Blends of ionomer with propylene copolymer and articles

Blends of (a) 80-93 weight percent of an ethylene/acid ionomer, and (b) 7-20 weight percent of a propylene/.alpha.-olefin copolymer are used to prepare peelable seals having nearly constant and predictable peel strength over an extended heat seal temperature range. Some of the seals so produced also show stress whitening.

TECHNICAL FIELD 
This invention relates to blends of an ionomer with a 
propylene/.alpha.-olefin copolymer, to heat-sealable films and/or 
laminates made from such blends, and to flexible film packages made from 
such films and/or laminates. Seals produced from such heat-sealable films 
and/or laminates are characterized by a nearly constant peel strength over 
an extended heat seal temperature range and by being peelable (i.e. having 
the seal failure occur) primarily at the interface of the sealing 
surfaces) rather than film-tearing. The blends, films and/or laminates of 
the present invention permit the manufacture of a more consistent finished 
product, i.e. a heat-sealed flexible film package having a seal of 
predictable and constant peel strength, in spite of inevitable variations 
in the heat seal temperature used in the production of such packages. 
Further, some of the seals produced using the blends of the present 
invention will be characterized by stress whitening, i.e. when stress is 
applied to the seal, either by peeling in the normal fashion or by an 
attempt to tamper with the seal, the film and/or laminate will change from 
a clear appearance to a cloudy or white appearance. 
BACKGROUND ART 
U.S. Pat. No. 4,346,196, granted Aug. 24, 1982 to Hoh et al., discloses 
80/20-20/80 blends of an ionomer dipolymer with an ionomer terpolymer and 
the use of such blends in the production of heat-sealable films for use in 
flexible film packages to create both tearable and peelable seals in the 
flexible film package. Hoh et al. does not use an ethylene/.alpha.-olefin 
copolymer in the blend, and while Hoh et al. does disclose that suitable 
heat seals can be achieved over a broad temperature range, the strength of 
such seals is temperature dependent. 
U.S. Pat. No. 4,279,344, granted July 21, 1981 to Holloway, discloses 
blends of an ionomer with a propylene/.alpha.-olefin copolymer and the use 
of such blends in the preparation of heat sealable films for use in 
laminated packaging structures to create peelable seals. Holloway, 
however, discloses blends that are high in the propylene/.alpha.-olefin 
copolymer (i.e. at least 65 weight percent) and low in the ionomer (i.e. 
at most 35 weight percent). In addition, Holloway declares his objective 
to be the creation of peelable seals of moderate strength that can 
tolerate temperatures necessary for retort sterilization (i.e. about 
250.degree. F.). Such is not the objective of the peelable seals of the 
present invention, which, in fact, are not retortable. In addition, 
Holloway's blend requires a seal temperature of about 450.degree. F., 
which is much higher than what would be used with the blends of the 
present invention. 
U.S. Pat. No. 3,819,792, granted June 25, 1974 to Ono et al., discloses 
blends C-2 or C-3 olefin homopolymer or copolymer with 
ethylene/methacrylic acid ionomer that can be high in ionomer, but only up 
to a maximum of 70 weight percent. Ono discloses such blends as being 
useful in the production of double wall tubing. No mention is made of 
possible use in heat sealable film. 
DISCLOSURE OF THE INVENTION 
This invention relates to blends of an ionomer with a 
propylene/.alpha.-olefin copolymer, to heat-sealable films and/or 
laminates made from such blends, and to flexible film packages made from 
such films and/or laminates. Seals produced from such films and/or 
laminates are characterized by a nearly constant peel strength over an 
extended heat seal temperature range, by being peelable (rather than film 
tearing), and by showing stress whitening, at least in some instances. By 
"nearly constant" there is meant a peel strength that varies not more than 
.+-.2.5 g/mm, and by "extended" there is meant a temperature range of at 
least 10.degree. C. Certain of the compositions of the present invention 
are also capable of being used to prepare fusion or film-tearing seals by 
substantially increasing the heat sealing temperature. Thus, a package can 
be prepared from films or laminates from such compositions, which packages 
will exhibit a peelable seal in one area of the package and a fusion seal 
in another. Such packages can be used in packaging snack foods and 
disposable medical products. 
In particular, the blends of the present invention comprise 80-93 weight 
percent of an ethylene/acid ionomer and 7-20 weight percent of a 
propylene/.alpha.-olefin copolymer, preferably 88-92 weight percent 
ionomer and 8-12 weight percent propylene/.alpha.-olefin copolymer. 
The ionomers used in the blends of the present invention can be dipolymer 
or terpolymer ionomers such as described in U.S. Pat. Nos. 3,264,272; 
3,404,134; and 3,355,319. When the ionomer is a dipolymer, the acid 
monomer should be greater than 12 but not more than 25 weight percent of 
the ionomer, preferably 13-18 weight percent and most preferably 14-16 
weight percent. When the ionomer is a terpolymer the third monomer should 
be from 5-25 weight percent of the ionomer, preferably 6-20 weight percent 
and most preferably 8-15 weight percent. The acid monomer in the ionomer 
should be 5-45% neutralized with a mono- or divalent metal ion, preferably 
10-30% and most preferably 15-25%, and the ionomer should be characterized 
by a melt index (measured according to ASTM D-1238, condition E) prior to 
neutralization of 1-100 g/10 minutes preferably 3-25 g/10 minutes and most 
preferably 5-20 g/10 minutes. The metal used for neutralizing the ionomer 
can be selected from those disclosed in the three U.S. patents cited above 
in this paragraph, and those patents are hereby incorporated herein by 
reference. 
Suitable acid monomers include monoethylenically unsaturated monobasic 
acids having 3-8 carbon atoms such as acrylic, methacrylic, ethacrylic, 
itaconic, alkyl hydrogen maleic or fumaric acids. Preferred acid monomers 
include acrylic and methacrylic acid because they are thermally stable and 
commercially available. Other monomers suitable for use in the preparation 
of the terpolymer include monoethylenically unsaturated copolymerizable 
monomers such as those disclosed in U.S. Pat. No. 4,321,337 at column 4, 
lines 28-44, which description is hereby incorporated herein by reference. 
(Meth) acrylate esters are preferred, with isobutyl acrylate being most 
preferred because of thermal stability and adhesion considerations. 
Suitable mono- and divalent ions for neutralization of the acid in the 
ethylene/acid ionomer include ammonium, lithium, sodium, potassium, 
calcium, magnesium and zinc, preferably sodium and zinc, with zinc being 
most preferred because of its superior adhesion characteristics. Mixtures 
of more than one acid comonomer and/or more than one other monomer can 
also be used in the preparation of the ionomer. Neutralization of the acid 
in the ionomer can be achieved during preparation of the ionomer or during 
preparation of the ionomer/copolymer blend, thereby eliminating a separate 
neutralization step. Similarly, the degree of neutralization of the acid 
in the ionomer can be adjusted to the proper range by blending more highly 
neutralized ionomer with an appropriate amount of unneutralized or 
partially neutralized corresponding acid copolymer. 
Blends of two acid copolymers, including terpolymers can be used as base 
resins for neutralization. 
The propylene/.alpha.-olefin copolymer should contain 1-12 weight percent 
.alpha.-olefin monomer, preferably 2-8 weight percent and most preferably 
3-5 weight percent, to promote a balance of seal characteristics, 
including seal strength and fusion or no fusion, and the melt flow rate 
(MFR) (as measured by ASTM D-1238, condition L) of this copolymer should 
be at least 4 g/10 minutes. Suitable .alpha.-olefin comonomers include 
ethylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, 
3-methylbutene-1, and 4-methylbutene-1, preferably ethylene and butene-1, 
with ethylene being most preferred because of low cost and commercial 
availability of such copolymers. Mixtures of copolymers can also be used. 
The ethylene/acid ionomer and the propylene/.alpha.-olefin copolymer are 
blended to form a molecular blend (i.e. an intimate admixture). The blend 
can be prepared by any of the common methods for blending polymeric 
materials. For example, solutions of the individual polymeric materials 
can be prepared, mixed with each other, and the solvent can be 
subsequently removed; the individual polymeric materials can be mixed with 
each other in molten form, e.g. by melt blending in an extruder; or the 
individual polymeric materials can be blended with each other in a high 
shear mixing device, e.g. a two-roll mill or a Banbury mixer. Preferably, 
the individual polymeric components will be melt blended with each other 
in an extruder and formed by melt extrusion, flat die extrusion, blown 
film extrusion or any other technique that will produce the desired shape. 
The blends of the present invention can be prepared as self-supporting 
films, as coextrusions, as laminates for film substrates or as coatings 
for conventional flexible packing materials, including films, foils, paper 
and webs. Materials of construction for such films, foils, papers and webs 
include organic polymers, metal foils, bleached and unbleached papers and 
board, glassine, non-woven fabrics, and composites of such materials. The 
blends of the present invention are particularly well suited for use with 
substrates made from polyolefin resins such as high density polyethylene 
and oriented polypropylene. When used as a laminate or coating, the blends 
of the present invention can be applied over the entire substrate or over 
only that portion of the substrate to be sealed. 
The blends of the present invention may also include minor amounts of 
antioxidants, slip agents, antiblocking agents, antifogging agents, 
antistats and other additives as may be commonly used in the preparation 
of polymeric compositions used in the preparation of heat sealable films 
and/or laminates (see, e.g. Fatty Amides by Arthur L. McKenna, Witco 
Chemical Corp. 1982, or "Modern Plastics Encyclopedia"). 
In the process of form-fill-seal packaging, a film is formed around a 
mandrel, sealed along the vertical seam, sealed along the bottom, filled 
with the package contents and sealed along the top, all this while the 
film is sliding over the mandrel. In this operation, it is necessary that 
the surface contacting the mandrel have an adequate degree of slip. 
Depending on the packaging machine used, the degree of slip necessary can 
be a coefficient of friction (C.O.F.) of 0.4 or lower, as measured by test 
method ASTM D-1894C. To achieve this level of C.O.F., it is usually 
necessary to add slip and/or antiblock additives to the compositions of 
this invention. Some types of antiblock additives are inorganic materials 
of fine particle size, such as silica or talc. Antiblocking properties and 
slip properties may also be conferred by organic additives, as discussed 
in "Fatty Amides" cited above. Several types of amides are discussed, such 
as primary amides, secondary amides, and bisamides. Secondary amides and 
bisamides are more effective additives for compositions containing 
ionomers. Examples of slip-modified ionomers are shown in U.S. Pat. Nos. 
3,474,063, 3,595,827; 3,597,382; 3,821,179; and Def. Publ., U.S. Patent 
Office 877,077 (August 1970). It should also be noted that the quantity of 
fatty amide required to produce a given level of C.O.F. is inversely 
dependent on the thickness of the film layer containing the additive. 
In the preparation of heat sealed flexible packages, it is generally 
preferred that the strength of the seal be such that rupture of the seal 
occurs within the heat sealable composition at the interface of the seal 
layers, rather than within the substrate, i.e. it is generally preferred 
that such seals be peelable, rather than film tearing. Whether a 
particular seal will be peelable will depend on the strength of the seal 
as compared with the strength of the substrate. Accordingly, it is 
important to be able to control the strength of the seal. With certain 
compositions, such as those disclosed in U.S. Pat. No. 4,346,196, the 
strength of the seal depends on the temperature at which the seal is 
prepared, i.e. the higher the sealing temperature, the higher the strength 
of the seal. Accordingly, the strength of seals prepared from such 
compositions can be controlled by controlling the sealing temperature. 
Unfortunately, it is not always easy or even practical to precisely control 
the sealing temperature, particularly on commercial packaging equipment. 
Sealing temperature variations can result from variations in ambient 
temperature, thickness of the substrate, thickness of the coatings, 
throughput of the packaging material, interruptions of the production 
line, etc. 
As will be seen in the Examples that follow, the blends of the present 
invention will produce seals having a nearly constant peel strength over 
extended heat seal temperature range. This can be represented graphically 
by plotting the peel strength vs. the sealing temperature for each 
composition. The blends of the present invention will exhibit a plateau at 
a peel strength well within the peelable range. As will also be shown in 
the Examples and the accompanying graphs, if one desires a film tearing 
seal, it is possible to achieve this result with certain of the 
compositions of the present invention by substantially raising the sealing 
temperature beyond the plateau region in the graphs. However, one of the 
unique features of the blends of the present invention is the plateu 
region, which permits one to achieve substantially constant peel strength 
over a wide range of sealing temperature. Accordingly, the blends of the 
present invention will most often be used in this plateau region. 
It will also be demonstrated in the following Examples that some of the 
blends of the present invention will produce seals that show stress 
whitening. Seals that show stress whitening can be produced only above 
certain seal temperatures, but such temperatures are at or below the 
plateau region described above, thus permitting the production of seals 
that are peelable (with predictable and constant peel strength) and will 
show evidence of tampering.

In each of the following Examples, all parts and percentages are by weight 
and all temperatures are in .degree.C. unless specified otherwise. 
Measurements not originally in SI units have been so converted and rounded 
where appropriate. All seals tested were prepared in a "Sentinel" heat 
sealer having two heated jaws, both 25.4 mm wide, the lower jaw being 
covered with a 10 mm thickness of silicone rubber. Two layers of 
Teflon.RTM.-coated glass cloth were interposed between each heated jaw and 
the film samples. Additionally, film samples were transported with a 
holder made of the same type Teflon.RTM.-coated glass cloth. The air 
pressure to the jaw activation pistons was set at 276 kPa, and the dwell 
time of the jaws in the closed position was set for three seconds. The 
maximum temperature of the interface of the film heat-seal surfaces was 
determined using a fine wire thermocouple with fast response recorder. 
Seal strength was determined by peeling apart the seal in an "Instron" 
tensile tester at a jaw separation rate of 127 mm/min., the "tail" of the 
sample being allowed free movement. As indicated above, data for several 
of the Examples is displayed graphically in the accompanying Figures. 
Wherever such data is reported the melt index (MI) of the acid copolymer 
was determined according to ASTM D-1238, condition E, and the melt flow 
rate (MFR) of the propylene copolymer was determined according to ASTM 
D-1238, condition L. 
EXAMPLE 1 
Three thousand six hundred grams of an ethylene/methacrylic acid (MAA) 
ionomer were dry blended with 400 g of a propylene/ethylene copolymer. The 
acid copolymer for the ionomer contained 15 wt. % methacrylic acid and had 
a melt index of 60 g/10 minutes. Zinc was used to neutralize 22% of the 
acid groups. The resulting ionomer had a melt index of 14 g/10 minutes. 
The propylene/ethylene copolymer had an ethylene content of 3 wt.% and a 
melt flow rate of 5 g/10 minutes. A uniform mixture of pellets of each of 
these polymers was fed to a 28 mm Werner and Pfleiderer corotating 
twin-screw extruder equipped with screws having a severe mixing profile. A 
melt temperature of 247.degree. C. was obtained at a throughput rate of 
12.7 kg./hr. Strands of the melt-blended material were quenched in an 
icewater bath and then cut into pellets. The melt index of the blend was 
determined to be 13.6 g/10 minutes. 
Blown film of 0.05 mm thickness and 127 mm lay flat width was prepared 
using a "Brabender" 19 mm diameter single screw extruder equipped with a 
25.4 mm blown film die. The melt temperature attained was 197.degree. C. 
Seals were prepared and tested as described above. A plot of peel strength 
vs. seal interface temperature is shown in FIG. 1. Note that a long 
plateau of nearly constant seal strength was obtained. Between 90.degree. 
and 114.degree. C., peel strength remains between 23.6 and 27.6 g/mm. At 
this level of seal strength, seal failure was at the interface of the 
sealing surfaces. At strengths above 31.5 g/mm, which were obtained at a 
temperature of 119.degree. C., the sealed film tore on attempted peeling. 
In addition, at sealing temperatures/seal strengths about 73.degree. 
C./10.8 g/mm, the peeled sample exhibited blushing or whitening. Thus, 
seals made above these conditions would show evidence of tampering. 
EXAMPLE 2 CONTROL BLEND WITH LOW MAA 
This experiment was carried out in a manner identical to that of Example 1, 
except the acid copolymer contained 9% MAA, and it was neutralized 18% 
with zinc to give an ionomer with melt index of 5 g/10 minutes. The blend 
had melt index of 4.7 g/10 minutes. Unlike the blend of Example 1, 0.05 mm 
film from this blend does not exhibit a plateau of seal strength, but 
tears at a low strength of 27.6 g/mm, as shown in FIG. 2. 
EXAMPLE 3 CONTROL BLEND WITH BORDERLINE MAA 
This experiment was carried out in a manner identical to that of Example 1, 
except the acid copolymer contained 12% MAA, and it was neutralized 38% 
with zinc to give an ionomer with melt index of 1.6 g/10 minutes. The 
blend had melt index of 1.6 g/10 minutes. A heat seal profile of 0.05 mm 
film from this blend is shown in FIG. 3. A short plateau of seal strength 
between 17.7-21.6 g/mm over a temperature range of 88.degree.-95.degree. 
C. is shown in FIG. 3. 
EXAMPLE 4 CONTROL WITH ONLY IONOMER 
This experiment was carried out in a manner identical to that of Example 1, 
except that no propylene/.alpha.-olefin copolymer was used. The lack of a 
seal strength plateau is shown in FIG. 4. In addition, the seals did not 
blush upon peeling. 
EXAMPLE 5 CONTROL BLEND WITH PROPYLENE HOMOPOLYMER 
This example was carried out in a manner identical to that of Example 1, 
except a propylene homopolymer having a melt flow rate of 2.8 g/10 minutes 
was used. A blend melt index of 15.0 g/10 minutes was obtained. As can be 
seen from FIG. 5, a heat seal plateau was not obtained, although seals 
formed at 83.degree. C. and above blushed on peeling. Fushion bonds were 
formed at 87.degree. C. and above. 
EXAMPLES 6-9 
These experiments were carried out in a manner identical to that of Example 
1, except that the proportion of ionomer and polypropylene/ethylene 
copolymer was varied as shown in the Table below. Example 6 shows a 
control blend with a low proportion of PP/E copolymer. Examples 7, 8 and 9 
show blends of the present invention, with Example 9 at the 20% limit for 
PP/E. 
______________________________________ 
Ionomer Blend MI 
Heat Seal 
Example 
Wt. % PP/E Wt. % (g/10 min) 
Profile, FIG. 
______________________________________ 
6 95 5 16.9 6 
7 92 8 13.2 7 
8 88 12 12.2 8 
9 80 20 13.8 9 
______________________________________ 
As can be seen from FIG. 6, when only 5% PP/E copolymer is blended with 95% 
ionomer, no plateau is obtained. As shown in FIGS. 7-9, with increasing 
amounts of PP/E in the blend, the level of seal strength in the plateau 
region decreased, until at 20%, the peel strength plateau was in the 5.1 
to 6.7 g/mm range, which is near the lower limit of peel strength 
generally required for most uses. 
EXAMPLES 10 AND 11 
To determine the effect of temperature and shear in the melt mixing step on 
the seal profile of film, a dry blend of the polymers used in Example 1 
was fed to an 88.9 mm diameter "Davis" single screw extruder equipped with 
a mixing screw. Two sets of processing conditions were used. In the first, 
the extruder was operated at 6 rpm and the product melt temperature was 
176.degree. C. The product had a melt index of 10.0 g/10 minutes. This 
single screw extruder imparted less shear to the polymer than did the twin 
screw extruder used in Example 1. A heat seal profile of seals from this 
blend prepared as described in Example 1 shows a plateau of about 13.8 
g/mm over a seal interface temperature range of 90.degree. to 122.degree. 
C. Seal strength rose to 27.6 g/mm at a seal temperature of 142.degree. 
C., but a fusion bond was not obtained. This set of mixing conditions thus 
gave a film with a plateau seal strength 54% of that obtained in Example 
1, and the plateau temperature range was also extended. 
In the second set of process conditions, the screw speed was increased to 
12 rpm. This caused the melt temperature to increase to 184.degree. C., 
and the blend melt index to increase to 10.6 g/10 minutes. Seals prepared 
from this blend gave a seal strength plateau of about 17.7 g/mm over a 
temperature span of 88.degree. to 122.degree. C., a significant increase 
in the plateau seal strength compared with that of material produced at 6 
rpm. At a seal temperature of 140.degree. C., seal strength rose to 33.5 
g/mm, but a fusion seal was not obtained. 
EXAMPLES 12 TO 14 CONTROL BLENDS 
To illustrate the effect of PP/E resin MFR on heat seal profile, 
experiments were carried out with three different PP/E resins, each 
containing 3% ethylene. Each was melt blended as described in Example 1 
with the ionomer described in Example 1 except that the quantities of 
copolymer and ionomer were 10% and 90%, respectively and the melt 
temperature was 205.degree. to 210.degree. C. The melt flow rates of these 
PP/E resins are shown below: 
______________________________________ 
Ex- PP/E PP/E MFR, Blend MI, 
Film Tear Seal 
ample Resin g/10 Minutes 
g/10 Minutes 
Temperature, .degree.C. 
______________________________________ 
12 A 3.5 13.3 82 
13 B 3.6 12.0 82 
14 C 3.8 12.5 91 
______________________________________ 
Seals were prepared and tested as described above. Heat seal profiles for 
these samples are shown in FIG. 10. The seal profiles show plateaus, but 
the seals were film tearing in the plateau region. Seals formed at 
74.degree. C. and higher blushed on peeling. In FIG. 10, data for resin A 
are shown as circles; data for resin B are shown as diamonds, and data for 
resin C are shown as squares. 
EXAMPLE 15 
This experiment was carried out in a manner identical to that of Example 12 
except that the melt temperature during preparation of the blend was 
268.degree. C. The melt blended product had a melt index of 12.2 g/10 
minutes. Heat seal profile determination showed a seal strength plateau of 
33.4-37.4 g/mm over a temperature span of 91.degree.-110.degree. C., and a 
film-tearing bond was formed at 114.degree. C. Seals formed at 74.degree. 
C. and higher blushed on peeling. 
EXAMPLES 16 AND 17 
The PP/E resins A and C described in Examples 12 and 14 were processed 
through the Werner and Pfleiderer extruder described in Example 1 at 
273.degree.-274.degree. C. and pelletized. Melt blends with ionomer were 
then prepared as described in Example except that the melt temperature was 
226.degree.-228.degree. C. and film samples were prepared at a melt 
temperature of 199.degree. C. Results of these processing steps are shown 
below: 
______________________________________ 
PP/E Resin Blend 
Ex- MFR After MI, Plateau Plateau Fusion 
am- Processing g/10 Seal Strength 
Seal Temp. 
Temp., 
ple g/10 Min. Min. Range, g/mm 
Range, .degree.C. 
.degree.C. 
______________________________________ 
16 4.9 13.4 29.5-33.5 
89-114 125 
17 5.4 13.2 19.7-23.6 
88-125 130 
______________________________________ 
This experiment demonstrates that resins which are high in molecular weight 
(low in MFR) initially can be thermally treated to lower their molecular 
weight (increase their melt flow rate), thus permitting the production of 
blends that will show a more desirable heat seal profile. 
EXAMPLES 18 AND 19 
A pellet blend as described in Example 1 was melt-mixed using a 63.5 mm 
"Prodex" single screw extruder equipped with a screw having a mixing 
torpedo. The melt temperature during mixing was 199.degree. C. and the 
blend had a melt index of 10.9 g/10 minutes. Film was extruded as 
described in Example 1 except that the melt temperature for Examples 18 
and 19 was 197.degree. C. and 206.degree. C., respectively. Results from 
these experiments are shown below: 
______________________________________ 
Plateau Plateau 
Seal Strength 
Seal Temperature 
Fusion Temperature 
Example 
Range, g/mm 
Range, .degree.C. 
.degree.C. 
______________________________________ 
18 12.8-16.7 84-118 (a) 
19 27.6-31.5 88-108 132 
______________________________________ 
(a) Maximum 35.4 g/mm peel strength at 144.degree. C., but fusion seal not 
obtained. 
A comparison of the plateau seal strength and fusion behavior in these 
experiments shows the importance of melt temperature in the film extrusion 
step. 
EXAMPLE 20 
A terpolymer of ethylene/10% isobutyl acrylate (IBA)/10% methacrylic acid 
having a melt index of 10 g/10 min. was simultaneously blended with the 
propylene copolymer described in Example 1 and neutralized 20% with 
magnesium to provide a blend containing 90% terionomer and 10% propylene 
copolymer. More specifically, magnesium acetate tetrahydrate, A.C.S. 
Grade, was ground to a fine particle size in a mortar and pestle. A dry 
blend containing 3000 g of the terpolymer, 335 g of the propylene 
copolymer, and 149.5 g of the pulverized magnesium acetate was fed to the 
extruder described in Example 1 and processed at a melt temperature of 
230.degree. C. The melt was vacuum-devolatized during processing. The 
pellets produced were dry blended and re-fed to the extruder to assure 
product uniformity. The blend produced had a melt index of 1.6. Blown film 
of this blend was prepared as described in Example 1 except that the melt 
temperature was 224.degree. C. Determination of the heat seal profile of 
this film showed a seal strength plateau of 6.3 to 10.2 g/mm over a 
temperature range of 84.degree.-110.degree. C. Seals made at 82.degree. C. 
and above blushed on peeling, and film tearing bonds were formed at 
119.degree. C. and above. 
EXAMPLES 21 TO 24 
Blends and film were prepared as described in Example 1 except that the 
ionomer was as described in the following table and the blends contained 
90% ionomer and 10% propylene copolymer. Seals were made and tested as 
described above with the following results: 
__________________________________________________________________________ 
Film Plateau 
% Comonomer(s) Blend Extr. 
Blush 
Seal Str. 
Temp. 
Fusion 
Fusion 
Example 
In Ethylene/ 
Neut. 
Neut. 
Temp. 
Blend MI 
Temp. 
Temp. 
Plateau 
Range 
Temp. 
Strength 
No. Acid Polymer 
Ion % .degree.C. 
g/10 Min. 
.degree.C. 
.degree.C. 
g/mm .degree.C. 
.degree.C. 
g/mm 
__________________________________________________________________________ 
21 15 MAA Zn 23 208 7.5 199 84 11.8-15.7 
89-124 
140 55.1 
22 15 MAA Zn 40 210 2.4 215 82 7.9-11.8 
90-135 
(a) (a) 
23 10 MAA Zn 20 208 10.8 176 64 14.2-18.1 
76-142 
(b) (b) 
10 IBA 
24 15 MAA Na 20 208 5.7 225 76 33.5-37.4 
91-135 
(c) (c) 
__________________________________________________________________________ 
(a) No fusion. Maximum peel strength 13.4 g/mm at 144.degree. C. 
(b) No fusion. Maximum peel strength 18.7 g/mm at 144.degree. C. 
(c) No fusion. Maximum peel strength 39.4 g/mm at 144.degree. C. 
As can be seen, the temperature at which peeled seals blush, the peel 
strength in the plateau region, the temperature range of the plateau 
region, and whether a fusion or film-tearing seal is formed, can all be 
controlled by varying the ionomer composition. 
EXAMPLES 25 TO 28 
Blends and films were prepared as described in Example 1 except that the 
propylene copolymer was as described in the following table and the blends 
contained 90% ionomer and 10% propylene copolymer. Seals were made and 
tested as described above with the following results: 
__________________________________________________________________________ 
Prop. Film Plateau 
% Ethylene 
Copoly. 
Blend Extr. 
Blush 
Seal Str. 
Temp. 
Fusion 
Fusion 
Example 
In Propylene 
MFR Temp. 
Blend MI 
Temp. 
Temp. 
Plateau 
Range 
Temp. 
Str. 
No. Copolymer 
g/10 Min. 
.degree.C. 
g/10 Min. 
.degree.C. 
.degree.C. 
g/mm .degree.C. 
.degree.C. 
g/mm 
__________________________________________________________________________ 
25 2.0 9 214 14.6 198 76 21.6-25.6 
91-108 
139 43.3 
26 3.0 8 214 14.6 198 76 21.6-25.6 
86-127 
137 39.4 
27 3.5 3.6 214 15.8 197 70 29.5-33.5 
88-100 
117 39.4 
28 3.5 7 214 16.8 198 68 19.7-23.6 
79-94 
119 37.4 
__________________________________________________________________________ 
Examples 25 and 26 show that propylene copolymer of the proper MFR gives 
desirable plateau seal strengths without having to use high temperature 
extrusion. 
EXAMPLE 29 
A dry blend was prepared containing 27.215 kg of the propylene copolymer 
described in Example 1 and 238.9 kg of a terpolymer of ethylene, 10% 
isobutyl acrylate, and 10% methacrylic acid, which terpolymer had a melt 
index of 10 g/10 minutes, and 6.03 kg of a zinc concentrate containing 30% 
zinc oxide, 1.5% anhydrous zinc acetate, 0.5% zinc stearate, and 68% 
ethylene/MAA copolymer, containing 90% ethylene and having a melt index of 
500 g/10 minutes. Dry pellets of each of these three components were fed 
to a 88.9 mm plasticating extruder at a feed rate of 31.75 kg of the 
pellet blend per hour. In the extruder the propylene copolymer pellets and 
the terpolymer pellets were melted and conveyed along with the zinc 
concentrate to the mixing section. The initial plasticating section of the 
screw was 7 diameters long and maintained at a temperature of about 
120.degree. C. At the inlet of the mixing section an activating liquid 
comprised of glacial acetic acid was injected into the molten stock by 
means of a nozzle penetrating the barrel wall. The mixing section was of 
the type described in U.S. Pat. No. 3,006,029 and was 13 diameters long. 
In the mixing section maintained at a temperature of 240.degree. to 
280.degree. C., the zinc concentrate reacted with the polymer melt to 
neutralize some of the acid groups of the terpolymer through the formation 
of a soluble salt. 
At the end of the mixing section, the mixture of ion crosslinked 
terpolymer, propylene copolymer and reaction by-products passed through a 
pressure control valve and a transfer line into a 2-inch diameter 
extraction extruder. The stock temperature before the valve was about 
265.degree. C. and the pressure 9.66 MPa (1400 p.s.i.). The extruder had 
two extraction zones, each about 4 diameters in length, in series. The 
first extraction zone was maintained at 686 mm of Hg and the second at 711 
mm. of Hg. The temperature of the melt was maintained between 250.degree. 
C. and 260.degree. C. The extraction zone removed most of the volatile 
constituents from the molten, ion crosslinked terpolymer. The polymer 
blend was extruded through a die in the form of strands, cooled in water 
and cut into pellets. The blend contained 10% of the propylene copolymer, 
90% of the terionomer, and had a melt index of 4.9 g/10 minutes. The 
carboxyl groups in the ionomer were neutralized 15.6%. 
High density polyethylene (0.950 density and 0.45 MI) was fed to a 6.35 mm 
"Welex" single-screw extruder, and the blend described above was fed to a 
50.8 mm "TEC" single-screw extruder. Melt temperatures were 222.degree. 
and 172.degree. C., respectively. The melt streams were combined in a 
Davis blown film coextrusion die with the blend outside. Film having a lay 
flat width of 584 mm was extruded at a blowup ratio of 2.5. The two-layer 
product film was made up to 0.048 mm of polyethylene and 0.013 mm of the 
blend. Heat seal profile testing of this composite film showed a plateau 
seal strength of 35.4-39.4 g/mm over a temperature range of 
95.degree.-112.degree. C. Seals formed at 78.degree. C. and higher blushed 
on peeling. Fusion seals were formed at temperatures of 139.degree. C. and 
higher. The seal formed at 139.degree. C. had a strength of 94.5 g/mm. 
EXAMPLE 30 
A three-layer, three-extruder feed block sheet coextrusion line was used to 
prepare a composite sheet. The sizes of the three single-screw extruders 
were: (A) 38.1 mm, (B) 25.4 mm, and (C) 31.8 mm. The output of these 
extruders entered a feed block and then a 152-mm wide die. The feed block 
was constructed so that the material from extruder (A) was cast against a 
controlled-temperature chill roll with the material from extruder B cast 
against the material from extruder A and the material from extruder C cast 
against the material from extruder B, thus producing a three layer 
structure, the three layers being designated, (a), (b), and (c) 
respectively in order outward from the chill roll. The cast composite 
sheet was then traversed over a second chill roll so that layer (c) was 
adjacent to the second chill roll. The first chill roll was operated at 
about 72.degree. C. and the second at 25.degree. C. 
Film-grade propylene homopolymer having a melt flow rate of 2.8 g/10 
minutes was processed through extruders (a) and (b) while the blend 
described in Example 29 was processed through extruder (C). Temperature 
settings for extruders, transfer lines, feed block, and die were 
215.degree. C. The extruders were set so that the layer thicknesses were: 
(a) 0.41 mm, (b) 0.05 mm, and (c) 0.05 mm. The sheet produced was then 
oriented at 155.degree. C. at a stretch rate of 2000%/minute and stretch 
ratios of 2.75X in the machine direction and 3.5X in the transverse 
direction. The seal strength profile of the oriented composite film was 
then determined as described above. A seal strength plateau of 24.8 g/mm 
was obtained over a temperature range of 105.degree.-130.degree. C. Seals 
formed in this range blushed on peeling. In another experiment employing 
the same base sheet polymer and a different batch of the same composition 
blend as described in Example 29, a maximum peel strength of 37.8 g/mm was 
obtained. 
EXAMPLE 31 CONTROL WITH ONLY IONOMER 
An oriented film structure similar to that of Example 30 was prepared, 
except the polymer blend layer (c) was composed of a 20% zinc-neutralized 
terionomer containing 10% IBA and 10% MAA which had a melt index of 5 
following neutralization. This oriented film gave a seal strength of only 
19.7 g/mm at 105.degree. C. No seal strength plateau was observed, nor did 
the seals blush on peeling. 
EXAMPLE 32 
An oriented film structure similar to that of Example 30 was prepared, 
except the polymer blend layer (c) was the composition of Example 1, but 
prepared by the method described in Example 29. This oriented film gave a 
plateau seal strength of 15.7-19.7 g/mm over a temperature range of 
96.degree.-129.degree. C. Seals formed in this temperature range blushed 
on peeling. 
EXAMPLE 33 
An oriented film structure similar to that of Example 30 was prepared, 
except that layer (b) was made from the propylene copolymer/terionomer 
blend described in Example 29, and layer (c) was the same as layer (c) 
described in Example 32. This oriented film provided a plateau seal 
strength of 26.0-29.9 g/mm over the temperature range of 
95.degree.-127.degree. C., which rose to a value of 38.4 g/mm fusion seal 
at a temperature of 139.degree. C. Seals formed at 86.degree. C. and 
higher blushed on peeling. 
EXAMPLE 34 LAMINATION OF TWO LAYER EXTRUSION 
The two-layer film described in Example 29 above was laminated to oriented 
polypropylene using an "Inta-Roto" coater/laminator in the following 
manner. The two-layer film was corona-treated on the high density surface 
by conventional means and slit to the proper width for lamination. A 
commercial single-component laminating adhesive, "Adcote" 333 supplied by 
Morton Chemical Company, was applied by gravure roll to one side of a 
commercial oriented polypropylene film of 0.019 mm thickness which had 
been corona-treated on both sides. The adhesive-coated film was passed 
through a drying oven held at 79.degree. C. to evaporate the solvent. 
Immediately exit the oven, the adhesive-coated polypropylene was nipped to 
the high density polyethylene side of the coextruded film using a 
combining roll held at a temperature of 71.degree. C., and then wound up 
after cooling. 
The resulting laminated film was evaluated under a different test procedure 
than described for the other examples. Rather than a 3-second seal time, 
0.5 seconds was used, and the seal bar temperature was recorded. The jaw 
activation pistons were activated with 207 kPa air pressure. These 
conditions are typical for form-fill-seal packaging of snack foods in 
commercial practice. Testing of the seals was carried out at 127 mm/minute 
jaw separation rate, but the "tail" of the sample was held in a T-peel 
configuration. This test procedure showed that a seal strength plateau of 
21.6 to 26.0 g/mm was obtained over a seal bar temperature range of 
143.degree. to 160.degree. C., and seals formed above 127.degree. C. bar 
temperature blushed on peeling. 
EXAMPLE 35 LAMINATION OF THREE LAYER EXTRUSION 
In another embodiment of Example 34, the same seal layer composition was 
compounded with 1% stearyl erucamide slip additive. The stearyl erucamide 
was provided from a concentrate containing 10% of this ingredient melt 
blended with 90% of an ethylene/methacrylic acid copolymer having 9% 
methacrylic acid and a melt index of 10 g/10 minutes. A pellet blend 
containing 10% of the concentrate and 90% of the seal layer resin was fed 
to the "Prodex" extruder described in Examples 18 and 19 and pellets of 
the modified resin produced. 
A three-layer blown film coextrusion apparatus was prepared with the 
following polymer feeds: (1) 0.944 density linear polyethylene having an 
MI of 0.25 plus a commercial white color concentrate, (2) the same 
polyethylene plus a commercial brown color concentrate, and (3) the seal 
layer composition with slip additive described above. A composite film 
having the following layer thicknesses was prepared: (2) 0.020 mm white 
polyethylene, (2) 0.015 mm brown polyethylene, and (3) 0.0076 mm seal 
layer. The white polyethylene surface was corona-treated and laminated to 
oriented polypropylene in a manner similar to that described in Example 
34. Determination of the seal characteristics gave results similar to 
those described in Example 34, except that bar temperatures were shifted 
to about 11.degree. C. lower for attainment of the same seal strength. The 
static coefficient of friction determined for the seal layer side of the 
coextruded film was 0.28, and the kinetic coefficient of friction was 
0.25, as determined by ASTM Method 1894C. 
EXAMPLE 36 EFFECT OF SLIP AND ANTIBLOCK ADDITIVES 
Another seal layer composition was prepared to contain both an antiblocking 
and a slip additive. A pellet blend was prepared which contained the 
following ingredients: (1) 81% of a terionomer containing 6.3% IBA, 9.8% 
MAA, and neutralized 12% with zinc to a melt index of 5 g/10 minutes, (2) 
9% of the propylene/ethylene copolymer of Example 1, and (3) 10% of a 
slip/antiblock concentrate containing 85% of an ethylene/methacrylic acid 
copolymer having 9% MAA and a melt index of 10 g/10 minutes, 10% 
N-oleylpalmitamide slip additive, and 5% silica antiblocking additive. The 
pellet blend was fed to an extruder, melt-compounded, and formed into 
pellets. These pellets were subsequently used for preparing first a 
three-layer coextrusion and then a laminate with polypropylene as 
described in the Example 35. 
INDUSTRIAL APPLICABILITY 
The blends of the present invention and the films and/or laminates of the 
present invention made from such blends are useful in the manufacture of 
peelable sealed flexible film packages which can be readily and manually 
opened at the seal layer interface upon application of a moderate, 
predictable and constant force. In addition, blends of the present 
invention that can be used to produce seals that will stress whiten when 
peeled are particularly well suited for packing items where the 
cleanliness, purity and/or integrity of the product is essential, e.g. 
foodstuffs, drugs and medical devices. 
BEST MODE 
Although the best mode of the present invention, i.e. the single best blend 
of the present invention, will depend on the particular desired end use 
and the specific requisite combination of properties for that use, the 
blend and processing conditions that will result in a product most 
preferred for its overall balance of properties is described in detail in 
Examples 29 and 36.