Patent Description:
A high-pressure jet mill, an ultrasonic homogenizer, a bead mill, and so on are available as devices for pulverizing and dispersing microparticles in slurry. Of these devices, a bead mill is capable of continuous processing and, due to being capable of pulverization and dispersion from micrometer size to nanometer size and so on, exhibits superior pulverization and dispersion functions. A bead mill is a device (a bead mill) in which a rotary member (a stirring rotor) rotates at high speed in a tightly sealed cylindrical container so that shearing force is generated between the cylindrical container and the stirring rotor, with the result that the particles in the slurry are pulverized and dispersed by the impact force of the beads suspended in the slurry.

For example, in a device (a bead mill <NUM>) of an invention disclosed in the Patent Literature <NUM>, a stirring rotor is provided in a lower portion of a cylindrical container, and by rotating the stirring rotor, pulverization processing is performed on particles and dispersion processing is performed on secondary particles formed from agglomerations of primary particles. To implement the pulverization and dispersion efficiently, the processing is performed by intermixing beads with a diameter of approximately <NUM> to <NUM> into the slurry. In the bead mill <NUM>, the beads are separated from the slurry on which the pulverization and dispersion processing has been completed by a bead separation device provided in an upper portion. Further, in a bead mill (a bead mill <NUM>) described in Patent Literature <NUM>, a mixture of slurry and beads is stirred inside a cylindrical container by a large bead separation device instead of a stirring rotor.

In a bead mill having this type of bead separation mechanism, pressure loss occurs in the device, e.g., when the slurry flows through a bead filling layer and when the slurry flows against centrifugal force generated as the bead separation device rotates, and therefore, in order to cause the slurry to flow through the bead mill having this type of bead separation device, it is necessary to apply comparatively high pressure of <NUM> to <NUM> MPa inside the mill.

Here, the pulverization processing refers to dividing single particles into a plurality of particles, while the dispersion processing refers to establishing a state in which primary particles are individually dispersed by separating secondary particles constituted by a plurality of particles. Note that the primary particles are individual crystalline or non-crystalline particles of a substance, and the secondary particles are formed when the surfaces of typically several to several thousand primary particles contact each other so as to form pseudo-particles. The beads used in the pulverization processing and dispersion processing are particles formed from a ceramic such as alumina or zirconia, a metal such as stainless steel, or plastic, and range in size from several tens of micrometers to several millimeters. The beads are generally preferably spherical. Further background art for the present invention is described in Patent Literatures <NUM>-<NUM>.

As noted above, a bead mill is capable of continuous processing and, due to being capable of pulverization and dispersion from micrometer size to nanometer size and so on, exhibits superior pulverization and dispersion functions. However, a bead mill has the following problems.

In a bead mill, the particles in the slurry are subjected to pulverization processing or dispersion processing by stirring the beads in a cylindrical container, and the beads are separated inside the cylindrical container. As described above, however, the push-in pressure applied thereto is high, while on the other hand, since a rotary driving portion of a rotary shaft for rotating the stirring rotor inside the cylindrical container comes into contact with the slurry, a rotating portion seal is required to prevent liquid leakage. To realize this rotating portion seal in the part where the pressure is comparatively high, a sealing structure realized by a mechanical sealing device is typically used.

A sealing device such as a mechanical seal is required to prevent slurry in a high-pressure container having a contact portion between a fixed component and a rotating component from leaking to the outside through a seal portion. To prevent leakage, it is necessary to apply pressure to the outside of the sealing device, and a mechanical seal is structured so as to house a sealing liquid. The seal contact portion component gradually becomes worn, which causes a problem in that the sealing performance deteriorates over time. As a result, a problem occurs in that the sealing liquid leaks into the slurry so as to contaminate the slurry. Another problem is that wear debris from the seal contact portion component (metal, ceramic, or the like) intermixes with the slurry. Furthermore, when the wear on the sealing device becomes severe, the sealing device has to be replaced, which costs money. Sealing portion wear occurs to a particularly large degree in slurry containing metal powder such as nickel, and this is a serious problem.

Another problem of a sealing device is that a mechanical seal has a complicated structure including a plurality of components, which is due to the existence of seams and uneven portions. In a bead mill having a sealing device, a problem occurs in that the slurry adheres to the seams and uneven portions. Especially when processing raw materials for foodstuffs and pharmaceuticals, problems occur in that due to putrefaction of solid matter, the product slurry cannot be used as a commercial product, and due to poor cleaning, the slurry is contaminated after changing the product type. Hence, problems occur due to wear of the sealing device and adhered substances, and therefore new technology for solving these problems is required.

The bead mill of the present invention does not include a rotating portion sealing device that contacts the slurry, and therefore the problem caused by wear of the contact members of the rotating portion sealing device, namely contamination of the product slurry with debris from the worn sealing components and the sealing liquid, is eliminated. The problem of particles in the slurry adhering to the rotating portion sealing device, making cleaning difficult, can also be solved.

<FIG> and <FIG> show a structural outline of a device of the present invention. The device is a bead mill in which a stirring rotor <NUM> rotates inside a cylindrical container constituted by a cylinder <NUM>, an upper lid <NUM>, and a lower lid <NUM>. A rotary shaft <NUM> is disposed in a vertical direction, and a slurry storage vessel <NUM> is provided above the cylindrical container. Note that the direction of the rotary shaft <NUM> does not have to be a perfectly vertical direction and may be inclined by up to approximately <NUM> degrees. The cylindrical container and the slurry storage vessel <NUM> are connected by a slurry flow passage <NUM> through which slurry passes, and the rotary shaft <NUM>, which is rotated by a driving device disposed above the cylindrical container, extends through the slurry storage vessel <NUM> and the slurry flow passage <NUM> into the cylindrical container. The stirring rotor <NUM> is fixed to the rotary shaft <NUM> in order to stir a mixture of slurry and beads in the cylindrical container. Further, a liquid feeding component that causes the slurry in the slurry flow passage <NUM> to flow downward is fixed to the rotary shaft <NUM>. The liquid feeding component is disposed either in the interior of the slurry flow passage <NUM> or in an uppermost portion of the cylindrical container. Due to the action of the liquid feeding component, a downward flow is formed in the slurry flow passage <NUM>, and as a result, leakage of the beads intermixed in the slurry in the cylindrical container can be prevented without the need for a sealing structure between the rotary shaft <NUM> and a fixed member (the upper lid <NUM>).

In <FIG>, a pumping component <NUM> that has a columnar shape with grooves formed therein and is provided in the interior of the slurry flow passage <NUM> is illustrated as an example of a suitable component shape for the liquid feeding component. <FIG> shows a detailed example of the structure thereof, in which grooves <NUM> are formed in a columnar portion <NUM>. Alternatively, as shown in <FIG>, a spiral projection <NUM> may be formed on the columnar portion <NUM>. The liquid feeding component does not necessarily have to be this shape, and any axial flow-type pumping mechanism may be used. Further, <FIG>, <FIG> and <FIG> illustrate a system in which a swirl promoting component (swirling blades <NUM>) for swirling the slurry is provided in the uppermost portion of the cylindrical container together with the pumping component <NUM>, and by causing the slurry to flow from a central portion to a peripheral portion using the swirl promoting component, the beads are pushed out to an outer peripheral portion of the cylindrical container by centrifugal force, while the slurry is sucked out from the slurry flow passage <NUM>.

<FIG> shows a specific example of this structure. <FIG> is a view showing the component from above, and illustrates an example in which rectilinear plates having receding angles in a rotation direction are disposed on an upper portion of a disc <NUM> as the swirling blades <NUM>. The swirling blades <NUM> may be rectilinear or curved. The swirling blades <NUM> preferably have a receding angle (<NUM> to <NUM> degrees) in the rotation direction. Note that when curved plates are used, the angle of the outermost part is viewed as the receding angle. Further, the component for swirling the slurry does not have to take the form of the swirling blades <NUM>, and instead, for example, a component having a plurality of grooves formed in a disc or, in the case of <FIG>, a component formed from only the swirling blades <NUM> without the disc <NUM> may be used. Moreover, as long as a function for swirling the slurry so that the slurry flows from the central portion toward the outer peripheral portion is realized, another shape may be used. Furthermore, as long as the upper portion of the cylindrical container includes a structure with which a sufficient downward flow is formed in the slurry flow passage <NUM> by the swirl promoting component for swirling the slurry, the liquid feeding component in the slurry flow passage <NUM>, such as the pumping component <NUM>, may be omitted so that only the swirl promoting component for swirling the slurry is disposed in the uppermost portion of the cylindrical container. By rotating the slurry in the upper portion of the cylindrical container at high speed, the slurry in the central portion is pushed out to the peripheral portion, and as a result, an effect of suctioning the slurry in the slurry flow passage <NUM> is realized.

In the device of the present invention, due to the effects of the rotary motion of the slurry in the cylindrical container and the rotation of the rotary shaft <NUM>, a vortex may be formed in the slurry storage vessel <NUM> such that the liquid surface enters the slurry flow passage <NUM>. In this case, air enters the mill, causing problems such as a reduction in the stirring efficiency of the beads and foaming of the slurry. These problems are particularly likely to occur when the stirring rotor <NUM> rotates at high speed or when highly viscous slurry is processed. In response to these problems, a component for preventing the slurry in the slurry storage vessel <NUM> from swirling may be disposed.

The component for suppressing swirling of the slurry may take any shape as long as swirling can be suppressed, but for example, a component (swirl prevention plates <NUM>) shown in <FIG> and <FIG>, in which a plurality of partition plates are disposed in a radial direction in order to halt rotation, is structurally simple and highly effective. The number of plates is preferably from <NUM> to <NUM>. Further, in addition to the swirl prevention plates <NUM>, as shown in <FIG>, a tube (a swirl prevention tube <NUM>) having a cylindrical shape, a polygonal shape, or another shape may be disposed around the rotary shaft <NUM> so as to reduce the effect of the rotation of the rotary shaft <NUM> on the slurry flow. Alternatively, although less effective, a comb tooth-shaped component may be disposed in the slurry in the slurry storage vessel <NUM>, for example, in order to suppress swirling of the slurry by creating flow resistance.

In method <NUM> according to the present invention, as shown in <FIG> and <FIG>, a centrifugal bead separation device is provided in the cylindrical container, and the slurry is supplied through a slurry passage port <NUM> in the lower lid <NUM> of the cylindrical container. The centrifugal bead separation device may take any form, but a centrifugal bead separation device used in experiments conducted by the inventors was a centrifugal bead separation device <NUM> shown in <FIG> or, as shown in detail in <FIG>, a device in which a plurality of plates (bead separation plates <NUM>) are fixed to an upper/lower pair of discs (an upper fixing disc <NUM> and a lower fixing disc <NUM>). The bead separation plates <NUM> were arranged at intervals of <NUM> to <NUM> between the outer peripheral portions thereof, and each had a receding angle of <NUM> to <NUM> degrees in the rotation direction. Instead of the form described above, a centrifugal bead separation device having a spiral impeller or the like can also be used in the present invention. In method <NUM>, the slurry passage port <NUM> in the lower lid <NUM> is used for slurry discharge, and in this case, a slit-type or screen-type bead separation device, such as a slit-type bead separation device <NUM> shown in <FIG>, is disposed. The slurry flows downward from the upper portion, whereupon the beads are separated and the slurry is discharged to the outside of the mill.

First, the bead mill of method <NUM> will be described in detail. A feature of this type is a structure including a component that causes the slurry to flow downward through the slurry flow passage <NUM> and a component that forms a slurry flow from the center toward the periphery in the slurry between the upper surface of the centrifugal bead separation device <NUM> and the upper lid <NUM> and prevents bead leakage by applying centrifugal force. By employing this structure, a bead mill not having a sealing structure in the rotating portion is formed. Note that in <FIG> and <FIG>, the stirring rotor <NUM> is disposed below the centrifugal bead separation device <NUM>, but the centrifugal bead separating component may itself be provided with a stirring function, and in this case, the stirring rotor <NUM> may be omitted.

In the example of <FIG>, which shows an embodiment of method <NUM> of the present invention, after performing stirring processing on the mixture of the slurry and the beads in the cylindrical container, the beads are separated from the slurry using centrifugal force. The centrifugal bead separation device <NUM> is fixed to the rotary shaft <NUM>. The slurry from which the beads have been separated by centrifugal force passes through a rotary shaft inner flow passage <NUM> formed in the interior of the rotary shaft <NUM>, and is discharged into the slurry storage vessel <NUM>. Next, the slurry is discharged from the slurry storage vessel <NUM> to the outside of the device through a slurry communication flow passage <NUM>. Note, however, that the slurry communication flow passage <NUM> does not necessarily have to be provided, and instead, a structure in which the slurry is sucked up from the slurry storage vessel <NUM> by a suction pipe or the like may be used. Some of the slurry in the slurry storage vessel <NUM> is fed downward by the pumping component <NUM> that is disposed on the rotary shaft <NUM> and has a function for feeding the slurry downward. By forming a downward flow of slurry in this manner, bead leakage into the slurry flow passage <NUM> is prevented.

In a case where microbeads of <NUM> or less are used or the like, the amount of beads flowing back through the slurry flow passage <NUM> may increase, and therefore, as shown in <FIG>, bead leakage into the slurry flow passage <NUM> must be suppressed by attaching a swirl promoting component such as the swirling blades <NUM> arranged radially to the upper surface of the centrifugal bead separation device <NUM> and exerting centrifugal force on the slurry in order to push the beads on the periphery of the slurry flow passage <NUM> out to the outer peripheral portion of the cylindrical container. The arrangement of the swirling blades <NUM> in this case is similar to the arrangement shown in <FIG>. Note that <FIG> is a view showing a combination of the swirling blades <NUM> of method <NUM> and the upper portion disc <NUM>, but the basic arrangement of the swirling blades <NUM> is the same. By employing a combination of the pumping component <NUM> and the swirling blades <NUM>, backflow of the beads due to pressure variation in the mill and so on can be suppressed. Alternatively, a component realized by forming radial grooves in the upper surface of the centrifugal bead separation device <NUM> or the like may be employed instead, as long as an identical function is realized thereby.

An outer peripheral diameter of the swirling blades <NUM> is preferably not less than <NUM> times an outermost peripheral diameter of the component of the centrifugal bead separation device <NUM> that swirls the slurry. More preferably, the outer peripheral diameter is from <NUM> times to <NUM> times the outermost peripheral diameter. These are optimum values for a ratio of the centrifugal force formed by the swirling blades <NUM> to the centrifugal force formed by the centrifugal bead separation device <NUM>. When the centrifugal force formed by the swirling blades <NUM> is too strong, the amount of slurry that circulates from the slurry storage vessel <NUM> to the cylindrical container through the slurry flow passage <NUM> may become too large, and as a result, the amount of slurry passing through the centrifugal bead separation device <NUM> may become excessive. Further, when the centrifugal force formed by the swirling blades <NUM> is too weak, a slurry flow flowing from the upper portion of the cylindrical container into the slurry flow passage <NUM> is formed. In this case, the component of the centrifugal bead separation device <NUM> that swirls the slurry may take any shape as long as the slurry is swirled thereby. Note, however, that components that are fixed to a disc or the like and have clear surfaces for pushing and separating the slurry in the rotation direction, such as the bead separation plates <NUM> shown in <FIG>, are preferable. The diameter of the outermost peripheral portion is defined as the diameter of the outermost portion of the component that swirls the slurry.

In the device of the present invention shown in <FIG>, the basic principle for preventing bead leakage according to the present invention is to prevent the slurry from flowing back from the slurry flow passage <NUM> by adjusting the pressure balance between the centrifugal bead separation device <NUM> and the swirling blades <NUM>. Depending on the operating conditions of the bead mill, however, disturbances in the flow through the bead mill may increase, causing the slurry to flow back into the slurry flow passage <NUM>. In order to respond to cases of such operating conditions, a component (a swirling slurry discharge component <NUM>) that causes the slurry to flow in a direction away from the rotational center of the rotary shaft <NUM> may be additionally disposed on the rotary shaft <NUM> at the outlet portion of the rotary shaft inner flow passage <NUM>, as shown in <FIG>. By disposing the final outlet of the slurry that flows out of the rotary shaft inner flow passage <NUM> in a position far from the rotational center, swirling is applied to the slurry flow. Due to the effect of dynamic pressure applied to the swirling slurry flow, a force for suctioning the slurry in the rotary shaft inner flow passage <NUM> acts thereon. Accordingly, the formation of a flow of slurry flowing into the centrifugal bead separation device <NUM> is promoted inside the cylindrical container, and as a result, a flow of slurry flowing back through the slurry flow passage <NUM> is less likely to occur, whereby bead leakage into the slurry storage vessel <NUM> can be suppressed.

The swirling slurry discharge component <NUM> may take any form as long as it is structured so as to swirl the slurry flow. However, a structure in which tubes having a circular shape, a square shape, or another shape are disposed at the slurry outlet of the rotary shaft inner flow passage <NUM>, which is divided into <NUM> to <NUM> locations, a structure in which a plurality of plates are disposed on an upper/lower pair of discs that apply centrifugal force to the slurry discharged from the rotary shaft inner flow passage <NUM>, or the like is preferable. For example, <FIG> shows a structure in which two cylindrical tubes (slurry rotating tubes <NUM>) are disposed at the slurry outlet of the rotary shaft inner flow passage <NUM>. In <FIG>, slurry outlets are provided in two locations of the rotary shaft inner flow passage <NUM>, and the slurry rotating tube <NUM> is disposed at each thereof. The slurry rotating tubes <NUM> are preferably disposed either radially in a diametrical direction from the rotation center, or disposed at receding angles in the rotation direction of the rotary shaft <NUM>. The receding angle is preferably within a range of <NUM> to <NUM> degrees. In the example of <FIG>, the slurry rotating tubes <NUM> are structured so as to draw an arc that recedes in the rotation direction.

Further, as a structure for applying centrifugal force to the slurry after the slurry is discharged from the rotary shaft inner flow passage <NUM>, an upper/lower pair of circular fixing discs may be disposed on the rotary shaft <NUM>, and a plurality of plates may be disposed thereon so that the slurry is pushed out in the outer peripheral direction by the motion of the plates. This structure is similar to the view of the centrifugal bead separation device shown in <FIG>. The diameter of the outer peripheral part of the slurry rotating tubes <NUM>, the plates, or the like is affected by the size of the bead mill, the slurry conditions, the diameter of the used beads, and so on, but is preferably <NUM> to <NUM> times the outer peripheral part of the component of the centrifugal bead separation device <NUM> that swirls the slurry. Furthermore, the bead separation plates <NUM> preferably have a receding angle of <NUM> to <NUM> degrees relative to the rotation direction.

In the device of the present invention shown in <FIG>, a component for preventing bead leakage is additionally disposed in the slurry storage vessel <NUM>. Likewise in a bead mill having the structure described above, in which the pumping component <NUM> and the swirling blades <NUM> are disposed as basic structures of the present invention, when the slurry is highly viscous, when beads of approximately <NUM> are used, and so on, the beads may flow back, albeit in a small amount, through the slurry flow passage <NUM>. As a measure for preventing this phenomenon, a screen <NUM> is disposed below the slurry liquid surface to prevent the beads from flowing out of the slurry storage vessel <NUM>. Note that when the slurry liquid surface is not flat, a part of the screen <NUM> may be above the liquid surface. Wire mesh may be disposed over the entire surface of the screen <NUM> or a part thereof. Gaps in the mesh forming the screen <NUM> are preferably <NUM> to <NUM> times the bead diameter.

The screen <NUM> is preferably fixed to the inner surface of the slurry storage vessel <NUM> so that there is no gap in a contact portion between the screen <NUM> and the slurry storage vessel <NUM>. However, there is a gap between the screen <NUM> and the rotary shaft <NUM>, and therefore, depending on the conditions, the beads suspended in the slurry may pass through the gap. When this phenomenon occurs, a component such as an under-screen swirling component <NUM> or a pumping component <NUM> is preferably disposed on the rotary shaft <NUM> to prevent the slurry from rising through the gap. Note that the under-screen swirling component <NUM> also has the effects of causing the slurry between the rotary shaft <NUM> and the screen <NUM> to flow downward and swirling the slurry so that the beads are prevented from approaching the gap between the rotary shaft <NUM> and the screen <NUM> by centrifugal force. As long as the under-screen swirling component <NUM> exhibits a function for causing the slurry to flow outward from the center by rotating, the shape thereof is not limited. A structure in which a plurality of radially arranged linear projections are mounted on a disc, i.e., a similar structure to the disc <NUM> and the swirling blades <NUM> disposed in the cylindrical container, as shown in <FIG>, a structure in which a plurality of radial grooves are formed in a disc as another shape, a structure in which a plurality of plates are arranged on a shaft, and so on may be used. The pumping component <NUM> is preferably identical to the pumping component <NUM> shown in <FIG>, for example, so as to be constituted by a groove formed in a cylindrical structure or a screw shape formed from a plurality of blades. Note that <FIG> shows both the under-screen swirling component <NUM> and the pumping component <NUM>, but it is possible to dispose only one thereof.

When the bead leakage suppression function of the under-screen swirling component <NUM> is sufficient, the slurry does not pass through the screen <NUM>, and bead leakage can be prevented by causing the slurry to pass only through the gap between the screen <NUM> and the rotary shaft <NUM>. In other words, below the screen <NUM>, the beads are pushed out in an outward direction from an outer peripheral portion of the under-screen swirling component <NUM> by the centrifugal force of the swirling slurry, and therefore there are no longer any beads in the slurry that rises through the gap between the screen <NUM> and the rotary shaft <NUM>. As a result of this effect, no beads leak above the screen <NUM> through the gap. Hence, by providing the under-screen swirling component <NUM>, the screen <NUM> may be a partition plate structured so that the slurry does not pass therethrough.

In the bead mill having this structure, a partition plate that divides the slurry stored in the slurry storage vessel <NUM> into upper and lower parts is disposed in the position of the screen <NUM>. Further, the rotary shaft <NUM> passes through an opening portion provided in the partition plate. Also, a component for swirling the slurry is disposed on the rotary shaft <NUM> below the opening portion. In the example of <FIG>, the under-screen swirling component <NUM> is disposed as this component. The under-screen swirling component <NUM> used to realize the bead mill of this embodiment may take any shape as long as sufficient centrifugal force is formed when the slurry is swirled thereby. However, a structure in which a pattern that promotes swirling is formed on the upper surface of a disc, as shown in <FIG>, is most preferable. A structure having a plurality of linear projections, as shown in <FIG>, or conversely a plurality of linear grooves may also be used.

Moreover, when the slurry in the slurry storage vessel <NUM> is swirled, a vortex may be generated, and as a result, the liquid surface of a central portion of the slurry may fall greatly below the screen <NUM>. As a countermeasure, the swirl prevention plates <NUM> may be mounted in the interior of the slurry storage vessel <NUM>, as described above. The swirl prevention plates <NUM> are vertical plates disposed so as to be oriented in the diametrical direction of the slurry storage vessel <NUM>, and are provided in a plurality. An appropriate number of swirl prevention plates is from <NUM> to <NUM>. By providing the swirl prevention plates <NUM>, the swirling motion of the slurry inside the slurry storage vessel <NUM> is suppressed so that the beads settle more easily. As a result, the beads can return to the cylindrical container more easily by riding the downward flow through the slurry flow passage <NUM>. The swirl prevention plates <NUM> are most typically structured so as to be fixed to the side surface of the slurry storage vessel <NUM>, but may be fixed to the bottom surface of the slurry storage vessel <NUM> instead. Furthermore, although not shown in <FIG>, the swirl prevention plates <NUM> are preferably adhered to the swirl prevention tube <NUM>, as shown in <FIG>. The effect of the motion of the rotary shaft <NUM> is further mitigated by the swirl prevention tube <NUM>, thereby further suppressing the slurry flow inside the slurry storage vessel <NUM>. The swirl prevention tube <NUM> is a cylindrical tube, a polygonal tube, or a tube having another shape, and is structured so as to isolate the rotary shaft <NUM> from the slurry on the periphery thereof in the interior of the slurry storage vessel <NUM>. Further, a hole or the like may be opened in a part thereof.

Note that as an even more preferable embodiment of method <NUM> of the present invention, the component for suctioning the slurry in the rotary shaft inner flow passage <NUM>, shown in <FIG>, the screen <NUM> for filtering the beads and the slurry rotation prevention component, shown in <FIG>, and so on are disposed in the interior of the slurry storage vessel <NUM>. Moreover, a combination of the structures shown in <FIG> and <FIG> is also within the scope of the present invention.

Next, using <FIG>, method <NUM> of the bead mill will be described. The bead mill having this device configuration includes, as main constituent components, the cylindrical container constituted by the cylinder <NUM>, the upper lid <NUM>, and the lower lid <NUM>, the stirring rotor <NUM> connected to the rotary shaft <NUM>, and the slit-type bead separation device <NUM> disposed in the slurry passage port <NUM> in the lower lid <NUM>, while the slurry storage vessel <NUM> is additionally disposed in the upper portion of the cylindrical container.

The slurry supplied from the slurry storage vessel <NUM> to the cylindrical container through the slurry flow passage <NUM> forms a mixture with the beads and undergoes stirring processing, whereupon the beads are separated before the slurry is discharged from the cylindrical container. In the bead mill of method <NUM>, a bead separation device of a type that separates the beads by passing the slurry through a narrower gap than the diameter of the used beads, such as the slit-type bead separation device <NUM>, is disposed. In the example of <FIG>, the gap opened between the slit-type bead separation device <NUM> and the slurry passage port <NUM> is adjusted so that the beads do not leak therethrough. Note that the bead separation device of the present invention may take any form as long as the slurry passes through a narrow gap formed therein, and a slit-type, a mesh screen-type, a parallel wire-type, or the like may be used.

In the bead mill having the structure described above, when the rotation speed of the stirring rotor <NUM> while stirring the beads is high or when the slurry is highly viscous, centrifugal force is exerted on the slurry by the rotary motion of the stirring rotor <NUM>, and as a result, the beads may rise through the cylindrical container up to the vicinity of the upper lid <NUM> and press against the slurry flow passage <NUM>. In the present invention, this problem is dealt with by disposing a component for applying centrifugal force to the slurry above the position in which the stirring rotor <NUM> is disposed in the cylindrical container. This component is realized by attaching the swirling blades <NUM> to the upper portion disc <NUM>, as shown in <FIG>, or the like. This structure is shown in detail in <FIG>. Here, the swirling blades <NUM> may be rectilinear or curved, and preferably have a receding angle of <NUM> to <NUM> degrees in the rotation direction. Further, the outer peripheral diameter of the swirling blades <NUM> is preferably larger than the outer peripheral diameter of the stirring rotor <NUM>.

Furthermore, due to the effects of rotation of the rotary shaft <NUM> and the pumping component <NUM> and swirling of the slurry in the cylindrical container, the slurry swirls inside the slurry storage vessel <NUM>, but when the swirling becomes violent, a large vortex may be formed such that air is drawn into the cylindrical container from the space in the slurry storage vessel <NUM>. As a result, it may become impossible to continue the processing due to foaming of the slurry, the stirring performed by the stirring rotor <NUM> may be insufficient, and so on. These problems are dealt with by disposing a rotation prevention component in the slurry storage vessel <NUM>. As shown in the example of <FIG>, by disposing the swirl prevention plates <NUM> and the swirl prevention tube <NUM> in the slurry storage vessel <NUM>, swirling of the slurry can be suppressed, and as a result, air can be prevented from infiltrating the cylindrical container. The swirl prevention plates <NUM> may also be disposed alone, although this leads to a slight reduction in effectiveness.

In a conventional bead mill, a mechanical sealing structure (typically, a mechanical sealing device) is disposed between the upper portion of the cylindrical container and the rotary shaft. The reason for this is that in order to respond to liquid resistance during the processing in the cylindrical container and pressure loss in the bead separation device, a state in which the interior of the cylindrical container is pressurized by pushing the slurry into the mill using a pump or the like is established, and therefore a sealing mechanism is required on the periphery of the rotary shaft. In the device of the present invention, on the other hand, pressure is applied to the interior of the cylindrical container by the pumping component <NUM> and so on disposed between the rotary shaft <NUM>, which is a rotating component, and the slurry flow passage <NUM>, which is a fixed component, and therefore differential pressure can be created between the interior and the exterior (in the case of the present invention, the slurry storage vessel <NUM> is on the exterior) of the cylindrical container without the need for a sealing mechanism. As a result, a mechanical sealing device can be omitted.

The bead mill according to the present invention can be applied to pulverization processing and dispersion processing of slurry containing a fine powder of ceramics, carbon nanotube, cellulose nanofiber, pigments, inks, paints, dielectric bodies, magnetic bodies, inorganic substances, organic substances, pharmaceuticals, foodstuffs, metals, and so on.

Two of the devices (a mill <NUM> using the centrifugal bead separation method and a mill <NUM> using the slit-type bead separation device) were manufactured, and processing experiments were performed thereon by introducing beads while varying the component configuration. In a first device of the present invention (method <NUM>: mill <NUM>), the experiment was performed with six component configurations, namely a mill 1a, a mill 1b, a mill 1c, a mill 1d, a mill 1e, and a mill 1f. The basic structure of the mills 1a to 1e was basically that shown in <FIG>. The gaps in the mesh of the screen <NUM> were set at <NUM> to <NUM>. In the mill 1d and the mill 1e, a component for adjusting the slurry flow through the gap between the screen <NUM> and the rotary shaft <NUM> was disposed. Further, in a mill <NUM>, a partition plate was disposed instead of the screen <NUM>, and in order to adjust the slurry flow through the gap between the partition plate and the rotary shaft <NUM>, the under-screen swirling component was disposed. The partition plate was disposed in the same position as the screen <NUM> of the mills 1b to 1e. In the configuration of the mill 1a, a further experiment was performed to determine a favorable outer peripheral diameter for the swirling blades <NUM>. The mill 1f was the mill shown in <FIG>. Table <NUM> shows the specifications of the mills.

In the mill 1a, the swirling blades <NUM> were disposed but nothing was disposed in the interior of the slurry storage vessel <NUM>, while in the mill 1b, only the swirling blades <NUM> and the screen <NUM> were disposed, and in the mill 1c, the screen <NUM> and the swirl prevention plates <NUM> were disposed in addition to the swirling blades <NUM>. Further, in the mill 1d, the under-screen swirling component <NUM> was disposed in addition to the configuration of the mill 1c. The under-screen swirling component <NUM> was structured as shown in <FIG>, and the outer peripheral diameter of the blades was <NUM>. Also in the mill 1d, the pumping component <NUM> was disposed in addition to the configuration of the mill 1c. Furthermore, in the mill 1f, in which a component for rotating the slurry flowing out of the rotary shaft inner flow passage <NUM> was disposed, the slurry rotating tube <NUM> shown in <FIG> was disposed, and the outer peripheral diameter thereof was set at <NUM>. Note that the outer peripheral diameter of the blades of the centrifugal bead separation device <NUM> was <NUM>.

Further, a second device (method <NUM>: mill <NUM>) was a bead mill having the contact-type, slit-type bead separation device <NUM> in the bottom portion of the mill, and basically having the structure shown in <FIG>. In a mill 2a, the swirling blades <NUM> were disposed, but neither the swirl prevention plates <NUM> nor the swirl prevention tube <NUM> were disposed, while in a mill 2b, both the swirl prevention plates <NUM> and the swirl prevention tube <NUM> were disposed in addition to the swirling blades <NUM>. The main specifications are shown on Table <NUM>.

Moreover, as comparative examples, the experiment was also performed using a mill I and a mill II in which none of the swirling blades <NUM>, the swirl prevention plates <NUM>, the swirl prevention tube <NUM>, the screen <NUM>, and so on were disposed in a mill having the same cylindrical container as the mill <NUM> and the mill <NUM>. The specifications of these mills are also shown on Table <NUM>. In the processing experiment undertaken on the mill 1a to the mill I of method <NUM>, the fluid supplied to the cylindrical container was water, while the fluid supplied to the mills 2a to II of method <NUM> was water and a highly viscous liquid with a viscosity of <NUM> mPa • s. The flow rate was set at <NUM>/hour.

First, with the device configuration of the mill 1a, the effect on bead leakage of the ratio of the outer peripheral diameter of the swirling blades <NUM> to the outer peripheral diameter of the component of the centrifugal bead separation device <NUM> that swirls the slurry was investigated. Six swirling blades <NUM> with a length of <NUM> and a height of <NUM> were disposed. Note that in a prior experiment conducted by the inventors, the receding angle of the swirling blades <NUM> was most preferably <NUM> to <NUM> degrees, and therefore, in this experiment, the receding angle was set at <NUM> degrees. An experiment was also performed to determine an appropriate outer peripheral diameter for the swirling blades <NUM> in the device configuration of the mill 1a. In the device configuration of the mill 1a, the outer peripheral diameter of the component that swirls the slurry is defined as the diameter of the outermost peripheral portion of the component, other than a near-parallel surface (an angle of no more than approximately <NUM> degrees) to the rotation direction, such as the plate that holds the swirling blades <NUM>. <FIG> is a view showing the structure of the centrifugal bead separation device <NUM> used in this experiment, and in this device, the component that swirls the slurry is the bead separation plates <NUM>. In the example of this case, the outer peripheral diameter of the bead separation plates <NUM> is preferably taken as the denominator of the outer peripheral diameter ratio. The experiment was performed with the outer peripheral diameter of the swirling blades <NUM> set within a range of <NUM> to <NUM> (outer peripheral diameter ratio: <NUM> to <NUM>) relative to an outer peripheral diameter of <NUM> for the bead separation plates <NUM>, and using <NUM> beads and water set at a flow rate of <NUM>/hour. Note that as an experiment condition, an outer peripheral speed of the bead separation plates <NUM> was set within a range of <NUM> to <NUM>/sec.

As shown in the experiment results on table <NUM>, at an outer peripheral diameter ratio of <NUM> and an outer peripheral speed of <NUM>/sec or less in the bead separation plates <NUM>, a very small amount of bead leakage occurred, whereas at an outer peripheral speed of <NUM>/sec or less, a considerable amount of bead leakage (<NUM>/min or more) occurred. Meanwhile, when the outer peripheral diameter was set at <NUM> (outer peripheral diameter ratio: <NUM>), only a very small amount of bead leakage occurred at <NUM>/sec, and therefore an improvement was observed. Further, when the outer peripheral diameter was set at <NUM> to <NUM> (outer peripheral diameter ratio: <NUM> to <NUM>), no bead leakage was observed. At <NUM> (outer peripheral diameter ratio: <NUM>), meanwhile, a very small amount of bead leakage (<NUM> or less over a one-hour operation) occurred at the maximum speed of <NUM>/sec. Favorable results were obtained at an outer peripheral diameter ratio of <NUM> or more, and therefore the range is preferably <NUM> to <NUM>. A range of <NUM> to <NUM> is even more preferable. On the basis of these results, the outer peripheral diameter of the swirling blades <NUM> of the mills 1a to <NUM> was set at <NUM> or <NUM>.

In the mills 1a to 1f and the mill I, the bead leakage situation was checked using beads with diameters of <NUM> and <NUM>. As regards the processing conditions, the beads were introduced using room temperature water until a filling ratio of <NUM>% was realized in the mill. The experiment was performed while varying the outer peripheral speed of the slurry swirling component (the bead separation plates <NUM>) of the centrifugal bead separation device <NUM> from <NUM> to <NUM>/sec at intervals of <NUM>/sec. The experiment results are shown on Table <NUM>. In the experiment using beads with a diameter of <NUM>, bead leakage was observed in the mill I of the comparative example when the outer peripheral speed of the bead separation plates <NUM> was <NUM>/sec.

On the other hand, bead leakage was not observed in any of the mills 1a to 1f, regardless of the conditions. Note that when the outer peripheral speed was <NUM>/sec, a very small amount of beads became intermixed in the slurry storage vessel <NUM> during the processing of the mills 1a and 1b. However, these beads did not flow out to the exterior of the mill. In the mills 1c to 1f, no beads became intermixed in the slurry storage vessel <NUM>.

In the experiment using beads with a diameter of <NUM>, intermixing of the beads in the slurry storage vessel <NUM> was observed in all mills during processing with the outer peripheral speed of the bead separation plates <NUM> set at <NUM>/sec or less, and in the experiment performed on the mill I of the comparative example, beads leaked to the outside of the device from the slurry storage vessel <NUM><NUM> minutes after the start of the processing at <NUM>/sec. In the experiment performed on the mill 1a, on the other hand, bead leakage did not occur until the outer peripheral speed of the bead separation plates <NUM> reached <NUM>/sec, and at <NUM>/sec, a small amount of beads leaked to the outside of the device from the slurry storage vessel <NUM><NUM> minutes after the start of the processing. At this point in time, as shown on Table <NUM>, a considerable amount of beads had accumulated in the interior of the slurry storage vessel <NUM>.

Hence, the beads showed a tendency to accumulate in the interior of the slurry storage vessel <NUM>, and in the mill 1a in which only the swirling blades <NUM> were disposed, although an effect for preventing bead leakage was achieved, the effect was somewhat limited. In the processing of the mill 1b, no bead leakage from the slurry storage vessel <NUM> was observed during processing performed with the outer peripheral speed of the bead separation plates <NUM> set at <NUM>/sec or more, and even during the processing performed at <NUM>/sec, only a very small amount of leakage was observed <NUM> minutes after the start of the processing. Hence, by disposing the screen <NUM>, it was possible to prevent bead leakage. Note, however, that a small amount of beads had accumulated in the slurry storage vessel <NUM> at the end of the processing.

In the experiment performed on the mill 1c, no bead leakage from the slurry storage vessel <NUM> was observed during the processing performed with the outer peripheral speed of the bead separation plates <NUM> set at <NUM>/sec or more, and even during the processing performed at <NUM>/sec, only a very small amount of leakage was observed <NUM> minutes after the start of the processing. Hence, by disposing the swirl prevention plates <NUM> in addition to the screen <NUM>, it was possible to prevent suspended bead leakage of the beads in the slurry storage vessel <NUM>. The amount of beads remaining the slurry storage vessel <NUM> following all of the processing was a very small amount. The reason for this is believed to be that since swirling of the slurry in the slurry storage vessel <NUM> is reduced such that suspension of the beads is suppressed, it becomes easier to feed the beads to the cylindrical container together with the slurry using the pumping component <NUM>. Note that the reason why a small amount of bead leakage occurred is believed to be that since the under-screen swirling component <NUM> and so on were not provided, the beads leaked upward through the space between the screen <NUM> and the rotary shaft <NUM>.

In the experiments performed on the mill 1d and the mill 1e, no bead leakage was observed during all of the processing performed with the outer peripheral speed of the bead separation plates <NUM> set at <NUM> to <NUM>/sec. This was due to the centrifugal effect of the under-screen swirling component <NUM> and the effect of the downward slurry flow formed by the pumping component <NUM>. Moreover, in the processing performed on the mill 1d and the mill 1e, the amounts of beads remaining in the slurry storage vessel <NUM> following the processing performed on the mill 1d and the mill 1e were much smaller than in the processing performed on the mills 1a, 1b, and I, while the amount of accumulated beads was slightly smaller than in the processing performed on the mill 1c.

In the experiment performed on the mill 1f, an effect of sucking out the slurry in the rotary shaft inner flow passage <NUM> was obtained by the slurry rotating tube <NUM>, thereby stabilizing the flow of slurry into the centrifugal bead separation device <NUM> so that bead leakage into the slurry storage vessel <NUM> was smaller than in the processing performed on the mill I of the comparative example and also the processing performed on the mills 1a to 1e.

The experiment performed on the mill <NUM> is an example in which the partition plate through which the slurry does not pass was disposed instead of the screen <NUM>. A component having the structure shown in <FIG> was disposed on the rotary shaft <NUM> as the under-screen swirling component <NUM>. The diameter of the under-screen swirling component <NUM> was set at <NUM>, i.e., <NUM> times the diameter of the bead separation plates <NUM> of the bead separation device, making it possible to generate enough centrifugal force to push out the beads in an outward direction, and as a result, no beads leaked upward from the slurry storage vessel even when all of the slurry passed through the space between the rotary shaft <NUM> and the partition plate. In an experiment performed by the present inventors, when the ratio of the diameter of the under-screen swirling component <NUM> to the diameter of the bead separation plates <NUM> was <NUM> or less, sufficient centrifugal force could not be secured, and a very small amount of bead leakage occurred. Further, when the ratio was <NUM> or more, the slurry flow in the interior of the slurry storage vessel <NUM> became excessive, leading to the formation of a vortex, and as a result, foaming of the slurry occurred.

In the mills 2a and 2b and the mill II, the processing experiment was performed using <NUM> beads together with water and highly viscous slurry with a viscosity of <NUM> mPa • s. The diameter of the swirling blades <NUM> of the mill 2b was <NUM>, which is larger than the diameter of the stirring rotor <NUM>, and it was therefore possible to form a sufficient downward flow in the interior of the slurry flow passage <NUM> by means of the slurry suctioning effect generated by the centrifugal force of the swirling blades <NUM>. Accordingly, the pumping component <NUM> was omitted. Note, however, that in order to increase the passage resistance in the slurry flow passage <NUM>, a cylinder (with no grooves or projections) having the same diameter as the pumping component <NUM> was disposed.

These experiment results are shown on Table <NUM>. In the mill II of the comparative example, when the outer peripheral speed of the stirring rotor <NUM> was set at a high speed of <NUM>/sec or more, the phenomenon whereby the beads are pushed against the upper lid <NUM> by the centrifugal force created by the stirring rotor <NUM> occurred. As a result, the beads entered the slurry flow passage <NUM> and then entered the slurry storage vessel <NUM>. The flow of slurry traveled from the slurry storage vessel <NUM> toward the cylindrical container, and therefore no beads were intermixed in the slurry after the processing. However, a problem occurred in that the pumping component <NUM> became worn. Moreover, when the outer peripheral speed of the stirring rotor <NUM> was <NUM>/sec or more during the processing using water and <NUM>/sec or more during the processing using highly viscous slurry, a large vortex was formed in the slurry storage vessel <NUM>, causing air to enter the mill, and as a result, slurry foaming occurred.

In the mill 2a, the disc <NUM> and the swirling blades <NUM> were disposed as components for swirling the slurry in the upper portion of the mill, and by rotating the slurry near the upper lid <NUM>, the beads were prevented from approaching the slurry flow passage <NUM>. Hence, the pumping component <NUM> did not become worn, and the beads did not flow back to the slurry storage vessel <NUM>. However, the effects of swirling of the slurry were not resolved, and therefore, when the outer peripheral speed of the stirring rotor <NUM> was <NUM>/sec or more during the processing using water, air entered the cylindrical container from the slurry storage vessel <NUM>, causing the slurry in the cylindrical container to foam, and as a result, the slurry flow deteriorated, making the processing impossible. In the mill 2b, on the other hand, both the combination of the swirling blades <NUM> and the disc <NUM> serving as the slurry swirling device and the swirl prevention plates <NUM> and swirl prevention tube <NUM> for preventing rotation were disposed, and therefore breakage of the cylinder and the foaming phenomenon did not occur in any of the processing.

Claim 1:
A bead mill in which a rotary shaft (<NUM>) is disposed in a vertical direction, a slurry storage vessel (<NUM>) is disposed above a container (<NUM>) in which stirring processing is performed on beads and slurry, a slurry passage port (<NUM>) is disposed in a lower portion of the container (<NUM>), and a slurry flow passage (<NUM>) through which the slurry can pass is disposed between an upper lid (<NUM>) of the container (<NUM>) and the slurry storage vessel (<NUM>), and in which the rotary shaft (<NUM>) extending from above the slurry storage vessel (<NUM>) into the container (<NUM>) through a space in the slurry flow passage (<NUM>), and a component that causes the slurry in the slurry flow passage (<NUM>) to flow downward being disposed on the rotary shaft (<NUM>), wherein
a flow promoting component (<NUM>) that swirls the slurry as the rotary shaft rotates is disposed in a higher position than either an uppermost portion of a stirring rotor (<NUM>) that is fixed to the rotary shaft (<NUM>) in an uppermost portion of the cylindrical container (<NUM>) or an upper portion of a centrifugal bead separation device (<NUM>) fixed to the rotary shaft (<NUM>), the bead mill being structured such that the slurry is supplied through the slurry passage port (<NUM>) in the cylindrical container (<NUM>), characterized in that the centrifugal bead separation device (<NUM>) and the component that causes the slurry in the slurry flow passage (<NUM>) to flow downward are disposed on the rotary shaft (<NUM>), a hollow passage through which the slurry that has passed through the centrifugal bead separation device (<NUM>) flows out into the slurry storage vessel (<NUM>) is disposed in the interior of the rotary shaft (<NUM>), and the slurry flows upward through the hollow passage.