IE914253A1 - Process for fabricating oriented polybenzazole films - Google Patents

Abstract

Films containing polybenzazole polymer dissolved in a solvent can be mechanically stretched to provide biaxial orientation. The resulting dope film can be coagulated. The polymer film has improved properties in the direction in which stretching occurs.

Description

PROCESS FOR FABRICATING ORIENTED POLYBENZAZOLE FILMS This invention relates to films oontaining polybenzazole polymers and processes for making them.

Polybenzazole polymers are typloally ς synthesized by polymerization in non-oxidizing dehydrating acid solutions to form visoous dopes containing the aotd and the polymer. Uniaxially oriented film may be synthesized from dope by extruding in onto a rotating drum that draws the film in the maohlne direction and rotates it down into a water bath to coagulate. Biaxially oriented films are synthesized by extruding the dope as a tube, which is blown or forced over a mandrel to impart some biaxial orientation, and is then immersed in water to ooagulate it. Examples of such processes are described in: Chenevcy, U.S. Patent 4,487,735 (December 11, 1984); Luslgnea et al., U.S. Patent 4.871,595 (Ootober 3» 1989); Chenevcy, U.S.

Patent 4,898,924 (February 6, 1990); Harvey et al., U.S. ?0 Patent 4,939,235 (July 3, 1990); Harvey ot al., U.S. Patent 4,963,428 (Ootober 16, 1990); Luslgnea et al., U.S. Patent 4,966,806 (October 30, 1990)> and Fujiwara, Japanese Kokai 63(1988)-74612 (published April 5, 1988). 39,489-F -1IE 914253 •2Improvements are needed in the processes for making polybenzazole films. Films made by the previously described prooesses tend to have very inconsistent gauge thickness. The biaxial orientation is less than complete, so that films still tend to have $ better properties in the machine direction and poorer properties in the transverse direction.

A further disadvantage of existing prooesses is that they Inherently oreate a multi-layered film. Each layer may oontain the same polymer, but molecules within the crystalline domains are oriented in a different direotion in eaoh layer. The different layers are subject to delamination from eaoh other.

An object of the invention is to find an improved prooess that can improve any one of: tho guage control of the polybenzazole film; the control over degree of orientation ln the polybenzazole film; or the delamination resistance of the polybenzazole film.

One aspect of the present invention is a process for making a polybenzazole film or sheet that has the steps oft (1) extruding a dope, that oontains a solvent and a polybenzazole polymer, to form a dope film or sheet; (2) stretching the dope film or sheet in the transverse direotion at a temperature and a rate at whioh the dope film or sheet does not tear; and (3) ooagulating the stretched dope film or sheet* whereby a polymer film or sheet is formed, 39,489-F -3Characterized In that the dope film ie stretched meohanioally using a device that grips the transverse edges of the dope film or sheet and draws the transverse edges apart from eaoh other. g A second aspect of the present Invention is a film or sheet that contains a lyotropic liquid orystalllne polybenzazole polymer and that has a tensile strength of at least 35 Ksi (241 MPa) in both the meohine dlreotion and the transverse direotion, oharaoterieed in that the crystalline domains on the faces of the film or sheet are not oriented in opposite uniform angles of + or - 0 with respect to the machino direction.

As used in this application, the term ”transverse means approximately at right angles with respect to the maohine dlreotion in whioh the dope film or sheet was extruded. 1 Ksi * 1000 psi} and 1 Ms! ® 2Q 1,000,000 psi.

The meohanioally stretched films and sheets may be used in structural materials or eleotronlc components as described in U.S. Patent 4,871,595 (October 3« 1989) and 11 Ency. Poly. Sol. A Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley A Sons 1988)· The present invention uses dopes containing 30 polybenzazole (PBZ) polymer. The polybenzazole polymer is preferably polybenzoxazole (PBO) or polybenzothiazole (PBT) or oopolymers thereof, dissolved in a solvent.

PBO, PBT and random, sequential and blook copolymers of 39,489-F 3IE 914253 -4PBO and PBT are described in references such as Wolfe et al., Liquid Crystalline Polymer Compositions Prooess and Products, U.S. Patent 4,703,103 ((JctoDer 27, 1987) ι Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Produots, U.S. Patent 4,533.692 (August 6, 5 1985); Wolfe et al., Liquid Crystalline Poly(2.6-Benzothlazole) Compositions, Process and Products. U.S. Patent 4,533,724 (August 6, 1985)f Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Patent 4,533,693 (August 6, 1985); Evers, Thermoxada10 tively Stable Artloulated p-Benzoblsoxazole and p-Benzoblsthlazole Polymers, U.S. Patent 4,359,567 (November 16, 1982)? Tsai et al., Method for Making Heterocyclic Block Copolymer. U.S. Patent 4,578,432 (Maroh 25, 1986); 11 Ency. Poly. Sol. & Eng., Polybenzothiazoles and Polybengoxazoles. 601 (J. Wiley & Sons 1988) and W. W. Adams et al., The Materials Solence and Engineering of Rigid-Rod Polymers (Materials Research Society 1989).

The polymer may contain AB-PBZ men units, as represented in Formula 1(a), and/or AA/BB-PBZ mer unite, as represented in Formula 1(b) 1(a) AB 39,489-F wherein: Each Ar represents an aromatio group. The aromatio group may be heterooyclio, suoh as a pyridlnylene group, but it is preferably carbooyolic. The aromatic group may be a fused or unfused polyoyolie system, but is preferably a Single six-membered ring. Slee is not critical, but the aromatio group preferably oontalns no more than 18 carbon atoms, more preferably no more than 12 oarbon atoms and most preferably no more than 6 oarbon atoms. Examples of suitable aromatic groups inolude phenylene moieties, tolylene moieties, Diphenylene moieties and bis-phenylene ether moieties. Ar1 in AA/BB-mer units is preferably a 1,2,4,5-phenylcne moiety or an analog thereof. Ar in AB-mer units Is preferably a 1,3,4-phenylene moiety or an analog thereof.

Eaoh I is independently an oxygen or a sulfur atom. 3q Each DM is independently a bond or a divalent organio moiety that does not interfere with the synthesis, fabrication or use of the polymer. The divalent organic moiety may contain an aliphatlo group, which preferably has no more than 12 oarbon atoms, but the divalent organic moiety is preferably 39,489-F -5IE 914253 an aromatio group (Ar) aa previously described, it is most preferably a 1,4-phenylene moiety or an analog thereof.

The nitrogen atom and the 2 moiety in each azole ring are bonded to adjaoent oarbon atoms in the aromatio group, such that a five-membered aeole ring fused with the aromatic group is formed.

The azole rings in AA/BB-mer units may be in cis- or trans-position with respeot to each other, as illustrated in 11 Ency. Poly. Sol. & Eng., supra. at 602.

The polymer preferably consists essentially of either AB-PBZ mer units or AA/BB-PBZ mer units, and more preferably oonsists essentially of AA/BB-PBZ mer units.

The polybenzazole polymer may be rigid rod, semi-rigid rod or flexible ooil. it is preferably rigid rod in tho case of an AA/BB-PBZ polymer or semi-rigid in the case of an AB-PBZ polymer. It is preferably a lyotroplo 2Q liquid-crystalline polymer.

Azole rings within the polymer are preferably oxazole rings (Z s 0), so that the polymer is a polybenzoxazolc polymer. Preferred mer units are illustrated in Formulae 2 (a)-(h). The polymer more preferably oonsists of mer units selected from those illustrated in 2(a)-(h), and most preferably consists of identioal mer units selected from these Illustrated in 2(a)-(d). 39,489-F 39.489-F 7IE 914253 Each polymer preferably oontains on average at least 25 mer units, more preferably at least 50 mer units and most preferably at least 100 mer units. The intrlnsio viaoosity of rigid AA/BB—PBZ polymers in methanesulfonio aoid at 25*C is preferably at least 10 dL/g, more preferably at least 15 dL/g and most preferably at least 20 dL/g. For some purposes, an intrinsic viscosity of at least 25 dL/g or 30 dL/g may be best. Intrlnsio viscosity of 60 dL/g or higher is possible, but the intrlnsio viscosity is preferably no mere than 40 dL/g. The intrlnsio visoosity of semi3θ rigid AB-PBZ polymers is preferably at least 5 dL/g, more preferably at least 10 dL/g and most preferably at least 15 dL/g.

The polymer or copolymer is dissolved in a solvent to form a dope solution. Some polybenzoxazole 39,489-F 8IE 914253 -9and polybenzothiazole polymers are soluble in cresol, but the solvent Is preferably an aoid capable of dissolving the polymer. The aoid is preferably non-oxidizing. Examples of suitable acids inolude polyphosphorio acid, methanesulfonlo acid and sulfuric 5 aoid, and mixtures of those acids. The aoid is preferably polyphosphorio aoid or methanesulfonic acid, and is more preferably polyphosphorio acid.

The dope should contain a high enough concentration of polymer for the polymer to coagulate to form a film of the desired thickness without substantial flaws. When the polymer is lyotropic llquldorystalline, then the concentration of polymer in the dope is preferably high enough to provide a dope having 15 liquid crystalline domains. The concentration of the polymer is preferably at least 7 weight peroent, more preferably at least 10 weight peroent and most preferably at least 14 weight percent. The maximum concentration is limited primarily by praetlaal factors, suoh as polymer solubility and dope viscosity. The concentration of polymer Is seldom more than 30 weight percent, and usually no more than 20 weight peroent.

Suitable polymers or copolymers and dopes can be synthesized by known procedures, suoh as those described in Wolfe et al., U.S. Patent 4,533,693 (August 6, 1985)J Sybert et al., U.S. Patent 4,772,678 (September 20, 1968)} Harris, U.S. Patent 4,847,350 (July 11, 1989)» and Ledbetter et al., An Integrated Laboratory Prooess for Preparing Rigid Rod Fibers from the Monomers, The Materials Sclenoe and Engineering of Rigid-Rod Polymers at 253-64 (Materials Res. Soo. 19Θ9)· In summary, suitable monomers (AA-monomers and BB39,489-F -10monomers or AB—monomers} are reaoted in a solution of nonoxidizing and dehydrating aoid under nonoxidizing atmosphere with vigorous mixing, and high shear at a temperature that Is inoreasea ln step-wise or ramped fashion from no more than 120°C to at least 19O*C. Examples of suitable AA-monomers include terephthalio acid and analogs thereof. Examples of suitable BBmonomers Include 4,6-diaminoresorcinol, 2,5diaminohydroquinone, 2,5-diamino-1,4-dlthiobenzene and analogs thereof, typically stored as aoid salts.

Examples of suitable AB-monomers Include 3-amino-4hydroxybenzoio acid, 3whydroxy-4-aminobenzoio aoid, 3-amino-4-thiobenzoie aoid, 3-thio-4-aminobenzoio aoid and analogs thereof, typically stored as aoid salts.

The present invention oonverts dopes into polymer films by a three-step prooess. In the first step, the dope is extruded as a dope film or sheet which Is relatively thick and is relatively narrow in the 2Q transverse direotion, as compared with the final desired film. The extrusion may optionally be through a slit die, such as a ooathanger die or τ-die, or through a tubular die, such as the counter-rotating die described in the previously-named references. An example of extrusion techniques is described in Chenevey, U.S. Patent 4,487,735 (Deeember 11, 1984).

The extrusion die preferably does not contain opposing surfaoes that move in relation to eaoh other 3° during extrusion to orient different layers of the film ln different discrete direotions, in the manner taught in U.S. Patents 4,487,735 and Harvey et al., U.S. Patent 4,939,235 (July 3, 1990). In other words, the die preferably does not subject the faoes of the dope film 39,489-F 10IE 914253 to transverse shear foroes during extrusion. The opposing surfaces moving with respect to eaoh other are reported to orient the nematic polyAer molecules at the surface of the film in opposite uniform angles defined as + or - Θ. The angle 6 is reportedly broadened by later steps in the process, so that the film or sheet oontains discrete layers with moleoules oriented in different directions. Those layers are undesirable because they increase the susceptibility of the film or sheet to delamination. The preferred dies also do not apply the twisting force and orientation that is applied by an anular die in which one surface rotates.

The extruded dope film is preferably left as a continuous sheet, rather than cutting into discrete sections. The dope film should not be coagulated. The dope film preferably does not contain dlsorete layers with different orientations. 2Q Optimal extrusion temperature varies aooording to many factors such as the solvent, polymer rigidity, moleoular weight and concentration, and dope viscosity. It should be high enough that the dope flows through the die well, and low enough that the dope is stable and handlable. It may be between 0eC and 300*C. The extrusion temperature for liquid crystalline dopes of about 14 weight percent cls-polybenzoxazole in polyphosphoric aoid is preferably at least 100*C, more preferably at least 130°C, and most preferably at least 3° 17O”C. It is preferably no more than 260eC, more preferably no more than 230*C and most preferably no more than 200*C. 39,489-F 11IE 914253 12The dope film or sheet should be thick enough that it oan be stretched as desired without leaving flaws after ooagulation. The optimuim thickness varies considerably depending upon the desired thickness of the final product and the desired stretch from the second step of the prooess. For most purposes, the dope film or sheet is preferably at least 1 mil thick, more preferably at least 5 mil thick and most preferably at least 25 mil thick. The dope film or sheet is preferably no more than 250 mil thiok and more preferably at most 100 roil thick. (Ordinarily, the term ’’film refers to an article no more than 10-15 mil thick, and the term sheet refers to an artiole at least 10-15 mil thick. In the interest of brevity, this Application shall use the term film to refer to both film and sheet.) it may optionally be desirable to extrude the dope film between two layers of a stretchable polymer 20 film which is inert with respect to the dope under process conditions. Examples of a suitable polymer film include Teflon™ fluorocarbon film and amorphous polyester film. The outer layers protect the dope from the atmosphere and prevent it from adhering Itself or other objeots if the dope is stored after extrusion.

In the seoond step, the dope film is mechanically stretched in at least the transverse direction. A mechanical device grips the transverse 3° edges of the dope film and pulls the transverse edges apart. The dope film may also be stretched in the machine direction and/or in any other direction. If the dope is stretched in multiple directions, then the stretching may be in a single direction at a time or may 39,489-F 12IE 914253 -13be simultaneous in two or more directions. Ordinarily, stretohing increases the tensile strength and modulus of the finished film in the direction Stretohed, but slightly deoreases those same properties perpendicular to the directions stretched.

Individual sheets of dope film may be stretched in a batoh fashion using commercially available equipment suoh as the T.M. Long” Film Stretcher, available from T.M. Long Co. Meohanical stretching is preferably carried out on a tentering apparatus, which continuously stretches a oontinuous dope film.

The dope film is tentered in a manner similar to known thermoplastic polymers. Ordinarily, the dope film travels continuously through a tenterlng devioe. Near the front of the device, gripping means such as clips grip the transverse edges of the dope film. As the dope film travels through the tentering device, the 2q gripping means move further apart, drawing the transverse edges of the dope film further apart. The tentering device may have zones, in whloh no stretohing occurs, before and/or after the stretohing zone.

Examples of tenterlng equipment and procedures are described in numerous literature references, such as Young, U.S. Patent 2,473,404 (June 14, 1949)ί Minioh, U.S. Patent 2,334,022 (November 9, 1943)1 Milne, U.S. Patent 2,618,012 (November 18, 1952); Tomlinson, U.S. Patent 3,571,846 (March 23, 1971); Levy et al., U.S. 3° Patent 4,104,769 (August 8, 1978) and Kwack, U.S. Patent 4,862,564 (September 5, 1989). Tenterlng devioes are also oommeroially available from souroes suoh as Marshall & Williams Co., Bruokner Maohinery Corp., and Crown Products. The materials that oome in contaot with 39,489-F -u dope ahould ba Inert with respeot to the dope under process conditions.

Some tentering machines are known whioh can simultaneously stretch film in the maohine direotion and the transverse direction. Alternatively, equipment that stretches film in the maohine direotion, suoh aa a series of rollers moving at different speeds, may be plaoed on the film line before or after the tenterlng apparatus.

Stretohing transversely improves the transverse tensile properties of the film after the dope is ooagulated. The transverse tensile strength and modulus lnorease with greater stretch, and the machine direotion tensile strength and modulus decline slightly with greater transverse stretch (except when the dope ie also stretched in the maohine dlreotion). The extruded film is preferably stretched to at least 1.5 times its 2Q original transverse width, more preferably at least 2 times, highly preferably at least 3 times, and more highly preferably at least 4 times and most preferably at least 5 times. The same preferred stretch applies to stretching in the machine direction. The maximum stretch is limited by the strength of the dope film or sheet, in most cases, it will be no more than about 50 times the original width of the dope film.

Stretching should be oarried out at a 3° temperature and at a rate at which the dope film can stretch without tearing. Liquid crystalline dope films containing polymer dissolved in polyphosphorie aoid may exhibit a phase change similar to a glass-transition temperature. The temperature of stretohing is 39,489-F -14IE 914253 -15preferably not below 5eC to 10*C below the glasstransition temperature, and is more preferably at least the glass transition temperature. The maximum temperature of atretohing should be low endugh that the dope film is stable. It is preferably low enough to minimize $ sagging of the dope film during stretching. The temperature of stretching ls preferably no more than 105*C above the glass-transition temperature of the dope, more preferably no more than 55‘C above and most preferably no more than 5’C above.

For liquid orystalline dopes containing polyphosphoric aoid (82 percent to 83 peroent F2O5) and 14 weight percent rigid rod polybenzoxazole or polybenzothiazole, the temperature for tenterlng is 15 preferably at least 20eC, more preferably at least 50°C and most preferably at least 75’C. It is preferably at most 175°C, more preferably at most 150’C and most preferably at most 125°C. The optimal rate of 2q atretohing varies widely depending upon a number of factors suoh as polymer struoture, molecular weight and concentration, solvent acid, ano dope temperature. It oan best be determined by experiment.

In the third step, the stretched dope film is ooagulated to yield a polybenzazole film. Ordinarily the stretched dope film is ooagulated by oontaoting the film with a liquid that is a nonsolvent for the polymer and a diluent for the solvent. The coagulating liquid may be organic, suoh as methanol, but it is preferably aqueous. The aqueous coagulant may be basic or slightly acidic, but ls preferably neutral. If the dope was extruded and stretohed between water-impermeable polymer face films, then the films should be stripped off of at 39,489-F -16least one side before ooagulating. If the dope was extruded end tentered between water-permeable films, then the entire structure may he Immersed to initially coagulate the film, although at leadt one face sheet Is preferably stripped off arter the initial coagulation in order to facilitate washing out residual solvent.

If the solvent oontains a volatile component, such as methanesulfonic acid, then the polymer may optionally be concentrated by evaporating the solvent.

Preferably, the volatile component Is not stripped off to the point that the polymer coagulates. Instead, the conoentrated dope is still preferably contacted with a nonsolvent to ooagulate the polymer.

After ooagulatlon the polybenzazole film is preferably washed for a period of time to substantially remove residual solvent. It is preferably dried under restraint to prevent it from curling or shrinking.

The coagulated film cay optionally be densified by heat treatment. The heat treatment is preferably under pressure. It is preferably at a temperature of at least i50*c, and more preferably at a temperature of at least 250’C.

The previously described steps may be integrated into a single continuous prooess in whloh the dope is extruded to form an extruded film, the extruded 3° film passes into a tentering maohine, and the tentered film is ooagulated within the tentering maohine or afterwards. The continuous process might optionally further oontain an apparatus to stretch the dope film in the maohine direction before or after tentering. 39,489-F -16IE 914253 -IT Alternatively, one or more of the steps may be broken apart from the others. For instance, the extruded film may be taken up on a roll and stored until ready for tenterlng. The tentered film may be stored or further processed before coagulation. Two or more layers of tentered film may be pressed together to form a thicker sheet before ooagulatlng. Reinforcing fibers may be pressed into a tentered film before ooagulation to form a prepreg. A tentered film may be plaoed over a mold or form before ooagulation.

The film reoovered from the present prooess contains polybenzazole polymer as previously described, and preferably consists essentially of polybenzazole polymer. It may be very thin, for instance suitable for membrane purposes, or thioker to be suitable for structural purposes. It is preferably at least 0.1 mil thick, and more preferably at least 0.2 mil thiok. It preferably has an average thickness variation of no more 2Q then 5 peroent, more preferably no more than 0.5 percent.

The optimal properties of the finished polybenzazole film will vary depending upon its intended use. The average tensile strength of the polymer film in the transverse direction is preferably at least 35 Ksi {240 Mpa), more preferablyat least 50 Ksi (345 Mpa), more highly preferably at least 70 Ksi (480 MPa), and most preferably at least 100 Ksi (690 MPa). The average 3° tensile strength Of the polymer film in the machine direction has similar preferred embodiments In a relatively balanced film. 39,489-F -17IE 914253 18The average tensile modulus of a relatively balanoed film in the maohine and transverse directions is preferably at least about 3 Msi (21 GPa), more preferably at least about 5 Msi (3^ GPa) and most preferably at least about 7 MPa (48 GPa). Films have j been made having even higher moduli in either the transverse or maohine direction, but not In both.

One reason that mechanical stretching is advantageous is that the degree of atretoh in eaoh direction may easily be seleoted. For instance, the film may be stretohed in the transverse direotion with essentially no stretch in the machine direotion. Alternatively, the film may be stretohed in the maohine and transverse direotlons in almost any ratio that the dope end equipment will permit, from essentially equal to muoh greater stretch In the maohine or transverse direotlons. 2Q Because meohanioal stretching permits a wide variety of stretching, the films made using meohanioal stretching may have a wide variety of tensile properties. The tensile strength and/or tensile modulus of the film may be at least as high in the transverse direction as it is in the maohine direotion. For insfeanoe, the average tensile strength and/or tensile modulus in the machine and transverse directions of a film with balanced properties preferably differ by no more than 10 percent, and more preferably differ by no 3° more than 5 percent. Alternatively, the tensile strength or modulus may be substantially higher in either the maohine direotion or the transverse direotion in a film with unbalanced properties. Films made using a slit die and the ourrent process are structurally 39.489-F 18IE 914253 -19different from films made using rotating anular dies and blown bubble in the prior art process. As previously explained, films that are made by extruding a tube from a rotating or oounter-rotating die ind blowing the tube oontain discrete layers of nematic polymer that are g oriented in a uniform angle of either * or - Θ with respect to the machine direction of the polymer. Those discrete layers are theroized to give the film more biaxial tensile properties. However, the laters also make the film more susoeptibie to delamination. See Luslgnea, Film Processing and Applications for RigidRod Polymers, The Materials Science and Engineering of Rigid-Rod Polymers at 256 (Materials Research Soolsty 1989). For instance, films made by the prooesses disclosed in U.S. Patents 4,898,924; 4,939,235; ie 4,963,428; and 4,966*806 contain polymer oriented at an angle -*-6 on one faoe, polymer oriented an angle -Θ on the other faoe, and a middle layer in whioh the polymer is substantially non-orlented.

Films which are extruded through a slit die and meohanioally stretched according to the preferred prooess of this invention have biaxial tensile properties that are equivalent to the properties realized by the prior art. However, the polymer of films of the present invention is not oriented ln a uniform preferred angle of + or -Θ. Some areas of the film do not oontain a plurality of discrete layers, but are more isotropio in the z direotion. This distinction may be advantageous in minimizing curling and/or delamination of the film with changing temperature. The advantage in delamination resistance tends to be greater when the dope film is stretched less and lesser when the dope film is stretohed more. 39,489-F -19IE 914253 The preferred films of the present Invention are anisotropic in the transverse and maohine directions, unlike films that are coagulated from an isotropio dope. The preferred films are also stronger than typioal films ooagulated from isotropic dopes.

The films are useful as coatings or structural materials or membranes are eleotronio substrates.

The prooess of the present invention is more 10 specifically illustrated in the following Examples.

Illustrative Examples The following examples are given to illustrate U the invention and should not be interpreted as limiting the Specification or the Claims. Unless stated otherwise, all parts and percentages are given by weight.

Example 1 - Batch Meohanical Stretching A solution of polyphosphoric acid (85 weight percent PgOs) containing 14 weight peroent cls-polybenzoxazole (about 25-40 intrinsic visocslty in & methanesulfonic aoid at 25’C) is extruded through a 6-inoh wide slit die with a 0.005 inoh gap using a ram extruder. The barrel temperature in the extruder is 18O“C and the die temperature is 16O’C. The speed of 3Q extrusion is 6.5 cm3/min. The dope film is taken up between two films of skived polytetrafluoroethylene (PTFE) that are 0.003 inch thick. The resulting produot is a sandwich containing 0.006 to 0.007 inoh of PBO between the PTFE films. 39,489-F -20IE 914253 -21Saveral 4-3/8 inch by 4-3/8 inch samples are out from the film. The samples are placed one at a time in a T.M. Long mechanical strataher having an air temperature of about 140eC and a plat’s temperature of about 125*C. The samples are held for 30 seconds bo g equilibrate temperature, and then are stretched In the transverse direction or the machine direction or both at a rate of 2 inoh/seo. until a desired stretch ratio is achieved. The samples are cooled with an air gun and reoovered.

The PTFE films are stripped off of each side of eaoh sample. Eaoh dope film is clamped on a steel hoop and immersed in deionized water for 48 hours. Eaoh sample is then dried on the hoop at 300’C for 1.5 hour. Dog-bone shaped test samples are out from eaoh sample and tested for tensile strength and tensile modulus in the transverse direction. The test method is set out in ASTM D 682-83· The tensile measurements are made using an Instrontensile tester. The results are set out in Table 1. The batch stretohing is recognized as a good bench-scale approximation of perfurmance in a continuous tentering apparatus. 39,489-F -21IE 914253 -22TABLB 1 Transverse stretch Ratio Transverse Tensile Strength (KSI) Transverse Tensile Modulus (KSI) 111 11.7 591 151 12.4 676 1:1 12.6 671 2.0:1 15.5 811 2.5:1 21.7 1262 3.0:1 24.4 1725 3.5:1 24.4 1858 Example 2 - Batch Mechanioal Stretching of PBO Filo A dope containing 14 weight peroent rigid rod 20 nis-polybenzoxazole (I.V. 20 to 40 dL/g) and polyphosphoric acid (About 82 to 84 percent P2O5) is extruded through a six-inch slit die with a barrel temperature of l80*C and a die temperature of 160°C. The film crosses and air gap. Each dope film is sandwiched between two 25 face eheets of 15 mil amorphous polyester (PETG) (KODAR* 6763 film). The multilayer structure is taken up upon a roll at a variable speed to provide variable draw upon film across the air gap. The oonditions for 2Q extrusion are set out in Table 2(A).

The dope film is out into samples of about 4 Inches by about 4 inohes Eaoh sample ls stretched either unixlaily or biaxially on a T.M. Long film stretcher at a rate of 2 inches/seo with a plate 39,489-F -22IE 914253 -23tenperature of about 105’C and an air temperature of about 90eC, The stretching ratio in the naohine and transverse directions are set out in Table 2(A) and Table 2(B). For instance, 1 by 2 means that the sample was etretohed to 2 times its original width in the transverse direction and was not stretohed in the machine direction, whereas 3 by 3 means that the sample was stretohed to 3 times its original width In the transverse direction and to 3 times its original length in the machine direction* Stretohed samples are oooled and ooagulated.

The samples are coagulated by immersing the entire multilayer structure for about 4 hours, then stripping off the face sheets and immersing in water for 24 hours.

Dog bone shape test samples are out in both tne transverse and machine directions and tested for tensile strength and modulus as desoribed in Example 1. The results are set out In Table 2(B). 39.489-F -24TJLBLE 2(A) Sample Barrel Press. (psi) Die Press. (pai) 1 2120 650 5 2 3090 690 3 2120 650 4 2120 650 5 2240 660 10 6 2200 680 7 2120 650 8 2120 650 9 1200- 1300 230 15 10 2120 650 CO - stretoh in maohine simultaneously (3 - stretch in machine sequentially Die Gap (in.) Draw Rate (cm/min) > · Stretoh Ratio 0.010 12.15 1 by 2 0.005 20.19 2 by 2® 0.010 12.15 2 by 2® 0.010 12.15 1 by 3 0.010 63-45 1 by 3 0.010 28.70 1 by 3 0.010 12.15 3 by 3® 0.010 12.15 2 by 3.5® 0.040 6.60 3 by 5® 0.010 12.15 4 by 4® and transverse directions and transverse direotlons 39,489-F -24IE 914253 TABLE 2(B) Sample Stretoh Ratio MD Tensile Strength (KSI) TD Tensile Strength (KSI) MD Tensile Modulus ’ (MSI) TD Tensile Modulus (MSI) 1 1 by 2 60.7 38.4 3-21 2.14 5 2 2 by 2® <0.9 39.7 4.01 2.26 3 2 by 2® 6S.3 51.0 4.29 3.31 4 1 by 3 35.2 71.3 2.19 3.69 s 1 by 3 34.6 34.4 3.55 1.27 1i 6 1 by 3 42.5 43.8 3.04 2.91 7 3 by 3® 88.5 14.4 3.27 1.16 8 2 by 3.5® 46.8 41.2 2.64 2.26 9 3 by 3® 33.7 CS.l 3.71 4.38 I! 10 4 by 4® 17.3 46.4 2.32 4.89 ® - stretoh in maohlne and transverse directions simultaneously φ - stretch in maohine and transverse directions sequentially Example 3 - Tenterlng of PBO film A solution containing 14 weight percent polybenzoxazole in polyphosphorio acid (84 percent P2O5) is extruded through a 6-inch slit die with a 0.020-lnoh gap. The extruder temperature is 160ec, and the die temperature is 18O6C. The extrusion speed is 9.4 cm3/min. The extruded dope travels across an air gap and is taken up between two 0.015 in sheets of amorphous polyester film to form a multilayered structure.

The multilayered structure is tentered at a temperature of 85*0 to 87*C and a rate of 5 ft./min. to stretoh it 4 times in the transverse 39,489-F -25IE 914253 26direotion. The etretohed film is coagulated and dried as desoribed in Examples 1 and 2. It is heated at 300*C for 1-1/2 hours before removing from the drying hoops. The tensile properties are tested as>desoribed in Example 1. The tensile strength of the film is about 42.6 Ksi in the machine direction and about 69.9 Ksi in the transverse direction. The tensile modulus of the film is about 2.03 Msi in the maohine direction and about 4.16 Msi in the transverse direction.

Example 4 - Tenter ing of PBO film The procedure of Example 3 is followed except as followsι (1) The extruder temperature is about 16OC and the extrusion speed is about 10.2 em3/mini (2) The film is drawn to three times its original length in the machine direction before tentering by drawing between a slow draw roller moving at 4 ft./min. and a fast draw roller moving at 12 ft./min. at a temperature of about 90’C} and (3) The resulting film is tentered in the transverse direction to 5 times its width at the completion of the machine direotion stretch.

The tensile strength of the film ia about 55.7 Ksi ln the maohine direction and about 65.1 Ksi in the traneverse direotion. The tensile modulus of the film is about 3.71 Msi in the maohine direotion and about 4.36 Msi in the transverse direotion. 39,489-F -27example 5 - PBO Film A solution containing 14 weight percent polybenzoxazole In polyphoaphorio aoid (83 to 85 peroent P2O5) is extruded through a 6-Inch slit die with a 0.030-inch gap. The extruder temperature is 160’C, and E the die temperature is 16O’C. The extrusion speed is 10.2 cm3/min. The extruded dope travels across an air gap and ia taken up between two 0.003 inch thick sheets of skived PTFE to form a multilayered structure.

The multilayered structure is out into 3.5 inches by 3.5 inches squares. The PTFE sheets are removed an eaoh dope film eample is stretched simultaneously m the maohine and tranverse directions.

The stretch ratio, temperature and speed are shown in Table 3 using an Iwamoto biaxial stretcher Model No. BIX-703. Each sample is heated for 90 seoonds to the proper temperature before stretching and is quenched in water at room temperature after stretohing. The samples 2Q are clamped on 16 inch diameter steel hoops, immersed in deionized water for at least hours, dried at 95*C for 4 hours, and heated at 300’C for 1.5 hours. 39,489-F -27IE 914253 -28TABLE 3(A) Sample Strctoh Ratio Stretoh Temp (’C) Stretoh Speed (mm/sec) Polymer Film Thickness (mm) 5 11 4 by 4 101 40 690-760 12 4 by 4 139 60 580-710 13 4 by 4 135 20 690-760 14 5 by 5 135 20 610-660 10 15 5 by 5 135 20 660-810 measired The tensile properties of the films are and set out in Table 3(B). TABLE 3(B) Sam MD Tens. Str. (K5I) ID Tens. Str. (KSI) MD Tens. MOd. (MSZ) TD Tens. Mod. (MSI) MD Tens. Str. (MPa) TD Tens. Str. (MPa) MD Tens. Mod. (OPa) TD Tens. Mod. (GPa) 11 114 75.3 8.57 6.16 785 519 59.1 42.5 12 107 71 8.81 4.84 738 490 60.8 33.4 13 105 69 8.56 5.58 724 480 59.0 38.5 14 94.5 78.6 7.35 7.45 651 541 50.7 51.4 15 75.7 64.2 5.63 5.04 522 443 38.8 34.8 39,489-F

Claims (12)

1. A process for making a polybenzazole film or sheet comprising that has the steps ofi (1) extruding a dope, that oontains a solvent and a polybenzazole polymer, to form a dope film or K J sheet} (2) stretching the dopo film or sheet in the transverse direction at a temperature and a rate at which the dope film or sheet does not tear; and 10 (3) ooagulating the stretched dope film or sheet, whereby a polymer film or sheet is formed, characterized in that the dope film is stretohed mechanically using a device that grips the transverse 15 edges of the dope film or sheet and draws the transverse edges apart from each other,

2. A process as described in Claim 1 wherein the dope is extruded in Step 1 through a die that does not apply transverse shear foroeo to the faoes of the dope film.

3. A process as described in any of the 25 preoeeding claims wherein the polybenzazole polymer is a 39,489-F -29IE 914253 lyotropic liquld-orystalline polymer in a concentration in the dope suitable to fora liquid orystalline domains.

4. A prooess as described in any of the preoeeding Claims wherein the dope filo is stretohed in $ the transverse direction to at least three times its original width.

5. A process as described in any of the preoeeding claims wherein the dope film is stretohed to

6. A process as described in any of the preoeeding olaims wherein the dope film ie stretched In Step (2) using a tenterlng equipment.

7. A prooess as described in any of the preoeeding olaims wherein the solvent in the dope is 20 polyphosphorie aoid.

8. A film or sheet that contains a lyotropic liquid orystalline polybenzazole polymer and that has a tensile strength of at least 241 MPa (35 Ksi) in both 25 the machine direotion and the transverse direction, characterized in that the crystalline domains on the faces of the film or sheet are not oriented in opposite uniform angles of ♦ or - Θ with respeot to the maohine direotion.

9. The invention as desorlbed in any on the preoeeding olaims wherein the polybenzazole polymer ls a lyotropic liquid orystalline polybenzoxazole or polybenzothiazole polymer. 39,489-F -30IE 914253 -3110. Th· invention as described in any of the proceeding claims wherein the polybenzazole polymer contains ser units represented by any of the Formulae» (e) 39,489-F -31IE 914253

10. At least three times its original length in the maohine direction.

11. A process for making a polybenzazole film or sheet, substantially as described herein by way of example.

12. A polybenzazole film or sheet whenever made by a process according to any of claims 1 to 7.