Laminated cook-in film
Abstract
A multi-layer structure, comprising a first polymeric film, laminated to a second polymeric film constructed separately from the first polymeric film, where: one, between the first and second polymeric films, can be contracted by heat, and the another, between the first and second polymeric films, cannot be contracted by heat; at least one of the aforementioned first and second polymer films is a barrier film, which has an oxygen permeance of no more than 150 cm3 / m2 or 24 hours at 23 ° C and 0% relative humidity (of according to ASTM 3985); said first polymeric film comprises: a first outer layer of polymeric film which, even when it has not been treated, has a surface energy of at least 0.034 J / m2; and at least 10 percent by weight of one, or more, polymers having a Vicat softening point of at least about 65 ° C; said first outer layer of polymeric film forms a first outer surface of said multi-layer structure; and said second polymeric film comprises an outer layer of the second polymeric film, which forms a second outer surface of said multi-layer structure.

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Projected expiry passed 22 December 2018, 7.8 years ago.
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2 claims: 2 independent, 0 dependent
- 1ES 2 229 558 T3 REIVINDICACIONES 1. Una estructura de capa múltiple, que comprende una primera película polimérica, laminada a una segunda película polimérica construida por separado respecto de la primera película polimérica, donde:una, de entre las películas poliméricas primera y segunda, se puede contraer mediante calor, y la otra, de entre las películas poliméricas primera y segunda, no se puede contraer mediante calor;al menos una, de las mencionadas películas poliméricas primera y segunda, es una película de barrera, que tiene una permeancia al oxígeno de no más de 150 cm 3 /m 2 · atm · 24 horas, a 23°C y al 0% de humedad relativa (de acuerdo con ASTM 3985);la mencionada primera película polimérica, comprende: una primera capa externa de película polimérica que, incluso cuando no ha sido tratada, tiene una energía superficial de, al menos, 0,034 J/m 2 ;y al menos un 10 por ciento en peso de uno, o más, polímeros que tienen un punto de reblandecimiento Vicat de al menos unos 65°C;la mencionada primera capa externa de película polimérica, forma una primera superficie externa de la mencionada estructura de capa múltiple;y la mencionada segunda película polimérica, comprende una capa externa de la segunda película polimérica, que forma una segunda superficie externa de la mencionada estructura de capa múltiple. 2. La estructura de capa múltiple de la reivindicación 1, donde la mencionada película polimérica es la película de barrera. 3. La estructura de capa múltiple de la reivindicación 2, donde la película de barrera tiene una permeancia al oxígeno de no más de 50 cm 3 /m 2 · atm · 24 horas, a 23°C y un 0% de humedad relativa. 4. La estructura de capa múltiple de la reivindicación 3, donde la película de barrera tiene una permeancia al oxígeno de no más de 25 cm 3 /m 2 · atm · 24 horas, a 23°C y un 0% de humedad relativa. 5. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 4, donde las mencionadas primera y segunda películas poliméricas están laminadas, de forma adhesiva, una a la otra. 6. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 5, donde la mencionada capa externa de la mencionada película polimérica tiene una energía superficial no tratada de, al menos, 0,036 J/m 2 . 7. La estructura de capa múltiple de la reivindicación 6, donde la mencionada capa externa de la mencionada película polimérica tiene una energía superficial no tratada de, al menos, 0,038 J/m 2 . 8. La estructura de capa múltiple de la reivindicación 7, donde la mencionada capa externa de la mencionada película polimérica tiene una energía superficial no tratada de, al menos, 0,040 J/m 2 . 9. La estructura de capa múltiple de la reivindicación 8, donde la mencionada capa externa de la mencionada película polimérica tiene una energía superficial no tratada de, al menos, 0,042 J/m 2 . 10. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 9, donde los mencionados uno, o más, polímeros de la mencionada capa externa de la mencionada primera película polimérica, tienen un punto de reblandecimiento Vicat de, al menos, 70°C. 11. La estructura de capa múltiple de la reivindicación 10, donde los mencionados uno o más polímeros de la mencionada capa externa, de la mencionada primera película polimérica, tienen un punto de reblandecimiento Vicat de, al menos, 75°C. 12. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 11, donde la mencionada capa externa de la mencionada película polimérica comprende, al menos, el 10 por ciento en peso de uno, o más, de un polímero que comprende unidades recurrentes derivadas de una a-olefina con 2 hasta 4 átomos de carbono, y unidades recurrentes derivadas de 1) un anhídrido insaturado, o
- 22) un monómero insaturado que comprende funcionalidad anhídrida; ES 2 229 558 T3 un polímero que comprende unidades recurrentes derivadas de ácido láctico; una poliamida; un poliéster; y un poliuretano. 13. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 11, donde la mencionada capa externa de la mencionada primera película polimérica, comprende al menos el 10 por ciento, en peso, de un interpolímero que comprende unidades recurrentes derivadas de, al menos, una α-olefina con 2 hasta 4 átomos de carbono y, al menos, el 2 por ciento en peso de unidades recurrentes derivadas de, al menos, un ácido insaturado con 3 hasta 18 átomos de carbono. 14. La estructura de capa múltiple de 13, donde el mencionado interpolímero tiene un punto de reblandecimiento Vicat, V, de V 111°C - 2,78°C(m A ) donde m A es el porcentaje en peso de unidades recurrentes en el mencionado interpolímero, derivadas del mencionado ácido insaturado con 3 hasta 18 átomos de carbono, con m A variando desde en torno al 2 hasta en torno al 25, incluidos. 15. La estructura de capa múltiple de la reivindicación 14, donde m A varía desde en torno al 4 hasta en torno al 15, incluidos. 16. La estructura de capa múltiple de la reivindicación 15, donde m A varía desde en torno al 6 hasta en torno al 12, incluidos. 17. La estructura de capa múltiple de la reivindicación 13, donde la mencionada, al menos una, α-olefina con 2 hasta 4 átomos de carbono, comprende etileno. 18. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 17, que comprende una imagen impresa, dispuesta entre las películas poliméricas primera y segunda. 19. La estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 18, donde la estructura de capa múltiple, tiene una contracción libre total de entre el 2% y el 40%, medida a 85°C. 20. Un tubo formado a partir de la estructura de capa múltiple, de cualquiera de las reivindicaciones 1 a 19, mediante sellar por pliegue la primera superficie externa a la segunda superficie externa. 21. Un tubo formado a partir de la estructura de capa múltiple de cualquiera de las reivindicaciones 1 a 19, por sellado a tope de la primera superficie externa a si misma, o a una cinta adhesiva aplicada sobre una junta, creada poniendo en contacto la mencionada primera superficie externa consigo misma. 22. Un proceso de envasado de un producto alimenticio que contiene proteínas, que comprende:a) sellar, o pinzar, un extremo de un tubo, formado mediante sellado por pliegue o sellado a tope, una estructura de capa múltiple, acorde a cualquiera de las reivindicaciones 1 a 19;b) introducir el mencionado producto alimenticio en el mencionado tubo;y c) sellar, o pinzar, el otro extremo del mencionado tubo para formar un envase.
Independent claims2
155 paragraphs in 9 sections, as filed
ES 2 229 558 T3
DESCRIPTION
Laminated film for internal firing.
Field of the invention
This invention relates generally to food packaging films, and more particularly to films in which food products can be cooked.
Background of the invention
Many food products are processed in thermoplastic film packages, subjecting the packaged product to elevated temperatures produced by, for example, immersion in hot water, or by exposure to steam. Often times such thermal processing is referred to as cook inside, and the films used in such processes are known as cook inside films.
A food product that is packaged and processed in this way can be refrigerated, shipped, and stored until the food product is to be consumed or, for example, sliced and repackaged into smaller parts, for retail display. Many sliced lunch meats are processed this way. Alternatively, the processed food can be immediately removed from the inner cooking container, for consumption, or for further processing (eg, for slicing and repackaging).
An internal cooking film must be able to withstand exposure to very severe temperature conditions, for extended periods of time, without compromising its ability to contain the food product. Indoor cooking processes typically involve a long cooking cycle. Immersion in hot water (that is, between about 55 ° to 65 ° C), for about 4 hours, is common; immersion in water from 70 ° to 100 ° C, or exposure to steam for up to 12 hours is not uncommon, although most interior cooking procedures do not normally involve temperatures exceeding about 90 ° C. During such extended periods of time, at elevated temperatures, any gaskets in a package formed by an inner cooking film preferably resist failure (ie, tearing into pieces).
Following the internal cooking process, preferably the film or package conforms, if not completely then at least substantially, to the shape of the contained food product. This is often accomplished by allowing the film to heat shrink, under bake conditions, to form a tightly tailored package. In other words, it is desirable that the inner cooking film has sufficient shrinkage energy so that the amount of thermal energy used to cook the product is also adequate to shrink the packaging film, comfortably around the contained product. Alternatively, the inner cooking film package may be made to contract around the contained food product, prior to initiating the inner cooking process, by, for example, placing the package in a heated environment prior to cooking.
The inner cooking film also preferably has sufficient adhesion to the cooked product to inhibit or prevent "outer cooking" (sometimes referred to as "purge"), which consists of water and / or juices that accumulate between the surface of the cookware. contained food product, and the contact surface of the packaging material with the food, during the internal cooking process. Preventing outside cooking can increase product yield, provide better tasting product, improve shelf life, and provide a more aesthetically pleasing packaged product. Films that adhere well to packaged food help reduce outside cooking.
Many internal cooking films are corona treated to increase the surface energy of the layers in contact with the food. However, corona treatment can be inconsistent, can result in a film with inconsistent adhesion, can result in a film that has a surface energy that decreases over time, and can interfere with the stability of a film.
Many types of meats are processed using the internal cooking procedure. Common examples include ham, hot dogs, some types of poultry, bologna, bologna, braunschweiger, and the like. However, such meats can vary substantially in fat and protein content. Obtaining adequate film adhesion to meat is more difficult relative to meats that are high in fat, low in protein, or have substantial levels of additives (starch, water, etc.). The adhesion of the film to the meat product is expected to be due to polar functionalities of the proteins, which are attracted to polar functionalities on the surface of the inner cooking film. For example, chicken has a relatively low fat content, and a relatively high protein content, therefore obtaining adequate film adhesion to chicken meat is relatively easy. However, ham, sausages, mortadella, bologna, or braunschweiger and the like, have relatively high fat content, and relatively low protein content; therefore obtaining adequate adhesion of the film to the meat is more difficult for such products (especially sausages, mortadella, bologna, or braunschweiger).
Some interior cook films currently available provide excellent adhesion to the meat product and do a good job of reducing exterior cook. Additionally, most movies
ES 2 229 558 T3 currently in use are capable of withstanding extended periods of time at the elevated temperatures described above; Correspondingly, such films are suitable for many interior cooking applications. However, some indoor cooking applications require even more stringent performance requirements. For example, some food products that are processed via the internal cooking process are sensitive to oxygen. Inner bake films for these products need to include one layer, or more, of oxygen barrier. Other internal cooking applications require that the film, or the packaging made from it, be printable and be able to retain any images printed on them.
One of the most problematic of these performance requirements is durability, when used in conjunction with a forming shoe (during the container molding process). When a film has a high degree of willingness to shrink in the transverse direction, it tends to "pinch" during the sealing stage of the process. This often causes such films with a high shrinkage disposition to break.
No interior cooking film currently available is expected to possess all of the following characteristics: (1) good adhesion to proteins, (2) extremely low oxygen permeance, (3) an ability to contract around the packaged product in a controlled manner, (4) a sealing layer with a softening point that is high enough to survive indoor cooking conditions, (5) an ability to be sealed, around a forming shoe, without pinching, (6) good resistance to clamp cuts, and (7) an ability to be printed, such that the printed image is protected during the internal cooking process, as well as in subsequent transportation and handling.
Summary of the invention
Briefly, the present invention provides a multilayer structure, including a first polymeric film, laminated to a second polymeric film. One of the two polymeric films can shrink by heat, and the other cannot shrink by heat. At least one of the films includes a barrier layer with an oxygen permeance of no more than about 150 cm<sup>3</sup>/ m<sup>2</sup>· Atm · 24 hours, at about 23 ° C and 0% relative humidity. (Units for oxygen permeance, as used throughout this document, are well known in the industry. To convert these to SI units, mol / m<sup>2</sup> SPa, we only need to multiply by a factor of 5, 097 x 10<sup>-15</sup>.) Each of the polymeric films includes an outer layer that forms an outer surface of the multi-layer structure (i.e., an outer layer of the first polymeric film, forms an outer surface of the multi-layer structures, while a layer outer surface of the second polymeric film, forms the other outer surface of the multilayer structure). The mentioned outer layer of the first polymeric film, even when untreated, has a surface energy of at least 0.034 J / m<sup>2</sup>, and includes at least about 10% (by weight) of a polymer having a Vicat softening point of at least about 65 ° C. The outer surface of the multi-layer structure formed from the outer layer of the first polymeric film (i.e., the first outer surface) can be sealed to itself, to the opposite outer surface (i.e., the second outer surface), or an optional adhesive tape, applied over a transverse seam joint, formed by contacting the first outer surface with itself. Each of the mentioned sealing techniques can result in the formation of a tube which, through additional sealing and cutting techniques, well known to those of ordinary skill in the art, can result in packages.
In another aspect, the present invention provides a multi-layer structure, including a first polymeric film, laminated to a second laminated polymeric film, at least one of which includes a barrier layer with an oxygen transmission coefficient of, no more than, about 150 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours, at about 23 ° C and 0% relative humidity. Each of the polymeric films includes an outer layer that forms an outer surface of the multilayer structure. The aforementioned outer layer of the first polymeric film includes at least one of, (1) a polymer that includes recurring units derived from an α-olefin with 2 to 4 carbon atoms, and at least 2 percent by weight of units. Recurrent units derived from an unsaturated acid with 3 to 18 carbon atoms, (2) an anhydride modified polymer, including recurring units derived from an α-olefin with 2 to 4 carbon atoms, (3) a polymer that includes recurring units derived from lactic acid, (4) a polyamide, (5) a polyester, and (6) a polyurethane. The sealing characteristics and the capabilities of the external surfaces of this multi-layer structure are the same as those stated for the multi-layer structure defined in the previous paragraph.
Both of the multi-layer structures just described are expected to possess each of the six characteristics discussed in the previous section of this document. As such, they are ideal for use as films, for use in many, if not all, interior cooking applications.
To aid in the understanding of the more detailed description of the invention that follows, certain definitions are provided immediately below. These definitions apply throughout this document, unless explicitly stated otherwise:
"Polymer" means the product of polymerization of one or more monomers, and is inclusive of homopolymers as well as copolymers, terpolymers, tetrapolymers, etc., and combinations and modifications of any of the foregoing;
ES 2 229 558 T3 "recurring unit" means the part of a polymer derived from a single reactive molecule; For example, a recurring unit of ethylene has the general formula - CH<sub>2</sub>CH<sub>2</sub>-;
"Homopolymer" denotes a polymer consisting essentially of a single type of recurring unit that repeats;
"Copolymer" denotes a polymer that includes recurring units derived from two reactants (usually monomers), and is inclusive of copolymers, terpolymers, tetrapolymers, and the like;
"Polyolefin" denotes a polymer in which some recurring units are derived from an olefinic monomer, which can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted (eg, olefin homopolymers, interpolymers of two or more olefins, copolymers of an olefin and a non-olefinic comonomer such as a vinyl monomer, and the like);
"(Meth) acrylic acid" refers to acrylic acid and / or methacrylic acid;
"(Meth) acrylate" means acrylate and / or methacrylate;
"Anhydrous functionality" means any group that contains a part of an anhydrous molecule, such as the derivative of maleic acid, fumaric acid, etc., whether mixed with one or more polymers, grafted onto a polymer, or subjected to polymerization with one more monomers;
"Oxygen permeance" (in the packaging industry, "permeance" is often referred to as "transmission rate") means the volume of oxygen (O2) b that passes through a given cross section of film (or layer of a film) b at a specified temperature and relative humidity, when measured according to a standard test such as ASTM D 1434 or D 3985;
"Longitudinal direction" means the direction along the length of a film, that is, in the direction of the film as it is cast during extrusion and / or coating;
"Transverse direction" means the direction through the film, and perpendicular to the machine direction;
"Free shrink" means the percent dimensional change, as measured by ASTM D 2732, in a 10 cm x 10 cm sample of film, being subjected to heat;
as a verb, "laminate" means to glue, or adhere (by means of, for example, adhesive bonding, pressure bonding, corona lamination, and the like) two or more items of film, manufactured separately, one to another so that they form a multi-layer structure; as a noun, "laminate" means a product produced by gluing, or adhesion, just described;
"Directly adhered", applied to film layers means adhesion of the subject film layer, to the subject film layer, without a bonding, adhesive, or other layer between the two;
"Between", when applied to film layers, means that the subject layer is arranged in the middle of two subject layers, regardless of whether the subject layer is directly adhered to the subject layers, or whether the subject layer is separated from the layers object by one, or more, additional layers;
"Inner layer", or "inner layer", means a layer of a film that has each of its major surfaces directly adhered to another layer of the film;
"Outer layer" refers to a layer of a film that has less than both of its major surfaces, directly adhered to other layers of the film;
"Inner layer" means the outer layer, of a film in which a product is packaged, that is closer, relative to the other layers of the film, to the packaged product;
"Outer layer" means the outer layer, of a film in which a product is packaged, which is the farthest, relative to the other layers of the film, from the packaged product;
"Barrier layer" denotes a film layer capable of excluding one, or more, gases (eg, O2);
"Misuse layer", means an external layer and / or an internal layer that resists abrasion, perforation, and other potential causes of reduction of the integrity of the container and / or quality of appearance;
"Tie layer" means an inner layer having the primary purpose of providing interlayer adhesion to adjacent layers, including otherwise non-adherent polymers;
"Raw coat" refers to any coat that is intended to increase resistance to misuse, strength,
ES 2 229 558 T3 the modulus, etc., of a multi-layer film and generally comprises polymers which are cheap, relative to other polymers in the film, which provide some objectives unrelated to resistance to misuse, the module, etc.,;
"Sealing layer" (or "sealing layer", or "heat sealing layer", or "sealing layer"), means (a) with respect to lap type seals, one or more outer film layer (s) (in general, up to the outer 75 μm of a film can be involved in sealing the film, to itself or to another layer) involved in sealing the film to itself, to another film layer of the same or another film, and / or other non-film item, or (b) with respect to fin-type seals, an inner film layer of a container, as well as support layers within 75 µm of the inner surface, of the innermost layer involved in sealing the film to itself;
as a noun, "sealing" means a bonding of a first region of a film surface, to a second region of a film surface (or opposing film surfaces), created by heating (for example, by means of a heated rod, hot air, infrared radiation, ultrasonic sealing, etc.) of the regions (or surfaces) down to at least their respective softening points;
"Clamp cut" means a reduction in package integrity due to either, or both, of the film gathering device, and the application of a pre-formed cable or clamp, used to seal one end of the package; and "cooking" means heating a food product, thereby effecting a change in one or more of the physical or chemical properties of the food product (eg, color, texture, flavor, and the like).
Films used in the food packaging industry are often divided into categories based on the number of layers that make up the film. Some films are made from a single polymer, or a blend of polymers, and therefore have only one layer. However, most films include more than one layer, and are referred to as multi-layer films. In general, the layers of a multilayer film can be classified as inner and outer layers. Usually. the inner layers are included to provide additional or different properties to the film. Additionally, any number of tie layers can be included in the film. Such tie layers may be present primarily on the outside of an inner layer, or they may themselves constitute a layer. Many tie layers include one or more polyolefins and / or polyurethanes, more preferably a modified ethylene / α-olefin copolymer, a modified ethylene / unsaturated ester copolymer, and / or a modified ethylene / unsaturated acid copolymer. Anhydride modified ethylene / α-olefin copolymer and anhydride modified ethylene / unsaturated ester copolymer are particularly preferred. Specific examples include anhydride grafted linear low density polyethylene, and ethylene anhydride grafted / vinyl acetate copolymer.
With respect to films used in internal cooking processes, generally one outer layer acts as a food contact layer, while the other acts as an outer layer. The former serves as the inner layer of a package formed from the film, and is in direct contact with the packaged food product. The second provides resistance against misuse, being arranged for this as the outermost layer of the container.
Some films, including many that are used in internal cooking processes, are oriented prior to use. Orientation involves stretching a film at an elevated temperature (the orientation temperature), followed by laying the film in an elongated configuration (eg, by baking). When an unconfined, unannealed, oriented polymeric film is subsequently heated to its orientation temperature, heat shrinkage occurs and the film returns almost to its original dimensions, ie, previously oriented.
An oriented film has an orientation ratio, which is the result of multiplying the extent to which the film has been expanded in various directions, usually two directions perpendicular to each other. Expansion in the longitudinal direction, sometimes referred to as the machine direction, occurs in the direction in which the film is cast during extrusion and / or coating. Expansion in the transverse direction means expansion across the width of the film, and is perpendicular to the longitudinal direction. Brief description of the drawings
Figure 1 is a greatly enlarged cross-sectional view of one embodiment of a multilayer structure in accordance with the present invention.
Figure 2 is a greatly enlarged cross-sectional view of another embodiment of a multilayer structure in accordance with the present invention.
Figure 3 is a greatly enlarged cross-sectional view of another embodiment of a multilayer structure in accordance with the present invention.
ES 2 229 558 T3
Figure 4 is an end view, not to scale, of a butt seal wrap of one embodiment of a multilayer structure in accordance with the present invention.
Figure 5 is an end view, not to scale, of another butt seal wrap of one embodiment of a multi-layer structure in accordance with the present invention.
Figure 6 is an end view, not to scale, of a sealing wrap, of one embodiment of a multilayer structure in accordance with the present invention.
Figure 7 is a perspective view, not to scale, of one embodiment of a packaged product according to the present invention.
Detailed Description of Illustrative Embodiments
The multilayer structure of the present invention involves at least two films that have been joined to form an integral structure. At least one of the films includes a barrier layer, more specifically a layer that has an oxygen permeance of no more than about 150 cm.<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours, at about 23 ° C (73 ° F) and 0% relative humidity. The presence of such a layer helps to ensure that the multilayer structure of the present invention can be used for those indoor cooking applications, where the exclusion of oxygen from the food product before, during, and / or after cooking , It is desirable.
Additionally, at least one of the films has an outer layer that inherently possesses a surface energy of at least 0.034 J / m.<sup>2</sup>, more preferably at least 0.038 J / m<sup>2</sup>, even more preferably at least 0.040 J / m<sup>2</sup>, and in the most preferred case at least 0.042 J / m<sup>2</sup>. ("Inherently possessed" means that the film does not need treatment to achieve the set level of surface energy.) Although this outer layer can be treated to further enhance its surface energy, by requiring that its inherent surface energy be relatively high (i.e. at least 0.034 J / m<sup>2</sup>), you get an advantage. Surface layers that need treatment to raise their surface energies (for example, to increase their adhesion to a closed food product), frequently lose some of that increase during processing. Specifically, since a film containing such a surface layer is molded into a container by being wrapped in a forming shoe, some of the surface functionalities created by the treatment process may disappear due to polishing. (This polishing phenomenon generally occurs more frequently in films that have a relatively high shrinkage force, that is, those films that have a transverse free shrinkage of at least 5%, and in particular those films that have a free shrinkage. of at least 7.5%.) However, since the outer layer described here has an inherently high surface energy (i.e. functionalities are inherent in the polymer, or polymers, of which the outer layer is formed, as opposed to being created after the layer is made), the film of the present invention does not suffer from a similar polishing problem.
In general, the multilayer structure of the present invention can have any total thickness, as long as it provides the desired properties, of the particular packaging operation in which it is to be used. However, the manifold structure of the present invention preferably has a total thickness (i.e., a combined thickness of all the layers) of between about 5 and about 500 jum, more preferably between about 10 and about 250 jum, even more preferably from about 25 to about 200 jum. Also preferably, it has a Young's modulus ranging from about 34 to about 3400 MPa, more preferably from about 70 to about 2100 MPa, and most preferably from about 280 to about 1400 MPa.
Referring to Figure 1, the multi-layer structure 10 includes a first polymeric film 11 and a second polymeric film 12. As exemplified in Figure 1, both films 11 and 12 are single-layer films, although either of these, or both, can be multilayer films. The surface of the first polymeric film 11 that is most distant from the second polymeric film 12, forms an outer surface 14 of a multilayer structure 10; the surface of the second polymeric film 12 that is most distant from the first polymeric film 11, forms the other outer surface 15 of the multilayer structure 10.
The first polymeric film 11, and a second polymeric film 12, are single-layer films; therefore its only layers are, correspondingly to the previously stated definitions, outer layers. Correspondingly, one of the polymeric film 11 and the second polymeric film 12 has a surface energy, even when untreated, of at least 0.034 J / m<sup>2</sup>, and includes at least 10% (by weight) of one, or more, polymers that have a Vicat softening point of at least about 65 ° C, while the other has an oxygen permeance of, not more than , about 150 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours, at about 23 ° C (73 ° F) and 0% relative humidity. To simplify the following discussion, it will be assumed that the first polymeric film 11 meets the requirements for surface energy and softening point, while the second polymeric film 12 will be assumed to have the required oxygen permeance.
The first polymeric film 11 preferably has a thickness of between about 1 to about 125 jum, more preferably from about 2.5 to about 50 jum, even more preferably between about 5 to about 25 jum, and in the case more preferably from about 7.5 to about 20 jum. The second polymeric film 12 preferably has
ES 2 229 558 T3 a thickness of between about 0.5 to about 75 pm, more preferably between about 1 to about 50 pm, even more preferably between about 2.5 to about 25 pm, and most preferably from about 5 until about 15 pm.
The first polymeric film 11 has a relatively high surface energy, even in the absence of a surface treatment (eg corona treatment). Specifically, its surface energy (untreated) is at least 0.034 J / m<sup>2</sup>, preferably at least 0.036 J / m<sup>2</sup>, more preferably at least 0.038 J / m<sup>2</sup>, even more preferably at least 0.040 J / m<sup>2</sup>, and in the most preferred case at least 0.042 J / m<sup>2</sup>. As previously discussed, films with high surface energies typically adhere better to food products. Correspondingly, in the multi-layer structure 10, the first polymeric film 11 acts as the food contact layer.
The first polymeric film 11 also includes one or more polymers, which have a Vicat softening point that is high enough to withstand internal cooking temperatures (i.e., its softening point is above the temperature at which the foodstuff to be cooked), but low enough to seal easily when subjected to normal heat sealing conditions. Specifically, the first polymeric film 11 includes at least about 10% (by weight), preferably at least about 25% (by weight), more preferably at least about 50% (by weight). ), most preferably at least about 75% (by weight) of at least one polymer having a Vicat softening point of at least about 65 ° C, preferably at least about 70 ° C , and more preferably at least about 75 ° C. Therefore, in addition to acting as the food contact layer, the outer surface 14 of the first polymeric film 11 is involved in sealing the multi-layer structure 10 to form the desired inner cooking container. (See below for additional description.)
In a preferred embodiment, the polymer, or polymers, which provide the first polymeric film 11 with its high surface energy, further have the mentioned Vicat softening point.
At least six classes of polymers have been identified that have the required Vicat softening point, and provide the desired surface energy discussed above. The first of these classes of polymers are interpolymers of one or more α-olefins with 2 to 4 carbon atoms (i.e., ethylene, propylene, and 1-butene), and one or more unsaturated acids with 3 to 18 carbon atoms. carbon. Recurring units derived from C3-18 unsaturated acids constitute at least 2 percent, by weight, of the interpolymer. Of the α-olefins mentioned, ethylene is preferred. Useful unsaturated acids have the general formula CH2 = CRCOOH, where R is hydrogen or an alkyl, cycloalkyl, aryl, alkoxy, etc. group with 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms. The specific identity of the R group is not important, as it does not interfere with the ability of the unsaturated acid to copolymerize with the α-olefin, and the resulting interpolymer has the properties previously discussed. Preferred unsaturated acids include methacrylic acid, and acrylic acid, with the latter being particularly preferred. Regardless of the identity of the α-olefin (s) and the unsaturated acid (s), the resulting interpolymer preferably has a melt index of between about 0.25 to about 50, more preferably from about 0.5 to about 10, and even more preferably from about 1 to about 5.
As previously mentioned, in a preferred embodiment, the polymer (s) that provide the first polymeric film 11 with its high surface energy, also have the required Vicat softening point (i.e., at least about 65 ° C, preferably at less than about 70 ° C, more preferably at least about 75 ° C). For some applications, those polymers having a Vicat softening point (V) defined by the formula may be preferred.
V> 111 ° C - 2.78 ° C (m<sub>TO</sub>) where M<sub>TO</sub> is the percentage of recurring units in the unsaturated acid-derived interpolymer, varying between about 2 to about 25, preferably varying from about 4 to about 15, more preferably varying from about 6 to about 12 (with all the above ranges being inclusive of extreme values). The y-intercept value of the Vicat softening point in the above formula is more preferably 113 ° C, even more preferably 115 ° C, even more preferably 117 ° C, and most preferably 120 ° C. Α-olefin / unsaturated acid interpolymers include ethylene copolymers of NUCREL ™ ARX 84-1 and ARX 84-2 / acrylic acid (DuPont de Numours; Wilimington, Del.), Exhibiting Vicat softening points of about 97 ° C and 100 ° C, respectively. (The former includes about 6% (by weight) of recurring units derived from acrylic acid, while the latter includes about 7% (by weight) of recurring units derived from acrylic acid.)
The second class of polymers that have Vicat softening points in the necessary range, and surface energy characteristics, are polyolefins that include anhydrous functionality, either in the central axis of the polymer, or hanging from it. In general, this class of polyolefins includes interpolymers of one or more α-olefins with 2 to 4 carbon atoms (i.e., ethylene, propylene, and 1-butene), and one or more anhydrides or unsaturated acids, interpolymers of one or plus α-olefins with 2 to 4 carbon atoms and one or more unsaturated monomers that include anhydrous functionality, and mixtures of polyolefins and one or more compounds that include anhydrous functionality. Examples of this class of polyolefins include BYNEL resin<sup>TM</sup> (DuPont), TYMOR ™ resin (Morton International Inc .; Chicago, Illinois), ADMER resin (Quantum Co .; Cincinnati, Ohio), and the LOTADER ™ series of
ES 2 229 558 T3 ethylene / alkyl / acrylate / maleic anhydride interpolymers (Elf-Atochem, Inc .; Buffalo, NY). Regardless of the identity of the α-olefin, or α-olefins, and the particular material (s) that include anhydride functionality, the resulting polymer, or mixture, preferably includes between about 0.1 and about 10 percent. of anhydrous functionality, more preferably between about 0.5 to about 7.5, percent by weight of anhydrous functionality, even more preferably between about 1 to about 5 percent by weight of anhydrous functionality, and most preferably between about 2 and about 4 percent by weight of anhydrous functionality.
The third class of useful polymers are homopolymers, and interpolymers, of lactic acid. In particular, where the multilayer structure is to undergo heat sealing, those polymers having a softening point of not more than about 200 ° C, preferably not more than about 190 ° C, more preferably not more than about 200 ° C, are preferred. 180 ° C, and most preferably no more than about 170 ° C.
The fourth class of useful polymers are polyamides (ie, nylons). Suitable polyamides, from which the outer layer can be molded, include one or more of the following: polyamide 6, polyamide 66, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 69, polyamide 610, polyamide 612, polyamide 6I, polyamide 6T, polyamide MXD / 6, and copolymers of these. Examples of preferred polyamides include 6/12 copolyamide, especially where the polymer includes from about 20 to about 80 percent by weight of recurring units derived from caprolactam, and from about 20 to about 80 percent. , by weight, of recurring units derived from laurolactam; polyamide 12; copolyamide 66/69/61, especially where the polymer includes (a) from about 10 to about 50 weight percent, more preferably from about 20 to about 40 weight percent , of recurring units derived from hexamethylene adipamide, (b) from about 10 to about 50 weight percent, more preferably from about 20 to about 40 weight percent, of recurring units derived from hexamethylene acylamide, and (c) from about 10 to about 60 weight percent, more preferably from about 10 to about 40 weight percent, of recurring units derived from hexamethylene isophthalamide, copolyamide 66/610; copolyamide 6/66; and copolyamide 6/69. Particularly where the first polymeric film 11 is to be involved in heat sealing, polyamides having softening points of not more than about 200 ° C, preferably not more than about 190 ° C, more preferably not more than about 180 ° C, and most preferably no more than about 170 ° C, may be preferable. Combining a relatively low-melting polyamide (for example, one that has a melting point of between about 120 ° and about 150 ° C, preferably from about 130 ° to about 150 ° C) with a higher melting polyamide (for example, one that has a melting point of between about 150 ° and about 200 ° C, preferably from about 160 ° to about 190 ° C) can result in a mixture having highly desirable characteristics. An example of such a blend is a 50:50 blend of 6/12 copolyamide and polyamide 12. Adding one or more polymers that are compatible with the polyamide, or polyamide blend, to modify the properties of the polyamide, may be beneficial to some applications. Polyolefins are an example of such a polymer.
Suitable polyolefins include polyethylene homopolymers and interpolymers, polypropylene homopolymers and interpolymers, and polybutene homopolymers and interpolymers. Preferred examples include ethylene / α-olefin copolymer, propylene / α-olefin copolymer, butene / α-olefin copolymer, ethylene / unsaturated ester copolymer, and ethylene / unsaturated acid copolymer. Specific examples of preferred polyolefins include one or more linear low density polyethylene (LLDPE), ethylene / vinyl acetate (EVA) copolymer, propylene / ethylene copolymer, and propylene copolymer. / butene. An ethylene / α-olefin copolymer includes recurring units derived from ethylene and one or more α-olefins with 3 to 18 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene , 4-methyl-1-pentene, and the like. The resulting polymer molecules include long chains, with relatively few side chain branches; additionally, the side branching that is present is short, compared to non-linear polyethylenes (eg low density homopolyethylene). Ethylene / α-olefin copolymers generally have a density in the range of about 0.86 g / cm<sup>3</sup> up to 0.94 g / cm<sup>3</sup>. LLPDE is generally understood to include the group of ethylene / α-olefin copolymers that falls in the density range of about 0.915 to about 0.94 g / cm<sup>3</sup>. Sometimes linear polyethylenes that have densities between about 0.926 to about 0.94 g / cm<sup>3</sup> They are referred to as Linear Medium Density Polyethylene (LMDPE). Lower density ethylene / α-olefin copolymers are often referred to as very low density polyethylene, VLDPE (very low density polyethylelne), which is commonly understood to be ethylene / butene copolymers, with a range density from about 0.88 to about 0.91 g / cm3 (Union Carbide Corp .; Danbury, Connecticut), and ultra-low density polyethylene, ULDPE (ultra-low density polyethylele), which are generally understood to be ethylene / octene copolymers (Dow Chemical Co .; Midland, Michigan).
Ethylene / α-olefin copolymers also include homogeneous polymers, which differ structurally from heterogeneous polymers (e.g., ULDPE, VLDPE, LLDPE, and LMDPE), in that they exhibit a common monomer sequence within a chain, a reflection of the distribution sequence of all the chains, and a similarity in the length of all the chains (ie, a narrower molecular weight distribution). Furthermore, homogeneous polymers are typically prepared using singular point type catalysts (eg, metallocenes), rather than Ziegler-Natta catalysts. Such singular point type catalysts typically have only one type of catalyst center, which is expected to be the basis for the homogeneity of the polymers so produced. Examples of commercially available homogeneous polymers include EXACT linear ethylene copolymers<sup>TM</sup>, catalyzed by metallocene / α-olefin (Exxon Chemical Co .; Baytown, Texas); linear ethylene copolymers
ES 2 229 558 T3
TAFMER<sup>TM</sup>/ α-olefin (Mitsui Petrochemical Corp.); and long chain AFFINITY ™ / α-olefin branched ethylene copolymers (Dow Chemical Co.).
The fifth class of useful polymers are polyesters. Although many polyesters have softening points that are too high, to make them good candidates for sealant layers in inner-cook films, those with melting points of no more than about 200 ° C, preferably no more than about 190 ° C. , more preferably no more than 180 ° C, and most preferably no more than about 170 ° C, they may be useful in accordance with the present invention. An exemplary polyester is KODABOND ™ Copolyester 5116 (Eastman Chemical Co .; Kingsport, Tenn.), Which has a melting point of about 180 ° C.
The sixth class of polymers found to be useful for connection to the first polymeric film 11 are polyurethanes, particularly those with melting points of no more than about 200 ° C, preferably no more than about 190 ° C, plus preferably not more than about 180 ° C, and most preferably not more than about 170 ° C. Those of ordinary skill in the art are familiar with numerous types of polyurethanes, including many that have melting points within the preferred ranges mentioned.
Although six classes of polymers useful in the first polymeric film 11 have been exemplified here, the skilled worker can probably imagine other types of polymers that meet the previously discussed softening point and adhesion requirements. Such additional classes of polymers can also be employed in the first polymeric film 11.
Of the foregoing classes of polymers, the first and fourth are preferred. Due to their relatively low cost, and excellent performance characteristics, the first class of polymers is particularly preferred. Most preferred among these are the NUCREL ™ ARX ethylene / acrylic acid copolymers.
In addition to the aforementioned requirements for adhesion and softening point, the polymer (or polymers) to be used in the first polymeric film 11 preferably have a melt flow index ranging from about 0.1 to 1000 g / 10 min. , more preferably from about 0.5 to 500 g / 10 minutes, and most preferably from about 1 to 50 g / 10 min., measured according to ASTM D-1238 (at 235 ° C and 1 kg) .
In addition to at least one of the preceding six classes of polymers, the first polymeric film 11 may include one, or more, of other polymers (as described in connection with polyamides, above). Examples of polymers that can be blended with at least one of the preceding six classes of polymers include polyolefins, polystyrenes, ethylene / vinyl alcohol copolymers (EVOH, ethylene / vinyl alcohol), and the like; in particular, preferred among these are polyolefins and polystyrenes. Preferred types of polyolefins have been previously described.
Blending one or more polymers with a relatively high Vicat softening point - that is, a Vicat softening point of between about 85 ° to about 160 ° C, preferably from about 90 ° to about 130 ° C, more preferably from about 95 ° to about 125 ° C, and most preferably from about 100 ° to about 120 ° C - with the polymer, or polymers, having a relatively low Vicat softening point (and chosen from one, of the six classes of polymers described above), it may be preferable for some applications such as, for example, where we want to increase the capacity, of the first polymeric film 11, to withstand internal cooking conditions. However, the first polymeric film 11 preferably includes only polymers having melting points of not more than about 200 ° C, preferably not more than about 190 ° C, more preferably not more than about 180 ° C, and in the more preferably not more than about 170 ° C. Furthermore, especially where the food product has a relatively high fat content, and a relatively low protein content (for example ham, sausages, mortadella, bologna, braunschweiger, etc.), the incorporation of non-polar polymers in the first polymeric film 11 it can reduce its ability to adhere to the food product; therefore, at least around 20% (by weight), preferably at least around 30% (by weight), more preferably at least around 40% (by weight), even more preferably around 50% (by weight), and in the most preferred case at least about 75% (by weight) of the first polymeric film 11, is derived from one or more polymers of the six classes set out above.
Preferably, the first polymeric film 11 includes at least one type of antioxidant that may be present in an amount of between about 50 to about 10,000 parts per million (ppm), preferably between about 100 to about 5,000 ppm, and more preferably between about 200. up to about 1,000 ppm. The presence of an antioxidant can be particularly useful when the first polymeric film 11, or a structure of multiples of 10, is to be irradiated. The presence of an antioxidant is preferred where the first polymeric film 11 includes an α-olefin / unsaturated acid interpolymer, which has a Vicat softening point that falls within the mentioned formula, because such polymers are expected to be more susceptible to crosslinking than previously available α-olefin / acrylic acid copolymers (eg ionomers). Sealing layers that include a crosslinked polymer are relatively difficult to heat seal; therefore, the presence of cross-linked polymers is normally undesirable.
Although a first polymeric film 11 may be blown, or melt, it is preferably oriented, and more preferably biaxially oriented. Orientation techniques are well known in the art. The first polymeric film 11 can have a Young's modulus ranging from about 20 to about 3400 MPa.
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If desired, or necessary to increase its adhesion to the food product, the outer surface 14 can be corona treated. This involves bringing the first polymeric film 11 into proximity with an ionized gas, containing oxygen or nitrogen, such as ambient air. Different forms of plasma treatment, known to those skilled in the art, can be used to perform corona treatment on the external surface 14. Exemplary techniques are described in, for example, US Patent Nos. 4,120,716 (Bonet) and 4,879,430 (Hoffman), the disclosures of which are incorporated herein by reference.
The second polymeric film 12 can be generally classified as a barrier film; specifically, at about 23 ° C and 0% relative humidity, it has an oxygen permeance of no more than about 150 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. In order of increasing preference, the second polymeric film 12 preferably has an oxygen permeance of no more than about 125 cm.<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 100 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 75 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 50 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 30 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 20 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, and 10 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours.
Representative examples of polymers that may be useful in the second polymeric film 12 include EVOH, polyvinylidene chloride (PVDC), polyamides, polyesters, and polyalkylene carbonates. Preferred polymers for use in the second polymeric film 12 include EVOH and polyamides, with the former being the most preferred. In particular, EVOH having from about 32 to about 48 mole percent, more preferably about 38 to about 44 mole percent, of recurring units derived from ethylene, can provide excellent barrier characteristics.
The second polymeric film 12 may be blown, cast, or oriented, preferably biaxially oriented, according to techniques well known in the art. Optionally, the second polymeric film 12 may be heat sealed, or annealed, at a temperature between about 60 ° to 200 ° C, preferably from about 70 ° to 150 ° C, and more preferably from about 80 ° to 90 ° C. .
In a preferred embodiment, the film that is to contact a packaged food product (i.e., the first polymeric film 11 in this case) cannot be heat-shrunk, and the other film (i.e., the second polymeric film 12 in this case case), is biaxially oriented, and can be heat-shrunk. In a preferred embodiment, the multilayer structure 10 has marginal free shrinkage in the transverse direction.
The second polymeric film 12 is laminated to the first polymeric film 11 by adhesive 13. Materials that can be used as the adhesive 13 include solvent-based resins (eg, polyurethanes), and solvent-free resins.
The multilayer structure 10 may have a longitudinal direction of free shrinkage of at least 1% and a transverse direction of free shrinkage of at least 1% (both average at 85 ° C). Additionally, the multilayer structure 10 may have free shrinkage (at 85 ° C) in at least one, between the longitudinal (L) and transverse (T) directions, of at least 2%, at least 5%, when minus 10%, at least 15%, at least 20%, at least 25%, and even up to 50%. Preferably, the multilayer structures 10 are biaxially oriented, and preferably have a free shrink (at 85 ° C) of between about 1 to about 20%, more preferably between about 2 to about 20%. around 15%, and even more preferably between around 3 to around 10%, in each of the L and T directions, and a total free contraction (L + T) of between around one 2 up to around 40%, preferably between around 2.5 to around 30%, more preferably between around 3 to around 20%, and even more preferably between around 5 to around 15% .
For certain applications, it may be preferred to orient, and then heat seal or anneal the multi-layer structure 10 (or alternatively one or both of the first polymeric film 11 and the second polymeric film 12), to provide free shrinkage. in the T direction (at 85 ° C) less than 10%, more preferably less than 5%. Heat sealing can be done at a temperature from about 60 ° to 200 ° C, preferably from about 70 ° to 150 ° C, and more preferably from about 80 ° to 90 ° C.
Although the multi-layer structure 10 is shown with the adhesive 13, laminating the first polymeric layer 11 to the second polymeric film 12, the adhesive 13 need not be present where some other laminating technique is employed. The ordinary skilled professional is aware of such techniques including, for example, corona lamination.
Although not necessary for its utility, the multilayer structure 10 can be irradiated, by subjecting it to radiation such as corona discharge, plasma, fire, ultraviolet, X-rays, gamma rays, beta rays, and high energy electronic treatment. . Such radiation can alter the surface of the multilayer structure 10, and / or induce crosslinking between molecules of the polymers contained therein. The use of ionizing radiation for cross-linked polymers present in a film structure is disclosed in US Patent No. 4,064,296 (Bornstein et al.), The teachings of which are incorporated herein by reference. Radiation doses are often measured in RAD units, one million RADS being designated by "MR", or in terms of the unit kiloGray (kGy), where 10 kGy represents 1 MR. To produce the crosslinking, the polymer is subjected to appropriate radiation doses of high-energy electrons (although the radiation is not limited to electrons from an accelerator, since any ionizing radiation can be employed), preferably using an electron accelerator. (although other accelerators, such as a Van de Graaff or resonant transformer, can be used). An adequate dose of electrons from
ES 2 229 558 T3 high energy, when measured by dosimetry techniques, is in the range of above about 16 to about 166 kGy, more preferably about 30 to about 139 kGy, and even more preferably from about 50 to about 100 kGy. The true amount of radiation used in a concrete multilayer structure depends on its components and the end use.
Referring now to Figure 2, the multilayer structure 20 includes a first polymeric film 21, and a second polymeric film 22. The surface of the first polymeric film 21 that is most distant from the second polymeric film 22 constitutes an outer surface 24 of a multilayer structure 20; the surface of the second polymeric film 22 that is most distant from the first polymeric film 21 constitutes the other outer surface 25 of the multilayer structure 20. The first polymeric film 21 is laminated to the second polymeric structure 22, by means of adhesive 23. As previously described, other means of lamination (eg corona lamination) can be used in place of adhesive 23.
Both films 21 and 22 are multi-layer films although, as previously described with respect to Figure 1, either or both can form single-layer films. More specifically, each of films 21 and 22 includes two layers. For the sake of simplicity, in the following discussion, the first polymeric film 21 is assumed to meet the requirements for surface energy and softening point, while the second polymeric film 22 is assumed to have the required oxygen permeance.
The first polymeric film 21 includes a seal layer 26 and a raw layer 27. The seal layer 26 is the outer layer that has the necessary surface energy described above (that is, an untreated surface energy of at least 0 , 34 U / m<sup>2</sup>) and includes at least about 10% (by weight) of one or more polymers that have the required Vicat softening point. One surface of the sealing layer 26 constitutes the outer surface 24 of the multi-layer structure 20. The sealing layer 26 can be made in the same way, and of the same materials, as previously discussed in connection with the first film. polymeric 11 of figure 1. The seal layer 26 preferably has a thickness of between about 1 to about 125 µm, and more preferably between about 2.5 to about 20 µm.
Raw layer 27 includes one, or more, of the following components: a polyolefin such as those described above, specifically EVA, ethylene / alkyl acrylate copolymers (eg, ethylene / methyl acrylate copolymers, ethyl acrylate , butyl acrylate, etc.), LDPE, and ethylene / α-olefin copolymers (eg LLDPE, VLDPE, etc.); a polystyrene, such as those described above; a polyamide, such as those described above; a polyester as described above; a polyurethane; EVOH; PVDC; a polyester; and a polycarbonate. Each of the foregoing includes interpolymers as well as homopolymers. Additionally, polymers mixed with starch may also be employed in the raw layer 27. The raw layer 27 preferably has a thickness of between about 1 to about 125 pm, more preferably between about 2.5 and about 50. pm, still more preferably between about 5 and about 25 jum, and most preferably between about 7.5 and about 20 pm.
Each or both of the seal layer 26 and the green layer 27 may include one or more polymers other than those discussed in the preceding paragraphs. Examples of polymers that can be blended with at least one of the preceding six classes of polymers include polyolefins, polystyrenes, EVOH, and the like; particularly preferred among these are polyolefins and polystyrenes such as those previously described.
One or more polymers with a relatively high Vicat softening point (i.e., a Vicat softening point of between about 85 ° to about 160 ° C, preferably from about 90 ° to about 130 ° C, more preferably from about 95 ° to about 125 ° C, and more preferably from about 100 ° to about 120 ° C), can be mixed with the polymer, or polymers, having a relatively low Vicat softening point (and chosen from one of the six classes of polymers described above). However, the seal layer 26 preferably includes only polymers having melting points of no more than about 200 ° C, preferably no more than about 190 ° C, more preferably no more than about 180 ° C, and in the most preferably no more than about 170 ° C. Also, the incorporation of non-polar polymers in the sealing layer 26 can reduce its ability to adhere to the food product; consequently, at least about 10% (by weight), preferably at least 20% throne (step, more preferably at least 30% throne (by weight), even more preferably at least about 50% % (by weight), and most preferably at least about 75% (by weight) of the seal layer 26, is derived from one or more polymers from the six classes set out above.
Optionally, a tie layer (not shown) can be disposed between seal layer 26 and raw layer 27. As with other films, seal layers can help maintain good interlayer adhesion between seal layer 26 and the raw layer 27. Where the polymers in the sealing layer 26 and the raw layer 27 are sufficiently similar in composition, a sealing layer is unnecessary.
As previously described with respect to the first polymeric film 11 of Figure 1, the first polymeric film 21 may include, in the sealing layer 26, at least one type of antioxidant, in an amount of between about 50 to about 10,000 ppm, preferably from about 10 to about 5,000 ppm, and more preferably from about 200 to about 1,000 ppm. The presence of an antioxidant can be particularly useful where the first polymeric film 21 and the multilayer structure 20 are to be irradiated. The presence of an antioxidant is especially preferred, where seal layer 26 includes an α-olefin / unsaturated acid interpolymer, which has a Vicat softening point that falls within the formula previously described (for reasons previously discussed).
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Although the first polymeric film 21 may be blown or melt, it is preferably oriented, more preferably biaxially oriented. The first polymeric film 21 can have a Young's modulus ranging from about 20 to 3,400 MPa. The outer surface 24 can be corona treated in a manner previously described, if desired.
The second polymeric film 22 includes the barrier layer 28 and the raw layer 29. The barrier layer 28, at about 23 ° C and 0% relative humidity, has an oxygen permeance of no more than about 150 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. Arranged in order of increasing preference, barrier layer 28 preferably has an oxygen permeance of no more than about 125 cm.<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 100 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 75 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 50 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 30 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 20 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, and 10 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. Representative examples of polymers that may be useful in the barrier layer 28 are the same as those discussed with respect to the second polymeric film 12 of Figure 1, namely EVOH, PVDC, polyamides, polyesters, and polyalkylene carbonates, EVOH and polyamides being preferred, in particular the former. In particular, EVOH having from about 32 to about 48 mole percent, preferably from about 38 to about 44 mole percent, of recurring units derived from ethylene can provide excellent barrier characteristics.
Raw layer 29 includes one, or more, polymers selected from the group set forth with respect to raw layer 27, above. The raw layer 29 preferably has a thickness of from about 1 to about 125 µm, more preferably from about 2.5 to about 50 µm, even more preferably from about 5 to about 25 µm, and more preferably. preferably from about 7.5 to about 20 jum.
The second polymeric film 22 may be blown, cast, or oriented, preferably biaxially oriented. Optionally, the second polymeric film 22 may be heat sealed or annealed at a temperature of from about 60 ° to 200 ° C, preferably from about 70 ° to 150 ° C, and more preferably from about 80 ° to 90 ° C.
The second polymeric film 22 is laminated to the first polymeric film 21, by the adhesive 23, which may be a material such as those described above in connection with the adhesive 13 of Figure 1.
The multilayer structure 20 can have free shrinkage, of at least 1% in both the L and T directions (both at the temperature of 85 ° C). Additionally, the multilayer structure 20 can have a free shrinkage (at a temperature of 85 ° C) in at least one of the L and T directions, of at least 2%, at least 5%, at least 10 %, at least 15%, at least 20%, at least 25%, even up to 50%. Preferably, the multilayer structure 10 is biaxially oriented, and preferably has a free shrinkage (at 85 ° C) of between about 1 to about 20%, more preferably from about 2 to about 20%. 15%, and even more preferably from about 3 to about 10%, in each of the L and T directions, and a total free shrink (L + T) of between about 2 to about 40 %, preferably between around 2.5 to around 30%, more preferably between around 3 to around 20%, and even more preferably between around 5 to around 15% .
The multilayer structure 20 can be irradiated as described above. A suitable dose of high energy electrons is in the range of from about 16 to about 166 kGy, more preferably about 30 to about 139 kGy, and even more preferably between 50 to about 100 kGy.
Referring now to FIG. 3, the multilayer structure 30 includes the first polymeric film 31, and the second polymeric film 32, with the latter having the printed image 42 disposed on one of its primary surfaces. The surface of the first polymeric film 31 that is most distant from the second polymeric film 32 constitutes an outer surface 34 of the multilayer structure 30; the surface of the second polymeric film 32 that is most distant from the first polymeric film 31 constitutes the other outer surface 35 of the multilayer structure 30. The first polymeric film 31 is laminated to the second polymeric film 32, by means of adhesive 33. As before, other means of laminating (eg corona lamination) can be used in place of adhesive 33.
Both films 31 and 32 are multi-layer films, although some or both may be single-layer films if desired. More specifically, each of films 31 and 32 includes three layers. For the sake of simplicity, the first polymeric film 31 is assumed to meet the requirements for surface energy and softening point, while the second polymeric film 32 is assumed to have the required oxygen permeance.
The first polymeric film 31 includes sealing layer 36, the first raw layer 37, and the second raw layer 38. The sealing layer 36 is the outer layer having the necessary surface energy described above (i.e., a surface energy untreated of at least 0.34 J / m<sup>2</sup>), and includes at least about 10% (by weight) of one, or more, polymers that have the required Vicat softening point. One surface of the sealing layer 36 constitutes the outer surface 34 of the multi-layer structure 30. The sealing layer 36 may be made in the same way, and of the same materials, as previously discussed in connection with the layer of seal 26 of figure 2. The sealing layer 36 preferably has a thickness of from about 1 to about 125 µm, more preferably from about 2.5 to about 50 µm, even more preferably from about 5 to about 25 µm, and most preferably between about 7.5 to about 20 μm.
ES 2 229 558 T3
The raw layers 37 and 38 include one or more of the polymers described as suitable relative to the green layer 27 of Figure 2. Each of the raw layers 37 and 38 preferably have a thickness of between 30 about 1 to about 125 pm, more preferably between about 2.5 to about 50 pm, even more preferably between about 5 to about 25 pm, and most preferably between about 7.5 to about 20 pm.
Any of the seal layers 36, or all of them, the first raw layer 36, and the second raw layer 38, can include one or more polymers, which can be blended with at least one of the above six classes of polymers. , including those previously discussed with respect to Figure 2, in particular polyolefins and polystyrenes.
One or more polymers with a relatively high Vicat softening point (i.e., a Vicat softening point of between about 85 ° to about 160 ° C, preferably from about 90 ° to about 130 ° C, more preferably from about 95 ° to about 125 ° C, and more preferably from about 100 ° to about 120 ° C), can be mixed with the polymer, or polymers, having a relatively low Vicat softening point (and chosen from one of the six classes of polymers previously described). However, the seal layer 36 preferably includes only polymers having melting points of no more than about 200 ° C, preferably no more than about 190 ° C, more preferably no more than about 180 ° C, and in the case more preferably not more than about 170 ° C. In addition, the incorporation of nonpolar polymers in the sealing layer 36 can reduce its ability to adhere to the food product; correspondingly, at least 10% (by weight), preferably at least 20% (by weight), and more preferably at least about 30% (by weight) of the sealing layer 36, is derived from one, or more, polymers from among the six classes set out above.
Optionally, to help maintain good interlayer adhesion, a tie layer (not shown) may be disposed between the seal layer 36 and the first raw layer 36, and / or between the first raw layer 37 and the second raw layer. gross 38.
Although not shown in Figure 3, other additional layers may also be present in the first polymeric film 31. Specifically, up to about 15, preferably up to 12, more preferably up to 9, and most preferably up to 5 additional layers may be present.
The first polymeric film 31 can include in the sealing layer 36, at least one type of antioxidant, in an amount of between about 50 to about 10.00 ppm, preferably from about 100 to about 5000 ppm, and more preferably from about 200 to about 1,000 ppm. The presence of an antioxidant can be useful, where the first polymeric film 31, or the structure of multiple every 30, is to be irradiated. The presence of an antioxidant is especially preferred, where the sealing layer 36 includes those α-olefin / unsaturated acid interpolymers of the type previously described.
Although the first polymeric film 31 may be blown or melt, it is preferably oriented, more preferably biaxially oriented. The first polymeric film 31 can have a Young's modulus ranging from about 20 to 3,400 MPa. The outer surface 34 may be corona treated in a manner previously described, if desired.
The second polymeric film 32 includes the barrier layer 39, the first raw layer 40, and the second raw layer 41. In the multi-layer structure 30, the bar layer 39 is disposed between the raw layers 40 and 41 Although preferred, it is not essential to the utility of the multilayer structure 30.
Barrier layer 39 at about 23 ° C and 0% relative humidity, has an oxygen permeance of no more than about 150 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. In increasing order of preference, barrier layer 39 preferably has an oxygen permeance of no more than about 125 cm.<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 100 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 75 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 50 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 30 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, 20 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, and 10 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. Representative examples of polymers that may be useful in the barrier layer 39 are the same as those set forth with respect to the second polymeric film 12 of Figure 1, namely EVOH, PVDC, polyamides, polyesters, and polyalkylene carbonates, with EVOH and polyamides being preferred, especially the former. In particular, EVOH having from about 32 to about 48 mole percent, preferably from about 38 to about 44 mole percent, of recurring units derived from ethylene can provide excellent barrier characteristics.
The raw layers 40 and 41 include one or more polymers described as useful, relative to the raw layer 29 of Figure 2. Each of the raw layers 40 and 41, preferably have a thickness of between about 1 to about 125 pm, more preferably between about 2.5 and about 50 pm, still more preferably between about 5 to about 25 pm, and most preferably from about 7.5 to about 20 pm.
Optionally, to aid in maintaining good intercoat adhesion, a tie layer (not shown) can be disposed between the barrier layer 39 and the first raw layer 40, and / or the second raw layer 41. Other layers additional, may also be present in the second polymeric film 32. Specifically, up to about 15, preferably up to 12, more preferably up to about 9, and most preferably up to about 5 additional layers may be present.
The second polymeric film 32 may be blown, cast, or oriented, preferably so oriented.
ES 2 229 558 T3 biaxial. Optionally, the subsequent polymeric film 32 can be heat sealed or annealed at a temperature between about 60 ° and 200 ° C, preferably between about 70 ° and 150 ° C, and more preferably between about 80 ° and 90 ° C.
Disposed on the first surface of the second polymeric film 32, opposite the outer surface 35, is the printed image 42. Although shown disposed on the second polymeric film 32, the printed image 42 (or, more precisely, the reverse of this ), may be disposed on the primary surface of the first polymeric film 31, opposite the outer surface 34. To help maintain good adhesion to the printed image 42, the first raw layer 40 (or the second raw layer 38 if the printed image 42 is disposed on the first polymeric film 31), may be corona treated, or it may be used an adhesive between layers. By positioning the printed image 42 within the multilayer structure 30, it is protected from scratches, and other aggressions normally encountered during shipping and display.
The second polymeric film 32 is laminated to the first polymeric film 31 by adhesive 33, which may be a material such as that described above in connection with the multi-layer structures of Figures 1 and 2. This is done after the printed image 42 is disposed on the second polymeric film 32 (or, if desired, the first polymeric film 31).
The multilayer structure 30 can have a free shrinkage of at least 5% in both the L and T directions (both at a temperature of 85 ° C). Additionally, the multilayer structures 30 can have a free shrinkage (at a temperature of 85 ° C), in at least one of the L and T directions of at least 5%, at least 10%, at least 15 %, at least 20%, at least 25%, and even up to 50%. Preferably, the multilayer structure 30 is biaxially oriented, and preferably has a free shrink (at 85 ° C) of from about 2 to about 20%, more preferably from about 3 to about 20%. about 15%, in each of the L and T directions, and a total free shrinkage (L + T) of between approximately 5 to 40%.
The multilayer structure 30 can be irradiated as described above. A suitable dose of high energy electrons, in the range of from about 16 to about 166 kGy, more preferably from about 30 to about 139 kGy, and even more preferably from about 50 to about 100 kGy.
In all the multilayer structures mentioned, the second polymeric film has been the barrier film. However, the present invention also encompasses embodiments in which the first polymeric film acts as the barrier film, as well as possessing the necessary adhesion and softening point characteristics. For example, a first polymeric film including a layer derived from, for example, EVOH or PVDC, could provide each of the adhesion, softening point, and barrier characteristics to the multilayer structure in which it is incorporated. In such circumstances, the second polymeric film can be formed from virtually any thermoplastic polymer.
In all the films of the foregoing multilayer structures, one or more of the layers of such films may, if desired, contain suitable amounts of additives. Examples of commonly employed additives include slip agents (eg, talc), filters, colorants, pigments, radiation stabilizers, antistatic agents, elastomers, and the like. The use of antioxidants in such films has been previously described.
In each of the preceding multilayer structures, the component films have been described as capable of heat shrinkage, or unable to heat shrink. Those of ordinary skill in the art are familiar with various methods available for making both of the aforementioned types of film. However, a brief discussion of the methodology will begin, for the convenience of the reader.
Non-shrink films can be made by a variety of methods, each of which results in a film where the polymer chains of one or more of the layers of that film are random, that is, not oriented. . Of course, if we form the film from materials that cannot be oriented, the result is a non-oriented film. More commonly, film casting, or co (extrusion) casting is employed. This process involves taking an extruded (or coextruded) film, immediately after extrusion, and without the standard cooling step, and stretching it while it is kept at a temperature above its orientation temperature; thereafter, the substantially non-oriented film is cooled.
Films that can be heat shrunk can also be made by a variety of methods. However, most of these methods involve the same general principles, differing in only a few details. In general, a film is (co) extruded and immediately cooled (by, for example, water cooling), below its orientation temperature. The non-oriented film is then stretched, in one of the L and T directions. This elongation is typically achieved by lay-out sizing, or other bubble techniques. The stretched film is then rapidly cooled so that it retains its stretched dimensions. This blocks the orientation of the polymer chains. Films that have been stretched to a greater extent tend to exhibit higher values of free shrinkage, shrinkage stress, and orientation stress release (as measured by ASTM D 2732-70, ASTM D 2838-81, and ASTM D 2838-81, respectively).
The two component films are laminated together to form the multi-layer structure of the present invention. This involves joining the separately constructed films together to form an essentially unitary structure.
ES 2 229 558 T3
Bonding is typically achieved through the use of a separate adhesive layer, or through the application of heat and pressure. (Of course, if heat is to be used to bond the shrinkable film to the non-shrinkable film, the amount of heat used is preferably not sufficient to raise the oriented film above its orientation temperature. ) True bonding can be achieved, either as batch treatment, or online.
Referring now to Figure 4, in a multi-layer structure 51, the first polymeric film 52 is laminated to the second polymeric film 53 by adhesive 54. In composition and arrangement, the multi-layer structure 51 substantially corresponds to the structure of multilayer 10 of figure 1.
The tube (or housing) 50 has been formed of the multi-layer structure 51, by fin sealing, of the first polymeric film 52 to itself. The flap closure 55 is created by folding the multilayer structure 51 so that one edge of the first polymeric film 52 is brought into contact with the opposite edge of it, followed by the application of heat to form a gasket. The flap closure 55 follows along substantially the entire length (not shown) of the tube 50.
Referring now to Figure 5, in the multi-layer structure 61, the first polymeric film 62 is laminated to the second polymeric film 63 by adhesive 64, which may be a pressure-sensitive type adhesive, an adhesive based hot melt, etc. In composition or arrangement, the multilayer structure corresponds substantially to the multilayer structure 10 of FIG. 1.
In each of the multilayer structures, the oxygen permeance preferably ranges from about 0.05 to about 150 cm.<sup>3</sup>/ m<sup>2</sup> Atm 24 hours, more preferably between about 0.1 to about 100 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, even more preferably between around 1 to about 75 cm<sup>3</sup>/ m<sup>2</sup> Atm24 hours, even more preferably between about 5 and about 50 cm<sup>3</sup>/ m<sup>2</sup> Atm 24 hours, and in the most preferred case between 10 and 30 cm<sup>3</sup>/ m<sup>2</sup> · Atm · 24 hours. Each of the preceding oxygen permeances is measured at about 23 ° C and 0% relative humidity.
Tube 60 has been formed from multi-layer structure 61 by first sealing polymer film 62 to adhesive 65, then folding multi-layer structure 61 so that one edge of the first polymer film is brought into contact with the edge. opposite of this. (Although the adhesive 65 is shown to be along the outside of the multi-layer structure 61, it may optionally be along the inside of such a structure.) The application of heat completes the formation of a joint between the first polymeric film. 62 to adhesive 65. The resulting joint continues along substantially the entire length (not shown) of tube 60.
Referring now to Figure 6, in the multilayer structure 71, the first polymeric film 72 is laminated to the second polymeric film 73 by the adhesive 74. In composition and arrangement, the multilayer structure 71 substantially corresponds to the multilayer structure 10 of Figure 1.
The tube 70 has been formed from the multilayer structure 71, folding the first polymeric film 72 to the second polymeric film 73, after folding the multilayer structure 71, so that a small part of the first polymeric film 72, is brought into contact with a small portion of the second polymeric film 73, followed by the application of heat to form a seal. The fold seal 75 continues along substantially the entire length (not shown) of tube 70.
Each of the tubes 50, 60 and 70 can be prepared from their corresponding multilayer structures. The respective structure is folded longitudinally passing over the molding part (sometimes called a "shoe") of, for example, a NISHIBE back sealing machine.<sup>TM</sup> HSP-250-SA (Nishibe Kikai Co. Ltd .; Nagoya, Japan), a TOTANI ™ FD-350C sealing machine (Totani Giken Kogyo Co, Ltd., Kyoto, Japan), a form-seal-pack - POLYCLIP horizontal stapling<sup>TM</sup> TSA-120 (Polyclip Corp .; Chicaho, III) or a vertical form-fill-seal machine ONPACK<sup>TM</sup> 2002 (Orihiro Co, Ltd .; Tomioka City, Japan). The multilayer structure is passed under and around the forming shoe to form a cylinder, with the circumference and diameter of the cylinder being determined by the size of the forming shoe. The multi-layer structure is overlaid in one of the ways described above, and a seal is created through the application of heat to the overlap area.
From the preceding discussion of tube formation, the reason for the aforementioned Vicat softening point limitation, imposed on at least one of the polymers of the first polymeric film, of the multilayer structure of the present invention can be seen. The first polymeric film must be sealed to an adhesive (a transverse seam), to the second polymeric film (a flap closure), or itself (a flap closure). Where the first polymeric film is to be sealed to the second polymeric film, or to an adhesive tape, it is desirable to ensure that, at least one of the polymers in the first polymeric film, and at least one of the polymers in the second polymeric film, or adhesive tape (wherever it is used), are compatible with sealing. In other words, it is preferable to provide a second polymeric film (or adhesive tape), with at least one polymer that is, from the point of view of composition and polarity, similar to the polymer of the first polymeric film, chosen from one of the following six classes described above. Otherwise, the strength of the longitudinal seal (ie, reverse seam) may be compromised. The reverse seam preferably has a seal strength of at least about 13.5 kPa, more preferably at least about 25 kPa, even more preferably about 40 kPa, even more preferably at least about 60 kPa, and most preferably at least about 80 kPa.
ES 2 229 558 T3
The flat width of passage (i.e., one half of the circumference) of any tubes 50, 60, and 70, can vary between about 2.5 to about 100 cm, preferably from about 5 to about 50 cm, more preferably from about 7 to about 30 cm, even more preferably from about 8.5 to about 25 cm, and most preferably from about 10b to about 20 cm. The particular flat pitch width of any given tube depends on the particular end-use application. Where a significant amount of food products is to be packaged, a larger flat width of the passage is preferred.
Any tubes 50, 60, and 70 can be further processed to form an inner cooking container in accordance with well known prior art techniques. Referring now to FIG. 7, the package 80 is formed from the wrapper 81 stapled at each of its ends, with only one staple 82 being illustrated in the perspective view shown. The housing 81 may be made of any of the previously described multi-layer structures (i.e. see Figures 1 through 3 and corresponding text, above) that has been formed into a tube (i.e. see Figures 4 through 6 and corresponding text, above). Specifically, housing 81 may be formed by stapling one end of such a tube, filling the resulting open container with the desired food product, then clipping the open end of the container.
Once formed, the package 80 can be used to store the enclosed food product (not shown) or, alternatively, the food product can be processed, for example cooked, still within the package 80. Preferably, the food product is protein, more preferably a meat product that includes one or more of ham, chicken, beef, sausages, and braunschweiger, more preferably at least one of ham, chicken, and beef.
Other packaging structures are possible, and readily apparent, to the ordinary skilled professional. The present invention is not limited to the specific structures described above.
Regardless of the specific form that a package according to the present invention takes, it preferably limits the amount of free moisture in the package (i.e. outside cooking) to no more than 5% (by weight), based on the weight of the product. food prior to cooking. In order of ascending preference, a package according to the present invention more preferably limits the amount of free moisture to no more than 3%, 1%, 0.75%, 0.5%, 0.25%, and 0.1 % (with all of the previous percentages being percentages by weight) when the container is used under standard cooking conditions.
Contents9
1 sheet
Sheet 1
16 members in 12 offices
Priority claims2
| Document | Office | Kind | Date |
|---|---|---|---|
| 19970070006P | United States of America | – | |
| 7000697 | United States of America | P |
Members16
| Document | Office | Kind | |
|---|---|---|---|
| CA2316979A1 | Canada | A1 | |
| WO9933653A1 | World Intellectual Property Organization (WIPO) | A1 | |
| AU2204599A | Australia | A | |
| EP1044106A1 | European Patent Office (EPO) | A1 | |
| BR9814596A | Brazil | A | |
| AU759209B2 | Australia | B2 | |
| NZ505435A | New Zealand | A | |
| US6656548B1 | United States of America | B1 | |
| EP1044106B1 | European Patent Office (EPO) | B1 | |
| AT276103T | Austria | T | |
| ATE276103T1 | Austria | T1 | |
| DE69826320D1 | Germany | D1 | |
| AR037481A1 | Argentina | A1 | |
| DK1044106T3 | Denmark | T3 | |
| ES2229558T3This record | Spain | T3 | |
| CA2316979C | Canada | C |
Numbers
- Publication
- 2229558
- Application
- 98966059
Titles2
- Spanish
- PELICULA LAMINADA PARA COCCION INTERIOR.
- English
- LAMINATED FILM FOR INTERNAL COOKING.
Classification
- CPC, 13
- B32B27/08
- B32B7/04
- B65D2581/34
- Y10T428/139
- Y10T428/1324
- Y10T428/1328
- Y10T428/1341
- Y10T428/1393
- Y10T428/1334
- Y10T428/31913
- Y10T428/31743
- Y10T428/3192
- Y10T428/31746
- IPC, 3
- B32B7 04
- B32B27 08
- B65D81 34