JPH0841728A - Highly elastic polybenzazol fiber - Google Patents

Abstract

PURPOSE:To produce a polybenzazole fiber useful as a source material for industrial materials and having excellent physical properties such as low fiber density and high elastic modulus. CONSTITUTION:This polybenzazole fiber having high elastic modulus is obtained by spinning a polyphosphoric acid solvent dope of polyparaphenylenebenzobisoxazole from a spinneret, drawing the spun fiber through an air gap, cooling the fiber, winding up the fiber by a godet roll, introducing the fiber into a coagulation bath, passing through a multi-stage extraction bath, washing by water, drying and winding up the fiber. The polybenzazole fiber has physical properties such as low density (<1.55g/cm<3>), a high strength (>=5.0GPa) and high modulus (>=200GPa) and <=1.0 in a ratio I(200)/I(010) of the peak value of the diffraction strength of an electron diffraction pattern obtained by revolving a section + or -25 deg. around the fiber axis. The section is obtained by cutting the fiber with a plane parallel to the fiber axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-modulus-strength polybenzazole fiber used as an industrial material.
More specifically, the present invention relates to a polybenzazole fiber having a low fiber density and remarkably excellent strength and elastic modulus.

[0002]

2. Description of the Related Art Polybenzazole fiber has a strength and elastic modulus more than twice that of polyparaphenylene terephthalamide fiber, which is a typical super fiber currently on the market. Therefore, it is expected as a next-generation super fiber.
It is known to manufacture fibers from polyphosphoric acid solutions of polybenzazole polymers. For example, US Pat. No. 5,296,185 and US Pat. No. 5,294,390 have been proposed for spinning methods, WO94 / 04726 for water washing and drying methods, and US Pat. No. 5,296,185 for heat treatment methods.

[0003]

The elastic modulus of the spun yarn of polybenzazole fiber produced by the conventional manufacturing method is about 16
In order to obtain a fiber having a high elastic modulus of not more than 0 GPa and not less than 200 GPa, heat treatment at 350 ° C. or more as described in US Pat. No. 5,296,185 is required. Such high temperature heat treatment not only causes energy consumption but also increases manufacturing cost. Also, from the viewpoint of physical properties, it is not desirable in the field in which the lightness such as the specific strength and the specific elastic modulus inevitably causes the increase of the density and the merit is light. The present invention overcomes such technical difficulties and provides a lightweight, high-strength, high-modulus polybenzazole fiber.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted intensive studies and found a solution to the problem with the aim of developing a lightweight, high-strength / high-modulus polybenzazole fiber. That is, a spinning dope composed of polybenzazole and polyphosphoric acid is spun from a spinneret. The yarn discharged into a so-called air gap (draw zone) has a very high elongation viscosity, and is called drawing rather than the concept of spinning. However, although the spun-doped benzazole molecular chain has an extremely long molecular relaxation time, the polyphosphoric acid molecule has a relatively short relaxation time, and therefore it is not unrelated to the relaxation of the doped molecular chain. Therefore, by controlling the molecular relaxation in the draw zone, a high-strength / high-modulus polybenzazole fiber can be obtained from spun yarn without heat treatment, and the high-strength / high-modulus polybenzazole fiber can be obtained. Found that they have microstructural features not available in the prior art.

The present invention will be described in detail below. The polybenzazole fiber in the present invention means a fiber made of polybenzazole polymer, and polybenzazole (PBZ)
The term "polybenzoxazole (PBO) homopolymer, polybenzothiazole (PBT) homopolymer and random, sequential or block copolymers of PBO and PBT". Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymers are, for example, described in "Liquid Crystalline Polymer C" by Wolfe et al.
ompositions, Process and Products "US Patent No. 47
03103 (October 27, 1987), "Liquid C
rystalline Polymer Compositions, Process and Produ
cts "US Pat. No. 4,533,692 (August 6, 1985)
Sun), "Liquid Crystalline Poly (2,6-Benzothiazole)
Composition, Process and Products "US Patent No. 45
No. 33724 (August 6, 1985), "Liquid Crys
talline Polymer Compositions, Process and Produc
ts "U.S. Pat. No. 4,533,693 (August 6, 1985)
Sun), Evers' Thermooxidative-ly Stable Articula
ted p-Benzobisoxazole and p-Benzobisthiazole Polym
res "U.S. Pat. No. 4,539,567 (November 16, 1982), Tasi et al.," Method for making Heterocyclic ".
Block Copolymer "US Pat. No. 4,578,432 (19
March 25, 1986), etc. The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers. The monomer unit consists of the monomer units described in structural formulas (a) to (h), and more preferably, essentially, structural formulas (a) to (h).
It consists of monomer units selected from (c).

[0006]

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[0007]

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Suitable solvents for forming the dope of PBZ polymer include cresol and non-oxidizing acids capable of dissolving the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and concentrated 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 1%.
It is 0% by weight, most preferably at least 14% by weight. The maximum concentration is limited by practical handling characteristics such as the solubility of the polynose and the viscosity of the dope. Due to these limiting factors, the polymer concentration is usually 20% by weight.
Never exceeds.

Suitable polymers, copolymers or dopes are synthesized by known methods. For example, Wolfe et al., US Pat. No. 4,533,693 (August 6, 1985), Sy.
U.S. Pat. No. 4,772,678 to Bert et al. (September 2, 1988)
Day 0, Harris U.S. Pat. No. 4,847,350 (198).
It is synthesized by the method described in July 11, 1997). PB
Z polymers are described in US Pat. No. 5,089,591 to Gregory et al.
According to the publication (February 18, 1992), it is possible to achieve a high molecular weight at a high reaction rate in a dehydrating acid solvent under relatively high temperature and high shear conditions.

The dope thus polymerized is supplied to the spinning section and discharged from the spinneret at a temperature of usually 100 ° C. or higher. A plurality of die holes are usually arranged in a circumferential shape or a lattice shape, but other arrangements may be used. The number of spinneret pores is not particularly limited, but the array of spinneret pores on the spinneret surface must be maintained at a pore density that does not cause fusion between the discharge yarns.

The spun yarn requires a sufficient draw zone length, as described in US Pat. No. 5,296,185, to obtain a sufficient draw ratio (SDR), and at a relatively high temperature (solidification of the dope). It is desirable to be uniformly cooled with a rectified cooling air having a temperature above the spinning temperature but below the spinning temperature). The length (L) of the draw zone needs to be the length at which solidification is completed in the non-solidifying gas, and is roughly determined by the single hole discharge amount (Q). In order to obtain good fiber properties, the draw-out stress in the draw zone must be 2g / d or more in terms of polymer (assuming stress is applied only to the polymer). On the other hand, when the yarn residence time in the draw zone becomes long, the polybenzazole molecular chain has an extremely long relaxation time, but polyphosphoric acid has a relatively short relaxation time. Proceed to. Since the system has extremely high molecular orientation and high elastic modulus, slight relaxation appears as a decrease in elastic modulus. We have found that preventing this is the decisive factor in improving the physical properties. That is, by satisfying the following formula, a fiber having a physical property and a structure which are not available in the past can be obtained. 0.7 x (0.00852 x C x V) ^0.5 ≤ 0.0112 x C x V (S x V) / Q ≥ 0.3 (2) 40 x Q ^0.5 ≤ L ≤ 80 x Q ^0.5 (3) where Q is the single hole discharge rate. (G / min), V is the spinning speed (m / min)
Min), C is the polymer concentration (weight ratio), S is the orifice outlet cross-sectional area (cm ² ), and L is the draw zone length (cm).

The yarn drawn in the draw zone is introduced into the coagulation bath. Since the spinning tension is high, it is not necessary to consider disturbance of the coagulation bath, and the coagulation bath of the following type may be used.
For example, a funnel type, an aquarium type, an aspirator type or a waterfall type can be used. The coagulating liquid is preferably phosphoric acid aqueous solution or water. Finally, 99.0% or more, preferably 99.5% or more, of phosphoric acid contained in the yarn is extracted in the extraction bath. The liquid used as the extraction medium in the present invention is not particularly limited, but water, methanol or the like, which is not substantially compatible with polybenzoxazole, is preferable. Alternatively, the extraction bath may be separated into multiple stages to reduce the concentration of the phosphoric acid aqueous solution in sequence and finally washed with water. Further, it is desirable to neutralize the fiber bundle with an aqueous solution of sodium hydroxide and wash it with water.

The extracted yarn is immediately or separately dried and wound up. The resulting fiber has a fiber density of 1.55 g / cm
Less than ^3, preferably 1.53 to 1.54 g / cm ³ , a strength of 5.0 GPa or more, preferably 5.5 GPa or more, further 6.2 GPa or more, and a surprisingly elastic modulus of 200 GPa or more, preferably 220 GPa or more. Further, the fiber was fixed by an epoxy resin substitution method, an ultrathin section was prepared on a plane parallel to the fiber axis, and mounted on a sample stage of an electron microscope. As shown in FIG.
Rotate +25 ° and take an electron diffraction image. An electron diffraction image of the fiber of the present invention is shown in FIG. Fiber of the invention (Fig. 2-b)
In the case of, the diffraction intensity ratio between the (200) plane and the (010) plane does not change even when the stage is rotated, and the intensity of the (200) plane is stronger than that of the (010) plane. However, the fibers produced by the conventional method (Fig. 2-a) showed opposite tendencies in the relative intensities of both diffraction planes, and at the same time,
The diffraction intensity ratio of the (010) plane changes when the stage is rotated. That is, the selective orientation in the fiber cross section is observed. The selective orientation in the fiber cross section observed in the fiber by the conventional method is also observed in p-aramid (Kazuyuki Yabuki et al .; The Textile Society of Japan, 32, T-55 (1976)), but it is not observed in the fiber of the present invention. . The definition of the index of the crystal plane in the present invention is ALFratini
AlFratini et al .; Material Research Socie
ty Symposia Proceedings, 134, p.431 (1989)).

The profile of the diffraction intensity of the fiber equator of FIG. 2 is shown in FIG. As shown in Fig. 3, when the baseline is drawn and the diffraction peak values are I (200) and I (110), I (200)
/ I (110) is 0.7 or less at any position in the case of a fiber having a high elastic modulus like the fiber of the present invention (Fig. 3-b), whereas the fiber having a low elastic modulus according to the prior art (Fig. 3). -A) is 0.
Indicates a value from 8 to 2.5. The reason for this is not well understood at present, but it is presumed that the ordering between molecules accompanying the relaxation phenomenon progresses and leads to selective orientation in the cross section.

The measuring method used in the present invention will be described. <Electron Diffraction Measurement Method> A Reichert Ultramicrotome Ultracut E equipped with a 5 mm monofilament fixed by an epoxy resin substitution method, embedded with epoxy resin, and equipped with a diamond in a plane parallel to the fiber axis was used for about 700 An ultrathin section of Å was cut out. A section cut out at a position of about 1/3 of the diameter was mounted on the sample stage of JEM-200CX, an electron microscope manufactured by JEOL Ltd., and an electron diffraction image was taken by rotating the sample stage at -25,0, + 25 °. At this time, the fiber axis must be aligned with the tilt rotation axis of the sample stage. With an acceleration voltage of 200KV,
The aperture was adjusted so as to have an effective diameter of about 1.4 μ on the objective surface, and an image was taken using a film for Fujifilm electron microscope. The diffraction intensity was read using a densitometer on the film after development and drying.

<Measurement Method of Density> The measurement was performed using a dry automatic densimeter Acupic (Pycnometer using helium gas) manufactured by Micromeritex.

[0018]

EXAMPLES Examples will be shown below, but the present invention is not limited to these examples. <Examples 1 to 3 and Comparative Examples 1 and 2> US Pat.
No. 3 polybenzoxazole 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 an acid was used for spinning. The dope is passed through a metal mesh filter material, then kneaded and defoamed by a biaxial kneading device, and then the pressure is raised, the temperature of the polymer solution is kept at 170 ° C., and 170 ° C. from a spinneret having 167 holes. The spinning yarn was spun in, and the discharged yarn was cooled with cooling air at a temperature of 60 ° C., and then the yarn was wound on a godet roll to give a spinning speed, and the temperature was kept at 22 ± 2 ° C. 10
% Phosphoric acid aqueous solution. Subsequently, the yarn was washed with ion-exchanged water in the second extraction bath, then immersed in a 0.1 N sodium hydroxide solution for neutralization. After further washing with a water washing bath, it was wound and dried in a drying oven at 80 ° C., and fiber physical properties and electron beam diffraction experiments were conducted. The results are shown in Table 1. It is recognized that the fiber of the present invention has a significantly improved elastic modulus and a unique microstructure as compared with the conventional fiber.

[0019]

[Table 1]

<Example 4> The fiber of Example 1 was washed with water in a washing bath and then passed through a drying step without winding. The drying conditions are as follows. Primary drying oven temperature 190 ℃ Drying time
60 seconds, second drying oven temperature 220 ℃ drying time 60 seconds, third drying oven temperature 240 ℃ drying time 60 seconds. The dry yarn had a water content of 0.4% by weight. Table 2 shows the measurement results of the fiber.

[0021]

[Table 2]

[0022]

According to the present invention, polybenzazole fiber having a high elastic modulus can be easily manufactured without a heat treatment step.

[Brief description of drawings]

FIG. 1 is a schematic view showing a rotation angle of an electron microscope sample stage of ultra-thin section of fiber (a: perspective view, b: cross-section of ultra-thin section viewed from fiber axis direction).

FIG. 2 is an electron diffraction image (a) of the fiber of the present invention at + 25 °, 0 ° and -25 ° and an electron diffraction image (b) of a conventional fiber.

FIG. 3 is a profile of electron beam diffraction intensity at each sample rotation angle on the fiber equator of the fiber (b) of the present invention and the conventional fiber (a).

[Explanation of symbols]

1: Ultrathin section, 2: Rotating sample spindle (fiber rolling), 3:
Electron beam, 4: electron beam diffraction intensity profile at sample stage + 25 ° (thick line), 5: electron beam diffraction intensity profile at sample stage 0 ° (thin line), 6: electron beam diffraction intensity at sample stage -25 ° Profile (dotted line), 7: peak height, 8: baseline.

Claims (4)

[Claims] 1. When a section of a polybenzazole fiber is cut in a plane parallel to the fiber axis and an electron diffraction image is taken, even if the section is rotated ± 25 ° around the fiber axis, the peak intensity ratio I ( 200) / I (010) are all 1.0 or less, high modulus polybenzazole fiber. 2. The polybenzazole fiber according to claim 1, which has a strength of 5.0 GPa or more and an elastic modulus of 200 GPa or more. 3. The high-modulus polybenzazole fiber according to claim 1, which has a density of less than 1.55 g / cm ³ . 4. The high elastic modulus polybenzazole fiber according to claim 1, wherein the polybenzazole is polyparaphenylenebenzobisoxazole.