JPS643818B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a curing agent for alkali silicate salts. Alkaline silicates are widely used as binders, adhesives, surface treatment agents, etc. in the fields of paints, refractories, and building materials, and sodium silicate has long been used as a hardening agent. However, due to recent increased interest in environmental issues, it has become a problem that this sodium silicofluoride is a deleterious substance and that it generates fluorine gas when heated, and various curing agents have been investigated to replace it. It's here. The conditions required for an alkali silicate as a curing agent include curing speed, strength of the cured product, heat resistance, water resistance, acid resistance, little expansion and contraction of the cured product, and no migration of the binder. It is. By the way, what has been considered so far,
For example, condensed aluminum phosphate relatively satisfies these conditions, and is particularly suitable for organic acid ions, phosphate ions, solutions consisting of aluminum ions, or organic acids as seen in Japanese Patent Publication No. 57-7587. A dried suspension of one or more of phosphoric acid, metallic aluminum, aluminum oxide, and aluminum hydroxide, or a fired product of this dried product, exhibits excellent hardening properties. be. However, such curing agents require the use of expensive raw materials, drying of the solution or suspension, and further calcination of the dried product to obtain more favorable curing properties. However, it has to be quite expensive and cannot be used as a substitute for inexpensive hardening agents such as sodium silicofluoride. On the other hand, fusible phosphorus or calcined phosphorus are known as inexpensive hardening agents for water glass, but because they are fired at high temperatures, their reaction with alkali silicate salts is slow; It is not necessarily appropriate. Further, heavy superphosphate lime is also known as a hardening agent, but the hardening reaction is too fast and it is difficult to secure sufficient working time, so its use is naturally limited. Therefore, the present inventors have repeatedly searched and researched an inexpensive water glass hardening agent that can be substituted for sodium silicofluoride. As a result, the by-product phosphorous fertilizer, which is produced at low cost as a fertilizer, has been found to be a substitute for the condensed phosphates. In comparison, it was found that although the water resistance was slightly inferior, it exhibited considerably good curing characteristics, and the present invention was completed based on this finding. The by-product phosphorous used in the present invention is a by-product when refining a wet phosphoric acid solution, and is produced by adding soda ash and lime to the wet phosphoric acid solution to form a precipitate. It is obtained by adding a small amount of phosphoric acid solution to the precipitate, drying it, and pulverizing it. Regarding the composition of this by-product phosphorous fertilizer, CaHPO ₄ , Ca(H ₂ PO ₄ ) ₂ , Ca ₃
( _PO4 ) ₂ , _FePO4 , _AlPO4 , _{NaH2PO4 , CaF2} ,
It is estimated that Ca ₅ (PO ₄ ) F ₂ etc. are included. Although it is not clear how these compositions work with alkali silicate salts to harden water glass, the main compositions that perform the hardening action are CaHPO ₄ , Ca
(H ₂ PO ₄ ) ₂ , Ca ₃ (PO ₄ ) ₂ , and the other compositions are considered to have an auxiliary function for curing.
Of course, the conjugation function between these compositions cannot be ignored. The curing properties of the curing agent of the present invention are that when commercially available by-product phosphorus is used as it is, curing is slightly faster, but when used after washing with water, curing is slower. Therefore, the curing time can be adjusted by the degree of washing with water, and the curing time can also be adjusted by the amount added, as with a normal curing agent. Furthermore, the curing time can also be adjusted by pulverizing commercially available by-product phosphorus and adjusting its particle size. Generally, the finer the powder, the faster the curing time. The ratio of the curing agent of the present invention to the alkali silicate salt will be explained below using the case of refractories as an example. (Specific example) Waxite aggregate 100 with the particle size composition shown in Table 1 below
Liquid No. 3 water glass (SiO ₂ 28.6%, Na ₂ O 9.6
%) was added, and unwashed products and water-washed products of the curing agent of the present invention (particle size: 200 mesh pass) were added at the ratios shown in Table 2, and the curing time was measured. The results are shown in Table 2. Note that the water-washed product refers to a product that is mixed in batches with twice the amount of water for about 1 hour and dried separately.

【table】

[Table] This is the time taken until the specimen loses its fluidity when pressed with fingers.
As is clear from the above table and the above,
Since the curing time of the curing agent of the present invention differs depending on whether it is washed with water or not, it may be treated as appropriate depending on the application, but generally it is 30% by weight (or less) based on liquid No. 3 water glass. "%" indicates "weight%".)
If more than 4% is added, the strength of the cured product, film strength, or adhesive strength will be weakened, which is undesirable, and if it is less than 4%, a sufficient curing function cannot be achieved. As mentioned above, the curing agent of the present invention does not have sufficient water resistance when used alone. Therefore, as a result of further research in order to improve the water resistance, it was found that when this and boric acid were used together, the water resistance was significantly improved. The proportion of boric acid used in such cases varies depending on the desired water resistance, but is preferably 10% or less based on liquid No. 3 water glass. If it exceeds 10%, the reaction between the hardening agent and the water glass will be too rapid, making it impossible to ensure sufficient workability. The present invention will be further explained below with reference to Examples. Example 1 To 100 parts of waxite shown in Table 1, 20 parts of liquid No. 3 water glass, 8 parts of water, and 3 parts of by-product phosphorous fertilizer (200 mesh) were added, and the same phosphorous fertilizer was added to the same amount. 3 parts of the product, which had been washed with a large amount of water, separated using a centrifuge, and dried, and the remaining part were added in the same proportions as above, were kneaded separately and uniformly, and then mixed into 20 x 20 x Pour into 80mm mold and heat at 30℃ for 24 hours.
After a period of time, the mold was removed, and the strength of the cured product in bending and compression of the dough was measured, and the external appearance was observed. Also, for comparison, 3 each of calcined phosphorus fertilizer (200 mesh passes) and molten phosphorus fertilizer (200 mesh passes)
After kneading, pouring, and demolding each part separately in the same manner as in the above-mentioned examples of the present invention, the same measurements and observations were performed. The results are shown in Table 3.

[Table] Example 2 40 parts of silica powder for 100 parts of liquid No. 3 water glass,
A total of 15 parts of 10 parts of bentonite and Example 1 plus 15 parts of the phosphorous by-product of washing (this first invention example), 11 parts of the same phosphorous and 4 parts of boric acid powder,
The remaining ingredients were added in the same proportions as above (this second invention example), and each was kneaded uniformly separately, then painted with a trowel on a slate board, and a calcium silicate heat insulating board with an apparent specific gravity of 0.2 was adhered. I let it happen. 110 of these
After drying at °C, it was immersed in water for 8 days, the adhesion state was examined, and the weight loss of the dried product before and after immersion was measured. The results are shown in Table 4.

[Table] Example 3 10 parts of No. 3 water glass and 2 parts of unwashed by-product phosphorus used in Example 1 were added to 100 parts of natural No. 6 silica sand (first invention example), In addition, the same amount of water was added to the same phosphorus fertilizer, mixed in batches, and the same phosphorus fertilizer solids were separated to obtain 50 parts of wet cake (water content: 42
%) with 0.5 part of boric acid added, dried and pulverized to form a hardening agent of 2 parts, and the rest added in the same proportions as above (this second invention example), and then kneaded separately and uniformly. After that, put it in a 50φ x 150mm molding tube,
After five strokes with a rammer, the mold was demolded, placed in a thermostat at 30°C, and taken out at predetermined intervals, and the change in compressive strength of the molded product over time was measured. The results are shown in Table 5.

[Table] Example 4 20 parts of liquid No. 3 water glass and 4 parts of unwashed by-product phosphorus used in Example 1 were added to 50 parts of natural No. 6 silica sand and 50 parts of silica powder (300 mesh powder). (this first invention example), and of the above, in place of 4 parts of the same phosphorous fertilizer, 2 parts of the same phosphorous fertilizer and 2 parts of boric acid powder, a total of 4 parts, and the remaining The mixtures added in the same ratio (this second invention example) were poured into a 20 x 20 x 80 mm mold, and the shrinkage rate of each cured product was measured with a caliper after 24 hours had elapsed. Next, the cured product was heat-treated at 300° C. for 1 hour, and after the same treatment, it was immersed in 35% HCl at room temperature for 24 hours, and after drying, the bending strength and weight change rate were examined. The results are shown in Table 6.

【table】

Claims (1)

[Scope of Claims] 1. A curing agent for alkali silicate consisting of by-product phosphorus. 2 Hardening agent for alkali silicate salts consisting of by-product phosphorus and boric acid.