Bowl-shaped plastic microwave dish

Bowl-shaped plastic dish for use in microwave ovens, the dish having a two-part structure composed of an inner shell and an outer shell, each shell having a circumferential, laterally projecting edge web, the inner and outer shells being spaced from one another to define a space containing air, and the shells being welded or glued to one another in the region of the webs to seal the air space.

BACKGROUND OF THE INVENTION 
The present invention relates to a bowl-shaped plastic microwave dish, for 
example in the form of a serving bowl, a partitioned dinner plate or the 
like. 
Microwave ovens are becoming increasingly more popular, particularly for 
home use, because, in a microwave oven, food can be cooked or thawed in 
the shortest possible time and can be reheated if desired. 
Correspondingly, the demand for dishes suitable for use in microwave ovens 
is increasing. 
In principle two types of microwave dishes are known. 
A first type includes simple plastic dishes having extremely thin walls 
which are used as throw-away packages. Such dishes are usually used for 
the sale of completely prepared and precooked foods which the end user 
merely heats in the microwave oven in the dish in question. After 
consumption of the food, this dish is discarded. 
Plastic dishes for repeated use in microwave ovens are known to be 
relatively solid and therefore also correspondingly stable. Such dishes 
are usually manufactured in an injection molding process or are pressed of 
a correspondingly high-grade plastic material. 
The latter category of dishes is comparatively expensive because, on the 
one hand, the plastic employed is of a relatively high quality and 
therefore very expensive and, on the other hand, the manufacture of such 
dishes in their respective molds is very time consuming and thus cost 
intensive. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a dish of this type 
which, with the smallest amount of material employed and low total 
manufacturing costs, has a stiffness and stability that permit repeated 
use without difficulty. 
The above and other objects are accomplished, according to the present 
invention, by a bowl-shaped plastic dish having a double shell structure 
composed of an inner shell and an outer shell, with the inner and outer 
shells being spaced from one another to delimit an enclosed air space, the 
dish having circumferentially and laterally projecting edge webs where the 
shells are welded or glued together. 
Due to the double shell structure of the dish and the firm connection of 
the two shells in the region of the edge webs which are stabilizing in any 
case, the smallest amount of material produces the highest degree of 
stiffness and strength so that such a dish is certainly able to withstand 
repeated home use. Due to the small amount of material employed, the dish 
itself is comparatively inexpensive and additionally offers a number of 
advantages which are realized because of its dual shell structure. 
For example, one of these advantages is that less energy is required than 
before to heat food in such a dish since the air enclosed between the 
inner and outer shell serves as an insulating layer. The same insulating 
effect brings about the further advantage that heated foods will remain 
hot for a longer period of time after removal from the oven. 
Due to the double shell structure, the shape of the dish offers 
considerably more possibilities than was the case in the past since inner 
and outer shell can be designed substantially independently of one 
another. Care must merely be taken that the inner and outer shells have 
practically the same shape in the region of their edge webs so that here a 
tight and firm bond can be produced. 
The inner and outer shells may also easily be given different colors. 
Due to the above-mentioned stiffness and strength, such a dish is also 
dishwasher proof and thus meets all requirements for dishes in modern 
household use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiment of the invention shown in FIGS. 1 to 4 is a plastic 
bowl-shaped dish 10 for microwave ovens which, as shown clearly in FIGS. 1 
and 2, is a serving dish. 
However, it must be pointed out here that the idea of the invention is not 
limited to any particular dish shape. This will be discussed in greater 
detail below with reference to the embodiment according to FIG. 8. 
As is particularly clear in FIGS. 3 and 4, dish 10 is composed of an inner 
shell 11 and an outer shell 12. As can be clearly seen each of shells 11 
and 12 is provided with a circumferential edge web, 13 and 14, 
respectively, in the upper region of dish 10. These webs also project 
laterally with respect to the dish and form a rim. In the region of these 
circumferential edge webs 13 and 14, inner shell 11 and outer shell 12 are 
firmly connected to one another, preferably by means of welding as 
indicated at 15 at the left-hand side of FIG. 4. As an alternative, inner 
shell 11 and outer shell 12 may, however, also be glued together by means 
of a suitable adhesive. 
Otherwise, inner shell 11 and outer shell 12 are spaced from one another so 
that an enclosed space 16 is formed between the two shells 11 and 12 and 
this space is filled with air. 
Inner shell 11 and outer shell 12 are each a one-piece, deep-drawn plastic 
part. 
Depending on the size of the total basic area of dish 10, its overall 
stiffness and stability can be increased by providing supporting bosses 
17, which are preferably drawn into outer shell 12 and extend to inner 
shell 11. They are fixed by welding to inner shell 11, as shown at 15, 
where bosses 17 contact shell 11. With these supporting bosses 17, the 
overall strength of dish 10 can be increased considerably in spite of the 
small amount of material employed and the consequently thin walls of inner 
shell 11 and outer shell 12. 
Such bosses 17 can be provided along the interior portion of dish 10, as 
shown in FIG. 3, and/or at edge webs 13 and 14, as shown in FIG. 4. 
The space 16 existing between inner shell 11 and outer shell 12, which is 
filled with air, serves as an insulating layer with the result that, on 
the one hand, food disposed in such a dish 10 can be heated comparatively 
quickly in a microwave oven since the heat losses through the walls of 
dish 10 are relatively low and, on the other hand, due to the insulating 
effect of the trapped air, there is the positive effect that the heated 
food is kept hot for a relatively long period of time. 
FIG. 5 shows an embodiment of the invention in which dish 10 again has the 
shape of a serving bowl. Here again, the inner shell 11 is provided with a 
circumferential, projecting edge web 13 and the outer shell with a 
corresponding edge web 14. Both edge webs 13 and 14 are again welded 
together at 15. Here again, supporting bosses 17 can be provided, and 
welded to inner shell 11 and web 13, to increase overall stability. 
In the illustrated embodiment, dish 10 may be provided with a covering lid 
18 likewise made of plastic. The upper supporting edge 19 of dish 10 is 
conically tapered on the outside so that it slopes downwardly in the 
direction toward the center of dish 10, with the shape of lid 18 being 
selected to correspond to web 13 and edge 19. This design provides a 
desirable, airtight seal for the contents of dish 10 by means of lid 18. 
If food disposed in closed dish 10 is to be heated in a microwave oven, it 
is necessary to permit air to escape from dish 10. 
This is accomplished in the embodiment according to FIG. 5 in that a type 
of "pressure relief" valve is integrated, on the one hand, in supporting 
edge 19 of dish 10 and, on the other hand, in lid 18. As can be clearly 
seen in FIG. 5, part of dish 10, in the region of its supporting edge 19, 
is provided with a groove 20 which widens toward the interior of dish 10 
and lid 18 is provided with a ventilation bore 21. When lid 18 is in 
place, ventilation bore 21 opens into a recess 22 in the upper surface of 
edge web 13 of inner shell 11. 
If, now, during heating of food a certain excess pressure develops in the 
interior of dish 10, which is closed by lid 18, this excess pressure is 
able to escape through groove 20, recess 22 and ventilation bore 21 as a 
result of the elasticity of supporting edge 19 and/or lid 18. 
In the embodiment of the invention shown in FIGS. 6 and 7, the upper 
supporting edge 19 of dish 10 is provided on the circumference of dish 10 
with two mutually vertically offset steps 23 and 24. Lid 18 is equipped on 
its interior, in the region of its closing edge 25, with correspondingly 
offset projections 26 and 27. 
If, as shown in FIG. 6, lid 18 is pressed completely onto supporting edge 
19 of dish 10, the interior of the dish is airtightly sealed. If, however, 
lid 18 is placed partially onto supporting edge 19 of dish 10 so that 
lower projection 27 is above lower step 24, the dish is still essentially 
closed while permitting air under pressure to pass. This means that in 
this closed position, in which only one step is engaged, food in dish 10 
can be heated in the microwave oven without developing an undesired excess 
pressure in the interior of dish 10. 
The airtight closed position for dish 10 shown in FIG. 6 is desirable for 
freezing food. 
FIG. 8 shows a microwave oven dish 10a which, in contrast to the above 
described configurations, is designed as a partitioned dinner plate. This 
dish 10a has basically a circular shape and is provided in its bowl-shaped 
interior with partition bars 28 and 29. These partition bars 28 and 29 
create various compartments 30 and 31 within the dinner plate. Plate 10a 
can additionally have edge webs as in the embodiments of FIGS. 1-7. 
As is clearly shown in FIG. 9, partition bars 28 and 29 may be provided 
exclusively in inner shell 11, but there also exists the possibility of 
equipping the respective outer shell 12 of dish 10a with corresponding 
protrusions 32 in the region of partition bars 28 or 29, as shown in FIG. 
10. In addition, it is possible to provide supporting bosses, like 17 in 
FIGS. 2-7, in the region between partition bars 28 or 29 and corresponding 
protrusions 32 in outer shell 12 and to connect these bosses with inner 
shell 11 by welding. Such bosses can also be provided in the flat regions 
and at the edge webs of dish 10a. 
The above statements show that the double shell structure according to the 
invention of a dish 10 or 10a according to the invention allows for 
manifold design possibilities which, on the one hand, serve to increase 
the inherent stiffness, stability and strength of the dish 10 or 10a 
itself and, on the other hand, also make it possible to influence in an 
extremely versatile way the exterior shape of such a dish 10 or 10a. 
For example, inner shell 11 may certainly have a different outline than 
outer shell 12; only in the region of the two edge webs 13 and 14 which 
are to be connected together, must inner shell 11 and outer shell 12 be 
congruent. There also exists the possibility of giving the inner shell 11 
a different color from outer shell 12. 
With all the stability of the entire dish 10 or 10a, inner shell 11 as well 
as outer shell 12 in themselves retain a certain elasticity so that it is 
easily possible to clamp a metal plate or the like into such a dish 10 or 
10a which, when used in a microwave oven, serves to produce a browning 
effect for meats or the like. 
Within the scope of the present invention, inner shell 11 and outer shell 
12 may also each be made of one piece as ejection molded items in which 
case, in order to retain the advantages mentioned repeatedly above, care 
must be taken that these injection molded pieces have relatively thin 
walls. 
The lids 18 shown in FIGS. 5 to 7 may of course have a double shell 
structure as well, similar to dish 10 so that the stated insulating effect 
also applies to the respective lid 18. A portion of such a lid, 18a, is 
shown in FIG. 11. This includes an inner lid shell 34 and an outer lid 
shell 35, the two lid shells having respective circumferential, laterally 
projecting edge webs via which lid shells 34 and 35 are welded or glued to 
one another at 15 to form a sealed air space 36. 
Recess 22 in wedge web 13 shown in FIG. 5 extends preferably around the 
entire periphery of edge web 13. This has the advantage that, 
independently of the position in which lid 18 is placed, ventilation bore 
21 always opens into circumferential recess 22. This means that it is not 
necessary to note at which point recess 22 is disposed when lid 18 is 
placed onto the dish. 
Each shell of a dish according to the invention, as well as the, or each 
part of the, lid, can be made of any known type of plastic suitable for 
use in a microwave oven. The plastic can be one of the high quality types 
mentioned at the outset since considerably less material is needed for the 
two shells than for the solid dishes known in the art. 
The invention now being fully described, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein. 
The present disclosure relates to the subject matter disclosed in German 
Application No. P 36 13 298.5 of Apr. 19th, 1986, the entire specification 
of which is incorporated herein by reference.