JP2020133028A - Finer meta-type wholly aromatic polyamide fiber and method for producing the same - Google Patents

Abstract

To provide a finer meta-type wholly aromatic polyamide fiber exhibiting high dispersibility in a resin medium because of having small variation in fiber diameter and having uniformity, smooth surface and long fiber length, and to provide a method for producing the same.SOLUTION: A meta-type wholly aromatic polyamide fiber having a fiber diameter of 5 to 30 μm is obtained by dry-spinning a meta-type wholly aromatic polyamide solution or wet-spinning the meta-type wholly aromatic polyamide solution into an aqueous coagulation bath containing an inorganic salt of 35 to 45 wt.% for coagulation. The meta-type wholly aromatic polyamide fiber is stirred in an inorganic salt-containing solvent.SELECTED DRAWING: Figure 1

Description

The present invention relates to a finely divided meta-type total aromatic polyamide fiber, and more specifically, a meta-type total aromatic polyamide fiber in which the meta-type total aromatic polyamide fiber is opened and split in the fiber axis direction to be finely divided. It relates to a group polyamide fiber and a method for producing the same.

Conventionally, it is well known that all aromatic polyamides produced from aromatic diamines and aromatic dicarboxylic acid dihalides are excellent in heat resistance and flame retardancy, and these all aromatic polyamides are amide-based polar solvents. It is also well known that it is soluble in and can be made into fibers from the polymer solution by methods such as dry spinning, wet spinning, and semi-dry semi-wet spinning.

Among such total aromatic polyamides, meta-type total aromatic polyamide fibers (hereinafter sometimes referred to as metaaramids) represented by polymethaphenylene isophthalamide are particularly useful as heat-resistant and flame-retardant fibers. By demonstrating these characteristics, it is used, for example, for disaster prevention and safety clothing such as protective clothing, and for industrial applications such as filters and electronic parts. In particular, as symbolized by recent advances in mobile communication devices and high-speed information processing devices, as electronic devices become smaller and lighter and have higher performance, they are smaller, lighter, and have higher capacity and higher performance that can withstand long-term storage. Expectations for batteries and capacitors are high, and they are widely applied, and parts development is progressing rapidly.

In order to respond to this, composite materials such as high-performance papers or resins typified by batteries / capacitor separators, electrically insulating papers, filter papers, and base materials for printed wiring boards have been developed. In the production of high-performance paper and composite materials using metaaramid, it is expected that the fineness of the fibers will improve the workability and dispersibility in structural materials.

As a spinning method for producing fine fine fibers, it is conceivable to reduce the pore diameter of the mouthpiece or to reduce the fineness of the spun fiber itself by increasing the draw ratio. However, an advanced technique is required to improve such a spinning method, and fine fibers having a fineness of about 0.1 dtex (fiber diameter 3 μm) or less are used for all aromatic polyamides, which cannot be melt-spun. Is impossible.

On the other hand, a method of finely reducing the produced fiber by processing has also been devised. Para-type total aromatic polyamide fibers represented by Twaron (registered trademark) can be fibrilized by beating or treatment with a specific chemical, and can be used as pulp.

For example, in Japanese Patent Application Laid-Open No. 3-152130 and JP-A-8-19633, a fibril having a large number of fine fibrils, which has been beaten by a homogenizer treatment under high pressure, is added to the papermaking raw material. It is disclosed that the paper sheet strength is improved by entanglement with each other, and a paper sheet having excellent heat resistance and electrical insulation can be obtained by reflecting the physical properties of the polymer itself.

Further, in Japanese Patent Application Laid-Open No. 2007-321310, an aramid dope obtained by dissolving aramid fiber waste in an amide-based solvent containing 30 to 150% by weight of an inorganic salt with respect to the aramid fiber waste is subjected to a shearing force by a beating action. A method for producing an aramid fibril by feeding and coagulating it in a precipitant is disclosed.

Further, in Japanese Patent Application Laid-Open No. 2010-222717, by applying cavitation energy by ultrasonic waves or high-pressure water flow to the fiber aggregate, at least a part of the fibers constituting the fiber aggregate is made into nanofibers, and the fibrillated fiber is produced. The manufacturing method to be given is disclosed.

In such a production method, since ultrafine fibers (fibrils) having a fiber diameter of several hundred nm or less and a fiber length of several μm or less can be obtained, it is expected that uniform dispersibility in structural materials will be improved. However, in reality, the obtained fibrillated fibers have many fluffs (branches) on the fiber surface, the fiber diameters vary greatly, and the fiber length itself is short, causing entanglement between the fibers and resulting in hairballs. As a result, the dispersion in the structural material becomes insufficient. From such a problem, in order to improve the dispersibility of fibers in a structural material or a solvent, the fiber diameter is several μm or less, but the fiber diameter is uniform so that entanglement between fibers does not occur, and the surface surface. Fine fibers with a smoothness and a fiber length of several mm are required.

Japanese Unexamined Patent Publication No. 3-152130 Special Fair 8-19633 Gazette JP-A-2007-321310 JP-A-2010-222717

As described above, in the use of reinforcing structural materials using short fibers, it is important to improve the dispersibility by increasing the fineness. However, there is a limit to ultrafineness in the spinning method by the conventional technique, and although ultrafine fibers can be obtained by fibrillation, it is difficult to give fibers having a uniform fiber diameter and a smooth surface. Therefore, fluffing due to entanglement of fibers Suppression was an issue.

An object of the present invention is to reduce the fineness of a meta-type total aromatic polyamide fiber, which cannot be achieved by such a background technique, because the fiber diameter is small, uniform, the surface is smooth, and the fiber length is long. It is an object of the present invention to provide a fineness meta-type total aromatic polyamide fiber that exhibits high dispersibility within and a method for producing the same.

As a result of diligent studies to solve the above problems, the inventor opened and cracked the fibers by stirring the meta-type total aromatic polyamide fibers produced under specific spinning conditions in a specific solution. It has been found that fibers occur and the desired fineness meta-type total aromatic polyamide fiber is obtained.

Thus, according to the present invention
A meta-type total aromatic polyamide fiber having a fiber diameter of 0.5 to 10 μm and a fiber length of 1 to 5 mm, wherein the surface of the meta-type total aromatic polyamide fiber is smooth. Type Total aromatic polyamide fiber and
A method for producing fine fiber made of meta-type total aromatic polyamide, in which a meta-type total aromatic polyamide solution is spun by dry spinning or in an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt to coagulate it. A method for producing a fineness meta-type total aromatic polyamide fiber, which comprises stirring a meta-type total aromatic polyamide fiber having a fiber diameter of 5 to 30 μm in an inorganic salt-containing solvent, which is obtained by wet spinning.
Is provided.

According to the present invention, a fineness meta-type total aromatic polyamide fiber having a fiber diameter of 0.5 to 10 μm and a fiber length of 1 to 5 mm can be obtained. Further, the fineness meta-type total aromatic polyamide fiber obtained by the present invention has a uniform thickness as compared with the conventionally known so-called fibrillated fiber, and the meta-type total aromatic polyamide fiber is cleaved and split. The surface is smooth because it is obtained.

Therefore, when the fineness meta-type total aromatic polyamide fiber obtained by the present invention is mixed with, for example, a structural material, it is possible to suppress fluffing in addition to high dispersibility due to fineness, and increase the adhesiveness of the structural material. Also, effective improvement of mechanical properties can be expected.

It is a surface photograph which exemplifies an example of the fineness meta-type total aromatic polyamide fiber obtained by this invention. It is a surface photograph which exemplifies another example of the fineness meta-type total aromatic polyamide fiber obtained by this invention. It is a surface photograph which exemplifies an example of the conventional fineness meta-type total aromatic polyamide fiber. It is a surface photograph which exemplifies another example of the conventional fineness meta-type total aromatic polyamide fiber. It is a surface photograph which exemplifies another example of the conventional fineness meta-type total aromatic polyamide fiber.

The "fine fiber" in the present invention is obtained by cleaving and splitting a thick fiber in the fiber axis direction, and is in the form of a short fiber having a fiber diameter of 0.5 to 10 μm and a fiber length of 1 to 5 mm. Refers to things.

In order to obtain such fibers, first, they are produced by dry spinning by a specific spinning method or wet spinning in which they are spun into an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt and coagulated. Here, the specific spinning method is a method in which the fiber structure becomes dense, and a method having a fine void structure in the fiber does not cause cleavage or splitting of the fiber and cannot be made fine. Therefore, it is necessary to adopt a dry spinning method in which the solvent is unilaterally extracted from the filament in the coagulation step, or a wet spinning method in which the solvent is spun into an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt and coagulated. Become.

Generally, the methods shown in (a) to (d) below are known as methods for producing metaaramid, and the metaaramid fibers produced by these methods form fine voids (porous structure) in the fibers. Therefore, it is not possible to make the fineness and uniform as in the present invention.
(A) A metaaramid polymer solution of an amide-based solvent is discharged from a spinneret into a high-temperature spinning tower, cooled with a low-temperature aqueous solution when it comes out of the spinning tower, and stretched in a plastic stretching bath. , A method of molding as a fiber having a very fine porosity and a density of 1.3 g / cm ³ or less (Japanese Patent Laid-Open No. 52-43930).
(B) A metaaramid polymer solution containing substantially no salts is discharged into a coagulation bath composed of an amide solvent and water and coagulated to form a fibrous substance (filament body), and then from the amide solvent and water. A method of washing with water and heat-treating after stretching in a plastic stretching bath (Japanese Patent Laid-Open Nos. 2001-303365, 2003-301326, 2003-342832, 2004-3049, JP-A-2004-3049, JP-A-2004-3049 2005-54315A, JP-A-2005-54335),
(C) A polymer solution composed of an amide solvent containing metaaramid and salts is discharged into a coagulation bath composed of an amide solvent and water and substantially free of salts to coagulate it as a porous linear body, followed by coagulation. A method of stretching in a plastic stretching bath composed of an aqueous solution of an amide-based solvent, washing the mixture with water, and then heat-treating it (Japanese Patent Laid-Open No. 2005-232598).
(D) A meta-aramid polymer solution containing calcium chloride and water produced by solution polymerization in an amide solvent and neutralizing with calcium hydroxide, calcium oxide, etc., in an amide solvent substantially free of inorganic salts. A method of spinning in an aqueous coagulation bath having a concentration of 45 to 60% by mass to form a fibrous substance (International Publication No. 2007/08900 Pamphlet).

On the other hand, the "fine fiber" in the present invention is a fine fiber obtained by cleaving and splitting a thick fiber in the fiber axis direction to make the fiber finer, and the fiber diameter is 0.5 to 10 μm and the fiber length is 1 to 5 mm. Refers to. Since the fineness fiber obtained by the present invention depends on the fiber diameter of the thick fineness fiber to be finely divided, it is difficult to obtain a fiber having a fiber diameter of 0.5 μm or less. Further, the fiber having a fiber diameter of 10 μm or more is a fiber that can be sufficiently obtained by a usual spinning method, and it is not necessary to apply the present invention.

As the meta-type total aromatic polyamide (hereinafter, meta-aramid) fiber used in the present invention, it is preferable to use one produced by the production method shown in the following (e) or (f).
(E) A polymetaphenylene isophthalamide solution is prepared by polymerizing metaphenylenediamine and isophthalate chloride in a low-temperature solution in N, N-dimethylacetamide, and then hydrochloric acid produced as a by-product in the solution is watered. A method for producing metaaramid fibers by neutralizing with calcium oxide to obtain a polymer solution containing calcium chloride and dry-spinning the obtained polymer solution (US Pat. No. 3,360,598).
(F) By contacting an organic solvent system (for example, tetrahydrofuran) containing a metaphenylenediamine salt and an isophthalate chloride, which is not a good solvent, with an aqueous solvent system containing an inorganic acid acceptor and a soluble neutral salt. A method in which a powder of a polymetaphenylene isophthalamide polymer is isolated (Japanese Patent Publication No. 47-10863), the polymer powder is redissolved in an amide solvent, and then wet-spun in an inorganic salt-containing aqueous coagulation bath (special). Kosho 48-17551).

In particular, in the production method (f), a wet spinning method is used in which a 15 to 25% by weight meta-type total aromatic polyamide solution is spun into an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt and coagulated. The obtained fiber is preferable.

Subsequently, a fine fineness method using the meta-aramid obtained by the method according to (e) or (f) above will be described.
Fine-fine fibers can be easily obtained by introducing the above-mentioned metaaramid fibers into an amide-based solvent containing an inorganic salt and subjecting them to shearing such as stirring. Lithium chloride, magnesium chloride, or lithium carbonate is preferably used as the inorganic salt, and dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethylacetamide (DMAc) are preferable as the amide solvent. Here, the concentration of the inorganic salt is preferably 1 to 10% by weight with respect to the solvent used, and the acceleration rate of fineness and the fiber diameter of the fineness can be adjusted by changing the concentration. The treatment temperature is preferably 0 to 30 ° C., and a temperature higher than this is unsuitable because the finely divided fibers are dissolved. The treatment time is appropriately adjusted according to the fiber diameter of the target fine fine fiber, but a treatment of about several hours is sufficient. The treated fibers are completely retained in shape by washing with water and collected by operations such as filtration.

The fineness meta-type total aromatic polyamide fiber thus obtained has a characteristic that the surface is smooth because it is obtained by cleaving and splitting a high-fineness meta-type total aromatic polyamide fiber. Here, "the surface is smooth" means a state in which fine fibrils do not exist on the fiber surface and fluffing does not occur due to entanglement of the fibril fibers even when kneaded, unlike the so-called fibrillated fibers conventionally known. To tell.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following contents. The physical property values in Examples and Comparative Examples were measured by the following methods.

[Fiber diameter and coefficient of variation]
Using a scanning electron microscope VE-8000 (manufactured by KEYENCE), 20 fibers were randomly measured at a magnification of 1000 times for a certain amount of fibers that had been split, and the average value was the fiber diameter. And said. In addition, the coefficient of variation was calculated from the average value and standard deviation. When the fiber cross section was not circular, the value having the largest fiber diameter in one fiber was defined as the fiber diameter.

[Fiber length]
Using a scanning electron microscope VE-8000 (manufactured by KEYENCE), 20 fibers were randomly measured at a magnification of 10 times for a certain amount of split fibers, and the maximum to minimum values were used. expressed.

[Example 1]
DMF / lithium chloride = 98/2 (weight ratio) of metaaramid fibers having a fiber diameter of 14 μm obtained by carrying out the same method as the dry spinning method of the meta-type total aromatic polyamide solution described in Example 1 of (e) above. The solution mixed in (1) was added to the solution to which a weight ratio of 200 times was added. The mixed solution was then stirred at 25 ° C. for 2 hours using a magnetic stirrer. The obtained aramid fibers were collected with a filter paper and washed with 5 times the amount of distilled water of the calcium chloride solution to obtain fine fine fibers.
A scanning electron micrograph of the obtained fiber is shown in FIG. After the treatment, the structure was cleaved in the fiber axis direction and finely divided, and it was confirmed that the fiber surface was smooth. The fiber diameter of the obtained fiber was 6.3 μm, and the coefficient of variation was 0.054. It was. The fiber length was 2 to 4 mm.

[Example 2]
A meta-aramid having a fiber diameter of 14 μm obtained by a method of spinning the meta-type total aromatic polyamide solution according to Example 1 of (f) above into an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt and coagulating it. The fibers were stirred at 25 ° C. for 6 hours using the same solution as in Example 1 and washed with water.
A scanning electron micrograph of the obtained fiber is shown in FIG. After the treatment, the structure was cleaved in the fiber axis direction and finely divided, and it was confirmed that the fiber surface was smooth. The fiber diameter of the obtained fiber was 5.3 μm, and the coefficient of variation was 0.15. It was. The fiber length was 1 to 4 mm.

[Comparative Example 1]
The metaaramid fiber having a fiber diameter of 14 μm obtained by the method described in Example 1 of (c) above was stirred and washed with water by the same method as in Example 1 above.
A scanning electron micrograph of the obtained fiber is shown in FIG. In this example, the fibers were swollen by the treatment liquid, and cleavage and splitting did not occur.

[Comparative Example 2]
The metaaramid fiber having a fiber diameter of 14 μm obtained by the method described in Example 1 of (d) above was stirred and washed with water by the same method as in Example 1 above.
A scanning electron micrograph of the obtained fiber is shown in FIG. In this example as well, the fibers were swollen by the treatment liquid, and cleavage and splitting did not occur.

[Comparative Example 3]
A scanning electron micrograph of the fibrillated para-aramid fiber described in JP-A-2010-222717 as an example of the fibrillated fiber is shown in FIG. Most of the fibers have a non-uniform fiber diameter, the fiber diameter is less than 0.5 μm, and the fiber length is about several μm. Moreover, the fiber surface is not smooth.

The fine fiber obtained by the present invention is obtained by cleaving the aramid fiber uniformly, and is a fiber having good heat resistance, chemical stability, and mechanical properties. Further, the meta-aramid fiber can be obtained by a simple operation by stirring. In addition, it is possible to obtain fibers having a fiber diameter of 0.5 to 10 μm and a fiber length of 1 to 5 mm, which are difficult to obtain by the conventional spinning method and fibrillation method, and the fiber diameter is uniform and the surface is smooth. Excellent dispersibility from to medium.

By using this fine fiber, it is possible to improve the mechanical, thermal, and chemical physical properties of a composite material having improved dispersibility in high-performance paper, rubber material, and resin material.

Claims (4)

A meta-type total aromatic polyamide fiber having a fiber diameter of 0.5 to 10 μm and a fiber length of 1 to 5 mm, wherein the surface of the meta-type total aromatic polyamide fiber is smooth. Total aromatic polyamide fiber. The fineness meta-type total aromatic polyamide fiber according to claim 1, wherein the coefficient of variation of the fiber diameter measured by the following method is 0.20 or less.
(Measurement method of coefficient of variation)
Using a scanning electron microscope VE-8000 (manufactured by KEYENCE), 20 fibers were randomly measured at a magnification of 1000 times, and the coefficient of variation was obtained from the average value and standard deviation. When the fiber cross section was not circular, the value having the largest fiber diameter in one fiber was defined as the fiber diameter. A method for producing fine fiber made of meta-type total aromatic polyamide, in which a meta-type total aromatic polyamide solution is spun by dry spinning or in an aqueous coagulation bath containing 35 to 45% by weight of an inorganic salt to coagulate it. A method for producing a fineness meta-type total aromatic polyamide fiber, which comprises stirring a meta-type total aromatic polyamide fiber having a fiber diameter of 5 to 30 μm in an inorganic salt-containing solvent, which is obtained by wet spinning. The method for producing a fineness meta-type total aromatic polyamide fiber according to claim 3, wherein lithium chloride, magnesium chloride, or lithium carbonate is used as the inorganic salt, and an amide solvent is used as the solvent.