JP2006057214A - Polybenzazole fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for industrially readily producing a polybenzazole fiber having a new fiber fine structure in which fiber structure is defect-free and the difference of the fiber structure between inner and outer layers is small. <P>SOLUTION: The inventors eliminate a defective structure such as amorphous which becomes hinderance to thermal vibration propagation of fiber to the utmost and succeed in suppressing unevenness of internal structure of the fiber to a dynamic diameter direction by adding a phosphorus additive for suppressing time gap existing in a skin part and a core part of polybenzazole filament when cooled and coagulated to a polymer dope. As a result, the inventors industrially obtained the polybenzazole fiber having high knot strength. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polybenzazole fiber excellent in durability in which a fiber structure suitable as an industrial material is homogeneous in the radial direction.

  Polybenzazole fiber has a strength and elastic modulus more than twice that of polyparaphenylene terephthalamide fiber, which is a representative super fiber currently on the market, and is expected as a next generation super fiber.

It is known to produce fibers from a polyphosphoric acid solution of a polybenzazole polymer. For example, Patent Document 1 and Patent Document 2 for spinning conditions, Patent Document 3 for washing and drying methods, and Patent Document 4 for heat treatment methods. The technical disclosures are made respectively.
US Pat. No. 5,296,185 US Pat. No. 5,385,702 International Publication No. W094 / 04726 US Pat. No. 5,296,185

  However, the polybenzazole fiber produced by the above-mentioned conventional production method breaks or fibrillates when it is processed into a fabric or the like even after heat treatment at 350 ° C. or more as described in US Pat. No. 5,296,185. This is a problem in operating the machine.

  Accordingly, the present inventors have intensively studied to develop a technique for easily producing a polybenzazole fiber having a property that hardly causes fibrillation.

  As means for realizing the ultimate physical properties of fibers, rigid polymers such as so-called ladder polymers have been considered, but such rigid polymers are not flexible and in order to have flexibility and processability as organic fibers. It is an essential condition that the polymer is linear.

  As shown by SGWierschke et al. In Material Research Society Symposium Proceedings Vol. 134, p.313 (1989), the most theoretical linear elastic polymer is cis-type polyparaphenylene benzobisoxazole. is there. This result was also confirmed by Tashiro et al. (Macromolecules vol. 24, p. 3706 (1991)). Among polybenzazoles, cis-type polyparaphenylenebenzobisoxazole has a crystal elastic modulus of 475 GPa (P Galen et al. Material Research Society Symposium Proceedings Vol. 134, p.329 (1989)), thought to have the ultimate primary structure. Therefore, in order to obtain the ultimate elastic modulus, the theoretical consequence is to use polyparaphenylene benzobisoxazole as a polymer.

  The fiberization of the polymer is performed by the method described in US Pat. No. 5,296,185 and US Pat. No. 5,385,702, and the heat treatment is performed by the method proposed in US Pat. No. 5,296,185. The nodule strength is at most 1.5 GPa. Therefore, the improvement of these methods was felt and the result of diligent research found that the desired physical properties could be easily achieved industrially by the following methods.

  As Ohta showed in Polymer Engineering and Science, 23, p697 (1983), there are so-called defect structures in the fiber such as voids, disordered crystal orientation, existence of molecular ends and amorphous parts. Furthermore, since the PBO fiber is produced through a solidification process, a time gap exists between the skin portion and the core portion of the filament when the dope filament is cooled and solidified, and therefore, there is a tendency that a difference between the inner and outer layers of the structure appears. In particular, the presence of this skin core structure is presumed to appear as internal strain of the fiber when the fiber is deformed in the bending direction, causing cracks and fibrillation. As a result, it appears as a decrease in nodule strength.

  A dope composed of polyparaphenylene benzobisoxazole (PBO) and polyphosphoric acid is spun from a spinneret. Thereafter, it is produced through solidification, neutralization, washing with water, drying, and heat treatment under tension. In order to increase the thermal conductivity, it is essential to eliminate as much as possible the defect structure such as amorphous, which hinders the thermal vibration transmission of the fiber. This time, for this purpose, polybenzazole fiber having a high knot strength was obtained industrially by succeeding in suppressing the nonuniform structure of the inner structure of the polybenzazole fiber in the radial direction.

  According to the present invention, a polybenzazole fiber having a novel fiber microstructure in which a fiber structure that has not been obtained so far is defect-free and the difference between the inner and outer layers of the fiber structure is small can be easily produced industrially. Since fibers with high practical strength can be obtained, the effect of expanding the field of use as industrial materials is enormous.

  In order to express the structural features described above, the points of the present invention can be realized by the following method. That is, a spun yarn obtained by extruding a polymer dope composed of polyparaphenylene benzobisoxazole from a spinneret into a non-solidifying gas was introduced into a coagulation bath to extract phosphoric acid contained in the dope yarn. Thereafter, neutralization, washing with water, drying and heat treatment were carried out. It was found that the fiber surface was heat-treated at a temperature of 500 ° C. or higher under a constant tension to obtain a polybenzazole having a dense fiber surface.

  The present invention will be further described in detail below. The polybenzazole fiber in the present invention refers to a PBO homopolymer, and a random, sequential or block copolymer with polybenzazole (PBZ) containing substantially 85% or more of a PBO component. Here, polybenzazole (PBZ) polymer is, for example, Wolf et al., “Liquid Crystalline Polymer Compositions, Process and Products” US Pat. No. 4,703,103 (October 27, 1987), “Liquid Crystalline Polymer Compositions, Process and Products” US Patent No. 4536992 (August 6, 1985), “Liquid Crystalline Poly (2,6-Benzothiazole) Compositions, Process and Products” US Pat. No. 4,533,724 (August 6, 1985), “Liquid Crystalline Polymer Compositions, Process and Products, US Pat. No. 4,453,393 (August 6, 1985), Evers “Thermooxidative-ly Stable Articulated p-Benzobisoxazole and p-Benzobisoxazole Polymers”, US Pat. No. 4,539,567 (November 16, 1982), Tsai “Method for making Heterocyclic Block Copolymer”, US Pat. No. 4578432 (March 25, 1986), and the like.

  The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers. The monomer units consist of monomer units described in structural formulas (a) to (h), and more preferably consist essentially of monomer units selected from structural formulas (a) to (c).

  Suitable solvents for forming a polymer dope consisting essentially of PBO include cresol and a non-oxidizing acid capable of dissolving the polymer. Examples of suitable acid solvents include polyphosphoric acid, methane sulfonic acid and high concentrations of sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.

  The polymer concentration in the solvent is preferably at least about 7% by weight, more preferably at least 10% by weight, and most preferably 14% by weight. The maximum concentration is limited by practical handling properties such as polymer solubility and dope viscosity. Due to their limiting factors, the polymer concentration does not exceed 20% by weight.

  Suitable polymers, copolymers or dopes are synthesized by known techniques. For example, Wolfe et al., U.S. Pat. No. 4,453,393 (August 6, 1985), Sybert et al., U.S. Pat. No. 4,772,678 (September 20, 1988), Harris, U.S. Pat. No. 4,847,350 (July 11, 1989). It is synthesized by the method described in 1. A polymer consisting essentially of PBO, according to Gregory et al., US Pat. No. 5,089,591 (February 18, 1992), has a high reaction rate at high reaction rates under relatively high temperature and high shear conditions in a dehydrating acid solvent. Molecular weight is possible.

  The dope polymerized in this way is supplied to the spinning section and discharged from the spinneret at a temperature of usually 100 ° C. or higher. A plurality of base pores are usually arranged in a circumferential shape or a lattice shape, but other arrangements may be used. The number of nozzle holes is not particularly limited, but the arrangement of the spinning holes on the spinneret surface needs to maintain a hole density that does not cause fusion between discharged yarns.

  In order to obtain a sufficient draw ratio (SDR), the spun yarn needs a sufficiently long draw zone length as described in US Pat. No. 5,296,185, and has a relatively high temperature (above the solidification temperature of the dope). It is desirable that the air is uniformly cooled with a rectified cooling air having a temperature equal to or lower than the spinning temperature. The length (L) of the draw zone needs to be a length that completes solidification in a non-solidifying gas, and is roughly determined by the single-hole discharge amount (Q). In order to obtain good fiber properties, the take-out stress of the draw zone needs to be 2 g / d or more in terms of polymer (assuming that only the polymer is stressed).

  The yarn drawn in the draw zone is then led to an extraction (coagulation) bath. Since the spinning tension is high, it is not necessary to consider the disturbance of the extraction bath, and any type of extraction bath may be used. For example, funnel type, water tank type, aspirator type or waterfall type can be used. The extract is preferably an aqueous phosphoric acid solution or water. Finally, 99.0% or more, preferably 99.5% or more of the phosphoric acid contained in the yarn is extracted in the extraction bath. There are no particular limitations on the liquid used as the extraction medium in the present invention, but water, methanol, ethanol, acetone, ethylene glycol, and the like that are substantially incompatible with polybenzazole are preferred. Further, the extraction (coagulation) bath may be separated into multiple stages, the concentration of the phosphoric acid aqueous solution is gradually reduced, and finally washed with water. Further, the fiber bundle is desirably neutralized with an aqueous sodium hydroxide solution and washed with water.

  In order to remove the structural difference between the inner and outer layers from the fiber structure, it is necessary to execute structure formation accompanying solidification almost simultaneously, regardless of the location of the fiber. However, since polybenzazole is relatively hydrophobic, there is a problem that structure formation proceeds non-uniformly when solidified with a polar solvent such as water or ethanol. As a result of intensive studies, it has been found that the crystal size and orientation are not uniform and non-uniform depending on the site inside the fiber. This non-uniform structure causes stress concentration when the fiber is deformed, and can also be a starting point of structural fracture, leading to a decrease in knot strength.

  Therefore, the inventors succeeded in suppressing the heterogeneity of the structure due to the above-described deviation in coagulation timing by mixing diphosphorus pentoxide again in the dope solution after polymerization. Although the mechanism of this effect is not clear, the inventors consider as follows: diphosphorus pentoxide is generally used as a desiccant. By adding diphosphorus pentoxide during coagulation, it acts as a hydrophilizing agent in the dope yarn, so that the coagulant quickly penetrates to the center of the fiber, resulting in structural heterogeneity between the fiber parts The inventors speculate that this can be suppressed.

  The amount of diphosphorus pentoxide to be added is preferably 5% or more and 30% or less, more preferably 10% or more and 25% or less, and most preferably 15% or more and less than 20% by weight with respect to the dope receipt. If the amount added is too large, the mechanical properties of the fiber are not improved, which is not preferable. If the amount added is small, the initial structure is not expressed.

[Evaluation method of crystal size and orientation]
Crystal size and orientation evaluation were measured using an X-ray diffraction method. As an X-ray source, a large synchrotron radiation facility SPring8 was used as an X-ray source, and a BL24XU hatch was used. The energy of the X-ray used is 10 keV (λ = 1.398Å). The X-rays taken out through the undulator were monochromatized through a monochromator (silicon crystal (111) plane) and then set to converge at the sample position using a phase zone plate. The size of the focal point is adjusted so that the diameter is 3 μm or less both vertically and horizontally. The sample fiber is placed on the XYZ stage so that the fiber axis is horizontal. The Thomson scattering intensity was measured by finely moving the stage while detecting using a separately installed Thomson scattering detector, and the point where the intensity reached the maximum was determined as the center of the fiber. Since the X-ray intensity is very high, the sample is damaged if the exposure time of the sample is too long. Therefore, the exposure time during X-ray diffraction measurement was 5 minutes. X-ray diffraction patterns were recorded using a Fuji imaging plate. Data reading was performed using Fuji microluminography. The recorded image data was transferred to a personal computer, and the line width was evaluated after cutting out data in the equator direction and the azimuth direction. The crystal size (ACS) was calculated from the half-value width β of the diffraction profile in the equator direction using the Scherrer equation [Equation 1] shown below. The measurement was carried out at random in the radial direction of one fiber and measured at 10 locations to obtain standard deviation and average value, and calculated based on the formula CV% = (standard deviation / average value) × 100.

[Formula 1] ACS = 0.9λ / βcos θ
Here, λ is the wavelength of the X-ray used, and 2θ is the diffraction angle.

  The orientation angle OA was the half width of the profile obtained by scanning in the azimuth direction. The inner / outer layer ratio of the crystal size was obtained by dividing the ACS evaluated by condensing X-rays on the resurface layer (skin portion) of the fiber and dividing it by the value of OA measured by condensing it at the center of the fiber. The inner / outer layer ratio of the orientation angle was obtained by dividing the OA evaluated by condensing X-rays on the resurface layer (skin portion) of the fiber and dividing it by the ACS value measured by condensing the central portion of the fiber. The measurement was carried out at random in the radial direction of one fiber, measured at 10 locations, standard deviation and average value were obtained, and calculated based on the formula CV% = (standard deviation / average value) × 100.

[Method of measuring nodule strength]
The nodule strength was determined by evaluating the nodule strength retention rate described below.
(Nodule strength retention rate of single fiber)
As for the strength and elastic modulus of the filament (single fiber), ten single yarns (filaments) were randomly extracted from one multifilament to be measured. When the number of filaments was less than 10, all single yarns (filaments) were measured.
In the measurement, about 2 m of each single fiber was taken out, 1 m of the fiber was used, the weight was measured, and the fineness (dTex) was converted into 10,000 m. When measuring the length of this single yarn fiber 1 m, a constant length sample was prepared by applying a load of about 1/10 of the single yarn fineness. Further, the remaining part of the fiber was used to make a knot in the middle of a single fiber, and then a tensile test was performed in the same manner as the strength of the fiber. At this time, how to make a knot was performed according to FIG. 3 described in JIS L1013. The direction of the knot is always the same, and is b in FIG.
Knot strength retention ratio = average value of single yarn knot strength / average value of single yarn strength × 100

  The following examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof.

[Example 1-4, Comparative example 1-2]
Obtained by the method shown in US Pat. No. 4,453,393, 14.0% by weight of polyparaphenylenebenzobisoxazole having an intrinsic viscosity of 24.4 dL / g measured with a methanesulfonic acid solution at 30 ° C. and a phosphorus pentoxide content of 83.17 A spinning dope consisting of% polyphosphoric acid was used for spinning. At this time, a predetermined amount of diphosphorus pentoxide was added to the dope after polymerization, and then mixed uniformly. Thereafter, the dope is passed through a metal mesh-like filter medium, and then kneaded and defoamed with a biaxial kneading apparatus, and then the pressure is increased to keep the polymer solution temperature at 170 ° C., and a spinneret having a pore number of 166 And then cooling the discharged yarn using a cooling nitrogen air whose temperature is adjusted to 60 ° C. and further cooling the discharged yarn to 40 ° C. by natural cooling. It was introduced into a prepared 30% aqueous phosphoric acid solution to prepare a fiber. Next, the fiber was wound around a gosset roll, the yarn was washed with ion-exchanged water in a second extraction bath at a constant speed, and then immersed in 0.1N sodium hydroxide solution for neutralization. Further, after washing with water in a water bath, it was wound up, dried in a drying oven at 80 ° C., and allowed to stand until the moisture content in the fiber was 2% or less. The results are shown in Table 1.

[Comparative Example 3]
Obtained by the method shown in US Pat. No. 4,453,393, 14.0% by weight of polyparaphenylenebenzobisoxazole having an intrinsic viscosity of 24.4 dL / g measured with a methanesulfonic acid solution at 30 ° C. and a phosphorus pentoxide content of 83.17 A spinning dope consisting of% polyphosphoric acid was used for spinning. At this time, diphosphorus pentoxide was added again to the dope just before the polymerization, and the mixture was uniformly mixed and then polymerized. Thereafter, the dope is passed through a metal mesh-like filter medium, and then kneaded and defoamed with a biaxial kneading apparatus, and then the pressure is increased to keep the polymer solution temperature at 170 ° C., and a spinneret having a pore number of 166 And then cooling the discharged yarn using a cooling nitrogen air whose temperature is adjusted to 60 ° C. and further cooling the discharged yarn to 40 ° C. by natural cooling. It was introduced into a prepared 30% aqueous phosphoric acid solution to prepare a fiber. Next, the fiber was wound around a gosset roll, the yarn was washed with ion-exchanged water in a second extraction bath at a constant speed, and then immersed in 0.1N sodium hydroxide solution for neutralization. Further, after washing with water in a water bath, it was wound up, dried in a drying oven at 80 ° C., and allowed to stand until the moisture content in the fiber was 2% or less. The results are shown in Table 1.

  From Table 1 above, it can be seen that the fiber of the present invention has a markedly lower equilibrium moisture content than the conventional fiber, and is extremely superior in physical properties. At the same time, it is recognized that it has a microstructure with very little defect structure on the skin-core.

  As described above, the present invention can industrially easily produce polybenzazole fiber having a unique fiber microstructure in which a fiber structure that has not been obtained so far is defect-free. As a result, the effect of increasing practicality and expanding the field of use is enormous. In other words, not only for high-density and high-performance circuit boards for mounting silicon chips, but also for tension members such as cables, electric wires and optical fibers, ropes, etc., rocket insulation, rocket casing, pressure vessels, space suits Aviation such as strings, planetary exploration balloons, impact materials such as space materials, bulletproof materials, cut resistant materials such as gloves, fire clothes, heat felt, plant gaskets, heat resistant fabrics, various seals, heat cushions, Heat-resistant flame-resistant members such as filters, rubber reinforcements such as belts, tires, shoe soles, ropes, hoses, fishing lines, fishing rods, tennis rackets, table tennis rackets, badminton rackets, golf shafts, club heads, guts, strings, sail cloths , Running shoes, marathon shoes, spike shoes, skate shoes, basketball Sports shoes such as golf balls, volleyball shoes, bicycles for competition (running) and its wheels, road racers, pis racers, mountain bikes, composite wheels, disc wheels, tension discs, spokes, brake wires, transmission wires, competition (running) ) Wheelchairs and their wheels, protectors, racing suits, sports materials such as skis, stocks, helmets, parachutes, friction materials such as avant belts, clutch facings, various building material reinforcements and other rider suits, speaker cones , Lightweight baby carriages, lightweight wheelchairs, lightweight nursing beds, lifeboats, life jackets, etc.

Claims (4)

A polybenzazole fiber characterized in that the CV% of the crystal size is 20% or less when measured using an X-ray beam formed to have a diameter of 3 μm or less in the radial direction of the single filament. 2. The polybenzazole fiber according to claim 1, wherein the CV% of the orientation angle is 10% or less when measured using an X-ray beam formed to have a diameter of 3 μm or less in the radial direction of the single filament. . The polybenzazole fiber according to claim 2, which has a crystal size of 3 nm or more and 15 nm or less when measured using an X-ray beam formed to have a diameter of 3 µm or less. The polybenzazole fiber according to claim 3, wherein the orientation angle is 1 ° or more and 9 ° or less when measured using an X-ray beam formed to have a diameter of 3 µm or less.