JP5287242B2 - Extra fine fiber and method for producing the same - Google Patents

Description

  The present invention relates to an ultrafine fiber and a method for producing the same, and more specifically, relates to an ultrafine fiber and a method for producing the same, which can obtain a high-quality fiber assembly even with an extremely low fineness.

  Extra-fine fibers have features such as a large specific surface area compared to general-purpose fibers, so they have advantages such as being lightweight, increasing the collection efficiency, and being flexible, such as in the medical field and high-performance filter members. Applications are expected in the field. As one of the methods for producing such ultrafine fibers, an electrospinning method is known. In order to reduce the fiber diameter in the electrospinning method, it is necessary to reduce the solution concentration or the molecular weight. is there. However, when the solution concentration is lowered, the evaporation of the solvent is delayed, and when it is collected as a fiber aggregate, it becomes a film-like form. Therefore, there is a limit to the fineness by lowering the solvent concentration.

Further, an electrostatic spinning method is disclosed in which a spinning state is stabilized by adding an alkali metal salt to a solution containing polyphmetaphenylene isophthalamide as a main component (for example, see Patent Document 1). However, even with such a method, if finer processing is performed, the occurrence of spindle-shaped defects (thick unevenness) in the fibers called beads is unavoidable, resulting in poor quality, fineness and high quality. The present condition is that the fiber assembly of this is not obtained.
JP 2006-336173 A

  The present invention has been made against the background of the above-described prior art, and provides an ultrafine fiber that can produce an extremely high-quality fiber assembly with almost no bead generation even with an ultrafine fiber, and a method for producing the same. It is to be an issue.

As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention comprises (1) a resin having an official moisture content of 0.1% to 5.0%, and contains 0.1 to 10% of salt with respect to the resin. .01-1 μm ultrafine fiber, (2) the resin is composed mainly of one or more resins selected from polyethylene, polyamideimide, polyimide, polyacrylonitrile, polybenzoxazole, polyimide benzoxazole, and polypropylene (1) the ultrafine fiber according to (1), (3) at least one solvent selected from N, N-dimethylacetamide, N, N-dimethylformamide and N-methyl-2-pyrrolidone An ultrafine fiber according to (1) or (2) obtained by an electrospinning method, and (4) a solution obtained by adding salt to a solution comprising a resin and an organic solvent. Then, the obtained solution is spun by an electrostatic spinning method to obtain the ultrafine fiber according to any one of (1) to (3), (5) (1) to (3) A non-woven fabric made of any one of ultrafine fibers.

The ultrafine fiber of the present invention and the production method thereof can provide a uniform fine fiber and a fine fiber aggregate over a wide field of view when the ultrafine fiber is a fiber aggregate. For example, the fiber diameter is 200 nm or less. As such, there is an advantage that a product having an extremely high quality of 20 to 25 beads per 10,000 μm ² can be obtained.

The present invention will be described in detail below.
The ultrafine fiber of the present invention is made of a resin having an official moisture content of 0.1 to 5.0%, and preferably contains a salt of 0.1 to 10% with respect to the resin. The present inventors have found that by adopting such a configuration, a high-quality fiber assembly with few beads can be obtained. Although it is not certain why the occurrence of beads can be suppressed by adopting such a configuration, it is considered as follows. In other words, the cause of the bead generation is that when the solution spun from the spinning nozzle is stretched toward the target, it is considered that an insufficiently stretched part is generated for some reason. If it is 0.1% to 5.0%, generally there are few hydrogen bonds, it is easy to stretch even if it becomes a low concentration during spinning, it is easy to be charged, and it is stretched along with the increase of coulomb repulsion by adding salt. It is believed that the stress becomes stronger, and these synergistic effects reduce the insufficiently stretched portions, that is, beads. More preferably, the official moisture content of the resin and the salt concentration are 0.2% to 4.5% official moisture content, 0.2% to 10% salt content, and more preferably 0.25% to official moisture content, respectively. 4.3%, salt content 0.25% to 9%, more preferably official moisture content 0.3% to 4.0% and salt content 0.3 to 8%.

The ultrafine fiber of the present invention preferably has an average fiber diameter of 0.01 to 1 μm. Within such a range, it is possible to exhibit high functions as ultrafine fibers for various applications and to satisfy the handling and strength. More preferably, it is 0.05-0.8 micrometer, More preferably, it is 0.7-0.2 micrometer.

The resin used for the ultrafine fiber of the present invention is not particularly limited as long as it has the above-mentioned official moisture content. For example, polyamideimide, polyimide, polyacrylonitrile, polybenzoxazole, polyimide benzoxazole, polylactic acid, polyethylene , Polypropylene, polyvinyl acetate, polyvinyl benzoate, polyurethane, polyhydroxybutyrate, polycarbonate, polymethyl methacrylate, polyacetal, polyethylene terephthalate, polybutylene terephthalate, polyvinyl isobutyl ether, polymethyl vinyl ketone, hexamethylene polyadipate, It is preferable that the main component is one or two or more resins selected from the above-mentioned resins such as polyphenylene sulfide. This is because these resins are excellent in stretchability in electrospinning as described above, and a high-quality fiber assembly with few beads can be obtained by adding a salt.

The salt used for the ultrafine fiber of the present invention is preferably dissolved in a solution, and is not particularly limited as long as it is soluble in the solvent used. For example, lithium chloride, sodium chloride, potassium chloride, Calcium chloride, ammonium chloride, sodium phosphate, calcium phosphate, sodium dihydrogen phosphate, sodium nitrite, aluminum nitrate, potassium nitrate, calcium nitrate, sodium nitrate, calcium acetate, sodium acetate, potassium carbonate, calcium carbonate, sodium carbonate, aluminum sulfate One or more salts selected from ammonium sulfate, potassium sulfate, calcium sulfate, sodium sulfate, barium sulfate and the like are preferable. If these salts are used, sufficient stretchability can be secured, and a high-quality fiber assembly with few beads can be obtained in the above-described resin. When the salt is not dissolved in the solution, the deposited salt becomes a foreign substance and becomes a defect in the fiber, so that a high-quality ultrafine fiber aggregate cannot be obtained. In addition to the above inorganic salts, quaternary ammonium salts such as dilauryldimethylammonium bromide, dimethyldimyristylammonium bromide, dimethyldistearylammonium chloride, dimethyldipalmitylammonium bromide, 1-butyl-3-methylimidazo 1-alkyl-3-methylimidazolium salts such as 1-ethyl-3-methylimidazolium hexafluorophosphate, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium tetra Aliphatic ionic liquids such as fluoroboric acid and N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bistrifluoromethanesulfonylimide can also be used.

  The ultrafine fibers of the present invention are acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dioxane, propanol, carbon tetrachloride, cyclohexane, cyclohexanone, methylene chloride, phenol, pyridine. , A highly volatile solvent such as trichloroethane, acetic acid, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N, N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidone (NMP), Ethylene carbonate, propylene carbonate, dimethyl carbonate, acetonitrile, N-methylmorpholine-N-oxide, butylene carbonate, γ-butyrolactone, diethyl carbonate, diethyl ether 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dioxolane, ethyl methyl carbonate, methyl formate, 3-methyl oxazolidine-2-one, methyl propionate, 2- It is preferably obtained by an electrospinning method using at least one solvent selected from solvents having relatively low volatility such as methyltetrahydrofuran and sulfolane. This is because these solvents can dissolve the above-mentioned resin and at the same time sufficiently dissolve the above-mentioned salt, thereby improving the quality of the fiber aggregate obtained from the ultrafine fibers of the present invention.

  The ultrafine fiber of the present invention is based on a production method in which a solution obtained by adding a salt to the above-described resin and organic solvent solution is prepared, and then the obtained solution is spun by an electrostatic spinning method to obtain an ultrafine fiber. preferable. This is because by adopting such a production method, a high-quality fiber assembly with few beads can be obtained.

  The concentration of the polymer solution used in the production method of the present invention is preferably 0.1 to 30% by weight, particularly preferably 1 to 25% by weight as the solid content concentration. This is because within such a range, it is possible to prevent film formation due to the delay in evaporation of the solvent and to obtain fine fibers.

    In the production method of the present invention, the applied voltage is preferably 3 to 100 kV, preferably 5 to 70 kV, and more preferably 5 to 50 kV. Note that the polarity of the applied voltage may be either positive or negative.

In the production method of the present invention, the spinning atmosphere is generally carried out in the air, but by performing electrostatic spinning in a gas having a higher discharge starting voltage than air such as carbon dioxide, it is possible to achieve a low voltage. Spinning, and abnormal discharge such as corona discharge can be prevented.
If water is the poor solvent for the polymer, polymer precipitation may occur. It is preferable to reduce moisture in the air and prevent polymer precipitation. However, when the absolute humidity is 2 g / m ³ or less, the evaporation of the solvent is suppressed, and the solvent remains in the obtained fine fiber aggregate, which causes the polymer to be redissolved and causes film formation. For this reason, the moisture in the air needs to be spun at an absolute humidity of 2 to 13 g / m ³ . More preferably, ³ to 11 g / m ³ is preferable.

The nonwoven fabric of the present invention preferably has 25 beads or less per 10,000 μm ² . It is because it is excellent in the value and performance as a product if it is this range. For example, when used as an air filter, pressure loss is reduced. More preferably, it is 23 or less, and still more preferably 20 or less.

Hereinafter, the present invention will be described in more detail based on examples. In addition, each physical property in an Example is calculated | required with the following method.

[Fiber diameter measurement method]
What is to be evaluated is photographed with a scanning electron microscope (SEM), 20 fibers are randomly selected from a large number of fibers projected on a 5000 times or 10,000 times SEM image, and the fiber diameter is measured. The average value of the measured 20 fiber diameters was calculated and defined as the (average) fiber diameter.

[Bead count measurement method]
What is to be evaluated is photographed with a scanning electron microscope (SEM), and the number of beads having a long diameter of 10 times or more and a short diameter of 5 times or more with respect to the fiber diameter is counted from a 1000 times SEM image. With respect to what evaluates this, 5 points | pieces were measured at random, the average value was computed, and it was set as the (average) bead number.

Example 1
N, N-dimethylacetamide was added to polyamideimide (official moisture content 2.6%) (logarithmic viscosity 1.38 dl / g) to a solid content concentration of 8%. 4% lithium chloride was added to the resin solution based on the polymer weight. The polyamideimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18 G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 22 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.11 μm. The number of beads was 12/10000 μm ² .

(Example 2)
N, N-dimethylacetamide was added to polyamideimide (official moisture content 2.6%) (logarithmic viscosity 1.34 dl / g) to a solid content concentration of 8%. 4% of dimelauryldimethylammonium bromide was added to the resin solution based on the polymer weight. The polyamideimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 18 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.14 μm. The number of beads was 4/10000 μm ² .

(Example 3)
N, N-dimethylacetamide was added to polyamideimide (official moisture content 2.6%) (logarithmic viscosity 1.38 dl / g) to a solid content concentration of 8%. 5% lithium chloride was added to the resin solution based on the polymer weight. The polyamideimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18 G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 27 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.10 μm. The number of beads was 15/10000 μm ² .

Example 4
N, N-dimethylacetamide was added to Ultem (General Electric Plastic) (official moisture content 1.25%) to a solid content concentration of 10%. 5% lithium chloride was added to the resin solution based on the polymer weight. The polyimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18 G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 23 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.12 μm. The number of beads was 12/10000 μm ² .

(Comparative Example 1)
N, N-dimethylacetamide was added to Conex (registered trademark) (official moisture content 5.5%) manufactured by Teijin Limited to a solid content concentration of 10%. 10% lithium chloride was added to the resin solution based on the polymer weight. The polyamideimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18 G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 30 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.06 μm. The number of beads was 36/10000 μm ² .

(Comparative Example 2)
N, N-dimethylacetamide was added to polyamideimide (official moisture content 2.6%) (logarithmic viscosity 1.38 dl / g) to a solid content concentration of 8%. 12.5% lithium chloride was added to the resin solution based on the polymer weight. The polyamideimide solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 28 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.14 μm. The number of beads was 2/10000 μm ² . However, the obtained ultrafine fibers could not be handled as a non-woven fabric and had very low quality.

(Reference example)
Nylon 6 (official moisture content: 4.5%) was added to a mixture of N, N-dimethylformamide and formic acid in a weight ratio of 5 to 95 to give a solid content concentration of 10%. 4% lithium chloride was added to the resin solution based on the polymer weight. This nylon solution was discharged to the fibrous material collecting electrode 5 for 20 minutes using the apparatus shown in FIG. An 18 G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 14 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10.5 cm. The absolute humidity in the air was 9.0 g / m3. The average fiber diameter of the obtained ultrafine fiber aggregate was 0.17 μm. The number of beads was 22/10000 μm ² .

  According to the ultrafine fiber of the present invention and the method for producing the same, a high-quality fiber assembly with few beads can be obtained even with an extremely low fineness, and there is little variation and high stability can be obtained. It is possible to expand to the industry and contribute to the industry.

Schematic cross-sectional view of an electrostatic spinning device SEM photograph of the ultrafine fiber assembly described in Example 1 SEM photograph of the ultrafine fiber assembly described in Comparative Example 1 SEM photograph of the ultrafine fiber assembly described in Comparative Example 2

Explanation of symbols

1: Electrostatic spinning device 2: Spinning nozzle 3: Solution tank 4: High voltage power supply 5: Counter electrode (collecting substrate)

Claims (3)

It consists of a resin with an official moisture content of 0.1% to 5.0%, contains 0.1 to 10% of salt with respect to the resin , has a long diameter of 10 times or more and a short diameter of 5 times the fiber diameter. An ultrafine fiber aggregate having an average fiber diameter of 0.01 to 1 μm, wherein the number of beads is 25 or less per 10,000 μm ² . The said resin has as a main component 1 type, or 2 or more types of resin selected from polyethylene, polyamideimide, a polyimide, a polyacrylonitrile, polybenzoxazole, a polyimide benzoxazole, and a polypropylene. Extra fine fiber assembly . 2. The method according to claim 1, wherein the solvent is obtained by an electrospinning method using at least one solvent selected from N, N-dimethylacetamide, N, N-dimethylformamide, and N-methyl-2-pyrrolidone. ultrafine fiber assembly according to 2.