Stock material or miscellaneous articles – Structurally defined web or sheet – Nonplanar uniform thickness material
Statutory Invention Registration
1997-09-26
2001-01-02
Jordan, Charles T. (Department: 3641)
Stock material or miscellaneous articles
Structurally defined web or sheet
Nonplanar uniform thickness material
C428S041800, C428S352000, C428S447000
Statutory Invention Registration
active
H0001935
ABSTRACT:
BACKGROUND OF THE INVENTION
Polyolefins and particularly polyethylenes are good base materials for films, coatings and release films. Such materials are easily formulated into films which exhibit desired slip, release, peelability and related characteristics. These films are known in the form of release films applied to adhesive materials, such as removable protective layers for adhesive strips and the like. The protective layer prevents premature adhesion from the strip and protects the covered area from dust, contamination, etc.
Polymer blends containing silicone are advantageous in the production of release films. However, films containing silicone have traditionally suffered from movement of the silicone within the film layers or across layers, also known as “migration”. For example, polyolefinic films containing silicone suffer from the tendency for the silicone to migrate from the surface of the film. Since it is the presence of silicone at the surface of the film which imparts desired physical characteristics (e.g., slip, release) to the film, any movement of the silicone away from the surface diminishes, if not completely removes, such advantageous characteristics.
Although the use of high dose corona treatment is known to inhibit migration of silicone within the surface of a film, the prior art does not disclose, teach or suggest the use of corona treatment in combination with embossing to substantially enhance the performance characteristics of silicone-containing polymeric films.
It has been discovered that the use of embossing techniques in combination with corona treatment of a silicone-containing polymeric film substantially improves the performance characteristics of such film as a release sheet. Such improved characteristics include lower peel forces, lower noise generated during the peel process, improved drape and tactile properties and increased bulk.
Traditional approaches to release films designed for use in connection with personal hygiene products include coated films and papers, which involves coating a paper with silicone and adhering it to a film. However, such traditional release films suffer from relatively high peel forces and inferior noise, drape and bulk characteristics. Moreover, such traditional, inferior performing films are relatively expensive.
Thus there remains a need for an economical polyethylenic-based film for use as a combination pouch and release sheet in connection with personal hygiene products, such as sanitary catamenial pads, which is capable of being extruded or coextruded with silicone and exhibits improved performance and aesthetic characteristics, and a method for producing same.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an improved combination pouch and release sheet composed of a silicone-containing embossed polyolefinic material. The film is corona treated to prevent migration of the silicone material within the film. Since the invention avoids the traditional need for a separate release paper and is produced using an in-line process, the combination pouch and release sheet of the present invention exhibits superior performance while being less expensive than such traditional release sheets.
The improved combination pouch and release film of the present invention comprises a single- or multiple-layer film. Preferably, a polyolefinic material containing a silicone component is used as a release material. The release material is extruded or coextruded with at least a polyolefinic film not containing silicone using traditional methods. Following extrusion (or coextrusion), the film is embossed to impart superior physical and aesthetic characteristics to the film. The release layer is then corona treated to prevent migration of the silicone in release layer. Corona treating the film either prior to or following embossing is contemplated by the combination pouch and release sheet of the present invention. Preferably, the film is embossed first and then corona treated; however, as previously mentioned, the film can be corona treated at any point, and even at multiple points, of the process. Embossing is accomplished via traditional embossing methods.
The resulting film exhibits superior drape, texture, gloss, noise and peel force characteristics. Moreover, unlike many release films, the superior release properties of the release film of the present invention are not diminished over time in contact with a pressure sensitive adhesive.
According to a method of the present invention, the improved combination pouch and release film of the present invention is produced by extruding a thin layer of a polyolefinic release material containing a silicone component. In one embodiment, the polyolefinic material containing silicone is coextruded onto a base film (preferably of non-silicone-containing polyolefin) to form a film and subsequently treated with a corona discharge. Corona treatment prevents the silicone material from migrating within the film. Either before or after corona treatment, but preferably before, the film is embossed to enhance the release, tactile and aesthetic characteristics of the resultant film. Again, the corona treatment step can even occur at multiple steps within the process either before and/or after embossing.
In another embodiment of the method of the present invention, a release material containing silicone and a base material not containing silicone are coextruded with a base film (also not containing silicone) to form an upper layer (release material), a core layer (base film) and a lower layer (base material). The multilayered film is then preferably embossed. Following embossing, the release material layer is subjected to corona treatment to fix the silicone within the release material. As discussed above, the release material layer can be corona treated to prevent migration of the silicone prior to embossing, and can even be corona treated both prior to and following embossing.
Due to the in-line corona treatment of the film, there is no need for the time and expense associated with the traditional steps of coating and curing the film. The present method features in-line recycling of the process remnants from the film into the core layer, thus providing yet additional cost savings. Remnants from the film of a two layer coextrusion are recycled into the base film.
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Tribble James D.
Wilhoit Darrel Loel
Baker Aileen J.
Jenkens & Gilchrist P.C.
Jordan Charles T.
Tredegar Corporation
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