GB2032876A

GB2032876A - Double-walled Plastics Containers

Info

Publication number: GB2032876A
Application number: GB7836730A
Authority: GB
Original assignee: BRUEMMER ESBE PLASTIC
Current assignee: BRUEMMER ESBE PLASTIC
Priority date: 1978-09-13
Filing date: 1978-09-13
Publication date: 1980-05-14
Also published as: SE7907323L; IT1123123B; IT7925635A0; BR7905830A; NL7906802A; DE2936138A1; FR2436079A1; JPS5541295A; ES484114A1; AR221247A1

Abstract

A container of the kind comprising mating inner and outer wall parts of plastics material with a pre-printed paper insert (3) interposed therebetween, the outer plastics wall part being transparent, is characterised in that one, preferably the inner, plastics wall part (1) is formed with a mouth flange (7) having an undercut portion, and the other (outer) plastics wall part (2) is formed at its mouth with a projecting lip portion (9), the edge of which is adapted to snap into and through the undercut to provide a substantially airtight joint, and in that the bottom wall of at least one, preferably the outer, plastics wall part (11) acts as a membrane to cater for expansion of trapped air. Apparatus for manufacturing said one (inner) plastics wall part, characterized by a mould having an upstanding boss defining an undercut face, an annular clamping ring for clamping the heated plastics material over the boss, and an annular forming tool slidable within the clamping ring for movement towards the mould face to squeeze and mould the plastics material around the boss and to fill against the undercut face. Apparatus for separating stacks of the inner plastics wall parts for feeding them individually to a required station in assembly apparatus, comprises a suction plug mounted on a movable arm and adapted be lowered into the uppermost wall part of a stack, and a push rod carried by the plug for subsequently ejecting the separated wall part from the suction plug after the plug is raised and carried by the arm over said required station. <IMAGE>

Description

SPECIFICATION Double Walled Container and Method and Apparatus for Manufacturing Same This invention relates to rounded containers for packaging foodstuffs such as yoghurt, jam, cottage cheese, etc, and particularly to containers intended to be hot filled, eg., with yoghurt and jam, or to have an instant dry food product sealed therein, to which hot or boiling water is added for eating after the seal is removed, e.g. soup.

By rounded is meant any container shape which, in plan, is continuously curved (e.g. circular or oval), or partly curved (e.g. square or rectangular with rounded corners).

At present the market is dominated by rounded containers made of polystyrene which is subsequently printed with details of the contents etc., and containers made of pre-printed paper usually with a coating of suitable plastics material.

The techniques available for printing on paper are more varied, and they are also easier to carry out than on plastics. However, lamination of the paper with appropriate plastic sheeting has the disadvantage that many working processes have to be taken into account, such as for example, the separate fabrication of a base and side wall for the container, and a strengthening rim around the edge of the side wall. This increases the cost of manufacture and also the possibility of rejects occurring is increased. Plastic containers, either injection moulded or heat-formed, can reproduce exactly all of the necessary features required, such as stacking spacers or rims, and also the appropriate formation of the base and side wall in one operation.However, the techniques available for printing onto these plastic containers are relatively costly because the plastic surface compared with a paper surface is much more difficult to print on.

A recent development to meet these problems has been to provide a container having separate mating inner and outer container wall parts of plastics material with a pre-printed paper wall part interposed between them, the outer plastics wall part being transparent. Such a container and a method and apparatus for assembling same has been described in our co-pending British Patent Application No. 43024/77 Serial No.

Thus, a container of this type enables printing to be readily carried out on the paper insert and the two mating plastics wall parts to be made of relatively thin plastics material, since structural strength is provided for by the paper insert.

However, particularly in the case where the container is to have an instant dry product sealed therein to which (after removal of the sealed lid) boiling water is added for eating, there are many considerations to take into account. Thus, it is important to ensure that the dry product has a prolonged shelf-life, which in most cases would mean that the container should be resistant to moisture and vapour (to ensure the dry product remains dry) and should be aroma and oxygen tight (to seal in the taste and freshness of the dry product). It is also important that at least the inner plastics wall part will not deform or shrink when the boiling water is added to the dry product.

The object of the present invention is to provide a rounded container of the kind having mating inner and outer wall parts of plastics material and a pre-printed paper wall part interposed between them, the outer plastics wall part being transparent, which is particularly suitable for a hot filled, or instant, dry product. It will be appreciated here that after hot filling, or after adding a measured quantity of dry product, into the open container, the latter is sealed in known manner by adhering, e.g. by welding, an aluminium foil or similar lid across the mouth of the container.

According to a first aspect of this invention, a rounded container of the kind referred to above is characterised in that one of said plastics wall parts is formed at its mouth with a flange which provides an undercut portion, and the other plastics wall part is formed at its mouth with a projecting lip portion, the edge of which is adapted to snap into and through the undercut to provide a firm contact between said portions and produce a substantially airtight joint, and in that the bottom wall of at least one of the plastics wall parts is adapted to act as a membrane to cater for expansion of air trapped between said plastics wall parts.

Preferably, one of the said plastics wall parts is selected from the materials polypropylene, polyethylene or a polyolefin and is provided with the flange providing the undercut portion, and comprises the inner plastics wall part of the container. The flange may comprise a projecting portion around the edge of which the undercut is provided as an inwardly directed downwardly projecting portion, the other plastics wall part having an outwardly projecting lip portion.

In manufacturing a rounded container in accordance with the first aspect of this invention problems arise in providing the undercut on saidone plastics wall part, which undercut is an important feature in achieving air-tightness between the mating inner and outer plastics wall parts.

A further object of this invention is to provide apparatus which overcomes this problem.

According to a second aspect of this invention, apparatus for manufacturing said one plastics wall part of a rounded container in accordance with the first aspect of this invention, is characterised by a mould which defines a cavity for the wall part and the mouth of which is an upstanding boss, the outer periphery of the boss defining an undercut face, an annular clamping ring for clamping a peripheral portion of a disc of the plastics material over the upstanding boss, and an annular forming tool slidable within the clamping ring and having an inner peripheral face dimension so as to clear the undercut face of the upstanding boss with such a spacing that, movement of the forming tool towards the mould face tends to squeeze and mould plastics material around the upstanding boss and to fill into and against said undercut face.

In one form of rounded container in accordance with the first aspect of this invention, there is no stacking distance or spacers for the plastics wall parts. This means that a problem arises in separating these for feeding them individually to their appropriate station of the container assembly apparatus and a still further object of this invention is to provide apparatus which overcomes this problem.

According to a third aspect of this invention, apparatus for separating stacks of plastics wall parts for feeding them individually to their required station in container assembly apparatus, is characterised by a suction plug of smaller diameter than the internal diameter at the wall part, means for raising and lowering said plug, an arm on which the plug is mounted and arranged for movement between a position over the stack and over said required station of the assembly apparatus, a push rod slidably carried in a guide on the plug, and means for actuating the push rod, the arrangement being such that, for an operation cycle, the arm is located over the stack, the suction plug is lowered into the uppermost wall part, suction is applied to deform and reduce the diameter of the latter onto the plug so separating the wall part, the plug is raised and carried by the arm over said required station where it is lowered into said station, the push rod being actuated to project from the bottom of the suction plug and suction being shut-off to release the wall part from the plug, the push rod and plug then being raised for a new cycle.

In order that the invention may be readily understood, one preferred embodiment of rounded container in accordance with the first aspect, and relevant parts of apparatus in accordance with the second and third aspects, will now be described with reference to the accompanying drawings in which~ Figure 1 is a half-sectional view of the rounded container, as assembled, Figure 2 is an enlarged sectional view of the mouth rim of the container showing the wall parts assembled together, Figure 3 is a developed view of the paper wall part, Figures 3a to c are views of various modifications of the paper wall part bent into its circular shape, Figure 4 is a sectional view of part of a moulding machine for forming the inner plastics wall part in one operational mode, Figure 5 is an enlarged detail of Figure 4, in another operational mode, Figure 6 is a plan view of apparatus for separating stacks of inner plastics wall parts, and Figure 7 is an enlarged sectional view on line VIl-VIl of Figure 6.

Referring to Figures 1 to 3, the rounded container, which in this case is circular in plan, comprises an inner wall part 1, a mating outer wall part 2 and a pre-printed paper wall part 3 interposed therebetween.

The inner wall part 1 is formed from polypropylene for the following reasons: i) polypropylene is tight against moisture and vapour so that the instant dry food product to be sealed therein will remain dry for prolonged periods, ii) polypropylene will not shrink or deform appreciably when the boiling water is added to the dry product therein, or a product is hot-filled Alternative plastics material with similar characteristics which would provide suitable alternatives to polypropylene are polyethylene or a polyolefin.

The outer wall part 2 is formed from PVC for the following reasons:~ (i) it is relatively cheap and transparent so as to allow the printing on the paper wall part to be clearly visible, (ii) it is tough, resilient and unbreakable therefore ensuring a durable outer surface to the container, (iii) it is oxygen and aroma tight (which characteristics are not present with polypropylene) and therefore, provided that the joint between inner and outer wall parts 1 and 2 is airtight, will retain the taste and freshness of the contained product over prolonged periods. An alternative to PVC is an acrylic plastics material e.g. Barex (RTM) or a polystyrene.

Referring to Figure 3, it will be seen that the developed shape of the paper insert comprises curved edges 4 and 5; these curves are developed from a cone the base of which is cut-off in a plane normal to the cone axis. Thus, when the insert is bent so that its end edges 6 abut and to be circular in plan, see Figure 3a, the curved edges 4 and 5 provide upper and lower edges lying in flat planes. If preferred, to prevent a tendency for the abutting edges 6 to deform the container from its circular shape, the edges 6 can be formed with mating curves (sec Figure 3b) or slanted (see Figure 3c).

It will be appreciated that due to the paper wall part 3, particularly if this is of thick paper or cardboard, the container is given a significant structural strength; this enables the inner and outer plastics wall parts, which are relatively more costly material, to be made relatively thin (of the order of 2 to 3 mm). Additionally, the paper insert provides the following advantages:~ i) it is opaque and significantly prevents light from penetrating to the contents thereby adding to the keeping quality of the dry product (polypropylene is also fairly transparent), and ii) it acts as an insulation layer for the PVC when hot filled or boiling water is added to the dry product, iii) because no adherence of the surfaces of the wall parts is necessary, the plastics wall parts 1, 2 can be easily separated and recycled.

As mentioned above, it is important that the joint between the inner and outer wall parts is airtight.

Referring to Figure 2, this is achieved by forming the mouth of the polypropylene inner wall part 1 with a flange comprising a horizontally outwardly extending portion 7 and a downwardly extending portion 8 providing an inwardly directed undercut. The mouth of the PVC outer wall part 2 is formed with an outwardly projecting horizontal projecting lip portion 9 which snaps into and through the undercut portion 8 to provide firm contact between the flange and lip.

To increase the effectiveness of this airtight joint, either or both of the following features may be employed.

i) the container wall parts 1 and 2 are assembled soon after heat forming of the polypropylene inner wall part 1; polypropylene tends to shrink over a time period of a few Slays (approximately 2 to 3) after forming and hence use is made of this characteristic to shrink the undercut part 8 into firm contact with the outer edge of the lip 9.

ii) normally, stacks of PVC container wall parts will be presented to the assembly apparatus, which are then separated and fed individually to their appropriate assembly station, and these stacks can be rolled over a laquer or wa bed so that, when assembled, the outer edge of each. lip 9 is sealed to its respective undercut part 8.

Also, if necessary, the projecting lip portion may be strengthened by strengthening ribs 9a during forming of the outer plastics wall part 2 (see Figure 1).

A problem which arises from the joint between the inner and outer wall parts being airtight is that when boiling water is added to the dry product the heat will cause air in the airtight space to expand. This is allowed for by making the bottom wall 10 of the PVC outer wall part concave and with a series of annular (or radial) grooves 11 so that said bottom wall will act as a membrane and tend to straighten. This ensures that, upon expansion, the bottom wall will not become convex (which of course would affect the stability of the container when placed on a flat surface).

It will be appreciated that the paper insert does not provide a bottom wall part, and hence, the membrane nature of the bottom wall 10 reduces the possibility of the PVC outer wall part deforming over said bottom wall; also to further reduce this possibility a significant air gap is left between the bottom walls of the parts 1 and 2.

It will be seen from Figure 1 that a chamfered side wall portion 12 is provided for the container.

This provides a distinctive appearance and also provides a more rounded bottom to the inner part 1 to facilitate eating of the contents with a spoon or the like. It is therefore necessary to provide means whereby the paper insert 3 can take up this chamfer during assembly. This is achieved by providing the insert with a series of regularly space slits 13 as shown in Figure 3, which slits include axial and transverse cuts to provide a series of individual tongues 14. Thus, when the insert 3 is bent to circular form and pushed into the outer wall part 2 during assembly, the chamfer portion 12 of said part causes adjacent edges of the individual tongues 14 to slightly overlap and take up the chamfer, this overlapping ensuring that the opaqueness provided by the paper insert is maintained.

Referring now to Figures 4 and 5, apparatus for forming the inner polypropylene wall part 1 includes a mould 1 5 providing a mould cavity 16, an outer annular clamping ring 17 in which is slidable, an annular forming tool 18 which is stepped to provide an annular rim portion 19 and a stop face 20. The rim portion 19 is dimensioned to clear by approximately 3 mm the outer diameter of an upstanding boss 22 extending around the mouth of the cavity, the outer peripheral face 23 of which is shaped for forming the undercut.

To form the part 1, a circular disc 21 of polypropylene approximately 8 mm thick, which has been heated to its forming temperature around 1 550C, is located over the mouth of the mould cavity 16 and its periphery is clamped down onto the mould face by the clamping ring 17, as shown in Figure 4. The forming tool 18 is then operated to cause the rim portion to move towards the mould face, during which movement it causes the polypropylene to be squeezed and moulded around the undercut face 23 of the upstanding boss 22 of the mould and to fill into and against said undercut face 23 (see Figure 5).

This operation also provides a controlled amount of stretch to the centre portion of the polypropylene disc 21 to overcome the tendency to sag into the mould cavity, and thereafter a plug 24 (Figure 4) is lowered in known manner to push the centre portion down into the cavity 16, after which forming pressure is applied. The resilient nature of the polypropylene enables the wall part, after forming and cooling, to be released from the mould without damage to its undercut portion 8.

Referring to Figures 6 and 7 of the drawings, the inner polypropylene walls parts 1 are supplied to the assembly machine, which has a number of assembly stations through which a circular table 25 rotates, as two spaced stacks 26. The container described with reference to Figures 1 to 3 has no stacking distance and, as mentioned above, because of this and because of static electricity normally present in the formings, the stacks are difficult to separate into individual components. To facilitate separation the apparatus of Figures 6 and 7 include two plugs 27 shaped to correspond to but of smaller diameter than the inner surface of the wall parts 1 and mounted at spaced positions corresponding to the spacing of the stacks 26 on a support bracket 28, which can be raised and lowered beneath a pivoted arm 29 by a pneumatic piston cylinder unit 30 mounted on the arm 29.The plugs are porous or have holes and are adapted to be connected as required to a source of vacuum.

Referring to Figure 7, each plug has an axial bore 31 in which a push rod 32 is mounted which can be raised and lowered by a pneumatic piston/cylinder unit 33.

In use of the apparatus, the arm is swung against a guide stop 34 to locate the plugs 27 over the respective stacks 26 whereupon they are lowered via unit 30 into the uppermost wall parts 1 of the stacks. Suction is applied to deform the wall parts onto their plugs, thereby releasing said uppermost wall parts from the stacks. The plugs 27 are then raised via the unit 30 and are swung by the arm 29 to locate over their assembly stations 35 (to each of which is rotated a subassembly comprising the outer wall parts 2 and paper inserts 3. The plugs are then lowered into their respective sub-assemblies, suction is released and the unit is actuated to raise the plugs 27 for another cycle.At the same time units 33 are actuated to push the parts 1 from their respective plugs 27 via the push rods 32, the latter being immediately after retracted into the plugs by their units 33 for the new cycle.

To ensure that the complete stacks 26 are not carried upwardly when the plugs 27 are raised after deforming the uppermost wall parts 1, stop fingers 37 are provided. As shown in Figures 6 and 7 these rest on two opposed wing portions 36 formed integrally with each mouth flange 7 of said wall parts. Due to the resilient nature of the wing portions 36, those of the two uppermost wall parts 1 lifted by the suction plugs 27 deform and ride under said fingers 37 which then act on the next upper parts 1 to hold the stacks down.

It will be appreciated that after hot filling with yoghurt or similar, or after filling with a dry instant food product, each container is sealed with a sealing foil (preferably aluminium) lid, which is appropriately adhered or welded arraround the flange part 7 of the container in a known manner.

Claims

1. A rounded container for sealing-in a hot filled or a dry food product to which hot or boiling water is added for eating and of the kind comprising mating inner and outer wall parts of plastics material with a pre-printed paper will part interposed therebetween, the outer plastics wall part being transparent, characterised in that one of said plastics wall parts is formed at its mouth with a flange which provides an undercut portion, and the other plastics wall part is formed at its mouth with a projecting lip portion, the edge of which is adapted to snap into and through the undercut to provide a firm contact between said portions and produce a substantially airtight joint, and in that the bottom wall of at least one of the plastics wall parts is adapted to act as a membrane to cater for expansion of air trapped between said plastics wall parts.

2. A container as claimed in Claim 1, characterised in that one of said plastics wall parts is selected from the materials polypropylene, polyethylene, or a polyolefin and has the flange providing the undercut portion.

3. A container as claimed in Claim 2, characterised in that said one plastics wall part provides the inner wall of the container and the flange provides an outwardly projecting portion around which the undercut is provided as an inwardly directed downwardly extending portion, and in that the outer plastics wall part has an outwardly projecting portion.

4. A container as claimed in Claim 3, characterised in that the wall parts are assembled within a time period during which the said one plastics wall part shrinks and hardens after forming, whereby when hardened its undercut portion is urged in firm sealing contact with the projecting lip portion of the other plastics wall part.

5. A container as claimed in Claim 3, or 4, characterised in that the edge of the projecting lip portion is coated with a suitable sealent or adhesive prior to its assembly to enhance the effectiveness of the airtight joint.

6. A container as claimed in any preceding Claim, characterised in that the paper wall part has no bottom wall and is developed with two opposed curved edges from the base of a cone cut-off in a plane normal to the cone axis.

7. A container as claimed in Claim 6, having a chamfered side wall, characterised in that the paper wall part is provided along its intended lower edge with a series of spaced slits which include axial and transverse cuts to form individual tongues, adjacent edges of which are caused to overlap during assembly into the outer wall part to take up the chamfer.

8. A container as claimed in any preceding Claim, characterised in that the bottom wall of the outer plastics wall part is formed to act as a membrane and to provide a concave outer surface.

9. A container as claimed in any preceding Claim, characterised in that the outer plastics wall is P.V.C. or an acrylic plastics, or a polystyrene.

10. Apparatus for manufacturing the said one plastics wall part of a container according to Claim 3, characterised by a mould defining a cavity for the wall part and the mouth of which is an upstanding boss, the outer periphery of the boss defining an undercut face, an annular clamping ring for clamping a peripheral portion of a disc of the plastics material over the upstanding boss, and an annular forming tool slidable within the clamping ring and having an inner peripheral face dimension so as to clear the undercut face of the upstanding boss with such a spacing that, movement of the forming tool towards the mould face tends to squeeze and mould plastics material around the upstanding boss and to fill into and against said undercut face.

11. Apparatus for separating stacks of plastics wall parts for containers according to any one of Claims 1 to 9, for feeding the wall parts individually to a required station in assembly apparatus, characterised by a suction plug of smaller diameter than the internal diameter at the wall part, means for raising and lowering said plug, an arm on which the plug is mounted and arranged for movement between a position over the stack and over said required station of the assembly apparatus, a push rod slidably carried in a guide on the plug, and means for actuating the push rod, the arrangement being such that, for an operation cycle, the arm is located over the stack, the suction plug is lowered into the uppermost wall part, suction is applied to deform and reduce the diameter of the latter onto the plug so separating the wall part, the plug is raised and carried by the arm over said required station where it is lowered into said station, the push rod being actuated to project from the bottom of the suction plug and suction being shut-off to release the wall part from the plug, the push rod and plug then being raised for a new cycle.

12. A rounded container constructed and arranged substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

13. Apparatus for manufacturing said one plastics wall part of a container according to Claim 12 constructed and arranged substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

14. Apparatus for separating stacks of plastics wall parts for containers according to Claim 12, constructed and arranged substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.