JPH0925154A - Production of artificial marble - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lumpy artificial marble having the density and surface hardness almost equivalent to those of natural marble by pressurizing the raw material consisting essentially of calcium carbonate to a specified value, heating the material to melt it, then cooling and solidifying the molten material. SOLUTION: The raw material consisting essentially of calcium carbonate is pressurized to >=4MPa, melted, then cooled and solidified to produce the marble. In this case, when the material is heated under low pressure, the material is thermally decomposed into calcium oxide and carbon dioxide, hence the m.p. is not revealed, however the m.p. is revealed at >=4MPa. The solidified body formed stable calcite at a high temp. An inert gas having a lower mol.wt. than carbon dioxide is injected through a passage for communicating the upper space in a production vessel with the outside of the vessel to increase the pressure. Besides, a boron nitride powder is preferably applied on the inner face of the vessel as a releasing material. Further, a colored pigment is mixed in the raw material, and a marble having a blue or wine-red color, which has not been found in nature, is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing artificial marble made of a substance having almost the same composition as that of naturally occurring marble.

[0002]

2. Description of the Related Art Marble is a natural material that has been widely used since ancient times as a material for interior decorations and statues, or as a building material. It gives a luster by polishing and has a warmth as a rock. Is an indispensable material for these applications because it is relatively easy to process.

However, the color tone is important because of these uses, and it is the actual situation that high-quality marble relies on imports from overseas such as Italy and Taiwan. Regarding the color tone, it is known that high-quality marble from Italy is white, gray is mainly from Taiwan, and black or green is also known. Further, when natural marble is cut into a plate shape and used, the surface pattern is also a major factor from the viewpoint of decorativeness.

Demand for marble is increasing due to the diversification and upsizing of buildings in recent years. However, due to the above-mentioned circumstances, high-quality natural products are expensive and not easily available. The alternative material has become popular. Although this alternative material such as resin is light in weight, it can be easily applied to buildings, but it has many drawbacks as compared with natural marble, such as low surface hardness, easy damage, and flammability.

Therefore, for example, in Japanese Patent Laid-Open No. 4-228464,
A method of producing artificial marble by sintering using a powder material having a composition similar to that of natural marble is disclosed. The main component of marble is calcium carbonate, which has a crystal structure called calcite, but calcite powder obtained by synthesis and limestone, which is another mineral with a different crystal structure called aragonite, are heated by CaCO. ₃ → CaO + CO ₂ thermal decomposition reaction occurs. Therefore, according to the method described in the above publication, a compression molded body of powder containing calcium carbonate as a main component is fired in a high-pressure gas atmosphere containing an inert gas as a main component, and the pressure Pkgf / cm ² at this time is fired. Temperature t ℃
On the other hand, P> (t−600) ^{3.5 /} 4.7 × 10 ⁶ 900 ≦ t <1200 is set. In this way, an artificial marble is produced by obtaining a sintered body while suppressing the decomposition reaction.

[0006]

However, in the method described in the above publication, since the powder is molded and sintered, pores are likely to remain, so that a solid body having a true density, that is, polished and glossed. Since it is not possible to obtain a solidified body that can be provided with, and it is not possible to add a pattern such as a flow pattern, it has sufficient characteristics as a material for construction, statues, and other ornamental materials. Has the problem that it cannot be obtained.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to manufacture artificial marble excellent in characteristics as a material for building materials, statues, ornaments, and the like. It is an object of the present invention to provide a method for producing artificial marble that can improve productivity.

[0008]

In order to achieve the above object, the manufacturing method according to claim 1 of the present invention comprises heating a raw material containing calcium carbonate as a main component under a pressure of 4 MPa or more. It is characterized in that it is melted by, and then cooled and solidified to produce marble. That is, as shown in FIG. 1, calcium carbonate, which is the main component of marble, does not have a melting point due to thermal decomposition into calcium oxide and carbon dioxide when heated at low pressure, but has a melting point at a pressure of 4 MPa or more. appear. Therefore, by utilizing the relationship shown in this state diagram, the raw material containing calcium carbonate as the main component is melted by heating under a high pressure of 4 MPa or more,
Then, by solidifying by cooling, a solidified product of calcium carbonate is obtained. There are two types of calcium carbonate, aragonite, which has a stable crystal structure at low temperature, and calcite, which is stable at high temperature and is the main component of marble, but when melted and cooled under high temperature and high pressure as described above, the latter A solidified product is obtained.

By thus melting and solidifying the raw material once, there are no internal pores as in the conventional manufacturing method by sintering, and therefore, a lump having the same density and surface hardness as natural marble can be obtained. Thus, it is possible to produce artificial marble having excellent properties as a material for construction, statues, and other materials for ornaments. The manufacturing method according to claim 2, wherein the raw material is housed in a container, and an inert gas having a smaller molecular weight than carbon dioxide is injected into the container through a communication passage for communicating an upper space in the container with the outside of the container. Then, the pressure is increased to 4 MPa or more, and in this state, heating and melting of the raw material and subsequent cooling and solidification are performed.

That is, when the raw material in the container is heated and melted in a high-pressure inert gas atmosphere, the composition of the melt varies in the state where carbon dioxide generated by thermal decomposition from the melt dissipates. Therefore, by using an inert gas having a molecular weight smaller than that of carbon dioxide, gas transfer due to natural convection between carbon dioxide generated on the surface of the melt and the inert gas above it is suppressed. Therefore, as a result of suppressing that carbon dioxide stays on the surface of the melt and dissipates outside the container, the progress of thermal decomposition of the melt is suppressed,
It is possible to manufacture artificial marble of almost the same material as natural marble.

In this case, as in the method according to claim 3,
It is preferable to apply boron nitride powder as a release material on the inner surface of the container. This improves the mold release when the solidified body is taken out from the container after cooling, which facilitates the production and improves the productivity, and the use of boron nitride that does not cause unnecessary reaction with the raw material improves the quality. The decrease is suppressed,
This also makes it possible to produce artificial marble of excellent quality.

On the other hand, in the method according to the fourth aspect, the color pigment is mixed with the raw material. As a result, it is possible to manufacture marble with a color tone that does not exist in nature, such as blue and wine red, and it is an artificial marble with excellent characteristics such as aesthetics and texture as a building material and a decorative material. Can be manufactured. In the method according to claim 5, massive limestone is used as at least a part of the raw material. As a result, the material cost becomes cheaper and the manufacturing cost can be reduced. By solidifying some lumpy limestone without completely melting it, artificial marble with a pattern in which white grains are scattered Etc. can be manufactured.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, calcium carbonate (CaCO ₃ ) which is the main component of marble will be described with reference to FIG. This figure shows a phase diagram of calcium carbonate under high pressure. When heated under atmospheric pressure, calcium carbonate is thermally decomposed into solid calcium oxide (CaO [s]) and carbon dioxide (gas). Therefore, it is understood that under atmospheric pressure, it has no melting point and cannot be made into a molten state. However, when pressure is applied, the decomposition temperature gradually rises as shown by the curve a in the figure, and in the pressurized state of 4 MPa or more, the melting point appears as shown by the curve b, and the melting curve b is In the exceeded temperature range C, the molten state is obtained.

Therefore, by utilizing the relationship shown in this phase diagram, a raw material containing calcium carbonate as a main component is added at 4 MPa.
By melting by heating under the above high pressure, then by cooling and solidifying while maintaining a high pressure state,
A solidified product of calcium carbonate is obtained. There are two types of calcium carbonate, aragonite, which has a stable crystal structure at low temperature, and calcite, which is stable at high temperature and is the main component of marble, but when melted and cooled under high temperature and high pressure as described above, the latter solidified product. Is obtained.

As the melt temperature rises, Ca
It seems that some of the CO ₃ changes to solid calcium oxide (CaO [s]), but at present, the details of the relationship between the amount and temperature / pressure are unknown. According to our experiments,
In the region close to the solid phase region A in the figure, the amount of CaO [s] generated is small, and further, the dissipation of carbon dioxide that accompanies this is suppressed as described below, so that it can be used for building materials and the like. It is possible to obtain high quality marble without any problems.

As a method of applying high pressure, a method of compressing by a press or the like can be considered, but since carbon dioxide decomposed and produced by heating is a gas, it is necessary to prevent the carbon dioxide from being dissipated as described above. Therefore, in the present embodiment, in order to prevent carbon dioxide from being dissipated, the raw material is stored in a container having a structure in which carbon dioxide is not easily dissipated, and the pressure at the triple point p in the state diagram of FIG. The raw material in the container is heated and melted while the inert gas is applied in the container.

FIG. 2 (a) shows an example of such a container structure. The container 1 is composed of a box-shaped container body (hereinafter, referred to as a crucible) 2 having an open upper surface, and a lid 3 that covers the crucible 2 from above. The crucible 2 is made of a gas impermeable material such as metal, glassy carbon, or alumina, and the inner surface of the side wall 2a is provided with a taper surface inclined so as to be located outward as it goes upward with respect to the bottom side, that is, a so-called draft angle is provided. It is formed as a surface.

After the mold release material is applied to the inner surface of the crucible 2, powder or small lumps containing calcium carbonate as a main component, or a raw material 4 in which these are mixed is filled. It is preferable to use, for example, a powder of boron nitride (BN) which is non-reactive with the raw material 4 as the release material. As the raw material 4, not only calcium carbonate powder industrially produced by the carbon dioxide reaction method, the soluble salt reaction method, etc., but also cheaper natural materials such as limestone and shells can be used, thereby reducing the manufacturing cost. can do. However, in the case of a natural material, particularly in the case of a constituent substance of a living organism such as a shell, since an organic component is contained, it is preferable to thermally decompose and remove this organic component before use. If the organic components remain, problems such as soot and tar-like substances adhering to the inside of the furnace and water accumulating at the bottom of the furnace tend to occur during heating in the high-pressure gas atmosphere furnace described later. .

After the raw material 4 is filled in the container 1 as described above, the lid 3 is put on the crucible 2 from above. The lid 3 is made of a gas impermeable material such as glassy carbon similar to the above, or a material having some gas permeability, and is formed in a box shape with an opened lower surface. The lid 3 is formed so that a predetermined gap 5 exists between the side wall 3a of the lid 3 and the side wall 2a of the crucible 2, and the upper end of the side wall 2a of the crucible 2 is partially cut out. Is provided, and the gap 5 and the notch 6 form a communication passage 7 that communicates the upper space in the container 1 with the outside of the container.

The filling amount of the raw material 4 into the container 1 is preferably as large as possible. That is, when the raw material 4 is melted, a space is created in the container 1 above the raw material 4, but this space is filled with carbon dioxide produced by partial pyrolysis of the raw material, It is preferable to fill the raw material 4 in a large amount so that this space does not become too large.

The container 1 filled with the raw material 4 as described above is
It is set in a high pressure inert gas atmosphere furnace (not shown). Then, after first performing an operation of replacing the inside of the furnace with an inert gas atmosphere, a high-pressure inert gas is further injected into the furnace and pressurized. At this time, the gas inside the container 1 is replaced through the communication passage 7, and the inert gas flows into the container 1 so that the inside of the container 1 is maintained in the high-pressure inert gas atmosphere. It should be noted that the gas pressure may be 4 MPa or more in the case of melting at 1250 ° C. from FIG. 1, but as described later, the higher pressure suppresses the dissipation of carbon dioxide due to natural convection. Therefore, it is advantageous. However, if the pressure becomes higher, the cost of the device becomes higher and the economy becomes worse. Therefore, it is recommended to perform the treatment at about 10 MPa.

The raw material 4 is heated and melted in the high-pressure inert gas atmosphere as described above. At this time, in order to suppress the dissipation of carbon dioxide generated by the decomposition of a part of the melted raw material, it is desirable that the gas to be pressurized has a molecular weight smaller than that of carbon dioxide (molecular weight: 44), such as argon (molecular weight : 40) or nitrogen (molecular weight: 28) is used. In particular, in the case of nitrogen, carbon dioxide is heavier than this, so the generated carbon dioxide gas 8 is near the surface of the molten CaCO ₃ melt 9, as shown in FIG. 2 (b). As a result of being easily retained in the
The amount of CaCO ₃ decomposed is reduced. On the other hand, in the case of argon, carbon dioxide is heavier than this, but since the difference between the two is small, dissipation to the outside of the container 1 is more likely to occur than above. The higher the pressure is, the larger the difference in gas density at the same temperature is. Therefore, a heavy carbon dioxide retention state is likely to occur below argon and nitrogen, and gas movement due to natural convection is reduced, resulting in carbon dioxide. Is further suppressed.

As described above, after melting the raw material under high pressure, the temperature is lowered to solidify, and the temperature is further lowered to around room temperature. Then, the pressure inside the furnace is reduced to atmospheric pressure, the container 1 is taken out from the furnace, and the solidified body is taken out from the container 1. At this time, since the above-mentioned draft is provided on the inner surface of the side wall 2a of the crucible 2 and the release material is applied to the inner surface, the solidified body, that is, the artificial marble can be easily recovered. .

As described above, in the present embodiment, the calcium carbonate-based material that cannot be melted and solidified under the atmospheric pressure is melted by heating in a high pressure inert gas atmosphere. By suppressing the pressure state and the dissipation of carbon dioxide due to the decomposition, calcite is stably present even at high temperature. As a result, it is possible to manufacture marble equivalent to natural by cooling and solidifying after melting.

When industrially synthesized calcium carbonate is used as the raw material 4, an almost pure white solid is obtained. In the case of natural limestone or the like, since the raw material contains impurities, a solidified product having a white to gray or greenish color tone is obtained. Furthermore, according to the above-mentioned manufacturing method, by adding a small amount of an inorganic pigment to the raw material 4, it is possible to manufacture marble having a color tone such as blue or wine red which does not exist in nature. it can. For example, in the case of blue, cobalt oxide should be 0.01-
0.1% by weight, 0.01% chromium oxide for green
Add ~ 0.1 weight percent. For pink coloring, 0.01 to 0.1 weight percent of chromium oxide and 10 weight percent or more of alumina are added. Further, in the case of red color, it is effective to add 0.5 wt% or more of cuprous oxide (Cu ₂₀ ) and 3 wt% or more of stannic oxide (SnO) as an oxidant.

When the calcium carbonate raw material is a powder, this pigment is mixed with a pulverizing mixer such as a ball mill to obtain a pigment having a uniform color tone as a whole. In the case of a raw material containing lumps such as limestone, by adjusting the processing time during the melting process and producing a solidified product without partially melting it, white colored calcite particles are added to the colored dough (matrix). A solidified body having a mixed pattern can be obtained. Further, after the pigment is added to the raw material powder, the crucible is filled into the crucible without being mixed so much to perform the melt solidification treatment, whereby a solidified body having a flow pattern associated with the flow of the melted raw material is obtained.

On the other hand, powders of hard oxide-based ceramics such as alumina and magnesia, nitrides such as silicon nitride and carbide ceramics such as silicon carbide are mixed,
It is also possible to impart characteristics that natural marble does not have, such as manufacturing artificial marble with high hardness. Thus, according to the present invention, it is possible to produce an artificial marble composed of the same lumpy calcite-based substance as natural marble, and further,
Since it is possible to obtain materials with color and characteristics that are not found in natural marble, it will contribute greatly to the development of these fields not only as a building material but also as a material for statues and other ornaments. be able to.

[0028]

【Example】

[Example 1] A calcium carbonate powder (calcite) having a purity of 99% or more was filled almost completely into an alumina crucible having a structure shown in Fig. 2 (a), and a glassy carbon powder was used. I put the lid on. After the whole was placed in the processing chamber of the high-pressure inert gas atmosphere furnace, the inside of the furnace was evacuated and the gas replacement operation with argon gas was performed.

Subsequently, the furnace was filled with argon gas at a pressure of 3 MPa, the heater was energized to heat at a temperature rising rate of 400 ° C./h, and at the same time, argon gas was injected and pressurized by the compressor to finally 2 at 1280 ℃ and 100MPa
Hold for hours. After the holding, the crucible was taken out after the temperature was lowered to about room temperature by cooling the furnace. Inside the crucible, a white solid of a translucent solidified solid was produced.
As a result of measuring the density, it was 2.6 g / cm ³ . In addition, as a result of crushing the obtained solidified body and investigating the constituent phases by an X-ray diffraction method, it was found to be mostly calcite. Also, when the Vickers hardness was measured, Hv = 150-170
It was equivalent to natural marble.

[Example 2] Limestone having a size of 3 to 4 cm, and powder obtained by crushing the limestone and passing through a 100-mesh sieve, and adding 0.1% by weight of chromium oxide to the whole. Were mixed and filled in a crucible in the state as shown in FIG. Boron nitride powder was applied to the inner surface of the crucible by spraying. Melt solidification treatment was carried out by the same operation as in Example 1 except that the holding time was shortened to 1 hour and the final holding pressure was 10 MPa.

When the obtained solidified body was cut and the cross section was observed, it was in a state in which white particles of about 2 cm were mixed in the green wave pattern-containing ground. As a result of analyzing the amount of chromium in the light green portion, it was about 0.01% by weight in terms of chromium oxide. Table 1 shows the conditions and results of Examples 3 to 8 in which melting and solidification was performed by substantially the same operation as each of the above Examples. In each case, a solidified product having a color tone that can be used for building materials and decorative articles was obtained.

[0032]

[Table 1]

[0033]

As described above, according to the present invention, a natural marble is obtained by heating and melting a calcium carbonate-based material that cannot be melted and solidified under atmospheric pressure under a pressure of 4 MPa or more and then cooled and solidified. It is possible to obtain a lump having a density and a surface hardness almost the same as those of the above, and it is possible to manufacture an artificial marble having excellent properties as a material for a building, a statue, and other materials for ornaments (claim 1).

By storing the raw material in a container and pressurizing it with an inert gas having a molecular weight smaller than that of carbon dioxide, the raw material is heated and melted and then cooled and solidified.
The progress of the thermal decomposition of the melt is suppressed, which makes it possible to produce artificial marble having substantially the same material as natural marble (claim 2). In this case, if boron nitride powder is applied to the inner surface of the container as a mold release material, the mold release when the solidified body is taken out from the container after cooling is improved, so that the production is facilitated and the productivity is improved, By using boron nitride that does not cause unnecessary reaction with the raw material, deterioration of quality is suppressed, and thereby artificial marble of excellent quality can be manufactured (claim 3).

On the other hand, by mixing a color pigment with a raw material, it becomes possible to produce marble having a color tone that does not exist in nature, such as blue or wine red, and is used as a building material or a decorative material. It is possible to produce an artificial marble having further excellent characteristics such as aesthetics and texture (claim 4). Further, it is also possible to use lumpy limestone as at least a part of the raw material, which makes it possible to reduce the manufacturing cost because the material cost is lower, and to partially lump the limestone completely. It is also possible to manufacture artificial marble having a pattern in which white particles are scattered by solidifying without melting (claim 5).

[Brief description of drawings]

FIG. 1 is a state diagram under high pressure of calcium carbonate, which is the main component of marble.

2A and 2B show a container for storing a raw material according to an embodiment of the present invention, wherein FIG. 2A shows a sectional view of the raw material-containing container, and FIG. 2B shows a heating and melting state of the raw material. FIG.

[Explanation of symbols]

 1 container 2 crucible (container body) 3 lid 4 raw material 7 communication passage

Claims (5)

[Claims] 1. A raw material containing calcium carbonate as a main component
A method for producing an artificial marble, which comprises melting by heating under a pressure of MPa or more and then cooling and solidifying to produce marble. 2. An inert gas having a molecular weight smaller than that of carbon dioxide is injected into the container through a communication passage for accommodating the raw material in the container and communicating a space on the upper side in the container with the outside of the container, and the pressure is 4 MPa or more. The method for producing artificial marble according to claim 1, wherein the raw material is heated and melted and then cooled and solidified in this state. 3. The method of manufacturing an artificial marble according to claim 2, wherein boron nitride powder is applied as a release material on the inner surface of the container. 4. The method for producing an artificial marble according to claim 1, wherein a color pigment is mixed with a raw material. 5. The method for producing artificial marble according to claim 1, 2, 3 or 4, wherein massive limestone is used as at least a part of the raw material.