JPS6257579B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new glass for melt-foaming molding which contains an alkali silicate as a main component. More specifically, the present invention relates to a glass for melt-foam molding, which is made of anhydrous modified alkali silicate and is suitable for producing an inorganic foam that has excellent water resistance, strength, and nonflammability, and has good heat insulation properties. In recent years, from the standpoint of energy conservation, there has been an increasing demand for insulation in general buildings and industrial equipment. In terms of materials, there are two types of insulation materials: organic and inorganic. Organic materials are widely used as excellent insulation materials in building materials and various heat insulating materials, but organic materials tend to burn easily and emit organic gases. However, from the viewpoint of safety in particular, there is an increasing demand for inorganic heat insulating materials that are nonflammable and have excellent heat resistance. Glass wool is a typical commercially available inorganic insulation material. Glass wool is a material that is mainly used in large quantities for general construction.It is lightweight and has excellent insulation properties in dry conditions, but as it is an aggregate of short fibers, it is highly breathable and has poor insulation properties in high humidity conditions. Sexuality decreases. Furthermore, since it does not have the ability to retain its shape, it tends to form voids after long-term use, and special construction is required to prevent this. Examples of hard inorganic heat insulating materials that have been put into practical use include lightweight calcium silicate and foam glass. Although lightweight calcium silicate materials have excellent heat insulation properties in a dry state, they have very high water absorption and hygroscopicity, making them unsuitable for use in high humidity conditions, and their uses are limited. Foam glass is relatively strong and has excellent long-term insulation properties, but it is currently used in very limited fields because it is expensive. On the other hand, it has been known for a long time that water glass (alkali silicate aqueous solution) is a cheap and abundant raw material, and that foam can be obtained by heating it. Various methods have been used. Since commercially available alkali silicate itself is water-soluble, the obtained foam has poor water resistance, and furthermore, a foam with excellent insulation performance and high strength enough to be used as a practical insulation material has not yet been developed. It has not yet been put into practical use. Among these drawbacks, many methods have been proposed to address water resistance. For example, a method of treating the finished foam with an acid or a metal salt (e.g., Japanese Patent Publication No. 49-12885), or a method of adding a modifier that imparts water resistance to the foaming stock solution (e.g., Japanese Patent Publication No. 12885/1983),
No. 54-57528), and it has become possible to impart water resistance, but still no foam obtained from this has been obtained that satisfies both the heat insulation performance and practical strength. Generally, the thermal conductivity of a foam can be lowered by lowering its bulk specific gravity, and better heat insulation performance can be obtained. Water glass-based foams are no exception to this, and better insulation performance can be obtained by lowering the bulk specific gravity, but this also results in a decrease in strength, and to date there are no foams that can be put to practical use. has not been obtained yet. In other words, water glass foams have the advantage that foams with low specific gravity and low thermal conductivity can be obtained relatively easily by heating and foaming the raw material alkali silicate aqueous solution using water evaporation. , the resulting foam has low mechanical strength (compressive strength, bending strength, impact strength) and low closed cell properties, so there are problems with water absorption, moisture absorption, moisture permeability, etc., which cannot be resolved for practical use. There are still many difficult issues that need to be addressed. The present inventors have conducted intensive research to solve the conventional problems in water glass foams using inexpensive alkali silicates as raw materials. By discovering glass, we succeeded in producing an inorganic foam that has excellent water resistance, mechanical strength, and good heat insulation properties, leading to the present invention. That is, the present invention is a new glass composition for melt-foam molding, which is an anhydrous alkali silicate represented by the general formula R ₂ O x SiO ₂ (R is an alkali metal) and has a value of x of 2 to 3.8. Provided is a glass for melting and foaming molding, which is made of an anhydrous modified alkali silicate imparted with water resistance and has a melting point of 700° C. or less, which is obtained by heating and melting a modifying agent and a modifying agent. The foam obtained by melt-foaming the glass of the present invention has excellent mechanical strength and water resistance that could not be obtained with conventional water glass foams, and has high closed-cell properties. It has excellent water resistance (water absorption resistance, moisture absorption, and moisture permeability), and also has excellent long-term insulation properties. The substantially anhydrous modified alkali silicate glass imparted with water resistance for use in melt-foam molding of the present invention can be obtained by heating and melting an anhydrous alkali silicate and a modifier. In general, alkali silicate is represented by the general formula R ₂ O xSiO ₂ , where R ₂ O is in the periodic table.
It is an alkali metal oxide belonging to Group Ia. The alkali silicate used in the present invention has x of 2 to 3.8
It is. Generally commercially available alkali silicates are No. 1 to No. 4, and the value of x is from 2 to 3.8. In addition, the alkali silicates that are generally commercially available as Calets are No. 1 to No. 3, and the value of x is 2 to 3.
3.3. Glasses with x of 4 or more have a high melting temperature and cannot be obtained in a normal alkali silicate melting furnace because the furnace would be damaged. Even if obtained, modified alkali silicate glass satisfies the melting point of the present invention. cannot be obtained. In addition, in order to impart good water resistance to alkali silicate with x less than 2, a large amount of modifying agent is required, and it is difficult to obtain modified alkali silicate glass that satisfies water resistance and melting point.
It is also economically disadvantageous. Further, R ₂ O is specifically Li ₂ O, Na ₂ O, K ₂ O, etc., but Na ₂ O is practically preferred. In the present invention, anhydrous modified alkali silicate glass means substantially anhydrous, and there is no problem even if a small amount of water is attached or adsorbed. The purpose of the modifier used in the present invention is to impart water resistance to the water-soluble alkali silicate, and at the same time, the type and amount thereof are selected so that the melting point of the reaction product is 700°C or less. do. Types of modifiers include various oxidants such as titanium oxide, tin oxide, zirconium oxide, aluminum oxide, calcium oxide, magnesium oxide, zinc oxide, strontium oxide, lead oxide, copper oxide, iron oxide, cobalt oxide, and nickel oxide. There are some materials, but considering economy and effectiveness, we use zinc oxide, aluminum oxide, calcium oxide, magnesium oxide,
At least one selected from the group of lead oxide, copper oxide, and iron oxide. In addition to the above-mentioned oxides, modifiers include those that produce oxides of a corresponding composition upon melting, such as various corresponding hydroxides, carbonates, sulfates, silicates, and the like. The amount of modifier added is based on the amount of alkali silicate anhydride.
Although it varies depending on the SiO ₂ /Na ₂ O molar ratio (x above) and the type of modifier, anhydrous silicon The amount is 3 to 30 parts by weight per 100 parts by weight of acid-alkali. If it is less than 3 parts by weight, it is difficult to obtain good water resistance, and if it exceeds 30 parts by weight, the melting point becomes too high and no improvement in water resistance can be expected, which is economically undesirable. The degree of water resistance required for a foam differs depending on its use, and therefore the water resistance required for glass naturally also differs, but when considering the general usage as a heat insulating material, The water resistance of the glass for foam molding is 3% by weight or less, preferably 2% by weight or less. Water resistance in the present invention represents the solubility of glass in hot water, and is determined by the following method. In other words, accurately weigh 1.5 g of glass powder with a uniform particle size of 14 to 25 mesh and place it in a 300 c.c. Erlenmeyer flask.
Pour in cc of heated distilled water and boil for 4 hours while stirring gently with a magnetic stirrer while refluxing using a hot water bath. After removing fine dissolved suspended matter by decantation, 1G1 of the glass sample was
The weight loss by boiling was determined by suctioning through a glass filter and weighing the weight before and after boiling, and the water resistance was expressed as a percentage of the weight before boiling. Here, the weight of the glass was determined by drying it at 150° C. for 1 hour, cooling it in a desiccator, and then weighing it. If the water resistance of the glass exceeds 3% by weight, the water resistance of the foam obtained from the glass will also be poor.
For example, when the foam is immersed in hot water, some of the glass components are eluted into the hot water, causing destruction of the cells, increasing water absorption and moisture permeability, and further leading to the collapse of the foam, which can lead to practical use. It becomes unusable. Therefore, in the present invention, "imparted with water resistance" means that the water resistance of the glass measured by the above method is 3% by weight or less. The melting point of the glass for melt foam molding of the present invention is 700℃
It is as follows. Glasses with melting points exceeding 700°C require high-temperature heating when producing the glass and producing foams using the glass, which is disadvantageous in terms of energy and equipment materials. Furthermore, when the melting point is 700°C or lower, heat-resistant metal materials can be advantageously used for the mold and the like. The melting point in the present invention represents the sintering temperature of glass powder, and is determined by the following method. 5 g of glass powder (100 mesh passes) is placed in a 30 c.c. porcelain crucible, kept in an electric furnace at a predetermined temperature for 10 minutes, taken out from the furnace and cooled, and the melting point is determined with the naked eye. The melting point was defined as the temperature at which sintering was completely uniform and no white scattering due to grain boundaries was observed. The glass of the present invention is obtained by heating and melting anhydrous alkali silicate and a modifier. There are various methods for this, but for example, it can be obtained by uniformly mixing anhydrous alkali silicate powder and modifier powder to a desired composition, and then heating and melting.
The melt reaction is carried out at a temperature of 900 to 1400°C for several tens of minutes to several hours depending on the composition of the alkali silicate and the type and amount of the modifier. In addition, in all conventional known techniques, as a means of imparting water resistance to alkali silicate, an aqueous alkali silicate solution and a modifier are reacted in the liquid to create a modified aqueous alkali silicate solution, and this is used directly or by adjusting the water content. Post-heat foaming is performed. At this time, although it is not impossible in principle to obtain the anhydrous modified alkali silicate glass of the present invention by completely removing water from the modified alkali silicate aqueous solution, the process becomes longer and the water removal process becomes difficult. It is clear that the energy consumption is large and the glass is completely disadvantageous in terms of cost compared to the glass of the present invention. Note that the presence of moisture makes it difficult to manage and control conditions during heat foaming, making it difficult to obtain a uniform foam. Next, a method for manufacturing a foam using the glass of the present invention will be explained. The foam can be produced by various methods, and for example, the foam can be obtained by crushing the glass of the present invention, uniformly mixing the glass with a foaming agent, and melting and foaming the resulting mixture. As the blowing agent, known ones such as metal carbonates and carbon can be used. Calcium carbonate, dolomite, basic magnesium carbonate, strontium carbonate, etc. are used as the carbonate, and activated carbon, carbon black, etc. are used as the carbon. When carbon is used, Fe ₂ O ₃ is used as a foaming aid.
It can be used in combination with oxides such as Sb ₂ O ₃ , As ₂ O ₃ and MnO ₂ , peroxides such as BaO ₂ , sulfates such as CaSO ₄ and ZnSO ₄ . One or more of these blowing agents is usually added in an amount of 0.2 to 5 parts by weight per 100 parts by weight of glass powder and mixed uniformly. A foam is obtained by filling a mold with this mixture or melting and foaming the mixture beforehand, followed by slow cooling by a conventional method. The heating temperature and time vary depending on the glass composition and type of blowing agent, but generally the heating temperature is the highest.
The temperature is 600 to 800°C, and the heating time is 5 to 90 minutes. In commercially available foam glass obtained by melt-foaming, general industrial glasses such as plate glass and bottle glass are usually used as the raw material glass, but all of them have a SiO ₂ /R ₂ O molar ratio of 5 or more. It is a silicate glass with a high melting point and requires high-temperature heating for production, resulting in very high costs for both glass production and foam production. In contrast, the glass of the present invention is characterized by a low melting point, and is not only advantageous in terms of energy costs because it is processed at a lower temperature, but also requires less expensive materials and structural equipment, and is easy to handle. It is clear that it is industrially advantageous. The present invention will be explained in more detail below using Examples. The physical properties of the foam described in the examples were measured by the following method. Bulk specific gravity: The value obtained by dividing the weight by the volume when the foam is 5 x 5 x 5 cm. Thermal conductivity: Measured according to ASTMC518. The temperature is 35℃. Closed cell ratio: Measured using an air pycnometer manufactured by Beckman. Sample size is 2.5×
It is 2.5×3.0cm. Compressive strength: The sample size was 5 x 5 x 5 cm, and other dimensions were measured according to ASTMC240. Bending strength: The sample is a rectangular parallelepiped with a height of 3 cm, a width of 3 cm, and a length of 10 cm.The distance between spans is 6 cm.
Measured according to ASTMC240. Water absorption rate: Measured according to ASTMC240, except that the sample size was 5 x 5 x 5 cm. Water resistance of foam: It was immersed in hot water at 90°C for 4 hours, and the following items were measured. The sample size is 5×
It is 5 x 5 cm. Water absorption: Weight of foam after 4 hours of immersion
The water absorption rate was calculated according to ASTMC240. Shape change: Observed with the naked eye. Examples 1 to 11 Glasses having the compositions listed in Table 1 were manufactured using various sodium silicate powders and modifiers. Blend the raw materials to the specified composition, mix them, and then heat to the maximum temperature.
The glass of the present invention was produced by melting at 1000 to 1300°C for about 2 hours to complete modification and then rapidly cooling. The melting point and water resistance of the glass of the present invention are also listed in Table 1. Next, this glass was made into a powder of 100 mesh passes, and the foaming agent and foaming aid listed in Table 2 were added and mixed uniformly. Pour an appropriate amount of this mixture into a stainless steel mold, preheat it in an electric furnace at 450℃ for 30 minutes, and then
Heat for ~120 minutes to the temperature shown in Table 2.
Hold for ~30 minutes. Next, it was slowly cooled and demolded to obtain a glass foam. Test pieces for measuring physical properties were cut out from the obtained foam, and various properties shown in Table 2 were measured. The obtained foam had excellent performance as a heat insulating material, as seen from the physical properties shown in Table 2. Comparative Examples 1 to 5 Glasses having the compositions shown in Table 3 were melted and modified at 1000 to 1500°C in the same manner as the glass used in the examples, and then rapidly cooled. Table 3 lists the water resistance and melting point of the glass. Next, foams were produced in the same manner as in Examples 1-11. Table 4 lists the manufacturing conditions, physical properties, and water resistance of the foam. The foams of Comparative Examples No. 1, No. 2, and No. 4 had poor water resistance, and a change in shape was observed in the foams of No. 1 and No. 4 after being immersed in hot water for 4 hours. On the other hand, No. 1,
The water absorption rate of foam No. 2 was significantly increased. As is clear from the comparison of Examples 1 to 11 and Comparative Examples 1 to 5 above, the foam obtained using the glass of the present invention has excellent water resistance and changes in shape even when immersed in hot water for 4 hours. was not recognized, and Example No. 2 and No.
4. As shown in No. 9, no significant change was observed in the water absorption rate. Comparative Examples No. 3 and No. 5 required high temperatures to manufacture the glass and foam. Comparative Example 6 The physical properties of the water glass foam obtained by the conventional technique are also shown in Table 4. Although it had excellent heat insulation properties, it had low strength and poor water resistance. The water glass foam was manufactured by the following method. No. 3 water glass aqueous solution (Na ₂ O, 3.3SiO ₂ , solid content
A modified water glass obtained by adding 4.7 parts by weight of boric anhydride to 100 parts by weight of 38.5%) at 90°C with stirring was placed in a mold, and heated at 450°C for 120 minutes to foam.

【table】

【table】

【table】

【table】

Claims (1)

[Claims] 1. Obtained by heating and melting an alkali anhydrous silicate having the general formula R ₂ O·xSiO ₂ (R is an alkali metal) and having a value of x of 2 to 3.8 and a modifier, A glass for melt-foam molding that is made of anhydrous modified alkali silicate with water resistance and has a melting point of 700°C or less. 2. The glass for melt foam molding according to claim 1, wherein R ₂ O is Na ₂ O. 3 Claim 1 in which the modifier is zinc oxide
Glass for melt-foam molding as described in Section 3. 4. Glass for melt foam molding according to claim 1, wherein the modifier is aluminum oxide. 5. Glass for melt foam molding according to claim 1, wherein the modifier is magnesium oxide. 6. Glass for melt foam molding according to claim 1, wherein the modifier is calcium oxide. 7. Glass for melt foam molding according to claim 1, wherein the modifier is lead oxide. 8. Glass for melt foam molding according to claim 1, wherein the modifier is copper oxide. 9. Glass for melt foam molding according to claim 1, wherein the modifier is iron oxide. 10. Melt-foam molding according to claim 1, wherein the modifier is a combination of at least two or more selected from the group of zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, lead oxide, copper oxide, and iron oxide. glass.