JPH08504007A - Low denier polybenzazole fiber and method for producing the same - Google Patents

Abstract

  (57) [Summary] Low denier polybenzazole fibers are described. Further, a method for producing the low denier polybenzazole fiber is also described. The method is to spin a fiber through a small orifice (0.0051 cm to 0.018 cm) of a low density spin dope with a spin-draw ratio of 12-60 and then wind the fiber at least 750 km without breaking.

Description

Description: Low denier polybenzazole fiber and method for producing the same The present invention relates to a polybenzazole (PBZ) fiber and a method for producing the same. Polybenzazole fibers include polybenzothiazole (PBT) fibers or polybenzoxazole (PBO) fibers. These PBZ fibers are high performance fibers with excellent chemical resistance, thermal stability and mechanical properties. These properties have made it the material of choice for high performance textile and composite applications. By spinning polybenzazole fibers from solutions of PBZ in various solvents (see, eg, Encyclopedia of Polymer Science and Technology, Vol. 11, pp. 6 01-635) nominal diameters of 16-20 microns A fiber having is obtained. In order to be effective in certain end uses, it is desirable to produce PBZ fibers with a diameter less than 12 microns. Heretofore, it was not known how to spin PBZ fibers having a diameter smaller than 12 microns uniformly. Another way to describe small diameter fibers is to call them low denier fibers. Denier is the weight (grams) of 9,000 meters of fiber. Denier is a direct numbering system, with smaller numbers indicating finer and higher numbers indicating coarser. Since denier is a unit of weight per length and diameter is a unit of length, denier and diameter are not interchangeable units when directly comparing numbers. The equation showing that relationship for a polybenzazole fiber having 1.58 denier is: Fiber diameter (μm) = (denier / square root of filament) × 9.4625 However, the terms denier and diameter may be used interchangeably when colloquially referring to small diameter, very fine fibers. One aspect of the present invention is: (1) spinning a lyotropic liquid crystalline polybenzazole dope containing a polybenzazole polymer and a solvent through an orifice of a spinneret to form a dope fiber, wherein the diameter of the hole of the orifice is 0.18. cm or less, (2) drawing the dope fiber across an air gap of 40.6 cm or less using a spin draw ratio of 12-60, (3) most of the fiber by contact with a non-solvent. A method for producing a low-diameter polybenzazole fiber, which comprises removing the solvent, and (4) winding the textured fiber at least 750 km. A second aspect of the invention is polybenzazole fibers having a diameter of 4-12 microns. Polybenzazole is available from Encyclopedia of Polymer Science TechnoIogy, Vol. It is a hard rod polymer as described in 11, pp. 601-635. The present invention uses fibers containing polybenzoxazole or polybenzothiazole polymers. Polybenzoxazoles, polybenzothiazoles and random, sequenced and block copolymers of polybenzoxazoles and polybenzothiazoles are described in the following references: Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, US Patent No. 4,703,103 (October 27, 1987), Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Prod ucts, US Patent No. 4,533,692 (August 1985 6 day), Wolfe et al., Liquid Crystalline Poly (2,6-Benzothiazole ) Compositlons, Pro cess and Products, US Patent No. 4,533,724 (August 6, 1985), Wolfe, Liqui d Crystalline Polymer Composltions, Process and Products, US Patent No. 4,53 3,693 (August 6, 1985), Evers, Thermooxidatively Stable Articulated p- Benzobisoxazole and p-Benzobisthiazole Polymers, US Pat. No. 4,359,567 (November 16, 1982), Tsai et al., Method for Making Heterocyclic Block Copolym er, US Patent No. 4,578,432 (March 25, 1986), 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988) and WW. Adams et al., The Materials Science and Engineering of Rigid -Rod Polym ers (Materials Research Society 1989). This polymer may contain an AB monomer unit represented by the following formula 1 (a) and / or an AA / BB monomer unit represented by the following formula 1 (b). In the above formula, each Ar represents an aromatic group. The aromatic group may be a heterocycle, for example a pyridinylene group, but is preferably a carbocycle. The aromatic group may be a fused or unfused polycyclic ring system, but is preferably a single 6-membered ring. Size is not critical, but the aromatic group preferably contains no more than about 18, more preferably no more than about 12, and most preferably no more than about 6 carbon atoms. Examples of suitable aromatic groups include phenylene moieties, tolylene moieties, biphenylene moieties and bisphenylene ether moieties. Ar ¹ in the AA / BB monomer unit is preferably a 1,2,4,5-phenylene moiety or a homologue thereof. Ar in the AB-monomer unit is preferably the 1,3,4-phenylene moiety or its homologues. Each Z is independently an oxygen or sulfur atom. Each DM is a divalent organic moiety that does not bind independently or interfere with the synthesis, processing or use of the polymer. The divalent organic moiety may contain an aliphatic group, which preferably has up to about 12 carbon atoms, but the divalent organic moiety is preferably an aromatic group (Ar) as described above. Is. It is most preferably a 1,4-phenylene moiety or its homologues. The nitrogen atom and Z moiety in each azole ring are bonded to adjacent carbon atoms in the aromatic group, forming a 5-membered azole ring fused with the aromatic group. The azole ring in the AA / BB monomer unit has 11 Ency. Poly. Sci. & Eng. May be in the cis or trans position relative to each other, as shown in particular at 602. The polymer preferably consists essentially of either AB-polybenzazole monomer units or AA / BB-polybenzazole monomer units, more preferably consisting essentially of AA / BB-polybenzazole monomer units. The molecular structure of the polybenzazole polymer may be a rigid rod, a semi-rigid rod, or a soft coil. Preferably, it is a hard rod in the case of AA / BB-polybenzazole polymer and semi-rigid in the case of AB-polybenzazole polymer. The azole ring in the polymer is preferably an oxazole ring (Z = O). Preferred monomer units are represented by the following formulas 2 (a) to (h). This polymer more preferably consists essentially of monomer units selected from those represented by 2 (a)-(h), most preferably selected from those represented by 2 (a)-(c). It consists essentially of many identical units. Each polymer preferably contains an average of at least about 25, more preferably at least about 50, and most preferably at least about 100 monomer units. The inherent viscosity of the hard AA / BB-polybenzazole polymer at 25 ° C in methanesulfonic acid is preferably at least about 10 deciliters / gram (dL / g), more preferably at least about 15 dL / g, most preferably at least about. It is 20 dL / g. For some purposes, an inherent viscosity of at least about 25 dL / g or 30 dL / g is best. Inherend viscosities of 60 dL / g or higher are possible, but are preferably about 45 dL / g or less. The inherent viscosity of the semi-rigid AB-polybenzazole polymer is preferably at least about 5 dL / g, more preferably at least about 10 dL / g, most preferably at least about 15 dL / g. The polymer is processed into fibers and films by spinning or extruding from a dope. If the freshly prepared polymer or copolymer is not available for spinning or extrusion, the previously prepared polymer or copolymer may be dissolved in a solvent to form a solution or dope. Although some polybenzoxazoles and polybenzothiazoles are soluble in cresol, the solvent is preferably an acid capable of dissolving the polymer. The acid is preferably one that does not oxidize. Examples of suitable acids are polyphosphoric acid, methanesulphonic acid, sulfuric acid and mixtures thereof. This acid is preferably polyphosphoric acid and / or methanesulfonic acid, more preferably polyphosphoric acid. The dope should contain a high enough concentration of polymer so that the polymer solidifies to form a solid product, but the viscosity of the dope should not be too high to handle. If the polymer is rigid or semi-rigid, the concentration of the polymer in the dope is preferably high enough to give a liquid crystalline dope. The concentration of polymer is preferably at least about 7 weight percent, more preferably at least about 10 weight percent, and most preferably at least about 14 weight percent. The maximum concentration is limited primarily by practical factors such as polymer solubility and dope viscosity. Due to these limiting factors, polymer concentrations are rarely above 30 weight percent, but usually below about 20 weight percent. Suitable polymers or copolymers and dopes can be prepared by known methods, such as Wolfe et al., US Pat. No. 4,533,693 (August 6, 1985), Sybert et al., US Pat. No. 4,772,678 (September 20, 1988), Harrls et al. Patent No. 4,847,350 (July 11, 1989), and Ledbetter et al., "An integrated Laboratory Process for Preparing Rigid Rod Fibers from the Monomers", T he Materials Science and Engineering of Rigid-Rod Polymers 253-64 (Mater ials Res Soc.1989). Suitable monomers (AA-monomer and BB-monomer or AB-monomer) can be mixed in a solution of an acid that does not oxidize and dehydrates in an atmosphere that does not oxidize, with vigorous mixing and shear, stepwise or rapidly at about 120 ° C. The reaction is carried out at temperatures increasing from the starting temperature to a final temperature of at least about 190 ° C. Examples of suitable AA-monomers include terephthalic acid and its homologues. Examples of suitable BB-monomers include 4,6-diaminoresorcinol, 2,5-diaminohydroquinone, 2,5-diamino-1,4-dithiobenzene and their homologues, usually stored as acid salts. . Examples of suitable AB-monomers are 3-amino-4-hydroxybenzoic acid, 3-hydroxy-4-aminobenzoic acid, 3-amino-4-thiobenzoic acid, 3-thio-4-aminobenzoic acid and their It includes homologues and is usually stored as the acid salt. Spinning PBO Polymer Preparation of PBO Dope PBO dope is a solution of PBO polymer in a solvent. Polybenzoxazole is soluble only in highly protic acid solvents such as methanesulfonic acid or polyphosphoric acid. The preferred solvent is polyphosphoric acid (PPA). The preferred concentration of PBO in polyphosphoric acid is about 14 weight percent. The intrinsic viscosity number of the PBO / PPA polymer should be 22-45 dL / g (based on measurement at a concentration of 0.05 g / dL in methanesulfonic acid at 25 ° C). The fibers may be spun from monofilament or multifilament lines. An example of an effective monofilament fiber spinning line is given in the JFWolfe review, page 625 (see Encyclopedia of Polymer Science and Engineering, 2nd edition, Vol. 11, pp. 601-635). The spinning device preferably comprises a spinneret having one or more orifices and means for pushing the dope into the orifices. If the spinneret contains many orifices, the device preferably further comprises a spinning die that delivers the dope to each orifice at about the same pressure and flow rate. The means for pushing the dope may be, for example, a pump, a piston or a single or multi-screw extruder. Spinnerets and spin dies are known as spinning blocks. Each part of the spinning block must be able to handle viscous, corrosive polymer dope solutions. Spinning of Dope Fiber After adding the dope to the spinning block, it is heated until the spinning temperature is reached. The spinning temperature is 135 to 180 ° C, the preferred spinning temperature is 140 to 170 ° C, and the most preferred spinning temperature is 150 to 160 ° C. The polymer dope is spun through an orifice hole with a diameter of 0.0051-0.018 cm (2-7 mils), preferably 0.0076-0.015 cm (3-6 mils), and most preferably 0.013 cm. The shear rate of this dope as it exits the spinning block is 300 to 4000 reciprocals second, the more preferred range of this shear rate is 500 to 3000 resec, and the most preferred shear rate is 1500 reversal. Seconds. Dope fibers are formed when spinning the PBO polymer dove through the spinneret. The dope fibers exit the spinning block and enter the space known as the "air gap" that exists between the exit side of the spinning block and the coagulation tank. The gas in this "air gap" may be air, but may also be another gas such as nitrogen, carbon dioxide, helium or argon. The temperature in this air gap is preferably about 0 ° C to 150 ° C, more preferably about 0 ° C to 100 ° C, most preferably 50 ° C to 100 ° C. The air gap is 0.64 to 41 cm (0.25 to 16 inches), the more preferred range is 1.3 to 15 cm (0.5 to 6 inches), and the most preferred range is 2.5 to 10 cm (1 to 4 inches). The spin-draw ratio is the ratio of the fiber winding speed divided by the dope extrusion rate. The extrusion rate is determined by the dope volumetric flow rate in the extruder or by the free fall rate of the spun dope from the spinneret. Here, the free fall velocity of the spun dope from the spinneret was used to determine the spin draw ratio. The spin-draw ratio of this spin is kept at 12-60, the preferred range is 13-25, and the most preferred spin-draw ratio is about 15. After the dope fiber exits the air gap and enters the coagulation / cleaning tank, or after being coagulated / cleaned and sprayed, the solvent (polyphosphoric acid) remaining in the fiber begins to phase separate from the PBO polymer in the fiber and coagulates. Diffuses in the agent. This phase separation process is known as coagulation. The coagulation or wash bath / spray used may contain water or a water / acid mixture, with the preferred acid being phosphoric acid at a concentration below 30 percent. Other coagulants or wash solutions include organic solvents such as acetone, methanol or acetonitrile. Washing, Drying and Heat Curing the Fiber After washing the fiber , it is dried and then heat cured. First, the fibers are dried to remove residual surface water. The fibers are dried and then heat treated. This heat treatment is preferably carried out in a furnace containing an inert gas such as nitrogen. Tension is applied to the fiber as it passes through the heat treatment element. The heat treatment is carried out at 300-650 ° C, the preferred temperature range is 400-650 ° C, the most preferred temperature is 600 ° C. The residence time of heat treatment depends on the temperature, but the higher the temperature, the shorter the required time. The heat treatment time is 1 second to 1 minute. The preferred time is 3 to 45 seconds, the more preferred heat treatment time is 5 to 20 seconds, and the most preferred time is 8 to 15 seconds. During this heat treatment the fibers are pulled. By following the processing conditions of the present invention, the fiber can be spun for a long time without causing damage to the fiber due to instability of the spinning process. The time for the spinning process to occur without failure is expressed in the length of the undamaged fibers collected (km). In the present invention, the amount of undamaged fibers collected is at least about 500 km, more preferably at least about 600 km, and most preferably at least about 800 km. The physical properties of the low denier fibers produced by the method of the present invention were measured. The low denier fiber produced by this method has a heat-treated tensile strength of 4.31GPa ~ 6.07GPa (625ksi ~ 880ksi), and the spun tensile modulus of this fiber is 172.4GPa ~ 30.2GPa (25msi ~ 45msi). ). These polybenzoxazole low denier fibers are effective when high performance chemical resistance, cut resistance, and flame retardant fibers are effective. In addition, the tensile and elastic properties make it valuable for composite applications. The following examples are given as an illustration of the present invention. However, it should be understood that the invention is not limited to this embodiment. Example 1-14% by weight PBO having an intrinsic viscosity (IV) of 22-40 dL / g (measured in methanesulfonic acid solution at 25 ° C., 0.05 g / dL) by polymerizing PBO in monofilament spun PPA. / PPA dope was prepared. This polymer dope was then used for fiber spinning. Fiber spinning was performed using a spinning block with four holes. The diameter of the hole or "orifice" in each spin was set. The fibers were spun at a barrel temperature of 150 ° C. The dope fiber exited the spinneret, crossed an air gap of 20 mm, and was then collected on a take-up spool immersed in water at 15 ° C. at various take-up speeds. The fibers were washed in running water for 48 hours, air dried for 24 hours, and vacuum dried for 4 hours. Then, it was heat treated at 450 ° C while pulling. The spinning conditions and fiber diameters are shown in the table below. Samples 1-7 were prepared from IV = 19 dL / g PBO dope. Example 2- Spinning with a Low Diameter Orifice Size Using the same method as in Example 1, 14 weights with an IV of 22-40 dL / g (measured in methanesulfonic acid solution at 25 ° C. at a concentration of 0.05 dL / g). A percent PBO / PPA dope was prepared. Fiber spinning was performed using the same equipment as in Example 1 with a spinneret having four holes. The fibers were spun at a barrel temperature of 150 ° C. and the dope fibers exiting the spinneret were crossed through a 20 mm air gap and collected on take-up spools immersed in water at 150 ° C. at various take-up speeds. The fibers were washed with running water for 48 hours, air dried for 24 hours and vacuum dried for 4 hours. Then, it was heat treated at 450 ° C while pulling. One fiber with a gauge length of 5.1 cm (2 inches) was drawn in an Instron tensile tester at an elongation rate of 0.01 / min. Test results are given in ksi (1000 pounds per square inch) or msi (1 million pounds per square inch). Here, 1 ksi = 6.895 MPa, 1 msi = 6.895 GPa. The results of fiber spinning and tensile strength and elastic modulus tests are shown in Table 2. Example 3- Multifilament spinning of low denier PBO fibers A PBO dope was prepared by polymerizing PBO in PPZ. 1000 g of this dope was used for fiber spinning using a multifilament fiber spinning device. The multifilament fiber spinning device included a mixing device for mixing and homogenizing the dope under vacuum and a spinning block for receiving the fibers and delivering the dope to a 36-hole (orifice) spinning die. A water tank containing two or more freely rotating wheels arranged in series was placed under the spinning die to receive the spinning dope and to solidify the dope fibers in water. The PBO dope was placed in the spinning machine, mixed for at least 4 hours and then transferred to the spinning block. The dope was then spun through a spinning die at 160 ° C. The spin block orifice size was approximately 0.01 cm (4 mils). The emerging dope fibers were traversed by an air gap of about 7.62 cm (3 inches), immersed in water, guided by a wheel at a distance of about 91.4 cm (3 feet), and then stretched by a fiber winding godet. The fiber was then sent to the winder. The thus spun fiber was washed with running water for 48 hours and then dried in a nitrogen-purged chamber. Heat treatment was performed while pulling a part of the fiber. The spun and dried fibers were observed under a microscope and mechanically tested. Tensile tests were performed with a gauge length of 25.4 cm (10 inches) and a thread twist factor of 6. Test results are given in ksi (1000 pounds per square inch) or msi (1 million pounds per square inch). Here, 1ksi = 6.895MPa and 1msi = 6.895GPa. The test results are shown in Table 3. This example shows that the tensile properties are much improved for fibers of less than 10 microns spun from a 0.1 cm (4 mil) hole die as compared to fibers prepared from a 0.05 (20 mil) hole die. Is shown. The smaller diameter fibers had 50% higher tensile modulus and 20% higher tensile strength than the spun state.

Claims (1)

[Claims]   1. The following process   (a) Lyotropic liquid crystalline poly containing polybenzazole polymer and solvent Spin the benzazole dope through the spinneret orifice to form the dope fiber. To make, where the diameter of this orifice hole is less than 0.18 cm,   (b) spin-draw ratio of 12 to 60 is used to remove the dope fiber from air of 40.6 cm or less. -Stretching across the gap,   (c) removing most of the solvent from the fiber by contacting it with a non-solvent, And   (d) winding at least 750 km of organized fibers, Of a low-diameter polybenzazole fiber having:   2. The method of claim 1, further comprising the steps of washing, drying and heat treating the fibers. How to list.   3. The diameter of the orifice hole is greater than 0.0051 cm and less than 0.18 cm, The method of claim 1.   4. The low-diameter polybenzazole fiber is polybenzoxazole fiber, The method according to claim 1.   Polybenzazole fibers having a diameter of 5.4-12 microns.   6. The polybenzazole according to claim 4, wherein the polybenzazole is polybenzoxazole. Ribenzazole fiber.   7. The polybenzazole according to claim 4, wherein the polybenzazole is polybenzothiazole. Benzazole fiber.   8. 5. The textured fibers of at least 500 km length are present. Polybenzazole fiber.   9. There is a well-structured fiber of at least 600 km long, The polybenzazole fiber according to claim 4.   Ten. 5. The textured fibers of at least 750 km length are present. Polybenzazole fiber.