JPH02126933A - Spherical calcium carbonate and production thereof - Google Patents

Abstract

PURPOSE:To obtain very stable spherical calcium carbonate having satisfactory shelf stability by coating spherical calcium carbonate contg. distributed sodium polystyrenesulfonate with a polymer of an ethylenic unsatd. compd. CONSTITUTION:Spherical calcium carbonate is crystallized in an aq. system contg. dissolved sodium polystyrenesulfonate. An ethylenic unsatd. compd. such as styrene or methyl methacrylate is polymerized on the spherical calcium carbonate as seed to coat the spherical calcium carbonate granules with a polymer of the ethylenic unsatd. compd. The shelf stability of the spherical calcium carbonate is remarkably improved and the spherical crystal form is maintained even in warm water or even after immersion in water over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to spherical calcium carbonate and a method for producing the same.

[Prior Art] Calcium carbonate, especially precipitated calcium carbonate, has traditionally been used as a filler for rubber, plastics, and paper, as a pigment for paints and inks, and as a pharmaceutical agent.

Used as an additive for cosmetics, foods, agricultural chemicals, etc.

Calcium carbonate has three types of crystals: calcite, which is a rhombohedral crystal, and vaterite, which is rod-shaped aragonite and spherical. Normally (at room temperature and normal pressure) calcite is the stable phase, but at room temperature and pressure, The difference in free energy between these three types of crystal shapes is small. Currently, what is industrially synthesized is rhombohedral calcite, which is a stable phase, and in some cases, rod-shaped aragonite exists as a metastable phase. Traditionally, by spheroidizing powders, various physical properties of powders such as dispersibility, filling properties, lubricity (sliding), extensibility (elongation), application properties, feel, and polishing properties have been improved, and desirable properties have been achieved. Attempts have been made to spheroidize various powders from the point of application, and with respect to calcium carbonate, the synthesis of spherical vaterite-type calcium carbonate is attracting attention.

[Problem that the invention seeks to solve]

Spheroidal vaterite-type calcium carbonate can be produced by the carbon dioxide blowing method (Japanese Patent Application Laid-Open No. 48-35159), the double decomposition method of salt (Japanese Patent Application Laid-open No. 55-95617), and the reaction between calcium chloride and sodium hydrogen carbonate. A method of coexisting ammonia in advance so that the slurry OpH value at the end is 6.8 (Japanese Patent Application Laid-open No. 150397/1983)
etc. have been proposed. However, these methods require complicated manufacturing processes and are unfavorable in terms of productivity and economy.
Moreover, the generated spherical vaterite type calcium carbonate has the disadvantage that in a system containing water, it easily loses its spherical crystal form and transforms (transitions) into a rhombohedral calcite type which is a stable phase. Such transformation from the spherical vaterite type to the rhombohedral calcite type not only causes the loss of the above-mentioned spherical properties, but also reduces the quality stability of the composition containing it.

In view of this, the present inventors proposed a method of carrying out a carbonation reaction in an aqueous system in which a water-soluble sulfonated polymer is dissolved as a method for industrially producing spherical calcium carbonate (Japanese Unexamined Patent Publication No. 62-91416). ) was proposed. According to this method,
It is possible to mass produce spherical vaterite-type crystal calcium carbonate that approximates a true sphere. However, in the scale-up production stage, it was found that there was room for improvement in the crystal shape stability of the above-mentioned spherical calcium carbonate.

The present invention was developed in view of these circumstances, and has a spherical shape similar to a pearl, a uniform particle shape, substantially composed of vaterite crystals, and excellent long-term storage stability in water. The object of the present invention is to provide a spherical calcium carbonate and a method for producing the same.

[Means for solving problems]

In order to achieve the above object, the first aspect of the present invention is to provide a spherical calcium carbonate crystal in which sodium polystyrene sulfonate is distributed throughout and coated with a polymer of an ethylenically unsaturated compound. A method for producing calcium carbonate, which includes the steps of: adding an aqueous sodium carbonate solution to an aqueous solution in which sodium polystyrene sulfonate and calcium nitrate are dissolved to crystallize spherical calcium carbonate crystals; A method for producing spherical calcium carbonate comprising the step of adding an ethylenically unsaturated compound and its polymerization catalyst to an aqueous solution in which the spherical calcium carbonate crystals are present, polymerizing the resulting polymer, and coating the spherical calcium carbonate crystals with the resulting polymer. is the second gist.

[Effect]

That is, in order to significantly improve the storage stability of spherical calcium carbonate obtained by the production method that is the basis of the present invention, the present inventors conducted a series of researches in which polystyrene was used as a water-soluble sulfonated polymer. It has been found that good results are obtained using sodium sulfonate. As a result of further research focusing on this, we crystallized spherical calcium carbonate in an aqueous system containing dissolved sodium polystyrene sulfonate, dispersed the obtained spherical calcium carbonate in water, and in this system, When seed polymerizing an ethylenically unsaturated compound using spherical calcium carbonate as a seed, the spherical calcium carbonate particles are coated with the polymer of the ethylenically unsaturated compound, which significantly improves the storage stability of the spherical calcium carbonate and allows it to be easily heated in hot water. The present invention was achieved by discovering that the spherical crystal shape can be maintained even when immersed in water for a long period of time.

The spherical calcium carbonate of the present invention is obtained using sodium polystyrene sulfonate, calcium nitrate, sodium carbonate, an ethylenically unsaturated compound, and a polymerization catalyst thereof.

The above sodium polystyrene sulfonate (hereinafter referred to as rpss)
, abbreviated as ) is not particularly limited, and any unit can be used as long as it consists of a repeating unit represented by the following general formula.

Further, the above-mentioned calcium nitrate and sodium carbonate are not particularly limited, and conventionally known ones can be used as they are.

Styrene (S
T), methyl methacrylate (MMA), butyl acrylate (BA), dimethylaminopropylacrylamide (DMAPAA), and the like. These may be used alone or in combination, and a combination of melamine and phenol can also be used. Therefore, the ethylenically unsaturated compounds according to the invention include:
It includes not only a narrow definition but also a combination of melamine and phenol.

The polymerization catalyst for the ethylenically unsaturated compound is not particularly limited, and peroxide catalysts such as benzoyl peroxide, cumene hydroperoxide, ammonium persulfate, and azobisbutyronitrile can be used.

In the present invention, spherical calcium carbonate is produced using the above-mentioned component raw materials and applying a carbonate solution formation method, for example, in the following manner. At the same time, calcium nitrate is dissolved in water to form an aqueous solution, and at the same time, sodium carbonate is dissolved in water to form an aqueous solution. Then, the above PSS is added and dissolved in either or both of these aqueous solutions. Next, the sodium carbonate aqueous solution is mixed with the calcium nitrate aqueous solution. This mixing may be performed by mixing the entire amount at once, or by dropping the aqueous sodium carbonate solution. As a result of such mixing, spherical calcium carbonate crystallizes and the aqueous solution becomes a suspension. therefore,
Spherical calcium carbonate consisting of vaterite crystals can be obtained in powder form by collecting the crystals by filtration or the like, washing with water if necessary, heating and drying according to a conventional method, and pulverizing if necessary. In this case, the amount of PSS added in the aqueous solution greatly influences the formation of the spherical calcium carbonate, and the amount added is r'
It is preferable to set the concentration of ss to 500 to 110,000 pp. More preferably 6000-1
It is within the range of up to 10,000 pp. That is, the above PS
This is because if the amount of S added is below the above range, the proportion of spherical crystals produced will be low. In addition, the concentrations of the calcium carbonate aqueous solution and the sodium carbonate aqueous solution may both be below the saturation concentration, but more preferably 0.20 to 1.
．． 00 mol/l, and it is preferable to mix solutions with such a concentration so that the amount of the re-compound is equivalent to cause the carbonation reaction.

In this case, if the liquid temperature exceeds 40°C, there is a tendency for some amorphous calcium carbonate crystals to precipitate.
It is desirable to maintain the temperature at ˚C. The end point of the carbonation reaction is preferably set at the time when the crystallization and growth of calcium carbonate crystals in the system reach a steady state (usually 30 to 60 minutes after mixing the re-solution).

Next, the spherical calcium carbonate particles obtained as described above are used as seed particles, and seed polymerization is performed on the surface of the spherical calcium carbonate particles to coat the spherical calcium carbonate particles with a polymer and encapsulate them. That is, the spherical calcium carbonate particles are dispersed in water, the ethylenically unsaturated compound (monomer) is dispersed therein, and at the same time, a polymerization initiator is added to initiate polymerization. Then, this polymerization is carried out for a predetermined time, for example, 2
Continue for about 4 hours. As a result, the surface of the spherical calcium carbonate is coated with the polymer and becomes, so to speak, in an encapsulated state. In this case, the proportion of the monomer used is set to be within the range of 5 to 500 parts, preferably 50 to 200 parts, per 100 parts by weight of spherical calcium carbonate (hereinafter abbreviated as "parts") on a solid content basis. It is preferable to do so. That is, if it is below the above range, the surface of the spherical calcium carbonate will be insufficiently coated with the polymer, whereas if it exceeds the above range, the viscosity of the solution will become too high and seed polymerization will not be carried out smoothly. After polymerization is carried out in this way, the polymerization liquid is centrifuged to separate the supernatant liquid system and the solid content system, and the solid content system is further filtered through a filter. Spherical calcium carbonate particles with type crystals are obtained. The surface of the spherical calcium carbonate obtained in this way is coated with a polymer, so it has extremely high storage stability.Therefore, even if it is immersed in water for more than a month, the crystal shape will not change. Moreover, even if it is boiled, its crystal form does not change.

〔Effect of the invention〕

As described above, the spherical calcium carbonate of the present invention is extremely stable because the spherical calcium carbonate in which sodium polystyrene sulfonate is distributed throughout is coated with a polymer of an ethylenically unsaturated compound. It has excellent storage stability.

Therefore, it maintains its spherical shape even if it is immersed in water for a long time or boiled. In addition, when producing spherical calcium carbonate whose surface is coated with a polymer, sodium polystyrene sulfonate present on the surface of the spherical calcium carbonate crystal acts as an intermediary between the ethylenically unsaturated compound and the crystal. , the coating of the crystals with the polymer of the ethylenically unsaturated compound is carried out smoothly.

Although this coating was observed under an electron microscope, it was found to be almost completely covered, but from a microscopic perspective, it appears that some crystals are exposed in some areas. Therefore, when the obtained surface-coated spherical calcium carbonate is immersed in hydrochloric acid (concentration IN), the hydrochloric acid solution enters from the slightly exposed portion, and a very small amount of carbon dioxide gas is generated. However, it is said that the entire crystal is covered almost completely, and as a result, even under the harsh conditions mentioned above (underwater or boiling), it is possible to maintain the spherical shape. It can maintain its shape for a long time.

Next, examples will be described together with comparative examples.

[Example 1] Polystyrene sulfonic acid (manufactured by NSC, VER3A-TL502, molecular weight 5) was added to Ca(No:+)z at a concentration of 10%.
0,000) was dissolved to prepare an aqueous solution. Pour 120g of this aqueous solution into a 200cc Erlenmeyer flask, and
It was immersed in a constant temperature bath of C and stirred.

When the temperature of the aqueous solution reached a steady state, the temperature was adjusted to 20°C using a roller pump. Next, 40 g of Naz Co3 aqueous solution having a concentration of 6.46% by weight was added dropwise at a speed of 2.087 minutes to cause a carbonation reaction. As a result, calcium carbonate crystals started to crystallize, and the aqueous solution turned into a Q-turbid liquid.

Next, the above suspension was filtered through a 0.2 μm membrane filter to remove the solid content, which was thoroughly washed with water and dried under reduced pressure to obtain powder crystals. As a result of observing this crystal with a scanning electron microscope (SEM), the average grain size was 3.
It was confirmed that it was a spherical calcium carbonate crystal of μm size. In addition, as a result of examining the above crystal form by X-ray diffraction method,
It was confirmed that 100% was vaterite.

Next, add a stirring bar to a 200cc four-loop flask.

An Aline condenser, a rubber stopper, and a stirring seal were attached, and the container was placed in a constant temperature bath. Next, 1.0 g of the spherical calcium carbonate powder crystals obtained as described above, 50 g of water, and 0.5 g of styrene monomer were added to the above flask, and the mixture was stirred at a speed of 300 rpm for 1 hour (liquid temperature: 20°C). ). Next, the temperature was raised to 70° C. and the atmosphere was replaced with nitrogen for 30 minutes. While stirring and nitrogen supply were continued in this manner, 0.1 g of potassium persulfate was added to initiate polymerization. After 30 minutes, nitrogen substitution was stopped, and polymerization was carried out at a temperature of 70°C for 24 hours.

After polymerization, the solution was separated into a supernatant liquid system and a solid content system using a centrifuge, and the solid content system was filtered through a 0.2 μm membrane filter. After washing with water, it was dried under reduced pressure to obtain polystyrene-coated spherical calcium carbonate powder crystals. As a result of observing the powder crystal thus obtained under SEM, it was confirmed that the surface of the spherical calcium carbonate crystal was almost completely covered with fine polystyrene particles. In addition, as a result of confirming the crystal structure by X-ray diffraction method, vaterite 10
It was 0%.

[Examples 2 to 4] The amount of the ethylenically unsaturated compound (styrene monomer) used was changed as shown in the table below. Other than that, polystyrene-coated spherical calcium carbonate powder crystals were obtained in the same manner as in Example 1. The results of X-ray diffraction of the crystal immediately after being obtained and after being left in water for a month were as shown in the table below.

[Examples 5 to 9] As ethylenically unsaturated compounds, those shown in the table below were used, and at the same time, the amounts used were changed as shown in the table. Other than that, plastic-coated spherical calcium carbonate powder crystals were obtained in the same manner as in Example 1. The results of X-ray diffraction of the crystal immediately after it was obtained and after being left in water for a month were as shown in the table below.

[Comparative Examples 1 to 4] Water-soluble polymers shown in the table below were used, and at the same time, the amount of ethylenically unsaturated compound (styrene monomer) used was changed as shown in the table below.

Other than that, polystyrene-coated spherical calcium carbonate powder (only one comparative example was not coated) was obtained in the same manner as in Example 1.

X of the crystal immediately after being obtained and after being left in water for a month
The results of line diffraction were as shown in the table below.

As is clear from the above table, the calcium carbonate crystals in all of the example fabrics are vaterite-type spherical calcium carbonate crystals, and even after being left in water for a month, the crystal morphology changes. It can be seen that it is rich in On the other hand, the comparative example product uses something other than PSS as a water-soluble polymer when producing the calcium carbonate crystal itself, so the calcium carbonate crystal that crystallizes is not a spherical vaterite type crystal. It was calcite, a rhombohedral crystal.

(Margin below) Procedural amendment (spontaneous) Special permission Agency long Government Sir 1゜ Display of incidents 1988 Patent Application No. 281018 2゜ name of invention Spherical calcium carbonate and its manufacturing method 3゜ person who makes corrections Relationship with the incident

Claims (3)

[Claims] (1) A spherical calcium carbonate characterized by coating a spherical calcium carbonate crystal in which sodium polystyrene sulfonate is distributed throughout with a polymer of an ethylenically unsaturated compound. (2) The spherical calcium carbonate according to claim (1), wherein the ethylenically unsaturated compound is at least one compound selected from the group consisting of styrene, methyl methacrylate, butyl acrylate, and dimethylaminopropylacrylamide. (3) Adding a sodium carbonate aqueous solution to an aqueous solution in which sodium polystyrene sulfonate and calcium nitrate are dissolved to crystallize spherical calcium carbonate crystals, and adding ethylene to the aqueous solution in which the spherical calcium carbonate crystals are present. 1. A method for producing spherical calcium, comprising the step of adding and polymerizing a sexually unsaturated compound and a polymerization catalyst thereof, and coating the spherical calcium carbonate crystals with the resulting polymer.