US3389194A - Method for mass producing small spherical particles - Google Patents

Description

June 18, 1968 R. SOMERVILLE METHOD FOR MASS PRODUCING SMALLSPHSRICAL PARTICLES 2 Sheets-Sheet 1 Filed June 20, 1966 INVENTOR.

a v I N Afro/war Geo/ye Ja/zwrw/fie June 18, 1968 R. SOMERVILLE 3,38

METHOD FOR MASS PRODUCING SMALL SPHERICAL PARTICLES Filed June 20, 1966 2 Sheets-Sheet Z Geo/ye A. Jamerw/le mvrsm'oa ATTORNEY United States Patent 3,389,194 METHQD FOR MASS PRODUCING MALL EPHERECAL PARTICLES George R. Somerville, San Antonio, Tex., assignor to Southwest Research Institute, San Antonio, Tex. Filed June 20, 1966, Ser. No. 558,796 5 Claims. (Cl. 264---4) ABSTRACT OF THE DISCLOSURE A method for mass producing capsules wherein there are a pair of concentric tubes opening into a conduit and filler and film material are fed into the inner and outer tubes, respectively, so as to extrude concentric rods of such materials from the ends of the tubes. A stream of carrier fluid is forced through the conduit and about the tube ends at a speed greater than the rate of extrusion so as to cause said rods to elongate and break off into individual se ments which form into fluid capsules of filler material within the film material. In a preferred practice, the temperature of the carrier fluid is reduced below the melting point of the film material to harden it while the capsules are suspended in the stream.

This invention relates generally to a method for manufacturing small spherical particles, and has s ecial utility in the manufacture of such particles in the form of capsules in which a filler material is contained within a seamless film material. More particularly, this invention relates to im roved techniques for producing such particles, and especially such capsules, on a mass production basis.

In accordance with one prior technique, capsules of the type described are mass produced by means of centritugal action. Thus, as shown and described in my prior Patent No. 3,015,128, a liquid film material is supplied to the interior of a rotating drum so as to extend across the inner ends of a bank of orifices disposed about and extending through the outer wall of the drum. Globules of the tiller material are then delivered to the film material across the orifices, and the speed of rotation of the drum is such that the resulting centrifugal force overcomes the adhesive forces of the film material at the orifices so that it forms a shell about each filler materia globule and is severed and flung outwardly from the orifices, As each capsule is so severed, additional film material forms across the orifice to receive an additional filler material globule, and all the fluid capsules are hardened in a suitable manner, such as within a bath of liquid hardening medium located to receive the capsules as they are flung from the orifices of the encapsulating drum.

Although this represents a substantial advance in the encapsulating art, it nevertheless has certain shortcoming when the filler material and film material have appreciably different densities-Thus, in this event, the centrifuging effect has a tendency to displace the globule of filler material off-center with respect to the shell of liquid film material. This eccentricity may be aggravated when the fluid capsules are flung into a liquid hardening medium, because of the impact of the capsule with the medium or collision with another capsule.

In accordance with another prior technique, the filler and film materials are extruded in the form of concentric fluid rods, which are caused to break off into individual fluid capsules by gravity or by vibration. Although this method is not as sensitive to density difierences between the filler and fiirn materials as the centrifugal method, it is nevertheless a much slower process and thus not capable of as high a rate of production. Furthermore, when the fluid capsules are hardened in a liquid hardening medium, there is the additional problem, above mentioned,

Patented .lune 18, 1968 of shifting the filler material off-center due to impact of the capsules with the medium as well as collision With one another. These latter problems increase as the extrusion rate is increased, because of the more severe impact of the fluid capsules with the fluid hardening medium.

A still further ditficulty encountered with the use of a liquid hardening medium, in these or other methods of forming spherical particles in which successive particles are directed toward the same point in the hardening medium, is their tendency to agglomerate.

There is often a need, in different types of known encapsulating methods, for accurately controlling the temperature of the fluid capsule when the film material is a hot melt. Shells of the film material are frequently of low strength when in the fluid state, and the rate at which they are cooled is critical. solidification at too rapid a rate may result in deformed capsules, whereas solidification at too low a rate may result in excessive capsule breakage.

An object of this invention is to provide a method for mass producing spherical particles, whether in solid or capsule form, which obviates one or more of the foregoing difliculties, while at the same time enabling a very high rate of production.

Another object is to provide a method for mass producing capsules having outer shells of substantially uniform thickness, even though the filler and film materials have substantially ditferent densities.

A more particular object is to provide such a method in which the fluid capsules may be hardened in such a manner as to avoid distortion.

A further object is to provide a method for mass producing small spherical particles, whether in solid or capsule form, in such a manner as to reduce the likelihood of their agglomerating in a liquid hardening medium, but without sacrificing the rates at which they may be produ-ced.

A still further object is to provide an encapsulating method in which the temperature of the shell of a hot melt may be conveniently controlled in a manner to prevent damage thereto.

These and other objects are accomplished, in accordance with the illustrative embodiments of this invention, by a method in which a rod of fluid material is extruded into a stream of carrier fluid which is chemically nonreactive and physically immiscible with such rod material and which is flowing at a speed greater than the rate of extrusion of the rod. More particularly, the speed of the carrier fluid is selected to cause the rod to elongate and break up into segments which form into individual spherical particles, which may then be hardened in a manner to be described. This stream of carrier fluid is also influential in separating the particles to minimize the possibility of collision prior to hardening. Still further, the size of the particles is inversely proportional to the speed of the carrier fluid, so that the latter may be regulated to form particles of different sizes.

In the mass production of particles in the form of capsules in which a filler material is encased within a seamless shell of film material, concentrically arranged fluid rods of the filler and film material are extruded into the stream of carrier fluid. As the film material breaks ofl from the rod, it quickly forms about the filler material which is broken ofl with it to form a fluid capsule, which is then conveyed by the stream of carrier fluid to a hardening area. Since this involves neither a centrifuging action nor any other action tending to move the filler material cit-center, the resulting capsule will have a shell of uniform thickness.

In one embodiment of the invention, the shell of film material comprises a hot melt which is hardened while suspended in the stream of carrier fluid. Thus, the carrier fluid is maintained at a temperature above the melting point of the film material as it flows past the extruded rod and then reduced below such point to harden the fluid capsules. As a result, the capsules are hardened before colliding with one another upon separation from the carrier fluid and collection. Also, of course, the heating of the carrier fluid permits the maintenance of a desired temperature gradient for the capsules.

In another embodiment, the shell is instead a material which is hardened by chemical reaction or by solvent extraction. In this case, the fluid capsules are introduced with the carrier fluid into a suitable liquid hardening medium. However, the carrier fluid in which the capsules are suspended will distribute them to random locations within the medium. Also, the stream of carrier fluid will agitate the medium to a certain extent, so as to further reduce the likelihood of the capsules colliding with one another before hardening in the medium. Still further, the carrier fluid is a liquid, such as water, collected in a vessel above the hardening medium contained therein, so that the fluid capsules settle gradually to random locations of the medium, thereby essentially eliminating impact.

The stream of carrier fluid is confined within a conduit connecting at its downstream end with the vessel for collecting the carrier fluid and separating the hardened capsules therefrom. The upstream end of the conduit is connected with a suitable means for pumping the carrier fluid therethrough at the desired speed. Preferably, the carrier fluid is recirculated from the vessel to the upstream end of the conduit by means of an auxiliary conduit connecting the vessel with the pumping means.

The concentric rods of fluid filler and film material are extruded from the ends of concentric tubes Which extend into the conduit. Preferably, these tube ends are arranged concentrically within the conduit and face toward its downstream end.

In the drawings where there is shown, by way of illustration, one embodiment of the invention:

FIG. 1 is a diagrammatic view of apparatus const-ructed in accordance with the first-mentioned embodiment of this invention; and

FIG. 2 is a diagrammatic view of apparatus constructed in accordance with the second-mentioned embodiment of the invention.

With reference now to the details of the above-described drawings, the first-mentioned embodiment of the apparatus shown in FIG. 1 comprises a conduit having anupstream section 10a of enlarged circular cross-section and a downstream section 1% of reduced circular crosssection and connected to the upstream section by means of a conical restriction 100 Inner and outer concentric tubes 11 and 12 extend concentrically within enlargedconduit section 10a for extruding fluid rods of filler and film material into the conduit. As shown in FIG. 1, the open ends of the tubes 11 and 12 terminate substantially adjacent the conduit restriction 100, while the opposite ends of the tubes extend through the closedend 13 ofconduit section 10a for connection withreservoirs 14 and 15. Thus, film material may be contained withinreservoir 14 for supplying it to the outer tube 12, and filler material may be contained within areservoir 15 for supplying it to the inner tube 11. These materials are kept in a fluid state as they are forced from the reservoirs, throughpipes 16 and 17 and into the tubes by means ofmetering pumps 18 and 18a, respectively.

Carrier fluid is forced into the upstream end of enlargedconduit section 10a so as to flow concentrically about the outer tube 12, and past the ends of the tubes, through the restriction 10, and into the reduced section 10b of the conduit. Obviously, as this carrier fluid flows through therestriction 10c, it velocity is increased, depending upon the relative sizes of the annular flowway Within thesection 10a and the flowway Within section 10b. At any rate, in accordance with this invention, the

velocity is increased at this area adjacent the ends of the tubes 11 and 12 to a value sufliciently greater than the extrusion velocity of the film and filler materials through these tubes as to cause the concentric rods extruded therefrom to elongate and break off into segments which form into fluid capsules. As these capsules are broken oil from the rod, they will flow suspended within the stream of carrier fluid through the reduced conduit section 1% As previously described, in this first embodiment of the invention, the film material which forms the shell of the capsule is a hot melt which is adapted to be hardened when cooled below its melting point. Thus, the stream of carrier fluid about the tubes is maintained at a temperature above the melting point of the film and filler material so that the fluid rods will remain liquid as they are extruded from the ends of the tubes and caused to break off and form into fluid capsules. These capsules then flow suspended within the stream of carrier fluid into and through the reduced conduit section 10b. As shown in FIG. 1, there is a counterflow heat exchanger 19 disposed about reduced section 1% for gradually decreasing the temperature of the carrier fluid from a point above the melting point of the film material to a point below such point. Thus, the suspended fluid capsules are caused to harden during their flow from the upstream to the downstream end of the reduced conduit section 1017. More particularly, the temperature gradient is in this way controlled during this time so as to avoid damage to the shell material, as might incur in the event the temperature of the film material was too rapidly or too slowly reduced.

Carrier fluid is supplied to the upstream end ofenlarged conduit section 10a by means of anauxiliary conduit 20 connected at its upstream end with a source of carrier fluid, to be described hereinafter, and at its downstream end with the upstream end of the enlarged conduit section. This carrier fluid is moved through the auxiliary conduit and into the main conduit 10 at the desired speed by means of apump 21 disposed within the auxiliary conduit upstream of aflowmeter 22 for indicating the flow rate of the carrier fluid. The temperature of this carrier fluid is raised to the desired level by means of aheat exchanger 23 in the auxiliary conduit between theflowmeter 22 and the upstream of reducedconduit section 10a.

The downstream end of reduced conduit section 1% is connected with a vessel 24 for collecting the carrier fluid and the capsules suspended therefrom. In this embodiment of the invention, it is contemplated that the carrier fluid will be a liquid, such as water, of higher specific gravity than the capsules. Thus, there is anoutlet 25 from the vessel above the connection thereto of conduit section 1012, so that the hardened capsules rise to the upper level of the carrier fluid so as to spill with it over the edge ofoutlet 25 onto ascreen conveyor 26. The hardened capsules will move on the conveyor from left to right so as to spill into a collection container 27, and abrush 28 is mounted beneath the right-hand end of thescreen 26 for wiping capsules from the screen which tend to stick to it.

As previously described, the carrier fluid is preferably recirculated from the vessel 24 to the upstream end of the main conduit 10. For this purpose acontainer 29 is mounted beneath the left-hand end of thescreen 26 to receive the carrier fluid which pases through it. Additional carrier fluid for make-up purposes may be introduced into thecontainer 29 through aline 30 connecting therewith. The lower end ofcarrier fluid container 29 is connected with the upstream end ofauxiliary conduit 20, so that carrier fluid may be recirculated into the main conduit 10. This recirculation of the carrier fluid has several advantages, particularly when it is of relatively expendable material, its recirculation permits the retention of some of its heat used in maintaining the film materialin a fluid state within at least a portion of conduit 10.

One or both of the tubes 11 and 12 may be adjusted longitudinally of the conduit 10, as well as with respect to one another in any conventional manner. In being adjustable relative to the conduit 10, the open ends of such tubes may be moved toward or away from the restriction c for adjusting the velocity at which the stream of carrier fluid moves about the extruded rods. The adjustment of the ends of the tubes relative to one another may be desirable in order to accomplish certain extrusion characteristics.

As previousl described, the carrier fluid is chemically nonreactive and physically immiscible with the film material which forms the shell of the capsule. At the same time, the film material is a hot melt which may be hardened in response to the lowering of the temperature of the carrier fluid from a point above to a point below its melting point. Still further, the filler material is asubstance which may be maintained in its fluid state at a temperature at which the film material is also maintained in its fluid state. Obviously, however, the filler material may or may not be hardened after extrusion. As an example of materials meeting these qualifications,

the film material may comprise a molten wax, the carrier fluid may be water, and the filler material may also be water. These substances were formed into capsules approximately 1,000 microns in diameter and containing approximately 57% by water with apparatus having the following structural and operational characteristics:

STRUCTURAL CHARACTERISTICS Inches Enlarged conduit section 0.580 I.D. Reduced conduit section 0315 ID. Outer tube 0.1875 0.D., 0.150 1.1). Inner tube 0.050 O.D., 0.030 I.D.

Outer ends of the inner and outer tubes flush with one another and located 1 /2" upstream of the conical restriction.

OPERATIONAL CHARACTERISTICS Upper carrier fluid temperature C. 80 Lower carrier fluid temperature C. 50 Filler material extrusion rate cc./min. 30 Encapsulating medium extrusion rate cc./min. 30 Carrier fluid rate g.p.m. 1 A Filler material temperature C. 80 Encapsulating medium temperature C.-- 80 The same film, filler and carrier fluid materials were used in forming capsules approximately 1500 microns in diameter and containing approximately 57% water employing the same apparatus and the following operational characteristics:

Upper carrier fluid temperature C. 80 Lower carrier fluid temperature C. 45 Filler material extrusion rate cc/min.-- 60 Encapsulating medium extrusion rate cc./min.- 60 Carrier fluid rate g.p.m. 2 Filler material temperature C. 85 Encapsulating medium temperature C. 85

The other embodiment of the apparatus shown in FIG. 2 is similar, in many respects, to the apparatus abovedescribed in connection with FIG. 1. Thus, it includes a conduit 10 having enlarged and reducedcylindrical sections 10a and 1021 connected by a restricted portion 100', and concentric tubes 11' and 12 extending concentrically withinenlarged conduit section 10a. As in the first-described apparatus, filler material is fed in a liquid state to inner tube 1.1 and film material is fed in a liquid state to outer tube 12' fromsupply reservoirs 15' and 14, respectively, throughpipes 17' and 16 having pumps 18' and 18a respectively, disposed therein. Also, carrier fluid is introduced into the upstream end ofenlarged conduit section 10a at the desired speed through anauxiliary conduit 20 connected at its opposite end to a source of supply of carrier fluid. As in the first embodiment of the invention, such carrier fluid is forced through the auxiliary conduit by means of apump 21, and the: flow rate thereof is measured by means of a meter 22'.

However, as previously mentioned, in. this second embodiment of the invention, the fluid capsules broken oflf from the fluid rods extruded through the tubes 11 and 12 are hardened either by chemical reaction or solvent extraction, so there is normally no need for heat exchangers either in the restricted conduit section 10b or in the auxiliary conduit 20'. Thus, in this second embodiment, the suspended fluid capsules flow entirely through the restricted conduit 10b in a fluid state and into avessel 31 adapted to contain a liquid hardening medium as well as to collect the carrier fluid and capsules.

In the illustrated embodiment of FIG. 2, it is contemplated that the carrier fluid will be a liquid having a lower specific gravity than the liquid hardening medium, and that the fluid capsules will have a specific gravity intermediate that of the fluid carrier and the hardening medium. Furthermore, the liquid carrier fluid and the hardening medium are also immiscible with one another so that they will stratify in thevessel 31 to establish ininterface 33. The end of the restricted conduit section 10b turns down to a level within the vessel below theupper level 32 of the carrier fluid, but above theinterface 33 between the carrier fluid and hardening medium. As a result, the liquid capsules will gradually fall through the carrier fluid to theinterface level 33. Also, this introduction of carrier fluid into thevessel 31 will agitate the fluid within the vessel so as to normally distribute the fluid capsules thereabout, and thus reduce the possibility of collision with one another prior to hardening at theinterface level 33.

Theinterface level 33 is maintained bylevel control 34 at the upperopen end 35a ofoverflow tube 35. The lower end oftube 35 is disposed above ascreen conveyor 36 similar to thescreen conveyor 26 shown in FIG. 1. Thus, the hardened fluid capsules and hardening medium spill over the openupper end 35a of the tube onto thescreen 36, where, as described in connection with the apparatus of FIG. 1, the capsules are moved by the conveyor from left to right so as to spill into acontainer 37 disposed beneath the right-hand end of the conveyor. Also, blade 38 is used to Wipe capsules from the conveyor in the event they have a tendency to stick to it.

The liquid hardening medium which spills over into thetube 35 and through thescreen 36 is collected within anothercontainer 39 having its lower end connected by apipe 40 to apump 41, which recirculates it through a pipe 42 into the lower end of thevessel 31 beneath theinterface 33. In the event there is a loss of hardening medium, as a result of whichinterface level 33 drops below the upper end oftube 35, thelevel control 34 will, through suitable means indicated by broken lines in FIG. 2, open avalve 43 Within a make-upline 44 for admitting additional liquid hardening medium into the pipe 46 and thus into the lower end of the vessel 3.1. When the interface level has thus been brought back up to the desired level, thelevel control 34 shuts the valve in the make-up The upstream end of auxiliary conduit 20' is connected to thevessel 31 above theinterface 33, but below theupper level 32 of the carrier fluid, so that carrier fluid will flow into the conduit 20' and thus to the pump 21' and throughflow meter 22 for recirculation into the upstream end of the main conduit 10. There may be need for ascrubber 45 in the auxiliary conduit in order to assure that there is no premature hardening of the film material within the main conduit 10.

As an example, this second embodiment of the invention may be used in the mass production of capsules comprising a filler material of hexane enclosed within a shell of aqueous sodium alginate. In this case, the carrier fluid may be naptha, and the hardening medium may be aqueous calcium chloride, which converts the sodium alginate to insoluble calcium alginate. In this event, the carrier fluid might be scrubbed by liquid-liquid contact with water in thescrubber 45.

This invention has been illustrated and described in connection with the mass production of seamless capsules, because, as previously noted, it is especially well suited to such use. However, as also previously described, it also has utility in the mass production of solid spherical particles, and the term particles, as used in the claims, contemplates either solid particles or particles in capsule form. As an example, it is contemplated that with suitable modification of the extruding means, this apparatus could be used in producing solid particles of wax. In this case, the carrier fluid could be water, which is immiscible with the wax and which may be maintained at a temperature level above the melting point of the wax as it flows past the extruding means and then lowered to a temperature level beneath the melting point of the wax after the fluid rod of the wax is elongated and broken off by means of the stream of carrier fluid into segments which form into spherical fluid particles.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. In a methad of mass producing small spherical particles, the steps of extruding a rod of fluid material within a confined stream of carrier fluid which is chemically nonreactive and physically immisicble with said material and which is flowing at a speed greater than the rate of extrusion of said rod and moving in the same direction as said rod so as to cause said rod to elongate and break off into segments which form into individual fluid particles, maintaining the carrier fluid at a temperature above the melting point of the extruded rod as said carrier fluid flows therepast, and then reducing the temperature of the carrier fluid below such melting point to cool and harden the fluid particles while suspended in said stream of carrier fluid and thereby produce said small spherical particles.

2. In a method of mass producing small spherical particles, the steps of extruding a rod of fluid material within a confined stream of carrier fluid which is chemically nonreactive and physically immisicble with said material and which is flowing at a speed greater than the rate of extrusion of said rod and moving in the same direction as said rod so as to cause said rod to elongate and break 01f into segments which form into individual fluid particles, and introducing the carrier fluid and the fluid particles suspended therein into a liquid hardening medium so as to harden the fluid particles within said hardening medium and thereby produce said small spherical particles.

3. In a method of mass producing capsules in which a filler material is contained within a seamless shell of film material, the steps of extruding concentrically arranged fluid rods of the film material and filler material within a confined stream of carrier fluid which is chemically nonreactive and physically immiscible with said film material and which is flowing at a speed greater than the rate of extrusion of said rods and moving in the same direction as said rods so as to cause said rods to elongate and break off into segments which form into indivdual fluid capsules, and then hardening the film material of said fluid capsules so as to thereby mass produce said capsules.

4. A method of the character defined in claim 3, including the steps of maintaining the carrier fluid at a temperature above the melting point of the film material as said carrier fluid flows past said extruded rods and then reducing the temperature of the carrier fluid below such melting point to cool and harden said film material while the fluid capsules are suspended in said stream of carrier fluid.

5. A method of the character defined in claim 3, including the step of introducing the carrier fluid and fluid capsules into a liquid hardening medium so as to harden the film material of said fluid capsules.

References Cited UNITED STATES PATENTS 2,265,801 12/1941 Cooke 264-11 2,874,473 3/1959 Mitchell 264-44 2,043,970 7/1962 Terenzi 264-14 X ROBERT F. WHITE, Primary Examiner.

R. B. MOFFIT, J. R. HALL, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,389,194 June 18, 1968 George R. Somerville It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 47, "2,043,970" should read -'3,042,970 same column 8 after line 47, insert the following references:

3,092,553 6/1963 Fisher 264-14X 3,111,708 11/1963 Watt 264-4 Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

Images