Recycle-ready lidding film

Abstract

To satisfy a continuing need for high-performance films that are recyclable while also providing excellent mechanical properties and heat resistance to meet the demands of high-performance packaging.SOLUTION: Provided is a laminated polypropylene-based film suitable for use as a lidding film, having an exterior film, a barrier layer, and a sealing layer. The lidding film has a total composition including high levels of polyolefin-based polymers and polypropylene-based polymers such that the material can be processed efficiently in a polypropylene recycling process. Advantageously, the film retains the properties required to suitably withstand sterilization and pasteurization processes and produce a high-quality packaged product.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to film structures, particularly to coverstock films and packaged products made therefrom. The coverstock films described herein can be recyclable in polyolefin-based streams. [Background technology]

[0002] Various preservation processes are used in the packaging industry to create safe food and health care products with long shelf lives. Some processes sterilize the product and / or packaging components by heat, chemical means, high pressure, irradiation, or a combination of these, which have the effect of killing any microorganisms and their spores. Some processes pasteurize foods using heat, which has the effect of reducing the microbial load. Preservation processes, such as sterilization or pasteurization, are performed just before filling and sealing the package, or after filling and sealing the package. Examples of these processes include, but are not limited to, retort / autoclaving, high pressure sterilization (HPP), hot filling, aseptic sterilization, and irradiation. These processes subject the packaging material to high temperatures, high pressure, or other harsh environments.

[0003] Specialized flexible packaging films are designed for applications incorporating these harsh preservation processes. Flexible packaging films used in pasteurization or sterilization applications often have many different layers, each layer contributing one or more properties to withstand the harsh conditions. For example, a packaging film may require high stiffness and high heat resistance to perform well in high speed packaging processes. In another example, a packaging film is designed to withstand the high temperatures and pressure changes of the sterilization process without losing the integrity of the seal, losing an adequate level of gas barrier, or becoming unattractive in appearance.

[0004] A typical flexible packaging film intended for sterilized or pasteurized (i.e., preserved) product applications may include a combination of materials such as polyesters and polyamides to provide good heat resistance, dimensional stability, and stiffness; aluminum foil to provide high barrier properties and stiffness; and / or polyolefins to provide suitable sealing properties. Unfortunately, when this wide variety of materials is combined in a single packaging film, it makes the film difficult to recycle.

[0005] Many consumers and consumer packaged goods manufacturers desire to use recyclable (i.e., recyclable) food packaging. In some cases, recyclable packaging structures are desired for regulatory compliance purposes. However, without additional compatibilizing chemicals, materials such as polyesters, polyamides, and foils may not be recyclable in current recycling streams for flexible packaging. Additionally, structures that contain metal are generally not suitable for applications where consumers may wish to use a microwave oven to heat the product within the package.

[0006] There is a continuing need for high performance films that provide excellent mechanical properties and heat resistance to meet the demands of high performance packaging, yet are recyclable. Summary of the Invention [Means for solving the problem]

[0007] Described herein is a flexible packaging film that can be used as a lidding in pasteurization or sterilization applications and is advantageously recyclable in polyolefin recycle streams. Despite having a high polyolefin content composition, the lidding film retains good appearance, excellent barrier properties, and airtight integrity while retaining characteristics that allow it to perform well in high speed packaging operations and to withstand harsh sterilization / pasteurization cycles.

[0008] The coverstock film herein comprises an outer polypropylene-based film, a barrier layer, and a seal layer. The coverstock film has a total composition comprising at least 80% by weight of a polyolefin-based polymer.

[0009] The coverstock film may have an oriented outer polypropylene-based film, which may be made of homopolymer polypropylene.

[0010] The covering film may have a barrier layer comprising a metal.The covering film may have a barrier layer comprising an inorganic oxide.

[0011] In some embodiments, the coverstock film has a total composition comprising at least 80% by weight of a polypropylene-based polymer. The coverstock film may have a total composition comprising at least 90% by weight of a polyolefin-based polymer.

[0012] The coverstock film may have a seal layer that is a peelable seal layer. The coverstock film may have a seal layer that comprises a polypropylene based polymer.

[0013] The coverstock film may further comprise an inner polypropylene-based film, which may be oriented.

[0014] The packages disclosed herein include a lidstock film, a second packaging component, a heat seal connecting a sealing layer of the lidstock film to a surface of the second packaging component, and a product sealed between the lidstock film and the second packaging component. In some embodiments, the product has been subjected to a sterilization process. In some embodiments, the product has been subjected to a pasteurization process. In some embodiments, the lidstock film has been subjected to a sterilization process. In some embodiments, the lidstock film has been subjected to a pasteurization process.

[0015] The packaging may include a hand peelable heat seal.

[0016] The package may have a second package component having a surface that includes a polypropylene-based polymer.

[0017] In some embodiments, the packaging has a total composition having at least 80% by weight of a polyolefin-based polymer. In some embodiments, the packaging has a total composition having at least 80% by weight of a polypropylene-based polymer. In some embodiments, the packaging has a total composition having at least 90% by weight of a polypropylene-based polymer.

[0018] The packaging has a moisture content of 3.0 cc / m when measured in accordance with ASTM F1927 at 23°C and 50% RH. 2 The covering film may include a covering film having an oxygen transmission value of less than 1000 nm.

[0019] The present disclosure may be more fully understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which: [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a plan view of one embodiment of a package incorporating a lidding film. [Diagram 2] FIG. 2 is a schematic side view of one embodiment of a covering material film. [Diagram 3] FIG. 2 is another schematic side view of one embodiment of the covering film. [Figure 4] FIG. 2 is another schematic side view of one embodiment of the covering film. [Diagram 5] 1 is a heat seal curve for the films of the examples and comparative examples described in the Examples and Data section. [Figure 6] 1 is a heat seal curve for the films of the examples and comparative examples described in the Examples and Data section. [Figure 7] 1 is a heat seal curve for the films of the examples and comparative examples described in the Examples and Data section. [Figure 8] 1 is a heat seal curve for the films of the examples and comparative examples described in the Examples and Data section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The drawings show some, but not all, embodiments. The elements depicted in the drawings are illustrative and are not necessarily to scale, and the same (or similar) reference numbers refer to the same (or similar) features throughout the drawings.

[0022] Current flexible packaging films designed to provide high performance in demanding applications contain many different materials. The construction generally includes layers that include polyester, polyamide, polyethylene, polypropylene, metal and / or ethylene vinyl alcohol copolymers. Each layer of the construction is designed to provide properties such as barrier properties, stiffness, heat resistance, dimensional stability, puncture resistance, seal strength, and visual appeal, to name a few. The challenging functional requirements of sterile or pasteurized product packaging and the diversity of materials in current constructions present significant obstacles when attempting to provide more sustainable, i.e. recyclable, packaging solutions.

[0023] The design of the lidding film is made difficult due to the high demands of these applications compared to other flexible packaging formats. Heat sealing equipment used to apply the lidding film to rigid containers (i.e. cups, trays, plates, etc.) typically only applies heat from the lid side. Furthermore, it becomes more difficult to form a heat seal on rigid packaging components that typically have rougher sealing surfaces. The process of applying the lid to the package involves a process that uses high heat, short dwell times, and high pressure. Thus, the lid experiences significantly higher heat compared to a sealing operation that heat seals two flexible films together. Typical flexible lidding structures are designed with high temperature resistant materials to withstand the heat sealing process without showing signs of degradation such as damage, sticking, or melting. In particular, materials such as polyester and polyamide are used as the outer material of the lidding film to impart sufficient heat resistance.

[0024] When moving to recyclable structures (i.e., based on polyolefin-based materials), there is a high risk that the lidding film will reach a point where the film begins to burn or distort before achieving a tight seal. Given this, developing a lidding film structure for products that utilize sterilization or pasteurization processes was an unexpected discovery for the inventors. Specifically, it was surprising to be able to use an outer layer of a film structure that includes high levels of polyolefins that 1) shows minimal or no signs of thermal distortion and 2) exhibits sufficient heat resistance to provide sufficient protection to the barrier layer so that it is not damaged during heat sealing.

[0025] In addition, the coverstock film is effective to withstand a curing treatment (i.e., pasteurization or sterilization). To be effective to withstand a curing treatment, the coverstock construction must provide sufficient protection to the barrier layer such that the barrier provided is not significantly reduced after the curing treatment. Specifically, the oxygen barrier of the coverstock film is less than 3.0 cc / m2 after exposure to retort conditions. 2 Another characteristic of a lidding film that is effective in withstanding a curing treatment is that the lid maintains a good heat seal (i.e., does not leak or weaken) to the other packaging components after the curing treatment.

[0026] The coverstock film disclosed herein is designed to contain high levels of polyolefin-based materials, specifically high levels of polypropylene-based materials.Despite the absence of many materials commonly used in coverstocks (i.e. polyester, polyamide, aluminum foil), the structure retains appropriate characteristics of barrier properties, heat resistance, appearance, and seal integrity.Advantageously, the structure is suitable for recycling in polyolefin-based mechanical recycling processes due to its essentially low levels of non-polyolefin materials.

[0027] Particularly surprising is the realization of a lidstock film that has both a seal layer design that has a heat seal initiation temperature low enough to match the only moderate heat resistance of the outer surface provided by the polyolefin material, and a seal layer that has sufficient integrity to withstand the high temperatures of the sterilization / pasteurization process along with other rigorous handling that the package may endure during distribution and use. The lidstock film can be formed into a package at a lower seal temperature and maintains an excellent appearance. Furthermore, the package structure maintains excellent barrier properties and seal integrity even after the film is formed into a package, filled with product, sealed, and subjected to a sterilization / pasteurization process.

[0028] In one or more embodiments, the covering film described herein contains at least 80% by weight of a polyolefin-based polymer and at least 50% by weight of a polypropylene-based polymer. Materials that are not polyolefin-based polymers are minimized. In one or more embodiments, the non-polyolefin-based polymer is less than 20% by weight, such as less than 10% by weight, less than 5% by weight, or even less than 1% by weight of the total covering composition. In one or more embodiments, the non-polyolefin-based polymer is excluded from the total covering composition. The outer surface of the covering film has a heat-resistant polypropylene-based film. The inner surface of the covering film has a seal layer that is a polypropylene-based polymer blend. The covering film includes a barrier layer that is typically not a polyolefin-based material. The film may also have other materials such as adhesives, inks, and coatings.

[0029] The coverstock film design elements described herein can be used to achieve a recyclable coverstock film. The film is suitable for recycling in polyolefin-based recycling processes due to its high polyolefin content. The film is also suitable for recycling in polypropylene-based recycling processes due to its high polypropylene content. Specifically, the film may have low or no levels of materials such as polyester, polyamide, chlorine-containing polymers, and aluminum foil. "Aluminum foil" as used herein is a metal web having a thickness of at least 1 micron, typically greater than 5 microns. The film may contain non-polyolefin-based polymers, such as those used in the adhesive or ink layers, but these are minimized and typically less than 10% by weight of the total composition. The film may contain non-polymer-based materials, such as barrier materials, but these are minimized and typically less than 10% by weight of the total composition.

[0030] packaging Described herein are packaging and coverstock films suitable for preservation, e.g., sterilization or pasteurization, packaging applications, and packages made therefrom. As used herein, a sterilization or pasteurization process is one that eliminates or reduces the microbial load of the product and / or packaging material such that the packaged product has an extended shelf life. The process can be carried out before filling the package, during filling the package, or after filling the package with the product and sealing it. The coverstock films can withstand harsh treatments and maintain their excellent performance, including but not limited to barrier and appearance.

[0031] The package includes at least one heat seal that allows for connection of the lidding film to another packaging component, forming the package, and sealing the package. An example of a package 100 is shown in Figure 1, including a lidding film 110, a second packaging component 120, and a heat seal 130. The heat seal 130 connects the sealing layer of the lidding film 110 to a surface of the second packaging component 120, and the product is sealed between the lidding film and the second packaging component.

[0032] The heat seal seals the package, protecting the product from contamination and preventing leakage. The heat seal withstands all the rough handling the package will endure during distribution, including stacking, vibration during transport, pressure fluctuations, dropping, etc. For convenience, the heat seal can be broken by the consumer manually, such as by peeling the lidding film from the second packaging component.

[0033] The packaging can be entirely composed of the coverstock film and the second packaging component described herein. The second packaging component can be a cup, tray, plate, or bowl, and has one or more cavities for holding the product. The packaging can also include other components, such as, but not limited to, labels, absorbents, and dividers. Any component of the packaging that is not the coverstock film described herein (i.e., the second packaging component) can also have a high level of polypropylene polymer. In some embodiments of the packaging, the second packaging component has at least 90% by weight of polypropylene-based polymer, so that the entire packaging (i.e., the coverstock film and all other packaging components) is recyclable in a polypropylene recycling process.

[0034] The lidstock film can be sealed to the second packaging component by a heat seal that has good integrity but can be peeled off by hand.As used herein, a seal is "peelable by hand" if the two objects attached by the heat seal can be separated by pulling with hand force, and the packaging components are separated at or near the heat seal.In other words, consumers can remove the lidstock film and / or access the contents of the package by separating the packaging components by their own strength, without using tools such as scissors or tearing the packaging material.

[0035] In some embodiments of the packaging, some components of the packaging cannot be recycled in a polyolefin or polypropylene recycling process. In that case, the components of the packaging can be separated prior to recycling and / or disposal. Separation of the packaging components can be accomplished by manually peeling the heat seal.

[0036] In some embodiments of packaging formed from the coverstock film, the packaging comprises at least 90% by weight polyolefin-based material or at least 80% by weight polyolefin-based material. In some embodiments of packaging formed from the coverstock film, the packaging comprises at least 90% by weight polypropylene-based material or at least 80% by weight polypropylene-based material. In some embodiments of packaging formed from the coverstock film, the packaging comprises at least 90% by weight polyolefin-based material and at least 80% by weight polypropylene-based material.

[0037] In some embodiments of the packaging, the surface of the second packaging component comprises a polypropylene-based polymer. When both the seal layer of the lidding film and the surface of the second packaging component to which the lidding film is sealed comprise a polypropylene-based polymer, a high integrity heat seal can be formed.

[0038] Lidding Film Described herein is a lidstock film suitable for packaging, and packaging and shelf-stable packaged products made therefrom. As used herein, a "lidstock film" is a film that can be used in a flat state to cover the opening of another packaging component, such as a cup or tray. The cup or tray is filled with a product, sealed with the lidstock film, and remains sealed throughout the shelf-life of the packaged product. The lidstock film may be exposed to harsh conditions as a result of a sterilization or pasteurization process applied to one or all of the packaging components, the product, or the sealed packaged product. Because the sterilization / pasteurization process is harsh, very specialized lidstock films are designed to withstand the process and maintain excellent barrier, good appearance, and seal integrity.

[0039] Various types of packaging materials can be used in the sterilization process, including cans, bottles, and flexible polymer-based packaging, such as the lidstock films described herein and laminated polypropylene-based films. Advantages of using flexible packaging, such as the lidstock films described herein, include reduced weight and reduced energy required to bring the contents of the package to the conditions required for sterilization. The lidstock films can have a thickness of about 2.5 mils (63.5 microns) to about 10 mils (254 microns), or about 3 mils (76.2 microns) to about 6 mils (152.4 microns).

[0040] Referring now to FIG. 2, an embodiment of a covering film 10 includes an outer polypropylene-based film 12, a barrier layer 14, and a seal layer 16. The outer polypropylene-based film 12 is located on one major surface of the covering film, which will be the exposed outer surface of the package to which the covering film is connected. In some cases, the outer polypropylene-based film 12 has an ink or another coating applied to the exposed surface. The seal layer 16 is located on the other major surface of the covering film, which will be the product contact surface when the covering film is formed into a package. The seal layer 16 is necessarily on the surface so that a heat seal can connect the seal layer to another package component. The barrier layer 14 is located on the interior of the surface of the covering film. The covering film has a total composition including at least 80% by weight of a polyolefin-based polymer. The covering film has a total composition including at least 90% by weight of a polypropylene-based polymer.

[0041] A "layer" as used herein is a uniform building block of a film. A layer may be continuous or discontinuous (i.e., patterned) across the length and width of the film. The term "film" as used herein is a single or multi-layer web having a small z-dimension (thickness) compared to the x- and y-dimensions (length and width), and is distinct from a piece of paper. A film is generally considered to have two opposing major surfaces that extend along its length and width. A film can be formed from an unlimited number of films and / or layers, which are bonded together to form a composite article. A portion of a packaging film may be referred to as a layer or film.

[0042] The cover material film comprises at least one polypropylene-based film. As used herein, a "polypropylene-based film" has a composition comprising at least 50% by weight, or at least 90% by weight, of a polypropylene-based polymer. In some cases, the polypropylene-based film may be essentially 100% polypropylene-based polymer.

[0043] The outer polypropylene-based film may be oriented. The term "oriented" as used herein indicates that the film has been heated to a temperature below the melting point of the material and stretched at least twice. This is typically accomplished by a double or triple bubble process, a tenter frame process, or an MDO (machine direction orientation) process using heated rolls. A typical blown or cast film process imparts some stretch to the film, but not enough to be considered oriented as described herein. The film may be biaxially or uniaxially oriented in either direction. The outer polypropylene-based film is preferably heat set (i.e. annealed) after orientation so that it is dimensionally stable under high temperature conditions that may be experienced during conversion of the coverstock film (i.e. printing or lamination) or during use of the coverstock film (i.e. heat sealing or retort sterilization). The outer polypropylene-based film may be manufactured using specific polymers and oriented using specific conditions that optimize the heat resistance of the film. The outer polypropylene-based film may include homopolymer polypropylene or may be manufactured exclusively from homopolymer polypropylene.

[0044] The outer polypropylene-based film may be an oriented polypropylene film, such as biaxially oriented polypropylene. The oriented polypropylene film may have one or more layers and may have a special coating, such as a matte lacquer. Any layer of the oriented polypropylene film may contain a pigment, such as titanium dioxide, to make the film opaque to visible light. The film may be a hollow biaxially oriented polypropylene, so that the film is opaque to visible light. The biaxially oriented polypropylene may be transparent to visible light. In some embodiments, the outer polypropylene-based film is a biaxially oriented polypropylene film that essentially comprises polypropylene. The outer polypropylene-based film may have a thickness of, but is not limited to, about 12, about 20, about 25, or about 30 microns.

[0045] Commercially available examples of films that can be used as the outer polypropylene-based film include Bicor™ NND20 (non-heat sealable, single-sided treated BOPP, available from Jindal Films), PL1 (non-heat sealable, single-sided treated BOPP, available from Polibak Plastik Film San.ve Tic.AS), and PPTE_LAM (non-heat sealable, single-sided treated, available from Poligal).

[0046] As used herein, the term "external" is used to describe a film or layer that is located on one of the major surfaces of the film in which it is contained. As used herein, the term "internal" is used to describe a film or layer that is not located on a surface of the film in which it is contained. An internal film or layer is adjacent to another film or layer on both sides.

[0047] The barrier layer of the coverstock film is usually coextensive with the coverstock film and comprises a barrier material. The barrier layer reduces the transmission of gases such as oxygen (i.e. comprises an oxygen barrier material). The barrier layer can also reduce the transmission of moisture (i.e. comprises a moisture barrier material). The barrier layer is typically an inner layer of the coverstock film to protect the integrity of this layer. The barrier material may be polymeric in nature such as polyamide, ethylene vinyl alcohol copolymer, or polyvinyl alcohol copolymer. The barrier material may be metallic such as a thin deposit of aluminum. The barrier layer may be a transparent inorganic oxide coating such as AlOx or SiOx. The barrier layer may be multi-layered and may comprise different layers of barrier material. The barrier layer may be a blend of multiple barrier materials. The barrier layer provides the specific barrier required to preserve the product within the package for an extended shelf life that may exceed several months or even a year.

[0048] The barrier layer can be disposed on a surface of the outer polypropylene-based film. In some embodiments of the coverstock film, the barrier layer is disposed on the inner surface of the outer polypropylene-based film facing the seal layer. Alternatively, the barrier layer may be provided on the surface of the inner film.

[0049] The barrier layer reduces the ingress of oxygen through the coverstock film during the shelf life of the packaged product (i.e., while the package is sealed). In some embodiments, the coverstock film is sealed to a thickness of 2 cm prior to exposure to pasteurization or sterilization. 3 / m 2 / day or less, 1cm 3 / m 2 / day, less than 0.5cm 3 / m 2 / day or less than 0.1cm 3 / m 2 / day (measured according to ASTM F1927 using conditions of 1 atmosphere, 23°C, and 50% RH). In some embodiments, after being subjected to a pasteurization or sterilization process, the coverstock film has an average oxygen transmission rate (OTR) value of less than 2 cm 3 / m 2 / day or less, 1cm 3 / m 2 / day, less than 0.5cm 3 / m 2 / day or less than 0.1cm 3 / m 2 / day. The average OTR value may be close to or below the minimum detection level of the test device.

[0050] The sealing layer of the coverstock film has a composition that allows for the formation of a heat seal, thereby forming a hermetically sealed package. As used herein, the term "heat seal" or "heat seal" refers to the connection of two or more surfaces by the brief application of both heat and pressure, or by an ultrasonic energy sealing process. As used herein, the term "heat seal" refers to the connection between two or more surfaces made by heat sealing. Heat sealing and ultrasonic sealing are well-known and commonly used processes for forming packages, and are well known to those skilled in the art.

[0051] The sealing layer of the coverstock film may be a peelable seal layer having a composition that allows the formed heat seal to be peeled by hand. There are various mechanisms by which peeling can occur, including adhesive failure and cohesive failure. Whatever the mechanism, peeling and separation of the packaging components occurs at or near the heat seal that connects the coverstock film to another packaging component. The sealing layer and / or coverstock film can be tested to form a manually peelable heat seal by sealing the film to itself (i.e., seal layer to seal layer) using heat seal conditions of 150°C, 1 second, 30 psi, and measuring the force to separate the film by ASTM F88 (grip separation at 100 mm / min). The seal is manually peelable if the maximum force to separate is less than 20 N / 15 mm.

[0052] The sealing layer is necessarily present on the surface of the covering film, which promotes the sealing function. During heat sealing, the sealing layer softens, allowing the formation of a heat seal bond at a sealing temperature lower than the heat resistance temperature of the outer polypropylene-based film. The sealing layer softens at a sealing temperature lower than the heat resistance temperature of the outer orientation film. The sealing layer must soften and form a heat seal under sealing conditions (time, temperature, and pressure) that do not cause excessive shrinkage or damage to the outer surface of the covering film.

[0053] The coverstock film is targeted to contain a large amount of polyolefin-based polymers, specifically polypropylene-based polymers, so that it can be accepted in the recycling process. Polyolefins have relatively low heat resistance compared to materials traditionally used for pasteurized or sterilized packaging film applications (i.e. polyester, aluminum foil, polyamide). As a result of the high polyolefin content and low heat resistance, the package must be formed using a heat sealing process at a low temperature to avoid shrinkage and melt-perforation. The challenge met by the coverstock film disclosed herein is to incorporate a sealing layer with a low heat seal initiation temperature (HSIT) and high seal strength and seal toughness (i.e. drop strength and burst strength) that will withstand both processing and normal distribution and handling. The sealing layer must also include materials approved for food contact under the conditions of use as mandated by government agencies for food safety.

[0054] The sealing layer may comprise a material that has a low heat seal initiation temperature (HSIT). In some embodiments of the coverstock film, the sealing layer contains a polypropylene copolymer that has a melting temperature of 135° C. or less.

[0055] The sealing layer can be formed by any known process. For example, the sealing layer can be a heat seal lacquer coated onto the other layers of the coverstock film. In another embodiment, the sealing layer is formed by an extrusion process in which a polymer melt is applied directly to the other layers of the coverstock film. In yet another embodiment, the sealing layer can be formed in an off-line co-extrusion process (i.e., cast film or blown film process) and then adhered to the other layers of the coverstock film using a lamination process. The sealing layer can be included in a multi-layer film that includes two, three, four, or more layers. In some embodiments, the sealing layer is a non-oriented layer.

[0056] Referring now to FIG. 3, an embodiment of a covering film 20 includes an outer polypropylene-based film 22, a barrier layer 24, and a seal layer 26. The seal layer 26 is in a coextruded multi-layer film 27. The outer polypropylene-based film 22 can be located on one major surface of the covering film and will be the exposed outer surface of a package that can be formed from the covering film. The seal layer 26 is located on the other major surface of the covering film and will be the product contact surface of a sealed package that can be formed from the covering film. The barrier layer 24 is located on the interior surface of the covering film 20. The covering film has a total composition including at least 80% by weight of a polyolefin-based polymer. The covering film can have a total composition including at least 90% by weight of a polypropylene-based polymer.

[0057] The structure of the coverstock film and any packaging made therefrom includes several different elements (exterior layers, barrier layers, seal layers, etc.), but the overall composition of the film or packaging needs to have a high level of a single material type (polyolefin, especially polypropylene) to facilitate recycling. As used herein, the term "total composition" is used to describe the coverstock film structure or packaging as a whole. Any materials, layers, or components that are connected to each other in some way are part of the overall composition of the article. The coverstock film may have a high level of polyolefin-based polymers. The coverstock film may have a high level of polypropylene-based polymers. The coverstock film described herein, and any packaging made therefrom, can be recyclable in a polypropylene recycling process if the article contains a large amount of polypropylene-based polymers. The recycling process for mixed polyolefins can also accept relatively high levels of polyolefins that are not polypropylene, so the article may also contain high levels of polyolefins that are not polypropylene and still be suitable for recycling.

[0058] As used herein, "polyolefin-based polymer" refers to a homopolymer or copolymer having at least one alkene monomer bond in the repeating backbone of the polymer. Primary examples of polyolefin-based polymers are polyethylene homopolymers and copolymers, and polypropylene homopolymers and copolymers. Other examples of polyolefin-based polymers are ethylene vinyl alcohol copolymers and cyclic olefin copolymers.

[0059] The covering film may have a total composition comprising at least 80% by weight of polyolefin-based polymer. In other words, taking into account all materials (polymeric and non-polymeric) within the entire covering film, at least 80% by weight is polyolefin-based polymer. The covering film may have a total composition comprising a minimum polyolefin-based polymer content of 80%, 82%, 84%, 86%, 88%, or 90% by weight. The covering film may have a total composition comprising a maximum polyolefin-based polymer content of 100%, 99%, 98%, 97%, 96%, or 95% by weight. For example, the covering film may have a total composition comprising 90% to 99% by weight of polyolefin-based polymer, or the covering film may have a total composition comprising 82% to 100% by weight of polyolefin-based polymer.

[0060] As used herein, a "polypropylene-based polymer" refers to a homopolymer or copolymer having at least one propylene monomer bond within the repeating backbone of the polymer. The propylene bond can be represented by the general formula: [CH 2 -CH(CH 3 )] n Such polypropylenes may be polypropylene impact copolymers, polypropylene random copolymers, or polypropylene homopolymers, may be syndiotactic or isotactic, and / or may be nucleated or non-nucleated. The polypropylene-based polymer may be a propylene alpha olefin copolymer.

[0061] The covering film may have a total composition comprising at least 70% by weight of polypropylene-based polymer. In other words, considering all materials (polymeric and non-polymeric) in the entire covering film, at least 70% by weight is polypropylene-based polymer. The covering film may have a total composition comprising a minimum polypropylene-based polymer content of 70%, 80%, 85%, 86%, 88%, or 90% by weight. The covering film may have a total composition comprising a maximum polypropylene-based polymer content of 100%, 99%, 98%, 97%, 96%, or 95% by weight. For example, the covering film may have a total composition comprising 70% to 98% by weight of polypropylene-based polymer, or the covering film may have a total composition comprising 80% to 100% by weight of polypropylene-based polymer.

[0062] In some embodiments, the covering film has a total composition that includes less than 10% by weight of polymers other than polyolefin-based polymers. In addition to having high polyolefin and polypropylene content, the covering film may have a low level of non-polyolefin-based polymers relative to the total composition. Non-polyolefin-based polymers that may be included in the covering film include polyamides, polyacrylates, and polyurethanes. These polymers may be present in the extruded layer or in the printed ink or adhesive layer. The covering film may have a total composition that includes less than 9%, less than 8%, less than 7%, less than 6%, or less than 5% by weight of polymers other than polyolefin-based polymers.

[0063] In some embodiments, the coverstock film does not include any polymer other than a polyolefin-based polymer, in other words, any non-polyolefin-based polymers that may be present in the coverstock film do not affect the basic and material properties of the film.

[0064] Referring now to FIG. 4, an embodiment of a coverstock film 30 includes an outer polypropylene-based film 32, a barrier layer 34, an inner polypropylene-based film 38, and a seal layer 36. The seal layer 36 is in a coextruded multi-layer film 37. The outer polypropylene-based film 32 can be disposed on one major surface of the coverstock film and will be the exposed outer surface of a package that can be formed from the coverstock film. The seal layer 36 is located on the other major surface of the coverstock film and will be the product contact surface of a package that can be formed from the coverstock film. The inner polypropylene-based film 38 and the barrier layer 34 are disposed on the inner surface of the coverstock film 30. In some embodiments, the location of the inner polypropylene-based film 38 and the barrier layer 34 may be altered from the location shown in FIG. 4. The coverstock film may have a total composition including at least 80% by weight of a polyolefin-based polymer. The coverstock film has a total composition including at least 80% by weight of a polypropylene-based polymer.

[0065] The barrier layer may be adjacent to or in contact with the inner surface of the outer polypropylene-based film. The barrier layer may be adjacent to or in contact with either surface of the inner polypropylene-based film.

[0066] The inner polypropylene-based film may be oriented. The film may be biaxially or uniaxially oriented in either direction. The inner polypropylene-based film is preferably heat set (i.e. annealed) so that it is dimensionally stable under high temperature conditions that may be experienced during conversion of the laminate or during use of the laminate (i.e. heat sealing or retort sterilization). If present, the inner polypropylene-based film may be the same as or different from the outer polypropylene-based film.

[0067] The inner polypropylene-based film may be an oriented polypropylene film, such as biaxially oriented polypropylene. The oriented polypropylene film may have one or more layers and may have a special coating, such as a matte finish. Any layer of the oriented polypropylene film may contain a pigment, such as titanium dioxide, to make the film opaque to visible light. The film may be a hollow biaxially oriented polypropylene, so that the film is opaque to visible light. The biaxially oriented polypropylene may be transparent to visible light. In some embodiments, the outer polypropylene-based film is a biaxially oriented polypropylene film that essentially comprises polypropylene.

[0068] In embodiments that include an inner polypropylene-based film, the inner polypropylene-based film may be the same as or different from the outer polypropylene-based film. Commercially available examples of films that can be used as the inner polypropylene-based film include Bicor™ NND20 (non-heat sealable, single-sided treated BOPP, available from Jindal Films), PL1 (non-heat sealable, single-sided treated BOPP, available from Polibak Plastik Film San.ve Tic.AS), and PPTE_LAM (non-heat sealable, single-sided treated, available from Poligal).

[0069] The barrier layer may be a coating or a deposition applied to one of the films used to construct the coverstock film. For example, the barrier layer 34 shown in the embodiment shown in FIG. 4 may be a silicon oxide material deposited on the inner polypropylene-based film 38, which is disposed between the outer polypropylene-based film 32 and the inner polypropylene-based film 38. Alternatively, the barrier layer 34 shown in the embodiment shown in FIG. 4 may be a silicon oxide material deposited on the outer polypropylene-based film 32, which is located between the outer polypropylene-based film 32 and the inner polypropylene-based film 38. Alternatively, the barrier layer 34 may be a silicon oxide material deposited on the side of the inner polypropylene-based film 38 facing the sealing layer 36 (this embodiment is not shown in the drawings).

[0070] Any of the embodiments of the coverstock film may include other materials and layers. For example, the film structure may include either an extruded tie layer or other adhesive layer intended to bond dissimilar materials. The film may also include an ink layer anywhere in the structure.

[0071] In some embodiments of the coverstock film, the outer film, the inner film, and the seal layer are free of polymers other than polyolefin-based polymers. EXAMPLES

[0072] Examples and Data A total of eight films were produced and tested. Six of the films were lidding films according to the films described herein, and these films were designated Example Films 1-6. Two of the films were comparative examples of lidding films, and these films were designated Comparative Films 1 and 2. Example Films 1-6 are recyclable lidding films suitable for packaging applications involving sterilization or pasteurization. Comparative Films 1 and 2 were used commercially as lidding films in packaging applications involving sterilization or pasteurization, but were not recyclable. The structures of all eight films are shown in Table 1.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] Samples of Example Films 1 and 2 were fully immersed in a hydrogen peroxide bath. The bath was heated to 60° C. and maintained at this temperature for 1 hour, after which time the heating was stopped and the bath was allowed to cool to room temperature. No visual changes were observed in the film samples, indicating that they were suitable for peroxide sterilization.

[0077] Burst strength of Example Films 1-6 and Comparative Example Film 1, another typical non-recyclable lidstock film. The films were tested using a Lorentzen and Wettre burst strength tester and ISO 2758:2014. Each sample was tested three times. The average burst strength is reported in Table 2. The burst strength of Example Films 1-6 was significantly greater than Comparative Example Film 1.

[0078] [Table 4]

[0079] The sealing and peeling performance of the films were tested using a method in which the lidding film was heat sealed to a preformed rigid cup having a polypropylene / EVOH / polypropylene structure. These types of cup and lid arrangements are typically used to package fruit pieces along with syrup or similar products. The lids were heat sealed to the empty cups at various sealing temperatures by a tray sealer with circular sealing jaws that matched the diameter of the round cup. After cooling, the packages were mounted in a tensile testing unit that allowed the lids to be peeled off at angles between 0° and 90° (approximately 30° to 45°) with tension clamps. The maximum and average peel strengths as the lids peel off are recorded. The maximum peel strength typically occurs at the first moment of opening, while the average peel strength takes into account the force required throughout the propagation of the peel across the seal. Figures 5 and 6 show the maximum and average peel strength curves, respectively, over a sealing temperature range of 110°C to 190°C.

[0080] In addition, the sealed cups were exposed to a water bath at 85°C for 30 minutes to mimic the thermal environment of a pasteurization process. After removal from the water bath, the cups were cooled and the peel strength was then measured again. Figures 7 and 8 show the maximum and average peel strength curves, respectively, of the heat-treated cups in the sealing temperature range of 110°C to 190°C.

[0081] The oxygen permeability of the example and comparative films was tested in several ways. The results of the tests are reported in Table 3. Flat samples of the films were tested according to ASTM F1927 using conditions of 23°C and 50% RH (flat sample OTR). Flat samples of the films were similarly tested after heat treatment (flat sample OTR after heating). The heat treatment for example films 1-5 was a water bath at 85°C for 30 minutes. The heat treatment for example film 6 was an autoclave treatment at 121°C for 30 minutes.

[0082] Additionally, the films were sealed onto lids of polypropylene cups filled with water, and the filled and sealed cups were subjected to heat treatment. The heat treatment for the cups with lids made with Example Films 1-5 and Comparative Example 2 was a water bath at 85°C for 30 minutes, while the heat treatment for the cup with lid made with Example Film 6 was an autoclave treatment at 121°C for 30 minutes. After heat treatment, the lids were removed from the cups and flat samples were tested for oxygen transmission rate according to ASTM F1927 (OTR of cup format after heating) under conditions of 23°C and 0% RH.

[0083] [Table 5]

[0084] The coverstock films described herein and shown in the examples are recyclable and stable in sterile peroxide baths, making them suitable for such aseptic processing. Using these structures, superior burst strength can be achieved compared to typical non-recyclable structures used in the same applications. Furthermore, the recyclable coverstock film structures offer the possibility of sealing to PP-based containers at relatively low temperatures. To achieve recyclability, the structures are modified from traditional structures to polyolefin-based structures, which can withstand heat treatments such as sterilization and pasteurization and retain good barrier properties. Products packaged using such coverstock films maintain the long shelf life of the product, similar to non-recyclable structures currently used in such applications.

[0085] Embodiment A. An outer polypropylene film; A barrier layer; A sealing layer; and having a total composition comprising at least 80 wt. % of a polyolefin-based polymer. B. A covering film according to any of the previous embodiments, wherein the outer polypropylene-based film is oriented. C. The coverstock film of any of the previous embodiments, wherein the outer polypropylene-based film comprises a homopolymer polypropylene. D. The covering film of any of the previous embodiments, wherein the barrier layer comprises a metal. E. The covering film of any of the previous embodiments, wherein the barrier layer comprises an inorganic oxide. F. The covering film of any of the previous embodiments having a total composition comprising at least 80% by weight of a polypropylene based polymer. G. The covering film of any of the previous embodiments, wherein the covering film has a total composition comprising at least 90% by weight of a polyolefin-based polymer. H. The covering film according to any of the previous embodiments, wherein said sealing layer is a peelable sealing layer. I. The cover material film of any of the previous embodiments, wherein the seal layer comprises a polypropylene based polymer. J. The covering film of any of the previous embodiments, further comprising an inner polypropylene-based film, said inner polypropylene-based film being oriented. K. A package comprising a covering material film according to any one of embodiments A to J, a second packaging component, a heat seal connecting the sealing layer of the covering material film to a surface of the second packaging component, and a product sealed between the covering material film and the second packaging component, wherein the product has been sterilized. L. A package comprising a covering material film according to any one of embodiments A to J, a second packaging component, a heat seal connecting the sealing layer of the covering material film to a surface of the second packaging component, and a product sealed between the covering material film and the second packaging component, wherein the product has been subjected to a pasteurization process. M. A package comprising a covering material film according to any one of embodiments A to J, a second packaging component, a heat seal connecting the sealing layer of the covering material film to a surface of the second packaging component, and a product sealed between the covering material film and the second packaging component, wherein the covering material film has been subjected to a sterilization treatment. N. A package comprising a covering material film according to any one of embodiments A to J, a second packaging component, a heat seal connecting the sealing layer of the covering material film to a surface of the second packaging component, and a product sealed between the covering material film and the second packaging component, wherein the covering material film has been subjected to a pasteurization treatment. O. The packaging of any of embodiments K-N, wherein the heat seal is manually peelable. P. The packaging of any of embodiments K-N, wherein the surface of the second packaging component comprises a polypropylene-based polymer. Q. The packaging of any of embodiments K-P, wherein the packaging has a total composition comprising at least 80% by weight polyolefin-based polymer. R. The packaging of any of embodiments K-Q, wherein the packaging has a total composition comprising at least 80% by weight of a polypropylene-based polymer. S. The packaging of any of embodiments K-R, wherein the packaging has a total composition comprising at least 90% by weight polypropylene-based polymer. When measured according to ASTM F1927 under conditions of T.23°C and 50% RH, the covering film has a viscosity of 3.0 cc / m 2 The packaging of any of embodiments K through S, having an oxygen transmission value of less than day. U. Outer polypropylene film; An inner polypropylene film; A barrier layer including an inorganic oxide; A seal layer; A covering film comprising: the inner polypropylene-based film is oriented; the outer polypropylene-based film is oriented and comprises homopolymer polypropylene; A coverstock film having a total composition comprising at least 80% by weight of a polyolefin-based polymer, said film being effective to withstand sterilization.

Claims

1. An outer polypropylene film; A barrier layer; A sealing layer; A covering film comprising: a covering material film having a total composition comprising at least 80% by weight of a polyolefin-based polymer.

2. 10. The covering film of claim 1, wherein the outer polypropylene-based film is oriented, the outer polypropylene-based film comprising a homopolymer polypropylene.

3. The covering film of claim 1 , wherein the barrier layer comprises a metal.

4. The covering film of claim 1 , wherein the barrier layer comprises an inorganic oxide.

5. 10. The covering film of claim 1 having a total composition comprising at least 80% by weight of a polypropylene-based polymer.

6. 10. The covering film of claim 1, wherein the covering film has a total composition comprising at least 90% by weight of a polyolefin-based polymer.

7. 2. The covering film of claim 1, wherein the seal layer is a peelable seal layer.

8. The covering film of claim 1 , wherein the seal layer comprises a polypropylene-based polymer.

9. 10. The covering film of claim 1, further comprising an inner polypropylene-based film, said inner polypropylene-based film being oriented.

10. An outer polypropylene film; An inner polypropylene film; A barrier layer including an inorganic oxide; A sealing layer; A covering film comprising: the inner polypropylene-based film is oriented; the outer polypropylene-based film is oriented and comprises homopolymer polypropylene; A coverstock film having a total composition comprising at least 80% by weight of a polyolefin-based polymer, said coverstock film being effective to withstand sterilization.

11. 13. A package comprising the lid material film of claim 1, a second packaging component, a heat seal connecting the sealing layer of the lid material film to a surface of the second packaging component, and a product sealed between the lid material film and the second packaging component, wherein the product has been subjected to a sterilization process.

12. 10. A package comprising the lidstock film of claim 1, a second packaging component, a heat seal connecting the sealing layer of the lidstock film to a surface of the second packaging component, and a product sealed between the lidstock film and the second packaging component, wherein the product has been subjected to a pasteurization process.

13. 13. A package comprising the lid material film of claim 1, a second packaging component, a heat seal connecting the sealing layer of the lid material film to a surface of the second packaging component, and a product sealed between the lid material film and the second packaging component, wherein the lid material film has been subjected to a sterilization process.

14. 13. A package comprising the lidstock film of claim 1, a second packaging component, a heat seal connecting the sealing layer of the lidstock film to a surface of the second packaging component, and a product sealed between the lidstock film and the second packaging component, wherein the lidstock film has been subjected to a pasteurization process.

15. 12. The package of claim 11, wherein the heat seal is manually peelable.

16. The package of claim 11 , wherein the surface of the second packaging component comprises a polypropylene-based polymer.

17. 12. The package of claim 11, wherein the package has a total composition comprising at least 80% by weight of a polyolefin-based polymer.

18. 12. The package of claim 11, wherein the package has a total composition comprising at least 80% by weight of a polypropylene-based polymer.

19. 20. The package of claim 17, wherein the package has a total composition comprising at least 90% by weight of a polypropylene-based polymer.

20. When measured according to ASTM F1927 under conditions of 23° C. and 50% RH, the covering film has a viscosity of 3.0 cc / m 2 12. The package of claim 11 having an oxygen transmission value of less than 100% by weight per day.

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