JPH0978349A - Production of polybenzazole fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the retention of the tenacity to be deteriorated, during drying and heat treatment, by treating the coagulated filament spun from the dope of a polybenzazole with a basic solution and drying the filament at a temperature depending on the fraction of the liquid remaining in the filament in a short time. SOLUTION: The dope of a polybenzazole mainly constituted with structural units of formula I to formula III in an acidic solvent is spun into filaments and coagulated through the air gap in the coagulation bath. Then, the filament is treated with a basic solution to develop the resistance to void formation thereby increasing the limitation temperature causing no void formation and dried at the temperature which is set relating to the fraction of the liquid remaining in the filament. This polybenzazole filament of excellent properties is obtained, even when the drying temperature is raised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a high-quality fiber comprising a polybenzazole polymer such as polybenzoxazole or polybenzthiazole, which has excellent strength and elastic modulus.

[0002]

2. Description of the Related Art Polybenzoxazole and polybenzthiazole polymers having lyotropic liquid crystallinity do not show thermoplasticity. These are fiberized by the dry jet wet spinning method. That is, a dope containing a polybenzazole polymer and an acid solvent is extruded from a spinneret and stretched in an air gap. Then, the polymer is coagulated by bringing it into contact with a non-solvent that does not dissolve the polymer, and the solvent is likewise diluted, desolvated and dried.

In order to improve productivity, it is preferable to dry many filaments in a short time at high speed. However, the polybenzazole fiber after desolvation contains a large amount of non-solvent of 25% by weight or more, and a volume change occurs when it is dried. When drying the filament at high speed in a short time,
When a large amount of non-solvent is left and when it is passed through a high temperature heating zone, defects occur in the drying process. This defect is not preferable because it causes a decrease in yarn strength. This defect can be prevented from appearing by drying in a low-temperature heating zone, but if drying is performed at a low temperature, it takes a lot of time to dry, which causes a problem in productivity.

Therefore, as a conventional method, as described in Japanese Patent Application No. 5-304111, polybenzazole fiber containing 25% by weight or more of a non-solvent is heated at 170 ° C. for 84.3 seconds at 200 ° C.
For 84.3 seconds and 240 ° C. for 79.3 seconds, the high-speed drying method can reduce the content of non-solvent to 1.5% by weight without causing defects and the drying time up to about 4 minutes. It is illustrated. However, the drying after the desolvation step by this conventional method still requires a long time. In order to shorten the time required for drying, it is necessary to increase the diffusion coefficient of the non-solvent inside the polybenzazole fiber. As a result of examining various methods for increasing the diffusion coefficient of the non-solvent inside the polybenzazole fiber, the most effective effect was the drying temperature. That is, since the drying time cannot be shortened sufficiently at the drying temperature that can be used in the conventional method, it is desired to develop a high-speed drying technique by further raising the limit temperature at which voids are not generated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a polybenzazole fiber which is free from defects in the fiber and has good quality and strength and elastic modulus in an extremely short drying time. To do.

[0006]

Means for Solving the Problems That is, in a method of spinning a filament from a dope composed of a polybenzazole polymer and an acidic solvent, coagulating, washing and drying, the spun dope filament is coagulated and then contacted with a basic solution. And then drying at a temperature set in relation to the residual liquid fraction in the filament to be subjected to the drying step.

The polybenzazole fiber is a fiber made of polybenzazole (PBZ) polymer. What is polybenzazole (PBZ)?
O) 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 described, for example, in "Liquid Cry" by Wolfe et al.
stalline Polymer Compositions, Process and Product
s '' US Patent 4,703,103 (October 27,1987), `` Liqui
d Crystalline Polymer Compositions, Process and Pro
ducts '' US Patent 4,533,692 (August 6,1985), `` Liq
uid Crystalline Poly (2,6-Benzothiazole) Compositio
ns, Process and Products '' US Patent 4,533,724 (Aug
(ust 6,1985), `` Liquid Crystalline Polymer Composit
ions, Process and Products '' US Patent 4,533,693 (A
(ugust 6,1985), Evers' `` Thermooxdatively Stable A
rticulated p-Benzobisoxazole p-Benzobisthiazole Po
lymers '' USPatent 4,359,567 (November 16,1982)
, Tsai et al. "Method for Making Heterocyclic Block C
opolymer Compositions, Process and Products '' USPa
tent 4,578,432 (March 25, 1986).

The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers. The monomer units are described in Structural Formulas (a)-(h). The polymer preferably consists essentially of rigid monomer units of the molecular chain itself selected from structural formulas (a)-(h), and more preferably consists essentially of structural formulas (a)-(c). Composed of monomer units.

[0009]

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[0010]

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Suitable acidic solvents for forming the PBZ polymer dope 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 the highly soluble polyphosphoric acids and methanesulphonic acids. The most suitable solvent is polyphosphoric acid.

The polymer concentration of the solution is preferably at least about 7% by weight, more preferably at least about 1%.
0% by weight, most preferably at least 14% by weight. The maximum concentration is limited by practical handling properties such as polymer solubility and dope viscosity. Due to these limiting factors, the polymer concentration usually does not exceed 20% by weight.

Suitable polymers, copolymers or dopes are synthesized by known methods. For example, Wolfe et al.
USPatent 4,533,693 (August 6,1985), Sybert et al.
S.Patent 4,772,678 (September 20,1988), Harris U.
S.Patent 4,847,350 (July 11,1989). PBZ
The polymer is US Patent 5,089,591 (Febru
ary 18, 1992), it is possible to increase the molecular weight at a high reaction rate in a dehydrating acid solvent under relatively high temperature and high shear conditions.

The dope is produced by a known dry-wet spinning method. That is, the fibrous dope discharged from the die is passed through gas and brought into contact with a thin solvent (insoluble solution) that does not dissolve the polymer (coagulation) to form a yarn. After coagulation, the residual acid solvent in the fiber is washed. The washed fibers typically have a residual liquid fraction of 25% to 200% by weight. The fluid used for cleaning may be a gas such as water vapor, but is preferably a liquid and most preferably an aqueous solution. Even if the fibers are contacted in a liquid bath,
You may contact by spraying.

The liquid bath is disclosed in JP-A-63-12710; JP-A-51.
Various forms described in JP-A-35716 and JP-B-44-22204 can be used. Also, for example
A combination of two roller spraying methods may be used as the fibers are run, as described in Guertin USP 5,034,250 (July 23,1991). The washed fiber contains about 30% by weight or more of the insoluble liquid due to the mutual diffusion with the solvent. As it is, or the insoluble liquid adhering to the fiber surface is removed and the fiber is contacted with a basic solution to remain in the fiber. Neutralize with acid solvent. The basic liquid may be a gas such as water vapor, but a liquid that is easy to handle is preferable, and an aqueous solution is more preferable.

Here, the basic solution is sodium hydroxide,
It is essential that calcium hydroxide, ammonia, sodium carbonate, calcium carbonate, etc. be dissolved in water or an organic solvent such as methanol, ethanol, and acetone to show basicity, but the basic solutions listed here are not limited. Absent. The concentration of the basic solution is preferably 0.001 N or more,
More preferably, the range is 0.01 N or more, desirably 0.1 N or more, and the range not exceeding 3.0 N is desirable. The contact time is preferably 0.1 seconds or longer, more preferably 1 second or longer, desirably 3 seconds or longer and not longer than 120 seconds. The higher the concentration, the shorter the contact time can be to a certain time.

The contact with the basic solution may be carried out by contacting with the liquid described above in a bath or spraying,
It is also possible to use a combination of methods of spraying while the fibers are running on the two rollers, or a combination of methods. In the coagulation and washing process described above, washing may be performed with a basic solution, but from an economical point of view, the residual acid in the yarn is neutralized by contact with the basic solution when the residual acid solvent concentration in the yarn is as low as possible. It is preferable. The residual solvent ratio is preferably 10,000 ppm or less, more preferably 5,000 ppm.
It is below ppm. Here, the neutralized base / acid molar ratio inside the fiber is at least 0.5, more preferably 0.75.
It is desirable that the range does not exceed 1.5. More preferably 1.25 and most preferably between 1.0 and 1.3. When it is 1.0 or more, the residual acid in the yarn is considered to be completely neutralized. For example, the phosphorus: sodium ratio when sodium hydroxide is used can be measured by an appropriate analyzer such as a fluorescent X-ray analyzer.

The purpose of neutralization is as follows: (1) The residual acid solvent inside the fiber acts as a catalyst that causes hydrolysis by heating or light irradiation during the drying or heat treatment steps, but suppressing this (2) The generation of voids is suppressed by reducing the surface tension of the residual cleaning liquid. FIG. 1 shows the maximum temperature at which no defect occurs in the fiber, which is determined based on the content of each residual insoluble liquid, in comparison with the technique disclosed in Japanese Patent Application No. 5-304111. By changing the properties of the residual non-soluble liquid, the occurrence of void defects, which causes a decrease in fiber strength during the drying process, was less likely to occur than in the conventional process.

After contact with the basic solution, a washing with a fluid capable of dissolving the basic solution is carried out in order to remove the basic solution. The fluid may be a gas such as steam, but is preferably a liquid that is easy to handle. It is important that the fluid used for washing the solvent is that the polymer solvent is easily soluble and that the one diffused in the filament can be removed later. An aqueous solution is preferable. The acidity of the liquid used for washing is preferably about pH 6-11.

The fibers which have been coagulated, washed, contacted with a basic solution and washed usually contain about 25% or more of the residual liquid. It is then contacted with a basic solution and the washed fibers are dried through a heating zone. For the heating zone, an electric furnace, a heating roller, heated air, a heated inert gas, a shock wave, superheated steam, or a heat medium such as oil can be used. You may hold | maintain at high temperature and use electromagnetic fields, such as a microwave, one part. Moreover, you may use it in these combinations. It is essential that the temperature of the fiber can be raised quickly.

In the drying step, the remaining liquid inside the fiber is dried to about 4% or less through a heating zone. This is because the shrinkage of the yarn in the radial direction after being wound in the package causes the cheese to come off and the edges of the cheese to be dried up to a permissible non-solvent content of 4%. For example, when using a two-stage heating zone, as shown in FIG.
Fiber with a non-solvent content of 8% by weight is used in the first heating element
The fibers dried at a temperature of 0 ° C. or lower to 10% by weight are dried by a second heating element at a temperature of 240 ° C. or lower to 3% by weight. From the industrial requirements, the heating time in the region shown in FIG. 1 in which no defects occur in the fiber is preferably 3 minutes or less. More preferably 120 seconds or less, most preferably 90 seconds.
It is less than a second.

The atmosphere of the heating zone is air or helium,
An inert gas such as argon or a gas fraction such as carbon dioxide may be high. The atmosphere of the heating zone is preferably used at atmospheric pressure, but the pressure may be changed. Further, increasing the wind speed in the heating zone is preferable because it promotes mass transfer from the fiber surface.

The average tensile strength of the fiber is expressed by the breaking strength per unit denier (g / d), preferably at least 7.3 g / d, more preferably at least 12.7 g.
/ D, more preferably at least 20 g / d, even more preferably at least 29.8 g / d, most preferably at least 45 g / d. In addition, the voids observed in the fiber with an optical microscope are shown in the photograph. Due to the large number of voids, the tensile strength of the fiber is about 9
Reduce to 5% or less. The average tensile modulus of the fiber is expressed by the initial tensile resistance per unit denier (g / d),
It is preferably at least 1100 g / d, more preferably 1600 g / d. This fiber can be heat treated to increase the tensile modulus, if desired. Apply a suitable spinning oil and wind it up into a package. The heat treatment may be performed online or may be rolled up once.

Although the mechanism for improving the resistance to void development by contact with a basic solution is not well understood, the surface tension characteristics of the non-solvent trapped in the voids of about 30 angstroms or less in the fiber are changed and the liquid is dried by drying. It is thought that this is because the residual stress after the breakage is reduced. Therefore, the temperature at which no defects occur in the fiber indicated by the dotted line in FIG. 1 is wider than that of the conventional technique indicated by the solid line. Even if the drying temperature is raised, a good polybenzazole fiber can be obtained, so that it can be dried in a short time. Further, contacting with a basic solution also has the effect of improving the retention of tensile strength by drying and heat treating the fibers.

[0025]

The following examples are for purposes of illustration only, and the present invention is not limited thereby. All quantities and percentages are by weight unless otherwise noted. The method for measuring the residual non-solvent content is as follows. Weigh about 1.0 g of fiber (W1)
Then, the fiber is dried in a static dryer at 230 ° C. for 30 minutes, weighed again (W0), and calculated by the following formula. Residual non-solvent content (%) = {(W1-W0) / W0} ×
The generation amount and dispersion state of 100 fiber defects were observed at 200 times using an optical microscope by placing a piece of fiber cut into about 4 cm on a slide glass. The defects are observed as black streaks (voids) along the fiber axis, and are distinguished from streaks (kinks) having an angle in the fiber axis direction in the present invention. The photograph shows an example of voids. Defect rank is 166 filaments, 18m
The number of defects per m was measured with an optical microscope, and there was no (0
Very small (1 to 2), very small to small (3 to 4), small (5 to 10), small to large (1)
1 to 15) and a very large number (16 or more) were classified into 6 ranks.

Example 1 A polyphosphoric acid solution prepared by dissolving 14% by weight of a cis-polybenzoxazole polymer having an intrinsic viscosity of 30 dL / g was
It was extruded from a spinneret kept at 0 ° C. The extruded filament was coagulated with ion-exchanged water at room temperature, and this yarn was introduced into the washing process and washed with water. In the neutralization step, a 0.1N solution of NaOH was used as the basic solution. After that, the thread was washed with water and drained with an air knife.
Was heated for 60 seconds, further passed through a heating roller at 225 ° C. for drying until the residual liquid fraction became 5.7%, and further dried by a heating roller at 255 ° C.
Table 1 shows the dry condition and the physical properties of the fiber. Table 1 to FIG. 1
Temperature condition that does not cause defects in
8%, heating zone temperature 220 ° C.), no defects occurred.
In addition, the drying time is dramatically faster than the conventional 4 minutes.

Comparative Examples 1 and 2 After coagulation and washing were carried out in the same manner as in Example 1, the yarn dried with an air knife was dried without neutralization. Table 1 shows the dry condition and the physical properties of the fiber. If you do not neutralize,
In the case where the fiber is dried without causing defects, the temperature that can be first applied to dry the yarn having a residual liquid fraction of 38% after washing is 190 ° C. or less, which is much higher than that of the present invention. It takes a long time (Comparative Example 1). When dried under the same drying conditions as in Example 1, the fiber is not contacted with the basic solution and is dried at a temperature at which defects are generated in the fiber, and the tensile strength of the fiber is lowered due to the occurrence of defects (Comparative Example 2). .

Comparative Example 3 In the same manner as in Example 1, coagulation, washing, contact with a basic solution, washing, and drying of the thread drained with an air knife were performed. Table 1 shows the dry condition and the physical properties of the fiber. In the case where the drying temperature condition which does not cause the defects shown in FIG. 1 is deviated, a large number of defects are generated in the fiber and the strength of the fiber is remarkably lowered.

[0029]

[Table 1]

Example 2 Spinning, washing and drying were carried out as in Example 1, but the concentration of NaOH solution was changed to 0.001 N in the neutralization step.
Table 2 shows the dry condition and the physical properties of the fiber. Table 2 to FIG. 1
Even when the basic solution is changed under the conditions of the claims of the present invention, such as the drying temperature condition in which the defect does not occur, the water content can be dried to the same extent as in Example 1.
In addition, the change in the basic solution has no significant effect on the drying condition and the physical properties of the fiber.

Example 3 Spinning, washing and drying were carried out as in Example 1, but the spinning speed was changed to 600 m / min. Table 2 shows the dry condition and the physical properties of the fiber. From Table 2, it is possible to dry quickly without generating voids even when the spinning speed is increased.

[0032]

[Table 2]

Examples 4 and 5 Spinning, washing and drying were carried out as in Example 1, but the drying device was changed in the drying step. Table 3 shows the dry condition and the physical properties of the fiber. In the case of the conditions of the claims of the present invention, such as those in the drying temperature condition where no defect occurs in Table 3 to FIG. It was able to dry quickly. Even if the drying device is changed, the drying condition can be improved by controlling the temperature of the heating zone.

[0034]

[Table 3]

[0035]

Industrial Applicability According to the present invention, it becomes possible to dry polybenzazole fiber in which the drying time is drastically shortened as compared with the conventional drying method without generating void defects in the fiber.

[Brief description of drawings]

FIG. 1 is a diagram comparing a relationship between a non-solvent content rate of a polybenzazole fiber used in the present invention and a drying temperature with that of a conventional technique.

[Explanation of symbols]

1: Void generation limit upper limit temperature when a basic solution is not contacted. 2: Void generation limit upper limit temperature when a basic solution is contacted. 3: Initial drying condition of the present invention (hatched portion)

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Claims (5)

[Claims] 1. A method of spinning filaments from a dope composed of a polybenzazole polymer and an acidic solvent, coagulating, washing and drying the spun dope filaments, coagulating them, and then contacting them with a basic solution, followed by a drying step. A method for producing a polybenzazole fiber, which comprises drying at a temperature set in relation to the residual liquid fraction in the filament to be subjected to. 2. The method for producing a polybenzazole fiber according to claim 1, wherein the drying introduction temperature is 190 ° C. or higher. 3. When the residual liquid fraction in the filament subjected to the drying step is 25% or more, the drying introduction temperature is 190 to
The method for producing a polybenzazole fiber according to claim 2, wherein the temperature is 220 ° C. 4. The method according to claim 1, wherein the filament is dried until the residual water content in the dried filament is 6% or less.
[3] A method for producing a polybenzazole fiber according to [3]. 5. The method for producing a polybenzazole fiber according to claim 1, wherein the drying time is 3 minutes or less.