Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Patent
1990-11-09
1992-02-18
Buffalow, Edith L.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
428 358, 428349, 428483, 428517, 428521, B32B 1900
Patent
active
050893203
DESCRIPTION:
BRIEF SUMMARY
Flexible packaging materials comprising layers of thermoplastic polymers are used to package a variety of products, particularly food. For example, cereals, potato chips and other snack foods are packaged in such materials. The packages are formed in packaging machines in which the material is sealed to itself by heated sealing jaws. However, when a package is opened by pulling apart one of the heat seals, normally at the top of the package, the heat seal is not reasealable without the application of heat as well as pressure. This invention provides a flexible packaging material that is resealable by the application of pressure alone at the area of a seal formed by a packaging machine.
The material of this invention comprises a substrate layer, a layer of tacky adhesive adjacent the substrate layer, and a skin layer covering the layer of tacky adhesive. When a seal formed by sealing the packaging material to itself is pulled apart, the tacky adhesive is exposed at the surface of the seal area, thereby permitting the material to be resealed to itself at the area of the seal by the application of manual pressure alone to reclose the package.
The substrate layer may comprise any material that is conventionally used for flexible packaging applications, such as plastic film, metal foil, paper or a combination thereof. Plastic film substrates may be single layer or multilayer and may be oriented or unoriented. The film can be polyamide, polyester, or olefin polymer or copolymer. Suitable substrates include poly(ethylene terephthalate) film, paper, oriented polypropylene film, and nonwoven materials.
As used herein, the term "tacky adhesive" refers to an adhesive that, in the practice of this invention, forms a resealable bond by the application of manual pressure alone at room temperature. The reseal strength is preferably between about 0.5 and 4 pounds per inch (0.1 and 0.7 kg/cm), more preferably between about one and two pounds per inch (0.18 and 0.36 kg/cm). Such adhesives may include cold seals and tacky lacquers. Cold seals are formed from aqueous latex emulsions of an elastomer. The tacky adhesive is preferably a pressure sensitive adhesive, which is a blend of an elastomer and a tackifier. The pressure sensitive adhesive preferably comprises from about 40 to 80 percent of a thermoplastic elastomer, 20 to 60 percent of a tackifier, and up to about 15 percent of other components, such as a fragrance and conventional additives, such as an antioxidant and an oil.
When the adhesive layer in the packaging material contains a fragrance, the fragrance is not appreciably noticeable until the material is formed into a package and the package is opened because the fragrance is essentially encapsulated in the packaging material. When the package is opened, the fragrance is liberated, thereby enhancing the appeal of the product in the package. Best results are obtained using an oil-based fragrance that is absorbed by the elastomer component of the adhesive.
Particularly suitable elastomers include styrene copolymers, such as styrene-butadiene copolymers sold under the trademark Stereon by Firestone and styrene-isoprene copolymers sold under the trademark Kraton by Shell Chemical Company. Other suitable elastomers include polyurethane and ethylene-vinyl acetate copolymers having a vinyl acetate content of about 18 percent or higher.
The tackifier may be any tackifier conventionally used with elastomers to form pressure sensitive adhesives. Suitable tackifiers include terpene resins, such as resins sold under the trademark Zonatac by Arizona Chemical Company, and petroleum hydrocarbon resins, such as resins sold under the trademark Escorez by Exxon Chemical Company.
The pressure sensitive adhesive is preferably coextrudable. The coextrudability of the pressure sensitive adhesive may be enhanced by utilizing a thermoplastic elastomer having a low melt index and by increasing the proportion of the elastomer in the adhesive. The melt index of the adhesive is preferably less than 30, more preferably less than 10, for coext
REFERENCES:
patent: 3655503 (1972-04-01), Stanley
patent: 4370369 (1983-01-01), Bonis
patent: 4438850 (1984-03-01), Kahn
patent: 4543139 (1985-09-01), Freedman
patent: 4615926 (1986-10-01), Hsu et al.
patent: 4673601 (1987-06-01), Lamping et al.
Bower William B.
Straus Steven J.
Yanidis Apostol
Zuscik Edward J.
Buffalow Edith L.
James River II Inc.
Teigland Stanley M.
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