JPS6320784B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnesia cement compositions. Magnesia cement is generally an aqueous composition made by mixing activated magnesia with magnesium chloride and/or magnesium sulfate, and has higher bending strength and hardness than other cements, as well as excellent surface gloss. In particular, since the cured product is nonflammable, it is attracting attention as a material that can replace conventional organic synthetic materials in the field of building materials and solve the problem of flammability. Furthermore, since magnesia cement has a relatively short curing time, it also has the advantage of being convenient for factory production of molded products such as plates and columns. However, on the other hand, magnesia cement suffers from a lack of water resistance due to the leaching of soluble salts after hardening, and its use in areas with high moisture or humidity must be avoided, resulting in the problem that its applications are extremely limited. It was hot. In order to solve this problem of lack of water resistance, it has been proposed, for example, to add polyphosphate to magnesia cement (US Pat. No. 3,320,077), but the improvement in water resistance is not sufficient; It tends to increase setting time and negate the benefits of magnesia cement. On the other hand, it is already known that magnesia cement can be heated to accelerate hardening in order to shorten the hardening time. There was a problem that the long-term strength and physical properties were inferior to that of the conventional method. The present invention has been made in order to solve the above-mentioned problems in magnesia cement, and provides a cured product with excellent water resistance, excellent hardening properties, especially heat hardening properties, and furthermore, An object of the present invention is to provide a magnesia cement composition having good long-term strength properties. The magnesia cement composition of the present invention comprises (a) 100 parts by weight of activated magnesia, and (b) 20 parts by weight of magnesium chloride.
~60 parts by weight and/or 15-100 parts magnesium sulfate
parts by weight, (c) a total amount of 7 to 35 parts by weight of zinc sulfate and zinc oxide in which the ratio of zinc oxide to 1 mol of zinc sulfate is 2.5 to 6 mol, and (d) 60 to 150 parts by weight of water. It is characterized by The activated magnesia used in the present invention preferably has a relatively high degree of activity. Such activated magnesia is usually obtained by firing magnesium hydroxide, magnesium carbonate, etc. at a temperature of 400 to 1000°C, but activated magnesia fired at a temperature of 600 to 900°C is preferably used. Magnesium chloride is used in an amount of 20 to 60 parts by weight per 100 parts by weight of active magnesia in terms of anhydride.
When the amount is less than 20 parts by weight, the initial strength of the magnesia cement immediately after hardening is low, and a so-called powder blowing phenomenon occurs in which excess magnesia blows out onto the surface.
When the amount is more than part by weight, excess magnesium chloride causes the so-called sweating phenomenon. Magnesium sulfate is 15% per 100 parts by weight of active magnesia in terms of anhydride.
~100 parts by weight are used. When it is less than 15 parts by weight, the strength of the cured product is generally low;
When the amount is more than 1 part by weight, the initial hardness after heat curing is particularly poor, and the cured product may lose its shape, for example, when the molded product is removed from the mold in the production of a molded product, which is not preferable. Magnesium chloride and magnesium sulfate may be used alone or in combination. When both are used together, the ratio is 1 mole of magnesium sulfate to 1 mole of magnesium chloride.
The amount is preferably 0.4 to 5 mol, and the total amount is preferably 25 to 75 parts by weight per 100 parts by weight of active magnesia. The magnesia cement composition of the present invention contains zinc sulfate and zinc oxide. The mixing ratio of zinc sulfate and zinc oxide is 1 mole of zinc sulfate to 1 mole of zinc oxide.
2.5 to 6 mol, and such a mixture is used in an amount of 7 to 35 parts by weight per 100 parts by weight of active magnesia. Water resistance is not improved even when zinc sulfate or zinc oxide is blended alone, and a combination of zinc sulfate or zinc oxide is required. In general, zinc oxide and zinc sulfate form hydrous double salt crystals in the presence of water, similar to magnesia cement.
It is known to harden at room temperature or under heating.
Although the magnesia cement composition of the present invention is not limited by any theory, it is believed that zinc oxide-zinc sulfate-based hydrous double salt crystals are generated during hardening of magnesia cement, and a nucleating agent or nucleating agent that promotes crystal growth of magnesia cement is used. In addition to acting as a seed crystal and improving its hardenability, zinc ions partially replace the magnesium ions in the magnesia cement crystals, and magnesium ions partially replace the zinc ions in the zinc oxide-zinc sulfate double salt crystals. replace,
It is thought that as a result of the magnesia cement crystals being modified in this way, water resistance is improved. Therefore, if the amount of zinc oxide relative to zinc sulfate used is too small, zinc sulfate will remain in the magnesia cement, causing a decrease in the water resistance of the hardened product.On the other hand, if the amount is too large, zinc oxide will remain. and reduce water resistance. This tendency becomes more pronounced as the amount of zinc sulfate and zinc oxide added to activated magnesia increases. When the blending amount of zinc oxide and zinc sulfate is too small, the effect as a nucleating agent as described above and the modification effect by mutual substitution of ions in the crystals will be poor, and when the amount is too large, the Since the amount of activated magnesia, magnesium chloride and/or magnesium sulfate is relatively reduced, the viscosity increases, which impedes moldability, and also has a detrimental effect on the long-term strength of the cured product, which is undesirable. . In the magnesia cement composition of the present invention,
The method of blending zinc oxide and zinc sulfate is not particularly limited. For example, it may be added to an aqueous solution of magnesium chloride and/or magnesium sulfate, or activated magnesia may be added to an aqueous solution of magnesium chloride and/or magnesium sulfate to form a slurry, and then added to this slurry. However, it is preferred that the zinc sulfate be used in the form of an aqueous solution. Water in magnesia cement compositions is typically 60 to 150 parts by weight per 100 parts by weight of active magnesia. This water is usually blended in the form of an aqueous solution of magnesium chloride, magnesium sulfate, zinc sulfate, etc., as described above, but is not limited to these methods. In the present invention, the obtained cured product is reinforced,
In addition, in order to prevent the occurrence of cracks, the magnesia cement composition may contain appropriate reinforcing materials such as natural fibers, synthetic fibers, mineral fibers, etc., and calcium carbonate, perlite,
It may contain fillers and aggregates such as vermiculite, sand, silica sand, gravel, etc. Furthermore, synthetic resin latex such as rubber latex and epoxy resin is blended,
It is also possible to further improve the water resistance of the resulting cured product. As described above, by blending zinc sulfate and zinc oxide in the magnesia cement composition of the present invention, the resulting cured product not only has excellent water resistance but also has good curing properties, especially heat curing properties. Moreover, the initial and long-term strength of the cured product is high,
Therefore, it can be used in a wide range of applications and has good demoldability, making it suitable for mass continuous production of molded products and the like. Examples of the present invention are listed below along with comparative examples, but the present invention is not limited to these Examples. In addition, parts mean parts by weight. Example 1 100 parts of activated magnesia (calcined at 800°C. The same applies below), 30 parts of magnesium chloride,
A magnesia cement slurry consisting of 5 parts zinc oxide, 2.5 parts zinc sulfate, and 100 parts water is poured into the formwork,
Then, after rapidly heating to a temperature of 80℃ and keeping at this temperature for 30 minutes, the molded part is placed in the formwork.

[Table] 2) The molded product developed cracks and was removed from the mold, but the molded product did not lose its shape. The bending strength immediately after demolding and after curing at room temperature was measured according to the bending test method for architectural boards (JIS A-1408). The results are shown in the table. Furthermore, after curing at room temperature for 28 days, the molded product was immersed in running water at room temperature (2 liters/min), and water resistance was evaluated from the weight loss rate. The results are shown in the table. Examples 2 to 4 Molded articles were obtained in the same manner as in Example 1 using magnesia cement slurries having the compositions shown in the table. The bending strength and weight loss rate are shown in the table. Comparative Examples 1 to 6 Molded articles were obtained in the same manner as in Example 1 using magnesia cement slurries having the compositions shown in the table. The bending strength and weight loss rate are shown in the table. As is clear from the above, even if a phosphate is added, the water resistance is only slightly improved, but according to the present invention, the water resistance is significantly improved, and furthermore, the cured product obtained by heat curing has high strength. has. Note that water resistance is not improved even when zinc oxide and zinc sulfate are used alone.

Claims (1)

[Claims] 1 (a) 100 parts by weight of activated magnesia, (b) 20 to 60 parts by weight of magnesium chloride and/or 15 to 100 parts by weight of magnesium sulfate, and (c) the ratio of zinc oxide to 1 mol of zinc sulfate is 2.5 to 6 mol. a total of 7 to 35 parts by weight of zinc sulfate and zinc oxide, and (d) 60 to 150 parts of water.
A magnesia cement composition comprising parts by weight.