JPS6144807B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing barium sulfate, and more particularly to a method for producing ultrafine barium sulfate whose primary particles have an average particle size of 0.01 to 0.08μ. Conventionally, barium sulfate has generally been produced by an aqueous reaction in which an aqueous sodium sulfate solution and an aqueous barium sulfide solution are reacted, but the barium sulfate obtained in this way usually has an average particle size of 0.3 to 0.8μ. It is large and has a wide particle size distribution. Therefore, since conventional barium sulfate generally has a large hiding power, when various molded products such as sheets, films, containers, industrial parts, and decorative items are manufactured from resin compositions containing this barium sulfate, the molded products are transparent. There are disadvantages that are inferior to gender. Similarly, when used as a transparent pigment or extender pigment in paints or printing inks, it is generally difficult to obtain a dry film with excellent transparency and surface gloss due to light scattering of barium sulfate particles. Furthermore, in the case of dark-colored paints, for example, barium sulfate causes the paint film to become cloudy due to light scattering, and the colored pigments themselves have poor dispersibility, which tends to cause secondary aggregation, resulting in a clear and glossy paint film. can't get it. For this purpose, a method for producing barium sulfate with an average particle size of approximately 0.1μ has already been proposed (Tokuko Kokō 50-
33984), the barium sulfate obtained by this method also has a large particle size depending on its use, and also has a wide particle size distribution. The present invention was made to solve the various problems described above, and provides a method for producing ultrafine barium sulfate whose average particle size is much smaller than conventional products and whose particle size distribution is extremely narrow. The purpose is to The method for producing barium sulfate according to the present invention involves continuously introducing a barium sulfide aqueous solution and a sulfuric acid aqueous solution into a reaction tank so that the barium sulfide concentration is always in excess of the sulfuric acid, and stirring vigorously for an average of 10 minutes or less. It is characterized by the reaction being carried out over a residence time.
The barium sulfate obtained in this way has an average primary particle size of 0.01 to 0.08 μ, and a particle size of 0.1
It has a particle size distribution in which the number of primary particles of μ or less accounts for 90% or more, preferably 95% or more of the total. In the method of the present invention, in the aqueous reaction in which a barium sulfide aqueous solution and a sulfuric acid aqueous solution are reacted, barium sulfide always has a ratio of 0.05 to 100% relative to sulfuric acid.
%, preferably 0.1 to 20% excess. If sulfuric acid temporarily becomes excessive with respect to barium sulfide during the reaction, the barium sulfate particles produced will adhere to each other and aggregate, making it difficult to obtain barium sulfate of the desired particle size. This is because the amount of processing liquid becomes unnecessarily large and is not practical. In the present invention, the concentration of the sulfuric acid aqueous solution supplied to the reaction tank is 0.2 to 5 mol/, preferably 0.5 to 2 mol/; if a sulfuric acid aqueous solution with too low concentration is used, it will be difficult to process after the reaction as described above. If a highly concentrated sulfuric acid aqueous solution is used, the reaction temperature will rise during the reaction and the particle size of the resulting barium sulfate will tend to increase, which is not preferable. The concentration of the barium sulfide aqueous solution supplied to the reaction tank is 0.1 to 2 mol/min, depending on the reaction temperature.
, preferably 0.2 to 1.2 mol/.
The reaction temperature is also not particularly limited, but is usually between 30 and 100°C.
℃, preferably 50 to 80℃. In the present invention, an aqueous reaction between a barium sulfide aqueous solution and a sulfuric acid aqueous solution is continuously introduced into a reaction tank,
For vigorous stirring, a pump equipped with an impeller, for example, is suitable as the reaction tank. The average residence time of the raw material aqueous solution in the reaction tank is not particularly limited, but it is usually 10 minutes or less, preferably 10 seconds or less, particularly preferably 1 second or less. The average reaction rate of barium sulfide is not particularly limited, but is preferably 80% or more, particularly 90% or more. After the reaction, for example, if the pump discharge liquid is filtered, washed with water, slurried, and spray-dried, the average particle size of the primary particles will be 0.01 to 0.08μ.
It is possible to obtain barium sulfate with a particle size of about 50 to 500μ. If necessary, crush this with a hammer. Since the wavelength of visible light is 380 to 780 nm, if the particle size is less than half the wavelength of light, that is, less than 0.19μ,
In theory, light can pass through the particles. As mentioned above, the ultrafine barium sulfate according to the present invention has an average primary particle size of 0.01 to 0.08μ, and as will be explained later, substantially all of the primary particles are transparent to light. Since it is less than half a wavelength, it is substantially transparent when dispersed as primary particles in a resin or resin solution. Therefore, the ultrafine barium sulfate of the present invention can be advantageously used in various resin products. For example, when obtaining various resin molded products such as sheets, films, containers, etc., by using the barium sulfate of the present invention as a filler or transparent pigment, molded products with extremely excellent transparency can be obtained. The ultrafine barium sulfate of the present invention can be suitably used as a transparent pigment or filler in the production of thermosetting resin molded products, and can also be used in all applications for forming resin dry coatings, such as paints and printing inks. It can be advantageously used in resin compositions for various purposes such as transparent pigments, extender pigments, and dispersion aids. That is, since the barium sulfate of the present invention is easily dispersed into primary particles under normal pigment dispersion conditions for paints, printing inks, etc., the resulting resin coating does not become cloudy due to light scattering of barium sulfate, and therefore, Even if a large amount of this is used as an extender pigment, an extremely transparent film with good surface gloss can be obtained. If used as an extender pigment in dark colored paints,
Due to its excellent transparency, coatings with vivid colors can be obtained. In particular, colored organic pigments are often used as dark pigments, but they generally do not have good dispersibility in vehicles, and furthermore, when conventional barium sulfate is used as an extender pigment, its light scattering Since the coating film has a whitish tinge, it is impossible to obtain a clear, glossy, dark-colored coating. However, the barium sulfate of the present invention not only has transparency but also has excellent dispersibility, making it impossible to obtain a colored coating. It also acts as a dispersion aid for organic pigments, thus making it possible to obtain a deep-colored resin coating with a much clearer and glossier color tone than in the past. Furthermore, according to the method of the present invention, after the aqueous reaction,
Ultrafine barium sulfate, which is filtered, washed with water, and slurried to a concentration of 200 to 600 g/min, has primary particles interconnected to form a three-dimensional three-dimensional network structure, and thus the slurry exhibits non-Newtonian viscosity. Barium sulfate, which is granulated by spray-drying such a slurry, has a three-dimensional structure in which primary particles are interconnected, and when this is dispersed in an ink or paint composition, barium sulfate becomes primary particles. In addition to being easily dispersed, it also forms the above-mentioned three-dimensional structure in the composition, giving the composition non-Newtonian viscosity. As a result, so-called "sag", which is often a problem with paints, inks, etc., is prevented and the durability of the coating film is improved. Therefore, in combination with the effect of improving the dispersibility of the pigment as described above, a resin composition with excellent workability can be obtained. As described above, the method of the present invention differs from conventional aqueous solution reactions in that an aqueous barium sulfide solution and an aqueous sulfuric acid solution are continuously introduced into a reaction tank while controlling the barium sulfide concentration to always be in excess. The reaction is preferably carried out for a short period of time under thorough stirring to suppress the particle growth of the barium sulfate produced in the reaction system, so barium sulfate with a primary particle size much smaller than conventional products and a narrow particle size distribution can be obtained. be. Furthermore, since barium sulfide is reacted in excess of sulfuric acid, the obtained barium sulfate can be used for various purposes without adjusting the pH. The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Example A Nitsuso Warman pump (manufactured by Taiheiyo Kinzoku Co., Ltd.) with a suction port diameter of 1.5 inches, a discharge port diameter of 1 inch, an internal volume of 850 c.c., and an impeller rotation speed of 2380 rpm was used as a reaction tank. /
), a sulfuric acid aqueous solution at a temperature of 20°C is sucked in at a constant rate of 700 g/hour, and the barium sulfide concentration of the pump discharge liquid is 6 g/hour, and the concentration is 120 g/hour.
(0.71 mol/hour), a barium sulfide aqueous solution at a temperature of 50°C is sucked into the pump at a rate of approximately 1200/hour while controlling the suction amount (barium sulfide concentration approximately 10
% excess), an average residence time of 0.17 seconds, and an average reaction rate of barium sulfide of 92%. After filtering the pump discharge liquid with a filter press and washing with water, the resulting cake was stirred at high speed in water to determine the concentration.
A 500 g slurry was prepared and dried using a spray dryer. Hereinafter, this will be referred to as the product of the present invention. For comparison, using the same reactor as above,
Sulfuric acid and barium sulfide were reacted under the same conditions as above, except that the flow rate of the barium sulfide aqueous solution was controlled so that the pH of the pump discharge liquid was 1.5.
The obtained slurry was added to an aqueous sodium hydroxide solution.
Neutralizes to pH7, and further increases sodium hydroxide concentration.
Sodium hydroxide was added to the mixture at a concentration of 10 g, and the mixture was aged at 70°C for 4 hours. Next, this slurry was filtered and washed with water using a filter press, treated in the same manner as the above-mentioned product of the present invention, and dried using a spray dryer. Hereinafter, this will be referred to as comparative product 1. Furthermore, for comparison, ultrafine barium sulfate was produced according to the method described in Japanese Patent Publication No. 50-33984. That is, 1.4 mol/aqueous sodium sulfate solution 1 was charged into a 5-volume reaction tank at a temperature of 50°C, and 3.3 g of sodium hexametaphosphate was added and dissolved therein. While stirring this mixed solution,
To this, 0.8 mol/barium sulfide aqueous solution 1.75
was added dropwise, and the mixture was reacted for 1 hour at a temperature of 50°C. After the addition was completed, the mixture was stirred for an additional 30 minutes. The obtained slurry was filtered and washed with water using a film press, and the water-containing cake was dried at a temperature of 100° C. for 24 hours and then ground to obtain fine barium sulfate. Hereinafter, this will be referred to as comparative product 2. For each of the 300 particles of the present invention product and comparative products 1 and 2 obtained as described above, the particle size in a certain direction was measured using an electron micrograph at a magnification of 100,000 times, and the particle size distribution was determined. are shown in Table 1. Note that, for example, the particle size of 0.02μ means that the actual particle size is 0.015μ or more and less than 0.025μ. Further, FIG. 1 shows a graph of the particle size distribution of the product of the present invention and comparative products 1 and 2. FIGS. 2, 3, and 6 are electron micrographs of the inventive product and comparative products 2 and 1, respectively. Figure 5 shows the decrease compared to

【table】

[Table] Electron micrographs of calcium carbonate, which is referred to as fine calcium carbonate, are also shown. The average particle size of the comparative fine calcium carbonate is 0.08μ. As is clear from Table 1, in the barium sulfate of the present invention, the average particle size of primary particles is 0.05μ, and particles with a particle size of 0.1μ or less account for 96.0% of the total. On the other hand, in the barium sulfate of Comparative Products 1 and 2, the average particle size of the primary particles is 0.09μ and 0.10μ, respectively, and the particles with a particle size of 0.1μ or less account for only 71.6% and 64.5% of the total, respectively. As described above, barium sulfate produced by the method of the present invention has a significantly smaller average particle size and a significantly narrower particle size distribution than conventional products. Next, Fig. 5 shows barium sulfate whose primary particles have an average particle size of 0.05μ obtained by the method of the present invention.
An electron micrograph (5000x magnification) of a slurry with a concentration of 400 g is shown. It is clear that the primary particles are interconnected to form a three-dimensional three-dimensional network structure. Reference examples showing the use of ultrafine barium sulfate according to the method of the present invention are listed below. Reference example 1 Baking type alkyd resin (Betsukosol J-524,
Non-volatile content 60%, manufactured by Dainippon Ink & Chemicals Co., Ltd.) 18.2
Weight parts and melamine resin (Supervecamine J-
820, non-volatile content 50%, Dainippon Ink & Chemicals Co., Ltd.
5.1 parts by weight of xylene and 25 parts by weight of the product of the present invention obtained in Example were added to a mixed varnish (alkyd resin/melamine resin solids ratio 7/3) consisting of 9.3 parts by weight (manufactured by Manufacturer).
The mixture was dispersed to obtain a paint with a pigment volume concentration of 30%. Add the above varnish to this to achieve a pigment volume concentration of 20% and
Got 10% paint. For comparison, instead of the barium sulfate product of the present invention, 25 parts by weight of the comparative products 1 and 2, and 15.8 parts by weight of the comparative fine calcium carbonate.
Paints were prepared using each part by weight. Each of the paints thus obtained was applied in parallel onto a glass plate using a 6 mil applicator.
After drying at room temperature, it was baked at 140°C for 20 minutes to form a coating film with a thickness of 68μ. Regarding this paint film, the 20°/20° specular reflectance was measured using a gloss meter to evaluate the surface gloss of the paint film, and the perpendicular light transmittance was measured using a Hunter system value. The transparency was evaluated. The results are shown in Tables 2 and 3. As is clear from the above, according to the barium sulfate product of the present invention, even when the pigment volume concentration reaches 30% (160 parts by weight per 100 parts by weight of resin), the surface gloss and transparency of the resulting coating film are lower than that of the resin alone. It is almost the same as the coating film. On the other hand, in the case of Comparative Products 1 and 2 and Comparative Fine Calcium Carbonate, there is a remarkable decrease in gloss and transparency as the amount added increases. Reference example 2 Baking type acrylic resin (acrylic resin A-
405, non-volatile content 50%, Dainippon Ink & Chemicals Co., Ltd.
Mixed varnish (acrylic resin/melamine resin solid content ratio 7/
3) Weighed 24.5 parts by weight of xylene and 70 parts by weight of the product of the present invention obtained in the above example into a commercially available mayonnaise bottle,
330 g of glass beads with a diameter of 1.5 mm were added and dispersed with a paint conditioner for 1 hour to obtain a paint. For comparison, paints were obtained in the same manner as above, using Comparative Products 1 and 2, comparative fine calcium carbonate, and commercially available white carbon, respectively, in place of the product of the present invention. However, the viscosity of white carbon increased under the above conditions and it was difficult to make it into a paint, so the amount of white carbon added per 100 parts by weight of resin was changed.
The amount was 20 parts by weight. The paint viscosity of each paint thus prepared was measured. The non-Newtonian viscosity was determined by measuring the viscosity (cps) at rotational speeds of 6 rpm and 60 rpm using a rotational viscometer with the rotor held constant, and the ratio was evaluated as thixotropy (TF). In addition, each paint was applied onto a glass plate using a 6 mil applicator to form a coating film in the same manner as in Reference Example 1, and the surface gloss and transparency of this coating film was evaluated in the same manner as in Reference Example 1. evaluated.

【table】

【table】

【table】

[Table] The results are shown in Table 4. As is clear from the above table, the paint containing the product of the present invention exhibited significantly higher thixotropy than Comparative Product 2 and Comparative Fine Calcium Carbonate, and on the other hand, the gloss and transparency of the paint film were also significantly superior. ing. Comparative product 1 and commercially available white carbon exhibit relatively high thixotropy, but comparative product 1 is inferior to the product of the present invention in both gloss and transparency, and white carbon has a significant reduction in the gloss of the coating film.

[Brief explanation of the drawing]

Figure 1 is a graph showing the particle size distribution of the invention product, comparative products 1 and 2, and Figures 2, 3, and 4 are electron micrographs of the invention product, comparison product 2, and comparative fine calcium carbonate, respectively. Photograph (100,000x magnification), Figure 5 is an electron micrograph (5000x magnification) showing barium sulfate slurry obtained by the method of the present invention, Figure 6
The figure is an electron micrograph (100,000x magnification) of comparative product 1.

Claims (1)

[Claims] 1. Continuously introduce a barium sulfide aqueous solution and a sulfuric acid aqueous solution into a reaction tank so that the barium sulfide concentration is always in excess of sulfuric acid in the range of 0.05 to 100%, mix rapidly, and maintain an average residence time of 1 second or less. The average particle size of the primary particles is 0.01 to 0.08μ.
A method for producing ultrafine barium sulfate, characterized by obtaining barium sulfate having m.