Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2001-09-14
2003-12-02
Bennett, Henry (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S451000, C034S557000, C427S372200, C427S379000
Reexamination Certificate
active
06655046
ABSTRACT:
The invention relates to a device and a process for the uniform drying of products in web form which have been obtained by coating, and, in particular, of thin films which essentially comprise organic raw materials and are manufactured on an aqueous basis.
The films or coatings to which this invention relates are based on organic raw materials or on mixtures of such substances. These are preferably water-soluble substances. Such organic raw materials include polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives, polyvinyl acetate, polyethylene glycol, alginates, carrageenan, xanthan, gelatin and other water-soluble polymers known to the skilled artisan, and also mixtures and copolymers of these substances. If desired, such films or coatings may also include fillers such as mannitol, lactose, calcium phosphate, glucose, sorbitol, etc., active substances such as drugs, aroma substances, menthol, etc., sweeteners such as cyclamate, flavours such as glutamate, and other ingredients, including in some cases volatile ingredients. These films may also have mucoadhesive properties.
For various application purposes, films are required which are very thin, i.e. having a thickness of between 10 and 500 &mgr;m, preferably between 50 and 200 &mgr;m. A problematic characteristic of such thin films is their high sensitivity to atmospheric humidity. At high atmospheric humidity, swelling may be observed in these films, which can cause an increase in volume and possibly the sticking together of two or more overlying films. Conversely, such films tend to become brittle and to fracture if atmospheric humidity is too low.
This behaviour can lead to problems, in particular with respect to the manufacture of such films. In manufacturing the films, typically, a procedure is used wherein a coating mass or composition is applied as an aqueous solution or dispersion to a web-shaped sheet material or paper which serves as carrier or support, and is subsequently subjected to drying. In the process, the coated support material is continuously passed through a drying oven. The zone dryers used for this purpose are typically provided with incoming-air nozzles which distribute the air over the entire width of the product web, i.e. transversely to the running direction of the product web. This leads to the edge regions having more contact with the moving air than the regions in the centre of the product web (cf. FIG.
2
).
Especially in the case of films or other coatings which are manufactured on an aqueous basis, this may result in overdrying in the edge region of the coated product web (relative to the running direction of the product web). If the drying conditions are chosen such that the region located in the centre (in longitudinal, that is, running direction) of the coated support web has been dried to a desired degree, in most cases the edge region is at the same time excessively dried (overdried). In the case of product webs which are processed with nonaqueous solvents, this effect is of no significance since the general aim is to expel all solvent residues from the product, i.e. the solvents are removed to a level of greater than or equal to 99%. There is therefore no “overdrying” at the edges.
The above-described overdrying of aqueous materials in the edge regions of the coated web-shaped support (=product web) may lead to shrinkage of the material at the edges of the product web and possibly even to detachment of the coating mass or of the dried thin film from the support since the extent of the shrinkage of the support and of the coating composition (or of the dried film) may be different.
The construction of the zone drier with the incoming air nozzles transverse to the running direction of the product web leads to a non-uniform drying and thereby to differences in the curing or cross-linking of the polymer chains in the case of films or other coatings produced on the basis of organic materials. During the further processing of the web material, this in turn leads to different chemical or physical behaviour of the coated product, depending on whether it has been cut from the centre or from the edge region of the product web.
It was thus the object of the present invention to provide processes and devices enabling the production of films or coatings of the kind mentioned whose moisture content, both in transverse and in longitudinal direction, is equal over the entire product web, and which avoid the disadvantages described. More particularly, the object is to enable the production of thin films of consistent quality, especially in terms of their moisture content.
Surprisingly, this object is achieved by a process for drying thin films or coatings by applying a coating mass, which is produced on an aqueous basis, to a support, the layer or film being transported through a drying device which has at least one drying zone, characterized in that in at least one drying zone, designated as moisture-compensation zone, air is supplied which has a moisture content corresponding to the constant moisture content of the film to be prepared or the layer to be prepared, by a process for manufacturing by applying a coating mass prepared on an aqueous basis and containing an organic substance to a support, transferring the composite of support and coating mass thus obtained into a drying device having at least one drying zone, and subsequent drying of the film, during which process the said film, located on the support, is conveyed through the drying device, characterized in that during the drying, in at least one drying zone, designated moisture-compensation zone, air is supplied having a moisture content which corresponds to the constant moisture content of the film to be prepared, as well as by a device for setting a constant moisture content of a coating mass applied to a web-shaped support, said device having a drying zone with a fresh air feed and a waste air return, characterized in that the fresh air feed is provided with a device enabling or capable of adjusting the moisture content of the air to a constant value, and a drying device comprising a plurality of drying zones arranged in tandem, through which the web-shaped support is transported, characterized by at least three zones arranged in tandem, namely at least one preheat zone, at least one drying zone and, at least one drying or designated moisture-compensation zone, wherein the fresh air feed is provided with a device enabling or capable of adjusting the moisture content of the air to a constant value, as well as by the embodiments of the invention described below.
In the inventive process for drying thin layers or films, the layer or film is, preferably continuously, passed through a drying device with at least one drying zone; in the process, in at least one drying zone, air is supplied which has a moisture content corresponding to the constant moisture content of the film to be prepared or the layer to be prepared. Such a drying zone is called moisture compensation zone.
In this manner, when passing through such a zone, the more strongly dried edge regions of the coated carrier web are moistened (or remoistened) and thus brought to the moisture content corresponding to the desired product moisture). The moisture content of the centre zone of the coated film web is not increased in the process. In this way it is accomplished that in the edge regions of the product web, the same moisture content occurs as in the centre zone of the product web. The film or coating thereby possesses uniform product properties over its entire surface. Detachment of the film or coating from the support web in the edge regions can thus be prevented.
“Constant moisture content” is understood to mean the desired moisture content of the product (film, coating) in its final condition after manufacture (predetermined moisture: 50-70% relative humidity, preferably 70%).
The manufacture of thin films or coatings is accomplished according to the present invention in that initially a coating mass is prepared which contains organic substanc
Brathuhn Rudi
Hoffmann Michael
Schäfer Wolfgang
Schwarz Peter
Bennett Henry
Hochberg D. Peter
LTS Lohmann Therapie-Systeme AG
Mellino Sean
O'Malley Kathryn S.
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