JPH07157920A - Method for heat-treating polybenzazole fiber - Google Patents

Abstract

PURPOSE:To improve physical properties such as strength, elongation and elastic modulus by heat-treating polybenzazole fiber under tension while bringing the fiber into contact with a heated gas stream. CONSTITUTION:This method for heat-treating polybenzazole fiber is to dry jet-wet spin a spinning dope of a polybenzazole through an air gap, then wash the resultant yarn with water, desolvate the yarn, dry the desolvated yarn, introduce the dried yarn into a heated container in which steam flows in a cocurrent or a countercurrent state and heat-treat the yarn under tension. Thereby, physical properties are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat treatment of polybenzazole fiber for the purpose of improving the physical properties of the fiber.

[0002]

2. Description of the Related Art Polybenzazole fibers such as polybenzoxazole are two types of polyparaphenylene terephthalamide fibers which are currently regarded as representatives of super fibers on the market.
Since it has more than double the elastic modulus, it is expected as a next-generation super fiber. Heat treatment is essential to obtain the highest elastic modulus of polybenzazole fiber. A general heat treatment method is described in J. Mater. Sci. 20, 2727 (198
5) and H.M. D. Ledbetter, S .; Rosenb
erg, C.I. W. Hurtig; Symposium
Proceedings of The Material
alsScience and Engineering
go of Rigid-Rod Polymers, Vo
l. 134, 253 (1989). The heat treatment method for these ordinary polybenzazole fibers must be treated at a temperature of 500 ° C. or higher because the rigidity of the polybenzazole fibers is extremely high. Therefore, the heat treatment machine according to the conventional method is huge and expensive, which is an obstacle to industrialization.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a new heat treatment method for eliminating the long-term heat treatment at a high temperature for improving the elastic modulus of polybenzazole fiber. Polybenzazole (PBZ) fiber is a fiber composed of polybenzoxazole (PBO) and polybenzthiazole (PBT).

[0004]

SUMMARY OF THE INVENTION The present invention is directed to the first aspect of heat treatment of polybenzazole by bringing it into contact with a gaseous heat treatment medium under tension and allowing the heat treatment gas to flow countercurrently or countercurrently in the heat treater. Characterize. More specifically, the present invention relates to a method of heat-treating a polybenzazole fiber by applying tension to it and bringing it into contact with a heat treatment medium. The heat treatment medium is a gas, which flows countercurrently or countercurrently in the heat treatment zone, and the relative velocity of the gas and the fiber is at least 5
The second characteristic is that it is m / sec. Further, the present invention is
In this method, tension is applied to the polybenzazole fiber to bring it into contact with a heat treatment medium, and then heat treatment is performed. The third characteristic is that the gas flows countercurrently or countercurrently in the heat treatment device, the relative velocity of the gas and the fiber is at least 5 m / sec, and the residence time of the fiber in the heat treatment zone is 3 seconds or less. .

The present invention uses a molded article containing polybenzazole (polybenzoxazole and polybenzthiazole). Polybenzoxazoles, polybenzthiazoles and random, alternating and block copolymers of polybenzoxazoles, polybenzthiazoles are described in the literature. For example, Wolf et al., Liquid Crystal Polymer Composites, Processes and Moldings, US Pat.
03 (October 27, 1985), Wolf et al., Liquid Crystal Polymer Composites, Processes and Moldings, US Pat. No. 4,533,692 (August 6, 1985), Wolf.
Et al., Liquid crystal poly (2,6-benzthiazole) composite, manufacturing method and molded article, US Pat. No. 4,533,724 (8).
June 6, 1985), Wolf et al., Liquid crystal polymer composite, manufacturing method and molded article, US Pat. No. 4,533,693.
No. (August 6, 1985), Evers, thermooxidatively stable parabenzoxazole and parabenzthiazole polymers, US Pat. No. 4,359,567 (Nov. 16,
1982), Tsai et al., Heterocyclic block copolymers, US Pat. No. 4,578,432 (March 25, 1986).
), 11 Ency. Poly. Sci. & En
g. , Polybenzthiazole and polybenzoxazole, 601 (J. Wiley & Sons 198).
8) and W. W. Adams et al., The Mater
ials Science and Engineer
ing of Rigid-Rod Polymers
(Materials Research Society
ty 1989) and the like. The polymer is an AB monomer unit represented by formula 1 (a) and / or formula 1
It consists of the AA / BB monomer unit represented by (b).

[0006]

[Chemical 1]

Here, Ar represents aromatic. The aromatic may be a heterocycle such as a pyridinylene group, but is preferably a carbocycle. The aromatic group may be a fused or unfused multi-carbon ring, but is preferably a single 6-membered ring. The size is not critical, but the aromatic groups are not more than 18 carbon atoms, more preferably not more than 12 carbon atoms and most preferably not more than 6 carbon atoms. Preferable aromatic groups include phenylene group, tolylene group, biphenylene group, bisphenylene ether group and the like. Ar1 in the AA / BB-mer unit is preferably a 1,2,4,5-phenylene group or the like. Ar in the AB monomer unit is preferably a 1,3,4-phenylene group or an analogue thereof. Each Z is an oxygen or sulfur atom. Each DM is a divalent organic group that does not interfere with independent synthetic polymerization. The divalent organic group may include an aliphatic group, but the number of carbon atoms in this aliphatic group is 12 or less. However, the divalent organic group is preferably the aromatic group described above. Most preferred is the 1,4-phenylene group or its analogues. The nitrogen and Z atoms of each azole ring combine with the carbon atoms forming the adjacent aromatic ring to form the 5-membered ring of the azole. The azole ring in the AA / BB monomer unit has 11 Ency. Polym. Sci. &
Eng. , Supra, page 602, it may be cis or trans.

The polymers of the present invention are preferably essentially A
It consists of a B-mer or an AA / BB-mer, and more preferably basically consists of an AA / BB-mer polymer. The molecular structure of polybenzazole polymer is rigid, quasi-rigid or flexible coil. It is preferably rigid in the case of AA / BB polymer and quasi-rigid in the case of AB polymer.
The azole ring in the polymer is an oxazole ring (Z =
O) is preferred. The polybenzazole polymer is preferably a polymer that forms lyotropic liquid crystals (lyotropic liquid crystals form liquid crystal domains when dissolved at a concentration above the critical concentration). Preferred monomer units are represented by the formulas 2, 3
It shows in (a)-(h). The polymer has the formula 2, 3 (a)-
It is preferably composed of the unit shown in (h). Most preferably, it consists of repeating units selected from formulas 2 (a)-(c).

[0009]

[Chemical 2]

[0010]

[Chemical 3]

Each polymer preferably comprises at least 25 mers, more preferably 50 mers, most preferably 100 mers. The intrinsic viscosity of the AA / BB polybenzazole polymer (by the established single point method measured at 25 ° C. dissolved in methanesulfonic acid) is preferably at least 10 dL / g, more preferably 1
It is 5 dL / g, most preferably 20 dL / g. Intrinsic viscosities of at least 25 or 30 dL / g are preferred for some purposes. An intrinsic viscosity of 60 dL / g or more can also be used, but it is preferably less than 45 dL / g. The intrinsic viscosity is most preferably around 33 dL / g. The intrinsic viscosity of the lyotropic liquid crystal quasi-rigid AB-polybenzazole polymer is preferably at least 5 dL /
g, more preferably at least 10 dL / g, most preferably at least 15 dL / g. The polymer can be formed into a fiber or film by spinning or extruding a dope.
The dope consists of polymer and solvent. The dope used for spinning or extrusion can be prepared by directly using the polymer dope or by dissolving a polymer or a copolymer. Some of polybenzoxazole and polybenzthiazole can be dissolved in cresol, but the solvent is preferably a soluble acid. The acid is preferably non-oxidizing. Preferred acids include polyphosphoric acid, methanesulphonic acid, sulfuric acid and / or mixtures thereof. The acid is preferably polyphosphoric acid and / or methanesulfonic acid. More preferred is polyphosphoric acid. The dope should contain the polymer in a sufficient concentration to solidify the polymer and form a solid. However, the concentration should not be so high that it cannot be handled. When the polymer is a rigid or quasi-rigid chain, the concentration of the doped polymer is preferably sufficient to form a liquid crystal. The polymer concentration is preferably at least 7% by weight, more preferably at least 10% by weight and most preferably at least 14% by weight. The maximum concentration is basically determined by practical factors such as the solubility of the polymer and the viscosity of the dope as described above. Due to these limiting factors, the polymer concentration is rarely 30% by weight.
But usually does not exceed 20% by weight.

Suitable polymers and copolymers can be synthesized by methods already known. US Patent No. 45 to Wolfe et al.
33693 (August 6, 1985) and Sybert et al. U.S. Pat. No. 4,772,678 (September 20, 1988) and H.
Arris U.S. Pat. No. 4,847,350 (July 11, 1
898) and U.S. Pat. No. 5,089,591 to Gregory.
(February 18, 1992) and Ledbetter et al. “An Integrated Laboratory”.
y Process for Preparing Ri
gid Rod Fibers from the M
onome ”The Material Science
e and Engineering of Rigi
254-64 (Mat of d-Rod Polymers)
rialsRes. Soc. , 1989), and the polymer can be synthesized. In summary, the preferred monomers (AA-monomer and BB-monomer or AB-monomer) react in a non-oxidizing solution and provide high shear under vigorous stirring under a non-oxidizing atmosphere at a temperature of 120 The dehydration reaction proceeds by gradually or gradually increasing the temperature from below ℃ to at least 190 ℃. Suitable examples of AA monomers include terephthalic acid or the like. Preferred examples of BB monomer include 4,6
-Diaminoresorcinol, 2,5-diaminohydroquinone, 2,5-diamino-1,4-dithiobenzene and the like. These are typically used as the hydrochloride salt. Preferable examples of AB monomer include 3-amino-4-hydroxybenzoic acid and 3-hydroxy-4.
-Aminobenzoic acid, 3-amino-4-thiobenzoic acid, 3-thio-4-aminobenzoic acid and the like are included, and these are usually used as hydrochlorides.

The polymer of formula 1 (b) preferably contains at least 85% terephthalic acid and / or its functional derivatives and less than 15% different difunctional acids. More preferably less than 10% of different difunctional acids are included. Formula 1
The polymer of (b) is preferably at least 85% 4,
It contains 6-diamino-1,3-benzenediol dihydrochloride and less than 15 mol% 2,5-diamino 1,4-benzenediol dihydrochloride. More preferably, it contains less than 10 mol% of 2,5-diamino 1,4-benzenediol dihydrochloride.

Preparation of PBO Dope PBZ dope is a solution of PBZ polymer and solvent. Polybenzazole polymers are soluble only in very strong protic acids such as methanesulfonic acid and polyphosphoric acid. The preferred solvent is polyphosphoric acid (PPA). PB
The concentration of O relative to polyphosphoric acid is about 14%. PBO
/ PPA-doped PBO intrinsic viscosity (0.05g / dL
Measured at 25 ° C with a methanesulfonic acid solution having a concentration of 22)
To 45 dL / g.

Preparation of Polybenzazole Fibers Polybenzazole fibers are preferably made in a continuous process of so-called polymerization and spinning. That is, the polymerized dope is sent to the direct spinning having the spinneret without being taken out from the polymerization kettle. Of course, you may take out from a polymerization kettle and spin dry and wet separately. In dry-wet spinning, the dope is extruded from the spinneret. The pores of the spinneret may be arranged in a circular arrangement, an orthogonal arrangement, or any other arrangement. The array of pores must be chosen so that the extruded dopes do not fuse together. There is no limit to the number of pores in the spinneret. It is important to make the temperature of all spun yarns extruded from the spinneret uniform. This is because the difference in temperature of individual filaments in the yarn is immediately reflected in the difference in filament tension. The spun and extruded dope fibers are immersed in a coagulation bath to separate the solvent from the polybenzazole polymer. There is an air gap between the spinneret and the coagulation bath. The gas in the air gap is usually air. However, it may be nitrogen, carbon dioxide, helium or argon. The preferred temperature of the air gap is preferably between 0 ° C and 150 ° C. More preferably, it is 0 ° C to 100 ° C. Most preferably 50-100
℃. After spinning, the spun yarn is contacted with a liquid known as a coagulating liquid to separate the solvent and polymer.

Coagulation is carried out in a bath or by spraying. If it is a coagulation bath, install it below the spinneret. Over 99.0% solvent is extracted in the coagulation bath. More preferably, 99.5% or more is extracted. Any coagulation bath / spray used contains water or a water / acid mixture. The preferred acid is phosphoric acid, preferably at a concentration of 30% or less. Other coagulation media also include organic solvents such as acetone, methanol and acetanilide. Any coagulation bath system can be used, for example, a solidification bath having a general roller in the bath or a funnel-shaped coagulation bath described in JP-A-51-35716 and JP-B-44-22204. Alternatively, a high-speed aspirator type coagulation bath described in US Pat. No. 4,298,565 or a waterfall-shaped coagulation bath described in US Pat. No. 4,869,860 is used. The solution concentration of the coagulated fiber is further reduced by washing the fiber with water. As mentioned above, any washing bath or spray contains water or a dilute water / acid mixture, with a preferred acid content being less than 5% phosphoric acid solution. Other water washing media also include organic solvents such as acetone, methanol, and acetanilide.

After being coagulated and washed with water, the fibers are dried and wound on a roll. The fiber thus obtained already has sufficient strength and elastic modulus as a spun yarn, but by further heat treatment, the elastic modulus of the polybenzazole fiber can be dramatically improved.

The heat treatment can be performed separately or continuously. A typical apparatus is a thin tube or a square shape, and the heat treatment machine is equipped with a feeding device and a discharging device. The heat treater must be able to supply the heating medium gas countercurrent or countercurrent to the fibers. Of course, it is also possible to provide a nozzle for supplying heated gas at the same time in the center of the heat treatment device and heat with a countercurrent and countercurrent heating medium gas. High-speed, high-temperature gas such as water vapor, nitrogen or other inert gas can be used as a heating medium for heat treatment for the purpose of improving the elastic modulus of the polybenzazole spun yarn. The inside of the heat treatment device in which the fibers come into contact with the heat transfer gas is hereinafter referred to as a heat treatment zone. The velocity of the gas as the heating medium is preferably higher than 10 m / sec. This is because the heat exchange between the fiber and the heated gas is determined by the difference in velocity as described by the following equation. ΔT ∝ L ^0.8 · u ^0.8 · t · (Ts-Tf) where L is the length of the heater or the heat treatment zone, u is the speed difference between the fiber and the heated gas, t is the residence time, Ts is the temperature of the heated gas, Tf Is the yarn temperature before heat treatment. In order to enhance the heat exchange between the heat transfer medium gas and the fiber, it is important to bring the heat transfer medium gas into contact with the fiber in a countercurrent or a countercurrent when the heat transfer medium is guided to the heat treatment device. If the flow is counter-current or counter-current, the relative velocity between the fiber and the heat medium gas increases, and the heat exchange effect increases. Of course, the counter flow has a higher relative velocity than the counter flow.
The velocity of the fibers passing through the heat treatment zone is preferably at least 20 m / min, more preferably at least 40 m.
/ Min. The heating gas velocity is preferably at least 5
m / sec, more preferably at least 10 m / sec.
The speed difference between the fibers and the heated gas is preferably at least 5 m
/ Sec is preferably 10 m / sec, more preferably 100 m / sec. The gas flow rate is calculated from the weight per hour measured by the anemometer. The flow velocity of the heat transfer gas in the heat treatment device having a nozzle in the center is calculated by the following equation for both countercurrent and counterflow. v = Q / d / 60 ² / 2S where v is the velocity m / sec, and Q is the flow rate kg of the heat transfer medium gas.
/ H, S is the cross-sectional area of the heat treatment device. The residence time of the fibers in the heating zone is preferably at most 20 seconds, more preferably at most 5 seconds, most preferably at most 3 seconds. The tension applied to the fibers during heat treatment is preferably between 0.1 and 10 g / d. Since the temperature of the fiber is instantaneously increased by using a heating gas such as high-speed and high-temperature steam, the negative heat treatment effect during heat treatment can be reduced. As a result, the heat treatment of the present invention can significantly reduce the temperature of the conventional method (normally 600 ° C.) and the processing time of the conventional method (normally 10 seconds). By using a countercurrent or counterflow high-speed, high-temperature heated gas, the temperature required for heat treatment can be lowered to 400 ° C., and the time required for heat treatment can be reduced to 3 seconds or less. The tensile modulus of the heat treated fibers according to the method of the invention is preferably at least 220 GPa, more preferably at least 250 GPa.

[0019]

EXAMPLES The effects of the present invention will be shown by the following examples. However, it goes without saying that the present invention is not limited to the examples shown below. (Example 1) 4,7-diamino-1,3-benzenediol dihydrochloride (50.0 g, 0.235 mol) and 200 g of polyphosphoric acid (P2O5 concentration 83.3% by weight) s) in a nitrogen atmosphere. The mixture was stirred under 40 ° C for 12 hours, and then the temperature was raised to 60 ° C for 20m for the purpose of dehydrochlorination.
Stirred under vacuum of mHg for 8 hours. Further terephthalic acid (39.0 g, 0.235 mol) and 103 g of P2O5
Under a nitrogen atmosphere at 60 ° C. for 8 hours, then 120 ° C.
Polymerization was carried out for 9 hours at 180 ° C. for 24 hours. The polymer dope thus obtained was spun. The intrinsic viscosity of the polymer was 21 dL / g. (The limiting viscosity was measured with methanesulfonic acid in a solvent city of 25 ° C.) A polymer dope of polybenzoxazole having a polymer concentration of the above dope of about 14% by weight was prepared. The polymer dope was fed to a twin-screw extruder through a wire netting filter for stirring and degassing. It was then extruded at 150 ° C. from a spinneret with 334 pores of diameter 0.20 mm. The discharge rate per single hole was 0.22 g / min. The extruded yarn was coagulated in a funnel type coagulating bath provided 20 cm below the spinneret. The atmosphere in the 20 cm space between the spinneret and the coagulation bath is dry air. The coagulated fiber was wound at a speed of 200 m / min.
The coagulated fiber was washed with water and dried. The dried fiber showed a moisture content of 0.4% by weight, an elastic modulus of 1100 g / d, a strength of 35 g / d and a breaking elongation of 3.8%.
The dried fiber was heat-treated under the conditions shown in Table 1. In the table, SJ means steam jet, dwell time means dwell time in heat treatment machine, GR1 means feed roll, and GR2 means take-up roll. When high-speed steam is used for heat treatment, 600 ° C. is required in the conventional method, whereas 370 ° C. is sufficient for the heat treatment effect. Further, it is advantageous for industrialization that the yarn processing speed can be increased to 200 m / min or more at about 20 m / min in the conventional method.

[0020]

[Table 1]

[0021]

[Table 2]

The measuring methods of the physical properties used in the present invention are as follows. Intrinsic Viscosity The intrinsic viscosity of polybenzbisoxazole was determined by the zero extrapolation method of the reduced viscosity measured at 30 ° C. in a methanesulfonic acid solution. Measurement of fineness A single yarn fineness measured after conditioning a fiber sample at 22 ° C. under the condition of RH65 ± 2% for 16 hours was measured by using Denier Computer DC-I 1B manufactured by SEARCH. The yarn fineness was measured by the lap reel method according to JIS L-1013 (1981). Tensile test The tensile test of monofilament and yarn is JIS L-10.
13 (1981).

[0023]

According to the present invention, it is possible to produce a large amount of polybenzazole fiber having high physical properties.

Front Page Continuation (72) Inventor Chi Chun Chau 48640 Midland Bluebird Drive, Michigan, USA 4205

Claims (1)

[Claims] 1. A method of heat-treating a polybenzazole fiber under tension by contacting it with a gas as a heating medium,
A heat treatment method for polybenzazole fibers, characterized in that heated gas flows in a heat treatment device in a countercurrent or a countercurrent.