Coating apparatus – Projection or spray type – Coating moving mass of solid particulate work
Patent
1995-03-07
1998-02-17
Czaja, Donald E.
Coating apparatus
Projection or spray type
Coating moving mass of solid particulate work
118 20, 118 24, 118 62, B05C 500
Patent
active
057187649
DESCRIPTION:
BRIEF SUMMARY
This application is a 35 U.S.C. 371 of PCT/DK95/00040 filed Jan. 27, 1995.
1. Field of the Invention
Coating of particulate materials is applied within various industries. Thus, for instance, in the pharmaceutical industry drug-containing tablets and pellets are provided with a coating. Thereby it is achieved that the active drug is released delayed after administration. This makes it possible to have the active substance released in specific areas of the intestine or to achieve a prolonged release of the active substance.
In the detergent industry an enzyme layer is provided on a carrying core of extender, which layer is protected against oxidation and attrition by a coating.
Also fertilizers, plant protecting agents, and several other chemical products are coated.
2. Background of the Invention and Prior Art
Special plants and apparatuses have been developed for coating purposes.
One embodiment of this prior art apparatuses comprises a cylindric reaction chamber having a perforated base plate and a spray nozzle in the top of the reaction chamber. By means of pressurized air blown through the base plate a fluidized layer of particles is maintained on said plate and the particles are wetted by the coating liquid which is atomized through the spray nozzle. To achieve the desired degree of encapsulation, uniformity and thickness of the coating layer it is necessary to circulate the batch of particles to be coated for a period between 0.5 and 24 hours. This type of apparatus has the drawback that the capacity is small, an agglomeration and sticking together of the particles is often experienced.
In an improved version of such an apparatus (see WO93/08923 and Ghebre-Sellassie, Isaac: Pharmaceutical Pelletizing Technology, New York and Basel, page 50 and thereafter) important constructive changes have been made. The spray nozzle is placed in the center of the base plate, and spraying of the coating liquid is only made in the direction of the main streams. Around the spray nozzle the base plate has in an annular area a higher perforation due to several larger apertures placed close to each other. The area more distant from the nozzle is perforated only to a minor degree; it has less and smaller apertures. Above the spray nozzle a vertical coating pipe is mounted in such a way that a narrow passage remains between the end of the pipe and the base plate. The diameter of the coating pipe corresponds to the diameter of the area having more pronounced perforation.
Thereby an annular down-flow bed is formed in the reaction chamber between the wall of the reaction chamber and the coating pipe, and a coating zone is formed in and above the coating pipe. The outer annular portion of the base plate is the bottom of the down-flow bed. Due to the only moderate perforation in the outer annular area, the amount of air penetrating the base plate in this section is smaller than the one passing through the interior portion below the coating pipe. Therefore, the column of particles which collects in the down-flow bed zone is only aereated by the weaker air-stream coming from below. On the contrary the stronger stream of air entering the coating pipe carries the particles coming from the down-flow bed upwards through the cloud of atomized droplets.
Thereby a more uniform coating of the particles is obtained, and the risk for agglomeration is decreased since the particles falling back into the down-flow bed after having passed through the cloud of atomized droplets have been predried and therefore have a lower tendency to stick together. However, with this apparatus only a limited production capacity can be obtained, making the apparatus unsuitable for treating large amounts of products, as necessary for instance in the detergent industry. Increase of capacity by increase of the amount of coating liquid sprayed through the nozzle involves an increased risk of agglomeration.
Agglomeration not only impedes product quality but causes operational problems due to partial or complete clogging of the particle flow into and through the coa
REFERENCES:
patent: 3110626 (1963-11-01), Larson et al.
patent: 3241520 (1966-03-01), Lindlof et al.
patent: 4117801 (1978-10-01), Dannelly et al.
patent: 4489504 (1984-12-01), Hammer
patent: 4858552 (1989-08-01), Glatt et al.
Ghebre-Sellassie: Pharmaceutical Pelletizing Technology, pp. 50-55 and 68-69.
Aeromatic-Fielder AG
Czaja Donald E.
Padgett Calvin
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