PACKAGE MATERIAL FOR MICROWAVE COOKING

Abstract: The present application is directed to a package material for microwave cooking which is obtained by integrally laminating a microwave heating element, which generates heat when irradiated with microwave, to a base material to form a sheet; and providing, on the sheet, many slits in the form of broken lines, in parallel, and in alternation between the adjacent ones.

Description: The present invention relates to a food packaging material for microwave cooking according to the preamble of claim 1. Heretofore, as disclosed in Japanese Patent Publication No. 15548/1985, a packaging material for microwave cooking has been constituted by first superposing an aluminum-deposited layer, which generates heat on the absorption of microwave, on a heat-resistant plastic film such as a polyethylene terephthalate film, and then integrally laminating a base material such as a paper to this aluminum-deposited layer. In cooking a food, the latter is wrapped in such a package material and is then placed in a microwave oven. Nowadays, such a cookery is often utilized. However, in the case of the cookery of using the above-mentioned packaging material, the food wrapped in the packaging material cannot be observed visually therethrough, and therefore a degree of the scorch is not confirmable. In addition, water vapor generated in the package is confined therein, so that an exothermic efficiency deteriorates, with the result that a scorch state on the food is bad disadvantageously. Furthermore, the above-mentioned packaging material has the drawback that it cannot pack the food so as to tightly fit to its shape. According to the document FR-A- 2 451 182 there is disclosed a generic food packaging material for microwave cooking. From this material, different containers of open or closed shape can be made, so that, in particular, the food prepared in the closed form can basically be stewed, but not gratinated. From the document FR-A- 2 146 198, a packaging material for roasting is known, from which containers for preparing food can be made. In the case of this material, open slits are provided partially, preferably on its lower side, in order to allow the escape of juices from the packaging container into a lower pan. This measure, however, does not at all suffice to allow gratinating. The object of the present invention is to provide a packaging material for microwave cooking by which suitable scorches can be marked on the outer surface of the cooked food. This object is achieved by the features defined in the characterizing part of claim 1. According to these features the packaging material is continuously provided with a plurality of open slits in the form of broken lines and arranged in parallel, with the gaps between the slits in each line being adjacent the slits in neighbouring lines. In such a manner the packaging material can stretch in the cross direction at right angles to the array direction of the slits and thus can wrap a piece of food so as to tightly fit its shape. Preferable embodiments of the invention are defined in the claims 2 and 3 respectively. In the following the invention is illustrated by embodiments with reference to the enclosed figures. Fig. 1 is a perspective view showing a packaging material for microwave cooking; Fig. 2 is an explanatory view showing a section of an essential part of one embodiment of the packaging material; Fig. 3 is an explanatory view showing another embodiment through its section; Fig. 4 is an explanatory view showing still another embodiment through its section; Fig. 5 is an explanatory view illustrating the state where a food is wrapped in the packaging material; Fig. 6 is an explanatory view illustrating a package morphology for transportation; Fig. 7 is a sectional view taken along the line VII - VII in Fig. 6; Fig. 8 is a perspective view showing the state where another food is wrapped in the packaging material; Fig. 9 is a sectional view taken along the line IX - IX in Fig. 8; and Fig. 10 is an explanatory view illustrating the state where still another food is wrapped in the packaging material. Fig. 1 is an explanatory view of a packaging material for microwave cooking. Reference numeral 1 in this drawing is a first heat-resistant plastic film layer comprising a polyethylene terephthalate film. On this first heat-resistant plastic film 1, a first metallic layer 2 of aluminum is vacuum vapor-deposited to form a heating element 3 in which the metallic layer 2 generates heat on absorbing microwave. Then, this heating element 3 is integrally laminated all over to a base material 4 such as a paper in order to form a sheet A in which the first heat-resistant plastic film layer 1, the first metallic layer 2 and the base material 4 are laminated together (see Fig. 2) On the sheet A, many slits 5 are provided in the form of broken lines, in parallel, and in alternation between the adjacent ones. The thus obtained packaging material for microwave cooking can stretch in a direction across at right angles to the array direction of the slits. Therefore, when a food B (e.g., a fish) to be cooked is wrapped in the packaging material and the latter is then sealed along its one edge 6 as shown in Fig. 5, the respective slits 5 are opened, so that packaging can be accomplished in conformity with the shape of the food B. And when the thus packed food B is placed in a microwave oven, water vapor can be released out through the open slits 5, and a suitable degree of the scorch can be obtained on the food B and net-like scorches can be marked thereon. In the course of transportation, the food B (see Fig. 5) packed in the package material of the present invention may be received in an outer bag C and then confined therein tightly by means of vacuum packaging. In this case, the food B is retained in the sheet A in a closely adherent state, and therefore when the food B is taken out from the outer bag C and is placed in the microwave oven, the above-mentioned effect can be more improved. The outer bag C may be made from a plastic film such as a polypropylene film or its laminate. Further, in the case that a back cutting or belly cutting dried fish as the food B is wrapped in the packaging material and is then cooked in the microwave oven, the said opened fish may be wrapped in the sheet A, as it is. However, as shown in Figs. 8 and 9, the opened fish (food B) may be folded with the interposition of one edge portion of the sheet A therebetween. In such a way, a use area of the sheet A is small, which fact is economical, and the inner surfaces of the folded fish can have scorches. In this case, the sheet A may be fastened with a label, or alternatively the whole of the packed food B may be subjected to a pillow deaeration packaging treatment so that the sheet A may adhere closely to the food B. Furthermore, in the case that some parts of the food B such as a tail and fins of the fish are liable to excessively scorch by heat, some portions alone of the food B for which suitable scorches are-desired may be wrapped in the sheet A, as shown in Fig. 10. This manner permits finely scorching the optional portions alone on the food B. The above-mentioned sheet A is not limited to the layer structure in which the heating element 3 is integrally laminated to either surface of the base material 4. As shown in Fig. 3, the packaging material further comprises a second metallic layer 2 and a second plastic film layer 1, wherein the second metallic layer 2 is laminated between the opposite side of the base material 4 and the second plastic film layer 1. Further, as shown in Fig. 4, the sheet A may be formed by laminating the second metalic layer 2 between the opposite side of the first plastic film layer 1 and the second plastic film layer 1. As described above, according to the present invention, the packaging material for microwave cooking comprises the sheet which is made by integrally laminating the heating element to the base material such as a paper, the heating element being composed of the heat-resistant plastic film layer and the heat-generating metallic layer. And on this sheet, many slits are provided in the form of broken lines, in parallel, and in alternation between the adjacent ones. Therefore, when a food is wrapped in the packaging material, the latter can be freely stretched in conformity with the shape of the food, and water vapor which generates by heating in a microwave oven is easily released through the opened slits, so that there can be avoided the conventional disadvantage that the surfaces of the food are softened with water. Instead, a suitable scorch state can be obtained, and net-like scorches can be marked on the food. In consequence, it is fair to say that the present invention can display the practically excellent effect.

Claims: A food packaging material for microwave cooking comprising a first metallic layer (2) formed by vacuum vapour deposition laminated between a first side of a first heat-resistant plastic film layer (1) and a first side of a base material (4), characterized in that said packaging material is continuously provided with a plurality of open slits (5) in the form of broken lines and arranged in parallel, with the gaps between said slits (5) in each line being adjacent said slits (5) in neighbouring lines in such a manner that said packaging material can stretch in the cross direction at right angles to the array direction of said slits (5) and thus can wrap a piece of food (B) so as to tightly fit its shape. A packaging material according to claim 1, characterized in that said packaging material further comprises a second metallic layer (2) and a second plastic film layer (1), wherein said second metallic layer (2) is laminated between the opposite side of said base material (4) and said second plastic film layer (1). A packaging material according to claim 1, characterized in that said packaging material further comprises a second metallic layer (2) and a second plastic film layer (1), wherein said second metallic layer (2) is laminated between the opposite side of said first plastic film layer (1) and said second plastic film layer (1).

Inventors: SADA, JUN C/O TOPPAN PRINTING CO., LTD., SASAKI, HIROAKI C/O TOPPAN PRINTING CO., LTD., SUZUKI, SHIGERU, TAKAHASHI, SUEO, TOYODA, MINORU C/O TOPPAN PRINTING CO., LTD.
Applicants: NIPPON SUISAN KAISHA, LTD., TOPPAN PRINTING CO. LTD.
Application year: 1987
Main classification: H05B6
IPC codes: B32B15, F24C7, A47J27, B65D81