JPS5812235B2 - Setsukou Shinjiyouketsuyouseni no Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing gypsum needle fibers, or whiskers.

Since whiskers are single crystals with very few lattice defects, they have extremely high strength compared to normal crystals.

For this reason, it has recently attracted particular attention as a new industrial material, and research and development of methods for its production and use are being actively conducted.

Things currently reported as whiskers include, for example,
Metals such as iron, copper, and tungsten, silicon carbide,
Examples include inorganic compounds such as alumina and silicon nitride.

Although these materials have excellent properties, they are expensive due to the manufacturing process, so their range of application is limited for use as general industrial materials.

For this reason, gypsum needle crystal fiber has recently attracted attention as an inexpensive needle crystal fiber.
A method for obtaining hemihydrate acicular crystal fibers by heating to a temperature of 150°C, and heating the obtained hemihydrate acicular crystal fibers until the hemihydrate gypsum is converted into soluble anhydrite or insoluble anhydrite, A method for obtaining soluble anhydrite acicular crystal fibers or insoluble anhydrite acicular crystal fibers is disclosed in Japanese Patent Application Laid-open No. 1973-
This is proposed in Publication No. 30626.

When the present inventors manufactured gypsum needle-like crystal fibers based on this proposed method, it was confirmed that the diameters of the obtained gypsum needle-like crystal fibers were mostly 3μ or more.

By the way, when using needle crystal fibers as reinforcing materials,
The reinforcing effect is related to the aspect ratio (length/diameter ratio), but as needle crystal fibers, gypsum needle crystal fibers with low strength tend to break when mixed with other materials; This trend is remarkable.

As a result, the aspect ratio of the fiber after crosstalk becomes smaller in the case of a long fiber with a large diameter than in the case of a short fiber with a small diameter.

Therefore, the resulting composite material exhibits better properties in terms of tensile strength, tensile modulus, bending strength, and bending modulus.

In view of the above points, the inventors of the present invention
Method No. 6 also has a small diameter (diameter of 2μ or less, especially 1μ or less)
As a result of various studies on the method of obtaining acicular gypsum crystal fibers, it was found that gypsum powder was hydrated while stirring in water, and the diameter was 1.
Dihydrate blue powder is added as necessary to an aqueous slurry in which extremely fine dihydrate gypsum of 5μ or less, preferably 5μ or less is dispersed, and the concentration of the aqueous slurry is adjusted to 35% or less,
It was discovered that when heated, gypsum needle crystal fibers with the desired small diameter were formed.

Next, representative examples among various experimental examples conducted by the present inventors will be described.

54/20 500g of calcined gypsum powder with 2% residue on 149μ sieve
When the mixture was added to water at 0.degree. C. and stirred, an aqueous slurry with a concentration of 10% in which fine dihydrate gypsum with an average diameter of 2 .mu.m and an average length of 15 .mu.m was dispersed was obtained.

One liter of this slurry was dispersed, placed in an autoclave equipped with a stirring device, and heated at 130° C. for 10 minutes while stirring at a speed of 120 rpm to produce gypsum hemihydrate needle crystal fibers.

Next, water vapor was released, the pressure inside the autoclave was lowered to normal pressure, and the slurry containing gypsum hemihydrate needles was taken out, filtered through hot water, washed with ethyl alcohol, and dried to give a diameter of 0.5 μm. Hemihydrate gypsum needle crystal fiber (
A) of the drawing was obtained.

In addition, the concentration of the fine dihydrate gypsum made earlier is 10%.
To the aqueous slurry, dihydrate blue powder with a 2% residue on a 149μ sieve was divided into 25, 50, 7
5 and 90%, respectively, and water was added to make 1 liter of a 10% strength aqueous slurry for each batch.

This slurry and 10% of dihydrate gypsum powder made separately
When acicular crystal fibers of gypsum hemihydrate were made from the slurry in the same manner as described above, fibers with diameters shown in B, C, D, E, and F in the drawings were obtained.

From the drawing, if less than 95% (weight) of dihydrate blue powder is added to the calcined gypsum powder in the raw material slurry, hemihydrate gypsum needle-shaped crystal fibers with a diameter of 2μ or less are obtained; It can be seen that as the amount of dihydrate blue powder added decreases, gypsum hemihydrate needle-like crystal fibers with smaller diameters can be obtained.

The aspect ratio of the obtained fiber is the largest at 90 when the dihydrate blue powder is 100%, and gradually decreases as the trihydrate content decreases, and when the dihydrate blue powder is 100%, it gradually becomes smaller.
% was 70.

In the above experimental example, a slurry adjusted to a concentration of 10% was heated, but similar results can be obtained when the concentration is adjusted to 35% or less.

However, if the concentration exceeds 35%, stirring becomes difficult, the aspect ratio of the resulting fibers becomes small, and non-fiber-like shapes coexist due to insufficient stirring.

In addition, when the raw material slurry concentration is low, it is possible to obtain a product with a small diameter and a long length, which is convenient in terms of quality, but from an industrial perspective, it is uneconomical if the concentration is low, so 0.2% or more It is preferable to

The reason why a small-diameter hemihydrate gypsum needle-like crystal fiber is obtained is not clear, but it is thought that the rate of dissolution of trihydrate gypsum in water in the raw material slurry has an effect.

That is, the conversion of dihydrate to hemihydrate gypsum in a dihydrate monohydrate system takes advantage of the difference in solubility in water between dihydrate gypsum and hemihydrate gypsum to dissolve the solid phase dihydrate gypsum. It is recrystallized as gypsum hemihydrate.

However, in this case, as in the experimental example, the dihydrate gypsum produced by stirring and hydrating calcined gypsum powder in water is extremely fine.

Therefore, the dissolution rate reaches saturation earlier in the heating process of the slurry than when dihydrate blue powder is simply made into an aqueous slurry, so it is thought that an extremely large number of new crystal nuclei of gypsum hemihydrate are generated. It is surmised that because this large number of new crystal nuclei suppresses crystal growth, needle-like hemihydrate crystal fibers with a small diameter can be obtained.

Furthermore, even if a certain amount of trihydrate gypsum powder is added to an aqueous slurry in which fine dihydrate gypsum is dispersed by stirring calcined gypsum powder in water and hydrating it, the new hemihydrate gypsum necessary for diameter reduction will not be produced. Since the number of crystal nuclei hardly changes, it is thought that a small-diameter hemihydrate gypsum needle-like crystal fiber can be obtained.

The present invention is based on the above knowledge, and is made by hydrating calcined gypsum powder in water while stirring it to form an aqueous slurry in which extremely fine dihydrate gypsum is dispersed, and adding trihydrate gypsum powder as necessary. In addition, the concentration of the aqueous slurry is adjusted to 35% or less, and heated under pressure while stirring until gypsum hemihydrate acicular crystal fibers are obtained, to obtain a slurry containing gypsum hemihydrate acicular crystals, hereinafter a conventional method. This is a method for producing a gypsum needle-like crystal fiber, characterized by obtaining a gypsum needle-like crystal fiber.

In the present invention, the calcined gypsum powder has a content of 10% or less on a 210μ sieve, preferably 10% or less on a 149μ sieve, and is hydrated with stirring in water to obtain extremely fine trihydrate. First, a dispersed raw material aqueous slurry is prepared, and the slurry concentration at this time is 35% or less, preferably 20% or less.

The reason for this concentration limitation is that if it exceeds 35%, stirring becomes difficult and the fine dihydrate gypsum produced will aggregate, making it difficult to obtain acicular crystal fibers of hemihydrate gypsum with a small diameter.

Furthermore, the lower the liquid temperature of the raw material aqueous slurry, the more fine dihydrate gypsum is produced, but a temperature around room temperature is usually used.

Note that if the liquid temperature exceeds 60°C, only large crystals of the dihydrate gypsum produced can be obtained, and therefore it is not possible to produce the small-diameter hemihydrate gypsum needle crystal fiber that is the object of the present invention. When the calcined gypsum powder is partially hydrated at 60℃ or below,
Even if the liquid temperature is raised to 60 to 80°C, the desired gypsum hemihydrate needle-like crystal fibers can be obtained.

At this time, as mentioned above, even if dihydrate blue powder is added to the aqueous slurry in which calcined gypsum powder is stirred and hydrated in water and fine dihydrate gypsum is dispersed, the amount of water required for diameter reduction is reduced. Since the number of new crystal nuclei of gypsum hardly changes, adding dihydrate blue powder is advantageous because it can reduce the cost of making calcined gypsum powder.

Therefore, in the present invention, dihydrate blue powder can be added to the aqueous slurry in which the fine dihydrate gypsum is dispersed, if necessary.

As mentioned above, when adding dihydrate blue powder to the aqueous slurry in which fine dihydrate gypsum is dispersed, it is preferably 95% by weight or less, preferably 90% by weight based on the calcined gypsum powder as the starting material.
Thereafter, more preferably 50% by weight or less of trihydrate gypsum powder is added.

The dihydrate blue powder at this time had a residue of 10
%, preferably 149μ sieve residue 10% or less.

Finally, the aqueous slurry adjusted to a concentration of 35% or less is heated under pressure while stirring to a temperature at which gypsum dihydrate converts to gypsum hemihydrate. It takes an extremely long time to make crystal fibers, and if the temperature exceeds 160°C, the hemihydrate gypsum needle crystal fibers will dehydrate and become non-crystalline anhydrite.
Preferably, heating is performed at a temperature of 10 to 160°C.

At this time, the pressure was applied by increasing the heating temperature of the aqueous slurry to 110°C.
The pressure necessary to bring the temperature to ~160°C, 110~16
The water vapor pressure at 0°C is 1.4 to 6.1 atm when the gas in the reaction tank (autoclave) is only water vapor.

The slurry containing gypsum hemihydrate acicular crystals obtained as described above is dried while being maintained at a temperature of 75 to 120°C, thereby forming gypsum hemihydrate acicular crystals as a product.

The hemihydrate gypsum acicular crystal fibers made through the process described above can be used as they are as reinforcing materials or fillers for various materials, but there is a risk that they will become hydrated and become non-assembled when they come into contact with moisture. Therefore, it is preferable to use the method described below to stabilize the product.

■ Colloids or high molecular weight substances such as a, gelatin, decomposed keratin, casein, hexametaphosphate, citrate,
After adding low molecular weight substances such as gluconate and acetate as water retarders, the gypsum hemihydrate needles were collected, or b. from the slurry containing the gypsum hemihydrate needles. Stabilize the surface of the gypsum hemihydrate by soaking or spraying the acicular crystal fiber in a liquid containing the water retardant or higher fatty acid, paraffin, or other hydrophobic substance mentioned in a above, and then drying it (in addition, According to method 1a, there is also the effect of lowering the temperature during drying of the slurry containing gypsum hemihydrate needle crystals to less than 75°C).

■ Hemihydrate acicular crystal fibers or a slurry containing the fibers are heated as they are, or after reducing the moisture content, heated at a temperature of 130 to 200°C, preferably 150 to 200°C, at which the hemihydrate gypsum converts to soluble anhydrite. It is called gypsum needle crystal.

■ Hemihydrate acicular crystal fibers or a slurry containing the fibers are heated as they are, or after reducing the water content, heated at a temperature of 200 to 1100°C, preferably 600 to 900°C, at which the hemihydrate gypsum converts to insoluble anhydrite. It is called gypsum needle crystal.

Among the anhydrite acicular crystal fibers obtained by the above methods (1) and (2), the soluble anhydrite acicular crystal fibers obtained by the method (2), in particular, can be further treated with a protective film similar to the method (2)-b. It is not affected by moisture at all.

The gypsum acicular crystal fibers of the present invention can be produced by a batch method, but since the fluidity of the produced fibers is greater than in the conventional method using only dihydrate gypsum as a starting material, it can be produced smoothly by a continuous method. can be manufactured.

The acicular crystal fibers of gypsum hemihydrate, soluble anhydrite, and insoluble anhydrite obtained by the method of the present invention have a small diameter of 2μ or less, so they can be mixed as reinforcing materials or fillers for plastics, etc. When used, a high aspect ratio is maintained even after mixing, resulting in a composite material with excellent physical properties.

According to the method of the present invention, gypsum fibers with a small diameter of 2μ or less can be manufactured, but it goes without saying that gypsum fibers with a larger diameter can be obtained by slightly changing the manufacturing conditions.

The present invention will be described below with reference to Examples.

Example 1 10% (by weight) of 149μ in water at 25°C while stirring
Calcined gypsum powder with a sieve residue of 2% was added and stirred for 30 minutes for hydration to produce a slurry in which fine trihydrate gypsum with an average diameter of 2 μm and an average length of 15 μm was dispersed.

This slurry was sent to a reaction tank, heated at 130°C (approximately 2.7 atm) for 5 minutes while stirring at 120 rpm, and then the water vapor was released and the liquid temperature in the reaction tank was cooled to 105°C. Then, the slurry was discharged from the bottom of the tank.

After filtering the slurry and washing with methyl alcohol,
When dried in a dryer maintained at a temperature of 10° C., semi-gypsum needle crystal fibers with an average diameter of 0.6 μm and an average length of 40 μm were obtained.

For comparison, a 20% aqueous slurry was made of trihydrate gypsum powder with a 2% residue on a 149μ sieve, and hemihydrate gypsum needle-like crystal fibers made in the same manner as described above had an average diameter of 3μ and an average diameter of 3μ. The length was 300μ.

The hemihydrate acicular crystal fibers produced by the method of the present invention and the comparative method were each heated at 700°C for 1 hour to form insoluble anhydrite acicular crystal fibers, which were added at 30% as a filler for vinyl chloride resin. However, the physical properties of the obtained vinyl chloride products (inventive product/comparative product) were as follows.
, the product of the present invention exhibits an excellent reinforcing effect.

In addition, the aspect ratio of the fiber after crosstalk is 2 for the product of this invention.
0, and the comparative product was 7.

Inventive product/Comparative product Specific tensile strength 1.09 Bending strength 1,18 Tensile modulus 1.42 Bending modulus 1,29 Example 2 Slurry in which fine dihydrate gypsum made by the method of Example 1 was dispersed The same amount of gypsum trihydrate powder with a 149μ sieve residue of 2% as the calcined gypsum powder was added to adjust the aqueous slurry to a concentration of 20%.

This slurry adjusted to 20% was fed into a reaction tank in the same manner as in Example 1, heated while stirring, then cooled, and the slurry was discharged from the bottom of the tank.

This slurry was filtered, washed, and dried to obtain hemihydrate gypsum needle crystal fibers with an average diameter of 0.7 μm and an average length of 50 μm.

Example 3 After filtering the hemihydrate acicular crystal slurry in the same manner as in Example 1, it was dried and calcined with hot air at 180°C in a hot air oven, resulting in an average diameter of 0.6μ and an average length of 40μ. Soluble anhydrite acicular crystal fibers were obtained.

Example 4 After filtering the hemihydrate acicular crystal slurry obtained in the same manner as in Example 1, it was dried and calcined with hot air at 800°C in a hot air oven, resulting in an average diameter of 0.6μ and an average length. A 40 μm insoluble anhydrite needle crystal fiber was obtained.

[Brief explanation of the drawing]

The drawing is a chart showing the results of experimental examples of the present invention.

Claims (1)

[Claims] 1. Hydrate calcined gypsum powder in water while stirring to form an aqueous slurry in which extremely fine dihydrate gypsum is dispersed, and add dihydrate blue powder as necessary to bring the concentration of the aqueous slurry to 35%.
% or less and heated under pressure while stirring until gypsum hemihydrate acicular crystals are obtained to obtain a slurry containing gypsum hemihydrate acicular crystals. A method for producing a gypsum needle-like crystal fiber.