Coating apparatus – Projection or spray type – Coating moving mass of solid particulate work
Reexamination Certificate
2002-10-22
2004-05-25
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
Coating moving mass of solid particulate work
C118S013000, C118S019000, C427S002180
Reexamination Certificate
active
06740162
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for treating particulate material with a coating medium, in particular for sugarcoating or film-coating of pharmaceutical or food preformed pieces, wherein the material is filled into a container, moved in the container by rotating the container, sprayed with the coating medium and the sprayed coating medium is dried by process air.
The invention further relates to an apparatus for carrying out the method comprising a container drivable to rotate about an axis, a spraying device for spraying the coating medium onto the material and supplying means for supplying process air.
Such a method and apparatus are known from the published German patent application DE 1 198 187.
Such methods and apparatus are used in the pharmaceutical, chemical, confectionary and food industries. In the pharmaceutical industry, medications are produced by sugarcoating making use of a sugared syrup. Film or polished tablets are produced on the other hand by film-coating, which are medications coated with a polymer coating.
The present invention however is not limited to sugarcoating or film coatings, but can also be used in granulation, where fine particles are coated with a medium to agglomerate the particles with one another.
In sugarcoating, the preformed pieces are normally coated with a sticky suspension or solution. In conventional methods, the particulate material to be coated is moved in a rotating container and the coating medium, i.e. the sticky suspension is poured onto the moving material in cycles. In further individual cycles, a distribution follows by which the suspension is uniformly distributed on the particulate material and subsequently, the coating medium is dried. These individual cycles each require about 5 to 10 minutes. After drying, the cycles of pouring, distributing, drawing, etc. are repeated.
In more recent methods for sugarcoating, the coating medium is sprayed onto the particulate material moved in the rotating container by means of a spray nozzle system.
In conventional methods of film-coating, the material to be coated is also moved in a rotating container and sprayed with the coating medium through a nozzle system, the coating medium normally being a solution, dispersion or a viscous suspension in the film-coating method. Subsequently, the material is dried.
The quality of the final coating of the particulate material depends on a uniform, rapid, however gentle circulation of the material to be coated, both in the sugarcoating and film-coating procedures. How the material is circulated in the container also has a considerable influence on the possible ways of applying the coating medium and the effectivity of drying. The application and drying in turn significantly influence the quality of the coating of the finally coated material.
A dragée vessel is known from the above-mentioned German patent application DE 1 198 187 for producing dragées for the confectionary and the pharmaceutical industry. A polishing arm is arranged in the dragée vessel which is connected to the open edge of the vessel or is driven by a shaft lying within the drive shaft of the dragée vessel. The dragée vessel is rotatable about an axis which is inclined to the vertical by an angle.
In the method carried out in this known dragée vessel, the material to be coated is moved in a container which is rotated about an inclined axis. The particulate material is circulated within itself due to the rotation of the container about its axis by which the material is mechanically carried along the rotating wall of the container. Thus descending layers of the material flow downwards on the layers ascending on the rotating wall. Due to the inclined disposition of the axis, a horizontal circulating motion is overlapped by upwardly inclined centrifugal forces. A disadvantage of this conventional apparatus is its limited capacity because the inclined disposition of the axis only allows a certain loading. In addition, when the charge amount is enlarged, inadequacies result with the supply of process air for drying the coating, because the process air only superficially passes the material which is circulated as a compact volume, however does not penetrate through the material.
For this reason, the apparatus in use today are almost exclusively those having a container rotated about a horizontal axis. These apparatus can be operated with larger charges. The disadvantage of apparatus with containers rotating about a horizontal axis however is that a mixing of the particulate material is less satisfactory due to the lack of centrifugal forces. This disadvantage is compensated by the use of mixing baffles or blades, which however represent a mechanical obstacle and promotes abrasion and therefore a damaging of the preformed pieces.
An apparatus with a container rotating about a horizontal axis is disclosed in the German product brochure of Glatt GmbH, Bühlmühle, “Glatt-Coater Type GC400-2000”.
Moving the particulate material to be coated in a container rotating about a horizontal axis is also a disadvantage with respect to spraying the material with the coating medium. Spraying in the known methods and apparatus of this type takes place either by spraying the medium from above onto the material moving therebelow. This so-called top-spray method however has the drawback that it necessarily leads to large spray losses.
To minimize the spray losses, it has therefore been attempted to immerse the spraying device in the circulating material. In apparatus and methods where the material is moved in a container rotated about a horizontal axis, it has however been found that the movement of the material is negatively influenced by the spraying device immersed in the material itself. A uniform movement and mixing of the particulate material is no longer ensured. Since the immersed, stationary, i.e. non-rotating spraying device again represents a mechanical obstacle to the moving material, the moving particles can be damaged by the mechanical obstacle due to too large friction.
In addition, the published German patent application DE 1 938 797 discloses an apparatus for coating granular material, such as pills, having a container for receiving the granular material and the coating material. The container is formed by a bottom shell rotatable about its middle point and a stationary drum joining with its inner surface to the periphery of the bottom shell smoothly in upward direction. According to the described method, the material to be coated is placed on the bottom shell and rotated at a speed such that the granular material is moved upwardly along the inner surface of the drum by centrifugal forces and from there is moved in circulation back to the bottom shell. The coating material is applied to the granular material circulating in this manner and drying air is blown in between the granular material. In this known apparatus, only the bottom of the container rotates, while the drum is stationary. A disadvantage is that the movement and mixing of the particulate material is insufficient. In addition, the upward moving material caused by centrifugal action flows back in counterflow to the ascending particles in this known method and apparatus. Impacts between the individual particles can cause damage, in particular when the granular particles are brittle. In addition, the ventilation with process air is not optimal in this type of method.
A multistage method is disclosed in the published German patent application DE 27 50 696 for applying a sprayable agent on a material composed of granular, flake, chip or fiber particles. The spray agent is sprayed onto the inner side of a curtain of particles formed to be rotationally symmetric to a vertical axis, which is made up of free falling particles or particles accelerated downwardly. The method is particularly used for coating wood shavings with a sprayable binding agent. The particles forming the curtain are deflected after passing through the direct spray zone and are thrown outwardly from the geometrical axis of the curtain
Crispino Richard
St. Onge Steward Johnston & Reens LLC
Tadesse Yewebdar
LandOfFree
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