Patent Publication Number: US-5289981-A

Title: Continuous dispersing apparatus

Description:
This is a continuation of parent application Ser. No. 705,301 filed May 24, 1991 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a continuous dispersing apparatus for mixing, finely grinding and dispersing a material to be processed. 
     (2) Background Information 
     As an apparatus for mixing, finely grinding and dispersing material to be processed, roll mills have been generally employed. A triple roll mill, which has been conventionally used as a roll mill, has a set of three rolls. The material is placed between a back roll and a middle roll and mixed by rotating both rolls. A front roll is positioned adjacent to the middle roll and the treated material is transferred from the middle roll to the front roll. The treated material is then scraped off and collected at the front roll. 
     According to the roll mill method, the material to be processed is dispersed by subjecting it to compressing-shearing-expanding actions through gaps or nips between the back and middle rolls and between the middle and front rolls. The compressing-shearing-expanding actions by means of the roll mill are conducted only at straight sections between two nips among the three rolls and thus the dispersion efficiency of these actions is low. 
     When the material to be processed is a high viscosity substance, if the gap between the rolls is very small at the beginning of the operation, the start of the rolls is difficult and metal parts may come into contact with each other and cause seizing, and the like. 
     In addition, since a conventional roll mill is of the batch type, it can not be operated continuously. A conventional roll mill is also generally open to the atmosphere allowing for the release of solvent vapor, etc. Further, the material is cooled only from the inside of the roll, and therefore can not be cooled efficiently. 
     Another known apparatus is a wet-type medium dispersing apparatus in which grinding elements such as balls, beads, etc. are stirred with a material to be processed in a vessel and shearing forces are applied to the material to be processed to disperse the material. However, the use of such grinding elements has the drawback that fragments or pieces of the grinding elements are often intermixed with the processed material discharged from the apparatus. Also, the structure of the apparatus is complex, and the processing is often difficult. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a continuous dispersing apparatus which does not use the conventional roll mill and which enables continuous treatment by mixing, grinding and dispersing of the material. 
     Another object of the present invention is to provide a continuous dispersing apparatus which can enhance the dispersing efficiency without using a grinding medium. 
     According to the present invention, the abovementioned objects can be accomplished by a continuous dispersing apparatus which comprises a vessel having an inlet at an upstream end for admitting a material to be processed and an outlet at a downstream end for discharging the processed material. A rotor is rotatably disposed within the vessel and spaced from the inner wall of the vessel to define therebetween a flow path for the material. The surface of the rotor is provided continuously with undulations having alternate crests and troughs which define a repeating pattern of compressing-shearing-expanding sections. Each compressing section is configured in such a manner that the space between the compressing section and the inner wall of the vessel becomes narrower gradually so that the material may be compressed as it flows past the compressing section from the inlet to the outlet through the path between the rotor and the vessel. Each shearing section is located downstream of a compressing section and opposite to the inner wall with a narrow space therebetween so that shearing forces may be applied to the material between the shearing section and the inner wall. Each expanding section is located downstream of a shearing section and configured in such a manner that the space between the expanding section and the inner wall becomes wider gradually so that the compression to the material may be released downstream of the shearing section. 
     Other objects and features of the present invention will become apparent to those skilled in the art upon reading the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view of one embodiment of a continuous dispersing apparatus according to the present invention; 
     FIG. 2 is a vertical sectional view of a part of another embodiment at an outlet section of a vessel of the continuous dispersing apparatus according to the present invention; 
     FIG. 3 is a developed view of a surface of a rotor of the continuous dispersing apparatus according to the present invention; 
     FIG. 4 is a cross-sectional view of another embodiment of the rotor; 
     FIG. 5 is a perspective side view of a further embodiment of the rotor; 
     FIG. 6 is a cross-sectional view showing an embodiment having two rotors; 
     FIG. 7 is a vertical sectional view of another embodiment of a continuous dispersing apparatus according to the present invention, in which a vessel can be moved in an axial direction; 
     FIG. 8 is a vertical sectional view of a part of an end portion of a vessel of another embodiment in which the vessel can be moved; and 
     FIG. 9 is a front view of an end portion of a vessel showing a further embodiment in which the vessel can be moved. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a casing which constitutes a vessel 1 is formed into a cone shape, but may also be formed into a cylindrical shape. The casing has an inlet 2 at one end for admitting a material to be processed and an outlet 3 at the other end for discharging the processed material. At the inlet section, a compressing-feeding means, such as a pump or the like (not shown), is mounted for feeding the material to be processed into the vessel. Around the vessel, a heat-exchange jacket 4 is mounted for circulating a temperature-controlling medium such as cooling water or the like. A rotor 5 is rotatably disposed inside the vessel 1 and is supported by a rotationally driven shaft 7 in such a manner that the rotor 5 may be rotated in close proximity to an inner wall 6 of the vessel 1. It is preferable to apply an axial force to the rotating shaft 7 by use of a force-applying means, such as a spring or the like (not shown), so that the rotor 5 applies a thrust in the direction opposite to the flow direction of the material being processed. The rotor 5 is formed into a substantially cylindrical shape, but may be formed into a polygonal column shape. 
     Between the rotor 5 and the inner wall 6 of the vessel, a flow path is formed for flowing the material to be processed. As shown in FIG. 2, a rotor plate 8 and a stator plate 9 may be provided at the downstream end of the flow path to form a narrow gap for preventing the free outflow of the material being processed and for applying sufficient compression to the material. 
     Also, as shown by chain line in FIG. 1, the rotary shaft 7 may be provided with a flow path at the center portion thereof and a circulating path 10 running through the flow path and the inner wall 6 of the rotor so that a temperature-controlling medium such as cooling water or the like may be passed through the circulating path 10. 
     The peripheral surface of the rotor 5, as shown in FIG. 3, is provided with undulations having alternate crests and troughs. The undulations define a repeating succession of distinct sections, namely, a compressing section 11, a shearing section 12 and an expanding section 13. The compressing sections 11 are formed between the troughs and crests of the undulations and slope gradually toward the vessel inner wall 6 in such a manner that the space between the compressing sections 11 and the inner wall 6 of the vessel 1 becomes narrower gradually so that the material to be processed is gradually compressed as the material to be processed is advanced in the direction of the arrow past the compressing sections. The shearing sections 12 are formed at the crests of the undulations and disposed oppositely to the inner wall 6 with a narrow space therebetween so that shearing forces are applied to the material to be processed between the shearing sections 12 and the inner wall 6. The expanding sections 13 are formed between the crests and troughs of the undulations and slope gradually away from the vessel inner wall 6 in such a manner that the space between the expanding sections 13 and the inner wall 6 becomes wider gradually so that the compression imparted to the material is relieved or released immediately downstream of the shearing sections 12. 
     The undulations defining the compressing section 11, shearing section 12 and expanding section 13 can be variously provided along the direction of transfer of the material to be processed. In the embodiment shown in FIG. 1, the rotor 5 has a compressing section, a shearing section and an expanding section continuously in the axial direction. In this embodiment, the compressing section and expanding section jointly form a hollow or annular groove between each two adjacent shearing sections. 
     The undulations defining the compressing section 11, shearing section 12 and expanding section 13 may be provided continuously in the circumferential direction of the rotor 5, as shown in FIG. 4. In this instance, the compressing section and expanding section form an axial groove in the axial direction of the rotor. These shapes may be formed in the axial direction and circumferential direction in combination to form the compressing section, shearing section and expanding section into a protrusion shape. 
     The undulations defining the compressing section, shearing section and expanding section may be provided helically around the peripheral face of the rotor. In this instance, the twist direction of the helical pattern is preferably formed in such a direction that the material to be processed is returned back to the inlet side when the rotor is rotated. 
     The space between the shearing section 12 and the inner wall 6 of the vessel, which is appropriately determined depending on the size of the material to be processed and conditions of the desired products, is mainly preferably within the range of from 0.5 to 0.02 mm. 
     FIG. 5 shows an embodiment in which a rotor 14 is partitioned into plural processing zones 15 in the axial direction. The compressing section 11, shearing section 12 and expanding section 13 are continuously provided in the circumferential direction of the rotor 14 in each processing zone. The phases of adjacent sets of compressing sections 11, shearing sections 12 and expanding sections 13 at the processing zones 15 are angularly shifted relative to one another along the length of the rotor. According to this embodiment, as the material to be processed is transferred from an upstream processing zone to an adjacent downstream processing zone during processing, the flow of the material meets a resistance and moves mainly in the circumferential direction as a whole, thereby ensuring that the material is sufficiently processed. 
     The rotors constructed as mentioned above may be provided in a plural number within the vessel. For example, as shown in FIG. 6, the apparatus may be constituted in such a manner that rotors 16, 17, like the rotor 5 shown in FIG. 4, are arranged in series within a vessel 18. By such an arrangement, the material to be processed flows back and forth between one rotor 16 and the other rotor 17, and the material is mainly moved in the circumferential direction as a whole resulting in sufficient processing of the material. 
     When the rotors 5, 14, 16 and 17 rotate, the material to be processed, which is fed with pressure into the vessel by use of a compressing-feeding means such as a pump or the like, is gradually compressed at the compressing section 11, then subjected to shearing forces between the shearing section 12 and the inner wall 6 of the vessel whereby the material is ground, then the compression of the material is released at the expanding section 13, then compressed again at the next compressing section 11, and then ground at the next shearing section 12, and so on. The material flows to the outlet 3 after the continuous processing by such actions, during which the material is finely ground to a desired size and uniform dispersion. 
     The surface of the rotor and the inner wall 6 of the vessel are preferably composed of abrasion resistance materials, for example, ultra rigid materials such as ceramic, tungsten carbide or the like. 
     It is preferable to design the apparatus so that the space between the rotor and the inner wall 6 of the vessel may be selectively varied depending on the properties of the materials to be processed. The adjustment of the space can be made by designing the apparatus in such a manner that the vessel and rotor are formed into a cone shape in which the diameters of the vessel and rotor vary from the inlet to the outlet, and either one or both of the vessel and rotor may be moved in the axial direction to adjust the dimensions of the space. 
     The embodiment shown in FIG. 7 shows an apparatus in which a vessel 19 is arranged to be shiftable in the axial direction. The vessel 19 has an inlet 20 at one end for feeding the material to be processed by a compressing-feeding means such as a pump or the like, and an outlet 21 at the other end. The vessel 19 has a jacket 22 for circulating a temperature-controlling medium such as cooling water or the like around the vessel 19, and a rotor 23 inside the vessel. The rotor 23 is rotated by a rotationally driven shaft 24. The inner wall 25 of the vessel 19 and the rotor 23 are formed into a cone shape whose diameter expands from the inlet 20 toward the outlet 21. Alternatively, the vessel and rotor may be formed into a cone shape having a diameter that reduces from the inlet to the outlet. On the rotor 23, a compressing section, a shearing section and an expanding section are continuously arranged as in the afore-described embodiments. 
     An inner end portion of the vessel 19 is slidably fitted to a flange 27 arranged at a stationary portion 26, and an appropriate sealing member 28, is provided at the sliding surface to permit the movement of the vessel 19 in the axial direction under a sealing condition. 
     Any suitable means of moving the vessel may be used. In the moving means shown in FIG. 7, a cylinder device 29, such as a hydraulic cylinder, a pneumatic cylinder or the like, is provided at the stationary portion 26, and a piston rod 30 of the cylinder device 29 is connected to the vessel 19. The vessel is moved in the axial direction by the extension and retraction of the piston rod by the operation of the cylinder device 29. 
     The moving means shown in FIG. 8 uses a thread device. In this embodiment, a male thread 32 is arranged at a flange 31 formed on the stationary portion 26, and a female thread 35 is arranged on a flange 34 formed on a vessel 33. The flange 34 has gear teeth about its periphery for engagement with a rotationally driven gear (not shown). The vessel can be moved in the axial direction by rotationally driving the flange 34 to effect corresponding rotation of the vessel 33. 
     FIG. 9 shows an embodiment using another thread device. In this embodiment, a vessel 36 is supported by a supporting member 37 and positioned transversely. A flange 38 is connected to the vessel 36 and carries a nut 39. A feed screw 40 is threadedly engaged with the nut 39. By rotating the feed screw 40 by an actuator 41 including a motor, a speed reducer or the like, the vessel 36 is moved in the axial direction. Here, if the vessel 36 is positioned in a vertical direction, the supporting member 37 is not necessary. 
     Alternatively, in the FIG. 7 embodiment, the rotor 23 can be moved by providing an appropriate moving means for moving the rotor in the axial direction at one end of the rotor 24. 
     According to the above construction, the rotor and the vessel are initially moved axially to separate from each other to enlarge the distance between the compressing, shearing and expanding sections and the inner wall of the vessel so that the start of the operation can be made easily even if the material to be processed has a high viscosity. Once the rotor starts to rotate, the vessel and rotor may be moved closer together to adjust the distance to a suitable value to effect processing of the material. 
     In the embodiments mentioned above, the vessels and rotors are arranged transversely. It is understood that the vessels and rotors may also be arranged in the vertical direction or an oblique direction. 
     In accordance with the present invention, the material to be processed is ground every time it passes through one of the shearing sections, and the material is processed continuously by this action during its travel from the inlet to the outlet. Accordingly, the dispersing efficiency of the material is extremely high. Further, since the processing can be carried out continuously in a sealed system, problems resulting from escape of solvent vapor or the like can be eliminated. Even if the material to be processed has a high viscosity, the problem in starting can be solved by adjusting the space at the shearing sections. Also the surface of the rotor and the inner wall of the vessel are not brought into contact with each other so as to prevent seizing.