JPH0260603B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for synthesizing acicular elestadite with a large aspect ratio. Erestadite is effective as a filler for improving the physical properties of thermoplastic resins such as PVC and polyolefins, and thermosetting resins such as epoxy and polyester, and particularly contributes to improving Young's modulus. However, conventional elestadite has a calcareous It is manufactured by hydrothermally reacting raw materials, silicic acid raw materials, and compounded raw materials containing only slag.
Its aspect ratio was approximately 10, and the improvement in strength was still insufficient. According to the single fiber reinforcement theory, the conditions for increasing the reinforcement strength of the filler are to increase the length of the filler and to decrease the diameter in the short direction. That is, increasing the aspect ratio, which is the ratio between the length and diameter of the filler, improves the reinforcement strength. For this reason, the present inventors conducted studies to increase the asvect ratio of elestadite crystals, and as a result, they discovered that adding a phosphoric acid-containing substance during the synthesis of elestadite increases the asvect ratio of elestadite crystals. Reached. That is, the gist of the present invention is to provide a method for synthesizing elestadite by a hydrothermal reaction of a blended raw material containing a calcareous raw material, a silicate raw material, and a plaster, in which a phosphoric acid-containing substance is added to the blended raw material during the hydrothermal reaction. A method for synthesizing elestadite characterized by adding 0.1 to 5.0% by weight of. As described above, the method of the present invention uses CaO, which contains calcareous raw material, silicic acid raw material, and plaster, respectively.
5 to 7:2 to 4:2 in terms of SiO ₂ and CaSO ₄
A phosphoric acid-containing substance is added to the raw materials prepared at a molar ratio of ~4.
0.1 to 5% by weight is added, an appropriate amount of water is added, and a synthesis reaction is carried out under hydrothermal conditions in an autoclave. The above hydrothermal conditions are preferably a saturated steam atmosphere of about 130 to 240°C, preferably in the range of 140 to 190°C. When the saturated steam atmosphere is below 130℃ and 240℃
If the temperature exceeds ℃, the production rate of elestadite decreases. As the calcareous raw material used in the present invention, slaked lime or quicklime, for example, is suitable, and either can be used even if it contains some impurities. Gypsum can be dihydrated, hemihydrated, or anhydrous, and can also be used even if it contains some impurities. As a silicic acid raw material, for example, crystalline or amorphous silicic acid containing 90% or more SiO ₂
Any powder containing 2,000 cm ² /g or more is preferable in order to increase the reactivity. Phosphoric acid-containing substances include various phosphoric acids and their salts such as orthophosphoric acid and pyrophosphoric acid. There is no difference depending on the phosphate cation, but
Alkali metals or alkaline earth metals are easy to use industrially. The amount of the phosphoric acid-containing substance added is in the range of 0.1 to 5.0% by weight based on the above-mentioned calcareous raw material, silicic acid raw material, and gypsum. If the amount added is less than 0.1% by weight, there will be no effect of the addition, and if it exceeds 5% by weight, the reaction rate will decrease and the crystallinity will decrease so that needle-shaped crystals will no longer be observed. The amount of water added during the above-mentioned hydrothermal reaction needs to be at least enough to wet the raw materials, and there is no problem even if a large amount is added, but if it is too large, it becomes inefficient. As described above, in the method of the present invention, by adding a phosphoric acid-containing substance to a blended raw material containing calcareous raw materials, silicic acid raw materials, and gypsum during synthesis, short hexagonal columnar crystals are formed through a hydrothermal reaction. Crystal growth in the direction, that is, the a-axis, is suppressed, and as a result, the length direction, that is, the c-axis, is relatively elongated, making it possible to synthesize a long crystal in the c-axis direction. The mechanism of such crystal growth is that in the above quantitative relationship, by adding a phosphate-containing substance, phosphate ions replace sulfate ions and silicate ions, enter the crystals of elestadite, and change the crystal growth rate. This seems to be due to Erestadite produced by the method of the present invention has a composition formula of 5~7CaO・_2~ 4SiO2・₂ ~4CaSO4・_nH2O
An example of elestadite is a hexagonal columnar crystal, as shown in the attached photograph, and its asvect ratio is approximately 10, whereas that obtained by conventional synthesis methods is approximately 10. 2-4
It is twice as large, and the surface area, that is, the area of contact with the resin, is accordingly large. Therefore, the elestadite according to the present invention is very useful as a filler for thermoplastic and thermosetting resins, and has extremely large industrial value. EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Powdered quicklime, Blaine 4000cm ² /g silica sand, dihydrated plaster, and sodium pyrophosphate were mixed to the composition shown in Table 1, and 6 times the weight of water was added to give 150%
The autoclave reaction was carried out at ℃ for 24 hours. The aspect ratios of the obtained crystals were observed using a scanning electron microscope, and the values are shown in Table 1 as No. 1 to No. 5.

[Table] Example 2 The same operations as in Example 1 were performed using the raw materials prepared according to the types and compositions shown in Table 2, and the results are shown in Table 2 as Nos. 6 to 9. The silica gel had a brane weight of 2500 cm ² /g, and the amount of sodium pyrophosphate added was 1.0% by weight.

【table】

[Table] Example 3 Using the raw materials prepared in Example 1, adding the phosphoric acid-containing substances shown in Table 3 (each amount added was 1% by weight) and carrying out the same operation as in Example 1, the obtained The aspect ratios of the crystals are shown in Table 3 as No. 10 to No. 13.

【table】 [Brief explanation of the drawing]

The attached photograph is a scanning electron micrograph showing the crystal structure of one example of estadite synthesized according to the present invention.

Claims (1)

[Claims] 1. In a method for synthesizing elestadite by hydrothermal reaction of a mixed raw material containing a calcareous raw material, a silicate raw material, and gypsum, 0.1 to 5.0% by weight of a phosphoric acid-containing substance is added to the mixed raw material during the hydrothermal reaction. Characteristic synthesis method of elestadite.