Note: Descriptions are shown in the official language in which they were submitted.
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BIAXIALLY ORIENTED XYGEN AND MOISTURE B~RRIER E'~LM
The present invention relates to a method for proclucing a
biaxially oriented oxygen and moisture barrier film which is
comprised of a core layer and an ethylene vinyl alcohol
copolymer barrier layer. More particularly, the invention
relates ~o a simple continuous method whereby the two layers are
combined by co-extrusion and biaxially oriented at the same
time.
Ethylene vinyl alcohol copolymer resins offer excellent
barrier properties with respect to such gases as oxygen, carbon
dioxide and nitrogen~ In addition, they are also effective
barriers against odors and the loss of flavor. Such resins,
hereinafter referred to as EVOH resins, are moisture sensitive
and the barrier properties are reduced in the presence of high
humidity. Polypropylene offers excellent barrier properties
with respect to moisture together wi~h good strength properties
and a high heat use temperature. When EVOH resins are
encapsulated by layers of polypropylene, they are protected from
moisture and therefore retain their barrier characteristics.
The biaxial orientation of ~VOH resins enhances their
barrier properties as well as reduces their susceptibility to
moisture. The biaxial orientation of polypropylene increases
its stiffness and enhances both its optical and other physical
propertie~ such as tensile strength, tear strength, and other
mechanical properties.
In the past, others have attempted to produce biaxially
oriented composite structures containing both polypropylene and
EVOH resins by first producing a polypropylene sheet and
orienting the sheet in the longitudinal direction. Then a layer
of EVOH resin was either laminated or extrusion coated onto the
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polypropylene and the composite was then orientecl in the
transverse direction. This methocl of production is costly and
only results in the orientation of the EVO~I resin in one
directionr thus not achieving the full benefit of biaxial
orientation.
U.S. Patent No. 4,239,326, issued December 16, 1980,
discloses a multl-layered barrier film comprising a barrier
layer of substantially pure ethylene vinyl alcohol copolymer
adhered between adjacent adherent layers consisting essentially
lO of a partially hydrolyzed vinyl acetate polymer or copolymer. A
layer of another material such as polypropylene can overlie the
partially hydrolyzed vinyl acetate layers. The patent discloses
co-extrusion of the EVOH and the partially hydrolyzed vinyl
acetate polymer to form the multi-layer structure and then
subsequent co-extrusion of ~he overlying material onto this
structure. The patent do~s not suggest that this construction
could be biaxially oriented and is otherwise distinguishable
from the present invention because the adhesive is different, it
does not mention controlling crystallinity of the EVOH, the
20 percent ethylene of the products mentioned is too low for
flexibility for biaxially oriented film, and, even if this film
was to be biaxially oriented, the operation would be a two step
operation whereas the operation of the present invention is a
one-step operation.
The present invention relates to a method of producing a
biaxially oriented oxygen and moisture barrier film which
comprises a first co-extruding at least one core layer of a
polyolefin selected from one group consisting of polyethylene,
polypropylene and copolymers of ethylene with o~her olefin
30 monomers, at least one layer of an ethylene vinyl alcohol
copolymer wi~h a melt flow rate oE at least about 8 yrams p~r 10
minutes, and at least one adhesive layer wherein t}lese layers
are combined into a composite sheet with the adhesive interposed
between the core layer and the ~VOH. Next, the composite sheet
is immediately cooled so that the crystallinity of the EVOH i5
no more than about 25~. Finally, the composite sheet is
biaxially oriented in the longitudinal direction to a degree of
about 2:1 to about 4:1 and in the transverse direction to a
degree of about 3:1 to about 7:1. In a preferred embodiment of
the invention, the ratio of the thickness of the adhesive to the
thickness of the core layer is about 1:8 to about 1:15~ The
invention also relates to a biaxially oriented oxygen and
moisture barrier film formed by the above method.
The ethylene vinyl alcohol (EVOH) copolymers used in the
present invention are the saponified or hydrolyzed produc~ of an
ethylene-vinyl acetate copolymer having, generally~ an ethylene
content of 25 to 75 mole percentO It is hlghly preferred that
the percent ethylene in the EVOH be at least 45 percent so that
the EVOH is flexible enough to be stretched during the
orientation process. The degree of hydrolysis should reach at
least ~6 percent, preferably at least 99 percent. It is highly
preferred that the degree of hydrolysis be greater than 96
percent because below that the barrier properties are less than
optimum. It is extremely important to the performance of the
present invention that the melt flow rate of the EVOH be at
least 8 grams per 10 minutes at 190C and a load of 2,160 grams.
If the melt flow rate is less than 8 grams per 10 minutes then
the viscosities of the EVOH, adhesive, and core layer cannot be
matched. It is important to match the viscosities of these
materials to avoid interfacial instability which causes waviness
_~_
of the melt and uneven distribution Oe the layers, otherwise
known as melt fracture. The visc091ty of these materials is
most easily and effectively matched by monitoring the melt 10w
rate o the materials. At EVOH melt Elow rates below 8 grams
per 10 minutes, melt fracture occurs. It does not occur if the
melt 10w rate is higher.
The core layer used in the present invention can be of a
polyolefin selected from the group consisting of polyethylene,
including low density polyethylene, high density polyethylene,
and linear low density polyethylene, polypropylene, and
copolymers of ethylene with other olefins. The preEerred
polymers for use as the core layer are polypropylene and
ethylene propylene copolymers containing predominately
propylene. The melt flow rate of the core layer must not be so
low that it is too stiEf and thus unorientable. For propylene
ethylene copolymers, it is preferred that the melt flow rate be
from about 2.5 to about 6.0 grams per 10 minutes at 230C and a
load of 2,160 grams. For polypropylene, it is preferred that
the melt flow rate be from about 2.5 to about 4.5. In this
range, the viscosities of the copolymer and the polypropylene
are most compatible with EVOH and the adhesive. Also, in this
range, orientation of the copolymer or the polypropylene results
in the best properties.
The adhesive used in the present invention should be
selected from the group consisting of maleic anhydride-modified
polymers and polymers similar thereto. Such polymers are
effective adhesives for adhering the core layer to the EVOH
layer and also have a viscosity similar to the above-described
EVOH and core layers. The preferred adhesives for use in this
inven~ion are maleic anhydride-modified polyolefins~ Examples
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of such polymers are the Admer~ QF-500 series manuactured by
Mitsui Petrochemical Company, the Modic~ P-300 series
manufactured by Mistubishi Petrochemical Comparly, and Plexar~
adhesives manufactured by Chemplex.
The pxocess for the manufacture of a biaxially oriented
three or more layer composite barrier sheet consists of four
distinct steps which together comprise a rela~ively simple
continuous operation. First, the composite sheet, consistiny of
polypropylene, for example, an adhesive layer, and an EVOH
barrier layer, is formed by co-extrusion of the above
components. One way of accomplishing this is to use three
extruders and have the materials fed into a combinin~ feed
block. Within the feed block, the materials are layered to form
tbe multi-layer melt stream wherein the adhesive is interposed
between the polypropylene and the EVO8. The melt stream is fed
into a slot cast sheet die or other type of die to form the
multi-layer sheet~ As ~he sheet exits the die, it is
immediately cooled by use of a cooling drum or a water bath to a
temperature satisfactory to maintain a 25 percent crystallinity
rate in the EVOH material.
The 25 percent crystallinity rate can be obtained by
maintaining the temperature of the cooling medium at 30 to 40C.
If the crys~allinity of the EVOH is higher than 25 percent at
this point in the process, the EVOH becomes ~oo stiff ~o stretch
properly in the orientation process and it will merely break
apart. It is preferable that the crystallini~y of the EVOH
should be at least about 20 percent in order to obtain
sufficient crystallinity in the final pro~uctr
Immediately after cooling, the composite sheet is fed into
an apparatus adapted for biaxial orientation of plastic
~L~t7~
mater ial. Any such apparatus can be used in the present
invention. One example would be to feed the composlte sheet
.into a set of differentlal speed heated rollers to stretch the
sheet in the longitudinal direction to a degree of about 2:1 to
about 4:1~ Next, the sheet can be fed to a tenter frame where
it is stretched in the transverse direction ~o a degree of about
3:1 ~o àbout 7:1.
If the degree of longitudinal orientation i~ less than
about 2:1, then uneven orientation occurs, and if it is more
than about 4 1, then fracture oE the sheet occurs. If the
degree of orientation in the transverse direction is less than
abou~ 3nl. then uneven orientation occurs, and more than about
7:1, then fracture of the sheet occurs. If polypropylene is
used as the core layer, then it is preferred that the machine
direction orientation rollers be at a temperature of from abou~
130 to about 140C and that the tenter frame for transverse
orientation be at about 150 to about 160C. If the propylene
ethylene copolymers are used in the core layer, then the
machine direction roller temperature should be about 125 to
about 130C and the tenter frame temperature should be about 130
ts about 135C.
After the sheet has been biaxially oriented, it is
subjectged to a heat setting treatment which allows the ~VOH to
crystallize. The crystallizing of the EVO~ impart~ high barrier
properties to the EVOEI layer and thus to the composite film.
Any known heat setting method can be used, but one example of
such a method is to pass the biaxially stretched sheet over a
series of heated rollsn
I is highly preferred that the ratio of the thickness of
the adhesive to ~he thickness of the core layer be about 1:8 to
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49~i~
about 1:15. If the ratio is less than about 1:~. then poor
adhesion between the EVOH and adhesive occur~, preventlng
satisfactory orientation. If the ratio is more than ahout 1:15,
then uneven flow dis~ribution of the adhesive occur~ and the
adhesion is poor.
EXAMPLES
The materials used in all of the following examples are:
Polypropylene: Homopolymer - Solvay Eltex HP405
318 melt flow rate
Copolymer - Solvay KS400, 5.7 mel~ flow
rate (4~ ethylene, 96~ propylene)
Ethylene Vinyl Alcohol Copolymer:
EV~D~ "F" Grade resin mada by Kuraray
Co., Ltd. - 1.5 melt index
EVAL~ "E" Grade resin made by Kuraray
Co., Ltd. - 5.6 melt index
EVAL~ "G" Grade resin made by Kuraray
Co., Ltd. - 15~1 melt index
Adhesive: Admer~ QF500~ - 4.2 melt flow rate
(a maleic anhydride-modified poly-
propylene~
All of the following examples attempted to produce a
biaxially oriented five layer composite barrier sheet of ABCBA
construction according to the same general process consistin~ o
the following four distinct steps:
1. A five layer composite sheet was co-extruded by the
use of three extruders. The sheet considered of a polyolefin (A
layer), an adhesive layer tB layer), an EVOH layer (C layer),
another adhesive layer (B layer), and another polyolefin layer
(A layer). The materials were fed into a combining feed block
where they were layered to form the five layer melt stream of
ABCBA construction. This melt stream was then fed into a slot
cast sheet die ~o form the five layer sheet. As the sheet
exited the die, it was immediately cooled by the use of a
cooling drum, or in some cases a water bath, to a temperature
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which maintained a 25 percent crystallinity rate ln the EVO}I
material.
2. Immediately after cooling, the composite sh~et was fed
into a set of diferential speed heatecl rolls (MDO) which
stre~ched the sheet in the longitudinal direction.
3. A~ter exiting the differential speed heated rollers
(MDO), the sheet was fed to a tenter frame. In the tenter
frame, the sheet was stretched in the transverse direc~ion.
4. After the sheet was biaxially stretched, it was passed
over a series of heated rolls which imparted a hea~ setting to
the composite sheet and allowed the EVOH layer to crystallize.
The crystallizing of the ~VO~ imparted high barrier properties
to the composite sheet.
The following examples specify which materials were used~
The orientation of the extruders was as follows in all cases:
Extruder #1: Always polypropylene
Extruder #2: Always EVOH
Extruder #3: Always Adhesive
Examples
In all cases in the following examples, the crystallinity
of the EVOH material as it exited the Aie was maintained below
25%. The crystallinity ranged from 18 to 22% in the examples.
The method of determination of the percent crystallinity is
based upon the linear relationship between the percent
crystallinity and the density of the filmO The percen~
crystallinity is empirically determinecl by measuring the density
of the total amorphous portion and the total crystalline portio~
of a par~icular grade of EVO~ film and using this information in
the formula set out below.
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The density is first measured by any accep~able method
such as ASTM D1505-68. Next, the total amorphous arld total
crystalline portions oE the EVOH are separated and their
densities measured according to the same procedure. For the
three grades of EVOH used in the following examples, the
densities of the amorphous and crystalline portions are as
follows:
Table
Density of Density of
Amorphous Crystalline
Grade Portion Portion
E Grade 1.110 1.148
F Grade 1.163 1.200
G Grade 1.094 1.130
The above densities are considered constants because they
do not change. The film density will change depending upon the
degree of the quenching treatment. In the following formula FD
is the film density, AD is the amorphous density constant, and
CD is the crystalline density constant. The percent
crystallinity of a film is determined by:
% Crystallinity = FD - AD X 100
CD - AD
Thus, it is clear that the percent crystallinity increases
linearly as the density of the film increases. The
crystallinity of the film can be controlled by controlling the
density of the film. This is what takes place in the quenching
step.
EXAMPLE I
Materials: Homopolypropylene
EVOH "E" Grade
Adhesive
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~xtruder #1: Melt Temp. 260C, RPM (revolutions per
minute~ 117.5
Extruder ~2: Melt Temp. 190C, RPM 25
Extruder # : Melt Temp. 185~C, RPM 29.5
Feedblock Temperature: 200C
MDO Rolls Temperature: 120C
Tenter Temperature: 165C
MDO OrientationO 2.0:1
Transverse Orientation: 3.0:1
The stretched film exhibited a fishnet effect due to the
fibrillation of the EVOH layer.
EXAMPLE II
Using the same conditions and materials as in Example I,
except that the RP~ of the Extruder #2 (EVO~) was reduced to 15
and the machine direction (MD) orientation was increased to
3.0:1, the same fishnet appearance was evident.
EXAMPLE III
Starting with the conditions and materials in Example II,
the degree of MD orientation was varied while the transverse
direction (TD) orientation was held constant. As the MD
orientation was decreased from 3.0:1 to 2.0:1, the fishnet
appearance decreased. At a 1.0:1 MD orientation and a 3.0:1 TD
orientation, the fishnet appearance disappeared. This, however,
only result2d in a uniaxially (transverse direction) oriented
sheet which exhibited non-uniform thickness and poor optical
proper~ies.
EXAMPLE IV
In observing the samples from Examples I through III, it
was noted that the reason for the fibrillation of the EVOH layer
might have been due to the lack of adhesion between the PP and
EVOH layers. To investigate this, the conditions and materials
used in Example I were selected as a base point. The melt
~4916~
temperature of the adhesive layer was increased in increments of
5~C until the melt temperature was the same as that of the
polypropylene. It was noted that the adhesion became better a~
the temperature was increased. However, fibrillation of the
EVOH layer was still present.
EXAMPLE _
Materials: Copolymer Polypropylene
EVOH "E" Grade
Adhesive
Extruder #1: Melt Temp. 240C, ~PM 95
Extruder $2: Melt TempO 190C, RPM 15
Extruder #3: Melt Temp. 2~0C, RPM 50
Feedblock Temperature: 180C
MDO Rolls Temperature: 120C
Tenter Temperature: 165C
MDO Orientation: 2~4:1
Transverse Orienta~ion: 4Ø1
The initial trials exhibited minor fibrillation of the
EVOH layer and uneven orientation of the polypropylene layer.
The RPM of the EVOH layer were increased to 30 to increase the
thickness. Fibrillation still resulted. The thicknesses of the
various layers were increased in increments of 0.5 times the
original up to two times the original. There was no appreciable
effect on fibrillation. Orientation temperatures were varied
until a limit on the low end was reached where transverse
stretching would not occur and on the high end until the
polypropylene would stick to the tenter frame clips.
Fibrillation still was evident. The conclusion reached from the
first five examples was that EVOH "E" grade could not be
satisfactorily biaxially oriented.
EXAMPLE VI
Materials: Copolymer Polypropylene
EVOH "G" Grade
Adhesive
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Extruder #1: Melt Temp. 240C, RPM as
~xtruder #2: Melt Temp. 185C, RMP ~0
Extruder ~3: Melt Temp. 250C, RMP 75
Feedblock Temperature: 185C
MDO Rolls Temperature: 120C
Tenter Temperature : 140C
MDO Orientation : 2.8:1
Transverse Orientation: 3.0:1
The above conditions were the starting conditions. The
composite sheet exhibi~ed extreme melt fracture upon exit from
the die. This melt fracture was occurrin~ in the EVOH layer and
was due to the difference in viscosities of the various
components. The difference in viscosities in turn affected the
flow properties through the feedblock and die. Various
combinations of heat and speed were investigated until the
following parameters were reached which in turn resulted in a
satisfactory biaxially oriented composite sheet.
Extruder #1: Melt Temp. 240C, RMP 95
Extruder #2: Melt Temp. 200C, RMP 20
Extruder #3: Melt Temp. 250C, R~IP 50
Feedblock Temperature: 200~
MDO Rolls Temperature: 129C
Tenter Temperature : 130C
~DO Orientation : 2.0:1
Transverse Orientation: 3.0:1
EXAMPLE VII
Materials: Homopolypropylene
EVOH "G" Grade
Adhesive
Extruder #1: Melt Temp. 260C, RPM 115
Extruder ~2: Mel~ Temp. 1~0C, RPM 20
Extruder #3: Melt Temp. 250C, RPM 80
Feedblock Temperature: 200C
MDO Rolls Temperature: 140C
Tenter Temperature : 150C
MDO Orien~ation : 4.4:1
Transverse Orientation: 3.0:1
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~.~749~L
Again, the above condi~ions were the starting conditions.
Althouyh the sheet going into ~he tenter frame looked good,
holes were torn in the sheet during transverse orientation.
This indicates either the sheet is too cold or the orientatlon
is too high. Various orientation ratios were investigated Erom
MDO ~.0:1 to 4.0:1 and transverse from 3.0:1 to 5.4:1. It was
noted that as the M~O ratio was increased from 2.0:1, the EVOH
started to fibrillate. At 4.0:1 MDO ratio, the EVO~ was totally
fibrillated. Increasing the trans~erse ratio and holding the
MDO at 2.0:1 did not have the same effect.
EXAMPLE VIII
In an attempt to match viscosities and 10w rates of the
various materials, the following changes were made in the
conditions used in Example VII.
Extruder #l: RPM 35
Extruder #2: ~PM 25
Extruder ~3: RPM 25
Tenter Temperature: 160C
MDO Orientation: 3.0:1
Transverse Orientation: 4.2:1
Using these conditions, an excellent biaxially oriented
sheeet was produced. The properties of this sheet are shown in
the Table. Orientation ranges from MDO 2.0:1 to MDO 4.0:1 and
transverse 3.0:1 to 7.0:1 were studied and satisfactory sheets
were produced. The properties of two different films made
hereunder are shown in the Table.
EXAMPLE IX
To further investigate the effects of parameters on the
ability to orient the sheet, the following was studied:
To determine the effect of Adhesive thickness: The PP RPM
was held constant. The adhesive RPM was decreased in 5 RPM
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increments to 25 RPM. At 25 RPM, fib~illation occurs.
To determine the eefect of PP thickness: The adhesive RPM
was held constant. The PP RPM was decreased to 7~ RPM. Uneven
flow distribution occurred. The adhesive RPM was set at 25 RPM.
The PP RPM was 70. Uneven flow distribution occurred.
EX~MPLE X
Materials: Homopolypropylene
EVOH "F" Grade
Adhesive
Extruder #1: Melt Temp. 260C, ~PM 35
Extruder ~20 Melt Temp. 210C, RPM 25
Extruder #3: Melt Temp. 250C, RPM 50
Feedblock Temperature: 210C
MDO Rolls Temperature: 140C
Tenter Temperature : 160C
~ DO orientation from 2.0:1 to 3.0:1 and transverse
orientation at 3.0:1 ~ere attempted and fibrillated film
resulted. Changes in Extruder #1 RPM to 80 and Extruder #2 RPM
to 40 did not have any effect. Various temperature conditions
did not have any effect. The conclusion was that the EVOH "F"
grade could not be satisfactorily biaxially oriented.
Final Thickness
This is a determination of the thickness of each layer in
the five layer composite sheet. The film was characterized by
both ligh~ microscopy and scanning electron microscopy (SEM)
techniques. For the SEM technique, the samples were notched and
fractured. Light microscopy samples were embedded in LDPE and
microtomed in thin sections. By using the thickness of the
individual layers, comparisons can be made between the
properties of oriented and unoriented films of the same
thickness.
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2 Transmls _on
It is known that the presence of oxygen callse~ ~oods to
degrade. The 2 transmission of a s~ructure is a measure of its
barrier to the penetration of oxygen to the materials packaged
with the film s~ructure~ This determination was carried out
according to ASTM Standard D3985-81.
MVTR
The Moisture Vapor Transmission is an indication of the
amount o H2O that will permeate to the packaged goods or
conversely the amount o~ moisture that can escape from a
packaged liquid product. Also the barrier properties of a
barrier material are deteriorated by the presence of moisture.
Therefore, it is desirable ~u prevent as much moisture as
possible Erom reaching the barrier layer. This test was carried
out according to ASTM Test Methods E398-70.
Ultimate Tens i le
The ultimate tensile strength is a measure of the strength
of the material. It is the amount of force per square inch of
material required to pull it apart. This test was carried out
according to ASTM D-882-73, Method Ao
Secant Modulus
The secant modulus is a measure of the stiffness of the
materialO A stiff material is required to provide good
machineability and handling in subsequent packaging operations,
and also to provide a crisp feel to packaged products. This
method was carried out according to ASTM D-618.
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TABLE
2 Tran~-
mission Ultimate Secant
Tenslle Modulus
Final cc/m2/24
Thick- hrs. @ 20C MVT~ MD TD MD TD
Example ness 0~ RH g/m Mpa Mpa ~ Mpa
Homopolymer12 12 3.0 30 250 18~8 5143
PP
Adhesive 1.3
EVOH G 3.5
Adhesive 1.3
~Iomopolymer 12
PP
~omopolymer13 13 3.3 91 233 1575 4089
PP
Adhesive
EVOH G 2
Adhesive
Homopolymer 13
PP
