This invention relates primarily to adhesive-based package seals and secondarily to a method of manufacturing such seals. More particularly, the present invention relates to decreasing the adhesive bond strength of adhesive-based peelable package seals to enable the adhesive to peel uniformly away from one package surface.
Contemporary food product component packages have a variety of different package seals which seal the food product component in one way or another in the package. Some package seals are recloseable and allow repeated access to the package contents without affecting the integrity of the package. Other seals are tamper-evident which indicate whether package has been opened prior to purchase of the package. Yet other seals are hermetic and provide an air-tight and liquid-tight barrier between the opposing package panels or sheets and further extend around a substantial portion of the perimeter of the package contents.
In some circumstances, the hermetic seal is peelable such that it is sufficiently strong to keep the package intact and the contents thereof in place, but is desirably weak to permit the user to easily gain access to the contents without the need for scissors or the like. These peelable seals can be formed by either heat sealing or adhesive sealing the package panels together. While some common packaging materials such as polyethylene, polybutene and polypropylene films are easily heat sealable, other packaging materials, such as polyvinyl chloride, polyamide, polyester and polyacrylonitrile films are not heat sealable. In order to obtain a peelable seal on these packaging films, either the composition of the film must be changed to include a heat sealable material or an adhesive must be used. Where a heat sealable component is added to the packaging film mixture, the cost and complexity of the resulting package may be increased. When adhesive sealing is used to establish a peelable, hermetic seal, a hot melt adhesive is typically applied to one of the two opposing package film sheets. The opposing package film sheet is subsequently attached to the first package film sheet. However, in this application, the adhesive does not separate completely or uniformly from either package film panel, but adheres to different portions of both opposing panels. When this occurs, the adhesive exhibits "stringing", that is, where segments of the adhesive remain adhered to both package panels and span the gap between them when the package is initially opened. This occurrence is known as "stringing". Further opening of the package results in the strands of adhesive rupturing and remnants of the adhesive remaining on both package panels. This "stringing" is undesirable from a visual perspective and sometimes leads to an inconsistent amount of digital force required to open the seal and pull the package panels apart.
The present invention therefore concerns itself with the establishment of peelable, adhesive-based hermetic seals between two sheets of packaging material which are not heat sealable in nature, such as polyester, polyvinyl chloride polyamide and polyacrylonitrile films. Specifically, it is directed to producing a peelable seal on polyacrylonitrile films, such as Barex, (an acrylonitrile methyl acrylate copolymer) which has been surface treated to substantially reduce the strength of the bond between the treated film and the adhesive such that the adhesive completely and uniformly separates from the treated film and remains on the untreated film and no "stringing" results.
Such a seal is accomplished by providing a sheet of polyacrylonitrile film, such as Barex, and surface treating either a portion or all of that film sheet with a corona discharge to increase the surface tension of the film. A hot melt adhesive may be applied to the treated film and a package is subsequently formed by combining the treated film and a similar, but untreated, Barex packaging film. The corona discharge treatment increases the surface tension of the film, yet unexpectedly decreases the strength of the adhesive bond such that when the package is opened the adhesive is completely and uniformly pulled away from the treated surface visually without any undesirable "stringing" resulting.
Accordingly, it is an object of the present invention to provide a food product package having an adhesive-based hermetic peelable seal in which the peelable seal area opens uniformly without the adhesive exhibiting "stringing".
It is another object of the present invention to provide a method for manufacturing a package from two opposing packaging film sheets and having a peelable seal which permits access to the contents of the package in which one of the package film sheet is treated by a corona discharge treatment prior to adhesion to the other opposing film sheet, the treated film sheet being subsequently adhered by an adhesive to the other film sheet such that the bond strength of the peelable seal at the sealed interface of the two film sheets requires a decreased opening force so that the adhesive easily and uniformly releases from the treated film when the package is opened.
It is a further object of the present invention to provide a food product package formed from a single sheet of polyacrylonitrile film which is separated into two opposing package portions by an integral hinge portion, one of the opposing package portions being subjected to a corona discharge treatment, a hot melt adhesive being applied to the treated package portion and the two opposing package portions being folded upon each other around the hinge member and adhered to each other, the adhesive forming, a peelable seal area having a decreased adhesive strength and which adhesive uniformly separates away from the treated package portion.
It is yet a further object of the present invention to provide a food product package composed of two opposing package films sealed together at least one peel seal area, one of the packaging films being treated by a corona discharge treatment prior to adhesions together, wherein the opening force required to separate opposing package panels at the seal interface thereof is substantially reduced compared to a similar peel seal formed between two untreated packaging films.
These and other objects of the present invention will become more readily apparent from a reading of the following detailed description taken in conjunction with the accompany drawings wherein like reference numerals refer to like parts.