JP2009040804A - Polyamide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aromatic polyamide fiber with excellent heat resistance and mechanical strength such as tensile strength and an elastic modulus. <P>SOLUTION: The aromatic polyamide X has a group represented by the formula 1, wherein Az represents a 6-20C bivalent aromatic group, as a terminal group and has inherent viscosity of 0.05-20 dL/g measured at 30°C in a concentrated sulfuric acid solution of 0.5 g/100 ml. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to polyamides, resin compositions and fibers having specific end groups.

  Aromatic polyamide has a structure in which rigid aromatic rings are connected, and as a material excellent in heat resistance, mechanical properties, chemical resistance, etc., in the form of fibers or films, electrical insulating materials, various reinforcing agents, bulletproof fibers Although it is one of the materials that are widely used and industrially extremely valuable, more advanced characteristics have been required for the resin depending on the intended use.

  As one of means for improving the basic physical properties of the fiber, a method of performing cross-linking by a chemical reaction between molecules is proposed. However, when the polymer is previously cross-linked, it gives a polymer insoluble in the solvent, making it difficult to form fibers, films and the like. Therefore, there is a method in which a crosslinking agent is added to the polymer solution in advance during the molding of the polymer, and a molded body is obtained by reacting during the heat treatment and hot stretching.

  Non-Patent Document 1 attempts to introduce a halogen atom into a polybenzobisthiazole molecular chain and introduce an intermolecular bond by a radical generated during heat treatment, and certainly an improvement in the shear modulus is observed. Patent Document 1 attempts to improve the thermal stability of the aromatic polyamide and control the degree of polymerization by sealing the end of the aromatic polyamide molecular chain with aniline. In Patent Document 2, an aromatic diisocyanate, an aromatic dicarboxylic acid and an aromatic polyamide oligomer having an unsaturated group polymerizable on the main chain are prepared, and heat curing is attempted by heating together with a radical generating catalyst. There has been no report on the introduction of cross-linking into a wholly aromatic polyamide by modifying the end group.

JP-A-4-16490 JP 7-228658 A Journal of polymer Science: Part A: Polymer Chemistry, vol. 30, 1111-1122 (1992)

  An object of the present invention is to provide an aromatic polyamide having excellent heat resistance and excellent mechanical strength such as tensile strength and elastic modulus, a resin composition containing an aromatic polyamide, a fiber, and a method for producing the same. .

  The inventor has intensively studied a method for introducing a crosslinked structure into an aromatic polyamide, and by introducing a crosslinked structure into the aromatic polyamide, the present inventors have excellent heat resistance and excellent mechanical strength such as tensile strength and elastic modulus. It has been found that aromatic polyamides and fibers can be provided.

（式中ｍ、ｎおよびｎ’は１０以上の整数である）
の反応スキームに示すように、末端基修飾芳香族ポリアミドの修飾末端基と芳香族ポリアミドのアミン末端が反応し架橋構造が形成されることを見出し、本発明に到達した。 That is, the present inventor modified the aromatic polyamide end with a compound having a specific structure and heat-treated, and then represented by the following formula (1):

(Wherein m, n and n ′ are integers of 10 or more)
As shown in the above reaction scheme, the present inventors have found that a modified end group of an end group-modified aromatic polyamide and an amine end of the aromatic polyamide react to form a crosslinked structure, and the present invention has been achieved.

  Moreover, it discovered that the moldability of the terminal modification aromatic polyamide before heat processing was favorable. Furthermore, it discovered that the fiber excellent in mechanical strength was obtained by bridge | crosslinking, and completed this invention.

で示される繰り返し単位を主として含有し、末端基として下記式（イ）

（式中、Ａｚは炭素数６〜２０の２価の芳香族基）
で表される基を有する、０．５ｇ／１００ｍＬの濃硫酸溶液で３０℃において測定した特有粘度が０．０５〜２０ｄＬ／ｇであるポリアミド（Ｘ）である。 The present invention provides the following formula (A)

Mainly containing a repeating unit represented by the following formula (I)

(In the formula, Az is a divalent aromatic group having 6 to 20 carbon atoms)
And a polyamide (X) having a specific viscosity of 0.05 to 20 dL / g measured at 30 ° C. with a concentrated sulfuric acid solution of 0.5 g / 100 mL.

で示される繰り返し単位を主として含有し、０．５ｇ／１００ｍＬの濃硫酸溶液で３０℃において測定した特有粘度が０．０５〜２０ｄＬ／ｇであるポリアミド（Ｙ）１００重量部、および(ii)上記ポリアミド（Ｘ）を０．０００１〜１００重量部とを含有する樹脂組成物（Ｚ）である。 The present invention also provides: (i) the following formula (a)

100 parts by weight of polyamide (Y) mainly containing a repeating unit represented by formula (II) and having a specific viscosity of 0.05 to 20 dL / g measured at 30 ° C. with a concentrated sulfuric acid solution of 0.5 g / 100 mL, and (ii) the above This is a resin composition (Z) containing 0.0001 to 100 parts by weight of polyamide (X).

  This invention is a fiber which consists of polyamide (X), and this invention includes the fiber which consists of a resin composition (Z).

  The present invention includes a dope (X) containing 100 parts by weight of polyamide (X) and 300 to 3000 parts by weight of solvent. The present invention also includes a dope (Z) containing 100 parts by weight of the resin composition (Z) and 300 to 3000 parts by weight of a solvent. The present invention further includes a method for producing a fiber comprising spinning a dope (X) or dope (Z).

  In the polyamide (X) of the present invention, the terminal is modified with a compound having a specific structure. Therefore, the polyamide (X) can be easily formed into a form such as a fiber, and the polyamide (X) can react with the amine terminal to form a crosslinked structure by heat treatment after the forming. As a result, fibers excellent in mechanical strength such as tensile strength and elastic modulus can be obtained. Moreover, the resin composition of this invention becomes a raw material of the fiber excellent in heat resistance, and can manufacture the fiber excellent in heat resistance. According to the present invention, a fiber molded body having excellent mechanical strength such as strength and elastic modulus can be obtained. The obtained fiber molded body is a high-strength heat-resistant fiber and a rope, belt, insulating cloth, thermosetting fiber as an elastic fiber It can be widely used in the fields of reinforcing materials for thermoplastic or thermoplastic resins, and protective clothing.

で示される繰り返し単位を主として含有し、末端基として下記式（イ）

（式中、Ａｚは炭素数６〜２０の２価の芳香族基）
で表される基を有する、０．５ｇ／１００ｍＬの濃硫酸溶液で３０℃において測定した特有粘度が０．０５〜２０ｄＬ／ｇであるポリアミド（Ｘ）である。 (About polyamide (X))
The polyamide (X) of the present invention has the following formula (a)

Mainly containing a repeating unit represented by the following formula (I)

(In the formula, Az is a divalent aromatic group having 6 to 20 carbon atoms)
And a polyamide (X) having a specific viscosity of 0.05 to 20 dL / g measured at 30 ° C. with a concentrated sulfuric acid solution of 0.5 g / 100 mL.

  "Containing mainly the repeating unit represented by the formula (a)" means that 80 to 100 mol% of the repeating unit of the formula (a) is contained in the polyamide, and more preferably 100 mol%.

  The repeating unit other than the repeating unit represented by the formula (A) includes a unit containing a paraphenylene group, a 3,4′-diphenylene ether group, and a 4,4′-diphenylene ether group in addition to the metaphenylene group. Is mentioned.

  The polyamide (X) has an inherent viscosity ηinh of 0.05 to 20 dL / g, preferably 0, as measured at 30 ° C. in a solution of 0.5 g / 100 mL dissolved in 98 wt% concentrated sulfuric acid. .1 to 5 dL / g, more preferably 0.5 to 2 dL / g.

  In the formula (A), examples of the divalent aromatic hydrocarbon group represented by Az include a group having a benzene ring or a naphthalene ring. Examples include a phenylene group, a tolphenylene group, a xylylene group, and a naphthylene group, and among them, a phenylene group is preferable.

で表される基であることが好ましい。 The terminal group represented by the above formula (A) is represented by the following formula (U)

It is preferable that it is group represented by these.

  The terminal group represented by the above formula (A) preferably has a terminal group concentration of 0.05 to 1500 eq / ton, more preferably a terminal group concentration of 100 to 240 eq / ton, more preferably 200 to 240 eq / ton. Preferably there is. The terminal group concentration can be determined from proton NMR analysis of polyamide dope.

  Polyamide (X) preferably has a specific viscosity of 0.5 to 2 dL / g and a terminal group concentration represented by the above formula (A) of 200 to 240 eq / ton.

  Since the polyamide (X) has a terminal group represented by the above formula (A), when heated, the terminal group represented by the formula (A) reacts to form a cross-linked structure in the polyamide. The mechanical strength is improved. Since the terminal group represented by the formula (A) does not form a crosslinked structure before heating, it can be easily formed into a fiber, a film or the like using polyamide (X).

で表されるジアミン成分と、下記式（ｂ）

（式（ｂ）中、ＸはＯＨ、ハロゲン原子、またはＯＲで表される基を表す。Ｒは炭素数１〜６の脂肪族炭化水素基、炭素数６〜１２の芳香族炭化水素基である）
で表されるジカルボン酸成分またはその酸無水物、
および下記式（ｃ）

（Ａｚは炭素数６〜２０の２価の芳香族炭化水素であり、ＸはＯＨ、ハロゲン原子、またはＯＲで表される基を表す。Ｒは炭素数１〜６の脂肪族炭化水素基、炭素数６〜１２の芳香族炭化水素基である。）
で表されるマレイミド成分（ｃ）から重合させることにより製造することができる。 Polyamide (X) has the following formula (a)

A diamine component represented by the following formula (b)

(In the formula (b), X represents a group represented by OH, a halogen atom, or OR. R represents an aliphatic hydrocarbon group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 12 carbon atoms. is there)
A dicarboxylic acid component represented by or an acid anhydride thereof,
And the following formula (c)

(Az is a divalent aromatic hydrocarbon having 6 to 20 carbon atoms, X represents a group represented by OH, a halogen atom, or OR. R is an aliphatic hydrocarbon group having 1 to 6 carbon atoms, (It is an aromatic hydrocarbon group having 6 to 12 carbon atoms.)
It can manufacture by polymerizing from the maleimide component (c) represented by these.

  When trying to obtain polyamide (X) containing a repeating unit other than the repeating unit represented by the formula (a), in addition to metaphenylenediamine as a diamine component, paraphenylenediamine, 3,4'-diphenylene ether diamine, Alternatively, 4,4′-diphenylene ether diamine is also used, and paraphenylene dicarboxylic acid is also used in addition to metaphenylene dicarboxylic acid as the dicarboxylic acid component.

The polymerization can be performed by a conventionally known method such as a solution polymerization method, an interfacial polymerization method, or a melt polymerization method. The degree of polymerization can be controlled by the ratio of the aromatic diamine component and the aromatic dicarboxylic acid component, and the preferred composition ratio is 8 ≦ (α) / {(β) + (γ)} ≦ 1.2.
0 <(γ) / (β) ≦ 1.0
(Wherein (α) represents the number of moles of the aromatic diamine component (a), (β) represents the number of moles of the aromatic dicarboxylic acid component (b), and (γ) represents the number of moles of the maleimide component (c))
It is.

(Resin composition)
The resin composition (Z) of the present invention contains polyamide (X) and polyamide (Y). Polyamide (X) is as described above.

で示される繰り返し単位を主として含有するポリアミドである。 Polyamide (Y) has the following formula (A)

It is a polyamide mainly containing the repeating unit represented by

  "Containing mainly the repeating unit represented by the formula (a)" means that 80 to 100 mol% of the repeating unit of the formula (a) is contained in the polyamide, and more preferably 100 mol%.

  The repeating unit other than the repeating unit represented by the formula (A) includes a unit containing a paraphenylene group, a 3,4′-diphenylene ether group, and a 4,4′-diphenylene ether group in addition to the metaphenylene group. Is mentioned.

で表されるジアミン成分と、下記式（ｂ）

（ＸはＯＨ、ハロゲン原子、またはＯＲで表される基を表す。Ｒは炭素数１〜６の脂肪族炭化水素基、炭素数６〜１２の芳香族炭化水素基である）
で表されるジカルボン酸成分またはその酸無水物から重合させることにより製造することができる。重合は、溶液重合法、界面重合法、溶融重合法など従来公知の方法で行うことができる。 Polyamide (Y) has the following formula (a)

A diamine component represented by the following formula (b)

(X represents a group represented by OH, a halogen atom, or OR. R represents an aliphatic hydrocarbon group having 1 to 6 carbon atoms and an aromatic hydrocarbon group having 6 to 12 carbon atoms)
It can manufacture by polymerizing from the dicarboxylic acid component represented by these, or its acid anhydride. The polymerization can be performed by a conventionally known method such as a solution polymerization method, an interfacial polymerization method, or a melt polymerization method.

The degree of polymerization can be controlled by the ratio of the aromatic diamine component and the aromatic dicarboxylic acid component, and the preferred composition ratio is 0.8 ≦ (α) / (β) ≦ 1.2.
(In the formula, (α) represents the number of moles of the aromatic diamine component (a), and (β) represents the number of moles of the aromatic dicarboxylic acid component (b).)
It is.

  The polyamide (Y) has an inherent viscosity ηinh of 0.05 to 20 dL / g measured at 30 ° C. at a concentration of 0.5 g / 100 mL in 98 wt% concentrated sulfuric acid, preferably 1 -20 dL / g, more preferably 1-10 dL / g.

  The content of the polyamide (X) in the resin composition (Z) is 0.0001 to 100 parts by weight, preferably 0.0001 to 30 parts by weight, more preferably 0 to 100 parts by weight of the polyamide (Y). 0.001 to 20 parts by weight, more preferably 0.01 to 15 parts by weight.

  The terminal group concentration represented by the above formula (A) in the resin composition (Z) is preferably 0.05 to 240 eq / ton, more preferably 1 to 50 eq / ton.

  The resin composition (Z) comprises 1) adding polyamide (X) to polyamide (Y), 2) mixing polyamide (Y) and polyamide (X), 3) polyamide (X) and polyamide (Y) 4) In-situ polymerization of polyamide (Y) with a solution of polyamide (X) can be prepared.

(Dope)
The dope (X) of the present invention contains 100 parts by weight of polyamide (X) and 300 to 3000 parts by weight, preferably 300 to 1500 parts by weight, more preferably 300 to 1000 parts by weight. The dope (Z) of the present invention contains 100 parts by weight of the resin composition (Z) and 300 to 3000 parts by weight, preferably 300 to 1500 parts by weight, more preferably 300 to 1000 parts by weight.

  Examples of the solvent include amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone, ether solvents such as tetrahydrofuran, or acid solvents such as 100% sulfuric acid, phosphoric acid, polyphosphoric acid, and methanesulfonic acid. The dope can be prepared by mixing the solvent and the polyamide (X) or the resin composition (Z). Moreover, dope can also be obtained directly by polymerizing polyamide in the presence of a solvent.

(fiber)
The present invention includes fibers made of polyamide (X). Moreover, this invention includes the fiber which consists of a resin composition (Z).
The strength of the fiber is preferably 400 to 650 mN / tex, more preferably 450 to 600 mN / tex. The end group concentration represented by the formula (A) in the fiber is preferably 0.05 to 240 eq / ton, more preferably 1 to 50 eq / ton. The end group concentration in the fiber can be measured by nuclear magnetic resonance spectroscopy (NMR).

(Fiber manufacturing method)
The fiber can be produced by spinning a dope containing polyamide (X) or a dope containing resin composition (Z).
Spinning may be performed by any of wet, dry and dry wet methods. As described above, in the spinning process, the orientation of the polyamide can be increased and the mechanical properties can be improved by performing flow orientation, liquid crystal orientation, shear orientation or stretch orientation.

  It is preferable to heat-treat after spinning. The polyamide can be crosslinked by heat treatment. The temperature during the heat treatment is preferably 100 ° C to 400 ° C, more preferably 200 ° C to 350 ° C. It is also preferable to apply tension to the fiber during the heat treatment. The tension is preferably 1 to 95%, more preferably 3 to 50%, and still more preferably 5 to 30% of the fiber breaking strength.

  You may extend | stretch in the case of heat processing. The draw ratio is preferably 2 to 40 times, more preferably 5 to 30 times. In view of mechanical properties, it is desirable to stretch as close as possible to the maximum draw ratio (MDR). The stretching temperature is preferably 100 ° C to 400 ° C, more preferably 200 ° C to 350 ° C. A fiber having excellent mechanical properties can be obtained by stretching and orientation at a high magnification at a high temperature.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples.
(1) End group concentration: Polymer dope was determined by proton NMR analysis using JEOL JEOL A-600 (600 MHz).
(2) Mechanical properties of the fiber: Tensylon universal testing machine 1225A manufactured by Orientec Co., Ltd. was used to conduct a tensile test on the obtained fiber with a single yarn, and the elastic modulus and strength were determined.

[Reference Example 1] Preparation of polyamide (Y) 300 parts by weight of dehydrated and purified NMP and 24.51 parts by weight of m-phenylenediamine were added to a well-dried three-necked flask equipped with a stirrer at room temperature and dissolved in nitrogen. Thereafter, 46.02 parts by weight of isophthalic acid dichloride was added with ice cooling and stirring. Thereafter, the temperature was gradually raised and finally reacted at 50 ° C. for 60 minutes. Then, 16.8 parts by weight of calcium hydroxide was added to carry out a neutralization reaction to obtain a dope containing polyamide (Y). The dope contained 379 parts by weight of NMP with respect to 100 parts by weight of polyamide (Y). The specific viscosity measured at 30 ° C. of a concentrated sulfuric acid solution having an aramid resin concentration of 0.5 g / 100 mL obtained by reprecipitation of the obtained dope with water was 1.56 dL / g.

で表される３−マレイミド酸クロライド１．４１重量部を添加した。その後徐々に昇温して最終的に６０℃、６０分反応させたところで水酸化カルシウム７．４１重量部を添加して中和反応を行い、ポリアミド（Ｘ）を含有するドープを得た。ドープは、１００重量部のポリアミド（Ｘ）に対して４００重量部のＮＭＰを含有していた。得られたドープを水にて再沈殿することにより得たアラミド樹脂の濃度０．５ｇ／１００ｍＬの濃硫酸溶液を３０℃で測定した特有粘度は０．６３３ｄＬ／ｇであった。式（２）由来の末端基の濃度は１４４ｅｑ／ｔｏｎであった。 [Reference Example 2] End group-modified polyamide (X)
In a well-dried three-necked flask equipped with a stirrer, 115 parts by weight of dehydrated NMP and 10.81 parts by weight of m-phenylenediamine were added at room temperature and dissolved in nitrogen. 20.30 parts by weight and the following formula (2)

1.41 parts by weight of 3-maleic acid chloride represented by the formula: Thereafter, the temperature was gradually raised and finally reacted at 60 ° C. for 60 minutes. Then, 7.41 parts by weight of calcium hydroxide was added to carry out a neutralization reaction to obtain a dope containing polyamide (X). The dope contained 400 parts by weight of NMP with respect to 100 parts by weight of polyamide (X). The specific viscosity measured at 30 ° C. of a concentrated sulfuric acid solution having an aramid resin concentration of 0.5 g / 100 mL obtained by reprecipitation of the obtained dope with water was 0.633 dL / g. The concentration of the end group derived from Formula (2) was 144 eq / ton.

[Example 1]
By adding 18.2 parts by weight of the end group-modified polyamide (X) prepared in Reference Example 2 to 300 parts by weight of the polyamide dope (Y) prepared in Reference Example 1, and stirring the mixture at 70 ° C. for 4 hours, the polyamide ( A mixed dope of Y) / polyamide (X) = 95/5 (weight ratio) was obtained. The amount of NMP relative to 100 parts by weight of the total amount of polyamide (Y) and polyamide (X) in the mixed dope was 383 parts by weight. The concentration of the end group derived from the formula (2) with respect to the total amount of polyamide (Y) and polyamide (X) was 7.2 eq / ton.

(Manufacture of fibers)
The obtained polymer dope was placed in a coagulation bath at a temperature of 50 ° C., which was an aqueous solution of 48% by weight of calcium chloride at a cylinder temperature of 80 ° C., using a cap having a hole diameter of 0.08 mm and a number of holes of 40, respectively. Extruded in minutes. The fiber taken out from the coagulation bath was washed with water in a 50 ° C. water bath, subjected to boiling water stretching in a 90 ° C. water bath, dried with a 150 ° C. drying roller, and then stretched on a 300 ° C. hot plate. First, the maximum draw ratio (MDR) in this drawing step was determined and drawn at 17 times, which is a 0.8 times draw ratio, to obtain a fiber molded body. The tensile strength of the obtained fiber was 519 mN / tex.
The tensile strength after heat-treating the obtained fiber at 300 ° C. for 3 minutes was 531 mN / tex. Moreover, the tensile strength after heat-treating the obtained fiber at 350 ° C. for 3 minutes was 563 mN / tex.

[Example 2]
In the same manner as in Example 1, 77.5 parts by weight of the end group-modified polyamide (X) prepared in Reference Example 2 was added to 300 parts by weight of the polyamide dope (Y) prepared in Reference Example 1, and the temperature was 4 at 70 ° C. By stirring for a time, a mixed dope of polyamide (Y) / polyamide (X) = 85/15 (weight ratio) was obtained. The amount of NMP relative to 100 parts by weight of the total amount of polyamide (Y) and polyamide (X) in the mixed dope was 398 parts by weight. The concentration of the end group derived from the formula (1) with respect to the total amount of the polyamide (Y) and the polyamide (X) was 21.6 eq / ton.

(Manufacture of fibers)
A fiber was produced in the same manner as in Example 1 to obtain a fiber molded body. The tensile strength of the obtained fiber was 500 mN / tex.
The tensile strength after heat-treating the obtained fiber at 300 ° C. for 3 minutes was 486 mN / tex. Moreover, the tensile strength after heat-treating the obtained fiber at 350 ° C. for 3 minutes was 491 mN / tex.

[Comparative Example 1]
300 parts by weight of the NMP aramid resin solution prepared in Reference Example 1 was spun in the same manner as in Example 1 to obtain a fiber molded body. Various physical properties of this fiber are shown in Table 1.
The tensile strength of the obtained fiber was 502 mN / tex.
The tensile strength after heat-treating the obtained fiber at 300 ° C. for 3 minutes was 461 mN / tex. Moreover, the tensile strength after heat-treating the obtained fiber at 350 ° C. for 3 minutes was 471 mN / tex.
The results are summarized in Table 1 below.

  Since the fiber of the present invention is excellent in heat resistance and mechanical properties, it can be widely used in the fields of ropes, belts, insulating fabrics, thermosetting or thermoplastic resin reinforcements, and protective clothing.

Claims (14)

The following formula (A)

Mainly containing a repeating unit represented by the following formula (I)

(In the formula, Az is a divalent aromatic group having 6 to 20 carbon atoms)
Polyamide (X) having a specific viscosity of 0.05 to 20 dL / g measured at 30 ° C. with a 0.5 g / 100 mL concentrated sulfuric acid solution having a group represented by The terminal group represented by the above formula (A) is represented by the following formula (U)

The polyamide (X) according to claim 1, which is a group represented by the formula:   The polyamide (X) according to any one of claims 1 to 2, wherein the end group concentration represented by the formula (A) is 0.05 to 1500 eq / ton.   The polyamide (X) according to any one of claims 1 to 3, wherein the specific viscosity is 0.5 to 2 dL / g, and the end group concentration represented by the formula (A) is 200 to 240 eq / ton. (I) The following formula (a)

100 parts by weight of polyamide (Y) mainly containing a repeating unit represented by formula (II) and having a specific viscosity of 0.05 to 20 dL / g measured at 30 ° C. with a concentrated sulfuric acid solution of 0.5 g / 100 mL, and (ii) Item 1. A resin composition (Z) containing 0.0001 to 100 parts by weight of the polyamide (X) according to item 1.   The resin composition (Z) according to claim 5, wherein the terminal group concentration represented by the above formula (A) in the resin composition is 0.05 to 240 eq / ton.   A dope (X) comprising 100 parts by weight of the polyamide (X) according to claim 1 and 300 to 3000 parts by weight of a solvent.   A dope (Z) containing 100 parts by weight of the resin composition (Z) according to claim 5 and 300 to 3000 parts by weight of a solvent.   A method for producing a fiber comprising spinning the dope according to claim 7 or 8.   The method for producing a fiber according to claim 9, wherein the fiber is heat-treated after spinning.   A fiber comprising the aromatic polyamide (X) according to claim 1.   A fiber comprising the resin composition (Z) according to claim 5.   The fiber according to claim 11 or 12, wherein the end group concentration represented by the formula (A) is 1 to 50 eq / ton.   The fiber according to claim 12 or 13, having a strength of 400 to 600 mN / tex.