IE50980B1

IE50980B1 - Foodstuff container sealed with an adhesive which is resistant to both freezer and oven temperatures

Info

Publication number: IE50980B1
Application number: IE963/81A
Authority: IE
Original assignee: Metal Box Co Ltd
Priority date: 1980-05-01
Filing date: 1981-04-30
Publication date: 1986-08-20
Also published as: IS1192B6; FR2481677B1; IN154114B; NZ196962A; CH652676A5; FR2481677A1; KE3358A; IS2633A7; DK193081A; AU542844B2; ZA812810B; IE810963L; SE8102716L; AU6986281A; NL8102143A; DE3117269A1; FI811293L; FI811293A7

Abstract

Freezerproof and ovenproof packaging containers of heat-resistant cardboard, preferably with an inner coating of polyethylene terephthalate, are provided with at least one closure part, which is closed by an adhesive agent which contains an aqueous emulsion of a vinyl/acryl polymer, for example a copolymer of ethylhexyl acrylate and vinyl acetate, and which adheres and does not become brittle at temperatures below freezing point, for example down to -40 DEG C, and which remains adhesive at high temperatures (for example up to 200 DEG C or above) and allows pulling off of the closure part. The packaging containers can be filled and closed by a process in which the adhesive agent is applied to the filled packaging containers and is dried by a hot gas, whereupon the closure part is closed to form a tight seal.

Description

This invention relates to containers for packaging foodstuffs and, more specifically, to containers of the so-called freezable-ovenable type which are intended for foodstuffs which are to be kept in a domestic freezer until required for consumption and which are then to be heated or cooked in a domestic oven. The containers must therefore be able to withstand temperatures from around -40°C, as in a domestic freezer, up to around 200°C as in a domestic oven.

Containers of this type are known, made of a paper board material which is resistant to elevated temperatures, and which is normally provided with a heat-resistant internal coating of a polyester material, typically polyethylene terephthalate. The board material may also have an external coating of clay to provide a good surface for printing. A problem arises when the containers are to be filled and sealed before sale of the goods to the public. It is important that the container should be easily openable when removed from the oven. If the sealing were effected by heat-sealing the polyester coating on a closure flap to the adjacent part of the container, which is in any case difficult to achieve reliably with the materials in - 2 50980 question, the flap could only be opened by a tearing operation in which the board material is torn apart, which is not easily performed especially on a hot container. If one attempts to use an adhesive, instead of heat-sealing, no adhesive has hitherto been known to provide an effective peelable seal at oven temperatures and yet to remain effective and non-brittle at freezer temperatures.

According to the present invention, there is provided a container for packaging foodstuffs, formed of a paper board material which is resistant to elevated temperatures and comprising at least one closure member which is sealed to a part of the container to close the container by means of an adhesive comprising an aqueous emulsion of a vinyl-acrylic copolymer, the said copolymer remaining adherent and non-brittle at sub-zero temperatures while remaining tacky and permitting the closure member to be peeled open at elevated temperatures.

Preferably the copolymer remains adherent and non-brittle at temperatures down to -40°C and remains tacky at temperatures up to 200°C. The preferred adhesive is a copolymer of ethyl hexyl acrylate and vinyl acetate. Preferably the paper board material is coated internally with polyethylene terephthalate.

The combination of the copolymer adhesive with the heat-resistant paper board has been found to enable a seal of the desired properties to be obtained as indicated above.

The container may be in the form of a carton having a hinged lid with at least one flap forming the closure member which is sealed to a side wall of the container to close the container. Alternatively the container may be in the form of an open-topped tray having a separate lid which is sealed to a peripheral rim of the tray to close the container. In another - 3 0980 alternative, the container may be in the form of a carton having two closure flaps at opposite ends or at opposite sides of the carton.

The invention also provides a method of packaging a foodstuff comprising the steps of placing the foodstuff in a container formed of a paper board material which is resistant to elevated temperatures and comprising at least one closure member, and moving the container successively past stations where (1) an adhesive comprising an aqueous emulsion of a vinyl/acrylic copolymer is applied to the closure member and/or to a part of the container to which it is to be sealed, (2) hot gas is directed at the adhesive to remove at least a substantial part of the aqueous content of the emulsion and (3) the closure member is closed against the said part of the container to form a seal which remains adherent and non-brittle at sub-zero temperatures while remaining tacky and permitting the closure member to be peeled open at elevated temperatures. In this connection, a further advantage of the adhesive is that it can rapidly be brought by application of the hot gas, preferably hot air, to a tacky state in which the seal can be made. The method can therefore be carried out rapidly on the production line, thus facilitating a high rate of production of the filled containers.

Preferably the adhesive comprises an aqueous emulsion of a copolymer of ethyl hexyl acrylate and vinyl acetate having a solids content of 50% to 60% and a pH value of from 4 to 6. Preferably the solids content is substantially 55% and the pH value substantially 5.

The adhesive may be applied by means of an applicator wheel to the closure member and/or to the part of the container to which it is to be sealed.

Specific embodiments of the invention will now be described in more detail by way of example with reference to the accompanying drawings, in which:- 4 5 09 80 Figure 1 is a perspective view of a carton, Figure 2 is a similar view of an open-topped tray with a lid, and Figure 3 is a diagrammatic perspective view of a part of a production line showing the sealing of cartons as shown in Figure 1.

As shown in Figure 1, a freezable-ovenable carton 10 of paper board coated on its internal surface with polyethylene terephthalate has a hinged lid 11 with three flaps 12, 13, 14 forming closure members. When the carton 10 has been filled with foodstuff, the lid 11 is folded down and the flaps 12, 13, 14 are sealed to the side walls 15, 16, 17 of the carton, as shown in Figure 3, by means of a strip of adhesive 18 applied to each side wall. The adhesive could, of course, be applied instead, or additionally, to the inside of the flaps 12, 13, 14.

Figure 2 shows an alternative type of freezable-ovenable container 20 in the form of an open-topped tray 21 of polyethylene terephthalate coated paper board having a peripheral rim 22 presenting a horizontal surface to which adhesive is applied. When the tray 21 has been filled, a separate flat lid 23 of the same coated board material is sealed by its peripheral region 24 to the rim 22.

The adhesive in each case is applied in the form of an aqueous emulsion of a copolymer of ethyl hexyl acrylate and vinyl acetate having a solids content of substantially 55% and a pH value of substantially 5.

Figure 3 illustrates one method by which the adhesive can be applied to the cartons 10 of Figure 1 and the seal can be completed. The cartons 10 are transported continuously along a production line past stations at which the cartons are filled, the adhesive is applied and then part-dried and the cartons are sealed. For the sake of clarity the means by which the cartons are conveyed past the stations on the production line have been largely omitted - 5 0980 from Figure 3, apart from a diagrairniatic indication of pushers 30. A filled carton 10 is shown at the top left hand corner of Figure 3 with its end flaps 13, 14 already closed and sealed. Figure 3 shows how flap 12 is now closed and sealed.

First the carton 10 is transported past an adhesive applicator 31 which applies the strip of adhesive 18 to the flap 12. The applicator is a wheel 40 rotating in contact with the underside of the flap 12, which is supported above by an abutment plate 41. The wheel 40 dips into a tank 42 containing the adhesive and is driven by a chain drive 43. After passing the applicator 31, the carton 10 is transported past a hot air delivery device 32 having a longitudinally extending nozzle 33 and receiving hot air from a heated tank 34. The hot air is directed against the adhesive strip 18 and rapidly removes at least the greater part of the water content, thus bringing the adhesive to a tacky state in which the desired seal can be made.

A bar 35 is provided to bend the flap 12 down to an inclined position close to the side wall 15.

The carton is then carried forward so that the flap 12 comes into contact with rollers 36 (only one of which is visible in Figure 3) which bend it down vertically into contact with the adhesive strip 18 and thereby seal it to the side wall 15, as seen at the right hand end of Figure 3. An inclined diabolo roller 37 steadies the carton during this stage of the operation.

The adhesive is rapidly dried to a tacky state by the hot air device 32 so that production can be at a high rate. The seal between the flaps 12, 13, 14 and side walls 15, 16, 17 remains effective at freezer temperatures and at oven temperatures of 200°C and higher. When removed from the oven, the container can readily be opened by peeling open the flaps and can then be resealed because the adhesive remains tacky.

Claims

1. A container for packaging foodstuffs, formed of a paper board material which is resistant to elevated temperatures and comprising at least one closure member which is sealed to a part of the container to close the container by 5 means of an adhesive comprising an aqueous emulsion of a vinyl/acrylic copolymer, the said copolymer remaining adherent and non-brittle at sub-zero temperatures while remaining tacky and permitting the closure member to be peeled open at elevated temperatures.

2. A container according to Claim 1, wherein the copolymer remains adherent ,0 and non-brittle at temperatures down to -40°C and remains tacky at temperatures up to 200°C.

3. A container according to Claim 2, wherein the adhesive is a copolymer of ethyl hexyl acrylate and vinyl acetate.

4. A container according to any one of the preceding claims wherein the 15 paper board material is coated internally with polyethylene terephthalate.

5. A container according to any one of the preceding claims in the form of a carton having a hinged lid with at least one flap forming the closure member which is sealed to a side wall of the container to close the container.

6. A container according to any one of Claims 1 to 4 in the form of an 20 open-topped tray having a separate lid which is sealed to a peripheral rim of the tray to close the container.

7. A container according to any one of Claims 1 to 4 in the form of a carton having two closure flaps at opposite ends or at opposite sides of the carton. - 7 50980

8. A method of packaging a foodstuff comprising the steps of placing the foodstuff in a container formed of a paper board material which is resistant to elevated temperatures and comprising at least one closure member, and moving the container successively past stations where (1) an adhesive comprising an 5 aqueous emulsion of a vinyl/acrylic copolymer is applied to the closure member and/or to a part of the container to which it is to be sealed, (2) hot gas is directed at the adhesive to remove at least a substantial part of the aqueous content of the emulsion and (3) the closure member is closed against the said part of the container to form a seal which remains adherent and non-brittle at 10 sub-zero temperatures while remaining tacky and permitting the closure member to be peeled open at elevated temperatures.

9. A method according to Claim 8 wherein the adhesive comprises an aqueous emulsion of a copolymer of ethyl hexyl acrylate and vinyl acetate having a solids content of 50% to 60% and a pH value of from 4 to 6. 15

10. A method according to Claim 9 wherein the solids content is substantially 55% and the pH value substantially 5.

11. A method according to any one of Claims 8 to 10 wherein the adhesive is applied by means of an applicator wheel to the closure member and/or to the part of the container to which it is to be sealed. 20

12. A container for packaging foodstuffs, substantially as hereinbefore described with reference to the accompanying drawings.

13. A method of packaging a foodstuff substantially as hereinbefore described with reference to the accompanying drawings. Dated this 30th day of April, 1981. BY:- TOMKINS & CO.,