CA2259004C - Highly oriented fluoropolymer films - Google Patents

Abstract

The present invention provides highly oriented multilayer films. They are produced by coextruding or laminating films having at least one layer of a fluoropolymer, at least one layer of a polyolefin homopolymer or copolymer and an intermediate adhesive layer of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof. With this structure the polyolefin layer allows the fluoropolymer layer to be stretched up to ten times its original length. Such a high orientation ratio for the fluoropolymer film increases t he mechanical strength, toughness, and water vapor barrier properties of the fi lm while using a thinner gauge fluoropolymer film. Coextrusion processing can b e done at higher temperatures, i.e. in the range of from at about 280 .degree. C to about 400 .degree.C. These temperatures allow films to be produced in the absence of polymer degradation and film melt fracture.

Description

30-3904 (4760) HIGHLY ORIENTED FLUOROPOLYMER FILMS
BACKGROUND OF THE INVENTION
1o FIELD OF THE IIwErTTION
The present invention relates to oriented multilayer films. More particularly, the invention pertains to coextruded or laminated films having at least one layer of a fluoropolymer such as poly(chlorotrifluoro ethylene) (PCTFE) homopolymer or copolymer, a layer of a polyolefin homopolymer or polyolefin containing 15 copolymer and an intermediate adhesive layer of a polyolefin having at least one fi~nctional moiety of an unsaturated carboxylic acid and/or anhydride thereof.
DESCRIPTION OE~'HLLPRIOR A»T
It is well known in the art to produce oriented polymeric films. See, e.g.
U.S.
20. patent 4,011,874. However, such films tend to expand in the direction perpendicular to the direction of stretching.
It is also known in the art to produce single layer and multilayer fluoropolymer films. See, e.g. U.S. patent nos. 4,677,017; 4,659,625 and 5,139,878.
25 However, fluoropolymers are difficult to orient due to their unique crystallization properties. More particularly, PCTFE is exceptionally difficult to orient due to its extremely fast crystallization rate and thermally induced self orientation. Its fast crystallization rate produces a highly crystalline structure that hinders orientation and actually prevents further WO 97/48553 PCTlUS97109170 orientation beyond a certain point Its thermally induced self orientation results in a film which, upon unconstrained heating, self extends in the machine or longitudinally stretched direction and shrinks in the transverse direction Most earlier attempts to stretch PCTFE films have failed either due to its high degree of film crystallinity, nonuniform crystailinity, self=orientation or a combination of these factors. Prior art studies of the orientation of PCTFE
homopolymer report a limit of a three to four times orientation or stretch ratio in either the machine direction (MD) or transverse direction (TD) For example, U.
S
1o patent 4,544,721 describes a substantially amorphous chlorotrifluoroethylene polymer monolayer film which is oriented at least 2 5 times its original length, but no more than five times in the MD. It also disclosed therein that attempts to stretch crystalline PCTFE result in films that contain holes or tears, or which are uneven in thickness. Other known attempts to stretch PCTFE homopolymer more t5 than five times its unstretched length result in film fibriiation and ultimate breakage See, e.g. U.S. patent 4,510,301 (orients film containing a copolymer of ethylene and chlorotrifluoroethylene) It would be desirable to produce a much more highly oriented, dimensionally stable 2o fluoropolymer film since as the higher the des;ree of attainable orientation is increased, the properties of mechanical strength, toughness, and water vapor barrier capability are significantly improved without increasing the film gauge. It would also be desirable to produce a multilayered film structure which is dimensionally stable and uniform across its entire width SUMMARY OF TI-ff: INVENTION
The invention provides a multilayer film which comprises at least one fluoropolymer layer and at least one polyolefin layer comprising at least one polyolefin homopolymer, polyolefin containing copolymer or blends thereof.
attached to a surface of the fluoropolymer layer by an intermediate adhesive layer comprised of at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof, which film has been uniaxially stretched at least five times in one linear direction, and wherein each of the fluoropolymer layer, adhesive layer and polyoiefin layer have a viscosity of less than or equal to about 10,000 Pascal seconds at a temperature in the range of from about 280 °C to about 400 °C.
to The invention also provides a method of producing an oriented, multilayer film which comprises coextruding at least one layer of a fluoropolymer, and at least one layer of a polyolefin homopolymer or a pol;yolefin containing copolymer attached to a surface of the fluoropolymer layer by a, coextruded intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least 15 one functional moiety of an unsaturated carboxylic acid or anhydride, wherein said coextruding is conducted at a temperature of from about 280 °C to about 400 °C;
casting the film and then stretching the filmy at least five times in either its longitudinal or transverse direction.
2o The invention further provides a method of producing an oriented, multiiayer film which comprises laminating at least one layer of a fluoropolymer to the surface of a layer of a poiyolefin homopolymer or a polyolefin containing copolymer by an intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid 25 anhydride and then stretching the film articae at least five times in either its longitudinal or transverse direction.
The invention still further provides an article which comprises a thermoformed Flm of the above multilayered film.

The present invention achieves a highly oriented fluoropolymer containing film by producing a multilayer structure by either a coextrusion or a lamination process.
Without the additional layers in the film structure, many fluoropolymers such as PCTFE can only be stretched to a maximum of five times its original length and usually only three times stretching. With this structure, the polyolefin layer allows the fluoropolymer containing layer to be stretched more than five times its original length, and usually up to ten times its original length.
1o It has been further found that when fluoropolymer films are coextruded with polyolefins and adhered with the above intermediate adhesive layer at a temperature range of from about 280 °C to about 400 °C, a stable, uniform film is produced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
For purposes of this invention, the terms "orienting" and "stretching" shall be used interchangeably. As used herein, "copolymers" shall include polymers having two or more monomer components.
The fluoropolymer layer may be comprised of PCTFE homopolymers or copolymers or blends thereof as are well known in the art and are described in, for example, U.S. patent numbers 4,510,301; 4,544,721; and 5,139,878.
Of these, particularly preferred fluoropolymers suitable to form multilayer barrier films of the present invention include homopolymers and copolymers of chlorotrifluoroethylene and copolymers of ethylene-chlorotrifluoroethylene. Such copolymers may contain up to 10%, and preferably up to 8 % by weight of other comonomers such as vinylidine fluoride and tetrafluoroethylene. Most preferred are chlorotrifluoraethylene homopolymers and copolymers of chlorotrifluoroethylene and vinylidine fluoride and/or tetrafluoroethylene. Such may also be purchased commercially as ACLON~ resin from AlliedSignal Inc. of Morristown, New Jersey.
5 Adjacent to the fluoropolymer layer is an adhesive layer, also referred to in the art as a "tie" layer, between each film layer. In accordance with the present invention, suitable adhesive polymers includes modified polyolefin compositions having at least one functional moiety selected from the group consisting of unsaturated polycarboxylic acids and anhydrides thereof. Such unsaturated carboxylic acid and anhydrides include malefic acid and anhydride, fumaric acid and anhydride, crotonic acid and anhydride, citracoruc acid and anhydride, itaconic acid an anhydride and the like. Of these, the most preferred is malefic anhydride. The modified polyolefins suitable for use in this invention include compositions described in U. S.
patents 3,481,910; 3,480,580; 4,612,155 and 4,751,270.
15 The preferred modified polyolefin composition comprises from about 0.001 and about 10 weight percent of the functional moiety, based on the total weight of the modified polyolefin. More preferably the functional moiety comprises from about 0.005 and about 5 weight percent, and most preferably from about 0.01 and about 2 weight percent. The modified polyolefin composition may 2o also contain up to about 40 weight percent of thermoplastic elastomers and alkyl esters as described in U.S. patent 5,139,878.
Adjacent the adhesive Layer is a polyolefin layer comprised of poly(a-olefins) and 25 copolymers and blends thereof, wherein the a-olefin monomers have from about 2 to about 10 and preferably from about 2 to about 6 carbon atoms. Non-limiting examples of polyolefins include polyethylenes, including ultralow, low, linear low, medium, high and ultrahigh density polyethylene; polypropylene; polybutyiene;
polybutene-1; polypentene-1; poly-3-methylbutene-1; poly-4-methylpentene-1;

WO 97148553 PCTlUS97/09170 polyhexene; copolymers of polyolefins; copolymers of olefins and other polymers such as polyvinyl chloride, polystyrene and polyurethane, etc., and mixtures of these. Of these, the preferred polyolefins are polyethylene and polypropylene with polypropylene being most preferred Although each layer of the multilayer film structure may have a different thickness, the thickness of each of the fluoropolymer and poiyolefin layers of the films in the post-stretched multilayer films structure is preferably from about 0.05 mils ( 1.3 ~tm) to about 100 mils (2540 Etm), and more preferably from about 0 05 mils ( l0 Vim) to about SO mils ( I 270 pm). The thickness of the post-stretched adhesive layer may vary, but is generally in the range of from about 0 02 mils to about l 2 mils (30S Vim), preferably from about O.OS mils ( 1.3 Vim) to about I 0 mils (2S
~tm), and most preferably from about 0.1 mils (25 Vim) to about 0 8 mils (20 Vim) While such thicknesses are preferred as providing a readily flexible film, it is to be t5 understood that other film thicknesses may be produced to satisfy a particular need and yet fall within the scope of the present invention; such thicknesses which are contemplated include plates, thick films, and sheets which are not readily flexible at raom temperature (approx. 20 °C. ).
2o In the preferred embodiment, each of the fluoropolymer layer, adhesive layer and polyolefin layer have on average no embedded particles having a diameter of greater than about 800 Nm, no more than about 22 particles having a diameter of from about 400 to about 800 ~tm, no more than about 2 I 5 panicles having a diameter of from about 200 to about 400 ~m and no more than about S38 particles 25 having a diameter of from about t 00 to about 200 ~m per square meter of film and wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have on average no more than about 0.36 embedded bubbles having a diameter of greater than about 3100 ~tm, no more than .about 22 bubbles having a diameter of from about 1500 to about 3100 Vim, and no~ more than about 161 bubbles having a diameter of less than about 1500 ~m per square meter of film This allows for an extremely clear film having less likelihood of breaking or tearing. Each of the each of the fluoropolymer layer, adhesive layer and polyolefin layer materials have a melt viscosity of less than or equal to about 10,000, preferably from about 3,000 to about 10,000 Pascal seconds at a temperature in the range of from about 280 °C to about 400 °C, and preferably from about 285 °C to about 370 °C These may be determined by using a Systronics Eagle Automatic Inspection System manufactured by Systronics, Inc.
to The multilayer films of the present invention can have a variety of structures so long as there is an adhesive layer between each polymer layer A typical film structure includes a three-layer structure, which comprises a thermoplastic polyoIefin layer, an adhesive layer and a fluoropolymer layer Another typical film t5 structure is a five-layer structure, which comprises a poiyolefin layer, an adhesive layer, a fluoropolymer layer, an adhesive layer and a polyoiefin layer These ace only two of many possible combinations of multilayer film structures, and any variation of the order and thickness of the layers of the fluoropoiymer and poiyolefin layer can be made The multilayer films of this invention may be produced by conventional methods useful in producing multiiayer films, including coextrusion and extension lamination techniques. Suitable coextrusion techniques are described in U.S. patents 5,139,878 and 4,677,017 except coextrusion in this invention is conducted at from about 280 °C to about 400 °C , preferably from about 285 °C to about 370 °C if coextrusion is performed at a higher temperature, the film polymers tend to degrade significantly and lose their film properties If coextrusion is done at a lower temperature, the film has a non-uniform, hazy pattern indicative of melt fracture. Coextrusion techniques include methods which include the use of a feed block with a standard die, a multimanifold die such as a circular die, as well as a multimanifold die such as used in forming multilayer films for forming flat cast films and cast sheets.
One advantage of coextruded films is the formation of a multilayer film in a one process step by combining molten layers of each of the film layers of fluoropoiymer, tie layer composition, and polyolefin, as well as optionally more film layers, into a unitary film structure. In order to produce a multilayer film by a coextrusion process, it is necessary that the constituents used to form each of the to individual films be compatible with the film extrusion process The term "compatible" in this respect means that the film-forming compositions used to form the films have melt properties which are sufficiently similar so as to allow coextrusion. Melt properties of interest include, for example, melting points, melt flow indices, apparent viscosity, as well as melt stability It is importam that such is compatibility be present to assure the production of a multilayer film having good adhesion and relatively uniform thickness across the width of the film being produced. As is known in the art, film-forming compositions which are not sufficiently compatible to be useful in a coextrusion process frequently produce films having poor interfacial lamination, poor physical properties as well as poor 2o appearance.
One skilled in the art can readily weigh the above-noted compatibility in order to select polymers having desirable physical properties and determine the optimal combination of relative properties in adjacent layers without undue 25 expet~imentation. If a coextrusion process is used, it is important that the constituents used to form the multilayer film be compatible within a relatively close temperature range in order to permit extrusion through a common die. It has been found that the variation of the quantity of the modified polyolefin within the tie layer composition provides an adhesive layer forming composition which is of sufficiently high melt viscosity, especially in the preferred range of compositions described above, to be particularly usefi~l in a coextrusion process with the fluoropolymer film forming composition, and with a film forming composition.
Alternatively, the multilayer films of the present invention can be produced by lamination whereby a multilayer film structure is formed from pre-fabricated film plies. The basic methods used in film laminating techniques are fusion, wet _ combining, and heat reactivating. Fusion, which is a method of laminating two or more film plies using heat and pressure without the use of other adhesives can only 1o be used where the films being laminated are comprised of polymers that readily form interfacial adhesion. Wet combining and heat reactivating are utilized in laminating incompatible films using adhesive materials.
Typically, laminating is done by positioning the individual layers of the inventive i5 film on one another under conditions of sufficient heat and pressure to cause the layers to combine into a unitary film. Typically the fluoropolymer, adhesive, and polyolefin layers are positioned on one another, and the combination is passed through the nip of a pair of heated laminating rollers by techniques well known in the art such as those described in U.S. patent 3,355,347.
2p Lamination heating may be done at temperatures ranging from about 120 °C to about 175 °C, preferably from about 150 °C to about 175 °C at pressures ranging from about 5 psig (0.034 MPa) to about 100 psig (0.69 MPa) for from about 5 seconds to about 5 minutes, preferably from about 30 seconds to about 1 minute.
Zs The multilayer film, whether comprising or three or more layer structure, may be stretched or oriented in any desired direction using methods well known to those skilled in the art. Examples of such methods include those set forth in U.S.
patent 4,510,301. In such a stretching operation, the film may be stretched uniaxially in either the direction coincident with the direction of movement of the film being withdrawn from the casting roller, also referred to in the art as the "machine direction", or in a direction which is perpendicular to the machine direction, and referred to in the art as the "transverse direction", or biaxially in both the machine direction and the transverse direction. The multilayered film of the invention are particularly useful for forming thermoformed three dimensionally shaped articles such as blister packaging for pharmaceuticals. This may be done by forming the film around a suitable mold and heating in a method well known in the art.
l0 We have unexpectedly found that the fluoropolymer films of the present invention have sufficient dimensional stability to be stretched at least five and preferably more than five times and more preferably from more than five times to about ten times in either the machine direction or the transverse direction or both.
15 Another noteworthy characteristic of the films of the present invention is that they exhibit improved tensile modulus, mechanical strength, and the most significantly of all, excellent barrier properties towards both water vapor and oxygen at 100%
relative humidity after being stretched five or more times its original length uniaxially in either machine direction or transverse direction.

Water vapor transmission rate (WVTR) may be via the procedure set forth in ASTM F1249. In the preferred embodiment, the multilayered film according to this invention has a WVTR of from about 0.001 to about 0.05 gm/100 in2/day per mil thickness of PCTFE, preferably from about 0.002 to about 0.02 gm/ 100 in2/day 25 per mil thickness of PCTFE, and more preferably from about 0.002 to about 0.01 gm/100 inZ/day per mil thickness of PCTFE. For example, a three layered film having a PCTFE/adhesive layer/ polyolefin layer structure which is oriented six times its original length in the machine direction possesses a WVTR of 0.0051 gm/100 inz/day per mil thickness of PCTFE which is 200% better than the unoriented equivalent sample (WVTR 0 01. 7 ~ml l00 in''/day per mil thickness) and almost 100% better than an equivalent film sample stretched only three times its original length (0.0098 gmI100 in2/day per mil thickness.
Oxygen transmission rate (OTR) may be via the procedure of ASTM D-3985 using an OX-TRAM 2120 instrument manufactured by Modern Controls, Inc., operated at 73 °F, 90% RH. In the preferred embodiment, the multilayered film according to this invention has an OTR of from about 0 1 to about 10 cc/ 100 in~/day per mil thickness of PCTFE, preferably from about 0 5 to about 5 cc1100 in~/day per ml!
to thickness of PCTFE, and more preferably from about 0 5 to about 3 cc/100 in2/day per mil thickness of PCTFE. The following non-limiting examples serve to illustrate the invention EXAMPLES
is The operation of the laboratory film stretcher employed in all of the following examples is based on the movement of two draw bars at right angles to each other upon hydraulically driven rods. These pairs of draw bars, to which the four edges of a film specimen are attached, form the two axes at right angles to each other along which a specimen is stretched in any desired stretch ratio Films can be 2o stretched in one or both directions independently or in both directions simultaneously. The stretching may be done at any selected constant rate adjustable from 0.51 to 50.8 cm per second or at any constant force from zero to I 1 3 kg per inch of edge before stretching. Nominal sample size before stretching is 10 cm by cm between grips for stretching under 4 times original size For stretching 25 between 4 times and 7 times original size, the sample size is 6 cm x 6 cm.
Specimens may be heated in a controlled manner during the stretching cycle, similar to the commercial tenter oven The following examples employed a constant stretch rate of 25.3 cm per second and a stretch temperature at 90 -100 °
C with six seconds pre-heating at a temperature within the same range WO 97!48553 PCTIUS97/09170 PCTFE homopolymer (HP)(390,000 M. W., density: 2 1 I gmlcc; melting temperature: 211 ° C; Zero Strength Test (A,STM D1430): 128, manufactured by AlliedSignal Inc. under the tradename Aclon " I-IP 128), was heated for four hours at 121 °C for drying, and then extruded through a 3.2 cm ( 1 l l4") diameter Killion single screw extruder (L/D=2411 ) equipped with three heating zones and two adapters The extruder temperature profile eras set at 277 ° C, 282 ° C, and 288 °
C for the zones 1 - 3, and the adapters were maintained at 288 ° C
The melt to temperature was measured at 286 ° C. After passing the extrudate through a coextrusion film die maintained at 282 ° C, it was cast on a roller maintained at 38 ° C, followed by a cooling roller set at 38 ° C The resultant film had a thickness of 25 ~tm although other films with various thic:knesses up to I50 um were also made Immediately after casting, the films were stretched ofI=line in a T M Long t5 laboratory stretcher set at 100 °C Cast film samples were cut to either 10 cm x l0 cm or 6 cm x 6 cm, depending on the intended stretching ratio These film samples were then Loaded into the laboratory stretcher equipped with grips along all four edges. After six seconds of preheating, the samples were then stretched to a desired stretch ratio, which was preset on the draw bar in the stretcher before the 2o experiment Films so obtained were then tesoed for various mechanical and physical properties as illustrated in Tables 1 and 2 In all attempts to stretch monolayer PCTFE homopolymer greater than three times its unstretched length, the film always fibrilated and ultimately broke.
EXAMP1:.E 2 A five layer laminate was coextruded using the PCTFE HP of Example I , a polypropylene) copolymer with polyethylene (melting temperature 148 °C;
melt flow rate MRF (ASTM D1238): 1.9 gm/10 min at 230 ° C, 3 2 % ethylene WO 97!48553 PC'T/US97I09170 content, manufactured by Shell Chemical Co under the tradename 6E20), and a malefic anhydride modified polyolefin tie resin (density: 0.88 gmlcc melt index 1 0 gmll0 min at 190 ° C, manufactured by Mitsui Petrochemical Industries, Ltd under the tradename "Admer") to make they following structurev poly(propylene)ltie resinIPCTFE HP/tie resin/ poly(propyiene) polypropylene) copolymer was extruded through a 3.8 cm ( 1112") diameter Killion single screw extruder (L/D=24/ 1 ) equipped with three heating zones and two adapters. The extruder temperature profiles were set at 238 ° C, 249 ° C, 260 to ° C for the zone 1 -3 and the adapters were' maintained at 260 ° C. The melt temperature was 256 ° C The malefic anhydride modified tie resin was extruded through a 3 2 cm { 1 1/4") diameter Killion single screw extruder equipped with four heating zones and twa adapters. The extruder temperature profiles were set at 238 ° C, 249 ° C, 260 ° C, 266 ° C for the zone l-4 and the adapters were maintained at 266 ° C. The resulting melt temperature was 263 °
C. The fluoropolymer was extruded following the same procedures described in Example The five layer extrudate, after passing through a coextrusion multilayer film die 2o maintained at 282 °C, was then cast on a roller kept at 38 °
C, followed by a cooling roll set at 38 ° C The resultant film had a thickness of 25 ~m although other films with various thicknesses up to 233 um were also made. Immediately after the casting the films were stretched according to the method set forth in Example 1. The post-stretching layer thickness of the PCTFE homopolymer layer is about 38% of the total thickness, while the poiy(propylene) layers and the tie layers consist of the remaining 62% of the; total post-stretching thickness In order to make direct comparison in the test properties, the PCTFE homopolymer layer was then carefully separated from the other layers in the multilayer film without any distortion or dimensional change .l3 This example illustrates that the PCTFE film, when coextruded with the tie and polypropylene layers can be stretched more than five times uniaxially in either machine direction (MD) or transverse direction (TD) with great ease without film breakage. The tensile modulus of the PCTFI~ film, when stretched more than five times its original length, is significantly higher than its counterparts as shown in Table I. As shown in Table II, the WVTR for PCTFE films oriented six times their original length in the MD was 0.0051 gm/100 inz/day per mil thickness of PCTFE, which is 200% better than the unoriented sample and almost 100% better than the to PCTFE film sample stretched only three times its original length t4 WO 97/48553 PCT/US97l09170 MECHANICAL PROPERTIES OF ORIENTED PCTFE HOMOPOLYMER
SAMPLE TENSILE MODULUS' ~', DEGREE OE EX.

MPa (psi) CRYSTAL-LINITYt2' (%) Cast Monolayerl OS4. l7 x 106 ( 36.3 1 153,0(10) PCTFE

Cast Five-Layer1067 95 x 10'' ( 1 38 0 SS,000) PCTFE

2X MD I 371.1 l x 106 ( 42 4 1 and 199,000) 2 3X MD 1722.5 x 106 (250,000)43 1 l and

2 4X MD 1860.3 x 106 (270,000)45.1 2 SX MD 241 I S x 10~ (350,000)4S. l 2 SX MD 2053.22 x 106 (298,000)45 6 '_' 6X MD 2618.2 x 106 (380,000)46.0 2 6X MD 2259.92 x 106 (328,000)45 5 7X MD 2232.36 x 106 (324,0()0)47.2 2 «' Tensile modulus in the direction stretched. For cast film samples, tensile modulus was measured in the machine direction (MD) using ASTM D-882 ~z' Degree of crystallinity determined by Differential Scanning Calorimetry (DSC).
DSC scans were obtained on a TA 9900 Automated DSC unit A 10 0 ~ 0 2 mg sample was crimped in an aluminum pan amd heated at a rate of SO °C/min in an to argon atmosphere. A DSC crystalline index was calculated from the ratio of the corrected heat of melting, ~H,", and the heat of fusion, ~Hm = 43 Jlg of a 100%
crystalline PCTFE.
~;5 TABLE: 2 BARRIER PROPERTIES OF ORIENTED PCTFE HOMOPOLYMER
SAMPLE WVTR~3', gm OTR'3', cc mi1/100EXAMPLE

mi1/100 in~lday inz/day at 73F, at 90%

100F, 100% RH RH

Cast PCTFE 0.017 4.7 1 and Homopolymer (control) 2X TD 0 01 14 3.8 1 and 3X TD 0.0098 3 2 I and 6X TD 0.005 i 2 7 ' ~" Both WVTR and OTR were measured in a MOCON instrument according to ASTM Test Method F 1249, the results of which are based on per mil thickness of PCTFE
Thus it can be seen that the uniaxiai orienta.bility of PCTFE film can be increased to l0 attain seven times in either the MD or TD through its coextrusion with poiyoleftns.
As illustrated in Table I, not only the tensile modulus, but also the degree of crystallinity of the coextruded PCTFE films significantly improved The degree of crystallinity of all films ranged from 36% to 49%, a significant increase as one increases the orientation ratio. As illustrated in Table 2, the barrier properties t5 improve significantly as the stretch ratio increases More specifically, the WVTR
for a six-time MD oriented film sample, at (0.005 I gm/ l00 in~/day per mil thickness of PCTFE) was 30% lower than the WVTR for the unoriented control film (0.017 gm/100 inz/day per mil thickness of PCTFE). This level of moisture barrier is the best ever known for a thermoplastic material, approaching the barrier 2o properties of the metal and glass, which are considered impermeable The OTR
t5

3 PCTlUS97l09170 was also dramatically reduced by about 57 °i° , from 4.7 cc/100 in2lday per mii thickness of PCTFE for the unoriented film sample to 2.7 cc/100 in2/day per mil thickness of PCTFE at SS °C and 90% RH for the sample oriented six times it original length.
#68266v2 t~

Claims (16)

What is claimed is:

1. A multilayer film which comprises at least one fluoropolymer layer and at least one polyolefin layer comprising at least one polyolefin homopolymer, polyolefin containing copolymer or blends thereof, attached to a surface of the fluoropolymer layer by an intermediate adhesive layer comprised of at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof, which film has been uniaxially stretched at least five times in one linear direction, and wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have a viscosity of less than or equal to about 10,000 Pascal seconds at a temperature in the range of from about 280°C to about 400°C; said film being prepared by coextruding the fluoropolymer layer, the layer of a polyolefin homopolymer or a polyolefin containing copolymer and the intermediate adhesive layer at a temperature of from about 280°C to about 400°C; casting the film and then stretching the film at least five times in either its longitudinal or transverse direction; and wherein each fluoropolymer layer, adhesive layer and polyolefin layer have on average per square meter of film no embedded particles having a diameter of greater than about 800µm, no more than about 22 particles having a diameter of from about 400 to about 800µm, no more than about 215 particles having a diameter of from about 200 to about 400µm and no more than about 538 particles having a diameter of from about 100 to about 200µm.

2. The multilayer film of claim 1 further comprising another layer of a polyolefin homopolymer or a polyolefin containing copolymer attached to another surface of the fluoropolymer layer by another intermediate adhesive layer comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof; said film being prepared by coextruding each fluoropolymer layer, each layer of a polyolefin homopolymer or a polyolefin containing copolymer and each intermediate adhesive layer at a temperature of from about 280°C to about 400°C;
casting the film and then stretching the film at least five times in either its longitudinal or transverse direction; and wherein each fluoropolymer layer, adhesive layer and polyolefin layer have on average per square meter of film no embedded particles having a diameter of greater than about 800µm, no more than about 22 particles having a diameter of from about 400µm to about 800µm, no more than about particles having a diameter of from about 200 to about 400µm and no more than about 538 particles having a diameter of from about 100 to about 200µm.

3. The multilayer film of claim 1 further comprising another layer of a fluoropolymer attached to another surface of the layer of the polyolefin homopolymer or polyolefin containing copolymer by another intermediate adhesive layer comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof; said film being prepared by coextruding each fluoropolymer layer, each layer of a polyolefin homopolymer or a polyolefin containing copolymer and each intermediate adhesive layer at a temperature of from about 280°C
to about 400°C; casting the film and then stretching the film at least five times in either its longitudinal or transverse direction; and wherein each fluoropolymer layer, adhesive layer and polyolefin layer have on average per square meter of film no embedded particles having a diameter of greater than about 800µm, no more than about particles having a diameter of from about 400 to about 800µm, no more than about 215 particles having a diameter of from about 200 to about 400µm and no more than about 538 particles having a diameter of from about 100 to about 200µm.

4. The multilayer film of claim 1 wherein the fluoropolymer is selected from the group consisting of chlorotrifluoroethylene homopolymers, chlorotrifluoroethylene containing copolymers and blends thereof.

5. The multilayer film of claim 1 wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have on average per square meter of film no more than about 0.36 embedded bubbles having a diameter of greater than about 3100µm, no more than about 22 bubbles having a diameter of from about 1500 to about 3100µm, and no more than about 161 bubbles having a diameter of less than about 1500µm.

6. The multilayer film of claim 1 wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have a viscosity of from about 3,000 to about 10,000 Pascal seconds at a temperature in the range of from about 280°C to about 400°C.

7. The multilayer film of claim 1 wherein the fluoropolymer is a poly(chlorotrifluoroethylene) homopolymer.

8. The multilayer film of claim 1 wherein the fluoropolymer is a poly(chlorotrifluoroethylene) containing copolymer.

9. The multilayer film of claim 1 wherein the polyolefin layer is selected from the group consisting of poly(propylene), poly(ethylene), poly(butylene), copolymers containing a polyolefin and mixtures thereof.

10. The multilayer film of claim 1 wherein the unsaturated carboxylic acid or anhydride is maleic anhydride.

11. The multilayer film of claim 1 which has been uniaxially stretched in its longitudinal direction.

12. The multilayer film of claim 1 which film has been uniaxially stretched in its transverse direction.

13. The multilayer film of claim 1 which has been uniaxially stretched from at least 5 times to about ten times in either its transverse or longitudinal direction.

14. A method of producing an oriented, multilayer film which comprises coextruding at least one layer of a fluoropolymer, and at least one layer of a polyolefin homopolymer or a polyolefin containing copolymer attached to a surface of the fluoropolymer layer by a coextruded intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride, wherein said coextruding is conducted at a temperature of from about 280°C to about 400°C; casting the film and then stretching the film at least five times in either its longitudinal or transverse direction.

15. A method of producing an oriented, multilayer film which comprises laminating at least one layer of a fluoropolymer to the surface of a polyolefin layer comprising a polyolefin homopolymer or a polyolefin containing copolymer by an intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid anhydride and then stretching the film article at least five times in either its longitudinal or transverse direction; wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have a viscosity of less than or equal to about 10,000 Pascal seconds at a temperature in the range of from about 280°C to about 400°C; and wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have on average no embedded particles having a diameter of greater than about 800µm, no more than about 22 particles having a diameter of from about 400 to about 800µm, no more than about 215 particles having a diameter of from about 200 to about 400µm, and no more than about 538 particles having a diameter of from about 100 to about 200µm per square meter of film.

16. An article which comprises a thermoformed film which comprises at least one fluoropolymer layer and at least one polyolefin layer comprising at least one polyolefin homopolymer, polyolefin containing copolymer or blends thereof, attached to a surface of the fluoropolymer layer by an intermediate adhesive layer comprised of at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof, which film has been uniaxially stretched at least five times in one linear direction, and wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have a viscosity of less than or equal to about 10,000 Pascal seconds at a temperature in the range of from about 280°C
to about 400°C; and wherein each fluoropolymer layer, adhesive layer and polyolefin layer have on average per square meter of film no embedded particles having a diameter of greater than about 800µm, no more than about 22 particles having a diameter of from about 400 to about 800µm, no more than about 215 particles having a diameter of from about 200 to about 400µm and no more than about 538 particles having a diameter of from about 100 to about 200µm.