JP2008169086A - Manufacturing process of alkaline earth metal carbonate particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of alkaline earth metal carbonate particles by which the shape and aggregativeness of the alkaline earth metal carbonate particles can be controlled and an acicular particle with an improved particle size distribution is prepared. <P>SOLUTION: The manufacturing process of an alkaline earth metal carbonate particles comprises reacting an alkaline earth metal salt solution with a carbonate solution in a solution containing an anti-aggregation agent using a double jet process to form the particles with an average aspect ratio of not less than 2. The process has a particle growth step subsequent to a nucleus formation step so that dispersing operation is conducted after the particle growth step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing alkaline earth metal carbonate particles having an acicular or columnar shape with improved particle size distribution.

  Alkaline earth metal carbonates such as calcium carbonate, strontium carbonate, and barium carbonate are used as additives for paper, rubber, resin, plastic, paint, cosmetics, pharmaceuticals, and other raw materials for dielectric ceramic materials and high-temperature superconductor materials. It is used in a wide range of industrial fields as an inorganic dope material for optical films.

  Alkaline earth metal carbonates are known to have different functions and characteristics depending on their physical properties. For example, spindle-like carbonates are used for the production of paints with low gloss and excellent wet ink coverage. It is said that calcium carbonate is suitable, and acicular calcium carbonate is suitable for the production of a paint having high gloss, opacity, ink inking properties and ink setting properties. In addition, when strontium carbonate is used as a raw material for producing strontium titanate, it has been reported that electrical characteristics are improved when particles having an average particle size of 0.8 μm or less are used. Furthermore, when applying to transparent resin or plastic material, in order not to impair the transparency, small particles of the order of μm or less are required.

  Thus, since it is necessary to select a particle shape and a particle size according to the objective, the industrial utility value of the alkaline earth metal carbonate particle | grains by which the form was controlled is high. Therefore, in order to precisely control the morphology of particles having anisotropic shapes such as needles and columns, which have a wide range of industrial applications, and to fully express the intended function, more uniform particles, that is, particle sizes There is a need for a technique that can produce particles with excellent distribution.

In general, a method for producing alkaline earth metal carbonate particles includes a “liquid-gas” method in which a carbon dioxide gas is reacted with a solution containing an alkaline earth metal ion called a carbon dioxide method, and an alkaline earth metal ion. And a solution containing carbonate ions and a solution containing carbonate ions are roughly classified into “liquid-liquid” methods. At present, the “liquid-gas” method is mainly carried out industrially. As a solution containing alkaline earth metal ions, alkaline earth metal hydroxides, specifically, Ca (OH) ₂ , Sr (OH) ₂ and Ba (OH) ₂ are often used, but these hydroxides are usually used as slurries because of their low solubility.

  In the “liquid-gas” method, a method of producing columnar calcium carbonate of 1 to 2 μm by changing the temperature of the calcium hydroxide slurry and the introduction rate of carbon dioxide gas in three stages (for example, see Patent Document 1), Before the carbonation reaction reaches 30%, water-soluble monosaccharides or oligosaccharides are added to the calcium hydroxide slurry to produce spindle-shaped calcium carbonate of 1 to 2 μm (see, for example, Patent Document 2), water. A method of producing a needle-shaped strontium carbonate having a thickness of 0.72 μm by defining the temperature of the strontium oxide slurry and the introduction rate of carbon dioxide (for example, see Patent Document 3) has been proposed.

  However, in the “liquid-gas” method, i) it is difficult to strictly control the dissolution rate of alkaline earth metal hydroxide in the slurry and the dissolution rate of carbon dioxide gas in the slurry during the reaction process, ii) the reaction process Iii) Since nucleation is carried out in a strontium hydroxide slurry, it is difficult to uniformly stir the reaction solution, and the ion concentration and supersaturation in the reaction solution Alkaline earth metal carbonate particles that can be prepared have a wide particle size distribution due to problems such as disproportionation and nuclei formed immediately by the influence of a higher salt concentration.

  For the problem i), for example, a method of producing a calcium carbonate crystal by directly reacting an aqueous solution containing carbonate ions and an aqueous solution of a calcium compound under ultrasonic irradiation (see, for example, Patent Document 4). , A method for producing acicular barium carbonate by simultaneously adding an aqueous solution of barium salt and an aqueous solution of alkali carbonate to reaction vessels through separate supply ports (see, for example, Patent Document 5), and similarly strontium, calcium, barium A method of producing needle-like and rod-like carbonates by reacting a metal ion source containing at least one selected from each ion of zinc, zinc and lead with a carbonate source in a liquid by a double jet method (for example, Patent Documents) 6)) and the like using a “liquid-liquid” method has been proposed.

  However, since these methods do not have technical means that can solve the problem shown in the section ii), the particle size distribution of the particles that can be produced is still unsatisfactory.

  For the problem described in the above item ii), a production method of reacting a carbonic acid source in a liquid of a metal ion source containing at least one selected from ions of strontium, calcium, barium, zinc, and lead, There has been proposed a method for producing a carbonate having a shape having an aspect ratio larger than 1, which includes a step of increasing the number of particles and a step of increasing the volume of the particle, and reacting by controlling the addition rate and time of the carbonic acid source (for example, patents) Reference 7).

  However, since this method is a single jet method for adding an ion source, it is a manufacturing method including the problem described in the item i), and a carbonic acid source is introduced into a metal ion source stored in a reaction vessel. Therefore, the problem described in the item iii) is unavoidable, and is insufficient as a technique for improving the deterioration of the particle size distribution.

  In addition, alkaline earth metal carbonates produced by the “liquid-gas” method originally have a very strong cohesion between primary particles (core particles), and a large number of primary particles aggregate to form a large secondary. Particles (coarse aggregates of primary particles) are formed, and the slurry of secondary particles is said to be impossible to disperse to primary particles even if stirring is continued for a long time. .

  For example, when calcium carbonate containing a large number of aggregates of such primary particles is used as a filler or pigment for rubber, plastic, paper, paint, etc., the secondary particles behave like primary particles. Insufficient dispersion, a decrease in strength, a decrease in gloss, a decrease in fluidity, and the like are caused, and the original effect that is manifested when primary particles are blended cannot be obtained. Similarly, even when calcium carbonate containing a large number of aggregates is subjected to an inorganic or organic surface treatment, only the surface of the secondary particles is treated, and a sufficient effect cannot be obtained. difficult.

  A number of methods for dispersing primary particle aggregates in such alkaline earth metal carbonate particles have been reported. Industrially, alkaline earth metal carbonate particles formed as aggregates are used in ball mills and sand grinder mills. For example, a method of pulverizing powerfully is employed.

  However, since this method is grinding and grinding using enormous energy, the aggregates are dispersed and the primary particles are destroyed at the same time. As a result, the surface state of the particles becomes unstable and added. Therefore, it is difficult to say that this is a preferable method because particles smaller than the desired primary particle size and secondary agglomerated particles incompletely dispersed are mixed and the particle size distribution becomes wide.

  In addition, in such a wet grinder such as a sand grinder, fine glass beads may be used as a grinding medium. However, in the grinding process of alkaline earth metal carbonate particles, the surface of these glass beads is also destroyed. Therefore, a large number of coarse glass pieces of several μm or more may be mixed in the alkaline earth metal carbonate particles after the dispersion treatment, and it is difficult to say that this is a preferable method.

Accordingly, there is a need for a method that can stably produce alkaline earth metal carbonate particles with less aggregated particles without the need for a pulverization process after the production of alkaline earth metal carbonate particles.
Japanese Patent Publication No.55-51852 JP 2001-139328 A JP 2006-124199 A JP 59-203728 A JP-A-5-155615 JP 2006-21988 A JP 2006-169038 A

  The present invention has been made in view of the above problems, and its purpose is to control the form and cohesiveness of alkaline earth metal carbonate particles, and to improve the particle size distribution having an acicular form. The object is to provide a method for producing earth metal carbonate particles.

  As a result of intensive research to solve the above problems, the present inventors have separated the nucleation step and the particle growth step of alkaline earth metal carbonate particles to give optimum conditions for each step, and at least By applying a dispersion treatment after the end of any step, the deterioration of the particle size distribution and the disproportionation of the shape caused by particle aggregation are prevented, and the average aspect ratio and average particle size of particles having a needle-like shape, and It has been found that the particle size distribution can be controlled. The present invention has been derived on the basis of knowledge obtained from such studies. In the present invention, the needle-like form includes a columnar form and a bar-like form.

  That is, the above object of the present invention is achieved by the following configuration.

  1. Alkaline earth metal which forms particles having an average aspect ratio of 2 or more by reacting an alkaline earth metal salt solution with a carbonate solution using a double jet method in a solution containing an anti-agglomeration agent A method for producing carbonate particles, comprising a particle growth step after a nucleation step, and performing a dispersion operation after the nucleation step is completed.

  2. 2. The method for producing alkaline earth metal carbonate particles according to 1 above, wherein the dispersing operation is performed after the nucleation step is completed and before the particle growth step is started.

  3. 2. The method for producing alkaline earth metal carbonate particles according to 1 above, wherein the dispersing operation is performed after completion of the particle growth step.

  4). 2. The method for producing alkaline earth metal carbonate particles according to 1, wherein the dispersing operation is performed from the end of the nucleation step to the start of the particle growth step and after the end of the particle growth step.

  5. 5. The alkaline earth metal carbonate according to any one of 1 to 4, wherein the dispersion operation is performed using at least one of a media disperser, an ultrasonic disperser, and a high-speed stirring disperser. A method for producing salt particles.

  6). The alkaline earth metal carbonate according to any one of 1 to 5 above, wherein a solvent of the solution containing the aggregation inhibitor, the alkaline earth metal salt solution, and the carbonate solution is substantially water. Particle production method.

  7. The method for producing alkaline earth metal carbonate particles according to any one of 1 to 6, wherein the aggregation inhibitor is a water-soluble polymer having an amide group.

  8). The method for producing alkaline earth metal carbonate particles according to any one of 1 to 7 above, wherein a coefficient of variation of a major axis diameter of the alkaline earth metal carbonate particles is less than 40%.

  9. 9. The method for producing alkaline earth metal carbonate particles according to any one of 1 to 8 above, wherein the coefficient of variation in minor axis diameter of the alkaline earth metal carbonate particles is less than 35%.

  10. 10. The method for producing alkaline earth metal carbonate particles according to any one of 1 to 9, wherein the aggregation inhibitor is removed using an ultrafiltration membrane after completion of the particle growth step.

  EFFECT OF THE INVENTION According to the present invention, it is possible to eliminate an adverse effect caused by aggregation during the formation of alkaline earth metal carbonate particles, and a method for producing alkaline earth metal carbonate particles having an acicular shape and an improved particle size distribution Can be provided.

  Embodiments of the present invention and details thereof will be described below, but the present invention is not limited thereto, and is specified by the description of the scope of claims.

  In the present invention, the nucleation step in the production process of alkaline earth metal carbonate particles is a process for generating nuclei particles, and the particle growth step is the step of generating particles with little generation of new nuclei particles. Means a growing process.

  In other words, the number of particles increases in the nucleation step and does not substantially increase in the particle growth step (the number of particles may decrease when Ostwald ripening is performed). Therefore, both processes can be distinguished by the presence or absence of new nuclear particles. Here, the fact that the number of particles does not substantially increase means that the number of particles at the end of the particle growth step is within 125% at the start of the particle growth step (when the ripening step is included, the end of the ripening step). To do.

The alkaline earth metal carbonate according to the present invention can be formed by reacting an alkaline earth metal ion and a carbonate ion. Examples of the alkaline earth metal ion source include Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Ra ²⁺ , and specific compounds in the case of Ca ²⁺ include CaCl ₂ and Ca (NO ₃ ). ₂ , CaSO ₄ , Ca (OH) ₂ , Ca (CH ₃ COO) ₂ , and hydrates thereof. The same applies to specific compounds in the case of Sr ²⁺ , Ba ²⁺ , and Ra ²⁺ . Examples of the compound that can be used as the carbonate ion source include Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , KHCO ₃ , (NH ₄ ) ₂ NO ₃ , NH ₄ HCO ₃ , (NH ₂ ) ₂ CO, and the like. Is mentioned.

  In the present invention, both alkaline earth metal ion source and carbonate ion source have a high solubility in a solvent, and a compound capable of preparing a solution having a high concentration is more preferable.

  As described above, as a method for producing an alkaline earth metal carbonate, a method in which carbon dioxide gas is introduced into a solution of an alkaline earth metal salt to cause a reaction (“liquid-gas” method), an alkaline earth metal, or A method of reacting a salt solution with a solution containing carbonate ions (“liquid-liquid” method) is known. In any method, when alkaline earth metal ions and carbonate ions react, precipitation of alkaline earth metal carbonate occurs immediately.

  Alkaline earth metal carbonate particles generated by the reaction start growing immediately after the generation of the core particles, so that the earlier generated core particles are more likely to grow, and the later generated core particles are less likely to grow. As a result, particle growth during the nucleation step is not preferable because it increases the particle size distribution of the nucleus particles and causes deterioration of the particle size distribution after the completion of particle growth.

  The broadening of the particle size distribution of the nuclei that occurs during the nucleation process depends greatly on the nucleation time and the nucleation temperature. That is, if the time of the nucleation process is long, the particle size distribution deteriorates due to the growth of the nucleation particles generated earlier, and if the temperature of the nucleation process is high, the growth rate of the nucleation particles increases. The difference in particle size from the nuclear particles generated from is amplified.

  In the present invention, the time for the nucleation step can be arbitrarily set, but it is preferably completed within 1800 seconds, more preferably within 300 seconds, and even more preferably within 120 seconds in order to prevent deterioration of the particle size distribution.

  Similarly, the temperature of the nucleation step can be arbitrarily set, but it is preferably performed at a temperature as low as possible in order to suppress the growth of nuclei particles during the nucleation step, specifically between −10 to 40 ° C. It is preferable to carry out with. At a lower temperature, the liquid in the reaction vessel freezes, special equipment is required for temperature control, and production costs increase.

  As a method for producing alkaline earth metal carbonate particles, a so-called carbon dioxide method in which only a carbon dioxide gas is introduced into an alkaline earth metal salt solution, a solution of an alkaline earth metal salt, and a solution containing carbonate ions are added simultaneously. Although there is a double jet method, in the present invention, it is preferable to use the double jet method in both steps of nucleation and particle growth.

  The double jet method referred to in the present invention is a method in which two types of solutions are dropped, injected, or injected onto the liquid surface of the liquid in the reaction vessel or into the liquid, respectively, using an appropriate liquid delivery device as required. In the present invention, an alkaline earth metal salt solution and a carbonate solution are added to a solution containing an anti-aggregation agent in the reaction vessel.

  In the present invention, the solvent of the solution containing the aggregation inhibitor, the alkaline earth metal salt solution, and the carbonate solution is preferably substantially water. Here, that the solvent is substantially water in the present invention means that the content of the solvent other than water is 10% by volume or less. When a solvent other than water, particularly an organic solvent, is contained in an amount of 10% by volume or more, there is a concern that the particle aggregability deteriorates.

  In the double jet method, it is possible to arbitrarily set or change the molar addition rate by changing the addition rate of the additive solution with a liquid delivery device or the like. Since the number of core particles formed per unit decreases, the production efficiency decreases, and when the number of core particles formed is increased by increasing the addition time, the generated core particles grow in parallel. to degrade.

  Therefore, in this invention, it is preferable to set the molar addition rate in the said nucleation process to 0.1 mol / min or more per 1 mol of alkaline earth metal carbonate formed in this process. Furthermore, 0.2-4 mol / min is preferable and 0.5-2 mol / min is more preferable. When the molar addition rate is higher than 4 mol / min, the stirring efficiency in the reaction vessel is relatively lowered, and non-uniform core particles are generated, or agglomeration may occur due to an increase in local core particle density. Will increase.

  In the particle growth step in the present invention, it is important to react alkaline earth metal ions and carbonate ions so that new core particles are not generated. Therefore, when the particle growth step is carried out by the double jet method, it is necessary to adjust the addition rate of the alkaline earth metal salt solution and the solution containing carbonate ions. It is necessary to adjust the carbon dioxide introduction speed.

  In the present invention, after completion of the nucleation step, the liquid temperature in the reaction vessel can be maintained higher than that in the nucleation step as necessary (aging step). Usually, in the aging process, a phenomenon in which particles having a small particle size dissolve and particles having a large particle size grow (Ostwald ripening) occurs. Therefore, in the present invention, the ripening step can be regarded as a part of the particle growth step. The particle growth step is preferably performed at a temperature equal to or higher than that of the nucleation step in order to increase the growth rate of the particles, and specifically, it is preferably performed between 0 to 60 ° C. Since a sufficient particle growth rate cannot be obtained at a temperature lower than 0 ° C., a long time is required for the particle growth step, and at 60 ° C. or higher, the diameter of the acicular particles becomes large and it is difficult to increase the aspect ratio.

  The present invention is characterized in that the dispersion operation is performed after the nucleation step and / or after the grain growth step. The dispersion operation is performed for the purpose of peptizing the aggregated particles generated in the nucleation process and / or the particle growth process into primary particles, and at least from the end of the nucleation process to the start of the particle growth process. It is preferable to be performed, and it is more preferable that it is performed both after the nucleation step and after the grain growth step and after the grain growth step. Furthermore, it can be carried out in the middle of the nucleation step and the particle growth step as necessary.

  Further, the dispersion operation can be performed in the reaction vessel, or the reaction solution can be temporarily transferred to another container during the dispersion operation. After the nucleation step is completed as in the present invention, the dispersion operation is performed in a solution state in the presence of an agglomeration inhibitor, thereby preventing excessive dispersion such that primary particles are destroyed and reaggregation of particles after peptization. can do.

  Since the time required for the dispersion operation varies depending on the aggregation state of the particles and the power of the disperser to be used, it is preferable to determine by confirming the peptization state. In order to confirm the peptization state of the aggregated particles, for example, a particle size measuring device or a turbidimeter can be used. When measuring changes in particle size and turbidity in the dispersion process with a particle size measurement device or turbidimeter, the particle size and turbidity decrease as the agglomerated particles are peptized, and most of the particles become primary particles. Then it converges to a certain value.

  In the present invention, it is preferable that the dispersion operation is carried out until the measured value is converged according to the above confirmation method that most particles have been peptized to the primary particles by the dispersion operation. As the dispersion operation time becomes longer, there is a concern about the deterioration of the particle size distribution due to Ostwald ripening between the particles. Therefore, in order to shorten the dispersion operation time, an appropriate coagulation inhibitor and a disperser should be selected, and Ostwald ripening. In order to reduce the influence of the above, it is important to keep the temperature of the reaction solution low during the dispersion operation.

  In the dispersion operation in the present invention, any of a media disperser, an ultrasonic disperser, a high-speed stirring disperser, or a combination thereof can be used.

  A media type dispersing machine is one in which beads or the like are introduced into the apparatus, and the particles are dispersed by collision or shearing between the bead particles. As a specific example of the apparatus that can be used in the present invention, Kotobuki Apex Mill, Ashizawa Kogyo LMZ and the like. In order to break up the agglomeration without pulverizing the primary particles, it is often preferable to use beads having a small particle size, and specifically, it is preferable to use beads having an average particle size of 0.3 mm or less, More preferably, beads having an average particle diameter of 0.1 mm or less are used. As the bead type, glass, titania, alumina, zirconia, or the like can be used.

  The ultrasonic disperser performs dispersion using energy generated when cavitation (vacuum bubbles) generated by ultrasonic waves is crushed. As specific examples of apparatuses that can be used in the present invention, SMT UH150 and Japan Examples include Seiki Seisakusho US-300T.

  The high-speed agitation type disperser disperses particles by the shearing force in the vicinity of the agitation blades that are agitated at a high speed. -3.7 and the like.

  In the present invention, the aspect ratio is the ratio (major axis diameter / minor axis diameter) of the length (major axis diameter) and the diameter (minor axis diameter) of particles having a needle-like morphology, and the average aspect ratio is , An arithmetic average value obtained by obtaining individual aspect ratios for 300 or more particles. When calculating the average aspect ratio, the average value of the major axis diameter and the minor axis diameter can also be obtained. The present invention is particularly useful for the production of an alkaline earth metal carbonate having an acicular form having an average aspect ratio of 2 or more.

  To obtain acicular particles with a high aspect ratio, there are a method of forming nuclei particles with a high aspect ratio in the nucleation process and a method of increasing the aspect ratio in the grain growth process, but the aspect ratio is increased in the nucleation stage. Attempts to do so often involve deterioration of the particle size distribution.

  In the present invention, the particle size distribution is more important than the aspect ratio as the characteristics of the core particles obtained in the nucleation step. This is because the formation of more uniform nucleus particles in the nucleation stage greatly contributes to the improvement of the particle size distribution after the grain growth. Therefore, in the present invention, it is preferable to use low aspect ratio particles in which the particle size distribution does not easily deteriorate at the nucleation stage, and the major axis diameter is selectively grown while suppressing the minor axis diameter growth in the grain growth process. Thus, it is preferable to form high aspect ratio particles.

Therefore, the alkaline earth metal carbonate particles according to the present invention have an average aspect ratio of nuclei particles at the end of the nucleation step of AR ₁ (= a ₁ / b ₁ ) and an average aspect ratio of the particles at the end of the particle growth step. Is AR ₂ (= a ₂ / b ₂ ), AR ₁ is preferably 1 or more and 2 or less, more preferably 1 or more and 1.5 or less. At the same time, AR ₂ / AR ₁ is preferably 2 or more, more preferably 3 or more, and still more preferably 5 or more. Here, a ₁ and b ₁ are the major axis diameter average value and minor axis diameter average value at the end of the nucleation step, respectively, and a ₂ and b ₂ are the major axis diameters of the particle at the end of the grain growth step, respectively. The average value and the minor axis diameter average value.

  In the present invention, the particle size is expressed by the diameter of a circle having an area equal to the projected area of the alkaline earth metal carbonate particles, and the average particle size is an arithmetic operation obtained by obtaining individual particle sizes for 300 or more particles. Mean average value. The particle size distribution is represented by a value obtained by multiplying the value obtained by dividing the standard deviation of each particle size used for obtaining the average particle size by the average particle size by 100.

Particle size distribution (%) = standard deviation of particle size / average particle size particle × 100
The present invention is useful for producing alkaline earth metal carbonate particles having an excellent particle size distribution. The alkaline earth metal carbonate particles according to the present invention preferably have a particle size distribution of 35% or less, and more preferably 30% or less. The average particle diameter is preferably 60 to 220 nm or less, more preferably 70 to 200 nm or less. The major axis, minor axis, and projected area of each particle required for calculating the average aspect ratio and the average particle size can be measured from an electron microscope image, and are obtained using an image analyzer as necessary. You can also

  In alkaline earth metal carbonate particles having an acicular shape, aggregation of particles joined in the major axis direction often occurs at the time of nucleation, which causes deterioration in distribution of the major axis diameter. On the other hand, since particle aggregation often occurs in the minor axis direction during particle growth, the distribution of minor axis diameter is deteriorated. When the particle cohesiveness is improved by the production method of the present invention, it is expected that both the major axis diameter and the minor axis diameter are improved. Specifically, a dispersion operation is performed between the end of the nucleation step and the start of the particle growth step (dispersion operation A), whereby the major axis diameter distribution is mainly performed, and the dispersion operation is performed after the end of the particle growth step (dispersion). By operation B), the distribution of the minor axis diameter can be improved mainly. That is, by implementing the dispersion operation A and the dispersion operation B in combination, the effect of improving the distribution of both the major axis diameter and the minor axis diameter can be obtained.

  When the distribution of the major axis diameter is defined by the same method as the particle size distribution, in the alkaline earth metal carbonate particles according to the present invention, the distribution of the major axis diameter is preferably 40% or less, and 30% or less. Is more preferable. The average value of the major axis diameter is preferably 150 to 450 nm, more preferably 200 to 450 nm, still more preferably 200 to 400 nm or less. Similarly, the short axis diameter distribution is preferably 35% or less, and more preferably 30% or less. Moreover, 20-80 nm is preferable, as for the average value of a short axis diameter, 20-70 nm is more preferable, and 20-60 nm is still more preferable.

  In the present invention, the molar ratio of the raw materials (alkaline earth metal salt and carbonate) consumed in the nucleation step and the particle growth step can be arbitrarily changed, but the needle-like particles having an average aspect ratio of 2 or more are used. For the formation, it is advantageous to reduce the molar ratio of the alkaline earth metal carbonate formed in the nucleation step to the alkaline earth metal carbonate at the end of particle formation. This is because the particle growth process greatly contributes to the formation of the anisotropic shape of the acicular particles. Therefore, in the present invention, the molar ratio of the alkaline earth metal carbonate formed in the nucleation step is preferably set to 50 mol% or less, more preferably 30 mol% or less, and more preferably 20 mol% or less.

  In the present invention, in order to prevent particle aggregation, it is necessary to add an aggregation inhibitor to the liquid in the reaction vessel at least before the start of the nucleation step. However, alkaline earth metal salt solution or carbonate solution It is also possible to add an anti-aggregation agent. The aggregation inhibitor that can be used in the present invention is a compound that has an adsorptivity to alkaline earth metal carbonate particles, acts as a steric hindrance, and can prevent aggregation between particles, and is a natural product. And a synthetic compound.

  Examples of the aggregation inhibitor that can be preferably used in the present invention include nitrogen-containing polymers such as polyamide, polyethyleneimine, and polyvinylpyrrolidone, neutral polymers such as polyvinyl butyral and polyvinyl alcohol, and cellulose-based polymers such as carboxymethylcellulose, methylcellulose, and hydroxyethylcellulose. A water-soluble polymer such as a polymer can be used. Among them, a polymer having an amide group is preferable as a compound. The average molecular weight of the polymer is not limited, but if the molecular weight is small, the aggregation suppressing effect is small, and if it is large, the reaction solution is thickened. The average molecular weight of the aggregation inhibitor used in the present invention is preferably 10,000 to 1,000,000, more preferably 30,000 to 500,000, and still more preferably 50,000 to 300,000.

  In addition, the addition amount of the anti-aggregation agent is preferably 0.1 to 15% by mass, more preferably 0.1 to 10% by mass, and more preferably 0.5 to 10% by mass with respect to the liquid or the addition solution in the reaction vessel. % Is more preferable.

  The anti-aggregation agent used may have a negative effect on product performance, such as when the final product is a hydrophobic paint or plastic. It can also be removed.

  In the present invention, in order to improve particle aggregability, at least a part of the nucleation step and the particle growth step can be performed under conditions where the liquid in the reaction vessel is in excess of alkaline earth metal ions. There is no particular limitation on the method for operating the liquid in the reaction vessel so that the alkaline earth metal ions are excessive, but the required amount of alkaline earth metal salt is separate from the alkaline earth metal salt solution added by the double jet method. Alternatively, a method of adding the solution into the reaction vessel or a method of adjusting the flow rate of the alkaline earth metal salt solution and the carbonate solution added by the double jet method is preferable.

  The excess amount of alkaline earth metal ions is preferably 0.001 to 0.5 mol / L as the molar concentration of alkaline earth metal ions dissolved in the liquid in the reaction vessel, 0.01 to 0.5 Mole / L is more preferable, and 0.01 to 0.2 mol / L is still more preferable. Outside this range, there is an increased concern about the occurrence of aggregation.

  In the present invention, the pH of the liquid in the reaction vessel can be arbitrarily set, but from the viewpoint of suppressing particle aggregation and anisotropic growth for forming acicular particles, a nucleation step or a particle growth step It is preferable to carry out at least a part of this under conditions of pH 9 or higher. Furthermore, a pH value of 9 to 13.5 is preferable, and a pH value of 10 to 13 is particularly preferable. Even if the pH value is higher than this, the effects on aggregation suppression and anisotropic growth are not changed.

  In the present invention, in order to form acicular particles, at least a part of the nucleation step or the particle growth step can be performed in the presence of a shape control agent. Examples of the compound that can be used for the form control agent include amines. Among them, primary amines and amino alcohols can be preferably used in the present invention.

  Examples of the form control agent applicable to the present invention include diamine compounds and amino alcohol compounds. Specifically, ethylene diamine, diethylene triamine, triethylene tetramine, propylene diamine, N, N-dimethylethanolamine, N, N. -Diethylethanolamine, 2- (2-aminoethylamino) ethanol, N-methyldiethanolamine, N-methylethanolamine, 2-aminoethanol and the like can be mentioned.

  In the present invention, the liquid in the reaction vessel may contain alcohol. Alcohol may be added to the liquid in the reaction vessel at any point in the nucleation step or the particle growth step, but it is preferably added at least before the start of the particle growth step. More preferably, the liquid contains alcohol.

  The alcohol used in the present invention can be mixed with water at an arbitrary ratio. Specifically, at least one of methanol, ethanol, n-propyl alcohol, and i-propyl alcohol is preferably used.

  When using a form control agent and alcohol, it is preferable to use in the range which does not exceed 10 volume% of the liquid in reaction container as the total amount of these solvents.

  In the present invention, the aggregation inhibitor can be removed using an ultrafiltration membrane after completion of the particle growth step. In other words, an ultrafiltration membrane having appropriate filtration characteristics is selected in consideration of the particle size of the formed particles and the molecular weight of the anti-aggregation agent, and concentration / dilution operations are performed using the ultrafiltration membrane after the particle growth process is completed. By doing so, it is possible to remove the aggregation inhibitor.

  Further, at the same time as removing the anti-aggregation agent, a desalting / washing treatment can be performed, or a substitution treatment with an appropriate solvent can be performed for various purposes. For example, when the alkaline earth metal carbonate particles are stored as a dispersion, the alkaline earth metal carbonate particles such as alcohol are more preferably substituted by replacing the solvent with a solvent having lower solubility than the solvent in the particle growth step. By substituting with a poor solvent, it is possible to prevent changes in particle size and shape due to Ostwald ripening during storage.

  In addition, when the produced alkaline earth metal carbonate particles are used as fillers or pigments for rubbers, plastics, paints, etc., it is possible to obtain a dispersion for an appropriate solvent without going through a drying step. In addition to omitting the step of pulverizing the solid, it is possible to avoid the dry aggregation caused by drying the particles, and to effectively develop the effect obtained when the primary particles are blended.

  The ultrafiltration membrane that can be used in the present invention is not particularly limited as long as it has a fractional molecular weight capable of separating alkaline earth metal carbonate particles and has resistance to a solvent.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Various conditions in the following embodiments can be appropriately changed without departing from the features and spirit of the present invention, and the scope of the present invention should not be construed as being limited by the following examples.

Example 1
[Production of alkaline earth metal carbonate particles]
<< Production of Particle-1: Present Invention >>
640 ml of an aqueous solution (solution A1) containing 5.3 g of strontium chloride hexahydrate and 19.2 g of polyvinylpyrrolidone (molecular weight: 130,000) as an aggregation inhibitor, 3.4 g of strontium chloride hexahydrate and polyvinylpyrrolidone ( A 140 ml aqueous solution (solution A2) containing 12.8 g (molecular weight: 130,000) was prepared. In addition, 200 ml (solution B1) of a 1.0 mol / L aqueous solution from strontium chloride hexahydrate and 200 ml (solution C1) of a 1.0 mol / L aqueous solution from sodium carbonate were prepared.

(Nucleation process)
The solution A1 was placed in a 2 L stainless steel reaction vessel and maintained at 5 ° C., and the pH was adjusted to 11.5 with a 5% aqueous sodium hydroxide solution while stirring at 1000 rpm. Subsequently, 40 ml each of the solution B1 and the solution C1 cooled to 4 ° C. were added to the solution A1 at a constant flow rate and an equal addition rate in 30 seconds using the double jet method.

(Distributed operation)
While maintaining the reaction solution after completion of the nucleation step at 5 ° C., dispersion operation was performed using an ultrasonic disperser (SMT UH150). The dispersion operation was performed until the turbidity of the reaction solution decreased and converged to a certain value.

(Particle growth process)
Next, solution A2 cooled to 5 ° C. was added while stirring the reaction solution, and the pH was adjusted to 11.5 with a 5% aqueous sodium hydroxide solution. Subsequently, 160 ml of the remaining amount of the solution B1 and the solution C1 held at 5 ° C. are added into the liquid in the reaction vessel using the double jet method while accelerating the flow rate according to the increase in the surface area accompanying particle growth at the same addition rate. Added over 160 minutes.

  After completion of the particle growth step, the membrane was washed with water using an ultrafiltration membrane, and further replaced with an ethanol solvent using an ultrafiltration membrane to produce particles-1.

  In addition, although the reaction liquid was extract | collected in the middle of a particle growth process and after completion | finish of a process, it confirmed using the electron microscope, but the production | generation of the new core particle in a particle growth process was not recognized. Moreover, it was identified from the electron microscope observation and X-ray diffraction spectrum of the obtained particle-1 that the particle-1 is strontium carbonate having an acicular shape.

<< Production of Particle-2: Present Invention >>
In the production of the particle-1, the dispersion operation after the completion of the nucleation step was not performed, but instead the dispersion operation was performed using an ultrasonic disperser (SMT UH150) after the completion of the particle growth step. Particle-2 was produced in the same manner as in Example 1.

<< Production of Particle-3: Present Invention >>
In the production of the particle-1, the particle-3 was produced in the same manner as in the production of the particle-1, except that the dispersion operation was performed using an ultrasonic disperser (UH150 manufactured by SMT) even after the particle growth step. .

<< Production of Particle-4: Present Invention >>
In the production of Particle-3, Particle-4 was produced in the same manner as in the production of Particle-3, except that Solution A3 prepared as follows was used instead of Solution A1.

  Solution A3: 640 ml of an aqueous solution containing 5.3 g of strontium chloride hexahydrate, 19.2 g of polyvinylpyrrolidone (average molecular weight 130,000) as an aggregation inhibitor, 4 ml of ethylenediamine, and 28 ml of ethyl alcohol.

<< Production of Particle-5: Present Invention >>
In the production of Particle-3, Particle-5 was produced in the same manner as in the production of Particle-3, except that Solution A4 prepared as follows was used instead of Solution A1.

  Solution A4: 640 ml of an aqueous solution containing 5.3 g of strontium chloride hexahydrate, 19.2 g of polyvinylpyrrolidone (average molecular weight 130,000) as an aggregation inhibitor, 4 ml of ethylenediamine, and 92 ml of ethyl alcohol.

<< Production of Particle-6: Comparison >>
In the production of Particle-1, Particle-6 was produced in the same manner as in the production of Particle-1, except that the solution A1 and the solution A2 were prepared and used except for the aggregation agent polyvinylpyrrolidone.

<< Production of Particle-7: Comparison >>
In the production of Particle-1, Particle-7 was produced in the same manner as in the production of Particle-1, except that the dispersion operation after the nucleation step was not performed.

<< Production of Particle-8: Comparison >>
Particles -8 were produced as follows without separating the nucleation step and the particle growth step.

  A 780 ml aqueous solution (solution A3) containing 8.7 g of strontium chloride hexahydrate and 32.0 g of polyvinylpyrrolidone (molecular weight: 130,000) as an aggregation inhibitor was prepared. Moreover, the solution B1 and the solution C1 were prepared similarly to manufacture of the said particle-1.

  The solution A3 was put in a stainless steel reaction vessel having a volume of 2 L and maintained at 5 ° C., and the pH was adjusted to 12 with a 5% aqueous sodium hydroxide solution while stirring at 1000 rpm. Subsequently, the solution B1 and the solution C1 maintained at 5 ° C. were added to the liquid in the reaction vessel for 200 minutes using the double jet method at an equal addition rate and a constant flow rate. Subsequently, after carrying out a dispersion operation using an ultrasonic disperser (SMT UH150), a water washing treatment is performed using an ultrafiltration membrane, and further, an ethanol solvent is substituted using an ultrafiltration membrane to thereby replace particles-8. Manufactured.

[Evaluation of alkaline earth metal carbonate particles]
(Observation of particle shape)
For each particle produced as described above, at least 300 particles were photographed with a scanning electron microscope and the shape thereof was observed, and the shape of the particles occupying the main body was a needle-like particle, a spherical particle, or an irregularly-shaped rugged shape. Classified into particles.

(Measurement of particle size and distribution)
About each particle | grain observed with the said scanning electron microscope, the short axis diameter and the long axis diameter were measured, and those average values and distribution were calculated | required by the above-mentioned method.

  The results obtained as described above are shown in Table 1. In addition, the particle-6 had severe particle aggregation, and the short axis diameter and the long axis diameter could not be measured.

  As is clear from the analysis results of each particle described in Table 1, acicular particles having excellent short axis diameter distribution and long axis diameter distribution can be produced by the production method defined by the present invention.

  Comparing the particles-1 of the present invention with the particles-6 to particles-8 of the comparative example, the constituent requirement of the present invention, that is, "the alkaline earth metal salt solution using the double jet method in the solution containing the aggregation inhibitor This is a production method of reacting with a carbonate solution, the production method having a particle growth step after the nucleation step, and carrying out a dispersion operation after the completion of the nucleation step. It turns out that this is a necessary condition.

  From the comparison of Particle-1 to Particle-3, it is preferable to perform the dispersion operation after the completion of the nucleation step because the effect of improving the distribution is greater than that performed after the completion of the particle growth step. It can be seen that it is more preferable to carry out the dispersing operation both after completion.

  Further, from the comparison of Particle-3 to Particle-5, when using a form control agent or alcohol, it is preferable that the total amount of these solvents is used within a range not exceeding 10% by volume of the liquid in the reaction vessel. I understand.

Example 2
In the method for producing particles-3 of Example 1, the dispersion operation after the nucleation step and after the particle growth step is changed from an ultrasonic disperser to a media disperser (Kotobuki Industrial Apex Mill) or a high-speed stirring disperser. Particle-9 and particle-10 were produced in the same manner as in the production of particle-3 except that (Primics TK homomixer MARKII) was changed.

  Dispersion operation with a media disperser or a high-speed stirring disperser was also performed until the turbidity of the reaction solution converged to a certain value. Analysis of Particle-9 and Particle-10 confirmed that the particles were excellent in distribution as in Particle-3.

Example 3
In the production of the particle-3 of Example 1, instead of the polyvinyl pyrrolidone as the aggregation inhibitor used in the solution A1 and the solution A2, polyvinyl alcohol (polymerization degree: 1700), polyethyleneimine (molecular weight: 70,000), hydroxyethyl cellulose ( Particles were prepared using a water-soluble polymer having a molecular weight of 120,000), and it was confirmed that particles with good distribution could be prepared. Further, from the comparison of these particles, particularly preferable results were obtained with a water-soluble polymer having an amide group such as polyvinylpyrrolidone used in the production of Particle-3.

Example 4
In the method for producing particles-3 of Example 1, instead of washing with water using an ultrafiltration membrane after the completion of the particle growth step, the particles were filtered, washed with water, dried and then dispersed in ethanol. 11 was produced.

  As a result of measuring the characteristics of Particle-11 in the same manner as in Example 1, it was confirmed that the minor axis diameter and the major axis diameter distribution were deteriorated due to particle aggregation generated in the drying process. That is, in the method for producing alkaline earth metal carbonate particles of the present invention, an ultrafiltration membrane may be used when a water washing treatment is performed for the purpose of removing excess anti-flocculating agent, form control agent, salt, and the like. It was confirmed that it is preferable in preventing the aggregation of particles.

Example 5
Barium chloride and calcium carbonate were prepared by changing the strontium chloride hexahydrate used in the production of the particles-1 to particles-8 of Example 1 to barium chloride and calcium chloride, respectively.

  About the obtained alkaline-earth metal carbonate particle, as a result of measuring each characteristic by the method similar to Example 1, the alkaline-earth metal carbonate particle manufactured with the manufacturing method of this invention is Example 1. Similar to the strontium carbonate particles according to the present invention described above, it was confirmed to have a needle-like shape and excellent particle size distribution.

Claims (10)

Alkaline earth metal which forms particles having an average aspect ratio of 2 or more by reacting an alkaline earth metal salt solution with a carbonate solution using a double jet method in a solution containing an anti-agglomeration agent A method for producing carbonate particles, comprising a particle growth step after a nucleation step, and performing a dispersion operation after the nucleation step is completed. 2. The method for producing alkaline earth metal carbonate particles according to claim 1, wherein the dispersing operation is performed between the end of the nucleation step and the start of the particle growth step. The method for producing alkaline earth metal carbonate particles according to claim 1, wherein the dispersion operation is performed after completion of the particle growth step. 2. The method for producing alkaline earth metal carbonate particles according to claim 1, wherein the dispersing operation is performed from the end of the nucleation step to the start of the particle growth step and after the end of the particle growth step. The alkaline earth metal according to any one of claims 1 to 4, wherein the dispersion operation is performed using at least one of a media disperser, an ultrasonic disperser, and a high-speed stirring disperser. A method for producing carbonate particles. The alkaline earth metal carbonate according to any one of claims 1 to 5, wherein a solvent of the solution containing the aggregation inhibitor, the alkaline earth metal salt solution, and the carbonate solution is substantially water. A method for producing salt particles. The method for producing alkaline earth metal carbonate particles according to any one of claims 1 to 6, wherein the aggregation inhibitor is a water-soluble polymer having an amide group. The method for producing alkaline earth metal carbonate particles according to any one of claims 1 to 7, wherein a coefficient of variation of a major axis diameter of the alkaline earth metal carbonate particles is less than 40%. The method for producing alkaline earth metal carbonate particles according to any one of claims 1 to 8, wherein a coefficient of variation in minor axis diameter of the alkaline earth metal carbonate particles is less than 35%. The method for producing alkaline earth metal carbonate particles according to any one of claims 1 to 9, wherein the aggregation inhibitor is removed using an ultrafiltration membrane after completion of the particle growth step.