JP2000007463A - Formation of inorganic foamed molding or coating film and inorganic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and surely forming an inorganic foamed molding or a coating film, which contains many bubbles independent of each other and having uniform particle size, and to provide an inorganic composition suitable as a material therefor. SOLUTION: This inorganic composition contains a binder composed of an aq. solution of an alkali metal silicate and egg shell powder, which is a finely crushed material of the egg shell. The inorganic foamed molding is formed by using the inorganic composition as the material and carrying out a pre- molding forming process and a foaming and molding process in this order. In the pre-molding forming process, the inorganic composition is shaped into a prescribed shape and dried and solidified to form the pre-molding. In the succeeding foaming and molding process, the pre-molding is heated to be foamed to form the inorganic foamed molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an inorganic foam molded article or an inorganic foam coating, and an inorganic composition suitable as a material for the molded article or the coating.

[0002]

2. Description of the Related Art Foams, that is, molded articles or coatings containing a large number of cells dispersed and separated from each other by partition walls, are lightweight, have excellent heat insulating properties, etc., and include a backing material or a core material for building materials. Is used in various fields. As such a foam, an organic foam made of a synthetic resin such as polystyrene or polyurethane is generally used, but in recent years, in particular, in view of fire resistance or fire resistance, inorganic foam including a binder component has been used. There is an increasing demand for non-combustible, highly heat-resistant inorganic foams substantially formed from only materials.

On the other hand, various methods for forming such an inorganic foam have been conventionally known and proposed. The most typical method is a method in which air is mixed in advance with an aqueous inorganic composition containing an inorganic binder such as cement, and the composition is solidified in a state where the composition is contained as bubbles. Although not a method of directly forming an inorganic foam, it is also common to use foamed (hollow) inorganic particles such as shirasu balloons and blend them into the composition in a relatively large amount.

Further, instead of the above-described method of introducing external air into the composition as air bubbles, a foaming agent that generates a gas by a chemical reaction or thermal decomposition is used, and this is foamed in the composition to form air bubbles. Methods of generating are also known. For example, Japanese Patent Application Laid-Open No. 7-291557 discloses that an inorganic composition using an aqueous solution (water glass) of an alkali metal silicate as a binder and a filler (also a curing agent) containing a specific fly ash is used. An addition of an aluminum powder as an agent is disclosed. The aluminum powder generates hydrogen gas due to the alkalinity of the binder and foams.

[0005] In addition, as for a method of forming an inorganic foam, a method using a special mineral material which rapidly expands in volume by heating to form air bubbles is also known. That is, according to the proposal of the present applicant, Japanese Patent Application Laid-Open No. 6-172058 discloses that an inorganic composition using water glass as a binder is provided with such a heat-swellable material such as synthetic swellable mica or synthetic smectite. (Powder)
After drying and solidifying (gelling), it is 400 ~ 500 ℃
To form a foam by heating at a temperature of

[0006]

By the way, the foam is
Its homogeneity, whether inorganic or organic, is important. However, even when the inorganic foam is formed according to any of the above-mentioned conventional techniques, it is difficult to make each cell a desired size, that is, to control the amount of air or gas in the cell. is there. Therefore,
The size of the bubbles becomes irregular, and in some cases, the bubbles merge with the adjacent bubbles to become large bubbles. As a result, in the obtained inorganic foam, there is a problem that variations in various properties such as heat insulation properties and specific gravity are increased.

Accordingly, an object of the present invention is to provide a method for easily and reliably forming an inorganic foam molded article or a coating containing a large number of cells which are independent of each other and have a uniform size. Another object of the present invention is to provide an inorganic composition suitable as a material for an inorganic foam molded article or an inorganic foam coating.

[0008]

According to a first aspect of the present invention, there is provided an inorganic composition comprising a binder comprising an aqueous solution of an alkali metal silicate and eggshell powder which is a finely ground egg shell. While forming and forming, a preformed body forming step of drying and solidifying the inorganic composition to form a preformed body, and a foaming forming step of heating the preformed body and foaming to form an inorganic foamed molded body. A method for forming an inorganic foam molded article, comprising:

Here, the alkali metal silicate has the general formula M
It is represented by ₂ O · nSiO ₂ . Wherein M is sodium (Na), potassium (K), or lithium (Li). N is the molar ratio between M ₂ O and SiO ₂ ,
Generally, it is 0.5 to 4.5. As such an alkali metal silicate, water glass of sodium silicate which is inexpensive and easily available can be suitably used.

[0010] The binder may contain a curing agent and a filler as required, and these may be dissolved in water to form a slurry. Examples of the curing agent include oxides of polyvalent metals such as magnesium oxide, lead oxide, zinc oxide, and calcium oxide; silicides (silicates) such as calcium silicate; silicides such as sodium silicofluoride; Phosphates such as aluminum phosphate, calcined products of phosphoric acid and metal oxide, or double salts thereof, and borates such as sodium or potassium borate and zinc borate are used. As the filler, for example, silica powder, kaolin, mica powder, calcium carbonate, sepiolite, and the like are used.

[0011] Eggshell powder is obtained by finely pulverizing eggshell such as chicken eggs (mainly chicken eggs) from which albumen and yolk have been removed.
It has an average particle size of about 20 μm to 20 μm and has fine pores. Eggshell powder is mainly calcium carbonate (CaCO
₃ ) and contains a small amount of calcium phosphate, silicate and a small amount of hard protein (keratin).

Drying is a treatment for removing water so that the formed inorganic composition does not foam.
Drying includes a treatment of allowing the composition to dry naturally and a treatment of heating at a temperature lower than the temperature at which the inorganic composition foams. The inorganic foam molded article is formed into a certain shape in a foamed state.

According to the first aspect of the present invention, a preform forming step and a foaming step are performed when forming the inorganic foamed article. In the preform forming step, an inorganic composition including a binder composed of an aqueous solution of an alkali metal silicate and eggshell powder that is a finely crushed eggshell is used. The inorganic composition is formed into a predetermined shape by being injected into a mold or the like. Then, when the water in the inorganic composition is removed by drying, the inorganic composition solidifies and becomes a preform having a predetermined shape. At this stage, no bubbles are contained in the preform.

In the subsequent foaming step, the preform is heated. The heating temperature varies depending on the type of the alkali metal silicate.
It is desirable that the temperature is not less than ° C. This is because, even if heating is performed at a lower temperature, uniform foaming is not performed. By this heating, the alkali metal silicate in the preform reacts with the eggshell powder. That is, each eggshell powder becomes a nucleus, and a protein which is a component of the eggshell powder is decomposed and gasified to generate a large number of bubbles. Here, the particle size of the eggshell powder is uniform,
The amount of gas generated per unit time from eggshell powder per piece is almost the same between eggshell powder. In addition, the decomposition and gasification of the protein occurs slowly so that the binder hardens before becoming large bubbles. As a result, an inorganic foam molded article that is independent of each other (not coalesced with adjacent cells) and includes many fine and uniform cells is obtained.

A second invention according to claim 2 is to coat an inorganic composition containing a binder composed of an aqueous solution of an alkali metal silicate and an eggshell powder, which is a finely ground egg shell, on a substrate surface, The gist of the present invention is a method for forming an inorganic foamed coating, in which after the inorganic composition is dried and solidified to form a foamable inorganic coating, the inorganic coating is heated and foamed. Here, the alkali metal silicate, the eggshell powder and the drying are the same as those described in the first invention. The inorganic foam coating covers an object (substrate) in a foamed state.

According to the second aspect of the invention, when forming the inorganic foam coating, first, the inorganic composition is coated on the surface of the substrate. This inorganic composition contains a binder composed of an aqueous solution of an alkali metal silicate, and eggshell powder that is a finely ground egg shell. Subsequently, moisture in the inorganic composition is removed by drying. This moisture removal solidifies the inorganic composition and forms a heat-foamable inorganic coating on the substrate. At this stage, the inorganic coating contains no air bubbles,
When heat is applied, it reacts in the same manner as in the first invention, resulting in an inorganic foam coating having a large number of independent cells.

A third aspect of the present invention is directed to an inorganic composition comprising a binder comprising an aqueous solution of an alkali metal silicate and an eggshell powder which is a finely ground egg shell. Here, the alkali metal silicate and the eggshell powder are the same as those described in the first invention.

According to the third aspect, the inorganic composition does not react under non-heating (for example, at normal temperature). Therefore, it is possible to shape the inorganic composition into a predetermined shape, coat the inorganic composition on the surface of the substrate, and dry and solidify the inorganic composition. Air bubbles are not contained in the dried and solidified inorganic composition. However, when the inorganic composition is heated, the alkali metal silicate and the eggshell powder react to generate gas and generate numerous bubbles. When the binder cures, an inorganic foam molded article or an inorganic foam coating containing a large number of cells that are independent of each other and are fine and uniform in size are obtained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment embodying the first and third inventions will be described below. As the aqueous solution of the alkali metal silicate, an aqueous solution of sodium silicate having a solid content of about 40% was used. Moreover, the average particle size is 1 as eggshell powder.
One having a thickness of 0 μm was used, and mica was used as a filler. Sodium silicate aqueous solution 1 in a container at room temperature
Then, 10 parts by weight of eggshell powder and 5 parts by weight of mica were added. Eggshell powder and mica were dispersed in the aqueous solution by stirring to prepare an inorganic composition. Using this inorganic composition, the following preformed body forming step and foam forming step were sequentially performed to form an inorganic foamed formed body.

In the preform forming step, the inorganic composition was formed into a predetermined shape by, for example, injecting the inorganic composition into a mold or the like prepared in advance. Subsequently, the inorganic composition was left at room temperature to remove water contained in the inorganic composition. The inorganic composition was solidified by the removal of water, and a preform having a desired shape was obtained. At this stage, no bubbles are contained in the preform.

In the subsequent foam molding step, the preform was heated to about 150 ° C. for about 5 minutes in a furnace. Then, the alkali metal silicate in the pre-formed body and the eggshell powder reacted to form an inorganic foamed shaped body. Here, since the inorganic composition and the preform had a white color, whereas the inorganic foamed molded product had a yellowish white color, it is considered that the following reaction occurred. That is, each eggshell powder becomes a nucleus, and a protein which is a component of the eggshell powder is decomposed and gasified to generate a large number of bubbles. The particle diameters of the eggshell powders are equal to each other, and the amount of gas generated from the eggshell powder per unit time per unit time is substantially the same between the eggshell powders. In addition, since the decomposition and gasification of the protein proceed slowly, the binder hardens before becoming large bubbles, and becomes an inorganic foam molded article.

As described above, a desired inorganic foam molded article could be formed only through a few and simple steps such as a pre-molded article forming step and a foam molding step. When the obtained inorganic foam molded article was cut and the internal state was examined, a large number of minute air bubbles having a uniform size were dispersed. In addition, there was hardly any thing that broke the partition and was connected to the next bubble. Many bubbles were separated by partitions and were independent. Further, the partition walls had sufficient hardness, and the inorganic foam molded article was hard and did not easily deform. As described above, since the inorganic foam molded article has little variation in various properties such as heat insulating properties and specific gravity, it can be suitably used for products requiring light weight, heat insulating properties, and the like, for example, inorganic heat insulating materials, inorganic building materials, and the like. . In addition, since such an inorganic foam molded article was obtained from the above-described inorganic composition, it was clarified that this inorganic composition was suitable as a material for the inorganic foam molded article.

(Second Embodiment) Next, a second embodiment embodying the second and third inventions will be described. In the second example, the same inorganic composition as that described in the first example was used, and a carbon fiber reinforced board was used as a substrate, and an inorganic foam coating was formed as follows.

The surface of the substrate was coated with an inorganic composition so as to have a substantially constant thickness. Subsequently, the inorganic composition was allowed to stand at room temperature and air-dried to remove moisture contained in the inorganic composition. The inorganic composition was solidified by the removal of water, and a heat-foamable inorganic coating was formed on the substrate. At this stage, no bubbles are contained in the inorganic coating. Subsequently, the substrate covered by the inorganic coating is
It was left in a 50 ° C. oven for about 5 minutes. By this heating, the alkali metal silicate and the eggshell powder in the inorganic coating react with each other, and the inorganic foam coating containing a large number of fine and uniform bubbles independent of each other, as in the first embodiment. Was formed.

The inorganic coating on the substrate keeps its form unless heated, but when it is heated, the inorganic coating naturally changes to an inorganic foam coating, and the following uses are considered. For example, an outer wall material is used as a base, and an inorganic coating is formed thereon. No heating is performed at this stage. In this way, if a fire occurs and heat is applied to the inorganic coating, the alkali metal silicate in the inorganic coating reacts with the eggshell powder to foam and form an inorganic foam coating. This inorganic foam coating exhibits heat insulation, fire resistance and the like, and can block a flame.

[0026]

As described above, according to the forming method of the first or second aspect of the present invention, a large number of air bubbles of uniform size can be reliably generated only through a few and simple steps. . The obtained inorganic foam molded article or inorganic foam coating is independent of each other, and contains a large number of cells having a uniform size in a dispersed state, and has little variation in various properties such as heat insulating property and specific gravity. It can be widely used in various other fields, including fields requiring properties and the like.

By using the inorganic composition according to the third invention,
Since it is foamed only by heating it, it is suitable as a material for the inorganic foam molded article of the first invention or the inorganic foam coating of the second invention.

Claims (3)

[Claims] 1. An inorganic composition comprising a binder comprising an aqueous solution of an alkali metal silicate and an eggshell powder which is a finely crushed eggshell is formed, and the inorganic composition is dried, solidified and preformed. A method for forming an inorganic foam molded article, comprising: a preformed article forming step of forming a body; and a foam molding step of heating and foaming the preformed article to form an inorganic foam molded article. 2. An inorganic composition comprising a binder comprising an aqueous solution of an alkali metal silicate and eggshell powder which is a finely crushed eggshell is coated on a substrate surface, and then the inorganic composition is dried, solidified and foamed. A method for forming an inorganic foamed coating, comprising forming a porous inorganic coating, and then heating and foaming the inorganic coating. 3. An inorganic composition comprising: a binder comprising an aqueous solution of an alkali metal silicate; and an eggshell powder which is a finely crushed eggshell.