JPH0978350A - Production of polybenzazole fiber and polybanzazole intermediately dried fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high-speed drying of polybenzazole filaments without damaging to the filaments by coagulating the filaments spun from the dope, washing them with water and drying them under specific conditions. SOLUTION: The spinning dope of a polybenzazole mainly constituted with structural units of formula I to formula III in a solvent (preferably polyphosphoric acid) is extruded from a spinneret and coagulated through the air gap in the coagulation bath into filaments, which are then washed with water. On the drying, more than 80% of the heating zone is kept at >=240 deg.C and the filaments are dried to some <=2% of the equilibrium moisture regain, preferably within 80 seconds. Thus, this polybenzazole fiber can be industrially produced with it compact installation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fibers of high-strength, high-modulus polybenzoxazole. More specifically, the present invention relates to a manufacturing method for efficiently drying a high-strength / high-modulus polybenzoxazole fiber in a short time, and an intermediate dry fiber for efficiently drying in a short time.

[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 make fibers from polyphosphoric acid solutions of polybenzazole polymers. For example, U.S. Pat. No. 5,296,185 and U.S. Pat. No. 5,294,390 are proposed for the spinning method, Japanese Patent Application No. 5-304111 is proposed for the drying method, and U.S. Pat. No. 5,288,445 is proposed for the heat treatment method. However, in the production of polybenzazole fiber, mass transfer is difficult because the molecule is rigid.
As described in No. 6, since the fiber is damaged when exposed to high temperature with a high water content in the fiber,
It was extremely difficult to raise the drying temperature to dry in a short time.

[0003]

The biggest problem in industrializing the polybenzazole fiber by the conventional technique is that the drying process requires a long time and the high-speed spinning equipment becomes large. The present invention overcomes such technical difficulties, develops a technique for drying at high speed without damaging the fiber, and provides a novel production method for industrially obtaining polybenzazole fiber at high speed. Is.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted intensive studies and found a solution for the purpose of economically producing polybenzazole fiber. That is, a spinning dope composed of polybenzazole and polyphosphoric acid is melt-spun from a spinneret, and a draft is applied to a yarn in a non-coagulating gas usually called an air gap, followed by coagulation and / or extraction and further drying. Then, polybenzazole fiber is obtained. In this process, it was discovered that the coagulation conditions determine the microstructure of the yarn to be dried and dominate the water drying phenomenon. Further, among coagulation conditions, in particular, it was found that the coagulation liquid temperature and coagulation liquid concentration conditions were dominant, and the inventors invented a method of drying at a high speed without damaging the fibers.
The purpose of the present invention is its manufacturing method. Furthermore, internal strain during drying, which is obtained by controlling the coagulation conditions, is unlikely to occur, and even if the drying is interrupted when only the fiber surface is dried and the center of the fiber contains a large amount of water, The residual stress level is low, and even if the water content in the fiber decreases thereafter, the strength does not decrease. Such fibers are unlikely to change in quality even in a manufacturing process in which spinning and drying are not directly connected, and it becomes possible to make the spinning / washing step and the drying / heat treatment steps at different production rates.

Hereinafter, the present invention will be described in detail. The polybenzazole fiber in the present invention refers to a fiber made of a polybenzazole polymer, and is a polybenzazole (PBZ)
"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 described in, for example, "Liquid Crystalline Polymer C" by Wolfe et al.
ompositions, Process and Products, U.S. Patent No. 47
03103 (October 27, 1987), "Liquid C
rystall-ine Polymer Compositions, Process and Pro
ducts "US Patent No. 4,533,692 (August 6, 1985)
Sun), "Liquid Crystalline Poly (2,6-Benzothiazole)
Composition, Process and Products, U.S. Patent No. 45
33724 (August 6, 1985), "Liquid Crys
talline Polymer Compositions, Process and Product
s "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). 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 essentially consist of 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.

[0009] The polymer concentration in the solvent is preferably at least about 7% by weight, more preferably at least 1% by weight.
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 their limiting factors, the polymer concentration is usually 20% by weight
Never exceed.

[0010] Suitable polymers, copolymers or dopes are synthesized by known techniques. See, eg, 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)
0) Harris U.S. Pat. No. 4,847,350 (198).
(July 11, 2009). PB
Z polymers are disclosed in US Pat. No. 5,089,959 to Gregory et al.
No. (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 way is supplied to the spinning section and discharged from the spinneret at a temperature of usually 100 ° C. or higher. The arrangement of the base pores is usually plural in a circumferential or lattice shape, but other arrangements are also possible. 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. Also, when spinning at high speed, so that the temperature of the cooling gas between the filaments is optimized,
It is necessary to adjust the hole arrangement and cooling airflow.

The filamentous dope discharged from the spinneret into a non-solidified gas (so-called air gap) is given a draft in the air gap. Providing a so-called quench chamber for cooling the yarn using cooling air in the air gap in order to enhance the cooling efficiency of the yarn is particularly effective for achieving stable production at a high spinning speed. The preferred cooling air temperature is about 10
The temperature is not lower than 120 ° C. and not higher than 120 ° C., but these depend on the polymer molecular weight and polymer concentration of the dope.

Next, the yarn is introduced into a coagulating liquid and coagulated and / or extracted. The coagulation conditions have a very important meaning in realizing the drying process of the present invention. The coagulation liquid is preferably a phosphoric acid aqueous solution which is an aqueous solution of a dope solvent from a practical viewpoint. The conditions for coagulation include the temperature of the coagulation liquid, the concentration of the coagulation liquid, the coagulation time, the tension applied to the dope filament during coagulation, the temperature of the dope filament entering the coagulation bath, the degree of orientation of the dope filament entering the coagulation bath, etc. There is. Of these, the most important are the temperature of the coagulation liquid,
It is the concentration of the coagulation liquid and the coagulation time. Of particular importance is the temperature of the coagulating liquid. The preferable temperature of the coagulating liquid is 30 ° C. or higher and 120 ° C. or lower. The temperature of coagulation liquid is 30 ℃
When it is less than the above range, the coagulation force is insufficient and the phase-separated structure of the inner layer portion of the fiber becomes rough, so that internal strain tends to occur during drying. If the temperature exceeds 120 ° C, the yarn path cannot be stabilized unless the dope filament is soft and continuously stretched. A more preferable coagulating liquid temperature is 35 ° C. or higher and 85 ° C. or lower. The concentration of the phosphoric acid aqueous solution used for coagulation is 6%
Above about 50% is preferable. By lowering the concentration of the coagulation liquid, sufficient coagulation power can be obtained, but in order to keep the concentration low, there is a problem of the cost of treating a large amount of low concentration phosphoric acid solution, so a concentration of less than 6% is from an industrial point of view. Not preferable. In the case of high-concentration coagulation, as in the case of low-temperature coagulation, the coagulation force is insufficient, the phase-separated structure of the inner layer portion of the fiber becomes rough, and internal strain during drying tends to occur. The concentration of the coagulating liquid is more preferably 10% or more and 45% or less, and further preferably 15%.
% Or more and 35% or less. The coagulation time depends on the coagulation temperature and the coagulation liquid concentration. In other words, conditions where the coagulation power is weak (low temperature / high concentration), whereas conditions where the coagulation power is high (high temperature / low concentration)
So it takes a long time. However, the coagulation time must be at least 0.01 second or longer, preferably 0.05 second or longer, and more preferably 0.1 second or longer. Also,
The coagulation time is preferably short from the viewpoint of making the equipment compact, and at most 10 seconds or less, preferably 5 seconds or less, more preferably 3 seconds or less.

The fibers which have been coagulated under these conditions and then washed with water have a fine structure suitable for drying in a short time.
The condition of washing with water after solidification is not a factor for a large structural change, but the phosphorus concentration is preferably 10,000 ppm or less, more preferably 7,000 ppm or less. In the water washing step, a neutralization step can also be performed. As the neutralizing agent, an alkali metal base can be used.The atomic ratio of the alkali metal to the phosphorus atom, which is the residual solvent in the fiber, should be 0.2 or more and 1.8 or less.
It is particularly preferable because it retains physical properties during post-processing of the fiber, but is not essential.

The polybenzazole fiber before drying (intermediate dry fiber) thus obtained has a small difference in the higher-order structure between the central portion and the surface layer portion of the fiber. The higher-order structure here can be evaluated by the size distribution of pores having a size of about several tens of angstroms in the fiber. As a method for evaluating this size distribution, a method of observing the heavy metal unevenly distributed in the water in the voids with a transmission electron microscope by impregnating a water-soluble heavy metal salt in an undried state, a thermal differential analysis of the undried fiber There is a method of measuring the temperature at which the water inside is frozen by cooling with a measuring device. The latter method is simple, but it is necessary to separate the water adhering to the fiber surface from the water inside the fiber. This operation has a moisture content of about 25% in the fiber.
It is possible to remove a part of water on the fiber surface and the fiber surface layer by drying at a tension of 2 g / d and a temperature of 180 ° C. The water content in the fiber here is defined by the weight fraction of the retained water with respect to the absolute dry weight of the fiber. The water content can be adjusted to 25% by changing the residence time in the drying device. At this time, the reason why the tension is set to 2 g / d is to prevent the void size inside from changing at the same time that the orientation of the fibers progresses when the tension during drying is high. The reason for setting the drying temperature to 180 ° C. is that the weight reduction rate is appropriate and the moisture content in the fiber can be easily adjusted. In general, the freezing point of water confined in pores is a thermodynamic action to lower the freezing point due to its surface tension. Report by Ishigiriyama et al. (Polymer Preprints, Japan Vol. 34, No. 9, p2645
(1985)), it is known that when the diameter of the pores becomes 100 angstroms or less, the freezing point is rapidly lowered, and water contained in the undried polybenzazole yarn
By comparing the SC curves, the size and distribution of voids within the fiber can be evaluated. From the results of the thermal differential analysis of the sample prepared as described above at 20 to −70 ° C., the fiber of the present invention has a single peak as shown by 2 in FIG. A fiber having a coagulation temperature of 25 ° C. and a phosphoric acid concentration of 22% in the coagulation liquid has two peaks as shown by 1 in FIG. The fiber having two peaks has a non-uniform structure in the fiber, and a void accompanied by a decrease in strength occurs when the fiber is dried at a high temperature of about 240 ° C. or higher. The void generation limit temperature of the fiber that has a substantially single peak is approximately 240 ° C.
On the other hand, the void generation limit temperature of the fiber which does not substantially have a single peak is about 230 ° C. or lower.

The drying time of the polybenzazole fiber can be shortened as the drying temperature increases. This is because the speed at which water molecules in the fibers move as clusters or monomolecular gas is proportional to the 1/2 power of the absolute temperature. However, in the conventional technique, when drying is carried out at a high temperature of 240 ° C. from the initial stage of drying when the amount of water in the fiber is 15% or more, voids are generated in the fiber, resulting in a problem that strength is lowered and photooxidation deterioration property is deteriorated. Was there. As described above, when the undried yarn having the uniform void size inside the fiber is dried at a high temperature of about 240 ° C. or more,
It was found that the strength did not decrease. The temperature that can be used in the drying process depends on the structure formed by solidification. The ideally coagulated undried yarn does not decrease in strength or generate voids even when dried at 300 ° C. or higher. When the solidification temperature is about 30 ° C. or higher, the strength can be prevented from lowering even when dried at a high temperature of 240 ° C. or higher.

The following are concrete evidences of the structural change of the fiber which causes such a phenomenon. The strain of the molecule in the drying step can be measured by Raman spectroscopy. Young et al. (J. of Materials Sc.25, 127 (1
990)), the method for measuring the molecular strain from the shift of the absorption peak at 1580 to 1640 cm-1. The present inventors spun at a spinning speed of about 400 m / min to obtain a phosphoric acid concentration of 2
An evaluation was carried out while allowing the fibers to be retained in a coagulation bath having a liquid temperature of 20 ° C. for 2% for 0.3 seconds and then thoroughly washed with water to be dried on a hot stage at 240 ° C. It was confirmed that the strain in the compression direction acts on the molecular chain to generate macroscopic voids, the strain is relaxed, and the shift of the absorption peak returns to the original, but when the coagulation conditions of the present invention are adjusted. At 240 ℃
No peak shift was observed during drying on the hot stage of No. 1 and the peak shift amount was 1 cm-1 even at 280 ° C.
The following was confirmed. The peak shift amount of Raman spectroscopy is measured, for example, by Jobin-Yvon Ramanor-U1000.
Can be used with an Argon laser light source.

In the drying process, the drying starts from the fiber surface portion. The volume change at this time causes internal strain, but when the difference in shrinkage between the inside of the fiber and the surface layer of the fiber becomes small, the strain of the molecular chain also becomes small. In the fiber of the present invention, void generation does not occur even if the fiber surface is left alone in a dry state. When the conventional fiber is left in a state where the internal strain in the intermediate dry state is large, a void is generated when the moisture in the inside evaporates and the strength is lowered. In the present invention, it has become possible to carry out a method in which the drying is interrupted and the fibers are once wound as a package and dried, or a process speed is reduced and drying is performed with a large number of spindles and a short treatment length.

An object of the present invention is to economically produce polybenzazole fiber by making the drying equipment compact. Therefore, it is preferable to set the drying temperature as high as possible, and it is preferable that as many portions as possible in the drying process are kept at high temperature. In particular, when drying continuously with a plurality of drying devices, it is necessary to devise to shorten as much as possible the portion where the yarn temperature of the connection between the devices decreases, and at least 80% or more of the total length of the drying process should be 2% or more.
It is preferable to keep the temperature at 40 ° C. or higher, more preferably 95
% Or more is preferably maintained at 240 ° C. or more. The drying temperature needs to be changed depending on the structure of the undried yarn, but at least about 240 ° C. or higher, more preferably 260
C. or higher, most preferably 280.degree. C. or higher. The upper limit of the drying temperature is preferably 290 ° C. or lower as long as the yarn converging property and antistatic property are realized by the oil agent. Even when the convergence of the yarn can be secured by a method such as charge adjustment, it is necessary to set the temperature to about 650 ° C. or lower at the highest because of the heat resistance of the polymer.

From the viewpoint of equipment cost, it is preferable that the drying time is at most about 80 seconds or less, and the fiber is dried to less than about 2% of the equilibrium moisture content of the fiber, more preferably 60.
Seconds or less, most preferably about 30 seconds or less.

As the heating zone in the drying step, radiation such as an electric furnace or flame, heating roller or heating air or heating inert gas, superheated steam, or heat medium such as oil can be used. You may hold | maintain at high temperature and may use electromagnetic fields, such as a microwave, and a shock wave partially. Moreover, you may use it in these combinations. It is important to be able to raise the temperature of the fiber quickly.

The drying step is preferably performed online from the water washing step. More preferably, it is dried to a water content not higher than the equilibrium moisture content, and then rolled up to obtain a product. On the other hand, you may dry to the moisture content which can be wound up in a drying process, and may continue to dry with the wound up package. Alternatively, it is also possible to unwind it from the wound package and continuously carry out drying and heat treatment. The water content that enables winding is preferably at most about 25%, more preferably about 15% or less, and further preferably about 4% or less.

EXAMPLES Examples are shown below, but the present invention is not limited to these examples. (Measurement of Water Content) The method for measuring the water content in the fiber is as follows. About 1.0 g of dried fiber is weighed (W1),
The fiber is dried in a static dryer at 230 ° C. for 30 minutes, weighed (W0) again, and calculated by the following formula. Moisture content (%) = {(W1-W0) / W0} × 100 (Thermal differential measurement) Thermal differential measurement (hereinafter referred to as DSC measurement)
Was measured using a MacScience DSC3100S.
As a sample, an incompletely dried filament bundle was quickly cut into a length of 1 to 5 mm, and 2 to 12 mg was weighed by a balance and placed in an aluminum pan. The water content of the sample used at this time must be adjusted to approximately 25% in advance. This is because when DSC measurement is performed in a state where a large amount of free water (water adhering to the outer surface of the yarn) is included, the free water coagulation becomes an obstacle and interferes with the measurement of the freezing point of water in the pores. . Particularly, the peaks existing at 0 ° C to -40 ° C are easily affected. The distribution of the freezing point is determined by the DSC during the cooling process.
It was carried out by measuring and evaluating the curve. Although essentially the same conclusion should be drawn from the measurement of the heating process, DSC
It was not suitable for actual evaluation because the peaks on the curve became dull. The rate of temperature decrease is 10 ℃ / min.
It was measured up to 70 ° C. An example of the DSC curve measured in this way is shown in FIG. The presence or absence of peak splitting allows the evaluation of the difference in pore distribution. (Void observation) The amount of fiber defects and the dispersion state are about 4
The fiber piece cut into cm was placed on a slide glass and observed at 200 times using an optical microscope.

Examples 1-8 and Comparative Examples 1 and 2, 3 obtained by the method shown in US Pat. No. 4,533,693
When the intrinsic viscosity measured with a methanesulfonic acid solution at 0 ° C. is 2
A spinning dope composed of 14.0% by weight of polybenzoxazole (4.4 dL / g) and polyphosphoric acid having a phosphorus pentoxide content of 83.17% was used for spinning. The dope is passed through a metal mesh filter material, then kneaded and defoamed with a biaxial kneading device, and then the pressure is raised to a polymer solution temperature of 175 ° C.
The spinning yarn was spun at 175 ° C. from a spinneret having 334 holes and the discharged yarn was cooled with cooling air having a temperature of 60 ° C. and then introduced into a coagulation bath. The spinning speed, coagulation bath temperature and phosphoric acid aqueous solution concentration in the coagulation bath were set to the conditions shown in Table 1.
Spinning, coagulation, water washing (neutralization), and drying were performed online. The drying device is a hot air drying type oven (wind speed 16m /
Sec) was used. The washing / drying conditions and the physical properties of the obtained fiber are also shown in Table 1.

[0024]

[Table 1]

As is clear from Table 1, spun yarn satisfying the coagulation conditions in the range of the present invention has physical properties without the occurrence of macroscopic voids and the like even under epoch-making high speed drying conditions which have never been obtained. Does not fall. With the technique of the present invention, polybenzazole fibers can be produced very efficiently with less capital investment.

Example 9 and Comparative Example 3 A sample subjected to the same spinning, coagulation and water washing (neutralization) as in Comparative Example 1 and Example 3 was dried at 180 ° C. for 34 seconds under a process tension of 2
The fiber was dried at g / d and the moisture content in the fiber was set to 25%, and the fiber was wound up and measured by DSC. 1 in FIG. 1 is the pattern of the intermediate undried yarn (Comparative Example 3) corresponding to Comparative Example 1, and 2 in the figure is the pattern of the sample (Example 9) corresponding to Example 3.

The samples of Comparative Example 3 and Example 9 were passed through a dryer, and the upper limit temperature at which voids were generated was examined. The temperatures at which voids were generated were 225 ° C. in Comparative Example 3 and 295 ° C. in Example 9, respectively.

Example 10 and Comparative Example 4 A sample subjected to the same spinning, coagulation and water washing (neutralization) as in Comparative Example 1 and Example 3 was passed through a dryer at 220 ° C. for 80 seconds and wound up. The water content at this time was 5.7% for the intermediate dry yarn (Comparative Example 4) corresponding to Comparative Example 1 and 5.1% for the intermediate dry yarn (Example 10) corresponding to Example 3. these,
Table 2 shows the water content and strength before and after being left for 42 hours in a dark place in a room where the temperature is 20 ° C and the humidity is 65 rh%.

[0029]

[Table 2]

As is clear from Table 2, the polybenzazole fiber of the present invention has excellent properties in that the yarn quality hardly changes with drying.

[0031]

Industrial Applicability According to the present invention, it is possible to manufacture polybenzazole fiber with a much more compact facility than the conventional one.

[Brief description of drawings]

1 shows a thermal differential analysis curve of an intermediate undried yarn of the present invention and a conventional polybenzazole fiber.

[Explanation of symbols]

1: Thermal differential analysis curve of conventional polybenzazole intermediate undried yarn (Comparative Example 3) 2: Thermal differential analysis curve of polybenzazole intermediate undried yarn of the present invention (Example 9)

Claims (5)

[Claims] 1. When a spinning dope composed of polyphosphoric acid and polybenzazole is extruded through a spinneret and the obtained dope filament is coagulated, washed with water, and then dried, the temperature of a portion of 80% or more with respect to the entire length of the heating zone. To 240 ° C. or higher, a method for producing a polybenzazole fiber. 2. A polyphosphoric acid aqueous solution of 6% or more and less than 50% is used as the coagulation bath, and the coagulation bath temperature is 30 ° C. or more and 120%.
The method for producing the polybenzazole fiber according to claim 1, wherein the temperature is set to be not higher than ° C. 3. The method for producing a polybenzazole fiber according to claim 1, wherein the water content in the fiber is dried to less than 2% within 80 seconds. 4. The moisture content in the fiber is set to 25% by drying at 180 ° C. under a tension of 2 g / d, and a thermal differential analysis (D
The method for producing a polybenzazole fiber according to claim 1, wherein the fiber in which a single in-fiber liquid coagulation peak is observed at 20 to -70 ° C when measured by SC) is subjected to a drying step. 5. A single fiber at 20 to -70 ° C. when measured with a differential scanning calorimeter (DSC) to have a moisture content in the fiber of 25% by drying at 180 ° C. under a tension of 2 g / d. A polybenzazole intermediate dry fiber characterized in that an internal liquid coagulation peak is observed.