EP0748746A1

EP0748746A1 - Easy-to-open thermoplastic package

Info

Publication number: EP0748746A1
Application number: EP96109304A
Authority: EP
Inventors: Bernard Chappuis; Joerg Staempli
Original assignee: GRACE AG; WR Grace and Co Conn
Current assignee: Cryovac LLC
Priority date: 1995-06-14
Filing date: 1996-06-11
Publication date: 1996-12-18

Abstract

The invention provides for an easy to open package wherein an article is enclosed between a lower thermoplastic web having an opening (1) and a rim (4) formed on the periphery of said opening and an upper thermoplastic web (7) superposed thereto that is sealed to the lower web in a sealing region that comprises said peripheral rim, said package being characterized in that the lower thermoplastic web has at least one recess (6) at a marginal zone of the peripheral rim providing in the upper web for an area of non-adhesion (8) that can be gripped with the fingers to initiate opening of the package.

Description

The present invention relates to an easy to open package wherein an article, typically a food product, is enclosed between two webs of thermoplastic material, the package is tightly sealed so as to protect the product packaged therein from abuse and exterior contamination during storage, shipment and display and yet it can be easily opened manually by the end consumer without resorting to knives, scissors or other implements.
A wide variety of products, particularly food products, are being offered in visually attractive packages made from two superposed thermoplastic webs, a lower or bottom web and an upper or top web, by different methods including the thermoforming method, the vacuum skin packaging method and other methods which can be generally considered as modifications of the above two general methods.
In these methods the lower, supporting, web has preferably a tray-like configuration defining a receptacle for the article to be packaged having an opening and a rim formed on the periphery of said opening. Said tray-like configuration is generally obtained by a thermoforming step, either in-line or off-line.
In the thermoforming process the upper web is then disposed over the receptacle containing the article to be packaged, the chamber containing the lower and upper webs is vacuumized and the upper web is sealed to the peripheral rim of the lower thermoformed web by means of a heat sealing platen, usually in the form of a sealing frame. If a modified atmosphere package is desired, the suitably selected gas mixture is injected into the chamber between vacuumizing and sealing.
In the vacuum skin packaging process the upper web is generally drawn into a concave mold cavity formed into a vertically movable heated molding platen so that it is heated while held by suction in contact with the heated ceiling and walls of the cavity. Then the vacuumization of the vacuum packaging chamber and the release of the suction applied to the cavity walls of the mold plate draws the upper web downwardly to contact with the contours of the product article and with the lower web. The upper web thus forms a tight skin all around the product and is bonded to the lower web by differential air pressure, thus sealing wherever the two webs contact each other. Depending on the temperatures and materials employed for the upper web, a heat sealing frame may be used to further seal the upper web to the peripheral rim of the lower web.
In said packages the requirement for sufficiently strong heat seals to maintain the integrity of the package through the distribution channels and storage, should be balanced with that for easily openable heat seals to allow the end user to open the package by applying ordinary human hand force.
Several methods involving the proper selection and combination of materials have been devised in order to achieve the desired compromise.
These methods are essentially based either on the concept of having an easily peelable seal layer that would, upon application of an ordinary force, delaminate from one of the two layers in contact therewith in the sealed package, or on the concept of having the sealing layer or one of the layers adjacent to the sealing layer, made of incompatible materials so that opening of the package is obtained by failure of the necessary cohesive force within said layer, upon the application of a tearing force from the outside.
For the purposes of the present application the term "easy to open package" is intended to refer to a package, and specifically heat sealed and bonded areas of a package, which, owing to the suitable selection of the composition of the upper and lower webs, and particularly that of the sealing layers and of the layers adjacent thereto, are readily openable without totally tearing or rupturing the packaging materials.
In any case independently on the easy to open mechanism involved, the opening of said packages still needs to be facilitated by a convenient means for pulling apart the package, i.e. a start for the end user to separate the two thermoplastic sheets one from another.
GB-B-1,360,808 discloses a package formed of superposed sealed webs of thermoplastic material with a corner of the package rendered easily openable by virtue of a paper insert between the webs in order to prevent localized sealing.
GB-B-1,510,115 also discloses a package formed of superposed sealed webs of thermoplastic material in which a corner is rendered easily openable by virtue of a patch of ink that should prevent the two webs from bonding to one another.
CA-B-1,164,260 describes a package wherein a corner of the lower web is bent downwardly by a punching device leaving the upper web without surface to adhere to at the sealing step.
Vacuum skin packaging machines are commercially available that provide for a pre-cut of a corner of the lower web which is then adhered to the upper web. To start opening the package, the pre-cut corner must first be detached from the rest of the lower web by bending it upwardly or/and downwardly along the precut.
However, even with these processes, it is often difficult to start the opening of the package because it is not readily apparent to the consumer where is the location at which opening of the package should be started and also because, even at the area of non-adhesion, the two webs tend to conform with one another and consequently it is not always easy for the consumer to be able to start the separation of the two thermoplastic webs at the unadhered corner. Furthermore in the case of the pre-cut corner, not always the corner can be easily detached from the rest of the tray and sometimes bending it downwardly may break the upper web without being able to remove it first.
In the light of the foregoing technical problem, it is a primary object of the present invention to eliminate the above drawbacks by providing an easy to open package in which it is readily apparent to the end user where to start the separation between the package webs, and gripping of the web to be torn apart and opening of the package is easier than with the presently known or commercially available means.
In addition, another object of the invention is to provide an easy to open package provided with means for pulling apart the package with enhanced properties of presentation and outward appeal of the packaged product.
Further objects of the invention are a method to manufacture said easy to open package and an apparatus to implement said method.
These and other objects are achieved by the present invention that provides as a first object thereof an easy to open package wherein an article is enclosed between a lower thermoplastic web having an opening and a rim formed on the periphery of said opening and an upper thermoplastic web superposed thereto that is sealed to the lower web at said peripheral rim, said package being characterized in that the lower thermoplastic web has at least one recess at a marginal zone of the peripheral rim providing in the upper web for an area of non-adhesion that can be gripped with the fingers to initiate opening of the package.
In a preferred embodiment said easy to open package is obtained by vacuum skin packaging.
In a second aspect the present invention relates to a method for producing an easy to open package provided with means for pulling apart the package according to the invention, comprising providing an easy to open package closable by adhering superposed lower and upper webs at a seal region, forming a recess in the lower web at a marginal zone in the seal region and sealing together said lower and upper webs at the seal region thereby providing for an area of non-adhesion in the upper web that can be gripped with the fingers to initiate opening of the package.
Further features and advantages of the invention will be more clearly understood from the following description of a preferred but not limitative embodiment of the easy to open package of the present invention, with reference to the accompanying illustrative drawings wherein :

Fig. 1 is a top schematic view of a package according to the present invention;
Fig. 2 is a perspective view of the same package;
Fig. 3 represents a general arrangement view of a packaging machine in accordance with the present invention;
Fig. 4 is a detail of two subsequent rows of packages being formed using the packaging machine in accordance with the present invention;
Fig. 5 is a detail of the means for creating the recess in a packaging machine in accordance with the present invention.

With reference to Fig. 1 and Fig. 2, the lower web has a substantially tray-like configuration with an opening (1), with a bottom (2) whence walls (3) extend typically diverging on the opposite side to the bottom, and a peripheral rim (4) all around the opening. The bottom may have an undulated surface which defines a plurality of canalizations or micro-channels intersecting one another to facilitate the extraction of air during the sealing operation; additional canalizations are defined by grooves (5), extending substantially parallel to one another toward the bottom such as to communicate to said micro-channels, again to facilitate the extraction of air. A recess (6) is formed in the lower web. The upper web (7) that is superposed to the lower thermoformed web and is sealed thereto in a seal region that comprises the peripheral rim, presents therefore an area of non-adhesion (8) in correspondence with the recess formed in the lower web. Said area of non-adhesion (8) can be easily gripped with the fingers and torn apart. Particularly in case of vacuum skin packages where the upper web is transparent, the identification of the point where to start the opening is immediate and no arrows or other signs need to be printed or fastened on the web to properly address the end user. The dimension of the recess and therefore of the area of non-adhesion in the upper web can be varied depending on the dimensions of the package and of the peripheral rim, provided however that it is sufficient to allow for an easy gripping by an ordinary hand. Generally packages from about 8 to about 20 cm in width and from about 15 to about 30 cm in length are manufactured with a rim width of from about 1 to about 3 cm. As an example in the case of the recess in the form of a half-moon or lunette shown in Fig. 1 and Fig. 2, a radius of at least about 0.7 cm, preferably at least about 0.8, and more preferably at least about 0.9 cm up to about 2.5 cm or even more depending on the rim width would be suitable. The shape of the recess is not critical provided that gripping of the non-adhesion area in the upper web can be easily achieved. Therefore round or oval shaped recesses are preferred as they better conform to the finger tips. The recess is preferably centered on the tray side in order to better balance the opening force applied and achieve a more uniform tearing apart of the upper web. However this is not strictly necessary and the recess may also be unsymmetrically positioned on the lower web side.
As indicated above in a preferred embodiment of the present invention the easy to open package is obtained by the vacuum skin packaging method, and in an even more preferred embodiment thermoforming of the lower web is carried out in-line by any suitable technique known in the art. It can be easily understood however that pre-formed trays can be used in the packaging method according to the present invention wherein the suitable recess has been created by known means.
In the most preferred embodiment of vacuum skin packaging with thermoforming of the lower web in-line, as schematically illustrated in Fig. 3, the manufacturing apparatus comprises a first reel (10) on which is wound the lower web material (11) and which is carried rotatably on a bed (12). Associated with the bed is a thermoforming station (13), typically comprising a heater element (14) facing a mold element (15), where the lower web is thermoformed in a tray-like configuration of the suitable shape and size. Suitable thermoforming methods, for example, include a vacuum forming or plug-assist vacuum forming method. In a vacuum forming method the lower web is heated, e.g. by a contact heater or infrared method and a vacuum is applied beneath the web causing the web to be pushed by atmospheric pressure down into a preformed mold. Alternatively, after heating the lower web , air pressure is applied above the web to push it down into a preformed mold by applied pressure. In a plug-assist vacuum forming method, after the web has been heated and sealed across a mold cavity, a plug shape similar to the mold shape impinges on the web and, upon application of vacuum, the lower web transfers to the mold surface.
The recess is preferably formed into the lower web after thermoforming. In such a case, downstream of the thermoforming station the apparatus has a means (16) for creating the recesses which is shown in detail in Fig. 5. This can be obtained e.g. by a punching unit comprising a stamp mold punch and a matrix shaped in the form desired that descends, punches out, and re-ascends once the recess has been created. Alternatively the recess can be created by any other means including for instance punching units carrying blades or knives or laser treatments. To avoid contamination of the packaged content with plastic scrap, the piece of thermoplastic material which is punched out or cut is preferably removed, e.g. by suction through the punching unit. Even if in a preferred embodiment of the process of the invention the recess is created after thermoforming, it may also be formed before thermoforming, particularly when thick lower webs are used as they would not be deformed in the subsequent thermoforming step. In such a case the means (16) should be positioned upstream the thermoforming station.
The apparatus has then a portion (17) for distributing products to be packaged in the trays either manually or automatically.
Downstream of this loading station, the apparatus has a packaging station (18) which carries rotatably a second reel (19) around which the upper web (20) is wound.
Within the packaging station the loaded tray is brought to a vacuumized condition and sealed by means of the upper web with a conventional vacuum skin packaging method such as described for instance in GB-A-1,307,054, GB-A-1,206,023, BE-A-898,216, EP-A-93,480, EP-A-270,208.
Since in actual practice the width of the lower web is such as to permit the forming of several trays parallel to one another (genearally two to four, and typically three), the sealed packages exit the packaging station (18) in the form of a continuous web having a plurality of mutually parallel packages as illustrated in Fig. 4. The packaging station (18) is therefore followed by cutting means (21) which subdivide the sealed package web exiting the packaging apparatus into individual packages.
Fig. 5 illustrates a detail of the means for creating the recesses according to a preferred embodiment of the invention. The punching stamp molds (22), three in a three lane thermoforming machine, are positioned downstream the thermoforming station (13), beneath the bed (12), and in the middle of each lane. They are automatically operated to raise, punch out the web against the corresponding suitable matrices (23) in the area corresponding to the peripheral rim of the end trays, thus forming in each tray at least one recess of the suitably selected shape and size.
In a preferred aspect the punching unit will create a hole in a part of the area between two subsequent thermoformed trays and the transverse severing of the sealed package web at the end of the packaging process to provide separate packages will then yield easy to open packages with a recess at a marginal zone of the peripheral rim of the lower web having half the size and shape of the hole, said recesses being positioned in the back side of one tray and correspondingly on the front side of the following one as illustrated in Fig. 4.
If such holes are provided in all the non thermoformed areas intercalating the thermoformed ones, then the obtained packages will have two recesses of similar shape on the opposite short sides.
The lower web used for the manufacture of the easy to open package according to the present invention preferably comprises a multilayered laminated structure having flexibility characteristics which may vary depending on the end use. Semi-rigid gas barrier structures are generally preferred. Typically they are polyvinyl chloride (PVC) or polystyrene (PS)-based laminates comprising a suitably selected sealant layer at the surface that will be sealed to the upper web. Thickness of the lower web is generally comprised between 100 and 450 µ, typically between 150 and 300 µ. The upper web may be a laminate comprising for example a substrate of e.g. unoriented polyethylene, irradiated or non-irradiated, a ionomer, a polyester, PVC, etc. or any other thermoformable material, a barrier layer, preferably ethylene-vinyl alcohol copolymer, and a suitably selected sealant layer. Thickness of typical upper webs to be used in vacuum skin packaging is from about 45 to about 250 µ, preferably from about 70 to about 180 µ. Suitable sealant layers for the lower and upper webs and suitable combinations thereof to provide for an easy to open package are for instance those described in US-A-4,382,513, US-A-4,665,130, US-A-4,666,778, US-A-5,023,121, EP-B-192,131, and European patent application no. 93250270.1, whose content is incorporated herein by reference.
The following example and comparative example show that the easy to open package provided with means for pulling apart the package according to the present invention allows for a much easier manual opening than the corresponding easy to open package provided with a conventional pre-cut corner adhered to the upper web as means for initiate the opening.
The prior-art comparative packages are made by the vacuum skin packaging process using a CRYOVAC® VS 44 machine. The machine is equipped with a knife to provide the corner of each tray with a pre-cut. The trays, which are obtained in-line by thermoforming, are 13 cm in width, 25 cm in length, and 1.2 cm in depth. The rim width is 1.5 cm in the front and back shorter sides of the tray and about 0.8 cm in the longer sides.
As the lower web a semi-rigid polyvinyl chloride sheet (200 µ thick) with a contact surface layer (9 µ thick) of a blend of 75 % EVA (12% VA), 20 % polybutene-1, and 5 % polypropylene is used, while the upper web is a flexible coextruded multi-layer film irradiated to a dosage of 12 MRad that consists of the following layers LDPE/Tie/EVOH/Tie/LDPE/Ionomer (wherein Ionomer stands for a Zinc partial salt of ethylene-methacrylic acid copolymer with MFI 14 g/10') with respective partial thicknesses (in µ) of 40/3/8/3/40/6
The packages according to the invention are produced using a modified CRYOVAC® VS 44 machine wherein the means for precutting the corners have been removed and replaced by means for creating two recesses in each tray, each one positioned in the middle of the short side of the tray, said recesses being in the form of a half-moon with a radius of about 1.1 cm.
The size of the trays and of the tray rims as well as the composition of the lower and upper webs and the machine conditions are identical.
While in both cases a seal of the desired seal strength is obtained, a statistically significative number of samples of the packages according to the present invention are tested in comparison with an equal number of packages according to the prior art by a panel of 8 people and judged to be much easier to open than the prior art packages.
Similar modifications could be easily carried out on different packaging machines such as for instance on a MULTIVAC CD 6000 machine and similar results in terms of openability would be expected.
Throughout the present application the shape of the thermoformed lower web has been described as being rectangular as this is the shape that is conventionally used. It will however be understood that virtually any shape of the superposed webs can be provided with the means for pulling apart the package according to the invention by creating a suitable recess in the lower web.

Claims

An easy to open package wherein an article is enclosed between a lower thermoplastic web having an opening (1) and a rim (4) formed on the periphery of said opening and an upper thermoplastic web (7) superposed thereto that is sealed to the lower web in a seal region that comprises said peripheral rim, said package being characterized in that the lower thermoplastic web has at least one recess (6) at a marginal zone of the peripheral rim providing in the upper web for an area of non-adhesion (8) that can be gripped with the fingers to initiate opening of the package.
The easy to open package of claim 1 obtained by vacuum skin packaging.
The easy to open package of claim 1 wherein the lower thermoplastic web has a tray-like configuration.
The easy to open package of claim 3 wherein the recess is centered on the tray side.
The easy to open package of claim 1 wherein said recess is in the shape of a lunette.
The easy to open package of claim 5 having a radius of at least about 0.7 cm, preferably at least about 0.8 cm and more preferably at least about 0.9 cm.
A method for producing an easy to open package provided with means for pulling apart the package according to claim 1, which comprises providing an easy to open package closable by adhering a lower thermoplastic web having an opening and a rim formed on the periphery of said opening and an upper thermoplastic web superposed thereto that is sealed to the lower web in a sealing region that comprises said peripheral rim, forming a recess in the lower web at a marginal zone in said peripheral rim and sealing together said lower and upper webs at the seal region thereby providing for an area of non-adhesion in the upper web that can be gripped with the fingers to initiate opening of the package.