High heat resistance and high toughness fiber and its manufacturing method

Abstract

To provide a highly thermostable and highly tough fiber excellent in balanced physical properties among strength, elongation, and thermostability.SOLUTION: A highly thermostable and highly tough fiber has breaking strength of 8.0 cN / dtex or more and less than 15.0 cN / dtex, breaking elongation of 5.0% or more and 20.0% or less, and dry heat dimensional change rate at 300°C of less than 5%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a high heat-resistant, high toughness fiber and a method for producing the same. More specifically, the present invention relates to a high heat-resistant, high toughness fiber characterized by an excellent balance of physical properties such as strength, elongation, and heat resistance, and a method for producing the same. [Background technology]

[0002] In recent years, advances in spinning technology have led to the industrialization of a variety of fibers. By selecting the chemical structure and spinning conditions that make up the fiber, fibers with physical properties tailored to the required performance and application can be developed and manufactured. High-strength, high-elasticity fibers can provide high-strength structures, but if the elongation is low, they cannot accommodate large deformations and break. There is a trade-off between the strength and elongation of these fibers, and it has been difficult to develop high-toughness fibers that satisfy both strength and elongation.

[0003] Examples of reports on high-toughness fibers include: For example, Japanese Patent Application Laid-Open No. 59-100710 (Patent Document 1) reports high-toughness polyethylene fibers with a strength of 15 to 25 g / de and an elongation of 15 to 25% by heat-shrinking ultra-drawn polyethylene fibers; Japanese Patent Application Laid-Open No. 2000-144527 (Patent Document 2) reports a method for obtaining polyester fibers with a strength of 8 to 9 g / de and an elongation of 10 to 15% by adjusting the oiling and bundling positions; and Japanese Patent Application Laid-Open No. 2008-308786 (Patent Document 3) reports polyester fibers with a strength of 8 to 10 cN / dtex and an elongation of 20 to 25% or more by controlling the temperature history on the spinning line; however, both are general-purpose fibers with relatively low heat resistance.

[0004] On the other hand, in addition to strength, heat resistance is also an essential property in material development. For example, fibers made from wholly aromatic polyamides (sometimes called aramid fibers) are particularly useful as high-strength, heat-resistant, and flame-retardant fibers.

[0005] For example, para-type wholly aromatic polyamide fibers composed of paraphenylene terephthalamide have high strength and high elastic modulus and are therefore widely used as industrial materials such as reinforcing materials for various matrices and ropes, etc. Also, meta-type wholly aromatic polyamide fibers composed of metaphenylene isophthalamide are flexible fibers in addition to heat resistance and are used in industrial applications such as disaster prevention safety clothing such as protective clothing and rubber reinforcing materials that require heat resistance.

[0006] The mechanical properties of these aramid fibers include a breaking strength of 15 to 20 cN / dtex and a breaking elongation of 1 to 5% for the para-type (Kevlar (registered trademark) manufactured by DuPont Co., Ltd., and Twaron (registered trademark) manufactured by Teijin Limited), and a breaking strength of 3 to 6 cN / dtex and a breaking elongation of 30 to 60% for the meta-type (Nomex (registered trademark) manufactured by DuPont Co., Ltd., and Conex (registered trademark) manufactured by Teijin Limited), and applications have been developed taking these fiber properties into consideration.

[0007] However, when using aramid fibers, para-type fibers are generally used in fields where heat resistance and higher strength are required, but these are limited to applications where deformation during use is unlikely.On the other hand, when flexibility is required in fields where heat resistance is also required, meta-type fibers are used, but this requires sacrificing strength. Therefore, it would be useful to obtain a synthetic fiber that has the heat resistance equivalent to that of aramid fiber while also having a good balance between strength and elongation, but this has not been achieved with conventional techniques. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 59-100710 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-144527 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-308786 Summary of the Invention [Problem to be solved by the invention]

[0009] In accordance with the above-mentioned background, an object of the present invention is to provide a highly heat-resistant and highly tough fiber that has high heat resistance and a good balance between strength and elongation. [Means for solving the problem]

[0010] As a result of extensive research into solving the above problems, the present inventors have found that by using a polymer obtained by copolymerizing a plurality of specific monomers in a specific ratio as a fiber, a highly heat-resistant, high-toughness fiber having high heat resistance and a good balance between strength and elongation can be obtained, and have completed the present invention.

[0011] That is, according to the present invention, 1. Breaking strength is 8.0cN / dtex or more but less than 15.0cN / dtex, and breaking elongation is 7.0% or more, 20.0% or less, and the dry heat dimensional change rate at 300°C is less than 5% The high heat resistance and high toughness fiber is a random copolymer of a wholly aromatic polyamide made of a copolymerized aramid polymer, and is composed of an aromatic diamine component and an aromatic dicarboxylic acid component, and contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl. A highly heat-resistant and tough fiber characterized by: 2 .Me The molar ratio of taphenylenediamine and / or isophthaloyl monomer units to paraphenylenediamine and / or terephthaloyl monomer units is in the range of 10 or more but less than 40:90 or less but more than 60. 1 to The high heat resistance and high toughness fiber described above, and 3.A method for producing a highly heat-resistant, highly tough fiber, the method comprising the steps of (1) to (5) using a copolymerized aramid polymer having a weight-average molecular weight of 400,000 to 1,000,000, the copolymerized aramid polymer comprising a structure containing metaphenylene terephthalamide units and / or metaphenylene isophthalamide units and paraphenylene terephthalamide units and / or paraphenylene isophthalamide units, wherein each of the amide units contains at least three types of structures selected from the group consisting of metaphenylene diamine, paraphenylene diamine, isophthaloyl, and terephthaloyl, the molar ratio of the metaphenylene diamine and / or isophthaloyl monomer units to the paraphenylene diamine and / or terephthaloyl monomer units being in the range of 10 or more but less than 40:90 or less but more than 60. (1) The copolymerized aramid polymer is dissolved in an amide-based solvent in an amount of 5 to 25% by mass to prepare a spinning dope, which is then passed through a spinneret; (2) The mixture is coagulated by being spun into an aqueous coagulation bath containing 1 to 20% by mass of an amide-based solvent, (3) The mixture is washed in an aqueous washing bath, and then stretched in a boiling water stretching bath at a ratio of 1.1 to 5.0 times. (4) Dry heat treatment is carried out at a temperature ranging from 100 to 250°C. (5) While applying heat treatment in the range of 290 to 380 ° C, hot stretching is performed at a stretch ratio in the range of 2.0 to 10.0 times. is provided. [Effects of the Invention]

[0012] The highly heat-resistant, high-toughness fiber obtained by the present invention has high heat resistance, with a dry heat dimensional change rate at 300°C of less than 5%, and is a high-toughness fiber with a breaking strength of 8.0 cN / dtex or more but less than 15.0 cN / dtex and a breaking elongation of more than 5.0% but not more than 20.0%. Because of its excellent balance of physical properties, the fiber can be suitably used in protective clothing applications where strength and flexibility are required, and in rubber reinforcement applications where elongation is required. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. The high heat resistant, high toughness fiber of the present invention is characterized by having a breaking strength of 8.0 cN / dtex or more but less than 15.0 cN / dtex, a breaking elongation of more than 5.0% but not more than 20.0%, and a dry heat dimensional change of less than 5% at 300° C. Examples of polymers constituting such high heat resistant, high toughness fibers include wholly aromatic polyamides (hereinafter sometimes referred to as aramids), which are specifically composed of meta- and para-aromatic diamine components and meta- and para-aromatic dicarboxylic acid components and are synthesized by copolymerization.

[0014] Particularly preferably used in the present invention, from the viewpoints of mechanical properties, heat resistance, and flame retardancy, is a wholly aromatic polyamide made of a copolymerized aramid polymer having a structure containing metaphenylene terephthalamide units and / or metaphenylene isophthalamide units and paraphenylene terephthalamide units and / or paraphenylene isophthalamide units.

[0015] In the high heat-resistant, high toughness fiber of the present invention, the wholly aromatic polyamide made of a copolymerized aramid polymer is randomly copolymerized and preferably contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, with the molar percentage of metaphenylenediamine and / or isophthaloyl monomer units being preferably 10 to less than 40 and the molar percentage of paraphenylenediamine and / or terephthaloyl monomer units being 90 to more than 60, and more preferably 20 to less than 40 and the molar percentage of paraphenylenediamine and / or terephthaloyl monomer units being 80 to more than 60. When both metaphenylenediamine and isophthaloyl monomer units are present, the total is the sum of these (metaphenylenediamine and isophthaloyl monomer units). Furthermore, when both paraphenylenediamine and terephthaloyl monomer units are present, the total is the sum of these (paraphenylenediamine and terephthaloyl monomer units).

[0016] If the mole percentage of metaphenylenediamine and / or isophthaloyl monomer units is 40 or more, the desired strength and thermal stability cannot be achieved. Furthermore, if the mole percentage of metaphenylenediamine and / or isophthaloyl monomer units is less than 10, the resulting polymer is insoluble in the amide-based solvent described below and therefore cannot be spun. Combinations of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl are shown in Table 1 below.

[0017] The present invention preferably contains at least three types of structures as shown in Examples 1 to 5. Note that, as described above, when the molar percentage of paraphenylenediamine and / or terephthaloyl monomer units is in the range of 10 to less than 40, and the molar percentage of metaphenylenediamine and / or isophthaloyl monomer units is in the range of 90 to more than 60, and when four types of structures as shown in Example 5 are contained, the solubility in an amide solvent, which will be described later, may decrease. Therefore, it is more preferable that the composition is composed of only three types of structures as shown in Examples 1 to 4.

[0018] In other words, it is more preferable that the high heat resistant, high toughness fiber consists of only three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl. It is particularly preferable that the high heat resistant, high toughness fiber consists of only three types of structures shown in Example 4. In other words, it is more preferable that the high heat resistant, high toughness fiber consists of only three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, and terephthaloyl.

[0019] [Table 1]

[0020] Examples of aromatic diamine components that serve as raw materials for wholly aromatic polyamides include metaphenylenediamine or paraphenylenediamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, and derivatives thereof having substituents such as halogens and alkyl groups having 1 to 3 carbon atoms on the aromatic ring.

[0021] Examples of raw materials for the aromatic dicarboxylic acid component constituting the wholly aromatic polyamide of the present invention include aromatic dicarboxylic acid halides. Examples of meta-type aromatic dicarboxylic acid halides include isophthalic acid halides such as isophthalic acid chloride and isophthalic acid bromide, and derivatives thereof having a substituent such as a halogen or an alkoxy group having 1 to 3 carbon atoms on the aromatic ring. Similarly, examples of para-type aromatic dicarboxylic acid halides include terephthalic acid halides such as terephthalic acid chloride and terephthalic acid bromide, and derivatives thereof having a substituent such as a halogen or an alkoxy group having 1 to 3 carbon atoms on the aromatic ring.

[0022] The polymerization method for the wholly aromatic polyamide of the present invention includes, but is not limited to, a method in which an organic solvent system (e.g., tetrahydrofuran) that is not a good solvent for the resulting polyamide containing metaphenylenediamine and isophthalic acid chloride is contacted with an aqueous solution system containing an inorganic acid acceptor and a soluble neutral salt, thereby isolating a powder of polymetaphenylene isophthalamide polymer (interfacial polymerization, JP-B-47-10863), or a method in which the above diamine and acid chloride are solution polymerized in an amide solvent, followed by neutralization with calcium hydroxide, calcium oxide, or the like (solution polymerization, JP-A-8-074121, JP-A-10-88421).

[0023] The weight-average molecular weight of the wholly aromatic polyamide copolymer (also referred to as copolymerized aramid polymer) used in the present invention must be 400,000 to 1,000,000, as determined by the analytical method described below, in order to form fibers with practically sufficient breaking strength. If the weight-average molecular weight is less than 400,000, not only will the breaking strength be significantly reduced, but stable spinning will also be impossible. Furthermore, if the molecular weight exceeds 1,000,000, the viscosity will be too high to handle when preparing and spinning a wholly aromatic polyamide solution described below, requiring specialized equipment.

[0024] The polymer within the molecular weight range specified in the present invention may be a mixture of a low molecular weight polymer and a high molecular weight polymer, and the overall molecular weight may be within the range specified by adjusting the mixing ratio. For example, if a polymer with a weight-average molecular weight of 200,000 is mixed with a polymer with a weight-average molecular weight of 800,000, and the weight-average molecular weight of the resulting polymer is 600,000, it can be used without any problems because it is within the molecular weight range specified in the present invention.

[0025] The wholly aromatic polyamide fiber of the present invention is produced using the wholly aromatic polyamide obtained by the above-mentioned production method through the following steps: spinning solution preparation step, spinning / coagulation step, washing step, boiling water drawing step, dry heat treatment step, and hot drawing step.

[0026] [Spinning solution preparation process] In the spinning solution preparation step, the wholly aromatic polyamide of the present invention is dissolved in a solvent to prepare a spinning solution (dope). An amide solvent is typically used to prepare the spinning solution, and examples of such solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc). Among these, NMP or DMAc is preferred from the viewpoints of solubility and handling safety.

[0027] The solution concentration can be appropriately selected from the viewpoints of the coagulation rate in the subsequent spinning and coagulation step and the solubility of the polymer, and is usually in the range of 5 to 25% by mass, more preferably in the range of 7 to 20% by mass to achieve stable spinning.

[0028] In the present invention, an inorganic salt may be incorporated into the dope, and the content of the inorganic salt is preferably 0 to 20% by mass relative to the dope, and more preferably 0 to 10% by mass in order to obtain stable spinnability.

[0029] If the inorganic salt content exceeds 20% by mass, the coagulation rate becomes too fast, resulting in the formation of numerous voids in the fiber, making it impossible to obtain a fiber with the desired physical properties. It is preferable to use chloride salts such as calcium chloride, magnesium chloride, and lithium chloride as the inorganic salt.

[0030] [Spinning and coagulation process] In the spinning and coagulation step, the dope obtained above is spun into a coagulation liquid and coagulated. The spinning device is not particularly limited, and a conventionally known wet spinning device can be used. As long as it can perform stable wet spinning, there is no need to particularly limit the number of spinning holes, the diameter of the spinning holes, the arrangement state, etc. of the spinneret. For example, a multi-hole spinneret for staple fiber having 10 to 30,000 spinning holes and a spinning hole diameter of 0.03 to 0.2 mm can be used.

[0031] The temperature of the dope when it is spun out from the spinneret is preferably in the range of 20 to 90°C, more preferably 70 to 90°C. The coagulation bath used to obtain the fiber of the present invention is an aqueous solution containing 1 to 20 mass % of an amide solvent, preferably 3 to 15 mass %. The temperature of this aqueous solution is preferably in the range of 50 to 90°C. The coagulation bath may also contain an inorganic salt such as calcium chloride or magnesium chloride, preferably in an amount of 30% by mass or more, more preferably 35 to 45% by mass. As described above, the dope is spun from the spinneret into the coagulation liquid and passed through the coagulation bath to obtain a coagulated thread.

[0032] [Washing process, boiling water stretching process] The coagulated yarn thus obtained is thoroughly washed in an aqueous washing bath and then sent to a boiling water drawing step. The draw ratio in the boiling water draw bath must be in the range of 1.1 to 5.0, and more preferably in the range of 1.1 to 3.0. By drawing within this range and increasing the molecular chain orientation, the strength of the final fiber can be ensured.

[0033] [Dry heat treatment process] The fibers that have been subjected to the above washing and drawing steps are preferably subjected to a dry heat treatment step. In the dry heat treatment step, the fibers that have been washed in the above washing step are dry heat treated at a temperature in the range of 100 to 250°C, preferably 100 to 200°C. The dry heat treatment is preferably carried out at a fixed length. The temperature of the dry heat treatment refers to the set temperature of a fiber heating means such as a hot plate or a heated roller.

[0034] [Hot stretching process] In the present invention, the fiber that has undergone the dry heat treatment step is subjected to a hot drawing step. In the hot drawing step, drawing is carried out while applying heat treatment in the range of 290 to 380°C. The treatment temperature is preferably in the range of 290 to 350°C. Temperatures below 290°C are inappropriate because high-ratio drawing is not possible, while temperatures above 380°C may cause discoloration of the fiber or breakage of the yarn. In the hot drawing step, the draw ratio must be in the range of 2.0 to 10.0 times, and preferably in the range of 3.0 to 10.0 times. The temperature of the hot drawing treatment refers to the set temperature of the fiber heating means, such as a hot plate or a heated roller.

[0035] The breaking strength of the high heat resistant and high toughness fiber obtained by the above method is 8.0 cN / dtex or more and less than 15.0 cN / dtex, and the lower limit is more preferably 9.0 cN / dtex or more.

[0036] If the breaking strength is less than 8.0 cN / dtex, the strength is insufficient to achieve the high toughness aimed at by the present invention. Furthermore, the breaking elongation must be greater than 5.0% and not greater than 20%, preferably 7.0% to 15.0%, and more preferably 10.0% to 15.0%. If the breaking elongation is less than 5.0%, the elongation is insufficient, and thus high toughness is not sufficiently exhibited. If the breaking elongation exceeds 20.0%, it becomes difficult to obtain sufficient strength.

[0037] The high heat-resistant, high toughness fiber of the present invention must have a dry heat dimensional change rate of less than 5%, preferably 4% or less, at 300° C. If the dry heat dimensional change rate is 5% or more, the fiber will not be able to exhibit its performance as a heat-resistant fiber. [Example]

[0038] The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples. The physical properties in the examples and comparative examples were measured by the following methods.

[0039] [Weight average molecular weight Mw] Analysis was performed using a high-performance liquid chromatograph equipped with a size exclusion chromatography column in accordance with JIS-K-7252, using dimethylformamide (containing 0.01 mol% lithium chloride) as the developing solvent. Sigma-Aldrich polystyrene sets (peak top molecular weights Mp = 400 to 2,000,000) were used as standard molecular weight samples.

[0040] [Single fiber fineness] Measurements were carried out in accordance with Method A of correct fineness in accordance with JIS-L-1015, and the results were expressed as apparent fineness.

[0041] [Breaking strength, breaking elongation] Measurement was carried out using a tensile tester (Instron, model: 5565) in accordance with JIS-L-1015 under the following conditions. (Measurement conditions) Grip spacing: 20mm Initial load: 0.044cN (1 / 20g / dtex) Pulling speed: 20 mm / min

[0042] [Dry heat dimensional change rate] Measurement was carried out in accordance with JIS-L-1013, Method B, to determine the dimensional change rate at 300°C.

[0043] [Example 1] After dissolving the amine monomer in NMP, the solution was cooled to 0°C and stirred with a mechanical stirrer while the acid chloride monomer was added. The metaphenylenediamine units were adjusted to 29 mol% of the total, the paraphenylenediamine and terephthaloyl monomer units to 71 mol%, and the mass concentration of the polymer after polymerization to the total solution was adjusted to 10.7%. The acid chloride monomer was terephthalic acid chloride, and the amine monomers were both metaphenylenediamine and paraphenylenediamine in a weight ratio of 4:3. After confirming that the increase in viscosity and solution temperature due to polymerization had stalled, an equal amount of calcium hydroxide to the acid chloride monomer was added and stirred until the solution became transparent, producing a polymer solution containing copolymerized aramid polymer. The weight-average molecular weight was 690,000.

[0044] This polymer solution was heated to 85°C and used as a spinning dope, which was then extruded from a circular spinneret with 100 discharge holes, each 0.1 mm in diameter, into a coagulation bath at 85°C for spinning. The composition of this coagulation bath was 43% by mass of calcium chloride, 10% by mass of NMP, and the remaining 47% by mass of water. The solution was passed through an immersion length (effective coagulation bath length) of 100 cm at a yarn speed of 5.0 m / min, and then drawn out into the air to obtain a coagulated yarn.

[0045] This coagulated yarn was washed in first and second water washing baths for a total immersion time of 200 seconds. The water temperatures in the first and second aqueous washing baths were 20°C and 30°C, respectively. This washed yarn was stretched 2.0 times in boiling water at 90°C, and then immersed in warm water at 90°C for 40 seconds for washing.

[0046] Next, the fiber was wound around a roller with a surface temperature of 170°C for dry heat treatment, and then stretched 2.2 times on a hot plate with a surface temperature of 335°C to obtain wholly aromatic polyamide fibers. The obtained fiber had a fineness of 1.3 dtex, a breaking strength of 10.5 cN / dtex, a breaking elongation of 15.0%, and a dry heat dimensional change at 300°C of 2.0%.

[0047] [Example 2] A polymer solution containing a copolymerized aramid polymer containing 33 mol% metaphenylenediamine units and 67 mol% paraphenylenediamine and terephthaloyl monomer units was synthesized by solution polymerization in accordance with Example 1. Terephthalic acid chloride was used as the acid chloride monomer. Furthermore, both metaphenylenediamine and paraphenylenediamine were used as amine monomers in a weight ratio of 2:1. The weight-average molecular weight was 620,000. This polymer solution was heated to 85°C to form a spinning dope, which was then extruded into a coagulation bath at 85°C through a circular spinneret with 100 circular nozzles and a 0.1 mm diameter. The composition of the coagulation bath was 45% by mass of calcium chloride, 12% by mass of NMP, and the remaining 43% by mass of water. The yarn was passed through the coagulation bath with an immersion length (effective coagulation bath length) of 100 cm at a yarn speed of 5.0 m / min, and then drawn out into the air to obtain a coagulated yarn.

[0048] This coagulated yarn was washed in first and second water washing baths for a total immersion time of 200 seconds. The water temperatures in the first and second aqueous washing baths were 20°C and 30°C, respectively. This washed yarn was stretched 2.0 times in boiling water at 90°C, and then immersed in warm water at 90°C for 40 seconds for washing.

[0049] Next, the fiber was wound around a roller with a surface temperature of 170°C for dry heat treatment, and then stretched 2.0 times on a hot plate with a surface temperature of 325°C to obtain wholly aromatic polyamide fibers. The obtained fiber had a fineness of 1.5 dtex, a breaking strength of 10.6 cN / dtex, a breaking elongation of 13.0%, and a dry heat dimensional change at 300°C of 2.1%.

[0050] [Example 3] A polymer solution containing a copolymerized aramid polymer containing 25 mol% metaphenylenediamine units and 75 mol% paraphenylenediamine and terephthaloyl monomer units was synthesized by solution polymerization according to Example 1. Terephthalic acid chloride was used as the acid chloride monomer. Furthermore, both metaphenylenediamine and paraphenylenediamine were used as amine monomers at a weight ratio of 1:1. The weight-average molecular weight was 580,000. This polymer solution was heated to 85°C to form a spinning dope, which was then extruded into a coagulation bath at 85°C through a circular spinneret with 100 circular orifices and a hole diameter of 0.1 mm. The composition of this coagulation bath was 40% by mass of calcium chloride, 10% by mass of NMP, and the remaining 50% by mass of water. The fiber was passed through the coagulation bath with an immersion length (effective coagulation bath length) of 100 cm at a yarn speed of 5.0 m / min and then drawn out into the air.

[0051] This coagulated yarn was washed in first and second water washing baths for a total immersion time of 200 seconds. The water temperatures in the first and second aqueous washing baths were 20°C and 30°C, respectively. This washed yarn was stretched 2.3 times in boiling water at 90°C, and then immersed in warm water at 90°C for 40 seconds for washing.

[0052] Next, the fiber was wound around a roller with a surface temperature of 170°C for dry heat treatment, and then stretched 1.5 times on a hot plate with a surface temperature of 325°C to obtain wholly aromatic polyamide fibers. The obtained fiber had a fineness of 1.5 dtex, a breaking strength of 12.0 cN / dtex, a breaking elongation of 13.0%, and a dry heat dimensional change at 300°C of 1.9%.

[0053] [Comparative Example 1] A polymer solution containing a copolymerized aramid polymer containing 66 mol% metaphenylenediamine units and 34 mol% paraphenylenediamine and terephthaloyl monomer units was synthesized by solution polymerization according to Example 1. The acid chloride monomers used were isophthalic acid chloride and terephthalic acid chloride in a weight ratio of 1:2. The amine monomer was metaphenylenediamine. The weight-average molecular weight was 580,000. This polymer solution was heated to 85°C to form a spinning dope, which was then extruded into a coagulation bath at 85°C through a circular spinneret with 100 circular nozzles and a 0.1 mm diameter. The composition of the coagulation bath was 40% by mass of calcium chloride, 10% by mass of NMP, and the remaining 50% by mass of water. The fiber was passed through the coagulation bath with an immersion length (effective coagulation bath length) of 100 cm at a yarn speed of 5.0 m / min and then drawn out into the air.

[0054] This coagulated yarn was washed in first and second water washing baths for a total immersion time of 200 seconds. The water temperatures in the first and second aqueous washing baths were 20°C and 30°C, respectively. This washed yarn was stretched 2.3 times in boiling water at 90°C, and then immersed in warm water at 90°C for 40 seconds for washing.

[0055] Next, the fiber was wound around a roller with a surface temperature of 170°C for dry heat treatment, and then stretched 2.0 times on a hot plate with a surface temperature of 325°C to obtain wholly aromatic polyamide fibers. The obtained fiber had a fineness of 2.0 dtex, a breaking strength of 6.3 cN / dtex, a breaking elongation of 12.0%, and a dry heat dimensional change at 300°C of 15%.

[0056] Comparative Example 2 A polymer solution containing a copolymerized aramid polymer containing 9 mol% metaphenylenediamine units and 91 mol% paraphenylenediamine and terephthaloyl monomer units was synthesized by solution polymerization according to Example 1. Terephthalic acid chloride was used as the acid chloride monomer. Both metaphenylenediamine and paraphenylenediamine were used as amine monomers in a weight ratio of 6:14. As the polymerization progressed, the solubility of the polymer decreased, and it no longer showed solubility in solvents such as NMP, making it impossible to spin.

[0057] Comparative Example 3 Measurement of the physical properties of a wholly aromatic polyamide fiber (Teijin Limited's "Conex (registered trademark)") in which metaphenylenediamine and isophthaloyl monomer units account for 100 mol % of the total fiber was performed. The fiber had a fineness of 2.2 dtex, a breaking strength of 4.8 cN / dtex, a breaking elongation of 39.0%, and a dry heat dimensional change at 300°C of 5.0%.

[0058] Comparative Example 4 Measurement of the physical properties of a wholly aromatic polyamide fiber (Twaron (registered trademark) manufactured by Teijin Limited) consisting of 100 mol% paraphenylenediamine and terephthaloyl monomer units revealed a fineness of 2.0 dtex, a breaking strength of 22 cN / dtex, a breaking elongation of 2.5%, and a dry heat dimensional change at 300°C of 0%. Since the breaking elongation of this fiber is less than 5.0%, it is insufficient to exhibit high toughness. Table 2 shows the physical properties of the fibers obtained in the above examples and comparative examples.

[0059] [Table 2] [Industrial Applicability]

[0060] The high heat-resistant, high toughness fiber obtained by the present invention has an excellent balance of physical properties including strength, elongation, and heat resistance, and therefore can be suitably used in applications where general-purpose fibers have been used at the expense of heat resistance, or where mechanical properties have been compensated for by combining multiple fibers.Furthermore, the fiber can be used in reinforcement applications to produce novel heat-resistant, high toughness materials that combine appropriate strength and flexibility, such as materials in the field of rubber reinforcement, which requires strength despite significant deformation.

Claims

1. A highly heat-resistant, high-toughness fiber having a breaking strength of 8.0 cN / dtex or more and less than 15.0 cN / dtex, a breaking elongation of 7.0% or more and 20.0% or less, and a dry heat dimensional change rate at 300°C of less than 5%, wherein the highly heat-resistant, high-toughness fiber is a random copolymer of a wholly aromatic polyamide made of a copolymerized aramid polymer, and is composed of an aromatic diamine component and an aromatic dicarboxylic acid component, and contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl.

2. A highly heat-resistant, highly tough fiber as described in claim 1, wherein the molar ratio of metaphenylenediamine and / or isophthaloyl monomer units to paraphenylenediamine and / or terephthaloyl monomer units is in the range of 10 or more but less than 40:90 or less but more than 60.

3. A method for producing a high heat resistant and high toughness fiber, A method for producing a highly heat-resistant and highly tough fiber, the method comprising the steps of (1) to (5) using a copolymerized aramid polymer having a weight average molecular weight of 400,000 to 1,000,000, the copolymer comprising a structure containing metaphenylene terephthalamide units and / or metaphenylene isophthalamide units, and paraphenylene terephthalamide units and / or paraphenylene isophthalamide units, wherein each of the amide units contains at least three types of structures selected from the group consisting of metaphenylene diamine, paraphenylene diamine, isophthaloyl, and terephthaloyl, the molar ratio of the metaphenylene diamine and / or isophthaloyl monomer units to the paraphenylene diamine and / or terephthaloyl monomer units being in the range of 10 or more but less than 40:90 or less but more than 60. (1) The copolymerized aramid polymer is dissolved in an amide solvent in an amount of 5 to 25% by mass to prepare a spinning dope, which is then passed through a spinneret. (2) The mixture is spun into an aqueous coagulation bath containing 1 to 20% by mass of an amide solvent and coagulated. (3) The film is washed in an aqueous washing bath and then stretched in a boiling water stretching bath at a ratio of 1.1 to 5.0 times. (4) Dry heat treatment is carried out in the range of 100 to 250°C. (5) While applying heat treatment in the range of 290 to 380°C, the film is hot stretched at a stretch ratio in the range of 2.0 to 10.0 times.

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