Note: Descriptions are shown in the official language in which they were submitted.
1~2i'
~3~
The inventiorl relates to a meth3d of forming a
film and the 'ilm pr3duced by the method. In addition,
the invention relates to a bag fabricated from the fiLm.
Generally, p31y~ers and copolymers Df vinylidene
chloride have f~und wide use as fi~ms and fi~m layers in
multilayer fiLms in connection with packagi~g foodsturfs
and other Db~ects. PDlyvinylidene chloride copolymer is
~nown in the art by the term "saran" and is particularly
relied upon as an oxygen barrier for p-eserving foodstuffs.
One typical prior art use of a fi~m incorporating
a layer of polyvinylidene chloride copolymer is for the
prote~tion and storage of primal and subprimal fresh
red meat cùt. One kno-wm multilaver film including
polyvinylidene chloride copolymer has outer layers of ethylene
vinyl acetate copDlymer and a core layer of viQylidene
chl~ride copolymer and is fabricated into a bag. The bag i9
heat-shrin~able. Typically, a meat cut is placed inside
the bag, the bag is evacuated and clipped closed, and then
the bag is he~t-shrunk to form a strong airtight p~ckage.
Such a multilayer film is described in Canadian patent
No. 982~23.
Gen~rally, it is know~ that p31y~inylidene
chloride copolymer can be produced by either e~ulsion or
s~spension polymerization. The suspension method as
compared t~ the emulsio~ method usually prDduces a resin
which is more stable and possesses a narrower particle size
distribution for g~3d ~ree flow properties, and has les~
-2-
`
~3~ 2214
inheren~ cDn-aminatiOn. The resins prDduced by the
suspension meth~d, h~wever, are cDstly as cD~pared to
the emulsiDn resins so that fDr cD~ercial prDduction
it is preferable t3 use emulsiDn resins from an ecDnomic
point Df view.
Both suspension and emulsion resins present
prDblems during the co~mercial pr~duction of films be-
cause P~lyvinylidene chloride cDpDlvmers can be degraded
by elevated temperatures. For this reason, it is a
CDmmOn practice in the art tD blend pDlyvinylidene
chloride copolymers with stabilizers, plasticizers, and
lubricants tD improve the cD~ercial extrusiDn of
polyvinylidene chlDride cDpolymers.
Generally, the extrusion Df a pDlyvinylidene
chlDride copolymer pr~duced by the e~ulsiDn meth3d has
the fDllowing draw~acksin cDnnection with its use in
forming a film:
1) A relatively large number of black particles
appear in the extrudate and the cDntinuDus appearance
of these particles fre~uently breaks the biDrientation
bubble.
2) A periodic slough-D~f of off-colDred
extrudate ~ccurs and this results in appearance
defects in the film beiLIg prDduced as well as breaks in
the bioriellt2tion bubble.
--3--
~ 3 12214
3) The resin flow in the h~pper f~r the
extrusion screw is uneven.
4) Non-cyclic pressure puLsations ~ccur in the
extruder and these cause pulsal~iDns in the DUtpUt rate
and unstable conditiDns along the extruder screw.
~ ne instant invention D~ercDmes these prDblems
and teaches the step ~f mixing, for example, pDlyvinylidene
ch~oride cDp~lymer pr~duced by the emulsiDn method with
apprDpriate stabilizers, plasticizers, and lubricant
al3ng with a selected ethylene vinyl acetate copDlymer.
~hen this mixture is extruded~ for example, as a core
layer Df a multilayer film having outer layers Df
ethylene vinyl acetate copolymers, the follDwing surprising
results occur.
(1) The number Df black particles în the
extrudate is decreased alDng with the number Df
biorientatiDn bubble breaks.
(2) The extruder head pressure fluctuatio~s are
reduced Dr eliminated and this indicates a more stable
~0 melt conditiDn.
(3) A greater Dutput per extruder screw
revDlutiDn ratio occurs.
(4) Most ~ilm prDperties dD nDt show a substantial
change as cDmpared tD a multilayer film having a core
layer with~ut the added ethylene vinyl acetate cDpolvmer~
~.~3~3
(5) The oxygen permeability rate of the
multilayer film remains almost: unchanged or increases
slightly.
(6) The adhesion bet:ween the film layers is
improved.
The invention can be used in connection with
polyvinylidene chloride copolymer produced by the emulsion
or suspension method as well as combinations of the
emulsion and suspension resins.
One embodiment of the instant invention is
a film comprising from about 60% to about 95% by
weight of a polyvinylidene chloride copolymer and from
about 5~ to about 40-~ by weight of an ethylene vinyl
acetate copolymer containing from about 5% to about 18%
by weight vinyl acetate and having a melt flow of from
about 0.1 to about 1.0 decigrams per minute. Preferably,
the ethylene vinyl acetate copolymer contains from
about 5% to about 15% by weight vinyl acetate to provide
a more acceptable o~ygen transmission barrier and for
economical production.
Another embodiment of the invention is the
aforementioned film wherein the polyvinylidene chloride
--5--
~21~
~3~ 3
copGlymer is ~rom about 80% to about 95~ by weight and
the ethy]ene uinyl acetate cDpDlymer is frDm about 5~l~ to
about 20% by weight and cDn~ains frD2 about 5% tD about
15% by weight vinyl acetate so that the total oxygen trans-
mission at room temperature of the film is le5s than about
3 cubic centimeter per 100 square inches-24 hours-atmosphexe.
A further embodiment of the invention is the
aLDrementioned film wherein the pDlyvinylidene chloride
cDpolymer is about 90% by weight and the ethylene vinyl
aceta~e cop~lymer is about 10% by weight and contains
from about 5% to about 18% by weight vinyl acetate so
that the total oxygen transmission at room temperature
of the film is about 2.3 CU~DiC centimeter
per 100 s~uare inches-24-hours-atmosphere. This e~bDd~ment
is particularly suited for film production using ethylene
vinyl acetate copolymers which ~ay have variable amounts
of vinyl acetate cDntent.
Yet a further embDdiment Df the invention is the
afDrementiDned film wherein the ~thylene vinyl acetate
copolymer cDntains about 12% vinyl acetate so that the total
oxygen transmissi~n at r~om temperature is about
2.4 cubic centimeter per 100 square inches- ~
24 hDurs-atmosphere. This embodiment is particularly
suited for film prDduction in which the amount of the
ethylene vinvl acetate cDpolymer being used need not be
cDntrolled precisely.
12214
Still ~ further embDdiment Df the invention is ame~hod
of producing a heat shl}nkable fit~ cDm2rising the steps
Df mixing tDgether fr~m about 60~, to about 95% by weight
a polyvinylidene chloride copDlymer and fr~m abDut 5% to
about 40% by weight of an ethylene vinyl acetate copolymer
cDntaining frDm about 5% tD about 18V/G by weight vinyl
acetate and having a melt fl3w of from about 0.1 to about
1.0 decigrams per minute, extruding the mlxture, and
biaxially Drienting the extrudate.
Preferably, the film of the invention is a heat
shrinXable multilayer film cDmprising outer layers of
ethylene vinyl acetate cDntaining from about 10% to about
1S% by wei~ht vinyl acetate and having a ~elt ~l~w of
Irom about 0.1 to about 1.0 decigram per minute and a core
layer comprising from about 60% to about 95% by weight of
a polyvinylidene chloride copoiymer and from 5% to about
40% by weight of an ethylene vinyl acetate copolymer
containing from about 5% tD about 18% by weight of vinyl
acetate and having a melt flow Df from about 0.1 tD about
1.0 decigrams per minute, ~referably,the aforementioned
multilayer film consists essentially of the three layers
The inventiDn acc~rdingly comprises the several
steps and relation of cne Dr more of such steps with
respect tD each Df.the others, all as exempliried in the
foll~wing detailed disclDsure, and the scope of the
applicatiDn of wnich will be indicated in the cla7ms.
12214
Generally, the three layer film of the instant
invention has an overall thickness of from about 2 to
3 mils and preferably about 2.4 mils. The biaxial
orientation can be carried out in accordance with ~nown
methods such as the method described in the U. S~ Patent
No. 3,555,60~ to Pahlke. This patent discloses a process
in which a polyethylene material defines an isolated
bubble maintained by simple nip rollers and the bubble
is subjected to heat and radial expansion due to internal
pressure near the draw point of the tubing, that is, the
point at which the polyethylene material is at or just
below its softening point. This process is generally
referred to as the "double bubble" method.
Generally, the polyvinylidene chloride copolymer
used in the invention comprises at least about 65% by weight
polymerized vinylidene chloride and the balance is a
polymer of vinyl chloride, acrylonitrile, an acrylate
ester such as methyl methacrylate, ox the like.
The film of the invention is preferably biaxially
oriented, but it can also be a slot cast film or a blown
film prepared by conventional methods.
In accordance with conventional practice, it is
understood that additives such as stabilizers, plasticizers,
and lubricants can be used for producing the film of the
invention ancl it is understood in the specification and
the claims that such additives can be present in accord-
ance with conventional practice.
Illustrative non-limiting examples of the
practice of the invention are set out below. Numerous
--8--
~ 3 12214
other examples can easily be evolved in the light of
the guiding principles and teachings contained herein.
The examples given herein are intended mainly tD
illus,rate the inventiDn and nDt in any sense tD limit
the ~nner in which the inventiDn can be practiced,
All percentages and parts stated herein are by
weight unless Dtherwise stated.
As used herein, the term l'phr" has the
conventional meaning of parts per 100 parts of polymer.
The materials described herein have their
properties determined in accordance with the following
test methods:
Melt F1DW - ASTM D -1238
Ethylene vinyl acetate copolymer - C~ndition E
PDlybutylene - CDndition E
PDlypropylene-ethylene copolymer - CDndition L
Density ASTM B-1505
The following polymers shown in Table 1 are
used in the examples:
~3~q~ 11214
Table 1
Melt Flow Density
Polymer dg /min . ~m/ c c - Descrip t ion
EVA A 0.3 Ethylene vinyl acetate
copolymer; 12% by wt.
vinyl acetate.
EVA B 0.7 Ethylene vinyl acetate
copolymer; 18% by wt.
vinyl acetate.
EVA C 0.5 Ethylene vinyl acetate
copolymer; 15% by wt.
vinyl acetate.
EVA D 1.0 Ethylene vinyl acetate
copolymer; 12% by wt.
vinyl acetate.
EVA E 0.6 Ethylene vinyl acetate
copolymer, 9~/O by wt.
vinyl acetate.
EVA F 0.3 Ethylene vinyl acetate
copolymer; 5% by wt.
vinyl acetate.
P-E A 12.0 0.899 Polypropylene-ethylene
copolymer; typically sold
commerci~lly as PP9818 by
Diamond Shamrock.
P-B A 2.0 0.91 Polybutylene copolymer;
typically sold commercially
as Witron~ 1200 by Witco
Chemical Co.
Elastomer A Ethylene-polypropylene
copolymer elastomer; typically
sold commercially as Vistalon~7
702 by Exxon Chemical Co.
-10-
3 1221~
The following polyvinylidene chloride polymers
shown in table 2 are used in the examples:
Table 2
Polyvinylidene Chloride Type and Commercial Designatlon by
Dow Chemical Company
PVDC A Emulsion type, Dow~ 5236.13
PVDC B Emulsion type, Dow~ 925
PVDC C Suspension type; Dow~ 468
PVDC D Suspension type
available from Kureha Chemical Co.
The following blends of polyvinylidene chloride
copolymers shown in table 3 are used in the examples:
Table 3
Blend 1
100 phr PVDC A
6.75 phr stabilizer, plasticizer, and lubricant
Blend 2
100 phr PVDC A
5.0 phr stabilizer, plasticizer, and lubricant
Blend 3
100 phr PVDC A
3.0 phr stabilizer and lubricant
Blend 4
100 phr PVDC B
6.75 phr stabilizer, plasticizer, and lubricant
. . .
~39~3 12214
Table 3 (cDntinued)
Blend 5
.
100 phr PVDC B
5.75 phr stabilizer, plasticizer, and lubricant
Blend 6
100 phr PVDC B
6.5 phr stabilizer, plasticizer~ and lubricant
Blend 7
90 phr PVDC A
10 phr PVDC C
6.75 phr stabilizer, plasticizer, and lubricant
Blend 8
90 phr PV~C B
10 phr PVDC D
6.5 phr stabilizer, plasticizer, and lubricant
'
.
-12-
~ 't~ 3 ~2~14
Examples 1 to 17
Examples 1 to 17 were carri~d out using an emulsion
type polyvinylidene chloride copoly~er in a core layer of
a three layer fiLm.
The multilayer film consisted essentially of outer
layers of ethylene vinyl acetate copolvmer and a core
layer as shown in tzble 4.
The multilayer film was produced by convention~l
metnods in accordance with the "double bubble" process
such ~s described in the U. S. patent no. 3,555,604 to
PahlhebY coextrusion of layers through a multilayer tubular
die. Reference is also had to the Canadian patent no.
982,923 which teaches a multilayer fiL~ including outer
layers of ethylene vinyl acetate and a core layer of
vinylidene chloride copolymer.
For the examples 4 to 12, and 17, the thicknesses
of the layers were not measured. The layers were controlled
to maintain thicknesses about the same as the corresponding
layers of the examples 1 to 3, 15 and 16.
12214
Table 4
First Outer Second Outer Core Layer
Layer - EVA C Layer - EVA A PVDC Blend EYA
Ex. % Thickness% Thickness % %
1 23.1 58.5 Blend 1 EVA C
95.0 5.0
2 24.3 54.5 Blend 2 EVA B
94.0 6.0
3 24.5 57.1 Blend 3 EVA B
90.0 10.0
4 Blend 4 EVA A
94.0 6.0
Blend 4 EVA A
90.0 10.0
6 31end 4 EVA A
85.0 15.0
7 . Blend 4 EVA A
80.0 20.0
8 Blend 4
100 . O --
9 Blend 5 EVA A
94.0 6.0
Blend 5 EVA A
90-0 10.~
11 Blend 5 EVA A
85.0 15.0
12 Blend 5 EVA A
80.0 20.0
13 25.0 4.0 Blend 6 -- -
100.O
14 24.6 55.0 Blend 6 EVA A
90, O 10 . O
-14-
12214
5~3
Table 4 (c~ntinued)
First Outer SecDnd Outer Core Laver
Layer - EVA C L2yer - EVA A P~3C Blend EV~
Ex. ~/~ Thickness ~c Thickness % . %
__ _
24.1 54.6 Blend 6 EVA A
65.0 35.0
16 25.4 53.3 Blend 6 EVA A
50.0 50.0
17 Blend 6 EVA A
40.0 60.0
EVA = ethylene vinyl acetate copolymer
TDtal film thickness is about 2.5 mils.
Example 18 to 37
Examples 18 tD 37 were carried out by the same
method as the examples 1 tD 17 and used a blend of
em~lsion and suspension types of p~lyvinylidene chloride
p~lymer. Table 5 shows the examples 18 tD 37.
The thicknesses Df the layers Df the examples 33 tD
37 were ccntr311ed tD be about the same as the
correspDnding layers Df the examples 18 to 32.
Examples 38 and 39
E~amples 38 and 39 were carried out by the same
method as the ex~mples 1 tD 17 except that the example
39 had four layers. Table 6 shows the examples 38
and 39. For the example 38, the first outer layer was EVA C
and for the example 39 the first outer layer was a blend of
40~ by weight of P-E A, 40% by weight of P-B A and 20~ by
weight of Elastomer A.
-15-
122~!,
~3~
Table ~
First Outer SecDnd Outer CDre Layer
Layer - EVA C ~ayer - EVA A F~DC Blend EVA
Ex. % Thickness ~/c Thickness_ _ % v/
18 25.5 57.9 Blend 7 EVA B
g5 5
19 24.2 54.9 Blend 8 EVA B
94 6
24.2 54.9 Blend 8 EVA C
94 6
21 24.2 54.9 Blend 8 EVA A
94 6
22 24.6 55.3 Blend 8 --
100
23 23.8 54.6 Blend 8 EVA B
92 8
24 23.8 54.6 31end 8 EVA B
23.8 54.6 Blend 8 EVA C
92
26 23.9 54.6 Blend 8 EV~oC
27 24.0 55.1 92 EVA8 A
28 25.1 54.1 90 .10
29 25.1 54.1 88 EVA2A
23.7 54.6 85 E~A15A
31 23.7 54.6 Blend 8 ~V2AoA
-16-
L__14
3 ~
Table5 (cDntinued)
First C~ter SecDnd ~uter _ C _e_~yer _
~ayer - EVA C laver - E~rA ,~ PVDC Blend E~A
Ex. % ~hickness ~/= Thickrless % %
32 23.4 55.0 Blend 8 EVA C
33 . Blend 8 EVA A
34 Blend 8 EVA A
Blend 8 EVA D
36 Blend 8 EVA E
37 Blend 8 EVA F
go 10
EVA = ethylene vinyl acetace c~p~lymer
TDtal film thickness is ab~ut 2.5 mils.
-17-
q~
12214
Table 6
.; Second First
First Outer Layer CDre L~yer Second Core Layer
Outer Layer EVA A EVA P~DC Blend EVA
Ex. 7 Thickness ~/~ Thickness ~/O Thickness % %
O _ _
- 38 25.254.2 -- Blend 7 E~A B
39 23.941.5E~A C Blend 7 EVA B
11.~ 95 5
. . : . .
EVA = ethylene vinyl acetate cop~lymer
TDtal film thickness is abDut 3 mils.
Test Results
The films of the tnree sets Df examples, that is,
examples 1 to 17, 18 tD 37, 38 and 39 were tested for
variDus pr~perties and the results ~f these tests are
given in the tables 7, 8, 9. For sDme ex~mples, s~me of
the parameters were nDt measured and conse~uently, are
not shown.
Several bags were formed by conventi3nal methods
from various films and Dund to be satisfactDry.
-18-
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-24-
12214
The examples surprisingly show that blends of
the polyvinylidene chloride copolymer and ethylene vinyl
acetate copolymer of the invention provide acceptable
levels of permeability for use in connection with the
storage of food stuff.
Typically, a three layer film including a core
layer of a blend of the invention having from about 5% to
about 20% by weight ethylene vinyl acetate copolymer con-
taining from about 5% to about 15% by weight vinyl acetate
has total oxygen permeability at room temperature of less
than about 3 cubic centimeter per 100 square inches-24
hours-atmosphere.
A three layer film including a core layer of a
blend of the invention having about 10% by weight ethylene
vinyl acetate copolymer containing from about 5% to about
18~ by weight vinyl acetate exhibits a total oxygen
permeability at room temperature of about 2.3 cubic
centimeter per 100 square inches-24 hours-atmosphere.
A three layer film including a core layer of a
blend of the invention having from about 5% to about 40%
by weight ethylene vinyl acetate copolymer containing
about 12% by weight vinyl acetate exhibits a total oxygen
permeability at room temperature of about 2.4 cubic
centimeter per 100 square inches 24-hours-atmosphere.
-25-
~39~3 12214
T~e oxygen permeability ~f the multilayered
films is determined by the pDlyvinylidene chloride
copoly~er and etkylene vinyl acetate copoly~er layer.
We wish it tD be understood that we do nDt
desire to be limited to the exact details ~f construction
shown and described, fo. DbviDus m3difications will occur
to a person skilled in the art.
Having tnus described the invention, what we
claim as new and desire to be secured by Letters Patent,
is as follows:
-26-
