JP7152261B2 - Para-type wholly aromatic polyamide fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thin para-type wholly aromatic polyamide fiber and a method for producing the same.

Wholly aromatic polyamide fibers are fibers that are excellent in strength, modulus, heat resistance, etc., and are used in various fields as industrial fibers by taking advantage of these high functionalities. And in recent years, as they are used in a wide range of applications, demands for their physical properties and properties are increasing more and more.

For example, when reinforcing materials such as lightweight and small semiconductor wiring boards, printed wiring boards, and medical catheter tubes with fibers, it is strongly required to reduce the fiber diameter in order to make the thickness extremely thin. However, since fibers with a small fiber diameter have low strength, they break during manufacturing or processing, and there are no thin fibers that can withstand practical use.

Further, from the standpoint of the characteristics of wholly aromatic polyamides, particularly strength and weight reduction, applications such as ropes, fishing nets, fishing lines, braids, etc. are expected.
Therefore, by making the reinforcing fiber to have a flat cross-section, it can be expected to achieve a reduction in size and weight.

Patent Documents 1 and 2 have so far proposed methods for obtaining a para-type wholly aromatic polyamide fiber having a flat cross section. However, there are problems that the resulting fiber has low tensile strength, uneven flatness, and low flatness, and is not satisfactory as a reinforcing fiber. strongly desired.

JP 2013-221729 A JP-A-3-163610

The present invention has been made in view of the above background art, and its object is to provide a thin fiber having a high degree of flatness, a high strength, a uniform thickness, and a method for producing the same. .

The present inventor has made intensive studies to solve the above problems, and has completed the present invention.

That is, the present invention
1. A para-type wholly aromatic polyamide fiber having a flat cross-sectional shape of a single filament perpendicular to the fiber axis direction, wherein the para-type wholly aromatic polyamide fiber satisfies the following conditions.
(a) The ratio (L/T1) of the longest axis (L) of the flat cross section to the longest axis (T1) orthogonal to (L) is greater than 5.0 and 20.1 or less. family of polyamide fibers.
(b) The longest axis (T1) is 3 μm or more and 30 μm or less.
(c) The coefficient of variation of the flatness of the flat cross section is less than 10%.
and preferably
2. The ratio (T2/T1) of the shortest axis (T2) perpendicular to the longest axis (L) excluding 3 μm at both ends of the flat cross section and the longest axis (T1) perpendicular to the longest axis (L) is 0.7 or more. 1. The para-type wholly aromatic polyamide fiber according to 1 above, which is 1.0 or less,
3. 1, wherein the ratio (A2/A1) of the single yarn cross-sectional area (A1) of the single yarn fiber to the area (A2) of the rectangle circumscribed by the circumference of the single yarn fiber is 1.00 or more and 1.25 or less. 3. or the para-type wholly aromatic polyamide fiber according to 2. again,
4. 4. The para-type wholly aromatic polyamide fiber according to any one of 1 to 3 above, wherein the single yarn strength per thickness of the single yarn fiber is 6.0 cN/μm or more, and
5. 5. The para-type wholly aromatic polyamide fiber according to any one of 1 to 4 above, wherein the polymer constituting the para-type wholly aromatic polyamide fiber is copolyparaphenylene/3,4'-oxydiphenylene/terephthalamide. .
The present invention also provides the following 6 manufacturing methods.
6. 2. The method for producing a wholly aromatic polyamide fiber according to claim 1 , wherein the spinneret ejection hole forming the shape of the fiber is flat, and the end (W1) of the flat short axis of the ejection hole The ratio (W2/W1) of the central portion (W2) is 0.1 or more and less than 1.0, and the ratio (L/W1) of the long axis (L) and the short axis end (W1) is 10 or more and 55 or less . A method for producing a para-type wholly aromatic polyamide fiber, wherein the air gap from the spinneret surface to the coagulating liquid is set to 10 mm or less, and then the fiber is drawn .
Furthermore,
7. A braid using the para-type wholly aromatic polyamide fiber according to any one of 1 to 5 above,
8. A composite using the para-type wholly aromatic polyamide fiber according to any one of 1 to 5 above,
9. A catheter using the para-type wholly aromatic polyamide fiber according to any one of 1 to 5 above.

The para-type wholly aromatic polyamide fiber having a flattened cross section of the present invention has a high monofilament strength and a uniform thickness and thin fiber. Therefore, the use of this fiber is useful for application to braids and composites, and makes it possible to reduce the weight and thickness of semiconductor wiring boards, printed wiring boards, catheter guides, and balloons.

An example of the shape of the ejection hole of the spinneret used for spinning the fiber of the present invention is shown. An example of the shape of the ejection hole of the spinneret used for spinning the fiber of the present invention is shown. An example of the shape of the ejection hole of the spinneret used for spinning the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown. An example of a single yarn cross-sectional shape perpendicular to the fiber direction of the fiber of the present invention is shown.

<Para-type Wholly Aromatic Polyamide>
The para-type wholly aromatic polyamide in the present invention is a polymer in which one or more divalent aromatic groups are directly linked via amide bonds. Aromatic groups also include those in which two aromatic rings are bonded via oxygen, sulfur, or an alkylene group, or those in which two or more aromatic rings are directly bonded. Further, these divalent aromatic groups may contain lower alkyl groups such as methyl group and ethyl group, halogen groups such as methoxy group and chloro group, and the like.

<Method for producing para-type wholly aromatic polyamide>
The para-type wholly aromatic polyamide in the present invention can be produced according to a conventionally known method. For example, it can be obtained by reacting an aromatic dicarboxylic acid dichloride (hereinafter also referred to as "acid chloride") component and an aromatic diamine component by low-temperature solution polymerization or interfacial polymerization in an amide-based polar solvent.

[Raw materials for para-type wholly aromatic polyamide]
(Aromatic dicarboxylic acid dichloride component)
The aromatic dicarboxylic acid chloride component used in the production of the para-type wholly aromatic polyamide is not particularly limited, and generally known ones can be used.
Examples thereof include terephthalic acid chloride, 2-chloroterephthalic acid chloride, 2,5-dichloroterephthalic acid chloride, 2,6-dichloroterephthalic acid chloride, 2,6-naphthalenedicarboxylic acid chloride and the like.

Moreover, these aromatic dicarboxylic acid dichlorides can be used not only in one type but also in combination of two or more types, and the composition ratio thereof is not particularly limited. Among these, terephthalic acid dichloride is preferable from the viewpoint of versatility and mechanical properties of the resulting fiber. In addition, in the present invention, a component that forms a bond other than the para position, such as isophthalic chloride, may be used.

(Aromatic diamine component)
The aromatic diamine component used in the production of the para-type wholly aromatic polyamide is not particularly limited, and generally known ones can be used. For example, p-phenylenediamine, 2-chloro-p-phenylenediamine, 2,5-dichloro-p-phenylenediamine, 2,6-dichloro-p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4' -diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, and the like.

Not only one type but also two or more types can be used, and the composition ratio is not particularly limited. In addition, in the present invention, a small amount of a component such as m-phenylenediamine that forms a bond other than the para-position may be used.

Among these, p-phenylenediamine is preferably used alone or in combination, and a combination of p-phenylenediamine and 3,4'-diaminodiphenyl ether is most preferable from the viewpoint of stability in high-temperature hot drawing. When p-phenylenediamine and 3,4′-diaminodiphenyl ether are used in combination, the composition ratio is not particularly limited, but is 30 to 70 mol % and 70 mol %, respectively, based on the total amount of aromatic diamines. It is preferably 30 mol %, more preferably 40 to 60 mol % and 60 to 40 mol %, and still more preferably 45 to 55 mol % and 55 to 45 mol %, respectively.

[Polymerization solvent]
Examples of the solvent for polymerizing the para-type wholly aromatic polyamide include organic polar amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and N-methylcaprolactam. , tetrahydrofuran, dioxane and other water-soluble ether compounds; methanol, ethanol, ethylene glycol and other water-soluble alcohol compounds; acetone, methyl ethyl ketone and other water-soluble ketone compounds; acetonitrile, propionitrile and other water-soluble nitrile compounds be done. These solvents can be used singly or as a mixed solvent of two or more. It is desirable that the solvent used above is dehydrated.

In the production of the para-type wholly aromatic polyamide used in the present invention, N-methyl-2-pyrrolidone (NMP) is used from the viewpoint of versatility, toxicity, handleability, solubility in the para-type wholly aromatic polyamide, etc. It is particularly preferred to use

[Other polymerization conditions, etc.]
In order to increase the solubility of the para-type wholly aromatic polyamide to be produced, an appropriate amount of a generally known inorganic salt may be added before, during, or at the end of the polymerization. Examples of such inorganic salts include lithium chloride and calcium chloride.

Also, the ends of the para-type wholly aromatic polyamide can be capped. When the terminal is blocked with a terminal blocking agent, for example, phthaloyl chloride and its substituted products, aniline and its substituted products, etc. can be used as the terminal blocking agent.

Moreover, in order to capture acids such as hydrogen chloride that are produced, aliphatic or aromatic amines, quaternary ammonium salts, etc. can be used in combination.

After completion of the reaction, if necessary, a basic inorganic compound such as sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, etc. may be added to carry out a neutralization reaction.

<Method for producing para-type wholly aromatic polyamide fiber>
In producing the para-type wholly aromatic polyamide fiber of the present invention, a wet spinning method or a semi-dry and semi-wet spinning method is employed to prepare a uniform spinning solution (polymer dope) containing a solvent, and Dispense.

[Shape of discharge hole]
The shape of the flat discharge hole for obtaining the wholly aromatic polyamide flat cross-section fiber of the present invention is such that the ratio (W2/W1) of the short axis end (W1) and the center (W2) is preferably 0.1 or more. It is less than 1.0, more preferably 0.1 or more and 0.9 or less, still more preferably 0.1 or more and 0.7 or less, and particularly preferably 0.1 or more and 0.6 or less.

If it exceeds 1.0, the central portion of the cross section perpendicular to the fiber direction is thick, the fiber tends to have a swollen shape, that is, the fiber has an elliptical shape, and it is difficult to form a thin fiber. If it is lower than 0.1, the yarn tends to break during production, and the strength is not satisfactory.

It has a discharge hole in which the ratio (L/W1) of the long axis (L) to the short axis end (W1) satisfies the range of 10 or more. It is preferably 20 or more, more preferably 30 or more.

The ends (W1), center (W2) and long axis (L) of the short axis of the discharge hole described above refer to the respective lengths of the flat discharge hole shown in FIGS. In the case of FIGS. 2 and 3, the diameter of the arc is W1. Also, both ends of the short axis may be straight lines or curved lines, and are not particularly limited. Furthermore, the short axis end and the central part are connected by a straight line or a curved line, and are not particularly limited.

[Air gap]
The air gap from the spinneret face to the solidified liquid must be 10 mm or less, preferably 5 mm or less, and still more preferably 3 mm or less. If the length is longer than 10 mm, the dope will be close to a circular shape due to stabilization of the surface energy, and flatness cannot be maintained.

[Spinning process]
In the production of the fibers of the present invention, the spinning solution (dope) prepared as described above is used to form fibers by a wet spinning method or a semi-dry and semi-wet spinning method with an air gap. That is, first, the spinning solution (dope) obtained above is discharged from a discharge hole (nozzle), and then brought into contact with a coagulating liquid in a coagulating bath to form a coagulated yarn.

A poor solvent for the para-type wholly aromatic polyamide is used as the coagulating bath. add a good solvent to control the solidification rate. It is preferable to use water as the poor solvent and a solvent for the para-type wholly aromatic polyamide dope as the good solvent. The mass ratio of good solvent/poor solvent is preferably in the range of 15/85 to 40/60, depending on the solubility and coagulability of the para-type wholly aromatic polyamide.

After pulling up the coagulated yarn from the coagulating liquid, the final para-type wholly aromatic polyamide fiber can be obtained by a known method. For example, the solvent is removed from the undrawn yarn formed by performing a water washing step, and if necessary, drawing is performed, and after a drying step or the like, the yarn is oriented by drawing if necessary, and the final fiber is can be obtained.

[Stretching process]
Stretching is then carried out. The stretching method is not particularly limited. The draw ratio is not particularly limited, but is preferably at least 6 times, more preferably 8 times or more. By controlling the draw ratio, the elongation and strength of the obtained wholly aromatic polyamide fiber can be controlled.

<Physical properties of para-type wholly aromatic polyamide fiber having a flat cross section>
The para-type wholly aromatic polyamide fiber having a flat cross section of the present invention has the following physical properties.

[Flatness of single filament cross section]
The para-type wholly aromatic polyamide fiber having a flattened cross section of the present invention is composed of the longest axis (L) of the single filament cross section of the flattened fiber and the longest axis (T1) orthogonal to L (T1 is also referred to as fiber thickness ) ratio (L/T1) is greater than 5.0, preferably 7 or more, more preferably 10 or more, and still more preferably 13 or more. If L/T 1 is less than 5, it cannot be said that the strength is sufficient for a thin wall.

The longest axis (L) of the single yarn cross section and the longest axis (T1) orthogonal to that L are each length of the flat cross section yarn shown in FIGS. 4 to 6 .

In addition, the shortest axis (T2) orthogonal to the longest axis (L) excluding 3 μm at both ends of the flattened monofilament cross section of the para-type wholly aromatic polyamide fiber having a flattened cross section of the present invention, and the single yarn The ratio (T2/T1) to the longest axis (T1) orthogonal to the longest axis (L) of the cross section is preferably 0.7 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less. , more preferably in the range of 0.9 or more and 1.0 or less.

The longest axis (L) and the shortest axis (T2) orthogonal to the longest axis (L) excluding 3 μm at both ends are each length of the flat cross-section yarn as shown in FIGS.

Furthermore, the ratio of the cross-sectional area (A1) of the flattened para-type wholly aromatic polyamide fiber of the present invention to the rectangular area (A2) circumscribed by the circumference of the single yarn ( A2/A1) is preferably 1.00 or more and 1.25 or less, more preferably 1.00 or more and 1.20 or less, still more preferably 1.00 or more and 1.15 or less, and particularly preferably 1.00 or more. It is in the range of 1.10 or less.

The flat cross-section yarn is required to maintain a uniformly thin thickness. (A2/A1) indicates the distortion of the flattened cross-section, and if it exceeds 1.25, extremely thick or thin portions are formed, so it cannot be said that thin-walled reinforcement is sufficient.

The single yarn cross-sectional area (A1) of the fiber and the area (A2) of the rectangle circumscribed by the circumference of the single yarn are the lengths of the flat cross-section yarns shown in FIGS.

[Thickness of single filament cross section]
In the para-type wholly aromatic polyamide fiber having a flat cross section of the present invention, the longest axis (L) of the single filament cross section of the flattened fiber and the length (T1) of the longest axis perpendicular to L are 30 μm or less. be. It is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less . If the thickness is larger than 30 μm, the thickness is too large and is not suitable for applications that require thinness, which is the object of the present invention.

[Single filament strength per thickness]
The para-type wholly aromatic polyamide fiber having a flat cross section of the present invention has a single filament tenacity per thickness of 6.0 cN/μm or more. It is preferably 8.0 cN/μm, more preferably 10.0 cN/μm.

If the monofilament strength per thickness is less than 6.0 cN/μm, the monofilament is easily broken, which is not preferable as a reinforcing fiber.

[Coefficient of variation of flatness]
The para-type wholly aromatic polyamide fiber having a flattened cross section of the present invention has a flatness coefficient of variation of less than 10% in the single filament cross section of the flattened fiber. Preferably less than 8%, more preferably less than 5%.

If the coefficient of variation is less than 10%, it means that there is no defect, and it is effective because the product can be stably reinforced.

If the coefficient of variation exceeds 10%, it means that there are extremely thin portions, and this is a drawback, and it is not preferable because it causes breakage of the single yarn.

As a method of flattening the fibers, there is a method of crushing with a roller, but this is not preferable because the coefficient of variation becomes high. This is not preferable because the higher the degree of flatness, the higher the coefficient of variation tends to be and the greater the variation in quality.

By satisfying the performance of the para-type wholly aromatic polyamide fiber having a flat cross section of the present invention described above, it can be used for applications such as ropes, fishing nets, fishing lines, etc., and braids, etc., for which there is a high demand for thinness, light weight, and miniaturization. , useful for fiber reinforced resin composites.

In addition, it is possible to reduce the weight and thickness of reinforcing materials such as semiconductor wiring boards and printed wiring boards, medical catheter tubes, catheter guides, and balloons.

EXAMPLES The present invention will now be described in more detail with reference to examples and comparative examples. However, these examples and comparative examples are intended to aid understanding of the present invention, and the scope of the present invention is not limited by these descriptions.

<Measurement/evaluation method>
In Examples and Comparative Examples, the following items were measured and evaluated by the following methods.
(1) Flatness, coefficient of variation, and various average values of para-type wholly aromatic polyamide fiber having a flattened cross section Any 10 single filaments of the flattened fiber are measured every 1 cm in the fiber axis direction N = Five pieces were cut, and the cross section of the single yarn was observed with a digital microscope (VHX-2000) manufactured by Keyence Corporation.
The longest axis (L) of the single filament cross section and the longest axis (T1) perpendicular to that (L) were measured, and the average value and coefficient of variation of the ratio (L/T1) were calculated. Coefficient of variation = standard deviation / average value x 100
In addition, the shortest axis (T2) orthogonal to the longest axis (L) of the single yarn cross section of the fiber, omitting 3 μm at both ends, and the shortest axis (T1) orthogonal to the longest axis (L) of the single yarn cross section were measured, and the ratio ( The average value of T2/T1) was calculated.
Furthermore, the cross-sectional area (A1) of the single yarn of the fiber and the area (A2) of the rectangle circumscribed by the circumference of the single yarn were measured, and the average value of the ratio (A2/A1) was calculated.

(2) Tensile strength of single yarn with respect to thickness of para-type wholly aromatic polyamide fiber having flat cross section Tensile tester (manufactured by INTESCO, trade name: INTESCO, model: 201X type), using a yarn test chuck, Measurement was performed under the following conditions. The measured single yarn strength was divided by the longest axis (T1) orthogonal to the longest axis (L) of the cross section of the single yarn to calculate the tensile strength with respect to the thickness.
[Measurement condition]
Temperature: Room temperature Test speed: 10 mm/min Distance between chucks: 25.4 mm

(3) Braided cord strength and braided cord appearance Braided cord strength was measured under the following conditions using the tensile tester described above.
A tensile tester (manufactured by INSTRON, trade name: INSTRON, model: model: 5565) was used to perform measurements under the following conditions using a thread test chuck according to the procedure of ASTM D885.
[Measurement condition]
Temperature: Room temperature Test piece: 75 cm
Twist factor: 1
Test speed: 250 mm/min Distance between chucks: 500 mm
Appearance Evaluation of Braided Cord: A 1 m long braided cord is hung with a weight of 50 g, and the surface of the braided cord is visually evaluated.

<Example 1>
[Step of preparing spinning solution]
A spinning solution (dope) of copolyparaphenylene/3,4′-oxydiphenylene terephthalamide (para-type wholly aromatic polyamide with a copolymer molar ratio of 1:1) was prepared.

[Spinning process]
The spinning solution (dope) was prepared so that the ratio (W2/W1) of the short axis end (W1) and the center (W2) of the flat discharge hole was 0.7, the long axis (L) and the short axis end ( W1) ratio (L / W1) is 15.0 through an air gap of 10 mm into a coagulation bath filled with an aqueous solution of NMP concentration of 30% by mass at 50 ° C. to obtain a coagulated yarn. . After that, the obtained coagulated thread was washed with water and dried.

[Stretching process]
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained by drawing 8 times at a drawing temperature of 500°C and winding. The resulting fiber had a fiber flatness of 5.2, a fiber variation coefficient of 4.2%, a fiber thickness of 5 μm, and a tensile strength to thickness of 7.3 cN/ μm , which were favorable. The resulting fiber properties are shown in Table 1.

[Manufacturing braids]
Four fibers obtained in Example 1 were twisted 75 times per meter and dipped in a hot-melt polyurethane adhesive. The coating amount was 80 parts per 100 parts of the fiber. After that, the four polyurethane adhesive-coated fibers were made into a string so that the braiding angle was 2015 degrees. This fiber was passed through a high-pressure press roll heated to 130° C. with a clearance of 0.1 mm, and the void inside was filled with a hot-melt adhesive. The strength of the braid was 43000 cN and the appearance of the braid was good.

[Resin composite]
When a resin composite was produced using the fiber obtained in Example 1 as a reinforcing material, a high-quality, high-strength, and thin resin product could be obtained.

[catheter]
A catheter was made using the fiber obtained in Example 1. It was good because it was thin and had a small diameter.

<Example 2>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that the air gap was changed to 2 mm. The obtained fiber had a fiber flatness of 7.3, a fiber variation coefficient of 4.0%, a fiber thickness of 4 μm, and a tensile strength to thickness of 7.7 cN/ μm , which were favorable. The resulting fiber properties are shown in Table 1.

<Example 3>
The ratio (W2/W1) between the end (W1) of the short axis and the center (W2) of the flat discharge hole is 0.7, and the ratio (L/ A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that W1) was changed to 20.0. The resulting fiber had a fiber flatness of 6.0, a fiber variation coefficient of 4.6%, a fiber thickness of 5 μm, and a tensile strength to thickness of 8.4 cN/ μm , which were favorable. The resulting fiber properties are shown in Table 1.

<Example 4>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 3, except that the air gap was changed to 2 mm. The obtained fiber had a fiber flatness of 8.8, a fiber variation coefficient of 4.5%, a fiber thickness of 4 μm, and a tensile strength to thickness of 9.4 cN/ μm , which were good. The resulting fiber properties are shown in Table 1.

<Example 5>
The ratio (W2/W1) between the end (W1) of the short axis and the center (W2) of the flat discharge hole is 0.4, and the ratio (L/ A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that W1) was changed to 30.0. The obtained fiber had a fiber flatness of 10.5, a fiber variation coefficient of 4.8%, a fiber thickness of 4 μm, and a tensile strength to thickness of 8.9 cN/ μm , which were favorable. The resulting fiber properties are shown in Table 1.

<Example 6>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 5, except that the air gap was changed to 2 mm. The resulting fiber had a fiber flatness of 14.6, a fiber variation coefficient of 4.4%, a fiber thickness of 3 μm, and a tensile strength to thickness of 9.8 cN/ μm . Although the degree of flatness was high, the fiber coefficient of variation and physical properties were good. The resulting fiber properties are shown in Table 1.

<Example 7>
The ratio (W2/W1) between the end (W1) of the short axis and the center (W2) of the flat discharge hole is 0.4, and the ratio (L/ A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that W1) was changed to 40.0. The resulting fiber had a fiber flatness of 13.7, a fiber variation coefficient of 4.9%, a fiber thickness of 4 μm, and a tensile strength to thickness of 10.3 cN/ μm . Although the degree of flatness was high, the fiber coefficient of variation and physical properties were good. The resulting fiber properties are shown in Table 1.

<Example 8>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 7, except that the air gap was changed to 2 mm. The resulting fiber had a fiber flatness of 18.9, a fiber variation coefficient of 4.2%, a fiber thickness of 3 μm, and a tensile strength to thickness of 10.7 cN/ μm . Although the degree of flatness was considerably high, the fiber coefficient of variation and physical properties were good. Table 1 shows the physical properties of the obtained fiber.

<Example 9>
The ratio (W2/W1) between the end (W1) of the short axis and the center (W2) of the flat discharge hole is 0.95, and the ratio (L/ A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that W1) was changed to 55.0. The resulting fiber had a fiber flatness of 17.0, a fiber variation coefficient of 7.8%, a fiber thickness of 3 μm, and a tensile strength to thickness of 11.4 cN/ μm . Although the degree of flatness was considerably high, the fiber coefficient of variation and physical properties were good. Table 2 shows the physical properties of the obtained fiber.

<Example 10>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 9, except that the air gap was changed to 2 mm. The resulting fiber had a fiber flatness of 20.1, a fiber variation coefficient of 6.8%, a fiber thickness of 3 μm, and a tensile strength to thickness of 12.4 cN/ μm . Although the degree of flatness was considerably high, the fiber coefficient of variation and physical properties were good. Table 2 shows the physical properties of the obtained fiber.

<Comparative Example 1>
Copolyparaphenylene 3, 3, A 4'-oxydiphenylene terephthalamide fiber was obtained. The resulting fiber had a fiber flatness of 4.2, a fiber variation coefficient of 4.5%, a fiber thickness of 10 μm, and a tensile strength to thickness of 4.3 cN/ μm . Flatness could not be maintained, and the flatness and cross-sectional area ratio deteriorated, and the tensile strength to thickness also decreased. Table 2 shows the physical properties of the obtained fiber.

<Comparative Example 2>
Copoly-paraphenylene 3 and 4 were prepared in the same manner as in Example 6, except that the ratio (L/W1) of the major axis (L) to the minor axis end (W1) of the flat discharge hole was 8.0. A '-oxydiphenylene terephthalamide fiber was obtained. The obtained fiber had a fiber flatness of 3.8, a fiber variation coefficient of 4.5%, a fiber thickness of 6 μm, and a tensile strength to thickness of 8.1 cN/ μm , which were favorable. The flatness could not be maintained, and the flatness and cross-sectional area ratio deteriorated. Table 2 shows the physical properties of the obtained fiber.

<Comparative Example 3>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 5, except that the air gap was changed to 15 mm. The resulting fiber had a fiber flatness of 3.9, a fiber variation coefficient of 6.8%, a fiber thickness of 14 μm, and a tensile strength to thickness of 3.1 cN/ μm . Flatness could not be maintained, and the flatness and cross-sectional area ratio deteriorated, and the tensile strength to thickness also decreased. Table 2 shows the physical properties of the obtained fiber.

<Comparative Example 4>
A copolyparaphenylene/3,4'-oxydiphenylene terephthalamide fiber was obtained in the same manner as in Example 1, except that the ejection holes were circular. The obtained fiber had a fiber flatness of 10, a fiber variation coefficient of 2.2%, a fiber thickness of 15 µm, and a tensile strength to thickness of 2.8c.
N/ μm . Table 2 shows the physical properties of the obtained fiber.

[Manufacturing braids]
Four fibers obtained in Comparative Example 4 were twisted 75 times per meter and dipped in a hot-melt polyurethane adhesive. The coating amount was 80 parts per 100 parts of the fiber. After that, the four polyurethane adhesive-coated fibers were made into a string so that the braiding angle was 2015 degrees.
This fiber was passed through a high-pressure press roll heated to 130° C. with a clearance of 0.1 mm, and the void inside was filled with a hot-melt adhesive. The strength of the braid was 38000 cN, which decreased due to the collision between the fibers during the pressing process.

[Resin composite]
When a resin composite was produced using the fiber obtained in Comparative Example 4 as a reinforcing material, it was not possible to obtain a thin resin product, which is the object of the present invention.

[catheter]
A catheter was made using the fiber obtained in Comparative Example 4. It was not possible to obtain a product having a thin thickness and a small diameter, which is the object of the present invention.

<Comparative Example 5>
The fibers having a circular cross-section obtained in Comparative Example 4 were crushed by nip rollers to obtain a flattened shape. The resulting fiber had a fiber flatness of 5.3, a fiber variation coefficient of 33.8%, a fiber thickness of 8 μm, and a tensile strength to thickness of 2.7 cN/ μm . In addition, the strength of the single yarn was remarkably lowered. Table 2 shows the physical properties of the obtained fiber.

Claims (9)

A para-type wholly aromatic polyamide fiber having a flat cross-sectional shape of a single filament perpendicular to the fiber axis direction, wherein the para-type wholly aromatic polyamide fiber satisfies the following conditions.
(a) The ratio (L/T1) of the longest axis (L) of the flat cross section to the longest axis (T1) orthogonal to (L) is greater than 5.0 and 20.1 or less. family of polyamide fibers.
(b) The longest axis (T1) is 3 μm or more and 30 μm or less.
(c) The coefficient of variation of the flatness of the flat cross section is less than 10%. The ratio (T2/T1) of the shortest axis (T2) perpendicular to the longest axis (L) excluding 3 μm at both ends of the flat cross section and the longest axis (T1) perpendicular to the longest axis (L) is 0.7 or more. The para-type wholly aromatic polyamide fiber according to claim 1, which is 1.0 or less. The ratio (A2/A1) of the single yarn cross-sectional area (A1) of the single yarn fiber to the area (A2) of the rectangle circumscribed by the circumference of the single yarn fiber is 1.00 or more and 1.25 or less. 3. The para-type wholly aromatic polyamide fiber according to 1 or 2. The para-type wholly aromatic polyamide fiber according to any one of claims 1 to 3, wherein the monofilament strength per thickness of the monofilament fiber is 6.0 cN/μm or more. The polymer constituting the para-type wholly aromatic polyamide fiber is copolyparaphenylene 3
, 4'-oxydiphenylene terephthalamide, the para-type wholly aromatic polyamide fiber according to any one of claims 1 to 4. 2. The method for producing a wholly aromatic polyamide fiber according to claim 1 , wherein the spinneret ejection hole forming the shape of the fiber is flat, and the end (W1) of the flat short axis of the ejection hole The ratio (W2/W1) of the central portion (W2) is 0.1 or more and less than 1.0, and the ratio (L/W1) of the long axis (L) and the short axis end (W1) is 10 or more and 55 or less . A method for producing a para-type wholly aromatic polyamide fiber, wherein the air gap from the spinneret surface to the coagulating liquid is set to 10 mm or less, and then the fiber is drawn . A braid using the para-type wholly aromatic polyamide fiber according to any one of claims 1 to 5. A resin composite using the para-type wholly aromatic polyamide fiber according to any one of claims 1 to 5. A catheter using the para-type wholly aromatic polyamide fiber according to any one of claims 1 to 5.

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