Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/58—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products
  • D01F6/74—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polycondensates of cyclic compounds, e.g. polyimides, polybenzimidazoles

Definitions

• Fibers prepared from polybenzoxazole (PBO) and polybenzothiazole (PBT) may be prepared by first extruding a solution of polybenzazole polymer in a mineral acid (a polymer "dope") through a die or spinneret to prepare a dope filament.
• the dope filament is then drawn across an air gap, with or without stretching, and then coagulated in a bath comprising water or a mixture of water and a mineral acid. If multiple filaments are extruded simultaneously, they may then be combined into a multif ilament fiber during or after the coagulation step.
• the filament or fiber is then washed in a washing bath to remove most of the mineral acid, and then dried.
• the physical properties of such filaments and fibers such as tensile strength, are known to be relatively high. However, further improvement in such properties is desirable.
• Polybenzazole dope filaments for use in the process of the present invention may be prepared by the extrusion of a polybenzazole dope through an extrusion die with a small diameter or a "spinneret".
• the polybenzazole dope comprises a solution of polybenzazole polymer in polyphosphoric acid.
• polybenzazole refers to polybenzoxazole (“PBO”) and polybenzothiazole (“PBT”). PBO, PBT and random, sequential and block copolymers of PBO and PBT are described in references such as Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S.
• Patent 4,703,103 (October 27, 1987); Wolfe et al., Liquid Crystalline Polv(2,6-Benzothiazole) Compositions, Process and Products, U.S. Patent 4,533,724 (August 6, 1985); Wolfe, Liquid Crystalline Polymer Com ⁇ positions, Process and Products, U.S. Patent 4,533,693 (August 6, 1985); Evers, Thermo- -oxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers. U.S. Patent 4,359,567 (November 16, 1982); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S.
• the polybenzazole polymer may be rigid rod, semi-rigid rod or flexible coil. It is preferably a lyotropic liquid-crystalline polymer, which forms liquid-crystalline domains in solution when its concentration exceeds a critical concentration.
• the intrinsic viscosity of rigid polybenzazole polymers in methanesutfonic acid at a temperature of 25°C is preferably at least about 10 dL/g, more preferably at least about 15 dL/g and most preferably at least about 20 dL/g.
• Suitable polybenzazole polymers or copolymers and dopes can be synthesized by known procedures, such as those described in Wolfe et al., U.S. Patent 4,533,693 (August 6, 1985); Sybert et al., U.S. Patent 4,772,678 (September 20, 1988); Harris, U.S. Patent 4,847,350 (July 11 , 1989); and Gregory et al., U.S. Patent 5,089,591 (February 18, 1992).
• suitable monomers are reacted in a solution of nonoxidizing and dehydrating acid under nonoxidizing atmosphere with vigorous mixing and high shear at a temperature that is increased in step-wise or ramped fashion from no more than 120°C to at least 190 C C.
• the dope may then be formed into a filament by extrusion through a spinneret, and drawing the filament across a gap. Suitable processes are described in the references previously incorporated and U.S. Patent 5,034,250.
• the spinneret preferably contains a plurality of holes. The number of holes in the spinneret and their arrangement is not critical to the invention, but it is desirable to maximize the number of holes for economic reasons.
• the spinneret may contain as many as 100 or 1000 or more, and they may be arranged in circles, grids, or in any other desired arrangement.
• the spinneret may be constructed out of ordinary materials that will not be degraded by the dope, such as stainless steel.
• Dope exiting the spinneret enters a gap between the spinneret and the coagulation bath.
• the gap is typically called an "air gap” although it need not contain air.
• the gap may contain any fluid that does not induce coagulation or react adversely with the dope, such as air, nitrogen, argon, helium or carbon dioxide.
• the dope is preferably drawn to a spin- -draw ratio of at least about 20, highly preferably at least about 40, more preferably at least about 50 and most preferably at least about 60.
• the spin-draw ratio is defined in this application as the ratio between the take-up velocity of the filaments and the capillary velocity (v c ) of the dope in the spinneret.
• the shear rate at the spinneret hole wall is preferably in the range of from 1800 to 6500 s '1 . The draw should be sufficient to provide a filament having the desired diameter.
• step (a) of the process of the invention the dope filament is contacted with water or a mixture of water and polyphosphoric acid under conditions sufficient to reduce the phosphorous content of the filament to less than about 10,000 ppm by weight. This may be carried out as a single operation in one washing apparatus, or the filament may travel through several baths or washing cabinets to reduce the phosphorous content to the desired level. If a mixture of water and polyphosphoric acid is used, the concentration of polyphosphoric acid in solution should be lower than that contained in the filament in order to effectively wash the filament. Such mixtures are preferably used in the initial stages of washing, since gradual removal of polyphosphoric acid from a multif ilament fiber tends to improve its physical properties.
• the filament is first "coagulated" in a coagulation bath containing water or a mixture of water and polyphosphoric acid, which removes enough of the solvent to prevent substantial stretching of the filament during any subsequent processing.
• the filament may then be further washed in a multi-step process.
• coagulation does not necessarily imply that the dope is a flowing liquid and changes into a solid phase.
• the dope may be at a temperature low enough so that it is essentially non-flowing before the coagulation step begins.
• the amount of solvent removed during the coagulation step will depend on the residence time of the filament in the coagulation bath, the temperature of the bath and the concentration of solvent therein. For example, using a 20 weight percent solution of polyphosphoric acid at a temperature of about 23°C, a residence time of about one second will remove about 70 percent of the solvent present in the filament.
• the wet, never-dried surface of the filament is relatively porous and provides paths to wash residual phosphorus from inside the filament.
• the pores close when they become dry and do not open even when they become wet again. The closed pores trap residual phosphorus inside the filament.
• the temperature of the coagulation bath is preferably at least about 10°C, more preferably at least about 25°C, and is preferably no greater than about 50°C, more preferably no greater than about 40°C.
• the residence time of the filament in the coagulation bath is preferably at least about 1 second, and is preferably no more than about 5 seconds.
• the concentration of acid in the coagulation bath is preferably at least about 0.5 percent by weight, more preferably at least about 20 percent, and is preferably no greater than about 40 percent, more preferably no greater than about 25 percent. For a continuous process, it is preferable to use as low a temperature and high a solvent content as is practical, so that the solvent may be removed as slowly as possible.
• the concentration of phosphorous in the ilament is preferably brought down as slowly as is practical in the coagulation and washing operations, given that for such processes, fewer steps and higher line speeds are desirable. It is believed that a slower reduction in the phosphorous concentration in the filament provides a filament which has better physical properties. It is also believed that this result is more efficiently achieved in a continuous multi-step operation, utilizing a series of baths or washing cabinets, by decreasing the concentration of acid in the washing bath as the filament proceeds down the washing line. Conveniently, the washing fluid residue collected after the last washing step may be used as the washing fluid in the next-to-last washing step, and so forth up the line, with washing fluid containing the highest acid concentration being used in the first washing step.
• the concentration of acid in the washing baths or cabinets is preferably at least about 0.2 percent by weight, and is preferably no greater than about 40 percent by weight.
• the residual concentration of phosphorous in the filament after step (a) of the process is preferably less than about 8,000 ppm, more preferably less than about 6,000 ppm, and most preferably less than about 4,000 ppm.
• the residual phosphorus content of a substantially dry filament may be measured using X-ray fluorescence techniques described in E.P. Bertin, Principles and Practice of X-Ray Spectrometric Analysis - Second Ed. (Plenum Press 1984). Suitable equipment is commercially available underthe trade name KEVEX 770 XRF and from Philips Electronic Instruments.
• the filament utilized in the process of the invention may be combined into a multif ilament fiber at any point during the process of the invention. Preferably, however, the filaments are combined just prior to, or during, coagulation. While the term "filament" is used throughout this application to describe the process of the invention, the process of the invention may of course also be carried out on a filament contained in a multifilament fiber, utilizing the same process parameters as described herein for use with a single filament.
• the filament is preferably under tension during at least part of the washing process. More preferably, tension is also applied throughout the coagulation and washing process, particularly when the fluid temperature is very high. The tension is preferably sufficient to prevent the filament from shrinking or relaxing.
• the dope filament is contacted with an aqueous solution of an inorganic base under conditions sufficient to convert at least about 50 percent of the acid groups present in the filament to the corresponding salt form (hereafter "neutralization step").
• neutralization step may likewise be carried out in a single operation, or the filament may travel through several baths or washing cabinets to reduce the phosphorous content to the desired level. Preferably, however, this step is carried out in a single washing cabinet as described above.
• suitable water-soluble bases include sodium hydroxide, ammonium hydroxide, sodium carbonate, and sodium bicarbonate.
• the percentage of acid groups which have been converted may be followed by any suitable technique, such as nuclear magnetic resonance spectroscopy (NMR) or Fourier transform infrared spectroscopy (FTIR).
• the concentration of base in the solution is preferably at least about 0.2 weight percent, more preferably at least about 0.4 weight percent, and is preferably no greater than about 1.2 weight percent, more preferably no greater than about 0.8 weight percent.
• the duration of this second step will depend on the concentration of the base, with longer residence times required for lower concentrations, but is preferably no greater than about 120 seconds, more preferably no greater than about 60 seconds.
• Preferably at least about 50 percent of the acid groups remaining after step (a) are converted to their salt form, more preferably at least about 75 percent, and most preferably at least about 95 percent are so converted.
• the preferred pH of the base solution used in the neutralization step will depend on the duration of the step, with a higher pH preferred with a shorter duration, but is preferably in the range of from 10 to 14, more preferably in the range of from 1 1 to 12.
• the process of the present invention is preferably run in a continuous fashion with a line speed of at least about 50 m/minute.
• the line speed is highly preferably at least o about 200 m/minute, more preferably at least about 400 m/minute and most preferably at least about 600 m/minute.
• the fibers were coagulated in a bath of water and polyphosphoric acid having an
• the fiber was dried under nitrogen at room temperature (23°C) for an additional 48 hours. A portion of the samples were heat-set through a nitrogen-purged tube furnace with a residence time of 2 seconds at 600°C. A constant tension of about 3.5 g/denier was maintained on the fiber during heat setting.
• Residual phosphorus was measured using X-ray fluorescence on a Philips PW1404/DY685 sequential spectrometer with scandium X-ray tubes and fiber samples which had been pressed into a pellet for analysis. The tensile strength retention and intrinsic viscosity of each fiber was then measured, both before and after heat-treatment. The retention of tensile strength (TSR), defined as (photo-aged tensile strength/initial tensile strength) x 100 percent, was used for expressing the retention of tensile strength after photo-aging, although separate samples were used for each measurement. Photo-aging was carried out in an Atlas Model G65A weatherometer with a xenon lamp and borosilicate filter. Fiber strands were mounted on sample holders and photo-exposed in the weatherometer. The exposure was 765 doewatt/m 2 with a 300 to 800 nm wave length for a total of 100 hours.
• fiber samples comprised of filaments with a denier of 1.5 denier per filament and a diameter of 1 1.5 microns were prepared, coagulated in water for 1 second, washed in water for 10 minutes, and contacted with a 0.1 N aqueous solution of a base for 10 minutes.
• the samples were subsequently washed with water at room temperature for 24 hours. The tensile strength of the samples were measured, and heat-treatment was carried out, as described in Examples 1-10.
• fiber samples comprised of filaments having a denier of 1.5 denier per filament and a diameter of 11.5 microns were prepared, coagulated, and washed for a period of time sufficient to give the residual levels of phosphorous shown in Table III. The samples were then contacted with a 0.1 N aqueous solution of a base for 5 minutes.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Artificial Filaments (AREA)
• Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)

Applications Claiming Priority (5)

Publications (2)

Family

ID=26980332

Family Applications (1)

Country Status (6)

Families Citing this family (10)

Family Cites Families (3)

• 1995
  • 1995-09-08 MX MX9702304A patent/MX9702304A/es not_active Application Discontinuation
  • 1995-09-08 CA CA 2199514 patent/CA2199514A1/en not_active Abandoned
  • 1995-09-08 EP EP95931706A patent/EP0783603B1/de not_active Expired - Lifetime
  • 1995-09-08 WO PCT/US1995/011229 patent/WO1996010661A1/en active IP Right Grant
  • 1995-09-08 CN CN 95195398 patent/CN1159836A/zh active Pending
  • 1995-09-08 DE DE69513844T patent/DE69513844T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events