Pellable seal package

An improved heat sealable, peelable seal package structure having walls defined by sheet members and having a region where a first wall portion overlaps upon a second wall portion. The overlapping portions are heat sealable together but are thereafter separatable by peeling. The surface of such first wall portion is comprised of an ethylene acid copolymer, preferably of the ionomer type, and the surface of such second wall portion is comprised of a polyblend of polyethylene and ethylene vinyl acetate copolymer.

BACKGROUND OF THE INVENTION 
In the art of packaging, typically a sealed plastic package must be torn, 
cut, or otherwise broken into in order to obtain access to the contents 
thereof. 
Particularly in the field of plastic packaging, or of packaging 
incorporating plastic film, heat sealed interfaces between thermally 
bondable plastic layers typically are either so tightly fused together as 
not to be delaminatable or peelable without film rupture, or, 
alternatively, the film interfacial bonding is so poor as not to provide 
the required sealing action and seal bond strength required for commercial 
purposes, particularly in the case of perishable food stuffs. 
Particularly, in the latter case, the package wall structure is important 
so that the provision of an effectively sealed package with a truly 
peelable seal is difficult to achieve and still have a container which is 
also adapted for wide spread commercial utilization. 
The idea of achieving a peelable seal seemingly has become even more 
difficult to achieve with the significant commercial usage of packaging 
films comprised of ethylene acid copolymers (including ionomers) which are 
characterized, among other properties, with good toughness and outstanding 
adhesion to a variety of substrates including metals (such as aluminum 
foil). Particularly in composite (e.g. laminate) structures, ionomer 
layers commonly serve as heat seal layers which bond well and irreversably 
to themselves. 
It is believed that ethylene acid copolymers (including probably ionomers) 
have been polyblended with certain other resins and formed into films for 
the purpose of providing products which would retain the desirable 
toughness and bonding characteristics of such copolymers and which would 
also provide peelability for ease in package opening. However, such 
polyblends appear to suffer from certain disadvantages. For one thing, the 
resulting polyblend films can have sealing problmes caused by the weakened 
capacity of such films to form commercially acceptable heat seals with 
other films. For another thing, it is sometimes difficult to retain the 
desired toughness properties in the resulting polyblended film. Other 
problems and disadvantages also exist. 
The packaging art needs improved means for producing durable heat seals 
between ethylene acid copolymer (including ionomer) films and other films 
and still have the resulting seals be peelable. 
BRIEF SUMMARY OF THE INVENTION 
The present invention relates to a class of plastic packages for food 
stuffs and the like having a peelable seal formed by heat sealing. 
More particularly, the present invention is directed to a class of 
containers whose walls are defined by at least one sheet member and which 
has at least one wall region where a first wall portion overlaps upon a 
second wall portion in an adjacent relationship. Such first and second 
wall portions are heat sealable together, yet such can be thereafter 
separated by peeling at ambient temperatures. 
In composition, the surface layer of such first wall portion which is 
adjacent such second wall portion is comprised of an ethylene acid 
copolymer, and the surface layer of such second wall portion which is 
adjacent such first wall portion is comprised of a polyblend which itself 
is comprised of polyethylene and ethylene vinyl acetate. 
In one aspect, such a container of this invention employs a formed product 
receiving member and a covering film. The receiving member is directly 
heat bondale to overlapping portions of the covering film around package 
perimeter regions to provide a gas tight seal of sufficient bond strength 
for general commercial usage. The so bonded perimeter region between 
covering film and product receiving member can be separated by manual 
peeling action when it is desired to open the sealed package. The surface 
composition of such respective overlapping wall portions are as above 
defined. 
In another aspect such a container of this invention employs a first film 
comprised of such an ethylene acid copolymer and a second film comprised 
of such a polyblend of polyethylene and ethylene vinyl acetate. 
Conveniently, such respective films are heat sealed together about their 
perimeter regions to define there-between a goods-receiving chamber. The 
sealed regions are peelable manually. 
In another aspect, such a container of this invention employs a single film 
or sheet consisting of a laminate structure of at least two layers such 
that the outer layer comprising one face thereof is comprised of such an 
ethylene acid copolymer, and the other layer comprising the opposed face 
thereof is comprised of such a polyblend of polyethylene and ethylene 
vinyl acetate. Various container structures using such a laminate sheet 
structure are possible. 
An object of the present invention is to provide an improved peelable seal 
heat sealed package. 
An object of the present invention is to provide an improved heat sealable 
package with a peelable seal. 
A further object is to provide such a package which is particularly well 
suited for the packing and storage of food products. 
A further object is to provide such a peelable seal package for food 
products and the like wherein interior surfaces of the package are 
comprised of material which has been previously approved by governmental 
regulatory agencies for food contact usage. 
A further object is to provide a package structure whose walls are 
comprised of sheet means whose surfaces are formed of continuously 
extending layers of plastic, one such layer being comprised of an ionomer 
another such layer being comprised of a polyblend as indicated above which 
is peelably heat sealable to such ionomer layer. 
Other and further aims, objects, purposes, advantages, uses, and the like 
for the present invention will be apparent to those skilled in the art 
from the present invention.

DETAILED DESCRIPTION 
Definitions 
By the term "peelable" as used herein in relation to a seal between two 
plastic film or sheet members reference is generally had to the capacity 
of a pair of truly sealed together film or sheet members in a face-to-face 
engagement with one another to separate and to release from such sealed 
engagement with each other while each retain substantially its original 
integrity through the application of a separating force which can be 
manually applied and which is exerted on portions of such members adjacent 
to the sealed together portion, such force being exerted so as to produce 
at least a pair of vector components which are opposed to one another in a 
direction which extends generally normally to the plain of such sealed 
together portion at the site of the delamination. 
By the term "heat sealed" or equivalent as used herein reference is had to 
a bond formed between two overlapping plastic film or sheet members with 
heat and pressure applied locally for sufficient time to produce such bond 
as those skilled in the art will appreciate. Such a bond is gas-tight, and 
preferably has impact toughness and resistance to separation. The exact or 
optimum temperature of heat seal formation varies somewhat with the film 
members being bonded together, as those skilled in the art will 
appreciate. 
Ethylene Acid Copolymer (EAC) 
As those skilled in the art appreciate, such a copolymer is produced by the 
high-pressure polymerization of ethylene and acrylic or methacrylic acid 
in the presence of free radical initiators. For melt processable 
applications, the copolymers reportedly contain up to 6.5 wt. % acrylic 
acid or up to 15 wt. % methacrylic acid. Melt index values reportedly 
range from about 2.5 to 500 (ASTM D 1238). 
The processing conditions used for ethylene-acrylic acid (EAA) or 
ethylene-methacrylic acid copolymers (EMAA) are generally similar to those 
used with LPPE. 
For direct food contact, EMAA resins should not contain over 20% 
methacrylic acid and EAA resins should not contain over 10% acrylic acid. 
Such copolymer resins are commercially available. For example, an EMAA 
resin is available from the duPont Company under the trade designation 
"ACR 0903", while an EAA resin is available from Dow Chemical under the 
trademark "Primacor 1410." 
Ethylene/(meth)acrylic acid copolymers in the form of sodium or zinc salts 
are sometimes known as "ionomers", as those skilled in the art appreciate. 
In heavier gauges, ionomer is used in skin packaging for heavy, high 
valued electronic and hardware products. In composite structures, ionomer 
is a heat seal layer, particularly in food packaging. Coextruded ionomer 
film is used in tear open pouches for pharmaceutical and food packaging. 
Coextruded or laminated ionomer/nylon film is thermoformed to deep draws 
for meat and drug packages. 
Ionomers are commercially available for example, from the duPont Company 
under trademarks as "Surlyn 1650" and "Surlyn 1601", and "Surlyn 1601B". 
Polyblend of PE and EVA 
Conveniently, the PE/EVA polyblend compositions employed in this invention 
are comprised of from about 99 to 67 weight percent of polyethylene, and 
correspondingly, from about 1 to 33 weight percent of ethylene vinyl 
acetate on a 100 weight percent polyblend basis, and preferably from about 
96 to 82 weight percent of polyethylene and correspondingly from about 4 
to 18 weight percent of ethylene vinyl acetate. 
A present more preferred embodiment employs such a polyblend which contains 
about 12 weight percent ethylene/vinyl acetate. Suitable polyblends of 
ethylene/vinyl acetate and polyethylene are available commercially. Such a 
polyblend, for example, is commercially available from the duPont Co., 
under the trademark "Elva 3130". 
In composite structures of this invention the bond strength (and 
consequently the peel force required to separate a heat seal) between an 
EAC layer and a PE/EVA layer appears to increase with increasing 
quantities of EVA in the PE/EVA layer, within the compositional ranges 
herein taught. 
Polyethylene (PE) is composed of long chains of the single recurring 
monomer, ethylene. The polyethylene can be conventionally made and 
processed for use in this invention. 
Ethylene-vinyl acetate (EVA) copolymer resins are derived from basic low 
density polyethylene (LDPE) technology and comprise a family of 
thermoplastic polymers containing from about 5 to 50% by weight of vinyl 
acetate incorporated into an ethylene chain of from about 50 to 95% by 
weight of ethylene. 
Processing of EVA is similar to that of low density polyethylene (LDPE), 
although a 50.degree. to 100.degree. F. lower temperature normally is 
used. 
Preferably the vinyl acetate content of EVA is in the 5 to 20 weight 
percent range, with the corresponding balance up to 100 weight percent 
being ethylene, since higher vinyl acetate contents apparently tend to be 
too tacky and soft for blown film in the polyblends with PE preferably 
used in this invention. 
The polyblends of PE/EVA can be conventionally made and processed into 
film, coextruded and laminated. 
Referring to FIGS. 1 and 2, there is seen one embodiment of a package 
structure of the present invention, such embodiment being herein 
designated for convenience by the numeral 10. Container 10 is seen to 
comprise a formed product receiving member 11 and a covering film 12. The 
configuration of the product receiving member 11 can be in any form 
desired, as those skilled in the art will appreciate, the shape in any 
given instance being consistent with the exterior configuration of the 
product to be housed therein. Similarly, the covering film 12 is 
configurated so as to have a perimeter 13 which is adapted to be 
positionable generally in overlying relationship to the perimeter 14 of 
the product receiving member 11. 
A preferred product receiving member 11, such as shown, for example, in 
FIG. 3, is seen to comprise a laminate structure of four mutually 
interbonded layers. The interior or innermost layer 16 of receiving member 
11 is comprised of a layer of a thermoplastic polymeric ionomer such as 
"Surlyn" which is available from E.I. duPont DeNemours & Co., Wilmington, 
Delaware. The outermost or exterior layer 17 of the receiving member 11 is 
comprised of a polyamide. One suitable polyamide polymer for this purpose 
is available from Allied Corp. under the trademark "Capram 77-K". 
Adjacent the layer 17 is a layer 25 of saran, which preferably used to 
provide an oxygen barrier as when a meat product is to be contained in 
package 10. A suitable coated film of polyamide and saran is available 
commercially from Allied Corp. If an oxygen barrier is not needed, then 
the saran layer can be eliminated. 
Adjacent the layer 16 is a layer of polyester adhesive 24 which functions 
to bond the "Surlyn" ionomer layer 16 to the substrate. The polyester 
adhesive can be applied to the polyamide or to the saran layer (if the 
latter is used). One suitable polyester adhesive is available commercially 
under the trade designation "56065" from duPont Packaging Finishes Co. 
As those skilled in the art will readily appreciate, the layer 17 can be 
conveniently formed initially by extrusion, after which succeeding layers 
are applied thereto by conventional processing as those skilled in the art 
will appreciate. After formation, this resulting laminate structure is 
generally thermoformable and is thermoformed conventionally into any 
desired dish-shape desired prior to incorporation into a container 10. 
Conventionally, before being thermoformed, this laminate is termed a 
forming web, as those skilled in the art will appreciate, since the 
polyamide layer is chosen so as to be thick enought to permit 
thermoforming of the entire laminate or forming web. Suitable 
thermoforming conditions involve temperatures in the range of from about 
60.degree. to 180.degree. C., though higher and lower temperatures may be 
employed, if desired. As illustrated, the internal surface portions of the 
thermoformed laminate comprising member 11 are thus comprised of the layer 
of "Surlyn" ionomer while the outer surface portions of such member 11 are 
comprised of the polyamide layer. 
The covering film 12 is generally flexible. Referring also to FIG. 3, film 
12 is seen to be a laminate structure having an outer layer 18 comprised 
of either a polyester (preferably a polyethylene terephthalate) or a 
polyamide. The thickness of layer 18 is not generally designed for 
thermoforming capability. The inner layer 19 is a polyblend of a 
composition comprised of ethylene/vinyl acetate and polyethylene as above 
described. 
The covering film 12 can be prepared by any convenient procedure. 
Preferably, and as shown in FIG. 3, the outer layer 18 of polyester or 
polyamide is covered with a layer 26 of saran for oxygen barrier 
resistance. This layer 26 can have a composition like layer 25 in member 
11, and it can be eliminated, if desired. 
A layer 27 of polyester adhesive (which can have a composition like layer 
24) bonds layer 18 to layer 19. Such adhesive can be used whether or not 
the saran layer 26 is included. Conventional methods of laminate 
manufacture known to those skilled in the art may be employed. Preferably, 
the covering film 12 is used directly as manufactured, although diecutting 
or similar procedure may be employed to define the perimeter 13 of the 
covering film 12 so as to match the perimeter 14 of the receiving member 
11. 
In accordance with the present invention, the ethylene vinyl 
acetate/polyethylene layer is directly heat bondable to portions of the 
receiving member 11 adjacent the perimeter 14 thereof after the receiving 
member 11 has been charged with a fill, such as a ring sausage 20, or the 
like. Surprisingly and unexpectedly, although the ethylene vinyl 
acetate/polyethylene layer 19 forms a gas tight bond with the "Surlyn" 
ionomer layer 16 which is secure for commercial purposes of shipping, 
storing, and the like, nevertheless, the ethylene vinyl 
acetate/polyethylene layer 19 can be delaminated from the portions of the 
"Surlyn" ionomer layer 16 bonded thereto by manual stripping action. For 
example, a loose flap including the PE/EVA layer 19 provided at corner 23 
of film 12 can be grasped between the thumb and forefinger of one hand 
while an adjacent loose flap portion provided at corner 22 of member 11 
including the "Surlyn" ionomer layer 16 can be grasped between the thumb 
and forefinger of the other hand. When the hands are pulled apart, 
delamination occurs so that ready access to the fill within the receiving 
member 11 is obtained. Flap regions for accomplishing delaminating can be 
in any desired form. As shown, for example, the flap of covering film 12 
can merely amount to an unbonded perimeter region (relative to layer 16). 
Alternatively, a pull tab or corner 22 (shown in phantom lines in FIG. 1) 
can be provided integrally with the receiving member 11 and another pull 
tab or corner 23 can be provided in integral association with the covering 
film 12. In heat sealing the covering film 12 to the receiving member 11, 
when tabs 22 and 23 are employed, it is preferred to orient the covering 
film 12 relative to the receiving member 11 so that the tab 23 is in 
adjacent opposed relationship to the pull tab 22 in the assembled 
container 10. 
EXAMPLE 1 (EMBODIMENT OF FIGS. 1-3 
For example, in an embodiment of the container of FIGS. 1-3, the film 12 
has a layer 18 with a thickness of 0.75 mils, a layer 19 with a thickness 
of 2.25 mils, and a layer 26 with a thickness of about 0.1 to 0.15 mils; 
and the receiving member 11 has a layer 16 with a thickness of 2.50 mils, 
a layer 17 with a thickness of 1.25 mils, and a layer 25 with a thickness 
of about 0.1 to 0.15 mils. 
Referring to FIG. 4, there is seen a two layered laminate film structure 30 
which is suitable for making a container structure of this invention. 
Laminate 30 has one face 31 thereof provided by a layer 32 comprised of an 
ethylene acid copolymer as herein described while the opposing face 33 
thereof is provided by a layer 34 comprised of a PE/EVA polyblend as 
herein described. 
Referring to FIG. 5 there is seen a three layered laminate film structure 
36 which is also suitable for making a container structure of this 
invention. Laminate 36 has one face 37 thereof provided by a layer 38 
comprised of an ethylene acid copolymer as herein described while the 
opposing face 39 thereof is provided by a layer 40 comprised of a PE/EVA 
polyblend as herein described. Between the layers 38 and 40 is positioned 
a mutually interbonded layer 41 comprised of another thermoplastic 
material, such as a polyamide or the like, the function of such a layer 41 
being to improve physical properties of the laminate 36 over the 
properties of, for example, the laminate 30, thereby to better adapt the 
laminate 36 for specialized applications, such as for meat packaging or 
the like. Selection of the particular thermoplastic for layer 41 depends 
upon the end use application contemplated and other factors. 
The laminate structures 30 and 36 can be prepared, if desired, by 
coextrusion. Alternatively such can be prepared by laminating procedures 
involving preformed film layers, in which procedure an adhesive layer can 
additionally be present between adjacent layers to achieve bonding 
therebetween. Mixed fabrication procedures can be used; for example, an 
ethylene acid copolymer/polyamide (nylon) laminate can first be coextruded 
and then a layer of PE/EVA polyblend preformed, can be laminated thereto 
with a polyester adhesive. The thicknesses of such laminates 30 and 36 is 
typically not such as to make the laminate rigid enough to be 
thermoformable. 
In place of a thermoplastic material for layer 41, one can employ various 
other film and sheet materials, such as metal foils, like aluminum, woven 
and non-woven fabrics (natural or synthetic), cellulosic paper, or the 
like. 
The laminates 30, and 36, or the like, can be used to make various 
containers of the invention. For example, referring to FIG. 6 there is 
seen a container embodiment which can be fabricated from a single sheet of 
either such laminate 30 or 36. 
In FIG. 6, a sheet of such a laminate is precut to provide a lip flap 45. 
The cut sheet is folded in upon itself to form side 46, and adjacent 
inner, faces thus formed are heat sealed together at their adjoining 
peripheries to form sides 47 and 48. When the flap 45 is folded over the 
adjacent outside surface portion of the resulting container 49, a contact 
between opposing faces 31 and 33 of, the laminate is achieved so that a 
heat seal between respective surface portions of ethylene acid copolymer 
and PE/EVA polyblend is achieved to produce a heat sealed joint which, in 
accord with the principles of this invention, is peelable. Thus, a single 
starting sheet of such a laminate is used to form a container structure. 
In FIG. 7, a sheet of such a laminate is precut to provide a lip flap 51. 
The cut sheet is folded in upon itself to form folded side edges 52 and 
53, respectively, and to provide an overlap in a central region 54 where 
the outside face is adjacent to the inside face. A heat seal is thus 
releasably formable between the overlapping faces in region 54. A heat 
seal is also formed between inside facial portions to provide a sealed 
side 55. The flap 51, when folded over the resulting adjacent outside 
surface portions of the thus formed container 56, permits a releasable 
(peelable) heat seal to be formed. 
Referring to FIG. 8, there is seen fragmentarily another embodiment of a 
container structure of this invention designated in its entirety by the 
numeral 60. Container 60 can, for example, utilize a heavy gauge sheet 61 
(comprised for example, a "Surlyn" polymer) and a similar sheet 62 
comprised of PE/EVA polyblend. The sheet 61 is adapted for the skin 
packaging or heavy high valve electronic and hardware products. The sheet 
62 is provided which is adapted to serve as a covering film and is edge 
configured to overlap upon rim (or lip) portions 63 of the central 
bag-like cavity 64 utilized for product holding defined in sheet 61. After 
packing with product, the covering film sheet 62 is positioned over the 
rim portions 63 and is heat sealed thereto. To open container 60, the 
sheet 62 is manually peeled away from the sheet 61. A tab 65 is optionally 
provided for sheet 62 to aid in peeling. 
Referring to FIGS. 9 and 10 there is shown another embodiment of a 
container structure of this invention which is herein designated in its 
entirety by the numeral 70. Container 70 is formed of two preformed 
laminate sheet members identified as 71 and 72, respectively, as shown in 
the fragmentary enlarged view depicted in FIG. 10. Laminate sheet 71 is 
seen to be comprised of an inner layer 73 comprised of a PE/EVA polyblend 
and an outer layer 74 bonded thereto comprised of a polyester. Layer 73 
can be, for example, about 1.5 mils in thickness while layer 74 can be 
about 0.5 mil in thickness. 
Sheet laminate 72 is seen to be comprised of an inner layer 76 and an outer 
layer 77 bonded thereto. Inner layer 76 is comprised of "Surlyn" while the 
outer layer 77 is comprised of polyester. Inner layer 76 is here 
illustratively about 1.5 mils while outer layer 77 is here illustratively 
about 0.5 mils, in thickness. 
Initially, the container 70 is formed by laminating together the opposed 
side edges 78 and 79 in the manner shown, for example, in FIG. 9, with the 
intended top portion 80 of container 70 being defined by the diagonal 
seals 81 and 82 which extend from their respective side edges 78 and 79 
inwardly to define a brief top edge 83 which itself is likewise sealed. 
Initially, the bottom edge 84 of the container 70 is left unsealed. 
Thus, a product or fill is placed into the container 70 through the bottom 
edge 84 and thereafter the bottom edge is sealed as illustrated by the 
phantom lines shown in FIG. 9. 
The unsealed tabs 85 on the outside of each of the diagonal seals 81 and 82 
(which tabs are comprised of the sheet laminates 71 and 72, as will be 
appreciated), are then available for finger gripping by someone desiring 
to open the container 70 for reasons of access to the fill therein. The 
opening can be achieved, in accordance with the present invention, by 
simply peeling away the opposed surfaces of the sheet laminate 71 from 
sheet laminate 72 in the region of the seals 81, 82, and 83. 
As those skilled in the art will understand, many different film materials 
can be bonded together by laminating or coextrusion (or the like)to 
produce laminate sheet constructions wherein a layer of ethylene acid 
copolymer or a layer of PE/EVA polyblend is on an outside face thereof. 
Thus, the laminate sheet constructions used as starting materials to make 
a container of this invention having a peelable seal structure can employ 
many different film forming thermoplastics. Suitable film forming plastics 
include acrylonitrile-butadiene-styrene (ABS); acrylonitrile methyl 
acrylate copolymer, rubber modified; cellulosics, such as cellulose 
acetate, cellulose tracetate, cellulose acetate butyrate, cellulose 
propionate, ethyl cellulose and regenerated cellulose (cellophane); 
fluoroplastics, such as ethylene-chlorotrifluoroethylene copolymer 
(E-CTFE), ethylene tetrafluoroethylene copolymer (ETFE); fluorinated 
ethylene propylene copolymer (FEP), perfluoroalkyl (PFA), 
polychlorotrifluoroethylene copolymers (CTFE), polytetrafluoroethylene 
(PTFE), polyvinyl fluoride (PVF), and polyvinylidene fluoride (PVDF); 
polyamides, such as nylon 6 (extruded or biaxially oriented), nylon 11, 
and nylon 12; polycarbonate; polyester (i.e., thermoplastic polyethylene 
terephthalate (PET)); polyethylene and ethylene copolymers, such as low 
density PE, medium density PE, high density PE, ultrahigh molecular weight 
PE and ethylene vinyl acetate copolymer; polyimide; polymethyl 
methacrylate, such as standard or type A (korad acrylic); polyethyl 
pentene; polypropylene, such as extrusion (cast) or biaxially oriented; 
polystyrene; polysulfone; polyethersulfone; polyurethane elastomer; 
polyvinyl chloride, such as nonplasticized sheets or films (calendering, 
extrusion, or solvent cast), or plasticized sheets or films (calendering, 
extrusion, or solvent cast); vinyl chloride-acetate copolymer 
(nonplasticized or plasticized); vinylidene chloride-vinyl chloride 
copolymer; vinyl nitrile rubber alloy; and the like. 
In addition, a laminate sheet construction used as starting structures for 
forming a container of the present invention can employ as one layer 
thereof paper or metal foil, such as aluminum or copper foil. Ethylene 
acid copolymer and PE/EVA each bond to paper or metal foil. For example, 
the layer 41 in the laminate 36 of FIG. 5 can be formed of metal foil or 
of cellulosic paper or of synthetic woven monofiliment, such as a 
polyester fabric, or the like as desired. 
A peeled seal of polyethylene and ethylene vinyl acetate copolymer layer to 
ethylene acid copolymer can be reformed, if desired through resealing with 
heat and pressure applied against such layers. A laminate incorporating a 
paper or foil layer is not heat formable, as those skilled in the art will 
readly appreciate. 
Although the teachings of my invention have herein been discussed with 
reference to various specific embodiments, it is to be understood that 
this is by way of illustration only and that others may wish to utilize my 
invention in different combinations, designs or applications.