EP0074161A2

EP0074161A2 - An easy open closure

Info

Publication number: EP0074161A2
Application number: EP82303165A
Authority: EP
Inventors: Milton A. Howe; Stephen F. Compton
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1981-08-21
Filing date: 1982-06-17
Publication date: 1983-03-16
Also published as: DK375082A; FI822893A0; FI822893L; EP0074161A3

Abstract

A pouch or bag (R) constructed from multi-layer thermoplastic film (F) for packaging cheese, luncheon meat and the like has a lip (Fl) around the mouth of the bag folded inwardly, the mouth flattened, and a transverse seal (S) applied across the bag between the fold line (12) and the folded under edge (E1) to close the bag (R) in a seal in which a portion of the outer surface (3) of the bag is sealed to itself thereby providing an easy open seal. Along one-half of the mouth a dead fold element (7) is enclosed within the fold and this element, when bent, aids in closing the package.

Description

This invention concerns packages, for example for food items such as cheese or luncheon meat, and relates to an easy open seal for such packages and to a method of making such a seal. The invention further relates to means to close such packages once they have been opened.
Cheese, luncheon meat, and similar products and commodities are packaged today in a thermoplastic film which is overwrapped about the article to be packaged and the film is heat sealed to itself to form closure seams. After the package has been heat sealed, it is a problem to open it without destroying the package and leaving it unsuitable for further use. The problem is compounded because the films for packaging such products as cheese and luncheon meat should be strong and abuse-resistant and should have desirable gas transmission properties yet at the same time be capable of being opened without destroying the package.
Numerous seal configurations which have been proposed in the past employ easy open features. For example, U.S. Patent 2,968,396 shows an opening-and- separating feature for a thermoplastic film package wherein a gusset type fold provides grippable pull-apart tabs. U.S. Patent No. 3,536,501 shows a package in which the edge of the closure flap is folded over so that the outer film layer is sealed to itself. French Patent No. 1,331,100 shows a package with a closure seal in which the edges of the mouth of the receptacle are folded outwardly and then has a heat seal placed through the four layers of film. U.S. Patent No. 3,655,503 shows a package closure seal in which multilayer films are sealed together so that, when pulled apart to open the package, the outer layer of one film ruptures and delaminates only in the seal area.
Another problem encountered in packages for cheese and luncheon meat is that often only a portion of the product is consumed at one time and it is desirable that the package be effectively reclosed to protect the remaining portion. Numerous reclosure elements have been proposed in the prior art including those disclosed in U.S. Patents Nos. 4,174,597: 4,138,932; 4,126,085; 4,ll7,934, all of which employ "twist tie" elements with dead fold characteristics, i.e., once bent or folded the element remains in its bent shape and does not spring back or tend to return to its original shape-It is an object of the present invention to provide a package and seal configuration improved over the aforementioned and other presently available designs, and to provide a closure and seal configuration which is easily opened by a relatively small opening force without destruction of the package. A subsidiary aim of the invention is to provide for reclosing of the package after opening of the seal.
Accordingly, one aspect of the present invention provides an easy open seal for an opening in a receptacle of thermoplastic film, said film having at least two layers,characterised in that the tensile or rupture strength of the outer surface layer is greater than the bond strength between the outer layer and its adjacent layer;in that there is at least one fold in said film, said fold being adjacent a film edge, said fold providing direct contact between two surface areas of said outer layer; in that a seal bonds said two surface areas, said seal being located between said fold and said film edge; and in that said fold provides a tab which may be pulled to rupture one of said outer layers at said seal and to cause said outer layer to delaminate from its adjacent layer to the edge of the film thereby opening said receptacle.
Preferably, there are two of said folds providing respective said tabs each having an outer layer bonded at said seal such that pulling said tabs apart will cause the outer layer of one of them to rupture and to delaminate from its adjacent layer. This provides for easy closing where the package is a bag.
Conveniently, the material of the outer surface layer is polyethylene or an ethylene-vinyl acetate copolymer and the material of the adjacent layer is nylon, a vinylidene chloride copolymer, a propylene homopolymer or copolymer, or a cross-linked copolymer of polyethylene and ethylene-vinyl acetate. These materials are very acceptable in practice for a multi-function laminate capable of being used with this invention.
More conveniently, said film comprises three layers of which the outer layer is an ethylene vinyl acetate copolymer, the middle layer is a copolymer of vinylidene chloride, and the outer layer is a cross-linked copolymer of ethylene and vinyl acetate. This provides optimum storage conditions for sandwiches and luncheon meats, with an easy open seal.
A second aspect of the invention provides a package comprising a product within a receptacle of flexible film having at least two layers, in which one side of the receptacle is closed by a seal of the double-tabbed type, just disclosed above, said seal being formed by opposed ends of said receptacle inwardly folded over at coinciding fold lines so that all of said surface-to-surface seals are being in-line within the same seal area located between the fold lines and product whereby the folded over edges provide said tabs. Such a package hermetically encloses the product and also allows easy gripping of the tabs for opening the seal.
Advantageously a strip-like dead fold element is enclosed by at least one of said folds whereby after said bag is opened it may be closed by bending said dead fold element. This dead fold element allows the package to be reclosed, after opening, by flattening the mouth of the package, rolling the dead fold element once or twice towards the product remaining in the package, and then folding the ends of the dead fold element in towards its centre. More advantageously, for optimum folding, the strip-like dead fold element extends along only one half of the mouth of the receptacle. Removal of film portions at the fold lines from near the ends of the fold line, reduces stresses on the side seals of a receptacle with the seal, upon opening.
A third aspect of the invention provides a method of making an easy open closure seal for an opening in a flexible receptacle of thermoplastic film, said film having at least two layers,characterised in that the tensile strength of the outer surface layer is greater than the bond strength between the outer layer and its adjacent layer;in that the film is folded along a fold line adjacent an edge which forms said opening so that surface areas of said outer layers are in direct contact; and in that said surface areas are then heat sealed together along a seal located between said film edge and fold line to form a pull tab by said film folded at the fold line whereby when said tab is pulled the outer layer will rupture and delaminate from the adjacent layer, said delamination continuing to said edge of said film to open said package.
Preferably the method is further characterised by the steps of: providing a receptacle in the form of a side seal bag constructed of flexible thermoplastic film having at least two layers; removing corner portions of said bag adjacent to the end opening of the bag so that two extended lip portions are formed; placing a strip-like dead fold element on an inner surface of at least one of said extended lip portions; folding said extended lip portions into said end opening so as to surround and encompass said dead fold element within the fold of the lip portion on which the element was placed, said folds bringing portions.of the outer surface of the bag into direct contact; and then flattening and heat sealing said folded lip portions to enclose said dead fold element within its respective fold and to close said bag, said heat seal being transverse across the width of the bag and being located between the fold line and the edge of each of the inwardly folded lips, said folds providing grippable tabs for pulling said folds apart to open said bag; and further characterised by filling said bag with a product prior to said application of the heat seal whereby an easy open package with a reclosable dead fold closure element is provided. This provides for insertion of the reclosable feature element during initial closing of the seal. More preferably the seal is formed between the dead fold element and the edge of the folded lip of the film, to allow easiest manipulation of the package during reclosing.
Alternatively the method is further characterised by the step of punching a hole through the tab between the fold line and the seal to allow a strip-like dead fold element to be introduced into the interior of the fold of the tab, for reclosing of the package after opening of the easy open seal. This hole allows the consumer to insert a suitable dead fold element through the hole before reclosing.
In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings in which:-

Figure 1 is an exaggerated schematic representation of the seal area, showing rupture of one outer layer and delamination thereof from an adjacent layer;
Figure 2 is a cross-section in exaggerated detail, of one embodiment of the package of the present invention;
Figure 3 is a top view of the embodiment shown in Figure 2;
Figure 4 is a top view of a flattened bag, prior to being provided with a dead-fold element and final seal; and,
Figure 5 is a top view of a flattened bag ready to receive a product before final sealing.

Referring first to Figure 2 there will be seen a product 6, which may be cheese or luncheon meat, enclosed by multilayer film F. The receptacle R made from the multilayer film F can be formed in several different manners and may be called a bag, pouch or package, but will be referred to herein by the generic term "receptacle".
In the preferred embodiment a seamless tube of the three-layer film F is closed at one end by an end seal 13 which forms the bottom of the receptacle R. The receptacle is then loaded with the product 6 and, to close the loaded receptacle, an inward fold is made at its open end or mouth along line 12 wherein edges El and E2 are folded under so that they mate or coincide when the mouth of the receptacle is flattened. In the flattened condition a heat seal is applied by compressing the four layers of material in the seal region A. All of the surfaces in contact in seal region A will be sealed to each other. This configuration leaves separable tabs 4 and 5 which may be gripped by the fingers to pull the seal apart. This causesthe rupture and delamination shown in Figure 1.
In Figure 1 region A represents the seal between film portions Fl and F2 of the film F, which seal actually closes the opening to the receptacle R. The actual seal is designated S in Figures 1 and 2. When the tabs 4 and 5 are grasped between the fingers and pulled apart a delamination occurs at the beginning of the seal S in the area A as shown in Figure 1, and the delamination between layer 3 and its adjacent layer 2 continues to the edge E of the film F so that the opening 20 now provides access to the interior of the receptacle through the ruptured outer layer 3 of film portion Fl of tab 4 and through the delamination between layer 3 and its adjacent layer 2 which continues to the edge E of the film portion Fl. From this opening the product 6 may be removed and reinserted into the receptacle.
Referring to Figure 1, it will be seen that the film F from which the receptacle is formed is a three-layer film having an inner layer 1, a middle or adjacent layer 2 and an outer layer 3. (In Figure 2 it can be seen that the outer layer 3 is on the outside of the receptacle). A preferred three-layer film is that disclosed in U.S. Patent No. 4,278,738. Relating this preferred film to the layers to Figure 1, the inner layer 1 is an ethylene-vinyl acetate copolymer which has been cross linked by irradiation and has a thickness of approximately 38 microns; middle layer 2 is a copolymer of vinylidene chloride having a thickness of approximately 5 microns; and oute_" layer 3 is a crosslinked ethylene vinyl acetate copolymer having a thickness of approximately 18 microns. The vinyl acetate content in the ethylene-vinyl acetate copolymer is approximately 10% and the vinylidene chloride copolymer is a copolymer of vinylidene chloride and vinyl chloride in a mixture of 10% suspension-polymerized and 90% emulsion-polymerized copolymers. The emulsion-polymerized copolymer consists of about 70% vinylidene chloride and 30% vinyl chloride and the suspension-polymerized copolymer consists of about 80% vinylidene chloride and 20% vinyl chloride.
Using the film described above, which is available in a seamless tube so that an end seal 13 can be applied to close the bottom of the bag, the top of the bag when folded in a configuration shown in Figure 2 has the appearance shown in Figure 3 when laid flat. In this position, a heat seal can be applied across the width of the bag in region A. The width of the seal is 3mm to 6mm in'width and can be applied by a sealing unit such as those made by the Vertrod Corporation of Brooklyn, New York or by any other heat seal. unit as these are well known in the art. A pressure of approximately twelve kg/cm is preferred and the sealing unit is set such that the temperature at the interfaces where sealing occurs is in the range of 107°C to 149°C. In a laboratory arrangement the total sealing time consists of approximately 0.6 seconds for preheating the seal bars, 0.3 seconds for the heated welding time as the pressure is applied to the region A, and approximately 0.1 seconds for release time. In a production operation the seal bars do not have time to cool and the preheat time will drop to approximately 0.1 second for a total sealing time of approximately 0.5 seconds.
A seal according to the foregoing will keep the package intact and will resist abuse yet the seal can be readily opened by grasping the tabs 4 and 5 of Figure 2 and pulling them apart whereupon one of the layers 3 as in Figure 1 ruptures and delaminates to film edge El or E2. Delamination is observed to occur rather than rerupture of the outer layer 3.
A reclosure feature is provided which can be a "twist-tie" strip or any piece of wire or other material which has dead-fold characteristics, i.e. it is substantially non-resiliently deformable. Strip 7 is located within one of the end folds as shown in cross section in Figure 2 or in the top view in Figure 3. Insertion of the dead-fold strip 7, for example by the consumer,can be facilitated by simply punching a hole as indicated by the dotted lines 21 in Figure 2 and inserting the dead-fold strip 7 into the hole. After the receptacle has been opened, it can be readily closed by rolling up the said receptacle material in the mouth area by rolling the dead fold strip 7 towards the product 6, as one rolls up the used end of a tube of toothpaste, and then crimping or bending the dead-fold strip to hold the roll of film material secure.
Another method of providing a reclosure feature is shown in Figures 4 and 5. In Figure 4 a receptacle R in the form of a side sealed bag is shown which has been formed by folding a sheet of film in its centre and sealing it along its sides by heat seals 26. At the open end of the bag the corners are removed by cutting along the dotted lines 27. When the corners are removed two opposed lips Fl and F2 (Figure 1) are formed which may readily be.folded inside the bag. When the upper lip Fl is folded in, the dead fold strip 7 is laid upon and may be secured to the upper surface of the lower lip for example by the strip 7 having an adhesive surface. After this, the lower lip is folded inwardly so the receptacle has the configuration shown in Figure 5 with the edges El, E2 of the lips Fl, F2 coinciding inside the receptacle, the lips having been folded along fold lines 12. The receptacle is now ready to receive a product and, when filled, has a transverse heat seal applied in the region A which closes and seals the receptacle with portions of the outer surface of the receptacle sealed to itself in the region A.
Film segments may be removed at 24 by punching or cutting. The removal of these segments tends to relieve the stress on the side seals when the fold tabs 4,5 are pulled apart and they direct the stress to seal region A to open the package.
Other materials which can be suitably used in the present invention are polyethylene and ethylene-vinyl acetate copolymers in general for the outer layer and the material of the adjacent layer can be selected from nylon, vinylidene chloride copolymers, propylene homopolymers and copolymers; and cross-linked polyethylene and ethylene-vinyl acetate copolymers. The chief criterion is that the tensile strength or rupture strength of the outer layer 3 is greater than the bond strength between layers 2 and 3. Likewise, the bond strength between layers 2 and 3 has to be less than the rupture or tensile strength of the adjacent layer 2 alone or of the combination of layers 1 and 2.
Other folding configurations are possible within the scope of the present invention as long as the fold results in the outer layer 3 being sealed to itself in a face-to-face relationship so that when the rupture occurs there is delamination to a nearby edge of the film resulting in an access opening to the interior of the package. For example, only one tab 4 may be provided but may, for example, be folded twice.

Claims

1. An easy open seal for an opening in a receptacle (R) of thermoplastic film (F), said film having at least two layers (2,3),characterised in that the tensile or rupture strength of the outer surface layer (3) is greater than the bond strength between the outer layer (3) and its adjacent layer (2); in that there is at least one fold (12) in said film, said fold being adjacent a film edge (El), said fold (12) providing direct contact between two surface areas of said outer layer (3); in that a seal (S) bonds said two surface areas, said seal being located between said fold (12) and said film edge (El); and in that said fold (12) provides a tab (4) which may be pulled to rupture one of said outer layers (3) at said seal (S) and to cause said outer layer (3) to delaminate from its adjacent layer (2) to the edge (El) of the film (Fl) thereby opening said receptacle (R).

2. A seal according to Claim 1, characterised in that there are two of said folds (12) providing respective said tabs(4,5) each having an outer layer (3) bonded at said seal (S) such that pulling said tabs (4,5) apart will cause the outer layer (3) of one of them to rupture and to delaminate from its adjacent layer (2).

3. A seal according to Claim 1 or 2, characterised in that the material of the outer surface layer (3) is polyethylene or an ethylene-vinyl acetate copolymer and in that the material of the adjacent layer (2) is nylon, a vinylidene chloride copolymer, a propylene homopolymer or copolymer, or a cross-linked copolymer of polyethylene and ethylene-vinyl acetate.

4. A seal according to Claim 1, 2 or 3 characterised in that said film comprises three layers (1,2,3) of which the outer layer (3) is an ethylene vinyl acetate copolymer, the middle layer (2) is a copolymer of vinylidene chloride, and the outer layer (1) is a cross-linked copolymer of ethylene and vinyl acetate.

5. A package comprising a product (6) within a receptacle (R) of flexible film (F) having at least two layers (2,3) characterised in that one side of said receptacle (R) is closed by a seal according to claim 2, alone or together with either of claims 3 and 4; and in that said seal (S) is formed by opposed ends (Fl,F2) of said receptacle inwardly folded over at coinciding fold lines (12) so that all of said surface-to-surface seals (S) are in-line within the same seal area located between the fold lines (12) and product (6) whereby the folded over edges (Fl,F2) provide said tabs (4,5).

6. A package according to Claim 5, characterised by further comprising a strip-like dead fold element (7,11) enclosed by at least one of said folds (12) whereby after said bag is opened it may be closed by bending said dead fold element.

7. A package according to Claim 6, characterised in that said strip-like dead-fold element (7) extends along approximately one-half of said mouth.

8. A package according to any one of the preceding claims, characterised in that portions (29) have been removed from near the ends of said fold or folds (12).

9. A method of making an easy open closure seal (S) for an opening in a flexible receptacle (R) of thermoplastic film (F), said film having at least two layers (2,3), characterised in that the tensile strength of the outer surface layer (3) is greater than the bond strength between the outer layer (3) and its adjacent layer (2); in that the film (F) is folded along a fold line (12) adjacent an edge (El) which forms said opening so that surface areas of said outer layers (3) are in direct contact; and in that said surface areas are then heat sealed together along a seal located between said film edge (El) and fold line (12) to form a pull tab (4) by said film (Fl) folded at the fold line (12) whereby when said tab (4) is pulled the outer layer (3) will rupture and delaminate from the adjacent layer (2), said delamination continuing to said edge of said film (F) to open said package.

10. A method of making an easy open seal according to Claim 9,.characterised by the steps of: providing a receptacle in the form of a side seal bag (R) constructed of flexible thermoplastic film (F) having at least two layers; removing corner portions (27) of said bag (R) adjacent to the end opening of the bag so that two extended lip portions (Fl,F2) are formed; placing a strip-like dead fold element (7) on an inner surface of at least one (F2) of said extended lip portions; folding said extended lip portions (Fl,F2) into said end opening so as to surround and encompass said dead fold element (7) within the fold of the lip portion (F2) on which the element (7) was placed, said folds bringing portions of the outer surface (3) of the bag (R) into direct contact; and then flattening and heat sealing said folded lip portions (Fl,F2) to enclose said dead fold element (7) within its respective fold and to close said bag (R), said heat seal (S) being transverse across the width of the bag and being located between the fold line (12) and the edge (E2) of each of the inwardly folded lips (Fl,F2), said folds providing grippable tabs (4,5) for pulling said folds (Fl,F2) apart to open said bag (R); and further characterised by filling said bag (R) with a product (6) prior to said application of the heat seal whereby an easy open package with a reclosable dead fold closure element (7) is provided.

11. A method according to Claim 10, characterised in that the seal (S) is formed between the dead fold closure element (7) and the edge (E2) of the lip (F2).

12. A method according to Claim 10 or 11, characterised by further including the step of punching out portions (24) of the folds at the fold line (12) adjacent the side seal to reduce stress on said side seals.

13. A method according to Claim 9, characterised by the step of punching a hole (21) through the tab (4) between the fold line (12) and the seal (S) to allow a strip-like dead fold element (7) to be introduced into the interior of the fold of the tab (4), for reclosing of the package after opening of the easy open seal.