JPH0453809B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel spherical basic magnesium carbonate that can be effectively used as a filler for synthetic resins, a carrier for cosmetics or agricultural medicines, and a method for producing the same. Conventionally, by spheroidizing powders, various powder physical properties such as filling properties, dispersibility, abrasiveness, and fluidity are improved, and favorable characteristics are imparted. is being attempted. Known examples of these spherical powders include spherical calcium carbonate (Japanese Patent Application Laid-open No. 57-92519, 57-92520, 57
-92521, 55-95617), spherical calcium sulfite (JP-A-53-14195), spherical alkaline earth metal silicate (Nikka-shi 5 , 727 (1976)), spherical calcium tungstate (Nikka-shi 10 , 1525 (1976)) etc. Conventionally, basic magnesium carbonate has been produced by using an aqueous slurry of orthomagnesium carbonate crystals as an intermediate raw material, heating and aging this at a temperature of 60 to 80°C for 1 to several hours, and separating the resulting crystals to 110 to 150°C.
A common method is to dry and ripen the product by heating it to ℃, and then convert it to basic magnesium carbonate according to the following reaction formula. 5 (MgCO ₃・3H ₂ O) heating --→ 4MgCO ₃・Mg(OH) ₂・4H ₂ O＋CO ₂ +10H ₂ O The magnesium orthocarbonate crystal required for this is (1)
Reaction of water-soluble magnesium salt (magnesium chloride or magnesium sulfate) with water-soluble carbonate (ammonium carbonate or sodium carbonate) (2) Thermal decomposition of magnesium bicarbonate (Mg(HCO ₃ ) ₂ ) (3) Magnesium hydroxide slurry It is regulated by either a reaction in which carbon dioxide is injected into the reactor. In the above-mentioned conventional method for producing basic magnesium carbonate, in order to obtain crystals of uniform size by maintaining uniformity in the reaction system, there is a step of precipitating orthomagnesium carbonate crystals, and a step of heating and ripening these crystals to form a base. In the process of converting magnesium carbonate into natural magnesium carbonate, the inside of the reaction tank is constantly stirred. Basic magnesium carbonate obtained by such conventional methods consists of plate-shaped microcrystals.
It is a very bulky powder with a bulk density of 0.2 to 0.3 g/ml, and when it is in a solution, its viscosity increases, and when it is in the form of a cake, it solidifies, and it must be dissolved to make a product. We had a problem that needed to be solved. Also,
Basic magnesium carbonate has a large amount of water of crystallization and carbon dioxide gas, and is known to be useful as a filler for flame retardant synthetic resins. Due to the above-mentioned properties of basic magnesium carbonate, it is extremely difficult to uniformly disperse and fill the resin in large quantities. In order to overcome the disadvantages or defects of the conventional basic magnesium carbonate powder as described above, it is sufficient to make the basic magnesium carbonate particles spherical.
It is difficult to make basic magnesium carbonate into a spherical shape, not only as a single crystal but also as a primary particle. must be made as fast as possible, without giving the crystals room to grow into their original shape. However, it is known that ``spherical'' aggregates can be obtained in some cases if the reaction temperature is increased to speed up the precipitation rate, or if stirring is stopped or slowed down to avoid destroying the aggregated particles. However, the ``spherical'' shape is made up of acicular basic magnesium carbonate crystals entwined, but it is chestnut-like and has an extremely wide particle size distribution, with a distorted shape. It is a mixture containing lumps. On the other hand, as a method for producing spherical basic magnesium carbonate, there is also a method of mechanically shaping it into a spherical shape using a binder without controlling the reaction conditions.
The presence of a binder is undesirable because it impairs the inherent chemical and physical properties of basic magnesium carbonate. As a result of intensive research in order to overcome the problems of the conventional basic magnesium carbonate powder as described above, the present inventors have developed a method by specifying the precipitation rate of orthomagnesium carbonate crystals as a basic magnesium carbonate precursor. We have discovered that spherical aggregated particles can be obtained and that the size of the spherical aggregated particles can be changed by controlling the uniformity within the reaction system during precipitation.
By performing the synthesis reaction while maintaining the reaction solution concentration, reaction temperature, and reaction rate within specific ranges, spherical basic magnesium carbonate with a narrow particle size distribution and a spherical or nearly spheroidal particle shape is always produced. In addition to being reliable, the resulting spherical basic magnesium carbonate has excellent properties as a powder, such as a large bulk density despite having a large specific surface area, and extremely good fluidity. As a result, when a high-concentration slurry is prepared, there is no significant increase in viscosity and it can be filled in large amounts into synthetic resins.It has been found that it has excellent properties as a filler, and can be effectively used in various fields. This led to the completion of the present invention. Therefore, based on this knowledge, the present invention provides that the shape of aggregated particles formed by agglomeration of fine primary particles is spherical or spheroidal with b/a≧0.7, where the major axis is a and the minor axis is b. Yes, the particle size of the aggregated particles is 5
60 μm, a bulk density of 0.4 to 0.7 g/ml, and a specific surface area of 10 to 40 m ² /g. Furthermore, as a typical method for producing the above-mentioned spherical basic magnesium carbonate, the present invention involves a reaction in which a water-soluble magnesium salt and an aqueous solution of sodium carbonate are reacted to synthesize basic magnesium carbonate, with each concentration being 1.5 mol/ml. , the temperature of the reaction system is 40-80
Keep at ℃, under stirring, addition rate of salt S (/min)
The present invention provides a method for producing spherical basic magnesium carbonate, which is characterized in that it is mixed under the condition that S/V≧0.1 with respect to the reaction volume V( ), and then left to ripen in the mother liquor. In the present invention, the reaction volume V is the sum of the volume of the magnesium salt aqueous solution and the volume of the sodium carbonate aqueous solution. The details of the present invention will be explained below. Examples of the water-soluble magnesium salt of the present invention include aqueous solutions of magnesium chloride and magnesium sulfate, and bittern. There is no strict limit to the concentration of the water-soluble magnesium salt and sodium carbonate aqueous solution, but too dilute solutions will increase the amount of processing liquid, making it uneconomical, and too concentrated solutions will make it difficult to ensure the uniformity of the reaction slurry. As a result, the final basic magnesium carbonate has many aggregated particles in which spherical bodies are linked together, resulting in a bulky basic magnesium carbonate with a wide particle size distribution. is preferably used in an amount of 0.5 to 1.5 mol/. The mixing ratio of the above magnesium salt aqueous solution and sodium carbonate aqueous solution is determined in order to increase the yield of Mg component.
It is best to charge a slight excess of sodium carbonate, and the molar ratio CO ^-- ₃ /Mg is preferably in the range of 1.0 to 1.1. In order to precipitate the spherical basic magnesium carbonate of the present invention, the temperature of the reaction system is 40 to 80°C, preferably 50°C.
Maintained at ~70°C, under stirring, salt addition rate S
(/min) to reaction volume V() S/V≧
It is extremely important to add so that S/V is 0.1, preferably 2≧S/V≧0.1. Note that the addition of a countersalt in this specification means that it is possible to add a water-soluble magnesium salt to an aqueous sodium carbonate solution, or to add a sodium carbonate aqueous solution to a water-soluble magnesium salt. , the former aspect is common. When the temperature of the reaction system is 40℃ or the ratio S/V of salt addition rate to reaction volume is 0.1 or less, the width is 1 to 20μ.
Relatively large acicular or columnar magnesium orthocarbonate with a length of 10 to 100 μm is generated, and the fine primary particles referred to in the present invention are not aggregated into a spherical shape, but are formed into spherical basic magnesium carbonate. No transformation occurs. Conversely, if the temperature of the reaction system is 80℃ or higher,
The result is platelet-shaped basic magnesium carbonate crystals similar to conventional basic magnesium carbonate. Also,
The upper limit of the S/V ratio is not particularly limited, but it is preferably 2≧S/V≧0.1, and in order to make the S/V ratio 2 or more, it is necessary to lower the concentration of the reaction solution, otherwise the slurry The viscosity increases rapidly, making it difficult to maintain uniformity of the reaction system. The stirring intensity in the reaction system is appropriate to maintain the precipitated magnesium orthocarbonate particles in a slurry state and to equalize the temperature and slurry concentration in the system. Too vigorous stirring beyond this level may cause the formation of spherical agglomerated particles. This is not preferable because it causes destruction and changes the shape of the basic magnesium carbonate finally obtained from a flat disk shape to a conventional fine plate shape. The stirring time in the reaction system varies depending on the shape of the reaction vessel, reaction volume, shape of the stirring blade, size, and stirring intensity, but it is desirable to keep it at the same time as the addition time of the salt or within 5 minutes after the addition is completed. Stirring for such a long period of time is not preferable because it prevents the precipitated fine primary particles from spherical agglomeration due to dissolution precipitation during the static aging process. Furthermore, in order to obtain the spherical basic magnesium carbonate of the present invention, a magnesium salt aqueous solution and a sodium carbonate aqueous solution are mixed under the above concentration, temperature, reaction rate, and stirring conditions, and then magnesium orthocarbonate consisting of precipitated fine primary particles is prepared. It is necessary to leave the slurry to mature without stirring in the mother liquor for generally 1 hour or more, particularly 2 to 4 hours, while maintaining the reaction temperature at the time of mixing. In the conventional production method of basic magnesium carbonate, in order to maintain uniformity in the reaction system and thereby obtain basic magnesium carbonate of uniform size, a slurry of magnesium orthocarbonate is converted and aged under stirring. was being carried out. Therefore, conventional basic magnesium carbonate had no choice but to have its original shape, that is, a plate-like crystal. However, the orthomagnesium carbonate slurry consisting of fine primary particles aggregates into spherical shapes by standing and ripening in the present invention, and is gradually converted into basic magnesium carbonate. The static aging time varies depending on other conditions and cannot be determined definitively, but in general, if it is shorter than 1 hour, especially 2 hours, the conversion to spherical shape and the conversion of orthomagnesium carbonate to basic magnesium carbonate will be incomplete; 4
Even if it is aged for more than an hour, the conversion will not proceed any further. In the present invention, in order to obtain spherical basic magnesium carbonate with a large average diameter, it is sufficient to slow down the reaction rate at a low temperature and shorten the stirring time after mixing.On the contrary, in order to obtain spherical basic magnesium carbonate with a small diameter, Spherical basic magnesium carbonate having a desired average diameter can be produced by appropriately selecting each reaction condition. The present invention provides basic magnesium carbonate with a new spherical structure that is clearly distinguishable from the structure of conventionally known basic magnesium carbonates, but the spherical basic magnesium carbonate has a large bulk density despite having a large specific surface area. Because it is spherical and has a narrow particle size distribution, it has excellent fluidity and dispersibility, and is useful as a filler for synthetic resins and as a carrier for cosmetics or agricultural medicines. The spherical basic magnesium carbonate is also useful as a raw material for highly active magnesium oxide, which has unique powder characteristics. Examples of the present invention will be described below. Example 1 500 ml of an aqueous magnesium chloride solution was added to 500 ml of an aqueous sodium carbonate solution at a rate of 2/min while stirring. At this time, the ratio S/V between the addition rate S (/min) and the reaction volume V () was 2. Stirring was continued for 60 seconds after the addition began. After the stirring was completed, the mixture was left to mature at the same temperature for 3 hours. Next, the precipitate was filtered and washed, and then dried at 120°C for 5 hours. The reaction temperature at this time was varied from 25℃ to 90℃, and the concentration ratios of sodium carbonate and magnesium chloride [Na ₂ CO ₃ ]/[MgCl ₂ ] were 0.52/0.50 and 0.73/
It was 0.70. All the results of X-ray diffraction of the dried product showed that it was basic magnesium carbonate. The properties of the basic magnesium carbonate obtained are shown in Table 1, and micrographs showing the shape are shown in FIGS. 1 to 6. If the reaction temperature is 40°C or less, the spherical basic magnesium carbonate referred to in the present invention cannot be obtained, but if the reaction temperature is in the temperature range of 40°C to 70°C, spherical basic magnesium carbonate can be obtained. When the reaction temperature is 80°C or higher, it becomes flat plate-like. The optimum reaction temperature in this example is in the range of 40 to 70°C, but as the reaction temperature increases, the particle size of the spherical particles becomes smaller. Both particle size distributions are very narrow.

[Table] Example 2 500 ml of a sodium carbonate aqueous solution with a concentration of 1.04 mol/k was kept at 60°C with 500 ml of a magnesium chloride aqueous solution with a concentration of 1.00 mol/kip held at the same temperature with stirring.
ml was added at a rate of 2/min. At this time S/
The V ratio was 2. Stirring was continued for 60 seconds after the addition began. After stirring, the mixture was left to mature at the same temperature for 1 to 4 hours, and the precipitate was then filtered and washed, and dried at 120°C for 5 hours. All the results of X-ray diffraction of the dried product showed that it was basic magnesium carbonate. The properties of the obtained powder are shown in Table 2, and micrographs showing the shape are shown in FIGS. 10 to 12.

[Table] If the static aging time is 1 hour, spherical aggregated basic magnesium carbonate will not be obtained, but only irregular aggregates of fine primary particles will be obtained. Basic magnesium carbonate aggregated into spherical shapes is obtained by dissolving and precipitating the primary particles. However, there is almost no difference when left standing for 4 hours or more. Example 3 A sodium carbonate aqueous solution with a concentration of 0.73 mol/kg was placed in a reaction tank with a capacity of 30 and equipped with a heating and stirring device.
12.5 and heated to 60°C. To this was added 12.5 ml of an aqueous magnesium chloride solution with a concentration of 0.7 mol/min heated to 60°C at a rate of 20/min. The S/V ratio at this time was 0.8. The mixture was stirred for 70 seconds from the start of addition, and then left to mature at the same temperature for 3 hours. After excessive washing, the precipitate was dried at 120°C for 5 hours. The obtained powder was confirmed to be basic magnesium carbonate by X-ray diffraction. A scanning electron micrograph showed that it was spherical (Fig. 13). Example 4 In Example 1, the concentration ratio [Na ₂ CO ₃ ]/
[MgCl ₂ ]=0.73/0.70, the reaction temperature was 60℃, the addition rate of the magnesium chloride aqueous solution was 50ml/min, and
At 100 ml/min, stirring was stopped at the same time as the addition was completed, and the mixture was left to mature at the same temperature for 3 hours. At this time S/
The V ratio was 0.05 and 0.1. The obtained powder was confirmed to be basic magnesium carbonate by X-ray diffraction. According to scanning electron micrographs, the shape is flat plate-like at S/V = 0.05 (Fig. 14), and spherical at S/V = 0.1 (Fig. 15).
Figure). Example 5 Properties of the spherical basic magnesium carbonate powder obtained in Examples 1 to 4 (bulk density, angle of repose, specific surface area)
And the properties as a slurry (viscosity of an aqueous slurry containing 20% basic magnesium carbonate on a weight basis) were compared with conventional basic magnesium carbonate. The bulk density was measured in accordance with JIS K 6220, the angle of repose was measured using a powder tester (Hosokawa Powder Engineering Institute), and the specific surface area was measured using a rapid surface area measuring device (BET 1-point method, Shibata Chemical Instruments Co., Ltd.). The particle size was measured using a Cirrus particle size distribution meter (laser light transmission method, Seishin Enterprises). The viscosity of the slurry was measured at 25°C using a B-type rotational viscometer.
The results are shown in Table 4.

【table】

[Table] Compared to conventional products, spherical basic magnesium carbonate has
The bulk density is about 2 to 3 times higher, so it can be filled in large quantities as a filler for synthetic resins, and although the bulk density is large, the specific surface area does not decrease much, depending on the particle size.
m ² /g, it is useful as a carrier for agricultural medicines, and when it is made into a slurry, it significantly reduces its viscosity. Example 6 (Application example) The spherical basic magnesium carbonate shown in FIG. 13 of Example 3 was blended with polymethyl methacrylate resin monomer (methyl methacrylate) in various proportions, and the viscosity of the composition was adjusted to type B. Measured using a rotational viscometer. For comparison, similar measurements were conducted using conventional basic magnesium carbonate that is commercially available. The results are shown in Table 5.

[Table] The spherical basic magnesium carbonate of the present invention can be filled in a much larger amount as a filler for polymethyl methacrylate resin than conventional basic magnesium carbonate. Add 500 ml of a sodium carbonate aqueous solution with a concentration of 1.04 mol/liter maintained at 70°C under stirring at a rate of 1 liter/min, and add 500 ml of a maznesium sulfate aqueous solution with a concentration of 1.00 mol/liter maintained at the same temperature at a rate of 1 liter/min, and at the same time as the addition ends. Stirring was stopped, and the mixture was left to mature for 1 hour. The precipitate was filtered and washed, and then dried at 120°C for 5 hours. As a result of X-ray diffraction, the dried product was spherical basic magnesium carbonate. Micrograph 1 showing the shape
It is shown in Figure 7.

[Brief explanation of drawings]

Figures 1 to 6 show [Na ₂ CO ₃ ]/[MgCl ₂ ]=
7 to 9 are micrographs of the particle structure of Example 1 showing the effect of reaction temperature at [Na ₂ CO ₃ ]/[MgCl ₂ ]=0.73/0.70. FIGS. 10 to 12 are micrographs of the particle structure of Example 2 showing the influence of the standing aging time at [Na ₂ CO ₃ ]/[MgCl ₂ ]=1.04/1.00. FIG. 13 is a micrograph of the particle structure of Example 3 at S/V ratio=0.8, FIG. 14 is a photomicrograph of the particle structure of Example 4 at S/V=0.05, and FIG. 15 is a photomicrograph of Example 4 at S/V=0.1. FIG. 16 is a micrograph showing the particle structure of conventional basic magnesium carbonate. The magnification of each photo is 5000x for Figure 6 and 5000x for Figure 1.
All except Figure 4 is 1500x and Figure 16 is 3500x.
It is 350 times more. FIG. 17 is a micrograph (1000x magnification) of the particle structure obtained in Example 7.

Claims (1)

[Claims] 1. The shape of aggregated particles formed by agglomeration of fine particles is such that when the major axis is a and the minor axis is b,
It is spherical or spheroidal with b/a≧0.7,
The particle size of the aggregated particles is 5 to 60 μm, and the bulk density is 0.4.
-0.7g/ml, spherical basic magnesium carbonate with a specific surface area of ^10-40m2 /g. 2 In a method of synthesizing basic magnesium carbonate by reacting a water-soluble magnesium salt with an aqueous sodium carbonate solution, the temperature of the reaction system is maintained at 40 to 80°C, and the addition rate of the salt is S (liters/min) while stirring.
A method for producing spherical basic magnesium carbonate, which comprises mixing under the condition of S/V≧0.1 with respect to the reaction volume V (liters), and further ripening the mixture by standing in a mother liquor.