Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-06-12
2004-03-16
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S515000, C428S516000, C428S520000
Reexamination Certificate
active
06706389
ABSTRACT:
BACKGROUND INFORMATION
1. Field of the Invention
The film described herein is useful in the packaging of a variety products, particularly perishable food products such as whole and cut produce, and exhibits excellent resistance to fogging.
2. Background of the Invention
Each year, thermoplastic packaging materials are used to enclose and protect an increasing number of products. Many of those products exhibit properties that call for packaging materials with special properties. Accordingly, numerous packaging materials are developed and introduced each year.
Because of their flexibility, strength, low weight, etc., thermoplastic films and packages made therefrom continue to capture an ever-increasing percentage of the packaging market. Nevertheless, because of the varied nature of the products being packaged, films with new and improved properties continually are in demand.
Products that contain moisture have presented a long-standing problem. Once such a product is packaged, water evaporating therefrom tends to condense on the inner surface of the package. This is particularly true where the packaged product is stored at subambient temperatures as is the case with, for example, produce.
As one might expect, manufacturers and retailers insist that products be displayed in a manner that is aesthetically pleasing and provides the customer with a clear view of the product. However, condensation reduces the ability of potential customers to see the product. Thus, a need for films and packages that resist this condensation (sometimes called “fogging”) has developed. Over the past several years, numerous solutions have been proposed. However, many such solutions have caused other problems.
The surfactants and wetting agents (often referred to as antifogging agents) commonly used to reduce the amount of condensation exhibited in thermoplastic films and packages tend to interfere with the ability of ink to adhere to the polymer(s) of the film or package. Because a significant portion of packages are printed to indicate source, contents, etc., particularly those designed for retail sale, good ink adhesion is a prerequisite.
Although antifoggng agents normally are applied to the surface of the film or package nearest to the food product they tend to migrate into the interior of the film or package. Where this migration continues to the outer surface of the film or package, the antifogging agent (which normally has a low surface tension) can interfere with adhesion between the ink and the film. This lowered adhesion can result in increased difficulty in printing the film and/or smearing of the printed ink onto other articles or consumers.
To exacerbate this film-to-ink adhesion problem, additives called slip agents often are used in film manufacturing processes. Slip agents are internal lubricants that exude to the surface of a film during and immediately after its manufacture so as to provide a thin coating that reduces the coefficient of friction (COF) that the film would otherwise possess. In addition to those slip agents used in the manufacture of the polymeric raw materials, film producers often add even more slip agents (such as fatty amides) during manufacture of the film itself. Although a film with a lower COF can be processed more easily, that same film is more difficult to print and, when printed, has lower film-to-ink adhesion than a similar film containing no slip agent.
Thus, a need remains for a film that has (1) good adhesion to ink, (2) a sufficiently low COF to be manufactured and processed easily, and (3) adequate resistance to fogging. Provision of such a film is highly desirable.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a packaging film that includes a heat sealable layer coated with one or more antifogging agents disposed in a binder, an antiblocking agent, and no more than about 800 parts per million (ppm) slip agent. The heat sealable layer includes a polymer that includes mer units derived from ethylene while the binder includes a polymer that includes mer units derived from an ester of (meth)acrylic acid and/or vinyl acetate monomers. The antiblocking agent can be in any layer of the film where it provides the desired effect. The film preferably includes slip agent in an amount of no more than, in ascending order of preference, about 750 ppm, about 700 ppm, about 650 ppm, about 600 ppm, and about 550 ppm. In certain situations, the amount of slip agent present can be as low as about 500 ppm, about 400 ppm, about 300 ppm, about 200 ppm, about 100 ppm, about 50 ppm, even about 25 ppm. In one embodiment, the film of the present invention can be essentially free of slip agent.
The film of the present invention can be a single layer film, i.e., the heat sealable layer is the only layer. Alternatively, the film of the present invention can be a multilayer film and, for certain end use applications, a film with more than one layer can be preferred. Layers that include a polymer with mer units derived from propylene and/or styrene can provide films with performance characteristics that differ from those of a single layer film.
In other aspects, the present invention provides a package made from the above-described film as well as a method of using the above-described film that includes introducing a product into a pouch made from the film and then sealing the pouch so as to form a package.
Films such as those just described exhibit a desirable COF and resist fogging, even when used to package moist products. Because the film of the present invention includes less slip agent than normally is present in films used for similar applications, it also can exhibit excellent adhesion any ink printed thereon.
The film of the present invention can be used to package a variety of products. It can be especially useful in packaging food products, particularly moist food products such as, for example, many types of produce. The film of the present invention can be especially useful in the packaging of cut lettuce, salad mixes, cut fruit, celery, and the like.
The following definitions apply hereinthroughout unless a contrary intention is expressly indicated:
“(meth)acrylic acid” includes both acrylic acid and/or methacrylic acid;
“polymer” means the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, tetrapolymers, etc.;
“copolymer” means a polymer formed by the polymerization reaction of at two different monomers and is inclusive of random copolymers, block copolymers, graft copolymers, etc.;
“interpolymer” means a polymer formed by the polymerization reaction of two or more different monomers and is inclusive of copolymers, terpolymers, tetrapolymers, etc.;
“ionomer” means a metal salt of an ethylene/(meth)acrylic acid copolymer,
“differing”, when used to describe the relative nature of two or more polymers, means differences in any one or more chemical or physical attributes including, but not limited to, identity and/or relative amounts of monomers, relative distribution of mer units, molecular weight, molecular weight distribution, melt flow, and density;
“package” means one or more packaging materials (e.g., a film) configured around a product;
“film” is used in its most generic sense to include all plastic web materials, although those having a thickness of 0.25 mm or less are most preferred;
“inner layer” means a layer of a multilayer film having both of its principal surfaces directly adhered to other layers of the film,
“outer layer” means a layer of a film having one (or, in the case of monolayer films, none) its principal surfaces directly adhered to another layer of the film;
“inside layer” means an outer layer of a multilayer film which is, relative to the other layers of the film, closest to the product being packaged;
“outside layer” means that layer of a multilayer film which is, relative to the other layers of the film, farthest from the product being packaged,
“between”, when used in conjunction with a subject layer and two or more object layers, means both direct adherence of the subject layer t
Bates Monty
Davis Mark
Luthra Narender P.
Pressley Woodrow W.
Cryovac Inc.
Nolan Sandra M.
Ruble Daniel B.
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