JP2007154355A - Meta-aromatic polyamide fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a meta-aromatic polyamide fiber having excellent high-temperature strength retention and a method for producing the fiber. <P>SOLUTION: The meta-aromatic polyamide fiber having excellent high-temperature strength retention has a carboxyl terminal content of <30 mmol/kg in the meta-aromatic polyamide constituting the fiber. The fiber is produced by polymerizing a meta-aromatic diamine and a meta-aromatic dicarboxylic acid halide at a ratio of 50.05-50.25 mol% of the aromatic diamine and 49.75-49.95 mol% of the aromatic dicarboxylic acid halide, and wet-spinning the obtained solution of the meta-aromatic polyamide while adding an amino-terminal blocking agent during or after the polymerization reaction as necessary. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a meta-type aromatic polyamide fiber excellent in heat-resistant strength retention and a method for producing the same.

  Meta-type aromatic polyamides have excellent heat resistance and dimensional stability because the molecular skeleton is almost composed of aromatic rings. In industrial applications, they have heat resistance and flame resistance as fibers, films and papers. Although it is used for important applications, further improvement in heat resistance has been demanded in recent years.

  The meta-type aromatic polyamide is an aromatic dicarboxylic acid according to the interfacial polymerization method described in Japanese Patent Publication No. 35-13247 (Patent Document 1) or the so-called low temperature solution polymerization method described in Japanese Patent Publication No. 35-14399 (Patent Document 2). It is produced by polymerizing acid halide and aromatic diamine and / or aromatic aminocarboxylic acid chloride in approximately equimolar amounts.

  However, when an aromatic diamine component and an aromatic dicarboxylic acid halide component are polymerized in equimolar amounts, -COOH and -COO- (hereinafter referred to as "carbo terminal") increase as terminal groups in the obtained polymer. Therefore, the heat resistant strength retention when this is spun into a fiber deteriorates.

  JP-A-62-177021 (Patent Document 3) discloses that in the production of a ternary or quaternary copolymer of an aromatic polyamide, the terminal in the polymer is an acid chloride such as acetic anhydride or benzoyl chloride. In addition, a method of sealing a terminal group by adding a primary or secondary monoamine such as propylamine, butylamine or aniline or a hydroxy compound such as phenol or cresol is described. Even when a stopper is added, it is difficult to block the end uniformly because of the high viscosity of the polymerization solution, and adding a terminal blocking agent prior to polymerization increases the low molecular weight component, which has a significant effect on spinnability. It was.

Japanese Patent Publication No. 35-13247 Japanese Patent Publication No. 35-14399 JP-A-62-177021

  The present invention has been made against the background of the state of the art as described above. The object of the present invention is to provide a meta-type aromatic polyamide fiber excellent in heat-resistant strength retention, and to Providing a method for industrially producing a type aromatic polyamide fiber.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors are able to improve heat resistance retention by using a meta-type aromatic polyamide fiber having a carbo terminal group amount of a certain amount or less. As a result, the present inventors have reached the present invention.

  That is, according to the present invention, as a means for achieving the above-mentioned problems, the amount of carbo terminal groups in the meta-type aromatic polyamide constituting the fiber is less than 30 mmol / kg (that is, less than 30 equivalents per 106 g of polymer). A meta-type aromatic polyamide fiber having good heat-resistant strength retention is provided. In a preferred embodiment of the present invention, a meta-type aromatic polyamide having a particularly excellent heat-resistant strength holding property of a heat-resistant strength holding rate represented by a silk factor holding rate of 60% or more after treatment at 250 ° C. for 100 hours. Fiber is provided.

  Further, according to the present invention, as a method for producing such a meta-type aromatic polyamide fiber having good heat-resistant strength retention, a polymer solution obtained from a polymerization reaction of a meta-type aromatic diamine and a meta-type aromatic dicarboxylic acid halide is used. When producing fibers by wet spinning, the ratio of the aromatic diamine to be polymerized and the aromatic dicarboxylic acid halide is 50.05 to 50.25 mol% of aromatic diamine, and aromatic dicarboxylic acid halide is 49.75 to 49.49. A meta type aromatic polyamide having a carbo terminal group content of less than 30 mmol / kg is formed by reacting at 95 mol%, and an amide solvent solution of the meta type aromatic polyamide is wet-spun and stretched and heat treated. A process for producing a meta-aromatic polyamide fiber, and further in the process, during or after the polymerization reaction, Manufacturing method is provided, which comprises adding a sealing agent of the amino-terminal against.

  Since the meta-type aromatic polyamide fiber of the present invention is excellent in heat-resistant strength retention, it is used in applications that require stricter heat resistance than conventional meta-type aromatic polyamide fibers, such as fire fighting clothes and furnace fronts. It is effective in the fields of protective clothing materials such as work clothes, filter materials for combustion gases, and materials for heat-resistant insulating paper.

Hereinafter, embodiments of the present invention will be described in detail.
The meta-type aromatic polyamide fiber according to the present invention is a fiber obtained by wet spinning from a solution of a meta-type aromatic polyamide obtained from the reaction of a meta-type aromatic diamine and a meta-type aromatic dicarboxylic acid halide exemplified below. However, the meta-type aromatic polyamide may have other copolymer components such as a para-type within a range not impairing the object of the present invention.

  Examples of the meta-type aromatic diamine used as a raw material for the meta-type aromatic polyamide include metaphenylene diamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, and the like, halogens and carbon atoms of 1 on these aromatic rings. Derivatives having a substituent such as an alkyl group of ~ 3 (for example, 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, 2,6-diaminochlorobenzene) and the like are used. be able to. Among them, metaphenylenediamine is used alone or mixed with other aromatic diamines and metaphenylenediamine is contained in an amount of 80 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more. The use of mixed diamines is preferred.

  Examples of the meta-type aromatic dicarboxylic acid halide include isophthalic acid halides such as isophthalic acid chloride and isophthalic acid bromide, and derivatives having substituents such as halogens and alkoxy groups having 1 to 3 carbon atoms on these aromatic rings, for example, 3-chloroisophthalic acid chloride, 3-methoxyisophthalic acid chloride and the like can be used. Among them, isophthalic acid chloride is used alone or mixed with the other aromatic dicarboxylic acid halide, and isophthalic acid chloride is 80 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more. The use of mixed carboxylic acid halides is preferred.

  Examples of copolymer components that can be used other than the diamine and carboxylic acid halide include aromatic diamines such as paraphenylene diamine, 2,5-diaminochlorobenzene, 2,5-diaminobromobenzene, and aminoanisidine. 1,5-naphthylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ketone, 4,4′-diamine diphenylamine, 4,4′-diaminodiphenylmethane, etc. Examples of the acid halide include terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 4,4′-biphenyldicarboxylic acid chloride, 4,4′-diphenyl ether carboxylic acid chloride, and the like. When the copolymerization amount of these copolymerization components is too large, the properties of the meta-type aromatic polyamide are liable to deteriorate. Therefore, it is preferably 20 mol% or less, particularly 0 to 10 mol%, based on the total acid component of the polyamide. Is appropriate.

  The meta-type aromatic polyamide particularly preferably used in the present invention is a polyamide in which 80 mol% or more, preferably 90 mol% or more, more preferably 95 to 100 mol% or more of all repeating units are composed of metaphenylene isophthalamide units. Particularly preferred is a homopolyamide in which all repeating units are composed of metaphenylene isophthalamide units.

  The polymerization reaction is usually a solution polymerization method in which these aromatic diamines and aromatic dicarboxylic acid halides are reacted in a polar amide solvent. In the present invention, in such a polymerization reaction, it is necessary to adjust the polymerization conditions so that the amount of carbo terminal group in the polymer is less than 30 mmol / kg, particularly preferably 5 to 20 mmol / kg. There is.

  The “carbo end group amount” referred to here is a value representing the number of moles of COOH and COO— present at the end of the polymer chain per 1 kg of the polymer, and an amount of CaCl 2 equal to 0.04 g of the polymer is 0. After dissolving in 7 g of DMAc, it can be determined by measuring with 1H-NMR.

  In order to obtain a meta-type aromatic polyamide having such a carbo end group amount, the ratio of the aromatic diamine to be polymerized and the aromatic dicarboxylic acid halide is such that the aromatic diamine is 50.05 mol% or more and the aromatic dicarboxylic acid halide 49 is used. .95 mol% or less is suitable, especially aromatic diamine 50.05 to 50.25 mol%, aromatic dicarboxylic acid halide 49.75 to 49.95 mol%, that is, aromatic diamine / aromatic The molar ratio of the group dicarboxylic acid halide is preferably in the range of 50.05 / 49.95 to 50.25 / 49.75.

  When the ratio of the aromatic diamine to be subjected to the polymerization reaction and the aromatic dicarboxylic acid halide is outside the above range, a meta-type aromatic polyamide having a carbo terminal group amount of less than 30 mmol / kg is obtained under good productivity and economy. For example, the method of sealing a carbo end group with a primary or secondary monoamine is difficult to achieve uniform end-capping because the polymerization solution is highly viscous even if an end-capping agent is added after polymerization. In the case of adding an end-capping agent, the low molecular weight component is increased, so that there is a problem that the effect on the spinnability is large. Therefore, it is not suitable for use in the present invention based on wet spinning.

  In the present invention, the degree of polymerization can be adjusted by adding an amino-terminal blocking agent during or after the polymerization reaction. Examples of such amino terminal blocking agents include acetic anhydride, propionic anhydride, butyric anhydride, caproic anhydride, isobutyric anhydride, phthalic anhydride, benzoic anhydride and the like, and acetyl chloride, And acid chlorides such as propionyl chloride, butyryl chloride, benzoyl chloride and caproyl chloride.

  The polymerization degree of such a meta-type aromatic polyamide (hereinafter sometimes referred to as “polymer”) is suitably in the range where the intrinsic viscosity (IV) measured using concentrated sulfuric acid at 30 ° C. as a solvent is 1.0 to 1.6. is there.

  In the present invention, a solution obtained by dissolving a polar amide solvent in a meta-type aromatic polyamide having a carbo end group amount of less than 30 mmol / kg, particularly preferably a carbo end group amount of less than 5-20 mmol / kg, is obtained in the present invention. Is spun from a spinneret into a fiber. As a spinning method of a meta-type aromatic polyamide solution, dry spinning is also known, but dry spinning is not only inferior in productivity in many respects, but it is difficult to obtain fibers having good physical properties and heat resistance. Therefore, it is not preferable.

  When producing the fiber of the present invention, polar amide solvents used for the preparation of a meta-type aromatic polyamide solution as a spinning dope include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide Examples include polar organic solvents such as (DMAc) and dimethyl sulfoxide (DMSO), among which NMP or DMAc is preferable.

  The meta-type aromatic polyamide solution described above is a neutralizing agent that forms a salt soluble in the solvent of hydrogen chloride produced as a by-product in the polymerization reaction, such as calcium carbonate, lithium carbonate, calcium hydroxide, lithium hydroxide, and the like. A spinning dope can be obtained by neutralizing with an alkali.

  In order to improve the spinnability, an aqueous solution of ammonia, solid sodium hydrogen carbonate, sodium hydroxide or potassium hydroxide, etc., in which the salt produced by the neutralization reaction in the polymerization process becomes insoluble in the solvent is used as a neutralizing agent. As a part, the obtained solution may be subjected to wet-spinning by adjusting the content of the inorganic salt by filtering the resulting solution (Japanese Patent Publication No. 35-14399, Japanese Patent Laid-Open No. 2001-114889). See the official gazette).

  Also, in order to control the penetration of the coagulation liquid into the fiber during wet spinning, the polymer concentration and water concentration are specified by adding a specific amount of amide solvent and water to the solution containing inorganic salt after neutralization. The range may be subjected to wet spinning as a spinning stock solution (see JP-A-2001-115333).

  In wet spinning, a conventionally known wet spinning apparatus is used, and the spinning solution is directly extruded into a coagulating solution to be coagulated into a fiber. The coagulated fibers are drawn out from the coagulation bath, adjusted in the residual solvent concentration in the fibers through a water washing step (preferably a multi-stage water washing step), then drawn in warm water, dried, heat set, etc. The

  The number of spinning holes of the spinneret used at this time may be for 50 to 1000 filaments, or 1000 to 30000 spinneret. The spinning hole diameter is generally 0.05 to 0.2 mm. The temperature of the meta-type aromatic polyamide solution during spinning is suitably in the range of 25 to 90 ° C. A conventionally known aqueous solution of an inorganic salt can be used as the coagulating liquid. For example, an aqueous solution having a calcium chloride concentration of 34 to 42% by weight and an NMP concentration of 5 to 10% by weight is preferred. The temperature of the coagulation liquid is suitably in the range of 80 to 95 ° C.

  The speed at which the coagulated fiber is drawn out from the coagulation bath can be in the range of 5 to 25 m / min, but is preferably in the range of 10 to 25 m / min from the viewpoint of the object of the present invention to improve productivity. The range of 1.0 to 11 seconds is appropriate for the fiber immersion time in the coagulation liquid.

  The fiber drawn from the coagulation liquid is sent to the hot water drawing step through the water washing step, and the water washing step is preferably performed in multiple stages. That is, the fiber drawn from the coagulation liquid is cooled to 60 ° C. or less, preferably 0 to 50 ° C., and then introduced into the first water-washing bath at 30 ° C. or less, preferably −20 to 20 ° C. The concentration of the organic polar solvent (for example, NMP) in the first washing bath is preferably in the range of 15 to 25% by weight, and the flow rate of washing water and the solvent concentration in the washing water are determined so that this concentration can be maintained. The immersion time of the fiber in the first washing bath is preferably 8 to 30 seconds. Subsequent to the first water washing bath, the fibers are washed by being introduced into a second water washing bath at 30 to 85 ° C. The amount of washing water replenished in these washing baths and the solvent concentration in the washing water, and the soaking time of the fibers in the washing bath are such that the amount of residual solvent in the fibers leaving the washing step is 12 to 25% by weight relative to the polymer, The calcium concentration in the fiber is appropriately selected and set so as to be 0.5% by weight or less.

  The fiber whose residual solvent amount and calcium amount have been adjusted in the water washing step is then subjected to a residual solvent while being drawn to 2.0 to 4.0 times, preferably 2.8 to 3.5 times, in the hot water drawing step. And the calcium salt is washed away. This stretching is preferably a multi-stage stretching of two or more stages, preferably three or more stages, in order to maintain a good process condition.

  The drawn fiber is dried at a temperature of 100 ° C. or higher, and then heat-set at a temperature of 250 to 400 ° C., preferably 270 to 350 ° C., with a heating roller, a hot plate or the like. This heat set is preferably a fixed length treatment, but may be a treatment under 10% or less of limited shrinkage or 1.1 times or less of stretching.

  The meta-type aromatic polyamide fiber of the present invention thus obtained is collected after being collected as a tow as necessary, wound up, or directly sent to a subsequent process to give a crimp as necessary. And it is supplied to a post process as a short fiber.

  According to the study by the present inventors, the high elongation retention rate when a meta-type aromatic polyamide fiber is exposed to a high temperature for a long time is governed by the amount of carbo terminal groups of the polymer constituting the fiber. I understood. And the meta type | mold aromatic polyamide fiber prepared so that the carbo terminal group amount of the polymer which comprises this fiber may be less than 30 mmol / kg, Most preferably, the carbo terminal group amount is 5-20 mmol / kg, 250 degreeC 100 hours after processing It was confirmed that the heat-resistant strength retention represented by the silk factor retention was 60% or more, and in a preferred embodiment, 65-90%. On the other hand, those having a carbo end group amount of 30 mmol / kg or more are not suitable for use in fields where heat resistance for a long time is required because the heat resistance retention is less than 60%.

Here, the silk factor (SF) is defined by the following formula (1), and is widely used as an index that comprehensively represents the mechanical properties of the fiber in terms of the work required to break the fiber. .
Further, the heat resistance retention rate of the fiber is expressed by the following formula (2), where the silk factor before heat treatment of the fiber is SF0 and the silk factor after heat treatment under free shrinkage tolerance is 100 hours in an atmosphere of 250 ° C. and SF100. Is required.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited by these Examples.
In addition, each characteristic value in an Example was measured with the following method. Intrinsic viscosity (IV) and end group composition are measured at the polymer stage, but it has been confirmed in many conventional measurement experiments that these measured values are not different from those measured with fibers.

<Intrinsic viscosity (IV)>
The polymer was dissolved in 97% concentrated sulfuric acid and measured at 30 ° C. using an Ostwald viscometer.
<Carbo terminal group amount>
An amount of CaCl2 equivalent to 0.04 g of polymer was dissolved in 0.7 g of DMAc, measured by 1H-NMR, and expressed as an equivalent amount (in moles) per kg of polymer.
<Fineness>
It measured based on JIS-L-1015.
<Strength and elongation>
The fibers constituting the tow were measured according to JIS-L-1074 at a test length of 20 mm, an initial load of 0.044 cN / dtex, and an extension rate of 20 mm / min.
<Heat resistant strength retention>
The silk factor SF0 before heat treatment of the fibers constituting the tow and the silk factor SF100 after 100 hours of treatment at 250 ° C. were determined and calculated by the above-described formula (2).

[Example 1]
In a reaction vessel equipped with a thermometer, a stirrer and a raw material inlet, 721.5 parts by weight of NMP having a moisture content of 100 ppm or less was placed, and 97.2 parts by weight (50.18 mol%) of metaphenylenediamine was added to this NMP. Dissolved and cooled to 0 ° C. To this cooled diamine solution, 181.3 parts by weight (49.82 mol%) of isophthalic acid chloride was added and reacted while gradually stirring. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 0.4 parts by weight of benzoyl chloride was added and stirring was continued for 40 minutes from the start of the reaction. Then, 66.6 parts by weight of calcium hydroxide powder having an average particle size of 10 μm was added and stirred for 40 minutes. Then, the reaction was terminated and the polymerization solution was taken out to obtain a transparent polymerization solution.

  Polymetaphenylene isophthalamide was isolated from this polymerization solution, and the intrinsic viscosity (IV) was measured. As a result, it was 1.25. When the amount of carbo terminal was evaluated by 1H-NMR, it was 13 mmol / kg. The polymer concentration of this solution was 20% by weight.

Next, the solution was degassed under reduced pressure to obtain a spinning stock solution, which was spun from a spinneret having 15,000 holes having a hole diameter of 0.07 mm into a coagulation bath at 85 ° C.
At this time, the composition of the coagulation bath was 40% by weight of calcium chloride, 5% by weight of NMP, and 55% by weight of the remaining water, and the yarn speed was 10 m / min at an immersion length (effective coagulation bath length) of 500 mm. After passing, it was once pulled out into the air.

  After cooling the fiber to 50 ° C., it is introduced into a first water-washing bath having a water temperature of 25 ° C., and then the residual solvent in the fiber is passed through a second water-washing bath having a water temperature of 45 ° C. and a third water-washing bath having a water temperature of 70 ° C. Washed with water until weight percent. At this time, the composition of the aqueous solution of the first washing bath was 22% by weight of NMP and 14% by weight of calcium chloride.

The fiber after washing was subsequently subjected to three-stage drawing in warm water at 98 ° C. with a first-stage draw ratio of 1.4 times, a second-stage draw ratio of 1.95 times, and a third-stage draw ratio of 1.1 times. When the fiber bundle after the hot water drawing was observed while running, the fluff was a good and glossy fiber of less than 1 / min.
This stretched fiber is dried through a drying roller at 70 ° C., preheated with a preheating roller at 200 ° C., then heat-set with a roller at 340 ° C., cooled to 30 ° C. with a cooling roller, coated with an oil, and wound up 33,000 dtex. A stretched tow of 15000 filaments was obtained.
Table 1 below shows the silk factor of the polymetaphenylene isophthalamide fiber constituting the drawn tow before and after heat treatment at 250 ° C. and the heat-resistant strength retention determined therefrom.

[Example 2]
In the same manner as in Example 1, 753.8 parts by weight of NMP was added, 85.7 parts by weight (50.06 mol%) of metaphenylenediamine was dissolved in this NMP, and cooled to 0 ° C. To this cooled diamine solution, 160.5 parts by weight (49.94 mol%) of isophthalic acid chloride was added and reacted while gradually stirring. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 0.2 parts by weight of benzoyl chloride was added and stirring was continued for 40 minutes from the start of the reaction. Then, 58.7 parts by weight of calcium hydroxide powder having an average particle size of 10 μm was added and stirred for 40 minutes. The reaction was terminated and the polymerization solution was taken out to obtain a transparent polymerization solution.

Polymetaphenylene isophthalamide was isolated from this polymerization solution, and the intrinsic viscosity (IV) was measured. As a result, it was 1.45. The amount of carbo terminal was evaluated by 1H-NMR, and found to be 28 mmol / kg. The polymer concentration of this solution was 17.8% by weight.
This spinning dope was coagulated, washed with water and stretched with hot water in the same manner as in Example 1. When the fiber bundle after the hot water drawing was observed while running, the fluff was a good and glossy fiber of less than 1 / min.

This stretched fiber is dried through a drying roller at 70 ° C., preheated with a preheating roller at 200 ° C., then heat-set with a roller at 340 ° C., cooled to 30 ° C. with a cooling roller, coated with an oil, and wound up 33,000 dtex. A stretched tow of 15000 filaments was obtained.
Table 1 below shows the silk factor of the polymetaphenylene isophthalamide fiber constituting the drawn tow before and after the heat treatment at 250 ° C. and the heat-resistant strength retention determined therefrom.

[Comparative Example 1]
In the same manner as in Example 1, 731.5 parts by weight of NMP was added, 93.4 parts by weight (50.03 mol%) of metaphenylenediamine was dissolved in this NMP, and cooled to 0 ° C. To this cooled diamine solution, isophthalic acid chloride (175.1 parts by weight (49.97 mol%)) was gradually added with stirring to react.The temperature of the solution rose to 70 ° C. The viscosity change changed. After stopping, 0.05 part by weight of benzoyl chloride was added and stirring was continued for 40 minutes from the start of the reaction. Then, 64.0 parts by weight of calcium hydroxide powder having an average particle size of 10 μm was added and stirred for 40 minutes to react. And the polymerization solution was taken out to obtain a transparent polymerization solution.

When polymetaphenylene isophthalamide was isolated from this polymerization solution and the intrinsic viscosity (IV) was measured, it was 1.61, and when the amount of carbo terminal was evaluated by 1H-NMR, it was 57 mmol / kg. The polymer concentration of this solution was 19.3% by weight.
This spinning dope was coagulated, washed with water and stretched with hot water in the same manner as in Example 1. When the fiber bundle after the hot water drawing was observed while running, the fluff was a good and glossy fiber of less than 1 / min.

This stretched fiber is dried through a drying roller at 70 ° C., preheated with a preheating roller at 200 ° C., then heat-set with a roller at 340 ° C., cooled to 30 ° C. with a cooling roller, coated with an oil, and wound up 33,000 dtex. A stretched tow of 15000 filaments was obtained.
Table 1 shows the silk factor and the heat-resistant strength retention ratio of the polymetaphenylene isophthalamide fiber constituting the drawn tow of Comparative Example 1 before and after heat treatment at 250 ° C.

  As is clear from the results shown in Table 1, fibers (Examples 1 and 2) having a carbo end amount per 1 kg of the polymer of the present invention of less than 30 mmol / kg had a silk factor retention of more than 60% after heat treatment. Therefore, there is little deterioration in mechanical performance when exposed to high heat for a long time, and it has excellent heat resistance strength retention. On the other hand, the fiber manufactured by the usual method (Comparative Example 1) has a carbo end amount of close to 60 mmol / kg, and the retention rate of the silk factor after heat treatment is much lower than 60%.

  Since the meta-type aromatic polyamide fiber of the present invention described above is excellent in heat-resistant strength retention, it can be used for applications requiring higher heat resistance than conventional meta-type aromatic polyamide fibers.

Claims (4)

  A meta-type aromatic polyamide fiber, wherein the amount of carbo terminal groups in the meta-type aromatic polyamide constituting the fiber is less than 30 mmol / kg.   2. The meta-type aromatic polyamide fiber according to claim 1, wherein the heat-resistant strength retention represented by a silk factor retention after treatment at 250 ° C. for 100 hours is 60% or more.   When producing a fiber by wet-spinning a meta-type aromatic polyamide solution obtained by polymerization reaction of a meta-type aromatic diamine and a meta-type aromatic dicarboxylic acid halide, the aromatic diamine and aromatic dicarboxylic acid halide to be polymerized Meta-type aromatic polyamide having a carbo end group content of less than 30 mmol / kg by reacting at a ratio of 50.05 to 50.25 mol% of aromatic diamine and 49.75 to 49.95 mol% of aromatic dicarboxylic acid halide A process for producing a meta-aromatic polyamide fiber, characterized in that the amide solvent solution containing the meta-type aromatic polyamide is wet-spun, drawn and heat-treated.   The process for producing a meta-aromatic polyamide fiber according to claim 3, wherein an amino-terminal blocking agent is added to the polymerization system during or after the polymerization reaction.