JP4266799B2 - Method for producing fine aramid fiber - Google Patents

Description

  The present invention relates to a method for producing fineness aramid fibers. More specifically, the present invention relates to a production method capable of efficiently producing fine fineness aramid fibers having a single yarn fineness of 1.1 dtex or less.

  Functional fibers having characteristics such as high strength, high elastic modulus, and high heat resistance represented by para-type wholly aromatic polyamide fibers (aramid fibers) have excellent physical and chemical properties. This is an industrially very useful fiber. Further, as these functional fibers are used for a wide range of applications in recent years, lower single yarn fineness has been demanded as a market demand. For example, fiber paper made by binding short fibers made of para-type wholly aromatic polyamide with a binder is required to be further thinned. To that end, it is necessary to make the single yarn fineness finer. It becomes.

  Para-type wholly aromatic polyamide fibers represented by polyparaphenylene terephthalamide (PPTA) are generally made into fibers by spinning an optically anisotropic solution into an inert gas and then bringing it into contact with a coagulation liquid. The way to do is taken. For this reason, when producing a fiber having a low single yarn fineness, it is necessary to extremely reduce the nozzle diameter of the die, and there is a problem that higher die processing accuracy and severe spinning conditions are required.

  On the other hand, in the case of a wholly aromatic copolyamide fiber having an ether group in a part of the molecular chain as described in Japanese Patent Publication No. 1-15605, an isotropic solution of the copolyamide polymer is drawn from the die. After spinning into an inert gas, it is brought into contact with a coagulation liquid to form an unstretched yarn, and then the unstretched yarn is first pre-stretched 1.1 to 2.0 times at a temperature of 100 ° C. or lower, followed by Stretched 1.5 to 3.0 times at a temperature exceeding 100 ° C. and not exceeding 400 ° C., further stretching 3.0 to 5.0 times at a temperature exceeding 400 ° C. and not exceeding 550 ° C. A method of sequentially stretching 10 to 14 times has been proposed. For this reason, when single yarn fineness of the same degree as PPTA is finally produced, the single yarn fineness when discharging from the die can be increased to 10 to 14 times, so that fibers with low single yarn fineness are produced. In this case, there are many advantages from the viewpoint of spinning conditions as compared with the PPTA.

  As a method for producing such a copolyamide fiber having a low single yarn fineness, a method in which solidification conditions are improved based on the method described in Japanese Patent Publication No. 1-15605 is proposed in Japanese Patent No. 2922327. Yes. In this method, unstretched yarn having a high degree of uniformity is formed by employing specific coagulation conditions, and a multifilament ultrafine copolyamide fiber is efficiently obtained by thermally stretching the yarn. However, this method focuses on obtaining a uniform copolyamide undrawn yarn, and details of fiber properties suitable for subsequent hot drawing (super drawing) of 8 times or more are not described in detail. According to the inventor's study, when a multi-fine ultra-fine aramid fiber of 1.1 dtex or less was produced, the single yarn was easily cut in the heat drawing process as compared with a fiber of 1.67 dtex, which is a normal single yarn fineness. In particular, it has been found that the process tone is significantly deteriorated when the single yarn fineness is smaller than 0.83 dtex. As described above, although the copolyamide fiber as described above easily forms a fiber having a single yarn fineness lower than that of PPTA fiber, the process condition at the time of hot drawing is not yet satisfactory, and further improvement is desired. ing.

Japanese Patent Publication No. 1-15605 Japanese Patent No. 2922327

  The present invention has been made against the background of the above-described prior art, and an object of the present invention is to provide a method capable of efficiently producing a fine fineness aramid fiber having a single yarn fineness of 1.1 dtex or less.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have conducted pre-drawing of an undrawn yarn made of a specific copolyamide so that the birefringence is in the range of 0.08 to 0.18, and then 280 ° C. It has been found that if the above-described heat stretching is performed, the process stability is improved and the above-mentioned problems of the present invention can be achieved, and the present invention has been achieved.

  Thus, according to the present invention, “90 mol% or more of all repeating units are composed of aramids of the following repeating units (Chemical Formula 1) and (Chemical Formula 2), and the fineness of the single yarn is 0.1 to 1.1 dtex. In producing the fineness aramid fiber, the undrawn yarn made of the aramid is pre-drawn at a temperature of 100 ° C. or lower so that the birefringence is in the range of 0.08 to 0.18, and then at a temperature of 280 ° C. or higher. A method for producing a fineness aramid fiber, characterized by hot drawing. "

  According to the production method of the present invention, the stability of the hot stretching process is improved, and fine fineness aramid fibers can be produced efficiently.

  The aramid targeted by the present invention is a wholly aromatic polyamide in which 90 mol% or more of all repeating units are composed of the above repeating units (Chemical Formula 1) and (Chemical Formula 2). In particular, the molar ratio of the unit represented by (Chemical Formula 1) and the unit represented by (Chemical Formula 2) (the former / the latter) is preferably in the range of 3/1 to 1/3. In addition, the hydrogen atom of the aromatic group in the formula may be substituted with a halogen atom and / or a lower alkyl group having 1 to 4 carbon atoms. The intrinsic viscosity of the aramid (measured in 97.5% sulfuric acid at 30 ° C.) is suitably in the range of 2.0 to 5.0.

  In the production method of the present invention, the above-mentioned aramid is spun and drawn into a fine-fineness aramid fiber. The single-fiber fineness is in the range of 0.1 to 1.1 dtex, particularly in the range of 0.5 to 0.8 dtex. For things. When the single yarn fineness exceeds the above range, stable production can be achieved without using the production method of the present invention. On the other hand, when the amount is less than the above range, the discharge amount from the spinneret becomes low, so that stable discharge becomes difficult, and the spinning property becomes unstable.

  The method for spinning the aramid is not particularly limited, and a conventionally known method may be employed. For example, an isotropic solution in which the aramid is dissolved in an amide solvent such as N-methyl-2-pyrrolidone (NMP), N, N′-dimethylacetamide, N, N′-dimethylformamide or the like is obtained from a spinneret. After being discharged once in an inert gas, it is solidified by being immersed in an aqueous coagulation bath. At that time, it is preferable to add lithium chloride, calcium chloride or the like to the isotropic solution from the viewpoint of solubility of aramid. Also, it is preferable to add the amide solvent and / or lithium chloride or calcium chloride to the aqueous coagulation bath.

  When the wet yarn (undrawn yarn) pulled up from the coagulation bath is subjected to the heat drawing step described later as it is, the desired process stability intended by the present invention cannot be obtained, so that it is predrawn in the wet state. It is important to do. The degree of pre-drawing should be such that the birefringence of the fiber that has been pre-drawn and then dried is in the range of 0.08 to 0.18, preferably in the range of 0.14 to 0.18. When the birefringence is less than 0.08, the fiber made of the above-mentioned aramid which is rigid and has high linearity is substantially difficult to form because it tends to exceed 0.08 even before the preliminary drawing. . When it exceeds 0.18, since the molecular orientation is too large, it becomes difficult to stretch at a sufficient magnification in the next thermal stretching, and fluff and yarn breakage are likely to occur, which is not preferable.

  The pre-stretching conditions are arbitrary as long as the birefringence is in the above range, but the temperature is preferably 100 ° C. or less, particularly 40 to 60 ° C. The stretching atmosphere may be an inert gas or warm water, but warm water is particularly preferable, and the stretching ratio is suitably in the range of 1.05 to 1.50 times, particularly in the range of 1.10 to 1.40 times. Is preferable.

  The pre-stretched yarn is hot-drawn at a temperature of 280 ° C. or higher, preferably 300 to 550 ° C. after drying. In this case, it is divided into two or more stages, for example, first-stage drawn at about 300 ° C., then 500 The second-stage drawing method at about 0 ° C. is particularly preferable because high-strength fibers can be produced stably. In addition, the draw ratio of the hot drawing is 8 to 14 times, particularly 10 to 14 times in terms of the total draw ratio that is the product of the preliminary draw ratio, and when the heat drawing is performed in two or more stages. The first stage stretching ratio is preferably about 1.5 to 2.5 times.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, each physical-property value in an Example was measured with the following method.
(1) Single yarn fineness, breaking strength, breaking elongation and modulus Measured according to JIS-L1013.
(2) Birefringence index (Δn)
Using a polarizing microscope “ECLIPSE E600W POL” manufactured by Nikon Corporation, measurement was performed by an interference fringe method using green light (wavelength 576 nm).

[Examples 1 to 4, Comparative Example 1]
112.9 parts of N-methyl-2-pyrrolidone (NMP) having a moisture content of 100 ppm or less, 1.506 parts of paraphenylenediamine and 2.789 parts of 3,4'-diaminodiphenyl ether are placed in a reaction vessel at room temperature, and nitrogen is added. After dissolving in, 5.658 parts of terephthalic acid chloride was added with stirring. The reaction was finally carried out at 85 ° C. for 60 minutes to obtain a transparent viscous polymer solution. Next, 9.174 parts of NMP slurry containing 22.5 wt% calcium hydroxide was added to carry out a neutralization reaction. The intrinsic viscosity of the obtained polymer was 3.33.

  Using the obtained polymer solution, it was extruded into a coagulation bath of an NMP aqueous solution (concentration: 30% by weight) from a spinneret having 1000 holes and wet-spun. At this time, the distance between the spinneret surface and the coagulation bath was 10 mm. After the fiber drawn from the coagulation bath was washed with water, the undrawn yarn was pre-drawn in a water bath under the conditions shown in Table 1, and then subjected to one-step drawing or two-step drawing on a hot plate. Table 2 shows the physical properties and process tone (number of yarn breaks) of the drawn yarns obtained.

  Since the fine aramid fiber produced by the production method of the present invention has a soft texture, it has been developed to take advantage of its high strength even in the field of clothing that has been difficult to develop due to its high modulus. Is possible. Moreover, in the field of papermaking, since the single yarn fineness is small, it is possible to provide a thinner fiber paper.

Claims (5)

When 90% by mole or more of all repeating units are composed of aramids having the following repeating units (Chemical Formula 1) and (Chemical Formula 2), and when producing a fine fineness aramid fiber having a single yarn fineness of 0.1 to 1.1 dtex, An undrawn yarn made of aramid is pre-drawn so that the birefringence is in the range of 0.08 to 0.18 at a temperature of 100 ° C. or lower, and then hot drawn at a temperature of 280 ° C. or higher. Manufacturing method of fineness aramid fiber.

  The method for producing a fine aramid fiber according to claim 1, wherein the preliminary drawing is performed in water.   The method for producing a fineness aramid fiber according to claim 1 or 2, wherein the predrawing ratio is 1.05 to 1.50.   The manufacturing method of the fineness aramid fiber in any one of Claims 1-3 which heat-stretches more than 280 degreeC in two steps or more.   The method for producing a fineness aramid fiber according to any one of claims 1 to 4, wherein the total draw ratio is 8 to 14.