CROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

[1] This application claims priority from commonly owned U.S. Provisional Patent Application 61/971 ,848 filed 28 March 2014, and titled "Thermoplastic Food Steamer and container", presently pending and incorporated by reference.

BACKGROUND

[2] In-flight meals in an airplane typically involve re-heating food that was previously prepared, cooked and then packaged. Because the food is often prepared and cooked days before it is consumed, the food is often chilled or frozen after being cooked, and then packaged inside a piece of foil or a plastic tray. Then, when the food is to be consumed in flight, the food is re-heated and then served.

[3] Unfortunately, preparing the food in this manner dries the food out, causing the food to look unappealing and the taste to become of inferior quality. Re-heating the food causes moisture in the food to escape. When food is frozen the humidity in the air surrounding the food causes more moisture to escape the food. Finally, re-heating the food causes some of the moisture remaining in the food to also escape the food.

SUMMARY

[4] In an aspect of the invention, a container for holding and heating food includes a plurality of cavities each disposed in a body of a wall, each having an opening through an interior surface of the wall, and each operable to hold moisture and to release the moisture through the opening when the body of the wall is warm. The body of the wall is disposed between the interior surface of the wall, which contacts the food when the container holds the food and the food is being heated, and the exterior surface of the wall, which is exposed to the environment surrounding the container.

[5] In another aspect of the invention, a container for holding and heating food includes a first wall, a second wall adjacent the first wall, and a cavity disposed between the first wall and the second wall. The cavity holds moisture and releases the moisture through a hole in the first wall when the first and second walls are warm. The first wall contacts the food when the container holds the food and the food is being heated. And, the second wall is exposed to the environment surrounding the container when the container holds food and the food is being heated.

[6] With the cavities in the body of a wall of a single-walled container, or with the cavity disposed between the first and second walls of a dual-walled container, moisture may be stored in the container and released toward the food when the food is heated. In this manner, re-heating the food does not dry out the food and allows the food to remain appetizing before and during consumption. In addition, moisture that might escape from the food while being stored in the container may be collected in the cavities or cavity, and then when the food is heated the moisture may be released from the cavity or cavities to be absorbed by the food.

BRIEF DESCRIPTION OF THE FIGURES

[7] FIG. 1 shows a perspective view of a container, according to an embodiment of the invention.

[8] FIG. 2 shows a partial cross-sectional view of the container shown in FIG. 1 , according to an embodiment of the invention.

[9] F^G. 3 is a photograph of a cross-section of a portion of a thermoplastic materia! having a microstructure that is included in the container shown in FIG. 1 , according to an embodiment of the invention. [10] FIG. 4 is schematic view of a process for generating the thermoplastic material having the microstructure shown in FUG, 3, according to an embodiment of the invention.

[11] FIG. 5 shows a partial cross-sectional view of a container similar to the container shown in FIG. 1 , according to another embodiment of the invention.

[12] Each of FIGS. 6 - 8, shows a cross-sectional view of a container, according to yet another embodiment of the invention.

DETAILED DESCRIPTION

[13] FIG. 1 shows a perspective view of a container 20 according to an embodiment of the invention. The container 20 includes a region 21 where food (not shown) is held while the food is stored and/or transported to where it will be heated for consumption, such as by a passenger travelling in a flying airplane. The container 20 includes a plurality of cavities 22 (only 7 labeled for clarity) disposed in a wall 24to hold moisture (here water but may be any liquid) and then to release the moisture into the region 21 when the respective wall 24 is warm. The wall 24 includes a side 26 and a bottom 27. The wall 24 also includes an interior surface 28 that contacts the food when the container holds the food and when the food is being cooked, an exterior surface 29, and a body (not shown in FIG. 1 ) that is disposed between the interior surface 28 and the exterior surface. The container 20 may also include a top (not shown) that covers (either sealingly or not) the interior surface 28 of the wall and isolates the interior surface 28 from the outside ambient environment.

[14] With the cavities 22 in the wall 24 and the side 26 of the container 20, moisture may be stored in the container 20 and released toward the food when the food is heated. In this manner, re-heating the food does not dry out the food and allows the food to remain appetizing before and during consumption. The released moisture can accomplish this in a couple ways. For example, while the food is heated the released moisture may be absorbed by the food, and/or the released moisture may retard the escape of moisture from food by reducing the difference between the humidity of the food and the humidity of the air surrounding the food. In addition, moisture that might escape from the food while being stored in the container 20 may be collected in the cavities 22, and then when the food is heated the moisture may be released from the cavities 22 to be absorbed by the food.

[15] Other embodiments are possible. For example, the wall 24 may not include a side 26 and simply include the bottom 27. As another example, the container 20 may include fewer cavities 22 in the side 26 than in the bottom 27, or the same number of cavities in the side 26 as the bottom 27. As another example, the container 20 may not include any cavities 22 in the bottom 27, and only include cavities in the side 26. This might be desirable when the food includes a sauce that one wants to keep from being collected and stored in a cavity, and thus unavailable for consumption with the food.

[16] Still referring to FIG. 1 , the side 26 of the wall 24 may be configured as desired. For example, in this and other embodiments, the side extends from the bottom 27 at an angle that is greater than or equal to 90 degrees for 1 .5 inches. In other embodiments, the side 27 may extend at an angle less than 90 degrees or much greater than 90 degrees, and for more or less than 1 .5 inches.

[17] FIG. 2 shows a partial cross-sectional view of the container 20 shown in FIG. 1 , according to an embodiment of the invention. In this embodiment, the container 20 is a single-walled container. More specifically, the interior surface 28 contacts the food when the container 20 holds the food and when the food is being cooked. The exterior surface 30 is exposed to the environment surrounding the container 20, such as the inside of an oven or box. And each of the cavities 22 does not extend through the exterior surface 30. When moisture is released from the cavities 22 the moisture travels through the cavities' 22 respective opening 32.

[18] The configuration of each of the cavities 22 may be any desired configuration. For example, in this and other embodiments each cavity 22 is cylindrical in shape and has a diameter of 1 millimeter. In addition, each cavity 22 extends into the body 34 of the wall 24 a length that is not the same length of each of the other cavities 22. For example, cavity 22a has a length of about 0.35 millimeters and the cavity 22b has a length of about 0.2 millimeters. In other embodiments, each of the cavities 22 may have the same length. In still other embodiments, each of the cavities 22 may be cylindrical in shape and have a diameter that is not the same as the diameter of each of the other cavities 22. For example, the diameters may range from 0.5 millimeters to 1 .0 millimeters. Or, the diameters may be shorter than 0.5 millimeters or longer than 1 .0 millimeter. In yet other embodiments, each of the cavities 22 may have a shape other than a cylinder. For example, each cavity 22 may have a square shape or a cone shape.

[19] Still referring to FIG. 2, the material of the wall 24 may be any desired material capable of withstanding temperatures encountered while heating the food. For example, in this and other embodiments the wall 24 includes polyethylene terephthalate (PET) that has been crystallized using conventional techniques. Crystallized, the PET can withstand temperatures up to about 500 degrees Fahrenheit. In other

embodiments, the wall 24 may include one or more of the following plastics:

polystyrene, polycarbonate, acrylonitrile butadiene styrene polycarbonate (ABS PC), polyethylene terephthalate (PET), glycol modified PET, polyethylene, polypropylene, NORYL (a blend of polyphenylene oxide and polystyrene), and polyvinyl chloride.

[20] The body 34 of the wall 24 may have any desired thickness and include any desired microstructure. For example in this and other embodiments, the body 34 is 0.4 millimeters thick and has a microstructure that includes many small, closed cells, such as that shown and discussed in greater detail in conjunction with FIGS. 3 and 4. In other embodiments, the body 34 may have a thickness that is less than 0.4 millimeters or greater than 0.4 millimeters, and may have a microstructure that does not include many small, closed cells. For example the microstructure may be solid (no cells) and/or may include open cells. The open-celled microstructure may be desireable when one wants the wall 24 to hold more moisture than the cavities 22 alone can hold.

[21] FIG. 3 is a photograph of a cross-section of a portion of a thermoplastic material 38 having a microstructure 38 that is included in the body 34 of the wail 24 in FIG. 2, according to an embodiment of the invention. The microstructure 38 includes a skin 40 (here two), and many (typically 10 ⁸ or more per cubic centimeter) microceiluiar bubbles 42 (only three labeled for clarity) whose cell sizes typically range from 0.1 to 500 micrometers and are closed. These many bubbles or closed-cells 42 form an interior that is sandwiched between the skins 40. Each skin 40 is a smooth, outer-layer whose microstructure does not include closed-cells 42 or at most far fewer closed-cells 42 than the interior of the material 38, and is thus substantially solid. In this and other embodiments, each skin 40 is integral to the closed-cells 42. More specifically, each skin 40 and the plurality of closed-cells 42 are formed during a single process, such as that shown and discussed in conjunction with FIG. 4, and from the same initial sheet of solid thermoplastic material. In other embodiments, the skin 40 may not be integral to the closed-cells 42, but formed after the closed-cells 42 have been formed.

[22] The size of each closed cell 42 may be any desired size, and the distribution of the closed cells 42 throughout the thickness of the material 38 may be any desired distribution. For example, in this and other embodiments the size of each closed cell ranges between 1 and 60 micrometers long at its maximum dimension that extends across the void within the cell, and the closed ceils may be uniformly dispersed throughout the interior of the material 36. Because the geometry of each closed-cell is rarely, if at ail, a perfect sphere, the size of each closed cell is arbitrarily identified as the length of the longest chord that extends through the void within the closed cell. For example, the size of an oblong ceil would be the length of the longest chord that extends in the same direction as the cell's elongation, and the size of a sphere would be the length of the sphere's diameter.

[23] With the many closed-cells 42 in the interior of the material 36, the material 36 is substantially thicker than and has a cross-sectional area substantially greater than, the same material before the closed-cells 42 are generated, but maintains the same amount of thermoplastic material. Thus, the material 36 has a relative density that ranges between 10% and 40%. The relative density is the density of the material 36 whose volume includes the closed-cells 42, divided by, the density of the same amount of material whose volume does not include any of the closed-cells 42 - i.e. is solid. With the relative density of the material 36 less than the density of the same material in solid form, the material 36 may be lighter but stiil may provide a strength and stiffness similar to the strength and stiffness of solid material,

[24] G. 4 is a schematic view of a process for generating the thermoplastic material 38 having the microstructure 38 shown in FIG, 3, according to an embodiment of the invention,

[25] in this and other embodiments, the process includes dissolving into the material 46 (here shown as a film rolled around a drum 48, but may be a block or thin sheet) a gas 50 that does not react with the material 46. The process also includes heating the material 46 with the dissolved gas at a temperature that is, is close to, or above the glass-transition temperature of the material and dissolved gas combination. The glass-transition temperature is the temperature at which the material 46 is easily malleable but has not yet melted. With the temperature at, near, or above the

glass-transition temperature, bubbles of the gas 50 can nucleate and grow in regions of the material 46 that are thermodynamicaily unstable - i.e. supersaturated. When the bubbles have grown to a desired size, the temperature of the material 46 is reduced below the glass-transition temperature to stop the bubbles' growth, and thus provide the material 46 with a microstructure having closed-cells whose size may range between 0,1 and 500 micrometers long,

[26] In the process, the first step 52 is to dissolve into the material 46 any desired gas 50 that does not react with the material 46. For example, in this and certain other embodiments of the process, the gas 50 may be carbon dioxide (CO ₂ ) because CO ₂ is abundant, inexpensive, and does not react with PET. In other embodiments of the process, the gas may be nitrogen and/or helium. Dissolving the gas 50 into the material 46 may be accomplished by exposing the material for a period of time to an atmosphere of the gas 50 having a temperature and a pressure. The temperature, pressure, and period of time may be any desired temperature, pressure, and period of time to dissolve the desired amount of gas 50 into the material 46. The amount of gas 50 dissolved into the material 46 is directly proportional to the pressure of the gas 50 and the period of time that the material 46 is exposed to the gas 50 at a specific temperature and specific pressure, but is inversely proportional to the temperature of the gas 50. For example, in this and certain other embodiments, the temperature may be 72° Fahrenheit, the pressure may be 725 pounds per square inch (psi), and the duration of the period may be 10 hours. This typically saturates the material 46 with the gas 50. In other embodiments, the pressure may range between 500 psi and 1000 psi, and the duration of the period may range between 4 hours and 48 hours.

[27] Because the layers of the rolled material film 48 that lie between adjacent layers or between a layer and the drum 48 are substantially unexposed to the atmosphere when the roll is placed in the atmosphere, a material 54 is interleaved between each layer of the roiled material film that exposes each layer to the atmosphere, In this and certain other embodiments, the material 54 includes a sheet of cellulose, and is disposed between each layer of the material film 48 by merging the sheet with the film and then roiling the combination into a single roll 58. The material 54 exposes each layer of the material film 48 by allowing the gas 50 to easily pass through it. After the gas 50 has saturated the material film 46, the material 54 may be removed from the roll 56 and saved as a roll 58 for re-use.

[28] The next step 60 in the process includes exposing the material film 46 with the dissolved gas 50 to an atmosphere having less pressure than the one in the first step to cause the combination of the material film 48 and the gas 50 dissolved in the material film 46 to become thermodynamicaily unstable - i.e. the whole material or regions of the material to become supersaturated with the dissolved gas 50. For example, in this and certain other embodiments, the reduction in pressure may be accomplished by simply exposing the material film 46 to atmospheric pressure, which is about 14.7 psi, in the ambient environment.

[29] When the combination of the material film 46 and the dissolved gas 50 becomes thermodynamicaily unstable, the dissolved gas tries to migrate out of the film 46 and into the ambient environment surrounding the film 46. Because the dissolved gas in the interior regions of the material film 46 must migrate through the regions of the material film 46 that are closer to the film's surface to escape from the material film 46, the dissolved gas in the interior regions begins to migrate after the dissolved gas in the surface regions begins to migrate, and takes more time to reach the ambient

environment surrounding the material film 46 than the dissolved gas 50 in the film's regions that is closer to the film's surface. Thus, before heating the material film 46 to a temperature that is, is close to or above its glass-transition temperature, one can modify the concentration of dissolved gas 50 in regions of the material film 46 by exposing for a period of time the material film 46 to an atmosphere having less pressure than the one in the first step. Because the concentration of dissolved gas 50 depends on the amount of gas that escapes into the ambient environment surrounding the material film 46, the concentration of dissolved gas 50 is inversely proportional to the period of time that the film 46 is exposed to the low-pressure atmosphere before being heated to, close to, or above its glass-transition temperature.

[30] In this manner, a skin, such as the skin 40 (FIG, 2), may be formed in the material film 46 when the film 46 is heated to a temperature that is, is close to or above its glass-transition temperature. For example, in this and certain other embodiments, the roll 56 of material film and interleaved material 54 can remain in a

thermodynamicaiiy unstable state for a period of time before removing the material 54 from the roil 56 and heating the film. This allows some of the gas dissolved in the region of the film adjacent the film's surface to escape. With the gas absent from this region of the film, this region becomes more thermodynamicaiiy stable than the regions that are further away from the film's surface. With a sufficient amount of thermodynamic stability in the region, bubbles won't nucleate in the region when the film is heated to, close to, or above its glass-transition temperature. Consequently, closed-cells 42 (FIG. 2) can be omitted from this region of the film, leaving a solid portion of the

microstructure that is integrai to the closed cell portion of the microstructure, such as the skin 40 (FIG. 2). Because the thickness of the skin 40 or solid portion depends on the absence of dissolved gas 50 in the region of the film 46, the thickness of the skin 40 or solid portion is directly proportional to the period of time that the film 46 spends in a thermodynamicaiiy unstable state before being heated to, close to, or above its glass-transition temperature. In this and certain other embodiments, the thickness of the integral skin ranges between 5 - 100 micrometers. [31] The next steps 62 and 64 in the process are to nucleate and then grow bubbles in the material 46 to achieve a desired relative density for the material film 46. The relative density is the density of the material film 46 with the closed cells divided by the density of the material 46 without the closed cells. Bubble nucieation and growth begin about when the temperature of the material film 46 is or is close to the glass-transition temperature of the material film 46 with the dissolved gas 50. The duration and temperature at which bubbles are nucleated and grown in the material 46 may be any desired duration and temperature that provides the desired relative density. For example, in this and certain other embodiments, the temperature that the PET material 46 is heated to is approximately 200° - 280° Fahrenheit, which is about 40° - 120° warmer than the glass-transition temperature of the material without any dissolved gas 50. The PET film 46 is held at approximately 200° - 280° Fahrenheit for approximately 30 seconds. This provides a relative density of the closed-cell film of about 18.5%. If the PET film 46 is held at 200° - 280° Fahrenheit for a period longer than 30 seconds, such as 120 seconds, then the bubbles grow larger, and thus the size of resulting closed-cells 42 (FIG. 2) are larger. This may provide a relative density of the closed-cell film of about 10% - 20%. If the PET film 46 is held at 200° - 280° Fahrenheit for a period shorter than 30 seconds, such as 10 seconds, then the bubbles remain small, and thus the size of resulting closed-cells 42 (FIG, 2) are smaller. This may provide a relative density of the closed-cell film of about 40%.

[32] To heat the material film 46 that includes the dissolved gas 50, one may use any desired heating apparatus. For example, in this and certain other embodiments, the PET film may be heated by a roll fed flotation/impingement oven, disclosed in U.S.

Patent Application Serial No. 12/423,790, titled ROLL FED FLOTATION/IMPINGEMENT AIR OVENS AND RELATED THERMOFORMING SYSTEMS FOR CORRUGATION- FREE HEATING AND EXPANDING OF GAS IMPREGNATED THERMOPLASTIC WEBS, filed 14 April 2009, now U.S. Patent 8,568,125, and incorporated herein by this reference. This oven suspends and heats a material film that moves through the oven, without restricting the expansion of the film. [33] The next step 88 in the process includes reducing the temperature of the heated material 46, and thus the malleability of the material 46 that occurs at, near, or above the glass-transition temperature, to stop the growth of the bubbles. The temperature of the heated material may be reduced using any desired technique. For example, in this and certain other embodiments, the material film 46 may be left to cool at ambient room temperature - i.e. simply removed from the heating apparatus, !n other embodiments the heated material film 46 may be quenched by drenching it with cold water, cold air, or any other desired medium.

[34] Other embodiments of the process are possible. For example, the material film 46 can be heated to a temperature that is or is close to its glass-transition temperature when the material film 48 is initially exposed to an atmosphere that causes the gas dissolved in the material film 48 to become thermodynamically unstable. This allows one to make a film that includes a skin having a minimal thickness.

[35] FIG. 5 shows a partial cross-sectional view of a dual-walled container 70 that is similar to the container 20 shown in FIG. 1 , according to another embodiment of the invention. The container 70 includes a first wall 72 where food (not shown) is held while the food is stored and/or transported to where it will be heated for consumption, a second wall 74 adjacent the first wall 72, and a cavity 76 disposed between the first wall 72 and the second wall 74. The cavity 76 holds moisture (here water but may be any liquid) and releases the moisture through a hole 78 (three shown in FIG. 5, but there may be fewer than three or more than three) in the first wall 72 when the first and second walls 72 and 74, respectively, are warm. The second wall 74 is exposed to the environment surrounding the container 70 when the container 70 holds food and the food is being heated.

[36] With the cavity 76, moisture may be stored in the container 70 and released through one or more of the holes 78 toward the food when the food is heated. In this manner, re-heating the food does not dry out the food and allows the food to remain appetizing before and during consumption. In addition, moisture that might escape from the food while being stored in the container 70 may be collected in the cavity 76, and then when the food is heated the moisture may be released from the cavity 76 to be absorbed by the food.

[37] Other embodiments are possible. For example, similar to the container 20 in FIG. 1 , the first wall 72 and the second wall 74 may not include a side and simply include a bottom. As another example, the first wall 72 may include one or more holes 78 in the side. As another example, the first wall 72 may not include any holes 78 in the bottom, and only include one or more holes 78 in a side. This might be desirable when the food includes a sauce that one wants to keep from being collected and stored in a cavity, and thus unavailable for consumption with the food.

[38] Still referring to FIG. 5, the one or more holes 78 may be configured as desired. For example, in this and other embodiments each hole 78 is cylindrical in shape and has a diameter of 1 millimeter. In other embodiments, each hole 78 may be cylindrical in shape and have a diameter that is not the same as the diameter of each of the other holes 78. For example, the diameters may range from 0.5 millimeters to 1 .0 millimeters. Or, the diameters may be shorter than 0.5 millimeters or longer than 1 .0 millimeters. In still other embodiments, each of the holes 78 may have a shape other than a cylinder. For example, each hole 78 may have a square shape or a cone shape.

[39] The material of the first and second walls 72 and 74, respectively, may be any desired material capable of withstanding temperatures encountered while heating the food. For example, in this and other embodiments each of the first and second walls 72 and 74, respectively, includes polyethylene terephthalate (PET) that has been

crystallized using conventional techniques. Crystallized, the PET can withstand temperatures up to about 500 degrees Fahrenheit. In other embodiments, the walls 72 and 74 may include one or more of the following plastics: polystyrene, polycarbonate, acry!onitri!e butadiene styrene polycarbonate (ABS PC), polyethylene terephthalate (PET), glycol modified PET, polyethylene, polypropylene, NORYL (a blend of

polyphenylene oxide and polystyrene), and polyvinyl chloride. In still other

embodiments, the first wall 72 may include a material that is different than the second wall 74. [40] Still referring to FIG. 5, each of the walls 72 and 74 may have any desired thickness and include any desired microstructure. For example in this and other embodiments, each of the walls 72 and 74 is 0.4 millimeters thick and has a

microstructure that includes many small, closed cells, such as that shown and discussed in greater detail in conjunction with FIGS. 3 and 4. In other embodiments, each of the walls 72 and 74 may have a thickness that is less than 0.4 millimeters or greater than 0.4 millimeters, and may have a microstructure that is solid and does not include many small, closed cells. In still other embodiments, the first wall 72 may have a thickness and a microstructure that is different than the thickness and microstructure of the second wall 74.

[41] Each of FIGS. 6 - 8, shows a cross-sectional view of a container 80, according to yet another embodiment of the invention. Similar to the container 70, the container 80 is a dual-walled container that includes a first wall 82, a second wall 84, a cavity 86 (shown in FIG. 8) and a plurality of holes 88 (only three labeled in each of FIGS. 6 - 8) through the first wall 82. The container 80 is formed from a single sheet 90 of material by folding the sheet along a region 92 and joining the ends 94 and 96. When joined, the first wall 82 nests in the second wall 84 and forms the cavity 86. The ends 94 and 96 may be joined using any desired technique, such as fusing the ends 94 and 96 together and adhering the ends 94 and 96 together. Like the container 70, the sheet of material has a microstructure that includes many small, closed cells, such as that shown and discussed in greater detail in conjunction with FIGS. 3 and 4.

[42] The preceding discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.