Coating processes – Particles – flakes – or granules coated or encapsulated – Solid encapsulation process utilizing an emulsion or...
Patent
1994-07-14
1996-01-30
Beck, Shrive
Coating processes
Particles, flakes, or granules coated or encapsulated
Solid encapsulation process utilizing an emulsion or...
427421, 118303, 118DIG5, 241 5, 241 39, 426577, B05D 700
Patent
active
054879167
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for coating particles in a spray-drying plant.
Coating of powder particles is desirable for many different reasons. Thus, e.g., coating may protect particles against humidity or oxidation. In connection with particles which are to be ingested, release of components from the particles during passage of the particles through the gastrointestinal system can be controlled by coating, e.g., in such a manner that the components in question are not released until after passage of the stomach. Coating of particles may also be a way of obtaining a slower release of active substances from the particles. Coating may cover an undesired taste, colour or texture of the particles. Furthermore, the coating may act as a protection against light and gasses.
As will be explained in the following, coating may also improve the possibility of spray-drying solutions or dispersions which are otherwise difficult or impossible to spray-dry, because the coating process may be utilized to expose the solutions or dispersions in a thin layer with a large surface, thus greatly enhancing evaporation.
Coating of powder particles may improve the handling of mixtures of powder products in which the individual components are to take part in a reaction which is initiated by decomposition of the coating.
BACKGROUND OF THE INVENTION
A known technique for coating powder particles comprises the use of a fluid bed plant. By means of this type of equipment, the powder particles are fluidized in air, the coating composition is atomized over the fluidized powder particles, and the coated particles are dried by continued passage in the fluid bed plant.
This type of fluid bed treatment is suitable only when coating powder particles have a size which is several times larger than the droplets of the atomized coating composition. When the particles are only a few times larger than the droplet size or smaller, an agglomeration occurs which results in the particles gluing together in clusters with large interstices of air, which is normally an undesired effect in a coating process.
In another technique, which is especially adapted for coating of relatively heavy particles in a fluid bed plant, a spray nozzle is placed at the bottom of a vertical tube in the center of fluidized powder particles and atomizes the coating composition upwards through the tube and concurrent with the powder particles, which particles are carried upwards through the same tube by means of an air flow. When the powder particles are coated, they are carried upwards, are dried, fall down into the fluidized powder particles and into the tube, and are coated with a new layer of the coating composition. This process is continued until the desired thickness of the coating layer has been obtained.
One problem associated with these two methods is that it is normally only possible to apply a very thin layer of a coating composition in each application stage. If a thicker layer of coating substance is applied at one time, the powder particles will tend to agglomerate due to sticky surfaces.
One known technique for coating of particles is to disperse powder particles in a liquid coating composition and spray-drying this mixed dispersion. However, in many cases, it is not realistic or at least not optimal to use this technique, in particular where the dispersion of the particles in the liquid coating composition will increase the viscosity to such an extent that spray atomisation of the dispersion becomes difficult or even impossible.
U.S. Pat. No. 3,615,723 describes a spray-drying process wherein the droplets, which are still tacky, are discharged at a screen where a mat is formed and dried. At least portions of the mat are subdivided into a particulate form (fines) and recirculated to the spray-drying chamber. The recirculated fines are added through a pipe discharging in a certain distance from the atomization zone. The dried, but still tacky droplets are discharged at the said screen in order to obtain an agglomeration of
REFERENCES:
patent: 3615723 (1971-10-01), Meade
patent: 4042653 (1977-08-01), Beyn
patent: 5075138 (1991-12-01), Tanaka et al.
patent: 5096744 (1992-03-01), Takei et al.
patent: 5100509 (1992-03-01), Pisecky et al.
Beck Shrive
Maiorana David M.
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