Note: Descriptions are shown in the official language in which they were submitted.
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EXTRUDABLE VINYLIDENE CHLORIDE POLYMER COMPOSITIONS
This invention relates to vinylidene chloride polymer (PVDC) compositions
having improved extrudability.
To control the generation of PVDC degradation products during melt-
processing, processing aids such as lubricants (for example, internal and
external types),
olefinic waxes and oils have been blended with the vinylidene chloride polymer
prior to
fabrication into a final product. However, it has been found that, after
prolonged periods of
extrusion under desirable processing conditions, an excessive degree of
adhesion develops
between the vinylidene chloride polymer and the metal surfaces of the extruder
screw and
die. This adhesion increases the residence time of the vinylidene chloride
polymer which
promotes degradation, resulting in the formation of die face buildup or die
slough generation,
and in the generation of carbon buildup on the screw and die metal surfaces.
It would be desirable to provide a vinylidene chloride polymer composition
which is capable of being extruded, in either powder or pellet form, without
having an
unacceptable level of degradation which results from excessive adhesion
between the PVDC
melt and the screw and die metal surfaces.
In a first aspect, the present invention is a vinylidene chloride polymer
(PVDC)
composition comprising (1 ) a vinylidene chloride polymer, (2) a glycerol
ester and (3) a
silicone polymer, the glycerol ester and silicone polymer being present in an
amount
2 0 sufficient to improve the extrudability of the vinylidene chloride
polymer.
In a second aspect, the present invention is a vinylidene chloride polymer
(PVDC) composition comprising (1) a vinylidene chloride polymer, (2) a
glycerol ester, (3) a
silicone polymer and (4) an epoxidized processing aid, the glycerol ester,
silicone polymer
and epoxidized processing aid being present in an amount sufficient to improve
the
2 5 extrudability of the vinylidene chloride polymer.
In a third aspect, the present invention is a vinylidene chloride polymer,
(PVDC) composition comprising (1 ) a vinylidene chloride polymer, (2) a
glycerol ester and
(3) a polyolefin, the glycerol ester, and polyolefin being present in an
amount sufficient to
improve the extrudability of the vinylidene chloride polymer.
3 0 The inventors have discovered that adding a glycerol ester and a silicone
polymer or a polyolefin and, optionally, an epoxidized processing aid to PVDC
improves the
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extrudability of the PVDC by reducing its degree of adhesion to the metal
surfaces of the
screw and die. The PVDC compositions of the present invention are considered
to possess
improved extrudability. As used herein, the term "improved extrudability"
means that, if
subjected to desirable processing conditions in an extruder, the polymer
composition is less
thermally sensitive and, consequently, the extrudate possesses a reduced level
of degraded
material in the form of die face buildup, slough generation and carbon buildup
on extruder
screw and die surfaces, reduced discoloration or less hydrogen chloride
evolvement and a
lower mechanical energy to extrude, that is, amount of energy expended to
extrude the
polymer due to friction and the viscosity of the polymeric composition, than a
PVDC
composition which does not contain the silicone/carrier polymer concentrate.
Vinylidene chloride polymers which can be employed in the practice of the
present invention are well-known in the art. See, for example, U.S. Patents
3,642,743 and
3,879,359. The most common PVDC resins are known as SaranT"" resins,
manufactured by
The Dow Chemical Company. As used herein, the term "vinylidene chloride
polymer" or
"PVDC" encompasses homopolymers of vinylidene chloride, and also copolymers
and
terpolymers thereof, wherein the major component is vinylidene chloride and
the remainder
is one or more monoethylenically unsaturated monomer copolymerizable with the
vinylidene
chloride monomer. Monoethylenically unsaturated monomers which can be employed
in the
practice of the present invention for preparing the vinylidene chloride
polymers include vinyl
2 0 chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic
acid, itaconic acid,
acrylonitrile, and methacrylonitrile. Preferred ethylenically unsaturated
monomers include
vinyl chloride, acrylonitrile, methacrylonitrile, alkyl acrylates, and alkyl
methacrylates. More
preferred ethylenically unsaturated monomers include vinyl chloride,
acrylonitrile,
methacrylonitrile, and the alkyl acrylates and alkyl methacrylates having from
1 to 8 carbon
atoms per alkyl group. Most preferred ethylenically unsaturated monomers are
vinyl
chloride, methylacrylate, ethylacrylate, and methyl methacrylate.
Preferably, the vinylidene chloride polymer is formed from a monomer mixture
comprising a vinylidene chloride monomer generally in the range of from 60 to
99 weight
percent and the monoethylenically unsaturated comonomer in an amount of from
40 to 1
3 0 weight percent, said weight percents being based on total weight of the
vinylidene chloride
interpolymer. More preferably, the amount of monoethylenically unsaturated
monomer is
from 40 to 4 weight percent, and most preferably, from 40 to 6 weight percent,
based on
total weight of the vinylidene chloride polymer.
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The glycerol esters which can be employed in the practice of the present
invention for preparing the vinylidene chloride polymer composition are those
having from 14
to 22 carbon atoms, such as, for example, glycerol monostearate, glycerol
monopalmitate,
glycerol monooleate, glycerol monolinooleate, glycerol monolinolenate and
their
corresponding di- and triesters. The preferred glycerol ester is glycerol
monostearate.
The amount of glycerol ester which can be employed in the present invention
depends on the composition of the vinylidene chloride polymer composition and
the
processing conditions to which the vinylidene chloride polymer composition is
exposed, but
in general, the amount is from 0.05 to 10, preferably from 0.2 to 5 and most
preferably 2
weight percent, based on the weight of the vinylidene chloride polymer
composition.
The silicone polymers which can be employed in the practice of the present
invention for preparing the vinylidene chloride composition include the high
viscosity silicone
fluids. The term "high viscosity silicone fluids" as used herein is intended
to represent a wide
range of polysiloxane materials having a high molecular weight. These high
viscosity
silicone fluids, often characterized as silicone gums, are comprised of 20 to
100 percent
siloxane polymers having an average molecular weight of 50,000 or above and
provide a
viscosity of 90,000 centipoise and above at ambient temperature. The preferred
polysiloxanes are polydimethyl siloxane, polydimethyldiphenyl siloxane and
polymethyl alkyl
aryl siloxane. It is known that these fluids are difficult to handle and feed
into conventional
2 0 blending equipment with solid thermoplastic polymers due to their high
viscosity. See, for
example, U.S. Patent 4,446,090.
The high viscosity silicone fluids are employed in the practice of the present
invention in the form of concentrates. The silicone polymer concentrate can be
prepared by
blending the high viscosity silicone polymer and a carrier polymer (for
example HDPE) in the
melt using conventional melt-processing techniques. Conventional melt-
processing
equipment which may be used includes heated two-roll compounding mills,
Brabender
mixers, Banbury mixers, single screw extruders, and twin screw extruders. It
is desirable
that the silicone polymer and carrier polymer be blended under conditions and
for a time
sufficient to produce a visually homogeneous blend of the silicone polymer and
carrier
3 0 polymer.
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The amount of silicone polymer employed in the practice of the present
invention for preparing the concentrate is from 0.1 to 99.9, preferably from
10 to 90 and,
most preferably, from 25 to 75 weight percent, based on the weight of the
concentrate.
The carrier polymers which can be employed in the practice of the present
invention for preparing the concentrate are those which are known in the art
for imparting ,
beneficial properties to vinylidene chloride polymers, such as, for example,
polyolefins,
oxidized polyolefins, ethylene vinyl acetate copolymers, and acrylate
copolymers.
Preferably, the carrier polymer is a polyolefin, more preferably, a
polyethylene and, most
preferably, a high density polyethylene (HDPE).
The amount of carrier polymer employed in the practice of the present
invention for preparing the concentrate is from 0.1 to 99.9, preferably from
10 to 90 and,
most preferably, from 25 to 75 weight percent, based on the weight of the
concentrate.
The most preferred silicone/carrier polymer concentrate is commercially
available from Dow Corning as a 50/50 weight percent blend of a high
viscosity, high
molecular weight polydimethyl siloxane and HDPE.
The silicone/carrier polymer concentrate of the present invention is typically
blended with the vinylidene chloride polymer in an amount sufficient to
provide from 0.01 to
10 weight percent silicone/carrier polymer concentrate in the blend.
Other types of silicone polymers which can be employed in the present
2 0 invention include low viscosity silicone fluids, such as those having a
viscosity of at least
about 100 centipoise at 25°C.
The amount of silicone polymer present in the vinylidene chloride polymer
composition of the present invention depends on the composition of the
vinylidene chloride
polymer composition and the processing conditions to which the vinylidene
chloride polymer
composition is exposed. In general, the amount of silicone polymer present in
the vinylidene
chloride polymer composition is from 0.005 to 5.0, preferably from 0.02 to 0.2
and most
preferably 0.1 weight percent, based on the weight of the vinylidene chloride
polymer
composition.
The epoxidized processing aids which can be used in the practice of the
3 0 present invention for preparing the vinyiidene chloride polymer
composition include the
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epoxidized vegetable oils, such as linseed oil, soybean oil, coconut oil,
safflower oil,
sunflower oil, and cotton seed oil; and the epoxidized fatty acid monoesters,
such as, octyl
stearate; and epoxidized diesters, such as the glycol ester of an unsaturated
fatty acid, such
as glycol dioleate.
The amount of epoxidized stabilizer which can be employed in the present
invention depends on the composition of the vinylidene chloride polymer
composition and
the processing conditions to which the vinylidene chloride polymer composition
is exposed,
but in general, the amount is from 0.1 to 10, preferably from 0.4 to 4 and
most preferably 1
weight percent, based on the weight of the vinylidene chloride polymer
composition:
A variety of conventional additives may also be incorporated into the
vinylidene chloride polymer composition. Additive type and amount will depend
upon several
factors. One factor is the intended use of the composition. A second factor is
tolerance of
the composition 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 expert in the art of polymer formulation and compounding.
Exemplary additives include plasticizers, heat stabilizers, pigments,
processing aids, lubricants, fillers, and antioxidants. Each of these
additives is known and
several types of each are commercially available.
Exemplary lubricants include fatty acids, such as stearic acid; esters, such
as
2 0 fatty esters, wax esters, glycol esters, and fatty alcohol esters; fatty
alcohols, such as
n-stearyl alcohol; fatty amides, such as N,N'-ethylene bis stearamide;
metallic salt of fatty
acids, such as calcium stearate, zinc stearate, magnesium stearate; and
polyolefin waxes,
such as paraffinic, and oxidized polyethylene. Paraffin and polyethylene waxes
and their
properties and synthesis are described in 24 Kirk-Othmer Encyc. Chem. Tech.
3rd Ed.,
2 5 Waxes, at 473-77 (J. Wiley & Sons 1980).
The additives may be incorporated into the vinylidene chloride polymer
composition by using conventional melt-processing, as well as dry blending
techniques for
thermally sensitive polymers. The vinylidene chloride polymer composition of
the present
invention can be melt-processed and extruded into any suitable final product,
for example, a
3 0 variety of films or other articles. As is well known in the art, the films
and articles are
fabricated with conventional coextrusion; for example, feedblock coextrusion,
multimanifold
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die coextrusion, or combinations of the two; injection molding; co-injection
molding; extrusion
molding; casting; blowing; blow molding; calendering; and laminating.
Exemplary articles include blown and cast, mono and multilayer, films; rigid
and flexible containers; rigid and foam sheet; tubes; pipes; rods; fibers; and
various profiles.
Lamination techniques are particularly suited to produce multi-ply sheets. As
is known in the
art, specific laminating techniques include fusion; that is, whereby self-
sustaining lamina are
bonded together by applications of heat and pressure; wet-combining, that is,
whereby two
or more plies are laminated using a tie-coat adhesive, which is applied wet,
the liquid driven
off, and in one continuous process combining the plies by subsequent pressure
lamination;
or by heat reactivation, that is, combining a precoated film with another film
by heating, and
reactivating the precoat adhesive so that it becomes receptive to bonding
after subsequent
pressure laminating.
The vinylidene chloride polymer compositions of the present invention are
particularly suited for fabrication into flexible and rigid containers both in
monolayer and
multilayer structures used for the preservation of food, drink, medicine and
other
perishables. Such containers should have good mechanical properties, as well
as low gas
permeabilities too, for example, oxygen, carbon dioxide, water vapor, odor
bodies or flavor
bodies, hydrocarbons or agricultural chemicals.
The monolayer structures comprise the vinylidene chloride polymer
2 0 composition of the present invention.
The multilayer structure comprises (1 ) one or more layers of an organic
polymer or a blend of two or more different organic polymers, the organic
polymer of one
layer being the same as or different from the organic polymer of another layer
and (2) one or
more layers of the vinylidene chloride polymer composition of the present
invention.
2 5 The multilayer structure can have three layers comprising (1 ) a first
outer
layer of the organic polymer or blend of two or more different organic
polymers, (2) a core
layer of the vinylidene chloride polymer composition of the present invention
and (3) a
second outer layer of an organic polymer which is the same as or different
from the organic
polymer of the first outer layer.
3 0 The multilayer structure can also have five or seven layers comprising one
or
more layers of the vinylidene chloride polymer composition of the present
invention, and the
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remaining layers comprising an organic polymer or'a blend of two or more
different organic
polymers, the organic polymer of one layer being the same as or different from
the organic
polymer of another layer.
Adhesive layers may be interposed between contiguous layers of the
multilayer structures, depending on the composition and method of preparing
the multilayer
structure.
Organic polymers which can be used in the practice of the present invention
for preparing the multilayer structure include polyolefins, polyamides,
polymers based on
aromatic monomers, and chlorinated polyolefins.
By the term "polyolefin" is meant a polymer or copolymer of ethylene, that is,
a polymer derived solely from ethylene, or ethylene and one or more monomers
copolymerizable therewith. Such polymers (including raw materials, their
proportions,
polymerization temperatures, catalysts and other conditions) are well-known in
the art and
reference is made thereto for the purpose of this invention. Additional
comonomers which
can be polymerized with ethylene include olefin monomers having from 3 to 12
carbon
atoms, ethylenically unsaturated carboxylic acids (both mono- and
difunctional) and
derivatives of such acids such as esters (for example, alkyl acrylates) and
anhydrides;
monovinylidene aromatics and monovinylidene aromatics substituted with a
moiety other
than halogen such as styrene and methylstyrene; and carbon monoxide. Exemplary
monomers which can be polymerized with ethylene include 1-octene, acrylic
acid,
methacrylic acid, vinyl acetate and malefic anhydride.
Polyolefins which can be employed in the practice of the present invention for
preparing the multilayer laminate structure include polypropylene,
polyethylene, and
copolymers and blends thereof, as well as ethylene-propylene-diene
terpolymers. Preferred
polyolefins are polypropylene, linear high density polyethylene (HDPE),
heterogeneously-
branched linear low density polyethylene (LLDPE) such as DOWLEXT""
polyethylene resin (a
trademark of The Dow Chemical Company}, heterogeneously-branched ultra low
linear
density polyethylene (ULDPE) such as ATTANET"" ULDPE (a trademark of The Dow
Chemical Company); homogeneously-branched, linear ethylene/a-olefin copolymers
such as
3 0 TAFMERT"" (a trademark of Mitsui Petrochemicals Company Limited) and
EXACTT"~ (a
trademark of Exxon Chemical Company); homogeneously-branched, substantially
linear
ethylene/a-olefin polymers such as AFFINITYT"" (a trademark of The Dow
Chemical
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Company) and ENGAGE~ a trademark of DuPont 'Dow Elastomers of polyolefin
elastomers,
which can be prepared as disclosed in U.S. Patents 5,272,236 and 5,278,272;
and high
pressure, free radical polymerized ethylene polymers and copolymers such as
low density
polyethylene (LDPE), ethylene-acrylic acid (EAA) copolymers such as
PRIMACORT""
(trademark of The Dow Chemical Company), and ethylene-vinyl acetate (EVA)
copolymers
such as ESCORENET"" polymers (a trademark of Exxon Chemical Company}, and
ELVAXT""
(a trademark of E.I. DuPont de Nemours & Co.). The more preferred polyolefins
are the
homogeneously-branched linear and substantially linear ethylene copolymers
with a density
(measured in accordance with ASTM D-792) of 0.85 to 0.99 g/cm3, a weight
average
molecular weight to number average molecular weight ratio (Mw/Mn) from 1.5 to
3.0, a
measured melt index (measured in accordance with ASTM D-1238 (190/2.16)) of
0.01 to
100 g/10 minutes, and an I10/I2 of 6 to 20 (measured in accordance with ASTM D-
1238
(190/10)).
In general, high density polyethylene (HDPE) has a density of at least about
0.94 grams per cubic centimeter (g/cc) (ASTM Test Method D-1505). HDPE is
commonly
produced using techniques similar to the preparation of linear low density
polyethylenes.
Such techniques are described in U.S. Patents 2,825,721; 2,993,876; 3,250,825
and
4,204,050. The preferred HDPE employed in the practice of the present
invention has a
density of from 0.94 to 0.99 g/cc and a melt index of from 0.01 to 35 grams
per 10 minutes
2 0 as determined by ASTM Test Method D-1238.
Polymers based on aromatic monomers which can be employed in the
practice of the present invention include polystyrene, polymethylstyrene,
polyethylstyrene,
styrene/methylstyrene copolymer, and styrene/chlorostyrene copolymer.
Polyamides which can be employed in the practice of the present invention
2 5 include the various grades of nylon, such as nylon-6, nylon-66 and nylon
12.
Adhesive materials which can be employed in the practice of the present
invention for preparing the adhesive layer include ethylene vinyl acetate
copolymers,
ethylene/ethyl acrylic acid ester copolymers, ionomers, modified polyolefins
as described in
U.S. Patent 5,443,874, acrylic-based terpolymer adhesives as described in U.S.
Patent
3 0 3,753,769 and adhesives formed by reacting an epoxy resin and an acidified
aminoethylated
vinyl polymer as described in U.S. Patent 4,447,494. The more preferred
adhesive materials
are maieic anhydride grafted polyethylene or polypropylene such as ADMER
(trademark of
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Mitsui Petrochemicals) adhesive resins, or ethylene-vinyl acetate copolymer
resins such as
ELVAXT"' (trademark of DuPont). The most preferred adhesive material is
ELVAXT"" 3175,
which is a 6 Melt Index, 28 percent vinyl acetate copolymer. The thickness of
the monolayer
and multilayer structures of the present invention is variable within wide
limits, depending on
the contemplated application. In general, the monolayer structure of the
present invention
has a thickness of from 0.05 to 10 mils, preferably, from 0.2 to 6 mils, most
preferably, from
0.4 to 1.8 mils. In general, the multilayer structure of the present invention
has a thickness
of from 0.05 to 200 mils, preferably from 1 to 100 mils, most preferably, from
2 to 80 mils,
with the PVDC polymer layer having a thickness of from 0.005 to 20 mils,
preferably from 0.2
to 10 mils, most preferably, from 0.2 to 8.0 mils.
The present invention is illustrated in further detail by the following
examples.
The examples are for the 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.
Examples 1-3 and Comparative Examples A and B
The following formulations of a vinylidene chloride copolymer (7.75 weight
percent methyl acrylate, 92.25 weight percent vinylidene chloride) prepared
using a
conventional high intensity blender were employed in the examples:
xam le 1
2 0 Vinylidene chloride copolymer 95.27 wt.
Epoxidized soybean oil 1.2 wt.%
Glycerol monostearate 2.0 wt.%
Oxidized polyethylene wax 0.18 wt.
Polyethylene wax 0.45 wt.%
High density polyethylene 0.90 wt.%
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Example 2
Vinylidene chloride copolymer 96.475 wt.%
Epoxidized soybean oil 1.0 wt.%
Glycerol monostearate 2.0 wt.%
Oxidized PE wax 0.1 wt.%
Polyethylene wax 0.1 wt.%
High Mw silicone/HDPE conc. 0.125 wt.%
Comparative Example A
Vinylidene chloride copolymer 96.27 wt.%
Epoxidized soybean oil 2.2 wt.%
Oxidized PE Wax 0.18 wt.%
P E wax 0.45 wt.
HDPE 0.90 wt.%
Comparative Example B
Vinylidene chloride copolymer 96.8 wt.%
Epoxidized soybean oil 1.2 wt.%
Glycerol Monostearate 2,0 ~,%
Extrusion Conditions:
9 hour trials, started with a clean system (screw, barrel, and die).
Rate: 42 Ib/hr, 17 RPM, 2.5-inch diameter 21:1 UD Extruder, monolayer cross-
head die.
Barrel Temperatures: 150°C (feed), 155°C (transition),
160°C (meter).
Die temperature: 173°C, Nosepiece: 175°C, Adaptor:
175°C, Feedthroat: 38°C.
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Extrusion trials were conducted on clean equipment, and the PVDC
formulations extruded for 9 hours each. At the end of the 9 hours, the screw
was stopped,
and full cooling put on the barrel and die. This froze the polymer in the die
without additional
degradation. The die was then dis-assembled, and the carbon tended to stick to
the polymer
when removed from the die. This allowed for a method to compare carbon
generation
between different PVDC copolymer formulations. The Comparative Example A
formulation
when extruded for 9 hours gave an outer portion of the die that was totally
covered with
black carbon. When Examples 1 and 2 formulations were extruded for 9 hours,
they both
gave an outer surface that was totally clean of carbon. The extrusion trial
with the
Comparative Example B formulation was stopped after 2 hours because of poor
quality film
due to heavy die lines, slough, and a rough surface to the film. This
indicates that the
external lubricants (for example, oxidized PE wax, PE wax, HDPE, silicone
concentrate) are
necessary in combination with the GMS.
Barrier Testing
Barrier properties were determined for monolayer blown films (1 to 2 mil) at
23°C and 60 percent relative humidity in accordance with ASTM Method D-
3985-81. The
barrier property of the film formed from the Example 1 formulation (0.085 cc-
mil/100 in2-atm-
day) was superior compared to that of the Comparative Example A formulation
(0.11 cc-
mil/100 in2-atm-day). This improvement in barrier is highly desirable. It is
surprising that
2 0 barrier properties and processing are both improved, because usually, an
improvement in
processability results in a detrimental effect on barrier properties. This is
due to the fact that
the improved stability of the GMS-containing formulation was obtained at a
reduced ESO
level (2.0 percent vs. i.0 percent). It is known that liquid stabilizers have
a detrimental effect
on barrier properties.
2 5 Thermal Stability
Two-roll mill testing was also performed to compare thermal stability of PVDC
copolymer formulations. In this test, 200 g of blended PVDC copolymer was
placed on two
heated, co-rotating rolls. The polymer then melted due to the heat and shear
created within
the sample. The time to significant degradation was compared between samples.
Testing
3 0 was done at 180°C roll temperature. The Comparative Example A
formulation evolved small
HCL bubbles after 11 minutes. The Example 1 formulation took 13.5 minutes to
reach the
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same level of gassing. This is a further indication of the improved thermal
stability provided
by the GMS-containing formulation.
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