Patent Grant
7582341
1. Field of the Invention
The present invention relates to multilayer films, specifically multilayer films that also can be used as packaging films. More specifically, the present invention is directed to multilayer films having relatively low haze and high gloss properties and associated methods of forming and using same.
2. Description of Related Art
Multilayered films are used in many industries to package all types of consumer goods, such as food, bottles, canned items, cleaning supplies, compact discs, and many more items. Numerous attempts have been made to manufacture packaging films that provide sufficient clarity and strength to allow consumers to clearly see the product through the packaging and also protect the product from the atmosphere or protect the atmosphere from the product.
Films can be used to wrap products directly or can be used to form bags that contain consumer products. Previous attempts have been made to use films that can be used to package consumer products that need transparent packaging, such as produce. Some of these films have been manufactured with an outer heat-resistant layer of elastomer, such as a styrene-butadiene copolymer, with an outer sealant layer of a metallocene-catalyzed ethylene/alpha-olefin copolymer. Films with these types of materials have generally been found to curl, making them very difficult to process through traditional film manufacturing machinery.
Another example film with an elastomer on an outer layer with polyolefins disposed on a second and third layer can be found in U.S. Pat. No. 5,523,136 by Fischer et al. titled “Packaging Film, Packages, and Methods of Using Them” (hereinafter “Fischer '136 Patent”). The Fischer '136 Patent describes a multilayer film with an elastomer on a first outermost layer with an ethylene layer as the central layer and as another outermost layer. Because the films described in the Fischer '136 Patent are not symmetrical in structure, the films also tend to curl, which makes them very difficult to machine.
To combat problems with curling, more structurally symmetrical films have been developed. An example of such a structurally symmetrical film can be found in U.S. Pat. No. 6,294,210 by Kuo titled “Oxygen Permeable Multilayer Film” (hereinafter “Kuo '210 Patent”). The Kuo '210 Patent describes a film that has a first layer of a homogeneous ethylene/α-olefin copolymer, a second layer of a polyolefin, and a third layer of the homogeneous ethylene/α-olefin copolymer that can be used to package produce and the like. Additional layers can be added as well. Because a thicker film must be used in some applications to provide the needed film strength, films made primarily of polyolefin tend to be hazy when they are produced with thicker film gauges.
To attempt to make stronger films, others have attempted to make packaging films with varying chemical compounds that are known for providing strength. An example packaging film that uses a chemical compound that is known to increase strength can be found in U.S. Pat. No. 6,060,136 by Patrick et al. titled “High Modulus Oxygen-Permeable Multilayer Film” (hereinafter “Patrick '136 Patent”). The Patrick '136 Patent describes a structurally sysmetrical multilayer film including a first layer of a homogeneous ethylene/alpha-olefin copolymer, a second layer of a thermoplastic elastomer, and a third layer of the homogeneous ethylene/alpha-olefin copolymer. Additional layers can be added. Thermoplastic elastomers are known to increase strength in films. The film of the Patrick '136 Patent is used for packaging food and requires a high oxygen transmission rate to ensure that the produce contained within the film receives enough oxygen to remain fresh. The core layer of the thermoplastic elastomer of a multilayer film is generally the center layer of the film, which is also generally the thickest layer. Because the thermoplastic elastomer material used in the center layer is relatively expensive, the cost of producing a film in accordance with the Patrick '136 Patent can be expensive. Films made with thermoplastic elastomers also lack optical properties that may be important in other applications.
A need exists for a packaging film that is economical to produce, and that can be manufactured on existing equipment without having to modify the equipment and, for example, without the need to use expensive crosslinking processes. There also is a continued need for a packaging film that is relatively thin, has good optical properties to allow a product to be seen easily through the packaging film, and has good mechanical properties to allow the packaging film to withstand outward forces being applied to the packaging without puncturing easily.
In view of the foregoing, embodiments of the present invention advantageously provide a packaging film that is relatively thin and has enhanced optical and mechanical properties. The enhanced optical and mechanical properties allow a product when substantially surrounded by the film to be seen clearly through the packaging film and also allow the packaging film to resist from being punctured easily when an outside force is applied to the packaging film. Embodiments of the present invention also advantageously provide a packaging film that is relatively inexpensive to produce and can be produced using known film manufacturing equipment.
More specifically, an embodiment of the present invention provides a combination product and shrink wrap packaging film that preferably includes a product that is substantially surrounded by the packaging film. The packaging film preferably contacts and substantially surrounds the product so that when the packaging film is heated to shrink the packaging film around the product, the packaging film encases the product so that the product is securely restrained by the packaging film. This type of film is commonly referred to as shrink-wrap film. The packaging film preferably includes a first outermost layer of elastomer, a second layer of polyolefin, and a third outermost layer of elastomer. The second layer of polyolefin preferably overlies and abuttingly contacts the first outermost layer of elastomer. The third outermost layer of elastomer preferably overlies and abuttingly contacts the second layer of the polyolefin so that the second layer of polyolefin is preferably positioned between the first and the third outermost layers of elastomer. The packaging film advantageously has enhanced optical and mechanical properties for a selected overall packaging film gauge thickness that allow the product to be seen more clearly through the packaging film and that increase modulus for the packaging film so that the packaging film is readily usable with packaging machinery, i.e., machinable, at relatively high speeds and provides packaging film having preselected optical and mechanical properties related to appearance, strength, and shrink. Conventional packaging machinery can be used, as understood by those of ordinary skill in the art.
Embodiments of the present invention also advantageously provide a packaging film that has enhanced optical and mechanical properties. The packaging film preferably includes a first layer of a sheet of elastomer, a second layer of polyolefin, and a third layer of a sheet of elastomer. The second layer of polyolefin preferably has a first surface that abuttingly contacts a first surface of the first layer of the sheet of elastomer. The third layer of the sheet of elastomer preferably abuttingly contacts a second surface of the second layer of polyolefin. The second layer of polyolefin is preferably positioned between the first and third layers of the sheets of elastomer.
The packaging film advantageously has enhanced optical properties and enhanced mechanical properties for a selected overall packaging film gauge thickness so that a product surrounded by the packaging film can be seen more clearly through the packaging film without the necessity of removing the packaging film and the packaging film is not easily punctured when an outside force is applied thereto. The packaging film of the present invention is advantageously capable of being readily usable with packaging machinery, i.e., machinable, at relatively high speeds and provides packaging film having preselected optical and mechanical properties related to appearance, strength, and shrink properties. For example, the packaging film of the present invention can have a 45° gloss in a range of about 70% to about 110%.
Methods of forming the packaging film with enhanced optical and mechanical properties are also advantageously provided. In one embodiment, the method of forming a packaging film having enhanced optical and mechanical properties advantageously includes positioning a first extruded layer of elastomer, a second layer of polyolefin and a third extruded layer of elastomer so that the first and third extruded layers of elastomer are the outermost layers of the packaging film. The packaging film can be produced by a blown film process, as understood by those of ordinary skill in the art of packaging films. As a step of the blown film process, the layered laminar structure is stretched and air is supplied to the layered laminar structure to produce a bubble. The bubble is then collapsed, typically by rollers, to form the packaging film. The packaging film preferably has a second layer of polyolefin positioned between and abuttingly in contact with first and third outermost layers of elastomer. The packaging film advantageously has enhanced optical and mechanical properties for a selected overall packaging film gauge thickness that allow a product surrounded by the packaging film to be seen more clearly through the packaging film and that increase modulus for the packaging film so that the packaging is readily usable with packaging machinery, i.e., machinable, at relatively high speeds and provides packaging film having preselected optical and mechanical properties for the packaging film related to appearance, strength, and shrink properties.
Another embodiment of a method of forming a packaging film having enhanced optical and mechanical properties so that a product surrounded by the packaging film can be seen more clearly through the packaging film and the packaging film is not punctured easily when an outside force is applied thereto. In this embodiment, the method preferably includes the step of positioning a first extruded layer of elastomer, a second extruded layer of polyolefin, and a third extruded layer of elastomer to form the packaging film. The packaging film is preferably formed by using a cast film process, as understood by those of ordinary skill in the art of packaging film production. As a step of the cast film process, the layered structure of the layers of extruded materials is rolled to form a packaging film. In the packaging film, the second layer of polyolefin is preferably positioned between and abuttingly contacts the first and the third layers of elastomer. The packaging film advantageously has enhanced optical and mechanical properties for a selected overall packaging film gauge thickness.
The enhanced optical and mechanical properties advantageously allow a product surrounded by the packaging film to be seen more clearly through the packaging film. The enhanced properties also increase modulus in the packaging film so that the packaging film is readily usable with packaging machinery, i.e., machinable, at relatively high speeds and provides packaging film having preselected optical and mechanical properties related to appearance, strength, and shrink properties.
The packaging film of the present invention has very low haze and high gloss properties that allow indicia on a product to be seen easily through the packaging film without having to remove the packaging film from the product. The packaging film also has high gloss values that make the combination product and film packaging more aesthetically appealing to consumers.
So that the manner in which the features and benefits of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope since it may include other effective embodiments as well.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Prime notation, if used, indicates similar elements in alternative embodiments.
As illustrated in
In embodiments of the present invention, the shrink-wrap packaging film 20 advantageously provides enhanced optical and mechanical properties for a selected overall packaging film gauge thickness. The enhanced optical and mechanical properties allow the product P to be seen more clearly through the packaging film 20 and increase modulus for the packaging film 20 that allow the packaging film 20 to be readily usable through packaging machinery, i.e., machinable, at relatively high speeds and provides packaging film having preselected optical and mechanical properties related to appearance, strength, and shrink properties. Conventional packaging machinery can be used, as understood by those of ordinary skill in the art of packaging film manufacturing.
In all embodiments of the present invention, the packaging film 20 is sufficiently durable to be useful as a packaging film 20. The packaging film 20 can withstand forces being applied thereto, such as puncture sources, chime cuts, i.e. from products rubbing together, users lifting the combination product P and packaging film 20 by the packaging film 20, and the like.
In all embodiments of the present invention, the elastomer can include a styrene butadiene copolymer. Suitable butadiene styrene copolymers for use in the present invention include those commercially identified as the K-Resin® Series from Chevron Phillips Chemical Company LP of 10001 Six Pines Drive, The Woodlands, Tex. 77380. The butadiene styrene copolymer known commercially as DK11 in the K-Resin® Series performed exceptionally well in initial tests. Another exemplary example butadiene styrene copolymer is known commercially as DK13, also in the K-Resin® Series. Other suitable elastomers can include polymethylpentene, polybutylene, polyisobutylene, ethylene propylene diene monomer terpolymer, styrene butadiene styrene copolymer, styrene ethylene butylene copolymer, styrene isoprene styrene copolymer, polybutene-1, isobutylene rubber, methyl acrylate butadiene styrene copolymer, acrylonitrile butadiene styrene copolymer, acrylonitrile alkylacrylate butadiene styrene copolymer, methyl methacrylate alkyl acrylate styrene copolymer, methyl methacrylate alkyl acrylate butadiene styrene copolymer, and the like. Elastomers having good optical characteristics, such as high clarity, are preferred. Other suitable elastomer materials will be known to those of ordinary skill in the art and are to be considered within the scope of the present invention.
In all embodiments of the present invention, the polyolefin can include such polyolefins as, for example, non-linear ethylene ethyl acetate copolymers, non-linear ethylene homopolymers (low-density polyethylene), and ethylene vinyl acetate copolymers, which can have densities, for example, greater than 0.920 grams per cubic centimeter. Beneficially, the non-linear ethylene ethyl acetate copolymers, non-linear ethylene homopolymers, and ethylene vinyl acetate copolymers can offer economic advantages to the manufacturer due to relatively low raw material costs and due to their suitability for shrink bundling applications without having to use an expensive cross-linking process. Another effective polyolefin is a linear low density polyolefin. Other polyolefins can include polyethylene homopolymer, polypropylene homopolymer, ethylene/α-olefin copolymer, propylene/ethylene copolymer, or ethylene/unsaturated ester copolymer. Other suitable polyolefin materials will be known to those of ordinary skill in the art and are to be considered within the scope of the present invention.
Although other thicknesses of film can be used as understood by those skilled in the art, the overall packaging film gauge thickness of packaging film 20 according to embodiments of the present invention can be preferably in a range of about 0.5 to about 3 mil, and more preferably in a range of between 0.6 to 1.25 mils, so that the packaging film 20 is more economical to manufacture without a reduction in clarity of the packaging film 20 and to provide optimal coverage performance over cost while maintaining adequate strength for a substantial portion of the applicable uses.
In an embodiment of the film 20 of the present invention, as perhaps best shown in
In embodiments of the film 20 of the present invention, the film 20 preferably has a haze, which is one of the enhanced optical properties, in a range of about 1% to about 10%, as shown in
In all embodiments of the present invention, packaging film 20 can include indicia I on the packaging film 20. The indicia I can make the combination product P and shrink-wrap packaging film 20 more aesthetically pleasing to consumers.
As shown in
Another mechanical property that is measured for embodiments of packaging films 20 of the present invention is the dart impact strength. The dart impact strength in all embodiments of the present invention is preferably in a range of about 300 grams to about 1000 grams so that the packaging film 20 will not puncture easily when an outside force is applied thereto, as shown in
An embodiment of the present invention also advantageously provides a packaging film 20 having enhanced optical and mechanical properties. The enhanced optical and mechanical properties enable a product P surrounded by packaging film 20 to be seen more clearly through packaging film 20, without the need to remove packaging film 20. The enhanced properties also prevent the packaging film 20 from being punctured easily when an outside force is applied thereto. Packaging film 20 preferably includes a first layer of a sheet of elastomer 21, a second layer of polyolefin 23, and a third layer of a sheet of elastomer 25. The second sheet of polyolefin 23 advantageously has a first surface abuttingly contacting a first surface of the first layer of the sheet of elastomer 21. The third layer of the sheet of elastomer 25 abuttingly contacts a second surface of the second layer of polyolefin 23 so that the second layer of polyolefin 23 is preferably positioned between the first and third layers of elastomer 21, 25. Packaging film 20 preferably has a 45° gloss in a range of about 70% to about 110%.
Several methods of forming the packaging film 20 with enhanced optical and mechanical properties also are provided according to the present invention. The packaging film 20 of the present invention can be manufactured using typical bubble blown film processes and machines 30 and cast film processes and machines 30′ without having to modify the machine or equipment, as can be seen in
In one embodiment illustrated in
It is understood that in the blown film manufacturing process, as shown in
If a flattened tube material is formed, the flattened tube material can then be converted to a roll stock of packaging film for sale to consumers, as shown in
The overall packaging film gauge thickness preferably is in a range of about 0.5 to about 3 mil, and more preferably in a range of between 0.6 to 1.25 mils, and the method can further include the step of printing indicia I on the packaging film 20 after the packaging film 20 has been formed, as shown in
Another embodiment of a method of forming a packaging film 20 having enhanced optical and mechanical properties 30′ so that for a selected overall packaging film gauge thickness, as shown in
The elastomer provided is preferably a styrene butadiene copolymer and the polyolefin is preferably selected from the group consisting of non-linear ethylene ethyl acetate copolymers, non-linear ethylene homopolymers, ethylene vinyl acetate copolymers, polyethylene, and polypropylene, as described herein. Other suitable elastomers and polyolefins are described herein and can also be used in the embodiments of forming a packaging film 20 in accordance with the present invention. The overall packaging film gauge thickness preferably is in a range of about 0.5 to about 3 mil, and more preferably in a range of between 0.6 to 1.25 mils, and the method further includes the step of printing indicia I on the packaging film 20 after the packaging film 20 has been formed, as indicated herein.
The film 20 produced in accordance with the present invention advantageously can be produced with a lower gauge, which allows manufacturers to use less material when manufacturing the film 20, thereby lowering manufacturing costs. Films 20 typically have a gauge of about 2 to about 3.5 mil thick. The film 20 of the present invention advantageously has a film gauge thickness is in a range of about 0.5 to about 3 mil, and more preferably in a range of between 0.6 to 1.25 mils. A mil is defined herein as a measurement of thickness. One mil is one thousandth of an inch. For example, a 0.80 stretch wrap is 0.8 thousandths of an inch thick. The 80 gauge is the equivalent of 0.80 mil. The 80 gauge or 0.80 mil thick stretch wrap performs well for many applications requiring packaging film 20.
To form the combination product P and film 20 embodiments of the present invention, the film 20 is first stretched out. During this stretched out orientation, the molecules with the elastomers and polyolefins are locked, or frozen, into their elongated state. A product P is then placed on the film 20 and the film 20 is then essentially wrapped around the product P. When heat is applied to the film 20 with the product P placed within the film 20, excess energy increases molecular motion within the chemical compounds that form the layers of the film 20. The elongated chemical molecules recoil, or shrink, back to their preferred random and disordered orientation. The result is a product P with the shrink-wrap packaging film 20 shrunk thereon. The film 20 securely restrains the product P within the film 20.
Tests were performed on twelve different samples of packaging film 20 manufactured in accordance with the present invention. Descriptions of the twelve samples can be found in Table 1 herein below. For the elastomer, a butadiene styrene copolymer known commercially as DK11 in the K-Resin® Series manufactured by Chevron Phillips Chemical Company was used in the test. A 3% antiblock additive was used in the elastomer layers to prevent the outer layers from sticking together once the finish packaging film 20 was made and formed into rolls. For the polyolefin, a low-density polyethylene was used. The layer percentages relate to the thickness of each layer used in the total film gauge thickness. For example, Sample A was a 1.0 mil thick packaging film 20 that was created with a 0.25 mil thick layer of butadiene styrene copolymer, a 0.50 mil thick layer of polyolefin, and a 0.25 mil thick layer of butadiene styrene copolymer. The test results are shown in the graphs shown in
Depending upon the desired characteristics of the packaging film 20 in accordance with an embodiment of the present invention, the optical and mechanical properties can be customized by increasing the amount of elastomer or polyolefin within the packaging film 20. For example, mechanical properties related to strength, such as tensile at yield, modulus, and ultimate tensile are generally higher for the packaging films 20 containing a higher amount of the elastomer and lower for those containing a higher amount of polyolefin, as shown in
As an advantage of the present invention, the shrink-wrap or other packaging films 20 made in accordance with the present invention are more economical to manufacture. The use of the elastomer in the film improves the physical properties of the film 20, so that a thinner packaging film 20 can be made. The performance properties of the packaging film 20 remains the same or are increased with a thinner gauged film 20. Because less material is needed to manufacture the film 20 and conventional equipment can be used, manufacturing costs are lowered.
As another advantage of the present invention, the films 20 provide evidence of tampering if someone attempts to remove the film 20 that has been heat sealed to a product P. The clarity of the film 20 allows users to easily determine if tampering has occurred.
In the drawings and specification, there have been disclosed a typical preferred embodiment of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification.
This application is a continuation-in-part application which claims the benefit of and priority to U.S. Non-Provisional patent application Ser. No. 10/760,337, filed on Jan. 20, 2004, now U.S. Pat. No. 7,083,838, which claims the benefit of and priority to U.S. Provisional Application No. 60/505,371, filed on Oct. 2, 2003, incorporated herein by reference in their entirety.
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