JP7315378B2 - Meta-type wholly aromatic polyamide fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a meta-type wholly aromatic polyamide fiber having a toughness value represented by the square root of the product of strength and elongation of 15 or more and having a small amount of residual solvent in the fiber, and a method for producing the same. More specifically, the present invention relates to a method for producing a meta-type wholly aromatic polyamide fiber having a toughness value of 15 or more and a residual solvent amount of 0.1% by mass or less in the fiber by wet-spinning a meta-type wholly aromatic polyamide dope having a weight average molecular weight of 200,000 to 600,000 containing an inorganic salt with a high-concentration inorganic salt coagulating solution.

Conventionally, it is well known that wholly aromatic polyamides produced from aromatic diamines and aromatic dicarboxylic acid dihalides are excellent in heat resistance and flame retardancy. Among such wholly aromatic polyamides, fibers of meta-type wholly aromatic polyamides (hereinafter sometimes referred to as meta-aramids) typified by polymetaphenylene isophthalamide are particularly useful as heat-resistant and flame-retardant fibers. Taking advantage of these properties, it is used for disaster prevention and safety clothing such as protective clothing, and for industrial applications such as filters and electronic parts.

In recent years, due to the sophistication of society, the need for lighter weight and higher strength has increased in each of the above applications, and spun yarns made of high-strength meta-aramid fibers with a fiber breaking strength exceeding 4.5 cN / dtex are suitably used.

Furthermore, in each of the above applications, there is an increasing demand for further improvement in workability and fatigue resistance, and in order to satisfy it, it is necessary to improve the elongation while ensuring the breaking strength of the fiber, that is, to increase toughness.

In particular, the elongation of fibers is one of the important factors in clothing applications, and clothing made of high-elongation fibers exhibits flexibility, leading to improved texture and comfort. Therefore, if a meta-aramid fiber having high elongation while satisfying breaking strength is obtained, its industrial value is extremely high.

It is also well known that meta-aramid is soluble in amide-based polar solvents and can be made into fibers from the polymer solution by methods such as dry spinning, wet spinning, semi-dry and semi-wet spinning. On the other hand, if the amide-based solvent remains in the fiber, it not only causes coloring and yellowing of the fiber in a high-temperature atmosphere, but also has an adverse effect on the human body when used for clothing. For this reason, the development of a spinning method for obtaining fibers with little residual solvent is important in the production of meta-aramid fibers.

Here, in the conventionally known dry spinning (for example, Japanese Patent Publication No. 35-14399), in the fibrous polymer solution spun from the spinneret, the solvent evaporates and dries from the vicinity of the surface of the formed fibrous material, so that a dense and strong skin layer is formed on the fiber surface. Therefore, even if the fibrous material is subsequently washed with water or the like, it is difficult to sufficiently remove the remaining solvent.

On the other hand, in wet spinning, a method has been developed in which the formation of a skin layer is suppressed and a fine void structure is formed inside the fiber, thereby effectively washing away the residual solvent. for example,
(a) A method in which a meta-aramid polymer solution substantially free of salts is discharged into a coagulation bath consisting of an amide solvent and water to be coagulated to form a fibrous material (filament), followed by drawing in a plastic drawing bath consisting of an amide solvent and water, followed by washing with water and heat treatment (JP-A-2001-303365, JP-A-2003-301326, JP-A-2003-342832, etc.);
(b) A method in which a polymer solution composed of an amide solvent containing meta-aramid and a salt is discharged into a coagulation bath composed of an amide solvent and water and substantially free of salts to solidify it as a porous linear body, which is then stretched in a plastic stretching bath composed of an aqueous solution of an amide solvent, and then subjected to heat treatment after washing with water (JP-A-2005-232598).
(c) A method in which a meta-aramid polymer solution containing water and calcium chloride produced by solution polymerization in an amide-based solvent and neutralized with calcium hydroxide, calcium oxide, etc. is spun in an aqueous coagulation bath containing substantially no inorganic salt and having an amide-based solvent concentration of 45 to 60% by mass to form a fibrous material (International Publication No. 2007/089008 pamphlet, International Publication No. 2011/118022 pamphlet).
etc. are exemplified.

The meta-aramid fibers produced by these spinning methods use a mixed solvent of amide solvent and water as a coagulation bath, and during the coagulation process, the diffusion of the solvent out of the system from the filaments and the infiltration of the coagulation liquid components into the filaments are strictly controlled to form a very fine void structure and suppress the formation of a skin structure. As a result, it is reported that the amount of residual solvent in the fiber after washing with water, drying, and heat treatment is all 0.1% by mass or less, and that it has the minimum necessary strength for use in each of the above applications.

However, the coagulation method using such a mixed solvent of amide solvent and water requires very strict setting of temperature, coagulation liquid composition, and polymer molecular weight condition, and the coagulation thread has a porous structure, so the breaking strength is very weak, and it needs to be handled under a special environment to increase the strength by stretching.

In addition, in each of the above-cited documents, the breaking elongation of the obtained fibers is often about 30%, and meta-aramid fibers with high elongation have not been reported. Therefore, in order to industrially obtain meta-aramid fibers with high toughness, that is, high strength and high elongation while reducing residual solvent, very strict process control is required, which makes stable production of meta-aramid fibers difficult.

Furthermore, as a wet spinning method for meta-aramid fibers, the following methods have been reported in addition to those mentioned above. for example,
(d) A wet spinning method in which meta-aramid polymer powder is redissolved in an amide solvent, and then 15 to 25% by mass of a meta-type wholly aromatic polyamide solution is spun into an aqueous coagulation bath containing 35 to 45% by mass of a high-concentration inorganic salt for coagulation (JP-B-48-17551).

In the above method, when the spun fibrous polymer is introduced into an aqueous coagulating bath or an aqueous coagulating bath containing a high concentration of inorganic salt, the solvent is unidirectionally desorbed from the vicinity of the surface of the fibrous polymer into the aqueous coagulating bath, forming a firm skin layer similar to dry spinning. Therefore, it is difficult to sufficiently remove the solvent remaining in the fiber, but since the skin layer provides high coagulated yarn strength, stable production is possible throughout the spinning process, and the final fiber strength exceeds 4.5 cN / dtex.

However, even with such a spinning method, a meta-aramid fiber that satisfies high strength and high elongation, that is, has high toughness, has not been reported. If a manufacturing method with high strength, high elongation and low residual solvent amount can be developed, it will be very useful industrially.

Japanese Patent Publication No. 35-14399 Japanese Patent Application Laid-Open No. 2001-303365 Japanese Patent Application Laid-Open No. 2003-301326 JP 2003-342832 A JP-A-2005-232598 International Publication No. 2007/089008 pamphlet International Publication No. 2011/118022 pamphlet Japanese Patent Publication No. 48-17551

An object of the present invention is to solve the problems in the prior art, and to provide a meta-aramid fiber having excellent properties such as heat resistance, flame retardancy, and mechanical properties, which has low residual solvent, high breaking strength, and high elongation, so that it can be suitably used for protective clothing.

As a result, the present invention is conducted on a firm consideration to solve the above issues, and when skillfully controlling the weight average molecular weight of the meta -type full aromatic polyamide, the amount of residual solvent is small and the intensity of fibers is small and the intensity of fibers is small and the intensity of fibers is small and the amount of fibers is small. The found that the toughness value indicated by the square root of the accumulation of 15 or more can be obtained, and the present invention has been completed, and the present invention has been completed.

That is, according to the present invention,
1.紡糸液が、塩化カルシウム、塩化マグネシウム、及び塩化リチウムからなる群から選ばれた少なくとも1種の無機塩を含む、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、及びジメチルアセトアミド（ＤＭＡｃ）からなる群から選ばれた少なくとも1種のアミド系極性溶媒溶液であり、凝固浴が、塩化カルシウム及び塩化マグネシウムからなる群から選ばれた少なくとも1種の無機塩を含む、ＮＭＰ水溶液であって、該紡糸液を該凝固浴中に紡出して凝固させることにより得られ、且つ下記測定方法にて測定した重量平均分子量が２０万～６０万のメタ型全芳香族ポリアミドからなる繊維であって、該繊維の破断強度と破断伸度との積の平方根で示されるタフネス値が１５～１８．４、繊維中に残存する溶媒量が０．１質量％以下であることを特徴とするメタ型全芳香族ポリアミド繊維、
(Method for measuring weight average molecular weight)
According to JIS-K-7252, analysis was performed using a high performance liquid chromatography apparatus equipped with a column for size exclusion chromatography, and dimethylformamide (containing 0.01 mol % of lithium chloride) was used as a developing solvent. As a standard molecular weight sample, a Sigma-Aldrich polystyrene set (peak top molecular weight Mp = 400 to 2000000) was used.
as well as,
2.メタ型全芳香族ポリアミドの濃度が１０～３０質量％、塩化カルシウム、塩化マグネシウム、及び塩化リチウムからなる群から選ばれた少なくとも1種の無機塩の濃度が１～２０質量％の、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、及びジメチルアセトアミド（ＤＭＡｃ）からなる群から選ばれた少なくとも1種のアミド系極性溶媒溶液を湿式紡糸することによりメタ型全芳香族ポリアミド繊維を製造するに際し、重量平均分子量が２０万～６０万のメタ型全芳香族ポリアミドを用い、該極性溶媒溶液を３０ ～４５質量％の塩化カルシウム及び塩化マグネシウムからなる群から選ばれた少なくとも1種の無機塩および３ ～１５質量％のＮＭＰを含む水性凝固浴中に紡出した後凝固せしめることを特徴とするメタ型全芳香族ポリアミド繊維の製造方法、
is provided.

According to the present invention, a meta-type wholly aromatic polyamide fiber having a small amount of residual solvent and a toughness value of 15 or more, which is indicated by the square root of the product of the strength and elongation of the fiber, can be obtained. In addition, since the amount of residual solvent contained in the fibers is small, not only is the coloring and yellowing of the fibers suppressed in a high-temperature atmosphere, but there is no adverse effect on the human body when used for clothing.

The present invention will be described in detail below.
The meta-type wholly aromatic polyamide constituting the meta-aramid fiber of the present invention is composed of a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid component, and within a range that does not impair the object of the present invention, other copolymerization components such as para-type may be copolymerized.

Particularly preferably used in the present invention is a meta-type wholly aromatic polyamide containing metaphenylene isophthalamide units as a main component from the viewpoint of mechanical properties, heat resistance, and flame retardancy. In the meta-type wholly aromatic polyamide composed of metaphenylene isophthalamide units, metaphenylene isophthalamide units preferably account for 90 mol% or more, more preferably 95 mol% or more, and particularly preferably 100 mol, of all repeating units.

Examples of the meta-aromatic diamine component that is a raw material for the meta-type wholly aromatic polyamide include metaphenylenediamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylsulfone, etc., and derivatives having substituents such as halogens and alkyl groups having 1 to 3 carbon atoms on the aromatic ring thereof, such as 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, and 2,6-diaminochlorobenzene. Among them, meta-phenylenediamine alone or a mixed diamine containing meta-phenylenediamine in an amount of 85 mol % or more, preferably 90 mol % or more, particularly preferably 95 mol % or more, is preferable.

Examples of raw materials for the meta-aromatic dicarboxylic acid component constituting the meta-type wholly aromatic polyamide include meta-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 having substituents such as halogens and alkoxy groups having 1 to 3 carbon atoms on the aromatic rings thereof, such as 3-chloroisophthalic acid chloride. Among them, isophthaloyl chloride itself or a mixed carboxylic acid halide containing 85 mol % or more, preferably 90 mol % or more, particularly preferably 95 mol % or more of isophthaloyl chloride is preferable.

As a method for polymerizing the meta-aramid, a method of isolating a polymetaphenylene isophthalamide polymer powder by contacting an organic solvent system (e.g., tetrahydrofuran), which is not a good solvent for the produced polyamide containing metaphenylenediamine and isophthalic acid chloride, with an aqueous solution system containing an inorganic acid acceptor and a soluble neutral salt (JP-B-47-10863), or a method of solution-polymerizing the above-mentioned diamine and acid chloride in an amide solvent, followed by neutralization with calcium hydroxide, calcium oxide, etc. Japanese Patent Application Laid-Open No. 8-074121, Japanese Patent Application Laid-Open No. 10-88421), etc., but not limited thereto.

The weight-average molecular weight of the meta-aramid used in the present invention must be in the range of 200,000 to 600,000 according to the analysis method described later, from the viewpoint of forming a fiber with a small amount of residual solvent and high toughness, that is, high strength and high elongation.

Further, in order to obtain a fiber that reliably achieves a residual solvent amount of 0.1% or less, a polymer having a weight average molecular weight in the range of 300,000 to 500,000 is preferable. Furthermore, a polymer having a weight average molecular weight in the range of 400,000 to 500,000 is particularly preferable in order to obtain a fiber having high strength, high elongation, especially toughness value of 15 or more, and reduced amount of residual solvent.

A mixture of a low molecular weight polymer and a high molecular weight polymer can also be used as the polymer having the molecular weight specified in the present invention, and the overall molecular weight may be the desired value by adjusting the mixing ratio. For example, if 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 overall weight-average molecular weight is 500,000, there is no problem in using the mixture in the present invention.

On the other hand, if the molecular weight is less than 200,000, a fiber with strength cannot be obtained, and the target toughness value cannot be achieved.

The meta-type wholly aromatic polyamide fiber of the present invention is produced by using the meta-aramid polymer obtained by the above production method, for example, through the following steps of spinning solution preparation, spinning and coagulation, washing, boiling water drawing, dry heat treatment, and hot drawing.

In the spinning solution preparation step, the meta-aramid polymer is dissolved in a solvent to prepare a spinning solution (dope). In preparing the spinning solution, an amide solvent is usually used, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc). Among these, it is preferable to use NMP or DMAc from the viewpoint of solubility and handling safety.

The concentration of the solution may be appropriately selected from the viewpoint of the coagulation rate and the solubility of the polymer in the spinning/coagulation step, which is the next step, and is usually in the range of 10 to 30% by mass. In order to achieve stable spinning, the range of 15 to 25% by mass is more preferable.

In the present invention, it is necessary to introduce an inorganic salt into the dope, and the dope preferably contains 1 to 20% by mass of the inorganic salt, more preferably 1 to 10% by mass of the inorganic salt in order to obtain stable spinnability, and particularly preferably 2 to 5% by mass of the salt in order to obtain a fiber having a residual solvent amount of 0.1% or less and a toughness of 15 or more.

Here, 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, making it impossible to obtain a fiber having the desired physical properties. As inorganic salts, chloride salts such as calcium chloride, magnesium chloride and lithium chloride are preferably used.

In the spinning/coagulating step, the dope obtained above is spun into a coagulating liquid and coagulated. The spinning device is not particularly limited, and a conventionally known wet spinning device can be used. The number of spinning holes in the spinneret and the arrangement state of the spinneret are not particularly limited as long as they can be stably wet-spun. For example, a multi-hole spinneret for staple fibers having 10 to 30,000 holes and a spinning hole diameter of 0.03 to 0.2 mm may be used. The temperature of the dope during spinning from the spinneret is suitably in the range of 20 to 90.degree. C., preferably 70 to 90.degree.

As the coagulation bath used to obtain the fiber of the present invention, an aqueous solution containing 30% by mass or more, preferably 35 to 45% by mass of an inorganic salt such as calcium chloride or magnesium chloride, and 1 to 20% by mass, preferably 3 to 15% by mass of an amide solvent is used at a temperature in the range of 50 to 90°C. A method using an aqueous solution of an amide-based solvent that does not substantially contain inorganic salts has also been devised. However, such a coagulating solution does not form a skin on the surface of the coagulated yarn, so it is not possible to obtain a yarn with necessary and sufficient strength.

The coagulated yarn thus obtained is thoroughly washed in an aqueous washing bath and sent to a boiling water drawing step. The stretching ratio in the boiling water stretching bath is suitably 1.5 to 5.0 times, more preferably 2.0 to 4.0 times. In the present invention, the strength of the finally obtained fiber can be ensured by stretching within the range of the magnification and increasing the molecular chain orientation.

A dry heat treatment step is preferably performed on the fibers that have undergone the washing and drawing steps. In the dry heat treatment step, the fibers washed in the above washing step are subjected to dry heat treatment at a temperature of preferably 100 to 250°C, more preferably 100 to 200°C. Here, the dry heat treatment is not particularly limited, but is preferably performed under a constant length. The temperature of the dry heat treatment mentioned above refers to the set temperature of fiber heating means such as a hot plate and a heating roller.

In the present invention, the fiber subjected to the dry heat treatment is subjected to a hot drawing process. In the hot drawing step, drawing is performed while applying heat treatment at 300 to 380°C. A suitable draw ratio is 1.2 to 5.0 times, more preferably 1.5 to 3.5 times.

The meta-aramid fiber obtained by the above method has a toughness value of 15 or more and a residual solvent amount of 0.1% by mass or less. A toughness value of 15 or more is required, and 16 or more is particularly preferable. The amount of residual solvent must be 0.1% by mass or less, preferably 0.05% by mass or less. Furthermore, it is especially preferable that it is 0.01 mass % or less. If the amount of residual solvent exceeds 0.1% by mass, not only will the fibers be colored or yellowed in a high-temperature atmosphere, but there is also concern about adverse effects on the human body when used for clothing.

The breaking strength of the meta-aramid fiber obtained by the above method is preferably 4.5 cN/dtex or more. If the strength is less than 4.5 cN/dtex, even if the amount of residual solvent is 0.1% or less, problems such as difficulty in processability and deterioration in product durability in more advanced applications occur.

Further, the single fiber fineness of the meta-aramid fiber obtained by the above method is preferably 0.5 to 10.0 dtex. If the fineness is less than 0.5 dtex, process passability is poor, and if the fineness exceeds 10.0 dtex, the single yarn is too thick to achieve the target residual solvent amount of 0.1% or less.

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. Each physical property value in Examples and Comparative Examples was measured by the following methods.

[Weight average molecular weight Mw]
According to JIS-K-7252, analysis was performed using a high performance liquid chromatography apparatus equipped with a column for size exclusion chromatography, and dimethylformamide (containing 0.01 mol % of lithium chloride) was used as a developing solvent. As a standard molecular weight sample, a Sigma-Aldrich polystyrene set (peak top molecular weight Mp=400 to 2,000,000) was used.
[Single fiber fineness]
In accordance with JIS-L-1015, measurement was carried out in accordance with the A method of regular fineness, and the apparent fineness was expressed.
[Breaking strength, breaking elongation]
Using a tensile tester (manufactured by Instron, model: 5565), measurements were made under the following conditions based on JIS-L-1015.
(Measurement condition)
Grip interval: 20mm
Initial load: 0.044cN (1/20g/dtex)
Tensile speed: 20mm/min [Toughness value]
Using values of breaking strength (cN/dtex) and breaking elongation (%) measured by the above method, it was calculated by the following formula.
Toughness value = (breaking strength x breaking elongation) ^1/2
[Residual solvent amount]
1 mg of fiber was weighed and the amount of residual solvent was measured by pyrolysis gas chromatography. In order to determine the amount of solvent, a calibration curve was prepared using a standard sample and calculated from peak area values.

[Example 1]
A meta-aramid polymer powder having a weight average molecular weight of 470,000 and calcium chloride powder synthesized by solution polymerization and washed with water were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 25% and the mass concentration of calcium chloride was 2.5%.

This polymer solution was heated to 80° C. and spun into a coagulation bath at 80° C. through a spinneret having a hole diameter of 0.1 mm and 100 circular ejection holes. The composition of this coagulation bath was 35% by mass of calcium chloride, 3% by mass of NMP, and 62% by mass of the remaining water.

The coagulated filaments were washed with water in the first and second water washing baths for a total immersion time of 250 seconds. The first and second aqueous washing bath temperatures used were 20° C. and 30° C., respectively. Next, the washed yarn was stretched 2.7 times in boiling water at 90°C, then immersed in warm water at 90°C for 40 seconds and washed.

Next, after being wound around a roller having a surface temperature of 170° C. and subjected to a dry heat treatment, it was drawn 1.5 times with a hot plate having a surface temperature of 340° C. to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.6 dtex, a strength of 4.9 cN/dtex, an elongation of 50.0% and a toughness value of 15.7. Moreover, the amount of residual solvent was 0.001% by mass or less (detection limit).

[Example 2]
A meta-aramid polymer having a weight average molecular weight of 470,000 synthesized by solution polymerization was dissolved in NMP to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 22% and the mass concentration of calcium chloride was 5.0%.
This polymer solution was spun in the same manner as in Example 1 to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.6 dtex, a strength of 4.7 cN/dtex, an elongation of 57.5% and a toughness value of 16.4. Moreover, the amount of residual solvent was 0.001% by mass or less (detection limit).

[Example 3]
A meta-aramid polymer powder having a weight-average molecular weight of 530,000 and calcium chloride powder synthesized by interfacial polymerization and washed with water were dissolved in NMP to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 22% and the mass concentration of calcium chloride was 2.5%.

This polymer solution was heated to 85° C. and spun into a coagulation bath at 83° C. through a spinneret having a circular pore diameter of 0.1 mm and 2000 holes. The composition of this coagulation bath was 38% by mass of calcium chloride, 5% by mass of NMP, and 57% by mass of the remaining water.

The coagulated filaments were washed in the first to third water washing baths for a total immersion time of 360 seconds. The first to third aqueous washing bath temperatures used were 20, 30 and 50° C., respectively. Next, the washed yarn was stretched 2.2 times in boiling water at 90°C, then immersed in hot water at 90°C for 50 seconds and washed.

Next, after being wound around a roller having a surface temperature of 170° C. and subjected to a dry heat treatment, it was drawn 2.25 times with a hot plate having a surface temperature of 340° C. to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.0 dtex, a strength of 4.5 cN/dtex, an elongation of 65.9% and a toughness value of 17.2. Moreover, the residual solvent amount was 0.014% by mass.

[Example 4]
A meta-aramid polymer powder having a weight average molecular weight of 470,000 and calcium chloride powder synthesized by solution polymerization and washed with water were dissolved in NMP to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 22% and the mass concentration of calcium chloride was 5.0%.

This polymer solution was heated to 87° C. and spun into a coagulation bath at 85° C. through a spinneret having a hole diameter of 0.1 mm and 100 circular ejection holes. The composition of this coagulation bath was 41% by mass of calcium chloride, 15% by mass of NMP, and 44% by mass of the remaining water.

The coagulated filaments were washed with water in the first and second water washing baths for a total immersion time of 250 seconds. The first and second aqueous washing bath temperatures used were 20° C. and 30° C., respectively. Next, the washed yarn was stretched 2.4 times in boiling water at 90°C, then immersed in warm water at 90°C for 40 seconds and washed.

Next, after being wound around a roller with a surface temperature of 170° C. and subjected to a dry heat treatment, it was drawn 1.8 times with a hot plate having a surface temperature of 340° C. to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.3 dtex, a strength of 4.6 cN/dtex, an elongation of 62.7% and a toughness value of 17.0. Moreover, the amount of residual solvent was 0.001% by mass or less (detection limit).

[Example 5]
A meta-aramid polymer powder having a weight average molecular weight of 480,000 and calcium chloride powder synthesized by solution polymerization and washed with water were dissolved in NMP to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 22% and the mass concentration of calcium chloride was 5.0%.

This polymer solution was heated to 85° C. and spun into a coagulation bath at 83° C. through a spinneret having a circular pore diameter of 0.1 mm and 100 holes as a spinning dope. The composition of this coagulation bath was 41% by mass of calcium chloride, 15% by mass of NMP, and 44% by mass of the remaining water.

The coagulated filaments were washed with water in the first and second water washing baths for a total immersion time of 250 seconds. The first and second aqueous washing bath temperatures used were 20° C. and 30° C., respectively. Next, the washed yarn was stretched 2.4 times in boiling water at 90°C, then immersed in warm water at 90°C for 40 seconds and washed.

Next, after being wound around a roller with a surface temperature of 170° C. and subjected to a dry heat treatment, it was drawn 2.0 times with a hot plate having a surface temperature of 330° C. to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 1.2 dtex, a strength of 5.3 cN/dtex, an elongation of 63.6% and a toughness value of 18.4. Moreover, the amount of residual solvent was 0.001% by mass or less (detection limit).

[Comparative Example 1]
A meta-aramid polymer having a weight average molecular weight of 780,000 synthesized by solution polymerization was dissolved in NMP to obtain a transparent polymer solution. At this time, the mass concentration of the meta-aramid polymer was adjusted to 22% with respect to the polymer solution.
The polymer solution was spun in the same manner as in Example 1 to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.5 dtex, a strength of 4.8 cN/dtex, an elongation of 38.9% and a toughness value of 13.7. Moreover, the residual solvent amount was 8.8% by mass.

[Comparative Example 2]
A meta-aramid polymer powder having a weight average molecular weight of 800,000 synthesized by solution polymerization and calcium chloride powder were dissolved in NMP to obtain a transparent polymer solution. At this time, the polymer solution was adjusted so that the mass concentration of the meta-aramid polymer was 22% and the mass concentration of calcium chloride was 2.5%.
This polymer solution was spun in the same manner as in Example 1 to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.2 dtex, a strength of 4.6 cN/dtex, an elongation of 44.8% and a toughness value of 14.4. Moreover, the residual solvent amount was 0.25% by mass.

[Comparative Example 3]
A meta-aramid polymer powder having a weight average molecular weight of 520,000 synthesized by solution polymerization was dissolved in NMP to obtain a transparent polymer solution. At this time, the mass concentration of the meta-aramid polymer was adjusted to 22% with respect to the polymer solution.
This polymer solution was spun in the same manner as in Example 1 to obtain a meta-type wholly aromatic polyamide fiber.

The resulting fiber had a fineness of 2.3 dtex, a strength of 5.6 cN/dtex, an elongation of 29.3% and a toughness value of 12.8. Moreover, the residual solvent amount was 1.52% by mass.
Table 1 shows the physical properties of the meta-type wholly aromatic polyamide fibers obtained in Examples and Comparative Examples.

According to the present invention, a meta-type wholly aromatic polyamide fiber having a toughness value of 15 or more and a residual solvent amount of 0.1% by mass or less can be obtained. Therefore, when used as a fabric, flexibility is exhibited due to the high elongation, leading to improvement in texture and comfort. In addition, since it has a low residual solvent, it not only suppresses the coloring and yellowing of fibers in a high-temperature atmosphere, but also has no adverse effect on the human body when used for clothing.

Furthermore, the production method of the present invention improves the operability because the viscosity of the polymer used is low. In addition, since it is a technique that gives a coagulated yarn with high strength without strict control of spinning conditions, stable production can be carried out, and its industrial value is extremely high.

Claims (4)

紡糸液が、塩化カルシウム、塩化マグネシウム、及び塩化リチウムからなる群から選ばれた少なくとも1種の無機塩を含む、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、及びジメチルアセトアミド（ＤＭＡｃ）からなる群から選ばれた少なくとも1種のアミド系極性溶媒溶液であり、凝固浴が、塩化カルシウム及び塩化マグネシウムからなる群から選ばれた少なくとも1種の無機塩を含む、ＮＭＰ水溶液であって、該紡糸液を該凝固浴中に紡出して凝固させることにより得られ、且つ下記測定方法にて測定した重量平均分子量が２０万～６０万のメタ型全芳香族ポリアミドからなる繊維であって、該繊維の破断強度と破断伸度との積の平方根で示されるタフネス値が１５～１８．４、繊維中に残存する溶媒量が０．１質量％以下であることを特徴とするメタ型全芳香族ポリアミド繊維。
(Method for measuring weight average molecular weight)
According to JIS-K-7252, analysis was performed using a high performance liquid chromatography apparatus equipped with a column for size exclusion chromatography, and dimethylformamide (containing 0.01 mol % of lithium chloride) was used as a developing solvent. As a standard molecular weight sample, a Sigma-Aldrich polystyrene set (peak top molecular weight Mp=400 to 2,000,000) was used. The meta-type wholly aromatic polyamide fiber according to claim 1, which has a breaking strength of 4.5 to 5.3 cN/ dtex . 3. The meta-type wholly aromatic polyamide fiber according to claim 1, wherein the solvent remaining in the fiber is at least one amide solvent selected from the group consisting of N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide. When producing meta-type wholly aromatic polyamide fibers by wet spinning a solution of at least one amide-based polar solvent selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc), in which the concentration of the meta-type wholly aromatic polyamide is 10 to 30% by mass and the concentration of at least one inorganic salt selected from the group consisting of calcium chloride, magnesium chloride, and lithium chloride is 1 to 20% by mass, the weight-average molecular weight is Using a meta-type wholly aromatic polyamide of 200,000 to 600,000, the polar solvent solution is~45mass%ofat least one inorganic salt selected from the group consisting of calcium chloride and magnesium chloride and three~15mass%ofA method for producing a meta-type wholly aromatic polyamide fiber, characterized by spinning in an aqueous coagulating bath containing NMP and then coagulating the fiber.