Wet milling method

Abstract

To provide a wet milling method for a milled material in which contamination by impurities from a milling medium is reduced.SOLUTION: A wet milling method has: a first process in which acid or an acidic compound is brought into contact with a dispersion solvent containing a milled material, and a mixed solution for wet milling is obtained; and a second process in which the mixed solution for wet milling is wet-milled by a milling medium in a wet milling device in which the milling medium is filled, and a wet-milled liquid is obtained. The milled material is a material which increases pH of the dispersion solvent by contacting the dispersion solvent, and in the second process, wet milling is performed in the state that pH of the mixed solution for wet milling is 9 or more and 11 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for wet grinding a material to be ground, which reduces the influence of contamination by grinding media. [Background technology]

[0002] Perovskite-type complex oxides, typified by barium titanate, have traditionally been used as raw materials for functional ceramics such as piezoelectric materials and multilayer ceramic capacitors. However, in recent years, multilayer ceramic capacitors have been required to have an increased number of layers and a higher dielectric constant in order to achieve higher capacitance, and this has led to a demand for nano-level microparticulation of perovskite-type complex oxides.

[0003] Various methods can be used to microparticulate perovskite complex oxides, and microparticulation is possible using, for example, grinders such as bead mills, ball mills, jet mills, etc. Among these, bead mills use minute beads as grinding media, and therefore exert little force on the perovskite complex oxide powder being ground, but because the particles frequently collide with the minute beads, they are frequently used as a method for microparticulating the particles while minimizing damage to them.

[0004] Several methods for milling perovskite-type composite oxides using a bead mill have been proposed. For example, Patent Document 1 describes using silicon nitride ceramic media to mill barium titanate-based semiconducting ceramic raw materials, thereby reducing the amount of contaminants caused by media wear. Patent Document 2 describes grinding the material to be milled with chemically soluble beads, such as YO or SiO, in acid, and then separating the abrasion powder generated from the beads through an acid dissolution process to obtain a high-purity milled product. Patent Document 3 also proposes a technology that uses acid-soluble oxide or carbonate particles as beads to mill an inorganic or organic slurry, and then adds an acidic substance to the slurry to dissolve the beads, thereby preventing contamination by bead components.

[0005] While the methods described in the above patent documents exist, methods have also been proposed for preventing contamination of the material to be ground due to wear of beads, not limited to when the material to be ground is a perovskite-type composite oxide. For example, Patent Document 4 describes that contamination caused by beads can be reduced by adjusting the pH of a mixture containing the material to be ground, beads, and a dispersion medium to 6.5 to 9. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-251086 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-51887 [Patent Document 3] Japanese Patent Application Publication No. 2018-58053 [Patent Document 4] International Publication No. 2020 / 179701 Summary of the Invention [Problem to be solved by the invention]

[0007] The grinding methods using bead mills cited in the above patent documents use beads as grinding media, and various methods are used to remove impurities in order to prevent the components constituting the beads from being mixed into the ground product as impurities due to wear on the bead surface. However, some contamination of the ground product was observed, and it was necessary to consider methods to further prevent contamination. In addition, depending on the pH of the mixture containing the ground product, there was also the problem that components derived from the ground product could be eluted, reacted, and mixed into the ground product as by-products.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for wet grinding a material to be ground that reduces contamination by impurities from the grinding media and by-products. [Means for solving the problem]

[0009] In light of the above-mentioned circumstances, the present inventors have conducted extensive research and found that when wet milling is performed using metal oxides such as zirconia or alumina as milling media, the surface of the milling media is worn due to collisions between the material to be milled and the milling media, leading to metal contamination of the milled product. However, when the pH of the dispersion solvent increases, the surface of the milling media becomes more susceptible to wear, and by adding an acid or acidic compound to the wet milling system to prevent the pH of the dispersion solvent from becoming too high during the wet milling process, wear on the surface of the milling media can be suppressed. Furthermore, when the pH of the dispersion solvent decreases, components derived from the material to be milled are eluted, causing side reactions to form impurities, leading to a deterioration in the quality of the material to be milled. This led to the completion of the present invention.

[0010] That is, the present invention (1) comprises a first step of contacting an acid or an acidic compound with a dispersion solvent containing a material to be pulverized to obtain a mixture for wet-pulverization; a second step of wet-grinding the mixture with grinding media in a wet-grinding apparatus filled with grinding media to obtain a ground wet-grinding solution; and The material to be ground is a material that increases the pH of the dispersion medium upon contact with the dispersion medium; and In the second step, the pH of the mixture for wet-grinding treatment is adjusted to 9 or more and 11 or less, and the wet-grinding treatment is carried out. The present invention provides a wet grinding method characterized by the above.

[0011] The present invention (2) provides the wet-grinding method according to (1), characterized in that the second step is carried out by supplying the wet-grinding mixture to the wet-grinding apparatus while discharging the wet-grinding mixture from the wet-grinding apparatus, and wet-grinding the wet-grinding mixture with the grinding media in the wet-grinding apparatus to obtain a ground wet-grinding solution.

[0012] The present invention (3) also provides the wet-grinding method according to (2), characterized in that the residence time of the wet-grinding mixture in the second grinding step is 1 to 1200 seconds.

[0013] The present invention (4) provides a wet-grinding method according to any one of (1) to (3), characterized in that the first step is carried out by contacting the wet-grinding treatment liquid obtained by carrying out the second step with an acid or an acidic compound to obtain a mixed liquid for wet-grinding treatment, and then the mixed liquid for wet-grinding treatment obtained is wet-grinded to carry out the second step, which is repeated one or more times.

[0014] The present invention (5) also provides any one of the wet-grinding methods (1) to (4), characterized in that in the first step, the pH of the dispersion solvent containing the material to be ground is lowered by 0.10 to 5 by bringing an acid or an acidic compound into contact with the dispersion solvent containing the material to be ground, thereby obtaining a mixture for wet-grinding treatment.

[0015] The present invention (6) also provides the wet-grinding method according to any one of (1) to (5), wherein the pH of the wet-grinding treatment liquid obtained by carrying out the second step is 9 or more and 11 or less.

[0016] The present invention (7) also provides the wet-grinding method according to any one of (1) to (6), wherein the acid or acidic compound is one or more selected from inorganic acids, organic acids, and acidic dispersants.

[0017] The present invention (8) also provides the wet-grinding method according to (7), wherein the inorganic acid is one or more acids selected from carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0018] The present invention (9) also provides the wet grinding method according to (7), characterized in that the organic acid is one or more selected from the group consisting of formic acid, acetic acid, citric acid, succinic acid and malonic acid.

[0019] The present invention (10) also provides the wet-grinding method according to (7), characterized in that the acidic dispersant is one or two compounds selected from the group consisting of polycarboxylic acid compounds, polyphosphoric acid compounds, and phosphonic acid compounds.

[0020] The present invention (11) also provides the wet grinding method according to any one of (1) to (10), wherein the grinding medium is one or more types of beads or balls selected from zirconia, alumina, silica, titania, and silicon nitride.

[0021] The present invention (12) also provides the wet-grinding method according to any one of (1) to (11), wherein the dispersion solvent is water or a mixed solvent of water and an aqueous organic solvent.

[0022] The present invention (13) also provides the wet-pulverization method according to any one of (1) to (12), characterized in that the material to be pulverized is a perovskite-type composite oxide.

[0023] The present invention (14) also provides the wet-grinding method according to (13), characterized in that the perovskite-type composite oxide is one or more selected from barium titanate, calcium titanate, magnesium titanate, strontium titanate, barium calcium titanate, barium strontium titanate, barium magnesium titanate, calcium magnesium titanate, calcium strontium titanate, and magnesium strontium titanate.

[0024] The present invention (15) also provides any one of the wet-grinding methods (1) to (14), characterized in that the content of the material to be ground in the dispersion solvent containing the material to be ground is 5 to 80 mass %.

[0025] The present invention (16) also provides the wet-grinding method according to any one of (1) to (15), characterized in that the volume ratio of the grinding media to the wet-grinding mixture is 10 to 90 volume %. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a wet grinding method for a material to be ground that reduces contamination by impurities from the grinding media and by-products. DETAILED DESCRIPTION OF THE INVENTION

[0027] The wet grinding method of the material to be ground of the present invention comprises the steps of: A first step of contacting an acid or an acidic compound with a dispersion solvent containing a material to be pulverized to obtain a mixture for wet pulverization; a second step of wet-grinding the mixture with grinding media in a wet-grinding device filled with grinding media to obtain a ground wet-grinding solution; and The material to be ground is a material that increases the pH of the dispersion medium upon contact with the dispersion medium; and In the second step, the pH of the mixture for wet-grinding treatment is adjusted to 9 or more and 11 or less, and the wet-grinding treatment is carried out. This is a wet grinding method characterized by the above.

[0028] The first step in the method for wet-pulverizing a material to be pulverized of the present invention is to obtain a mixture for wet-pulverization by bringing an acid or an acidic compound into contact with a dispersion solvent containing the material to be pulverized.

[0029] The dispersion solvent used in the wet grinding method for a material to be ground according to the present invention is not particularly limited as long as the material to be ground is uniformly finely ground by the grinding medium, and examples thereof include water and a mixed solvent of water and an aqueous organic solvent. Examples of the water include pure water, ion-exchanged water, tap water, and industrial water. Among these, pure water and ion-exchanged water are preferred, and pure water is particularly preferred, from the viewpoint of preventing contamination of the material to be ground. Examples of the aqueous organic solvent include methanol, ethanol, propanol, butanol, ethylene glycol, and toluene. Among these, ethanol is particularly preferred because it is easy to handle and allows the material to be ground more uniformly. The water content in the mixed solvent of water and an aqueous organic solvent is preferably 50% by mass or more.

[0030] The material to be ground in the wet-grinding method for a material to be ground of the present invention is a material that increases the pH of the dispersion solvent when it comes into contact with water or a mixed solvent of water and an aqueous organic solvent. When wet-grinding is performed using metal oxides such as zirconia or alumina as the grinding medium, the surface of the grinding medium becomes more susceptible to wear as the pH of the dispersion solvent increases. Therefore, in the wet-grinding method for a material to be ground of the present invention, since the material to be wet-grinded increases the pH of the dispersion solvent when it comes into contact with the dispersion solvent, an acid or acidic compound is mixed into the wet-grinding system before grinding to prevent the pH of the dispersion solvent from becoming too high during the wet-grinding process.

[0031] Examples of the material to be pulverized in the wet-pulverization method for a pulverized material of the present invention include perovskite complex oxides. Perovskite complex oxides are compounds that increase the pH of a dispersion solvent when they come into contact with water or a mixed solvent of water and an aqueous organic solvent, which is the dispersion solvent. The perovskite complex oxide is not particularly limited as long as it is a perovskite complex oxide having an ABO3 structure, but perovskite complex oxides in which the A-site element is at least one selected from Ba, Ca, Mg, and Sr and the B-site element is at least one selected from Ti, Sn, Pb, and Zr are preferred.Examples of such perovskite complex oxides in which the A-site element is at least one selected from Ba, Ca, Mg, and Sr and the B-site element is at least one selected from Ti, Sn, Pb, and Zr include barium titanate, calcium titanate, magnesium titanate, strontium titanate, barium calcium titanate, barium magnesium titanate, barium strontium titanate, calcium magnesium titanate, calcium strontium titanate, magnesium strontium titanate, barium stannate, calcium stannate, magnesium stannate, strontium stannate, barium calcium stannate, barium magnesium stannate, barium strontium stannate, calcium magnesium stannate, calcium strontium stannate, magnesium strontium stannate, barium zirconate, calcium zirconate, magnesium zirconate, strontium zirconate, barium calcium zirconate, Examples of suitable stannates include barium magnesium stannate, barium strontium zirconate, calcium magnesium zirconate, calcium strontium zirconate, strontium magnesium zirconate, barium titanate stannate, calcium titanate stannate, magnesium titanate stannate, strontium titanate stannate, barium calcium titanate stannate, barium magnesium titanate stannate, barium strontium titanate stannate, calcium magnesium titanate stannate, calcium strontium titanate stannate, strontium magnesium titanate stannate, barium zirconate, calcium titanate zirconate, magnesium zirconate, strontium titanate zirconate, barium calcium titanate zirconate, barium magnesium titanate zirconate, barium strontium titanate zirconate, calcium magnesium titanate zirconate, calcium strontium titanate zirconate, and strontium magnesium zirconate.

[0032] The average particle size of the perovskite complex oxide to be used as the material to be pulverized is preferably 0.010 to 1 μm, more preferably 0.020 to 0.5 μm. The perovskite complex oxide having an average particle size within the above range is preferred because it is easy to obtain and handle. In the present invention, the average particle size of the perovskite complex oxide to be used as the material to be pulverized means the BET-equivalent particle size, which is calculated from the specific surface area measured by the BET method, assuming that the particles are spherical.

[0033] The BET specific surface area of ​​the perovskite complex oxide to be ground is preferably 0.10 m 2 / g or more, more preferably 0.5 to 50m 2 The BET specific surface area of ​​the perovskite complex oxide is preferably within the above range, since it is easy to obtain and handle.

[0034] The method for preparing the perovskite complex oxide to be used as the material to be pulverized is not particularly limited, and examples thereof include an organic acid salt method such as an oxalate method, a coprecipitation method, a hydrolysis method, a hydrothermal synthesis method, a solid phase method, etc. Commercially available perovskite complex oxides can also be used as the perovskite complex oxide to be used as the material to be pulverized.

[0035] When perovskite-type composite oxides obtained by the organic acid salt method, particularly the oxalate method or the solid-phase method, come into contact with the dispersion solvent, water or a mixed solvent of water and an aqueous organic solvent, a large amount of alkaline (A-site) components are eluted from the particle surface, resulting in a large increase in the pH of the dispersion solvent upon contact with the dispersion solvent. Therefore, when the material to be ground is a perovskite-type composite oxide obtained by the organic acid salt method, particularly the oxalate method or the solid-phase method, the pH of the dispersion solvent becomes too high when the material to be ground comes into contact with the dispersion solvent, so it is necessary to lower the pH of the dispersion solvent using an acid or an acidic compound. Therefore, as the perovskite-type composite oxide to be ground, perovskite-type composite oxides obtained by the organic acid salt method, such as the oxalate method, or the solid-phase method are preferred because they enhance the effects of the present invention.

[0036] Furthermore, perovskite complex oxides obtained by hydrolysis or hydrothermal synthesis have low elution of alkaline (A-site) components from the particle surface when they come into contact with the dispersion solvent, water or a mixture of water and an aqueous organic solvent, resulting in a low increase in the pH of the dispersion solvent upon contact with the dispersion solvent. However, even when the material to be ground is a perovskite complex oxide obtained by hydrolysis or hydrothermal synthesis, the pH of the dispersion solvent becomes too high if the grinding time is long or the number of grinding treatments is increased, so it is necessary to lower the pH of the dispersion solvent using an acid or an acidic compound. Therefore, even when the pH of the dispersion solvent becomes too high due to the grinding conditions or repeated grinding, the effects of the present invention can be achieved by performing the first and second steps of the wet grinding method for a material to be ground of the present invention using a perovskite complex oxide obtained by hydrolysis or hydrothermal synthesis as the material to be ground.

[0037] The acid used in the wet-pulverization method for a pulverizable material of the present invention may be an inorganic acid or an organic acid. The inorganic acid is preferably one or more selected from carbonic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and hydrofluoric acid. When carbonic acid is used as the inorganic acid, carbon dioxide is introduced into a dispersion solvent containing the pulverizable material to generate carbonic acid in the dispersion solvent, thereby bringing the dispersion solvent containing the pulverizable material into contact with the carbonic acid. The organic acid is preferably one or more selected from formic acid, acetic acid, citric acid, succinic acid, and malonic acid. Furthermore, an acidic compound used in the wet-pulverization method for a pulverizable material of the present invention may, for example, be an acidic dispersant. An acidic compound is an acid that, when contacted with a dispersion solvent that is water or a mixed solvent of water and an aqueous organic solvent, generates H in the dispersion solvent. + Acidic dispersants refer to compounds that produce the above. Examples of acidic dispersants include polycarboxylic acid compounds, polyphosphoric acid compounds, and phosphonic acid compounds. Among these, from the viewpoint of further suppressing contamination by impurities from the grinding medium in the second step, the acid or acidic compound is preferably carbonic acid, hydrochloric acid, nitric acid, or acetic acid.

[0038] In the first step of the wet-grinding method for a pulverized material of the present invention, an acid or an acidic compound is contacted with a dispersion solvent containing the pulverized material to obtain a wet-grinding mixture. Examples of methods for contacting an acid or an acidic compound with a dispersion solvent containing the pulverized material include adding an aqueous acid solution to the dispersion solvent containing the pulverized material and mixing them together, introducing carbon dioxide into the dispersion solvent containing the pulverized material to generate carbon dioxide in the dispersion solvent, and contacting the dispersion solvent with carbon dioxide, and adding a dispersion solution of an acidic compound to the dispersion solvent containing the pulverized material and mixing them together. The pulverized material is a material that increases the pH of the dispersion solvent upon contact with the dispersion solvent, so in the first step, an acid or an acidic compound is contacted with the dispersion solvent containing the pulverized material to lower the pH of the dispersion solvent.

[0039] The dispersion solvent containing the pulverized material may be prepared by mixing the unpulverized material with the dispersion solvent. Alternatively, the wet-pulverized liquid obtained in the second step may be used as the dispersion solvent containing the pulverized material.

[0040] The content of the material to be pulverized in the dispersion solvent containing the material to be pulverized is preferably 5 to 80% by mass, more preferably 10 to 70% by mass. When the content of the material to be pulverized in the dispersion solvent containing the material to be pulverized is within the above range, the pulverization efficiency is improved, the yield is high, and the size of the obtained particles is uniform, resulting in high-quality particles.

[0041] When the material to be ground is a perovskite complex oxide, upon contact with water or a mixed solvent of water and an aqueous organic solvent, the A-site elements dissolve into the dispersion solvent, raising the pH of the dispersion solvent, for example, making the dispersion solvent strongly alkaline, exceeding pH 11. The inventors have found that if the material to be ground is ground with grinding media while the pH of the wet-grinding mixture is high, the grinding media dissolves into the dispersion solvent, resulting in contamination of the finely ground perovskite complex oxide with impurities from the grinding media. The inventors have also found that if the pH of the wet-grinding mixture is too low, impurities derived from the dissolved A-site elements are easily produced as by-products, leading to contamination of the finely ground perovskite complex oxide. Therefore, in the first step, an acid or acidic compound is contacted with a dispersion solvent containing the material to be ground, which increases the pH of the dispersion solvent upon contact with the dispersion solvent, to obtain a wet-grinding mixture containing the material to be ground, with the pH adjusted to between 9 and 11. That is, in the first step, an acid or acidic compound is brought into contact with a dispersion solvent containing the material to be ground, which increases the pH of the dispersion solvent upon contact with the dispersion solvent, thereby obtaining a mixture for wet grinding treatment with a pH adjusted to an optimal range.

[0042] In the first step, it is preferable to obtain a mixture for wet-grinding treatment by contacting the dispersion solvent containing the material to be pulverized with an acid or an acidic compound to lower the pH of the dispersion solvent containing the material to be pulverized by 0.10 to 5, and particularly by 0.50 to 4. By obtaining a mixture for wet-grinding treatment in which the pH of the dispersion solvent containing the material to be pulverized is lowered within the above range, the effect of preventing elution of the grinding media and contamination by by-products in the second step is enhanced.

[0043] In the first step, the pH of the wet-milling mixture obtained by contacting the dispersion solvent containing the material to be milled with an acid or acidic compound is 9 or more and 11 or less. The lower limit of the pH range of the wet-milling mixture is 9 or more, preferably greater than 9, more preferably greater than 9.1, even more preferably greater than 9.1, particularly preferably greater than 9.2, and most preferably greater than 9.2, while the upper limit is 11 or less, preferably less than 11, and more preferably 10.9 or less. These upper and lower limits can be combined. If the pH of the wet-milling mixture is less than 9, impurities derived from A-site elements are easily produced as by-products, leading to contamination of the milled perovskite-type composite oxide. Furthermore, if the pH exceeds 11, the milling media will dissolve in the dispersion solvent, and the milled perovskite-type composite oxide will be contaminated by impurities derived from the milling media. When the pH of the mixture for wet-milling treatment is within the above range, the wear on the surface of the milling media during the wet-milling treatment is suppressed, and the effect of reducing impurities derived from A-site elements is enhanced.

[0044] In the first step, for example, the pH of the dispersion medium containing the material to be ground is 11 or higher, preferably 12 or higher, and the pH is adjusted to 9 or higher, lower than the pH before mixing with the acid or acidic compound, preferably to a pH greater than 9 and less than 11, by contact with an acid or acidic compound to obtain a mixture for wet grinding.

[0045] In the first step, when preparing a dispersion solvent containing the material to be ground by mixing the unground material with the dispersion solvent, for example, first, the dispersion solvent is placed in a mixing container, and then the pH of the dispersion solvent is monitored to control the amount of the material to be ground and the amount of the acid or acidic compound to be mixed into the dispersion solvent (if carbon dioxide is introduced into the dispersion solvent to bring carbon dioxide into contact with it, the amount of carbon dioxide introduced into the dispersion solvent) so that the pH of the dispersion solvent is close to the target pH, and the unground material to be ground and the acid or acidic compound are brought into contact with the dispersion solvent continuously or intermittently, thereby performing the first step and preparing a mixture for wet grinding. Furthermore, when wet-grinding the material to be ground multiple times in the first step, the wet-grinding liquid obtained in the second step is used as the dispersion solvent containing the material to be ground. For example, while the wet-grinding liquid obtained in the second step is introduced into a mixing vessel, the pH of the dispersion solvent is monitored, and the amount of the wet-grinding liquid obtained in the second step and the amount of the acid or acidic compound mixed (when carbon dioxide is introduced into the dispersion solvent to bring carbon dioxide into contact with the dispersion solvent, the amount of carbon dioxide introduced into the dispersion solvent) is controlled so that the pH of the dispersion solvent is close to the target pH. The wet-grinding liquid obtained in the second step and the acid or acidic compound are continuously or intermittently introduced into the mixing vessel to prepare a wet-grinding mixed liquid.

[0046] The wet-grinding mixture obtained by carrying out the first step is a dispersion medium in which the material to be ground has been dispersed and whose pH has been adjusted with an acid or an acidic compound. In other words, the wet-grinding mixture obtained by carrying out the first step is a dispersion medium containing the material to be ground and whose pH has been adjusted with an acid or an acidic compound.

[0047] The second step in the method for wet-grinding a material to be ground of the present invention is to wet-grind the wet-grinding mixture obtained in the first step using grinding media to obtain a ground wet-grinding solution.

[0048] In the second step, the wet-grinding mixture is introduced into a grinding device filled with grinding media, and the wet-grinding mixture and the grinding media are mixed and stirred, thereby wet-grinding the wet-grinding mixture containing the material to be ground.

[0049] The wet-grinding apparatus used in the wet-grinding method of the present invention is not particularly limited as long as it can agitate the liquids in the wet-grinding apparatus, i.e., the material to be pulverized, the dispersion solvent, and the grinding medium, and cause the material to be pulverized, the dispersion solvent, and the grinding medium to flow. In the wet-grinding method of the present invention, examples of the wet-grinding apparatus that pulverizes the material to be pulverized while stirring the material to be pulverized, the dispersion solvent, and the grinding medium include a bead mill and a ball mill.

[0050] The grinding media used in the wet grinding method of the present invention for a material to be ground is not particularly limited as long as it can uniformly grind the material to be ground and can be easily separated from the material to be ground after grinding, but it is preferable that the grinding media be one or more selected from the group consisting of zirconia, alumina, silica, titania, and silicon nitride. Furthermore, the grinding media are preferably in the form of beads or balls, from the viewpoint of effectively grinding the material to be ground.

[0051] In the second step, when beads are used as the grinding media, the diameter of the beads is preferably 0.005 to 10.0 mm, particularly 0.01 to 6.0 mm. When balls are used as the grinding media, the diameter of the balls is preferably 0.05 to 20 mm, particularly 0.1 to 10 mm.

[0052] In the second step, the stirring speed when stirring the wet-grinding mixture and grinding media in the wet-grinding processor depends on the scale of the grinding processor, but for example, on a 0.1 L scale, a peripheral speed of 2 to 14 m / s is preferred, and 3 to 13 m / s is particularly preferred. By keeping the stirring speed when stirring the wet-grinding mixture and grinding media in the wet-grinding processor within the above range, the material to be ground can be effectively ground by the grinding media moving in the wet-grinding mixture.

[0053] In the second step, the stirring conditions for stirring the wet-grinding treatment mixture and grinding media in the wet-grinding treatment device are, for example, when a bead mill is used as the wet-grinding treatment device, such that the volume ratio of grinding media to the wet-grinding treatment mixture is 10 to 90% by volume, particularly 20 to 80% by volume, and the stirring speed is preferably a peripheral velocity of 2 to 14 m / sec, particularly 3 to 13 m / sec.

[0054] In the second step, the temperature at which the material to be pulverized in the wet pulverizing treatment device is pulverized is preferably 5 to 60°C, particularly 10 to 50°C, in order to obtain a fine perovskite-type composite oxide.

[0055] In the second step, the pH of the wet-milling solution obtained by wet-milling with milling media is preferably 9 to 11, more preferably greater than 9 but less than 11, and particularly preferably 9.1 to 10.9. Having the pH of the wet-milling solution within this range further suppresses elution of the milling media and by-products derived from A-site elements, thereby preventing contamination by impurities. The pH of the wet-milling solution obtained by performing the second step can be adjusted by, for example, appropriately selecting the wet-milling conditions, such as milling time, residence time, and stirring speed, or by selecting the pH of the wet-milling mixture before milling.

[0056] After the wet-pulverization treatment in the second step, the wet-pulverization treatment liquid containing the pulverization media is filtered or the like to separate the pulverization media from the wet-pulverization treatment liquid containing the pulverization media, thereby obtaining a wet-pulverization treatment liquid.

[0057] The wet-pulverization treatment according to the wet-pulverization method of the present invention for a pulverizable material may be repeated any number of times as desired. Specifically, the wet-pulverization treatment liquid obtained in the second step is used as a dispersion medium containing the pulverizable material in the first step, and the first and second steps can be repeated at least once, preferably 1 to 1,000 times, and more preferably 2 to 100 times. The pulverization treatment in the second step exposes new surfaces of the pulverizable material, and the pH of the wet-pulverization mixture increases relative to the pH of the dispersion medium containing the pulverizable material prior to the pulverization treatment. For example, if the second step alone is performed for a long period of time or multiple times in order to pulverize the pulverizable material to a desired particle size, the pH of the wet-pulverization mixture may increase too much. Therefore, the wet-grinding treatment mixture obtained in the second step is used as a dispersion solvent containing the material to be ground in the first step, and the dispersion solvent containing the material to be ground is again contacted with an acid or an acidic compound to obtain a wet-grinding treatment mixture with a lowered pH.In the second step, the wet-grinding treatment mixture is again wet-grinded with grinding media to obtain a ground wet-grinding treatment mixture.By repeating this process one or more times, even if wet-grinding is performed multiple times, the increase in pH of the wet-grinding treatment mixture can be suppressed, the elution of grinding media into the wet-grinding treatment mixture is further suppressed, and contamination by the grinding media can be prevented.

[0058] In the wet-grinding method of the present invention for the material to be ground, the wet-grinding treatment liquid obtained by carrying out the second step (the final second step if the first and second steps are repeated multiple times) can be dried, centrifuged, filtered, etc. to separate the dispersion solvent and obtain the desired wet-grinding treatment powder.

[0059] In one embodiment of the wet-grinding method of the present invention (hereinafter referred to as embodiment (1) of the wet-grinding method of the present invention), in the second step of the wet-grinding method of the present invention, the wet-grinding mixture is supplied to a wet-grinding treatment device, and while the wet-grinding treatment liquid is discharged from the wet-grinding treatment device, the wet-grinding mixture is wet-grinded with grinding media in the wet-grinding treatment device to obtain a ground wet-grinding treatment liquid.

[0060] The wet-grinding method according to the first embodiment of the present invention comprises a first step of contacting an acid or an acidic compound with a dispersion solvent containing a material to be pulverized to obtain a mixture for wet-grinding treatment; a second step of supplying the wet-pulverization mixture to a wet-pulverization apparatus filled with pulverization media, while discharging the wet-pulverization mixture from the wet-pulverization apparatus, and wet-pulverizing the wet-pulverization mixture with the pulverization media in the wet-pulverization apparatus to obtain a pulverized wet-pulverization mixture; and The material to be ground is a material that increases the pH of the dispersion medium upon contact with the dispersion medium; and In the second step, the pH of the mixture for wet-grinding treatment is adjusted to 9 or more and 11 or less, and the wet-grinding treatment is carried out. This is a wet grinding method characterized by the above.

[0061] In the wet-grinding method of the present invention, for example, a wet-grinding mixture is supplied to one end of a wet-grinding device such as a bead mill while the wet-grinding mixture is discharged from the other end of the device, and the wet-grinding mixture is wet-grinded with grinding media to obtain a ground wet-grinding liquid. The type of wet-grinding device is not particularly limited, and may be either vertical or horizontal.

[0062] The residence time of the wet-grinding mixture in the second grinding step according to embodiment (1) of the wet-grinding method of the present invention is 1 to 1200 seconds, preferably 2 to 900 seconds. The residence time of the wet-grinding mixture refers to the value obtained by dividing the volume (L) of the wet-grinding mixture present in the wet-grinding treatment device during the wet-grinding treatment by the supply rate (L / sec) of the wet-grinding mixture supplied to the wet-grinding treatment device per unit time.

[0063] In the wet-pulverization method of the present invention, the first and second steps are carried out once using an unpulverized material to be pulverized, thereby obtaining the target wet-pulverized product (single pass).

[0064] In addition, in embodiment (1) of the wet-milling method of the present invention, the wet-milling solution obtained in step (2) is contacted with an acid or an acidic compound to obtain a wet-milling mixture, and step (1) is then repeated. The resulting wet-milling mixture is then wet-milled, and step (2) is repeated one or more times to obtain the desired wet-milled product (multiple passes). In embodiment (1) of the wet-milling method of the present invention, by performing steps (1) and (2) in multiple passes, the pH of the wet-milling solution can be adjusted to 9 or higher and 11 or lower, more preferably greater than 9 and lower than 11, and particularly preferably 9.1 or higher and 10.9 or lower, even when wet-milling is performed multiple times. This further suppresses elution of milling media into the wet-milling solution and by-products derived from A-site elements, thereby preventing contamination by impurities.

[0065] In the wet-pulverization method of the present invention, the average particle size of the pulverized material after pulverization, for example, the perovskite-type composite oxide, determined from the BET-equivalent particle size, is preferably 0.005 to 0.9 μm, and more preferably 0.01 to 0.4 μm. In addition, the BET specific surface area is preferably 1.1 to 200 m. 2 / g, preferably 2.5 to 100m 2 The mixing ratio of the material to be ground and the dispersion solvent, the volume ratio of the grinding medium to the wet grinding treatment mixture, the degree of adjustment of the initial pH and the pH after addition of the acid or acidic compound, the stirring speed, and other grinding conditions can be appropriately selected so that the resulting mass is 0.01g / g.

[0066] To manufacture a multilayer ceramic capacitor using the perovskite complex oxide obtained by the wet grinding method of the present invention, the perovskite complex oxide powder is first mixed and dispersed in a suitable solvent with conventional additives, including minor component elements, organic binders, plasticizers, dispersants, and other compounding agents to form a slurry, which is then formed into a sheet. This produces a ceramic sheet for use in manufacturing a multilayer ceramic capacitor. To fabricate a multilayer ceramic capacitor from the ceramic sheet, first, a conductive paste for forming internal electrodes is printed on one side of the ceramic sheet. After drying, multiple ceramic sheets are stacked and pressed together in the thickness direction to form a laminate. Next, the laminate is heated to remove the binder and fired to obtain a fired body. The fired body is then coated with a Ni paste, Ag paste, nickel alloy paste, copper paste, copper alloy paste, or the like and baked to obtain a multilayer ceramic capacitor.

[0067] Furthermore, the perovskite complex oxide powder obtained by the wet grinding method of the present invention for grinding a material can be blended with a resin such as an epoxy resin, polyester resin, or polyimide resin to form a resin sheet, resin film, adhesive, or the like, which can be used as a material for printed wiring boards and multilayer printed wiring boards, as well as a co-material for suppressing the difference in shrinkage between internal electrodes and dielectric layers, an electrode ceramic circuit board, a glass ceramic circuit board, a circuit peripheral material, and a dielectric material for inorganic EL.

[0068] Furthermore, the perovskite complex oxide obtained by the wet grinding method of the present invention for the material to be ground is suitable for use as a catalyst used in reactions such as exhaust gas removal and chemical synthesis, or as a surface modifier for printing toner that imparts antistatic and cleaning effects. [Example]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The properties in the examples were measured by the following methods. (1) Zirconium oxide (ZrO2) content Measurement was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) using an ICAP6000 manufactured by Thermo Fisher Scientific. (2) Average particle size The cumulative 50% (D50) value of the volume frequency particle size distribution measured by the laser diffraction scattering method using the MT3300EX manufactured by Microtrac Bell was used as the average particle size. (3) BET specific surface area It was determined by the BET method. (4) Alkaline earth metal salt content Measurement was carried out by X-ray diffraction (XRD) using a Bruker D8 ADVANCE.

[0070] Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-2 75 g of barium titanate having an average particle size of 40 nm was added to 300 g of pure water and stirred to prepare a 20 mass % slurry. The pH of this slurry was 13. While stirring this slurry at 10°C in a jacketed stirring tank, carbon dioxide gas was added while adjusting the pH of the slurry to the pH shown in Table 1. Note that no carbon dioxide gas was added in Comparative Example 1-2. The resulting slurry was wet-milled in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and then re-introduced into the wet mill, counting as one pass. Milling was repeated for a total of 15 passes. Carbon dioxide gas was added to the slurry after each milling run, adjusting the pH of the slurry to the pH shown in Table 1. This process was repeated 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO content, average particle size, BET specific surface area, and alkaline earth metal salt (barium carbonate) content of the obtained dry powder were measured, and the results are shown in Table 1.

[0071] [Table 1]

[0072] In Table 1, BT refers to barium titanate. As shown in Table 1, the barium titanate powders of each Example, obtained by adding carbon dioxide to adjust the pH of the slurry to between 9 and 11, have a lower barium carbonate content in the dry powder than Comparative Example 1-1, obtained by adjusting the pH to less than 9. It is also clear that the barium titanate powders of each Example have a lower ZrO2 content in the dry powder than Comparative Example 1-2, in which the pH was not adjusted and the slurry pH was greater than 11.

[0073] Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-2 75 g of barium titanate having an average particle size of 200 nm was added to 300 g of pure water and stirred to prepare a 20 mass% mixed slurry. The pH of this slurry was 13. While stirring this slurry at 10°C in a jacketed stirring tank, carbon dioxide gas was added while adjusting the pH of the slurry to the pH shown in Table 2. Note that no carbon dioxide gas was added in Comparative Example 2-2. The resulting slurry was wet-pulverized in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) loaded with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and then re-introduced into the wet mill, counting as one pass. The milling process was repeated for a total of 15 passes. Carbon dioxide gas was added to the slurry after each milling run, adjusting the pH of the slurry to the pH shown in Table 2. This process was repeated 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO content, average particle size, BET specific surface area, and alkaline earth metal salt (barium carbonate) content of the obtained dry powder were measured, and the results are shown in Table 2.

[0074] [Table 2]

[0075] In Table 2, BT refers to barium titanate. As shown in Table 2, the barium titanate powder of each Example, obtained by adding carbon dioxide to adjust the pH of the slurry to between 9 and 11, had a lower barium carbonate content in the dry powder than Comparative Example 2-1, obtained by adjusting the pH to less than 9. It was also found that the barium titanate powder of each Example had a lower ZrO2 content in the dry powder than Comparative Example 2-2, in which the pH was not adjusted and the slurry pH was greater than 11.

[0076] Examples 3-1 to 3-3 and Comparative Examples 3-1 to 3-2 75 g of strontium titanate having an average particle size of 40 nm was added to 300 g of pure water and stirred to prepare a 20 mass % slurry. The pH of this slurry was 12. While stirring this slurry at 10°C in a jacketed stirring tank, carbon dioxide gas was added while adjusting the pH of the slurry to the pH shown in Table 3. Note that no carbon dioxide gas was added in Comparative Example 3-2. The resulting slurry was wet-milled in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and then re-introduced into the wet mill, counting as one pass. Milling was repeated for a total of 15 passes. Carbon dioxide gas was added to the slurry after each milling run, adjusting the pH of the slurry to the pH shown in Table 3. This process was repeated 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO content, average particle size, BET specific surface area, and alkaline earth metal salt (strontium carbonate) content of the obtained dry powder were measured, and the results are shown in Table 3.

[0077] [Table 3]

[0078] In Table 3, ST refers to strontium titanate. As shown in Table 3, the strontium titanate powders of each Example, obtained by adding carbon dioxide to adjust the pH of the slurry to between 9 and 11, had a lower barium carbonate content in the dry powder than Comparative Example 3-1, obtained by adjusting the pH to less than 9. It was also found that the strontium titanate powders of each Example had a lower ZrO2 content in the dry powder than Comparative Example 3-2, in which the pH was not adjusted and the slurry pH was greater than 11.

[0079] [Examples 4-1 to 4-3 and Comparative Examples 4-1 to 4-2] 75 g of barium strontium titanate having an average particle size of 40 nm was added to 300 g of pure water and stirred to prepare a 20 mass % slurry. The pH of this slurry was 12. While stirring this slurry at 10°C in a jacketed stirring tank, carbon dioxide gas was added while adjusting the pH of the slurry to the pH shown in Table 4. Note that no carbon dioxide gas was added in Comparative Example 4-2. The resulting slurry was wet-milled in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and re-introduced into the wet mill, counting each pass as one. Milling was repeated for a total of 15 passes. Carbon dioxide gas was added to the slurry after each milling run, adjusting the pH to the pH shown in Table 4, and the resulting slurry was wet-milled again 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO content, average particle size, BET specific surface area, and alkaline earth metal salt (barium carbonate) content of the obtained dry powder were measured, and the results are shown in Table 4.

[0080] [Table 4]

[0081] In Table 4, BST refers to barium strontium titanate. As shown in Table 4, the barium strontium titanate powders of each Example, obtained by adding carbon dioxide to adjust the pH of the slurry to between 9 and 11, had a lower barium strontium carbonate content in the dry powder than Comparative Example 4-1, obtained by adjusting the pH to less than 9. It was also found that the barium strontium titanate powders of each Example had a lower ZrO2 content in the dry powder than Comparative Example 4-2, in which the pH was not adjusted and the slurry pH was greater than 11.

[0082] Examples 5-1 to 5-3 and Comparative Examples 5-1 to 5-2 75 g of barium calcium titanate having an average particle size of 60 nm was added to 300 g of pure water and stirred to prepare a 20 mass % slurry. The pH of this slurry was 12. While stirring this slurry at 10°C in a jacketed stirring tank, carbon dioxide gas was added while adjusting the pH of the slurry to the pH shown in Table 5. Note that no carbon dioxide gas was added in Comparative Example 5-2. The resulting slurry was wet-milled in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and re-introduced into the wet mill, counting as one pass. Milling was repeated for a total of 15 passes. Carbon dioxide gas was added to the slurry after each milling run, adjusting the pH of the slurry to the pH shown in Table 5. This process was repeated 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO content, average particle size, BET specific surface area, and alkaline earth metal salt (barium carbonate) content of the obtained dry powder were measured, and the results are shown in Table 5.

[0083] [Table 5]

[0084] In Table 5, BCT refers to barium calcium titanate. As shown in Table 5, the barium calcium titanate powders of each Example, obtained by adding carbon dioxide to adjust the pH of the slurry to between 9 and 11, had a lower barium calcium carbonate content in the dry powder than Comparative Example 5-1, obtained by adjusting the pH to less than 9. Also, the barium calcium titanate powders of each Example had a lower ZrO2 content in the dry powder than Comparative Example 5-2, in which the pH was not adjusted and the slurry pH was greater than 11.

[0085] Examples 6-1 to 6-15 75 g of barium titanate having an average particle size of 40 nm was added to 300 g of pure water and stirred to prepare a 20 mass% mixed slurry. The pH of this slurry was 13. While stirring this slurry at 10°C in a jacketed stirring tank, an acid shown in Table 6 was added while adjusting the pH of the slurry to the pH shown in Table 6. The resulting slurry was wet-milled in a wet mill (Ashizawa Finetech Co., Ltd., Star Mill LMZ) with 136.80 g of 0.05 mm zirconia beads (40% of the vessel volume) at an agitator peripheral speed of 11 m / sec and a slurry flow rate of 50 ml / min. The milled slurry was returned to the jacketed mixing vessel and then re-introduced into the wet mill, counting each pass as one. The milling process was repeated for a total of 15 passes. The acid listed in Table 6 was added to the slurry after each milling run, adjusting the pH of the slurry to the pH listed in Table 6. The resulting slurry was then wet-milled 15 times. The crushed slurry was dried in a dryer at 120°C to obtain a dry powder. The ZrO2 content, average particle size, and BET specific surface area of ​​the obtained dry powder were measured, and the results are shown in Table 6.

[0086] [Table 6]

[0087] In Table 6, BT refers to barium titanate. The barium titanate powder obtained by adjusting the pH to between 9 and 11 by adding the acids shown in Table 6 has a low ZrO2 content in the dry powder, and it can be seen that contamination from the grinding media is suppressed.

Claims

1. a first step of contacting an acid or an acidic compound with a dispersion solvent containing a material to be pulverized to obtain a mixture for wet pulverization; a second step of wet-grinding the mixture with grinding media in a wet-grinding apparatus filled with grinding media to obtain a ground wet-grinding solution; and The material to be ground is a material that increases the pH of the dispersion medium upon contact with the dispersion medium; and In the second step, the pH of the mixture for wet-grinding treatment is adjusted to 9 or more and 11 or less, and wet-grinding treatment is carried out. A wet grinding method characterized by:

2. 2. The wet-grinding method according to claim 1, wherein the second step is carried out by wet-grinding the wet-grinding mixture with the grinding media in the wet-grinding apparatus while supplying the wet-grinding mixture to the wet-grinding apparatus and discharging the wet-grinding mixture from the wet-grinding apparatus, thereby obtaining a ground wet-grinding mixture.

3. 3. The wet-grinding method according to claim 2, wherein the residence time of the wet-grinding mixture in the second grinding step is 1 to 1200 seconds.

4. 2. The wet-grinding method according to claim 1, wherein the first step is carried out by contacting the wet-grinding solution obtained by carrying out the second step with an acid or an acidic compound to obtain a mixed solution for wet-grinding, and then the mixed solution for wet-grinding obtained is wet-grinded to carry out the second step, and this process is repeated one or more times.

5. 3. The wet-grinding method according to claim 1, wherein in the first step, the pH of the dispersion solvent containing the material to be ground is lowered by 0.10 to 5 by contacting the dispersion solvent containing the material to be ground with an acid or an acidic compound, thereby obtaining a mixture for wet-grinding treatment.

6. 3. The wet-grinding method according to claim 1, wherein the pH of the wet-grinding solution obtained by carrying out the second step is 9 or more and 11 or less.

7. 3. The wet grinding method according to claim 1, wherein the acid or acidic compound is one or more selected from inorganic acids, organic acids, and acidic dispersants.

8. 8. The wet-grinding method according to claim 7, wherein the inorganic acid is one or more acids selected from the group consisting of carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid.

9. 8. The wet-grinding method according to claim 7, wherein the organic acid is one or more selected from the group consisting of formic acid, acetic acid, citric acid, succinic acid and malonic acid.

10. 8. The wet-grinding method according to claim 7, wherein the acidic dispersant is one or two selected from the group consisting of polycarboxylic acid compounds, polyphosphoric acid compounds, and phosphonic acid compounds.

11. 3. The wet grinding method according to claim 1, wherein the grinding medium is one or more beads or balls selected from the group consisting of zirconia, alumina, silica, titania and silicon nitride.

12. 3. The wet grinding method according to claim 1, wherein the dispersion solvent is water or a mixed solvent of water and an aqueous organic solvent.

13. 3. The wet grinding method according to claim 1, wherein the material to be ground is a perovskite-type complex oxide.

14. 14. The wet-grinding method according to claim 13, wherein the perovskite-type composite oxide is one or more selected from the group consisting of barium titanate, calcium titanate, magnesium titanate, strontium titanate, barium calcium titanate, barium strontium titanate, barium magnesium titanate, calcium magnesium titanate, calcium strontium titanate, and magnesium strontium titanate.

15. 3. The wet grinding method according to claim 1, wherein the content of the material to be ground in the dispersion solvent containing the material to be ground is 5 to 80% by mass.

16. 3. The wet-grinding method according to claim 1, wherein the volume ratio of the grinding media to the wet-grinding mixture is 10 to 90% by volume.

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