Sealing container

[0002] This application is a continuation-in-part of copending application Ser. No. 29/051,122, filed Mar. 4, 1996, now U.S. Pat. No. D 390,109, entitled “Microwave Container”, listing the inventors as Edward Tucker, George Luekan, Luke Gross, Mark Cruz, and Jack Melvan, which is incorporated herein by reference. This application is a continuation-in-part of copending application Ser. No. 29/054,729, now U.S. Pat. No. D 388,325, filed May 20, 1996, entitled “Container for Food or the Like”, listing the inventors as Edward Tucker, George Luekan, Luke Gross, Mark Cruz, and Jack Melvan which is incorporated herein by reference.

[0003] The invention relates to sealing containers and more particularly, to a closure device and corner tab feature for such containers.

[0004] Rigid thermoplastic food containers may be classified into two distinct categories. The first category of containers are the containers that the consumer acquires during the purchase of dairy or deli foods at a retail store. This category of container is often referred to as an “inexpensive” container since usually the consumer's intention is to purchase the food in the container irrespective of the type of container. Since the consumer pays the retail price necessary to purchase the food, they often think of the container as an inexpensive item which they may save for re-use at a later date.

[0005] With respect to this first category of container, a group includes the inexpensive convenience containers which consumers frequently acquire when purchasing deli foods. Generally, these “deli” containers need only to perform the function of providing a highly visible display and to provide containment of solid foods, such as, bakery items, salads or fruit at refrigeration temperature to ambient temperature. Often, the material of choice is a high clarity grade of APET (amorphous polyethylene terephthalate) or PS (polystyrene) and the containers are manufactured into many shapes by a thermoforming process so as to provide wall thicknesses of about 10-20 mils. This wall thickness range represents the low end of wall thicknesses generally seen in rigid thermoplastic food containers and as a consequence the containers can be made very inexpensively. Thus, the consumer may deem the container disposable, i.e. discardable without significant monetary loss that can be attributed to the cost of acquiring the container. In addition, the weight to volume ratio (i.e. the weight of the container over the volume of the container) of these containers is approximately 33.8-37.2 grams/liter for the total of the top and bottom of the container.

[0006] Since these deli containers have no elevated temperature requirements and thus can be formed from APET or PS, their low heat distortion temperature makes them highly unsuitable for microwave cooking applications. Furthermore, because the containers are not designed to provide a secure seal for liquid foods, the containers may leak if inverted while attempting to contain such foods during re-use by the consumer. Also, because the materials of construction are generally brittle, these containers will generally crack if stressed mechanically and thus are not very durable. Although these “deli” containers are inexpensive, their lack of heat resistance, durability and poor sealing characteristics severally limit their use.

[0007] “Dairy” containers also represent another group of thermoplastic containers that can be characterized as “inexpensive”. These containers are designed to hold butters, fresh and processed cheeses, yogurts, and read-serve sauces at retail. Often these containers are filled by a food producer while the food contents are hot enough to flow freely into the container. In these cases, the materials of choice for such containers are generally PP (polypropylene) or HDPE (high density polyethylene) owing to their elevated temperature performance characteristics. The container bottoms are manufactured by an injection molding or thermoforming process. The container bottoms made by injection molding have a wall thickness of about 20-40 mils. The container bottoms made by thermoforming have a wall thickness of about 10-20 mils. Like the “deli” containers, the “dairy” containers can be made very inexpensively and as such the consumer may deem the container disposable after limited re-use. The weight to volume ratio of the injection molded containers is approximately 43.9-57.4 grams/liter for the total of the top and bottom of the container. The weight to volume ratio of the thermoformed containers is approximately 37.2 -54.1 grams/liter for the total of the top and bottom of the container.

[0008] These dairy containers almost always are formed into a round, somewhat cylindrical shape which is well suited to the requirements of high speed labeling equipment. The cylindrical shape is an inefficient shape compared to other shapes such as a rectangle or square with regard to storage space utilization.

[0009] Also the dairy containers should prevent moisture loss, oxygen permeation, and odor absorption which if not prevented would undesirably alter the food contents. The food producer solves these problems by completely enclosing the head space above the food by application of a lidding material, such as, foil or thermoplastic barrier film which is continuously sealed to the upper lip of the container bottom. The container generally will also include a removable rigid thermoplastic lid that is placed over the continuously sealed lidding foil or film so that puncture protection is provided. The lid has a wall thickness of about 10 to 20 mils. The rigid thermoplastic container lid usually engages the container bottom so as to provide a crude fit, but it does not have to provide a secure leakproof seal since the lidding material accomplishes this function. Thus when the consumer goes to re-use the container, they may find that the container's seal is unsuitable for rough transport and handling of liquid foods, since the lidding material has been peeled off during consumption of the original contents and only the crude fitting rigid lid remains.

[0010] The lid is usually made from a softer polyethylene material which often does not have the same heat resistance of the container bottom. Thus, when the consumer goes to re-use the container, they may find that the lid is easily distorted during microwave heating.

[0011] Finally, the dairy container materials are usually highly pigmented to provide opacity in order to prevent light-induced oxidation of fat-containing dairy products so as to extend store shelf-life. The consumer may prefer a see-through container which allows easy recognition of food contents during re-use of the container. Thus, dairy containers would be unsuitable in this regard. Although these dairy containers are inexpensive, their round shape, lack of a heat resistant lid, poor sealing characteristics, and opacity severely limit their re-use after the original food contents have been consumed.

[0012] For example, many consumers choose to take their lunch to work. While in transit, containers are frequently resting on uneven surfaces or being jostled from ordinary movements, and as a result, the contents of an inexpensive container may leak onto clothing, upholstery, and/or other food. In addition, the inexpensive containers may not be suitable for microwave use, and the food must be removed from the container and placed on dishware suitable for microwave cooking before being heated.

[0013] The second category of food containers consists of expensive durable containers which may utilize more expensive plastic materials and thick container walls. These containers address the shortcomings of the inexpensive containers in that they may be suitable for microwave, dishwasher, and freezer use and provide a secure seal which will not leak. However, these containers may employ costly materials. In addition, due to their sophisticated design elements, these containers generally require heavier construction to enable manufacture within the limitations associated with the injection molding process from which these containers are made. These containers have wall thicknesses of about 20 to 80 mils. Thus, this second category of containers become too expensive for disposable use. As a result, a consumer taking his or her lunch to work in an expensive durable container must be burdened with also transporting the container from work to home. The weight to volume ratio of these containers is approximately 67.6-219.6 grams/liter for the total of the top and bottom of the container.

[0014] Thus, it would be advantageous if a container were available that possessed the durability, sealing characteristics and features (i.e. microwaveable, freezable, and dishwasher safe) of the expensive containers at a cost which affords the user the option to dispose of it either after very limited use or after extended use.

[0015] It is a general object of the present invention to provide a tight sealing container at a price appropriate for disposable use. Another object of the present invention is to provide a semi-transparent container to ensure satisfactory visibility of the container contents. Another object of the present invention is to provide a container that is suited for microwave use. A further object of the invention is to create a container that is top-shelf dishwasher safe. Another object of the present invention is to provide a container that maintains its sealing characteristics while in freezer type temperatures.

[0016] A further object of the present invention is to provide a corner tab feature that will facilitate removing the container top from the container bottom. Another object of the invention is to provide a container top which may be positioned in a manner to permit container venting.

[0017] Another object of the present invention is to provide a container top which will receive a container bottom during container stacking. Another object of the invention is to provide a container bottom which is nestable with other container bottoms. A further object of the present invention is to provide a container top which is nestable with other container tops.

[0018] Another object of the present invention is to provide a sealable container which reduces manufacturing costs, while enabling diverse shapes other than round, such as, rectangle or square.

[0019] Other objects and advantages of the invention will become apparent upon reading the following description and upon reference to the drawings.

[0020] The present invention consists of an inexpensive tight sealing plastic container suited for microwave cooking, top-shelf dishwashing and freezer use. The container utilizes a cut-back closure device of which the retaining bead of the container bottom maintains the container top in a secure position. The container top is slightly larger than the container bottom. The difference in sizes provides an interference fit and forms a nearly leak proof seal along the inside vertical sealing wall of the container. The container top provides gripping tabs which facilitate the separation of the container top from the container bottom and permit container venting.

[0021] For a more complete understanding of this invention reference should now be had to the embodiments illustrated in greater detail in the accompanying drawings and described below by ways of examples of the invention. In the drawings:

[0022] FIG. 1 is a bottom perspective view of a container having a top and bottom for food or the like;

[0023] FIG. 2 is a top plan view;

[0024] FIG. 3 is a side elevation view;

[0025] FIG. 4 is an end elevation view;

[0026] FIG. 4A is a partial cross-sectional view (similar to the view of FIG. 16B) of stacked container bottoms;

[0027] FIG. 5 is a bottom plan view;

[0028] FIG. 6 is a perspective view of the container bottom;

[0029] FIG. 7 is a top plan view of the container bottom;

[0030] FIG. 8 is a side elevation view of the container bottom;

[0031] FIG. 9 is an end elevation view of the container bottom;

[0032] FIG. 10 is a bottom plan view of the container bottom;

[0033] FIG. 11 is a bottom perspective view of the container top;

[0034] FIG. 12 is a bottom plan view of the container top;

[0035] FIG. 13 is a side elevation view of the container top;

[0036] FIG. 14 is a cross-sectional view taken along line 14—14 of FIG. 2;

[0037] FIG. 15 is a top plan view of the container top;

[0038] FIG. 15A is a top plan view of another embodiment of a tab for the container top;

[0039] FIG. 15B is a bottom plan view of the tab in FIG. 15A;

[0040] FIG. 15C is a cross sectional view of the tab in FIGS. 15A and 15B;

[0041] FIG. 15D is a top plan view of another embodiment of a tab for the container top;

[0042] FIG. 15E is a bottom plan view of the tab in FIG. 15D;

[0043] FIG. 15F is a cross sectional view of the tab in FIGS. 15A and 15B.

[0044] FIG. 16 is a cross-sectional view taken along line 16-16 of FIG. 7;

[0045] FIG. 16A is an enlarged partial view of area 16A in FIG. 16;

[0046] FIG. 16B is the view of FIG. 16A with dimensional parameters;

[0047] FIG. 16C is another embodiment of the closure device for the container bottom;

[0048] FIG. 17 is a cross-sectional view taken along line 17-17 of FIG. 12;

[0049] FIG. 17A is an enlarged partial view of area 17A in FIG. 17;

[0050] FIG. 17B is the view of FIG. 17A with dimensional parameters;

[0051] FIG. 17C is the view of FIGS. 16A and 17A in an engaged position;

[0052] FIG. 17D is the view of FIG. 17A in a stacked formation;

[0053] FIG. 17E is a cross-sectional view of the container bottom in FIG. 16 and the container top in FIG. 17 in a stacked formation;

[0054] FIG. 18 is a bottom perspective view of another embodiment of a container having a top and bottom for food or the like;

[0055] FIG. 19 is a top plan view of the container in FIG. 18;

[0056] FIG. 20 is a side elevation view of the container in FIG. 18;

[0057] FIG. 21 is a bottom plan view of the container in FIG. 18;

[0058] FIG. 22 is a perspective view of the container bottom in FIG. 18;

[0059] FIG. 23 is a top plan view of the container bottom in FIG. 22;

[0060] FIG. 24 is a side elevation view of the container bottom in FIG. 22;

[0061] FIG. 25 is a bottom plan view of the container bottom in FIG. 22;

[0062] FIG. 26 is a cross-sectional view of the container bottom taken along line 26—26 of FIG. 23;

[0063] FIG. 27 is a bottom perspective view of the container top in FIG. 18;

[0064] FIG. 28 is a bottom plan view of the container top in FIG. 27;

[0065] FIG. 29 is a side elevation view of the container top in FIG. 27;

[0066] FIG. 30 is a top plan view of the container top in FIG. 27;

[0067] FIG. 31 is a cross-sectional view of the container top taken along line 31—31 of FIG. 28.

[0068] Referring to FIG. 1, the container 100 consists of a flexible plastic container bottom 102 which is sealingly closed by a flexible plastic container top 104.

[0069] As illustrated in FIG. 6, the container bottom 102, has a bottom surface 120, four sidewalls 122, 124, 126, 128, a stacking recess 130, a denesting shoulder 134, and a closure device 136.

[0070] The sidewalls 122, 124, 126, 128 extend upwardly and slightly outwardly from the periphery of the bottom surface 120. At the termination of the sidewalls, an outwardly and substantially horizontally extending denesting shoulder 134 is provided which merges into the base of the closure device 136. The bottom surface 120 provides a stacking recess 130 extending upwardly to an upper substantially horizontal surface 132.

[0071] Referring to FIG. 16A, the closure device 136 comprises an inner vertical sealing wall 150, a retention bead 140, an outer vertical wall 162 and a skirt 142. The terms “inner” and “outer” are used with respect to the reference line 137 shown in FIG. 16A. The terms “inwardly” and “outwardly” are used with respect to the reference line 137 and moving in a clockwise direction 139 as shown in FIG. 16A.

[0072] The vertical sealing wall 150 extends from the denesting shoulder 134 and merges into the retention bead 140. The retention bead 140 may include an upwardly and outwardly extending cut-back portion 152, an inner vertical portion 153, an upwardly and inwardly extending lead-in portion 154, a horizontal rim surface 156, a downwardly and outwardly extending lead-in portion 158, an outer vertical portion 159, and a downwardly and inwardly extending cut-back portion 160.

[0073] The outer vertical wall 162 joins the retention bead 140 and the skirt 142. The skirt 142 may include a first downwardly and outwardly extending portion 164, a second downwardly and outwardly extending portion 166 of a more vertical position than the first portion 164, and a substantially horizontal lip 168.

[0074] As shown in FIG. 4A the container bottoms may be stacked together in a nested formation. When the container bottoms 102 are nested, the denesting shoulder 134 of the upper container bottom rests on the upwardly and inwardly extending lead-in portion 154 of the lower container bottom. The inner vertical sealing wall 150 of the container bottom 102 is designed of a necessary length to maintain an air space 170 between the sidewalls 122 of the lower container bottom and the sidewalls 122 of the upper container bottom such that the interlocking of container bottoms is avoided. The height of the vertical sealing wall 150 is dictated by the draft angle of the sidewall 122. Furthermore, the container bottoms 102 provide a low stacking height when nested together to facilitate packaging and minimize storage space.

[0075] FIG. 16B represents a container bottom closure device 136 of the present invention. The representative dimensions of the various parameters are given as follows:

[0076] FIG. 16C represents another embodiment of a closure device 136A for the container bottom. The closure device 136A is the same as closure device 136 except the inner vertical portion 153A is longer than the inner vertical portion 153 of closure device 136. The representative dimensions of the parameters which are different from FIG. 16B are given as follows:

[0077] The container top 104 as illustrated in FIG. 11 comprises a bottom surface 300, an inner stacking bead 302, an outer stacking bead 304, gripping tabs 306 and a closure device 308.

[0078] Referring to FIG. 17, each stacking bead 302, 304 may include an inner vertical portion 310 and an outer vertical portion 312 and a horizontal portion 314 such that an inverted “U” shape is formed. The inner stacking bead 302 runs continuously along the bottom surface 300 forming a substantially rectangular ring as viewed in FIG. 12. The outer stacking bead 304 also runs continuously along the bottom surface 300, forming a substantially rectangular ring outside the perimeter of the inner stacking bead 302 and inside the perimeter of the closure device 308.

[0079] As depicted in FIG. 17E, the inner stacking bead 302 of the container top 104 is adapted to fit within the stacking recess 130 of the container bottom. The outer bead 304 is designed to secure the perimeter of the bottom surface 120 of the container bottom 102. The stacking beads 302, 304 keep the closed containers in vertical alignment when placed in a stacked position thereby minimizing shelf space within a cabinet, refrigerator or freezer while providing for a stable stack.

[0080] The gripping tabs 306 are formed adjacent to the corners of the container top, outside the perimeter of the closure device 308. As viewed in FIG. 12, the tabs 306 are located at opposite corners of the container top 104 such that a tab in the top left-hand corner of the container top would have a corresponding tab in the lower right-hand corner of the container top.

[0081] Referring to FIGS. 12-15, each tab 306 comprises three upper inverted “U” shaped ribs 316 and two lower “U” shaped ribs 318 all of which extend outwardly from the periphery of the container top. The ribs 316, 318 have a reinforcing and stiffening effect which provide a means of leverage in separating the container top 104 from the container bottom 102. The ribs 316, 318 further provide a frictional gripping surface to minimize slippage when grasping the tab 306.

[0082] The gripping tab may also include cross-ribs to improve the grip on the tab. The cross-ribs may be perpendicular to the other ribs or the tab may only include the cross-ribs. Referring to FIGS. 15A-15C, the tab 306A includes three upper inverted “U” shaped ribs 316A and two lower “U” shaped ribs 318A. In addition, the tab 306A also includes upper cross ribs 317A on the upper ribs 316A and lower cross ribs 319A on the lower ribs 318A. If necessary, the tab may include another set of cross-ribs located near the outside edge of the tab. In another embodiment, the tab includes the upper and lower ribs 316A, 318A and the upper cross ribs 317A, but not the lower cross ribs 319A. In a further embodiment, the tab includes the upper and lower ribs 316A, 318A and the lower cross ribs 319A, but not the upper cross ribs 317A. In yet another embodiment, the upper and lower ribs 316A, 318A are eliminated from the tab and instead the tab includes the upper cross ribs 317A and/or the lower cross ribs 319A.

[0083] Furthermore, the tab 306B may include an indented portion on the tab or on the ribs to improve the grip on the tab. Referring to FIGS. 15D-15F, the tab 306B includes three upper inverted “U” shaped ribs 316B and two lower “U” shaped ribs 318B. In addition, the tab 306B also includes an indented portion 321B on the lower ribs 318B. If necessary, the tab may include another set of indented portions near the outside of the tab. The tab may be manufactured with the indented portion in the indented position 323B. In other embodiments, the tab may be manufactured with the indented portion in the neutral position 323C or the extended position 323D and when the user grips the tab, the indented portion collapses to indented position 323B. The indented portion collapses because the material is thinner at the indented portion than the surrounding portions of the tab.

[0084] In another embodiment, the indented portion(s) could be located on the upper rib(s) 316B. In a further embodiment, the upper and lower ribs 316B, 318B are eliminated from the tab and instead the tab includes indented portion(s).

[0085] Referring to FIGS. 11, 12 and 14, the tabs 306 provide a recess 320 in the downwardly and inwardly extending cut-back portion 372 of the closure device 308 adjacent to the base of the tab 306. As a result, the recess 320 provides less interference contact with the container bottom 102 during the removal or engagement of the container top 104 while still providing an adequate cut-back portion to maintain proper sealing of the closure device.

[0086] By utilizing the tab 306 and the recess 320, less force is required to remove the container top 104 from the container bottom 102. For example, the force required to close the container top 104 onto the container bottom 102 is approximately 27 pounds. However, the force required to open the container top 104 from the container bottom 102 using the tab 306 is approximately 1.8 pounds. Similarly, the force required to close the container top 604 onto the container bottom 602 in FIGS. 18-31 is approximately 31 pounds and the force required to open using the tab is approximately 1.6 pounds. These forces demonstrate the advantage of the tab and the leverage which the tab provides in opening the container. The lower opening force also reduces the possibility for container failure due to stress and fatigue.

[0087] In addition, the lower opening force may be beneficial when the container is used in a freezer. Some materials which may be used to make the container may become brittle at or near freezer temperatures. Consequently, if the container is removed from the freezer and immediately opened, the material for the container (and thus the container) are subject to the failure if the opening force is too high. Therefore, the lower opening force reduces the possibility of failure when the container is removed from the freezer and immediately opened.

[0088] The tab recess 320 also permits container venting by allowing the corner of the container top 104 to be removed from the container bottom 102 while still maintaining a seal around the remaining perimeter of the container. This feature is useful in microwave cooking where the container top 104 prevents food from splattering onto the inside surface of the microwave while still allowing the container to vent.

[0089] In one embodiment depicted by FIG. 17A, the container top closure device 308 may include an upwardly and inwardly extending lead-in portion 360, an inner vertical sealing portion 362, an upwardly and outwardly extending cut-back portion 364, an upwardly and inwardly extending portion 366, a horizontal surface 368, a downwardly and outwardly extending portion 370, a downwardly and inwardly extending cut-back portion 372, an outer vertical portion 374, a downwardly and outwardly extending lead-in portion 376 and a substantially horizontal lip 378. The terms “inner” and “outer” are used with respect to the reference line 381 shown in FIG. 17A. The terms “inwardly” and “outwardly” are used with respect to the reference line 381 and moving in a clockwise direction 383 as shown in FIG. 17A.

[0090] FIG. 17B illustrates the container top closure device 308 shown in FIG. 17A of the present invention. The representative dimensions of the various parameters are given as follows:

[0091] As shown in FIG. 17D, when container tops 104 are stacked together in a nested formation, the closure device 308 of the upper container top 104 rests upon the closure device 308 of the lower container top 104. More specifically, the lead-in portions 360, 376 of the upper container top 104 rest upon the upwardly and inwardly extending portion 366 and the downwardly and outwardly extending portion 370 of the lower container top 104 respectively. The portions in contact 360, 366, 370, 376 prevent the container tops 104 from interlocking as well as provide horizontal support for retaining the nested stack in a secure position.

[0092] As shown in FIG. 17C, the closure device 308 of the container top 104 is engaged with the closure device 140 of the container bottom 102. The closure devices are engaged by positioning the lead-in portions 360, 376 of the container top over the lead-in portions 154, 158 of the container bottom. A vertical force is then applied to the container top 104 to overcome the interference between the closure devices 140, 308. The cut-back portions 364, 372 of the thinner container top 104 deflect horizontally while passing over the lead-in portions 154, 158 of the container bottom 102. Once beyond the lead-in portions 154, 158 of the container bottom 102, the cut-back portions 364, 372 of the container top 104 retract inwardly against the cut-back portions of the container bottom 152, 160. The retracting forces of the cut-back portions 364, 372 of the container top 104 cause the container top 104 to move downwardly until the horizontal surface 368 of the container top 104 rests against the horizontal rim surface 156 of the container bottom 102. In addition, the force created by the expanded cut-back portions 364, 372 causes the container top 104 to audibly snap into place, indicating that the container is securely closed. In the engaged position, as shown in FIG. 17C, the cut-back portion 364 of the container top 104 is still deflected from its relaxed position. Thus, the cut-back portion 364 exerts a force against the inner sealing wall 150 of the container bottom 102 and forms a seal 402.

[0093] The container top 104 is also designed slightly larger than the container bottom 102. This difference in size forms an interference fit between the cut-back portion 364 of the container top 104 and the inner sealing wall 150 of the container bottom 102. In one embodiment, the range of interference fit is 5 to 80 mils. As a result, when the two pieces are engaged, a strong inside seal 402 is formed around the inside perimeter of the container. Due to variations resulting from the thermoforming process and the polypropylene material, it is beneficial to have additional sealing points. Thus, the closure devices may have several other sealing areas when the container top engages the container bottom. Referring to FIG. 17C, a second seal 404 may occur where the inwardly extending portion 366 engages the lead-in portion 154, a third seal 406 may occur where the horizontal surface 368 engages the horizontal rim surface 156, a fourth seal 408 may occur where the outwardly extending portion 370 engages the lead-in portion 158 and a fifth seal 410 may occur where the cut-back portion 372 engages the cut back portion 160.

[0094] Both the container bottom 102 and the container top 104 may be made of a plastic material. More particularly, the top and bottom may be fabricated by thermoforming a clarified polypropylene homopolymer material. In one embodiment, the container is made from clarified polyprohomo with the tradename 3289M and sold by Fina Oil and Chemical Co. which has the following properties:

[0095] In another embodiment, the container may be fabricated by thermoforming a clarified random copolyer polypropylene material, such as Pro-fax SR-256M from Monteli North America Inc., Wilmington, Del., U.S.A., which has the following properties:

[0096] Furthermore, if the material is transparent or semi-transparent, it permits satisfactory visibility of the container contents.

[0097] Alternative plastic materials which would be suitable for fabricating the container by thermoforming include PS (polystyrene), CPET (crystalline polethylene terephthalate), APET (amorphous polethylene terephthalate), HDPE (high density polyethylene), PVC polyvinyl chloride), and PC (polycarbonate). A disadvantage of PS and APET is that their limited heat resistance makes these materials unsuitable for microwave cooking. A disadvantage of HDPE is lack of see-through clarity though this material is readily recyclable by current waste handling practices. A disadvantage of CPET is that it lacks see-through clarity though its heat resistance is suitable for convection oven use. Fabrication using PC will yield a container with enhanced functional performance over PP (polypropylene) except that its cost may be prohibitive for a limited, re-use disposable product.

[0098] The container bottom 102 is formed from a starting sheet thickness in the range of 15 to 120 mils and preferably 25-40 mils. In one embodiment, the container bottom 102 is formed from a starting sheet thickness of approximately 40 mils. Referring to FIG. 16, the wall thickness of the container bottom will vary due to the thermoforming process. The representative dimensions of various locations for different starting sheet thicknesses are given as follows:

[0099] The container bottom 102 has a sufficient thickness to withstand the heat of microwave cooking and remain sturdy during lifting while laden with hot food and also withstand the heat of top-shelf dishwashing without deforming.

[0100] The container top 104 is formed from a starting sheet thickness in the range of 7 to 60 mils and preferably 12-18 mils. In one embodiment, the container top is formed from a starting sheet thickness of approximately 15 mils. Referring to FIG. 17, the wall thickness of the container top will vary due to the thermoforming process. The representative dimensions of various locations for different starting thicknesses are given as follows:

[0101] The thinner container top reduces material costs and increases flexibility to more easily accommodate its removal from and engagement onto the container bottom. The container top 104 will maintain adequate flexibility for proper sealing even during typical freezer temperatures. Furthermore, the lack of surface detail in the container material provides for easy washing. The size of the container 100 as depicted in FIGS. 1 through 5 is approximately 6 inches in length, 5 inches in width and 2.5 inches in height.

[0102] FIGS. 18-31 illustrate another embodiment of the present invention similar to that described in FIGS. 1-17E except that the container is of a different size. The container 600 consists of a container bottom 602 and a container top 604. The container 600 is approximately 6.5 inches in length, 6.5 inches in width and 2 inches in height.

[0103] The container bottom 602 is formed from a starting sheet thickness in the range of 18 to 140 mils and preferably 22-35 mils. In one embodiment, the container bottom 602 is formed from a starting sheet thickness of approximately 35 mils. Referring to FIG. 26, the wall thickness of the container bottom 602 will vary due to the thermoforming process. The representative dimensions of various locations for different starting sheet thicknesses are given as follows:

[0104] The container top 604 is similar to the container top 104 except the overall size corresponds to container bottom 602. Specifically, the dimensional parameters including the starting sheet thicknesses and the finished wall thicknesses are the same as for the container top 104 noted above.

[0105] The weight to volume ratio (i.e., the weight of the container over the volume of the container) for the container 100 shown in FIGS. 1-17 is approximately 33.8 grams/liter for the total of the top and bottom of the container. The weight to volume ratio for the container 600 shown in FIGS. 18-31 is approximately 50.7 grams/liter for the total of the top and bottom of the container.

[0106] The container may include additional features. For example, the container top and/or the container bottom may have an area which allows the user to write information, such as, the date. The write-on area could be an opaque color, such as, an opaque white, which would receive a contrasting color from a writing instrument, such as, a marker with black ink. The write-on area could be incorporated into the material for the container or could be applied to the material, such as, by printing.

[0107] Another feature which can be included on the container are volume marks. The container bottom can have marks on the side of the container indicating a specific volume, such as, ounces, pints, cups, or milliliters. For example, the marks may indicate one ounce, two ounces, etc. and include the appropriate text. The marks may be formed into the material or the marks may be applied to the material, such as, by printing.

[0108] The container may also include a visual indication of closure between the container top and the container bottom. The visual indication may be a color change in the area where the container top engages the container bottom. In one embodiment, the closure device on the container top may be a first color, such as, a translucent blue and the closure device on the container bottom may be a second color, such as, an opaque yellow. When the closure devices are occluded, the first and second colors produce a third color, such as, a green which is visible to the user to indicate that the container is sealed. Alternatively, the color change can result from the appearance or loss of a color as a result of hindrance by the closure portions. Examples of color change closures and techniques for forming a color change seal are shown in U.S. Pat. Nos. 4,186,786, 4,285,105, 4,829,641, 4,907,321, 5,248,201, 5,356,222, 5,252,281 and 5,427,266 which are incorporated herein by reference. In another embodiment a visual indication of closure can be provided to the container by forming complimentary patterns in the mating areas of the bottom and lid. When the lid is placed on the bottom of the container and pressed into a closed position the complimentary patterns form a combined visual indication that the lid and bottom have been mated or sealed. This embodiment is particularly well suited for containers manufactured by use of thermoforming manufacturing processes or in mold labeling where separate imprints can be placed in the mating areas of the lid and bottom of the container to form a visual indication of sealing. For example if a simple “X” pattern is desired the lid can have a repeating “\” pattern which overlays upon sealing a “/” pattern on the container bottom to form upon mating a repeating “X” pattern.

[0109] The colors may be incorporated into the material for the container or a portion of the container, such as in the closure area, or the colors may be applied to the material, such as, by printing. The actual inclusion of a color change closure or visual indication closure can be effected by use of established commercially available techniques. For example, if the container top and the container bottom are to have a different color at the interface where the top attaches to the bottom the two respective surfaces can be fashioned with a color or design by use of screen printing (also known as silk-screen printing), pad printing (also known as transfer pad printing)or ink jet printing. The printing may be performed on the unformed material or the printing may be performed on the formed container. In addition, another approach for forming a color or pattern on the top and bottom surfaces where such mate includes the use of coextruded sheet material which is then thermoformed. The aforementioned techniques are well known for use in providing decorative surfaces to plastic surfaces.

[0110] Furthermore, the colors or patterns may be incorporated into the material by using in-mold labeling during the thermoforming process. The process for in-mold labeling for thermoforming involves the following steps. The label, such as an opaque yellow label, is positioned in a predetermined location on the thermoforming cavity for the part. The plastic is then positioned over the label and over the thermoforming cavity. The part is then formed and the label is embedded into the part. As an example, the closure device on the container top may include a translucent blue in-mold label and the closure device on the container bottom may be an opaque yellow in-mold label. When the closure devices are occluded, the in-mold labels produce green which is visible to the user to indicate that the container is sealed.

[0111] The container may also include an audible indication of closure or a tactile indication of closure. In one embodiment, the closure device on the container top includes interior protrusions which engage exterior detents on the closure device on the container bottom. When the closure devices are engaging, the closure devices will make a clicking sound and cause a vibration in the container which is perceptible to the user to indicate that the container is sealed. Examples of audible closures and/or tactile closures disclosing techniques to provide this functionality are shown in U.S. Pat. Nos. 4,944,072, 5,070,584, 5,138,750, 5,140,727, 5,154,086, 5,363,540, 5,403,094 and European applications EP A 90314084.5 and EP A 92301996.2 which are incorporated herein by reference.

[0112] The container bottom may also include vertical ribs on the sidewalls. The vertical ribs would increase the strength of the sidewalls and allow the sidewalls to be thinner.

[0113] The container may also include a rough exterior surface to reduce slipping and improve grasping by the user. For example, the exterior of the container bottom may have a textured surface, as opposed to a smooth surface, to improve handling by the user, especially if the user's hands are wet or greasy.

[0114] The container top may also include a shape to hold an aluminum can, water bottle or second container in either a horizontal or vertical position. For example, the container top may include a two upwardly extending arms or a cradle surface which would hold the second container in a horizontal position. As another example, the container top may include a circular recess which would hold the second container in a vertical position.

[0115] The container may include a clip-on drink container. For example, the container bottom may have two outwardly extending arms and a bottom platform which would hold a drink container.

[0116] The container top may include a dome surface to increase the volume of the container and/or to allow the user to create a vacuum in the container upon sealing. For example, in order to create a vacuum, the user may depress the dome surface during the closing of the container. The dome surface will attempt to return to its relaxed position and create a vacuum.

[0117] In addition, the container may include a self-venting feature. The pressure in the sealed container may increase when the sealed container and contents are heated in a microwave oven. Thus the container top may include a self-venting mechanism which opens when the pressure in the container exceeds a predetermined value.

[0118] The container bottom may include a peelable lid with a super seal. Specifically, in a commercial use, the container bottom may include an interior peelable lid which is glued to the closure device.

[0119] In another embodiment, the peelable lid would release or vent when the sealed container and contents are heated in a microwave oven. Specifically, the heat would weaken the glue and allow the pressure to escape and /or the glue would be the weakest point of the container and allow the pressure to escape.

[0120] The container may be divided to separate various foods in the container. The divider would permit the user to store one food in one compartment and another food in another compartment. The divider may be integral with the container or a separate component. In addition, only the container bottom may include a divider or both the container bottom and the container top may each include a divider.

[0121] The container may also include a temperature indicating strip which would indicate the temperature of the container and contents. In one embodiment, the temperature strip could indicate the approximate temperature of the container and contents. In another embodiment, the temperature strip could indicate whether the container and content are within one of several temperature ranges. In a third embodiment, the temperature strip could indicate whether the container and contents are either hot or cold.

[0122] While the invention is described in connection with these embodiments, it will be understood that it is not intended to limit the invention to these embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.