JPS5811369B2 - 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 gypsum such as phosphate gypsum has been produced, and effective ways to use these gypsum are being developed. These materials are equally desired today, and therefore various studies are being 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 filling material used for this has traditionally been as small as possible in diameter and with an aspect ratio (
It is well known that composite materials such as gypsum synthetic resins with larger length/diameter ratios have better properties.

On the other hand, when gypsum fibers are kneaded with other materials, the fibers naturally break, and it is clear that the longer the fiber length becomes, the stronger the tendency of such fibers to break.

Therefore, by increasing the aspect ratio of the gypsum fibers after kneading,
It is understood that in order to improve the properties of the obtained composite material such as gypsum fiber-synthetic resin, it is most preferable to predict the breakage of the fibers during kneading and to reduce the diameter of the fibers.

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

By the way, the method for obtaining acicular crystals or fibrous crystals of gypsum is disclosed in Japanese Patent Application Laid-Open No. 49-306, which has already been published.
There are various proposals including No. 26.

However, in these known methods, a trihydrate gypsum aqueous slurry is heated under pressure to form molded clay gypsum crystal fibers, but when the present inventors actually carried out the method,
The average diameter of the fibers thus obtained was all 3 microns or more, and it was confirmed that it was impossible to produce fibers smaller than this based on the prior art.

The present applicant has also conducted various studies to solve the problem of reducing the diameter of gypsum fibers, and first calcined trihydrate gypsum powder in a high-temperature gas stream to make calcined gypsum, and then stirred it in water. We have proposed a method for obtaining extremely thin gypsum fibers with an average diameter of 0.4 μm or less by mixing them to form an aqueous slurry of trihydrate gypsum, and then pressurizing and heating the slurry.

However, the method for producing the above-mentioned small-diameter gypsum fibers proposed by the present applicant requires special equipment because trihydrate gypsum is calcined in a high-temperature gas stream. This paper further researched a method for obtaining fine-diameter gypsum fibers from calcined gypsum that was calcined using ordinary firing equipment such as a flat pot or rotary kiln instead of a gas firing furnace.

As a result, the present inventors focused on the highly active soluble anhydrous gypsum in calcined gypsum, and increased its content to 40% by weight (hereinafter referred to as
It was discovered that α-type earth water gypsum crystal fibers with an extremely small diameter can be obtained by increasing the weight percentage to a value greater than or equal to % (% by weight).

That is, in this invention, Sansuimen gypsum powder is calcined to produce calcined gypsum containing 40% or more of soluble anhydride, hydrated with stirring in water to form an aqueous slurry of Sansuimen gypsum, and then the slurry is made into an aqueous slurry of Sansuimen gypsum. It is characterized by being heated under pressure to form α-type soil water gypsum crystal fibers.

This invention will be explained in detail below. Most of today's calcined gypsum is calcined to a flat surface, and some of it is calcined in rotary kilns, but calcined gypsum produced by either calcining method still contains a large amount of soluble anhydrous gypsum in the product. It has occurred.

Therefore, if this calcined gypsum is used as it is, its degree of activation will be too high, causing various problems.

For example, the pouring time is short and workability is poor, bubbles are generated during curing, and mechanical strength is also insufficient.

For this reason, all commercially available calcined gypsum is aged for a certain period of time after calcination, and this process appropriately hydrates the metastable soluble anhydrous gypsum to create stable hemihydrate gypsum and suppress the activity of calcined gypsum. .

Therefore, currently commercially available calcined stone contains almost no soluble anhydrous gypsum.

By the way, the present inventors focused on such highly active soluble anhydrous gypsum, and conducted research on reducing the diameter of gypsum fibers using calcined gypsum containing this as a raw material. It has been discovered that the diameter of gypsum fibers can be reduced by using the following methods.

That is, the present inventors hydrated calcined gypsum obtained by various calcining methods so as to have different soluble anhydride gypsum contents, and used this as an aqueous slurry of sanhydrite gypsum to obtain α-type earth water gypsum acicular crystal fibers. As a result, it was confirmed that as the content of soluble anhydrous gypsum in the calcined gypsum increases, the diameter of the obtained gypsum fibers becomes smaller.

As for the reason for this, through previous experiments, the inventor found that highly active calcined gypsum is highly soluble trihydric sulfur crystal,
In other words, it generates trihydric crystals with loose crystallinity, and as a result, generates a large number of fine crystal nuclei necessary to obtain small-diameter fibers, and the growth of these numerous nuclei generates needle-shaped crystals with a small diameter as a whole. It is presumed that this is a cause for concern.

Sansuimen gypsum, which is the raw material for baked gypsum in this invention, may be any of natural gypsum, chemically grown gypsum, and dehydrated gypsum.
There are no particular limitations.

The calcining method is not particularly limited either, and for example, any method such as a hot air dryer, rotary kiln, flat calcining, etc. can be used, but 40% or more of the trihydric gypsum must be soluble anhydrous gypsum.

The reason why the content of soluble anhydrous gypsum is set to 40% or more in this invention is that calcined gypsum with a content less than 40% has insufficient activity and gypsum fibers with the desired small diameter cannot be obtained.

In experiments conducted by the present inventor, gypsum fibers obtained by hydrating calcined stone containing less than 40% of soluble anhydrite had an average diameter of more than 0.4μ, whereas soluble anhydrite The gypsum fibers obtained by hydrating calcined gypsum with a content of 40% or more had an average diameter of 14μ or less, and some had an average diameter of 0.1μ.

Note that the aspect ratios at this time were all in the range of 50 to 150.

For this reason, it is essential that the calcined gypsum used in the present invention contains 40% or more of soluble anhydrite, and the higher the content, the thinner the fibers can be obtained.

In addition, if trihydric gypsum coexists in calcined gypsum, the trihydric gypsum obtained by the hydration reaction will become coarse, and if insoluble anhydrous gypsum coexists in this, it will remain as an unreacted material during hydration. Care must be taken to reduce the content of gypsum and insoluble anhydrous gypsum.

Furthermore, if there are aggregates or granules in the calcined gypsum after calcination, they may be crushed if necessary, but in this case, an aqueous phase of the soluble anhydrous gypsum is formed and the content of soluble anhydrous gypsum is reduced. It must be ensured that it does not fall below 40%.

After calcination of Sansuimenko, it is necessary to hydrate it as soon as possible, and when storing it, it is preferable to keep it in a sealed state.

The calcined surface 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 industrial water and other water can be widely used. I can do it.

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 generated dihydrate gypsum will aggregate, making it impossible to obtain semi-aqueous acicular crystals with a small diameter.

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

The temperature at this time is approximately 120 to 150℃ according to the usual method.
After that, the reaction was completed as -tan80~1
After cooling to 00°C, it is quickly passed through the mouth and then dried at 80°C or higher to finally obtain the gypsum needle-like crystal fine fiber of the present invention.

Since the α-type clay gypsum crystal fibers thus produced are crystallographically the same as 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.

The gypsum fibers obtained by the above method have an average diameter of 0.4μ or less, and in some cases even reach 0.1μ, and therefore, these fine fibers can be used, for example, as reinforcing materials and fillers for plastics. In this case, the physical properties of the composite material will be further improved.

Note that Figure 1 shows the relationship between the soluble anhydride content in the raw calcined gypsum of Examples 1 to 3 described later and the diameter of the obtained fibers, and Figure 2 shows the relationship between Examples 1 to 3. α being
Hemihydrate gypsum fibers and α-hemihydrate gypsum fibers with an average diameter of 0.6 to 3μ obtained using dihydrate gypsum as starting materials are fired for 1 hour to obtain insoluble anhydrous gypsum fibers, and the insoluble anhydrous gypsum fibers are made from polypropylene. It was added to the resin at a ratio of 40% by weight, kneaded, and then a test piece was prepared in a conventional manner using an injection molding machine and a tensile strength test was performed. The relationship between the average diameter of the gypsum fibers and the tensile strength. This is what is shown.

This invention will be explained in detail below.

Example 1 Flue gas desulfurization dihydrate gypsum with 8% attached moisture and 10% residue on a 149μ particle size sieve was air-dried for 5 days and nights in a 40°C dryer, and the gas temperature was 1.
The mixture was calcined in a hot air dryer at 30° C. for 1 to 16 hours to obtain two types of calcined gypsum containing 10% and 25% of soluble anhydrous gypsum of 40-b as shown in Table 1.

Separately, a portion of calcined gypsum containing 92% soluble anhydrous gypsum was exposed to air at a temperature of 25°C and a humidity of 60 to 70% for 2 hours.
After aging for 4 hours, calcined gypsum containing 1% soluble anhydrous gypsum was obtained.

The eight types of calcined gypsum obtained here were hydrated with stirring to a slurry concentration of 5%, and then 13.
The mixture was pressurized and heated to 5°C to obtain α-type soil water gypsum fibers.

The average diameters of these fibers were as follows.

Example 2 Commercially available calcined gypsum products made from natural trihydrate gypsum and dehydrated dihydrate gypsum were used as comparative examples. A flat calcined product made from water gypsum was calcined in a hot dryer at a gas temperature of 180° C. for 3 hours to obtain calcined gypsum.

Using the calcined gypsum obtained here, α-type earth water gypsum fibers were obtained in the same manner as in Example 1.

The average diameter of this fiber was measured and was as shown in Table 2.

Example 3 Exhausted gypsum with an attached moisture content of 8% and a particle size of 149 μm or less was calcined in a rotary kiln to obtain three types of calcined gypsum shown in Table 3.

Using the calcined gypsum obtained here, α-type earth water gypsum fibers were obtained in the same manner as in Example 1.

The average diameter of the gypsum fibers was measured and was as shown in Table 3.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the soluble anhydride gypsum content in calcined gypsum obtained using various firing apparatuses and gypsum fibers. FIG. 2 is a diagram showing the relationship between gypsum fiber diameter and tensile strength in a polypropylene molded product using gypsum fiber as a filler.

Claims (1)

[Claims] 1 Calcinate dihydrate gypsum powder to obtain 40% soluble anhydrous gypsum.
Calcined gypsum containing at least % by weight is hydrated with stirring in water to form an aqueous slurry of trihydrate gypsum, and then
A method for producing small diameter gypsum needle-like crystal fibers, which comprises pressurizing and heating the slurry to obtain α-type earth water gypsum crystal fibers.