CA1202157A - Spirally cross-oriented film and method for producing spirally cross-oriented film - Google Patents
Spirally cross-oriented film and method for producing spirally cross-oriented filmInfo
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- CA1202157A CA1202157A CA000423550A CA423550A CA1202157A CA 1202157 A CA1202157 A CA 1202157A CA 000423550 A CA000423550 A CA 000423550A CA 423550 A CA423550 A CA 423550A CA 1202157 A CA1202157 A CA 1202157A
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- oriented film
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Abstract
SPIRALLY CROSS-ORIENTED FILM AND METHOD
FOR PRODUCING SPIRALLY CROSS-ORIENTED FILM
ABSTRACT OF THE DISCLOSURE
A novel spirally oriented film is produced by a novel method comprising extruding an orientable material in tubular form and longitudinally stretching the extruded tube while simultaneously axially rotating the tube to spirally orient the molecular configuration of the tube and form a spirally oriented film. Thereafter, the tube, preferably, is collapsed and internally self-welded to form a spirally cross-oriented unitary lay-flat film.
FOR PRODUCING SPIRALLY CROSS-ORIENTED FILM
ABSTRACT OF THE DISCLOSURE
A novel spirally oriented film is produced by a novel method comprising extruding an orientable material in tubular form and longitudinally stretching the extruded tube while simultaneously axially rotating the tube to spirally orient the molecular configuration of the tube and form a spirally oriented film. Thereafter, the tube, preferably, is collapsed and internally self-welded to form a spirally cross-oriented unitary lay-flat film.
Description
,$~ 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 ~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 `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-
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 ~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 `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-
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improved method for producing a spirally oriented film; the improvement comprising; extruding a tube of an orientable thermoplastic film from a die; heating said orientable film to a temperature within an orientation temperature range of said film;
transversely orienting said film; cooling said transversely oriented film; reheating said transversely oriented film to a temperature within an orientation temperature range of said film and simultaneously longitudinally stretching and axially rotating said film to spirally orient said film.
transversely orienting said film; cooling said transversely oriented film; reheating said transversely oriented film to a temperature within an orientation temperature range of said film and simultaneously longitudinally stretching and axially rotating said film to spirally orient said film.
2. An improved method for producing a spirally cross-oriented film; the improvement comprising; extruding a tube of an orientable thermoplastic film having a tacky self-weldable inner surface; heating said orientable film to a temperature within an orientation temperature range of said film; transversely orienting said film; cooling said transversely oriented film; reheating said transversely oriented film to a temperature within an orientation temperature range of said film and simultaneously longitudinally stretching and axially rotating said oriented film to spirally further orient said film; and collapsing said film to self-weld said inner surface of said film and form a spirally cross-oriented film having an effective angle of cross-orientation greater than 20°.
3. The method of claim 1, wherein a multiply tube is co-extruded.
4. The method of claim 2, wherein a multi-ply tube is co-extruded.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US39120782A | 1982-06-23 | 1982-06-23 | |
| US391,207 | 1982-06-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1202157A true CA1202157A (en) | 1986-03-25 |
Family
ID=23545711
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000423550A Expired CA1202157A (en) | 1982-06-23 | 1983-03-14 | Spirally cross-oriented film and method for producing spirally cross-oriented film |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS58224722A (en) |
| AU (1) | AU1197683A (en) |
| CA (1) | CA1202157A (en) |
-
1983
- 1983-03-02 AU AU11976/83A patent/AU1197683A/en not_active Abandoned
- 1983-03-14 CA CA000423550A patent/CA1202157A/en not_active Expired
- 1983-05-26 JP JP9161683A patent/JPS58224722A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58224722A (en) | 1983-12-27 |
| AU1197683A (en) | 1984-01-05 |
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