EP0464654A2

EP0464654A2 - Dispersion apparatus

Info

Publication number: EP0464654A2
Application number: EP91110604A
Authority: EP
Inventors: Susumu Kajiura
Original assignee: ASADA IRON WORKS Co Ltd; Dai Nippon Toryo KK
Current assignee: ASADA IRON WORKS Co Ltd; Dai Nippon Toryo KK
Priority date: 1990-07-03
Filing date: 1991-06-26
Publication date: 1992-01-08
Anticipated expiration: 2011-06-26
Also published as: DE69106951D1; EP0464654B1; DE69106951T2; JPH0686924A; EP0464654A3; JPH0673620B2

Abstract

A dispersion apparatus comprising a container which receives therein a suspension liquid including paint, a rotating shaft (16) extending vertically into the inside of the container (1), a vessel (2) provided at a position in the container and a rotor (5) placed just below the vessel, in a rotatable manner, so as to form a chamber (8) in association with the vessel (2), wherein a gap (9) which permits a mill base (A) to pass therethrough, but doesn't permit the mixing medium (B) to pass, is formed between the lower end surface of the vessel (2) and the upper end surface of the rotor (5), and an opening (10) is formed in the ceiling portion of the vessel.

Description

The present invention relates to a dispersion apparatus for dispersing a suspension liquid containing fine solid particles such as paint, ink, ceramics or the like in a coloidal form.
A medium type dispersion machine has been generally used to prepare paint, ink, ceramics or the like. The medium type dispersion machine is such one capable of dispersing a suspension liquid containing solid particles such as pigment, i.e. a mill base by using a medium such as sand, hard glass beads, ceramic beads, or steel balls. As such type of dispersion machine, a sand mill, a ball mill or an atriter is well known.
The sand mill is of a type that sand, hard glass beads or ceramic beads are mainly used as a medium and is constructed in such a manner that a mill base which has been subjected to premixing (which means previously stirring and mixing before a regular dispersion process) is forcibly supplied to a container (which is referred to as a mill) with use of a pump, and aggregations in the mill base are dispersed by utilizing colliding forces of materials constituting the medium which are forcibly moved by stirring blades provided in the container. While the dispersion machine is advantageous by used because of its having a large dispersing function, the fine solid particles and liquid have to be previously mixed with each other by agitation (premixing) to prepare the mill base in which the materials are uniformly mixed. The reason why the premixing is required is because the sand mill is a so-called continuous treatment type dispersion machine wherein the mill base is forcibly supplied to the container with a pump while the mill base having been subjected to a treatment is taken out from the container. Use of this system disadvantageously requires much labor for washing because it is necessary to connect a stirring/mixing (premixing) device in which fine solid particles are previously mixed with liquid, to the container of the sand mill with a pipe wherein a pump is disposed in the pipe.
The ball mill or the atriter is a so-called batch treatment type dispersion machine wherein steel balls are mainly used as a medium, and each predetermined amount of fine solid particles and liquid is put in a mill or a container called a tank so that the stirring and mixing of the materials are conducted in the container on every occasion. The batch treatment type dispersion machine unnecessitates the premixing of the mill base unlike the sand mill which is the continuous treatment type dispersion machine. However, in this dispersion machine, the container itself constitutes a grinding section in which a large amount of a medium is filled. Accordingly, not only the surface areas of the inner wall of the container and the outer circumferential potion of the medium must be large, but also the liquid naturally remains in the gaps between the materials as the medium, whereby it is difficult to completely wash the inner wall of the container and the medium. For instance, there is difficulty in the preparation of a white paint after the preparation of a black paint by using the same dispersion machine. Further, noises caused by this dispersion machine in operation are large, and the temperature of the container rises remarkably.
To improve the disadvantages of the conventional dispersion apparatus, there have been proposed dispersion machines called a basket mill wherein a basket-like body is used (such dispersion machines are disclosed in, for instance, Japanese Examined Patent Publication No. 16687/1987 and Japanese Unexamined Patent Publication No. 210020/1989). These dispersion machines are so constructed that a basket-like body receiving therein a medium is immersed in a mill base; the medium in the basket-like body is forcibly moved by stirring blades disposed in the basket-like body; convection blades located at just below the basket-like body are operated to forcibly move by convection the mill base in the container into the basket-like body, whereby the mill base in the container is caused to enter into the basket-like body from its upper portion while the mill base is discharged outside through net portions formed in the side wall portion and the bottom portion of the basket-like body; thus the mill base is dispersed. In the basket mill, the grinding chamber is formed in the basket-like body, so that the size of it is remarkably smaller than that of the ball mill or the atriter. Further, since the liquid can be scattered due to a centrifugal force solely by the idle revolution of the basket-like body, washing operation can be relatively simple. In addition, noises in operation of the basket mill and the temperature rise of the container can be reduced. However, it has a disadvantage that fine solid particles and liquid have to be previously mixed and stirred (premixed) in the same manner as the sand mill. If the basket mill is operated under the condition that the premixing is insufficient, a non-dispersed portion of the mill base deposits on the outer surface and the net portions of the basket-like body to cause the clogging of the net portions. Such phenomenon prevents the mill base from dispersing and causes a part of the medium flying out the basket-like body. The basket-like body is unsuitable for dispersing the mill base in the preparation of an abrasion resistance material or ceramics because the basket-like body is easily worn.
It is an object of the present invention to eliminate the above-mentioned disadvantages and to provide a dispersion apparatus in which the advantage of a basket mill is optimally utilized.
In accordance with the present invention, there is provided a dispersion apparatus comprising a container for receiving therein a suspension liquid including fine solid particles, a rotating shaft extending vertically into the inside of said container, and a mixing means including a mixing medium, provided at the lower portion of the rotating shaft, said dispersion apparatus being characterized in that said mixing means comprises a vessel provided at a position in said container and a rotor placed just below said vessel, in a rotatable manner, so as to form a chamber in association with the vessel, wherein a gap which permits a mill base to pass therethrough, but doesn't permit the mixing medium to pass, is formed between the lower end surface of the vessel and the upper end surface of the rotor, and an opening is formed in the ceiling portion of the vessel.
In accordance with the present invention, it is desirable that the inner surface of the ceiling portion of the vessel is lowered toward the center line of the vessel.
It is further preferable that stirring blades are disposed in the chamber which is formed by the vessel and the rotor. Further, at least one blade is preferably attached to either the rotor or the vessel at a position near the outlet of the gap.
In drawings;

Figure 1 is a cross-sectional view of the dispersion apparatus, which is for explaining the principle of the present invention;
Figure 2 is a front view of an embodiment of the dispersion apparatus having the construction as shown in Figure 1;
Figures 3 through 7 are respectively cross-sectional views of an important portion of each of other embodiments of the dispersion apparatus of the present invention;
Figure 8 is a cross-sectional view taken along a line VIII-VIII in Figure 7; and
Figures 9 and 10 are respectively perspective views showing modified embodiments of the rotor used for the dispersion apparatus of the present invention.

Preferred embodiments of the dispersion apparatus of the present invention will be described with reference to the drawings.
In a preferred embodiment of the dispersion apparatus of the present invention, a container 1 receives therein a vessel 2 and a rotor 5 rotatably placed just below and close to the vessel so that a chamber 8 is formed in association with the vessel and the rotor. A gap 9 which permits a mill base to pass therethrough but doesn't permit a medium for dispersion to pass is formed between the lower end surface of the vessel and the upper end surface of the rotor. Further, an opening 10 is formed in the ceiling portion of the vessel.
As shown in Figures 1 and 2, the container 1 is in an upright cylindrical shape and it may have a cover 11 at its top. The container 1 may be provided with at least one jacket 12 at its outer circumferential wall, whereby it is possible to heat or cool the inside of the container 1 during operations. It is further desirable that a discharge valve 13 is attached to the bottom portion of the container 1.
The vessel positioned in the container 1 is detachably attached to supporting bars 15 which depend downward from a transmission casing 14 so that the vertical and rotational movements of the vessel are prevented.
The rotor just below the vessel is rotatably positioned. In order to provide the rotor to be rotatable, it is preferable to attach the rotor to the free end (the lower end) of a rotating shaft (stirring shaft) 16 which is rotatably supported by the transmission casing 14 and is extended into the container 1 through the entire portion of the vessel from its opening 10. Another means to make the rotor rotatable may be employed. However, the above-mentioned means is advantageous in that the vessel can vertically be moved or can be swung along with the rotor when the transmission casing 14 is vertically moved or the head portion of the casing 14 is swung.
The rotating shaft 16 can be rotated by a driving means 17 such as a variable speed motor attached to the transmission casing 14; hence, the rotor can be rotated just below the vessel in the container 1 through the revolution of the rotating shaft 16. The transmission casing 14 is vertically movable with respect to a base table 18, and it is capable of swinging around a cylinder shaft 18a by means of hydraulic cylinders.
The container 1 of the dispersion apparatus as shown in Figures 1 and 2 is adapted to receive a suspension liquid including fine solid particles such as paint, ink, ceramics, which is referred to as a mill base A. Further, a medium B for dispersion consisting of a large number of particles is received in the chamber 8 which is formed of the vessel and the rotor. The amount of the mill base A is such an amount that the vessel is completely immersed in the mill base A. Further, it is desirable that the size of the particles which constitute the medium B is in a range of about 0.5 mm in diameter-3.0 mm in diameter, and the amount of the medium B to be put in the chamber 8 is in a range of about 60%-85% of the apparent cubic volume of the chamber. As the medium B, hard glass beads, steel balls or the like is preferably used.
When the rotating shaft 16 is rotated in the direction as indicated by an arrow mark, the rotor attached to the free end (the lower end) of the rotating shaft is also rotated. Then, the mill base A is moved by convection in the container 1 as shown by an arrow mark in Figure 1, and a part of the mill base A is caused to flow in the vessel through the opening 10 formed in the ceiling portion of the vessel. Since the medium B is moved in the vessel due to the force of rotation of the rotor, the mill base in the chamber is passed through the spaces formed by the large number of particles, as the medium B, and is discharged outside the chamber through the gap 9. By repeating the above-mentioned movement, the mill base which may be insufficiently dispersed, in the vessel is uniformly stirred, mixed and dispersed due to the collision of the large number of particles which constitute the medium B, a relative movement between the rotor and the medium, a relative movement between the vessel and the medium, dispersion at the gap 9 formed between the vessel and the rotor and the stirring function at the inner surface of the rotor. Accordingly, even though relatively large solid particles are contained in the mill base A, they are crushed and dispersed due to the rotation of the rotor until they pass through the gap 9, and there is no danger of clogging at the gap 9. It is preferable that the rotor is rotated at a circumferential speed of about 6 m/sec-15 m/sec.
The above-mentioned embodiment is for such case that the mill base is stirred, mixed and dispersed in the container 1 by the rotation of the rotor while the vessel is stopped. However, a shaft for driving the vessel may be separately arranged to rotate the vessel in the direction opposite the rotor.
Regarding to putting the mill base A in the container 1, solid particles and liquid which are raw materials for the mill base A may be directly put into the container 1 because the dispersion apparatus of the present invention is of a batch-treatment type dispersion machine (wherein the solid particles and the liquid are put together in the container on every occasion and they are stirred and mixed on that occasion) in the same manner as the ball mill or the atriter, and it is unnecessary to previousely mix the solid particles and the liquid. Further, the dispersion apparatus of the present invention need not to take care of wearing of the vessel and the rotor unlike the conventionally used basket mill using a basket-like body. Accordingly, there is no trouble of treating the mill base containing a wear resistance material or ceramics.
The length t of the gap 9 formed between the lower end surface of the vessel and the upper end surface of the rotor is preferably determined to be about 1/2 times-1/3 times as large as the particle diameter of the solid particles as the medium B. When the length t of the gap exceeds this value, the medium B easily bite in the gap 9 resulting in the breakage of the vessel or the rotor. On the other hand, when the length t is less than that value, the discharge rate of the mill base becomes excessively small so that the function of the dispersion of the mill base decreases.
The size of the opening 10 formed in the ceiling portion of the vessel is preferably about 6 times-20 times as large as the particle diameter of the medium B plus the diameter of the rotating shaft 16 extending downwardly through the opening 10. Further, it is preferable to form a gap having a size of at least about three pieces of the medium particles between the outer circumference of the rotating shaft 16 and the inner circumference of the opening 10. Thus, the size of the opening 10 is determined as mentioned above in order to satisfy the demands that the mill base A must be effectively introduced in the vessel; the function of dispersing the mill base must not be reduced, and the biting of the medium B in the gap formed between the outer circumference of the rotating shaft 16 and the inner circumference of the opening 10 must be minimized.
The shape of the chamber 8 formed of the vessel and the rotor is not particularly limited, and it may have a substantially circular shape in vertical cross-section as shown in Figures 1 and 7; it may have a shape wherein the inner diameter of the vessel is equal to that of the rotor as shown in Figure 3; or it may have a substantially inversed triangular shape with its top cut in cross section wherein the inner diameter at the lower part is smaller than that of the upper part as shown in Figures 4 through 6.
It is preferable that the inner surface of the ceiling portion of the vessel is so formed as to be lowered toward the center line of the chamber 8 as indicated by numeral 21 in Figures 1 and 7; as indicated by numeral 31 in Figure 3, and as indicated by numeral 41 in Figures 4 through 6, because the provision of the downwardly inclined inner surface of the ceiling portion of the vessel causes the movement of the large number of solid particles in the vessel in such a manner that they are guided by a surface portion 21, 31 or 41 which declines downwardly to thereby move them downwardly along the rotating shaft 16; they move outwardly in the rotor due to the centrifugal force of the rotating rotor; they move upwardly along the inner surface of the side wall portion of the vessel; and they reach again the inclined surface portion 21, 31 or 41 in the ceiling portion of the vessel.
Figures 3 through 6 respectively shows an important portion of each of other embodiments of the dispersion apparatus of the present invention. In Figure 3-6, the same reference numerals designate the same parts as in Figures 1 and 2. Stirring blades for stirring the medium are attached to the rotating shaft extending in the chamber 8 formed of a vessel 3 and a rotor 6, or a vessel 4 and a rotor 7.
The stirring blade assembly indicated by numeral 32 in Figure 3 or by numeral 42 in Figure 4 is of a cross-bar type wherein two sets of four bars are attached, in a vertical relation and in equal angular positions, to the rotating shaft 16 extending in the chamber 8 which is formed of a vessel 3 and a rotor 6, or which is formed of a vessel 4 and a rotor 7.
The stirring blade assembly indicated by numeral 43 in Figure 5 or numeral 44 in Figure 6 is of a circular plate type, or of a type of an inversed cone with its top cut. The stirring blade assembly shown in Figure 7 is provided with four stirring blades 22 on the upper surface of the rotor so as to perpendicularly cross to each other. Figure 8 is a plane view of the embodiment shown in Figure 7. Each of the stirring blades 22 may be formed by raising a part of the upper surface of the rotor 5 by a certain height. Thus, by arranging the stirring blades in the chamber in each of the embodiments, the medium B consisting of a large number of solid particles in the chamber 8 is forcibly stirred by the stirring blades rotated in accordance with the rotation of the rotor 5 or the rotating shaft 16.
Referring to Figures 4 through 6, the rotor 7 is provided with blades 71 at or near the outlet of the gap 9 which is formed between the lower end surface of the vessel 4 and the upper end surface of the rotor 7.
The blades may be formed on the side of the vessel 4. With such arrangement of the blades 71 at or near the outlet, the mill base is easily discharged through the gap 9 which is formed between the vessel and the rotor 7 positioned just below the vessel when the rotor 7 is driven. Further, the mill base is easily introduced into the vessel 4 through the opening 10. Thus, the stirring and mixing function, i.e. the dispersing function to the mill base is remarkably increased.
In the present invention a gap or gaps may be formed in the side wall of the rotor so as to allow the mill base to pass therethough, but to prevent the medium from passing, whereby the amount of discharge of the mill base from the chamber can be increased. Figures 9 and 10 show examples of the above-mentioned structure. In Figure 9, the rotor is formed by stacking a plurality of ring-like bodies with a gap between two adjacent ring-like bodies. In Figure 10, the rotor is provided with a rolled screen with a large number of apertures, made of a wear resistant material. In the present invention, stirring blades may be provided at the lower portion of the rotor so that the mill base can easily be introduced into the chamber 8 through the opening 10.
After the stirring, mixing and dispersing operations in the container have been finished, the transmission casing 14 is raised until the rotor separates from the liquid level in the container 1 and the rotor is caused to rotate. Then, the mill base in the chamber 8 is discharged outside 8 due to the centrifugal force and is recovered in the container 1.
In each of the embodiments of the dispersion apparatus of the present invention, the liquid remaining in the container 1 can be discharged by simply opening the discharge valve 13 which is disposed at the bottom part of the container and the discharged liquid can easily be recovered.
In a case that there is no discharge valve 13 at the bottom part of the container 1, the casing 14 is raised with respect to the base table 18; the vessel and the rotor are brought to the outside of the container 1, and the container is inclined, whereby the liquid in the container can be recovered, after the completion of the dispersing operation.
In a case that complete washing of the vessel, the rotor, the rotating shaft 16 and the medium in the chamber is required, the vessel, the rotor and the rotating shaft 16 and so on are dipped in a washing liquid, which may be put in the container 1 or may be put in a separate container, and the same operation as the dispersing operations are conducted. In the case that the washing liquid is put in the container 1 used for the dispersion, the washing of the container 1 can be effected at the same time of the washing of the vessel and the rotor.
In accordance with the present invention, dispersing operations can be carried out by putting directly fine solid particles and liquid into the container 1 without subjecting them to a premixing treatment wherein the fine solid particles and the liquid are previously stirred for mixing. Accordingly, the dispersing operation is very effective.
Further, the degree of the wearing of the vessel and the rotor is less than that of the conventional basket mill using a basket-like body, so that the dispersion apparatus of the present invention minimizes the trouble of wearing in the preparation of a wear resistance material or ceramics. In addition, the dispersion apparatus of the present invention suppresses problems of noise and temperature rise in the container during operations.
In accordance with preferred embodiments of the present invention, the medium B is circulated in the chamber 8 so that the mill base can sufficiently be dispersed. Further, the degree of dispersion of the mill base can be further improved. Further, the function of dispersing the mill base can be remarkably improved.

Claims

A dispersion apparatus comprising a container (1) for receiving therein a suspension liquid including fine solid particles, a rotating shaft (16) extending vertically into the inside of said container, and a mixing means including a mixing medium, provided at the lower portion of the rotating shaft, characterized in that the mixing means comprises a vessel (2,3,4) provided at a position in said container and a rotor (5,6,7) placed just below said vessel, in a rotatable manner, so as to form a chamber (8) in association with the vessel, wherein a gap (9) which permits a mill base (A) to pass therethrough, but doesn't permit the mixing medium (B) to pass, is formed between the lower end surface of the vessel (2,3,4) and the upper end surface of the rotor (5,6,7), and an opening (10) is formed in the ceiling portion of the vessel (2).
The dispersion apparatus according to Claim 1, wherein the inner surface (21,31,41) of the ceiling portion of the vessel (2,3,4) is lowered toward the center line of the vessel.
The dispersion apparatus according the Claim 1, wherein stirring blades (22,32,42) are disposed in the chamber (8) formed by the combination of the vessel (2,3,4) and the rotor (5,6,7).
The dispersion apparatus according to Claim 1, wherein at least one blade (71) is attached either to the rotor (7) or to the vessel at a position near the outlet of the gap (9).