JPH06104571B2 - Method for producing calcium carbonate crystals - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing calcium carbonate crystals, and more specifically, a method for producing spherical calcium carbonate crystals useful as a filler or pigment for paper or paints. Regarding

(Prior Art) Conventionally, calcium carbonate, especially precipitated calcium carbonate, has been used as a filler for rubber, plastics, paper, paint,
It is used as a pigment for inks and as an additive for pharmaceuticals, cosmetics, foods, agricultural chemicals, etc.

Calcium carbonate includes hexagonal calcite-type crystals, orthorhombic aragonite-type crystals, and pseudo-hexagonal vaterite-type crystals as polymorphs. Cubic or spindle-shaped calcite-type crystals or needle-shaped aragonite-type crystals are mostly used for such applications. Although these calcium carbonates have the characteristics of high purity and relatively uniform particle size distribution, on the other hand, they have a low bulk specific gravity, and because they have a spindle shape, a cubic shape, etc., they are dispersible when made into a slurry. However, it is not always sufficient and it is difficult to obtain a high-concentration slurry.

On the other hand, in the case of spherical calcium carbonate crystals, for example, vaterite-type spherical calcium carbonate crystals, from the morphological characteristics, the dispersibility of the slurry is improved and the closest packing can be easily taken. It is expected that high concentration can be achieved. When it is used as a pigment or filler for paper, paint, rubber, or plastics, it also has the effects of improving coatability and filling properties, and thus the glossiness, whiteness, or It is thought that this will lead to improvements in printing characteristics and the like.

From the above viewpoint, conventionally, spherical calcium carbonate crystals,
In particular, various methods for industrially producing vaterite-type spherical calcium carbonate crystals have been studied, and as such a method, for example, a carbon dioxide-containing gas is introduced into a calcium hydroxide aqueous suspension containing a magnesium compound. , A method for obtaining spherical calcium carbonate by adding condensed phosphoric acid or its alkali metal salt when a certain carbonation rate is reached (JP-A-60-90822), or a reaction between calcium chloride and calcium hydrogen carbonate. In JP-A-54-150397, there has been proposed a method of obtaining vaterite-type spherical calcium carbonate by previously allowing ammonia to coexist so that the pH value of the slurry at the end of the reaction becomes 6.8.

However, in any of those methods, the manufacturing process is very complicated as compared with the conventional method for manufacturing cubic or spindle-shaped calcium carbonate crystals, and therefore, it is necessary to refurbish the manufacturing apparatus (crystallizer, etc.). However, it is hard to say that it is always satisfactory in terms of productivity and economic efficiency.

(Problems to be Solved by the Invention) The present inventor, in view of the problems of the conventional techniques as described above, has conducted earnest research to find a method for industrially producing spherical calcium carbonate crystals, and as a result, In the solution for precipitating the calcium carbonate crystals, the water-soluble sulfonated polymer described below is allowed to coexist, so that spherical calcium carbonate crystals composed of vaterite type crystals or mainly composed of the crystals (hereinafter, simply referred to as The present invention has been completed based on the knowledge that spherical calcium carbonate crystals composed of vaterite type crystals) can be easily and reproducibly manufactured.

That is, the object of the present invention is industrially advantageous in that spherical calcium carbonate can be used in a very simple manner without any complicated steps and operations, and can also be used as it is in a conventional crystallizer. It is to provide a method for manufacturing by means.

Another object of the present invention is to stably supply spherical calcium carbonate crystals, which are useful as fillers and pigments for rubber, plastics, paper, paints, etc., at a low cost by adopting the above-mentioned improved method. If you can do it, you have to do it.

(Means for Solving Problems) The above-mentioned object is to precipitate polystyrene from an aqueous solution in a crystalline form by adding polystyrene sulfonic acid, styrene sulfonic acid and the following general formula to the solution. (Here, R ₁ , R ₂ , R ₃ , and R ₄ each independently represent hydrogen, a methyl group, or a carboxyl group, provided that R ₁ , R ₂ , and
Any one or two of R ₃ and R ₄ is a carboxyl group, and when it has two carboxyl groups, it may be in the form of an anhydride. ) A method for producing spherical calcium carbonate crystals, characterized in that at least one water-soluble sulfonated polymer selected from the group consisting of a copolymer with at least one monomer represented by Reached by.

According to such a method of the present invention, spherical calcium carbonate crystals composed of vaterite-type crystals are enhanced by simply adding a small amount of the water-soluble sulfonated polymer as described above to an aqueous solution that will crystallize calcium carbonate crystals. It can be obtained with high yield and reproducibility.

The water-soluble sulfonated polymer used in the present invention is (meth)
Polymer (Polyelectrolyte) type water treatment with acrylic acid type polymer [poly (meth) acrylic acid, copolymer of acrylic acid and acrylic acid ester] or maleic acid type polymer (polymaleic acid, copolymer of ethylene and maleic acid) It is also known as an agent (scale inhibitor), and one of the scale-inhibiting effects of these polymer-type water treatment agents is a crystal habit effect, that is, suppression of crystal growth of scale components (calcium carbonate, etc.) and modification of crystal form. It is also known to be based on.

However, when these polymers are used for adjusting the crystallization state of calcium carbonate, as will be shown later in Comparative Examples, even if they are scale inhibitors, (meth) acrylic acid-based polymers or maleic acid-based polymers are actually spherical. It is difficult to produce calcium carbonate crystals, and the industrial production of the spherical crystals is only possible by using the water-soluble sulfonated polymer of the present invention. It has been clarified for the first time in consideration of the present invention that there are remarkable differences in specific effectiveness.

Also, Journal of the American Chemical
Society (Journal of the American Chemical Socie
ty), Vol. 79, pp. 4898-4900 (1957), "On the influence of polyelectrolytes on the crystallization of calcium carbonate".
However, in this case, only sodium polymethacrylate is used as the polymer electrolyte, and its crystal habit effect also varies significantly depending on the amount used, and it is extremely reproducible. Cannot be said.

On the other hand, a sulfonated polymer similar to that used in the present invention for controlling the crystal precipitation state of inorganic salts is also known from US Pat. No. 3,770,390. However, the known method targets inorganic salts for fertilizers having relatively high solubility in water, such as potassium nitrate, ammonium sulfate, etc., and makes crystals of those salts larger,
However, nothing is said about calcium carbonate, and about changing its crystal form from a usual spindle or cubic form to a spherical form.

In the method of the present invention, the polymer (polymer electrolyte) to be coexisted in the aqueous solution for crystallization for producing spherical calcium carbonate crystals is polystyrene sulfonic acid, styrene sulfonic acid, and a monomer represented by the general formula (I). One or more water-soluble sulfonated polymers selected from copolymers with monomers and salts thereof.

Here, the polystyrene sulfonic acid includes not only a homopolymer of styrene sulfonic acid but also sulfonated polystyrene obtained by sulfonation of polystyrene. Similarly, the term "copolymer of styrene sulfonic acid and a monomer of the general formula (I)" means that a styrene-containing copolymer obtained by sulfonation of a copolymer of a styrene and a monomer of the general formula (I). A polymer is included. In the case of sulfonation of these styrene components, the degree of sulfonation is generally 80 mol%.
The above is preferable.

Examples of the monomer of the general formula (I) include maleic acid, maleic anhydride, acrylic acid, methacrylic acid, fumaric acid,
Examples thereof include itaconic acid and citraconic acid, with maleic acid or maleic anhydride being most preferred. Generally, the copolymerization amount of these monomers is preferably such that their proportion in the total polymer is 50 mol% or less. When the copolymerization amount exceeds 50 mol%, the spherical crystal forming ability of the polymer tends to be somewhat lowered.

The molecular weight of the water-soluble sulfonated polymer used in the present invention is
The range of 500-600,000 is common, preferably 1000-
It is in the range of 500,000, more preferably 5,000 to 100,000.

Examples of the polymer salt include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, ammonium salt and organic amine salt, but they are partial salts. May be.

The production of spherical calcium carbonate crystals by the method of the present invention using the water-soluble sulfonated polymer as described above is performed by precipitating calcium carbonate from an aqueous solution, for example, calcium carbonate aqueous solution and sodium hydrogen carbonate aqueous solution are mixed to obtain calcium carbonate. Method, a method of mixing a carbonate solution such as a method of mixing an aqueous solution of calcium nitrate and an aqueous solution of sodium carbonate to obtain calcium carbonate, dissolving calcium carbonate in hot water, filtering off the insoluble portion, and then allowing the filtrate to cool. According to the method of concentrating to precipitate calcium carbonate, or the method of blowing carbon dioxide gas into a calcium hydroxide aqueous suspension, a trace amount of the above-mentioned sulfonated polymer is contained in the aqueous solution containing or will contain calcium carbonate. Other than the addition, it can be carried out in the same manner as those ordinary crystallization methods.

The amount of sulfonated polymer added to the aqueous solution is generally 10
ppm or more, preferably 50 to 300 ppm. If the amount of the sulfonated polymer is less than 10 ppm, the effect of forming spherical crystals is not sufficient, while even if it exceeds 300 ppm, no further improvement in the effect of forming spherical crystals is observed, and the amount of polymer used is unnecessarily high. It is uneconomical only to increase.

Here, a specific embodiment of the spherical calcium carbonate crystal preparation according to the method of the present invention will be described by taking the carbonate solution compounding method as an example.

In the carbonate solution compounding method, a calcium compound such as calcium chloride, calcium nitrate, calcium iodide, or calcium bromide is carbonated with a carbonate compound such as sodium carbonate, sodium hydrogen carbonate, potassium carbonate, or ammonium carbonate. It is carried out by This carbonation reaction is carried out by mixing an aqueous solution of a carbonate compound with stirring in an aqueous solution of a calcium compound, but in the method of the present invention, one or both of the aqueous solutions are mixed with water-soluble sulfone prior to the mixing. One or two or more of the polymerized polymers should be added.

The concentration of the calcium compound and the carbonate compound in the aqueous solution may be either a saturated concentration or less, more preferably 0.
The concentration is in the range of 20 to 1.0 mol / l, and a solution having such a concentration is generally mixed so that the amounts of both compounds are almost equivalent to carry out the carbonation reaction.

If the liquid temperature during the carbonation reaction exceeds 40 ° C, some amorphous calcium carbonate crystals tend to precipitate, so keep the temperature below that, especially at 15 to 30 ° C as in the usual case. Is desirable.

The end point of the carbonation reaction is preferably at the time when the precipitation and growth of the calcium carbonate crystals in the system reach a steady state (usually, 30 to 60 minutes after the mixing of both solutions).

Thus, a suspension containing calcium carbonate crystals was obtained, and the crystals were collected by filtration, washed with water if necessary, dried by heating according to a conventional method, and further pulverized if necessary to obtain the objective. Spherical calcium carbonate crystals consisting of vaterite type crystals are isolated and obtained in powder form.

(Effects of the Invention) According to the present invention having the above-mentioned constitution, the obtained calcium carbonate crystals are spherical, and therefore, when they are used as pigments and fillers for paper coating, conventional spindle-shaped or cubic It is possible to increase the slurry concentration as compared with the case of calcium carbonate, which results in improved dryness, and
The gloss, whiteness, and smoothness of the resulting paper are improved, and at the same time, the printability is improved. Furthermore, since the slurry coatability is good, it is expected that the coating speed will be increased and the production efficiency will be improved. Currently, for paper coating, clay composed of scaly crystals is mainly used, but it is not only expected that the spherical calcium carbonate crystals according to the present invention are comparable in performance to clay. However, it is more advantageous in terms of price and is therefore useful as a substitute for clay.

Further, due to its excellent dispersibility and mechanical properties, good results can be expected when it is used as an additive in a wide range of fields such as rubber, plastics, synthetic resins, pharmaceuticals and foods.

As described above, the present invention does not require any major reworking of the conventional calcium carbonate crystal production process, production apparatus, or the like, and is simply a simple addition of the sulfonated polymer to the aqueous solution for calcium carbonate crystallization. This method has made it possible to produce spherical calcium carbonate composed of high-quality vaterite-type crystals with good reproducibility and at low cost, and its industrial significance is enormous.

Hereinafter, the present invention will be described more specifically with reference to examples.
In each of the examples, the crystal structure of calcium carbonate is X using Geiger Flex 2027 (manufactured by Rigaku Denki).
It was identified by line diffraction, and the shape and size of the crystal were observed and measured with an optical microscope and a scanning electron microscope S-450 type (manufactured by Hitachi, Ltd.).

Example 1 To 500 ml of a 0.08 mol / l calcium chloride aqueous solution, 60 mg of sodium polystyrene sulfonate (a homopolymer of sodium styrene sulfonate, molecular weight 10,000) (60 pp at a total reaction solution concentration) was added.
m) was added, and the mixture was heated to 40 ° C. with stirring and maintained at the liquid temperature. To this aqueous solution, 500 ml of 0.08 mol / l sodium hydrogen carbonate aqueous solution was added dropwise at a rate of 100 ml / min. After the completion of dropping, the mixture was stirred for about 1 hour, then the obtained suspension was suction-filtered, washed with water, and then air-dried at about 100 ° C. for 1.5 hours to obtain 2.2 g of spherical calcium carbonate crystals.

80% of the calcium carbonate crystals consisted of vaterite type crystals and had an average particle size of 18 μm.

Comparative Example 1 When carbonation was carried out in the same manner as in Example 1 except that sodium polystyrene sulfonate was not added to the calcium chloride aqueous solution, 2.1 g of indefinite calcium carbonate crystals mainly composed of calcite type crystals were obtained. Was obtained.

Examples 2 and 3 Carbonation was carried out in the same manner as in Example 1 except that the concentrations of the calcium chloride aqueous solution and the sodium hydrogen carbonate aqueous solution were 0.20 mol / l or 1.0 mol / l, respectively, and the reaction temperature was 20 ° C., The spherical calcium carbonate crystals shown in Table 1 were obtained.

Examples 4, 5 Sodium polystyrene sulfonate added amount of 150mg or 300mg (150ppm or 300ppm as the total reaction solution concentration)
Spherical calcium carbonate crystals were obtained in the same manner as in Example 2, except that The results are shown in Table 2. The results of Example 2 are shown in Table 2 again.

Examples 6 to 9 Similar to Example 2 except that calcium nitrate was used as the calcium compound and sodium carbonate and sodium carbonate were used as the carbonate compound, and the concentration of the aqueous solution and the reaction temperature were as shown in Table 3. Carbonation was carried out to obtain spherical calcium carbonate shown in Table 3.

Examples 10-12 As sulfonated polymers, the molecular weight is 5,000, 10,000, 5
Spherical calcium carbonate crystals were similarly obtained in the same manner as in Example 7 except that 0,000 or 500,000 soda polystyrene sulfonate was used, respectively. The results are shown in Table 4. The results of Example 7 are shown in Table 4 again.

Example 13 and Comparative Examples 2 and 3 In the same manner as in Example 1 except that various polymers (polymer electrolytes) shown in Table 5 were added to the aqueous solution in place of sodium polystyrene sulfonate, calcium carbonate was prepared. Crystals were obtained. The results are shown in Table 5. The results of Example 1 are shown in Table 5 again.

Example 14 To a beaker of 21 was added 1000 g of deionized water and 100 g of calcium carbonate (JIS reagent special grade), and a water-soluble sulfonated polymer [trade name Versace TL70, National Starch and Chemical Co., sodium polystyrene sulfonate ( Polystyrene sulfonate salt, degree of sulfonation
90%), 6.0 mg (60 ppm in the aqueous solution) of a 1% by weight aqueous solution having a molecular weight of 70,000] was added, and the mixture was heated to 80 ° C. and sufficiently stirred. After cooling, this aqueous solution was filtered to remove the insoluble portion, and the filtrate was concentrated under reduced pressure with a rotary evaporator to precipitate calcium carbonate crystals. This crystal was a spherical crystal consisting of 70% of vaterite crystal (average particle size: approx.
15 μm).

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (magnification: 1000) showing the appearance of calcium carbonate crystals obtained by the method of the present invention (Example 7).
Times). FIG. 2 is a scanning electron micrograph showing the appearance of the calcium carbonate crystals obtained in Comparative Example 3 (magnification: 1000
Times).

Claims (1)

[Claims] 1. When crystallizing calcium carbonate from an aqueous solution, polystyrene sulfonic acid, styrene sulfonic acid and the following general formula are added to the aqueous solution. (Here, R ₁ , R ₂ , R ₃ , and R ₄ each independently represent hydrogen, a methyl group, or a carboxyl group, provided that R ₁ , R ₂ , and
Any one or two of R ₃ and R ₄ is a carboxyl group, and when it has two carboxyl groups, it may be in the form of an anhydride. ) A method for producing spherical calcium carbonate crystals, characterized in that at least one water-soluble sulfonated polymer selected from the group consisting of a copolymer with at least one monomer represented by .