JPH11117126A - High-elasticity polybenzazole fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polybenzazole fiber that has high strength and high elasticity and is useful as an industrial material. SOLUTION: The objective polybenzazole fiber of high elasticity has a convex inflexion point in the range of 0.004-0.02 (Å<-2> ) of the square of the scattering vector of the Guinea plots constituted from the equatorial streak of the small angle X-ray scattering. The polybenzazole is dissolved in polyphosphoric acid and the resultant spinning dope is extruded through the orifice into non- coagulating gas. After it cools down <=50 deg.C, the dope filament is coagulated by bringing it into contact with a non-aqueous coagulating agent, then the filament is washed with water and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polybenzazole fiber having excellent strength and elastic modulus, which is suitable as an industrial material, and a method for producing the same.

[0002]

2. Description of the Related Art Polybenzazole fiber has twice the strength and elastic modulus of polyparaphenylene terephthalamide fiber, which is a typical super fiber currently on the market, and is expected as a next-generation super fiber.

[0003] By the way, it is conventionally known to produce fibers from a polybenzazole polymer in polyphosphoric acid. For example, there are U.S. Pat. No. 5,296,185 and U.S. Pat. No. 5,538,702 for spinning conditions, and W094 / 047 for a washing and drying method.
No. 26 and a heat treatment method are proposed in US Pat. No. 5,296,185.

[0004]

However, the elastic modulus of the high-strength polybenzazole fiber obtained by the above-mentioned conventional manufacturing method generally remains at 290 GPa even after heat treatment at 350 ° C. or more as described in US Pat. No. 5,296,185. It is. Although extremely high elastic modulus has been reported at the laboratory level, fiber yarns (aggregates of filaments) having a modulus of 5.0 GPa or more but having a modulus of 290 GPa or more can undergo molecular relaxation under special spinning conditions. Except for an example realized by suppression (JP-A-8-325840), an easy production technology at a level that can be called an industrial technology has not yet been obtained.

[0005] The inventors of the present invention have intensively studied to develop a technique for easily producing polybenzazole fiber having the ultimate elastic modulus as an organic fiber material.

Means for realizing the ultimate physical properties of fibers include:
Rigid polymers such as so-called ladder polymers have been considered, but these rigid polymers are not flexible,
In order to have flexibility and processability as an organic fiber, a linear polymer is an essential condition.

[0007] SGWierschke et al.
ciety Symposium Proceedings Vol.134, p.313 (1989
As shown in (1), cis-polyparaphenylenebenzobisoxazole has the highest theoretical elastic modulus among linear polymers. This result was also confirmed by Tashiro et al. (Macromolecules.vol.24, p.3706 (1991)). Of the polybenzazoles, cis-type polyparaphenylenebenzobisoxazole had a crystal elastic modulus of 475 GPa.
(P. Galen et al. Material Research Society Symposium Pr.
oceedings Vol. 134, p. 329 (1989)), which was considered to have the ultimate primary structure. Therefore, in order to obtain the ultimate elastic modulus, it is a theoretical conclusion that polyparaphenylene benzobisoxazole is used as a material for the polymer.

The fiberization of the polymer is disclosed in US Pat. No. 5,296,185.
No. 5,385,702, and the heat treatment is performed by the method proposed in US Pat. No. 5,296,185. The elastic modulus of the yarn (fiber yarn) obtained by such a method is at most. It is 290 GPa, which is just 61% of the crystal elastic modulus. Accordingly, the need for research on the improvement of these methods was keenly felt, and it was found that the desired physical properties could be industrially easily achieved by the following methods.

[0009]

That is, the present invention provides a convex inflection when the square k ² of a scattering vector in a Guinier plot composed of equatorial streaks of small-angle X-ray scattering is within the range of 0.004 to 0.02 (Å ⁻² ). Having points and crystal orientation parameters
<sin ² φ> is a high elastic modulus polybezazole fiber characterized by having a modulus of less than 0.025, and the elastic modulus of the fiber is 290 G
High elastic modulus polybenzazole fiber characterized by having a strength of Pa or more and a strength of 5.0 GPa or more. Also, a spin dope composed of polybenzazole and polyphosphoric acid is extruded from a die into a non-coagulating gas, and after the dope filament reaches a temperature of 50 ° C. or less, it is brought into contact with a non-aqueous coagulant to coagulate. A method for producing a high-modulus polybenzazole fiber, characterized by washing and drying the filament, and further comprising, after washing and drying, heating the filament at a temperature of 500 ° C. or more under a constant tension. For producing high modulus polybenzazole fibers.

A spin dope composed of polyparaphenylene benzobisoxazole (PBO) and polyphosphoric acid is spun from a spinneret. Thereafter, the dope filament is subjected to a coagulation step, and the obtained filament is produced through neutralization, washing, drying, and heat treatment under tension. In the doped yarn (assembly of doped filaments) in the draw zone before entering the coagulation bath, the molecular chains of PBO are in a liquid crystal state and are in a highly oriented state in the stretching direction. Generally, in order to increase the elastic modulus of a fiber, it is necessary to increase the crystal orientation in the fiber. For that purpose, it is necessary to solidify the dope yarn while keeping the molecular chains highly oriented in the draw zone. But,
When water or phosphoric acid aqueous solution as used in the prior art is used as a coagulant, the penetration rate (diffusion rate) of water molecules into the inside of the doped yarn in the coagulation process is too fast, and is formed once in the draw zone. The resulting microstructure was disturbed, and as a result, there was a defect that the elastic modulus did not increase even if heat treatment was performed under tension through washing, neutralization, and drying. According to the present invention, by using a non-aqueous coagulant, the dope yarn is coagulated while maintaining the high orientation state formed in the draw zone to form fibers. The microstructure of the fiber thus obtained is characterized in that the microfibrils constituting the fiber have a uniform diameter compared to the conventional production method and are regularly aligned in a direction perpendicular to the fiber axis. Further, it has been found that by heat-treating the fiber under tension, a fiber having a high strength and a high elastic modulus, which has not been obtained until now, can be easily obtained.

The fiber has a strength of 5.0 GPa or more and an elastic modulus of 290 GPa or more, preferably a strength of 5.0 GPa or more and an elastic modulus of 350 GPa or more, or a strength of 6.2 GPa or more and an elastic modulus of 30 GPa or more.
It is more than 0GPa.

The present invention aims to provide a high-strength and high-modulus polybenzazole fiber which overcomes the technical difficulties so far and achieves a nearly crystalline elastic modulus. The points of the present invention can be realized by the following relatively simple method in order to express the above-mentioned structural characteristics. That is, a dope of a polymer substantially consisting of polyparaphenylene benzobisoxazole is extruded from a spinneret into a non-coagulating gas, and the obtained spun yarn is introduced into a coagulation bath to coagulate the yarn. Drying and winding are performed, but the discharged yarn is cooled to 50 ° C. or less, and then brought into contact with a coagulation liquid. Further, as a coagulant, a non-aqueous system other than water or phosphoric acid aqueous solution and substantially against polybenzobisoxazole is used. It is characterized in that a heat treatment is carried out under a tension at a temperature of 500 ° C. or higher using a solvent having no compatibility.

Hereinafter, the present invention will be described in more detail. The polybenzazole fiber in the present invention is a PBO homopolymer,
And a random, sequential or block copolymer with polybenzazoles (PBZ) containing substantially 85% or more of a PBO component. Here, the polybenzazole (PBZ) polymer is described in, for example, “Liquid
Crystalline Polymer Compositions, Process and Pro
ducts "U.S. Pat. No. 4,703,103 (October 27, 1987)
Sun), "Liquid Crystalline Polymer Compositions, P
rocess and Products "U.S. Pat.
August 6, 5), “Liquid Crystalline Poly (2,6-Benz
othiazole) Compositions, Process and Products, U.S. Patent No. 4,337,724 (August 6, 1985), "Liquid
Crystalline Polymer Compositions, Process and Pro
ducts "U.S. Pat. No. 4,453,693 (August 6, 1985)
Sun), Evers "Thermooxidative-ly Stable Articula
ted p-Benzobisoxazole and p-Benzobisoxazole Polyme
rs "U.S. Pat. No. 4,539,567 (November 16, 1982)
Sun), Tsai et al. “Method for making Heterocyclic Blo
ck Copolymer "U.S. Pat. No. 4,578,432 (March 25, 1986).

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

[0015]

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[0016]

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Suitable solvents for forming the dope of the polymer consisting essentially of PBO include cresol and non-oxidizing acids capable of dissolving the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic 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 concentration of the polymer in the solvent is preferably at least about 7% by weight, more preferably at least 10% by weight.
%, Most preferably 14% by weight. The maximum concentration is limited by practical handling properties such as, for example, polymer solubility and dope viscosity. Due to these limiting factors, the polymer concentration does not exceed 20% by weight.

A suitable polymer, copolymer or dope is synthesized by a known method. For example, U.S. Pat. No. 4,453,693 to Wolfe et al. (August 6, 1985); U.S. Pat. No. 4,772,678 to Sybert et al. (September 20, 1988);
US Patent No. 4,847,350 to rris (July 11, 1989)
And synthesized by the method described in Polymers consisting essentially of PBO are disclosed in US Pat. No. 5,085,959 to Gregory et al.
According to (February 18, 1992), it is possible to increase the molecular weight at a high reaction rate under a relatively high temperature and high shear condition in a dehydrating acid solvent.

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

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 requires a relatively high temperature (dope of dope). It is desirable that the cooling air is uniformly cooled by the rectified cooling air having a temperature equal to or higher than the solidification temperature and equal to or lower than the spinning temperature. The length (L) of the draw zone needs to be long enough to complete solidification in a non-coagulating gas, and is roughly determined by the single hole discharge amount (Q). As a requirement for forming a desired structure in the spun yarn, it is important that the filament is cooled to 50 ° C. or lower, preferably 45 ° C. or lower, and then brought into contact with a coagulating liquid. If the temperature is 50 ° C. or more, there is a problem that the crystal orientation of the fiber is not sufficiently improved due to the relaxation effect. In order to obtain good fiber properties, the draw-out stress of the draw zone is desirably 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 a coagulation bath. Since the spinning tension is high, no consideration is required for disturbance of the coagulation bath, and any type of coagulation bath may be used. For example, funnel type, water tank type, aspirator type or waterfall type can be used. As the coagulation liquid, a liquid which is non-aqueous and has substantially no compatibility with polybenzazole is used. As the non-aqueous coagulation liquid, aldehydes, ketones, alcohols containing 10 or less carbon atoms in the molecule or a liquid mixture thereof are preferable, and ethanol, methanol, propanol, butanol, ethylene glycol, and acetone are more preferable. Or a mixed liquid thereof. After coagulation, 99.0% or more, preferably 99.5% or more of phosphoric acid contained in the yarn is finally extracted in a washing bath. Alternatively, the coagulation bath may be separated into multiple stages and finally washed with water. In order to further increase the microfibril arrangement and crystal orientation of the coagulated fiber, polyphosphoric acid, a coagulant, a neutralizing agent, or water is contained inside the fiber during or during the coagulation, washing, neutralization, and drying steps. Tension may be applied to the yarn. Further, the fiber bundle is neutralized with an aqueous sodium hydroxide solution,
It is desirable to wash with water.

The use of a non-aqueous coagulation liquid having substantially no compatibility with polybenzazole makes the fine structure of the fibers after washing different from the conventional production method using water or a phosphoric acid aqueous solution as a coagulant. That is, when the small-angle X-ray scattered image of the washed yarn is measured by a method described later, an equatorial streak appears, but a characteristic appears in the scattering angle dependence of the scattering intensity. FIG.
FIG. 2 shows a Guinier plot showing the scattering angle dependence of small-angle scattering of the washed fiber prepared by the conventional method, and FIG. 2 shows a Guinier plot of the washed fiber prepared by the method of the present invention as in FIG. In the Guinier plot of the fiber prepared by the method of the present invention, a clear convex inflection point occurs in the range of 0.004 <k ² <0.02 (Å ⁻² ). According to the theory of small-angle X-ray scattering, the origin of the inflection point convex upward is interpreted as the existence of a regular array of microfibrils constituting the microstructure of the fiber in a direction perpendicular to the fiber axis. Of course, the microstructure of the washed fiber produced by the conventional method is also made of microfibrils, but as shown in FIG. 1, the Guinier plot shows an inflection point along a straight line over a wide range from 0.003 <k ² <0.04 (Å ⁻² ). Is not present. This means that the washed fibers produced by the method of the present invention have a microstructure in which the diameter of the microfibrils is uniform and the arrangement of the fiber axes in the vertical direction is high.

Further, when the crystal orientation of the washed yarn is measured and compared by the method described later, the fiber yarn produced by the conventional method has an orientation parameter <sin ² φ> of 0.025 or more, whereas the fiber yarn produced by the method of the present invention has the orientation parameter <sin ² φ> of 0.025 or more. In the case of the treated fiber, it is less than 0.025.
Therefore, the crystal orientation of the spun yarn of the present invention is higher than that of the conventional production method.

After the water-washed yarn is dried, it is subjected to a heat treatment under tension at 500 ° C. or more, whereby the elastic modulus is 290 GPa or more and the strength is 5.0 G
Fiber yarn of Pa or more can be obtained. It is considered that the solidification proceeded without disturbing the microstructure by using the solidification method of the present invention. It is understood that the characteristic microstructure of the washed fiber is an essential precursor for changing into a fiber having a higher elastic modulus and strength through the next heat treatment step.

[0026]

【Measuring method】

<Measurement method of small-angle X-ray scattering> Small-angle X-ray scattering was performed by the following method. X-rays to be used for the measurement were generated using Rotaflex RU-300 manufactured by Rigaku Corporation. The device was operated at a fine focus of 30 kV x 30 mA output using a copper counter-cathode as a target. The optical system was a point converging camera manufactured by Rigaku Corporation, and the X-rays were monochromatic using a nickel filter. As a detector, an imaging plate (FDL UR-V) manufactured by Fuji Photo Film Co., Ltd. was used. The distance between the sample and the detector may be any suitable distance between 200 mm and 350 mm. Helium gas was filled between the sample and the detector to suppress interference background scattering from air and the like. Exposure time is 2
Hours to 24 hours. For reading of the scattering intensity signal recorded on the imaging plate, digital micrography (FDL5000) manufactured by Fuji Photo Film Co., Ltd. was used. The resulting data, Guinier plot with respect to the equatorial direction of the scattering intensity I after performing background correction (the natural logarithm ln scattering intensity after background correction (I) with respect to the square k ² of the scattering vector Plot). Where the scattering vector k is k = (4π / λ) sin θ, and λ is X
The wavelength of the line is 1.5418 ° and θ is half the scattering angle 2θ.

<Measurement Method of Crystal Orientation> The crystal orientation of the washed fiber yarn was measured by X-ray diffraction. The X-rays to be used for the measurement were generated using a rotor flex RU-200 manufactured by Rigaku Corporation. The target was monochromated with a nickel filter using a copper counter cathode. Driving with normal focus of output 40kVx100mA. The optical system used was a 3-slit optical system small angle X-ray scattering device manufactured by Rigaku Corporation. The pinhole diameter was 0.15 mm. Only one yarn was subjected to the measurement in order to remove the disorder of the orientation resulting from the arrangement of the yarns. The exposure time was between 10 minutes and 1 hour. The diffracted X-ray was detected at a position 80 mm from the sample using the above-mentioned imaging plate.
Indexing of diffraction points is described by Fratini et al. (Material Research Soc.
(ietyiety Symposium Proceedings Vol.134, p.431 (1989))
According to the proposed crystal model. After the background correction from the intensity distribution in the azimuthal direction of the diffraction point along the Debye ring of the (200) plane, the orientation parameter <sin ² φ defined by [Equation 1]
> Evaluated.

[0028]

(Equation 1) Here, I (φ) is the azimuth distribution of the diffraction intensity after background correction measured along the Debye ring of the (200) plane, and φ is the azimuth measured from the equator.

[0029]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

<Examples 1, 3, 4 and Comparative Examples 1, 2, 3, 4> 30 ° C. obtained by the method described in US Pat.
24.4 dL / g intrinsic viscosity measured with methanesulfonic acid solution
A spin dope consisting of 14.0% (by weight) of polyparaphenylene benzobisoxazole and polyphosphoric acid having a phosphorus pentoxide content of 83.17% was used for spinning. The dope is passed through a metal mesh filter medium, and then kneaded and defoamed with a kneading device consisting of two shafts, and then the pressure is increased. Spin at 170 ° C,
After cooling the discharged yarn using cooling air at a temperature of 60 ° C., and further cooling the discharged yarn to 40 ° C. by natural cooling, it was introduced into a coagulation bath maintained at a temperature of 30 ± 2 ° C. The spinning speed was constant by winding the wire around a gusset roll provided in a coagulation bath. Subsequently, the yarn was washed with ion-exchanged water in a second extraction bath, and then immersed in a 0.1 N sodium hydroxide solution to perform a neutralization treatment. After washing in a washing bath, take up and dry in a drying oven at 80 ° C.
Heat treatment was performed at a temperature of 600 ° C./d for 1.4 seconds. Table 1 shows the results. <Example 2> A tension of 2.4 GPa was applied for 0.2 seconds to an undried state to the washed fiber yarn manufactured under the same conditions as in Example 1. Further, the same drying and heat treatment as in Example 1 were performed.

[0031]

[Table 1]

From Table 1 above, it can be understood that the fiber of the present invention shows a remarkable improvement in strength and elastic modulus as compared with the conventional fiber, and is extremely excellent in physical properties. The fibers of the present invention include tension members such as cables, electric wires and optical fibers, ropes, etc., as well as rocket insulation, rocket casing, pressure vessels, space suit strings, planetary exploration balloons, etc. Shock-resistant materials such as materials and bullet-proof materials, cut-resistant materials such as gloves, fire-fighting clothing, heat-resistant felts, gaskets for plants, heat-resistant fabrics, heat-resistant fabrics, various types of sealing, heat-resistant cushions, filters, etc., belts and tires , Soles, ropes, hoses, rubber reinforcements, fishing lines, fishing rods, tennis rackets, table tennis rackets, badminton rackets, golf shafts, club heads, gut, strings, sail crosses, sports (running) shoes, spike shoes, Competition (running) bicycles and their wheels, spokes, brake wires, transmission wires, competition (running) Sport-related materials such as wheelchairs and their wheels, skis, stocks, helmets, etc., abrasion-resistant materials such as avance belts, clutch farthings, reinforcing materials for various building materials and other rider suits, speaker cones, lightweight baby carriages, lightweight wheelchairs, lightweight Nursing beds, lifeboats,
Can be used for a wide range of applications such as life jackets.

[0033]

According to the present invention, polybenzazole fibers having both high strength and high elasticity, which have not been obtained conventionally, can be industrially easily produced, and the practical use as industrial materials is enhanced. The effect of expanding is enormous.

[Brief description of the drawings]

FIG. 1 is a Guinier plot of a washed yarn produced according to the prior art.

FIG. 2 is a Guinier plot of a washed yarn manufactured using the technology proposed this time.

Claims (5)

[Claims] 1. The square k ² of a scattering vector in a Guinier plot composed of equatorial streaks of small-angle X-ray scattering is equal to 0.
A high-modulus polybezazole fiber having a convex inflection point in the range of 004 to 0.02 (Å ^-2 ). 2. The crystal orientation parameter <sin ² φ>
2. The high elastic modulus polybenzazole fiber according to claim 1, wherein the fiber is less than 0.025. 3. The fiber according to claim 1, wherein said fiber is under a constant tension.
The heat treatment at 0 ° C. or more increases the modulus of elasticity to 290 GPa or more and the strength to 5.0 GPa or more.
The high-modulus polybenzazole fiber described in the above. 4. A spin dope comprising polybenzazole and polyphosphoric acid is extruded from a die into a non-coagulating gas,
A method for producing a high-modulus polybenzazole fiber, comprising: after a dope filament reaches a temperature of 50 ° C. or less, contacting with a non-aqueous coagulant to coagulate, and then washing and drying the filament. 5. The method for producing a high-modulus polybenzazole fiber according to claim 3, wherein the filament is heat-treated at a temperature of 500 ° C. or more under constant tension after washing and drying.