JP3065467B2 - Method for drying polybenzazole fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improved method for drying polybenzazole (PBZ) fibers containing polybenzoxazole (PBO) or polybenzothiazole (PBT).

[0002]

BACKGROUND OF THE INVENTION Non-thermoplastic lyotropic liquid crystalline polybenzazole is typically produced by a dry-wet spinning method. A solution (dope) composed of a polybenzazole polymer and an acid solvent is discharged from a die as described in USP 07/985079 (a method for spinning polybenzazole fiber) and USP 07/985078 (a method for high-speed spinning polybenzazole fiber). At the time of spinning, the fiber is stretched in a gas and then brought into contact with a liquid of a solvent having a low concentration that does not dissolve the polymer for desolvation, thereby spinning. This process is known as coagulation. USP08 / 110149
After coagulation, the residual solvent in the fibers is washed with water, as shown in (Improved method for washing coagulated polybenzazole fibers). The polybenzazole fiber after washing has a large amount of water of 30% by weight to 200% by weight. The residual moisture percentage here is expressed by the following equation. Residual moisture percentage (%) = (weight of fiber before drying−weight of fiber after drying) / weight of fiber after drying × 100 The fiber after water washing must be dried. One of the reasons is to avoid defects generated during heat treatment. Although heat treatment is performed to improve physical properties using dried fibers, PBZ fibers having a residual moisture content of about 12% by weight or more typically have defects when heat treated at 400 ° C. all right. For this reason, during the heat treatment, the residual moisture content usually needs to be about 12% by weight or less. Conventionally, as a method of reducing the residual moisture content before heat treatment to 12% or less, it was necessary to dry the material at 65 ° C. for 40 hours or more. Such low-temperature and long-time drying is not acceptable in terms of cost and industry. But,
When the fiber is heated at a high temperature to increase the drying speed, there is a problem that void defects occur in the fiber. This defect must be avoided as much as possible. Therefore, there is a need for an improved process that dries quickly without causing defects.

[0003]

SUMMARY OF THE INVENTION The present invention is directed to a method of drying polybenzazole fiber which has improved the above problems and has a remarkably increased drying rate without causing defects such as voids in the fiber. Is what you do.

[0004]

Means for Solving the Problems The present inventors have studied a method for drying polybenzazole fibers after washing with water at as high a temperature as possible without causing defects, and have reached the present invention. That is, a polybenzazole fiber having a residual moisture content of 30% by weight or more is dried by the method described below to obtain about 1%.
This is a rapid drying method that makes the residual moisture content of 2% by weight or less and minimizes the defect of the fiber. One of them is to successively dry at two or more different temperatures at different drying temperatures, set the drying temperature in relation to the residual moisture content in the fiber, and set the drying temperature at each stage to the previous value. This is a drying method in which the drying temperature is set higher than the drying temperature of the stage, and the fibers during drying have a non-contact drying residence time different from the set temperature (Preparation method 1). The second is that polybenzazole fiber having a residual moisture content of 30% by weight or more is continuously dried in two or more stages at different drying temperatures, and the drying temperature is changed to the residual moisture in the fiber. The drying temperature of each stage is selected to be higher than the drying temperature of the previous stage, and the drying temperature is about 12% by weight.
This is a rapid drying method that has the following residual moisture content and minimizes defects of the fiber (Production method 2).

Further, there is provided a drying method according to the above-mentioned production method 1, wherein the final residual moisture content is 10% by weight or less. This is the drying method of Production Method 1, in which the final residual moisture content is 6% by weight or less. The drying method according to Production Method 1, wherein the final residual moisture content is 4% by weight or less. A drying method according to production method 1, wherein the final residual moisture content is 2% by weight or less. The drying method according to Production Method 1, wherein the total residence time of drying is 20 minutes or less. The drying method according to Production Method 1, wherein the total residence time for drying is 15 minutes or less.
The drying method according to Production Method 1, wherein the total residence time for drying is 10 minutes or less. The drying method according to Production Method 1, wherein the drying temperature is two stages. A drying method according to production method 1, wherein the drying temperature is three stages. The drying method according to production method 1, wherein the initial drying temperature is at least 140 ° C. or higher. The drying method according to production method 1, wherein the initial drying temperature is at least 150 ° C. or higher. The drying method according to production method 1, wherein the initial drying temperature is at least 170 ° C. or higher. The drying method according to production method 1, wherein the initial drying temperature is at least 180 ° C or higher.
The drying method according to production method 1, wherein the polybenzazole fiber is a polybenzazole fiber. The drying method according to production method 1, wherein the polybenzazole fiber is a polybenzazole fiber. A polybenzazole fiber dried by the method described in Production Method 1. The above-mentioned polybenzazole fiber which is a polybenzazole fiber. The above-mentioned polybenzazole fiber which is a polybenzothiazole fiber is preferable.

[0006] This is a drying method of Production Method 2 in which the final residual moisture content is 10% by weight or less. Final residual moisture content is 6% by weight
This is the drying method of Production Method 2 below. This is the drying method of Production Method 2 in which the final residual moisture content is 4% by weight or less. This is a drying method of Production Method 2 in which the final residual moisture content is 2% by weight or less. This is a drying method of Production Method 2 in which the total residence time is 14 minutes or less. This is a drying method of Production Method 2 in which the total residence time is 10 minutes or less. The drying method according to Production Method 2, wherein the total residence time is 7 minutes or less. A drying method according to production method 2, wherein the drying temperature is two stages. A drying method according to Production Method 2, wherein the drying temperature is three stages. The drying method according to production method 2, wherein the initial drying temperature is at least 140 ° C. or higher. The drying method according to Production Method 2, wherein the initial drying temperature is at least 150 ° C. or higher. The drying method according to Production Method 2, wherein the initial drying temperature is at least 170 ° C. or higher. The drying method according to production method 2, wherein the initial drying temperature is at least 180 ° C. or higher.
The drying method according to production method 2, wherein the polybenzazole fiber is a polybenzoxazole fiber. The drying method according to Production Method 2, wherein the polybenzazole fiber is a polybenzothiazole fiber. A polybenzazole fiber dried by the method described in Production Method 2. The polybenzazole fiber is a polybenzoxazole fiber. Preferably, the polybenzazole fiber is a polybenzothiazole fiber.
This drying method will be described with reference to the drawings.

FIG. 1 shows the residual moisture content and the drying temperature of the polybenzazole fiber. The solid line 10 indicates the boundary between the safety zone 30 where no defect occurs and the danger zone 20 where the defect occurs. This solid line 10 is a non-damage drying (NDD) line of the polybenzoxazole fiber. FIG. 2 shows FIG.
Indicates that the drying temperature is increased (horizontal line portion) so as to continuously reduce the residual moisture content in the safety region 30 (perpendicular line portion). FIG. 3 shows two cases of drying along the solid line in FIG. Line 1 is a case where a defect occurs, and line 2 is a case where no defect occurs. Polybenzazole (PBZ) refers to polybenzoxazole (PBO) homopolymer, polybenzothiazole (PBT) homopolymer and their PBO, PB
T means a random, sequential or block copolymer. Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymers are, for example, Wolfe
`` Liquid Crystalline Polymer Compositions, Proc
ess and Products '' US Patent 4,703,103 (October 27,
1987), `` Liquid Crystalline Polymer Compositions,
Process and Products '' USPatent 4,533,692 (August
6,1985), `` Liquid Crystalline Poly (2,6-Benzothiaz
ole) Compositions, Process and Products '' USPat
ent4,533,724 (August 6,1985), `` Liquid Crystalline
Polymer Compositions, Process and Products '' USPa
tent 4,533,693 (August 6,1985), Evers `` Thermooxi
datively Stable Articulated p-Benzobisoxazole and
p-Benzobisthiazole Polymers '' USPatent 4,359,567
(November 16,1982); Tsai et al., “Method for Making He
terocyclic Block Copolymer '' USPatent 4,578,432
(March 25, 1986). The structural unit contained in the PBZ polymer is preferably selected from a lyotropic liquid crystal polymer.

The monomer units are described in structural formulas (a) to (h) in chemical formulas 1 and 2. The polymer preferably consists essentially of monomer units selected from structural formulas (a)-(h), and more preferably consists essentially of structural formula (a)
-Consisting of monomer units selected from (c). Suitable solvents for forming the dope of the PBZ polymer include:
Includes non-oxidizing acids that can dissolve cresol and its polymers. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and high concentrations of sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.

[0009]

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[0010]

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[0011] The polymer concentration in the solution is preferably at least about 7% by weight or more, more preferably at least about 10% by weight or more, and most preferably at least about 14% by weight or more. The maximum polymer concentration is limited by practical handling properties, for example, polymer solubility and dope viscosity. Due to their limiting factors, the polymer concentration does not usually exceed 20% by weight.

A suitable polymer, copolymer or dope is synthesized by the following known method. For example, Wolf
e et al., USPatent 4,533,693 (August 6,1985), Sybert
US Patent 4,772,678 (September 20,1988), Harr.
See USPatent 4,847,350 (July 11,1989) for is.
PBZ polymers are available from US Patent 5,089,591 by Gregory et al.
According to (February 18, 1992), it is possible to increase the molecular weight at a high reaction rate under relatively high temperature and high shear conditions in a dehydrating acid solvent.

As described in the prior art, the dope is produced by a known dry-wet spinning method. In other words, the fibrous dope that has been discharged from the spinneret passes through the gas,
The spinning is performed by contacting (coagulation) with a liquid of a thin solvent having a concentration that does not dissolve the polymer. After coagulation, the residual solvent in the fiber is washed with water. The fibers after washing are usually from 30% by weight to 200% by weight.
It has a residual moisture content of% by weight. As already explained, the washed fibers must be dried. One of the reasons is that it is necessary to avoid defects generated during the heat treatment. To do so, set the residual moisture content of the fiber to 1
It is preferably at most 2% by weight, preferably at most 10% by weight, more preferably at most 6% by weight, most preferably at most 2% by weight. Conversely, the temperature for rapidly drying the PBZ fiber is preferably selected to be the highest as long as no defect occurs. The lower the residual moisture content in the fiber, the higher the drying temperature can be made without causing defects. That is, it is possible to raise the drying temperature without generating defects as the drying is performed continuously to reduce the residual moisture content.

The most suitable method for increasing the drying rate of the PBZ fiber is to increase the temperature in the safety zone where no defects occur with a decrease in the residual moisture content, so that the best method is provided within the danger zone where defects occur. Drying at a temperature. As a result of examining the relationship between the residual moisture content of the PBO fiber and the drying temperature, the non-damage drying (NDD) line 10 shown in FIGS.
I got This NDD line indicates the maximum drying temperature at which no defect occurs in the fiber in relation to a specific residual moisture content, and is a boundary between the safety zone 30 and the danger zone 20. For example, the highest temperature to be dried first can be simply selected according to the residual moisture content of the fiber at that time. At this time, the maximum drying temperature that minimizes the residence time should be selected so that the residual moisture content is about 12% by weight or less. The number of stages of the drying temperature is selected according to the process conditions of the equipment, etc., but the subsequent drying temperature is set higher than the preceding drying temperature so as to minimize the residence time and keep the residual moisture content at about 12% by weight or less. More than steps are required.

FIG. 2 shows that the temperature of the PBO fiber having an initial residual water content of 40% by weight or more is gradually increased to 5% by weight.
The following shows a multi-stage drying process of 23 stages for drying.
In this drying process, drying is performed along the NDD line as much as possible within the safety area of the NDD line. This method allows the fastest drying without creating defects in the fibers. Since the morphology and physical properties of the dried PBZ fiber depend on the dope composition, polymer structure and process conditions, the maximum temperature at which no defects occur will vary. Therefore, the NDD line of the PBZ fiber changes depending on the following factors and their sizes. a) Defects in the fiber that enter the manufacturing process prior to drying b) Porosity in the fiber c) Manufacturing conditions d) Residual chemicals and impurities such as solvents in the fiber e) Additives and process aids in the fiber In practice, a pair of heated rolls suitable for drying are typically used. The fiber is multiply wound on this heated roll to increase the contact time. The contact time is the time during which the heating roll (which may be another device) at the set temperature is in direct contact with the fiber. At this time, the temperature of the fiber in contact with the roll is estimated to be the same as the surface temperature of the roll. The surface temperature of the heating roll is estimated to be the same as the set temperature of the roll,
For example, when set to 180 ° C., the surface temperature of the roll becomes the same. Here, the set temperature of the heating device is set as the actual heating temperature.

Next, the contact time with the heating roll will be described. When the fiber is dried by a pair of heating rolls, it moves between the rolls, and in the case of two pairs of heating rolls, it also moves between the pair. The time when the fiber is not in contact with the roll is defined as the non-contact time. The total residence time during drying is the contact time (C
T) and the non-contact time (NCT). When the fiber is not in contact with the heating roll, the temperature of the fiber is lower than the heating roll temperature. Therefore, it is presumed that the time during which the fibers are substantially dried at the heating roll temperature is short, and the drying proceeds during NCT between the heating rolls, but is not as efficient as during CT. One way to increase the drying efficiency is to insulate the cabinet in which the heating rolls are installed, and to blow heated air or heated nitrogen, helium, argon, carbon dioxide, etc., which does not cause defects in the fibers, into the cabinet. Then, there is a method of making the inside of the cabinet the same as the set temperature of the heating roll. As another method of further increasing the drying efficiency, there is a method in which the fibers are continuously passed through a roll of a subsequent drying cabinet following the preceding drying cabinet and a plurality of drying cabinets in which the ambient temperature is set high. By combining the above methods, the drying efficiency is further improved, and the total residence time can be all handled in the same manner as CT. As mentioned, the drying efficiency of CT is higher than that of NCT. By these methods of increasing the drying efficiency, the residence time to reach the target residual moisture content can be reduced, and the residence time is reduced to about 2/3 as compared with the case other than the above method (including NCT). be able to.

When the CT and NCT need to be considered, the total residence time is preferably about 10 minutes or less, more preferably about 5 minutes or less in view of industrial requirements to keep the residual moisture content to about 12% by weight or less. Most preferably it should be less than about 3 minutes. In the case where the residence time can be expressed only by CT, the total residence time is preferably about 6 minutes or less, more preferably about 3.3 minutes in view of industrial requirements to keep the residual moisture content to about 12% by weight or less. Below, most preferably less than about 2 minutes. When the CT and NCT need to be considered, the total residence time is preferably about 20 minutes or less, more preferably about 15 minutes or less, most preferably about 15 minutes or less, from the industrial demand to keep the residual moisture content to about 2% by weight or less. Should be no more than about 10 minutes. In the case where the residence time can be expressed only by CT, the total residence time is preferably about 14 minutes or less, more preferably about 10 minutes or less in view of industrial requirements in order to keep the residual moisture content to about 2% by weight or less. Most preferably it should be no more than about 7 minutes.

In the above description, to obtain a specific residual moisture content, it is preferable to start from a specific minimum temperature. Thus, the initial temperature is at least about 140 ° C. or higher, preferably at least about 150 ° C. or higher, more preferably at least about 160 ° C., and most preferably at least about 180 ° C. To reduce the residence time, the running speed of the fibers should be as high as possible. As shown in Fig. 2, if the selected temperature during the process of drying does not exceed the NDD line temperature within the safety zone, no voids are generated. Normal,
Final drying temperature does not exceed 300 ° C, preferably 280 ° C
And more preferably not more than 260 ° C.

An important point of drying is when the residual moisture content reaches a predetermined level. Drying is performed at most up to a residual moisture content of 12% by weight or less, preferably up to a residual moisture content of 10% by weight or less, more preferably at most 8% by weight or less, at most before leaving the drying apparatus. Drying is preferably continued at most to a residual moisture content of at most 6% by weight, more preferably at most to a residual moisture content of at most 4% by weight, most preferably at most to a residual moisture content of at most 2% by weight. The dried yarn may be heat treated to improve the physical properties of the fiber. Heat treatment of PBZ fiber is USP07 / 9
85068 and USP 07/985067. According to the method described above, it is possible to dry quickly with minimizing the defects in the PBO fiber.

[0020]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, all percentages shown below are percentages by weight. The method for measuring the residual moisture content is as follows. About 0.5
g of fiber is weighed (w1) and placed in an oven at 250 ° C. for 30 minutes.
After partial drying, it is weighed again (w0) and calculated by the following equation. Residual moisture percentage (%) = (w1-w0) / w0 × 100 The amount of voids in the fiber and the state of dispersion are determined by cutting a fiber sample to a length of 3 inches, placing the fiber sample on a slide glass, and using a light microscope at a magnification of 200 times. Was observed. Voids usually look like spots or dark streaks along the fiber axis, their size,
Numbers and thicknesses vary. No void amount, slight void,
It was ranked as many, many.

A spin dope in which cis-polybenzoxazole having an intrinsic viscosity of 30 dl / g was dissolved in polyphosphoric acid at 14% was extruded at 160 ° C. from a 166-hole nozzle having an orifice diameter of 0.22 mm. The fibrous dope extruded from the nozzle passed through an air gap of 22 cm, passed through a coagulation bath adjusted to about 22 ° C., and was further continuously washed with rollers. Subsequently, a pair of rolls set at the same temperature were installed in a cabinet, and three drying devices were successively dried at a higher temperature in a later stage. FIG. 3 shows a drying profile of an example described below.

<Embodiment 1> In FIG. 3, line 2 has a speed of 20.
It is a drying profile of the fiber 2 running at 0 m / min.
First, at 170 ° C. (residence time: 84.3 seconds), the residual moisture content was 2
0% or less, then 200 ° C. (residence time 84.3
) And dried at 240 ° C. (residence time 79.3 seconds) to a residual moisture content of 3% or less. The fiber finally had a total residence time of 4.1 minutes and a residual moisture content of 3.0.
%Met. Under these conditions, when the residence time at 240 ° C. was further increased to 158.6 seconds, the final residual moisture content became 1.0% or less. The drying profile of this fiber 2 is NDD line
And does not enter the danger zone 20. The fiber has a tensile strength of 38.0-39.3 g / d and a tensile modulus of 1616-
It was 1,624 g / d and elongation at break was 2.86 to 3.00%. No void was observed in this fiber. If the cabinet is not insulated (total residence time is CT and NCT
The first pair of heating rolls at 180 ° C., the second stage heating roll at 200 ° C., and the third stage heating roll at 220 ° C.
When the temperature is set to 4.degree.
In contrast, if the cabinet is insulated and the inside thereof is set to the same temperature as the set heating roll (total residence time is only CT) under the same conditions, it takes about 2. It can be dried in 78 minutes. As described above, when the residence time can be represented only by CT, the residence time can be reduced to about ／ of the case where the residence time is not otherwise.

<Comparative Examples 1 to 3> In FIG. 3, line 1 is a drying profile of the fiber 1 running at a speed of 200 m / min. First, at 180 ° C. (residence time: 42 seconds), the residual moisture content is 2
Dry to 5% or less, then 240 ° C (residence time 121 seconds)
And dried to a residual moisture content of 15% or less. Line 1 is at point 5
Crosses the NDD line and enters the danger zone 20. The fiber has a tensile strength of 33.8 g / d and a tensile modulus of 1671 g / d.
d, elongation at break was 2.46%. Observation of voids revealed that the fiber had many voids. The above results are shown in the table together with Comparative Examples 2 and 3.

[0024]

[Table 1]

[0025]

According to the present invention, it has become possible to provide a method for drying polybenzazole fibers with a remarkably increased drying rate without generating void defects in the fibers.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the residual moisture content and the degree of dryness of polybenzazole fibers used in the present invention.

FIG. 2 is a diagram showing that the drying temperature is increased so as to continuously reduce the residual moisture content in the safety region in FIG.

FIG. 3 is a diagram showing a case where a defect occurs in the fiber (dotted line) and a case where no defect occurs (solid line) in FIG. 1;

[Explanation of symbols]

10: NDD line of polybenzazole fiber. 20: dangerous area where a defect occurs, 30: safety area where no defect occurs.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Chi Chun Chau 48640 Midland, Michigan USA Midland Bluebird Drive 4205 Examiner Yoko Nakajima (58) Field surveyed (Int.Cl. ⁷ , DB name) D01F 6/74

Claims (2)

(57) [Claims] 1. A polybenzazole fiber having a residual moisture content of 30% by weight or more is dried by the following method to obtain
A method for drying a polybenzazole fiber to have a residual moisture content of not more than weight%. (1) Continuously, stepwise drying at two or more different temperatures at different drying temperatures, setting the temperature in relation to the residual moisture content of the fiber, and setting the drying temperature of each step to be lower than the temperature of the preceding step. Set higher. (2) The fiber during drying has a non-contact residence time at a temperature different from the set temperature. 2. Polybenzazole fibers having a residual moisture content of 30% by weight or more are continuously dried at different drying temperatures.
Drying stepwise at a temperature equal to or higher than the step, selecting the drying temperature in relation to the residual moisture content of the fiber, and drying at a temperature of each step higher than the temperature of the previous step, and drying by 12% by weight.
A method for drying polybenzazole fiber having the following residual moisture content.