Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1998-05-04
2002-12-31
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S034100, C428S034300, C428S034800, C428S035200, C428S035700, C428S036910, C428S200000, C428S474700, C428S474900, C383S109000, C383S113000, C426S127000
Reexamination Certificate
active
06500559
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermoplastic film that can be used to make packages for a wide variety of food and non-food products.
BACKGROUND OF THE INVENTION
Vertical form/fill/seal (VFFS) packaging systems have proven to be very useful in packaging a wide variety of flowable products. An example of such systems is the Onpack™ flowable food packaging system sold by W. R. Grace & Co.-Conn. through its Grace Packaging group. The VFFS process is known to those of skill in the art, and described for example in U.S. Pat. No. 4,589,247 (Tsuruta et al), incorporated herein by reference. A flowable product is introduced through a central, vertical fill tube to a formed tubular film having been sealed transversely at its lower end, and longitudinally. The pouch is then completed by sealing the upper end of the tubular segment, and severing the pouch from the tubular film above it.
The choice of packaging materials is important, and should be matched to the intended end use of the pouch.
Several properties are often desirable in such pouches.
Dimensional stability is of great importance in VFFS systems. In such systems, the equipment fills a pouch to a certain level. If the film stretches, too much product is put into the pouch. This phenomenon makes it difficult to standardize pouch dimensions, which leads for example to difficulty in packing off of pouches in shipping boxes of pre-determined size.
Sometimes a pouch material is used to package a product, such as an aqueous liquid food product, at an elevated temperature of 170 to 210° F. This is known as a hot fill process. Sometimes the pouch, after filling, is exposed to retort conditions. In either case, the dimensional stability of the package is severely tested, and the possibility of package distortion increases.
The package material is preferably stiff (i.e. has a high modulus), especially at high temperatures. This is often necessary because the film tracks more easily on a packaging machine. Also, a hot fin seal can stretch undesirably; therefore, to preserve seal integrity, the ability to package at high speeds is limited by the degree to which hot seals will elongate or stretch. If a heavy load, e.g. 5 to 20 pounds of shredded cheese, is thrust into a pouch with transverse seals just formed, these seals are still hot and the pouch, or the seal area of the pouch, can deform. More uniform package length is related to more uniform package weight, which is important to the food processor in order to provide packages with consistent weights.
Good tensile strength is necessary in films used for such applications. Where flowable foods are packaged, as in many VFFS applications, the hydrostatic pressure of many oil and water based foods requires a tough, impact and abuse resistant packaging material that will maintain its structural integrity during the packaging process, and subsequent distribution and storage.
For hot fill and retort applications, heat resistance is essential to avoid package distortion or degradation of the film itself, or of the transverse and longitudinal seals associated with the VFFS process.
Oxygen barrier properties are also essential in end-uses where the product is susceptible to oxidative degradation.
Depending on the packaging process, form of the package, and nature of the product, physical properties such as barrier to ultraviolet light, surface printability, clarity, flatness, thermoformability, and low tear initiation and propagation (for easy-open packages) may become significant.
The inventors have found that a combination of many of these properties is possible through the use of at least one layer consisting essentially of amorphous polyamide in a multilayer thermoplastic film.
SUMMARY OF THE INVENTION
In a first aspect, a multilayer film comprises a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a second aspect, a multilayer film comprises a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a third aspect, a method of packaging a food product comprises providing a rollstock film, the film comprising a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer; forming the film into a tube in a vertical/form/fill/seal process; filling the tube with a food product; and closing the tube to form a sealed pouch containing the food product.
In a fourth aspect, a package comprises a flowable food product; and a pouch containing the food product, the pouch made from a film comprising a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a fifth aspect, a method of packaging a food product comprises providing a rollstock film, the film comprising a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer; forming the film into a tube in a vertical/form/fill/seal process; filling the tube with a food product; and closing the tube to form a sealed pouch containing the food product.
In a sixth aspect, a package comprises a flowable food product; and a pouch containing the food product, the pouch made from a film comprising a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicryst
Hofmeister Frank M.
Kennedy Thomas D.
Musco Carlo E.
Satterwhite Paul J.
Sharps G. Vince
Cryovac Inc.
Miggins Michael C.
Pyon Harold
Quatt Mark B.
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