Films blown by the inflated bubble method of alloys of vinylidene chloride interpolymers and olefin polymers

Blends of a vinylidene chloride polymer, an olefin polymer, and a compatibilizer polymer are successfully fabricated into films using the well-known inflated bubble technique, by using blow-up rates in the range of about 1.5 to 5.0 and a drawn-down ratio upwards of 6, preferably upwards of 8, but not exceeding the critical draw-down ratio of 13. At a draw-down ratio exceeding 13, the physical properties of the polymer blend are seriously diminished.

FIELD OF THE INVENTION 
Blown films are prepared from blends or alloys of a vinylidene chloride 
polymer, an olefin polymer and a minor amount of a compatibilizing 
polymer. 
BACKGROUND OF THE INVENTION 
The present invention relates to a process for blowing films of 
compatibilized blends of at least two normally incompatible polymers. More 
particularly, the present invention relates to compatibilized and melt 
processible blends of a vinylidene chloride interpolymer and an olefin 
polymer which are blown as films using the inflated bubble technique. 
Vinylidene chloride interpolymers are well known as excellent barriers to 
mass transport of atmospheric gases and moisture vapor. These 
interpolymers have limited areas of application, however, because of poor 
melt processing characteristics. In particular, vinylidene chloride 
interpolymers in a melt plasticized state have poor heat stability and low 
melt strength. These same interpolymers, when fabricated, tend to be 
brittle and to have low impact strength. 
Olefin polymers, such as high density polyethylene (HDPE), low density 
polyethylene (LDPE), linear low density polyethylene (LLDPE), and 
ultra-low density polyethylene (ULDPE), generally have better melt 
processing characteristics than vinylidene chloride interpolymers. That 
is, they are melt processible over a wider range of temperatures. The 
olefin polymers are readily fabricated into articles. They also provide 
rigidity without brittleness when so fabricated. Notwithstanding such 
processing advantages, the olefin polymers are excessively permeable to 
atmospheric gases. 
Efforts to combine the best features of vinylidene chloride interpolymers 
and olefin polymers in a polymer-polymer blend useful in blown films have 
been unsuccessful until now. Lack of success has been studied by comparing 
physical properties of the polymer-polymer blend with those of the blend 
components in a straight line volume fraction relationship (hereinafter 
referred to as "the rule of mixtures"). The physical properties of the 
polymer-polymer blends have generally been poorer than those predicted by 
following the rule of mixtures. 
Various explanations have been advanced to explain the aforementioned lack 
of success. One such explanation was that mixing procedures used to 
disperse one polymer in a second polymer were inadequate. 
It is now believed thatthe lack of success may be attributed to inherent 
physical incompatibility of vinylidene chloride interpolymers with olefin 
polymers. A compatibilizer (such as an ethylene copolymer containing as a 
copolymerized moiety an oxygen-containing monomer) can be used in creating 
a compatible blend or alloy of vinylidene chloride interpolymers and 
polyethylenes; it is known that such blends can be easily compression 
molded into films with good oxygen barrier properties. 
EPO Application No. 85111781.2 discloses compatibilized blends, such as 
described immediately above, which are heat-molded under compression into 
films having good oxygen barrier properties. 
Japanese patent application No. Sho 52-40290, filed Apr. 11, 1977 discloses 
blends of vinylidene chloride resins and polyolefin type resins or 
polystyrene type resins which are melt-extruded, then cooled, and after 
being cooled are biaxially stretched by tentering or by inflation. 
It is well-known in the relevant arts that vinylidene chloride polymers and 
copolymers are lacking in sufficient melt strength to be inflated, while 
molten, by the bubble blowing technique. For this reason it has been 
customary to extrude such VCl.sub.2 polymers through a circular die, then 
after being cooled (frozen), the solidified tube can be tentered or 
inflated so as to biaxially stretch the film. 
It has now been discovered that blends of vinylidene chloride polymers and 
olefin polymers which have been compatibilized with a compatibilizing 
polymer can be blown as films using the inflated bubble technique wherein 
the stretching of the film is performed while the extruded tube of film is 
still molten, i.e., it is inflated before it has been cooled, if the 
process is controlled within certain process parameters. 
SUMMARY OF THE INVENTION 
The present invention concerns a process for blowing films of a 
compatibilized blend of polymers comprising: (a) a vinylidene chloride 
interpolymer, the interpolymer having polymerized therein vinylidene 
chloride in an amount of from about 40 to about 98 percent by weight of 
interpolymer and at least one monoethylenically unsaturated monomer 
copolymerizable therewith in an amount of from about 60 to about 2 percent 
by weight of interpolymer; (b) an olefin polymer and (c) a compatibilizing 
amount of a compatibilizing polymer, said compatibilizing polymer being 
selected from the group consisting of (i) ethylene interpolymers having 
polymerized therein from about 97 to about 60 weight percent of ethylene 
and from about 3 to about 40 weight percent of at least one oxygen 
containing species copolymerizable therewith; and (ii) olefin polymers 
having halogen chemically affixed thereto in an amount of from about 24 to 
about 44 percent by weight of polymer. 
The film-blowing may be done using an apparatus designed for the blowing of 
films of olefin polymers using the inflated bubble technique wherein an 
extruded molten tube is inflated to stretch the polymer while it is still 
molten, and wherein the so-inflated (stretched) tube is then cooled 
(solidified) before passing through nip rolls which axially tense the tube 
and flatten the solidified tube before it is collected in or on a 
collection device, such as a take-up roller. It is critical, in the 
present invention, that the blow-up ratio (B.U.R.) in the inflation step 
be in the range of about 1.5:1 to about 5:1 (preferably about 2:1 to about 
4:1) while maintaining the draw-down ratio (D.D.R.) to a maximum in the 
range of about 8:1 to about 13:1 (preferably about 9:1 to about 11:1). 
Furthermore, since the vinylidene chloride polymers are, when molten, 
susceptible to accelerated degradation when in contact with iron, such 
degradation releasing halogen values which are detrimental to the extruder 
and extrusion die, it is necessary to use materials of construction which 
substantially avoid having iron in contact with the molten vinylidene 
chloride polymers. A film-blowing apparatus made of steel, with 
appropriate surfaces electroless-plated with nickel metal or 
chrome-plated, can be used, for example, as a means for substantially 
avoiding contact of iron with molten vinylidene chloride polymers during 
the film-blowing process.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 depicts an extruder, not to scale, for film-blowing using the 
entrapped bubble technique. It is shown that a heated extrusion barrel (1) 
contains an extrusion screw (2) having a pointed tip (3) and communicates 
through passageway (4) with a die-head (5) which contains a gas inlet (6) 
in the center of annular die (7) which provides an annular port (8) for 
extrusion of a molten tube of polymer flowing through conduit (4) from the 
extrusion barrel (1). In a film-blowing operation the extruder (1) forces 
a molten tube of polymer through annular port (8) and the tube becomes 
axially stretched by nip rolls (not shown) located distal to, and in axial 
alignment with, the extruding tube. The nip rolls are at an appropriate 
distance from the annular die to provide for inflation (i.e. radial 
stretching) of the tube, and cooling of the tube so that the polymer is 
below its melting point and does not fuse to itself or stick to the nip 
rolls; the nip rolls flatten the tube as it pulls it, thus "closing" the 
bubble. Rapid cooling (if needed) may be provided by a cooling gas blown 
around the circumference of the bubble. From the nip rolls, the polymer 
may be gathered on take-up rolls or otherwise collected. Inflation of the 
tube while it is still molten is done by injecting an inflation gas into 
the tube through inlet (6) under controlled pressure to steadily provide 
the required blow-up ratio. The extrusion may be done vertically upward 
(as in FIG. 1) or vertically downward. 
Vinylidene chloride interpolymers suitable for use with the present 
invention are those which have polymerized therein an amount of vinylidene 
chloride monomer and an amount of monoethylenically unsaturated monomer 
copolymerizable therewith. The vinylidene chloride interpolymers are 
desirably melt processible. 
The amount of polymerized vinylidene chloride monomer is suitably from 
about 40 to about 98 percent by weight of interpolymer, beneficially from 
about 50 to 96 percent by weight of interpolymer, and desirably from about 
60 to about 94 percent by weight of interpolymer. 
The vinylidene chloride interpolymer comprises one or more 
monoethylenically unsaturated monomers which are copolymerizable with the 
vinylidene chloride monomer. The amount of monoethylenically unsaturated 
monomer is suitably from about 60 to about 2 percent by weight of 
interpolymer, beneficially from about 50 to about 4 percent by weight of 
interpolymer, and desirably from about 40 to about 6 percent by weight of 
interpolymer. 
Monoethylenically unsaturated monomers suitable for copolymerization with 
vinylidene chloride include vinyl chloride, alkyl acrylates, alkyl 
methacrylates, acrylic acid, methacrylic acid, itaconic acid, 
acrylonitrile and methacrylonitrile. The unsaturated monomers are 
desirably selected from the group consisting of vinyl chloride, alkyl 
acrylates and alkyl methacrylates, the alkyl acrylates and alkyl 
methacrylates having from about 1 to about 8 carbon atoms per alkyl group. 
The alkyl acrylates and alkyl methacrylates beneficially have from about 1 
to about 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl 
methacrylates are preferably selected from the group consisting of methyl 
acrylate, ethyl acrylate and methyl methacrylate. 
Olefin polymers suitable for use in the present invention are those olefin 
homopolymers and interpolymers which can be compatibilized with the 
vinylidene chloride interpolymers through the use of the compatibilizing 
polymers of the present invention. 
Beneficially, the olefin polymers are selected from the group consisting of 
(1) low density polyethylene (LDPE), (2) medium density polyethylene 
(MDPE), (3) high density polyethylene (HDPE), (4) polypropylene (PP), (5) 
poly 1-butene (PB), (6) generally linear interpolymers of ethylene (LLDPE) 
having polymerized therein from about 70 to about 99 weight percent of 
ethylene and from about 1 to about 30 weight percent of at least one 
1-alkene, said alkene having from 3 to 14 carbon atoms, (7) copolymers of 
two or more alpha-olefins, having from 3 to 14 carbon atoms per molecule, 
(8) rubbery ethylene-propylene-diene monomer interpolymers, and mixtures 
thereof. 
Low density polyethylenes (such as made by the well-known I.C.I. process) 
which are useful in the present invention generally have a density of from 
about 0.913 to about 0.938 grams per cubic centimeter. The low density 
polyethylenes also have a melt index of from about 0.1 to about 200 grams 
per 10 minutes as measured in accordance with American Society for Testing 
and Materials (ASTM) Test D-1238(E). 
Medium density polyethylenes which are useful in the present invention have 
a density of from about 0.938 to about 0.950 grams per cubic centimeter. 
The medium density polyethylenes also have a melt index of from about 0.08 
to about 200 grams per 10 minutes (ASTM Test D-1238(E)). 
High density polyethylenes which are useful in the present invention have a 
density of from about 0.950 to about 0.965 grams per cubic centimeter. The 
high density polyethylenes also have a melt index of from generally about 
0.01 to about 200 grams per 10 minutes (ASTM Test D-1238(E)). 
For purposes of the present invention, useful polypropylenes are the 
normally solid isotactic polypropylenes. The isotactic polypropylenes have 
an insolubility in hot heptane of greater than about 90 percent. These 
polypropylenes also have a melt flow rate (ASTM D-1238) of from about 0.3 
to about 100 grams per 10 minutes at a temperature of 230.degree. C. with 
a load of 2160 grams. The polypropylene beneficially has a melt flow rate 
of from about 0.3 to about 50 grams per 10 minutes. 
Any poly 1-butene (PB) is believed to be suitable for use in the percent 
invention so long as it meets the other requirements for the olefin 
polymer. 
For purposes of the present invention, the linear interpolymers of ethylene 
(a.k.a. as LLDPE) have polymerized therein an amount of ethylene and an 
amount of at least one 1-alkene to provide a density in the range of about 
0.87 to about 0.938 gms./cc. The amount of ethylene is suitably from about 
70 to about 99 percent, by weight of the interpolymer. The amount of 
1-alkene is suitably from about 1 to about 30 percent, by weight of 
interpolymer. Preferably the LLDPE is one having a sufficient amount of 
1-alkene interpolymerized therein to give a density of less than about 
0.915 gm./cc, a.k.a. ULDPE (ultra-low density polyethylene). 
The 1-alkene is selected from the group of 1-alkenes which have from 3 to 
about 14 carbon atoms per molecule. The 1-alkene is beneficially selected 
from the group of 1-alkenes which have from 3 to about 10 carbon atoms per 
molecule. The 1-alkenes having from 3 to 10 carbon atoms per molecule 
include, e.g., propene, butene, hexene and octene. Preferably the 1-alkene 
is one or more selected from the C.sub.4 -C.sub.8 range. 
Linear copolymers of ethylene and another olefin are described in U.S. Pat. 
No. 4,076,698, the teachings of which are incorporated herein by reference 
thereto. 
Alpha-olefin interpolymers suitable for use with the present invention have 
polymerized therein two or more monomers selected from the group of 
alpha-olefin monomers having from about 3 to about 14 carbon atoms per 
molecule. The alpha-olefin monomers are represented by the general formula 
R-CH.dbd.CH.sub.2 wherein R is an alkyl group of 1 to 12 carbon atoms, 
especially 2 to 6 carbon atoms. 
Examples of suitable alpha-olefin monomers include propylene, butene-1, 
pentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, 
4-methyl-pentene-1, 4-methyl-hexene-1 and 4,4-dimethyl-pentene-1. 
The compatibilizing polymer is selected from the group consisting of (i) 
ethylene interpolymers having polymerized therein from about 97 to about 
60 weight percent of ethylene and from about 3 to about 40 weight percent 
of at least one oxygen containing species copolymerizable therewith; and 
(ii) olefin polymers having halogen chemically affixed thereto in an 
amount of from about 24 to about 44 percent by weight of polymer. 
Preferably, the compatibilizing polymer is an ethylene copolymer or 
terpolymer formed by interpolymerizing ethylene with at least one of alkyl 
acrylate, alkyl methacrylate, vinyl alkylate, and carbon monoxide. 
The compatibilizing polymer must be capable of compatibilizing a blend of 
the vinylidene chloride interpolymer and the olefin polymer. For the 
purposes of this application the blend of vinylidene chloride interpolymer 
and olefin polymer is considered compatibilized when the blend has 
mechanical properties which are generally better than those suggested by 
the rule of mixtures. One measure of compatibility is the impact strength 
of the blend which should be better than suggested by the rule of mixtures 
in order to say the blend is compatibilized. The oxygen permeability of 
compatibilized blends is very dependent on the process used in forming a 
film. The draw-down ratio (DDR) and the blow-up ratio (BUR) are critical 
and these depend largely on the viscosity of the polymer blend and the 
shear rate encountered in the extrusion die. 
Beneficially the compatibilizing polymer will meet two additional criteria. 
First, it will be melt processible with the vinylidene chloride 
interpolymer. Second, it will preferably have a melt viscosity which is 
sufficiently close to that of the vinylidene chloride interpolymer and to 
the olefin polymer for viscosity compatibility to allow adequate mixing to 
occur. In the present invention it is preferred that the compatibilizing 
polymer have a melt flow rate in the range of about 0.1 to about 5 gms./10 
min. 
Two factors, which must be carefully monitored are processing time and 
processing temperature. In melt processing polymers, it is generally 
recognized that as processing temperatures increase, processing times must 
decrease in order to avoid undesirable results such as polymer 
degradation. This is especially true for vinylidene chloride 
interpolymers. 
Vinylidene chloride interpolymers may be melt processed at temperatures of 
up to about 200.degree. C. provided processing time is less than about one 
minute. Temperatures greater than about 200.degree. C. may be employed 
provided the processing time is sufficiently short and provided the 
vinylidene chloride polymer is not in contact with iron or black plate 
steel. For example, vinylidene chloride polymers are melt processible at 
temperatures as high as about 230.degree. C. at processing times of less 
than about ten seconds when the vinylidene chloride polymer forms an inner 
layer in a coextruded structure. 
Melt index or melt viscosity differences affect the final oxygen 
permeability of the blends. Ideally, the polyolefin melt viscosity should 
be nearly equal or greater than the vinylidene chloride interpolymer melt 
viscosity. Using a typical vinylidene chloride interpolymer with a 
molecular weight of about 90,000 grams per mole, the Rabinowitch corrected 
viscosity of the polyolefin should be .gtoreq.12,000,.gtoreq.8,000, 
.gtoreq.5,000,.gtoreq.3,000 poise at shear rates of 40, 100, 200, and 400 
sec.sup.-1 at 177.degree. C., respectively. 
The first class of compatibilizing polymer, (i), are ethylene interpolymers 
having polymerized therein from about 97 to about 60 weight percent of 
ethylene and from about 3 to about 40 weight percent of at least one 
oxygen containing species copolymerizable therewith. The said ethylene 
interpolymer is suitably selected from the group consisting of (a) 
ethylene interpolymers having polymerized therein from about 97 to about 
60 weight percent of ethylene and from about 3 to about 40 weight percent 
of at least one ethylenically unsaturated carboxylic acid monomer 
copolymerizable therewith, the interpolymer being esterified after 
preparation thereof; (b) copolymers of ethylene and at least one alkyl 
acrylate; (c) copolymers of ethylene and at least one alkyl methacrylate; 
(d) copolymers of ethylene and carbon monoxide; (e) interpolymers of 
ethylene carbon monoxide and (1) an ester of an ethylenically unsaturated 
carboxylic acid or (2) vinyl acetate; (f) copolymers of ethylene and vinyl 
acetate; (g) ethyl oxazoline modified copolymers of ethylene and acrylic 
acid; (h) interpolymers of ethylene, carbon monoxide and acrylic acid; (i) 
interpolymers of ethylene, carbon monoxide and methacrylic acid; and (j) 
interpolymers of ethylene, carbon monoxide and vinyl acetate. 
Beneficially, the ethylene interpolymer is either (a), (b), (c), (d), (e), 
or (f). 
Desirable results are obtained when the compatibilizer ethylene 
interpolymer has polymerized therein from about 97 to about 60 weight 
percent of ethylene and from 3 to about 40 weight percent of at least one 
ethylenically unsaturated carboxylic acid monomer copolymerizable 
therewith, the interpolymer being esterified after preparation thereof. 
Suitable ethylenically unsaturated carboxylic acid monomers copolymerizable 
with ethylene for use as a compatibilizer include acrylic acid, 
methacrylic acid, and the like. Preferably, the unsaturated carboxylic 
acid monomer is acrylic acid. 
Most preferably the compatibilizing ethylene interpolymer is selected from 
the group consisting of ethylene/alkyl acrylate and ethylene/alkyl 
methacrylate copolymers wherein the alkyl group contains from 1 to 8 
especially from 1 to 4 carbon atoms, wherein the said ethylene comprises 
about 60% to about 97% by weight of the interpolymer. 
Ethylene/acrylic acid compatibilizer copolymers are suitably prepared as 
outlined in U.S. Pat. Nos. 3,520,861 and 4,351,931 the teachings of which 
are incorporated herein by reference thereto. Methods of esterifying such 
copolymers are well-known in the prior art. 
Preferred ethylene/acrylic acid compatibilizer copolymers, prior to 
esterification, have polymerized therein acrylic acid in an amount of from 
about 6 to about 30 percent by weight of the copolymer. The 
ethylene/acrylic acid copolymers also have a melt index, measured in 
accordance with American Society for Testing and Materials (ASTM) Test 
D-1238 of from about 0.01 to about 100 decigrams per minute. 
Compatibilizer copolymers of ethylene with either alkyl acrylates or alkyl 
methacrylates are readily prepared using conventional technology. One 
process for preparing such copolymers is disclosed in U.S. Pat. No. 
2,497,323, the teachings of which are incorporated herein by reference 
thereto. 
Compatibilizer copolymers of ethylene and carbon monoxide are also readily 
prepared using conventional technology. Processes for preparing 
ethylene/carbon monoxide copolymers are disclosed in U.S. Pat. Nos. 
4,024,325; 4,024,326; and 4,143,096, the teachings of which are 
incorporated herein by reference thereto. 
Compatibilizer interpolymers of ethylene, carbon monoxide and (1) an ester 
of an ethylenically unsaturated carboxylic acid or (2) vinyl acetate are 
prepared using the process suitable for preparation of copolymers of 
ethylene and carbon monoxide. 
Ethyl oxazoline modified copolymers of ethylene and acrylic acid are 
suitably prepared by contacting ethylene/acrylic acid copolymers with an 
excess of ethyl oxazoline at a temperature of from about 110.degree. to 
about 120.degree. C. for a period of from about 2 to about 24 hours. 
High pressure, free-radical initiated, processes for producing copolymers 
of ethylene and vinyl acetate; interpolymers of ethylene, carbon monoxide, 
and acrylic acid; interpolymers of ethylene carbon monoxide and 
methacrylic acid; and interpolymers of ethylene, carbon monoxide, and 
vinyl acetate are well-known in the art and need not be detailed here. 
The second class of compatibilizing polymers are olefin polymers having 
halogen chemically affixed thereto in an amount of from about 24 to about 
44 percent by weight of polymer. Olefin polymers having halogen chemically 
affixed thereto suitably have chlorine as the halogen. 
The term "olefin polymer" is meant to include olefin homopolymers and 
olefin interpolymers. Suitable olefin polymers are formed from one or more 
olefin monomers having from 2 to about 14 carbon atoms. 
Beneficial compatibilizing chlorinated olefin polymers include olefin 
homopolymers formed from a mono-olefin monomer having from 2 to 4 carbon 
atoms. Exemplary of such olefin homopolymers are polyethylene, 
polypropylene and polybutylene. Preferred olefin homopolymers are the 
polyethylene resins. The olefin homopolymers have chlorine chemically 
affixed thereto. 
Beneficial compatibilizing chlorinated olefin polymers also include olefin 
interpolymers formed from at least one mono-olefin monomer having from 2 
to 4 carbon atoms and up to 98 weight percent of at least one 1-alkene 
monomer having from 4 to 14 carbon atoms. A preferred group of olefin 
interpolymers contain at least about 90 mole percent of ethylene and about 
10 mole percent of at least one 1-alkene having from 4 to 14 carbon atoms. 
Exemplary of suitable 1-alkenes are butene-1, octene, 1,7-octadiene and 
the like. Another preferred olefin interpolymer comprises 2 mono-olefin 
monomers having from 2 to 4 carbon atoms. Exemplary of such interpolymers 
are interpolymers of ethylene and propylene. The olefin interpolymers have 
chlorine chemically affixed thereto. 
The compatibilizing olefin polymers having chlorine chemically affixed 
thereto suitably have a chemically combined chlorine content of from about 
24 to about 44 percent by weight of polymer. The resins also have a heat 
of fusion of from about 2 to about 13 calories per gram and a melt 
viscosity of from about 8,000 to about 20,000 poise. Melt viscosity is 
determined using a capillary rheometer at a temperature of 190.degree. C., 
a shear rate of 145 reciprocal seconds and a capillary size of 0.127 by 
5.08 centimeters. 
The compatibilizing chlorinated olefin polymers, prior to chlorination, 
suitably have a weight average molecular weight of less than about 
1,000,000 grams per mole, beneficially between about 20,000 and 300,000 
grams per mole. 
The compatibilizing olefin polymers are suitably prepared under the 
influence of catalyst systems comprising admixtures of strong reducing 
agents, such as triethyl aluminum, and compounds of groups IV-B, V-B and 
VI-B metals of the Periodic System, such as titanium tetra-chloride, and 
the like, and then chlorinated. 
Chlorinated polyethylene resins desirable for use as compatibilizers with 
the present invention are prepared by suspension chlorination as disclosed 
in U.S. Pat. No. 3,454,544, the teachings of which are incorporated herein 
by reference thereto. 
The compatibilized blends of the present invention are readily prepared by 
using conventional melt processing techniques provided two conditions are 
met. First, melt processing must be accomplished at a temperature below 
that at which decomposition of the vinylidene chloride interpolymer 
becomes significant. Second, sufficient shear must be generated during 
melt processing to provide a visually homogeneous blend within a 
reasonable mixing time. 
Conventional melt processing equipment which may be used includes heated 
two-roll compounding mills, Brabender mixers, Banbury mixers, single screw 
extruders, twin screw extruders, and the like. Desirable results are 
obtained when an extruder, either single screw or twin screw, is used for 
melt processing the compatibilized blends of the present invention. 
A factor in determining satisfactory mixing times is temperature. As noted 
hereinbefore, an upper limit on temperature is the temperature at which 
decomposition of the vinylidene chloride interpolymer becomes signficiant. 
A lower limit on temperature is dictated by the polymer blend component 
which has the greatest melting point. If the temperature does not exceed 
the melting point of that polymer blend component, a visually homogeneous 
melt will be difficult, if not impossible, to obtain. 
Another factor in determining satisfactory mixing times is mixing 
efficiency of the melt processing equipment. Certain melt processing 
equipment mixes more efficiently than other melt processing equipment. 
Selection of melt processing equipment which will produce a visually 
homogeneous melt within a reasonable processing time is, however, not 
difficult and can be accomplished without undue experimentation. 
The polymeric components of the compatible blends are generally available 
either in finely divided powder form or in pellet form. Either form is 
suitable for purposes of the present invention. The pellet (or granule) 
form, if available, is preferred over the powder form. In this disclosure 
a powder is that which has substantially all particles of less than 1 mm 
diameter. 
A variety of additives may be added to the compatibilized blends of the 
present invention. Additive type and amounts thereof will depend upon 
several factors. One factor is the intended use of the blends. A second 
factor is tolerance of the blends for the additives. That is, how much 
additive can be added before physical properties of the blends are 
adversely affected to an unacceptable level. Other factors are apparent to 
those skilled in the art of polymer formulation and compounding. 
Additives which may be incorporated into the compatibilized blends of the 
present invention are selected from the group consisting of plasticizers, 
heat stabilizers, light stabilizers, pigments, processing aids, lubricants 
and the like. Each of these additives is known and several types of each 
are commercially available. 
Factors which determine the specific physical properties of the blown films 
of the present invention are not only in the selection of the polymer 
components and their ratio to each other, but also in the film-blowing 
parameters. It has been found that the oxygen barrier property increased 
with decreasing draw-down ratios (DDR); however, if the DDR is decreased 
too much, so that there is insufficient axial stretching of the film 
during the inflation of the molten film the physical strength of the 
ultimate film is somewhat decreased. Whereas some utility exists for such 
"weaker" films, such as those prepared at below a DDR of about 6:1, it is 
preferred that the DDR be maintained in the range of about 8:1 to about 
13:1 (the critical limit). A DDR in the range of about 9:1 to about 11:1 
is most preferred. At a DDR of greater than about 13:1 one encounters an 
unexpected sharp and detrimental decrease in physical properties. The 
blow-up ratio (BUR) is also critical and needs to be between about 1.5:1 
to about 5:1, preferably about 2:1 to about 4:1. Low die shear rates are 
preferred in obtaining superior oxygen barrier properties. 
The temperature employed in preparing, and extruding, the subject blends is 
generally in the range of about 285.degree. F.-410.degree. F., but is 
preferable in the range of about 300.degree.-350.degree. F. If the 
temperature is too low for a given blend, then excessive shear time is 
likely to be encountered in the mixing or extruding operation, giving poor 
results. If the temperature is higher than needed for good mixing and easy 
extrusion, then thermal decomposition is detrimentally accelerated. 
The present invention is illustrated in further detail by the following 
examples and comparative examples. The examples and comparative examples 
are for purposes of illustration only and are not to be construed as 
limiting the scope of the present invention. All parts and percentages are 
by weight unless otherwise specifically noted. 
Blend Preparation 
Three polymeric components (a) a vinylidene chloride interpolymer, (b) an 
olefin polymer and (c) a compatibilizing polymer, each of which was in 
pellet (or granule) form, were dry blended to form a visually uniform 
admixture. Blending was accomplished by placing the components in a bag 
and then shaking them. More sophisticated equipment could have been used 
but was not necessary. The admixture was then fed to an extruder via a 
rate controlled feeding mechanism. 
Alternately, melt blends of vinylidene chloride polymer, polyethylene, and 
a compatibilizer comprising an ethylene copolymer (e.g. ethylene/alkyl 
acrylate copolymer) were prepared from dry blends at various ratios of the 
blend components to each other, melted and homogenized on a heated 
two-roll mill (350.degree. F), cooled to room temperature, and ground to 
pellet-sized granules. 
Compression Molding to Prepare Impact Test Specimens 
Pellet-sized particles of melt-blended samples were compression-molded on a 
Pasadena Hydraulic Press equipped with water-cooled lower platens for 
cooling. Samples were melted between sheets of polyethyleneterephthalate 
at 350.degree. F. for 30 seconds with the platens closed but not 
pressured; then the platens were pressured to about 3 tons platen pressure 
for 1 minute and then at about 15 tons for 30 seconds. The samples were 
then cooled for 5 minutes under 5 tons of platen pressure. 
Oxygen Permeability Testing 
Oxygen permeability of the compression molded samples was measured using an 
instrument commercially available from Modern Controls, Incorporated, 
under the trade designation Oxtran 1050. Oxygen permeability measurements 
were made at 25.degree. C. 
Temperature dependence of permeability is known to be represented by an 
equation of the form P=P.sub.o raised to the exponent of (-E.sub.a /RT) 
where 
P=permeability 
P.sub.o =a constant 
E.sub.a =activation energy of permeation 
R=gas constant 
T=absolute temperature 
From the equation, it is apparent that permeability increases rapidly with 
increasing temperature. Accordingly, an Arrhenius plot at several elevated 
temperatures (log P vs 1/T, wherein P and T are as identified hereinabove) 
can be used to extrapolate to permeabilities at lower temperatures. 
Extrapolation is valid so long as there are no transitions over the range 
of temperatures selected for taking measurements. 
Those skilled in the art recognize that oxygen permeability values obtained 
from compression molded samples may vary from the values obtained by 
testing samples prepared in a different manner. Compression molded sample 
data are, however, a valid basis for comparison. 
Polymers used in preparing polymer blends of the examples and comparative 
examples are set forth hereinafter in Table I. 
TABLE I 
______________________________________ 
Polymer Components 
Code Polymer Description 
______________________________________ 
VDC A vinylidene chloride copolymer resin 
having polymerized therein about 85 
percent vinylidene chloride and about 15 
percent vinyl chloride, both percentages 
being based upon copolymer weight. The 
copolymer had a melt point of about 
161.degree. C. and a weight average molecular 
weight of about 90,000 grams per mole. 
The copolymer was commercially available 
from The Dow Chemical Company as Saran 
B-2000. 
LDPE-A A low density polyethylene resin having 
a density, determined in accordance with 
American Society for Testing and Materi- 
als (ASTM) Test D-792, of 0.921 grams 
per cubic centimeter and a melt index 
(ASTM Test D-1238) of 0.22 decigrams per 
minute. The resin was commercially 
available from The Dow Chemical Company 
under the trade designation PE 133. 
LDPE-B Similar to LDPE-A above except the 
density was about 0.920, M.I. was about 
2.0 and trade designation was PE 529. 
LDPE-C Similar to LDPE-A above except the 
density was about 0.920, M.I. was about 
6.0 and trade designation was PE 752. 
LDPE-D Similar to LDPE-A above exept the 
density was about 0.922, M.I. was about 
1.2 and trade designation was PE 681. 
HDPE A high density polyethylene resin having 
a density (ASTM Test D-1505) of 0.965 
grams per cubic centimeter and a melt 
index, (ASTM Test D-1238) of 0.7 deci- 
grams per minute. The resin was commer- 
cially available from The Dow Chemical 
Company under the trade designation HDPE 
69065. 
LLDPE A linear low density polyethylene resin 
having a density of 0.919 grams per 
cubic centimeter (ASTM Test D-792) and a 
melt index of 2.3 grams per ten minutes 
(ASTM Test D-1238). The resin was 
commercially available from The Dow 
Chemical Company under the trade desig- 
nation Dowlex .TM. 2047. 
ULDPE A linear low density polyethylene resin 
having a density of about 0.914 per 
cubic centimeter and a melt index of 
about 1.1 grams per ten minutes; trade 
designation Dowlex .TM. 4001. 
EMA An ethylene/methyl acrylate copolymer 
having polymerized therein 80 percent 
ethylene and 20 percent methyl acrylate, 
both percentages being based upon 
copolymer weight. The copolymer had a 
melt index (ASTM Test D-1238) of 2.4 
grams per ten minutes and a density 
(ASTM Test D-1505) of 0.942 grams per 
cubic centimeter. The copolymer was 
commercially available from Gulf Oil 
Chemical Company under the trade desig- 
nation. PE 2205. 
EEA-1 An ethylene/ethyl acrylate copolymer 
having polymerized therein 85 percent 
ethylene and 15 percent ethyl acrylate, 
both percentages being based upon 
copolymer weight. The copolymer had a 
melt index (ASTM Test D-1238) of 1.5 
grams per ten minutes and a density 
(ASTM Test D-1505) of 0.930 grams per 
cubic centimeter. The copolymer was 
commercially available from Union 
Carbide under the trade designation DPDA 
6182. 
EEA-2 An ethylene/ethyl acrylate copolymer 
having polymerized therein about 90 
percent ethylene and about 10 percent 
ethyl acrylate, both percentages being 
based upon copolymer weight. The 
copolymer had a melt index (ASTM Test 
D-1238) of 1.5 grams per 10 minutes and 
an estimated density of about 0.93 grams 
per cubic centimeter. 
EEA-3 An ethylene/ethyl acrylate copolymer 
containing about 8.6% EA, with M.I. 
about 2.6. 
EEA-4 An ethylene/ethyl acrylate copolymer 
containing about 13.6% EA, with M.I. 
about 10.7. 
EEA-5 An ethylene/ethyl acrylate copolymer 
containing about 6.7% EA, with M.I. 
about 11.4. 
EEA-6 An ethylene/ethyl acrylate copolymer 
containing about 11.0% EA, with M.I. 
about 28.4. 
______________________________________ 
The examples which follow are for illustration purposes, but the scope of 
the invnetion is not limited to the particular examples shown. 
EXAMPLE 1 
Some representative blends of a VDC polymer, a polyethylene, and a 
compatiblizer are as follows (all are given in weight percent): 
TABLE II 
______________________________________ 
Blend % VDC Polyolefin; % 
Compatibilizer; % 
______________________________________ 
A 10 LDPE-A; 80 EMA; 10 
B 25 LDPE-A; 65 EMA; 25 
C 40 LDPE-A; 50 EMA; 10 
D 65 LDPE-A; 25 EMA; 10 
E 45.5 LDPE-D; 45.5 
EEA-1; 9 
F 25 LDPE-B; 65 EMA; 10 
G 40 LDPE-B; 50 EMA; 10 
H 25 LDPE-C; 65 EMA; 10 
I 40 LDPE-C; 50 EMA; 10 
J 40 LDPE-A; 50 EEA-5; 10 
K 40 LDPE-A; 50 EEA-6; 10 
L 40 LDPE-A; 50 EEA-4; 10 
M 40 LDPE-A; 50 EEA-3; 10 
N 40 LDPE-A; 50 EEA-2; 10 
O 40 LDPE-A; 50 EMA; 10 
P 40 LDPE-B; 50 EEA-3; 10 
Q 40 LDPE-B; 50 EEA-2; 10 
R 40 ULDPE; 50 EEA-4; 10 
S 40 LLDPE; 50 EEA-2; 10 
T 40 ULDPE; 50 EEA-2; 10 
U 40 HDPE; 50 EEA-2; 10 
V 40 ULDPE; 50 EEA-3; 10 
______________________________________ 
The above blends, when fabricated into blown-films by the inflated bubble 
technique described supra, using a BUR in the range of 1.5-5.0 and a DDR 
upwards of 6 experience a sharp drop in physical properties if the 
critical DDR limit of about 13 is exceeded and follow the general shape of 
the curve shown in FIG. 2. 
EXAMPLE 2 
For comparison purposes a given blend, i.e. Blend E of Example 1 above is 
shown below using blow-up ratios within, and outside of, the presently 
claimed invention and using draw-down ratios within, and outside of, the 
presently claimed invention. 
TABLE III 
______________________________________ 
Blow-up Draw-down Oxygen 
Test Ratio.sup.1 Ratio.sup.2 
Permeability.sup.3 
______________________________________ 
I 0.6* 3.3* 10.7 
II 1.0* 9.0 8.3 
III 1.6 8.7 4.6 
IV 2.7 12.0 3.9 
V 3.5 14.0* 3.8 
VI 4.7 8.9 2.9 
______________________________________ 
*These are for comparison, not within the present claims 
.sup.1 Blowup Ratio = film tube diameter/die diameter 
.sup.2 Drawdown Ratio = cross sectional area ratio of die gap to film 
.sup.3 Oxygen Permeability is ccmil/100 in.sup.2day-atm at 25.degree. C. 
In Test I both the B.U.R. and D.D.R. were too low and the oxygen 
permeability was poor. In Test II the B.U.R. was low and the oxygen 
permeability was poor. In Test V the oxygen permeability was good, but the 
D.D.R. was too high as indicated in Example 1 above.