Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By extrusion spraying or gravity fall through orifice
Reexamination Certificate
2001-02-22
2003-06-10
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By extrusion spraying or gravity fall through orifice
C264S005000, C264S011000, C264S012000, C425S006000, C366S176100
Reexamination Certificate
active
06576023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing emulsions for use in food, drugs, cosmetics or the like, emulsions for DDSs (Drug Delivery Systems), and microspheres (fine particles) which are solid fine particles or liquid fine particles used as a microcapsule, an ion exchange resin, a chromatography carrier or the like.
2. Description of the Relevant Art
Techniques in which a biphasic system, for which a separated state is thermodynamically stable, is formed, such as that composed of a water phase and an organic phase which are emulsified to obtain a semi-stable emulsion, are conventionally known.
As general emulsification methods, there have been described in “Science of Emulsions” (Asakura-shoten, 1971), the methods of using a mixer, a colloid mill, a homogenizer, etc., and the method of dispersion with sound waves, which are all well known.
The general methods mentioned above have a disadvantage in that the diameters of dispersed phase particles in a continuous phase are distributed over a wide range.
Therefore, a method of using filtration by means of a membrane comprising polycarbonate (Biochemica et Biophysica Acta, 557 (1979), North Holland Biochemical Press); a method using repeated filtrations through a PTFE (polytetrafluoroethylene) membrane (Proceedings of the 26th Autumn Meeting of the Society of Chemical Engineers, Japan, 1993); and a method of manufacturing homogenous emulsions by transferring a dispersed phase into a continuous phase through a porous glass membrane having uniform pores (Japanese Patent Application Laid-Open No. 2-95433) have been proposed. In addition, as a method of manufacturing emulsions using a nozzle or a porous plate, a laminar-flow dripping method (KAGAKU KOOGAKU Vol. 21, No. 4, 1957) is also known.
The method using filtration through a membrane comprising polycarbonate and the method using repeated filtrations through a PTFE membrane theoretically cannot manufacture emulsions comprising particles larger than the membrane pores and cannot separate particles smaller than the membrane pores. These methods are therefore especially unsuitable for producing emulsions comprising large particles.
In the method using a porous glass membrane having uniform pores, when the average diameter of the membrane pores is small, particle diameters are distributed in a narrow range and thus homogenous emulsions can be obtained. When the average diameter of the membrane pores is increased, however, particle diameters become distributed over a wide range so that homogenous emulsions cannot be obtained.
In addition, in the laminar-flow dripping method, particle sizes become 1,000 &mgr;m or more and are distributed over a wide range so that homogenous emulsions cannot be obtained.
Therefore, the inventors of the present invention formerly proposed an apparatus which can continuously produce homogenous emulsions in International Publication No. WO97/30783. The structure of this apparatus is shown in
FIGS. 8 and 9
.
FIG. 8
is a vertical sectional view of this apparatus.
FIG. 9
shows a perspective exploded view wherein a base and a plate are shown taken apart. In this apparatus for producing emulsions, a supply port
102
for a continuous phase, a supply port
103
for a dispersed phase, and a withdrawal port
104
for emulsions are formed in a body
101
supported by a case
100
. A bulkhead member
106
provided between the body
101
and a base
105
separates the supply port
103
for a dispersed phase from the withdrawal port
104
for emulsions. In addition, an opening
107
for a dispersed phase is formed in the center part of the base
105
and a gap is formed between the base
105
and a plate
108
placed opposite the base
105
. The dispersed phase and the continuous phase are separated in a boundary section
109
formed in the base
105
and the dispersed phase and the continuous phase are mixed in a microchannels
110
formed in the boundary section
109
.
The dispersed phase supplied to the inside of the bulkhead member
106
through the supply port
103
enters a gap between the plate
108
and the base
105
through the opening
107
. The dispersed phase then enters the continuous phase through the microchannel
110
, and thereby emulsions are formed.
As an art related to producing microspheres (fine particles) other than in emulsions, there is known a spray drying method. Spray drying method may be of three types, i.e., a centrifugal nozzle method, a pressure nozzle method and a two-fluid nozzle method. However, in each method, a turbulent flow is formed by rotating a nozzle at high speed or making a liquid flow at high speed, and the liquid is caused to form microspheres (fine particles) through a shear stress caused by the turbulent flow.
As an apparatus for manufacturing microspheres, there is also known a granulation apparatus. Granulation apparatuses of many types are known, for example: a pumping type, a centrifugal flow type, a fluidized bed type, an air current type, a stirring type or the like. However, in methods employing each of these types of granulation apparatus, microspheres (liquid drops) are formed through a shear stress caused by a turbulent flow.
In the conventional apparatus for producing emulsions, the spray dryer or the various granulation apparatuses as mentioned above, a penetrating hole of a porous membrane or a nozzle from which microspheres are pumped has a circular shape or a nearly circular shape with respect to the opening shape.
In the case where the opening shape of the portion from which the dispersed phase is pumped into the continuous phase is circular or nearly circular, since the force of a vertical direction uniformly acts on the boundary surface of the dispersed phase which is pumped from the opening, the dispersed phase is difficult to separate from the opening. Therefore, in the conventional arts, as mentioned above, a turbulent flow is formed, the dispersed phase is forced to separate from the opening through a shear stress caused by the turbulent flow, and thereby fine particles are produced.
However, in the case where microspheres (fine particles) are formed through a shear stress caused by the turbulent flow, since the dispersed phase is difficult to separate from the opening as liquid drops as mentioned above, the problem arises wherein the particle diameters of the manufactured microspheres are not uniform.
In the known apparatus in relation to, as well as particle diameter, there is another problem that relates to production efficiency. For example, in the apparatus for producing emulsions shown in
FIGS. 8 and 9
, it is necessary to linearly form the microchannels on the periphery of the opening which is provided in the center part of the base. The number of microchannels per a base is at most 5000 in a case of small microchannels. The number is further decreased as the size of the microchannels is increased. Therefore, it is not easy to disperse homogenous particles of the dispersed phase into the continuous phase at high efficiency and as a result there is room for improvement with respect to the production cost.
SUMMARY OF THE INVENTION
To solve the above-mentioned problems, according to the present invention, there is provided a method for manufacturing microspheres comprising the steps of separating a dispersed phase and a continuous phase by a bulkhead in which a penetrating hole is formed, applying higher pressure to the dispersed phase than the continuous phase, and thereby pumping the dispersed phase into the continuous phase, wherein a non-uniform shear stress is made to act toward the boundary surface of the dispersed phase which is pumped into the continuous phase through the penetrating hole, so that microspheres are formed.
When the non-uniform shear stress acts toward the boundary surface of the dispersed phase which is pumped into the continuous phase through the penetrating hole, the dispersed phase is easy to separate and form into microspheres, so that microspheres having a uniform particle
Fujita Hiroyuki
Kikuchi Yuji
Kobayashi Isao
Nakajima Mitsutoshi
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Japan as represented by Director of National Food Research Insti
Theisen Mary Lynn
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