JPS5941938B2 - Method for improving flow value of gypsum slurry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of a gypsum slurry composition obtained by adding water to gypsum hemihydrate, which not only has particularly excellent workability but also provides a non-colored and high-strength cured product. It is an object of the present invention to provide a gypsum slurry composition.

Conventionally, gypsum has been used as an inorganic material for various purposes, and there are many products such as gypsum board, gypsum block, and gypsum plaster.Most of these products are made from hemihydrate gypsum, which is mixed with water. It is made from a slurry or plastic material with the addition of necessary fillers, additives, etc.

This slurry or plastic material usually begins to coagulate eventually with the evaporation of water, and further hardening progresses to form a cured body of the final product.

However, in order to obtain a desirable molded article from this slurry or plastic material, it is necessary to impart sufficient fluidity to the slurry or plastic material, and for this purpose, the amount of water mixed is usually increased.

However, when a large amount of water is mixed in, although the fluidity of the slurry or plastic material is improved, the strength of the cured product decreases, which is not preferable.

Therefore, in order to increase the strength of the cured product, methods such as mixing a water reducing agent such as calcium lignin sulfonate, etc., are used to maintain high fluidity and increase the strength of the cured product by reducing the amount of mixed water. However, these methods have the disadvantage that the cured product is likely to be colored due to the additives.

The present inventors have conducted various studies on the modification of gypsum products, and found that mixing silica sol into gypsum slurry significantly increases the flow value, but the setting time of gypsum slurry is shortened and the known The present invention was completed by discovering that the setting time can be delayed by further mixing a setting retarder.

An object of the present invention is to provide a gypsum slurry composition that has a high flow value and a delayed setting time, and which, after curing, forms a hardened gypsum body that is uncolored and has high strength.

The gypsum slurry composition of the present invention includes an aqueous slurry of gypsum hemihydrate, silica sol in an amount of 1 to 15% by weight as SiO□, and silica sol in an amount of 0.05 to 0.5% by weight, respectively, based on the gypsum hemihydrate in the slurry. It is characterized by containing a setting retarder.

The hemihydrate gypsum used in the present invention is a normal powdered hemihydrate gypsum obtained by firing hydric gypsum, and CaSO4.0.5
It has a composition of H2O.

In addition, the aqueous slurry of gypsum hemihydrate used in the present invention is
Although it is obtained by adding and mixing water to the above-mentioned gypsum hemihydrate, it may contain any other additives, fillers, etc. depending on the purpose as long as the purpose of the present invention is achieved.

The silica sol used in the present invention has a particle size of approximately 2 to 300 m.
Colloidal silica particles having an active silanol group on the surface are stably dispersed in water, a hydrophilic organic solvent, or a mixture thereof.

Examples of the silica sol used include acidic silica sol that does not substantially contain an alkali component and has a pH of about 2 to 6, alkaline silica sol stabilized with an alkali, and the like.

These silica sols use water, a hydrophilic organic solvent, or a mixture thereof as a dispersion medium and usually have a concentration of about 5 to 50% as SiO2.

Examples of hydrophilic organic solvents as dispersion media include methanol, ethanol, impropatol, acetone, methyl ethyl ketone, and the like.

The alkali-stabilized silica sol usually contains small amounts of alkali metal components, primary, secondary and tertiary amines,
When a water-soluble nitrogen-containing organic compound such as a quaternary ammonium hydroxide represents Li, Na, K or the ammonium cation group of the nitrogen-containing organic compound as M, 810
The molar ratio of 27M20 is 20 or more, preferably 50 to 100
A silica sol within a range of 0 is usually used.

Examples of the setting retarder used in the present invention include citric acid, oxalic acid, their sodium and potassium salts, and polysaccharides such as sucrose.

When the silica sol is added to an aqueous slurry of hemihydrate gypsum, it has the effect of improving the flow value of the slurry and also has the effect of increasing the strength of the hardened slurry. The amount of silica sol contained in the aqueous slurry of gypsum is S
A suitable amount is 1 to 15% by weight as iO2.

Although it can be used at 1% by weight or less, if it is 0.65% by weight or less it is not substantially effective in improving the flow value, and 15% by weight or less is not effective in improving the flow value.
Above this, the strength of the hardened gypsum body decreases.

It is preferably about 3 to 10% by weight.

Generally, the flow value increases with increasing amount of colloidal silica added.

However, if the content of the silica sol is increased to more than 3 as SiO2, the setting time of the gypsum hemihydrate slurry will be shortened, and the workability will be significantly reduced unless the work is completed in a short time.

When the setting retarder used in the present invention is added to the slurry containing gypsum hemihydrate and silica sol, the above-mentioned drawbacks are overcome, and the setting time of the slurry is delayed while the improvement effect due to the inclusion of silica sol is maintained5. act.

However, if the content is less than 0.05% by weight based on gypsum hemihydrate, the above effects will be poor, and if the content is more than 0.5% by weight, the strength of the cured product will decrease, which is not preferable.

Of course, if it is desired to significantly delay the setting time even if the strength of the cured product decreases, it may be added at a content higher than the above content.

The gypsum slurry composition of the present invention may include any other components in addition to the above-mentioned components, as long as the object of the present invention is achieved.
Fibrous reinforcements, aggregates, fillers, pigments, etc. may also be added.

The gypsum slurry of the present invention may be prepared by adding and mixing gypsum hemihydrate, water, silica sol, a setting retarder, etc. in any order, but the gypsum slurry may be prepared by adding silica sol and a setting retarder to mixed water in advance. The preferred method is to prepare a gypsum and mix it with gypsum hemihydrate.

When using silica sol, the dispersion medium can also be a component of the water added, so the amount of water to be added is determined by taking into account the dispersion medium from the silica sol.

According to the present invention, colloidal silica has the effect of increasing the flow value of the aqueous slurry of gypsum hemihydrate, so as long as it has sufficient workability and fluidity, it is possible to reduce the amount of water mixed in when preparing the slurry. Therefore, a hardened product with even higher strength can be obtained from a slurry of gypsum hemihydrate with a reduced amount of mixed water.

Furthermore, in applications where the cured product does not require particularly high strength, the amount of filler mixed can be increased as long as the slurry has sufficient workability and fluidity.

The effect that the cured product obtained by curing the slurry of the present invention has significantly higher strength than the cured product from a slurry that does not contain colloidal silica is due to the active silanol groups on the particle surface of colloidal silica. This is thought to be due to the fact that silica particles are involved in bonding between gypsum particles, and the voids between gypsum particles are filled with high-strength silica material, resulting in the formation of a composite material.

However, despite the existence of colloidal silica with such binding strength, it is surprising that an aqueous slurry of gypsum hemihydrate containing colloidal silica has a high flow value before curing. Although the complete theory behind this has not yet been determined, it is believed that colloidal silica dispersed in the slurry is present near the gypsum particles and acts as a lubricant before hardening.

Furthermore, the fact that the aqueous slurry of gypsum hemihydrate containing colloidal silica remains colorless even after curing is due to the fact that this slurry does not contain any colored organic substances, and the combination of gypsum and silica is not a colored substance. This is thought to be due to

The gypsum slurry composition of the present invention is extremely useful not only for construction purposes such as wall materials and board materials, but also for a wide variety of applications such as gypsum plasters, gypsum boards, and gypsum blocks.

Examples will be described below along with comparative examples, but the technical scope of the present invention is not limited thereto.

Comparative Example By adding 60 parts by weight of water to 100 parts by weight of gypsum hemihydrate, slurry of Arashi ■ was prepared.
, an aqueous silica sol with a S i 02 concentration of 30% by weight so that the total amount of water mixed is 60 parts by weight based on the gypsum hemihydrate, and 1.5% by weight as 5i02 and 3.0% by weight with respect to the gypsum hemihydrate.
Slurries of Arashi ① to ② were prepared by adding and mixing so that the weight % and 6.0 weight % were obtained.

Further, 0.1% by weight of gypsum hemihydrate was mixed with citric acid as a setting retardant to the slurry of step 5 above to obtain a slurry of Arashi 1.

Next, the setting time and flow value of these slurries were measured according to JISR5201 physical property testing method for cement, and the compressive strength and bending strength of the hardened product obtained by curing the slurry were measured according to the method of JISR5201. The results shown in Table 1 were obtained.

Example 1 Slurries of Boiled ■ and ■ were prepared by adding citric acid to the slurries of Comparative Example 5 and ■ and adding 0.1% by weight of gypsum hemihydrate. The physical properties of the slurry and the properties of the cured product were measured, and the results shown in Table 2 were obtained.

In both cases, citric acid has a setting retarding effect.

Furthermore, after immersing these cured bodies in water at room temperature for 24 hours, they were taken out and the wet compressive strength was measured.
Good results shown in the table were obtained.

Example 2 Slurries of Japanese cabbage ■ and ■ were prepared by adding and mixing sodium citrate as a setting retardant to the slurry of Comparative Example 5■ in the amount listed in Table 2 relative to gypsum hemihydrate. When the setting onset time, flow value and compressive strength were measured in the same manner as above, the results shown in Table 2 were obtained.

The results in the same table show that sodium citrate also has an effective setting retardation effect on slurries added with silica sol, and that an improved gypsum slurry with good workability can be obtained by adding it in combination with silica sol. .

Claims (1)

[Claims] 1. An aqueous slurry of gypsum hemihydrate contains silica sol in an amount of 1 to 15% by weight as SiO2 and a setting retarder in an amount of 0.05 to 0.5% by weight, respectively, based on the gypsum hemihydrate in the slurry. Characteristic gypsum slurry composition.