JP3120913B2 - Heat treatment method of polybenzazole fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment of polybenzazole fiber for improving 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 super fibers in the market.
It has more than twice the modulus of elasticity and is expected to be the next generation super fiber. Heat treatment is indispensable for obtaining the highest elastic modulus of the polybenzazole fiber. The usual heat treatment method is described in J. Mater. Sci. 20, 2727 (198
5) and H. D. Ledbetter, S.M. Rosenb
erg, C.I. W. Hurtig; Symposium
Proceedings of The Materi
alsScience and Engineerine
go of Rigid-RodPolymers, Vo
l. 134, 253 (1989). These conventional heat treatment methods for polybenzazole fibers must be treated at a temperature of 500 ° C. or higher because the rigidity of the polybenzazole fibers is extremely high. For this reason, the heat treatment machine according to the conventional method is huge and expensive, which is an obstacle to industrialization.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new heat treatment method for eliminating a long-time heat treatment at a high temperature for improving the elastic modulus of polybenzazole fiber.

[0004]

The first feature of the present invention is that the heat treatment of polybenzazole is brought into contact with a gaseous heat treatment medium and the heat treatment medium is steam. More specifically, the present invention provides for tensioning the polybenzazole fiber into contact with the heat treatment medium, the heat treatment medium being steam, the heat treatment zone being brought into contact with the fiber in countercurrent or countercurrent to the fiber, and the velocity of the water vapor and the fiber. A second feature is that the difference is at least 5 m / sec. The present invention also provides a method for applying tension to the polybenzazole fiber and bringing the fiber into contact with the heat treatment medium, the heat treatment medium being steam, the heat treatment zone being brought into contact with the fiber in a countercurrent or countercurrent to the fiber, and a speed difference between the steam and the fiber being at least 5 m. / Sec, and the residence time in the heat treatment zone is 3 seconds or less.
In addition, a method of applying tension to the polybenzazole fiber and bringing the heat treatment medium into contact with the heat treatment medium, and bringing the heat treatment zone into contact with the fiber in countercurrent to the heat treatment medium. The method in which the medium is water vapor and the heat treatment zone is brought into contact with the fiber in a counterflow, the tension is applied to the polybenzazole fiber and the heat treatment medium is brought into contact with the heat treatment medium. The method of contacting, wherein the polybenzazole fiber is a polybenzoxazole fiber in the heat treatment method, the speed of steam as a heating medium is at least 10 m / sec in the heat treatment method, and the heating medium is Is characterized in that the water vapor velocity is at least 100 m / sec.

[0005] The substances used in the present invention are polybenzazole (polybenzoxazole and polybenzthiazole).
Contains polymer. Polybenzoxazoles, polybenzothiazoles and random or block copolymers thereof are disclosed in Wolfe et al., US Pat. No. 4,703,103.
(October 27, 1987), US Patent No. 4,533,692.
(August 6, 1985), US Pat. No. 4,533,724 (8
6, 1985), US Patent 4,533,693 (August 6).
1985) and Evers U.S. Pat.
7 (November 16, 1982) and US Pat. No. 4,578,432 to Tsai et al. (March 25, 1986), and 11
Ency. Poly. Sci. & Eng. , Poly
Benzothiazoles and Polybe
nzoxazoles, 601 (J. Wiley &
Sons 1988) and W.S. W. Adams et al. T
he Materials Science and
Engineering of Rigid-Rod
Polymers (Materials Research
rch Society, 1989). In the polymer of the present invention, 85 mol% or more is composed of the repeating unit represented by Chemical Formula 1 or Chemical Formula 2.

[0006]

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[0007]

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Here, Ar represents an aromatic. The aromatic may be a heterocyclic ring such as a pyridinylene group, but is preferably carbocyclic. The aromatic group may be a fused or unfused multi-carbon ring, but is preferably a single six-membered ring. Its size is not critical, but the aromatic group should have no more than 18 carbon atoms, more preferably no more than 12 carbon atoms, and most preferably no more than 6 carbon atoms. Preferred aromatic groups include a phenylene group, a tolylene group, a biphenylene group, a 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 mer unit is preferably a 1,3,4-phenylene group or an analog thereof. Each Z is an oxygen or sulfur atom. Each DM is an independent divalent organic group that does not interfere with the synthetic polymerization. The divalent organic group may include an aliphatic group, but the aliphatic group has 12 or less carbon atoms. However, the divalent organic group is preferably an aromatic group as described above. Most preferred is the 1,4-phenylene group or an analog thereof. The nitrogen and Z atoms of each azole ring combine with the carbon atoms forming the adjacent aromatic ring to form a 5-membered ring of the azole. The azole ring in the AA / BB mer unit is 11 Ency. Polym. Sci. & E
ng. , Supra, p. 602, the cis position or the trans position. The polymer is preferably an AB polybenzazole unit or an AA / BB polybenzazole unit, and more preferably an AA / BB polybenzazole unit. The molecular structure of the polybenzazole polymer is a rigid straight chain, a rigid straight chain equivalent thereto, or a flexible coil. In the case of an AA / BB polybenzazole polymer, a rigid straight chain is preferable, and in the case of an AB polybenzazole polymer, a rigid straight chain equivalent thereto is preferable. The polybenzazole polymer is preferably a polymer that forms a lyotropic liquid crystal. (The lyotropic liquid crystal forms a liquid crystal domain when dissolved at a concentration higher than the limit concentration.) The azole ring in the polymer is an oxazole ring (Z = O)
Is preferred. Preferred units are shown in Chemical Formulas 3 to 10. The polymer is preferably composed of a monomer unit represented by Chemical Formulas 3 to 10. Most preferably, it comprises a repeating unit selected from chemical formulas 3 to 6.

[0009]

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[0010]

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[0011]

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[0012]

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[0013]

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[0014]

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[0015]

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[0016]

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The number average degree of polymerization of each polymer is 25 or more, preferably 50 or more, and more preferably 100 or more.
The intrinsic viscosity of the AA / BB polybenzazole polymer measured at 25 ° C. dissolved in methanesulfonic acid is preferably at least 10 dL / g, more preferably 15 dL / g.
g, most preferably 20 dL / g. For some purposes, an intrinsic viscosity of at least 25 or 30 dL / g is preferred. Intrinsic viscosities of 60 dL / g or more can be used, but are preferably less than 45 dL / g. Most preferably, the intrinsic viscosity is about 33 dL / g. The limiting viscosity of the AB polybenzazole polymer is 5 dL / g or more, preferably 10 dL / g.
dL / g or more, more preferably 15 dL / g or more.

The polymer is produced into fibers or films by spinning or extruding from a dope. The dope is a polymer solution in a solvent. If the polymer or copolymer cannot be immediately subjected to spinning or extrusion, it can be dissolved in a solvent to form a solution or a dope and then spun and extruded. Polybenzazole and polybenzthiazole dissolve in cresol. The acid is preferably non-oxidizing. As the solvent, polyphosphoric acid, methanesulfonic acid, sulfonic acid, or a mixture thereof is preferred. Further, polyphosphoric acid and / or methanesulfonic acid are preferable, and polyphosphoric acid is more preferable. The dope needs to have a concentration sufficient for coagulation to form a solid, but if the concentration is too high, it becomes difficult to control the viscosity of the dope. When the polymer is a rigid or similar rigid straight chain, the polymer concentration in the dope is set to a concentration sufficient for a liquid crystalline dope. The polymer concentration is preferably at least 7% by weight, more preferably at least 10% by weight, further preferably at least 14% by weight. The maximum concentration is constrained by various conditions, such as polymer solubility and dope viscosity described above. Depending on these conditions, the polymer concentration may rarely be 30% by weight or more, but is usually 20% by weight or less.

Wolfe et al., US Pat. No. 4,533,693.
(August 6, 1985) and US Pat.
772678 (September 20, 1988) and Harris
U.S. Pat. No. 4,847,350 (July 11, 1898) and Gregory U.S. Pat.
H., 1992) and Ledbetter et al.
integrated Laboratories Proc
ess for Preparing Rigid R
od Fibers from the Monom
e "The Material Science an
d Engineering of Rigid-Ro
d Polymers 254-64 (Matrial
s Res. Soc. , 1989) can be synthesized. In summary, suitable monomers (AA-monomer and BB-monomer or AB-monomer)
Monomer) reacts in a non-oxidizing solution, giving high shear with vigorous stirring under a non-oxidizing atmosphere,
The temperature is raised stepwise or at a gradient from 120 ° C. or lower to at least 190 ° C. to advance the dehydration reaction. A
Suitable examples of the A monomer include terephthalic acid or the like. Suitable examples of BB monomers include 4,6-diaminoresorcinol, 2,5-diaminohydroquinone, 2,5-diamino-1,4-dithiobenzene and the like. These are typically used as hydrochlorides. Preferred examples of the AB monomer include 3-amino-4-hydroxybenzoic acid, 3-hydroxy-4-aminobenzoic acid, 3-amino-4-thiobenzoic acid,
-Thio-4-aminobenzoic acid and the like, which are commonly used as hydrochlorides. The polymer of Formula 2 is preferably at least 85% terephthalic acid and / or
Or less than 15% of a different difunctional acid from its functional derivative. More preferably it contains less than 10% of different bifunctional acids. The polymer of formula 2 is preferably at least 85
% Of 4,6-diamino-1,3-benzenediol dihydrochloride and less than 15 mol% of 2,5-diamino-1,4-benzenediol dihydrochloride. More preferably, it contains less than 10 mol% of 2,5-diamino-1,4-benzenediol dihydrochloride.

Adjustment of PBZ dope PBZ dope is a solution comprising a PBZ polymer and a solvent. Polybenzazole polymers are only soluble in very strong protic acids such as methanesulfonic acid and polyphosphoric acid. The preferred solvent is polyphosphoric acid (PPA). PB
The concentration of O 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
To 45 dL / g.

Preparation of Polybenzazole Fiber Polybenzazole fiber is preferably made by a so-called continuous polymerization and spinning process. That is, the polymerized dope is sent to the direct spinning having a spinneret without being removed from the polymerization kettle once. Of course, after taking out from the polymerization kettle, dry-wet spinning may be separately performed. In dry-wet spinning, the dope is extruded from a spinneret. The arrangement of the pores of the spinneret may be a circular arrangement or a lattice arrangement. The arrangement of the pores must be chosen so that the extruded dopes do not fuse together. The number of pores in the spinneret is not limited. It is important to keep the temperature of all spun yarns extruded from the die uniform. This is because differences in the temperature of the individual filaments in the yarn are immediately reflected in differences in the tension of the filaments.

After the spinning, the extruded dope fibers are immersed in a coagulation bath to separate the solvent from the polybenzazole polymer. An air gap exists between the spinneret and the coagulation bath. The gas in the air gap is usually air. However, nitrogen, carbon dioxide, helium or argon may be used. The preferred temperature of the air gap is between 0 ° C and 100 ° C. More preferably, the temperature is from 50 ° C to 100 ° C. After passing through the air gap, the extruded dope fibers are immersed in a coagulation bath to remove the solvent from the polybenzazole polymer.

The coagulation is performed in a bath or by spraying. In the case of a coagulation bath, it is installed below the spinneret. More than 99.0% of the solvent is extracted in the coagulation bath. More preferably, 99.5% or more is extracted. Any coagulation bath / spray used includes water or a water / acid mixture. A preferred acid is phosphoric acid at a concentration of 30% or less. Other coagulating 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 U.S. Pat. No. 4,298,565 or a waterfall-shaped coagulation bath described in U.S. Pat. No. 4,869,860.

The solution concentration of the coagulated fibers is further reduced by washing the fibers with water. Water or a dilute water / acid mixture, especially 5% or less, aqueous phosphoric acid can be used as any water bath or spray. Other washing media also include organic solvents such as acetone, methanol and acetanilide. After coagulation and washing, the fiber is dried and wound up in a roll. The fiber thus obtained already has sufficient strength and elastic modulus as a spun yarn, but the polybenzazole fiber can dramatically improve the elastic modulus by further heat treatment. The heat treatment can be performed separately or continuously. A high-speed, high-temperature gas, such as water vapor, nitrogen or other inert gas, can be used as a heating medium for the heat treatment performed for the purpose of improving the elastic modulus of the polybenzazole spun yarn. The velocity of the gas as the heating medium is desirably greater than 10 m / sec. This is because the heat exchange between the fiber and the heated gas is determined by its speed difference as described by equation 1.

[0025]

(Equation 1)

Where L is the heater length or heat treatment zone, u is the velocity difference between the fiber and the heated gas, t is the residence time,
Ts is the temperature of the heated gas, and Tf is the yarn temperature before the heat treatment. What is important for efficient heat exchange between the heat treatment medium and the yarn is that the gas for heat treatment needs to flow through the heat treatment machine as countercurrent or countercurrent to the fiber. The efficiency of heat exchange depends on the speed difference between the yarn and the heating gas. It goes without saying that the counterflow has a larger velocity difference than the counterflow. Further, by supplying a gas for heating to the center of the heat treatment machine, it is possible to cause the heat treatment machine to have a countercurrent and a countercurrent at the same time. The speed of the fibers passing through the heat treatment zone is preferably at least 20 m / min, more preferably at least 40 m / min. The velocity of the heated gas is preferably at least 5 m / sec, more preferably at least 10 m / sec. The speed difference between the fiber and the heated gas is preferably at least 5 m / sec, more preferably 10 m / sec. The speed difference between the yarn and the fiber is preferably at least 5 m
/ S, more preferably at least 10 m / min.
The amount of the heated gas used is measured as Kg / hour by a flow meter. If the heat treatment machine has both countercurrent and countercurrent, the velocity of the gas is calculated by the following equation.

[0027]

(Equation 2)

Here, v is the gas velocity in m / sec, Q is the amount of gas used in Kg / h, d is the vapor density, and S is the cross-sectional area of the heat treatment machine. The residence time of the fibers in the heating zone is preferably at most 20 seconds, more preferably at most 5 seconds, and most preferably at most 3 seconds. The tension applied to the fibers during the heat treatment is preferably between 0.1 and 10 g / d.

Since the temperature of the fiber is instantaneously increased by the use of a heating gas such as steam at high speed and high temperature, the negative heat treatment effect at the time of heat treatment can be reduced. As a result, the temperature of the conventional method (normally 600 ° C.) and the processing time of the conventional method (normally 10 seconds) can be greatly reduced by the heat treatment of the present invention. By using a counter-current or counter-current high-speed and high-temperature heating gas, the temperature required for the heat treatment can be reduced to 400 ° C., and the time required for the heat treatment can be reduced to 3 seconds or less. The tensile modulus of the heat treated fiber according to the method of the present invention is preferably at least 220 GPa (31.9 ms).
i), more preferably at least 250 GPa (3
6.3 msi).

[0030]

EXAMPLES The effects of the present invention are shown by the following examples. However, it goes without saying that the present invention is not limited to the embodiments described below. (Example 1) A polyphosphoric acid polymerization dope of polybenzoxazole (at a concentration of about 14% by weight) was fed to a twin screw extruder through a wire mesh filter to perform stirring and degassing. It was then extruded at 150 ° C. from a spinneret with 334 pores of 0.20 mm diameter. The discharge rate per single hole was 0.22 g / min. The extruded yarn was coagulated in a funnel-type coagulation 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 has a moisture content of 0.4% by weight, 1
It exhibited an elastic modulus of 100 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 Tables 1 and 2. In the table, SJ denotes a steam jet, stay time denotes a stay time in the heat treatment machine, GR1 denotes a feed roll, and GR2 denotes a winding roll. When high-speed steam is used for the heat treatment, the conventional method requires a temperature of 600 ° C., whereas a heat treatment effect of 370 ° C. is sufficient. What is more advantageous for industrialization is that the yarn processing speed can be increased to 200 m / min or more from 20 m / min in the conventional method.

[0031]

[Table 1]

[0032]

[Table 2]

The methods for measuring physical properties used in the present invention are as follows. Intrinsic Viscosity The intrinsic viscosity of polybenzbisoxazole was determined by a zero extrapolation method of the reduced viscosity measured at 30 ° C. in a methanesulfonic acid solution.

Measurement of fineness The fiber yarn sample was conditioned at 22 ° C. under the conditions of RH 65 ± 2% for 16 hours, and the single yarn fineness measured was measured using a denier computer DC-I1B manufactured by Search. The yarn fineness was measured by a wrap reel method according to JISL-1013 (1981).

Tensile test The tensile test of a single fiber or a yarn was conducted according to JIS L-10.
13 (1981).

Claims (3)

(57) [Claims] 1. A method for heat treating a polybenzazole fiber by contacting the fiber with a gas as a heating medium under tension.
A method for heat treating polybenzazole fiber, wherein the gas is water vapor. 2. A gas as a heating medium flows in a counter-current or a counter-current in a heat treatment apparatus, and has a velocity of at least 5 m /
The method for heat treating polybenzazole fiber according to claim 1, wherein the time is seconds. 3. The method for heat treating polybenzazole fiber according to claim 1, wherein the heat treatment time is 3 seconds or less.