JPS6015548B2 - food containers for microwave cooking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to food packaging, and more particularly to a food container for use in microwave cooking of food, the invention comprising a food container for use in the microwave cooking of food, which comprises a structure that provides color to the exterior surface of the food contained therein; Relating to food containers equipped with

In the field of microwave cooking, it is a common problem to make the outer surface and color of the food being cooked to more closely resemble food prepared by conventional methods.

Unless special structures are created that impart color to the outer surface of the food, the outer surface of the food cooked in the open microwave remains undercooked. This is because when food is heated with microwave radiation, it has the effect of cooling the surface of the food. It is therefore a general objective in the field of microwave cooking of foods to perfect an economical and efficient method for coloring the exterior of foods cooked in microwave ovens. Accordingly, various attempts are generally known in the prior art to incorporate layers into containers used for microwave cooking of foods, these layers being designed to be specifically heated by microwave radiation. Ru. Such layers are generally made of semiconductor materials such as tin oxide. US patents showing the use of such layers include, for example, US Pat. No. 3,853,612 and US Pat. No. 3,965,323. Another example of a method used to obtain color heating from microwave radiation is U.S. Pat. No. 2,582,174;
No. 669 and No. 400,384 P1 are disclosed. Furthermore, at least one method of heating food products in a microwave oven is known that uses ferromagnetic metals. An example is disclosed in US Pat. No. 2,830,162'. Additionally, at least one U.S. patent includes:
It has been taught to incorporate conductive films as porcelain dishes or other heavy containers for use in coloring foods cooked in microwave ovens.
However, the examples disclosed in that patent, US Pat. No. 3,783,22, relate to tin oxide films; other materials disclosed therein are cellulose fiber and silicon carbide. There are no examples in the prior art of containers used to color food products in microwave ovens that use elemental metals or that use very thin conductive films on low-cost, disposable substrates. . The improvement according to the invention is that in a food cooking container used for microwave cooking of food, a layer of electrically conductive elemental metal is incorporated into the container, which when exposed to microwave radiation heats up rapidly and covers the surface of the food in the container. It all boils down to making the metal layer thin enough to give it color.

The main object of the present invention is to provide a means for coloring food prepared in an open microwave oven, which can be incorporated into a throwaway package or container for pre-packaged or frozen food. It is to be.

Another object of the invention is to construct a suitable food package incorporating structures for coloring the exterior surface of food products to be cooked in a microwave oven.

Yet another object of the present invention is to incorporate an arrangement for coloring and coloring foods during microwave cooking, the operation of which is efficient and economical.

Other objects, advantages, and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

In FIG. 1, a food container for microwave cooking constructed in accordance with the present invention is indicated generally by the reference numeral 10.

The container, as shown in FIG. 1, is a generally tray-shaped package with four side walls that receives a pre-prepared amount of food material. Container 10
The container 101 has shallow side walls and a wide base as shown, and may or may not have a lid thereon, or may be of any desired shape depending on the contents to be supported by the container 101. You can also do that. The container is specifically designed to be disposable and is therefore comprised of economically available ingredients. Figure 2 shows the package 1 in Figure 1.
A cross-sectional view of the packaging material comprising 0 is shown.

This packaging material, designated by the reference numeral 12 in FIG. 2, generally comprises three layers. The top layer, which is designed to be the layer closest to the food product as shown in FIG. 2, is a high temperature resistant protective layer 14. Under this protective layer 14,
A very thin layer 16 of conductive material such as a vapor deposited conductive elemental metal is formed, for example a thin layer of elemental aluminum. The combination of a protective layer 14 and a metal layer 16 adhered thereto is attached to a base layer 18 of structural substrate material. The function of each of these layers is discussed below. The function of the base material 18 is to provide structural rigidity to and support the physical shape of the package 10, whatever the shape of the package 10.

The substrate material layer 18 is preferably formed of a low density material that has sufficient thermal stability to withstand microwave oven cooking temperatures and relatively high insulation properties. Materials suitable for use as the base material are paper, glassine materials, plastics, porcelain, and various coated papers. Preferred materials for use in disposable containers include coated kraft paper and other common kraft paper combinations commonly used in cardboard cartons and packaging. The function of the protective layer 14 is to prevent the food product inside the container 10 from coming into contact with either the metal layer 16 or the base material layer 18.
Protective layer 14 also serves as a base material to which metal layer 16 is deposited during the fabrication of package material 12. Suitable materials for use in making protective layer 14 include polyester, polyethylene, nylon, cellophane, polysulfone, and other relatively stable plastic materials. It is important that the material of the protective layer 14 is sufficiently stable at high temperatures to not deteriorate during operation of the microwave oven at the temperature selected to cook the desired food product. Polyester has been found to be a particularly suitable material for use as the protective layer 14 due to its stability and surface smoothness. The packaging material 12 also includes a metal layer 16 that is adhered to the rear surface of the protective layer 14 and to the food contact surface of the base material 18. Metal layer 16 is formed as a vacuum deposited film of a conductive elemental metal, which coats protective layer 14 prior to bonding protective layer 14 to substrate material 18 as described above.
Preferably, it is deposited on the lower surface of the . The main characteristic of the metal layer 16 concerns its mechanical thickness. This means that it is extremely thin. In fact, under current technology, it is virtually impossible to mechanically measure the exact thickness of the metal film layer 16. Therefore, in the common art of vacuum deposition, it is common practice to measure the thickness of a vacuum deposited layer of conductive metallic material with respect to the surface resistivity of the metallic layer itself. The reason why it can be done in this way is
Unlike traditional thick metal films and foils, these deposited metal layers are very thin and therefore have a fairly high resistance to current flow that can be easily measured. Once the resistivity of the metal layer has been measured, it can be determined that the resistivity is moderate based on the amount of metal material applied to a given square area during deposition of the metal layer on the substrate, in this case the protective layer The mechanical thickness of this layer can be approximated with great certainty. It should be understood, however, that the film of metal layer 16 is of such a thickness that it is impossible to directly measure its size, and such measurements must be made indirectly. Such films are generally thin and easily visible to the human eye when deposited on transparent materials. Metal layer 1 of the package of the invention
Films of type 6 serve in food packaging and perform a coloring function during microwave oven cooking.

In conventional microwave cooking, it is generally considered to be an undesirable practice to include appliances or packages that incorporate significant amounts of electrically conductive elemental metals. Many microwave oven manufacturers provide instructions with oven warnings against using aluminum or similar metal appliances in microwave ovens. Such a warning is included to avoid reflection problems since microwaves cannot penetrate such metal appliances and are reflected back from them. Such reflections can result in areas of food not being cooked in the oven, and in some cases can damage the klystron of the microwave oven. Also, traditional foil products such as aluminum foil do not generate heat when exposed to microwave radiation, so such materials may not act as a heat source to surface and color food products when exposed to microwaves. easily recognized. However, surprisingly, if the metal layer 16 is sufficiently thin, it will not interfere with the operation of the microwave oven, and as is clear, the microwaves incident thereon will not be completely reflected, so that the microwave oven will not actually interfere with the operation of the microwave oven. It was found that the heating was done very efficiently.

Therefore, when the container 10 of the invention containing a food product is placed in a microwave oven and exposed to microwave radiation, the metal layer 16 heats rapidly to a relatively high temperature. metal layer 1
The heat generated by the container serves to color the surface of the food contained in the container. This coloring effect is particularly effective in food containers designed for cooking in microwave ovens. In experiments conducted using containers and metal layers 16 used to cook food in microwaves, various thicknesses of metal layers 16 have been successfully used.

Approximately 0. It has generally been found that a metal layer 16 having a surface resistivity between t and 80/in2 provides satisfactory results for containers according to the present invention. As mentioned above, the thickness of this material cannot be directly measured mechanically, and if the resistivity of the aluminum film of metal layer 16 is 1.50/in2, then the thickness of this aluminum film is 200 to 300 Å.
Approximate calculations showed that. Using these numbers as a basis for calculation, in the case of aluminum metal, 0. The thickness is believed to be approximately 700 to 40 A thick with a surface resistivity of 80 to 80/in2. Films such as metal layer 16 are most efficiently deposited on the substrate, in this case the protective layer 14, by using vacuum deposition.
attached to.

Such techniques involve melting elemental metal material in a vacuum chamber and passing a substrate through the vacuum chamber accessing the molten metal material. The molten metal material releases metal vapor, which is deposited on the substrate as it is passed through the chamber, and the amount of material deposited on the substrate is controlled by the speed at which the substrate is moved through the vacuum chamber. Such vacuum deposition techniques are believed to be the most efficient way to make metal layer 16 usable in the present invention. An advantage of such materials is that many types of materials that can be used in the present invention are now readily available, such as polyester coated with aluminum. The exact upper limit of metal layer 16 that can be used in the present invention is not easily determined using currently available products.

For example, the thinnest pinhole-free film or foil of aluminum material available has a thickness of about 0.00025 inches (0.0065 ribs). This thickness corresponds to about 65000A. Experiments have shown that this thickness is too large to cause the foil to heat up when exposed to microwaves. The difference between the thinnest foil available, which is 0.00025 inch foil, and currently commercially available vacuum deposited films is currently about two orders of magnitude, and materials between these thicknesses can be made to order. But it's not easily available. It is contemplated that the metal films used within the metal layer 16 of the present invention will function at slightly greater thicknesses than those described herein. However, the exact limits of mechanical thickness are currently unknown. To be technically useful in forming the metal layer 16 of the present invention, the metal layer 16 must be of such a thickness that it heats easily and rapidly when exposed to microwave radiation. No.

Such heating of the metal layer 16 must be rapid, and by rapid we mean within a time sufficient to coat the exterior surface and color of the food during the normal cooking time of the food in a microwave oven. This means that heating must occur and a temperature sufficient for it must be reached. For example, about 20/
It has been found that a vacuum deposited metal layer 16 having a surface resistivity of square inches can reach temperatures of over 200 degrees within 30 seconds. Similarly, a metal layer 16 having a surface resistivity equal to about 40/in2 will reach temperatures in excess of 2000°C in 20 to 3 hours. There appears to be a generally linear relationship between the surface resistivity of the metal film used as metal layer 16 and the time required to achieve a certain temperature for that metal layer when exposed to microwave radiation. It will be done.
The higher the surface resistance of the metal layer, the faster the metal layer 16 will heat up when exposed to microwave radiation. In either case, the metal layer 16 to be used in the container 10 of the invention is
During the time it takes to cook a food placed in a 0.0000000000000000000000000000000000 temperature, the exterior surface of the food is generally at least 2000F (93oo) and reaches its coloring temperature within a short enough time to color the exterior surface of the food. It is necessary to maintain FIG. 3 shows another embodiment of a food container constructed in accordance with the present invention. The container of FIG. 3, designated generally by the reference numeral 22, is intended to enclose a sausage 20 or similar sausage-shaped material. This container 22 is formed as a thin material wrap around the outside of the sausage 20. FIG. 4 shows an enlarged cross-sectional view of the packaging material of package 22. FIG. Similar to container 10, this container 22 is provided with a protective layer 28 behind which a vacuum deposited metal layer 26 is arranged. The combination of protective layer 28 and metal layer 26 is encased within a substrate material 24 that includes the exterior of container 22 .
This substrate material 24 of container 22 is similar to substrate material 18 of container 10.
is chosen to be considerably more flexible than The container 22 of FIGS. 3 and 4 functions similarly to the container 10 of FIGS. 1 and 2. When exposed to microwave radiation, the container 22 serves to color the exterior surface of the sausage 20 contained therein. This kind of exterior and coloring effect is sausage 2.
It is very useful in the sausage making field as it sterilizes and seals the outer surface of the sausage. Using a container 22 constructed in accordance with the present invention, sterilization and sealing can be accomplished in an efficient and economical manner by placing the finished sausage 20 in the container 22 and exposing it to microwave radiation in a process plant. be able to. It is clear that metal layer 16 can be used to construct many types of containers within the scope of the present invention.

It is therefore clear that a large number of disposable containers can be constructed for use in microwave cooking of frozen or other pre-packaged convenience foods. Furthermore, the metal layer 16 can also be incorporated into containers such as dishes, metal cutlery, and stew pots that are not disposable in nature but are household items, and can be used to cook food in a microwave oven. It is also clear that the housewife can easily use this metal layer again and again during cooking. It will also be appreciated that a container including a metal layer 16 according to the present invention may be any of a wide variety of wrappers used to wrap food products, such as the sausage package 22 of FIGS. 3 and 4. However, a particular advantage of the present invention is that layer 16, whether formed of metal or other conductive material, is capable of configuring a disposable container with an arrangement for heating and coloring foods in a microwave oven. It means that it can be done. microphone. Known containers for food preparation and coloring in waves are large, bulky and relatively expensive, which are totally unsuitable for packaging food and can only be used as dishes or cooking utensils. Not available. By combining the readily available and economical materials of the containers of the present invention, it is possible to package food for consumers and cook the food in a microwave oven to improve its surface and color and then wrap the package with bran. ．． A food package is constructed that can be used as you like. This was not possible with known technology. Additionally, the conductive coated polyester paperboard material that is the preferred material for such packaging is relatively lightweight yet has a density of 4.5 mm, making the use of absorbed microwave energy less convenient for heavy equipment or glassine equipment. make it more efficient than in the case of Porcelain and glassine utensils require a considerable amount of heating before they feel hot to the touch. Therefore, the first
Food packages, such as container 10 of FIGS. 1 and 2, are suitable for use in microwave oven-cooked foods and for coloring devices by allowing a twill-type device to operate effectively and efficiently. bring about significant advances in the field. Furthermore,
It is also clear that when using metal layer 16 in a container according to the invention, many metals other than aluminum can be used as this metal layer.

However, it is considered important that the material used for this metal layer 16 is an elemental metal and that the metal is electrically conductive. Other suitable metals for use in metal layer 16 include copper, tin, lead, silver, gold, nickel, and zinc, some of which are not recommended for single-use containers due to cost. It is clear that this will not be selected.
It is also clear that combinations or alloys of these metals can also be used in the present invention. The exact thickness of the metal layer 16 required to obtain a coloring effect varies depending on the metal used as the metal layer 16, but any metal is most efficiently used when this layer is constructed by vacuum deposition, and the thickness of the metal layer 16 is It is clear that the surface conductivity of 16 is approximately the same for different metallic materials when this layer is used in a container according to the invention. The present invention is not limited to the specific structure or arrangement of each part described above,
It is to be understood that all such variations are included within the scope of the claims.

[Brief explanation of drawings]

1 is a perspective view of a food package constructed according to the present invention; FIG. 2 is an enlarged cross-sectional view of the material of the package of FIG. 1;
FIG. 3 is a perspective view of another embodiment of a food package constructed in accordance with the present invention, and FIG. 4 is an enlarged cross-sectional view of the material of the package of FIG. 10... Container, 12... Package material, 14...
- Protective layer, 16... Layer of conductive elemental metal, 18...
Base material layer, 20... sausage, 22... container, 24... base material material, 26... metal layer, 28...
protective layer. FIGIF! G. 2 FIG. 3 FIG4

Claims (1)

[Claims] 1. In a food cooking container used for microwave cooking of food, a base material formed into a structure of an appropriate shape to support the desired food, and a structure formed on the food contact surface of the base material. a protective layer and a layer of electrically conductive elemental metal disposed between the protective layer and the substrate material, the metal layer being heated when exposed to microwave radiation to cause the metal to be heated within the container. at least about 0.4Ω to make the food and color
1. A food cooking container, characterized in that the food preparation container is formed to a thickness having an electrical resistivity of /in2.