Note: Descriptions are shown in the official language in which they were submitted.
- 1 329288
,
VINYLIDENE CHLORIDE INTERPOLYMER
The present invention relates to a vinylidene
chloride interpolymer posses~ing an improved
combination of properties. Specifically, this
invention relates to an improved barrier resin
comprising a mixture of a vinylidene chloride
interpolymer and a unique combination oP additives,
which resin has improved barrier to atmospheric gases
and has, after being subject to a heat history during
processing, a reduced level of carbon contamination and
. good extrudability e.g., color.
Vinylidene chloride interpolymers are well-
known in the prior art. In the past, vinylidene
chloride interpolymers have been produced by an
emulsion or ~uspension polymerization process. Both
the emulsion and suspension polymerization processes
produce an aqueous dispersion of polymer particles
having a relatively small particle diameter. The
polymer particles are recovered from the aqueous
dispersion by drying or other means for removing a
majority of the aqueous phase. In the past, the
practice has been to extrude the vinylidene chloride
36,369A-F -1_
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interpolymer directly from the form in which it is
recovered.
In an effort to improve the extrudability o~
compounds comprising vinylidene chloride interpolymers,
such compound~ are fabricated mainly from vinylidene
chloride interpolymers and an adequate amount of
modifiers such as stabilizers, plasticizers, etc. When
using no modifiers with the resin, the melt viscosity
of the resin is sufficiently high that the load on the
extruder screw is too large and the extruded compound
is subject to thermal decomposition and discoloration
due to the close proximation of the compound's thermal
decomposition point and melting point. Moreover, the
decomposed interpolymer may generate an undesirable
level of carbon contamination in the extrudate, which
could have an effect upon the gas barrier of the
extrudate.
In order to industrially extrude and process
the compound of vinylidene chloride resin by using a
conventional screw-type extruder without thermal
. .
decomposition and discoloration of the product, a
-~ 25 relatively large amount of a stabilizer and plasticizer
would inevitably have to be incorporated in the resin.
The larger amount of stabilizer and plasticizer would
lower the melting point of the vinylidene chloride
resin, with an accompanied reduction of melt viscosity
and improvement of thermal stability of the compound,
but with a decrease in barrier to atmospheric gases.
. ~,,
In some instances, it is desirable to form the
vinylidene chloride interpolymer into pellets prior to
final extrusion. With the increased demand for
pellets, the processing conditions in which pellets are
, . -, .
36,369A-F -2-
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exposed has become more demanding. Although
satisfactorily extrudable for a period, it has been
found that attempts to extrude vinylidene chloride
interpolymer pellets over long periods on certain
extrusion equipment have also proven unsatisfactcry due
to an undesirable level oP carbon contamination in the
extrudate, and discoloration of the extrudate.
It is desirable to produce a vinylidene
chloride interpolymer which interpolymer, in either
powder or pellet form, is capable of being extruded
without having an unacceptable level of carbon
contamination, as well as having good color. It is to
this goal that the present invention is directed.
In the case of packing perishable foods such as
processed meats and cooked foods which are highly
sensitive to permeated oxygen through the packing
-` material, better barrier resins is demanded. It is to
this goal that ano~her aspect of the present invention
is directed.
~'
It would also be desirable to produce an
` article from a vinylidene chloride interpolymer which
exhibits a decreased permeability to atmospheric gases.
The present invention concerns a process for
improving the extrudability of a thermally sensitive
resin comprising the step of blending into a generally
3 homogeneous mixture a vinylidene chloride interpolymer
and a unique combination of additives which comprises
an extrusion aid selected from the group consisting of
~` oxidized polyethylene; oxidized polypropylene; or
mixtures thereof, in an amount of from about 0.01 to
about 0.5 weight percent; an ethylene-vinyl acetate
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~ 1 329288
copolymer present in an amount of from about 0.01 to
about 2 weight percent; a paraffin wax present in an
amount of from about 0.005 to about l weight percent;
and an epoxidized oil or resin present in an amount of
from about 0.1 to about 3 weight percent, all weight
percentages being based on the total weight of the
mixture.
Additionally, the present invention concerns a
composition comprising a generally homogeneous mixture
of a vinylidene chloride interpolymer and a unique
combination of additives which comprises an extrusion
aid selected from the group consisting of oxidized
polyethylene; oxidized polypropylene; or mixtures
thereof, in an amount of from about 0.01 to about 0.5
weight percent; an ethylene-vinyl acetate copolymer
present in an amount of from about 0.01 to about 2
weight percent; a paraffin wax present in an amount of
from about 0.005 to about 1 weight percent; and an
epoxidized oil or resin present in an amount of from
about 0.1 to about 3 weight percent, all weight
. percentages being based on the total weight of the
~ mixture.
::'25
Vinylidene chloride interpolymers suitable for
use in the present invention are those vinylidene
chloride interpolymers formed from vinylidene chloride
and an amount of one or more monoethylenically
unsaturated monomers copolymerizable with vinylidene
chloride.
The vinylidene chloride interpolymers have
selectively polymerized therein vinylidene chloride in
, 35 an amount of from about 40 to about 98 weight percent,
beneficially from about 50 to about 96 weight percent,
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and desirably from about 60 to about 94 weight percent,
based on total weight of the vinylidene chloride
interpolymer.
The vinylidene chloride interpolymer is
selected to comprise one or more monoethylenically
unsaturated monomers copolymerizable with vinylidene
chloride. The amount of monoethylenically unsaturated
monomer is suitably from about 60 to about 2 weight
percent, beneficially from about 50 to about 4 weight
percent, and deqirably from about 40 to about 6 weight
percent, based on total weight of the vinylidene
chloride interpolymer.
Monoethylenically unsaturated monomers suitable
-~ for use in the present invention include vinyl
chloride, alkyl acrylates, alkyl methacrylates, acrylic
acid, methacrylic acid, itaconic acid, acrylonitrile,
^ and methacrylonitrile. The ethylenically 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 preferably have from about 1 to about 4
carbon atoms per alkyl group. The alkyl acrylates and
alkyl methacrylates are most preferably selected from
the group consisting of methylacrylates,
ethylacrylates, and methyl methacrylates.
~`
Methods of forming the vinylidene chloride
interpolymers suitable for use in the present invention
are well-known in the prior art. The vinylidene
chloride interpolymer is generally formed through an
emulsion or suspension polymerization process.
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Exemplary of such proce~ses are U.S. Patents 2,558,728;
3,007,903; 3,642,743; ana 3,~79,359; and the methods
described by R. A. Wes~ling, in Pol~vinylidene
Chlor-de, Gordon and Breach Science Publisherq, New
York, 1977, Chapter 3.
Typically, the monomeric
materials are emulsified or ~u~pended in an aqueous
phase. The aqueous phase containq a polymerization
initiator and a surfac~ active ~gent capable of
emulsifying or suspending the monomeric materi~lq in
the aqueous phase. The polymerization of the monomeric
materials is usually carried out witn heating and
agitation.
After polymeri~ation is complete, the resulting
suspension or emulsion of vinylidene chloride
interpolymer has a majority o~ an aqueou~ phase. The
resultant polymeric m~ttrial is vacuum stripped.
Thereafter, the slurry is cooled down~ unloaded and
dewatered, and the re~in is collected and further
dried.
The inventors have found that a particular
combination of additives yields a resin, in either
powder or pellet form, which when extruded provides an
article having good color characteristicq, low carbon
contamination, and low permeability to oxygen.
The preferred vinylidene chloride interpolymer
formulation comprises the following additives. An
extrusion aid of oxidized polyethylene; oxidized
polypropylene; or mixtures thereof is employed.
Oxidized polyethylene and oxidized polypropylene are
well-known in the prior art. Oxidized polyethylene and
oxidized polypropylene are generally prepared by
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forming the ethylene or propylene polymer through
methods well-known in the art, and subsequently
exposing said polymer to oxygen at an elevated
temperature and for time sufficient to achieve the
desired degree of oxidation. Preferably, oxidized
polyethylene is employed as an extrusion aid.
Suitably, Allied 629A oxidized polyethylene,
commercially available from Allied Corp., is the
oxidized polyethylene.
The extrusion aid is incorporated into the
vinylidene chloride interpolymer in the useful range of
from about 0.01 to about 0.5 weight percent, preferably
in the range of from about 0.02 to about o.o8 weight
percent, most preferably in the range of from about
0.03 to about 0.04 weight percent.
An ethylene-vinyl acetate copolymer is employed
as an additional extrusion aid; suitably, EVA 3180~
ethylene-vinyl acetate copolymer which contains about
28 percent vinyl acetate and is commercially available
~ from E. I. DuPont de Nemours Co. The EVA 3180~ or an
;l equivalent ethylene-vinyl acetate copolymer is
`; 25 incorporated into the vinylidene chloride interpolymer
in the range of from about 0.01 to about 2 weight
percent, preferably in the range of from about 0.1 to
~` about 1.5 weight percent, and most preferably in the
range of from about 0.5 to about 1 weight percent.
A paraffin wax is employed as an extrusion aid.
For example, a paraffin, commercially available from
Bohler Industries under the trade designation Bohler
1421, may be incorporated into the vinylidene chloride
interpolymer. The paraffin wax is present in an amount
in the range of from about 0.005 to about 1 weight
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percent, preferably in the range of from about 0.1 to
about 0.2 weight percent.
Epoxidized oils and resins are suitably
employed as plasticizers, stabilizers and lubricants;
for example, Vikoflex 7177~ epoxidized soybean oil which
contains oxirane groups is commercially available from
Viking Chemical Co. The epoxidized soybean oil or an
equivalent epoxidized soybean oil is incorporated into
the vinylidene chloride interpolymer in the range of
from about 0.1 to about 3 weight percent, preferably,
from about 0.5 to about 2 weight percent, and most
preferably, from about 0.8 to about 1.2 weight percent.
In a preferred embodiment of the present
invention, the additive package comprises an additive
comprising at least one inorganic base. Preferred
inorganic bases are magnesium hydroxide, tetrasodium
pyrophosphate, magnesium oxide, and calcium hydroxy
phosphate (commonly referred to tricalcium phosphate),
with magnesium hydroxide being most preferred. An
exemplary magnesium hydroxide is Kisuma 5BT~,
commercially available from the Kyowa Chemical Co.
When the inorganic base is included in the
additive package, it is suitably present in an amount
of from about 0.01 to about 5 weight percent of the
total mixture weight. Preferably, the inorganic base
is present in an amount of from about 0.1 to about 4
weight percent of the total mixture weight. Most
preferably, the inorganic base is present in an amount
of from about 0.5 to about 2 weight percent of the
total mixture weight.
36,369A-F -8-
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The inventors have found that a specific
combination of additives provides particularly
beneficial results. The combination comprises the
following: an oxidized polyethylene, such as Allied
629A, in an amount of about 0.03 weight percent; an
ethylene-vinyl acetate copolymer, such as EVA 3180~, in
an amount of about 0.65 weight percent; a paraffin wax,
such as Bohler 1421, present in an amount of about 0.12
weight percent; an epoxidized oil, such as Vikoflex
7177~, in an amount of about 1.0 weight percent; and
magnesium hydroxide, such as Kisuma 5B~M, in an amount
of about 0.65 weight percent.
The exact quantities of the compounds of the
additives blended with the vinylidene chloride
interpolymer should be selected to provide a resin
having an oxygen permeability according to the Dow
permeability index of no more than about 0.09 units,
the Dow index being calculated as follows: units are in
(cc-mil)/(100 in2.day-atm), wherein cc is the cubic
centimeters of oxygen, mil is the sample thickness, in2
is the surface area of the sample, day represents a 24
hour time period, and atm is atmospheric pressure in
atmospheres. Beneficially the oxygen permeability of
mixtures according to the present invention will be
less than about 0.08 Dow unit. The selection of
suitable proportions to satisfy the above criteria is
known by skilled artisans.
The additive package may contain additional
additives well-known to those skilled in the art.
Exemplary of additives which may be incorporated in the
package are light stabilizers such as hindered phenol
derivatives; pigments such as titanium dioxide and the
36,369A-F -9_
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like. Each of these additives is known and several
types of each are commercially available.
Blending of the vinylidene chloride and the
additive package can be accomplished by using
conventional melt processing, as well as dry blending
techniques.
For melt blending, two conditions must be 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 generally homogenous extrudate
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 blending the vinylidene chloride interpolymer
and the additives.
When dry blending, the components should form a
visually uniform admixture. Suitable dry blending
equipment includes Hobart mixers, Welex mixers,
Henschel High Intensity mixers, and the like.
After being blended into a mixture, the
3 vinylidene chloride interpolymer and additive package
is then extruded. In one embodiment, the mixture is
physically blended and then melt processed into any
suitable final product.
In a preferred embodiment of the present
invention, the mixture of vinylidene chloride
36,369A-F -10-
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interpolymer and additive package is pelletized.
Methods of forming the mixture into pellets are well-
known to those skilled in the art. Any method capable
of forming the mixture into pellets is suitable for use
in the present invention. For the purposes of this
application, the terms "pellet" or "pellets" refer to
particles having a minimum cross-sectional dimension of
at least 1/32 inch, preferably of at least 1/16 inch,
and most preferably of at least 1/8 inch, said pellets
suitably have a maximum cross-sectional dimension of at
least 1/2 inch, preferably of at least 3/8 inch, and
most preferably of at least 1/4 inch. Exemplary of a
method suitable for use in forming the pellets of the
mixture are extrusion through a strand die and
pelletization by chopping the extruded strand into
pellets.
Applicants have discovered that the process and
composition according to the present invention improves
the extrudability of the vinylidene chloride
~; interpolymer and allows for the satisfactory extrusion
of vinylidene chloride interpolymer pellets formed
therefrom. The pellets are considered to possess
improved extrudability when the mixture of vinylidene
chloride interpolymer and additives can be formed into
an article which possesses less carbon contamination
and less discoloration than from pellets formed from
the vinylidene chloride interpolymer alone.
3o
The process of the present invention can be
used to form a variety of films or other articles. As
is well known in the art, the films and articles are
fabricated with conventional coextrusion, e.g,
feedblock coextrusion, multimanifold die coextrusion,
or combinations of the two; injection molding;
36,369A-F -11-
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extrusion molding; and lamination techniques. Articles
formed therefrom include blown and cast, mono and
multilayer, films; 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, i.e., whereby self-
sustaining lamina are bonded together by applications
of heat and pressure; wet combining, i.e., whereby two
or more plies are laminated using a tie coat adhesive,
~; which is applied wet, the liquid driven off, and
combining by subsequent pressure laminating in one
continuous process; or by heat reactivation, i.e.,
combining a precoated film with another film by heating
and reactivating the precoat adhesive so that it
becomes receptive to bonding after subsequent pressure
l laminating.
Exemplary articles include rigid containers
used for the preservation of food, drink, medicine and
other perishables. Such containers should have good
mechanical properties, as well as low gas
permeabilities to, for example, oxygen, carbon dioxide,
water vapor, odor bodies or flavor bodies, hydrocarbons
or agricultural chemicals. Most organic polymers such
; as the polyolefins, styrene polymers and the like, by
them~elves, do not possess sufficent resistance to
transmission of atmospheric gases and vapors.
3 Consequently, multilayer sheet structures employed in
packaging materials have organic polymer skin layers
laminated on each side of a vinylidene chloride
interpolymer barrier layer, generally with glue layers
used to promote adhesion between the barrier layer and
dissimilar material layers.
:,
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Artiçles formed from the preferred formulation
exhibit decreased oxygen permeabilty.
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 1-6
,
Blends of vinylidene chloride are prepared with
, various additives as set forth in Table 1.
, A vinylidene chloride interpolymer is formed
; through a suspension polymerization process. The
vinylidene chloride interpolymer is formed from a
monomer mixture comprising about 94 weight percent
20 vinylidene chloride and about 6 weight percent methyl
acrylate, based on total monomer mixture weight. The
copolymer has a weight average molecular weight of
100,000.
The interpolymer produced as described above is
melt blended into a generally homogeneous mixture with
the various quantities of the following additives: (a)
Vikoflex 7177~ epoxidized soybean oil commercially
30 available from Viking Chemical Co; (b) ethylene-vinyl
acetate copolymer commercially available from E. I.
DuPont de Nemours under the trade designation EVA 3180~;
(c) a paraffin wax commercially available from Bohler
Industries under the trade designation Bohler 1421; and
35 an oxidized polyethylene commercially available under
the trade designation as Allied 629A from Allied Corp.
36,369A-F -13-
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The mixtures described imMediately above are, in
some examples, melt blended with one of the following
inorganic bases: (a) magnesium hydroxide, commercially
available from the Kyowa Chemical Co., under the trade
designation Kisuma 5B~U; (b) tetrasodium pyrophospahate
commercially available Prom Monsanto Chemical Co.;
magnesium oxide, commercially available from Merck &
Co., under the trade designation Maglite S 3331; and (d)
10 calcium hydroxy phpsphate commercially available from
Monsanto, under the trade designation polymer grade
tricalcium phosphate.
The mixture of vinylidene chloride interpolymer
15 and additives is pelletized. Pelletizing is
accomplished using a commercially available strand die
and cutter. The pellets have an average length of about
0.130 inch and an average diameter of about 0.145 inch.
The pellets are extruded through a 2 1/2"
extruder having a length to diameter ratio of 21/1. The
extruder has the following set temperatures: (a) first
zone temperature = 174C; (b) second zone temperature-
168C; (b) third zone temperature = 163C; and (c) die
25 temperature= 165C.
The molten blend is extruded through a single
tape die to form a tape which is tested.
30 Extrudability Testin~
~ As the resin decomposes, it discolors i.e.,
- becomes brownish. The extrudate tape is also visually
inspected to determine its color. Color is
35 qualitatively rated on a scale of 1 to 5 over a
36,369A-F -14-
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continous range of discoloration, wherein 1 represen~s a
creamy color and 5 a rather dark brown.
Carbon Contamination Testin~
The decomposition of the extruded resin into
carbon is determined on the root of the extruder screw
heel, on the extruder die, and in the extrudate tape.
When evaluating the root of the extruder screw heel and
lO the extruder die, pellets are extruded in a continuous
process for a period of about 2 hours. The extent of
carbon formation is qualitatively rated on a scale of l
to 5 over a continous range of carbon buildup, wherein 1
represents generally no visible carbon on the surface
15 and 5 represents a layer of carbon generally completely
covering the surface.
Carbon contamination in the extrudate tape is
determined by counting specks of carbon over a one
20 minute period every during the two hour extrusion trial.
The extent of carbon formation is qualitatively rated on
a scale of 1 to 5 over a continous range of carbon
buildup, wherein l represents less than 20 carbon speck
counts per minutes and 5 represents greater than 100
25 carbon ~pecks counts per minute.
OxY~en PermeabilitY Testin~
~- The samples in examples are measured for oxygen
30 permeability. The oxygen permeability of blends
according to the present invention is measured according
to a Dow permeability index, the Dow index being
calculated as follows: units are in (cc-mil)/(100
in2-day-atm), wherein cc is the cubic centimeters of
35 oxygen, mil is the sample thickr.ess, in2 is the surface
36,369A-F -15-
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1 329288
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area of the sample, day represents a 24 hour time
period, and atm is atmospheric pressure in atmospheres.
Oxygen permeability of the extrudate tapes is
measured using an instrument commercially available from
Modern Controls, Incorporated, under the trade
designation Oxtran 1050. Oxygen permeability
measurements are made at 23 Centigrade.
: 25
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- 36,369A-F -16-
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~ 1 329288
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* = not an example of the present invention.
** = not measured.
1 VdMA = All examples are carried out with a
vinylidene chloride copolymer of 94 weight percent
vinylidene chloride and 6 weight percent methyl
acrylate, having a weight average molecular weight
of 100,000.
2 OP = oxidized polyethylene, commercially available
from Allied Corp., under the trade designation
Allied 629A. Weight percent is based upon the
total mixture weight.
10 3 Wax = paraffin wax, commercially available from
Bohler Industries, under the trade designation
Bohler 1421. Weight percent is based upon the total
mixture weight.
4 ESO = epoxidized soybean oil, commercially
available from Viking Chemical Company, under the
trade designation Vikoflex 7177~. Weight percent is
based upon the total mixture weight.
5 EVA = ethylene-vinyl acetate, commercially
available from E.I. DuPont de Nemours Co., under
the trade designation EVA 3180~. Weight percent is
based upon the total mixture weight.
20 6 Inorganic Bases: (a) Mg(OH)2 = magnesium hydroxide,
commercially available from the Kyowa Chemical Co.,
under the trade designation Kisuma 5BT~; (b) TSPP =
tetrasodium pyrophospahate commercially available
from Monsanto Chemical Co.; (c) TCP - commercially
available from Monsanto, under the trade
designation polymer grade tricalcium phosphate.
Weight percent is based upon the total mixture
weight.
7 Color = according to visual inspection.
8 Carbon contamination = according to visual
inspection of (a) the extruder screw, (b) the
extruder die, and (3) the extrudate. Carbon
formation on the screw and die is rated on a scale
of 1 to 5 over a continous range of carbon buildup,
wherein 1 represents generally no visible carbon on
the surface and 5 a represents a layer of carbon
generally completely covering the surface. Carbon
contamination in the extrudate tape is
qualitatively rated on a scale of 1 to 5 over a
continous range of carbon buildup, wherein 1
represents less than 20 carbon speck counts per
, .
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_19_
minutes and 5 represents greater than lO0 carbon
specks counts per minute.
9 2 perm. = oxygen permeabilty measured in cubic
centimeters of oxygen times mils of thicknes~
divided by the product of (a) 100, (b) area in
square inches, (c) 24 hours and (d) the atmospheric
pressure in atmospheres.
.1
As can be seen from the above table, the
compositions of the present invention possess good color
10 characteristics, low carbon contamination, and low
permeability to oxygen.
Although the invention has been described in
considerable detail, with reference to certain preferred
embodiments thereof, it will be understood that
variations and modifications can be effected within the
spirit and scope of the invention as described above and
as defined in the appended claims.
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