Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-06-04
2001-04-17
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S518000, C428S035400, C428S036600, C428S036700
Reexamination Certificate
active
06218024
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multilayer plastic films suitable for packaging food products such as cheese, processed meat and raw meat.
BACKGROUND OF THE INVENTION
There is a need in the food packaging industry for packing film with improved structural integrity and which can be made into bags. Food products such as cheese, processed meat and raw meat are preferably packed by using film with high barrier resistance to moisture and oxygen. A typical way of protecting such food products from moisture and oxygen is by shrink packaging in high barrier film. A useful film with good moisture and oxygen barrier properties for this purposes comprises a copolymer of vinylidene chloride with a monomer such as methyl acrylate, vinyl chloride or other unsaturated monomer or hydrolysed ethylene vinyl acetate (EVOH) or any other barrier polymer which can be fabricated in the form of film and has good oxygen and moisture barrier properties.
It is known to provide a multilayer shrink film with the following structure, namely a first outer layer, a bonding layer, a barrier layer, a further bonding layer and a further outer layer to achieve the desired properties. A known multilayer film of this kind having good moisture and oxygen barrier properties for use in packaging food products has a core layer of a barrier polymer such as a copolymer of vinylidene chloride or hydrolysed ethylene vinyl acetate (EVOH) or other barrier polymer. A multilayer plastic film from which bags are to be manufactured must meet a number of criteria, such as being heat sealable, delamination resistant, and have good moisture and oxygen barrier properties. For heat shrinkable uses, the film must also be capable of shrinking from about 30 to about 50 percent at 90 degrees C. in both longitudinal and transverse directions. The film should also be capable of withstanding physical abuse during transportation.
A significant property of EVOH and polyvinylidene chloride (PVDC) based films is their barrier resistance to oxygen and other gasses. Compared to PVDC based films, EVOH based films have better barrier properties at low relative humidity, i.e. 30 to 40 percent, than commonly used multilayer films.
U.S. Pat. No. 4,469,742 (Oberle et al) describes a multilayer cook-in film with six layers. The middle barrier layer is of EVOH, selected because of its superior oxygen barrier properties compared to PVDC.
However, EVOH is hydrophillic, and therefore EVOH based films are moisture sensitive. As the moisture content of an EVOH based film increases, the permeation rate increases, i.e. barrier properties decrease, which is in contrast to PVDC based films because the permeability of PVDC does not vary with humidity, i.e. PVDC is not moisture sensitive. Accordingly therefore, EVOH based films are often produced in a multilayer structure or buried under moisture barrier materials such as polyolefins or sometimes with polyamides in order to protect an EVOH layer from moisture.
If a material with a much higher barrier layer for moisture compared to polyolefins or polyamide is used to protect an EVOH layer in a multilayer film from both the environmental and product sides thereof, the barrier properties and consequently the shelf life of the product can be increased significantly.
However, U.S. Pat. No. 4,161,562 (Yoshikawa et al) teaches that, in multilayer barrier films, a barrier layer of crystalline polymers such PVDC or EVOH has a tendency to crack if the thickness exceeds 15 microns, due to low temperature brittleness of these polymers.
It is therefore an object of the present invention to provide a multilayer plastic film which is at least substantially free from the problems referred to above.
SUMMARY OF THE INVENTION
According to the invention, a multilayer plastic film has a series of component layers and bonding layers bonding said component layers together, the component layers including an inner hydrolysed ethylene vinyl acetate copolymer (EVOH) layer, an adjacent polyvinylidene chloride (PVDC) layer, and outer layers comprising a polyolefin homopolymer, copolymer or ionomer.
The inner EVOH layer may have a thickness in the range of from about 2 to about 20 microns, preferably from about 5 to about 15 microns.
The adjacent PVDC layer may comprise from about 85 to about 98 percent by weight of vinylidene chloride, and may be selected from the group consisting of vinylidene chloride—methyl acrylate copolymer, vinylidene chloride-vinyl chloride copolymer and a copolymer of vinylidene chloride with an unsaturated monomer. The adjacent PVDC layer may have a thickness in the range of from about 2 to about 30 microns preferably from about 5 to about 15 microns.
A first outer layer may have a thickness in the range of from about 10 to about 40 microns, preferably from about 15 to about 25 microns. The first outer layer may comprise at least one material selected from the group consisting of low density polyethylene, linear low density polyethylene, metallocene-based linear low density polyethylene, polypropylene, copolymers of polypropylene, high-density polyethylene, ionomers, and mixtures thereof.
A second outer layer may have a thickness in the range of from about 10 to about 40 microns preferably from about 15 to about 25 microns.
The second outer layer may comprise at least one material selected from the group consisting of low density polyethylene, linear low density polyethylene, metallocene-based linear low density polyethylene, polypropylene, copolymers of polypropylene, high-density polyethylene, ionomers, and mixtures thereof.
Each bonding layer may have a thickness in the range of from about 1 to about 10 microns, and may be selected from the group consisting of ethylene vinyl acetate, ethylene methyl acrylate, and ethylene acrylic acid copolymer and ethylene vinyl acetate—maleic anhydride copolymer.
The thickness of the film may be in the range of from about 25 to about 300 microns, preferably from about 50 to about 100 microns.
An adjacent PVDC layer may be provided on each side of the EVOH layer.
Thus, in a multilayer plastic film in accordance with the invention, the EVOH is “locked up” in an adjacent PVDC layer. PVDC has better barrier properties not only for moisture and oxygen but also for aroma compared to polyolefins and polyamides which have conventionally been us ed to protect an EVOH layer in known multilayer plastic films.
A multilayer plastic film in accordance with the invention can be produced by methods such as blown film, cast film, lamination, extrusion coating and extrusion coating lamination. A multilayer plastic film in accordance with the invention can also be used to produce bottles and other containers by blow molding.
The present invention also provides a method of producing a multilayer plastic film including extruding multilayer plastic material in tubular bubble form to provide a multilayer plastic film having a series of component layers and bonding layers bonding said component layers together, said component layers including an inner hydrolysed ethylene vinyl acetate copolymer (EVOH) layer, an adjacent polyvinylidene chloride (PVDC) layer, and outer layers comprising a polyolefin homopolymer, copolymer or ionomer, and cooling and collapsing the tubular film to sheet form.
The above method may also include subsequently returning the collapsed film to a second tubular bubble form, stretching the second tubular bubble radially and longitudinally to produce a biaxially oriented heat shrinkable film, and collapsing the second tubular bubble to a further sheet form. The further sheet form may be partially cross-linked by exposure to high energy electrical radiation to improve the sealing properties of a sealing layer.
The present invention further provides a method of producing a multilayer plastic film including extruding multilayer plastic film in cast form to provide a multilayer plastic film having a series of component layers and bonding layers bonding said component layers together, said component layers including an inner hydrolysed ethylene vinylacetate copolymer
Planeta Mirek
Tamber Harinder
Delbridge Robert F.
Macro Engineering & Technology Inc.
Zirker Daniel
LandOfFree
Multilayer plastic film does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multilayer plastic film, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multilayer plastic film will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2518020