Patent Application
20100031881
The invention is directed towards a rotor processor for coating or layering micronized particles with a polymer in a rotor processor. An improvement to the processor is directed to a powder feed system for introducing dry polymers and dry glidants into the rotor chamber and onto the circulating particles.
Coating of small particulates, commonly known as cores, beads, crystals, pellets, granules or seeds, is well known for creating spherical particles, such as pharmaceuticals. The typical size for such particles is 50-10,000 microns. The coating material is normally a polymer, which may be a copolymer or monomer. A rotor processor is commonly used for such coating. This processor has a cylindrical stator chamber with a rotatable disc mounted therein, and a narrow annular slit between the inner wall of the stator and the perimeter edge of the rotor. The rotor forms a floor in the chamber upon which particles are supported. The width of the slit is sufficiently narrow so as to prevent particles in the chamber from falling through the slit. Rotation of the rotor imparts centrifugal force to the particles, which are thrown to the wall of the stator, wherein air forced upwardly through the slit lifts the particles upwardly. The width of the slit governs the air velocity for a given air flow, which creates an upward draft which carries the particles upwardly. The upward movement of the particles continues, as long as the air velocity exceeds the transport velocity required to fluidize the particles. The air passing through the slit has a relatively high velocity, and then expands into the larger volume of the chamber, thereby losing velocity. As the particles lose their transport velocity, they fall back toward the center of the rotor and return to the rotor surface. Thus, the rotating rotor and the upwardly flowing air create a circulating bed of particles within the chamber.
The particles are coated or layered during circulation through the bed. In the conventional layering process, a polymer, copolymer or monomer is dissolved in a solvent, which is then sprayed onto the particles in the chamber while the particles are circulating. The airflow also functions to dry the solution on the cores, with the layer thickness being built up as the particles continue circulating through the bed for repeated exposure to the sprayed solution.
Some polymers have an adhesive nature. In prior art coating processes, these polymers generally are diluted to 2-15% solids content to minimize agglomeration due to the adhesive nature. Furthermore, glidants are normally suspended in the polymer spray solution/dispersion so as to prevent or inhibit agglomeration during the coating process. Examples of glidants include titanium dioxide, calcium carbonate, magnesium stearate or any metal stearate, fumed or colloidal silica, sodium lauryl sulfate, graphite or any other finely divided material capable of reducing the adhesive nature of some polymers. Such glidants normally must be added to the polymer spray solution/dispersion in concentrations of 5-100%, based on the polymer solids in the solution/dispersion. These suspensions must be continuously agitated to prevent settling. The glidants in solution/dispersion often cause buildup in the spray guns, and thus blockage during processing, as well as problems with settlement in the solution/dispersion lines and other flow problems leading to inconsistent delivery during the coating process.
With the conventional polymer layering process, the polymers must be soluble so as to dissolve in a suitable solvent so as to be applied as a dilute liquid. Typical soluble polymers will be 5-15% solids in solution, by weight. In a pharmaceutical application, the polymers may function for modified release of active ingredients and/or for taste masking. In this type of application, polymers may be layered on the cores for 5-25% weight gain. In the case of organic solvent soluble polymers, as much as 5 kg of solvent must be used for each 1 kg of product coated. In scaled production, this is a very large amount of solvent per coated batch. For example, in a 5 kg batch of cores coated to a 25% weight gain with a 5% solids solution, a 25 kg solution is required, with the polymer application being approximately 2.5 grams of polymer substances per minute. Thus, the conventional layering process with dissolved polymers in solvent solution is slow and requires large volumes of solvents.
In the conventional rotor processors, such as the GX or GXR sold by Applicant, the expansion chamber of the processor is normally maintained at a slightly negative pressure. Pulse filters are provided at the top of the processor and are connected to a positive compressed air source. The product powder port is located above the rotor chamber to drop powder downwardly by gravity and/or pulled into the processor by the negative internal pressure onto the circulating particles. The powder port is an opening without a closure or seal. Occasionally, the filter pressure may exceed the chamber pressure, in which case the powders are forced out of the open powder port. Some powders are toxic, which presents a hazardous situation. Also, the loss of powder from the processor is a wasteful cost.
Accordingly, a primary objective of the present invention is the provision of an improved rotor processor for supplying dry powder polymers or glidants to the particle bed in the rotor chamber.
Another objective of the present invention is the provision of an improved powder feed system for a rotor processor which introduces dry powders into the rotor chamber for application to particles in the circulating bed.
A further objective of the present invention is the provision of an improved rotor processor having a powder feed system with a precise screw conveyor, and eductor, and a ball mounted powder conduit.
Still another objective of the present invention is the provision of an improved rotor processor wherein dry powders are introduced into the rotor chamber at a level circumferentially spaced from the liquid spray gun of the rotor chamber.
Yet another objective of the present invention is the provision of an improved rotor processor having separate spray and powder zones in the rotor processor through which circulating particles sequentially and repeatedly pass.
A further objective of the present invention is the provision of an improved rotor processor for dry powders which introduces the powders into the rotor chamber under a positive pressure.
Another objective of the present invention is the provision of an improved rotor processor for application of dry powders to the circulating particle bed which is effective and efficient.
These and other objectives will become apparent from the following description of the invention.
The rotor processor of the present invention includes a stator and a rotor rotatably mounted in the stator to define a rotor chamber. A gap between the peripheral edge of the rotor and the interior cylindrical wall of the stator allows air to flow upwardly during the operation of the processor to facilitate circulation of the particles within the rotor chamber. A spray gun extends through the stator wall and into the rotor chamber to spray a liquid onto the bed of particles. A dry powder feed system extends through the stator wall and into the rotor chamber to direct dry powder into the bed of particles. The spray gun and the powder feed system define separate spray and powder zones within the circulating bed of particles, which pass repeatedly and sequentially through the zones to build a coating or layering onto the particles. The powder is introduced under positive air pressure. Depending on the coating process, the powder may be a dry polymer or a dry glidant.
The rotor processor of the present invention is generally designated by the reference numeral 10 in the drawings. The processor includes a lower portion defining a rotor chamber 12, a central portion defining an expansion chamber 14, and an upper portion 16 housing the pulse filter. The expansion chamber 14 and pulse chamber filter 16 are conventional.
The present invention is directed towards the rotor chamber 12, which is defined by a substantially cylindrical stator 18 having a concave or dish-shaped rotor 20. The internal wall of the stator 18 has a ledge 22. The perimeter edge of the rotor 20 extends over the upper surface of the ledge 22, and when the rotor processor 10 is operating, the rotor 20 lifts off of the ledge 22 to define a small gap through which air flows upwardly. This gap structure and function is disclosed in Applicant's co-pending application Ser. No. 11/669,544 filed Jan. 31, 2007 and entitled ROTOR PROCESSOR.
The rotor 20 is mounted on a shaft 24 which is drivingly connected to a motor 26 via gears and a drive belt (not shown).
The stator 18 and rotor 20 may be in the form of an insert which can be removably clamped beneath the expansion chamber 14. The stator 18 includes a spray gun port 28, a powder port 30, a sample port 32, and a discharge port 34. Depending upon the size of the processor 10, multiple spray gun ports 28 and powder ports 30 may be provided. The powder port 30 is spaced circumferentially from the spray port 28, but generally at the same elevation relative to the rotor chamber 12. As best seen in
A spray gun is attached to the spray gun port 28 in any convenient manner, such as with a ball mount or universal joint connector. Similarly, a powder feed system 35 is attached to the powder port 30 with a ball mount or universal joint connector. The powder feed system 35 is mounted on a cart 36 for quick and easy connection and disconnection to the processor 10. The system 35 includes three principle components, a powder feed conveyor 38, an eductor 40, and a flexible Teflon® or stainless steel conduit 42 extending from the eductor 40 to the ball mount. The feed conveyor 38 precisely transfers the powder from a container (not shown) to the eductor 40. One example of a conveyor 38 is the KT20 K-Tron screw conveyor sold by Applicant. The eductor 40 is connected to a source of pressurized air so that the powder is transmitted from the eductor 40, through the conduit 42 and pushed into the rotor chamber 14 under a positive pressure. Preferably, the pressure ranges between 10-100 psi. The feed rate of the conveyor 38 preferably is in the range of 1-20 grams/minute, ±0.5 grams/minute, depending upon the size of the processor 10.
The spaced apart spray port 28 and powder port 30 effectively define separately spray and powder zones within the rotor chamber 12 through which particles sequentially and repeatedly pass when the processor 10 is operating. More particularly, when the motor 26 is actuated to rotate the rotor 20, the centrifugal force of the rotor 20 is imparted to particles sitting on the rotor, which defines a floor for the chamber 12. The particles are thrown outwardly towards the wall of the stator 18, wherein the air flowing upwardly through the gap creates an upward draft that carries the particles upwardly, until the transport velocity required to lift the particles exceeds the air velocity of the upward draft. As the air leaves the confines of the gap, it expands into the larger volume of the chamber 12, thereby losing its high initial velocity, such that the particles lose transport velocity and fall back toward the center of the rotor 12 onto the rotor surface. The air velocity at the slit or gap must exceed the transport velocity of the particles at all times during operation of the processor 10, in order to prevent particles from falling downwardly through the gap. As the particles circulate in the rotor chamber 12, they are coated by liquid from the spray gun and dry powder from the powder feed system 35 until a desired layer thickness is achieved. Additional drying air is introduced into the processor from above the bed, to further enhance evaporation. The delivery of a large amount of drying air from the top of the particle bed allows for rapid evaporation of the coating solution, while keeping the cores in contact with the rotor plate and maintaining the small gap between the rotor and the stator.
The improved rotor processor 10 of the present invention can be used with dry polymer powders or dry glidant powders. Applicant's co-pending application Ser. No. ______, describes a dry polymer coating process, while Applicant's co-pending application Ser. No. ______, filed on ______, describes a dry glidant process. These applications are incorporated herein by reference.
The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.
This application claims priority under 35 U.S.C. §119 of provisional applications Ser. No. 61/087,083 filed Aug. 7, 2008 and 61/087,089 filed Aug. 7, 2008, which applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61087083 | Aug 2008 | US | |
| 61087089 | Aug 2008 | US |
