JPS6242872B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnesia cement compositions. Hardened magnesia cement is dense, has excellent mechanical properties, and is nonflammable, so 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. has been done. Generally, to cure magnesia cement in a short time, it is enough to heat a compound containing highly active magnesia, but in this case, cracks may occur in the cured product during curing, reducing its mechanical strength. many. On the other hand, if it is cured slowly at a low temperature, cracks will not occur in the cured product during curing, but
When used in dry, high-temperature conditions for a long period of time, the cured product tends to develop fine cracks and lacks heat resistance. In order to solve these problems, it has been proposed to mix long glass fibers several millimeters in length or mix glass powder into magnesia cement. Although this method can prevent cracks from forming in the cured product during heat curing to a certain extent, if the cured product is exposed to high temperatures for a long period of time, minute cracks will still occur.
Heat resistance is not improved at all. The present invention has been made to solve the above-mentioned problems, and provides a cured product that does not crack even when rapidly cured by heat, and has excellent long-term thermal stability and mechanical strength. The purpose is to provide a magnesia cement composition. The magnesia cement composition of the present invention is a magnesia cement composition comprising activated magnesia and magnesium chloride and/or magnesium sulfate, in which 25 glass fibers have a maximum fiber length distribution of 0.1 to 0.3 mm for 100 parts by weight of activated magnesia.
40 parts by weight and 10 to 80 parts by weight of an alkaline earth metal carbonate. As already known, the magnesia cement composition of the present invention contains 20 to 60 parts by weight of magnesium chloride or 15 to 60 parts of magnesium sulfate in terms of anhydride based on 100 parts by weight of active magnesia.
When magnesium chloride and magnesium sulfate are used together, the ratio is usually 0.4 to 5 mol of magnesium chloride per 1 mol of magnesium sulfate, and the total amount is 100 parts by weight of active magnesia. 25 to 75 parts by weight. In the present invention, the magnesia cement composition further contains 25 to 40 parts by weight of short glass fibers having a maximum fiber length distribution in the range of 0.1 to 0.3 mm per 100 parts by weight of active magnesia. When the maximum fiber length distribution is larger than 0.3 mm, it becomes difficult to uniformly disperse the magnesia cement into the composition, and as a result, the amount of compounding is limited. The heat resistance that suppresses the occurrence of cracks is not developed. Especially when used with long glass fibers,
The short fibers are not sufficiently dispersed in the matrix of the magnesia cement composition between the long fibers, and the heat resistance of the cured product cannot be improved. Preferably, all short fibers have a fiber length of 1 mm or less. The maximum distribution of fiber length is
Even if it is smaller than 0.1 mm, the heat resistance of the cured product will not be improved. In particular, when used in combination with long fibers, the contact area with the magnesia cement matrix is too small, making it ineffective in improving the heat resistance of the cured product.
Glass fiber is used as the short fiber. The effect of improving the heat resistance of the cured product by adding short fibers becomes even more remarkable when an alkaline earth metal carbonate is used together with the short fibers. This is thought to reduce the shrinkage/expansion properties of the magnesia cement matrix, particularly the shrinkage/expansion properties in the direction perpendicular to the longitudinal direction of the fibers, and thus prevent the formation of fine cracks within the matrix. The amount of alkaline earth metal carbonate is 10 to 80 parts by weight per 100 parts by weight of active magnesia. When it is less than 10 parts by weight, the above effects are not sufficient, and when it exceeds 80 parts by weight,
This is because the viscosity increases when water is added, making it impossible to knead thoroughly. Preferred specific examples of the alkaline earth metal carbonate include calcium carbonate, magnesium carbonate, etc., and the particle size thereof is preferably 10 μm or less so as to be sufficiently dispersed between the fibers. In the present invention, as described above, long glass fibers conventionally used in magnesia cement compositions may be blended as a reinforcing agent, or mats or woven materials of the above fibers may be impregnated. good. Furthermore, additives such as water-insoluble phosphates, various aggregates, and fillers may be added to improve the water resistance of the cured product. As is conventionally known, the magnesia cement composition of the present invention contains activated magnesia.
For every 100 parts by weight, 40 to 150 parts by weight of water is mixed, and after kneading, it is shaped into a desired shape and heated to a temperature of about 60 to 100°C to harden. As described above, the magnesia cement composition of the present invention uses short glass fibers having a maximum distribution in a specific range in combination with an alkaline earth metal carbonate, suppresses contraction and expansion in the magnesia cement matrix, and forms a cured product. In addition to providing long-term heat resistance to the product, the cured product does not crack even during rapid heating and curing, and forms a cured product with excellent mechanical strength. Examples of the present invention are listed below along with comparative examples, but the present invention is not limited to these Examples in any way. Note that parts are parts by weight. Example 1 100 parts of activated magnesia (calcined at 700°C), 85 parts of magnesium chloride hexahydrate, and sodium tripolyphosphate
Prepare a magnesia cement paste by mixing with an aqueous solution consisting of 0.7 parts and 60 parts of water, and further add 20 parts of calcium carbonate and the following fibers with a fiber length of 1 mm or less and a maximum distribution in the range of 0.1 to 0.3 mm. 10 parts of short glass fibers with length distribution were mixed. This was poured into a mold, rapidly raised to 80°C, and heated for 15 minutes to harden. During curing, no cracks were generated in the cured product, and after cooling, it was possible to remove the product from the mold without losing its shape. A cured product was obtained by curing at room temperature for 4 weeks. Fiber length distribution of short glass fibers 0.1 mm or less 8.5% More than 0.1 mm and less than 0.2 mm 36.5% More than 0.2 mm and less than 0.3 mm 25.5% More than 0.3 mm and less than 0.4 mm 14.5% More than 0.4 mm and less than 0.5 mm 7.5% 0.5 mm More than 0.6mm and less than 3.3% More than 0.6mm and less than 0.7mm 0.75% More than 0.7mm and less than 0.8mm 1.0% More than 0.8mm and less than 0.9mm 0.25% More than 0.9mm and less than 1.0mm 2.0% Example 2 Activated magnesia (700 A magnesia cement paste was prepared by mixing 100 parts of magnesium chloride hexahydrate (calcined at
Further, 40 parts of calcium carbonate and 5 parts of the short glass fiber
parts were mixed. This was impregnated into 13 parts of chopped strand pine, laminated and cured at room temperature.
A cured product was obtained after curing for 4 weeks. Example 3 Magnesia cement paste was prepared by mixing 100 parts of activated magnesia (calcined at 700°C) with an aqueous solution consisting of 50 parts of anhydrous magnesium sulfate and 100 parts of water, and further mixed with 30 parts of magnesium carbonate and 10 parts of the short glass fibers.
parts were mixed. This was impregnated into 11 parts of chopped strand glass mat, laminated and cured at room temperature. A cured product was obtained by curing at room temperature for 4 weeks. Comparative Example 1 The same magnesia cement paste as in Example 1 was heat-cured under the same conditions as in Example 1 without adding magnesium carbonate and short glass fibers.
During curing, many fine cracks were generated in the cured product. A cured product was obtained by curing at room temperature for 4 weeks. Comparative Example 2 5 parts of the short glass fibers alone were added to the same magnesia cement paste as in Example 2, and 12 parts of chopped strand glass mat was impregnated and laminated.
After curing at room temperature, a cured product was obtained by curing for 4 weeks. Comparative Example 3 A cured product was obtained in exactly the same manner as in Example 2, except that 7.5 parts of crushed glass was added instead of the short glass fibers. After leaving each cured product obtained in the above manner in dry air at 100°C for two weeks, the surface condition was observed, and the bending test method for architectural boards (JIS
A bending test was conducted based on A1408). Also,
A bending test was also conducted on the cured product that was not subjected to drying treatment. The results are shown in the table below.

[Table] According to the magnesia cement composition of the present invention,
The bending strength of the cured product was almost unchanged before and after the high temperature drying treatment, but according to the composition of the comparative example, the mechanical strength of the cured product significantly decreased after the high temperature drying treatment.

Claims (1)

[Claims] 1 Activated magnesia, magnesium chloride and/or
Or, in a magnesia cement composition consisting of magnesium sulfate, 25 to 40 parts by weight of glass fibers having a maximum fiber length distribution of 0.1 to 0.3 mm for 100 parts by weight of activated magnesia, and 10 to 80 parts by weight of an alkaline earth metal carbonate. A magnesia cement composition comprising: