High heat-resistant toughness fiber and method for producing the same

Abstract

To provide a heat-resistant high-toughness fiber having an excellent balance of strength, elongation and heat resistance.SOLUTION: A heat-resistant high-toughness fiber has a breaking strength of 7-15 cN / dtex, a breaking elongation of 10-30% and a melting point of 290°C or higher.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, with the development of spinning technology, various fibers have been industrialized, and by selecting the chemical structure and spinning conditions constituting the fiber, fibers having physical properties corresponding to required performances and applications have been developed and manufactured. High-strength and high-elastic fibers can provide a high-strength structure, but when the elongation is low, they cannot be relaxed against large deformations and break. The strength and elongation of these fibers are in a trade-off relationship, and it has been difficult to develop high-toughness fibers that satisfy both strength and elongation.

[0003] Examples of reports on high-toughness fibers are as follows. For example, Japanese Patent Application Laid-Open No. 59-100710 (Patent Document 1) reports high-toughness polyester fibers having a strength of 15 to 25 g / de and an elongation of 15 to 25% by subjecting super-stretched polyethylene fibers to heat shrinkage treatment. Further, Japanese Patent Application Laid-Open No. 2000-144527 (Patent Document 2) reports a method for obtaining polyester fibers having a strength of 8 to 9 g / de and an elongation of 10 to 15% by adjusting the positions of oiling and focusing. Further, Japanese Patent Application Laid-Open No. 2008-308786 (Patent Document 3) reports polyester fibers having 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, but all of them are general-purpose fibers and have relatively low heat resistance.

[0004] On the other hand, heat resistance is cited as a performance required in material development in addition to strength. For example, fibers made of wholly aromatic polyamide (sometimes referred to as 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 thus are widely used as reinforcing materials for various matrices and industrial materials such as ropes. Also, meta-type wholly aromatic polyamide fibers composed of metaphenylene isophthalamide are flexible fibers in addition to having heat resistance, and are used, for example, in disaster prevention safety clothing applications such as protective clothing and industrial applications such as rubber reinforcing materials that require heat resistance.

[0006] The mechanical properties of these aramid fibers include, for the para-type, a breaking strength of 15 to 20 cN / dtex and a breaking elongation of 1 to 5% (such as "Kevlar" (registered trademark) manufactured by DuPont Co., Ltd. and "Twaron" (registered trademark) manufactured by Teijin Limited), and for the meta-type, a breaking strength of 3 to 6 cN / dtex and a breaking elongation of 30 to 60% (such as "Nomex" (registered trademark) manufactured by DuPont Co., Ltd. and "Conex" (registered trademark) manufactured by Teijin Limited). Application development has been carried out considering these fiber properties.

[0007] However, when using aramid fibers, in fields where heat resistance is required and even higher strength is demanded, generally the para-type is used, but it is limited to applications that are less likely to involve use deformation. On the other hand, in fields where heat resistance is required and flexibility is demanded, the meta-type is used, but it is necessary to sacrifice strength. Therefore, it is useful to obtain synthetic fibers that have heat resistance equivalent to that of aramid fibers and also have a balanced characteristic of strength and elongation, but this has not been achieved by the prior art.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a high heat-resistant and high toughness fiber having a balance between strength and elongation while having high heat resistance as described in the foregoing background.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventors have found that by using a polymer obtained by copolymerizing a plurality of specific monomers at a specific ratio as a fiber, a heat-resistant high toughness fiber having a balance between strength and elongation while having high heat resistance can be obtained, and thus the present invention has been completed.

[0011] That is, according to the present invention, 1. The heat-resistant high-tenacity fiber contains at least three structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, A heat-resistant high toughness fiber characterized in that the breaking strength is 7 to 15 cN / dtex, the breaking elongation is 15~ 30%, and the melting point is 290°C or higher, 2. The heat-resistant high toughness fiber according to 1 above, wherein the dry heat dimensional change rate at 250°C is less than 2%. 3. The heat-resistant high toughness fiber according to 1 or 2 above, wherein the heat-resistant high toughness fiber is composed of a copolyaramid polymer having a structure containing a metaphenylene terephthalamide unit and and me a paraphenylene isophthalamide unit, and a paraphenylene terephthalamide unit and / or a paraphenylene isophthalamide unit. 4. The heat-resistant high toughness fiber contains at least three structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, and the molar ratio of the metaphenylenediamine and / or isophthaloyl monomer unit to the paraphenylenediamine and / or terephthaloyl monomer unit is in the range of 40 or more and less than 70: more than 30 and 60 or less. and has a breaking strength of 7 to 15 cN / dtex, an elongation at break of 10 to 30%, and a melting point of 290 °C or higher. Heat-resistant high toughness fiber, and 5. A method for producing a heat-resistant high toughness fiber, Composed of a structure containing meta-phenylene terephthalamide units and / or meta-phenylene isophthalamide units, and para-phenylene terephthalamide units and / or para-phenylene isophthalamide units, each of the amide units contains at least three structures selected from the group consisting of meta-phenylenediamine, para-phenylenediamine, isophthaloyl, and terephthaloyl. The molar ratio of meta-phenylenediamine and / or isophthaloyl monomer units to para-phenylenediamine and / or terephthaloyl monomer units is in the range of 40 or more and less than 70:60 or less and more than 30, and a copolymerized aramid polymer having a weight average molecular weight of 400,000 to 1,000,000 is used to produce in the following steps (1) to (5) and satisfy the production conditions of (6). A method for producing a high heat-resistant toughness fiber. (1) Dissolve the copolymerized aramid polymer in an amide-based solvent in the range of 10 to 30% by mass to form a spinning dope, and pass it through a spinneret. (2) Spin it into an aqueous coagulation bath containing 1 to 20% by mass of an amide-based solvent and coagulate it. (3) Wash it with water in an aqueous washing bath, and then stretch it in a boiling water stretching bath in the range of 1.1 to 5.0 times. (4) Perform dry heat treatment in the range of 100 to 250 °C. (5) While applying heat treatment in the range of 290 to 380 °C, perform hot stretching in the range of a stretching ratio of 2.0 to 10.0 times. (6) The total stretching ratio of the boiling water stretching ratio and the hot stretching ratio is 7 times or more. is provided.

Effect of the Invention

[0012] The high heat-resistant toughness fiber obtained in the present invention has heat resistance capable of withstanding a use environment of 250 °C or higher, and is a high toughness fiber with a breaking strength of 7 to 15 cN / dtex and a breaking elongation of 10 to 30%. Since the balance of physical properties is excellent, it can be suitably used in applications such as protective clothing that compensates for strength and flexibility, and rubber reinforcement applications that require elongation.

Embodiment for Carrying Out the Invention

[0013] The following is a detailed description of the present invention. The high heat-resistant toughness fiber of the present invention is characterized in that its breaking strength is 7 to 15 cN / dtex, its breaking elongation is 10 to 30%, and its melting point is 290°C or higher. Examples of the polymer constituting such high heat-resistant toughness fiber include wholly aromatic polyamides (hereinafter sometimes referred to as aramids), specifically those composed of meta-type and para-type aromatic diamine components and meta-type and para-type aromatic dicarboxylic acid components, and are synthesized by copolymerization.

[0014] Particularly preferably used in the present invention is a wholly aromatic polyamide composed of a copolymerized aramid polymer having a structure containing a meta-phenylene terephthalamide unit and / or a meta-phenylene isophthalamide unit, and a para-phenylene terephthalamide unit and / or a para-phenylene isophthalamide unit, from the viewpoints of mechanical properties, heat resistance, and flame retardancy.

[0015] In the high heat-resistant toughness fiber of the present invention, the wholly aromatic polyamide composed of the copolymerized aramid polymer is randomly copolymerized, preferably containing at least three types of structures selected from the group consisting of meta-phenylenediamine, para-phenylenediamine, isophthaloyl, and terephthaloyl, and the molar percentage of the meta-phenylenediamine and / or isophthaloyl monomer units is preferably 40 or more and less than 70 of the total, and the molar percentage of the para-phenylenediamine and / or terephthaloyl monomer units is preferably 60 or less and more than 30 of the total. More preferably, the molar percentage of the meta-phenylenediamine and / or isophthaloyl monomer units is 50 or more and less than 70 of the total, and the molar percentage of the para-phenylenediamine and / or terephthaloyl monomer units is 50 or less and more than 30 of the total. Particularly preferably, the molar percentage of the meta-phenylenediamine and / or isophthaloyl monomer units is 50 or more and less than 67 of the total, and the molar percentage of the para-phenylenediamine and / or terephthaloyl monomer units is 50 or less and more than 33 of the total.

[0016] When the molar percentage of the m-phenylenediamine and / or isophthaloyl monomer unit is 70% or more, the desired strength cannot be achieved. Further, when the molar percentage of the m-phenylenediamine and / or isophthaloyl monomer unit is less than 40%, the resulting polymer cannot be dissolved in the amide-based solvent described later and thus cannot be spun. The combinations of m-phenylenediamine, p-phenylenediamine, isophthaloyl, and terephthaloyl are shown in Table 1 below. The present invention preferably includes at least three types of structures as shown in Examples 1 to 4, and particularly preferably includes four types of structures as in Example 5.

[0017]

Table 1

[0018] Examples of the aromatic diamine component as a raw material for the wholly aromatic polyamide include m-phenylenediamine or p-phenylenediamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, etc., and derivatives having substituents such as halogen and an alkyl group having 1 to 3 carbon atoms on these aromatic rings.

[0019] Examples of the raw material for the aromatic dicarboxylic acid component constituting the wholly aromatic polyamide of the present invention include aromatic dicarboxylic acid halides. 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 halogen and an alkoxy group having 1 to 3 carbon atoms on these aromatic rings. Similarly, examples of the para-type aromatic dicarboxylic acid halide include terephthalic acid halides such as terephthalic acid chloride and terephthalic acid bromide, and derivatives having substituents such as halogen and an alkoxy group having 1 to 3 carbon atoms on these aromatic rings.

[0020] As a method for polymerizing the wholly aromatic polyamide of the present invention, an organic solvent system (for example, tetrahydrofuran) that is not a good solvent for the produced polyamide containing metaphenylenediamine and isophthaloyl chloride and an aqueous solution system containing an inorganic acid acceptor and a soluble neutral salt are brought into contact with each other to isolate a powder of a polymetaphenylene isophthalamide polymer (interfacial polymerization, Japanese Patent Publication No. Sho 47-10863), or a method of solution-polymerizing the above diamine and acid chloride in an amide solvent and then neutralizing with calcium hydroxide, calcium oxide, etc. (solution polymerization, Japanese Patent Laid-Open No. Hei 8-074121, Japanese Patent Laid-Open No. Hei 10-88421), etc. are mentioned, but it is not limited thereto.

[0021] In addition, from the viewpoint of being able to form fibers having a breaking strength that can withstand practical use, the weight average molecular weight of the wholly aromatic polyamide copolymer (also referred to as a copolymerized aramid polymer) used in the present invention needs to be 400,000 to 1,000,000 according to the analysis method described later. When the weight average molecular weight is less than 400,000, not only does the breaking strength decrease significantly, but stable spinning cannot be performed. Further, when the molecular weight exceeds 1,000,000, when preparing and spinning the wholly aromatic polyamide solution described later, the viscosity is too high, making it difficult to handle and requiring dedicated equipment.

[0022] For the polymer within the molecular weight range defined in the present invention, a mixture of a low molecular weight polymer and a high molecular weight polymer can be used, and as long as the overall molecular weight is a value within the molecular weight range defined by adjusting the mixing ratio. For example, when a polymer having a weight average molecular weight of 200,000 and a polymer having a weight average molecular weight of 800,000 are mixed and the weight average molecular weight of this mixed polymer is 600,000, there is no problem in using it because it is within the molecular weight range defined in the present invention.

[0023] The wholly aromatic polyamide fiber of the present invention is produced through the spinning solution preparation process, spinning and coagulation process, washing process, boiling water stretching process, dry heat treatment process, and heat stretching process described below using the wholly aromatic polyamide obtained by the above production method.

[0024] [Spinning Solution Preparation Process] In the spinning solution preparation process, the wholly aromatic polyamide of the present invention is dissolved in a solvent to prepare a spinning solution (dope). When preparing the spinning solution, an amide-based solvent is usually used, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), etc. Among these, from the viewpoints of solubility and handling safety, it is preferable to use NMP or DMAc.

[0025] As for the solution concentration, an appropriate concentration may be appropriately selected from the viewpoints of the coagulation rate in the subsequent spinning and coagulation process and the solubility of the polymer, and usually it is necessary to be in the range of 10 to 30% by mass. In order to achieve stable spinning, it is more preferable to be in the range of 15 to 25% by mass. In the present invention, an inorganic salt may be introduced into the dope, and it is preferable to contain 0 to 20% by mass of the inorganic salt with respect to the dope. In order to obtain stable spinnability, 0 to 10% by mass of the inorganic salt is more preferable.

[0026] If the inorganic salt content exceeds 20% by mass, the coagulation rate becomes too fast, and a large number of voids are formed in the fiber, so that fibers having the desired physical properties cannot be obtained. As the inorganic salt, it is preferable to use chloride salts such as calcium chloride, magnesium chloride, and lithium chloride.

[0027] Here, in the spinning and coagulation process, 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 stably perform wet spinning, there is no particular need to limit the number of spinning holes, the spinning hole diameter, the arrangement state, etc. of the spinneret. For example, a multi-hole spinneret for staple fiber with 10 to 30,000 spinning holes and a spinning hole diameter of 0.03 to 0.2 mm can be used.

[0028] [Spinning and Coagulation Process] In the spinning and coagulation process, 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 stably perform wet spinning, there is no particular need to limit the number of spinning holes, the spinning hole diameter, the arrangement state, etc. of the spinneret. For example, a multi-hole spinneret for staple fiber with 10 to 30,000 spinning holes and a spinning hole diameter of 0.03 to 0.2 mm can be used.

[0029] In addition, the temperature of the dope when spinning 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 fibers of the present invention is an aqueous solution containing 1 to 20% by mass of an amide-based solvent, preferably an aqueous solution containing 3 to 15% by mass. The temperature of this aqueous solution is preferably in the range of 50 to 90°C.

[0030] Moreover, the coagulation bath can contain an inorganic salt such as calcium chloride or magnesium chloride, preferably 30% by mass or more, more preferably 35 to 45% by mass. As described above, the dope is spun from the spinneret into the coagulating liquid and passed through the coagulation bath to obtain a coagulated fiber.

[0031] [Washing step, boiling water stretching step] The coagulated fiber thus obtained is sufficiently washed in an aqueous washing bath and sent to the boiling water stretching step. The draw ratio in the boiling water stretching bath needs to be in the range of 1.1 to 5.0 times, more preferably in the range of 1.1 to 3.0 times. By performing the stretching within this ratio range and increasing the molecular chain orientation, the strength of the finally obtained fiber can be ensured.

[0032] [Dry heat treatment step] Preferably, a dry heat treatment step is performed on the fiber that has undergone the above washing and stretching steps. In the dry heat treatment step, the fiber washed in the above washing step is dry heat treated in the range of 100 to 250°C. Preferably, it is dry heat treated in the range of 100 to 200°C. Also, the dry heat treatment is preferably performed under a fixed length. The temperature of the above dry heat treatment refers to the set temperature of fiber heating means such as a hot plate or a heating roller.

[0033] [Thermal stretching step] In the present invention, a thermal stretching step is performed on the fiber that has undergone the above dry heat treatment step. In the thermal stretching step, stretching is performed 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. If it is less than 290°C, high magnification stretching cannot be performed, so it is unsuitable. If it exceeds 380°C, there is a possibility of fiber discoloration and thread breakage. In the heat drawing process, the draw ratio needs to be in the range of 2.0 to 10.0 times, preferably in the range of 3.0 to 10.0 times. Note that the temperature of the heat drawing treatment refers to the set temperature of fiber heating means such as a hot plate and a heating roller.

[0034] And, the total draw ratio of the boiling water draw ratio and the heat draw ratio in the present invention needs to be 7 times or more. If the total draw ratio is less than 7 times, the target strength cannot be achieved. Therefore, the boiling water draw ratio and the heat draw ratio need to be appropriately adjusted in view of the process conditions. The breaking strength of the high heat-resistant toughness fiber obtained by the above method is 7 to 15 cN / dtex, and the lower limit is more preferably 8.0 cN / dtex or more.

[0035] When the breaking strength is less than 7.0 cN / dtex, it is insufficient as the strength for the high toughness aimed at by the present invention. Also, the breaking elongation needs to be 10% to 30%, preferably 15% to 25%, and more preferably 20% to 25% or more. When the breaking elongation is less than 10%, the elongation is not sufficient, so the high toughness property cannot be sufficiently exhibited. When the breaking elongation exceeds 30%, it becomes difficult to obtain sufficient strength.

[0036] The melting point of the high heat-resistant toughness fiber of the present invention needs to be 290 °C or higher, preferably 300 °C or higher. When the melting point is lower than 290 °C, the performance as a heat-resistant fiber cannot be exhibited.

[0037] Also, in the high heat-resistant toughness fiber of the present invention, the dry heat dimensional change rate at 250 °C is preferably less than 2%, more preferably 1.5% or less, still more preferably 1.0% or less, and particularly preferably 0.5% or less. When the dry heat dimensional change rate becomes 2% or more, the performance as a heat-resistant fiber cannot be exhibited.

Examples

[0038] Hereinafter, the present invention will be described in detail by way of examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples. Each physical property value in the examples and comparative examples was measured by the following method.

[0039] [Weight average molecular weight Mw] In accordance with JIS-K-7252, analysis was carried out using a high-performance liquid chromatography apparatus equipped with a column for size exclusion chromatography, and measurement was performed using dimethylformamide (containing 0.01 mol% lithium chloride) as the developing solvent. As the standard molecular weight sample, a polystyrene set manufactured by Sigma-Aldrich (peak top molecular weight Mp = 400 to 2,000,000) was used.

[0040] [Single fiber fineness] In accordance with JIS-L-1015, measurement was carried out in accordance with Method A for positive fineness, and the apparent fineness was indicated.

[0041] [Breaking strength, elongation at break] Using a tensile testing machine (manufactured by Instron, model: 5565), measurement was carried out in accordance with JIS-L-1015 under the following conditions. (Measurement conditions) Grip interval: 20 mm Initial load: 0.044 cN (1 / 20 g / dtex) Tensile speed: 20 mm / min

[0042] [Dry heat dimensional change rate] In accordance with JIS-L-1013, measurement was carried out in accordance with Method B, and the dimensional change rate at 250 °C was determined.

[0043] [Melting point of fiber] The melting point of the fiber was determined by thermomechanical analysis in accordance with JIS-K-7197. Among the peaks of the obtained sample, the peak top temperature of the peak detected on the high temperature side or the temperature at which peak detection became impossible due to fiber melting was defined as the melting point.

[0044] [Example 1] By interfacial polymerization according to Japanese Patent Publication No. 47-10863, a copolymerized aramid polymer powder was synthesized in which the meta-phenylenediamine and isophthaloyl monomer units accounted for 67 mol% of the total, and the para-phenylenediamine and terephthaloyl monomer units accounted for 33 mol%. At this time, both isophthaloyl chloride and terephthaloyl chloride were used as the acid chloride monomers so that the weight ratio was 2:1. Also, both meta-phenylenediamine and para-phenylenediamine were used as the amine monomers so that the weight ratio was 2:1. The weight average molecular weight was 800,000. This polymer powder and calcium chloride were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a transparent polymer solution. At this time, the mass concentration of the copolymerized aramid polymer in the polymer solution was adjusted to 16%, and calcium chloride was adjusted to 3%.

[0045] This polymer solution was heated to 85 °C to obtain a spinning dope, and was extruded and spun from a spinneret with a circular discharge hole having a pore diameter of 0.1 mm and 100 holes into a coagulation bath at 85 °C. The composition of this coagulation bath was 44% by mass calcium chloride, 3% by mass NMP, and the remaining water was 53% by mass. After passing through at a yarn speed of 5.0 m / min with an immersion length (effective coagulation bath length) of 100 cm, it was once drawn out into the air.

[0046] This coagulated yarn was washed with water in the first to second water washing baths, and the total immersion time at this time was 200 seconds. The temperatures of the first to second aqueous washing baths were 20 °C and 30 °C water, respectively. This washed yarn was stretched 2.4 times in boiling water at 90 °C, and then immersed in warm water at 90 °C for 40 seconds and washed.

[0047] Next, after heat treatment by winding around a roller with a surface temperature of 170 °C, it was stretched 4.5 times on a hot plate with a surface temperature of 325 °C to obtain wholly aromatic polyamide fibers. The obtained fibers had a fineness of 1.3 dtex, a breaking strength of 10.4 cN / dtex, an elongation at break of 23%, a melting point of 307 °C, and a dry heat dimensional change rate at 250 °C of 1.00%.

[0048] [Example 2] By interfacial polymerization according to Example 1, a copolymerized aramid polymer powder in which the meta-phenylenediamine and isophthaloyl monomer units are 60 mol% of the whole and the para-phenylenediamine and terephthaloyl monomer units are 40 mol% was synthesized. At this time, both isophthaloyl chloride and terephthaloyl chloride were used as the acid chloride monomers so that the weight ratio was 3:2. Also, both meta-phenylenediamine and para-phenylenediamine were used as the amine monomers so that the weight ratio was 3:2. The weight average molecular weight was 640,000. This polymer powder and calcium chloride were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a transparent polymer solution. At this time, the mass concentration of the copolymerized aramid polymer in the polymer solution was adjusted to 16% and calcium chloride was adjusted to 3%.

[0049] This polymer solution was heated to 85 °C to obtain a spinning dope, and it was discharged from a spinneret with a circular orifice diameter of 0.1 mm and 100 holes into a coagulation bath at 85 °C for spinning. The composition of this coagulation bath was 44 mass% calcium chloride, 3 mass% NMP, and the remaining water was 53 mass%. After passing through at a yarn speed of 5.0 m / min with an immersion length (effective coagulation bath length) of 100 cm, it was once drawn out into the air. This coagulated yarn was washed with water in the first to second water washing baths, and the total immersion time at this time was 200 seconds. The temperatures of the first to second aqueous washing baths were 20 °C and 30 °C water, respectively. This washed yarn was stretched 2.5 times in boiling water at 90 °C, and then immersed in warm water at 90 °C for 40 seconds for washing. Next, it was wound around a roller with a surface temperature of 170 °C for dry heat treatment, and then stretched 3.5 times with a hot plate with a surface temperature of 330 °C to obtain wholly aromatic polyamide fibers.

[0050] The obtained fibers had a fineness of 1.8 dtex, a breaking strength of 9.2 cN / dtex, an elongation at break of 22%, a melting point of 319 °C, and a dry heat dimensional change rate at 250 °C of 0.70%. The obtained fibers had a fineness of 1.8 dtex, a breaking strength of 9.2 cN / dtex, an elongation at break of 22%, a melting point of 319 °C, and a dry heat dimensional change rate at 250 °C of 0.70%.

[0051] [Example 3] By interfacial polymerization according to Example 1, a copolymerized aramid polymer powder was synthesized in which m-phenylenediamine and isophthaloyl monomer units were 56 mol% of the whole, and p-phenylenediamine and terephthaloyl monomer units were 44 mol%. At this time, both isophthaloyl chloride and terephthaloyl chloride were used as acid chloride monomers so that the weight ratio was 5:4. Also, both m-phenylenediamine and p-phenylenediamine were used as amine monomers so that the weight ratio was 5:4. The weight average molecular weight was 450,000. This polymer powder and calcium chloride were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a transparent polymer solution. At this time, the mass concentration of the copolymerized aramid polymer in the polymer solution was adjusted to 20%, and calcium chloride was adjusted to 2%.

[0052] This polymer solution was heated to 85 °C to obtain a spinning dope, and was extruded and spun from a spinneret with a circular orifice having a pore diameter of 0.1 mm and 100 holes into a coagulation bath at 85 °C. The composition of this coagulation bath was 44 mass% calcium chloride, 3 mass% NMP, and the remaining water was 53 mass%. After passing through at a yarn speed of 5.0 m / min with an immersion length (effective coagulation bath length) of 100 cm, it was once drawn out into the air.

[0053] This coagulated yarn was washed with water in the first to second water washing baths, and the total immersion time at this time was 200 seconds. The temperatures of the first to second aqueous washing baths were 20 °C and 30 °C water, respectively. This washed yarn was stretched 2.4 times in boiling water at 90 °C, and then immersed in warm water at 90 °C for 40 seconds and washed.

[0054] Next, after winding around a roller with a surface temperature of 170 °C and performing dry heat treatment, it was stretched 4.0 times on a hot plate with a surface temperature of 315 °C to obtain wholly aromatic polyamide fibers. The obtained fibers had a fineness of 1.54 dtex, a breaking strength of 11.1 cN / dtex, an elongation at break of 24%, a melting point of 313 °C, and a dry heat dimensional change rate at 250 °C of 0.30%.

[0055] [Comparative Example 1] By interfacial polymerization according to Example 1, a copolymerized aramid polymer powder in which the meta-phenylenediamine and isophthaloyl monomer units are 75 mol% of the whole and the para-phenylenediamine and terephthaloyl monomer units are 25 mol% was synthesized. At this time, both isophthaloyl chloride and terephthaloyl chloride were used as the acid chloride monomers so that the weight ratio was 3:1. Also, both meta-phenylenediamine and para-phenylenediamine were used as the amine monomers so that the weight ratio was 3:1. The weight average molecular weight was 610,000. This polymer powder and calcium chloride were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a transparent polymer solution. At this time, the mass concentration of the copolymerized aramid polymer in the polymer solution was adjusted to 21% and calcium chloride was adjusted to 3%.

[0056] This polymer solution was spun under the conditions of Example 1 to obtain wholly aromatic polyamide fibers. At this time, the boiling water draw ratio was 2.4 times and the hot plate draw ratio was 3.0 times. The obtained fibers had a fineness of 1.7 dtex, a breaking strength of 4.6 cN / dtex, an elongation at break of 33%, a melting point of 333 °C, and a dry heat dimensional change rate at 250 °C of 0.87%.

[0057] [Comparative Example 2] By interfacial polymerization according to Japanese Patent Publication No. Sho 47-10863, a copolymerized aramid polymer powder in which the meta-phenylenediamine and isophthaloyl monomer units are 33 mol% of the whole and the para-phenylenediamine and terephthaloyl monomer units are 67 mol% was synthesized. At this time, both isophthaloyl chloride and terephthaloyl chloride were used as the acid chloride monomers so that the weight ratio was 1:2. Also, both meta-phenylenediamine and para-phenylenediamine were used as the amine monomers so that the weight ratio was 1:2. Since this polymer did not show good solubility in solvents such as NMP, it could not be spun.

[0058] [Comparative Example 3] When physical properties of wholly aromatic polyamide fibers (Teijin Limited's "Conex") in which the meta-phenylenediamine and isophthaloyl monomer units are 100 mol% of the whole were measured, the fineness was 2.2 dtex, the breaking strength was 4.9 cN / dtex, the breaking elongation was 40%, the melting point could not be measured (400 °C or higher), and the dry heat dimensional change rate at 250 °C was 0.20%.

[0059] [Comparative Example 4] When physical properties of wholly aromatic polyamide fibers (Teijin Limited's "Twaron" (registered trademark)) consisting of 100 mol% of para-phenylenediamine and terephthaloyl monomer units were measured, the fineness was 2.0 dtex, the breaking strength was 21 cN / dtex, the breaking elongation was 3%, the melting point could not be measured (400 °C or higher), and the dry heat dimensional change rate at 250 °C was 0%. The physical properties of the fibers obtained in the above Examples and Comparative Examples are shown in Table 2.

[0060] [Table 2] [Industrial Applicability]

[0061] The high heat-resistant toughness fibers obtained in the present invention have an excellent balance of physical properties of strength, elongation, and heat resistance. Therefore, they can be suitably used in applications where general-purpose fibers were used at the sacrifice of heat resistance, or in applications where mechanical properties were compensated by a combination of multiple fibers. Further, they can be applied to a novel high heat-resistant toughness material having appropriate strength and flexibility in reinforcing material applications, for example, a material in the rubber reinforcement field where a large amount of deformation is involved and strength is required.

Claims

**Claim 1**: A high heat-resistant toughness fiber contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, has a breaking strength of 7 to 15 cN / dtex, an elongation at break of 15 to 30%, and a melting point of 290 °C or higher. **Claim 2** The high heat-resistant toughness fiber according to claim 1, wherein the dry heat dimensional change rate at 250 °C is less than 2%. **Claim 3** The high heat-resistant toughness fiber according to claim 1 or 2, wherein the high heat-resistant toughness fiber is composed of a copolyaramid polymer having a structure containing metaphenyleneterephthalamide units and metaphenylenisophthalamide units, and paraphenyleneterephthalamide units and / or paraphenylenisophthalamide units. **Claim 4** A high heat-resistant toughness fiber contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, the molar ratio of metaphenylenediamine and / or isophthaloyl monomer units to paraphenylenediamine and / or terephthaloyl monomer units is in the range of more than 40 and less than 70: more than 30 and not more than 60, the breaking strength is 7 to 15 cN / dtex, the elongation at break is 10 to 30%, and the melting point is 290 °C or higher. **Claim 5** A method for producing a high heat-resistant toughness fiber, using a copolyaramid polymer having a structure containing metaphenyleneterephthalamide units and / or metaphenylenisophthalamide units, and paraphenyleneterephthalamide units and / or paraphenylenisophthalamide units, each of the amide units contains at least three types of structures selected from the group consisting of metaphenylenediamine, paraphenylenediamine, isophthaloyl, and terephthaloyl, the molar ratio of metaphenylenediamine and / or isophthaloyl monomer units to paraphenylenediamine and / or terephthaloyl monomer units is in the range of more than 40 and less than 70: more than 30 and not more than 60, and a weight average molecular weight of 400,000 to 1,000,000, and producing by the following steps (1) to (5) and satisfying the production conditions of (6). Dissolve the copolyaramid polymer in an amide solvent in the range of 10 to 30% by mass to obtain a spinning dope, and pass it through a spinneret. Spin it into an aqueous coagulation bath containing 1 to 20% by mass of an amide solvent for coagulation. Wash it with water in an aqueous washing bath, and then stretch it in a boiling water stretching bath in the range of 1.1 to 5.0 times. Perform dry heat treatment in the range of 100 to 250 °C. While applying heat treatment in the range of 290 to 380 °C, perform hot stretching at a draw ratio in the range of 2.0 to 10.0 times. The total draw ratio of the boiling water draw ratio and the hot draw ratio is 7 times or more.

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