Production method for aqueous dispersion slurry of inorganic particles

Abstract: The present invention provides production methods for aqueous dispersion slurry of inorganic particles which are so stable as not to increase in viscosity, gel or sediment even if stored for a long time and whose average particle diameter is 0.01 to 2 µm. As such production method, 2 production methods are available: A production method (A) having a preliminary dispersion process in which the inorganic particles are added to ad dispersed in an aqueous medium and a main dispersion process in which dispersed slurry out of the preliminary dispersion process are collided with each other under a pressure of 100 to 3,000 kg/cm 2 ; and A production method (B) in which the inorganic particles are added to an aqueous medium within a kneading tank of a kneader in which mixing blades rotate around respective subsidiary spindles and the subsidiary spindles revolves around a spindle and dispersed at a solid concentration of 30 to 70wt%.

Description: FIELD OF THE INVENTION This invention generally relates to aqueous dispersion slurry of inorganic particles and production methods thereof. Aqueous dispersion slurry produced by the production method according to this invention are free from such problems as increase in viscosity, gelation and separation/sedimentation during storage, i.e., highly stable. For this reason, such aqueous colloidal dispersion slurry may be suitably used, for example, as raw materials for cosmetics, paint, coating materials and polishing slurry for semiconductor wafers. BACKGROUND OF THE INVENTION As raw materials for cosmetics, paint, coating materials and polishing slurry for semiconductor wafers, raw materials of high purity with a minimal concentration of impurities, such as inorganic particles synthesized by a vapor phase method, such as fumigation, (hereinafter referred to as "vapor phased inorganic particles") have been used. However, as the vapor phased inorganic particles are intensive in secondary coagulation, when the vapor phased inorganic particles are dispersed in the water, coagula of such vapor phased inorganic particles should be destroyed and fused in the water. If the coagula are not completely destroyed or fused, problems, such as increase in viscosity of the aqueous dispersion slurry as the time passes, gelation and consequent loss of fluidity, and sedimentation and separation of the coagula. As a result, the aqueous dispersion slurry of inorganic particles can no longer be applied to those uses as described above. As a method of dispersing the vapor phased inorganic particles in an aqueous medium, a method using dispersion equipment of high-speed mixing type (e.g., whirling blender, and high shearing mixer) as disclosed in USP5116535 (Japanese Unexamined Patent Publication No. 3-50112) has been known. Also, a method using equipment combining a powder introduction type mixer/disperser (e.g., jet stream mixer) with a toothed colloid mill, a dissolver or a skim mixer (Nippon Aerosil Co., Ltd.; Catalog No. 19: How to Handle Aerosil, p. 38) has also been known. However, both of these methods are disadvantageous in that a long-time processing is required and that vapor phased inorganic particles can not be completely destroyed or fused. As regards the method of dispersing pulverized silica or fumed silica in an aqueous medium, a method of pulverizing and dispersing the vapor phased inorganic particles using a high-pressure homogenizer to 100 nm or less in average secondary particle diameter has been disclosed in the Japanese Unexamined Patent Publication No. 9-142827 (opened on June 3, 1997) and in the Japanese Unexamined Patent Publication No. 9-193004 (opened on July 29, 1997), which were opened after the date of application of the Japanese Patent Application No. 9-132881 over which the present invention claims priority. However, these publications contain no description of the dispersion of inorganic particles other than the pulverized silica and the fumed silica. In EP-0 766 997 A a production method of dispersions with small size particles is disclosed. Using a orifice-type injector bigger sized particles of the original dispersions are reduced in size. In US 5,116,535 A a production method for aqueous colloidal dispersions of fumed silica is disclosed. Fumed silica is admixed with water in a way such that the concentration exceeds the desired one. Subsequently, the mixture is diluted with water to the desired concentration. In EP-0 773 270 A a production method for polishing slurries having an average particle size of 5 to 30 nm is disclosed. Under these circumstances, development of a method of producing the aqueous dispersion slurry of various inorganic particles has been wanted. SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a production method for aqueous dispersion slurry of inorganic particles of 0.01 to 2 µm in average diameter which are highly stable with no increase in viscosity, no gelation or no sedimentation even if stored for a long time. These and other objects of the present invention are achieved by a production method according to independent claim 1. The dependent claims treat further advantageous developments of the present invention. PRODUCTION METHOD The production method is a production method for the aqueous dispersion slurry of inorganic particles which is characterized by that inorganic particles are added to an aqueous medium within a kneading tank of a kneader in which a mixture of the inorganic particles and the aqueous medium is to be kneaded by rotation of mixing blades around respective subsidiary spindles and revolution of the subsidiary spindles around a spindle, and the inorganic particles are dispersed through such kneading at a solid concentration of 30 to 70wt%. Here, the kneader in which mixing blades rotate around respective subsidiary spindles and the subsidiary spindles revolve around a spindle is generally called "a planetary kneader." In the production method, the concentration of the inorganic particles in dispersion in an aqueous medium should be 30 to 70wt%, preferably be 35 to 60wt%, and more preferably be 40 to 50wt%. If the solid concentration of the inorganic particles is less than 30wt%, the dispersion efficiency will drop to such an extent that coagula may be left in the obtained aqueous dispersion slurry, and as a result, such coagula may sediment and separate during storage or gel due to increase in viscosity. On the other hand, if the solid concentration of the inorganic particles exceeds 70wt%, load on the disperser will become too large to maintain mixing in motion. If mixing is forced in such state, the inorganic particles may be excessively disperse, and as a result, a large quantity of coarse particles of 10 µm or more in particle diameter may be produced due to re-coagulation. In the production method, it is preferable that the inorganic particles should be dispersed in an aqueous medium while continuously and intermittently added. If the inorganic particles are added in a required quantity at a time in the beginning, there will be problems that it is difficult to uniformly disperse the inorganic particles and the mixer may be stopped by an excessively large load. As an ideal method of adding the inorganic particles, it is preferable that the inorganic particles should be quickly added until the solid concentration reaches approx. 20wt% and then continuously and intermittently added while monitoring current value of (load on) the kneader not to be too large. As a hopper for supplying the inorganic particles, a screw transfer type or the like may be named. Preferably, the aqueous dispersion slurry out of the dispersion process in the production method should be diluted after the kneading process. The extent of such dilution depends on the type of the dispersed inorganic particles or the solid concentration in the kneading process. Preferably, the solid concentration should be decreased by 5wt% or more down from the solid concentration in the kneading process. If the solid concentration in the kneading process is maintained, as this solid concentration is too high, the inorganic particles are not only difficult to be processed but also may quickly gel due to increase in viscosity during storage. As a dilution method, additionally applying an aqueous medium directly into the kneader is preferable as this way of dilution makes it easy to remove the dispersion slurry from the kneader. In the production method, it is possible to perform the dispersion processing by using another kneader or disperser after the kneading process to improve the uniformity. In this case, for example, corres type high-speed mixer/disperser, homo-mixer, high-pressure homogenizer or bead mill can preferably be used for this purpose. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view showing a planetary kneader, wherein FIG. 1 (a) is a top view thereof, and FIG. 1 (b) is a side view thereof. DETAILED DESCRIPTION OF THE INVENTION Now, the present invention will be described in detail. 1. INORGANIC PARTICLES As a production method of the inorganic particles used in production method according to the present invention, such as a vapor phase method, a wet method and a sol gel method may be named. As the vapor phase method, a fumed method (high-humidity flame hydrolysis method), and a Nanophase Technologies Corporation method (metal evaporation and oxidation method) may be named. Furthermore, a production method in which natural inorganic compounds are pulverized, refined and/or classified can be named. Preferably, the inorganic particles should be produced by the vapor phase method, and more preferably, by the fumed method. The inorganic particles produced by the vapor phase method are highly purified and therefore favorable. The inorganic particles produced by the fumed method are highly purified and also comparatively economical and therefore particularly favorable. As the inorganic particles preferably used in production method, metallic oxides may be exemplified, such as silicon oxide, aluminum oxide, titanium oxide, ziruconium oxide, antimony oxide, chromium oxide, germanium oxide, vanadium oxide, tungusten oxide, iron oxide, manganese oxide and cerium oxide. More preferable among these metallic oxides are silicon oxide, aluminum oxide, titanium oxide and cerium oxide. These metallic oxides may be used singly or as a mixture of two or more. As the particularly favorable inorganic particles used in production method, metallic oxides may be exemplified, such as aluminum oxide, titanium oxide, ziruconium oxide, antimony oxide, chromium oxide, germanium oxide, vanadium oxide, tungusten oxide, iron oxide, manganese oxide and cerium oxide. More preferable among these metallic oxides are aluminum oxide, titanic oxide and cerium oxide. These metallic oxides may be used singly or as a mixture of two or more. Typically, the inorganic particles to be dispersed are in a form of powder existing as coagula (called "secondary particles") of small particles (called "primary particles"). The average diameter of these primary particles is normally 0.005 to 1 µm. 2. DISPERSION PROCESS AND EQUIPMENT In the production method, a kneader which performs a planetary motion, i.e., mixing blades rotate around respective subsidiary spindles and at the same time the subsidiary spindles revolve around a spindle can be used. Such kneader should preferably be equipped with high-speed rotation dispers (blades) as well. Here, the equipment in which the mixing blades perform the planetary motion will be described. FIG. 1 schematically shows a planetary kneader in which mixing blades performs a planetary motion, wherein FIG. 1 (a) is a top view of such planetary kneader, and FIG. 1 (b) is a side view of such planetary kneader. A kneading tank 10 of the kneader shown in this figure is provided with a mixing blade 11a which rotates around a subsidiary spindle a in a direction indicated by an arrow, a mixing blade 11b which rotates around a subsidiary spindle b in a direction indicated by an arrow, and a spindle c which revolves these 2 subsidiary spindles a and b in a direction indicated by an arrow. That is, it is so constructed that the mixing blades 11a and 11b "rotate" around the respective subsidiary spindles a and b, while the subsidiary spindles a and b "revolve" around the spindle c. As the mixing blades 11a and 11b provided as described above move with complicated loci, the dispersion slurry within the kneading tank 10 can be uniformly kneaded and the coagula can be completely divided. As a result, a large quantity of the inorganic particles can be efficiently dispersed in a comparatively small quantity of aqueous medium. In FIG. 1, 2 subsidiary spindles a and b are shown. However, it is acceptable that single subsidiary spindle is provided or 3 or more subsidiary spindles are provided instead of 2 subsidiary spindles. Furthermore, when a plurality of subsidiary spindles are provided, each subsidiary spindle may be positioned at regular intervals or at irregular intervals. Also in FIG. 1, 2 mixing blades are provided as a pair on each subsidiary spindle. However, it is acceptable that single mixing blade is provided on each subsidiary spindle, or 3 or more mixing blades are provided as a pair on each subsidiary spindle. It is also acceptable that a high-speed blade is provided on a spindle coaxially with or differently from the subsidiary spindle of the mixing blades to improve the ability of dividing and dispersing the inorganic particles. In FIG. 1, both the spindle c and the subsidiary spindles a and b rotate counterclockwise viewed from the top. However, it is acceptable that the spindle c and the subsidiary spindles a and b are set differently from each other in the rotational direction to have different loci of the mixing blade motion. In FIG. 1, the mixing blades 11a and 11b are curved and twisted between the ends (twisted shape). However, it is accepted that the mixing blades 11a and 11b are differently shaped in any way as long as such shape ensures that the dispersion slurry within the kneading tank can be uniformly kneaded and the coagula can be completely divided and as a result a large quantity of the inorganic particles can be efficiently dispersed in a comparatively small quantity of an aqueous medium. Among those planetary kneaders which satisfy the requirements described above, in addition to those kneaders named above, are Universal Mixer/Stirrer ("Universal Mixer/Stirrer" is a tread mark) of Dalton Co., Ltd., Universal Mixer ("Universal Mixer" is a tread mark) of Powlex Co., Ltd., Planetary Kneader/Mixer ("Planetary Kneader/Mixer" is a tread mark) of Ashizawa Co., Ltd., T.K. Hibis Disper Mix ("T.K. Hibis Disper Mix" is a tread mark) of Tokushu Kika Kogyo Co., Ltd., and Planetary Disper ("Planetary Disper" is a tread mark) of Asada Iron Works Co., Ltd. Preferably, the equipment used in the production method should be provided with a lining of resin, such as polyurethane, Teflon or epoxy resin, to protect the aqueous dispersion slurry from metallic contamination after production. Still preferably, the liquid contacting portions, such as inner walls and mixing blades, of such equipment should be provided with a lining of ceramic, such as zirconia, to prevent metallic contamination and increase wear resistance. The production method may be performed for plural times on single equipment or one or more times on a combination of plural, different equipment. 3. ADDITION OF ACID OR ALKALI In the production method, an acid or an alkali should preferably be added at least to the aqueous medium before the dispersion process, to the dispersion slurry during the dispersion process, or to the dispersion slurry after the dispersion process to adjust the pH of the aqueous dispersion slurry to be finally in a range of 2 to 12. As a result of this addition, the dispersion stability of the resultant aqueous dispersion slurry becomes much higher. The pH of the aqueous dispersion varies depending on the intended use. However, such pH should preferably be in a range of 3 to 11. If the pH is set to be less than 2 or more than 12, the inorganic particles tends to be dissolved or coagulated due to insufficient colloidal stability. The acid or the alkali may be added in any one of the stages described above or in any 2 or 3 of such stages. In whatever stage the acid or the alkali is added, preferably, the aqueous medium or dispersion slurry should be continuously stirred while the acid or alkali is added. If the acid or the alkali is added after the dispersion, a part of the inorganic particles of the dispersion slurry may be coagulated due to a shock of localized increase in concentration. To prevent this, it is preferable that the dispersion process should be performed again or high-speed mixing processing should be performed by using a homo-mixer, a disper or the like after the addition of the acid or the alkali. As acids, inorganic acids, such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, or organic acids, such as acetic acid, phthalic acid, acrylic acid, methacrylic acid, crotonic acid, polyacrylic acid, maleic acid and sorbic acid, may be used. Among of these, hydrochloric acid, nitric acid and acetic acid, which are univalent acids, are preferable. As alkalis, inorganic bases, such as potassium hydroxide, sodium hydroxide, lithium hydroxide and ammonia, and amines, such as ethylenediamine, trirthylamine and piperazine, may be used. 4. PREFERABLE RANGE OF AQUEOUS DISPERSION SLURRY The average diameter of the inorganic particles of the aqueous dispersion slurry produced by the method of the present invention is in a range of 0.01 to 2 µm, should preferably be in a range of 0.02 to 1 µm, and should more preferably be in a range of 0.03 to 0.8 µm. If such diameter is smaller than 0.01 µm, the viscosity of the aqueous dispersion slurry of the inorganic particles will be excessively high, and good dispersion stability can not be obtained. If such diameter is larger than 2 µm, the dispersion stability will be so low as to cause sedimentation. This particle diameter can be controlled by setting a suitable condition in the main dispersion process and/or by selecting a suitable raw material of the inorganic particles. When the high-pressure homogenizer is used, the particle diameter can be controlled by the pressure, number of processing times, etc. of the high-pressure homogenizer. When the planetary kneader is used, the particle diameter can be controlled by the number of rotations of the mixing blades, the number of revolutions of the subsidiary spindles, the mixing time, etc. The inorganic particles dispersed in the aqueous dispersion slurry obtained by the production method according to the present invention are composed of primary particles and secondary particles or of secondary particles alone. The average diameter of the inorganic particles can be measured by using Laser Particle Diameter Analysis System Model LPA-3000S/3100, which is controlled based on a dynamic light scattering method, of Otsuka Denshi Co., Ltd. SPECIFIC DESCRIPTION Now, the present invention will be specifically described by referring to examples and reference examples. However, the present invention is not limited to such examples. In the following description, "part" means "part by weight," and "%" means "percent by weight or wt%." The average particle diameter of the inorganic particles in the aqueous dispersion slurry of the inorganic particles were measured by using Laser Particle Diameter Analysis System Model LPA-3000S/3100 of Otsuka Denshi Co., Ltd. PRODUCTION METHOD [EXAMPLE 1] Fumed aluminum oxide C (Degusa Co., Ltd.) of 10 kg was continuously added for 1 hour to 8.6 kg of ion exchange water in which 1.4 kg of 1N nitric acid had been dissolved while the mixture was kneaded by a planetary kneader having liquid contacting portions of the stirrer and container coated with urethane resin (Universal Kneader ("Universal Kneader" is a tread mark) Model 30DM of Dalton Co., Ltd.) with the subsidiary spindles and spindle of the stirrer in rotation at 60 rpm and 20 rpm, respectively. After such addition, the mixture was further kneaded for another 1 hour at 50% solid concentration. Thus obtained slurry was further dispersed for another 1 hour at 2,000 rpm by using a non-planetary disperser (T.K. Homodisper ("T.K. Homodisper" is a tread mark) of Tokushu Kika Kogyo Co., Ltd.). Thus obtained slurry was diluted with ion exchange water, and aqueous dispersion slurry of aluminum oxide with 30% solid concentration were obtained. Thus obtained aqueous dispersion slurry were subjected to metallic analysis by atomic absorption spectroscopy. As a result, there was a little metallic contamination with 0.5 ppm of iron. The pH and average particle diameter of the aqueous dispersion slurry of fumed aluminum oxide were 4.3 and 0.12 µm, respectively. The aqueous dispersion slurry were left for 30 days at 25°C, but none of increase in viscosity, gelation or sediment was recognized. [EXAMPLE 2] Fumed titanium dioxide (P25, Nippon Aerosil Co., Ltd.) of 2 kg was continuously added for 1 hour to 2 kg of distilled water in which 100 g of acetic acid had been dissolved while the mixture was kneaded by a planetary kneader having liquid contacting portions of the stirrers and container coated with urethane resin (Universal Kneader ("Universal Kneader" is a tread mark) Model 5DM of Dalton Co., Ltd.) with the subsidiary spindles and spindle of the stirrer in rotation at 90 rpm and 30 rpm, respectively. After such addition, the mixture was further kneaded for another 1 hour at 50% solid concentration. Thus obtained slurry was diluted with ion exchange water, and aqueous dispersion slurry of titanium dioxide with 40% solid concentration were obtained. The pH and average particle diameter of thus obtained aqueous dispersion slurry of titanium dioxide were 6.5 and 0.16 µm, respectively. The aqueous dispersion slurry were left for 30 days at 25°C, but none of increase in viscosity, gelation or sediment was recognized. [EXAMPLE 3] Fumed silicon oxide (Aerosil #50 ("Aerosil #50 " is a tread mark) of Nippon Aerosil Co., Ltd.) of 6 kg was continuously added for 30 minutes to 8kg of distilled water in which 60g of potassium hydroxide granules had been dissolved while the mixture was kneaded by using a planetary kneader having liquid contacting portions of the stirrers and container coated with urethane resin (T.K. Hibis Disper Mix ("T.K. Hibis Disper Mix" is a tread mark) Model HDM-3D-20 of Tokushu Kika Kogyo Co., Ltd.) with the twisted blades rotated around the respective subsidiary spindles and the subsidiary spindle revolved around the spindle at 10 rpm and 30 rpm, respectively. After such addition, the mixture was further subjected to kneading for another 1 hour at 43% solid concentration while the twisted blades were rotated around the respective subsidiary spindles at 30 rpm and at the same time to disper procesing with the corres type high-speed rotary blades of 80 mm in diameter rotated around the respective subsidiary spindles at 2,000 rpm and the spindle rotated at 10 rpm for both the kneading and disper processing. Thus obtained slurry was diluted with ion exchange water, and aqueous dispersion slurry of silicon oxide with 30% solid concentration were obtained. The pH and average particle diameter of the aqueous dispersion slurry of silicon oxide were 10.5 and 0.23 µm, respectively. The aqueous dispersion slurry were left for 30 days at 25°C, but none of increase in viscosity, gelation or sediment were recognized. [EXAMPLE 4] Aqueous dispersion slurry of silicon oxide were obtained by the same method as the example 3 except that fumed silicon oxide was added to 8 kg of distilled water in which 60 g of potassium hydroxide granules had not been dissolved and then the mixture was subjected to further kneading and disper processing for another 1 hour by using blades and potassium hydroxide was added as 10% solution at 10 minutes before ending such additional processing. The pH and average particle diameter of the aqueous dispersion slurry of silicon oxide were 10.3 and 0.21 µm, respectively. The aqueous dispersion slurry were left for 30 days at 25°C, but none of increase in viscosity, gelation or sediment were recognized. [REFERENCE EXAMPLE 1] (COMPARISON TO EXAMPLE 3) Aqueous dispersion slurry were formulated by the same method as the example 3 except that a disperser with the stirrers only in rotation (T.K. Homo Disper ("T.K. Homo Disper" is a tread mark) of Tokushu Kika Kogyo Co., Ltd.) was used as a kneader instead of T.K. Hibis Disper Mix of Tokushu Kika Kogyo Co., Ltd. with the stirrers in both rotation and revolution (planetary mechanism). Complete dispersion slurry could not be obtained. The pH and average particle diameter of the aqueous dispersion slurry were 10.6 and 2 µm or more, respectively. The aqueous dispersion slurry were left for 2 days at 25°C, and gelled and lost fluidity. [REFERENCE EXAMPLE 2] (COMPARISON TO EXAMPLE 2) Aqueous dispersion slurry were formulated by the same method as the example 6 except that 6 kg of distilled water in which 100 g acetic acid had been dissolved, instead of 2 kg of distilled water in which 100 g acetic acid had been dissolved, to adjust the solid concentration during kneading to 25%. Complete dispersion slurry could not be obtained. The pH and average particle diameter of the aqueous dispersion slurry were 6.7 and 2 µm or more, respectively. The aqueous dispersion slurry were left for 2 days at 25°C, and gelled and lost fluidity. [REFERENCE EXAMPLE 3] (COMPARISON TO EXAMPLE 2) Aqueous dispersion slurry were formulated by the same method as the example 2 except that 0.6 kg of distilled water in which 100g acetic acid had been dissolved, instead of using 2 kg of distilled water in which 100 g acetic acid had been dissolved, to adjust the solid concentration during kneading to 74%. During continuous addition of the inorganic particles, the mixer was stopped due to overload, and further continuous kneading operation was impossible.

Claims: A production method for aqueous dispersion slurry in which inorganic particles are dispersed at a solid concentration of 30 to 70 wt %, characterized by inorganic particles being dispersed in an aqueous medium to an average particle diameter of 0.01 to 2 µm by using a method in which said inorganic particles are added to an aqueous medium within a kneading tank (10) of a kneader in which mixing blades (11a and 11b) are rotated around respective subsidiary spindles (a and b) and said subsidiary spindles (a and b) are revolved around a spindle (c). The production method for aqueous dispersion slurry according to claim 1, wherein said inorganic particles are synthesized by a vapor phase method. The production method for aqueous dispersion slurry according to claim 1, wherein said inorganic particles are synthesized by a fumed method. The production method for aqueous dispersion slurry according to claim 1, wherein said inorganic particles are at least one of silicon oxide, aluminum oxide, titanium oxide and cerium oxide. The production method for aqueous dispersion slurry according to claim 1, wherein an average particle diameter of said inorganic particles dispersed in an aqueous medium is 0.02 to 1 µm. The production method for aqueous dispersion slurry according to claim 1, wherein an average particle diameter of said inorganic particles dispersed in an aqueous medium is 0.03 to 0.8 µm. The production method for aqueous dispersion slurry according to claim 1, wherein at least a part of inorganic particles contacting portions of said kneader used in the production method is provided with a lining of resin.

Inventors: HATTORI MASAYUKI, ITO NOBUYUKI, HATTORI, MASAYUKI, ITO, NOBUYUKI
Applicants: JSR CORP, JSR CORPORATION
Application year: 1998
Main classification: B01F5
IPC codes: B01F3, C09D17, B01F5, C09C1, C09C3, B01F13