Microwave ovens provide a convenient means for heating a variety of food items. It is common for the food being heated to be contained by a package comprising microwave energy interactive material (“MEIM”) mounted to a substrate that is transparent to microwave energy. The MEIM may be discontinuous to achieve the desired heating effect of the food item. For example, the MEIM may be discontinuous by virtue of the MEIM defining a pattern. Examples of discontinuous MEIM and associated manufacturing methods are disclosed in prior U.S. Patents.
As a more specific example regarding packaging material in which the MEIM is aluminum that is mounted to a polymer film, it is known to patternize the aluminum in order to achieve a desired heating effect in a microwave oven. For example, it is known to use a rotogravure printing press to apply a pattern of solvent-based resist coating to a continuous layer of aluminum (“precursor aluminum”) that was previously mounted to and is being carried by the polymer film. The solvent-based resist coating is applied in the same pattern that is intended to be defined by the resultant patternized aluminum.
After printing, the solvent-based resist coating is dried by evaporating its solvent. The web is then drawn through a caustic bath of 50% sodium hydroxide. The resist coating is resistant to the caustic bath so that the caustic bath does not react with the protected portion of the aluminum, wherein the protected portion of the aluminum is superposed with the resist coating. In contrast, the caustic bath reacts with the unprotected portion of the aluminum, wherein the unprotected portion of the aluminum is not superposed with the resist coating. The caustic bath deactivates the unprotected portion of the aluminum by converting it to aluminum oxide. The aluminum oxide is relatively transparent to light as compared to pure aluminum. In further contrast to aluminum, aluminum oxide is an electrical insulator that is transparent to microwave energy.
The web is rinsed with water immediately after the web is drawn out of the caustic bath. The web is then wet-bond laminated to paperboard to create packaging material. The aluminum, aluminum oxide and resist coating are positioned between the paperboard and the polymer film in the packaging material
The above-described step of evaporating the solvent of the solvent-based resist coating may be a limiting factor in the manufacturing of the packaging material. There is a desire for improvements to manufacturing line speeds, efficiency, quality and/or over-all costs.
An aspect of this disclosure is the provision of a method for at least forming a microwave energy transparent area in a layer of microwave energy interactive material (“MEIM”). The method may include partially coating the layer of MEIM with thermoset polymeric material. For example, the thermoset polymeric material may be printed onto a first portion of the layer of MEIM. Then, the thermoset polymeric material on the first portion of the layer of MEIM may be cured, for example, by exposure to ultraviolet (“UV”) light. That is, the thermoset polymeric material may advantageously be a UV-cured material. The cured thermoset polymeric material is for protecting the first portion of the layer of MEIM. In contrast, a second portion of the layer of MEIM is neither covered by nor protected by the cured thermoset polymeric material. The method may further include applying an agent to the coated layer of the MEIM, so that the agent transforms the second portion of the layer of MEIM into a microwave energy transparent area. In contrast, the cured thermoset polymeric material is for protecting the first portion of the layer of MEIM from the agent, so that the first portion of the layer of MEIM remains microwave energy interactive. For example, the agent may be a deactivating agent, so that the deactivating agent deactivates the second portion of the layer of MEIM.
The first portion of the layer of MEIM, which remains microwave energy interactive, may be referred to as resultant MEIM. The microwave energy transparent area, or more specifically the second portion of the layer of MEIM, which was deactivated, may be referred to as deactivated MEIM. Each of the resultant and deactivated MEIMs may be arranged in a pattern.
The resultant and deactivated MEIMs may both be parts of a packaging material that further includes a substrate. The resultant and deactivated MEIMs may be connected to the substrate, such as by a layer of adhesive material. The resultant and deactivated MEIMs may be adjacent to one another on the substrate. The packaging material may further include the thermoset polymeric material in a superposed configuration with the resultant MEIM. The thermoset polymeric material of the packaging material is typically transparent to microwave energy. In an embodiment of this disclosure, the deactivated MEIM is not covered by the thermoset polymeric material.
The substrate of the packaging material may be a first substrate, and the packaging material may further include a second substrate, so that the thermoset polymeric material and the resultant and deactivated MEIMs are positioned between the first and second substrates. The first substrate may be a polymeric film, and the second substrate may be paper, such as paperboard. The packaging material may be configured in any suitable conventional manner.
In one aspect of this disclosure, the deactivated MEIM may be referred to as microwave energy transparent material.
The foregoing presents a simplified summary of some aspects of this disclosure in order to provide a basic understanding. The foregoing is not an extensive summary and is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. The purpose of the foregoing summary is to present some concepts of this disclosure in a simplified form as a prelude to the more detailed description that is presented later. For example, other aspects will become apparent from the following.
In the following, reference is made to the accompanying drawings, which are schematic and not drawn to scale. The drawings are exemplary only, and should not be construed as limiting the inventions.
Exemplary embodiments are described below and illustrated in the accompanying drawing, in which like numerals refer to like parts. The embodiments described provide examples and should not be interpreted as limiting the scope of the invention. Other embodiments, and modifications and improvements of the described embodiments, will occur to those skilled in the art and all such other embodiments, modifications and improvements are within the scope of the present invention. For example, features illustrated or described as part of one embodiment can be used in the context of another embodiment to yield a further embodiment, and these further embodiments are within the scope of the present invention.
A system for forming a laminated packaging material 10 is illustrated in
The precursor web 12 comprises, consists of or consists essentially of microwave energy interactive material 20 (“MEIM”) mounted to a primary substrate 24 that supports the MEIM and is typically transparent to microwave energy. The primary substrate 24 may be a polymeric film 24 that may comprise, consist of or consist essentially of polyethylene terephthalate, or any other suitable polymeric material may be used, as discussed in greater detail below.
In the first embodiment, the MEIM 20 is operative for reflecting a substantial portion of impinging microwave energy (sometimes referred to as a microwave energy shielding element). For example, the MEIM 20 may be configured as a patch of metal foil having a thickness of from about 5 to about 10 micrometers, for example, about 7 micrometers. Such foil is typically formed from a conductive, reflective metal or metal alloy, for example, aluminum, copper, or stainless steel, but other suitable materials may be used. As a more specific example, the MEIM 20 may be a layer of aluminum foil that is mounted to the substrate 24 in a conventional manner. Specifically, the precursor web 12 may be a laminate comprising the MEIM 20 and the primary substrate 24 joined to one another by way of adhesive material 19 (
Alternatively, the MEIM 20 may be a high (greater than about 1.0) optical density evaporated material having a thickness of from about 300 to about 700 or more angstroms. For example, the precursor web 12 may be formed by depositing the MEIM 20 either directly or indirectly onto the primary substrate 24, such as by way of vacuum deposition or in any other suitable manner. More generally, the MEIM 20 may be mounted to the primary substrate 24 in any suitable manner.
The MEIM-side 20 of the precursor web 12 is selectively coated in a predetermined manner with a thermoset polymeric resist coating 26 by drawing the precursor web past or through at least one coater 28. In the first embodiment, the thermoset polymeric resist coating 26 may be an ultraviolet-curable (“UV-curable”) resist coating 26. The coater 28 may any suitable coater for depositing the UV-curable resist coating 26 in any suitable discontinuous arrangement (e.g., pattern). In
In the example of
In the first embodiment: the UV-curable resist coating 26 has a viscosity suitable for allowing the UV-curable resist coating to be printed for facilitating the disclosed method of the first embodiment; the MEIM 20 of the precursor web 12 is a continuous layer of aluminum 20 (“precursor aluminum”) that is sufficiently thick for reflecting impinging microwave energy; and the coater 28 prints the UV-curable resist coating 26 directly onto the outer face of the aluminum 20 in a pattern. The printed pattern is the same as (e.g., substantially the same as) the pattern of the resultant patternized aluminum of the resultant web 16.
The UV-curable resist coating 26 printed on the MEIM 20 is cured by drawing the coated web 12 in sufficiently close proximity to and past at least one ultraviolet (“UV”) light source 40. The UV light source(s) 40 may be conventional. The UV light source(s) 40 cause the UV-curable resist coating 26 printed on the MEIM 20 to become a cured thermoplastic resist coating 41. As should be apparent from the foregoing, the cured thermoplastic resist coating 41 may be a UV-cured resist coating 41. The UV-cured resist coating 41 is adhered to and carried by the MEIM-side 20 of the web 12.
The UV-curable resist coating 26 is typically immediately (e.g., substantially immediately) cured after the printing by exposure to the UV energy provided by the at least one UV light source 40. The UV-curable resist coating 26 is typically exposed to sufficient UV energy from the UV light source(s) 40 so that the UV-curable resist coating 26 is immediately (e.g., substantially immediately) cured (e.g., substantially fully cured) as soon as the UV-curable resist 26 coating is carried past the UV light source(s) 40 by the traveling web 12. Typically, as soon as the UV-curable resist coating 26 is fully cured by passing the UV light source(s) 40, the resulting UV-cured resist coating 41 is nearly or approximately (e.g., substantially) 100% solids so that the UV-cured resist coating typically does not include any solvent that has to be dried (e.g., evaporated). Due to the lack of drying and the relatively quick speed of curing of the UV-curable resist coating 26, it is believed that the use of the UV-curable resist coating 26 will increase manufacturing speeds as compared to the use of solvent-based resist coatings. In the first embodiment, the UV-cured resist coating 41 is transparent to microwave energy. In an alternative embodiment, the precursor web 12 may consist solely of the MEIM 20, wherein the MEIM may be in the form of a metallic foil, and the metallic foil with the UV-cured resist coating 41 thereon may be referred to as a laminate.
After formation of the UV-cured resist coating 41, the coated web 12 is drawn through, or otherwise exposed to, a caustic dispersion 42 that may be contained in an upwardly open container 44 (e.g., a caustic bath). In the first embodiment, the UV-cured resist coating 41 is sufficiently resistant to the caustic dispersion 42 (e.g., 50% sodium hydroxide dispersion) so that the caustic dispersion does not react with the protected portion of the MEIM 20, wherein the protected portion of the MEIM is adhered to and superposed with the UV-cured resist coating 41. In contrast, the caustic dispersion 42 reacts with the unprotected portion of the MEIM 20, wherein the unprotected portion of the MEIM is neither adhered to nor superposed with the UV-cured resist coating 41. When the MEIM 20 is aluminum, the caustic dispersion 42 typically deactivates the unprotected portion of the aluminum by converting it to aluminum oxide, wherein the aluminum oxide is the MEIM (e.g., aluminum) in a deactivated condition. The aluminum oxide is relatively transparent to light as compared to pure aluminum. In contrast to aluminum, aluminum oxide is an electrical insulator that is transparent to microwave energy.
Optionally and depending upon factors such as the strength of the caustic dispersion 42 and the duration of the exposure thereto, at least some of the aluminum oxide may be etched away or otherwise removed from the web 12. The caustic dispersion 42 may be more generally referred to as an agent, or a deactivating agent. Examples of suitable deactivating agents are disclosed in U.S. Pat. No. 4,865,921, which is incorporated herein by reference in its entirety.
As the web 12 is drawn out of the caustic bath 44, the web typically carries some of the caustic dispersion 42. The web 12 is then drawn through or past a conventional rinsing station 46. In the rinsing station 46, the web 12 is rinsed with water and/or one or more other fluids, or the like, so that the resultant web 16 (e.g., laminate) is absent of (e.g., substantially absent of) any caustic dispersion 42.
The resultant web 16 comprises the precursor web 12 (e.g., polymeric film), a pattern of resultant MEIM 50 (e.g., aluminum), a pattern of deactivated MEIM 52 (e.g., aluminum oxide) and the UV-cured resist coating 41. The pattern of the resultant MEIM 50 of the resultant web 16 corresponds to, and is superposed with, the pattern of the UV-cured resist coating 41 of the resultant web. Examples of patterns of the resultant MEIM 50 in the resultant web 16 are discussed in greater detail below. Any other suitable patterns of the resultant MEIM 50, such as any suitable conventional patterns, are also within the scope of this disclosure.
The resultant web 16 may be drawn through or past a conventional lamination station 60, wherein the resultant web may be laminated (e.g., wet-bond laminated) to the substrate 18 (e.g., paper, or more specifically paperboard) to create the packaging material 10. The substrate 18 may be drawn from a roll, and the packaging material 10 may be formed into another roll. In the packaging material 10, the resultant MEIM 50, deactivated MEIM 52 (e.g., microwave energy transparent material) and UV-cured resist coating 41 are typically positioned between the additional substrate 18 and the primary substrate 24. The laminating at the lamination station 60 may comprise joining the resultant web 16 and the substrate 18 to one another by way of adhesive material 62 (
UV-cured resist coating 41 (
As shown in
The second sections 252 of the resultant MEIM 50 are in the form of metal foil segments 110 arranged in clusters in a lattice-like configuration. Only a few of the foil segments 110 are identified by their reference numeral in
In the embodiment shown in
At least partially reiterating from above, it is within the scope of this disclosure for the resultant web 16 to be in the form of, and to be used as, packaging material. In this regard and in accordance with an embodiment of this disclosure, the packaging material 10, 16 may be formed into, or otherwise incorporated into, any suitable packages, such as cartons, trays, wraps, bags, or the like. Food products to be heated in microwave ovens may be contained in or otherwise associated with the packages. The substrate-side 24 (e.g., polymeric film side) of the precursor web 12 will typically be the interior surface of packages formed from the packaging material 10, 16. However, a variety of differently configured packaging materials and packages are within the scope of this disclosure.
As nonlimiting examples, the primary substrate 24 may be a polymeric film having a thickness from about 35 gauge to about 10 mil. The thickness of the polymeric film may be from about 40 to about 80 gauge, from about 45 to about 50 gauge, or about 48 gauge. Examples of polymeric films that may be suitable include, but are not limited to, polyolefins, polyesters, polyamides, polyimides, polysulfones, polyether ketones, cellophanes, or any combination thereof Reiterating from above, the polymeric film may comprise polyethylene terephthalate. Examples of polyethylene terephthalate film that may be suitable for use as the primary substrate 24 include, but are not limited to, MELINEX®, commercially available from DuPont Teijan Films (Hopewell, Va.), and SKYROL, commercially available from SKC, Inc. (Covington, Ga.). Polyethylene terephthalate films are used in commercially available packaging materials, for example, MicroRite® packaging material available from Graphic Packaging International. Other non-conducting primary substrate 24 materials such as paper and paper laminates, metal oxides, silicates, cellulosics, or any combination thereof, also may be used.
The resultant web 16 (e.g., laminate) may be laminated or otherwise joined to another material, such as, but not limited to, the substrate 18, or a surface of a wall of a package or other suitable structure. In one example, the resultant web 16 may be laminated or otherwise joined to a substrate 18 in the form of paper or paperboard. The paper may have a basis weight of from about 15 to about 60 lb./ream (lb./3000 sq. ft.), for example, from about 20 to about 40 lb./ream, for example, about 25 lb./ream. The paperboard may have a basis weight of from about 60 to about 330 lb./ream, for example, from about 80 to about 200 lb./ream. The paperboard generally may have a thickness of from about 6 to about 30 mils, for example, from about 12 to about 28 mils. In one particular example, the paperboard has a thickness of about 20 mils (0.020 inches). Any suitable paperboard may be used, for example, a solid bleached sulfate board, for example, Fortress® board, commercially available from International Paper Company, Memphis, Tenn., or solid unbleached sulfate board, such as SUS® board, commercially available from Graphic Packaging International.
If desired, the resultant web 16 or packaging material 10 may further include or otherwise be used in conjunction with other microwave energy interactive elements and/or structures such as, but not limited to, one or more susceptor layers (e.g. layers of aluminum) configured for absorbing at least a portion of impinging microwave energy and converting it to thermal energy (i.e., heat) through resistive losses in the layer of aluminum, or the like. Alternatively, the MEIM 20 and resultant MEIM 50 may be sufficiently thin for functioning as susceptors that absorb at least a portion of impinging microwave energy and convert it to thermal energy (i.e., heat) through resistive losses.
The above-disclosed patterns (e.g., of the resist coating 26, resultant MEIM 50, deactivated MEIM 52, and first and second sections 152, 252) are provided as examples only, and other patterns are within the scope of this disclosure. For example, one or more of the above-disclosed patterns may be tailored to the desired end uses of the packaging materials 10 and 16, or the like.
The above examples are in no way intended to limit the scope of the present inventions. It will be understood by those skilled in the art that while the present disclosure has been discussed above with reference to exemplary embodiments, various additions, modifications and changes can be made thereto without departing from the spirit and scope of the inventions, some aspects of which are set forth in the following claims.
This application claims the benefit of U.S. Provisional Application No. 61/858,775, filed Jul. 26, 2013, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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61858775 | Jul 2013 | US |