ULTRASONICALLY WELDABLE POLYMERIC LIDS AND MICROWAVABLE POLYMERIC CONTAINERS

Abstract

Embodiments herein relate to an ultrasonically weldable polymeric lid for a microwaveable polymeric container. In an embodiment, a lid for microwaveable containers can include a polymeric ring. The polymeric ring can define a central aperture having an inner diameter. The polymeric ring can also include a recessed shelf contacting the inner diameter of the central aperture and an ultrasonic bonding surface disposed to the outside of the recessed shelf. The lid can include a peelable film disposed on the recessed shelf and occluding the central aperture. The peelable film can be removably bonded to the recessed shelf, and can include a tab attached to an edge of the peelable film. In some cases the lid can contain substantially no metal content. Other embodiments are also included herein.

Description

FIELD

Embodiments herein relate to ultrasonically weldable polymeric lids for microwaveable polymeric containers.

BACKGROUND

Sealed plastic food containers can be created through heat sealing a film to a plastic container, generating a container with hybrid plastic-metal seams, or through induction welding to create a container having a combination of plastic and metal components bonded together.

In the example of heat sealing, a film can be fed across a multi-lane cup filling line, the film can be cut to fit the cups and sealed over the product, and then the skeletal remains of the film can be removed. The sealing time and index rate of such a process can require many sealing lanes to generate high throughput.

In comparison, plastic containers with metal ends can be sealed by a seaming process to achieve higher throughputs. However, the containers including both plastic and metals are more difficult to recycle through a single-stream recycling system, as the components thereof can be difficult to separate.

SUMMARY

Embodiments herein relate to ultrasonically weldable polymeric lids and microwaveable polymeric containers. In an embodiment, a lid for microwaveable containers can include a polymeric ring. The polymeric ring can define a central aperture having an inner diameter. The polymeric ring can also include a recessed shelf contacting the inner diameter of the central aperture and an ultrasonic bonding surface disposed to the outside of the recessed shelf. The lid can include a peelable film disposed on the recessed shelf and occluding the central aperture. The peelable film can be removably bonded to the recessed shelf, and can include a tab attached to an edge of the peelable polymeric film. The lid can be all polymeric and contain substantially no metallic content. However, in some embodiments, the peelable film may be of a metallic structure, either laminated with a polymer, or laminated within layers of polymer, which is totally removed from the polymeric ring prior to microwaving.

In another embodiment, a microwaveable food package is contemplated. The microwaveable food package can include a cup that can have a bottom, a side wall, and a top edge. The microwavable food package can include a lid for microwavable containers. The lid can include a polymeric ring, where the polymeric ring can define a central aperture having an inner diameter. The polymeric ring can include a recessed shelf contacting the inner diameter of the central aperture and an ultrasonic bonding surface disposed to the outside of the recessed shelf. The lid can include a peelable film disposed on the recessed shelf and occluding the central aperture. The peelable film can be removably bonded to the recessed shelf, and can include a tab attached to an edge of the peelable film. The lid can contain substantially no metal content. However, in some embodiments the peelable film may be of a metallic structure, either laminated with a polymer, or laminated within layers of polymer, which is totally removed from the polymeric ring prior to microwaving.

This summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which is not to be taken in a limiting sense. The scope herein is defined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE FIGURES

Aspects may be more completely understood in connection with the following drawings, in which:

FIG. 1 shows a schematic representation of a microwaveable container in accordance with the embodiments herein.

FIG. 2 shows a schematic representation of the cross-section of the microwavable container of FIG. 1 along line 2-2′.

FIG. 3 is an additional embodiment of the cross-section of microwavable container as presented in FIG. 2.

FIG. 4 is an additional embodiment of the cross-section of microwavable container as presented in FIG. 2.

FIG. 5 is a schematic representation of ultrasonic weld components in accordance with the embodiments herein.

FIG. 6 is an additional schematic representation of ultrasonic weld components in accordance with the embodiments herein.

FIG. 7 is an additional schematic representation of ultrasonic weld components in accordance with the embodiments herein.

FIG. 8 is an additional schematic representation of ultrasonic weld components in accordance with the embodiments herein.

FIG. 9 is an additional schematic representation of ultrasonic weld components in accordance with the embodiments herein.

FIG. 10 is a schematic representation of a microwavable food container in accordance with the embodiments herein.

FIG. 11 is a schematic representation of an ultrasonic weld in accordance with the embodiments herein.

While embodiments are susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the scope herein is not limited to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope herein.

DETAILED DESCRIPTION

Embodiments herein relate to ultrasonically weldable polymeric lids and microwaveable polymeric containers. In various embodiments, the lids and container can be lacking in any significant metallic content resulting in packages that are microwave and radiofrequency safe and easily recyclable. As used herein, the term “microwaveable” in reference to a container shall refer to a container that can be safely subjected to microwave radiation without potentially dangerous effects such as arcing.

Referring now to FIG. 1, a microwavable container 100 in accordance with the embodiments herein is shown. The microwavable container 100 can include a lid 102 and a cup 104. The lid 102 can include a polymeric ring 106, where the polymeric ring 106 can include a central aperture 108 having an inner diameter 110. The polymeric ring 106 can include a recessed shelf 112 adjacent to an edge of the inner diameter of the central aperture 108. The lid 102 can also include a peelable polymeric film 114 disposed on the recessed shelf 112, that occludes the central aperture 108. The peelable polymeric film 114 can be removably bonded to the recessed shelf 112 of lid 102. The lid 102 can also include a tab 116 attached to an edge of the peelable polymeric film 114. Tab 116 can be used to aid in removing peelable polymeric film 114.

In some embodiments, the lid 102 can contain substantially no metal content. In some embodiments, the lid can contain less than 0.1 weight percent (wt. %) metal content. In some embodiments, the lid can contain less than 0.01 wt. % metal content. In some embodiments, the lid can be 100% free of metal content. In some embodiments, the lid can lack materials having an electrical conductivity of greater than 0.5×10⁶ siemens/m. However, in some embodiments, the peelable film can be a foil structure, or a laminated metal film to a contact sealable peelable layer. As such, in some embodiments, the lid, other than the peelable film, can contain less than 0.1 weight percent (wt. %) metal content. In some embodiments, the lid, other than the peelable film, can be 100% free of metal content.

Referring now to FIG. 2, a partial cross-sectional view is shown of components of lid 102 and cup 104 as taken along line 2-2′ of FIG. 1. Lid 102 can include a peelable polymeric film 114 disposed on the recessed shelf 112 of polymeric ring 106. In some embodiments, the peelable polymeric film 114 can be removably bonded to the recessed shelf 112. In some embodiments, the peelable polymeric film 114 can be heat sealed to the recessed shelf 112. In some embodiments, the peelable polymeric film 114 can be bonded to recessed shelf 112 with an adhesive. In some embodiments, peelable polymeric film 114 is designed to be positioned within the recessed shelf 112 such that it does not come into contact with the outer edge 201 of recessed shelf 112.

FIG. 2 shows polymeric ring 106 with an ultrasonic bonding surface 202 disposed on the underside of polymeric ring 106 and to the outside of the recessed shelf 112. Ultrasonic bonding surface 202 can be substantially flat, as shown. Ultrasonic bonding surface 202 can form an ultrasonic weld with cup 104 at opposing ultrasonic bonding surface 204. In some embodiments, an ultrasonic weld can be actuated through an energy director bead 206 disposed on the opposing ultrasonic bonding surface 204 of cup 104, as shown in FIG. 2. Alternatively, an ultrasonic weld can be actuated through an energy director bead 206 disposed on the ultrasonic bonding surface 202 of lid 102, as shown in an additional embodiment shown in FIG. 3. Ultrasonic bonding surface 202 and opposing ultrasonic bonding surface 204 can be welded together to form an ultrasonic weld between lid 102 and cup 104, as will be discussed below.

The profile of energy director bead 206 can be designed to initiate the melt flow of the polymers within the lid 102 and cup 104 during an ultrasonic welding process. Energy director bead 206 can be a raised bead off of either the ultrasonic bonding surface 202 or opposing ultrasonic bonding surface 204, as shown in FIGS. 2 and 3. Energy director bead 206 can assume a hemispherical shape, a triangular shape, a square shape, and the like. In some embodiments energy director bead 206 can be pointed, rounded, tiered, terraced, conical, frustoconical, or the like.

In some embodiments, energy director bead 206 can have a height of between 0.01 mm and 3 mm off of either the ultrasonic bonding surface 202 or opposing ultrasonic bonding surface 204. In some embodiments, the energy director bead 206 can have a height of 0.01, 0.05, 0.1, 0.5, 1, 2, or 3 mm off of either the ultrasonic bonding surface 202 or opposing ultrasonic bonding surface 204.

In some embodiments, polymeric ring 106 can include a downward pointing wall 208 disposed to the outside of the ultrasonic bonding surface 202. The downward pointing wall 208 can include an inner surface 210 and an outer surface 212. The downward pointing wall 208 can include an inward facing point 214 that is disposed on an inner surface 210 of the downward pointing wall 208. The inward facing point 214 can include a sloped bottom surface 216. In some embodiments, after the lid 102 and cup 104 have been welded together at the ultrasonic bonding surface 202 and opposing ultrasonic bonding surface 204, a flange 218 can be formed at the outer diameter of microwavable container 100. However, in some embodiments, welding together the ultrasonic bonding surface 202 and opposing ultrasonic bonding surface 204 can result in no flange at the outer diameter of the microwavable container 100.

FIG. 4 shows polymeric ring 106 with an ultrasonic bonding surface 202 disposed on the underside of polymeric ring 106 and to the outside of the recessed shelf 112. The embodiments of FIG. 4 is similar to FIG. 2. However, the embodiment of FIG. 4 lacks the inward facing point 214 shown in FIG. 2 and the sloped bottom surface 216.

Referring now to FIGS. 5-9, additional embodiments of the ultrasonic weld components between polymeric ring 106 of lid 102 and cup 104 are shown. FIG. 5 shows the interface 500 between polymeric ring 106 and cup 104. In FIG. 5, ultrasonic bonding surface 202 is substantially flat, while opposing ultrasonic bonding surface 204 includes a pointed or triangular energy director bead 206 extended from the surface. Creating an ultrasonic weld between the polymeric ring 106 and cup 104 of the embodiment shown in FIG. 5 can create a flange 218 to the outer perimeter of microwavable cup 104.

FIG. 6 shows the interface 600 between polymeric ring 106 and cup 104. In FIG. 6, ultrasonic bonding surface 202 is substantially flat, while opposing ultrasonic bonding surface 204 includes a pointed or triangular energy director bead 206 extended from the surface and a sealing notch 602 at the interior perimeter of cup 104. In this case, an ultrasonic weld formed from components shown in the interface 600 of FIG. 6 would result in no flange formation at the perimeter of cup 104.

FIG. 7 shows the interface 700 between polymeric ring 106 and cup 104. In this embodiment, a portion of a sonotrode 720 is shown. The sonotrode 720 can be used to deliver energy sufficient to cause welding between the polymeric ring 106 and the cup 104. In some embodiments, the bottom surface of the sonotrode 720 can include an energy directing point or bead 706.

FIG. 8 shows the interface 800 between polymeric ring 106 and cup 104. In FIG. 8, ultrasonic bonding surface 202 includes an energy director bead 206 having a square shape extended from the surface. The opposing ultrasonic bonding surface 204 includes a corresponding groove 802 that is designed to be the reciprocal shape to energy director bead 206 to create a close fit. Energy director bead 206 and corresponding groove 802 can be designed to form a tongue and groove joint during ultrasonic welding of the lid 102 to the cup 104. It will be appreciated that energy director bead 206 and corresponding groove 802 can be square shaped, triangle shaped, hemisphere shaped, and the like. An ultrasonic weld formed from components shown in the interface 800 of FIG. 8 would result in no flange formation at the perimeter of cup 104.

FIG. 9 shows interface 900 between polymeric ring 106 and cup 104. In FIG. 9, ultrasonic bonding surface 202 is substantially flat, while opposing ultrasonic bonding surface 204 includes a triangular energy director bead 206 extended from the surface. The ultrasonic bonding surface 202 and opposing ultrasonic bonding surface 204 can form a tongue-and-groove joint upon ultrasonic welding of the polymeric ring 106 to the cup 104. Polymeric ring 106 of FIG. 9 shows a downward pointing wall 208 that extends past the ultrasonic weld interface. Downward pointing wall 208 can include an inner surface 210 and an outer surface 212. The outer surface 212 of downward pointing wall 208 can include one or more threads 902 to serve as a point of removable attachment for a re-sealable lid (not shown).

Referring now to FIG. 10, a microwavable food package 1000 is shown in accordance with the embodiments herein. The microwavable food package 1000 can include a lid 102 and a cup 104. The cup 104 can include a bottom 1004, a side wall 1002, and a top edge 1006, defining an inner volume, the food package further comprising a food material 1008 disposed within the cup. The lid 102 can have an outer diameter 1010. The lid 102 can include a polymeric ring 106, having a central aperture 108 with an inner diameter 110. The polymeric ring can include a recessed shelf 112 in contact with the inner diameter 110 of the central aperture 108.

The lid 102 of microwavable food package 1000 can include a peelable polymeric film 114 disposed on the recessed shelf 112 to occlude the central aperture 108. The peelable polymeric film 114 can be removably bonded to the recessed shelf 112, and can include tab 116 attached to an edge of peelable polymeric film 114. Tab 116 can be used to remove peelable polymeric film 114. As discussed above, lid 102 can contain substantially no metal content. Additionally, microwavable food package 1000 can include any of the features discussed above in reference to FIGS. 1-9.

Referring now to FIG. 11, an ultrasonic weld is shown in accordance with various embodiments herein. FIG. 11 shows an ultrasonic weld 1102 between polymeric ring 106 of lid 102 and cup 104. To form the ultrasonic weld 1102, a region of the ultrasonic bonding surface 202 can be welded to the opposing ultrasonic bonding surface 204. As will be discussed below, ultrasonic weld 1102 can include a region where the polymeric material of lid 102 and the polymeric material of cup 104 melt into one another to form a welded area of polymer content that permanently joins the polymeric ring 106 to the cup 104.

Ultrasonic Welding

In some embodiments, incorporating an ultrasonic welding process into a continuous, high-speed, high-throughput sealing system is provided. The systems embodied herein can be used to achieve a throughput of greater than 300 units per minute during automatic assembly. The system can be designed to also incorporate a steam flush step prior to welding the lid to the cup, or container. The steam flush can be used to create a vacuum in the container to drive out residual oxygen.

Lids can be ultrasonically welded to the cups using a down-stacker device, which can be a scroll feeder, a chute feeder, and the like. In some embodiments, the lids may need to be further positioned prior to the ultrasonic welding process using a roller, a press head, a screw chuck, and the like, to engage the components for contact. In some embodiments, the cups can be designed with a sidewall contour such that they are easily stackable prior to being fed into the down-stacker device.

The ultrasonic welding process can advantageously expel contaminants from between the lid and cup at the weld area, through vaporization or through sonic cutting, to create a clean and reliable seal in the ultrasonic weld. The ultrasonic welding process can thus prevent sealing over or around contaminants between the lid and cups, thereby preventing a weakening in the ultrasonic weld.

The microwavable containers embodied herein can be constructed using an ultrasonic welding process to create permanent seal between a polymeric lid and a polymeric cup. The ultrasonic weld between the polymeric ring of the lid and the polymeric top edge of the cup can be actuated through an energy director bead integral to either the polymeric ring or the polymeric top edge of the cup. As discussed herein, the energy director bead can be shaped like a square, a triangle, a hemisphere, and the like. In some embodiments, the energy director bead can assume a design where the angle between the surface from which it extends and the exterior surface of the energy director bead is around 60°.

The lid and cup can ideally be formed from the same polymer so that they both have the same melt flow index and are therefore compatible with each other during the ultrasonic welding process. In some embodiments, the polymer composition of the lid and the polymer composition of the cup can be different if they have substantially similar melt flow indices. Polymers suitable for use herein, can include but are not limited to, polycarbonates, polyvinylchlorides, polyethylenes, polyethylene terephthalates, polypropylenes, and polyamides.

The ultrasonic welding process can result in a dimensional change in the height of the final ultrasonic weld as compared to the individual lid and cup components prior to ultrasonic weld formation. The change the final ultrasonic weld height as compared to the height of the individual components prior to weld formation can be used as a measure of weld quality and to validate seal integrity. During quality control checks, a control unit can adjust the power and time of exposure to the ultrasonic horn to create a final ultrasonic weld having optimal strength and seal integrity as required for the intended application. Thus, the ultrasound horn can be used as an intelligent feedback mechanism to detect the quality of the final ultrasonic weld. Any ultrasonic welds that do not meet a threshold height can be rejected and removed for further inspection and system optimization.

Peelable Polymeric Membrane

Peelable polymeric membranes embodied herein can be affixed to the lid prior to the ultrasonic welding process. Placing the peelable membrane prior to combining the lid and cup during the ultrasonic welding process can prevent contamination from drips or product transfer during filling of the cup. In some embodiments, the peelable polymeric membrane can be applied upon manufacture of the lid using a cut-in-place application from a die cut heat and placement tool during a heat sealing process. The application can be performed on a liner transfer belt and vacuum wheel placement mechanism, or on an indexing line where the lid is stopped and the peelable polymeric membrane is cut and placed on the recessed shelf of the lid.

In some embodiments, the heat sealing process can include applying the peelable polymeric membrane by cutting, placing, and sealing all in the same operation. In some embodiments, the heat sealing process can include tack sealing the peelable polymeric membrane off of a rotary system before moving on to a secondary sealing operation. In some embodiments, the peelable polymeric membrane can be applied by an adhesive process. In some embodiments, the adhesive process can include applying a peelable, pressure-sensitive label having an adhesive coating at the outer perimeter and securing it to the lid by applying pressure to the outer perimeter. In some embodiments, little to no skeletal waste is generated during the application of the peelable polymeric membrane. Exemplary sealing systems include, but are not limited to those offered by Rychiger, Ball Corporation, and Soudronic.

In some embodiments, the peelable film is placed in an injection molding tool, as per an in-mold label application, and the polymeric ring injected around the peelable film. The structure of the peelable film is such that the film remains peelable post forming of the part.

Polymeric Containers

The container embodiments herein can be used for many applications in addition to microwavable food containers discussed above. In some embodiments, the ultrasonic welding process described herein can be used to create an easy-open container for hot and cold foods, beverages, retort containers, and the like. In some embodiments, the container embodiments herein can be used for packaging foods such as soups, beverages, sauces, cookies, crackers, bread, and the like. In some embodiments, the ultrasonic welding process described herein can be used to create an ultrasonic weld between a lid and container during any of a high pressure processing, hot fill processing, cold fill processing, and the like. In some embodiments, the ultrasonic welding process described herein can be used to create a hermetic seal within a container.

The polymeric lids and containers discussed herein can be created from polymers including, but not limited to polycarbonates, polyvinylchlorides, polyethylenes, polyethylene terephthalates, polypropylenes, and polyamides. As discussed above, the polymeric containers discussed herein can contain substantially no metal content. Such containers offer a microwave-friendly design. Polymers such as those suitable for use herein have little to no dielectric influence on the microwave heating of the product inside the container. Thus, the containers can be compatible with various microwave or other electromagnetic wave processing steps during food processing. Additionally, containers having substantially no metal content can be recycled using a single-stream recycling system, with no need to separate the components from one another.

In various embodiments a method of filling and sealing food containers is included herein. The method can include filling a container such as those described herein with a food product. Many different food products can be filled into the container including, but not limited to, soups, sauces, ready to eat meals, juices, vegetable products, pasta and sauces, desserts, and the like. Various amounts (weights/volumes) of food products can be put into each container. In some embodiments the amount can be from about 25 ml (or 25 grams) to about 3 liters (or 3 kilograms). The method can also include aligning a lid such as those described herein with the filled container and placing the lid onto the top surface of the container. The method can also include ultrasonically welding the lid to the container forming a filled and sealed food container. The method can also include measuring the height of the sealed food container around the perimeter of the same after, or at the same time as, the step of ultrasonically welding.

The method can also include sterilizing the filled and sealed food container. Many different techniques of sterilizing or pasteurizing the filled and sealed food container can be used, including but not limited to, cooking, retort cooking, pressure-based sterilization, application of microwave and/or radiofrequency energy to the container, and the like. In some embodiments, microwave and/or radiofrequency energy can be applied for a time and at an intensity to produce a desired degree of sterilization of the food product within the filled and sealed food container. In some embodiments, method can include submerging the filled and sealed food container within a liquid medium prior to applying microwave and/or radiofrequency energy to the container.

The embodiments described herein are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices. Aspects have been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope herein.

It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

It should also be noted that, as used in this specification and the appended claims, the phrase “configured” describes a system, apparatus, or other structure that is constructed or configured to perform a particular task or adopt a particular configuration to. The phrase “configured” can be used interchangeably with other similar phrases such as arranged and configured, constructed and arranged, constructed, manufactured and arranged, and the like.

All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated by reference. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate any publication and/or patent, including any publication and/or patent cited herein.

Claims

1. A lid for microwaveable containers comprising a polymeric ring, the polymeric ring defining a central aperture having an inner diameter;a recessed shelf contacting the inner diameter of the central aperture; andan ultrasonic bonding surface disposed outside of the recessed shelf; a peelable film disposed on the recessed shelf and occluding the central aperture, the peelable film removably bonded to the recessed shelf; anda tab attached to an edge of the peelable film; wherein the lid contains substantially no metal content.

2. The lid of any of claim 1, wherein the lid contains less than 0.1 wt. % metal content.

3. The lid of any of claim 1, wherein the lid contains less than 0.01 wt. % metal content.

4. The lid of any of claim 1, wherein the lid is 100% free of metal content.

5. The lid of any of claim 1, the peelable film comprising a peelable film.

6. The lid of any of claim 1, the peelable film comprising a coated foil.

7. The lid of any of claim 1, the peelable film comprising a polymeric laminated metal film.

8. The lid of any of claim 1, wherein the lid lacks materials having an electrical conductivity of greater than 0.5×106 siemens/m.

9. The lid of any of claim 1, wherein ultrasonic bonding surface is substantially flat.

10. The lid of any of claim 1, further comprising an energy director bead disposed on the ultrasonic bonding surface.

11. The lid of any of claim 10, the energy director bead comprising a hemispherical shape.

12. The lid of any of claim 10, the energy director bead comprising a triangular shape.

13. The lid of any of claim 10, the energy director bead comprising a height between 0.01 mm and 3 mm.

14. The lid of any of claim 1, the polymeric ring comprising a downward pointing wall disposed to the outside of the ultrasonic bonding surface, the downward pointing wall having an inner surface and an outer surface.

15. The lid of any of claim 14, further comprising an inward facing point disposed on an inner surface of the downward pointing wall, the inward facing point comprising a sloped bottom surface.

16. The lid of any of claim 14, further comprising threads disposed on the outer surface of the downward pointing wall.

17. The lid of any of claim 1, comprising an outer diameter of about 2 inches to about 5 inches.

18. The lid of any of claim 1, wherein the peelable film is removably bonded to the recessed shelf.

19. The lid of any of claim 1, wherein the peelable film is heat sealed to the recessed shelf.

20. The lid of any of claim 1, wherein the peelable film is bonded to the recessed shelf with an adhesive.

21. The lid of any of claim 1, wherein the polymeric ring comprises at least one of polycarbonates, polyvinylchloride, polyethylene, polyethylene terephthalate, polypropylene, and polyamides.

22. A microwaveable food package comprising a cup comprisinga bottom,a side wall, anda top edge; anda lid for microwaveable containers comprisinga polymeric ring, the polymeric ring defining a central aperture having an inner diameter;a recessed shelf contacting the inner diameter of the central aperture; andan ultrasonic bonding surface disposed outside of the recessed shelf; a peelable film disposed on the recessed shelf and occluding the central aperture, the peelable film removably bonded to the recessed shelf; anda tab attached to an edge of the peelable film; wherein the lid contains substantially no metal content.

23. The microwaveable food package of claim 22, the cup defining an inner volume, the food package further comprising a food material disposed within the cup.