Note: Descriptions are shown in the official language in which they were submitted.
LINEAR POLYETHYLENE S}IRIN~ FILMS
ABSTRACT OF THE INVENTION
A multi-layered thermoplastic film having improved physical
characteristics is formulated through utilization of a linear low density
polyethylene or linear medium density polyethylene resin as a core and/or
an intermediate layer constituent.
IELD OF THE INVENTION
This invention relates to heat shrinkable, thermoplastic pack-
aging films. In particular, the present invention is directed to shrink
films utilizing linear low density polyethylene or linear medium density
polyethylene resins as a constituent of a core and/or an intermediate
layer in a multi-layer film.
BACKGROUND OF THE INVF.NTION
The present invention is directed to new and useful heat shrink-
able film formulations. One distinguishing feat~re of a shrink film is
the fil~'s ability, upon exposure to a certain temperature, to shrink or~
if restrained from shrinking, to generate shrink tension within the film.
The manufacture of shrink films, as is well known in the art,
may be generally accomplished by extrusion of the resinous materials
which have been heated to their flow or melting point from an extrusion
die in tubular or planar form. After a post extrusion quenching to cool,
the extrudate is then reheated to its orientation temperature range. The
orientation temperature range for a given film will vary with the
different resinous polymers and blends thereof which comprise the film.
However, the orientation temperature range may generally be stated to be
above room temperature and below the melting point of the film.
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The terms "orienLed" or "orientation" are used herein to des-
cribe the process and resultant product characteristics obtained ~y
stretching and immediately cooling a resino~s polymeric material which
has been heated to its orientation temperature range so as to revise the
molecular configuration of the material by physical alignment of the
molecules to improve mechanical properties of the film such as , for
example, shrink tension and orientation release stress. Both of these
proper~ies may be measured in accordance with ASTM D 2~38-69 (reapproved
1975). When the stretching force is applied in one direction uniaxial
orientation results. When the stretching force is applied in two
directions biaxial orientation results. Orientation is also herein used
interchangeably with "heat shrinkability" with these tèrms designating a
material which has been stretched and set by cooling at its stretched
dimensions. An oriented (i.e., heat shrinkable) material will tend to
return to its original unstretched dimensions when heated to an appro-
priate temperature below its melting temperature range.
Returning to the basic process for manufacturing the film as
discussed above, it can be seen that the film once extruded and initially
quen~hed to cool is then reheated to its orientation temperature range
and oriented. The stretching to orient may be accomplished in many ways
such as, for example, by "blown bubble" techniques or "tenter framing".
These terms are well known to thos'e in the art and refer to orientation
steps whereby the material is stretched in the cross or transverse
direction (TD) and in the longitudinal or machine direction (~). After
being stretched, the film is rapidly cooled to quench and thus set or
lock-in the oriented molecular configuration.
After locking-in the oriented molecular configuration the film
may then be stored in rolls and utilized to tightly package a variety of
items. In this regard, the product to be packaged is first enclosed in
the heat shrinkable material by heat sealing the shrink film to itself
where necessary. Thereafter, the enclosed product is subjected to ele-
vated temperatures by, for example, passing the product through a hot air
or hot water tunnel. This causes the film to shrink around the product
to produce a tight wrapping that closely conforms to the contour of the
product.
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The above general outline for manufacturing films is not
meant to be all inclusive since this process is well known to
those in the art. For example, see United States Patent Nos.
4,274,900; 4,229,241; 4,194,039; 4,188,~43; 4,048,428; 3,821,182
and 3,022,543.
~ any variations on the above discussed general processing
theme are available to those in the art depending upon the end use
for which the film is to be put and the characteristics desired to
be instilled in the film. For example, the molecules of the film
may be cross-linked during processing to improve the films abuse
resistance and other characteristics. Cross-linking and methods
for cross-linking are well known in the ar-t. Cross-linking may be
accomplished by irradiating the film or, alternatively, may be
accomplished chemically through the utilization of peroxides.
Another possible processing variation is the application of a fine
mist of silicone spray to the interior of the freshly extruded
material to improve the further processability of the material.
A method for accomplishing such internal application is disclosed
in copending Canadian application serial No. 403,969 filed
May 28, 1982.
The polyolefin family and, in particular, the polyethyl-
ene family of shrink films provides a wide range of physical and
performance characteristics such as shrink force (the amount of
force that a film exerts per unit area of its cross-section during
shrinkage), the degree of free shrink (the reduction in linear
dimension in a specified direction that a material undergoes when
subjected to elevated temperatures while unrestrained), tensile
strength (-the highest force that can be applied to a unit area of
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film before it begins to tear apart), sealability, shrink
-temperature curve (the relationship of shrink to temperature),
tear initiation and resistance (the force at which a film will
begin to tear and continue to tear), optics (gloss, haze and
transparency of material), and dimensional stability (the ability
of the film to retain its original dimensions under diEferent
types of storage condi-tions). Film characteristics play an
importan-t role in the
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selection o~ a partic~llar film and they differ for each type of packaging
application and ~or each package. Consideration must be given to the
product size, weight, shape, rigidity, number of product components,
other packaging materials which may be used along with the film, and the
type of packaging equipment available.
In view of the many above discussed physical characteristics
which are associated with polyethylene films and in further view of the
numerous applications with which these films have already been associated
and those to which they may be applied in the future, it is readily dis-
cernible that the need for ever improving any or all of the above des-
cribed physical characteristics of ~hese films-is great and, naturally,
ongoing.
OBJECTS OF T}~ INVENTION
Accordingly, it is a general object of the invention to provide
a heat shrinkable polyolefin film that will be an improvement over ~hose
films already utilized in the prior art.
It is another object of the present invention to provide a
polyolefin film having improved shrink tensions.
In another object of the present invention is to provide an
improved polyolefin shrink film having improved optical qualities.
A still further obiect of the invention is to provide a poly-
olefin shrink film having a wide shrink temperature range.
Another object of the present invention is to proYide an im-
proved polyolefin shrink film having improved sealability.
Furthermore, yet another object of the present inven~ion is to
provide a polyolefin shrink film having improved resistance to tear
propagation.
An even further object of the invention is to provide a poly-
olefin shrink film ha~ing an improved machineability.
Yet another object of the present invention is to provide an
improved polyethylene shrink film which utili~es either a linear low
density or a linear medium density polyethylene as a consti~ent of a
core andfor an intermediate layer.
These and other objects are achieved by the polyolefin shrink
film which is disclosed herein.
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DEFINI~IONS
~ n1ess sl~ecifically set forth and defined or limited, the terms
"polymer" or "polymer resin" as used herein generally inclllde homopoly-
mers, copolymers, terpolymers, block, graft polymers, random, and alter-
nating polymers.
The term "melt flow" as used herein or "melt flow index" is the
amount, in grams, of a thermoplastic resin which can be forced through a
given orifice under a specified pressure and temperature within ten
minutes as described in ASTM D 1238.
The term "core" or "core layer" as used herein means a layer in
a multi-layer film which is enclosed on both sides by additional layers.
The term "skin" or "skin layer" as used herein means an outer
(i.e., surface) layer of a multi~layer film.
The term "intermediate" or "intermediate layers" as used herein
means a layer of a multi-layer film which is neither a core layer nor a
skin layer.
The term "low density polyethylene" (LDPE) as used herein
refers to homopolymers of ethylene having a density of from O.910 to
0.925.
The term "linear low density polyethylene" (LIDPE) as used
herein refers to a copolymer of ethylene and 8% or less of butene, octene
or hexene having a density of from 0.910 to 0.925 and in which the
molecules comprise long chains with few or no branches or cross-linked
structures.
The term "linear medium density polyethlyene" (LMDPE) as used
herein refers to a copolymer.of ethylene and less than 8% butene, octene
or he~ene having a density of from 0.926 to 0.940 and in which the
molecules comprise long chains with few or no branches or crcss-linked
structures.
The term "ethylene vinyl acetate copolymer" (EVA) as used
herein refers to a copolymer formed from ethylene and vinyl accetate
monomers wherein the ethylene derived units are present in major amounts
and the vinyl accetate derived units are present in minor amounts.
The ter~ "ethylene propylene copolymer" ~EPC) as used herein
refers to a copolymer formed from ethylene and propylene monomers wherein
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the propylenf~ derived uni~s are present as a major constituen~ and ~he
ethy]ene dcrived units ~re presen~ as a minor consti~uent.
The term "proplyerle homopolymer" (PP) as used herein refers to
a thermoplastic resin having a density of approximately O.90 and made by
polymerizing propylene with suitable catalysts as is well known in the
art.
SU~RY OF THE INVENTION
It has been discovered that a flexible, heat shrinkable thermo-
plastic packaging film having a desirable combination of physical
characteristics such as shrink tension, optical characteristics, cut-
~bility, sealability, shrink temperature range, and tear resistance has
been achieved by ~he multi-layer flexible, thermoplastic packaging film
of the present invention. This multi-layer film has a "core" layer that
comprises a linear low density polyethylene resin. It is believed that
linear medium density polyethylene resin may be substituted for the
linear low density polyethylene resin. A preferred three layer embodi-
ment also comprises, in addition to the above identified "core" layer,
two skin layers each comprising a blend of a propylene homopolymer and an
ethylene propylene copolymer. Preferably, the multi-layer film is
oriented so that it is heat shrinkable in at least one direction.
The multi-layer film may be combined with other polymeric
materials for specific applications. For instance, relatively thin
layers may be added on either or both sides of the basic preferred three
layer structure to improve seal strength or to lower gas and moisture
permeability.
Another embodiment of the present invention envisions a five
layered film structure. A preferred five layer structure comprises the
same core and skin layers as the above discussed three layer structure
and additionally includes two intermediate layers each comprising a blend
of an e~hylene vinyl acetate copolymer and either an ionomer resin, or a
linear low density polyethylene. It is presently believed that a linear
medium density polyethylene may also be substituted for the linear low
density polyethylene of ~he intermediate layer.
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BRIEF DESCRIPTION OF TIIE DRAWINGS
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Figure I is a cross sectional vie~ of a preferred three layered
embodiment of the present invention.
Figure II is a cross sectional view of a preferred five layered
embodiment of the present invention.
DESC~IPTION OE THE PREFERRED E~IBODI~ENTS
Referring to Figure I, which is a cross sectional view of a
three layered preferred embodiment of the present invent_on, it is seen
that this embodiment comprises core layer 2 and skin layers 1 and 3. The
preferred thickness ratio of the three layers of 1/3/1 is demonstrated in
Figure I. A preferred core layer 2 constituent comprises a linear low
density polyethylene polymer. However, it is believed that linear medium
density polyethylene polymer may be substituted as a core layer constit-
uent without substantial alteration of the characteristics of the final
film product. The core l~yer 2 comprises linear iow density (alterna-
tely, linear medium density) polyethylene or the core layer 2 may com~
prise a copolymeric blend of linear low density (alternately, linear
medium density) polyethylene with either an (a) ethylene propylene co-
polymer or (b) ethylene vinyl acetate copolymer or (c) ethylene vinyl
acetate copolymer blended with an ionomer resin or (d) low density poly-
ethylene. Thus the various blend formulations for core layer 2 may, in
accordance with the present invention, be selected from the following
groups.
(1) 10-100% LLDPE blended with from 0-90~ EPC or
(2) 10-100% IMDPE blended with 0-90% EPC or
(3) 10-80~ LLDPE blended with 20-90% EVA or
(4) 10-80% L~PE blended with 20-90~ EVA or
(5) 10-80% LLDPE blended with 10-80% EVA and 10-80% ionomer
resin or
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(6) 10-~0% LMDPE blended with 10-80% EVA and
10-80% ionomer resin or
(7) 10-80% LLDPE blended with 20-90% LDPE or
(8) 10-80% LMDPE blended with 20-90% LDPE
LLDPE is herein utilized as an abbreviation for linear
low density polyethylene as defined above. LMDPE is herein
utilized as an abbreviation for linear medium density polyethylene
as defined above. EPC is herein used as an abbreviation for an
ethylene propylene copolymer as defined above. EVA is herein
utilized as an abbreviation for an ethylene vinyl acetate copolymer
as defined above. The term ionomer resin is used herein to broadly
describe the group of ionomer resins. One o:E the most notab]e of
the ionomer resins is marketed under the trade mark Surlyn by du
Pont.
My experimentation has revealed that an especially
preferred core layer formulation consists essentially of linear
low density polyethylene. This material may be obtained from the
Dow Chemical Company under the trade mark Dowlex 2045.
Returnin~ to Figure 1 and, in particular, to skin layers
1 and 3, appropriate skin layer formulations may be selected from
the following groups:
(1) EPC or
(2) 70-90% EPC blended with 10-30% PP or
(3) 70-90% EPC blended with 10-30% LLDPE or
(4) 70-90% EPC blended with 10-30% LMDPE~
All abbreviations are as stated above with regard to the
core layer formulations. ~dditionally, PP is used herein as an
abbreviation for a propylene homopolymer as defined above.
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Experimentation has also determined that a particularly preferred
skin layer formulation consists essentially of a blend of 20% PP
with 80~ EPC.
The propylene homopolymer may be obtained from the
Hercules Chemical Company under the trade mark PD064. The
ethylene propylene copolymer may be obtained Erom the Soltex
Chemical Company under the trade mark 42X01 or alternatively, from
the Solvay Chemical Company under the trade mark KS400.
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Throu~hout this specification and claims all percentages are
"by weight" pc~ccnta6cs.
Throughout the specification and claims all references to
density are in gm/cc.
In summary, my experimentation has determined that a particu-
larly preferred embodiment of the present invention comprises a core
layer consisting essentially of linear low density polyethylene and skin
layers consisting essentially of a blend of 20% of propylene homopolymer
with 8070 ethylene propylene copolymer.
Although the above-discussed three layer formulations are
generally preferred over structures having more than three layers as a
resul~ of the economics of manufacture, I have also produced various five
layer formulations which are also satisfactory from a physical character-
istics point of view. }[owever, the cost of manufacturing a five layer
film is generally greater than that of a three layer film.
~ igure II, which is a cross sectional view of a preferred five
layer film of the present invention, demonstrates the preferred layer
thickness ratio of 2/2/1/2/2. The core layer 6 may comprise any of the
core layer formulations discussed above with regard to the core layer 2
o~ the three layer embodiment. Additionally, the core layer may consist
essentially of either (1) an ethylene propylene copolymer (EPC) or (2) an
ethylene vinyl acetate copolymer (~VA).
The skin layers 4 and 8 of the five layer embodiment may com-
prise any of the skin layer formulations discussed above with regard to
the s~in layers 1 and 3 of the three layered embodiment of Figure I.
The five layered embodiment of Figure II also includes inter-
mediate layers 5 and 7. These intermediate layers may comprise any of
the formulations disclosed above with regard to core layer 2 of the three
layer embodiment. Additionally, the formulation of the intermediate
layers 5 and 7 may be selected from the following additional groups.
(1) EVA or
(2) 20-80% LLDPE blended with 20-80% ionomer resin or
(3) 20-80% L~PE blended with ~0-80% ionomer resin.
My experimentaticn has revealed that a particularly preferred
five layer strueture will comprise skin layers 4 and 8 which consist
essentially of an ethylene propylene copolymer (EPC), intermediate layers
S and 7 consisting essentially of a blend of 90% ehylene vinyl acetate
G~ .
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copolymer with 10% ionomer resin and a core layer 6 consisting
essentially of a linear low density polyethylene. The EPC may be
obtained from the Soltex Chemical Company under the trade mark
Soltex 42X01. The EVA may be obtained from the du Pont Chemical
Company under the trade mark Alathon 3137. The ionomer resin may
be obtained from the du Pont Chemical Company under the Surlyn
trade mark and is trade marked Surlyn 1601. The LLDPE may be
obtained from the Dow Chemical Company under the trade mark
Dowlex 2045.
Those skilled in the art will readily reco~nize that all
of the above disclosed, by weight, percentages are subject to
slight variation. Additionally, these percentages may vary
slightly as a result of the inclusion or application of additives
such as the silicon mist discussed above or agents such as slip
and anti-block agents. A preferred anti-block agent is silica
which is available from Johns Manville under the trade mark Whlte
Mist. Preferred slip agents are Erucamide (available from Humko
Chemical under the trade mark Kemamide E), and Stearamide
(available from the Humko Chemical Company under the trade mark
Kemamide S) and, N, NL Dioleoylethylenediamine (available from
Glyco Chemical under the trade mark Acrawax C). A preferred
Silicon spray is a liquid polyorganosiloxane manufactured by
General Electric under the trade mark General Electric SF18
polydimethylsiloxane.
The general ranges for application of these additives
are as follows:
(1) Silica - 250 - 3000 PPM
(2) Acrawax C: 200 - 4000 PPM
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(3) Erucamide: 200 - 5000 PPM
(4) Stearamide: 200 - 5000 PPM
(5) Silicon Spray: .5 mgft2 _ and up.
When utilized within the specification and claims of the
instant application the term "consisting essentially of" is not
meant to exclude slight percentage variations or additives and
agents of this sort.
Additional layers and/or minor amounts of additives o
the types described above may be added to either the 3-layer or
5-layer structure of the present invention as desired but care
must be taken not to adversely alter the desirable shrink tensions,
shrink properties,
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optics and other char~cteristics of the multi~layer film of the present
invention.
In the prefcrre~ process or making the multi-layer linear low
or linear medium density polyethlyene shrink film of the present inven-
tion the basic stcps are blending the polymers for the various layers,
coextruding the layers to form a multi-layer film, and then stretching
the film to biaxially orient. These steps and additional desirable steps
will be explained in detail in the paragraphs which follow.
The process begins by blending the raw materials (i.e. poly-
meric resins3 in the proportions and ranges desired as discussed above.
The resins are usually purchased from a supplier in pellet form and can
be blended in any one of a number of commercially available blenders as
is well known in the art. During the blending process any additives
and/or agents which are desired to be utilized are also incorporated.
The blended resins and applicable additives and/or agents are
then fed into the hoppers of extruders which feed the coextrusion die.
For the three-layer film at least three extruders need to be employed if
each layer is to have a different composition. Two extruders are fed the
materials desirable for the inner and outer skin layers and the other-
extruder is fed the linear low or linear medium density polyethylene
material which is desired for uti~ization in the core layer. Additional
extruders may be employed, if desired. Preferably the materials are
coextruded as a tube having a diameter which is dependent on the racking
ratio and desired rinal diameter. This coextruded tube is relatively
thick and is referred to as the "tape". Circular coextrusion dies are
well k~own in the art and can be purchased from a number of manufactures.
In addition to tublar coextrusion, slot dies could be used to coextrude
the material in planar form. Well known single or multi-layer extrusion
coating processes could also be employed if desired.
An additional process step which may be lltilized is to
irradiate the tape or unexpanded tubing or sheet by bombarding it with
high-energy electrons from an accelator to cross-link the materials of
the tape. Cross-linking greatly increases the structural strength of the
film or the force at which tke material can be stretched before tearing
apart when the film materials are predominately e~hyelene such as poly-
ethylene or etheylene-vinyl acetate. Irradiation also improves the
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optical properties of the film and changes the properties oE the
film at higher temperatures. If an irradiation step is employed
a preferred irradiation doseage level is in the range of 0.5MR to
12.0MR. MR is an abbreviation for megarads~ A megarad is 1 x ]0
rads with a rad being the quantity of ionizing irradiation that
results in the absorption of 100 ergs of energy per gram of
irradiated material regardless of the source of the radiation.
In some instances, it may be desirable to stretch the multi-layer
film first and then irradiate it, or, if sequential coating is
employed one layer or a group of layers could be irradiated and
then another layer or layers could be added before the final step
of stretching and orienting.
As stated above, an additional optional process step is
the application of a fine silicon spray to the interior oE the
newly extruded tapea The details of this process step are
disclosed in Canadian application serial No. 403,369.
Following coextrusion, quenching to cool, and if desired
irradiation, the extruded tape is reheated and is continuously
inflated by internal air pressure into a bubble thereby transEorm-
ing the narrow tape with thick walls into a wide film with thinwalls of the desired film thickness. This process is sometimes
referred to as the "trapped bubble technique" of orientation or as
"racking". After stretching, the bubble is then deflated and the
film is wound onto semi-finished rolls called "mill rolls". The
racking process orients the film, by stretching it transversely
and, to some extent, longitudinally to rearrange the molecules and
thus impart shrink capabilities to the film and modify -the film's
physical characteristics. Additional longitudinal or machine
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direction stretching may be accomplished by revolving the de:Elaterollers which aid in the collapsing of the "blown bubble" at a
speed greater than that of the rolls which serve to -transport the
reheated "tape" to the racking or blown bubble area. All of these
methods of orientation are well known in the art.
To further disclose and clarify the scope of my
invention to those skilled in the art the following examples are
presented.
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EXA~LE I
A Eive layered structllre having an approximate layer thickness
ratio of 2/2/1/2/2 was extruded by supplying four extruders. Extruder
no. 1 which supplied the die orfices for both intermediate layers was
provided with a blend of 90% ethylene vinyl acetate copolymer (12% vinyl
acetate) [Alathon 3137 ~Melt Index 0.5)] and 10% ionomer resin ~Surlyn
1601 (0.940 density, ~elt Index 1.4)]. The blend also contained 1100 PPM
Erucamide lKemamide E~ and 1100 PPM Stearamide lKemamide S]. Extruder
No. 2 which supplied the die orfice for the core layer was provided with
lQ0% linear low density polyethylene [Dowlex 2045 (0.920 density, Melt
Index 1.0)]. Extruders No. 3 and 4 each supplied a die orfice for a skin
layer and both were provided with 100~ ethylene propylene copolymer
(3.5% ethylene) lSoltex 42X01 (Melt Flow 4.5)] having blended therewith
1100 PP~ Erucamide [Kemamide E], 1100 Stearamide ~Kemamide S], and 1100
PPM silica [White Mist].
Extruder No. 1 was maintained at a temperature range of from
390-425F. Extruder No. 2 was maintained at a temperature range of from
410-470F. Extruder No. 3 was maintained at a temperature range of ~rom
3~0-370F and Extruder No 4 was maintained at a temperature range of
from 345-3~5F. The ciruclar die was maintained at a temperature range
of from 390-435F.
After extrusio~ of the layers through the 10 inch ciruclar die
orifice the tublar extrudate which had a tape thickness of approximately
15 mil. and a tubular width of approximately 9 5/8" was quencbed to cool
by passing through a cold water bath at approximatley 37 feet per minute.
The tube was then reheated to orient by passing through a heating zone or
oven at 38 feet per minute. The oven was heated by horizontal, vertical,
and steam heating elements. In this example the horizontal heating
element was maintained at 200F. The vertical heating elements was
maintained at 300~ and the steam element, which supplied heat by being
passed through pipes or cans located within the oven, was supplied with
steam at 2 p.s.i.
A~ter being heated as described above, the tubular extrudate
was inflated and transversely stretched approximately to 4.8 to 1 and
longitudinally stretched approximatley 4.3 to 1. Thereafter the film was
cooled by water quenching to 'ock-in the oriented structure ~inal ~ilm
gauge was approximately 7~ gauge.
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The experimental data which was obtained for this film formu-
latiou is reported in Table I which follows the description of the re-
maining examples.
EXAMPIE II
A five layered structure having an approximate layer thickness
ratio of 2/2/1/2/2 was extruded by supplying four extruders. Extruder
No. 1 which supplied the die orifices for both intermediate layers was
provided with a blend comprising 50% ethylene vinyl acetate copolymer
(12% vinly acetate) lAlathon 3137 (Melt Index 0.5)] and 50% linear low
density polyethylene [Dowlex 2045 (0.920 density, Melt Index 1.0~] also
having 1100 PPM Erucamide [Kemamide E~. Extruder No. 2 which supplied
the die orifice for the core layer was provided with 100% linear low
density polyethylene [Dowlex 2045 (0.920 density, Melt Index 1.0)].
Extruders No. 3 and 4 each supplied a die orifice for a skin layer and
both were p~ovided with 100% ethylene propylene copolymer (2.7% ethylene~
ARCO K-193 (Melt Flow 2.3)~ having 1100 PPM Erucamide lKemamide E] and
1100 PPM silicon lWhite Mist].
Extruder No. 1 was maintained at a temperature range of from
405 to 415F. Extruder No. 2 was maintained at a temperature range of
from 400-475~. Extruder No. 3 was maintained at a temperature range of
from 355-435F and Extruder No. 4 was maintained at a ternperature from
355-410~. The circular die was maintained at a temperature range of
from 390-425F.
After extrusion of the layers through the 10" circular die
orifice the tubular extrudate having an approximate tape width of 8 3/4"
and thickness of 17 mil and was quenched to cool by passing through a
cold water bath at approximately 39 feet per minute. The tubular extru-
date was then reheated to orient by passing through a heating zone or
oven at approximately 38 feet per minute. The oven was heated by horizon-
tal, vertical and steam elements. In this example the hori~ontal heating
element was maintained at 212F. The vertical heating element was main-
tained at 343F and the steam element, which supplied heat by being
passed through pipes or cans located within the oven, was supplied at 7
psi .
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After being heated the tubular extrudate was inflated and
transvers~ly stretched approXimately 4.8 to 1 and longitudinally
stretched approxirn3tely 4.5 to 1. Thereafter the film was cooled by
water quenching to lock-in the oriented molecular structure. Final film
thickness was approximately 75 gauge.
The data obtained upon testing of this material is located in
Table I below.
EXAMPLE III
A three layered structure having an approximate layer thickness
ratio cf 1/3/1 was extruded by supplying 4 extruders. Extruders nurnber 1
and ~. which supplied the die orifice for th~ core layer were provided
with 100% linear low density polyethylene lDowlex 2045 (0.920 density,
Melt Inde~ 1.0)~ having 330~ PPM Erucamide IKemamide E~. Extruders No. 3
and 4 each supplied a die orifice for a skin layer and both were provided
with a blend of 80% ethylene propylene copolymer (3.5% ethylene) ISoltex
h2X01 (Melt Flow 4.5)~ and ~0~ propylene homopolymer [Hercules PD064
(0.906 density, Melt Flow 3.5)] and having 3300 PPM Erucamide lKemarnide
E] and 1100 PPM silica [White Mist] and 1650 PPM Acrawax C.
The temperature of extruder number 1 was set in the temperature
range of from 395-485F. Extruder number 2 was set in the temperature
range of from 425-470. Extruder number 3 was set in the temperature
range of from 370-375F. Extruder number 4 was set in the temperature
range of from 370-375F. The circular die was set at a temperture of
385F. The actual temperature ranges at which the extruders and die were
maintained weIe not recorded for this example.
After extrusion of the.layers through the 10 inch circular die
orifice the tubular extrudate was quenched to cool by passing through a
cold bath at ~Ipproximately 39.5 feet per minute. Upon extrusion of the
ta~e a fine siXicon mist was applied to the interior of the extruded tube
at the rate of 5-7 mg. ft. . The cooled tubular extrudate was then
reheated to orient by passing through a heating zone or oven at approx-
imately 37.7 feet per Minute. The oven was heated by a horizontal,
vertical and steam heating elernents. Xn this example the horizontal
element was maintained at 200~F. The vertical elemen~ was maintained at
30~F. and the steam element, which supplied heat by being passed through
pipes or cans located within the oven9 was supplied at 3.5 p.s.i.
Y14~C15/b ~ D ~G?~k
6~ ~
3~ 7
After being heated the tnbular extrudate was transversely
stretched approximately 4.8 to 1 and longitudinally stretched approx-
imately 4.5 to 1. Thereafter the film was cooled by water quenching to
lock-in th~ oriented structure. Final film gauge was approximately 75
~auge.
The data obtained l~pon testing this film is tabulated in Table
I below.
_BLE I
Example I II III_
Layer Ratio 1 2/2/l/2/2 2/2/1/2/2 1/3/1
Tensile Strength x 100 (PSI)
MD . g7.1 125.2 124.6
rD 110.5 105.1 130.7
Elongation (%)2
MD 86 98 113
TD 3 65 107 102
Modulus x 1000 (PSI)
MD 90.3 98.3 96.5
TD 4 101.4 99.4 97.6
Tear Propagation (gms.)
MD 4.10 4.33 9.60
TD 5 4.01 5.53 9.83
Tear Xesistanc~ (lbs~)
MD (~.70 0.61 0.60
TD G.90 0.83 0.67
Shrink Properties
at 200F
Free Shrink (%)6
MD 16 14 12
TD 18 20 17
Shrink Tension (PSI)7
MD 239 304 2~8
TD 327 457 509
At 260F 6
Free Shrink (%)
MD 52 4g 48
TD 5~7 57 54
Shrink Tension (PSI)7
MD 220 345 434
TD ` 365 422 538
at 280F
Free Sbrink (~)6
MD 71 66 62
67 68 64
Shrink Tension (PSI)
MD 237 34~ 432
TD 8 304 362 584
Opti~s
Haze 1%) 2.5 2.1 2.0
Gloss (45) 94 88 8B
Total Transmission 92.5 92.2 92.2
Y14LC16/b ~_~ ~
Footnote to Table I
ASTM D 882
ASTM D 882
ASTM D 882
ASTM D 1938
ASTM D lOO~
5ASTM D 2732
7ASTM D 2838
ASTM D 1003
All of the above tabulated Table :~ data are averages
obtained by procedures in accordance with the designated ASTM
standard.
It should be understood that the detailed description
and specific examples which indicate the presently preferred
embodiments of the invention are given by way of illustration
only since various changes and modifications within the spirlt
and scope of the invention will become apparenl to those of
ordinary skill in the art upon review of t.he above de-tailed
description and examples.
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