EP0208352A1

EP0208352A1 - Lid for a container and packing consisting of a container with a lid

Info

Publication number: EP0208352A1
Application number: EP86200995A
Authority: EP
Inventors: Dirk Zijlstra; Waldur Hansen
Original assignee: Wavin BV
Current assignee: Wavin BV
Priority date: 1985-06-11
Filing date: 1986-06-09
Publication date: 1987-01-14
Also published as: NL8501681A; AU5854786A; JPS61287554A

Abstract

In a lid (1) for a container (5) comprising a rim portion (2) for connecting the lid (1) to the container (5) and a middle portion (3) lying inside the said rim portion (2)and being movable in the axial direction relative to the rim portion (2) the middle portion (3) is joined to the rim portion (2) via a bellows-shaped intermediate portion (4) extending substantially in the axial direction. This makes it possible that, when a packing consisting of a container (5) closed by such a lid and filled with a product is subjected to a heat treatment, such as sterilization, the expansion of the gases contained in the packing is entirely taken by the lid (1). The lid may additionally be provided with a closable opening (9) which opening is preferably closed by a drop (10) of a meltable plastics composition.

Description

The invention relates to a container lid comprising a rim portion for connecting the lid to the container and a middle portion lying inside said rim portion and being movable in the axial direction relative to the rim portion.
A lid of this type is known in various forms. In a particular form the middle portion of the lid is joined to the rim portion via an intermediate portion having a plurality of concentric ridges and grooves. When this lid is placed on a container the middle portion may be forced downwardly in order to press air out of the container. The air can escape from the container by passing between the rim portion of the lid and the container. After the downward force on the middle portion is released a partial vacuum is created in the container and the lid is sealed in place.
For some products, such as foodstuffs, it is often necessary for products in the packing to be subjected to heat treatment, such as sterilization. If in such cases the packing consists of a container closed by a lid, the lid is usually of metal or sometimes of glass or other material and is for example fitted on the container by a screw connection. In order to obtain hermetically sealed packing after the heat treatment, a sealing ring of rubber or rubber-like material is placed between the lid and the container.
To make it possible to subject a product in a packing consisting of a container and a lid fitted to the container to heat treatment, such as sterilization, various requirements are imposed on the packing.
During the heat treatment the volume of the gases contained in the packing increases. These gases must be able to escape from the packing by passing between the lid and the container. In order to prevent the product also contained in the package from accompanying the escaping gases and being lodged between the lid and the holder, so that after the heat treatment the packing will leak, a fairly large empty space must be left under the lid.
In addition, it is necessary for the container to be non-deformable in view of the fact that after the heat treatment a considerable negative pressure will be produced in the packing through the contraction of the contents and the condensation of the water vapour which drove the air out of the container during the heat treatment. The packing must be able to withstand this negative pressure without being deformed, since a deformed packing has an unattractive appearance and therefore is difficult or impossible to sell. The containers are therefore often made of glass or metal. This means that the packing is relatively expensive and in addition fairly heavy.
In order to reduce the pressure differences in a packing which is subjected to a heat treatment, the packing may be provided with means for varying its inside volume. For this purpose a lid of the above-mentioned type could be used. However, this type of lid is still relatively rigid and the distance over which the middle portion of the lid may be moved is relatively small. Consequently, the possible variation of the inside volume of a container closed by such a lid is relatively small. This means that during heat treatment a certian portion of the expanding gases in the packing have to escape from the packing by passing between the rim portion of the lid and the container.
Thus, a container closed by a lid of the abovementioned type presents almost the same disadvantages as a container closed by a screw cap. Also in this case the container must be made of a rigid material such as glass or metal.
The invention now seeks to provide a lid of such a type that the container can be made of a modern packing material of slight wall thickness and a relatively low modulus of elasticity, which on the one hand has a relatively low resistance to deformation but on the other hand is light and easily worked, while its price is advantageous.
This aim is achieved with a lid of the type defined above which is characterized in that the middle portion is joined to the rim portion via a bellows-shaped intermediale portion extending substantially in axial direction.
Through the use of a lid of this type it is possible for the expansion of the gases contained in a container closed by this lid to be entirely taken by the packing during the heat treatment. Since no gases now have to escape from the packing, the container can be almost completely filled, which means that the empty space under the lid is relatively small. This in turn has the consequence that during the heat treatment the increase of the inside volume of the packing through the expansion of the gases contained in the latter is relatively slight.
Through the elimination of large pressure differences in the packing, it is now possible to make the container of a light material, for example a plastics material, thus enabling a considerable saving in the weight of the packing to be achieved.
The heating of the contents of a container closed by the lid causes the bellows to expand, whereby the inside volume of a packing is increased, while on subsequent cooling the bellows is redeformed in the opposite direction through the contraction of the contents of the packing.
The average diameter of the bellows-like intermediate portion advantageously decreases from the rim portion in the direction of the middle portion, so that on the one hand the lids can easily be stacked without their unstacking in the packing machine causing any disturbance, while on the other hand the stacking of filled packings is also easily possible.
The bellows-shaped intermediale portion may have helical ridges and grooved in order to make it more easily deformable in axial direction.
It is particularly advantageous for the middle portion to have substantially the shape of a cone having an obtuse apex angle or of a truncated cone. Thus the lid may have a certain signal action.
In order to obtain a good connection between the lid and the container, the rim portion may be at least partly provided, on the side which comes into contact with the container, with a layer which can adhere to the material of the container, this layer preferably consisting of a plactics composition meltable through the action of heat and/or pressure.
The invention likewise relates to a packing consisting of a container and lid according to the invention.
The lid is preferably joined to the container by welding or be means of an intermediate layer applied to the rim portion of the lid and adhering to the material of the container, such as a plastics composition meltable through the action of heat and/or pressure.
The packing may be provided with a closable opening, which is preferably provided in the lid, for the purpose of allowing the escape of any larger amounts of gas formed during the heat treatment of the packing. This opening is advantageously adapted to be closed by means of a drop of a meltable plastics composition. In the case of a packing with a closable opening the lid according to the invention will have a certain signal action. As the expanding gases and gases formed in the packing during the heat treatment will escape through the opening the pressure inside and outside the packing will remain the same during the heat treatment. Upon cooling of the packing and after closing of the opening a negative pressure will be produced in the packing through the contraction of the contents and the condensation of the water vapour which drove the air out of the packing during the heat treatment, so that the middle portion of the lid will be pulled inwards. If the packing is not correctly closed or in case of inadequate heat treatment the negative pressure will not be produced or will disappaear through the action of bacteria. This causes the middle portion of the lid to stay in its original position or to move outwards from the pulled-back position. Thus, practically all posible defects of the filled and closed packing will be signalized.
The invention will now be explained with the aid of one example of embodiment and with reference to the drawings.

Figure 1 is a section of a preferred embodiment of a lid according to the invention;
Figure 2 is a top plan view of the lid shown in Figure 1;
Figure 3 is a section of a container with the lid shown in Figure 1;
Figure 4 shows an enbodiment of a lid according to the invention and having an intermediale portion with helical ridges and grooves;
Figure 5 shows another possible embodiment of lid according to the invention;
Figure 6 shows an embodiment of a lid according to the invention, with a conical middle portion, and
Figure 7 shows an embodiment of a lid according to the invention, with a frustoconical middle portion.

The embodiment of the lid 1 according to the invention, which is shown in Figures 1 and 2, comprises a rim portion 2 and a middle portion 3. The rim portion 2 is intended for joining to a container.
The middle portion 3 is joined to the rim portion 2 via a bellows-like intermediate portion 4. The middle portion is thus movable in the axial direction relative to the rim portion 2. In this embodiment the average diameter of the bellows-like intermediate portion 4 decreases from the rim portion 2 in the direction of the middle portion 3. The lids can thus be easily stacked and during unstacking in a packing machine the risk of failure is slight.
Figure 3 shows a filled container 5 which is closed by the lid 1 described above. The rim portion 2 of the lid is completely joined to a top rim portion 6 of the container 5.
The lid 1 is fastened to the radially extending top rim 7 of the container 5 by welding or by means of an intermediate layer 8 adhering to the rim portion 2 of the lid and to the material of the container. This intermediate layer 8 may consist of a plastics composition which is meltable through the action of heat and/or pressure, and which can be applied to the bottom face of the radially extending part of the rim portion 2 of the lid during the production of the latter.
When a packing consisting of a filled container 5 closed by the lid 1 is subjected to heat treatment, such as sterilization, the gas contained in the packing will expand. Gas may in addition escape from the packet product. This increase of the volume of the contents of the packing is taken by the upward movement of the middle portion 3 of the lid 1, which is joined via the bellows-like intermediate portion 4 to the rim portion 2, whereby the internal volume of the packing is enlarged. The pressure in the packing is thus raised only slightly.
After the heat treatment the contents of the packing will cool and contract. The middle portion 3 will then move in the opposite direction adn the internal volume of the packing will become smaller again, so that after the heat treatment there will be only a slight or no negative pressure in the packing.
Through the elimination of large differences in pressure in the packing, the container 5 can be made of light material, such as plastics material.
Since the packing is well closed during the heat treatment and thus none of the packed product can escape between the container and the lid. the container 5 can be almost completely filled.
In order to permit the escape of any larger amounts of gas which might be formed in the packing during the heat treatment, the lid may be provided with a closable opening 9. Closure can be effected with the aid of a drop 10 of a plastics composition meltable through the action of heat, this material being liquid during the heat treatment, so that gas can escape, and being solid at temperatures below the heat treatment temperature.
Figure 4 shows a lid in which the bellows-like intermediate portion 4a has helical ridged and grooves. This makes the intermediate portion more easily deformable in axial direction. It also facilitates the removal of the lid from the mould for forming the lid, particularly when the lid is formed by thermoforming. By rotating the lid it may be removed from the mould. The lid of figure 4 is otherwise similar to the lid shown in Figure 1.
Figure 5 shows a lid in which the average diameter of the bellows-like intermediate portion 11 is constant over practically the entire height. This lid is otherwise similar to the lid shown in Figure 1.
The lid shown in Figure 6 is provided with a middle portion 12 in the form of a cone having an obtuse apex angle. This middle portion 12 itself is likewise movable in the axial direction and has two stable positions. The conical middle portion 12 is joined via a bellows-like intermediate portion 14 to the rim portion 2. The lid shown in Figure 4 has a middle portion 13 in the form of a truncated cone, which also has two stable positions. The middle portion 13 is joined via a bellows-like intermediate portion 14a to the rim portion 2.
The lids shown in Figures 6 and 7 may also be provided with a closable opening, which may be closed by a drop of a plastics composition meltable through the action of heat.
The conical or frustoconical middle portion 12 or 13 respectively thus has a signal action. During the heat treatment expanding gases and gases formed in the packing will escape through the opening 9, while the pressure inside and outside the packing will remain the same.
Upon cooling of the packing and after closing of the opening 9 by the drop 10 of a plastics composition a negative pressure will be produced in the packing through the contraction of the contents of the packing and the condensation of water vapour which drove the air out of the packing during the heat treatment. If the packing is correctly closed, the portion 12 or 13 will be drawn inwards, after the heat treatment, because of the negative pressure produced in the packing. If the packing is not correctly closed, no negative pressure will be produced after the heat treatment, and the middle portion 12 or 13 will stay in its original position. In the event of inadequate heat treatment of the contents of the packing, the negative pressure in the packing will disappear through the action of bacteria, so that middle postion 12 or 13 will move outwards. Thus, practically all possible defects of the filled and closed packing will be signalized.
It is noted that also the lids according to the invention with a flat middle portion and provided with a closable opening may have such a signal action. However, the signal action of the lids of Figures 6 and 7 is better visible.
In order to improve the fastening of the lid 1 on the container 5, the upstanding part of the rim portion 2 may be provided with one or more annular ribs 15 fitting into corresponding grooves 16 in the wall of the container 5 when the lid is fitted to the latter.
Through use of a lid having a bellows-like intermediate portion according to the invention it is thus made impossible for large differences in pressure to occur in a packing consisting of a container closed by the lid according to the invention during the heat treatment of the packing. This means that the packing need be resistant only to low positive or negative pressures, so that the container and also the lid can be made of a modern packing material, such as a plastics material. This material is light and easily worked, and its price is favourable.
The packing with the lid according to the invention has another advantage, particularly when the lid is provided with a closable opening. After the heat treatment the space between the product in the packing and the lid will be very small because of the negative pressure in the packing. Consequently, it will be possible to obtain a stack of filled packings with very little empty space and the transportation and storage costs will be less than with common packings.
The lid according to the invention can obviously however also be used in combination with containers of rigid material, such as glass.

Claims

1. A lid for a container, comprising a rim portion (2) for connecting the lid (1) to the container (5) and a middle portion (3; 12; 13;) lying inside said rim portion (2) and being movable in the axial direction relative to the rim portion (2), characterized in that the middle portion (3; 12; 13) is joined to the rim portion (2) via a bellows-shaped intermediate portion (4; 4a; 11; 14; 14a) extending substantially in the axial direction.

2. Lid according to Claim 1, characterized in that the average diameter of the bellows-shaped intermediate portion (4; 4a) decreases from the rim portion (2) in the direction of the middle portion (3).

3. Lid according to Claim 1 or 2, characterized in that the bellows-shaped intermediate portion (4a) has helical ridges and grooves.

4. Lid according to one of Claims 1 to 3, characterized in that the middle portion (12; 13) has substantially the shape of a cone having an obtuse apex angle or of a truncated cone.

5. Lid according to one of Claims 1 to 4, characterized in that the rim portion (2) is provided at least partially, on the side coming into contact with the container (5), with a layer (8) adapted to adhere to the material of the container (5), said layer (8) preferably consisting of a plastics copmposition meltable by the action of heat and/or pressure.

6. Lid according to one of Claims 1 to 5, characterized in that the lid (1) consists of plastics material.

7. Packing consisting of a container and a lid fitted to the container, according to one of Claim 1 to 6.

8. Packing according to Claim 10, characterized in that the lid (1) is fastened to the container (5) by welding or by means of an intermediate layer (8) adhering to the rim portion (2) of the lid (1) and to the material of the container (5), said intermediate layer (8) preferably consisting of a plastics composition meltable by the action of heat and/or pressure.

9. Packing according to Claim 7 or 8, characterized in that the packing is provided with a closable opening (9), preferably in the lid (1).

10. Packing according to Claim 9, characterized in that the opening (9) is closed by a drop (10) of a meltable plastics composition.