Bowl for heating food Description

A widely used method to protect food from spoilage and thus to obtain a longer shelf life is found in heating the food. Normally temperatures above yo degrees Celsius are applied. Once sufficiently long exposed to sufficiently high temperatures, the preserved food can be placed in a hermetically sealed containerto guarantee the hygienic condition of the heated food during transport, storage and so on.

A common method is to place the food in a plastic tray before heating and to seal it hermetically before heating by attaching a plastic sheet to the top of a horizontally oriented flange around the perimeter of the tray. This prevents outside contaminations from reaching the food after heating. Examples of this can be found in patents US 3,997,677 and US 2008/0251518 Ai.

A disadvantage of this method is that the hermetically sealed packaging comes under pressure during the heating of the food. This is caused by air trapped in the packaging that expands under the influence of heating and is caused by steam that is released from the heated food. As the container is hermetically sealed, the heat generated pressure cannot escape. The packaging used commonly are thermoplastic plastic trays. Commonly used thermoplastics lose stiffness at temperatures above 70 degrees Celsius. In combination with the high internal pressure, this means that the trays can deform strongly. To prevent this undesired deformation, the trays have extra thick walls: thicker than necessary for the other functioning of the tray, such as serving or consuming the food.

A further disadvantage is that during heating the covering sheet will become convex. This places a peeling force on the attachment of the sheet to the flange of the tray. In order to withstand this stress state during heating without loss of integrity, the bond between tray and covering sheet must also be mechanically strong at high temperatures. This implies that the bond will be even stronger at room temperatures and can no longer be broken manually. This does not benefit the ease of use.

However, the installation of a one-way valve built into the sheet that can release

overpressure as in EP 1340695 A1 built into the covering sheet, is not a solution. During cooling, the expanded air will cool down and the steam will condense. This creates negative pressure that causes the tray to implode during cooling.

A well-known solution to this problem is to create a two-way valve. The valve allows air to escape during heating and the valve allows air to flow in during cooling. An example is US 2017/0036843 Ai. However, this solution cannot guarantee that the packaging is

hermetically sealed or remains sealed after cooling. If the time between the cooling of the heated food and its consumption is long, as is the case with food intended for the supermarket, this is a crucial shortcoming.

The invention described below solves the above problems. It essentially provides the function of a two-way valve that can be hermetically sealed. The invention is based on a packaging consisting of the combination of a tray with a horizontally oriented flange (2) attached to the top of the side walls (1) around the circumference of the tray to which a cover sheet is attached. Preferably, the sheet and the tray are of thermoplastic material and the method of attachment is thermal or ultrasonic welding. By adding a hinging section to the horizontal flange to which the cover sheet is attached (10), this hinging section (3) can be rotated out of the plane of the flange (2).

This rotating movement is triggered by a pressure difference between the interior of the sealed tray and its surroundings. In case of overpressure (where the sheet will be convex), as well as negative pressure (where the sheet will be concave), the sheet will introduce a tensile stress into the flange. By placing the hinge in a section of the flange, this tensile stress will pull the hinging section up and make it rotate from its horizontal position in a more vertically oriented position. Preferably the hinge should be placed in a corner of a chamber of the tray. In case the tray has several chambers, several corners can be provided with a hinge. See figures 4a, b, c, and d for the function of the hinging section in its different positions.

The attachment pattern (7) runs over the hinging part forming the connection between the cover sheet and the flange. The attachment pattern is the geometric shape of the contact surface that creates the atachment. The attachment forms a boundary between the interior of the packaging and its surroundings. So this dividing line is also present in the hinging section of the flange. See figure 5. The hinging section on the interior side of the attachment has a perforation (11). This perforation can have the shape of one or more round holes, cracks or other cuts. In the initial position, the hinging section (3) is in horizontal position and the perforation is covered by the cover sheet. When the hinging section is in a more vertical position, the sheet is necessarily moved away from the perforation - leaving it uncovered - so that the perforation forms a channel between the interior of the packaging and its surroundings. Any over- or negative pressure that may occur can thus be removed, as the hinging section is brought into a more vertical position from its neutral horizontal position by negative pressure or overpressure. Preferably the perforation is close to the hinge, so that only a small angular change (e.g. a change of two or more degrees) of the position of the hinging section is required to form the channel with the outside world. In this way, large pressure differences - and thus deformations - are avoided. The shell wall thickness can now be minimised.

in addition, no major forces are now exerted on the attachment between the cover sheet and the flange. This means that the attachement can be so weak that it can be peeled off manually after cooling.

After the aforementioned pressure differences have disappeared, the hinging section returns to the horizontal position. This covers the perforation in the hinging section again with the cover sheet and seals the packaging.

By then moving the hinging section downwards, the sheet is pulled tight over the hinge.

Not only is the perforation covered by the sheet, but the hinge forms a second blockage. This creates an extra threshold for contact between the environment and the interior of the packaging. By fixing the hinging part in its downward position, the integrity is guaranteed. In a preferred version of the invention, the fixation of the hinging section in its downward position is irreversible. Once hinged downwards, the packaging remains hermetically sealed. In a preferred version, a vertically oriented locking finger (5) located under the flange (2) is used for this purpose. A locking hole (9) is located in the hinging part (3). The locking hole is dimensioned in such a way that its end can be forced over the end of the locking finger in a rotating movement around the hinge line (10). The material around the locking hole must therefore be elastically deformed so that the end of the locking hole can hinge past the end of the locking finger. For this purpose, the distance from the end of the locking hole to the hinge line is less than the distance from the end of the locking finger to the hinge line. The side of the locking finger which first encounters the end of the locking hole during the locking process may be rounded to facilitate forcing the locking hole across the end of the locking finger. By orienting the side of the locking fingerthat meets the first end of the locking hole at right angles to that end during opening, it is impossible to open the fastener.

By placing a tear-off line (8) in the hinging section, the closure can still be broken by tearing the hinging section apart around the locking hole. The tearing will be visible and re-closing is no longer possible, with which the tearing testifies of the breaking of the hermetic closure.

In a preferred version, the angle with the hinging section {3) has a shoulder (4) that serves to keep the stack height of empty stacked trays small. The downward reaching closing finger {5) is positioned at the bottom of the shoulder (4). When stacking, the closing finger will rest on the shoulder of the scale below and act as a stacking cam between two successive trays. See figures y, 8 and 9. The size of the stack height is now equal to the length of the closing finger minus the depth of the shoulder (4). This makes it possible to make the closing finger long and thus choose the end of the closing finger low, which makes it possible to make the whole of the hinging part (3) fit geometrically, while keeping the stack height low. The closing finger has such a length that in the corner with the hinging part (3) the stack height is equal to the stack height due to the length of the stacking finger (6) in the other corners.

List of figures

Figure i

T ray, top view

Here i is a side wall, 2 a horizontally oriented flange, 3 a hinging section of the flange and 4 a stacking shoulder under the hinging part of the flange.

Figure 2

Tray, bottom view

Here 2 is a horizontally oriented flange, 3 a hinging section of the flange, 5 a locking finger and 6 a stacking ridge.

Figure 3

Tray, attachment pattern Here 7 is a attachment pattern with which a cover sheet is connected to the tray.

Figure 4 a

Functioning of the hinging section, neutral postion Figure 4 b

Functioning of the hinging section, open position

A channel with its surroundings is fromed

Figure 4 c

Functioning of the hinging section, closed position Figure 4 d

Functioning of the hinging section, locked postion Figure 5

Detail hinging section with attachment pattern

Here 3 is the hinging part of the flange, 7 the attachment pattern with which the sheet is attached to the scale, 8 a tear line, 9 a locking hole and 10 the hinge line and 11 a perforation.

Figure 6

Details closure

Here 5 is the locking finger, 9 the locking hole and 10 the hinge line.

Figure 7 a

Stacking

The line AB is the line along which the cross section is drawn in the figure 7 b and in Figure 7 b

Stacking, cross-section Figure 8

Stacking, cross-section hinging section

Here 4 is the shoulder, 5 the locking finger and 9 the locking hole.

Figure 9

Stacking, cross-section other corners

Here 6 is the stacking ridge.