JPS597680B2 - Method for manufacturing gypsum needle-like crystal small diameter fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular gypsum crystal fibers, and particularly to a method for producing gypsum fibers whose diameter is extremely small.

Since gypsum acicular crystal fibers have a needle-like or fibrous form, it has recently been expected to be used as a reinforcing material for synthetic resins, a reinforcing material for paint lacquer, etc., and a material for improving durability.

In other words, in recent years, with the regulation of exhaust gas from thermal power plants, a large amount of so-called flue gas desulfurization gypsum has been produced as a by-product, and in addition to this, chemical by-product gypsum such as phosphate gypsum has been produced, and there is a need to develop methods for the effective use of these gypsum. is equally desired today.

For this reason, various studies have recently been conducted on the use of these gypsums in the form of needle-like crystals as reinforcing materials and fillers for plastics, etc., as described above.

However, in such cases, the gypsum filler used in this case has traditionally been made to have as small a diameter as possible and a large aspect ratio (length/diameter ratio), since the characteristics as a composite material are better. It is well known that

Furthermore, when gypsum fibers are kneaded with other materials, the fibers naturally break, but this tendency becomes stronger as the fibers become longer.

Therefore, the aspect ratio of the fibers after kneading is clearly larger for small diameter short fibers than for large diameter long fibers.

For this reason, in the production of gypsum fibers used as fillers, reducing the diameter of the fibers has become a major technical issue today.

By the way, the method for obtaining acicular crystals or fibrous crystals of gypsum is already disclosed in the recently published Japanese Patent Application Laid-Open No. 49-3.
There are various proposals including No. 0626, but when the present inventors actually carried out these known methods, the average diameter of the obtained fibers was all 3μ or more, and those smaller than this were It has been confirmed that this is not possible based on the conventional technology.

Furthermore, the present applicant had previously proposed a method capable of producing even gypsum needle-like crystal fibers with an extremely small diameter of 0.5 to 1μ.
As a result of intensive research to obtain needle-like crystal fibers with even smaller diameters, the present invention has now been completed.

That is, in this invention, trihydrate gypsum powder is calcined in a high-temperature gas stream to produce calcined gypsum, which is hydrated while stirring in water to form an aqueous slurry of trihydrate gypsum, and then the aqueous slurry is heated under pressure. The method is characterized in that α-type hemihydrate gypsum crystal fibers are obtained.

The details of this invention will be explained below. Various methods have been known to obtain calcined gypsum by calcining Sansui gypsum, and it is generally well known that the properties of calcined gypsum produced depending on the calcining method vary.

Therefore, the present inventors focused on the properties of raw calcined gypsum while conducting intensive research to reduce the diameter of gypsum needle crystals.

That is, the present inventors discovered that among various conventionally known calcination methods, gypsum calcined by the so-called air flow calcination method, in which the gypsum is calcined in a high-temperature gas stream, has a low water vapor partial pressure in the hot gas. This study focuses on the fact that as the crystal structure becomes finer, its crystal structure becomes irregular, and as a result, crystal growth is suppressed and the crystal is highly reactive.

In fact, other kettles, rotary kilns, fluidized beds, etc. are used for calcining, or hot air drying ovens are used.
Furthermore, we performed X-ray diffraction under the same conditions on various types of calcined gypsum, such as those obtained using airflow calcination.
When the half-value width at 5.7 3 degrees was measured, the half-value width of the calcined gypsum obtained by the airflow calcination was 0.3.
In contrast, the half-value width of calcined gypsum obtained by methods other than airflow calcination was all 0. 2 5
degree or less, and it was found that the crystals of calcined gypsum produced by the airflow calcining method had an irregular structure.

For these reasons, the present inventors actually obtained gypsum needle crystals as an aqueous slurry using calcined gypsum obtained by the above-mentioned so-called air flow calcination method, in which calcination is performed in a high-temperature gas stream, and found that the average of the fibers was It has been confirmed that the diameter can be reduced to 0.4μ or less, and in some cases to an average of about 0.1μ.

This fact is based on the knowledge of the present inventors that, by obtaining calcined gypsum by the airflow calcining method, the crystallinity of the trihydrate gypsum obtained thereby also becomes loose, and therefore its dissolution rate becomes slow. During the crystallization process of α hemihydrate gypsum, the degree of supersaturation of trihydrate gypsum becomes extremely large, and a large number of fine crystal nuclei are generated here, making the final hemihydrate gypsum needle crystal fibers fine. It is assumed that the diameter will increase.

Since the raw material Sansui gypsum used here is air-flow calcined, its particle size must be small so that it can be calcined in an extremely short time. If so, it is better to keep it below 1rrLTL.

When using dehydrated gypsum, phosphate gypsum, etc. as raw materials, these usually contain 5 to 30% of attached water, but any of these can be used as is.

However, if the amount of adhering water is 30% or more, the stability of the device and the quality of the calcined gypsum will be affected, so the adhering water must be removed by drying before calcining.

The temperature of the hot gas used in the present invention may be any temperature necessary to air-flow calcining most of the trihydrate gypsum;
A range of from 1100°C to 1100°C is preferred.

These gas temperatures are naturally varied depending on the particle size of the raw material trihydrate gypsum and the proportion of attached moisture.

Increasing the flow rate of the gas flow increases the heat transfer rate between the gas and the particles, which shortens the calcination time, but if it becomes higher than necessary, the trihydrate gypsum will not be sufficiently calcined. This is actually not desirable since it will be collected.

According to experiments, a suitable flow rate is 10 to 150 m/s.
It is ec.

Furthermore, the shorter the firing time, the greater the degree of structural irregularity of the crystals, and the more reactive calcined gypsum can be obtained. is sufficient.

When the calcined gypsum produced in this way coexists with trihydrate gypsum, the trihydrate gypsum obtained by the hydration reaction becomes coarse.
Furthermore, if type (2) type anhydrous gypsum coexists, it will remain as an unreacted product during hydration, so the total of hemihydrate gypsum and soluble anhydrous gypsum should exceed 90% of the total.

Various types of calcining equipment are possible, but any type of calcining equipment is suitable as long as the trihydrate gypsum is dispersed and conveyed in a hot gas stream, and most of it is calcined as calcined gypsum. May be used.

The calcined gypsum obtained as described above is then dispersed in water to make an aqueous slurry, but the water used here is not limited to distilled water, and a wide variety of industrial water and other water can be used. .

The temperature of the slurry during hydration is kept at 60'C or lower and stirred according to a conventional method.

The slurry concentration is usually 35% or less, preferably 20% or less.

If the slurry concentration exceeds 35%, not only will stirring become difficult, but the produced trihydrate gypsum will aggregate, making it impossible to obtain hemihydrate gypsum needle crystals with a small diameter.

Thereafter, this is placed in an autoclave, and is pressurized and heated to produce α-type hemihydrate gypsum crystal fiber.

The temperature at this time is approximately 120 to 150 °C to complete the reaction, and then it is cooled to -80 to 100 °C, quickly passed through the mouth, and dried at 80 °C or higher, and finally A gypsum acicular crystal fine fiber according to the present invention is obtained.

Since the α-type hemihydrate gypsum crystal fibers thus produced are crystallographically identical to gypsum needle crystals obtained by conventionally known methods, they are then heated to 200 to 1100°C, preferably 600 to 900°C. Then, insoluble anhydrous gypsum fibers are obtained.

In addition, chemical properties such as stability and water resistance can be imparted by surface-treating this with a polymeric substance such as casein or a salt such as citric acid or silicate.

As mentioned above, the gypsum fibers obtained by the present invention can have an average diameter of 0.4μ or less, and in some cases even 0.1μ or less, so if they are used as reinforcing materials or fillers for plastics, etc. A high aspect ratio was obtained even after kneading, and the applications of gypsum fibers were further expanded.

Example 1 Flue gas desulfurized trihydrate gypsum with attached water content of 8% and particle size of 149μ or less was heated using the air flow calcining device shown in the figure until the total content of hemihydrate gypsum and soluble anhydrous gypsum reached 95% or more. Calcined.

In addition, in the figure, the raw material dihydrate gypsum supplied from the screw 1 quantitative feeder 2 is dispersed and introduced into the turbulent jet pipe 4 and the vortex chamber 5, and is carried by air current, passes through the duct 6, and is collected by the cyclone 7. .

Hot gas is supplied from hot air stove 3, and the gas temperature is 800°C.
1 gas flow velocity is 80 m/se at turbulent jet tube 40 section
c, vortex chamber 5 at 25 m/sec, drying and calcination time approximately 0.5 sec.

In addition, the inlet gas temperature of cyclone 7 at this time is 280
It was ℃.

The exhaust gas emitted by the cyclone 7 is sucked by a fan 8, passes through a dust collector 9, and is discharged from the stack 10.

The calcined gypsum obtained here was hydrated to a slurry concentration of 5%, stirred, and then mixed in an autoclave for 1. It was pressurized and heated to 35°C to obtain α-type hemihydrate gypsum fibers.

The average diameter and average length of the obtained gypsum fibers were measured and were as shown in the following table.

In addition, in order to compare the same trisui gypsum as above with different calcination methods, we used a conventional flat pot and rotary kiln, and as another example, a hot air dryer. However, in this case, the layer thickness 10mm, gas temperature 180℃, gas flow rate 5m/sec
, drying and calcining for 2 hours to obtain calcined gypsum, and using the calcined gypsum thus obtained, α
A molded hemihydrate gypsum was made, and the average diameter and average length of the gypsum fibers were measured and compared in the same table.

Example 2 The temperature of the hot gas supplied from the hot stove 3 was 700°C, the gas flow rate was 90 m/sec at the turbulent jet pipe 40 section, 28 m/sec at the swirl chamber 5, and the gas temperature at the inlet of the cyclone 7 was 240°. As C, other conditions were the same as in Example 1, and flue gas desulfurized dihydrate gypsum with an attached moisture content of 9.5% and a particle size of 149 μm or less was calcined to obtain calcined gypsum.

This calcined gypsum was subjected to the same method as in Example 1 to obtain α-type hemihydrate gypsum fibers.

The average diameter of the obtained gypsum fibers was 0.2μ, and the average length was 2
It was 5μ.

[Brief explanation of drawings]

The figure shows an airflow calcining apparatus used in Examples 1 and 2 of the present invention. 3...Hot air generator, 4...Turbulent jet tube, 5...Swirl chamber, 7...Cyclone.

Claims (1)

[Claims] 1. Calcined gypsum dihydrate powder in a high-temperature glass air stream to obtain calcined gypsum, which is hydrated and cured in water while stirring to form an aqueous slurry of gypsum dihydrate.Then, the aqueous slurry is heated under pressure to form α-type gypsum. A method for producing a small diameter gypsum acicular crystal fiber, characterized by obtaining a hemihydrate gypsum crystal fiber.