JP2011137266A - Polybenzazole fiber multifilament - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polybenzazole fiber multifilament having improved post-processing property while maintaining heat resistance and flame retardancy. <P>SOLUTION: The polybenzazole fiber includes a tensile strength of ≤4.5 GPa, the variation B(%) of strength of single filaments constituting a multifilament defined by the following formula: B(%)=(σ/average tensile strength of single filaments)×100 of ≤0.2% and a number of constituent filaments is ≥30. The polybenzazole fiber multifilament has a stickiness degree K of single filaments to each other constituting the multifilament of ≤5%, wherein K=((b-a)/b)×100 (wherein a is the total number of single filaments; and b is a structural number of multifilament). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polybenzazole fiber multifilament, more specifically, various post-processability such as fiber cutting, heat resistance, and flame retardancy, as compared with a conventional polybenzazole fiber multifilament. The present invention relates to a polybenzazole fiber multifilament that can be developed for use.

  The polybenzazole fiber is extruded from a spinneret by a dope containing a polybenzoxazole or polybenzothiazole polymer and an acid solvent, and then immersed in a solidifying liquid (for example, water or a mixture of water and an inorganic acid). In order to solidify and then remove the acid solvent, it is produced by a method of washing in a water washing bath, further neutralizing the acid remaining in the yarn through an aqueous bath of an inorganic base, and then drying (for example, (See Patent Document 1).

  Polybenzazole fibers have the highest level of performance among organic fibers in all respects, in terms of strength, elastic modulus, heat resistance and flame retardancy. For this reason, it has been developed for various applications utilizing these characteristics. However, among the applications that make use of heat resistance and flame retardancy, the excellent properties of polybenzazole fiber, such as high strength and high elastic modulus, conversely make fiber cutting difficult and cause deterioration in post-processability It has become. Therefore, in these fields, improvement of post-processability of polybenzazole fiber is desired.

  As a method for improving the post-processability of the polybenzazole fiber, a method of greatly reducing the strength of the fiber can be considered. For example, a polybenzazole dope in which polybenzazole is dissolved in a solvent is spun from a spinneret, and the spun dope filament is brought into contact with the vapor of a polybenzazole coagulant and then immersed in a coagulation bath. A polybenzazole fiber having a significantly reduced fiber strength is disclosed (for example, see Patent Document 2).

  By using the above method, it is possible to significantly reduce the strength of the polybenzazole fiber multifilament. However, a phenomenon occurs in which the variation in strength between the single yarns constituting the multifilament increases or the single yarns constituting the multifilament partially stick to each other.

  That is, when many high-strength single yarns coexist, some high-strength single yarns cause deterioration in post-workability. Moreover, sticking of single yarns is a problem from the point of product quality. Therefore, a polybenzazole fiber multifilament in which these problems are improved is desired.

Japanese Patent No. 3564822 Japanese Patent Laid-Open No. 2008-50711

An object of the present invention is to provide a polybenzazole fiber multifilament having excellent post-processability such as fiber cutting while maintaining excellent heat resistance and flame retardancy.
Furthermore, there is provided a polybenzazole fiber multifilament in which the filaments (single yarns) constituting the multifilament have less sticking to each other and the strength of all the filaments (single yarns) constituting the multifilament is reduced more uniformly. There is.

The polybenzazole fiber multifilament of the present invention capable of solving the above-mentioned problems has the following configuration.
That is, the present invention is a polybenzazole fiber multifilament composed of at least 30 filaments, the tensile strength is 4.5 GPa or less, and the variation B in tensile strength between the filaments is 0.2%. It is the polybenzazole fiber multifilament characterized by the following.

  Moreover, it is preferable that the sticking degree K of the filaments (single yarn) constituting the multifilament is 5% or less.

  The polybenzazole fiber multifilament of the present invention maintains the excellent heat resistance and flame retardancy of the polybenzazole fiber, and the strength of all single yarns constituting the multifilament is more uniformly reduced. And the sticking of the single yarn which comprises a multifilament is suppressed. Therefore, since the quality is good and the high strength of the polybenzazole fiber, it can be used for various applications where the post-processability is poor and the use has not spread.

Hereinafter, the present invention will be described in detail.
The polybenzazole fiber used in the present invention means a fiber made of a polybenzazole polymer. The polybenzazole (hereinafter also referred to as PBZ) is selected from polybenzoxazole (hereinafter also referred to as PBO), polybenzothiazole (hereinafter also referred to as PBT), or polybenzimidazole (hereinafter also referred to as PBI) 1 Means more than one polymer.

  In the present invention, PBO means a polymer containing an oxazole ring bonded to an aromatic group. The aromatic group is not necessarily a benzene ring, and may be a biphenylene group, a naphthylene group, or the like. Furthermore, PBO is not only a homopolymer of poly (p-phenylenebenzobisoxazole) but also a copolymer or aromatic compound in which a part of the phenylene group of poly (p-phenylenebenzobisoxazole) is substituted with a heterocyclic ring such as a pyridine ring. Polymers comprising a plurality of oxazole ring units bonded to a group are widely included. This is the same for PBT and PBI. And (i) a mixture of two or more selected from PBO, PBT, or PBI, (ii) two or more block or random copolymers selected from PBO, PBT, or PBI, or These mixtures are also included.

  The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers that form liquid crystals at a specific concentration. The polymer is composed of monomer units described in the following structural formulas (a) to (f), preferably consisting essentially of monomer units selected from the structural formulas (a) to (d). is there. In addition, these monomer units may partially include monomer units having a substituent such as an alkyl group or a halogen group.

  Suitable solvents for forming the polymer dope include cresol and non-oxidizing acids that can dissolve the polymer. Suitable acid solvents include, for example, polyphosphoric acid, methanesulfonic acid and high concentration sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most preferred solvent is polyphosphoric acid.

  The polymer concentration in the dope is preferably 7% by mass or more, more preferably 10% by mass or more, and particularly preferably 14% by mass or more. The maximum concentration of polymer in the dope is limited by practical handling properties such as polymer solubility and dope viscosity. Due to these factors, the polymer concentration usually does not exceed 20% by weight.

  In the present invention, suitable polymers or copolymers and dopes can be synthesized by known methods.

  For example, Wolfe et al U.S. Pat. No. 4,533,693 (1985.8.6), Sybert et al U.S. Pat. No. 4,772,678 (1988.9.22), Harris U.S. Pat. No. 4,847. , 350 (1989. 7.11), or Gregory et al., US Pat. No. 5,089,591 (1992.2.18).

  In these patent documents, suitable monomers are stepwise or constant from about 60 ° C. to 230 ° C. in a non-oxidizing and dehydrating acid solution in a non-oxidizing atmosphere under high speed stirring and high shear conditions. It is described that the reaction is carried out at an elevated temperature.

  The dope thus polymerized is supplied to the spinning section and discharged from the spinneret at a temperature of usually 100 ° C. or higher. Normally, a plurality of nozzle discharge holes are arranged in a circumferential shape or a lattice shape, but other arrangements may be used. The number of discharge holes in the die is not particularly limited, but is preferably 30 or more. It is important that the discharge holes on the spinneret surface have a hole density that prevents fusion between the spun yarns (dope filaments). Moreover, it is preferable that each discharge hole of a nozzle | cap | die is equidistant.

  The spun yarn requires a sufficiently long draw zone length as described in US Pat. No. 5,296,185 to obtain a sufficient draw ratio (SDR) and a relatively high temperature (solidification temperature of the dope). It is desirable to cool uniformly with the rectified cooling air having a spinning temperature equal to or lower than the above. The length (L) of the draw zone is required to be a length that completes solidification in a non-solidifying gas, and is roughly determined by the discharge amount (Q) of a single hole. In order to obtain good fiber properties, it is desirable that the draw zone take-out stress is 2.2 g / dtex or more in terms of polymer (assuming that only the polymer is stressed).

  The feature of the polybenzazole fiber multifilament of the present invention is that the tensile strength is 4.5 GPa or less, and the variation B of the tensile strength of at least 30 filaments (single yarn) constituting the multifilament is 0.2%. It is as follows. Furthermore, it is preferable that the sticking degree K of single yarns constituting the multifilament is 5% or less.

The variation B (%) in the strength of the single yarn constituting the multifilament is defined as follows.
A single filament of at least 90% of the number of multifilaments is extracted, and all the extracted single yarns are measured with a tensile tester in accordance with JIS L 1013. From the tensile strength, the variation of the tensile strength, that is, the standard deviation σ is obtained, and the value of the variation B (%) is calculated using the following equation. As the fineness in the single yarn measurement, the single yarn fineness calculated by dividing the fineness of the multifilament by the number of constituent filaments is used.
B (%) = (σ / average tensile strength of single yarn) × 100

Further, the degree of sticking K between the single yarns constituting the multifilament is defined as follows. When multifilaments cut to 5 mm are placed on a slide, paraffin oil is dropped and separated into single yarns using tweezers, the total number of single yarns excluding fibers that are not easily separated by sticking is a When the number of components is b, the degree of sticking between single yarns is calculated using the following formula, and the average value evaluated three times is K.
Degree of sticking between single yarns constituting multifilament (%)
= ((B−a) / b) × 100

  A suitable production method for producing the polybenzazole fiber multifilament of the present invention will be described below.

  The dope filaments extruded from the spinneret with a polybenzazole dope containing solvent are focused and immersed from the coagulating liquid-containing liquid before solidification before the inside of the bundle of dope filaments of the focused polybenzazole fiber. It is important to spray the vapor of the coagulant of polybenzazole from the circumferential direction. Thereby, the tensile strength of each single yarn which comprises a multifilament can be reduced significantly and more uniformly.

  For example, when the polybenzazole coagulant is water, examples of the method of bringing the dope filament bundle into contact with water vapor include a method of passing through a water vapor atmosphere and a method of spraying water vapor.

  In the method of passing a bundle of polybenzazole fiber dope filaments in a steam atmosphere, each single yarn located outside the bundle of filaments can be in contact with the steam atmosphere. However, each single yarn located inside the bundle of filaments is obstructed by the accompanying flow and cannot sufficiently come into contact with water vapor. Therefore, there is a difference in the contact state of water vapor between the single yarns located outside and inside the bundle of filaments. As a result, there is a difference in the decrease in tensile strength of each single yarn.

  On the other hand, as a method of spraying water vapor on the bundle of dope filaments, there is a method using a slit nozzle. However, in the method in which two slit nozzles are installed in the facing direction, water vapor is applied only from two directions, so that it is difficult to uniformly bring water vapor into contact with each single yarn of the dope filament bundle. In order to make water vapor contact more uniformly with each single yarn constituting the bundle of filaments, a method of spraying water vapor from the circumferential direction from the outside to the inside of the spun dope filament bundle is suitable. is there.

Further, the focused density D (number of filaments / cm ² ) of the spun dope filaments at a position where the vapor of the polybenzazole coagulant is sprayed from the circumferential direction to each single yarn of the bundle of dope filaments is 2, It is also important that it is 000 or less.

The focusing density D of the doped filament is defined by the following equation.
D = A × (L1 / L2) × (L1 / L2)
D (number of filaments / cm ² ): the concentration density of the dope filaments at the position where the vapor of the coagulant of polybenzazole is sprayed, A (pieces / cm ² ): hole density of the spinneret, L1 (cm): from the spinneret Distance to position where dope filament is focused in coagulation bath, L2 (cm): Distance from position where polybenzazole coagulant vapor is sprayed to position where dope filament is focused in coagulation bath

  The inventors of the present invention have described the polybenzazole until it is solidified by immersing it in a liquid (coagulation bath) containing a polybenzazole coagulant while focusing the dope filament of polybenzazole extruded from the spinneret. When spraying the vapor of the sol coagulant from the circumferential direction, it is possible to uniformly contact each single yarn with the vapor of the coagulant of polybenzazole without contacting each single yarn constituting the multifilament. I found it important.

For that purpose, the degree of focusing of the dope filament at the portion where the vapor is sprayed is most important. If the degree of focusing of the dope filament in the portion where the vapor is sprayed, that is, the value of D defined above is 2,000 (number of filaments / cm ² ) or less, the polybenzazole wound up through the subsequent process In the multifilament of fibers, sticking of single yarns is not observed. On the other hand, when the value of D exceeds 2,000 (number of filaments / cm ² ), sticking of single yarns is observed.

Here, the technical meaning of the value of D will be described.
Assuming that the dope filament is focused at the point where the dope filament is focused in the coagulation bath, the hole density at the position where the vapor of the polybenzazole coagulant is sprayed is calculated from the hole density of the spinneret, and the value is calculated as The focused density D of the dope filament is assumed.

The hole density at the position where the vapor of the coagulant of polybenzazole is sprayed, that is, the focused density D (number of filaments / cm ² ) of the dope filament is equal to the hole density (A: pieces / cm ² ) of the spinneret. To the position where the dope filament is focused in the coagulation bath (L1: cm) and the distance from the position where the vapor of the polybenzazole coagulant is sprayed to the position where the dope filament is focused in the coagulation bath (L2: cm) is multiplied by the square of the ratio (L1 / L2).

  When the value of D is too high, that is, when the concentration of the dope filament is dense at the position where the vapor of the polybenzazole coagulant is sprayed, the vapor of the polybenzazole coagulant sprays from the circumferential direction. The frequency with which the single yarns in the multifilament come into contact with each other and the single yarns stick to each other due to the force applied or the fluctuation of the force increases.

  Therefore, it becomes difficult to make vapor contact with each single yarn, and it becomes difficult to lower the strength of the single yarn constituting the multifilament more uniformly.

On the other hand, when the value of D is low, that is, when the degree of focusing of the dope filament is sparse at the position where the vapor of the coagulant of polybenzazole is sprayed, the coagulation of each single yarn constituting the multifilament with polybenzazole The agent can be contacted more uniformly. However, if the value of D is too low, the distance between the position where the dope filament is focused in the coagulation bath and the position where the vapor is sprayed becomes large, so that the yarn sway becomes prominent and yarn breakage tends to occur.
Therefore, it is preferable to reduce the value of D from the viewpoint of preventing the occurrence of yarn sway and yarn breakage.

  It is also important to prevent the spouted dope filament from coming into contact with the vapor outlet of the polybenzazole coagulant. When the two come into contact with each other, there is a problem that the yarn breaks or the single yarns constituting the multifilament come into contact with each other and stick to each other.

  As a coagulant for polybenzazole, at least one of water, methanol, ethanol, acetone, and ethylene glycol is preferable, and water is more preferable in terms of simplicity.

  The reason why the fiber strength is lowered is not clear, but the change in the crystal structure of the fiber is considered to be the main reason. When the coagulation liquid is water, acceleration of polymer hydrolysis is considered to be one of the factors.

  The temperature of the steam treatment varies depending on the type of coagulant, but in the case of water, the temperature of the water vapor is preferably 50 to 200 ° C. The upper limit of the temperature of the water vapor is more preferably 160 ° C., particularly preferably 130 ° C., from the viewpoint of a decrease in the tensile strength of the polybenzazole fiber. On the other hand, the lower limit of the temperature of the water vapor is more preferably 60 ° C., particularly preferably 70 ° C. from the viewpoint of productivity such as yarn breakage.

  When the temperature of the steam treatment is less than 50 ° C., the effect of reducing the strength is reduced. On the other hand, when the temperature of the steam treatment exceeds 200 ° C., yarn breakage frequently occurs and the productivity tends to be remarkably lowered. If the coagulant has a lower boiling point than water, the temperature may be lower, and if the coagulant has a higher boiling point than water, the temperature may be higher, and can be appropriately selected in consideration of the boiling point and the vapor pressure.

  In order to process the steam used in the steam treatment in a short time, the content of the steam component is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass with respect to all gas components % Or more.

  The steam-treated filament is then led to a coagulation (extraction) bath for polybenzazole solvent extraction and complete coagulation of the filament. The coagulation bath is not particularly limited, and any type of coagulation bath may be used. For example, a funnel type, water tank type, aspirator type or waterfall type coagulation bath can be used.

  Finally, the solvent is extracted so that the solvent remaining in the filament in the coagulation bath is 1% by mass or less, preferably 0.5% by mass or less. In the present invention, the liquid used as the solvent extraction medium is preferably water, methanol, ethanol, acetone, ethylene glycol, or the like that is substantially incompatible with polybenzazole.

  As the extract, a phosphoric acid aqueous solution or water is simple and desirable. Further, a method of separating the coagulation (extraction) bath in multiple stages, gradually decreasing the concentration of the phosphoric acid aqueous solution, and finally washing with water can be employed. In the coagulation (extraction) step, it is a preferred method to neutralize the filament bundle with an aqueous sodium hydroxide solution and then wash with water. Thereafter, drying and heat treatment can be performed to obtain a fiber that can be distinguished into two layers of a sheath and a core.

  The fiber is then dried and further subjected to a heat treatment step as necessary. The drying temperature may be a temperature at which the polybenzazole coagulant or solvent is easily dried, and is preferably 150 to 400 ° C., for example. The upper limit of the drying temperature is more preferably 300 ° C, particularly preferably 270 ° C. On the other hand, the lower limit of the drying temperature is more preferably 200 ° C, and particularly preferably 220 ° C. Moreover, you may heat-process under tension as needed for the purpose of improving an elasticity modulus.

  The heat treatment temperature is preferably in the range of 400 to 700 ° C. The upper limit of the heat treatment temperature is more preferably 680 ° C, particularly preferably 630 ° C. On the other hand, the lower limit of the heat treatment temperature is more preferably 500 ° C, and particularly preferably 550 ° C. The tension applied during the heat treatment is preferably in the range of 0.3 to 1.2 gf / dtex. The upper limit of the tension applied during the heat treatment is more preferably 1.1 gf / dtex, particularly preferably 1.0 gf / dtex. On the other hand, the lower limit of the tension applied during the heat treatment is more preferably 0.5 gf / dtex, and particularly preferably 0.6 gf / dtex.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. In addition, the following method was employ | adopted for various measurements.

(1) Intrinsic viscosity [η]
Using methanesulfonic acid as the solvent, the viscosity of the polymer solution prepared to a concentration of 0.5 g / L was measured in an oven at 30 ° C. using an Ostwald viscometer.

(2) Strength and elastic modulus of fiber Measured with a tensile tester in accordance with JIS L 1013. The tensile strength and tensile modulus shown in the table indicate the results of measuring multifilaments.
Furthermore, at least 90% or more of the number of multifilament constituent yarns are extracted from one multifilament, and all the extracted single yarns are subjected to a tensile tester in accordance with JIS L 1013. It was measured.
And the dispersion | distribution, ie, standard deviation (sigma), was calculated | required from the measurement result of the intensity | strength of each obtained single yarn, and the value of the dispersion | variation B was calculated | required using the following formula | equation.
B (%) = (σ / average tensile strength of single yarn) × 100

  As the fineness in the single yarn measurement, the single yarn fineness calculated by dividing the fineness of the multifilament by the number of constituents was used.

(3) Degree of sticking between the single yarns constituting the multifilament Fibers that are not easily separated when they are placed on a slide with multifilaments cut to 5 mm, and paraffin oil is dropped and separated into single yarns using tweezers. When the total number of single yarns excluding a is a and the number of multifilaments is b, the degree of sticking (%) between single yarns defined by the following formula is calculated, and the average value evaluated three times Is K (%). K (%) represents an average value of three measurements.
Degree of sticking between single yarns constituting multifilament (%)
= ((B−a) / b) × 100

(4) Heat resistance of fiber When a temperature is increased from normal temperature at a temperature increase rate of 20 ° C./min in air, using a thermogravimetric analyzer (TA Instruments, TGA Q50), mass The temperature at which the retention rate [(sample mass at a certain temperature / original sample mass) × 100] was 90% was defined as heat resistance (° C.).

(5) Flame retardancy of fiber Based on JIS K7201, it evaluated by the limiting oxygen index (Limiting Oxygen Index: LOI).

(6) Post-processability of the fiber The sample which bundled the obtained fiber so that the number of single yarns might be 16,600 was produced. The obtained sample is positioned horizontally, and both ends of the sample are fixed in a state where a tension of 500 gf is applied. Subsequently, an unused feather blade (carbon steel, blade thickness 0.245 mm, product number FAS-10) manufactured by Feather Safety Razor Co., Ltd. was installed from the top of the sample so that the surface of the blade is in contact with the sample. Further, the single blade was reciprocated in a direction of 90 ° with respect to the fiber axis direction of the sample, and the number of reciprocations until the entire filament of the sample was cut was evaluated.

  Note that a load of 70 gf was applied to the back surface of the single blade, and the amplitude width of the reciprocating motion of the single blade was 1 cm, and the single blade was reciprocated once per second. The evaluation was performed three times, and the average value was rounded off.

(Comparative Example 1)
Using a spinning dope (PBO concentration 14 mass%) in which poly (p-phenylenebenzobisoxazole) (hereinafter abbreviated as PBO) having an intrinsic viscosity [η] of 24 dL / g was dissolved in polyphosphoric acid, Was spun under the condition of 11.5 μm (corresponding to a single yarn fineness of 1.65 dtex).

That is, a spinning dope is spun from a spinneret (nozzle) having a spinning temperature of 175 ° C., a hole diameter of 0.15 mm, a hole number of 166, and a hole density of 4 / cm ² , and the spun dope filament is quenched at a quench temperature of 60 ° C. The interior was cooled by passing through it, and after passing through the quench chamber, the filament was focused and immersed in the first coagulation / washing bath to coagulate the multifilament.

  Then, it washed with water until the residual phosphorus density | concentration in a filament was set to 5,000 ppm or less, neutralized with 1 mass% NaOH aqueous solution for 5 seconds, and also washed with water for 20 seconds. Then, it dried and wound up until the moisture content became 1.5 mass%, and obtained the multifilament of the polybenzazole fiber.

(Example 1)
During the period from the exit of the quench chamber to the immersion in the first coagulation / cleaning bath, water vapor is spouted from a device (water vapor applying device) that applies water vapor from the circumferential direction to a large number of dope filaments before focusing. A polybenzazole fiber multifilament was wound up in the same manner as in Comparative Example 1 except that it was attached.

  In addition, saturated steam at a temperature of 98 ° C. is introduced into the steam applicator, the slit width of the steam spout section of the steam applicator is 4 mm, and the steam spout is located at a position where L1 / L2 = 6. It was installed so that water vapor was sprayed from a direction of 30 ° with respect to the traveling direction (so that the direction in which water vapor was sprayed did not counteract the traveling direction of the multifilament).

(Examples 2-8, Comparative Examples 5-7)
A multifilament of polybenzazole fiber was wound up in the same manner as in Example 1 except that L1 / L2, the number of holes of the spinneret (nozzle), and the hole density were changed as shown in Table 1. .

(Comparative Example 2)
A multifilament of polybenzazole fiber was wound up in the same manner as in Comparative Example 1 except that the space from exiting the quench chamber to dipping in the first washing bath was filled with a steam atmosphere.
A cylinder having an inner diameter of 5 mm and a length of 5 cm was installed at the outlet of the quench chamber, water vapor was introduced into the cylinder to fill the cylinder with a water vapor atmosphere, and the multifilament was allowed to pass through the cylinder. The temperature of the filled water vapor was 98 ° C. saturated water vapor.

(Comparative Example 3)
The size of the cylinder installed at the exit of the quench chamber was changed to a cylinder with an inner diameter of 5 mm and a length of 1 m, and the same procedure as in Comparative Example 2 was conducted except that steam was introduced into the cylinder and the interior of the cylinder was filled with a steam atmosphere. The multifilament of polybenzazole fiber was wound up.

(Comparative Example 4)
The cylinder installed at the exit of the quench chamber has a diameter of 10 cm and a length of 1 m. Further, two slit nozzles (slit width of 1 mm) are installed at the exit of the quench chamber in the facing direction, and saturated steam at a temperature of 98 ° C. is supplied to the slit nozzle. The polybenzazole fiber multifilament was wound up in the same manner as in Comparative Example 1 except that the multifilament was introduced and passed between the slit nozzles.
In addition, the slit nozzle was installed so that water vapor could be sprayed from a direction of 30 ° with respect to the traveling direction of the multifilament (so that the direction of spraying water vapor would not counteract the traveling direction of the multifilament).

Example 9
The polybenzazole fiber multifilament wound up in Example 2 was heat-treated while applying tension. The heat treatment temperature was 600 ° C., the tension was 2.5 gf / dtex, and the heat treatment time was 3 seconds.

(Example 10)
The multifilament of polybenzazole fiber wound up in Example 7 was heat-treated while applying tension. The heat treatment temperature was 600 ° C., the tension was 2.5 gf / dtex, and the heat treatment time was 3 seconds.

  Table 1 shows the production conditions and evaluation results of the polybenzazole fiber multifilament obtained above.

  Although the polybenzazole fiber multifilaments obtained in Examples 1 and 5 were slightly large in yarn swinging under the spinneret at the time of production and the yarn breakage frequency was slightly high, the polybenzazole fibers obtained in each Example Multifilaments suppress the sticking of single yarns that make up multifilaments while maintaining the excellent heat resistance and flame resistance of polybenzazole fibers, and the tensile strength of all the single yarns that make up multifilaments It can be seen that the value is more uniformly and greatly reduced. Moreover, the fiber can be easily cut and it can be seen that the post-processability is improved.

  The polybenzazole fiber multifilament of the present invention maintains the heat resistance and flame retardancy of the polybenzazole fiber, and the tensile strength of all single yarns constituting the multifilament is more uniform and greatly increased. Due to the decrease, post-processability is superior to conventional products. Therefore, it becomes easy to develop in various uses that require heat resistance, flame retardancy, and post-processability as important characteristics, and the industrial contribution is great.

Claims (2)

  A polybenzazole fiber multifilament composed of at least 30 filaments, having a tensile strength of 4.5 GPa or less and a tensile strength variation B between the filaments of 0.2% or less. And polybenzazole fiber multifilament.   The polybenzazole fiber multifilament according to claim 1, wherein the degree of sticking K between the filaments constituting the multifilament is 5% or less.