Note: Descriptions are shown in the official language in which they were submitted.
,$~ a3f~3~ c:~
ab~ ~
~~~ElD OF rHE l~;~Tr ~ O~
Tbe fie]d of the present invel)tion is that of oriented tubularly
e~truded iilms and improved rnethods for their production. More specifi-
cally the present invention is directed to a spirally oriented film and a
rnethod for its production. Even more specifically the preseDt invention
is directed to a spirally cross-oriented iilm and a method for its
production.
BACKGROUND OF T}E INVENTlON
The quest for an improved method for producing a film material
having irnproved pbysical cbaracteristics such as overall strength and
tear resistance has been ongoing for guite some time. ~or many years it
has been kDown that the stretchiDg of an orientable thermoplastic
material under certain conditions, now well known in the art, would
result in the orientation, i.e. alignment, of the molecules of the
material in the direction of stretching. One method whereby this
stretching may be accomplished is kno~rn as the "bubble" process. The
bubble process is a well knowr3 process for forming an oriented thermo-
plastic film wherein an extruded tube of thermoplastic material ~hich is
heated to its orientation temperature range is sequentially inflated by
internal pressure, cooled and collapsed into lay-f]at configuration. The
collapsed tube may subseguently be wound up in roll fashion for storage.
The tube is usually extruded vertically. After extrusion a volume of air
is trapped within the tube. The internally trapped air causes the
extruded tubing to assume a bubble or balloon-like configuration so as to
enlarge, stretch and orient the tube in both the transverse and longitu-
dinal directions. The bubble may be forrrled through utilization of two
sets of pinch rolls which may also serve to collapse the tube and form a
lay-flat ~ilm. The thic~ness of the filnl may, to some deree, be
controlled by varying the volume o~ the internally trapped air and heDce
Y]6LC2/sb
lZ(?;i:`~5~
~ degree ol enlarging aDd stretching, by varyiDg the rate o~ ex~rusioD
and/or by varying the speed oi revolution of the piDch rolls wbich col-
lapse the tube into a lay-f~at configuration.
The terms "oriented" and/or "orientation" are used berein to
describe the process and resultant product characteristics obtained by
stretchiDg a resinous orieotable polymeric thermoplastic material which
is heated to its orientation temperature range and tben cooled iD order
to lock-in or freeze the molecular alignment of the material in the
direction of stretching. This action improves the mechanical properties
of the film, such as, for example, shrink tension and orientation release
stress. Both of these properties may be measured in accordance with ASTM
D 2838 69 (reapproved 1975). The orientation temperature range or a
given film will ~ary with the different resinous thermoplastic materials
or 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 thermoplastic material or blend of
materials:- Orientation temperature ranges for the materials encompassed
by the present application are ~ell known to those skilled in the art.
When the stretching force is applied in one direction unia~ial orienta-
tion results. When the stretching force is applied in two directions
biaxial orientation results.
The terms "polymer" and "polymeric" are used herein to include
polymers, ionomers, copolymers, interpolymers, homopolymers, block or
graph polymers and blends thereof.
The term "cross-oriented" is used herein to describe a multi-
layer film comprising two or more layers in which at least two of the
la~yers are oriented at an angle with respect to each other.
The term "spirally oriented" is used herein to describe an
oriented film wherein the ph~sical alignment ol the molecular configura-
tion of the ~ilm assumes 3 subs~antially spiral configuration.
Y]6LC3/sb ~5
OLher metbods of streLching are known Lo tilose in the art. For
exam~.le, it has been recogrlized in t~e art that the extruded tubing may
be ]ongitudinally stretched by revo]ving the pinch rolls which initiall~
col~apse the tubing after extrusion at a rate in excess of the linear
velocity with which the tubing em~rges from the exLrusion die. If the
temperature of the extruded tubing is maintained within its orieDtation
temperature range during the stre~ching tbe molecules of the tubing will
be oriented in the direction of stretching. Films manufactured by this
metbod are generally referred to as hot stretched. It has also been
recognized in the art that the extruded tubing may be longitudinally
stretched by revolving one of the pairs of pinch rolls which transport a
tubular extrudate, which has been extruded, cooled and reheated to its
orientation temperature range, at a rate in excess of the rate of revolu-
tion of a preceding pair of pinch rolls. Films manufactured by this
method are generally referred to as cold stretched films. Either of
these methods accomplishes some degree of orientation of the stretched
tubular extruded film in the longitudinal or tubular direction. However,
if a high degree of orientation is desired the later procedure should be
followed since it results in a greater degree of orientation. ~urther-
more, it is also well known that the transverse stretching of an extruded
tubular film which is heated to a temperature within its orientation
temperature range results in the stretching and consequent orientation of
the tubular extruded film in the transverse or lateral direction. A
greater degree of transverse orientation occurs if the extruded mater;al
is first cooled and then reheated to its orientation temperature range
(i.e. cold stretched) prior to being subjected to transverse stretchiDg
and expansion. If the transverse stretching is coupled ~ith longitudinal
stretching, as is the case in the bubble process, a biaxial orientation
is imparted to the resu~tant ex~ruded film.
Stre-~ching to orient a thermoplastic material is widely utilized
within the art since it is well ~nown that an oriented material exhibits
increased tear resistance in the direction transverse to the
direction of stretching and orientation. Further discussion of
film orientation may be found at Volume I, Chapter 10 of the
Science and Technology of Films, copyrigh-ted in 1968 by John Wiley
and Sons. This book was edited by Orville Sweeting.
Unfortunately, it is also well known that an oriented
material exhibits li-ttle or no increase in tear resistance in the
direction of stretching and orientation. In the past attempts to
overcome this problem have led to the utilization of linearly
cross-oriented films. However, the methods for processing a
linearly cross-oriented film have been somewhat complex. For
example, the work of Reifenhauser et al. has resulted in United
States Patent Nos. 3,726,743 and 3,926,706. Additionally, the work
of Kubat et al. resulted in United States Patent No. 4,076,56~.
While -these patents do disclose methods for producing linearly
cross-oriented films those skilled in the art, upon reviewing these
patents, will recognize that these methods are quite unwieldy and
cumbersome.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to pro-
vide a me-thod for forming a film from a -tubular extruda-te whereby
-the aforementioned disadvantages are obvia-ted.
The invention provides an improved method for producing
a spirally oriented film; the improvement comprising; extruding a
tube of an orien-table -thermoplastic film from a die; heating said
orientable film -to a temperature wi-thin an orien-tation tempera-ture
range of said film; transversely orienting said film; cooling said
transversely orien-ted film; reheating said transversely orien-ted
--5--
~L ~
film to a tempera-ture wi-thin an orien-tation tempera-ture range of
said film and simultaneously longitudinally stretching and axia]ly
rotating said orien-table film to spirally orient said film.
The spirally oriented film has improved strength and
tear resistance properties.
Further details and the broad scope of applicability of
the presen-t invention will become apparent to those of ordinary
skill in the art from the details disclosed hereinafter. However,
it should be understood tha-t the following detailed description
which indicates a presently preferred embodiment of the present
invention is only given for purposes of illustration since various
changes and modifications well within the scope of the present
invention will become apparent to those of ordinary skill in the
art upon review of the following detailed description.
In a preferred embodiment of the present invention the
inner surface of the tubular extrudate comprises an adhesive tacky
self-weldable material. In this embodiment the collapse of the
tubular extrudate by
--6--
`le dfflate rolls occurs under Lelnperature and pressure conditions ~hich
promote Lhe self-welding oI the inner surlace of the tubu~ar extrudate to
itself. Upon comp]etio~ of the col]apsing aDd inLer~al selI-we]ding of
the imler surface of the tubular extrudate to itself, the tubular extru-
date is Lransormed into a unitary ]ay-f]at filTn co-nprising at least two
layers which, as a result of the spiral orientation of the tubular extru-
-
date, are spirally cross-orienLed with respect to each other. ~berefore,
the fiDal lay-flat film will exhibit, as a result of the presence of the
spirally cross-oriented layers, the improved physical characteristics of
increased strength and increased tear resistance in both the longitudinal
and transverse directions.
BRIEF DESCRIPTI~N OF THE_ RAWINGS
~ IG. I is a schematic cross-sectional view of one embodiment of
the present invention wherein an orientable tubular extrudate is, upon
extrusion, simultaDeously longitudinally stretched and circularly rotated
to spirally orient the molecular configuration of the tubular film.
DepeDding on the materials utilized, this embodiment can also produce a
spirally cross-oriented film.
~ lG. II is a sebematic cross-sectional ~iew of a more preferred
embodiment of the present inVeDtiOn whereiD a previously extruded and
cooled orientable tubular extrudate is reheated to its orientation temper-
ature range, longitudianlly stretched and circularly rotated to spirally
orient the molecular configuration of the tubular film. As is the case
with the embodiment of ~igure I, the more preferred embodiment of ~igure
II, depending upon the materials utili~ed, may also produce a spirally
cross-orienLed film.
Y16~C7/sb
5~
D~hllED l)ESCRIPI~70~ A~ ~ PREFERRED E~DIMFNT
TUrlliDg now to the ligures, iD which like reference r)umerals
represent like materials or apparatus and, ;D particular, to FIG. I which
represents a schematic cross-sectional view of one embodirnent of the
present invention, it can be seen tQat tubular extrudate 3 is extruded
from the orifice of circular ar~ular die 1 as indicated by arrow l7. ~he
extrudate is provided to circular die I by conventional, well known
extruders, not shown. The tubular extrudate may be a monolayer in which
case the tubular extrudate 3 need only be provided through a single
extrusion channel as at 2. In the case of a coextruded multi-ply struc-
ture the second ply may be provided through a second ex~rusion chanDel
2a. Otber plies may be provided through utilization of additional extru-
sion channels and extruders as is well known in the art.
After extrusion, tubular extrudate 3 is cooled by ~uench;ng
means, not sho~7n, well known in the art and collapsed as indicated at 5 by
deflate rolls 6 revolving as indicated by 6a. Deflate rolls 6 are
revolved at a speed which is in excess of the speed of extrusion of
tubular extrudate 3 from circular die orifice 1. The excess speed of
revolution of deflate rolls 6 results in the loDgitudinal stretching of
tubular extrudate 3. The quenching meaDS is adjusted so that during the
stretchiDg the temperature of the tubular extrudate 3 is maintaiDed
within its orientation temperature range. Thus, the tubular extrudate
will be longitudinally oriented. As was stated above quenching means are
well known in the art. However, an example of such a cooling means is
the cascading water quenching means.
Of principal importance to the present invention is that the
deflate rolls 6 are constructed so as to continuously axially rotate as
indicated by arrow 7 with respect to the orifice of circular die 1.
Preferably, any acco~lpanying transporting and storing apparatus, for
Y~61C~sb
,~ ~9,rl,~g~ ~9
~ p1e 9, is also axially rotated in unisoD with def]ate rolls 6 The
continuous axial roLation of the def~aLe rolls 6 imparts a spiral char-
acter to the loDgitudinal stretching and conse~uent orientation of the
molecules of the tubular extrudate 3. Accordingly, upon collapse of the
tubular extrudate 3 to form a lay-flat configuration as at 8, both of the
superimposed layers of the collapsed lay-flat configuration 8 will exhibit
a degree of spiral orientation. Since a spiral orientation configuration
comprises e]ements of both longitudinal and transverse stretching and
orientat;on, the spirally oriented layers will exhibit improved tear
resistance in both the longitudinal and transverse directions. ~hus, the
spirally oriented film will exhibit an overall improvement in strength as
a result of the improved tear resistance in both the transverse and
longitudinal directions.
FIG. II illusLrates a preferred embodiment of the present
invention. In this embodiment a source 10 of stored, previously extruded
and cooled tubing 11 is supplied through pinch rolls 12 revolving as
demonstrated by arrows 12a. The lay-flat tubing ll is thereafter inflated
as at 13 to form a tubular structure 3. Xeating element 14 is utilized
to increase the temperature of the tubular structure 3 to within its
orientation temperature range. AdditioDally, it should be noted that
deflate rolls 6 are revolved at a speed in excess of that of pinch rolls
12 so as to longitudinally stretch and orient the molecular configuration
of tubular structure 3. Deflate rolls 6 and, preferably, storage roll 16
are also simultaneously axially rotated in unison, as ;n the embod;ment
of FIG. I and as indicated by arrow ~, so as to spira~ly orient the
molecu]ar configuration of tubular structure 3. ~he remaining steps of
this preferred embodiment are the same of those of the embodiment of FIG.
I. ~his embodiment is preferred to that of FIG. I since a greater degree
Y16LC9/sb
of ~ nta~ioD is obtair)ed if the extruded tuhing has first b~eu c~o~ed
and is then reheated to its orientation temperature range prior to being
oriented.
,
Orientable therMoplastic materia~s which may be utilized within
the scope ol the present in~ention are well ~nown in the art. Examples
of such orientable thermoplastic materials are polymers and polymeric
blends of the following monomers: the mono-olefiDs and conjugated di-
olefiDs, e.g., ethy]ene, propyle~e, butene-l, isobulene, 1,3, butadiene,
isoprene and other aliphatic rnono aDd di-olefins; the halogen substituted
olefins, e.g., vinyl chloride, vinylidene chloride; the mono/vinylidene
aromatic compounds, e g., styrene, alpha methylstyrene, chlorostyrene and
other aromatic olefins; and other unsaturated monomers such as acryoni-
trile acrylamide and the like. Ionomer resins aDd nylon may also be
utilized. A preIerred orientable therMoplastic material is a polymer of
vinylidene chloride and vinyl chloride which is comprised of at least
50~, by weight, of vinylidene chloride derived units. ~his material is
wel] known ;n the art for its o~gen impermeability characteristics. ~he
orientation temperature ranges ~or these materials are known to those
skil]ed in the art.
In yet an even more preferred embodiment o~ the present inven-
tion a spirally cross-oriented film is produced. An important feature of
this embodiment is that the extruded monolayer or, in the case of a
coextruded multi-ply structure the innermost ply, comprises a polymeric
self-weldable adhesive resinous thermoplastic material having a low
melting point, preferrably betweeD 160F and 200F. In the case of an
extruded monolayer the self-weldable material must also be orieDtable.
lf a multi-ply structure is co-extruded the ilmer~ost ply ma~ but does
not have to be orientable. A preferred adhesive, self-~leldable material
is a copoly~ler of ethylene and vinyl acetate ~hich ~las froM ~0 to 40%,
/o
Y]6LC]O/sb
~q~
y wcight, oI vinyl acetate derived units. Otber particularly elfective
adhesive selI-we]dable resins broadly include uusatura~ed ester polymers
such as ethylene/unsaturated ester copolymers; e.g., et~ylene/vinyl
acetate copolymers, ethylene/vinyl propiouate copolyn)ers, etbylene/methyl
methacrylate copolymers, ethylene/ethyl methacrylate copolymers, ethylene/
ethyl acrylate copoly~ers, ethylene/isobutyl acrylate copolymers, and the
like; unsaturated carboxylic acid copolymers, e g., ethylene/unsaturated
carboxylic acid copolymers ehtylene/acrylic acid copolymers, ethylene/
methacrylic acid copolymers, ethylene/maleic acid copolymers, ethyleDe/
fumaric acid copoly~ers, ethylene/itaconic acid copolymers, and the like;
low molecular weight polyethylene, low molecular weight polypropyleDe and
other low molecular weight olefin polymers. Still other useful adhesive
self-weldable ma~erials include ionomer resins, aDd vinylidene chloride
polymers, e.g., viDylidene/vinyl chloride copolymers, i.e. a pol}~er of
viDylidene chloride and vinyl chloride comprising at least 50%, by weight,
of vinylidene chloride derived units.
ln this embodimeDt the collapsing of tubular extrudate 3 by
deflate rolls 6 briDgs the tacky self-weldable i~ner surface of tubular
extrudate 3 into iDtimate pressurized contact with itself. ~he collaps-
ing and pressure a~plying action of deflate rolls 6 when utilized with
tubular extrudates such as those disclosed above haviug an inDer surface
which is adbesive and self-weldable, results In the self-welding of the
superimposed inner surface of the tubular extrudate 3 to itself so as to
produce a unitary rnultilayer film as at 8 or 15 in ~igures I and II,
respectively. Since the tubular extrudate 3 is spirally oriented, the
unitary multilayer film, upon collapsing and interDal self-welding, will
comprise two spirally orieDted layers which are spirally cross-oriented
with respect to eacb other. If necessary, deflate rolls 6 may be heated
to ful-ther assist in the self-welding of the inner surface of spirally
~//
~]6~C]~/sb
j7
iented tubu]ar ex~rudaLe 3. ~er col]apse and internal sel~-~e]ding
of the syirally oriented tubular exLrudate 3 iDto the spirally cross-
orien~ed film as at ~ or 15, the fil~ may be transported to aDd stored on
rolls 9 or ]~. The spirally cross-oriented unitary multilayer film is
characterized by increased s~rength and tear resistaDce in both the
transverse and IoDgitudinal film directions- ~be most preferred erDbodi-
ment for obtaining a spirally cross-orien~ed film is that at Figure II
since, as was stated above, this embodiment results in a greater degree
of orientation.
Experimentation which ùtilized a coextrnded tubular extrudate
having an outer polypropylene ply and an~inner ethylene vinyl acetate ply
determined that, through utilization of the present inventive process, it
is difficult to impart an angle of spiral cross-orientation of greater
than 20. This limitation, which varies with the materials utilized,
arises from the fact that if the deflate rolls 6 are axially rotated 7 at
too great a speed the tubular extrudate 3 will be physically twisted
rather than merely having a spirally oriented molecular configuration.
Since it may generally be stated that the greater the angle of cross-
orientation the greater the overall strength and tear resistance of the
final film iu both the transverse and longitudinal directions, further
modification of the embodiment depicted by ~IG. II to further increase
the overall strength and tear resistance of the spirally cross-oriented
film may be help~ll when the finished film product is to be exposed to
the most delnanding conditions. A modification which has been found
useful is to subject the tubing 1~ of the embodiment of ~IG. II to some
transverse orientation, for example by the bubble process described
above, prior to its further processing in accordance ~7ith the embodiment
of ~IG. Il. It is believed that s~ch action effectively increases the
angle of spiral cross-orientation and, thus, results in an even stronger
and more tear resistant product.
~6~C12/sb
s~
Of course, numerous modifications of -the present inventive concept
will be readily discernable to -those of skill in the art in view of the
present disclosure. For example, the film ma-terials may be irradiated, as
is well known in the art, if a cross-linked final structure is desired.
Modifications of this sort are intended to be within the scope and spirit
of ~he present invention.
~13-
