Description of the Related Art Containers having a tray portion and a lid portion come secured to each other to protect the contents of the container from outside elements and or to prevent spillage of the contents. If the tray, the lid, or both expand or contract due to thermally induced dimensional changes, temperature changes, load stresses, or other interactions, the lid will no longer fit on the tray. It is desired that the container lid still fit on the tray both before and after one or both change size.

Plastic baking trays shrink in the oven during baking, as a result, prior art lids have been designed to fit the tray either before or after baking but not both before and after baking.

It is desirable to have tray lids that will attach to the tray both before and after the tray changes sizes due to thermally induced shrinkage. The tray lid should be securely locked onto the tray such that a good seal is maintained to protect the food therein.

In other applications a tray may have a first size before it is filled and a second size after it is filled. It is desirable to have tray lids that will attach to the tray both before and after the tray changes sizes due to stresses applied to or removed from the tray.

Summary of the Invention A container having a tray with a lid attached thereto is provided wherein the tray, the lid or both have two sets of engagement mechanisms in different locations, such that when the tray or lid is a first size a first set of engagement mechanisms are employed and when the tray and or lid is a second size a second set of engagement mechanisms are employed to secure the lid to the tray.

For example plastic trays are well suited for baking a variety of food products.

However, one problem with such trays is that they shrink when subjected to heat at typical baking temperatures. In the past, separate covers would have to be provided to keep the food fresh. One cover would be used before baking and one after baking.

The use of two covers substantially increases the cost of packaging and can lead to a level of inconvenience and dissatisfaction on the part of consumers.

The present invention solves these problems by providing a tray and a single lid to cover the food both before and after baking to keep the food fresh. A feature of the invention is to provide a tray and a lid arrangement with dual sets of closure elements, one set used before thermal shrinkage has occurred and the other used after the tray has experienced thermal shrinkage.

In one embodiment, the two sets of closure elements are provided on the lid so that one set fits and seals with the tray before baking and the other set fits and seals with the tray after thermal shrinking has occurred.

In another embodiment, the two sets of closure elements are provided on the tray and cooperate with members on the lid.

The invention can be used in conjunction with any of a variety of tray and lid designs and with trays and lids made of a variety of different plastic materials. Those skilled in the art can use well known techniques to measure or calculate shrinkage and then use the invention to produce products that require only a single cover.

Objects of the Invention It is an object of the invention to provide one lid that fits a tray of a first size before baking and also fits the same tray after it thermally shrinks to a second size due to baking.

It is an object of the invention to seal plastic baking trays with a single lid before and after baking food in the tray.

It is an object of the invention to provide a lid which is easy to open and close at two tray sizes.

It is an object of the invention to provide a lid with two sizes of engagement perimeters one for the size of the tray before baking and one for the size of the tray after baking.

It is an object of the invention to provide a tray with two sizes of engagement perimeters one for engaging the lid before baking and one for engaging the lid after baking.

It is an object of the invention to provide lids, which fit trays, subjected to thermal shrinkage.

It is an object of the invention to provide lids, which fit trays, subjected to thermal expansion.

It is an object of the invention to provide trays, which fit lids, subjected to thermal shrinkage.

It is an object of the invention to provide trays, which fit lids, subjected to thermal expansion.

It is an object of the invention to provide trays, which fit lids, subjected to stress shrinkage.

It is an object of the invention to provide trays, which fit lids, subjected to stress expansion.

It is an object of the invention to provide lids, which fit trays, subjected to stress shrinkage.

It is an object of the invention to provide lids, which fit trays, subjected to stress expansion.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.

Brief Description of the Drawings Fig. 1 is a top perspective view of a lid with two locking perimeters.

Fig. 2 is a bottom view of a lid two locking perimeters.

Fig. 3 is a top view of a tray for engaging the lids of Fig. 1 and 2.

Fig. 4 is a bottom perspective view of lid with a one locking perimeter.

Fig. 5 is a side perspective view of a tray with two lid locking perimeters for engaging the lid of Fig. 4.

Fig. 6 shows a top view of the tray rim with two concave tracks therein.

Fig. 7 shows a bottom view of the lid with one convex track therein.

Fig. 8 is a top perspective view of a dome lid.

Fig. 9 is a top perspective view of a flat lid Fig. 10 is a top perspective view of a drop lid Description of the Preferred Embodiments Some containers have components such as lids and trays which engage each other to hold contents within the containers and keep foreign objects out. In some uses the container components will change size during the life of use and the lid will no longer engage the tray. In cases where only one component, such as the tray, is subjected to baking, the tray will experience thermoplastic shrinkage. Thereafter the tray and lid engagement will not be aligned and the lid can not be secured to the tray.

Although in the example above the tray changed size due to thermoplastic shrinkage, either the tray or the lid may be subjected to a change in size due to many forces such as thermal expansion and contraction, pressure changes, or load stresses.

In order to have a container in which the lid and tray will engage both before and after one or more or its components changes size, a container having two engagement portions on either the lid or tray or both are provided.

Figure 1 is a perspective view of the outside of tray lid 10. The. (id 10 has a flat rim 12 in a plane on which the lid 10 can rest when laid down. An outer perimeter riser 14 begins at and is generally perpendicular to the plane of the rim 12, the riser 14 defining an outer perimeter of the lid 10. Locking tabs 16 extend inward toward the center of the lid 10 from the riser 14.

Figure 3 shows a top view of a tray 40 having a bottom surface 46 a base wall 44 and a rim 42 having a rim edge 41 defining a perimeter of the tray 40.

The locking tab 16 on the lid 10 slides over the rim edge 41 of rim 42 on tray 40 and engages the top of the outer locking tab 16 to lock the tray lid 10 onto tray 40.

The tray lid 10 is prevented from further movement on tray 40 by rim 42 engaging the runner 22 and the coplanar top of the locking tabs 26 which extend perpendicularly inward from riser 24 and define the upper limit of the length of riser 14. The lid 10 is therefore secured from movement either upward or downward to the range between the bottom of inner locking tabs 26 and the top of outer locking tab 16.

A riser 24 extends parallel to riser 14 on an inner perimeter as defined by the inner side of runner 22. The riser 24 extends from runner 22 to runner 30, which is parallel to rim 12. The runner 30 limits the movement of the tray rim 42 to a range between the top of inner locking tabs 26 and runner 30.

In Fig. 1 a perspective view of the tray lid 10 is shown, opposing sides are symmetric as shown by Fig. 2, a bottom view of the tray lid 10.

The lid 10 is easily removable from the tray 40 buy exerting a force on the removal tab 48 which provides leverage to deform the lid 10 such that either the outer 16 or inner 26 locking tabs are removed from under the tray rim 42.

Riser 38 extends between the lid surface 36 and the runner 30. Riser 38 gives the lid 10 added height such that the lid surface 36 does not come into contact with the contents of the tray 40 particularly when the tray is filled to a level over the top of the tray rim 42.

Riser 38 can be longer and attached to a dome lid surface 136 as in Fig. 8, which extends high above the rim 12. Riser 38 may be shorter and attached to a flat lid 236, which is closer to rim 12 as in Fig. 9. Riser 38 may also be of an intermediate height and have a drop lid 336, which drops below the maximum height of riser 38 as in Fig. 10.

Although the outer and inner locking tabs 16,26 are shown as one large outer tab 16 on a first level and two smaller inner tabs 26 on a second level any number of tabs and any number or sizes of tabs may be used.

Outer and inner locking tabs 16,26 may also be used in the corners of the lids 10. In the embodiment shown in Fig. 1 a corner locking tab 16 is shown. In the embodiment shown the corner with the removal tab 48 does not have a locking tab for ease of removing the lid 10 from the tray 40.

Further, although the outer and inner locking tabs 16,26 are shown occupying mutually exclusive portions of the length of the sides of the lid 10 the inner and outer locking tabs may overlap lengthwise.

Alternatively the lid 10 may have a rim 42 as shown on tray 40 in Fig. 3 and the tray 40 may have two sets of locking tabs as shown on the lid 10 to reverse their roles. In this manner the tray has two locking positions to latch the lid to. One position

is used before baking and the other after the tray shrinks during baking. Since the tray 40 shrinks the lid 10 will first occupy the smaller inner diameter locking portion of the tray 40 before baking and then larger outer diameter portion after baking.

In another embodiment, as shown in Fig. 4 and 5, a lid 50 may have one locking perimeter defined by riser 54 having concave locking portions 56. The lid 50 has a flat rim 52 and a flat cover portion 58. A tray 60 has a flat rim 62 and a riser 72 perpendicular to the rim 62. The riser 72 defines a first perimeter of the tray 60. The riser 72 has a concave portion 76 which aligns with the concave portion 56 of the lid 60 to lock the lid in place on the tray 60 before the tray 60 is baked.

Tray 60 has a runner 64 parallel to the rim 62 and extending perpendicularly from riser 72 to define a second perimeter ending at riser 74 with extends downward from runner 64. Riser 74 has a concave portion. 78 which aligns with the concave portion 56 of the lid 50 to lock the lid in place on the tray 60 after the tray 60 is baked.

Since the tray shrinks during baking, after baking the concave portion 78 will be at a perimeter equal to the perimeter concave portion 76 before backing.

The tray 60 also has a lip 66 extending perpendicularly from the riser 74 and forming the outer boundary of the tray which may engage outer rim 52 on lid 50 to limit the downward movement of the lid 50.

The lid 50 has a riser 54 long enough to extend the concave portion 56 to the depth of either the concave portion 76 or 78 on tray 60.

The means for engaging the lid 50 to the tray 60 need not be by concave portions 56 and concave portions 76,78 of the lid 50 and tray 60 respectively, convex portions may be used. Further, other locking means may be employed such as the tabs and lips of the first embodiment or any other means for locking the lids to the trays.

Although the concave 56 and concave 76,78 portions of the lid 50 and tray 60 have been shown at the corners of the lid 50 and tray 60 other positions around the perimeter of the lid 50 and tray 60 may be used.

Figs. 6 and 7 show another embodiment of the invention. This embodiment is similar to that shown in Figs. 4 and 5 but with the concave portions being continuous around the perimeter. In Fig. 6 a tray 80 has a bottom 81, sides 82 and risers with concave tracks 84 and 85 forming inner and outer perimeters. Figure 7 shows a lid 90 having a top 91, sides 92, a rim 93 and a perimeter with a convex track 94. The concave track 94 on lid 90 will engage one of the concave tracks 84 or 85 on tray 80 depending on whether the tray expands or contracts due to temperature induced expansion or contraction, thermal shrinking, or stress due to load factors or pressures.

Similarly the lid could be supplied with the double track and the tray the single track.

Also the concave portions can be reversed forming convex portions. In a further embodiment only a portion of the track needs to have the concave or convex deformations. For example, there can be one or more convex or concave portions on a side for a rectangular container. Also the concave or convex portions may be just in the corners.

Many other combinations of engagement means are possible as well as the numbers of perimeters used on the trays and lids. In addition to concave or convex portions engaging each other, a zip lock style engagement mechanism or other mechanisms may be used.

In another embodiment both the tray and the lid may have two perimeters defined by two risers such that lids from Fig. 1 could be modified to engage trays of Fig. 5.

The above examples have been shown with the trays subjected to thermoplastic shrinking, however the trays or lids may be subjected to changes in size due to a variety of other causes, including, but not limited to, loading stresses from contents in the container, temperature induced thermal expansion or contraction when heated or frozen, changes in pressure or any combination of the above.

The trays and lids may be made of the same materials which expand or contract at the same rates or of different materials which expand or contract at different rates.

Although in all of the above embodiments the trays and lids have been shown with rectangular shapes, the trays and lids may be oval, circular, triangular or have as many sides or shapes as are desired.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is: