Thermoplastic C.sub.2 -.alpha.-olefin copolymer blends and films

A polymer blend and mono-and multilayer films made therefrom having improved properties such as heat sealing or puncture resistance wherein the blend has a first polymer of ethylene and at least one .alpha.-olefin having a polymer melting point between 55 to 75.degree. C.; a second polymer of ethylene and at least one .alpha.-olefin having a polymer melting point between 85 to 110.degree. C. and a third thermoplastic polymer having a melting point between 115 to 130.degree. C.; and optionally a fourth polymer e.g. EVA, having a melting point between 90 to 100.degree. C.

BACKGROUND OF THE INVENTION 
The invention relates to thermoplastic C.sub.2 -.alpha.-olefin copolymer 
resin blends and flexible films thereof having heat sealing and puncture 
resistance properties. Such blends are useful for making films 
particularly heat shrinkable, oriented films for packaging food and 
non-food articles, but especially fresh or frozen foods such as meat, 
poultry or cheese. 
Manufacturers and wholesalers utilize flexible thermoplastic packaging 
films to provide economical, sanitary containers which help protect and/or 
preserve the freshness and wholesomeness of their products. These films 
are often sold in bag form. For example, a single or multilayer 
thermoplastic film may be made into bags by a packaging manufacturer using 
film stock comprising a tubular film or one or more flat sheets or webs of 
film by well known processes involving e.g. cutting, folding and/or 
sealing the film to form bags which may then be shipped to processors for 
use in packaging operations. These films and bags may be printed with 
customer logos, product data or other information and may also be 
uniaxially or biaxially oriented, heat shrinkable, or irradiated, or may 
contain film layers which are abuse resistant or puncture resistant, or 
which are crosslinked or which enhance or retard or prevent transmission 
of light, gases, or liquids therethrough. Frequently, multilayer films 
having one or more barrier layers to oxygen and/or moisture such as saran 
(a polyvinylidene chloride copolymer), a modified saran e.g. containing 
methyl acrylate polymer units, ethylene vinyl alcohol copolymer, nylon, or 
acrylonitrile may be used with a heat sealing layer such as a copolymer of 
ethylene and vinyl acetate (EVA) to produce bags for packaging oxygen 
and/or moisture sensitive foods e.g. fresh red meat. Such bags help 
preserve meat in its original condition by preventing or reducing moisture 
loss and chemical changes in the meat structure due to oxidation 
reactions. A typical packaging bag produced from a tubular film stock will 
have one or two sides which have been heat sealed by the bag manufacturer 
in the bag forming process. For food packaging bags often will have one 
open side to allow a food processor to insert ham, turkey, chicken, 
cheese, primal or subprimal meat cuts, ground beef, fruits, vegetables, 
bread or other food products into the bag. The food processor then makes a 
final seal thereby enclosing the bag. This final seal may follow gas 
evacuation of the bag by vacuum means or replacement of the gaseous 
environment within the bag by a particular gas or mixture of gases which 
may be inert or reactive with the enclosed product to provide some 
advantage such as to assist product preservation. This final seal is 
frequently a heat seal similar to the initial seals produced by the bag 
manufacturer although the actual heat sealing equipment may vary. 
Thus, 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. 
The strength of seals of heat shrinkable bags may be measured by 
determining the time for a seal to fail when under certain conditions the 
seal is immersed in hot water e.g. at 95.degree. C. i.e., the hot water 
seal strength ("HWSS") may be measured by a test such as that described as 
the "restrained shrinkage-seal strength test" in Funderburk et al U.S. 
Pat. No. 3,900,635 which patent is hereby incorporated by reference. 
Once a 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. However, heat sealing techniques are now also commonly employed 
to produce the final closure of the bag. 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. 
Generally, impulse seals may be made faster than hot bar seals because of 
the quick cool down of the impulse ribbon following the heat impulse. 
Impulse seals are also generally narrower than hot bar seals which lead to 
an improved package appearance, but narrower seals also leave less margin 
for error in the production of continuous sealed edges. Since typically 
less area is bonded in an impulse seal relative to a hot bar seal, the 
performance of the sealing layer of the thermoplastic film is more 
critical. 
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 made from cross-linkable polymer resins 
causes the various irradiated resin layers in the film to crosslink. Under 
controlled conditions, crosslinking by irradiation raises and may also 
broaden the temperature range for heat sealing, and depending upon the 
film composition may also enhance puncture resistance of the film. 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 package is made of heat 
shrinkable film and is to be immersed in hot water to shrink the film 
against the packaged article since such shrinkage increases the stress on 
these seals. Thus, there is a continuing need for monolayer and 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. 
Copolymers of ethylene and vinyl esters such as vinyl acetate have 
previously been disclosed as useful materials in monolayer and multilayer 
thermoplastic films and are known for providing heat sealing properties. 
For example, U.S. patent application Ser. No. 07/419,061 (Georgelos et al) 
filed Oct. 10, 1989, which application is hereby incorporated by 
reference,disclose EVA blends useful for their heat sealing properties. 
U.S. Pat. No. 4,064,296 (Bornstein et al) discloses a heat shrinkable 
multilayer film having an oxygen barrier core layer of hydrolyzed 
ethylene-vinyl acetate (EVOH) and outer layers of EVA. 
U.S. Pat. No. 4,178,401 (Weinberg et al) discloses an oriented, heat 
shrinkable packaging film having a blended self-welding layer said to have 
superior seal strength and abuse resistance. Blends of EVAs with different 
melt flows are disclosed with e.g. a first EVA having a melt flow of less 
than 5.0 blended with a second EVA having a melt flow of at least 28. The 
film may also be crosslinked by irradiation. 
U.S. Pat. No. 4,247,584 (Widiger et al) discloses heat sealable food bags 
made from multilayer films having a heat sealing layer comprising a blend 
of EVAs with 10 to 90 weight percent of the blend comprising a first EVA 
having 2-12% VA and a melt index of 0.2 to 10 dg/min. and 90 to 10 weight 
percent of the blend comprising a second EVA having 8-30% VA and a melt 
index of 0.2 to 5. 
An example of a typical fresh red meat bag currently in commerce is a film 
having three layers which are coextruded and oriented. The core or middle 
layer of the film is an oxygen and moisture barrier material, the outer 
layer provides abrasion resistance and is formulated to provide support 
for the film during the expansion of the primary tube for orientation, and 
the inner layer provides heat seal properties and contributes to puncture 
resistance. 
The core or barrier layer of this film is a relatively small percentage of 
total film thickness and is made of polyvinylidene chloride (PVDC) or 
vinylidene chloride methylacrylate copolymer (VDC-MA or MA-Saran). 
The outer layer of this film is thicker than the core layer and is a blend 
of very low density polyethylene (VLDPE) and ethylene vinyl acetate (EVA). 
VLDPE, also called ultra low density polyethylene is a class of 
ethylene-alpha olefin copolymers having a density which generally is 
recognized to range from less than 0.915 g/cm.sup.3 down to about 0.860 
g/cm.sup.3. The EVA and VLDPE components contribute to the shrink 
properties of the film and the VLDPE component contributes to the abrasion 
and puncture resistance. The VLDPE also adds plastic orientation strength 
to minimize breaks of the secondary bubble during expansion of the 
softened primary tube. 
By far, the thickest film layer is the inner or heat seal layer. In the 
commercial film noted above, this layer is over 60% of the total film 
thickness and comprises a blend of VLDPE and EVA. The heat seal layer 
provides a significant contribution to the puncture resistance properties 
of the film. Another desirable film characteristic provided by this layer 
is the heat seal temperature range. It is preferred that the temperature 
range for heat sealing the film be as broad as possible. This allows 
variation in the operation of the heat sealing equipment as opposed to a 
film having a very narrow heat sealing range. For example, it is desirable 
for a suitable film to heat seal over a temperature range of 350.degree. 
F. to 550.degree. F., providing a heat sealing window of 200.degree. F. 
While films of the general structure and composition as described above 
have been in commercial use for many years, efforts continue to improve 
upon such films and in particular to increase puncture resistance while 
maintaining ease of processability, a broad heat seal temperature range 
and a high degree of both machine direction (MD) and transverse direction 
(TD) shrink. 
Recent developments for improving properties of a heat shrinkable film 
include U.S. Pat. No. 5,272,016 (Ralph). The '016 Patent improves 
properties of a multilayer nonoxygen barrier film by forming the outer 
layers of a blend of EVA, VLDPE and a plastomer. 
U.S. Pat. No. 5,397,640 discloses a multilayer oxygen barrier film wherein 
at least one outer film layer is a three component blend of VLDPE, EVA and 
a plastomer. 
U.S. Pat. No. 5,403,668 discloses a multilayer heat shrinkable oxygen 
barrier film wherein one of the film outer layer is a four component blend 
of VLDPE, LLDPE, EVA and plastomer. 
Recent manufacturing changes in catalysts and processes have provided 
increasing numbers of polymeric resins having different melting 
characteristics and melting points, and narrower molecular weight 
distribution ratios (MWD). MWD is the ratio of M.sub.w /M.sub.n, where 
M.sub.w is the weight-average molecular weight of the resin and M.sub.n is 
the number-average molecular weight. For example, older commercialized 
VLDPE resins have a MWD generally in the range of about 3.5 to 8.0, 
although some VLDPE resins outside this range have been commercialized. 
Improvements in catalysis technology has been able to produce many resins 
which reduce this ratio generally to below 3 to the range of about 1.5 to 
about 2.5 and most typically to about 2.0. This reduction in the MWD means 
that the polymer chains of these VLDPE resins are more uniform in length. 
Whereas those having a higher MWD may be said to comprise polymer chains 
of more varied lengths. Other differences in resin properties have been 
attributed to differences in distribution along an ethylene backbone 
resulting in materials produced from single-site catalysts having a lower 
melting point than a multisite catalyst produced VLDPE of comparable 
density and melt index. Also, in the case of the above-noted commercial 
film wherein the heat seal layer is primarily a blend of EVA and VLDPE, it 
was found that using a more narrow M.sub.w /M.sub.n VLDPE having a lower 
melting point in place of a broader M.sub.w /M.sub.n VLDPE having a higher 
melting point considerably decreased the operable heat sealing range. For 
example, where the sealing layer used only a very narrow M.sub.w /M.sub.n, 
lower melting point VLDPE in the blend, the heat seal temperature was in 
the order of 400.degree. F. to about 475.degree. F. giving a sealing 
window of only 75.degree. F. 
Past attempts at providing improved heat sealing in films, while making 
some progress, leave much to be desired. Variability in heat sealing 
equipment and process parameters continue to produce bags with weak seals 
which are subject to burn through, which fail to seal through folds, and 
which produce leaking bags having discontinuous seals. It would be highly 
desirable to have biaxially stretched, heat shrinkable films and bags 
whose heat sealing layer in particular and film construction in general 
allows greater flexibility and variability in heat sealing process 
parameters while producing strong, integral, continuous seals rapidly and 
with a lower failure rate relative to prior art films and bags. 
Accordingly, one object of the present invention is to provide a novel 
polymeric blend having improved heat sealing properties. 
Another object of the invention is to provide a polymer blend having an 
improved combination of properties. 
Another object of the invention is to provide a flexible film having 
improved heat sealing properties. 
Another object of the present invention is to provide a heat shrinkable 
biaxially oriented monolayer film having improved puncture resistance 
and/or a broad heat sealing range. 
Another object of the invention is to provide a heat shrinkable biaxially 
oriented multilayer film having a broad heat sealing range. 
Another object of the invention is to provide a heat shrinkable biaxially 
oriented multilayer film having improved puncture resistance. 
Another object of the present invention is to provide a heat shrinkable 
biaxially oriented multilayer film having an improved combination of 
puncture resistance and a broad heat sealing range. 
Yet another object of the present invention is to provide a heat 
shrinkable, biaxially oriented multialyer film having a puncture 
resistance and heat sealing range suitable for use in the packaging of 
fresh bone-in meats. 
A still further object of the present invention is to provide a heat 
shrinkable, biaxially oriented multilayer film having an improved 
combination of optical properties, heat sealing properties and puncture 
and abrasion resistance. 
SUMMARY OF THE INVENTION 
According to the present invention, a novel polymeric blend, film, and 
biaxially stretched, heat sealable, heat shrinkable, thermoplastic 
flexible film comprising at least one heat sealable layer and suitable for 
use in making bags for packaging e.g. food articles such as primal and 
subprimal meat cuts is provided. The novel blend is suitable to being 
formed into a wide variety of articles including packaging films useful 
for packaging food and nonfood items alike. The inventive polymer blend in 
its various embodiments has excellent heat sealing properties, optical 
properties, puncture and abrasion resistance, heat shrinkability, 
flexibility as well as good combinations of such properties. 
The inventive blend has a first polymer of ethylene and at least one 
.alpha.-olefin having a polymer melting point between 55 to 75.degree. C.; 
a second polymer of ethylene and at least one .alpha.-olefin having a 
polymer melting point between 85 to 110.degree. C. and a third 
thermoplastic polymer having a melting point between 115 to 130.degree. C. 
which is preferably selected from the group of ethylene homopolymers such 
as HDPE and LDPE, and ethylene copolymers with at least one 
.alpha.-olefin; and optionally and preferably a fourth polymer such as a 
copolymer of ethylene with an alkyl acrylate or vinyl ester e.g. EBA or 
EVA, having a melting point between 80 to 105.degree. C., preferably 90 to 
100.degree. C. 
Beneficially, the present invention provides a polymeric blend having an 
improved combination of properties especially for forming a heat sealing 
layer comprising a blend of copolymers of ethylene and at least one 
.alpha.-olefin, said blend having a broadened heat seal range to enhance 
sealability without sacrificing puncture resistance, and other desirable 
properties. 
Advantageously, the present invention produces films and bags less subject 
to seal failure relative to commercially available prior art films and may 
increase the impulse sealing temperature range. 
DETAILED DESCRIPTION OF THE INVENTION 
By the term "heat sealing layer" is meant a layer which is heat sealable to 
itself, i.e., be 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 bag form. 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 food body sealed within the tube. 
As used herein, "antioxidant" means an additive which retards oxidation, 
i.e., cross-linking, of that layer on irradiation. The heat sealing layer 
of the present invention may utilize antioxidants to inhibit crosslinking 
as further taught by Evert et al, U.S. Pat. No. 5,055,328 whose teachings 
and description is hereby incorporated by reference. 
Various copolymers of ethylene and at least one alpha olefin are employed 
in the film of the invention. It is to be understood that use of the term 
"copolymer of ethylene" means that the copolymer is predominantly 
comprised of ethylene and that at least 50% by weight of the copolymer is 
derived from ethylene monomer units in forming the copolymer. Suitable 
alpha olefins include C.sub.3 to C.sub.10 alpha-olefins such as propene, 
butene-1, pentene-1, hexene-1, methylpentene-1, octene-1, decene-1 and 
combinations thereof. The invention contemplates use not only of 
bipolymers, but copolymers of multiple monomers such as terpolymers e.g. 
ethylene-butene-1-hexene-1 terpolymer. The ethylene .alpha.-olefin 
copolymers used in the present invention may have various molecular 
weights, molecular weight distributions (M.sub.w /M.sub.n) and melt 
indices. Typically, the ethylene .alpha.-olefin copolymers used will have 
a melt index of less than 2 dg/min.(ASTM D-1238, condition E 190.degree. 
C.), preferably 1.0 dg/min. or less. 
The invention in all of its embodiments utilizes at least three different 
polymers having at least three different melting points. The term "melting 
point" means the peak melting temperature of the dominant melting phase as 
measured by Differential Scanning Calorimetry (DSC) with a 5.degree. 
C./min. heating rate according to ASTM D-3418. At least two, and 
preferably all three, of the required polymers of the inventive blend are 
ethylene .alpha.-olefin copolymers. It is preferred that the three 
required polymers of the invention be present in an amount of at least 10% 
by weight each in the blend. 
It is believed that useful physical properties, especially heat sealing 
range, are improved by selecting at least three polymers having melting 
points which are at least 5-10.degree. C. apart to provide melting 
characteristics over a broad temperature range which leads to a broadened 
heat sealing range and enhanced properties. The first and third polymers 
have peak melting points which are at least 40.degree. C. apart. 
The first polymer of the inventive blend has a melting point between 55 to 
75.degree. C., and comprises an ethylene alpha olefin copolymer. Examples 
of suitable first polymers include copolymers of ethylene with at least 
one C.sub.3 -C.sub.10 .alpha.-olefin, such as C.sub.2 C.sub.4 and C.sub.2 
C.sub.6 copolymers. Exemplary suitable first polymers may have a density 
of 0.900 g/cm.sup.3 or less, a melt index of about 1.5 dg/min. or less, 
and an M.sub.w /M.sub.n of less than 3, preferably about 2. Preferred 
commercially available first copolymers include those sold under the 
trademark TAFMER A-0585X and EXACT 9036. TAFMER is a trademark of Mitsui 
Petrochemical Co., Tokyo, Japan. EXACT is a trademark of EXXON Chemical 
Co., Houston, Tex., for their ethylene .alpha.-olefin polymers produced 
using metallocene single-site catalysts. These resins typically have a low 
level of crystallinity; 10-15% is typical. 
For the present invention, it is preferred that the first polymer of the 
heal sealing layer comprise a copolymer of ethylene having a melt index 
(M.I.) between about 0.2 and 2 (more preferably 0.2 to 0.7) dg/min. as 
measured by ASTM D-1238, at 190.degree. C. under a total load of 2.16 Kg 
(condition E). 
Regarding the suitable amount to be employed of the first polymer in the 
blend, the first polymer may comprise at least 10% and preferaby from 
about 20 to 35 weight % of the total weight of the required first, second 
and third polymer components, and preferably of the total polymer content 
of the polymer blend. Use of lesser amounts reduces shrinkability in those 
embodiments where heat shrinkability is desired and use of higher amount 
makes orientation more difficult and may increase extractable moieties to 
amounts which are undesirable for certain applications. When a preferred 
four component blend is used the first polymer will be present in an 
amount of from about 20 to 35% based upon the weight of the layer 
comprising the blend. 
The second polymer of the inventive blend has a melting point of from 85 to 
110.degree. C. and comprises a copolymer of ethylene and at least one 
alpha olefin. Examples of suitable second copolymers include copolymers of 
ethylene and at least one C.sub.3 to C.sub.10 alpha olefin, such as 
C.sub.2 C.sub.4, C.sub.2 C.sub.6, C.sub.2 C.sub.8 and C.sub.2 C.sub.4 
C.sub.6 copolymers. Exemplary suitable second polymers may have a density 
of at least about 0.900 g/cm.sup.3 and higher, preferably from 0.900 to 
0.915 g/cm.sup.3 ; a melt index of 2 dg/min. or less, preferably less than 
1.0 dg/min.; and a M.sub.w /M.sub.n of less than 3.5 preferably about 2. 
Preferred second copolymers include AFFINITY PL 1840, PL 1880, and Exact 
3032. AFFINITY is a trademark of Dow Chemical Co. of Midland, Mich., USA 
for its ethylene polymers produced using constrained geometry catalysts. 
Exact is a trademark of Exxon Chemical Co. of Houston, Tex., USA for their 
metallocene catalyst produced polymers. 
For the present invention, it is preferred that the second polymer of the 
heal sealing layer comprise a copolymer of ethylene having a melt index 
(M.I.) between about 0.5 and 2.5 (more preferably 0.7 to 1.5) dg/min. as 
measured by ASTM D-1238, at 190.degree. C. under a total load of 2.16 Kg 
(condition E). 
Regarding the suitable amount to be employed of the second polymer in the 
blend, the second polymer may comprise at least 10% and preferaby from 
about 30 to 70 weight % of the total weight of the required first, second 
and third polymer components, and preferably of the total polymer content 
of the polymer blend. Use of lesser amounts reduces puncture resistance in 
those embodiments where puncture resistance is desired. When a preferred 
four component blend is used the second polymer will be present in an 
amount of from about 25 to 60%, preferably greater than 30%, based upon 
the total weight of the layer comprising the four polymer blend. 
The third polymer of the inventive blend has a melting point of from 115 to 
130.degree. C. and comprises a thermoplastic polymer, preferably a 
copolymer of ethylene and at least one alpha olefin. Examples of suitable 
third polymers include copolymers of ethylene and at least one C.sub.3 to 
C.sub.10 alpha olefin, such as C.sub.2 C.sub.4, C.sub.2 C.sub.6, C.sub.2 
C.sub.8 and C.sub.2 C.sub.4 C.sub.6 copolymers; LDPE; HDPE; and propylene 
copolymers. Exemplary suitable third polymers may have a density of at 
least about 0.900 g/cm.sup.3 and higher, preferably from 0.900 to 0.930 
g/cm.sup.3, more preferably from 0.900 to 0.915 g/cm.sup.3 ; a melt index 
of 2 dg/min. or less, preferably 1.0 dg/min. or less; and a M.sub.w 
/M.sub.n of from about 2 to 12 or more, preferably greater than 3.5. 
Preferred third copolymers include ATTANE XU 61509.32. ATTANE is a 
trademark of Dow Chemical Co. of Midland, Mich., USA for its ethylene 
ULDPE(VLDPE)polymers. 
For the present invention, it is preferred that the third polymer of the 
heal sealing layer comprise a polymer of ethylene having a melt index 
(M.I.) between about 0.2 and 2 (more preferably 0.2 to 0.7) dg/min. as 
measured by ASTM D-1238, at 190.degree. C. under a total load of 2.16 Kg 
(condition E). 
Regarding the suitable amount to be employed of the third polymer in the 
blend, the third polymer may comprise at least 10% and preferably from 
about 10 to 30 weight % of the total weight of the required first, second 
and third polymer components, and preferably of the total polymer content 
of the polymer blend. Use of lesser amounts reduces heat sealing 
properties in those embodiments where heat sealability is desired and use 
of higher amounts reduces puncture resistance and may decrease 
shrinkability undesirably for certain applications. When a preferred four 
component blend is used the third polymer will be present in an amount of 
from about 10 to 30% based upon the weight of the layer comprising the 
blend. 
The optional and preferred fourth polymer of the inventive blend has a 
melting point of from 80 to 105.degree. C., preferably 90 to 100.degree. 
C. Suitable fourth polymers that may be employed in the heat sealing layer 
of the monolayer and multilayer films of the present invention include 
copolymers of ethylene and unsaturated esters having adhesive and/or heat 
sealing properties. Such copolymers are predominantly (&gt;50 wt. %) 
ethylene. Suitable copolymers include ethylene vinyl esters and ethylene 
alkyl acrylates such as ethylene-vinyl acetate, ethylene-vinyl propionate, 
ethylene-methyl methacrylate, ethylene-ethyl methacrylate, ethylene-ethyl 
acrylate, and ethylene n-butyl acrylate. Preferred copolymers are 
ethylene-vinyl esters such as ethylene-vinyl acetate, ethylene-vinyl 
formate, ethylene-vinyl propionate, and ethylene-vinyl butylate. 
Especially preferred is ethylene-vinyl acetate (EVA). Many different EVA 
resins are commercially available having a wide range of vinyl acetate 
contents and melt flow indices. 
Suitable vinyl ester or alkyl acrylate content of the preferred fourth 
polymer components used in the present invention include 4-28 (preferably 
4-18) weight percent vinyl ester or alkyl acrylate based on the total 
copolymer weight. 
For the present invention, it is preferred that the fourth polymer of the 
heal sealing layer comprise a copolymer of ethylene and a vinyl ester 
having a melt index (M.I.) between about 0.1 and 2 (more preferably 0.1 to 
0.5) dg/min. as measured by ASTM D-1238, at 190.degree. C. under a total 
load of 2.16 Kg (condition E). It is preferred that the fourth polymer 
when present comprise from about 10 to 30 weight % of the total weight of 
four polymer components, and preferably of the total polymer content of 
the polymer blend. 
A most preferred EVA copolymer is that sold by the Exxon Chemical Company 
of Houston, Texas under the brand designation ESCORENE LD 701.06 with the 
following reported properties, a density of 0.93 g/cm.sup.3, a vinyl 
acetate content of 10.5 wt. % and a melt index of about 0.19 dg/min., and 
a melting point of about 97.degree. C. 
It should be noted that the above reported melt indices are initial values 
for the pelletized resins as received by the manufacturer. Such as 
received pellet values are intended as used herein unless otherwise noted. 
Crosslinking, especially irradiative crosslinking, is known to increase 
the average molecular weight by formation of longer chains of molecules 
than originally present. Therefore, crosslinking will also reduce the melt 
index of a polymer from its initial value to a lower value since the melt 
index is not only a measure of viscosity but also an indirect measure of 
molecular weight. Also, the melt blended material will also have its own 
melt index which is not to be confused with that of the original copolymer 
components of the blend. 
Advantageously, the present invention utilizes a polymeric blend material 
in the heat sealing layer which has a broad range of melt behavior and 
characteristics which are believed to enhance seal formation and strength 
while providing excellent puncture resistance. Beneficially, such 
polymeric material may provide a broad combination of desirable properties 
having important commercial advantages for production and use 
thermoplastic films, particularly biaxially stretched films having heat 
shrinkability properties at 90.degree. C. Advantageously such films may 
have excellent puncture resistance, high shrinkability, high tensile 
strengths, good modulus, low haze, high gloss, excellent optical 
properties, and importantly a broad sealing range and good seal strength. 
Beneficially combinations of these desirable attributes are present in 
various embodiments of the invention. The blend has a sufficient film 
strength to withstand orientation (especially a tubular double-bubble type 
biaxial orientation process). The blend also resists "burn through" during 
heat sealing operations and produces strong fusion bonds as described 
below. Such polymer blends of the invention provide sufficient polymeric 
material having chain lengths suitable for diffusion and entanglement 
between adjacent layers during heat sealing operations to form strong 
integral fusion bonds. 
It will be appreciated by those skilled in the art that materials of broad 
molecular weight or materials which are polymodal in molecular weight 
distribution are contemplated, as are blends of materials which have very 
narrow molecular weight distributions. 
An advantage of the present invention is that use of the presently 
disclosed blends facilitates a broad heat sealing range for irradiated 
films. 
Upon exposure to irradiation sufficient to cause cross-linking, heat 
sealable layers generally tend to diminish their heat sealing ability. 
However, an antioxidant may be added to the heat sealable inner layer of 
the tubular article to inhibit cross-linking within the polymer, thereby 
reducing the adverse effects of over-irradiation upon the heat sealing 
properties. Addition of an antioxidant further allows the irradiation 
dosage to be sufficiently high to allow other layers of the multilayer 
film to retain the beneficial effects of irradiation. Beneficially, films 
of the present invention may be crosslinked by use of chemical agents or 
by irradiation, preferably at a level between 1 and 10 Mrad, more 
preferably 2-6 Mrad. 
The heat sealing layer of the present invention will comprise a blend of at 
least three different polymers, at least two of which are copolymers of 
ethylene and at least one .alpha.-olefin, and optionally and preferably a 
fourth polymer which preferably is a copolymer ethylene and at least one 
unsaturated ester. 
As generally recognized in the art, resin properties may be further 
modified by blending in additional resins or additives such as colorants, 
processing aids, antiblock agents and slip agents, etc. and it is 
contemplated that the specific polymer blends as described above may be 
further blended with resins such as very low density polyethylene (VLDPE), 
linear low density polyethylene (LLDPE), low density polyethylene (LDPE), 
high density polyethylene (HDPE), ionomers, polypropylene, ethylene 
acrylates or esters; or may be formed into multilayer films with one or 
more additional layers of such resins or blends thereof. 
The 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 
into any or all layers. 
Advantageously, in one embodiment of the present invention a blend of a 
first polymer having a melting point between 55 to 75.degree. C. 
comprising a copolymer of ethylene and at least one .alpha.-olefin; a 
second polymer having a melting point between 85 to 110.degree. C. 
comprising a copolymer of ethylene and at least one .alpha.-olefin; and a 
third polymer having a melting point between 115 to 130.degree. C. 
comprising a thermoplastic polymer; and the blend may otherwise be: i) 
free from EVA; ii) have less than 15% by wt. EVA; iii) have greater than 
25% EVA; or iv) have from 15% to 25% EVA, based upon the total weight of 
the blend layer. 
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. For example, according to the present 
invention, in extrusion or coextrusion of the polymer blends of the 
invention, barrel and die temperatures may range between about 145.degree. 
C. and 185.degree. C. However, variations are expected which may depend 
upon such factors as variation of polymer resin selection, use of other 
resins e.g. in the blend or in separate layers in a 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. 
Blends of the present invention may be manufactured into various useful 
articles e.g. cast films using e.g. a slot die, or conventional blown 
films where a tubular film is produced directly from the die melt, molded, 
thermoformed, blow molded sheets, rigid solid, hollow or foamed bodies may 
also be produced. In a preferred embodiment, extrusion by a trapped bubble 
or double bubble process of the type described in U.S. Pat. No. 3,456,044 
is used. In a preferred process for making an oriented or heat shrinkable 
film, a primary tube comprising the inventive plastic blend is extruded, 
and after leaving the die is inflated by admission of air, cooled, 
collapsed, and then preferably oriented by reinflating to form a secondary 
bubble with reheating to the film's orientation (draw) temperature range. 
Machine direction (M.D.) 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 (T.D.) orientation is obtained by radial 
bubble expansion. The oriented film is set by rapid cooling. Suitable 
machine direction and transverse direction stretch ratios are from about 
3:1 to about 5:1 with a ratio of about 4:1 preferred. 
Films of the present invention may be monolayer or multilayer films 
preferably of 10 mils or less. Multilayer films have the following 
preferred layer thicknesses. The thickness of the heat sealable inner 
thermoplastic first layer is typically between about 0.5 and about 2.0 
mils. Thinner layers may perform the aforedescribed functions, 
particularly in in structures of 5 or more layers. Thicker layers may not 
appreciably improve processability of the film and may reduce total film 
performance. Accordingly, they would be uneconomical. 
The barrier layer thickness is preferably between about 0.1 and about 0.5 
mils. Thinner barrier layers may not perform the intended functions and 
thicker layers do not appreciably improve performance. 
In the barrier layer embodiment of this invention the outer thermoplastic 
layer of the enclosing multilayer film is on the opposite side of the core 
layer from the inner layer, and in direct contact with the environment. In 
a preferred three layer embodiment of the invention this outer layer is 
directly adhered to the core layer. Since it is seen by the use/consumer, 
it must enhance optical properties of the film. Also, it must withstand 
contact with sharp objects so is termed the abuse layer and provides 
abrasion resistance. 
The outer layer is preferably formed of a blend of ethylene vinyl acetate 
as at least the major constituent, more preferably at 50% weight percent 
EVA and most preferably at least 70 weight percent EVA. Also, the outer 
layer preferably has between about 3% and about 18% vinyl acetate content 
to provide good shrinkability. 
Alternatively, the outer layer may be formed of other thermoplastic 
materials as for example polyamide, styrenic copolymers e.g. 
styrene-butadiene copolymer, polypropylene, ethylene-propylene copolymer, 
ionomer, or an alpha olefin polymer and in particular a member of the 
polyethylene family such as linear low density polyethylene (LLDPE), very 
low density polyethylene (VLDPE and ULDPE), HDPE, LDPE, an ethylene vinyl 
ester copolymer or an ethylene alkyl acrylate copolymer or various blends 
of two or more of these materials. 
The thermoplastic outer layer thickness is preferably between about 0.5 and 
1.0 mils. Thinner layers may be less effective in performing the abuse 
resistance function. 
Unless otherwise noted, the following physical properties are used to 
describe the present invention, films and seals and are measured by either 
the test procedures described below or tests similar to the following 
methods. 
Average Gauge: ASTM D-2103 
Tensile Strength: ASTM D-882, method A 
1% Secant Modulus: ASTM D-882, method A 
Percent Elongation: ASTM D-882, method A 
Molecular Weight Distribution: Gel permeation chromatography 
Gloss: ASTM D-2457, 45.degree. Angle 
Haze: ASTM D-1003-52 
Melt Index: ASTM D-1238, Condition E(190.degree. C.) 
Melting Point: ASTM D-3418, DSC with 5.degree. C./min. heating rate. 
Vicat Softening Point: ASTM D-1525-82 
All ASTM test methods noted herein are incorporated by reference into this 
disclosure. 
DYNAMIC PUNCTURE RESISTANCE 
The dynamic puncture resistance procedure is used to compare films for 
their resistance to bone puncture. It measures the energy required to 
puncture a test sample with a sharp pyramidal metal point made to simulate 
a sharp bone end. A Dynamic Ball Burst Tester, Model No. 13-8, available 
from Testing Machines, Inc., Amityville, Long Island, N.Y., is used, and a 
modified tip is installed on the tester probe arm for use in this test 
procedure. The modified tip is constructed from a 3/8 inch (0.95 cm) 
diameter conical tip having a configuration of a right circular cone with 
the angle between the cone axis and an element of the conical surface at 
the vertex being about 65.degree.. Three equally spaced and abutting 
planar surfaces are machined to a smooth finish on the cone surface to 
form a pyramidal shaped point. At least six test specimens approximately 4 
inches (10 cm) square are prepared, a sample is placed in the sample 
holder, and the pendulum is released. The puncture energy reading is 
recorded. The test is repeated until at least 6 samples have been 
evaluated. The results are calculated in cm-kg per mil of film thickness 
and are averaged. 
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. 
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.

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. In the following examples, all layers were 
extruded (coextruded in the multilayer examples) as a primary tube which 
was cooled upon exiting the die e.g. 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. All percentages are by weight unless indicated 
otherwise. 
EXAMPLE 1 
In Example 1, a biaxially stretched, heat shrinkable, monolayer film of the 
present invention was made and its physical properties tested. 
Thermoplastic resins generally in pellet form were mixed together to form 
an inventive blend of: a first polymer comprising a copolymer 
predominantly of ethylene with butene-1 monomer and having a reported 
density of about 0.885 g/cm.sup.3, a melt index of 0.5 dg/min., a melting 
point of 68.degree. C. which is available under the trademark Tafmer 
A0585X from Mitsui Petrochemical Industries, Ltd. of Tokyo, Japan; a 
second polymer comprising ethylene-.alpha.-olefin copolymer sold by Dow 
Chemical Company of Midland, Mich., U.S.A. under the trademark Affinity PL 
1840 which is reportedly a copolymer of ethylene and octene-1(9.5%) having 
a melt index of about 1.0 dg/min. and a density of about 0.908 g/cm.sup.3, 
and a melting point of about 103-106.degree. C.; a third polymer 
comprising 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.; and a fourth polymer 
comprising a copolymer of ethylene and vinyl acetate(EVA) available from 
Exxon Chemical Company of Houston Tex., U.S.A. under the trademark 
Escorene LD 701.06 and having 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.; 4.0% by weight of a slip 
processing aid sold under the trademark Ampacet 500301 by Ampacet Corp. of 
Tarrytown, N.Y., U.S.A.; and 2.0% by weight of a slip processing aid sold 
under the trademark Ampacet 100510 by Ampacet Corp. of Tarrytown, N.Y., 
U.S.A. 
The blended resins were melt plastified in an extruder and a monolayer 
thermoplastic tube was extruded. The extruder barrel and extrusion die 
temperature profile was set at about 335.degree. F. (168.degree. C.) to 
about 360.degree. F. (182.degree. C.). The extruded primary plastic tube 
was then cooled, reheated, biaxially stretched, and cooled according to a 
double bubble process and the resultant biaxially stretched film wound on 
a reel. The machine direction (M.D.) draw or orientation ratio was about 
4.9:1 and the transverse direction (T.D.) bubble or orientation ratio was 
about 4.2:1. The draw point or orientation temperature is below the 
melting point for each layer to be oriented and above that layer's Vicat 
softening point. The draw point temperature of the film of example 1 is 
believed to have been about 160 to 175.degree. F. (71-79.degree. C.). Draw 
point temperature, bubble cooling rates and orientation ratios are 
generally adjusted to maximize bubble stability with use of higher 
throughput rates and lower draw point temperatures believed to provide 
films having higher puncture resistance relative to use of lower 
throughputs or higher orientation temperatures. 
The average gauge was measured to be about 2.25 mil (57 microns). Haze and 
45.degree. gloss were measured and are reported as 3.4% and 86 Hunter 
Units(HU). The Heat shrinkability if the fresh film was determined to be 
46% in the machine direction (M.D.) and 54% in the transverse direction 
(T.D.) at 90.degree. C. 
Those skilled in the art of manufacturing biaxially oriented films know of 
different and various processes of such manufacture and the present 
inventive films include biaxially oriented or biaxially stretched films 
regardless of the method used for their production as well as uniaxially 
oriented and unoriented films including slot cast and hot blown films. 
The above film sample is also usefully crosslinked by irradiation e.g. at a 
level of 2-6 megarads (Mrad) after biaxial stretching (which irradiative 
process is hereinafter referred to as post-irradiation), in the manner 
generally described in Lustig et al, U.S. Pat. No. 4,737,391 which is 
hereby incorporated by reference. 
EXAMPLES 2-3 
In Example 2, a biaxially stretched, heat shrinkable, coextruded, 
multilayer film of the present invention was made and its physical 
properties tested. Example 3 is a comparative example of a similar 
commercially acceptable multilayer film having a similar structure except 
that the heat sealing layer comprises the blend of the invention. 
Examples 2-3 are three layer films. One extruder was used for each layer. 
Each extruder was connected to an annular coextrusion die from which heat 
plastified resins were coextruded forming a primary tube having a first 
inner layer, a second core layer and a third outer layer. The first and 
third layers being directly attached to opposing sides of the second core 
layer. The first/second/third layer ratio was about 62:10:28. 
In Examples 2-3, for each layer, the resin mixture was fed from a hopper 
into an attached single screw extruder where the mixture was heat 
plastified and extruded through a three layer coextrusion die into a 
primary tube. The extruder barrel temperatures for the second (core) layer 
was between about 255-285.degree. F. (124-141.degree. C.); for the first 
(inner) layer was about 300-330.degree. F. (149-166.degree. C.); and for 
the third (outer) layer was about 300-340.degree. F. (149-171.degree. C.). 
The extrusion die had an annular exit opening of 31/2 inch diameter with a 
0.040 inch gap (8.89 cm.times.0.102 cm). The coextrusion die temperature 
profile was set from about 320.degree. F. to 335.degree. F. 
(160-168.degree. C.). The extruded multilayer primary tube was cooled by 
spraying with cold tap water (about 7-14.degree. C.). 
The cooled primary tube was flattened by passage through a pair of nip 
rollers. In Examples 2-3, a flattened tube of about 315/16 to 37/8 inches 
(9.8 to 10 cm) 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 4.8:1 to 4.9:1 and the transverse direction 
(T.D.) bubble or orientation ratio was about 4.6:1 to 4.7:1 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 predominant 
glass transition point and is believed to be about 178.degree. F. 
(81.degree. C.) for Example 2 and about 185.degree. F. (85.degree. C.) for 
Example 3. 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 2-3 having an average gauge of 2.5 to 2.25 
were biaxially oriented and had an excellent appearance. 
For Example 2, the first layer comprised an inventive blend of: about 24 
wt. % of a first polymer comprising a copolymer predominantly of ethylene 
with butene-1 monomer and having a reported density of about 0.885 
g/cm.sup.3, a melt index of 0.5 dg/min., a melting point of 68.degree. C. 
which is available under the trademark Tafmer A0585X from Mitsui 
Petrochemical Industries, Ltd. of Tokyo, Japan; about 29.1 wt. % of a 
second polymer comprising ethylene-.alpha.-olefin copolymer sold by Dow 
Chemical Company of Midland, Mich., U.S.A. under the trademark Affinity PL 
1840 which is reportedly a copolymer of ethylene and octene-1(9.5%) having 
a melt index of about 1.0 dg/min., a density of about 0.908 g/cm.sup.3, 
and a melting point of about 103-106.degree. C.; about 19.2 wt. % of a 
third polymer comprising 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.; and about 19.3 
wt. % of a fourth polymer comprising a copolymer of ethylene and vinyl 
acetate (EVA) available from Exxon Chemical Company of Houston Tex., 
U.S.A. under the trademark Escorene LD 701.06 and having 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.; 4.0% 
by weight of a processing aid sold under the trademark Ampacet 500301 by 
Ampacet Corp. of Tarrytown, N.Y., U.S.A.; and 4.4% by weight of a 
processing aid sold under the trademark Ampacet 100031 by Ampacet Corp. of 
Tarrytown, N.Y., U.S.A. 
The heat sealing layer was the first layer of the multilayer film and the 
inner layer of the film tube. For Comparative Example 3, the heat sealing 
layer comprised a blend of about 69.1 wt. % of an ethylene octene-1 
copolymer sold by Nova Chemicals Ltd. of Calgary, Alberta, Canada under 
the trademark Novacor D032-07 which is a C.sub.2 C.sub.8 copolymer 
reportedly having a density of about 0.912 g/cm.sup.3, a melt index of 
about 1.0 dg/min., a melting point of about 122.degree. C.; about 22.5 wt. 
% of the above noted LD 701.06 EVA; about 4.4 wt. % of the above noted 
Ampacet 100031 processing aid; and about 4 wt. % of the above noted 
Ampacet 500301 processing aid. 
For Examples 2-3, each core layer comprised a 3:1 blend of commercially 
available vinylidene chloride-methylacrylate copolymer and vinylidene 
chloride-vinyl chloride copolymer. 
For Example 2, the third (outer) layer comprised: about 47 wt. % of a 
commercially available ethylene-.alpha.-olefin copolymer sold by Dow 
Chemical Company of Midland, Mich., U.S.A. under the trademark Affinity PL 
1840 which is reportedly a copolymer of ethylene and octene-1 having a 
melt index of about 0.5 dg/min and a density of about 0.908 g/cm.sup.3 and 
a melting point of about 103-106.degree. C.; about 24.3% of a copolymer of 
ethylene and vinyl acetate (EVA) available from Exxon Chemical Company of 
Houston, Tex., U.S.A. under the trademark Escorene LD 701.06 having 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.; about 24.3% of a copolymer of ethylene with butene-1 
monomer and having a reported density of about 0.885 g/cm.sup.3 a melt 
index of 0.5 dg/min., a melting point of 68.degree. C. which is available 
under the trademark Tafmer A0585X from Mitsui Petrochemical Industries, 
Ltd. of Tokyo, Japan; 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 example 3, the third layer comprised about 80.6 wt. % of the above 
noted Novacor D032-07 copolymer; about 15 wt. % of the above noted EVA; 
and about 4.4 wt. % of the above noted Ampacet 100031 processing aid. 
The multilayer films of Examples 2-3 were irradiated after orientation by 
electron beam according to methods well known in the art to a level of 5.3 
and 4.5 Mrad, respectively. 
Physical properties of the irradiated multilayer films were tested and are 
reported in Table 1. 
TABLE 1 
__________________________________________________________________________ 
TENSILE 
STRENGTH 
ELONGATION IMPULSE 
AVG. at RT .times. 
AT BREAK 
1% SECANT SHRINK SEAL 
GAUGE 
10.sup.3 psi 
at RT MODULUS 
DYNAMIC 
at 90.degree. C. 
GLOSS 
RANGE 
Ex. 
mil (Mpa) % MPa PUNCTURE 
% HAZE 
at 45.degree. 
min./max. 
No. 
(.mu.) 
MD/TD MD/TD MD/TD cmKg/.mu. 
MD/TD 
% Angle 
(volts) 
__________________________________________________________________________ 
2 2.5.dagger. 
13.2/15.0 
218/187 213/225 
0.13 42/49 
5.5 77 32-50 
(63.5) 
(91/103) 
3* 
2.25 13.5/14.7 
186/179 ND 0.08 23/36 
ND ND 34-48 
(57.2) 
(93/101) 
4 2.5.dagger. 
14.6/14.4 
184/176 ND 0.09 40/46 
5.9 81 34-50 
(63.5) 
(101/99) 
5 2.59 12.6/12.1 
191/196 ND 0.09 40/47 
6.1 76 34/49 
(65.8) 
(87/83) 
6 2.57 14.1/13.5 
184/178 ND 0.09 40/46 
6.3 76 34/49 
(65.3) 
(97/93) 
7 2.58 15.0/13.9 
172/179 ND 0.11 47/52 
5.8 75 35/50 
(65.5) 
(103/96) 
__________________________________________________________________________ 
ND = Not Determined 
RT = Room Temperature (20-23.degree. C.) 
* = Typical Values 
.dagger. = Nominal Thickness 
Referring now to Table 1, Comparative Example 3 presents physical property 
values which are acceptable for food packaging film which are commercially 
useful for packaging processed meats. Example 2 of the present invention 
has comparable or better values for shrink, puncture resistance and 
impulse seal range relative to Comparative Example 3 for multilayer films 
of substantially the same gauge thickness. Multilayer films of the present 
invention demonstrate excellent tensile strengths, elongation at break 
values and 1% secant modulus values as well as very good haze and gloss 
properties. The elongation at break of the inventive film is also good. 
Film of the invention processed well. 
The films of the present invention have desirable sealing properties. The 
impulse seal range test demonstrates broader sealing range than that of 
the control. 1 and 2 volt differences in sealing range values are 
significant and the 2 volt extension on both ends of the range is believed 
to translate into broader ranges for many commercially available sealers 
other than the Sentinel. 
In controlled field tests, bags formed from the films of Examples 2 and 3 
were laminated with 7 mil (178 micron)thick films and used to package 
shortloins and evacuated and sealed with commercial impulse sealing 
machines. During the sealing operation, air was evacuated from the 
shortloin containing bag and the evacuated bag was temporarily sealed by 
mechanically clamping near the mouth end and then spaced inwardly from the 
clamp the bag was impulse sealed. The excess film was severed from the 
sealed bag by a knife cutting across the mouth end between the impulse 
seal and the clamp. The inventive film tested out with no burn through 
leakers, no bone puncture failures and only a 16% failure at load-off for 
shortloins held overnight compared to a 27% failure for films similar to 
comparative example 3 and 15% for another commercially successful film for 
this application. 
The above tests for leakers, and impulse seal range demonstrate films 
having a heat sealing layer can be made according to the present invention 
to produce better seals. These seals are stronger, and less subject to 
failure due to variations in heat sealing process parameters and equipment 
and have a desirable combination of high shrinkability at low temperatures 
e.g. 90.degree. C., high puncture resistance and a broad sealing range. 
EXAMPLES 4-7 
For all the Examples 4-7, biaxially stretched, heat shrinkable 3-layer 
coextruded films similar to the inventive film of example 2 were made 
under similar conditions. The layer ratio was the same as for Example two 
and the formulations were the same except as follows. Example 4 had the 
same formulation as Example 2. In Example 5, Affinity.TM. PL 1880 from Dow 
Chemical Co. was substituted for PL 1840 copolymer in both the first and 
third layers. PL 1880 is a copolymer of ethylene and octene-1 having the 
following reported properties; density of 0.902 g/cm.sup.3 ; 1 M.I.; a 
melting point of 100.degree. C.; a Vsp of 83.degree. C.; and a M.sub.w 
/M.sub.n &lt;3.0. In Example 6, Affinity.TM. 58000.02 from Dow Chemical Co. 
was substituted for PL 1840 copolymer in both the first and third layers. 
58000.02 is a copolymer of ethylene and octene-1 having the following 
reported properties; density of 0.908 g/cm.sup.3 ; M.I. of 0.9; a melting 
point of 105.degree. C.; and a M.sub.w /M.sub.n &lt;3.0. In Example 7, 
Exact.TM. 3032 from Exxon Chemical Co. was substituted for PL 1840 
copolymer in both the first and third layers. Exact.TM. 3032 is a 
terpolymer of ethylene, hexene-1, and butene-1 having the following 
reported properties; density of 0.902 g/cm.sup.3 ; M.I. of 1.2; a melting 
point of 94.degree. C.; a Vsp of 79.degree. C.; and a M.sub.w /M.sub.n 
&lt;2.5. All of the films of examples 4-7 were irradiated to a level of about 
5 Mrad according to methods well known in the art. 
Physical properties of the irradiated multilayer films were tested and are 
reported in Table 1. 
Referring now to Table 1, Examples 4-7 all present physical property values 
which are acceptable for food packaging films which are commercially 
useful for packaging articles e.g. fresh or processed meats. 
Examples 2-7 are three layered films. However, multilayered films of two or 
four or more layers are contemplated by the present invention. The 
inventive multilayer films may include tie or adhesive layers as well as 
layers to add or modify various properties of the desired film such as 
heat sealability, toughness, abrasion resistance, tear resistance, 
puncture resistance, optical properties, gas or water barrier properties, 
shrinkability, and printability. These layers may be formed by any 
suitable method including coextrusion, extrusion coating, and lamination. 
In another embodiment of the invention, the three required blend components 
are not strickly in a single blend but may be placed into two adjacent 
layers e.g. by coextrusion, coating lamination, or lamination. In this 
embodiment of the invention a first heat sealing layer comprises a polymer 
such as the above mentioned third polymer having a melting point of from 
about 115 to 130.degree. C. Optionally this first layer may further 
comprise either or both of the aforementioned first or fourth polymers 
having respective melting point of 55 to 75.degree. C., and 80 to 
105.degree. C. (preferably 90 to 100.degree. C.). Most preferably this 
first layer will comprise a combination of the first, third and fourth 
polymers specified above, especially two copolymers of ethylene and at 
least one alpha olefin and one copolymer of ethylene and a vinyl ester or 
alkyl acrylate(most desirably EVA). In this alternative embodiment, in 
direct contact with the first layer is a second layer which comprises a 
blend of the first and second polymers described above i.e. a first 
polymer having a melting point of 55 to 75.degree. C. in combination with 
a second polymer having a melting point of 85 to 110.degree. C. This 
inventive two layer film may be usefully employed as a blown film, cast 
film or may be axially stretced in one or two directions to produce a heat 
shrinkable film of two layers it may also through lamination processes or 
coextrusion be part of a multilayer film structure having 3 or more layers 
but may find special utility as a 5 layer film or 7 or greater layer film. 
An example of a preferred structure includes a first heat sealing layer 
having a blend of EVA and Attane XU 61509.32; a second layer comprising a 
blend of Exact 3033 (preferably 60%) and Tafmer A-0585X (preferably 40%); 
a third core layer comprising a gas barrier resin such as EVOH or saran; a 
fourth layer comprising the same blend as the second layer; and a fifth 
layer comprising a blend similar to the first layer. A suitable layer 
ratio would be 10%/50%/6%/24%/10%. In an alternative preferred embodiment, 
the first and fifth layers would comprise a blend if the first, third, and 
fourth polymers i.e. a plastomer (55-75.degree. C. m.p.)+a polyethylene 
homo- or copolymer (115-130.degree. C. m.p.)+ an EVA (90-100.degree. C. 
m.p.). 
In another aspect of the invention, one or more alternative layers having 
gas barrier properties may be incorporated into a multilayer film as 
either an intermediate or surface layer or both. For example, ethylene 
vinyl alcohol copolymer (EVOH), vinylidene chloride-methylacrylate 
copolymer, nylon such as nylon 6 or amorphous nylon, vinylidene 
chloride-vinyl chloride copolymer, acrylonitriles were other materials 
having oxygen barrier properties may be used in one or more layers such as 
the core layer. Blends of resins having gas barrier properties may also be 
used e.g. a blend of nylon with EVOH. Typical gas barrier films will have 
a gas barrier layer having an oxygen transmission of less than 15 cc/100 
in.sup.2 for 24 hrs. at 1 atm. 
While this invention has been described with reference to certain specific 
embodiments, it will be recognized by those skilled in the art that many 
variations are possible without departing from the scope and spirit of the 
invention.