JP6153150B2 - Wet classification method - Google Patents

Description

  The present invention relates to a wet particle classification apparatus.

  In recent years, particles used in the electronic material region are required to have monodispersity, and high-precision classification is also required for further improvement of characteristics. In wet classification, particles can be classified more easily than dry classification. Examples of the wet classification means include a cyclone, a sedimentation method, and a water sieve using static electricity.

  First, the sedimentation method that has existed since ancient times has a gap in the distance between the particles that are above and the particles that are below. For this reason, classification is easy when the particle diameters are greatly different, but classification is impossible at a time when the particle diameters are close, and theoretically it is difficult to completely separate them. Further, when small-diameter particles are present in the lower part of the apparatus, they cannot be separated.

  Therefore, several methods have been devised as countermeasures. In Patent Documents 1 to 4, different from normal wet classification, there is a method in which a liquid is gently poured from below, and classification is performed by balancing the ascending flow and the gravity sedimentation. In this method, even if there is a distance between the upper particles and the lower particles, the particles converge to a certain place according to the particle diameter, so that classification is easy.

  However, in such a classification method, as the particle diameter becomes smaller, the descending speed of the particles becomes gentler. Therefore, it is necessary to extremely slow the flow of the liquid, which is difficult to control. In the case of resin particles, even if the particle size is about 10 μm, it takes about 10 days to form a layer structure according to the particle size. More days are required depending on the particle size and specific gravity. That is, such a method has a drawback that it takes an extremely long time compared with a normal sedimentation method.

  Patent Document 5 discloses a method in which particles to be classified are treated with a bead mill and then classified with a special cyclone using a voltage. Patent Document 6 discloses a method of classifying with an airflow cyclone after passing particles through a device having a potential applying mechanism.

  Patent Document 7 discloses a method of classifying particles having different zeta potentials by flowing a slurry in a tank to which an electric current is applied.

  However, such a classification method is useful when the zeta potential is different for each particle diameter, but is difficult in other cases.

JP 2000-301022 A JP 2001-087673 A JP 10-015430 A JP 10-015429 A JP 2011-125801 A JP 2003-190836 A JP 2005-334865 A

  In recent years, in the electronic material region, the coefficient of variation of particles such as plastics having an average particle size of about 1 μm to 10 μm C.I. V. There is a request to reduce (Coefficient of Variation) to 3% or less. However, in the conventional wet classification as described in Patent Documents 1 to 7, it is either difficult to satisfy this requirement or a long time is required.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a wet classification method capable of improving the conventional problems and classifying particles having the same specific gravity with high accuracy and in a short time.

  The wet classification method according to the present invention is a wet classification method for classifying particles in a slurry, and a slurry layer containing particles to be classified in a solvent and a liquid layer containing no particles are stacked in a tank. A laminating step and a classifying step of collecting particles from the tank by moving particles from the slurry layer toward the liquid layer side by gravity, and in the laminating step, the specific gravity of either the slurry layer or the liquid layer is determined. The specific gravity of the upper layer of either the slurry layer or the liquid layer is made larger.

  According to the wet classification method of the present invention, in the stacking step, the slurry layer and the liquid layer are stacked in the tank, and the specific gravity of the lower layer is made larger than the specific gravity of the upper layer. While suppressing the generation of a boycott flow (substitution flow) with the slurry layer, the majority of particles can be moved from the slurry layer to the liquid layer side under substantially the same conditions. In addition, the movement (sedimentation or levitation) of particles from the slurry layer toward the liquid layer by gravity can be realized by appropriately setting the specific gravity of the particles, the solvent, and the liquid layer, for example. And since the moving speed of the particle | grains by the influence of gravity changes with particle diameters, the particle | grains in a slurry can be isolate | separated up and down according to a particle size by leaving a tank for a predetermined time in a classification process. As a result, even particles having the same specific gravity can be classified with high accuracy and in a short time.

  Moreover, this invention can laminate | stack a slurry layer on the upper layer of a liquid layer in a lamination process, and can make the specific gravity of a slurry layer smaller than the specific gravity of a liquid layer. In this way, if a liquid layer having a large specific gravity is formed in the lower layer and a slurry layer having a small specific gravity is formed in the upper layer, the particles in the slurry are separated vertically according to the particle size by allowing the particles to settle by gravity. be able to.

  Moreover, this invention can make the specific gravity of particle | grains larger than the specific gravity of a solvent and a liquid layer in a lamination process. Thus, by making the specific gravity of the particles larger than the specific gravity of the solvent and the liquid layer, the particles can be appropriately settled by gravity.

  Moreover, this invention can make the ratio of specific gravity of the slurry layer with respect to a liquid layer into the range of 0.80 or more and less than 1.00 in a lamination process. By making the specific gravity of the slurry layer smaller than the specific gravity of the liquid layer, generation of boycott flow can be suppressed, but if the specific gravity ratio of the slurry layer and the liquid layer becomes too large, the movement of particles in the slurry layer The difference between the speed and the moving speed of the particles in the liquid layer is increased, and the particles are likely to accumulate in the upper layer of the liquid layer and aggregate. Thus, by setting the specific gravity ratio of the slurry layer to the liquid layer in the range of 0.80 or more and less than 1.00, it is possible to suppress the generation of the boycott flow while suppressing the aggregation of particles.

  Moreover, this invention can laminate | stack a slurry layer and a liquid layer via the partition member which partitions the inside of a tank up and down in a lamination process, and can remove a partition member from a tank in a classification process. In this way, the boycott flow between the slurry layer and the liquid layer can be prevented by separating the slurry layer and the liquid layer by the partition member in the stacking step, and the partition member is removed in the classification step. Thus, the particles in the slurry can be moved to the liquid layer side under substantially the same conditions.

  Further, the present invention forms a liquid layer and a slurry layer in a tank in which an upper electrode is disposed in the upper portion and a lower electrode is disposed in the lower portion in the stacking step, and the upper electrode and the lower electrode are formed in the classification step. A voltage can be applied. When a voltage is applied to the upper electrode and the lower electrode to generate an electric field in the tank, the particles in the slurry are charged according to the relationship between the polarity of the charged zeta potential and the polarity of the upper electrode and the lower electrode. Electrophoresis is performed on the electrode side or the lower electrode side. At this time, since the zeta potential is considered to depend on the particle diameter, the electrophoresis speed varies depending on the particle diameter. Therefore, by combining the movement of particles by gravity and electrophoresis, the difference in the movement speed of the particles according to the particle size can be further widened, so that the particles in the slurry can be classified with higher accuracy and in a shorter time. it can.

  According to the present invention, even particles having the same specific gravity can be classified with high accuracy and in a short time.

It is a flowchart which shows the wet classification method which concerns on embodiment. It is the longitudinal cross-sectional schematic diagram which showed notionally the classification apparatus used for the wet classification method which concerns on 1st Embodiment. It is a longitudinal cross-sectional schematic diagram of the wet classification apparatus which concerns on 1st Embodiment which showed the sedimentation state of the particle | grains in a classification process. It is a longitudinal cross-sectional schematic diagram of the wet classification apparatus which concerns on 1st Embodiment after leaving it to stand for a predetermined time in a classification process. It is the longitudinal cross-sectional schematic diagram which showed notionally the classification apparatus used for the wet classification method which concerns on 2nd Embodiment. It is the longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on 2nd Embodiment which showed the sedimentation state of the particle | grains at the time of extracting a partition plate in a classification process. It is a longitudinal cross-sectional schematic diagram of the wet classification apparatus which concerns on 2nd Embodiment after leaving to stand for the predetermined time in a classification process. It is the longitudinal cross-sectional schematic diagram which showed notionally the classification apparatus used for the wet classification method which concerns on 3rd Embodiment. It is the graph which showed the sedimentation curve when acrylic particles were sedimented by the sedimentation balance method. It is a graph which shows the particle size dependence of the zeta potential in an acrylic particle. It is the longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on 3rd Embodiment which showed the sedimentation state of the acrylic particle at the time of a classification | category process extracting a partition plate and applying an electric field. It is a longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on 3rd Embodiment after leaving to stand for a predetermined time in a classification process. It is the longitudinal cross-sectional schematic diagram which showed notionally the classification apparatus used for the wet classification method which concerns on 4th Embodiment. It is the longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on the 4th Embodiment which showed the floating state of the particle | grains in a classification process. It is a longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on 4th Embodiment after leaving to stand for the predetermined time in a classification process. It is the longitudinal cross-sectional schematic diagram which showed notionally the classification apparatus used for the wet classification method which concerns on 5th Embodiment. It is the longitudinal cross-sectional schematic diagram of the wet-classification apparatus which concerns on the 5th Embodiment which showed the movement state of the acrylic particle at the time of applying an electric field in a classification process. It is a longitudinal cross-sectional schematic diagram of the wet classification apparatus which concerns on 5th Embodiment after leaving to stand for the predetermined time in a classification process. It is a table | surface which shows the measurement result of an Example. It is a graph showing the frequency (CV) of each sample. It is a graph showing the number of particles in 1 microliter of each sample.

  Hereinafter, preferred embodiments of a wet classification method according to the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a flowchart showing a wet classification method according to the embodiment. As shown in FIG. 1, this embodiment is a wet classification method for classifying particles in a slurry, and a slurry layer in which particles to be classified are contained in a solvent and a liquid layer in which particles are not contained in the solvent are stored in a tank. A stacking step S1 for stacking the particles inside, and a classification step S2 for recovering the particles from the tank by moving the particles from the slurry layer toward the liquid layer side by gravity. In the stacking step S1, the specific gravity of the lower layer of either the slurry layer or the liquid layer is made larger than the specific gravity of any of the upper layer of the slurry layer or the liquid layer. In the present invention, the specific gravity means specific gravity for water at room temperature.

[First Embodiment]
FIG. 2 is a schematic longitudinal sectional view conceptually showing the classification device used in the wet classification method according to the first embodiment. As shown in FIG. 2, the classifier 11 includes a tank 12 into which slurry is injected. The tank 12 is made of, for example, a resin material such as silicone or acrylic, an inorganic material such as glass, a metal material, or the like, and has a bottomed cylindrical shape, and has an upper end opened. In addition, the tank 12 includes those formed in a cylindrical shape having a circular bottom surface and those formed in a rectangular tube shape having a polygonal bottom surface.

  As shown in FIG. 2, in the stacking step S1, after injecting the solvent into the tank 12 to form the liquid layer α1, the slurry is injected into the tank 12 to form the slurry layer α2 in the upper layer of the liquid layer α1. .

  At this time, the specific gravity of the slurry layer α2 (specific gravity of the solvent and the entire slurry) is made smaller than the specific gravity of the liquid layer α1 (specific gravity of the solvent). Thus, by adjusting the specific gravity of the liquid layer α1 and the slurry layer α2, the liquid layer α1 and the slurry layer α2 can be stably laminated. The slurry layer α2 is laminated on the upper layer of the liquid layer α1, for example, by gently pouring the slurry onto the liquid layer α1 formed in the tank 12 so that the liquid layer α1 and the slurry layer α2 are not mixed.

  The specific gravity ratio of the slurry layer α2 to the liquid layer α1 (specific gravity of the slurry layer α2 / specific gravity of the liquid layer α1) is not particularly limited, but is preferably in the range of 0.80 or more and less than 1.00, More preferably, it is in the range of 0.90 or more and 0.99 or less. In the classification step S2, in order to suppress the generation of a boycott flow between the liquid layer α1 and the slurry layer α2, it is preferable to set the specific gravity ratio to less than 1.00. By reducing the specific gravity ratio, the sedimentation rate of the particles in the liquid layer α1 becomes smaller than the sedimentation rate of the particles in the slurry layer α2. Therefore, by setting the specific gravity ratio to 0.80 or more, it is possible to suppress the difference between the sedimentation rate of the particles in the slurry layer α2 and the sedimentation rate of the particles in the liquid layer α1 from being excessively increased. It is possible to suppress congestion and aggregation between the slurry layer α2 and the liquid layer α1. Therefore, by setting the specific gravity ratio in the range of 0.80 or more and less than 1.00, generation of a boycott flow can be suppressed while suppressing aggregation of particles. Furthermore, the effect can be further improved by making this specific gravity ratio into the range of 0.90 or more and 0.99 or less.

  Moreover, it is preferable that the specific gravity of the particles in the slurry forming the slurry layer α2 is larger than the specific gravity of the solvent in the slurry forming the slurry layer α2 and the solvent forming the liquid layer α1. By adjusting the specific gravity between the particles and the solvent in this way, the particles in the slurry can be precipitated from the slurry layer α2 toward the liquid layer α1 by gravity. In addition, particles that settle in the solvent forming the slurry layer α2 and in the solvent forming the liquid layer α1 can be appropriately separated in accordance with the particle size.

  The volume ratio of the slurry layer α2 to the liquid layer α1 (volume of the slurry layer α2 / volume of the liquid layer α1) is not particularly limited, but is preferably in the range of 0.01 to 1.00, More preferably, it is in the range of 0.10 or more and 0.50 or less. By making this volume ratio 1.00 or less, it is possible to suppress a decrease in classification accuracy. By making this volume ratio 0.01 or more, it is possible to suppress a decrease in the amount of recovered particles. Therefore, by setting the volume ratio in the range of 0.01 or more and 1.00 or less, the classification accuracy and the amount of recovered particles can be improved. Furthermore, the effect can be further improved by making this volume ratio into the range of 0.10 or more and 0.50 or less.

  The concentration of the particles in the slurry layer α2 is not particularly limited, but is preferably in the range of 1% by mass to 20% by mass. By setting this concentration to 1% by mass or more, it is possible to suppress a decrease in the amount of recovered particles. By setting this concentration to 20% by mass or less, the promotion of particle aggregation can be suppressed. When the particles are aggregated, it becomes difficult to separate the particles vertically according to the particle size in the classification step S2, and the classification accuracy tends to be lowered. Therefore, by setting the concentration to 1% by mass or more and 20% by mass or less, the amount of collected particles and the classification accuracy can be improved.

  Note that the particles in the slurry layer α2 can be improved in dispersibility in the slurry by performing a surface treatment with a dispersant as needed or by dispersing the particles in a solvent having a dispersant.

  As the liquid of the liquid layer α1 and the solvent of the slurry layer α2, any material can be used as long as the above conditions are satisfied, but water, alcohols such as ethanol, methanol, isopropyl alcohol, and the like are preferable. Among these, water is preferable because it is inexpensive. A specific gravity / viscosity adjusting agent such as glycerin or glucose may be added to the solvent.

As the particles of the slurry layer α2, any material can be used as long as the above conditions are satisfied . As the particles of the slurry layer α2, particles such as plastic particles, inorganic particles, and metal particles can be used. Examples of these plastic particles include acrylic particles and vinyl resin particles. Cross-linked acrylic particles obtained by seed polymerization using acrylic particles as seeds can also be suitably used . In addition, the average particle diameter of the particles of the slurry layer α2 is preferably in the range of 1 μm to 10 μm from the viewpoint of sedimentation speed.

  FIG. 3 is a schematic vertical cross-sectional view of the wet classifier according to the first embodiment, showing the sedimentation state of particles in the classification process. FIG. 4 is a schematic longitudinal sectional view of the wet classifier according to the first embodiment after being left for a predetermined time in the classification process.

As shown in FIG. 3, in the classification step S2, first, the tank 12 is left for a predetermined time. Then, since the specific gravity of the particles of the slurry layer α2 is larger than that of the solvent of the slurry layer α2 and the solvent of the liquid layer α1, the particles of the slurry layer α2 settle by gravity toward the liquid layer α1 from the slurry layer α2. I will do it. The sedimentation rate of the particles is expressed by the Stokes equation of Equation (1).

  As is clear from the equation (1), the sedimentation rate of the particles varies depending on the particle size. The larger the particle size, the faster the sedimentation rate, and the smaller the particle size, the slower the sedimentation rate. For this reason, when the tank 12 is left for a predetermined time, as shown in FIG. 4, the particles are separated vertically according to the particle diameter. For example, let us consider a case where the slurry layer α2 includes particles having a large particle size, particles having a medium particle size, and particles having a small particle size. In this case, if the tank 12 is left for a predetermined time, most of the large-sized particles settle to the lower layer area A1 of the tank 12, and most of the medium-sized particles settle to the middle layer area A2 of the tank 12, Most of the particles having a particle size settle in the upper layer region A3 of the tank 12. The relationship between the sedimentation height of the particles corresponding to the particle size and the standing time can be specified by obtaining in advance through experiments or calculations.

  Then, after leaving the tank 12 for a predetermined time, the solvent in the height region in which the particles to be collected have settled is collected from the tank 12. For example, when collecting particles having a large particle size, the solvent in the lower layer region A1 of the tank 12 is collected, and when collecting particles having a medium particle size, the solvent in the middle layer region A2 of the tank 12 is collected and small particles are collected. When it is desired to collect particles having a diameter, the solvent in the upper layer region A3 of the tank 12 is collected. The solvent can be recovered by, for example, dividing the inside of the tank 12 up and down with one or a plurality of partition plates, and sucking the solvent from the area partitioned by the partition plates, or dropping from the upper opening of the tank 12. This can be realized by sucking the solvent with a suction pipe. Moreover, the predetermined time which leaves the tank 12 is about 5 to 30 hours.

  As described above, in the wet classification method according to the first embodiment, in the stacking step S1, the slurry layer α2 is stacked on the liquid layer α1, and the specific gravity of the slurry layer α2 is smaller than the specific gravity of the liquid layer α1. doing. For this reason, in the classification step S2, while suppressing the generation of a boycott flow (substitution flow) between the liquid layer α1 and the slurry layer α2, the majority of the particles from the slurry layer α2 to the liquid layer α1 under substantially the same conditions. Can sink to the side. Since the sedimentation speed of the particles due to the influence of gravity varies depending on the particle size, the particles in the slurry can be separated vertically according to the particle size by leaving the tank 12 for a predetermined time in the classification step S2. As a result, even particles having the same specific gravity can be classified with high accuracy and in a short time.

[Second Embodiment]
Next, a wet classification method according to the second embodiment will be described. The wet classification method according to the second embodiment is basically the same as the wet classification method according to the first embodiment, but the first is that the slurry layer and the liquid layer are partitioned using a partition plate. This is different from the wet classification method according to the embodiment. For this reason, below, only the part which is different from the wet classification method which concerns on 1st Embodiment is demonstrated, and description of the same part as the wet classification method which concerns on 1st Embodiment is abbreviate | omitted.

  FIG. 5 is a schematic longitudinal sectional view conceptually showing a classification device used in the wet classification method according to the second embodiment. As shown in FIG. 5, the classification device 21 includes a tank 22 into which slurry is injected and a partition plate 25 that partitions the tank 22 in the vertical direction. The tank 22 is made of, for example, a resin material such as silicone or acrylic, an inorganic material such as glass, a metal material, or the like, and has a bottomed cylindrical shape, and has an upper end opened.

  The tank 22 is divided into two in the vertical direction, and is composed of a lower tank 23 arranged at the lower part and an upper tank 24 arranged at the upper part.

  A packing 23 a having a predetermined height and having elasticity is attached to the upper end edge of the lower tank 23. A packing 24 a having a predetermined height and having elasticity is attached to the lower end edge of the upper tank 24. And the lower tank 23 and the upper tank 24 are supported by the tank support apparatus (not shown) so that the packing 23a and the packing 24a may closely_contact | adhere.

  The partition plate 25 is preferably formed in a thin flat plate shape and has a thickness of about 1 mm to 5 mm. The partition plate 25 is inserted between the packing 23 a of the lower tank 23 and the packing 24 a of the upper tank 24, thereby completely partitioning the tank 22 in the vertical direction between the lower tank 23 and the upper tank 24. It is possible. As described above, since the packing 23a and the packing 24a have elasticity, the partition plate 25 can be inserted between the packing 23a and the packing 24a while maintaining the airtightness between the packing 23a and the packing 24a. At the same time, the partition plate 25 can be removed from between the packing 23a and the packing 24a.

  As shown in FIG. 5, in the stacking step S <b> 1, the slurry layer β <b> 2 is formed on the liquid layer β <b> 1 via the partition plate 25. More specifically, first, the partition plate 25 is removed from the tank 22. Next, a solvent is injected into the tank 22 to form a liquid layer β1 in the lower layer of the tank 22. Next, the partition plate 25 is inserted into the tank 22. At this time, it is preferable not to create a space between the liquid layer β1 and the partition plate 25. Next, the slurry is injected into the tank 22 to form the slurry layer β2 in the upper layer of the tank 22. Thereby, in the laminating step S1, the slurry layer β2 can be easily laminated on the upper layer of the liquid layer β1 without mixing the liquid layer β1 and the slurry layer β2. Further, in the laminating step S1, the slurry layer β2 Can be prevented from settling into the liquid layer β1.

  The conditions of the liquid layer β1 and the slurry layer β2 are the same as the conditions of the liquid layer α1 and the slurry layer α2 in the wet classification method according to the first embodiment.

  FIG. 6 is a schematic vertical cross-sectional view of a wet classifier according to a second embodiment showing a sedimentation state of particles when the partition plate is removed in the classification process. FIG. 7 is a schematic vertical cross-sectional view of a wet classifier according to a second embodiment after being left for a predetermined time in the classifying step.

  As shown in FIG. 6, in the classification step S <b> 2, first, the partition plate 25 is removed from the tank 22. Then, the particles in the slurry layer β2 settle from the slurry layer β2 toward the liquid layer β1 due to gravity. As described above, in the stacking step S1, the partition plate 25 prevents the particles of the slurry layer β2 from being settled into the liquid layer β1, and therefore, in the classification step S2, the partition plate 25 is removed from the tank 22. The sedimentation of the particles of the slurry layer β2 into the liquid layer β1 can be started under substantially the same conditions. In this embodiment, as a method for removing the partition plate 25, the partition plate 25 is completely removed from the tank 22. However, if the partition plate is moved within a range where the effects of the present invention can be obtained, there is no problem and a part of the partition plate is removed. May be left in the tank.

  Then, when the tank 22 is left for a predetermined time, as shown in FIG. 7, the particles are separated vertically according to the particle diameter. For example, let us consider a case where the slurry layer β2 includes particles having a large particle size, particles having a medium particle size, and particles having a small particle size. In this case, if the tank 22 is allowed to stand for a predetermined time, most of the large-sized particles settle to the lower layer region B1 of the tank 22, and most of the medium-sized particles settle to the middle layer region B2 of the tank 22. Most of the particles having a particle size settle in the upper layer region B3 of the tank 22.

  Then, after the tank 22 is left for a predetermined time, the solvent in the height region where the particles to be collected are settled is collected from the tank 22. For example, when collecting particles having a large particle size, the solvent in the lower layer region B1 of the tank 22 is collected, and when collecting particles having a medium particle size, the solvent in the middle layer region B2 of the tank 22 is collected, When it is desired to collect particles having a diameter, the solvent in the upper layer region B3 of the tank 22 is collected.

  As described above, according to the wet classification method according to the second embodiment, the following operational effects can be obtained in addition to the operational effects of the wet classification method according to the first embodiment.

  That is, in the stacking step S1, by separating the slurry layer β2 and the liquid layer β1 by the partition plate 25, it is possible to prevent the boycott flow between the slurry layer β2 and the liquid layer β1, and in the classification step S2, By removing the partition plate 25, particles in the slurry can be settled to the liquid layer β1 side under substantially the same conditions.

[Third Embodiment]
Next, a wet classification method according to the third embodiment will be described. The wet classification method according to the third embodiment is basically the same as the wet classification method according to the second embodiment, but the particles in the slurry are classified using the particle size dependence of the zeta potential. This is different from the wet classification method according to the second embodiment. For this reason, below, only the part which is different from the wet classification method according to the second embodiment will be described, and the description of the same part as the wet classification method according to the second embodiment will be omitted.

  FIG. 8 is a schematic longitudinal sectional view conceptually showing a classification device used in the wet classification method according to the third embodiment. As shown in FIG. 8, the classification device 31 includes a tank 32 into which slurry is injected, a partition plate 35 that partitions the inside of the tank 32 in the vertical direction, an upper electrode 36 that is disposed above the tank 32, and the tank 32. A lower electrode 37 disposed in the lower part, and a voltage control unit 38 for applying a voltage to the upper electrode 36 and the lower electrode 37 are provided.

  The tank 32 is formed, for example, in a cylindrical shape from a resin material such as silicone or acrylic, or an inorganic material such as glass. The upper end is opened and the lower end is covered by the lower electrode 37.

  The tank 32 is divided into two in the vertical direction, and includes a lower tank 33 disposed in the lower part and an upper tank 34 disposed in the upper part.

  An elastic packing 33 a having a predetermined height is attached to the upper end edge of the lower tank 33. An elastic packing 34 a having a predetermined height is attached to the lower end edge of the upper tank 34. And the lower tank 33 and the upper tank 34 are supported by the tank support apparatus (not shown) so that the packing 33a and the packing 34a may closely_contact | adhere.

  Similar to the classification device 21 of the second embodiment, the partition plate 35 is formed in a thin flat plate shape, and is attached to the packing 33 a attached to the upper edge of the lower tank 33 and the lower edge of the upper tank 34. It can be inserted into and removed from the packing 34a.

  The upper electrode 36 is made of, for example, a conductive material such as a conductive polymer or metal in order to apply an electric field to the slurry injected into the tank 32. The upper electrode 36 is disposed on the inner upper side of the upper tank 34. In order to dispose the upper electrode 36 on the inner upper side of the upper tank 34, for example, a protrusion (not shown) is provided on the upper inner wall of the upper tank 34, and the upper electrode 36 is inserted into the tank 32 from the upper opening of the tank 32. What is necessary is just to insert and place in this protrusion. The upper electrode 36 is formed with a plurality of through holes 36 a in order to allow the slurry injected into the tank 32 to pass smoothly through the tank 32.

  The lower electrode 37 is made of, for example, a conductive material such as a conductive polymer or a metal in order to apply an electric field to the slurry injected into the tank 32. For example, the lower electrode 37 has a larger outer diameter than the tank 32 and is in close contact with the lower end edge of the tank 32 in order to configure the bottom of the tank 32. The lower electrode 37 has an upper surface exposed in the tank 32 in order to apply an electric field to the slurry injected into the tank 32.

  The voltage control unit 38 is electrically connected to the upper electrode 36 and the lower electrode 37. The voltage control unit 38 can change the magnitude of the voltage applied to the upper electrode 36 and the lower electrode 37 and change the polarity of the voltage applied to the upper electrode 36 and the lower electrode 37. It is possible.

  Here, before explaining the wet classification method according to the third embodiment, the particle size dependence of the zeta potential will be briefly explained by taking acrylic particles as an example.

  FIG. 9 is a graph showing a sedimentation curve when acrylic particles are sedimented by a sedimentation balance method. FIG. 10 is a graph showing the particle size dependence of the zeta potential in acrylic particles.

  First, after the slurry containing acrylic particles is stirred by a bead mill, the sedimentation curve as shown in FIG. 9 is obtained by sedimentation of the acrylic particles by a sedimentation balance method. The sedimentation curve shown in FIG. 9 is obtained by setting the peripheral speed of the bead mill to 6.65 m / s, stirring the slurry for 30 minutes, and then applying a voltage of 30 V to sediment the acrylic particles. The relationship between weight and elapsed time is shown.

  Next, the experimental conditions of the sedimentation balance method and the data of the sedimentation curve are substituted into the equations (2) and (3), and the zeta potential ζ for each particle size is calculated. In Equation (3), the zeta potential ζ is expressed by a quadratic equation, but may be expressed by a primary equation or a higher-order equation of the third or higher order.

The thus the relationship between the particle diameter D _p of the calculated zeta potential ζ and acrylic particles shown in FIG. 10. As shown in FIG. 10, the acrylic particles are charged with a negative (−) zeta potential ζ, and the absolute value of the zeta potential ζ increases as the particle size increases, and the absolute value of the zeta potential ζ decreases as the particle size decreases. The value is getting smaller. From this, it can be seen that the zeta potential ζ varies depending on the particle size.

  Next, a wet classification method for classifying acrylic particles in the slurry using the classifier 31 will be described.

  As shown in FIG. 8, in the stacking step S1, the slurry layer γ2 is formed on the liquid layer γ1 via the partition plate 35. More specifically, first, the partition plate 35 is removed from the tank 32. Next, a solvent is injected into the tank 32 to form a liquid layer γ1 in the lower layer of the tank 32. Next, the partition plate 35 is inserted into the tank 32. At this time, it is preferable that no space is formed between the liquid layer γ1 and the partition plate 35. Next, the slurry is injected into the tank 32 until the liquid level of the slurry layer γ2 is higher than the upper electrode 36 so that the upper electrode 36 is immersed in the slurry, and the slurry layer γ2 is formed in the upper layer of the tank 32. . At this time, the slurry for forming the slurry layer is charged in advance with negative (−) acrylic particles. The acrylic particles are charged by, for example, bead milling the acrylic particles or adding functional groups to the acrylic particles. In this embodiment, the acrylic particles are used for charging, but there is no particular limitation as long as the particles can be charged.

  The conditions for the liquid layer γ1 and the slurry layer γ2 are the same as the conditions for the liquid layer α1 and the slurry layer α2 in the wet classification method according to the first embodiment.

  FIG. 11 is a schematic vertical cross-sectional view of a wet classifier according to a third embodiment showing the sedimentation state of acrylic particles when the partition plate is removed and an electric field is applied in the classification process. FIG. 12 is a schematic longitudinal sectional view of a wet classifier according to a third embodiment after being left for a predetermined time in the classifying step.

  As shown in FIG. 11, in the classification step S <b> 2, first, the partition plate 35 is removed from the tank 32, and a negative (−) polarity voltage is applied to the upper electrode 36 by the voltage control unit 38 to lower the lower electrode 37. By applying a positive (+) polarity voltage to the liquid layer γ1 and the slurry layer γ2, an electric field in the vertical direction is applied.

  As a result, the acrylic particles in the slurry layer γ2 settle faster due to gravity in the case of particles having a large particle size than particles having a small particle size. Furthermore, since the electrophoresis of acrylic particles is faster for particles having a large particle size than for particles having a small particle size, the sedimentation rate for particles having a large particle size is higher than the sedimentation rate for particles having a small particle size.

  Then, when the tank 32 is left for a predetermined time, the acrylic particles are separated vertically according to the particle diameter, as shown in FIG. For example, let us consider a case where the slurry layer γ2 contains a large particle size acrylic particle, a medium particle size acrylic particle, and a small particle size acrylic particle. In this case, if the tank 32 is allowed to stand for a predetermined time, most of the large-sized acrylic particles settle to the lower layer region C1 of the tank 32, and most of the medium-sized acrylic particles settle to the middle layer region C2 of the tank 32. Most of the acrylic particles having a small particle size settle in the upper layer region C3 of the tank 32.

  Then, after the tank 32 is left for a predetermined time, the solvent in the height region in which the particles to be collected are settled is collected from the tank 32. For example, when collecting acrylic particles having a large particle size, the solvent in the lower layer region C1 of the tank 32 is collected, and when collecting acrylic particles having a medium particle size, the solvent in the middle layer region C2 of the tank 32 is collected, When it is desired to collect acrylic particles having a small particle size, the solvent in the upper layer region C3 of the tank 32 is collected.

  As described above, according to the wet classification method according to the third embodiment, the following operational effects can be obtained in addition to the operational effects of the wet classification method according to the second embodiment.

  That is, an electric field is generated in the tank 32 by applying a voltage to the upper electrode 36 and the lower electrode 37, and the sedimentation rate difference of the particles according to the particle size is further increased by combining the sedimentation of particles due to gravity and electrophoresis. Since it can be spread, the particles in the slurry can be classified with higher accuracy and in a shorter time.

[Fourth Embodiment]
Next, a wet classification method according to the fourth embodiment will be described. The wet classification method according to the fourth embodiment is basically the same as the wet classification method according to the first embodiment. However, the liquid layer and the slurry layer are turned upside down and the floating of particles by gravity is used. This is different from the wet classification method according to the first embodiment. For this reason, below, only the part which is different from the wet classification method which concerns on 1st Embodiment is demonstrated, and description of the same part as the wet classification method which concerns on 1st Embodiment is abbreviate | omitted.

  FIG. 13 is a schematic longitudinal sectional view conceptually showing a classification device used in the wet classification method according to the fourth embodiment. As shown in FIG. 13, in the wet classification method according to the fourth embodiment, the classification device 11 used in the wet classification method according to the first embodiment is used.

  As shown in FIG. 13, in the stacking step S1, the slurry is injected into the tank 12 to form the slurry layer δ1, and then the solvent is injected into the tank 12 to form the liquid layer δ2 above the slurry layer δ1. .

  At this time, the specific gravity of the slurry layer δ1 (specific gravity of the solvent and the whole slurry) is set to be larger than the specific gravity of the liquid layer δ2 (specific gravity of the solvent). Thus, by adjusting the specific gravity of the slurry layer δ1 and the liquid layer δ2, the slurry layer δ1 and the liquid layer δ2 can be stably stacked.

  The specific gravity ratio of the liquid layer δ2 to the slurry layer δ1 (specific gravity of the liquid layer δ2 / specific gravity of the slurry layer δ1) is not particularly limited, but is 0.80 or more and 1 for the same reason as in the first embodiment. The range is preferably less than 0.00, and more preferably in the range of 0.90 to 0.99.

  For the same reason as in the first embodiment, the specific gravity of the particles in the slurry forming the slurry layer δ1 is smaller than the specific gravity of the solvent in the slurry forming the slurry layer δ1 and the solvent forming the liquid layer δ2. It is preferable to do so. By adjusting the specific gravity between the particles and the solvent in this manner, the particles in the slurry can be floated from the slurry layer δ1 toward the liquid layer δ2 by gravity. Moreover, the particles floating in the solvent forming the slurry layer δ1 and the solvent forming the liquid layer δ2 can be appropriately separated in accordance with the particle size.

  The volume ratio of the slurry layer δ1 to the liquid layer δ2 (volume of the slurry layer δ1 / volume of the liquid layer δ2) is not particularly limited, but is 0.01 or more and 1 for the same reason as in the first embodiment. The range is preferably 0.000 or less, and more preferably 0.10 or more and 0.50 or less.

  The concentration of the particles in the slurry layer δ1 is not particularly limited, but for the same reason as in the first embodiment, the concentration is preferably in the range of 1% by mass to 20% by mass.

  FIG. 14 is a schematic vertical cross-sectional view of a wet classifying apparatus according to the fourth embodiment of the house board showing the floating state of particles in the classification process. FIG. 15 is a schematic vertical cross-sectional view of a wet classifier according to a fourth embodiment board after being left for a predetermined time in the classification process.

  As shown in FIG. 14, in the classification step S2, first, the tank 12 is left for a predetermined time. Then, since the specific gravity of the particles of the slurry layer δ1 is smaller than that of the solvent of the slurry layer δ1 and the solvent of the liquid layer δ2, the particles of the slurry layer δ1 are separated from the slurry layer by gravity, contrary to the first embodiment. It floats from δ1 toward the liquid layer δ2.

  As apparent from the above formula (1), the ascending speed of the particles varies depending on the particle diameter, and the ascending speed increases as the particle diameter increases, and the ascending speed decreases as the particle diameter decreases. For this reason, when the tank 12 is left for a predetermined time, as shown in FIG. 15, the particles are separated vertically according to the particle diameter. For example, let us consider a case where the slurry layer δ1 includes particles having a large particle size, particles having a medium particle size, and particles having a small particle size. In this case, if the tank 12 is left for a predetermined time, most of the large-sized particles float up to the upper layer area D1 of the tank 12, and most of the medium-sized particles float up to the middle layer area D2 of the tank 12. Most of the particles having a particle size float in the lower layer region D3 of the tank 12. The relationship between the flying height of the particle corresponding to the particle size and the standing time can be specified by obtaining in advance through experiments and calculations.

  Then, after the tank 12 is left for a predetermined time, the solvent in the height region where the particles to be collected are levitated is collected from the tank 12. For example, when collecting particles with a large particle size, the solvent in the upper layer region D1 of the tank 12 is collected, and when collecting particles with a medium particle size, the solvent in the middle layer region D2 of the tank 12 is collected, When it is desired to collect particles having a diameter, the solvent in the lower layer region D3 of the tank 12 is collected.

  As described above, in the wet classification method according to the fourth embodiment, in the stacking step S1, the liquid layer δ2 is stacked on the upper layer of the slurry layer δ1, and the specific gravity of the slurry layer δ1 is larger than the specific gravity of the liquid layer δ2. doing. For this reason, in the classification step S2, it is possible to suppress the generation of a boycott flow (substitution flow) between the liquid layer δ2 and the slurry layer δ1, and the majority of the particles from the slurry layer δ1 to the liquid layer δ2 under substantially the same conditions. Can float to the side. Since the particle floating speed due to the influence of gravity varies depending on the particle size, the particles in the slurry can be separated vertically according to the particle size by leaving the tank 12 for a predetermined time in the classification step S2. As a result, even particles having the same specific gravity can be classified with high accuracy and in a short time.

[Fifth Embodiment]
Next, a wet classification method according to the fifth embodiment will be described. The wet classification method according to the fifth embodiment is a method of classifying particles based on the relationship between particle sedimentation by gravity and electrophoresis.

  FIG. 16 is a schematic longitudinal sectional view conceptually showing a classification device used in the wet classification method according to the fifth embodiment. As shown in FIG. 16, the classification device 51 includes a tank 52 into which slurry is injected, an upper electrode 53 disposed above the tank 52, a lower electrode 54 disposed below the tank 52, and an upper electrode 53. And a voltage control unit 55 that applies a voltage to the lower electrode 54.

  The tank 52 is formed in a cylindrical shape from, for example, a resin material such as silicone or acrylic, an inorganic material such as glass, and the like. The upper end is opened and the lower end is covered with the lower electrode 54.

  The upper electrode 53 is made of, for example, a conductive material such as a conductive polymer or metal in order to apply an electric field to the slurry injected into the tank 52. The upper electrode 53 is disposed on the inner upper side of the tank 52. The upper electrode 53 is formed with a plurality of through holes 53a in order to allow the slurry injected into the tank 52 to pass smoothly through the tank 52.

  The lower electrode 54 is made of, for example, a conductive material such as a conductive polymer or a metal in order to apply an electric field to the slurry injected into the tank 52. The lower electrode 54 has a larger outer diameter than the tank 52 and is in close contact with the lower end edge of the tank 52, for example, in order to configure the bottom of the tank 52. The lower electrode 54 has an upper surface exposed in the tank 52 in order to apply an electric field to the slurry injected into the tank 52.

  The voltage control unit 55 is electrically connected to the upper electrode 53 and the lower electrode 54. The voltage control unit 55 can change the magnitude of the voltage applied to the upper electrode 53 and the lower electrode 54 and change the polarity of the voltage applied to the upper electrode 53 and the lower electrode 54. be able to.

  Next, a wet classification method for classifying acrylic particles in the slurry using the classifier 51 will be described.

  As shown in FIG. 16, in the stacking step S1, slurry is injected into the tank 52 to form the slurry layer ε1, and then the solvent is injected into the tank 52 until the upper electrode 53 is immersed in the solvent. The liquid layer ε2 is formed on the upper layer. In the slurry forming the slurry layer ε1, acrylic particles are charged to minus (−) in advance. The acrylic particles are charged by, for example, bead milling the acrylic particles or adding functional groups to the acrylic particles.

  At this time, the specific gravity of the slurry layer ε1 (specific gravity of the solvent and the whole slurry) is set to be larger than the specific gravity of the liquid layer ε2 (specific gravity of the solvent). Thus, by adjusting the specific gravity of the slurry layer ε1 and the liquid layer ε2, the slurry layer ε1 and the liquid layer ε2 can be stably stacked.

  The specific gravity ratio of the liquid layer ε2 to the slurry layer ε1 (specific gravity of the liquid layer ε2 / specific gravity of the slurry layer ε1) is not particularly limited, but is 0.80 or more and 1 for the same reason as in the first embodiment. The range is preferably less than 0.00, and more preferably in the range of 0.90 to 0.99.

  Further, the specific gravity of the particles in the slurry forming the slurry layer ε1 forms the solvent and liquid layer ε2 in the slurry forming the slurry layer ε1, so that the particles in the slurry forming the slurry layer ε1 settle by gravity. The specific gravity of the solvent to be increased.

  The volume ratio of the slurry layer ε1 to the liquid layer ε2 (volume of the slurry layer ε1 / volume of the liquid layer ε2) is not particularly limited, but is 0.01 or more and 1 for the same reason as in the first embodiment. The range is preferably 0.000 or less, and more preferably 0.10 or more and 0.50 or less.

  The concentration of the particles in the slurry layer ε1 is not particularly limited, but is preferably in the range of 1% by mass to 20% by mass for the same reason as in the first embodiment.

  FIG. 17 is a schematic vertical cross-sectional view of a wet classifier according to a fifth embodiment showing a movement state of acrylic particles when an electric field is applied in the classification process. FIG. 18 is a schematic vertical sectional view of a wet classifier according to a fifth embodiment after being left for a predetermined time in the classification process.

  As shown in FIG. 17, in the classification step S <b> 2, the voltage control unit 55 applies a positive (+) polarity voltage to the upper electrode 53 and applies a negative (−) polarity voltage to the lower electrode 54. The vertical electric field is applied to the slurry layer ε1 and the liquid layer ε2.

  Then, since the acrylic particles in the slurry layer ε1 are negatively charged (−), they attempt to move from the lower electrode 54 side to the upper electrode 53 side by electrophoresis. However, since the acrylic particles are also affected by gravity, the direction of movement changes depending on the magnitude of the influence of gravity. That is, the acrylic particles having a small particle diameter have a lower gravitational effect than the electrophoresis, and thus move upward from the lower electrode 54 side to the upper electrode 53 side. On the other hand, since acrylic particles having a large particle size have a large influence on the influence of electrophoresis, they do not move up from the lower electrode 54 side to the upper electrode 53 side at a high speed, but settle down due to gravity and stagnation. Or move up at low speed.

  For this reason, small particle size acrylic particles move up at high speed, large particle size acrylic particles settle, stagnant or move up at low speed, medium particle size acrylic particles move up at medium speed. To do.

  Then, when the tank 52 is left for a predetermined time, as shown in FIG. 18, the acrylic particles are separated vertically according to the particle diameter. For example, consider the case where the slurry layer ε1 contains acrylic particles having a large particle size, acrylic particles having a medium particle size, and acrylic particles having a small particle size. In this case, if the tank 52 is left for a predetermined time, most of the small-diameter acrylic particles move up to the upper layer area E1 of the tank 52, and most of the medium-sized acrylic particles rise to the middle layer area E2 of the tank 52. Most of the acrylic particles having a large particle diameter do not move upward from the lower layer region E3 of the tank 52.

  Then, after the tank 52 is left for a predetermined time, the solvent in the height region in which the particles to be collected are moving upward is collected from the tank 52. For example, when collecting acrylic particles having a small particle size, the solvent in the upper layer region E1 of the tank 52 is collected, and when collecting acrylic particles having a medium particle size, the solvent in the middle layer region E2 of the tank 52 is collected, When it is desired to collect acrylic particles having a large particle size, the solvent in the lower layer region E3 of the tank 52 is collected.

  As described above, according to the wet classification method according to the fifth embodiment, even when particles are classified using the balance between the sedimentation of particles due to gravity and the upward movement of particles due to electrophoresis, the slurry layer By adjusting the specific gravity between ε1 and the liquid layer ε2, it is possible to suppress the occurrence of a boycott flow (substitution flow) between the slurry layer ε1 and the liquid layer ε2 in the classification step S2. Can be classified on time.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  For example, in the second embodiment, the partition member is used as a partition member that partitions the inside of the tank up and down. However, any member may be used as long as the inside of the tank can be partitioned up and down. It may be a shape. For example, the inside of the tank may be divided up and down by a membrane, and the inside of the tank may be divided up and down by a partition member having a smaller diameter than the inner diameter of the tank.

  In the third embodiment, the particles are charged negatively, a negative polarity voltage is applied to the upper electrode, and a positive polarity voltage is applied to the lower electrode, so that the particles settle. As described above, the charge polarity of the particles and the voltage polarity applied to each electrode can be appropriately changed. For example, when a particle is negatively charged, a positive polarity voltage is applied to the upper electrode, and a negative polarity voltage is applied to the lower electrode, so that the particles can be electrophoresed to float. In addition, when the particles are positively charged, by applying a negative polarity voltage to the upper electrode and applying a positive polarity voltage to the lower electrode, the particles can be electrophoresed to float. On the other hand, when the particles are charged positively, by applying a positive polarity voltage to the upper electrode and applying a negative polarity voltage to the lower electrode, electrophoresis can be performed so that the particles settle.

  In the fifth embodiment, the particles are settled by gravity and the particles are moved up by electrophoresis. However, the particles may be lifted by gravity and moved down by electrophoresis. In this case, the specific gravity of the particles is made smaller than the specific gravity of the solvent so that the particles float by gravity, and the upper electrode is applied with a voltage of the same polarity as that charged to the particles so that the particles move down by electrophoresis. And a voltage having a different polarity from the pole charged in the particles may be applied to the lower electrode. It is also possible to float the particles by gravity and move the particles up by electrophoresis.

  Further, the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment can be appropriately combined. For example, in the first embodiment or the fourth embodiment, by applying an electric field in the tank as in the third embodiment, particles in the slurry are also utilized by utilizing the particle size dependence of the zeta potential. Classification may be performed. Further, in the second embodiment or the third embodiment, classification may be performed by causing particles in the slurry to float by reversing the specific gravity relationship between the liquid layer and the slurry layer as in the fourth embodiment.

  Next, examples of the present invention will be described. In addition, this invention is not limited to the Example demonstrated below.

  In the examples, pure water was injected into a 25 cm high volume flask to form a liquid layer, and then slurry was injected to form a slurry layer on top of the liquid layer. The liquid layer was 23 cm high and the slurry layer was 2 cm high.

  The slurry used was a solvent in which ethanol and water were mixed in a one-to-one ratio and contained 2.5% by mass of crosslinked acrylic particles having an average particle diameter of 2.85 μm and a specific gravity of 1.26. The crosslinked acrylic particles were synthesized by seed polymerization using acrylic particles having an average particle size of 600 nm as seeds.

  The specific gravity of the liquid layer was 1.00, and the specific gravity of the slurry layer was 0.94.

  After being left for 15 hours at 20 ° C., samples were taken from the volumetric flask in approximately 3 cm increments from above. The region from 4 cm to the top is sample 1, the region from 4 cm to 7 cm is sample 2, the region from 7 cm to 10.3 cm is sample 3, the region from 10.3 cm to 13.6 cm is from sample 4, 13.6 cm The region up to 17 cm was sample 5, the region from 17 cm to 20.3 cm was sample 6, and the region from 20.3 cm to 23.6 cm was sample 7.

  The particle diameter of the particles contained in each sample was measured using an FPIA 3000 (Flow Particle Image Analyzer) manufactured by Sysmex Corporation. As measurement conditions, 36000 particles were analyzed, and particles having a circularity of less than 95% were excluded as aggregated particles.

  FIG. 19 is a table showing the measurement results of the example. 20 is a graph showing the frequency (CV) of each sample. FIG. 21 is a graph showing the number of particles in 1 μl of each sample.

  As shown in FIGS. 19 to 21, there are many small particles in the region from 4 cm to the top, and many medium particles in the region from 4 cm to 7 cm. It was found that many particles having a large particle size exist in the region up to 3 cm. From this, it was found that by adjusting the specific gravity of the liquid layer and the slurry layer and leaving it for a predetermined time, the particles can be separated vertically according to the particle size, and can be classified with high accuracy.

  DESCRIPTION OF SYMBOLS 11 ... Classification apparatus, 12 ... Tank, 21 ... Classification apparatus, 22 ... Tank, 23 ... Lower tank, 23a ... Packing, 24 ... Upper tank, 24a ... Packing, 25 ... Partition plate, 31 ... Classification apparatus, 32 ... Tank, 33 ... Lower tank, 33a ... Packing, 34 ... Upper tank, 34a ... Packing, 35 ... Partition plate, 36 ... Upper electrode, 36a ... Through hole, 37 ... Lower electrode, 38 ... Voltage controller, 51 ... Classifier, 52 ... tank, 53 ... upper electrode, 53a ... through hole, 54 ... lower electrode, 55 ... voltage controller, α1, β1, γ1, δ2, ε2 ... liquid layer, α2, β2, γ2, δ1, ε1 ... slurry layer.

Claims (4)

A wet classification method for classifying particles in a slurry,
A laminating step of laminating a slurry layer containing particles to be classified in a solvent and a liquid layer not containing the particles in a tank;
A classification step of collecting the particles from the tank by moving the particles from the slurry layer toward the liquid layer by gravity;
Have
In the laminating step, the specific gravity of any one of the lower layer of the slurry layer and the liquid layer is made larger than the specific gravity of any of the upper layers of the slurry layer and the liquid layer , and an upper electrode is disposed on the upper side and a lower portion on the lower side. Forming the liquid layer and the slurry layer in a tank in which electrodes are arranged , and laminating the slurry layer and the liquid layer via a partition member that partitions the tank up and down ,
In the classification step, a voltage is applied to the upper electrode and the lower electrode, and the partition member is removed from the tank .
Wet classification method. In the stacking step, the slurry layer is stacked on the liquid layer, and the specific gravity of the slurry layer is made smaller than the specific gravity of the liquid layer.
The wet classification method according to claim 1. In the lamination step, the specific gravity of the particles is larger than the specific gravity of the solvent and the liquid layer.
The wet classification method according to claim 2. In the lamination step, the specific gravity ratio of the slurry layer with respect to the liquid layer is in a range of 0.80 or more and less than 1.00.
The wet classification method according to claim 2 or 3.

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