Multilayer plastic film, useful for packaging a cook-in foodstuff

A multilayer, preferably biaxially oriented, film suitable for processing and/or packaging cook-in foods such as ham, roast beef and poultry having an excellent combination of oxygen barrier, heat seal and optical properties comprising at least five essential sequential layers with a first layer of a copolymer of propene and at least one C.sub.2 -C.sub.8 .alpha.-olefin having a propene content of at least 60 wt. % and preferably having a melting point <140 .degree. C.; a second layer of (1) a first copolymer of ethylene and at least one C.sub.4 -C.sub.8 .alpha.-olefin having a density of from 0.900 to 0.915 g/cm.sup.3 and a melt index of less than 1.0 dg/min., (2) a second copolymer of ethylene with from 4 to 18%, preferably 4 to 12%, of a vinyl ester or alkyl acrylate, (3) an anhydride-modified third copolymer of ethylene with at least one .alpha.-olefin, a vinyl ester or an alkyl acrylate, and (4) optionally a fourth copolymer of ethylene and at least one C.sub.3 -C.sub.8 .alpha.-olefin having a density less than 0.900 g/cm.sup.3 and a melting point less of less than 85.degree. C.; a third EVOH layer; a fourth layer like the second layer; and a fifth layer of a first copolymer of ethylene with at least one C.sub.4 -C.sub.8 .alpha.-olefin having a density of from 0.900 to 0.915 g/cm.sup.3 and a melt index of less than 1.0 dg/min., and a second copolymer of ethylene with from 4 to 18%, preferably 4 to 12%, of a vinyl ester or alkyl acrylate, and optionally a third copolymer of ethylene and at least one C.sub.3 -C.sub.8 .alpha.-olefin having a density less than 0.900 g/cm.sup.3 and a melting point less of less than 85.degree. C.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements in the art of packaging 
foodstuffs, especially cook-in foods such as for example ham, beef, and 
turkey breasts. 
In discussing plastic film packaging, various polymer acronyms are used 
herein and they are listed below. Also, in referring to blends of polymers 
a colon (:) will be used to indicate that the components to the left and 
right of the colon are blended. In referring to film structure, a slash 
"/" will be used to indicate that components to the left and right of the 
slash are in different layers and the relative position of components in 
layers may be so indicated by use of the slash to indicate film layer 
boundaries. Acronyms commonly employed herein include: 
PP -Polypropylene homopolymer 
PE -Polyethylene (an ethylene homopolymer and/or copolymer of a major 
portion of ethylene with one or more .alpha.-olefins) 
EVA -Copolymer of ethylene with vinyl acetate 
PVDC -Polyvinylidene chloride (also includes copolymers of vinylidene 
chloride, especially with vinyl chloride) 
EVOH -A saponified or hydrolyzed copolymer of ethylene and vinyl acetate 
EAA -Copolymer of ethylene with acrylic acid 
Various published patent documents disclose different types of packaging 
films for cook-in and other processing or packaging applications. 
U.S. Pat. No. 4,724,185 (Shah) discloses a five layer coextruded oriented 
film having a core layer of an EVOH-nylon blend attached to outer layers 
of a blend of linear low density polyethylene, linear medium density 
polyethylene, and EVA using intermediate layers of an acid 
anhydride-modified adhesive resin. The film is irradiated. 
U.S. Pat. No. 4,726,984 (Shah) discloses a five layer coextruded oriented 
shrink film having a core layer of EVOH attached by adhesive layers to 
opposing outer layers of a blend of ethylene propylene copolymer(2-5 wt. % 
C.sub.2) and polypropylene. 
U.S. Pat. No. 4,469,742 (Oberle) discloses a cook-in six layer heat 
shrinkable film having examples which includes a structure of C.sub.3 
C.sub.2 random copolymer/EVA/anhydride graft adhesive/EVOH/anhydride graft 
adhesive/EVA. The EVA may be replaced with ethylene homopolymer or 
copolymer such as LLDPE. The film may be irradiatively cross-linked and 
extruded. A comparative example of a five layer film is also presented 
which has a structure of C.sub.3 C.sub.2 random copolymer/EVA/anhydride 
graft adhesive/EVOH/EVA. 
U.S. Pat. No. 4,857,399 (Vicik) discloses a four layer shrink film 
comprising an ethylene-propylene random copolymer as a meat contact first 
layer, a blend of EVA and an anhydride-modified adhesive resin as an 
intermediate second layer, an EVOH-nylon blend barrier core layer, and a 
blend of anhydride-modified adhesive and EVA as a fourth layer. 
U.S. Pat. No. 5,382,470 (Vicik) discloses a biaxially stretched oriented 
heat shrinkable film for food packaging having an EVOH-nylon 6/66 
copolymer core layer connected by intermediate adhesive layers to opposing 
outer layers. The adhesive layers are disclosed to be specific blends of 
resins including VLDPE, EVA, and anhydride-modified PE or EVA adhesive 
resins. The outer layers may comprise a blend of VLDPE, EVA and 
plastomeric ethylene .alpha.-olefin copolymer. 
U.S. Pat. No. 5,397,613 (Georgelos) discloses a heat shrinkable film of at 
least 50% shrink having a C.sub.2 .alpha.-olefin 
layer(.rho.=0.88-0.905;m.p. &lt;100.degree. C.;M.sub.w M.sub.n &lt;3) which may 
have EVA and another C.sub.2 .alpha.-olefin blended therein. This film may 
be on both sides of a barrier layer which may be EVOH. 
U.S. Pat. No. 4,888,223 (Sugimoto et al) discloses a corona treated, heat 
shrinkable, multilayer, tubular film having a possible structure of 
polyolefin/modified polyolefin/gas barrier/modified polyolefin/polyolefin 
where the inner meat contact layer is corona treated at a level of at 
least 35 dynes/cm. The inner layer may be a polypropylene copolymer. The 
modified polyolefin may be a maleic anhydride grafted LLDPE. The gas 
barrier may be EVOH. 
EP 561,428 (Fant et al), claims a multilayer film comprising a core layer 
of an ethylene vinyl alcohol copolymer; two outer polymeric layers; two 
interior layers of an acid- or acid anhydride modified polyolefin adhesive 
polymeric material to bond the outer layers to the core layer. A dependent 
claim specifies that both outer layers may comprise C.sub.3 C.sub.2 
copolymer. 
EP 457 598 (Shah et al) discloses a polyamide based multilayer film for 
packaging cheese. This polyamide film is disclosed as having "an oxygen 
transmission rate of no more than 500 cc/m.sup.2, 24 hrs., atm". Example 5 
purportedly discloses a 1 mil (25.4 micron) thick biaxially oriented film 
having a core layer comprising a blend of about 70% EVOH and about 30% of 
a polyamide in combination with polypropylene or propylene copolymer based 
outer layers and this film has a reported shrinkage at 220.degree. F. 
(104.degree. C.) of 24% in two directions. 
PCT 94/07954 (Kaeding), assigned to DuPont, has broad claims drawn to a 
shrink film comprising a blend of a first polyolefin (.rho.&lt;.0.92 
g/cm.sup.3 ; M.sub.w /M.sub.n of 1-4; m.p&lt;115.degree. C.; single narrow 
m.p.) with a second polyolefin having a m.p. that is 10.degree. C. greater 
than the m.p. of the first polyolefin and an orientation temperature at 
least 2.degree. C. less than its m.p.. Also, disclosed are multilayer 
structures having a core layer of the above with a C.sub.3 C.sub.2 
copolymer or polypropylene outer layer. 
Various multilayer thermoplastic films have been commercialized for 
packaging meats, cheeses and cook-in foodstuffs. Three to six layer films 
are common. Typical structures include: PP/Adhesive/Nylon, 
EVA/PVDC/EVA:PE, PE:EVA/PVDC/PE:EVA, 
Ionomer/EVA/Adhesive/EVOH/Adhesive/EVA, 
PE:EVA/PE:Adhesive:EVA/EVOH/PE:Adhesive:EVA/PE:EVA, 
Nylon/EVA/Adhesive/EVOH/Adhesive/EVA, C.sub.3 C.sub.2 
copolymer/EVA/Adhesive/EVOH/Adhesive/EVA, and variations thereof where 
polyethylene copolymers are blended into one or more of the EVA layers. 
Some packaging films are heat shrinkable at 90.degree. C. and others are 
not. Some are irradiatively crosslinked and/or corona treated or not. Some 
of the nonshrinking films have an oxygen barrier comprising one or more 
layers of nylon or EVOH or a blend of EVOH with nylon. Such known 
nonshrinking films include structures of the type EVA:PE/Nylon, 
EVA:PE/Nylon/EVOH/Nylon/EVA:PE, EVA:PE/PVDC/Nylon, EVA:PE/EVOH/Nylon, and 
EVA:PE/Nylon/EVA. The nonshrinking EVOH containing films generally have a 
relatively thick EVOH containing layer, generally greater than 0.5 mil 
(12.7 microns). Thin EVOH barrier layer, multilayer heat shrinkable, 
oriented films have been taught in U.S. Pat. No. 5,382,470 and U.S. 
application Ser. No. 08/191,886; filed Feb. 3, 1994, both of which are 
hereby incorporated by reference in their entireties. 
Of the foregoing nonshrinking films, those containing EVOH have a typical 
oxygen permeability of less than 10 cm.sup.3 per m.sup.2 at 1 atm, 0% 
relative humidity and 23.degree. C. and are considered high barrier films. 
The terms "barrier" or "barrier layer" as used herein mean a layer of a 
multilayer film which acts as a physical barrier to gaseous oxygen 
molecules. Physically, a barrier layer material will reduce the oxygen 
permeability of a film (used to form the bag) to less than 70 cm.sup.3 per 
square meter in 24 hours at one atmosphere, 73.degree. F. (23.degree. C.) 
and 0% relative humidity. These values should be measured in accordance 
with ASTM standard D-1434. 
Also known are films suitable for packaging foodstuffs that are heat 
shrinkable at 90.degree. C. which contain nylon or a blend of EVOH and 
nylon. Axially stretched, especially biaxially stretched, films which are 
"heat shrinkable" as that term is used herein have at least 10% 
unrestrained shrinkage at 90.degree. C. (10% in both the machine direction 
(M.D.) and transverse direction (T.D.) for biaxially stretched films). 
Such known films include structures of the following 
types:Ionomer/PE/Nylon, Ionomer/EVA/Nylon, EAA/Nylon:EVOH/Ionomer, and 
PE/EVOH:Nylon/PE. Some of these EVOH containing heat shrinkable films have 
an oxygen permeability in the high barrier range. 
Also, recycling of PVDC polymers is difficult, particularly where the waste 
polymer is mixed with other polymers having different melting points. 
Attempts to remelt film containing PVDC frequently results in degradation 
of the PVDC component. For this reason EVOH has been employed as an 
alternative barrier layer. However, use of EVOH in multilayer structures 
frequently leads to undesirably poor optical properties, especially high 
haze, and to film structures which are difficult to process and orient. 
EVOH is a very stiff material and layers containing EVOH often delaminate 
from adjoining layers or crack during processing and orientation thereby 
exhibiting lines, streaks, and other undesirable optical properties. 
Commercially available bags are made by transversely sealing a tubular 
stock of either monolayer or multilayer film and cutting off the tube 
portion containing the sealed end, or by making two spaced apart 
transverse seals on a tubular stock and cutting open the side of the tube, 
or by superimposing flat sheets of film and sealing on three sides, or by 
end folding flat sheets and sealing two sides. 
Generally heat sealing of thermoplastic film is accomplished by applying 
sufficient heat and pressure to adjacent film layer surfaces for a 
sufficient time to cause a fusion bond between the layers. 
A common type of seal used in manufacturing bags is known to those skilled 
in the art as a hot bar seal. In making a hot bar seal, adjacent 
thermoplastic layers are held together by opposing bars of which at least 
one is heated to cause the adjacent thermoplastic layers to fusion bond by 
application of heat and pressure across the area to be sealed. For 
example, bags may be manufactured from a tube stock by making one hot bar 
seal transverse to the tube. This seal may also be referred to as a bottom 
seal. Once the bottom seal is applied, the tube stock may be transversely 
cut to form the mouth of the bag. 
Once a food product such as meat or poultry is inserted into the bag, the 
package is typically evacuated and the bag mouth sealed. At one time, the 
standard method for sealing a bag was to fasten a clip around the mouth of 
the bag. Although this method is still used, more recently, heat sealing 
techniques have been employed to seal bags. For example, a bag mouth may 
be hot bar sealed or it may be sealed by another common type of heat seal 
known as an impulse seal. An impulse seal is made by application of heat 
and pressure using opposing bars similar to the hot bar seal except that 
at least one of these bars has a covered wire or ribbon through which 
electric current is passed for a very brief time period (hence the name 
"impulse") to cause the adjacent film layers to fusion bond. Following the 
impulse of heat the bars are cooled (e.g. by circulating coolant) while 
continuing to hold the bag inner surfaces together to achieve adequate 
sealing strength. 
One problem which occurs during impulse heat sealing of known films is that 
the film in the seal area often becomes extruded during sealing. This 
results in thinning of the film in the seal area and therefore reduces the 
strength of the film at the seal or in extreme situations, allows the 
thinned film to be too easily severed or pulled apart. Those skilled in 
the art refer to severely extruded seals as "burn through" seals. Thus, a 
"burn through" seal does not have adequate strength or integrity to seal 
in or protect the packaged product. One attempt to solve this "burn 
through" problem is to irradiate the film prior to manufacture of the bag. 
Irradiation of a multilayer film causes the various irradiated layers in 
the film to crosslink. Under controlled conditions, crosslinking by 
irradiation raises and may also broaden the temperature range for heat 
sealing, and may also enhance the puncture resistance of the film. 
Disadvantageously, if the heat sealing layer of the thermoplastic film is 
crosslinked too heavily, the highly crosslinked layer is more difficult to 
melt or fusion bond which makes it difficult to achieve strong seals, 
particularly by impulse sealing the bag mouths after filling with meat or 
poultry. All of the bag seals (including those made by both the bag 
manufacturers and the food processor and by whatever means including 
either or both hot bar seals and impulse seals must maintain their 
integrity to preserve and protect the enclosed food product. 
There must be a strong continuous seal to prevent unwanted egress and 
ingress of gaseous, liquid or solid materials between the bag exterior and 
interior. This is particularly necessary when the food-containing package 
is made of heat shrinkable film and is to be cooked in steam or hot water 
and/or immersed in hot water to shrink the film against the packaged food 
since such shrinkage increases the stress on these seals. Thus, there is a 
continuing need for multilayer films which can be made into bags having 
strong seals especially when formed by hot bar sealing or impulse sealing. 
Such films should provide strong seals able to withstand a range of 
temperatures and also be able to produce such seals over a wide sealing 
temperature range without burn through. 
Variations in sealing temperatures, times and pressure are known to exist 
not only from one brand and/or type of sealers to another but also between 
different sealing machines sold by the same manufacturer under the same 
brand identification. Such variations, which may be due to factors such as 
variation in the manufacturer's product or varying equipment settings or 
installation, increase the desirability for films which may be heat sealed 
to produce strong integral seals over a wide range of temperatures and 
therefore be usefully sealed on different sealing machines. 
Another problem encountered during heat sealing is that of inadvertent 
folding. Normally, a heat seal is made by applying heat and pressure 
across two sheets or portions of film e.g. the two opposing sides of a 
flattened tube, however, occasionally the area to be sealed will be 
inadvertently folded to produce a section of film having four or six 
sheets or film portions which are pressed between the opposing sealer 
bars. In such situations it is desirable to be able to seal the film 
without burn through. A wider impulse heat sealing temperature range is 
indicative of a greater latitude in sealing through folds than a narrower 
range. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a multilayer film having a low 
oxygen permeability. 
It is still another object of the invention to provide a film having low 
permeability to water vapor. 
It is another object of the invention to provide a multilayer film having 
controllable meat adhesion. 
It is another object of the invention to provide a multilayer film 
containing EVOH which is delamination resistant. 
It is another object of the invention to provide a film of sufficient 
integrity to withstand the cook-in process with intact seals and film 
layers. 
It is another object of the invention to provide a heat sealable film 
capable of forming high strength fusion bonds. 
It is another object of the invention to provide a multilayer film 
containing EVOH which has high shrinkage values at 90.degree. C. or less. 
It is a further object of the invention to provide an irradiatively 
crosslinked, multilayer film having an EVOH core layer having a broad 
impulse heat sealing voltage range. 
It is yet another object of the invention to provide an EVOH containing 
multilayer film having good optical properties. 
It is a further object of the invention to provide a chlorine-free 
packaging film. 
It is an object of the invention to provide a film for packaging foods such 
as hams which are cooked and shipped in the same film. 
It is another object of the invention to provide a packaged cook-in 
foodstuff using a multilayer film having a oxygen barrier layer. 
The above and other objects, benefits and advantages of the invention will 
be apparent from the disclosure below which is exemplary and nonlimiting. 
It is not necessary that each and every object listed above be found in 
all embodiments of the invention. It is sufficient that the invention may 
be usefully employed. 
According to the present invention an article such as a foodstuff, 
especially ham, is packaged in a multilayer, thermoplastic, flexible film 
of at least five layers arranged in sequence (first, second, third, 
fourth, fifth) and in contact with one another. The first layer comprises 
at least 50% by weight of a copolymer of propene and at least one 
.alpha.-olefin selected from the group consisting of ethylene, butene-1, 
methylpentene-1, hexene-1, octene-1 and mixtures thereof having a propene 
content of at least 60 wt. %. The second layer is comprised of a blend of 
(i) at least 10% of a first copolymer of ethylene and at least one C.sub.4 
-C.sub.8 .alpha.-olefin having a copolymer density of from 0.900 to 0.915 
g/cm.sup.3 and a melt index of less than 1.0 dg/min., and (ii) at least 
10% of a second copolymer of ethylene with from 4 to 18% of a vinyl ester 
or alkyl acrylate, and (iii) at least 10% of an anhydride-modified third 
copolymer of ethylene with at least one .alpha.-olefin, a vinyl ester or 
an alkyl acrylate, and optionally from 0 to 30% of a fourth copolymer of 
ethylene and at least one C.sub.3 -C.sub.8 .alpha.-olefin having a density 
less than 0.900 g/cm.sup.3 and a melting point less of less than 
85.degree. C. The second layer may also optionally contain a propene 
copolymer as described above for the first layer. The third layer is a 
core layer which comprises at least 80 weight percent, preferably at least 
90 weight percent, ethylene vinyl alcohol copolymer having an ethylene 
content of about 38 mole percent or higher. In a preferred embodiment this 
third layer may have a thickness of about 0.05 to 0.3 mil (1.7-7.62 
microns),and preferably 0.14 to 0.2 mil (4.1-5.1 microns). The fourth 
layer may be the same or different from the second layer but is comprised 
of a blend of resins as described above for the second layer. The fifth 
layer comprises a blend of (i) at least 30% of a first copolymer of 
ethylene with at least one C.sub.4 -C.sub.8 .alpha.-olefin having a 
copolymer density of from 0.900 to 0.915 g/cm.sup.3 and a melt index of 
less than 1.0 dg/min.; (ii) at least 10% of a second copolymer of ethylene 
with from 4 to 18% of a vinyl ester or alkyl acrylate; and (iii) 
optionally from 0 to 30% of a third copolymer of ethylene and at least one 
C.sub.3 -C.sub.8 .alpha.-olefin having a density less than 0.900 
g/cm.sup.3 and a melting point less of less than 85.degree. C. Preferably, 
the inventive film will be heat sealable having at least one layer which 
is crosslinked, preferably by irradiation. In a highly useful embodiment 
of the invention, the film will be heat shrinkable at temperatures such as 
90.degree. C. or lower, and may have shrinkage values in one or both of 
the MD and TD directions of at least about 20%, and advantageously e.g. 
for packaging cook-in foods such as ham or poultry breasts may be at least 
30%. 
In one embodiment of the invention, a process for making the 
above-described film is claimed. The film is useful to process and/or 
package articles, especially foodstuffs such as ham, beef, poultry, or 
processed meat which may be cooked in the film.

DETAILED DESCRIPTION OF THE INVENTION 
The inventive film, bag, process and package of the present invention may 
be used as a heat sealable, oxygen and moisture barrier film for holding a 
foodstuff during cooking and/or for packaging for sale of such a foodstuff 
after a pasteurization or cooking period. 
The present invention is particularly well adapted to processing and 
packaging pasteurizable foods, and has particular utility in packaging 
cook-in hams. "Cook-in" is the term used to indicate a film or bag in 
which a foodstuff is pasteurized or cooked. This film or bag is used to 
hold together, protect and/or form the shape of the foodstuff by a food 
processor (manufacturer) during the cooking or pasteurization process 
after which the film may be removed (sometimes termed "stripped"), or may 
be left on as a protective barrier during shipping, and optionally even 
left on during retail sale. 
Some of the benefits of the inventive film include: relatively low 
permeability to oxygen and water vapor; high delamination resistance and 
an unexpectedly good combination of delamination resistance especially at 
elevated temperatures simulating cook-in conditions and orientability 
resulting in good low temperature heat shrinkability; resistance to 
degradation by food acids, salts and fat; high shrinkage values at low 
temperatures (90.degree. C. or lower); residual shrink force which forms 
and maintains a compact product; controllable meat adhesion; good to 
excellent heat sealability especially over a broad voltage range on 
commercial sealers; low levels of extractables with compliance with 
governmental regulations for food contact; low haze; high gloss; does not 
impart off tastes or odors to packaged food; good tensile strength; a 
surface which is printable; high heat seal strength and a long lasting 
seal especially at cook-in temperatures; and good machinability. 
Advantageously, a preferred embodiment of the invention has low O.sub.2 and 
low water vapor permeabilities in combination with high meat adhesion 
which prevents undesirable cook-out of liquid during processing, good heat 
sealability and high low temperature (90.degree. C. or less) shrinkage 
values. In an especially preferred embodiment, the inventive film has at 
least 20% (more preferably about 30% or higher) shrinkage values in at 
least one direction at 90.degree. C. or less, and preferably at least 25% 
in both directions. Also, preferred films are heat sealable over a broad 
voltage range, and preferably heat shrinkable at low temperatures in 
combination with such broad range heat sealability. 
Also, the oxygen barrier properties of the inventive film reduces or 
eliminates losses from spoilage e.g. by rancidity due to oxidation. The 
inventive films and bags are particularly useful for packaging cook-in 
foodstuffs, but may also be employed as packaging for a wide variety of 
food and non-food articles. 
The present invention may be employed as bags in the various typical sizes. 
By "flatwidth" is meant the transverse width of a flattened tubular film. 
The flatwidth is also equal to 1/2 of the circumference of the tubular 
film. 
The invention in all of its embodiments comprises or utilizes a multilayer 
thermoplastic polymeric flexible film of 10 mils (254 microns) or less 
having a propene-based copolymer layer for food contact which provides 
heat sealability, an EVOH gas barrier layer, an outer abuse resistant 
layer, and adhesive layers which utilize a combination of high molecular 
weight, low molecular weight, highly branched and substantially linear 
polymers to produce a surprisingly orientable film having high 
delamination resistance even under cook-in conditions. The EVOH containing 
layer controls the gas permeability of the film. The propene-based 
copolymer containing layer controls the adherability of the film to an 
enclosed food, which for meat is termed "meat adhesion", and also controls 
heat sealability and seal strength, particularly at elevated temperatures 
and over time. The adhesive layers control delamination resistance to the 
EVOH core layer, and beneficially enhance orientability. 
Such films will preferably have a thickness of about 2-3 mils (50.8-76.2 
microns), although suitable films for packaging foodstuffs as thick as 4 
mils (101.6 microns) or as thin as 1 mil (25.4 microns) may be made. 
Typically, films will be between about 1.5-3 mil (38.1-76.2 microns). 
Especially preferred for use as films for packaging cook-in meats are 
films wherein the multilayer film has a thickness of between about 2 to 3 
mils (50.8-76.2 microns). Such films have good abuse resistance and 
machinability. Films thinner than 2 mils are less abuse resistant and more 
difficult to handle in packaging processes. Advantageously, preferred 
films are heat shrinkable. Preferred films may also provide a beneficial 
combination of one or more or all of the properties including low haze, 
high gloss, high shrinkage values at 90.degree. C. or less, good 
machinability, good mechanical strength and good barrier properties 
including high barriers to oxygen and water permeability. 
Suitable films of the present invention may have low haze and high gloss 
e.g. less than 20% haze and a gloss greater than 50 Hunter Units(H.U.) at 
45.degree.. Advantageously, some preferred embodiments of the present 
invention may have haze values of less than 10-12% and preferably less 
than 6%, and very high gloss values e.g. greater than 65 Hunter Units and 
preferably greater than 75 H.U.. 
The inventive article is preferably a heat shrinkable multilayer film which 
must have at least five layers. These five essential layers are termed the 
first layer, the second layer, the third layer, the fourth layer, and the 
fifth layer. The first layer and fifth layer are disposed on opposing 
sides of the third layer and are preferably attached thereto by the second 
and fourth adhesive layers, respectively. These five layers are essential 
to the film of this invention. When the film is in tube or bag form these 
layers comprise the wall of the tube or bag. This wall in cross-section 
has the first layer comprising an outer layer disposed closest to the 
tube's (or bag's) interior surface with the fifth layer being an opposing 
outer layer typically disposed closest to the tube's (or bag's) exterior 
surface. 
It is contemplated according to the present invention that tubular films 
having more than five layers may be constructed and that such additional 
layers may be disposed as additional intermediate layers lying between the 
third layer(also called the core layer) and either or both of the first 
and fifth layers, or these additional layers may comprise one or more 
surface layers and comprise either or both the interior or exterior 
surface of the tube. Preferably, the first layer will comprise the 
interior surface layer of the tube where in use it will contact a 
foodstuff encased by the tube. 
Beneficially, this first layer will be heat sealable to facilitate 
formation of bags and hermetically sealed packages. Advantageously, the 
first layer as the interior surface layer will, when used to package 
foodstuffs, be suitable for contact with foodstuffs containing protein, 
water and fat without evolving or imparting harmful materials; off tastes 
or odors to the foodstuff. Beneficially, the first layer may be the 
interior surface layer and may consist essentially of a propene 
.alpha.-olefin copolymer. If desired, an ionomeric resin may be used 
either alone or blended in one or more of the layers but such use is 
unnecessary to produce a film suitable for packaging cook-in foodstuffs. 
Advantageously, the heat sealing layer and indeed the entire film may be 
free of ionomer polymer yet provide entirely satisfactory performance 
without the added expense of using costly ionomer resin. 
Also, it is preferred that the fifth layer will comprise the exterior 
surface of the tube or bag. As the exterior surface layer of the tube or 
bag, the fifth layer should be resistant to abrasions, abuse and stresses 
caused by handling and it should further be easy to machine (i.e. be easy 
to feed through and be manipulated by machines e.g. for conveying, 
packaging, printing or as part of the film or bag manufacturing process). 
It should also facilitate stretch orientation where a high shrinkage film 
is desired, particularly at low temperatures such as 90.degree. C. and 
lower. 
Advantageously, the first layer will be predominantly comprised of 
propylene copolymers having a propylene(propene) content of 60 wt. % or 
more. Such layer is preferably an interior surface layer of the tube or 
bag. 
The surface layers function to protect the core layer from abuse and may 
also protect it from contact with moisture which may impact or alter the 
gas barrier properties of the core layer EVOH and/or nylon. 
Beneficially, in the present invention there are intermediate adhesive 
layers on either side of the EVOH core layer(third layer). The second 
layer of this film is generally an unusually thick adhesive layer which in 
addition to providing delamination resistance between the adjacent EVOH 
layer and the opposing layer, also contributes to ease of orientation and 
facilitates formation of a biaxially stretched film having high shrinkage 
values particularly at low temperatures (90.degree. C. or lower) in 
combination with optical properties which are superior to many prior art 
films. Use of an adhesive layer directly adhered to either side of the 
core layer produces a film which is extremely resistant to delamination 
and which may be oriented to produce film having high shrinkage of 30% or 
higher at 90.degree. C. or less. 
In a preferred embodiment, the EVOH core layer directly adheres to the 
second and fourth layers which function as adhesive layers and in turn are 
optionally directly adhered respectively to either (or preferably both) 
the interior(first) and exterior(fifth) layers. In a most preferred 
embodiment the film article consists essentially of five polymeric layers 
viz the interior(first) layer, the adhesive(second) layer, the core(third) 
layer; the adhesive(fourth) layer and the exterior(fifth) layer. This 
preferred embodiment provides a desirable combination of properties such 
as low moisture permeability, low O.sub.2 permeability, controllable meat 
adhesion, high gloss, good mechanical strength, chlorine-free 
construction, and desirable shrink forces in a low temperature heat 
shrinkable, multilayer packaging film which is delamination resistant, 
heat sealable and which can be biaxially oriented. The core layer may 
optionally have processing aids or plasticizers. Nylon may optionally be 
incorporated in amounts up to 20 wt. %. 
Typical layer thicknesses for the essential layers of the inventive heat 
shrinkable film may be about 5-40% first (typically interior surface) 
layer, 25-70% second (adhesive) layer, 3-13% third (core) layer, 1-35% 
fourth (adhesive) layer and 10-50% fifth (exterior) layer, although films 
with differing layer ratio thicknesses are possible. The first layer is 
typically an outer surface layer of the film and in a tubular construction 
is the interior surface layer of the tube. The function of the first layer 
is to provide a layer which has controllable meat adhesion and a surface 
which is heat sealable to itself (or to the second outer layer if a lap 
seal is desired) on commercially available equipment and (for food 
packaging) to provide a hygienic surface for contact with the foodstuff. 
In the present invention, to fulfill these functions the thickness of the 
first layer need not be great, but for an advantageous combination of ease 
of processing and seal performance this layer will preferably be from 
0.1-1.2 mils thick. It is important that this heat sealable layer be 
continuous, e.g. over the interior surface of the tube, and that it be 
extruded at a sufficient thickness to allow heat sealing (if desired). 
Preferably, the first layer is an outer heat sealing layer which allows the 
film to be formed into bags. By the term "heat sealing layer" is meant a 
layer which is heat sealable to itself, i.e., capable of fusion bonding by 
conventional indirect heating means which generate sufficient heat on at 
least one film contact surface for conduction to the contiguous film 
contact surface and formation of a bond interface therebetween without 
loss of the film integrity. Advantageously, the bond interface must be 
sufficiently thermally stable to prevent gas or liquid leakage 
therethrough when exposed to above or below ambient temperatures during 
processing of food within the tube when sealed at both ends, i.e., in a 
sealed bag form. For use in cook-in applications the heat seals should 
withstand elevated temperatures up to about 160.degree.-180.degree. 
F.(71.degree.-82.degree. C.) or higher for extended periods of time e.g. 
up to 4 to 12 hours in environments which may range from heated humidified 
air or steam to submersion in heated water. Finally, the bond interface 
between contiguous inner layers must have sufficient physical strength to 
withstand the tension resulting from stretching or shrinking due to the 
presence of a food body sealed within the tube and optionally subjected to 
pasteurization or cook-in temperatures and conditions. 
Unless otherwise indicated in the present application, percentages of 
materials used in individual layers are based upon the weight of the 
indicated layer. The percentage of comonomer content of a particular 
polymer is based upon the weight of the indicated polymer. 
The first layer especially as the interior surface layer of a tube 
according to the present invention also provides good machinability and 
facilitates passage of the film over equipment (e.g. for inserting 
foodstuffs). This layer may be coated with an anti-block powder. Also, 
conventional antiblock additives, polymeric plasticizers, or slip agents 
may be added to the first outer layer of the film or it may be free from 
such added ingredients. When this layer is corona treated, optionally and 
preferably no slip agent will be used, but it will contain or be coated 
with an anti-block powder or agent such as silica or starch. In one 
embodiment of the invention the first outer layer consists essentially of 
a propene copolymer, or blends thereof. 
Suitable propene copolymer resins for use in the first layer have a propene 
content of at least 60 weight percent, optionally at least 80 wt. %. 
Optionally and preferably these copolymers will have a content of at least 
90 wt. % propene. Copolymerized with propene will be at least one 
.alpha.-olefin selected from the group consisting of ethylene, butene-1, 
hexene-1, methylpentene-1, octene-1 and mixtures thereof in an amount up 
to 40 wt. %. Preferred are bipolymers of propene and ethene (C.sub.3 
C.sub.2 copolymers) as well as C.sub.3 C.sub.4 bipolymers and C.sub.3 
C.sub.2 C.sub.4 terpolymers. Most preferred are C.sub.3 C.sub.2 copolymers 
especially bipolymers. A preferred C.sub.3 C.sub.2 copolymer may have a 
propene content of at least 90% and optionally at least 95 wt. %. 
Preferred propene copolymers have a melting point between about 
126.degree. C. to 145.degree. C., more preferably between about 
129.degree. C. to 136.degree. C. Preferred are random copolymers of 
propylene. A preferred copolymer is commercially available from Solvay & 
Cie as a bioriented film grade resin under the trademark Eltex P KS 409. 
This resin is reportedly a random copolymer of propylene and ethylene 
having a melting point of less than 136.degree. C., a density (p) of about 
0.895 g/cm.sup.3, a Vicat softening point of about 120.degree. C. (ASTM 
1525 (1 Kg)) and a melt index at 230.degree. C. and 2.16 Kg of about 5 
dg/min. 
The first layer of the inventive film comprises a propene copolymer and has 
controllable meat adhesion. The meat adhering attribute of the film may be 
controlled by the absence, presence, and/or extent of surface energy 
treatment e.g., by corona discharge. 
Films of the present invention which had not had their interior surface 
layer (first layer) corona treated will have a typical surface energy of 
at least 29 dynes per cm and typically less than 33. Corona treatment of 
the first layer can raise the surface energy to levels of at least 33 
dynes/cm, preferably at least 34 dynes/cm. Most preferably levels of from 
about 35 to 38 dynes/cm will be usefully employed to produce films of the 
invention having high meat adhesion. Films that have high meat adhesion 
lessen cook-out of meat juices which if not prevented may lead to loss of 
product weight. Also, cook-out can produce an undesirable package 
appearance for applications where the processing/packaging film is 
intended to be left on the product for post-processing sale and use. 
Inventive films with low meat adhesion find utility in cook and strip 
applications where the film is typically removed from the encased 
foodstuff directly after cooking or pasteurization. The product after 
removal of the film is further processed or repackaged. Low meat adhesion 
films of the invention typically have a surface energy of less than 33 
dynes/cm.. 
The core layer functions as a controlled gas barrier, and provides the 
necessary O.sub.2 barrier for preservation of the article to be packaged. 
It should also provide good optical properties when stretch oriented, 
including low haze and a stretching behavior compatible with the layers 
around it. It is desirable that the thickness of the core layer be less 
than about 0.45 mil (10.16 microns) and greater than about 0.05 mil (1.27 
microns) to provide the desired combination of the performance properties 
sought e.g. with respect to oxygen permeability, shrinkage values 
especially at low temperatures, ease of orientation, delamination 
resistance, and optical properties. Suitable thicknesses are less than 15% 
e.g. from 3 to 13% of the total film thickness. Preferably, the thickness 
of the core layer will also be less than about 10% of the total thickness 
of the multilayer film. 
The core layer comprises EVOH which will control the oxygen permeability of 
the film. For perishable food packaging, the oxygen (O.sub.2) permeability 
desirably should be minimized. Typical films will have an O.sub.2 
permeability of less than about 20 cm.sup.3 /m.sup.2 for a 24 hour period 
at 1 atmosphere, 0% relative humidity and 23.degree. C., and preferably 
less than 15 cm.sup.3 /m.sup.2, more preferably less than 10 cm.sup.3 
/m.sup.2. 
EVOH is prepared by the hydrolysis (or saponification) of an ethylene-vinyl 
acetate copolymer, and it is well known that to be an effective oxygen 
barrier, the hydrolysis-saponification must be nearly complete, i.e. to 
the extent of at least 97% (use of which is likewise preferred for the 
present invention). EVOH is commercially available in resin form with 
various percentages of ethylene and there is a direct relationship between 
ethylene content and melting point. 
In the practice of this invention, the EVOH component of the core layer has 
a melting point of about 175.degree. C. or lower. This is characteristic 
of commercially available EVOH materials having an ethylene content of 
about 38 mole % or higher. Suitable EVOHs having an ethylene content of 38 
mole % have a melting point of about 175.degree. C. With increasing 
ethylene content the melting point is lowered. A melting point of about 
158.degree. C. corresponds to an ethylene content of 48 mole %. Preferred 
EVOH materials will have an ethylene content of 44 mole %. EVOH copolymers 
having higher ethylene contents may be employed and it is expected that 
processability and orientation would be facilitated, however gas 
permeabilities, particularly with respect to oxygen may become undesirably 
high for certain packaging applications which are sensitive to product 
degradation in the presence of oxygen. 
The amount of EVOH in the core layer may be adjusted by blending in nylon 
to vary orientation parameters or the gas permeability e.g. O.sub.2 of the 
films of the invention. The thickness of the core layer may also be varied 
from about 0.05 to about 0.30 mils (1.3-7.62 microns). Also, while it is 
preferred that the core layer consist essentially of EVOH, the present 
invention recognizes the possibility not only that up to 20% by weight 
nylon may be present, but also other additives including polymers may be 
blended into the core layer to purposefully affect core layer properties 
such as gas permeability or moisture resistance in minor amounts. 
When blending the EVOH of the oxygen barrier layer with nylon, nylon 6/66 
is the preferred polyamide in the blend. Nylon 6/66 is a copolymer of 
nylon 6 and nylon 66. Nylon 6 is polyepsilon caprolactam. Nylon 66 is the 
polymer derived from adipic acid and hexamethylene diamine. 
Nylon 6/66 is manufactured by different companies, in some instances with 
different percentages of the two monomers, possibly by different methods 
and presumably with different operating parameters. Accordingly, the 
properties of various nylon 6/66 copolymers may differ significantly. For 
example, the melting temperature decreases as the nylon 66 content is 
increased from 5% to 20 mole %. 
When other nylons such as type 6,12 are used as the polyamide in the 
polymer blend of the oxygen barrier layer, numerous gels develop in the 
core layer of the five layer film and in some instances cracks develop. 
The gels may be due to EVOH-nylon 6,12 incompatibility or chemical 
reaction between the two polymers. The cracks probably develop because the 
polymer blend is not stretching uniformly during the orientation. These 
numerous gels and cracks are undesirable in films for commercial use to 
package foodstuffs and indicate potential weak spots in the film integrity 
and permeability properties. 
A preferred nylon is a nylon 6/66 copolymer having a melting point of about 
195.degree. C., which has a reported nylon 6 component content of about 85 
mole % and a nylon 66 component content of about 15 mole % and which is 
commercially available from Allied Chemical Co. of Morristown, N.J., 
U.S.A. under the trademark CAPRON XTRAFORM.TM. 1539F. 
The core layer must be at least 80% by weight EVOH and optionally may 
contain from 0-20 wt. % of nylon. Use of greater amounts of nylon (e.g. 
greater than 10% and particularly greater than 20%) results in undesirably 
high oxygen permeability. 
The second and fourth layers are disposed on either side of the core layer 
and provide good interlayer adhesion characteristics to the multilayer 
structure. Either or both of these layers may also contribute to the 
shrinkability and/or optical properties of the inventive film. The 
composition of each of the second and fourth layers comprises at least 10% 
of a first copolymer of ethylene and at least one C.sub.4 -C.sub.8 
.alpha.-olefin, said copolymer having a density of from 0.900 to 0.915 
g/cm.sup.3 and a melt index of less than 1.0 dg/min.. This first copolymer 
is a very low density polyethylene. 
The expression very low density polyethylene ("VLDPE") sometimes called 
ultra low density polyethylene ("ULDPE"), as used herein refers to 
substantially linear polyethylenes having densities below about 0.915 
g/cm.sup.3 and, possibly as low as 0.86 g/cm.sup.3, and having at least 
one melting point of at least 90.degree. C. This expression does not 
include ethylene alpha olefin copolymers of densities below about 0.90 
g/cm.sup.3 with elastomeric properties and referred to as elastomers. Some 
elastomers are also referred to by at least one manufacturer as "ethylene 
alpha olefin plastomers", but other manufacturers have characterized VLDPE 
as an ethylene .alpha.-olefin with plastomeric properties. However, as 
hereinafter explained, ethylene alpha-olefin elastomers or plastomers may 
be advantageously used in the practice of this invention as a minor 
constituent in certain layers of this multilayer film. VLDPE does not 
include linear low density polyethylenes (LLDPE) which have densities in 
the range of 0.915-0.930 gm/cm.sup.3, but it is contemplated that LLDPE 
may optionally be blended into one or more of the layers. VLDPE's as the 
term is used herein may be made by a variety of processes including 
solution or fluidized bed processes using a variety of catalysts including 
traditional Ziegler-Natta, single-site constrained geometry or metallocene 
catalysts. 
VLDPE comprises copolymers (including terpolymers) of ethylene with 
alpha-olefins, usually 1-butene, 1-hexene or 1-octene, and in some 
instances terpolymers, as for example of ethylene, 1-butene and 1-hexene. 
A process for making VLDPEs is described in European Patent Document 
publication number 120,503 whose text and drawing are hereby incorporated 
by reference into the present document. 
As for example described in Ferguson et al. U.S. Pat. No. 4,640,856 and 
Lustig et al. U.S. Pat. No. 4,863,769, VLDPEs are capable of use in 
biaxially oriented films and have superior properties to comparably made 
films having LLDPEs. These superior properties include higher shrink, 
higher tensile strength and greater puncture resistance. 
Suitable VLDPEs include those manufactured by Dow Chemical Company, Exxon 
Chemical Company and Union Carbide Corporation. 
The composition of each of the second and fourth layers also comprises at 
least 10% of a second copolymer of ethylene with from 4 to 18% of a vinyl 
ester or alkyl acrylate, and, and at least 10% of an anhydride-modified 
third copolymer of ethylene with at least one .alpha.-olefin, a vinyl 
ester or an alkyl acrylate, and from 0 to 30% of a fourth copolymer of 
ethylene and at least one C.sub.3 -C.sub.8 .alpha.-olefin having a density 
less than 0.900 g/cm.sup.3 and a melting point less of less than 
85.degree. C. The preferred second copolymer is an ethylene vinyl acetate 
copolymer. 
The expression "ethylene vinyl acetate copolymer" (EVA) as used herein 
refers to a copolymer formed from ethylene and vinyl acetate monomers 
wherein the ethylene derived units (monomer units) in the copolymer are 
present in major amounts (by weight) and the vinyl acetate derived units 
(monomer units) in the copolymer are present in minor, by weight, amounts. 
The composition of the second layer may be identical or different from that 
of the fourth layer within the parameters of the above defined structure. 
For example the specific first, second and third polymers used may differ 
from one layer to the other or they may be partially or completely the 
same or in the same or different amounts. Also, the optional fourth 
polymer and other ingredients not required by this invention may also be 
present in one or both layers, and the relative thicknesses of each layer 
may vary. Beneficially the second layer will often be thicker than the 
fourth layer to provide good moisture barrier properties in addition to 
good shrinkability. The optional fourth component is often referred to as 
a "plastomer". 
The first copolymer of either or both of the second and fourth layers may 
comprise from 10 to 70% of each respective layer. The second copolymer of 
either or both of the second and fourth layers may comprise from 10 to 40% 
of each respective layer. The third copolymer of either or both of the 
second and fourth layers may comprise from 10 to 60% of each respective 
layer. The fourth copolymer of either or both of the second and fourth 
layers may comprise at least 10% of each respective layer. 
The fifth layer provides mechanical strength, shrinkability, abrasion 
resistance and resists burn through during heat sealing. This fifth layer 
is typically sufficiently thick to provide support, heat shrinkability, 
and impart strength to the packaging film wall in order to withstand the 
shrinking operation, handling pressures, abrasion, and packaging with a 
foodstuff. As an outer surface layer of the film, the fifth layer provides 
a desirable glossy appearance. Advantageously, the fifth layer comprises 
at least 30%, preferably at least 40% of a first copolymer of ethylene 
with a minor proportion of one or more C.sub.4 -C.sub.8 alpha-olefins, 
which may provide a water vapor barrier which resists moisture permeation. 
High moisture barrier properties are desirable to avoid weight loss and 
undesirable drying of the enclosed food product. This first copolymer has 
a density of from 0.900 g/cm.sup.3 to 0.915 g/cm.sup.3 and a melt index of 
less than 1.0 dg/min. and is often termed a VLDPE. 
The fifth layer further comprises at least 10 wt. % of a second copolymer 
of ethylene with from 4 to 18% (based on the weight of the second 
copolymer) of a vinyl ester or alkyl acrylate. Preferably, this second 
copolymer comprises EVA. Optionally, included in this fifth layer is from 
0 to 30% of a third copolymer of ethylene and at least one C.sub.3 
-C.sub.8 .alpha.-olefin having a density less than 0.900 g/cm.sup.3 and a 
melting point less than 85.degree. C. This third copolymer is often termed 
a "plastomer" and may also have a average molecular weight distribution 
(M.sub.w /M.sub.n)less than 3, e.g. about 2. Processing aides such as slip 
agents, anti-block agents and the like may also be incorporated into the 
fifth layer as well as into other layers. Such processing aids are 
typically used in amounts less than 10% and preferably less than 5% of the 
layer weight. A preferred processing aid for use in the outer layer of the 
film is a fluoroelastomer. The above ingredients are admixed together and 
extruded to provide a uniformly blended layer having good strength, 
processability, high shrinkage characteristics and good optical properties 
including high gloss. Addition of the third copolymer, in particular, 
contributions to good optical and shrink properties. Advantageously, the 
fifth layer may consist essentially of the first and second copolymers 
with or without the third copolymer and with or without a minor amount 
(&lt;10%) of processing aid. 
The multilayer film of the invention may be made by conventional processes 
including e.g. slot cast or blown film processes, but preferably will be 
made by an orientation process, especially under conditions to produce a 
film which is heat shrinkable at 90.degree. C. or less. For example, a 
packaged foodstuff having a heat shrinkable film enclosure according to 
the invention will advantageously cling to the foodstuff even after 
opening. Non-shrink bags have a tendency to fall away from the sides of 
the enclosed product once the vacuum is broken by either intentional or 
accidental opening. Once the film separates from the enclosed article 
surface, oxygen comes into contact with the article surface and product 
defects on susceptible products such as ham may occur. Some prior art 
films and bags are nonshrink bags which suffer from this defect thereby 
causing spoilage and waste when used to package perishable foodstuffs. 
The five layer film of this invention may be manufactured by coextrusion of 
all layers simultaneously for example as described in U.S. Pat. No. 
4,448,792 (Schirmer) or by a coating lamination procedure such as that 
described in U.S. Pat. No. 3,741,253 (Brax et al.) to form a relatively 
thick primary multilayer extrudate either as a flat sheet or, preferably, 
as a tube. This sheet or tube is oriented by stretching at orientation 
temperatures which are generally below the melting points for the 
predominant resin comprising each layer oriented. Stretch orientation may 
be accomplished by various known methods e.g. tentering which is commonly 
employed to orient sheets, or by the well-known trapped bubble or double 
bubble technique for orienting tubes as for example described in U.S. Pat. 
No. 3,456,044 (Pahlke). In this bubble technique an extruded primary tube 
leaving a tubular extrusion die is cooled, collapsed and then preferably 
oriented by reheating and inflating to form an expanded secondary bubble 
which is again cooled and collapsed. Preferred films are biaxially 
stretched. Transverse direction (TD) orientation is accomplished by the 
above noted inflation to radially expand the heated film which is cooled 
to set the film in an expanded form. Machine direction (MD) orientation is 
preferably accomplished with the use of sets of nip rolls rotating at 
different speeds to stretch or draw the film tube in the machine direction 
thereby causing machine direction elongation which is set by cooling. 
Orientation may be in either or both directions. Preferably, a primary 
tube is simultaneously biaxially stretched radially (transversely) and 
longitudinally (machine direction) to produce a multilayer film which is 
heat shrinkable at temperatures below the melting points of the major 
polymeric components, e.g. at 90.degree. C. or lower. Axially stretched, 
especially biaxially stretched, films which are "heat shrinkable" as that 
term is used herein have at least 10% unrestrained shrinkage at 90.degree. 
C. (10% in both the machine direction (M.D.) and transverse direction 
(T.D.) for biaxially stretched films). According to the present invention 
one or more of the essential five film layers may be oriented either 
uniaxially or biaxially by axial stretching at temperatures low enough to 
produce low temperature, high shrink multilayer films. Such heat 
shrinkable multilayer films will have at least 10% shrink in at least one 
direction at 90.degree. C., but preferably will have at least 20% shrink 
at 90.degree. C. in at least one direction (preferably both directions) 
and advantageously may have at least 30% shrink at 90.degree. C. in at 
least one direction, and preferably may have at least 25% in both M.D. and 
T.D. directions, and beneficially may have at least 10% shrink at 
74.degree. C. in both M.D. and T.D. directions and preferably at least 15% 
(more preferably at least about 20%) in at least one direction at 
74.degree. C. 
The general annealing process by which biaxially stretched heat shrinkable 
films are heated under controlled tension to reduce or eliminate shrinkage 
values is well known in the art. If desired, films of the present 
invention may be annealed to produce lower shrinkage values as desired for 
the particular temperature. The stretch ratio during orientation should be 
sufficient to provide a film with a total thickness of between about 1.0 
and 4.0 mils. The MD stretch ratio is typically 21/2-6 and the TD stretch 
ratio is also typically 21/2-6. An overall stretch ratio (MD stretch 
multiplied by TD stretch) of about 61/4x-36x is suitable. 
The preferred method for forming the multilayer film is coextrusion of the 
primary tube which is then biaxially oriented in a manner similar to that 
broadly described in the aforementioned U.S. Pat. No. 3,456,044 where the 
primary tube leaving the die is inflated by admission of a volume of air, 
cooled, collapsed, and then preferably oriented by reinflating to form a 
secondary tube termed a "bubble" with reheating to the film's orientation 
(draw) temperature range. Machine direction (MD) orientation is produced 
by pulling or drawing the film tube e.g. by utilizing a pair of rollers 
traveling at different speeds and transverse direction (TD) orientation is 
obtained by radial bubble expansion. The oriented film is set by rapid 
cooling. In the following examples, all five layers were coextruded as a 
primary tube which was cooled upon exiting the die by spraying with tap 
water. This primary tube was then reheated by radiant heaters with further 
heating to the draw temperature (also called the orientation temperature) 
for biaxial orientation accomplished by an air cushion which was itself 
heated by transverse flow through a heated porous tube concentrically 
positioned around the moving primary tube. Cooling was accomplished by 
means of a concentric air ring. 
In a preferred process for making films of the present invention, the 
resins and any additives are introduced to an extruder (generally one 
extruder per layer) where the resins are melt plastified by heating and 
then transferred to an extrusion (or coextrusion) die for formation into a 
tube. Extruder and die temperatures will generally depend upon the 
particular resin or resin containing mixtures being processed and suitable 
temperature ranges for commercially available resins are generally known 
in the art, or are provided in technical bulletins made available by resin 
manufacturers. Processing temperatures may vary depending upon other 
process parameters chosen. However, variations are expected which may 
depend upon such factors as variation of polymer resin selection, use of 
other resins e.g. by blending or in separate layers in the multilayer 
film, the manufacturing process used and particular equipment and other 
process parameters utilized. Actual process parameters including process 
temperatures are expected to be set by one skilled in the art without 
undue experimentation in view of the present disclosure. 
As generally recognized in the art, resin properties may be further 
modified by blending two or more resins together and it is contemplated 
that various resins may be blended into individual layers of the 
multilayer film or added as additional layers, such resins include 
ethylene-unsaturated ester copolymer resins, especially vinyl ester 
copolymers such as E-VAs, or other ester polymers, very low density 
polyethylene (VLDPE), linear low density polyethylene (LLDPE), low density 
polyethylene (LDPE), high density polyethylene (HDPE), nylons, ionomers, 
polypropylenes, or blends thereof. These resins and others may be mixed by 
well known methods using commercially available tumblers, mixers or 
blenders. Also, if desired, well known additives such as processing aids, 
slip agents, antiblocking agents, pigments, etc., and mixtures thereof may 
be incorporated into the film. 
In some preferred embodiments of the invention it is preferred to crosslink 
the entire film to broaden the heat sealing range. This is preferably done 
by irradiation with an electron beam at dosage levels of at least about 2 
megarads (MR) and preferably in the range of 3 to 8 MR, although higher 
dosages may be employed. Irradiation may be done on the primary tube or 
after biaxial orientation. The latter, called post-irradiation, is 
preferred and described in U.S. Pat. No. 4,737,391 (Lustig et al.). An 
advantage of post-irradiation is that a relatively thin film is treated 
instead of the relatively thick primary tube, thereby reducing the power 
requirement for a given treatment level. 
Alternatively, crosslinking may be achieved by addition of a chemical 
crosslinking agent or by use of irradiation in combination with a 
crosslinking enhancer added to one or more of the layers, as for example 
described in U.S. Pat. No. 4,055,328 (Evert et al.). The most commonly 
used cross-linking enhancers are organic peroxides such as 
trimethylpropane and trimethylacrylate. 
These performance levels are desirable for shrink packaging foodstuffs such 
as roast beef, poultry breasts and ham which are susceptible to 
discoloration and spoilage in the presence of oxygen. 
The following are examples and comparative examples given to illustrate the 
present invention. 
Experimental results and reported properties of the following examples are 
based on the following test methods or substantially similar test methods 
unless noted otherwise. 
Tensile Strength: ASTM D-882, Method A 
% Elongation: ASTM D-882. Method A 
Haze: ASTM D-1003-52 
Gloss: ASTM D-2457, 45.degree. angle 
1% Secant Modulus: ASTM D-882, Method A 
Oxygen Gas Transmission Rate (O.sub.2 GTR) : ASTM D-3985-81 
Water Vapor Transmission Rate (WVTR): ASTM F 1249-90 
Elmendorf Tear Strength: ASTM D-1992 
Gauge: ASTM D-2103 
Melt Index: ASTM D-1238, Condition E (190.degree. C.) (except for 
propene-based (&gt;50% C.sub.3 content)polymers tested at Condition 
TL(230.degree. C.)) 
Melting point: ASTM D-3418, DSC with 5.degree. C./min heating rate 
Surface Energy (Wetting Tension):ASTM D-2578-84 
Shrinkage Values: Shrinkage values are defined to be values obtained by 
measuring unrestrained shrink of a 10 cm square sample immersed in water 
at 90.degree. C. (or the indicated temperature if different) for five 
seconds. Four test specimens are cut from a given sample of the film to be 
tested. The specimens are cut into squares of 10 cm length in the machine 
direction by 10 cm. length in the transverse direction. Each specimen is 
completely immersed for 5 seconds in a 90.degree. C. (or the indicated 
temperature if different) water bath. The specimen is then removed from 
the bath and the distance between the ends of the shrunken specimen is 
measured for both the M.D. and T.D. directions. The difference in the 
measured distance for the shrunken specimen and the original 10 cm. side 
is multiplied by ten to obtain the percent of shrinkage for the specimen 
in each direction. The shrinkage of four specimens is averaged for the 
M.D. shrinkage value of the given film sample, and the shrinkage for the 
four specimens is averaged for the TD shrinkage value. As used herein the 
term "heat shrinkable film at 90.degree. C." means a film having an 
unrestrained shrinkage value of at least 10% in at least one direction. 
Shrink Force: The shrink force of a film is that force or stress required 
to prevent shrinkage of the film and was determined from film samples 
taken from each film. Four film samples were cut 1" (2.54 cm) wide by 7" 
(17.8 cm) long in the machine direction and 1" (2.54 cm) wide by 7" (17.8 
cm) long in the traverse direction. The average thickness of the film 
samples was determined and recorded. Each film sample was then secured 
between the two clamps spaced 10 cm apart. One clamp is in a fixed 
position and the other is connected to a strain gauge transducer. The 
secured film sample and clamps were then immersed in a silicone oil bath 
maintained at a constant, elevated temperature for a period of five 
seconds. During this time, the force in grams at the elevated temperature 
was recorded. At the end of this time, the film sample was removed from 
the bath and allowed to cool to room temperature whereupon the force in 
grams at room temperature was also recorded. The shrink force for the film 
sample was then determined from the following equation wherein the results 
is obtained in grams per mil of film thickness (g/mil): 
EQU Shrink Force (g/mil)=F/T 
wherein F is the force in grams and T is the average thickness of the film 
samples in mils. 
Impulse Seal Range: 
The impulse sealing range test determines the acceptable voltage ranges for 
impulse sealing plastic films. A Sentinel Model 12-12AS laboratory sealer 
manufactured by Packaging Industries Group, Inc., Hyannis Mass., U.S.A. 
was used. This impulse sealer is equipped with a replacement sealing 
ribbon for a Multivac AG100 brand packaging machine. The ribbon is 
available from Koch Supplies of Kansas City, Mo. In this test, two four 
inch wide (T.D. direction) samples are cut from a tubular film. The 
impulse sealer is equipped with controls for coolant flow, impulse voltage 
and time, and seal bar pressure. These controls except for impulse voltage 
are set at the following conditions: 
0.5 seconds impulse time (upper ribbon only) 
2.2 seconds cooling time 
50 psi (345 kPa) jaw pressure 
0.3 gallon per minute (1 liter per minute) of cooling (about 75.degree. F. 
(22.degree. C.)) water flow 
One of the samples is folded in half for use in determining a minimum 
sealing voltage. This folding simulates folding which may inadvertently 
occur during conventional bag sealing operations. The folded sample which 
now has four sheets or portions of film (hereinafter referred to as "sheet 
portions") is placed into the sealer and by trial and error the minimum 
voltage to seal the bottom two sheet portions to each other was 
determined. 
The maximum voltage is then determined for a sample having two sheet 
portions by placing it in the sealer and then activating the seal bar. The 
film sample is manually pulled with about 0.5 lbs. of force and the 
voltage which does not cause burn through or significant distortion of the 
seal is determined. 
Seal Strength Test: 
Five identical samples of film are cut 1 inch (2.54 cm) wide and at least 5 
inches (77 cm) long with a 1 inch (2.54 cm) wide seal portion centrally 
and transversely disposed. Opposing end portions of a film sample are 
secured in opposing clamps in a temperature controlled chamber of an 
Instron 4501 Universal Testing Instrument. The film is secured in a taut 
snug fit between the clamps without stretching prior to beginning the 
test. The test chamber door is closed and the chamber is heated to the 
test temperature at which time the instrument is activated to pull the 
film via the clamps traverse to the seal at a uniform rate of 5 inches 
(127 cm) per minute until failure of the film (breakage of film or seal, 
or delamination and loss of film integrity). The lbs. at break are 
measured and recorded. The test is repeated for five samples and the 
average lbs. at break reported. 
Unless otherwise indicated, the impulse seals tested for seal strength were 
made using the equipment described in the impulse seal range test 
description above with controls similarly set but having a cooling time of 
about 8 seconds. 
The hot bar seals of various tested films were made similar to one another 
using settings of at 500.degree. F. (260.degree. C.) and 0.5 seconds dwell 
time. 
Seal Creep: 
The Seal Creep to Failure Test is designed to be an accelerated cook-in 
simulation to determine resistance to seal failure and/or loss of film 
integrity of a processing film over time. In the test, five samples of 1/2 
inch (12.7mm) wide film is cut from one or more similar sealed films with 
the cuts made perpendicular to the seal so that each film sample contains 
a 1/2 inch wide seal and five inches of film on either side of the seal. 
This produces samples which are each 10 inches (25.4 cm) long by 1/2 inch 
(12.7 mm) wide with a seal in the middle. The opposing top and bottom long 
portions of a film sample containing a centrally disposed seal are 
securely attached to respective flat plate clamps which extend over the 
width of the film end. The top film clamp is attached to a fixture while 
the opposing bottom clamp has an attached weight (for a total weight of 
about 1 lb. (454 g). The weighted clamp and lower film portion including 
the seal area are submersed into a circulating bath of temperature 
controlled water set at 165.degree. F. (74.degree. C.). The film seal area 
is positioned about 2-3 inches below the surface of the water and the film 
strip with attached weight is perpendicular to the surface of the water. 
Upon submersion, a timer is started and the film and weight are observed 
and the time noted at which the weight drops signifying film seal failure 
and/or loss of film integrity. The film and weight are observed 
continuously for the first fifteen minutes and then checked at least every 
15 minutes thereafter up to a total test period of 180 minutes. The 
average for five test samples is reported. Minimum and maximum values 
measured for the set may also be reported. 
Following are examples and comparative examples given to illustrate the 
invention. 
In all the following examples, unless otherwise indicated, the film 
compositions were produced generally utilizing the apparatus and method 
described in U.S. Pat. No. 3,456,044 (Pahlke) which describes a 
coextrusion type of double bubble method and in further accordance with 
the detailed description above. All percentages are by weight unless 
indicated otherwise. 
Examples 1.varies.6 
In Examples 1-3, three biaxially stretched, heat shrinkable, multilayer 
films of the present invention were made. The layers of each multilayer 
film were coextruded and biaxially stretched according to a coextrusion 
type of tubular orientation process. 
Examples 1-3 are five layered films. However, films of six or more layers 
are also contemplated by the present invention. The inventive multilayer 
films may include additional layers or polymers to add or modify various 
properties of the desired film such as heat sealability, interlayer 
adhesion, food surface adhesion, shrinkability, shrink force, wrinkle 
resistance, puncture resistance, printability, toughness, gas or water 
barrier properties, abrasion resistance and optical properties such as 
gloss, haze, freedom from lines, streaks or gels. These layers may be 
formed by any suitable method including coextrusion, extrusion coating and 
lamination. 
For Examples 1-3, one extruder was used for each layer and the heat 
plastified resins from each extruder were introduced to a 5 layer spiral 
plate coextrusion die from which the resins were coextruded at an 
first/second/third/fourth/fifth layer thickness ratio of about 
16:43:11:9:21 for Examples 1-3. 
In Examples 1-3, for each layer, the resin or resin mixture was fed from a 
hopper into an attached single screw extruder where the resin and/or 
mixture was heat plastified and extruded through a five layer coextrusion 
spiral plate die into a primary tube. The extruder barrel temperatures for 
the third (core)layer was about 350.degree.-400.degree. F. 
(177.degree.-204.degree. C.); for the first (inner)and second 
(intermediate) layer was about 300.degree. F.(149.degree. C.) ; for the 
fourth (intermediate) layer was about 340.degree. F. (171.degree. C.) and 
for the fifth (outer) layer was about 330.degree.-340.degree. F. 
(166.degree.-171.degree. C). The extrusion die had an annular exit opening 
of 3 inch diameter with a 0.060 inch gap (7.62cm.times.0.152 cm). The 
coextrusion die temperature profile was set from about 340.degree. F. to 
410.degree. F. (171.degree.-210.degree. C.). The extruded multilayer 
primary tube was cooled by spraying with cold tap water (about 
7.degree.-14.degree. C.). 
The cooled primary tube was flattened by passage through a pair of nip 
rollers whose speed was controlled to neck down the primary tube to adjust 
the tube circumference or flatwidth. In Examples 1-3, a flattened tube of 
about 41/8 inches (10.5cm) flatwidth was produced. The cooled flattened 
primary tube was reheated, biaxially stretched, and cooled. 
The cooled film was flattened and the biaxially stretched and biaxially 
oriented film was wound on a reel. The machine direction (M.D.) draw or 
orientation ratio was about 3.7:1 to 3.8:1 and the transverse direction 
(T.D.) bubble or orientation ratio was about 2.8:1 to 2.9:1 for all the 
films. The draw point or orientation temperature was below the predominant 
melting point for each layer oriented and above that layer's glass 
transition point. Draw point temperature, bubble heating and cooling rates 
and orientation ratios are generally adjusted to maximize bubble stability 
and throughput for the desired amount of stretching or orientation. The 
resultant films of Examples 1-3 having an average gauge of 2.5 to 2.7 (See 
Table 2) were biaxially oriented and had an excellent appearance. 
Examples 4 and 5 were made by irradiating at a level of 4 Mrad by electron 
beam after orientation and according to methods well known in the art to 
cause crosslinking, especially of the polymeric second and fourth adhesive 
layers and the outer (fifth) polymeric layer. These examples (4 and 5) 
were also corona treated to make the first layer have adherability to 
proteinaceous foodstuffs such as meat. This property termed "meat 
adhesion" is important for applications where it is desirable to retain 
juices within the meat during cooking or pasteurization while in the bag. 
This is called preventing "cook-out" in which pockets of fat and juices 
can form causing an undesirable appearance, loss of juices and loss of 
weight. In other applications (often termed "cook and strip") it is 
desirable to be able to easily remove the bag from a product following 
cooking or pasteurization; and in these applications the film is not 
corona treated and the inner layer advantageously does not adhere to the 
enclosed foodstuff e.g. meat. In these applications a worker may easily 
remove the bag after processing for further processing, repackaging for 
retail sale or for use. 
For all of the Examples 1-3, the first layer (which was the interior 
surface of the tubular film) comprised a random copolymer of propene and 
ethene having a DSC melting point of 133.degree. C., a reported density of 
0.895 g/cm.sup.2, a melt index of 5 g/10 min., and which is commercially 
available under the trademark Eltex P KS 409 from Solvay & Cie of 
Brussels, Belgium. In examples 1, 2,and 3, the first layer comprised, 
respectively, 100%, 90%, and 80% by weight of the propene-ethene random 
copolymer, and 0%, 10%, and 20% by weight of an LLDPE-based adhesive. The 
LLDPE-based adhesive was an extrudable rubber-modified, anhydride-modified 
linear low density polyethylene based tie layer resin having the following 
reported properties: density of 0.912 g/cm.sup.3, melt index of 1.5 
dg/min., a Vicat softening point of 98.degree. C., a melting point of 
about 125.degree. .C, and is available under the trademark Plexar.RTM. 
PX380 from Quantum Chemical Corporation, Cincinnati, Ohio, U.S.A.. 
The fifth layer of Examples 1-3 (which was the exterior surface of the 
tube) contained an ethylene-.alpha.-olefin copolymer of very low density 
polyethylene sold by Dow Chemical Company of Midland, Mich., U.S.A. under 
the trademark Attane XU 61509.32 which is a copolymer of ethylene and 
octene-1 reportedly having a melt index of about 0.5 dg/min and a density 
of about 0.912 g/cm.sup.3, with a Vicat softening point of 95.degree. C. 
and a melting point of about 122.degree. C. Also in the fifth layer was a 
copolymer of ethylene and vinyl acetate (EVA) as a component of the blend 
of resins. This EVA is available from Exxon Chemical Company of Houston 
Tex., U.S.A. under the trademark Escorene LD 701.06 and has the following 
reported properties: 10.5% vinyl acetate content; 0.93 g/cm.sup.3 density; 
0.19 dg/min. melt index; and a melting point of about 97.degree. C. In 
Examples 1, 2 and 3, the fifth (outer) layer compositions were identical 
and comprised 70.6% of the ethylene-.alpha.-olefin copolymer which was 
blended with 25% of the EVA copolymer and 4.4% by weight of a slip 
processing aid sold under the trademark Ampacet 100031 by Ampacet Corp. of 
Tarrytown, N.Y., U.S.A. 
For Examples 1-3, the second and fourth (intermediate) layers were each 
identical blends comprising 17.5% of the same EVA copolymer used in the 
fifth layer with 42.5% of the same very low density polyethylene used in 
the fifth layer, and 40% of the same extrudable rubber-modified, 
anhydride-modified linear low density polyethylene based tie layer 
adhesive resin (Plexar.RTM. PX380) used in the first layer. The second and 
fifth layers of each of Examples 1-3 were identical to one another except 
that the fourth layers of examples 1-3 were all thinner than the 
corresponding second layers. 
For Examples 1-3, each core layer comprised a 90:10 percent by weight blend 
of a saponified ethylene-vinyl acetate copolymer (EVOH) with a nylon. A 
premix was formed by blending 90% EVOH with 10% nylon. This premixed blend 
was then added to an extruder hopper for extrusion as the core layer. The 
EVOH was a commercially available copolymer sold by Eval Company of 
America of Lisle, Ill., U.S.A. under the trademark EVAL E105A and had the 
following reported properties: an ethylene content of 44 percent by 
weight, a melt index of 5.5 dg/min, a density of 1.14 and a melting point 
of 165.degree. C. The nylon was a commercially available nylon 6/66 
copolymer sold by Allied Chemical Company under the trademark CAPRON 
XTRAFORM 1539F and had a reported nylon 6 content of 85 mole % and nylon 
66 content of 15 mole % with a DSC melting point of about 195.degree. C., 
and a density of 1.13 g/cm.sup.3. 
Comparative Example 6 is not of the invention, but is a prior art example 
of a commercial film used for cook-in packaging of e.g. hams. The 
comparative film of Example 6 is believed to be a six layer film of the 
structure C.sub.3 -.alpha.-olefin copolymer/EVA/Adhesive/EVOH(44 mole % 
ethylene)/Adhesive/EVA. All of the examples including the comparative 
example are heat shrinkable at 90.degree. C. Example 6 is believed to have 
a composition and layer thicknesses of about 0.5 mil for the 1st (C.sub.3 
copolymer)layer; 0.6 mil for the combined 2nd (EVA) layer and 3rd 
(adhesive) layer; 0.2 mil for the 4th (EVOH)layer; and combined 1.2 mils 
for the 5th (adhesive) and 6th (EVA) layer. 
Layer formulations of Example 1-5 are reported in Table 1. Physical 
properties of the films of Examples 1-6 were measured and are reported in 
Tables 2-4. 
TABLE 1 
__________________________________________________________________________ 
Layer Composition 
First Layer 
Second Third Layer Fifth Layer 
Ex. No. 
(Inner) 
Layer (Core) 
Fourth Layer 
(Outer) 
__________________________________________________________________________ 
1 100% C.sub.3 C.sub.2 
42.5% VLDPE 
90% EVOH 
Same as 2nd 
70.6% VLDPE 
17.5% EVA 
10% Nylon 
Layer 25% EVA 
40% Adhesive* 4.4% Processing Aid 
2 90% C.sub.3 C.sub.2 
Same as 
90% EVOH 
Same as 2nd 
70.6% VLDPE 
10% Adhesive* 
Ex. 1 10% Nylon 
Layer 25% EVA 
4.4% Processing Aid 
3 80% C.sub.3 C.sub.2 
Same as 
90% EVOH 
Same as 2nd 
70.6% VLDPE 
20% Adhesive* 
Ex. 1 10% Nylon 
Layer 25% EVA 
4.4% Processing Aid 
4 Same as 
Same as 
Same as 
Same as 
Same as 
Ex. 1 Ex. 1 Ex. 1 Ex. 1 Ex. 1 
5 Same as 
Same as 
Same as 
Same as 
Same as 
Ex. 3 Ex. 3 Ex. 3 Ex. 3 Ex. 3 
__________________________________________________________________________ 
*The adhesive is a rubbermodified, anhydridemodified LLDPE adhesive 
(Plexar PX 380). 
TABLE 2 
__________________________________________________________________________ 
SHRINK FORCE 
SHRINK FORCE 
Avg TENSILE at 90.degree. C. 
at RT 
at 74.degree. 
at RT 
GAUGE 
FLAT ELONGATION 
STRENGTH .times. 10.sup.3 
SHRINK 
SHRINK gm/mil 
gm/mil 
gm/mil 
gm/mil 
Ex. mil WIDTH 
AT BREAK % 
psi at RT 
at 90.degree. C. 
at 74.degree. C. 
(Kg/cm) 
(Kg/cm) 
(Kg/cm) 
(Kg/cm) 
No. (micron) 
(mm) at RT MD/TD 
(MPa) MD/TD 
% MD/TD 
% MD/TD 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
__________________________________________________________________________ 
1 2.53 314 ND ND 17/35 
8/20 84/163 
57/149 
36/168 
22/159 
(64.3) (33/64) 
(22/59) 
(14/66) 
(9/63) 
2 2.77 298 ND ND 20/35 
10/23 114/173 
77/155 
81/158 
59/154 
(70.4) (45/68) 
(30/61) 
(32/62) 
(23/61) 
3 2.69 298 ND ND 21/36 
9/24 113/170 
59/88 
88/173 
72/165 
(68.3) (45/67) 
(23/35) 
(35/68) 
(28/65) 
4 2.31 ND 105/215 7.0/7.0 14/31 
5/18 51/168 
35/149 
43/155 
37/144 
(58.7) (20/66) 
(14/59) 
(17/61) 
(15/57) 
5 2.66 ND 144/217 8.5/7.0 19/34 
9/21 121/157 
83/149 
85/166 
68/157 
(67.6) (48/62) 
(33/59) 
(33/65) 
(27/62) 
6 2.48 337 126/85 6.5/6.6 30/42 
12/19 77/115 
60/92 
68/108 
54/78 
(63.0) (30/45) 
(24/36) 
(27/43) 
(21/31) 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
TABLE 3 
__________________________________________________________________________ 
1% Secant 
TEAR HOT H.sub.2 O 
Modulus 
STRENGTH 
DYNAMIC 
PUNCTURE 
O.sub.2 GTR.dagger.* 
GLOSS 
EX. 
MD/TD 
MD/TD PUNCTURE 
95.degree. C. 
at RT 
HAZE 
AT 45.degree. 
No. 
MPa g/.mu. 
cmKg/.mu. 
.mu./seconds 
0% RH 
% ANGLE 
__________________________________________________________________________ 
1 ND ND ND ND 11 7.3 
71 
(64) 
2 ND ND ND ND ND 19.1 
44 
3 ND ND ND ND ND 22.3 
45 
4 323/293 
1.3/1.1 
0.04 79.2/22** 
12 9.2 
68 
(71) 
5 293/268 
1.0/1.4 
0.04 66.3/14 
14 19.3 
45 
(69) 
6 352/375 
0.55/0.55 
0.03 69.6/29 
13 18.4 
53 
(61) 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
RH = RELATIVE HUMIDITY 
.dagger.Oxygen gas transmission rate (O.sub.2 GTR) in units of cm.sup.3 
per meter.sup.2 per 24 hours at 1 atmosphere for the film tested. 
*For O.sub.2 GTR the film thickness is below the rate in microns (). 
**Average of 5 values; a sixth value in excess of 120 seconds for a 89.mu 
film was also obtained. 
TABLE 4 
__________________________________________________________________________ 
SEAL CREEP 
SEAL STRENGTH 
SEAL STRENGTH 
IMPULSE 
TO FAILURE 
Impulse Seal 
Hot Bar Seal 
SURFACE 
SEAL RANGE 
at 165.degree. F. (74.degree. C.) 
at 160.degree. F. (71.degree. C.) 
at RT/160/170/180/190.degree. F. 
Ex. 
ENERGY 
min./max. 
avg./min./max. 
at 40 v/43 v/46 v/49 v 
(RT/71/77/82/88.degree. C.) 
No. 
(dynes/cm) 
(volts) 
(minutes) 
(g/cm) (g/cm) 
__________________________________________________________________________ 
1 31 ND ND ND ND 
2 ND ND ND ND ND 
3 32 ND ND ND ND 
4 34 44/46 115/&lt;1/180 
697/731/738/708 
1939/958/ND/ND/677 
5 35 35/46 137/26/180 
627/606/618/633 
1630/1010/ND/ND/688 
6 36 32/50 1/&lt;1/4 604/506/590/564 
ND/792/677/717/651* 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
*This was a factory seal and the sealing method was undetermined. 
The results in Table 2 demonstrate that films according to the present 
invention have good physical properties. The elongation at break, tensile 
strength, unrestrained shrink, and shrink force properties of Examples 1-5 
of the invention are comparable to commercially available films for 
packaging cook-in foods as exemplified by comparative Example 6. Although 
comparative Example 6 has slightly better unrestrained shrink values than 
the films of the Examples 1-5, all of the inventive films have adequate 
and excellent unrestrained shrink values for many utilities including 
packaging of foodstuffs. The elongation at break and tensile strength 
values of the Examples 4 and 5 are generally as good or better than those 
reported for the comparative film of Example 6. For packaging articles, 
the reported elongation at break values for the example films of the 
invention have very good extensibility which is adequate to accommodate 
any stretching encountered under typical packaging and process conditions. 
The shrinkage values for Examples 1-5 are good for a film containing EVOH. 
The transverse direction values are all greater than 30.degree. at 
90.degree. C. and shrinkage at lower temperatures of 74.degree. C. are 
similar to the 74.degree. C. shrinkage values for comparative Example 6. 
The present invention is capable of producing films with even higher 
shrinkage values in both directions at the test temperatures. Therefore 
the inventive films may have desirably high shrinkage values which may be 
greater than 20% in either or both directions at 90.degree. C. and 
beneficially may be greater than 30%. High shrinkage especially at 
90.degree. C. or lower is an advantage in packaging articles to provide 
close contact between the film and the enclosed article surface which 
prevents or lessens damage which may be caused by contact with oxygen or 
by movement of the article within the package. A further advantage is that 
good shrinkage values may be obtained at a lower temperature thereby using 
a shrinking process which has lower energy requirements. 
Also the shrink forces reported for Examples 1-5, especially the residual 
shrink forces, are at levels desirable to hold the film in close contact 
with the enclosed article not only during possible processing subsequent 
to packaging e.g. pasteurization, but also at room temperature. The 
residual shrink force at room temperature is important e.g. when a package 
may be opened exposing one end to the deleterious effects of exposure to 
the environment. Films and bags having a high residual shrink force such 
as those values reported for Example 1-5 of the invention have continued 
close contact between film and article even after opening. The measured 
values of Examples 1-5 indicate that the film would be kept in close 
contact with an enclosed article and continue to maintain its protective 
functions. 
Referring now to Table 3, the inventive films of Examples 4 and 5 
demonstrate lower modulus values indicating a softer film yet having 
superior tear strength to the tested commercially available comparative 
film sample and similar puncture resistance values. The oxygen barrier 
properties of the test films are all excellent for applications requiring 
low permeability (a high barrier) to oxygen. The optical properties of 
Examples 1-5 show that the inventive films of Examples 1 and 4 which have 
an unblended first layer that consists essentially of a propene copolymer 
have superior low haze and high gloss relative to the blended structures 
of Examples 2, 3 and 5. Comparative Example 6 is also believed to have an 
unblended first layer, however, the comparative example has a much hazier 
and less glossy appearance than the inventive examples having an unblended 
first layer. 
Referring now to Table 4, the film samples of Examples 4 and 5 were corona 
treated whereas Examples 1-3 were not. The difference in surface energy or 
wetting tension is shown by the dynes per cm values. The surface energy 
values obtained for the films of Examples 1 and 3 indicate films suitable 
for cook and strip applications or films for use where meat adhesion is 
not a required or desired property. The surface energy value for 
comparative Example 6 suggests that this film has been corona treated. The 
impulse seal range for the irradiatively crosslinked Examples 4-5 are all 
sufficiently broad for use and sealing by commercially available sealing 
equipment including hot bar or impulse sealers. 
The seal creep to failure and seal strength data demonstrates a film having 
strong seals and superior high resistance to delamination relative to the 
film of the comparative example. The first set of seal strength data 
demonstrates that impulse seals of the inventive films may be made over a 
range of voltages from 40-49 volts which are unexpectedly superior at 
elevated temperatures to the prior art film of comparative Example 6. The 
second set of seal strength data examines hot bar seals made at 
500.degree. F. (260.degree. C. ) and 0.5 seconds dwell time relative to 
the factory seal on the commercially available bag of Example 6. Again the 
inventive films show unexpectedly high and superior seal strength. 
Surprisingly, the seal creep at failure test demonstrates the dramatic 
superiority of the hot bar seals of the films of the present invention to 
the comparative example factory seal at a typical cook-in temperature of 
165.degree. F. (740C. ) . The unexpectedly good seal strength, 
particularly under simulated cook-in temperatures and conditions, is 
believed to be due to the particular inventive formulation-structure 
combination employed in the multilayer film. 
The films of examples 4 and 5 were formed into bags for processing and 
packaging cook-in food. These bags along with bags of comparative example 
6 were stuffed with ground meat and cooked at 165.degree. F. (74.degree. 
C. ) in steam heat for eight hours followed by chilling overnight. The 
meat adhesion, purge control, delamination resistance, and seal strength 
characteristics of the films were all evaluated. The films of examples 4 
and 5 were as good or better than the comparative example in all the above 
characteristics, and demonstrated good purge control, high delamination 
resistance, good meat adhesion, and good seal strength. None of the tested 
films of examples 4 and 5 delaminated during either thermal processing or 
after film removal from the cook-in product. None of the films of examples 
4 and 5 exhibited seal failure over the 8 hour cook period or after 
chilling overnight. Bags of examples 4 and 5 were also subjected to a more 
severe cook procedure of stuffing and cooking at a temperature of 
180.degree. F. (82.degree. C. ) in steam heat for 8 hours to further test 
the heat seals and none of these bags showed seal failure. 
Examples 7-10 
A five layer tubular film designated here as Example 7 was made by a 
biaxial stretching orientation process. This process was similar to that 
disclosed above for making the films of Examples 1-3, except as noted 
below. Example 8 is the film of Example 7 which has been irradiated by 
electron beam to a level of about 4 Mrad. Example 9 is the irradiated film 
of example 8 which has also been corona treated. Example 10 is a 
comparative example (not of the invention) which is further described 
below. 
These examples demonstrate the effect of certain properties of irradiation 
and corona treatment to, respectively, cross-link and surface 
treat(incorporate polar groups into) the film. It also demonstrates use of 
a core layer which consists essentially of EVOH and use of a sealing layer 
using a higher melting point propene copolymer. In all of the examples 
below, a core layer 100 wt. % EVOH (EVAL E105A) was used having an 
ethylene content of 44 mole %. 
The films of Examples 7-9 each had an inner heat sealable layer which 
comprised 100% by weight of an propylene-ethylene copolymer which was sold 
by FINA Oil and Chemical Company of Dallas, Tex., U.S.A. under the 
trademark FINA 7371. This C.sub.3 C.sub.2 copolymer reportedly had a 
melting point of about 143.degree. C. (as measured by a differential 
scanning calorimetry (DSC), and a reported melt index of 3.5 g/10 
minutes(at 230.degree. C./2.16Kg). This resin also had a reported 
density(p) of 0.9 g/cm.sup.3. 
The extruder barrel temperatures for the third (core)layer was about 
355.degree.-365.degree. F. (179.degree.-185.degree. C.); for the first 
(inner)and fourth (intermediate) layer was about 350.degree.-375.degree. 
F.(177.degree.-191.degree. C. ); for the second (intermediate) layer was 
about 320.degree. F. (160.degree. C. ) and for the fifth (outer) layer was 
about 340.degree. F. (171.degree. C. ). The coextrusion die temperature 
profile was set from about 350.degree. F. to 365.degree. F. 
(177.degree.-185.degree. C.). 
For Examples 7-9, the second and Fourth (intermediate) layers were each 
identical blends comprising 17% of the same EVA copolymer with 53% of the 
same very low density polyethylene used in Example 1, and 30% of an 
extrudable anhydride-modified linear low density polyethylene based tie 
layer adhesive resin (Plexar.RTM. PX 360) having a melt index of 2 dg/min. 
, a density of 0.925 g/cm.sup.3, and a melting point of about 125.degree. 
C. 
The fifth layer of Examples 7-9 (which was the exterior surface of the 
tube) contained 73.1 weight % of an ethylene-.alpha.-olefin copolymer of 
very low density polyethylene sold by Dow Chemical Company of Midland, 
Michigan, U.S.A. under the trademark Attane XU 61509.32 which is a 
copolymer of ethylene and octene-1 reportedly having a melt index of about 
0.5 dg/min and a density of about 0.912 g/cm.sup.3, with a Vicat softening 
point of 95.degree. C. and a melting point of about 122.degree. C. Also 
blended in the fifth layer was 22.5 wt. % of EVA(LD 701.06) and 4.4% by 
weight of the fluoroelastomer slip processing aid described in Example 1. 
As in Examples 1-5, the first(inner) and fifth(outer) layers were connected 
to opposing sides of a third(core) layer (which comprises EVOH) by second 
and fourth (intermediate) layers which act in part as adhesive layers. 
The EVOH core layer controlled the permeability of the film with regard to 
gases such as oxygen. 
The inventive films of Examples 7-9 have a five layer structure which, if 
one refers to the Plexar resin containing layers as Adhesive (Ad) layers, 
may generally be identified as 100% C.sub.3 C.sub.2 /Ad/100% EVOH 
/Ad/73.1% EVA:22.5% VLDPE: 4.4% Proc. Aid. The 100% C.sub.3 C.sub.2 layer 
is the inner layer of the tubular film. This film has relative layer 
thicknesses (1st to 5th layers) of 8.3%/63.7%/8.4%/3%/16.6%(the combined 
4th and 5th layers were measured to be 19.6% with the 4th layer believed 
to be about 3%). 
For Example 10 the layers and their composition were identical to example 7 
except that a higher melt index ethylene .alpha.-olefin VLDPE was 
substituted for the 0.5 M.I. VLDPE(XU61509.32). The components were 
described more fully above with respect to Examples 1-3 and 7. The VLDPE 
(XU61520.01) used in the first, second and fourth layers of Example 10 was 
an ethylene-octene-1 copolymer having a reported density of 0.912 
g/cm.sup.3, a melt index of 1.0 dg/min., and a melting point of about 
123.degree. C., which was available from Dow Chemical Company under the 
trademark ATTANE XU 61520.01. The film of the Example 10 extruded very 
poorly and could not be made into a tubular film. The absence in the 
formulation of at least 10% of the copolymer of ethylene and at least one 
C.sub.4 -C.sub.8 .alpha.-olefin having a melt index of less than 1.0 
dg/min. and a density of from 0.900 to 0.915 g/cm.sup.3 produced an 
unstable primary tube having poor dimensional stability and low melt 
strength which was insufficient to make a tubular biaxially stretched 
film. No film was able to be made and therefore no results are reported. 
Various properties of the films of Examples 7-9 were measured and are 
reported in Tables 5 and 6 below. 
TABLE 5 
__________________________________________________________________________ 
TENSILE SHRINK FORCE IMPULSE 
AVG. STRENGTH SHRINK 
SHRINK 
at 90.degree. C. 
at RT 
SURFACE 
SEAL 
GAUGE 
at RT GLOSS 
at 90.degree. C. 
at 74.degree. C. 
g/mil 
g/mil 
ENERGY 
RANGE 
EX. 
mil .times. 10.sup.3 psi 
O.sub.2 GTR.dagger. 
HAZE 
at 45.degree. 
% % (Kg/cm) 
(Kg/cm) 
dynes/ 
VOLTS 
NO. 
(.mu.) 
(mPa) at RT 
% ANGLE 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
cm Min/Max 
__________________________________________________________________________ 
7 2.82 ND 7.3 2.4 87 14/30 
7/17 108/194 
80/166 
30 ND 
(71.6) (71) (43/76) 
(31/65) 
8 3.06 ND ND 4.2 82 ND ND ND ND 30 50+/50+ 
(77.7) 
9 3.24 9.7/8.9 
8.2 5.7 78 18/31 
8/17 107/195 
72/178 
37 50+/50+ 
(82.3) 
(67/61) 
(76) (42/77) 
(28/70) 
__________________________________________________________________________ 
ND = Not Determined 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
.dagger. = Oxygen gas transmission rate (O.sub.2 GTR) in units of cm.sup. 
per meter.sup.2 per 24 hours at 1 atmosphere and 0% relative humidity for 
the film tested. For O.sub.2 GTR film thickness is listed below the rate 
in microns (). 
TABLE 6 
______________________________________ 
SEAL STRENGTH 
lbs/inch 
EX. (Kg/cm) 
NO. at 160.degree. F. 
at 170.degree. F. 
at 180.degree. F. 
at 190.degree. F. 
______________________________________ 
7 ND ND ND ND 
8 6.80 5.40 4.68 5.25 
(1.2) (0.97) (0.84) (0.94) 
9 5.16 4.57 4.07 3.52 
(0.92) (0.82) (0.73) (0.63) 
______________________________________ 
Referring to Tables 5 and 6, good physical properties are shown. Strong, 
oxygen barrier films were made having excellent optical properties. Very 
low haze and high gloss values are demonstrated. The surface energy values 
reflect that the film of Example 9 has been corona treated to provide a 
surface capable of high meat adhesion. The impulse seal range is 
peculiarly high and off the test scale and this is believed due to a 
combination of sealing through a relatively thick (i.e. greater than 2.6 
mil (66 .mu.))film coupled with use of a high melting point propene 
copolymer to form the first (sealing) layer. Good shrinkage values at both 
90.degree. C. and 74.degree. C. are demonstrated with good shrink force 
values at both elevated and room temperatures. Hot bar seals were made of 
the irradiated films of Examples 8 and 9 and again demonstrate 
unexpectedly strong seals over a wide range of elevated temperatures. 
Examples 11-16 
Five layer tubular films designated here as Examples 11,12, and 14-16 were 
made by a biaxial stretching orientation process. This process was 
generally similar to that disclosed above for making the films of Examples 
1-3, except as noted below. The layer formulations of the film examples 
are listed in Table 7. The resins used in these examples were the same as 
used in Examples 1-3, except that the second, fourth and fifth layers all 
included a resin designated in Table 7 as "Plastomer". This plastomer 
resin was a copolymer of ethylene and at least one C.sub.3 -C.sub.8 
.alpha.-olefin having a density less than 0.900 g/cm.sup.3 and a melting 
point less than 85.degree. C. In particular, the plastomer resin used was 
a commercially available copolymer predominantly of ethylene copolymer 
with butene-1 monomer and component having a reported density of about 
0.885 g/cm.sup.3, a melt index of 0.5 dg/min and a melting point of 
68.degree. C. and available under the trademark Tafmer A0585X from Mitsui 
Petrochemical Industries, Ltd. of Tokyo, Japan. Examples 11 and 12 were 
similarly made films that were processed to slightly different flatwidths. 
Both films were irradiated by electron beam to a level of about 4 Mrad, 
and neither film was corona treated. Examples 14-16 were irradiated to 
different levels of 4 Mrad, 5 Mrad, and 6 Mrad, respectively. The films of 
examples 14-16 were all corona treated. Example 13 is a comparative 
example (not of the invention) which is further described below. 
These examples demonstrate the effect of addition of the optional plastomer 
component to the film as well as the effect on certain properties of 
irradiation and corona treatment to, respectively, cross-link and surface 
treat(incorporate polar groups) the film. It also demonstrates use of a 
core layer which consists essentially of EVOH and use of a sealing layer 
using a preferred low melting point propene copolymer. In all of the 
examples below, a core layer 100 wt. % EVOH was used having an ethylene 
content of 44 mole %. 
As in Examples 1-5, the first(inner) and fifth(outer) layers were connected 
to opposing sides of a third(core) layer (which comprises EVOH) by second 
and fourth (intermediate) layers which act in part as adhesive layers. 
The EVOH core layer controlled the permeability of the film with regard to 
gases such as oxygen. 
The inventive films of Examples 11, 12, and 14-16 each have a five layer 
structure with the 100% C.sub.3 C.sub.2 layer being the inner layer of the 
tubular film. These films have relative layer thicknesses (1st to 5th 
layers)of 11.8%/43.1%/7.3%/3%/34.8% (the combined 4th & 5th layers were 
measured to be 37.8% and the 4th layer is believed to be .about.3). 
Example 13 is a comparative example of a prior art, commercially available 
film believed to have a six layer structure as described above for 
comparative example 6, except that comparative example 13 is not corona 
treated. 
Various properties of the films of Examples 11-16 were measured and are 
reported in Tables 8, 9, and 10 below. 
TABLE 7 
__________________________________________________________________________ 
Layer Composition 
Ex. 
First Layer 
Second Third Layer 
Fourth 
Fifth Layer 
Sixth 
IRRADIATED 
No. 
(Inner) 
Layer (Core) 
Layer (Outer).dagger. 
Layer 
(Mrad) Corona 
__________________________________________________________________________ 
11 100% C.sub.3 C.sub.2 
37.5% VLDPE 
100% EVOH 
Same as 
55.6% VLDPE 
-- 4 NO 
17.5% EVA 2nd Layer 
25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
12 100% C.sub.3 C.sub.2 
37.5% VLDPE 
100% EVOH 
Same as 
55.6% VLDPE 
-- 4 NO 
17.5% EVA 2nd Layer 
25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
13** 
100% C.sub.3 - 
EVA Adhesive 
100% EVOH 
Adhesive EVA 
Yes NO 
olefin 
14 100% C.sub.3 C.sub.2 
37.5% VLDPE 
100% EVOH 
Same as 
55.6% VLDPE 
-- 4 YES 
17.5% EVA 2nd Layer 
25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
15 100% C.sub.3 C.sub.2 
37.5% VLDPE 
100% EVOH 
Same as 
55.6% VLDPE 
-- 6 Yes 
17.5% EVA 2nd Layer 
25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
16 100% C.sub.3 C.sub.2 
37.5% VLDPE 
100% EVOH 
Same as 
55.6% VLDPE 
-- 8 Yes 
17.5% EVA 2nd Layer 
25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
__________________________________________________________________________ 
**Comparative example believed to be irradiated but not corona treated. 
*The adhesive is a rubbermodified, anhydridemodified LLDPE adhesive 
(Plexar PX 380). 
.dagger.The exterior outer layer for examples 11-17, except comparative 
example 13 which is believed to be a six layer film with the sixth layer 
as the exterior outer layer. 
TABLE 8 
__________________________________________________________________________ 
TENSILE 
ELONGATION 
STRENGTH SHRINK FORCE 
SHRINK FORCE 
Avg AT BREAK 
.times.10.sup.3 psi 
SHRINK 
SHRINK 
at 90.degree. C. 
at RT 
at 74.degree. C. 
at RT 
GAUGE 
FLAT 
% at RT at 90.degree. C. 
at 74.degree. C. 
gm/mil 
gm/mil 
gm/mil 
gm/mil 
Ex. 
mil WIDTH 
at RT (mPa) % % (Kg/cm) 
(Kg/cm) 
(Kg/cm) 
(Kg/cm) 
No. 
(micron) 
(mm) 
MD/TD MD/TD MD/TD 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
__________________________________________________________________________ 
11 2.61 329 85/150 10.8/7.8 
27/36 
12/20 
186/158 
101/132 
130/146 
85/138 
(66.3) (74/54) (73/62) 
(40/52) 
(51/57) 
(33/54) 
12 2.64 378 113/134 9.9/8.0 
23/34 
11/20 
139/172 
82/136 
101/162 
78/150 
(67.1) (68/55) (55/68) 
(32/54) 
(40/64) 
(31/59) 
13 2.67 302 149/92 5.6/6.2 
29/41 
10/20 
ND ND ND ND 
(67.8) (39/43) 
14 2.59 240 137/181 9.7/7.4 
24/36 
12/21 
146/140 
85/121 
105/145 
71/133 
(65.8) (67/51) (58/55) 
(33/48) 
(41/57) 
(28/52) 
15 2.64 241 105/167 9.2/7.1 
24/35 
12/21 
128/145 
79/134 
101/151 
73/142 
(67.1) (63/49) (50/57) 
(31/53) 
(40/59) 
(29/56) 
16 2.41 241 106/146 9.4/6.9 
23/35 
12/20 
129/141 
80/133 
94/139 
74/132 
(61.2) (65/48) (51/56) 
(31/52) 
(37/55) 
(29/52) 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
TABLE 9 
__________________________________________________________________________ 
1% Secant 
TEAR HOT H.sub.2 O 
Modulus 
STRENGTH 
DYNAMIC 
PUNCTURE GLOSS* 
EX. 
MD/TD 
MD/TD PUNCTURE 
95.degree. C. 
O.sub.2 GTR.dagger. at RT 
HAZE* 
AT 45.degree. 
No. 
MPa g/.mu. 
cmKg/.mu. 
.mu./seconds 
0% RH 
50% RH 
% ANGLE 
__________________________________________________________________________ 
11 278/250 
0.71/1.8 
ND 71/&gt;120 
ND ND 11 64 
12 248/242 
0.94/1.2 
ND 74/58.dagger..dagger. 
ND ND 6 73 
13 351/371 
0.55/0.91 
0.03 67/20 9 ND 15 60 
(64) 
14 392/384 
1.2/1.8 
0.03 71/&gt;120 
ND 13 11 69 
(58) 
15 391/373 
1.4/1.2 
0.03 74/&gt;120 
ND 12 11 69 
(64) 
16 389/392 
1.9/1.8 
0.03 61/&gt;120 
ND 8 10 71 
(69) 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
RH = RELATIVE HUMIDITY 
.dagger.Oxygen gas transmission rate (O.sub.2 GTR) in units of cm.sup.3 
per meter.sup.2 per 24 hours at 1 atmosphere for the film tested. For 
O.sub.2 GTR the film thickness is below the rate in microns (). 
*Values for powder coated film (Values for Example 13 after wiping off 
powder were 11 and 65). respectively). 
.dagger..dagger.Average of three values; three other values obtained were 
in excess of 120 seconds for film having an average thickness of 80 
microns (.mu.). 
TABLE 10 
__________________________________________________________________________ 
IMPULSE 
SEAL RANGE 
SEAL STRENGTH 
IMPULSE 
at 1 second Impulse Seal 
SURFACE 
SEAL RANGE 
dwell Hot Bar Seal 
at 160.degree. F. (71.degree. C.) 
Ex. 
ENERGY 
min./max. 
max. RT/160.degree. F./190.degree. F. 
at 35 v/40 v/45 v/50 v 
No. 
(dynes/cm) 
(volts) 
(volts) 
(g/cm) (g/cm) 
__________________________________________________________________________ 
11 31 ND ND 2145/1090/854 
ND 
12 30 ND ND 2551/1190/929 
ND 
13 30 35/50 39 1420/869/572* 
ND 
14 37 40/&gt;50 38 ND 584/645/758/754 
15 37 42/&gt;50 40 ND 677/803/842/851 
16 36 42/&gt;50 43 ND 570/686/788/785 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23.degree. C.) 
*The seal tested was a factory seal and the factory sealing method is 
undetermined. 
Referring now to Tables 8, 9, and 10, the films of Examples 11-12 and 14-16 
have very good physical properties typically as good or better than those 
measured for the comparative Example 13. The comparative film had slightly 
higher shrinkage values, but these values for all films were acceptable 
for commercial applications. Surprisingly, relative to the comparative 
commercial film example 13, the inventive films all demonstrate much 
improved tear strength, and a better appearance including lower haze, 
higher gloss, and have better resistance to hot water punctures. All films 
demonstrate suitable oxygen barrier properties. The surface energy 
measurements indicate values suitable for high meat adhesion for Examples 
14-16, and that comparative Example 13 was not corona treated. This 
comparative example and non-corona treated Examples 11-12 are suitable for 
use in nonadhering applications such as cook and strip process 
applications. The films of examples 14-16 all had similar flatwidths of 
about 240 mm. 
The impulse seal ranges of inventive films 14-16 were measured and 
determined to be desirably broad and sufficient for commercial heat 
sealing operations. Also, the maximum voltage for impulse seals using a 
one second dwell time was measured for the films of Examples 14-16. The 
results indicate that higher irradiation levels raise the maximum 
burn-through resistance of the inventive film. For comparison, the one 
second dwell time, maximum impulse seal voltage was measured for the film 
of comparative Example 6 and a maximum value of 39 volts was obtained. 
The seal strengths of hot bar seals made at 500.degree. F. with a 0.5 
second dwell time for the inventive films of Examples 11 and 12 are 
unexpectedly superior to the factory seals of the commercially suitable 
comparative film of Example 13. Furthermore the seal strengths of the 
impulse seals of examples 14-16 are surprisingly and unexpectedly superior 
to those measured for the six layer film of example 6. 
Examples 17-23 
Five layer tubular films designated here as Examples 17-22 were made by a 
biaxial stretching orientation process. This process was generally similar 
to that disclosed above for making the films of Examples 1-3. The layer 
formulations of the film examples are listed in Table 11. 
In examples 17-19 the resins used in layers 2-5 were the same as used in 
Examples 1-3, except that the second, fourth and fifth layers all included 
a resin designated in Table 11 as "Plastomer". The plastomer resin used in 
this set of examples was a copolymer of ethylene and at least one C.sub.3 
-C.sub.8 .alpha.-olefin having a density less than 0.900 g/cm.sup.3 and a 
melting point less than 85.degree. C. In particular, the plastomer resin 
used was a commercially available copolymer predominantly of ethylene with 
a minor proportion of butene-1. This plastomer copolymer has a reported 
density of about 0.888 g/cm.sup.3, a melt index of 0.8 dg/min., and a 
melting point of 68.degree. C. The plastomer is also believed to have a 
narrow molecular weight distribution (M.sub.w /M.times..sub.n) of about 2 
and was available from Exxon Chemical Company of Houston, Tex., U.S.A. 
under the trademark Exact 9036. Examples 17-19 were similarly made films 
having the same formulations and structures except that the composition of 
the first layer was varied. 
In Example 17, the first layer (inner surface layer of the tube) was made 
of 100 wt. % of a propylene terpolymer. This C.sub.3 C.sub.2 C.sub.4 
terpolymer was commercially available from Sumitomo Chemical Company, 
Limited of Tokyo, Japan under the trademark Excellen WS 709N and 
reportedly had minor proportions of ethylene (1.5%) and butene-1 (14.7%); 
a melt index of 8 dg/min. (230.degree. C./2.16Kg); and a melting point of 
about 133.degree.-134.degree. C. 
In Example 18, a film similar to that of example 17 was made except the 
first layer substituted a C.sub.3 C.sub.4 bipolymer having a reported melt 
index of 6.5 dg/min.(at 230.degree. C./2.16 Kg); a melting point of about 
131.degree. C.; and a butene-1 content of 14% by weight. This copolymer 
was commercially available from Shell Oil Company, Atlanta, Ga., U.S.A. 
under the trademark CEFOR SRD4-141. 
In Example 19, the first layer of Example 18 was modified to comprise a 
blend of 70 wt. % of the noted C.sub.3 C.sub.4 polymer with 30 wt. % of an 
anhydride-modified LLDPE adhesive having a reported melt index of 2 
dg/min; a density of 0.925; a melting point of about 125.degree. C. and 
was commercially available from Quantum Chemical Company, Cincinnati, 
Ohio, U.S.A. under the trademark Plexar PX 360. 
Examples 17-19 were each irradiated at 4 Mrad and the first layer surface 
was corona treated. Examples 20 and 21 are comparative examples (not of 
the invention) which are further described below. 
Examples 17-23 demonstrate variation of the first and second layer 
compositions as well as the effect of addition of an optional plastomer 
component to the film. The effect on certain properties of irradiation and 
corona treatment to, respectively, cross-link and surface 
treat(incorporate polar groups) the film is also evidenced. Also, the 
examples 17-19 demonstrate use of a core layer which consists essentially 
of a blend of EVOH and nylon 6/66 copolymer and use of a sealing layer 
using a preferred low melting point propene copolymer. 
In each of the examples 17-19 and 22-23, a core layer of EVOH was used 
having an ethylene content of 44 mole %; a melt index of 5.5 dg/min.; and 
a melting point of about 165.degree. C. This EVOH copolymer is 
commercially available from Eval Company of America of Lisle, Ill., USA 
under the trademark EVALCA E 105A. In each of the examples 20-21, a core 
layer of EVOH was used having an ethylene content of 44 mole %; a melt 
index of 1.6 dg/min.; and a melting point of about 165.degree. C. This 
EVOH copolymer is commercially available from Eval Company of America of 
Lisle, Ill., USA under the trademark EVALCA E 151B. 
Examples 20 and 21 each used the same C3C.sub.2 copolymer in the first 
layer and the same VLDPE, EVA and processing aid in the fifth layer; and 
the same adhesive in the second and fourth layers as described for 
Examples 1-3. The second and fourth layers of Examples 20 and 21 used 
different EVA resins. The second and fourth layers of example 20 used 60% 
of an EVA copolymer (EVA A) having a 6.1 wt. % vinyl acetate (VA) content; 
a density of 0.928 g/cm.sup.3' ; a melt index of 0.3 dg/min; and a melting 
point of 102.degree. C. in combination with 40% adhesive. This EVA 
copolymer A is commercially available from EXXON under the trademark 
ESCORENE LD317.09. The second and fourth layers of Example 21 used 55% of 
EVA A in combination with 15% of the same LD701 EVA (EVA B) used in the 
fifth layer; and 30% of adhesive. 
As in Examples 1-5, the first(inner) and fifth(outer) layers were connected 
to opposing sides of a third(core) layer (which comprises EVOH) by second 
and (intermediate) layers which act in part as adhesive layers. 
The EVOH core layer controlled the permeability of the film with regard to 
gases such as oxygen. 
The inventive films of Examples 17-22 each had a five layer structure with 
the propene copolymer-containing layer being the inner layer of the 
tubular film. These films have been biaxially stretched to a machine 
direction (M.D.) orientation (draw) ratio of about 31/2:1 and to a radial 
or transverse direction (T.D.) orientation ratio of about 3:1. The 
relative layer thicknesses (1st to 5th layers) of the extruded primary and 
any resultant film of examples 17-19 are believed to be 
14.1%/49.7%/9.6%/7.2%/19.4%. The relative layer thicknesses (1st to 5th 
layers) of the extruded primary and any resultant film of examples 20-23 
are believed to be 12.8%/51.3%/6.4%/3%/26.6%. 
Examples 20-21 are comparative examples of a five layer structure which was 
biaxially stretched, as described above for examples 17-19, and had the 
formulations indicated in Table 11. Example 22 is an example of the 
invention similar to Example 14, except that it was not irradiated or 
corona treated. Example 23 is a comparative example (not of the invention) 
where the formulation was identical to that of Example 22 except that the 
first layer was modified by substituting 100 wt. % of polypropylene 
homopolymer (PP)(Escorene.RTM. PP 4092 available from Exxon Chemical Co.) 
for the propene copolymer of Example 22. The PP had a density of about 
0.90 g/cm.sup.3 ; and a melt index (condition L) of 2.3 dg/min. 
Referring now to a comparison of the examples, it was determined that the 
inventive film of Example 22 extruded and processed very well forming a 
stable orientation bubble resulting in a biaxially stretched film of good 
appearance. The film made in example 22 had an average gauge of 2.11 mil 
(53.6 .mu.); a flatwidth of 157/8 inches (40 cm) and an M.D./T.D. 
shrinkage value at 90.degree. C. of 30%/39%. Attempts to process the 
formulation of Example 23 into a biaxially stretched film failed. The 
polypropylene homopolymer layer appeared to be very hard. Although a 
primary tube extruded well, attempts at biaxially stretch orienting film 
from the primary tube resulted in a bubble break as the first layer 
composition was changed to polypropylene homopolymer. Subsequent attempts 
to form a stable bubble from primary tubes of the test formulation failed 
due to bubble rupture during inflation. This demonstrates the 
unsuitability and undesirability of polypropylene homopolymer as the main 
or sole constituent of the film layer, especially the first layer. 
Various properties of the films of Examples 17-22 were measured and are 
reported in Tables 12-14 below. 
TABLE 11 
__________________________________________________________________________ 
Layer Composition 
First Layer 
Second Third Layer Fifth Layer 
Ex. No. 
(Inner) Layer (Core) Fourth Layer 
(Outer) 
__________________________________________________________________________ 
17 100% C.sub.3 C.sub.2 C.sub.4 
37.5% VLDPE 
90% EVOH 
Same as 2nd Layer 
55.6% VLDPE 
17.5% EVA 
10% Nylon 25% EVA 
30% Adhesive* 4.4% Processing Aid 
15% Plastomer 15% Plastomer 
18 100% C.sub.3 C.sub.4 
Same as Ex. 17 
Same as Ex. 17 
Same as Ex. 17 
Same as Ex. 17 
19 70% C.sub.3 C.sub.4 
Same as Ex. 17 
Same as Ex. 17 
Same as Ex. 17 
Same as Ex. 17 
30% Adhesive** 
20 100% C.sub.3 C.sub.2 
60% EVA A 
100% EVOH 
Same as 2nd Layer 
70.6% VLDPE 
40% Adhesive* 25% EVA 
4.4% Processing Aid 
21 Same as Ex. 20 
55% EVA A 
Same as Ex. 20 
Same as Ex. 20 
Same as Ex. 20 
15% EVA B 
30% Adhesive* 
22 Same as Ex. 14 
Same as Ex. 14 
Same as Ex. 14 
Same as Ex. 14 
Same as Ex. 14 
23 100% PP Same as Ex. 14 
Same as Ex. 14 
Same as Ex. 14 
Same as Ex. 14 
__________________________________________________________________________ 
*The adhesive is a rubbermodified, anhydridemodified LLDPE adhesive 
(Plexar PX 380). 
**The adhesive is an anhydridemodified LLDPE adhesive (Plexar PX 360). 
TABLE 12 
__________________________________________________________________________ 
TENSILE 
ELONGATION 
STRENGTH SHRINK FORCE 
SHRINK FORCE 
Avg AT BREAK 
.times.10.sup.3 psi 
SHRINK 
SHRINK 
at 90 C. 
at RT 
at 74 C. 
at RT 
GAUGE 
FLAT 
% at RT at 90 C. 
at 74 C. 
gm/mil 
gm/mil 
gm/mil 
gm/mil 
Ex. 
mil WIDTH 
at RT (mPa) % % (Kg/cm) 
(Kg/cm) 
(Kg/cm) 
(Kg/cm) 
No. 
(.mu.) 
(mm) 
MD/TD MD/TD MD/TD 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
MD/TD 
__________________________________________________________________________ 
17 2.58 ND 202/192 8.7/7.3 
26/39 
13/24 
110/156 
77/134 
85/157 
67/139 
(65.5) (60/50) (43/61) 
(30/53) 
(33/62) 
(26/55) 
18 2.95 ND 139/165 7.7/6.9 
33/40 
16/24 
133/138 
86/118 
102/150 
83/137 
(74.9) (53/48) (52/54) 
(34/46) 
(40/59) 
(33/54) 
19 2.68 ND 208/213 9.1/7.2 
26/36 
12/22 
121/148 
84/136 
89/138 
73/129 
(68.1) (62/49) (47/58) 
(33/54) 
(35/54) 
(29/51) 
20 2.39 400 127/134 7.4/8.0 
21/35 
9/18 
103/181 
73/131 
76/158 
67/133 
(60.7) (51/55) (41/71) 
(29/52) 
(30/62) 
(26/52) 
21 2.15 406 117/134 7.5/7.9 
19/34 
9/18 
100/179 
66/128 
78/155 
70/136 
(54.6) (52/55) (39/70) 
(26/50) 
(31/61) 
(28/54) 
__________________________________________________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23 C.) 
TABLE 13 
__________________________________________________________________________ 
1% Secant 
TEAR HOT H.sub.2 O 
Modulus 
STRENGTH 
DYNAMIC 
PUNCTURE GLOSS 
EX. MD/TD 
MD/TD PUNCTURE 
95 C. HAZE 
AT 45 
No. MPa g/.mu. cmKg/.mu. 
.mu./seconds 
% ANGLE 
__________________________________________________________________________ 
17 310/504 
1.1/1.4 
0.04 64.5/24 
6.4 64 
18 311/314 
1.4/1.3 
0.06 75.2/38* 
10.8 
69 
19 316/309 
0.91/0.94 
0.04 77.0/25 
19.2 
49 
20 330/345 
1.1/1.2 
ND 64.3/28** 
3.4 81 
21 322/339 
0.90/0.93 
ND 61.0/20 
5.4 81 
__________________________________________________________________________ 
ND = NOT DETERMINED 
*Reported value is average of 4 samples; Two other samples tested &gt;120 
seconds for 86.1.mu. average thickness films. 
**Reported value is average of 5 samples; One other sample tested &gt;120 
seconds for a 66.3.mu. average thickness film. 
TABLE 14 
______________________________________ 
IMPULSE 
SEAL STRENGTH 
SEAL Hot Bar Seal 
Impulse Seal 
SURFACE RANGE RT/160 F.(71 C.)/ 
at 160 F. (71 C.) 
Ex. ENERGY min./max. 
190 F.(88 C.) 
at 35v/40v/45v/50v 
No. (dynes/cm) 
(volts) (g/cm) (g/cm) 
______________________________________ 
17 36 43/47 1470/946/683 
ND 
18 36 43/50 2050/983/629 
ND 
19 36 42/49 ND ND 
20 ND ND 1240/883/760 
290/252/270/357 
21 ND ND 1590/770/713 
309/256/266/304 
______________________________________ 
ND = NOT DETERMINED 
RT = ROOM TEMPERATURE (.about.20-23 C.) 
*The seal tested was a factory seal and the factory sealing method is 
undetermined. 
Referring now to Tables 11-14, Examples 17-19 all show results of tests 
which demonstrate that the films produced have useful properties for 
packaging articles. The examples not only demonstrate that the first layer 
may utilize bipolymers and terpolymers, but that the core layer may be 
varied to include a nylon polymer such as nylon 6/66 copolymer. Propene 
polymers suitable for use in the invention have at least 60 wt. % of 
propene polymerized with various amounts of one or more .alpha.-olefin 
comonomers. Preferably, the melting point of such propene-based polymers 
is less than 140.degree. C. 
It is seen that addition of adhesive to the first layer of example 19 
produced a film with suitable properties but the optical properties and 
tear strength were not as good as the films of examples 17 and 18. The 
films of comparative examples 20 and 21 demonstrate inferior impulse seal 
strength as seen by comparison to earlier samples 4-6 and 14-16 of the 
invention. This inferior impulse seal strength is believed to be due to 
the absence in the second and fourth layers of at least 10 wt. % of an 
ethylene copolymer with at least one C.sub.4 -C.sub.8 .alpha.-olefin which 
has a copolymer density of 0.900 to less than 0.915 g/cm.sup.3 a melt 
index of less than 1.0 dg/min. and a melting point of at least 90.degree. 
C. 
Films, bags and packages of the present invention may also employ 
combinations of characteristics as described in one or more of the claims 
including dependent claims which follow this specification and where not 
mutually exclusive, the characteristics and limitations of each claim may 
be combined with characteristics or limitations of any of the other claims 
to further describe the invention. 
The above examples serve only to illustrate the invention and its 
advantages, and they should not be interpreted as limiting since further 
modifications of the disclosed invention will be apparent to those skilled 
in the art in view of this teaching. All such modifications are deemed to 
be within the scope of the invention as defined by the following claims.