JPS6221814A - Poly(p-phenylene terephthalamide) fiber and production thereof - Google Patents

Abstract

PURPOSE:To produce the titled fiber having high strength and suitable for cutting, by coagulating a sulfuric acid dope of poly(p-phenylene terephthalamide) with a specific organic solvent, and taking up the coagulated fiber from the coagulation bath at a specific speed. CONSTITUTION:A sulfuric acid dope of poly(p-phenylene terephthalamide) is coagulated with an organic solvent compatible with sulfuric acid, having a solubility parameter of <=11 and free from hydrogen atom capable of forming hydrogen bond (e.g. pyridine, dioxane, tetrahydrofuran, anisole, etc.). The concentration of the sulfuric acid dope is >=15wt%, preferably >=17wt%. The coagulated fiber is taken out of the coagulation bath at a speed to apply a draft of >=1.5, preferably 3-10 to the fiber. The fiber produced by this process has a single filament strength of >=20g/denier and a refractive index gradient (TRIV) of -0.2--0.005 measured by polarized light oscillating perpendicular to the fiber axis.

Description

Detailed Description of the Invention (1) Industrial Application Field The present invention relates to a poly(P-phenylene terephthalamide) (hereinafter sometimes abbreviated as rPPTAJ) fiber having a novel microstructure and a method for producing the same. More specifically, the present invention relates to a PPTA fiber that has a novel structure not seen in known PPTA fibers and therefore has extremely high strength and excellent machinability, and a method for producing the same.

(2) Prior Art PPTA is a polymer that has been known for a long time, and due to its rigid molecular structure, it was expected that fibers with excellent heat resistance and mechanical properties could be obtained.

However, since PPTA is poorly soluble in organic solvents,
Cipriani proposed a basic method of wet spinning using concentrated sulfuric acid as a solvent (Special Publication No. 38-18573!11).
, Cipriani's method itself was not industrialized. On the other hand, it has long been known both theoretically and experimentally that when a rigid polymer is dissolved in a solvent, it forms a liquid crystal under a certain degree of polymerization, a certain concentration, and a certain temperature. , J., Flory: Proc., Roy, S.
oc, +A234+Page 73 (1956)).

If a polymer solution exhibiting optical anisotropy in a liquid crystal state can be ejected from a nozzle and solidified without disturbing the orientation of the liquid crystals generated inside the nozzle, it is possible to achieve high strength, high modulus, and highly molecular It is easily expected that fibers with oriented chains can be produced. In fact, Kuuorek proposed a wet spinning method for a concentrated solution of these aromatic polyamides with a rigid and linear molecular structure in a liquid crystal state (Japanese Patent Publication No. 8474/1984 tIVI), which brought him into the limelight once again. Ta. However, even with Kuwolek's method, in order to obtain useful high strength, the as-spun fibers must be further heat-stretched, and this heat-stretching inevitably results in an increase in modulus as well as an increase in strength. On the other hand, it had the disadvantage of extremely lowering elongation.

Blaze is a method of producing as-spun fibers by air-discharge wet spinning of an increased concentration of an optically anisotropic dope with improved elongation compared to Kuwolek's method. (Unexamined Japanese Patent Publication No. 47-39)
458 Publication), and furthermore, high modulus can be achieved by subjecting this fiber to tension heat treatment (Japanese Unexamined Patent Publication No. 47
-43419).

The major structural feature of blaze is that these fibers not only have a high orientation of the crystal C axis in the fiber length direction, but also have a crystal V axis orientation in the radial direction of the fiber cross section. (For example, Japanese Patent Application Laid-Open No. 47-394
PPTA fiber obtained by the blaze method is commercially available as Kevlar or Kevlar 49, and is used as a reinforcing material for rubbers, plastics, etc. It is used.

(3) Problems to be Solved by the Invention However, it has been pointed out that one of the drawbacks of these fibers is that they are difficult to cut. Special scissors have even been developed to cut these fibers and woven fabrics without forming them into composite materials. However, even with the new tools, the problem has not been completely resolved, and cutting remains difficult. A more serious problem arises when fibers are used as reinforcing fibers in composite materials, and existing cutting equipment is inadequate, so cutting with lasers or high-energy water jets is being considered. However, these devices are expensive and still contain technical problems. For example, the fibers may come loose at the cut surface, making it impossible to obtain an accurate end face, or the fibers may be pulled out, causing the composite material to partially collapse or become distorted. As an extreme example, when used as a reinforcing material for a timing belt, there are parts of the belt where the fibers are not cut properly on the end face, and as a result, the fibers are pulled out during use, causing damage to the main body on which the belt is attached. It has even become tangled in equipment, causing malfunctions.

The present invention was born out of a completely unexpected phenomenon that occurred in the course of research aimed at improving these drawbacks of conventional PPTA fibers.

(4) Means for solving the problem The inventors
Various studies have been carried out with the aim of creating PPTA fibers that are both high strength and easy to cut, but it has not been possible to achieve this goal using conventional techniques such as blaze. However, in the previously known literature such as Blaze, no one has tried to make PP with a specific organic solvent.
When the sulfuric acid dope of TA is coagulated, the conventional I) P T
It is possible to obtain fibers with a new structure that could not be found in A fibers (specifically, a structure in which the crystal axis is oriented in the circumferential direction), and fibers with such a structure have high strength. However, they found that this fiber was easy to cut with a knife, and further research found that this fiber had significantly improved resistance to compressive forces not found in conventional aramid (PPTA) fibers. Through repeated efforts, the present invention was completed.

That is, the invention of the present application No. 1 is a fiber consisting essentially of poly (P-phenylene terephthalamide) having a single fiber strength of at least 20 g/denier, which is refracted by polarized light vibrating in the direction perpendicular to the fiber axis. gradient of rate (TRI
v) is -0,2 to -0,005.

In the second invention of the present application, a dope in which poly(P-phenylene terephthalamide) is dissolved in sulfuric acid or a solvent mainly composed of sulfuric acid to a polymer concentration of at least 15% by weight is poured into a gas through a spinneret and then into a coagulation bath. Extrude inside,
In a method for producing poly(P-phenylene terephthalamide) fibers in which a coagulated thread is drawn out of a coagulation bath and a coagulant is removed, the coagulant contains hydrogen atoms that are compatible with sulfuric acid and have the ability to form hydrogen bonds. using one or more organic solvents having a solubility parameter of 11 or less, or a mixture of these with sulfuric acid, and at a rate such that a draft of at least 1.5 is imparted. This is a method for producing poly (P-phenylene terephthalamide) fiber, which is characterized by drawing out a coagulated filament from a coagulation bath.

The fibers of the present invention consist essentially of PPTA.

Here, "substantially" means a small amount of polymers other than PPTA (for example, poly-(m-phenylene terephthalamide), poly-(p-phenylene terephthalamide), poly-(p- phenylene isophthalamide), poly(m-phenylene isophthalamide), poly(polymethylene ethylene refthalamide), aliphatic polyamide, alicyclic polyamide, polyester, polyimide, polyurethane, polyurea, etc.] are blended, PPT
A has other repeating units (e.g., nuclear-substituted p-phenylene unit, nuclear-substituted or unsubstituted biphenylene unit (i, 0-phenylene unit, m-phenylene unit,
Poly)methylene units, viridiref units, bonding units such as esters, urethanes, ureas, ethers, thioethers, etc.) are copolymerized, and various additives and compounding agents (e.g.
This means that dyes, antioxidants, ultraviolet absorbers, brighteners, pigments, etc.) may be added.

The fiber of the present invention is claimed to have a single fiber strength of 20 g/denier or more. This is because, when used as an industrial fiber, the value generally increases as the strength increases.

Single fiber strength is measured according to the method disclosed in JP-A-47-39458. The single fiber strength is preferably 25 g/denier or more. Such high-strength fibers can be conveniently produced by spinning with a specific draft using the so-called gap spinning method in which the spinneret and coagulation bath are separated.

The greatest feature of the fiber of the present invention is that
TRh (the gradient of the refractive index of the fiber due to polarized light vibrating in the direction perpendicular to the fiber axis) measured by the method described in Publication No. 2 is in the range from -0.2 to -0,005, that is, smaller than 0. That's true. The definition and measurement method of TRh are as follows.

The average refractive index distribution observed from the side of the fiber can be measured by the interference fringe method obtained using a transmission quantitative interference microscope (for example, an interference microscope Interfaco manufactured by Karlspusuys Jena, East Germany). This method is applicable to fibers with a circular cross section.

The refractive index of a fiber is characterized by its refractive index (NV) for polarized light oscillating in the direction perpendicular to the fiber axis. All measurements described here are performed using green light (wavelength λ = 546 mμ).
) is carried out using the refractive index (NV ) obtained using

The fibers to be tested use optically flat glass slides and coverslips, with an inert encapsulation for the fibers with a refractive index (N8) that gives a shift of the interference fringes within the range of 0.2 to 2 wavelengths. immersed in the agent. The refractive index of the mounting medium (Nl
l ) is a value at 20° C. measured using an Atsube refractometer using green light (wavelength λ = 546 mμ) as a light source. Several fibers are immersed in this encapsulant so that the single fibers do not come into contact with each other. Furthermore, the fibers should have their fiber axes perpendicular to the optical axis of the interference microscope and the interference fringes. Photograph this interference fringe pattern and
Analyze at 00x to 2000x magnification.

In Figure 3, the refractive index of the fiber encapsulant is N, the average refractive index between s' and s'' of the fiber is NV, the thickness between S' and 8'' is t, and the wavelength of the light beam used is λ. When the distance between parallel interference fringes on the ground (corresponding to 1λ) is D, and the deviation of the interference fringes due to fibers is d, the optical path difference R is expressed as R;□λ=(Nv NB ) t.

Center of fiber r. The distribution of the average refractive index (NV) of the fiber at each position can be determined from the optical path difference from the optical path difference to each position from the outer circumference rQ to the outer circumference rQ.

The thickness t can be calculated by assuming that the obtained fiber has a circular cross section. However, due to variations in manufacturing conditions or accidents after manufacturing, there may be cases where the cross section is not circular. In order to eliminate this inconvenience, it is appropriate to use a portion to be measured where the displacement of the interference fringes is symmetrical with the fiber axis as the axis of symmetry. The measurement is from 0 (center of fiber) to 0, where r is the radius of the fiber.
．． The average refractive index at each position can be determined by performing the measurement at intervals of 0.05 r between 95 r and 0.05 r. The central refractive index Nv0 due to polarized light vibrating in the direction perpendicular to the fiber axis is the value of the refractive index at "=0 (center of the fiber). The refractive index gradient (TRIV) due to polarized light vibrating in the vertical direction of the fiber axis is as follows. It is expressed by the formula.

Here, TRIv, Nvo, Nvo, and s are each
These are the refractive index gradient due to polarized light vibrating in the vertical direction of the fiber axis, the center refractive index, and the average refractive index at two positions of the radius.

The fact that the TRIV measured in this way is negative for the fiber of the present invention means that the crystalline axis of PPTA has priority in the circumferential direction in the cross section of the fiber, as schematically shown in Figure 1B. This is thought to be due to the fact that the fibers are symmetrically oriented, and as far as the present inventors know, PPTA fibers with such a structure have not yet been reported. All conventionally known PPTA fibers are
Either the TRIv was 0 or positive and the crystal axes were oriented in the radial direction of the cross section as shown in A in FIG. 1, or the structure was such that the b-axis was not oriented.

It is believed that the crystal axis orientation behavior observed in PPTA fibers is deeply related to hydrogen bonding during the coagulation process, similar to the long-known orientation behavior of cellulose. As far as we know, when a sulfuric acid dope of PPTA is coagulated in water (which has a very high hydrogen bonding capacity) or an aqueous coagulation bath, regardless of the polymer concentration or optical properties in the dope, Basically, the crystal axis is oriented perpendicular to the solidification plane (that is, in the case of fibers, in the radial direction). However, if the agglomerated structure is disturbed due to the solidification rate or the tension during solidification, the apparent orientation of the axes may become random. When a solvent with a solubility parameter exceeding 11 is used as a coagulation bath, such as an amide solvent such as lydimethylformamide or dimethylacetamide, using a hydrogen-bonding a-containing solvent such as methanol, ethylene glycol, or glycerin outside the waterside. It was found that only fibers with crystallographic axes oriented in the radial direction were obtained in the same way as in hydrogen coagulation baths. In addition, regarding the solubility parameter, for example, J. Macromol.

5ctence-Rev, Macromol, C
hem, Vol. C15, No. 2, pp. 279-393 (1
976).

On the other hand, the fiber of the present invention is an organic solvent that is compatible with sulfuric acid and does not have hydrogen atoms capable of forming hydrogen bonds, and has a solubility parameter of 11 or less.
For example, pyridine, dioxane, tetrahydrofuran,
It is obtained when a sulfuric acid dope of PPTA is coagulated with anisole or the like, and coagulation in such a system has never been carried out to the best of the knowledge of the present inventors.

The fiber of the present invention preferably has a TR of -0.1 to 0.01.
Should have IV. - When the TRIv is smaller than 0,005, preferably 10, and the TRIv smaller than the old one, the cutting strength with a knife becomes significantly higher than that of conventionally known fibers (i.e., TRIv≧0), even though the tensile strength is greater. It is characterized by being small and very easy to cut. The lower limit of TRIV is -0.2, but in many cases it is difficult to obtain a TRIv lower than about -0.1, so it is preferably -0.1 or more. negative TR
At present, it is not known at all what mechanism is involved in the unique structure of the circumferential orientation of the crystal axis expressed by IV, which surprisingly reduces the cutting strength with a knife.

The fibers of the present invention include at least 1.408/crl
Those having a density of 1 are preferred. Density is 1.40g/
c11! If the fiber is smaller, it indicates that the fiber contains many cracks or voids, has extremely low crystallinity, or has an uneven agglomerated structure, and its strength is low, making it of no practical value. reduce Such low density fibers may be obtained, for example, by wet spinning directly from a spinneret into a coagulation bath, or by spinning with very low draft or polymer concentration. For a more desirable level of strength, PPTA fibers with a density of at least 1.43 g/cm are preferred. PPTA of the present invention
The density of the fibers can be measured in a conventional manner using toluene and carbon tetrachloride at 25° C. using a density gradient tube.

The fibers of the present invention have a logarithmic viscosity (η+
nh: Dissolved in 98% sulfuric acid at a concentration of 0.5 g/di,
(a value measured using a conventional method at 25°C) is desirable. This is because fibers made of PPTA with a high degree of polymerization have greater strength. More preferably, ηi
nh≧4.0.

The fibers of the present invention are not particularly limited in their thickness, but fibers with a diameter of 0.1 to 10 deniers are generally preferred because they have better tensile strength and knot strength.

The fiber of the present invention can only be produced by a specially designated method and conditions, and this production method constitutes the second invention of the present application.

In producing the fibers, it is first necessary to prepare a dope in which PPTA is dissolved in sulfuric acid or a solvent mainly composed of sulfuric acid to a polymer concentration of at least 15% by weight. At this time, as described above, PPTA may be copolymerized with other components if necessary, or may be blended with other polymers in small amounts. Furthermore, since PPTA generally causes a slight decrease in the degree of polymerization in a doped state, the degree of polymerization of the charged PPTA may be determined in consideration of this point.

In order to ensure the desired level of physical properties in the fibers of the present invention, the PPTA charge will preferably have a logarithmic viscosity of about 3.5 or higher. PPTA can be obtained, for example, by the method described in Japanese Patent Publication No. 35-14399.

The solvent used to prepare the dope is sulfuric acid or a mixture based on sulfuric acid. From the viewpoint of solubility, the sulfuric acid is preferably concentrated sulfuric acid with a concentration of about 96% by weight or more. It may also be so-called fuming sulfuric acid.

Examples of substances that can be mixed with sulfuric acid include chlorosulfuric acid, fluorosulfuric acid, dichloroacetic acid, acetic acid, phosphorus pentoxide, and nitrobenzene. Polymer concentration is 15%
It is necessary that it is above.

This is because fibers spun from dopes with a polymer concentration of less than 15% by weight generally have low density and low strength. The polymer concentration is preferably 17% by weight or more. At such polymer concentrations, the dope often requires slight warming. As the temperature increases, the rate of deterioration of the polymer in the dope increases.
It is not desirable to be exposed to high temperatures for too long. Typically, a dope in the range of room temperature to 120"C is used. The dope used in the present invention often exhibits optical anisotropy. The dope contains conventional additives, such as antioxidants. , an ultraviolet stabilizer, etc. may be blended.

The dope thus prepared must be extruded through a spinneret into a gas and then into a special coagulation bath. It may be advantageous, especially for industrial production, to degas, filter and meter the dope before passing it through the spinneret. The shape of the spinneret, the number of holes, the size of the holes, etc. are not particularly limited. The hole size is usually 0.01 to 0.5
■Those with a heavy diameter are used. The linear speed of the dope extruded from the spinneret is not particularly limited, and may be determined solely based on requirements such as productivity and draft requirements described below. It is important that the dope stream extruded from the spinneret first passes through a gas. This is because when the fibers are suddenly extruded from a spinneret into a coagulation bath without passing gas, it is virtually impossible to increase the draft, and the resulting fibers have a low density due to non-uniform coagulation. This is because the strength and modulus are also small. Gases include air, nitrogen,
Examples include argon, oxygen, carbon dioxide, etc.
Air is the most preferred because of its economic advantages and ease of use.

gas thickness (i.e., the gap between the spinneret surface and the coagulation bath surface)
is selected to be about 0.2 to 201 m. This is because the smaller the thickness, the more likely the resulting fiber will have high strength and high modulus. However, if the thickness is too small, the spinnability will be poor, so the thickness of the gas is preferably 0.5 to 10 mm.

The dope stream forced into the gas must then be forced into a special coagulation bath where it undergoes coagulation. In the present invention, the coagulant is one or more organic solvents that are compatible with sulfuric acid, do not have hydrogen atoms capable of forming hydrogen bonds, and have a solubility parameter of 11 or less. Mixtures or mixtures thereof with sulfuric acid are used.

Specific examples include dioxane, pyridine, tetrahydrofuran, trioxane, anisole, mixtures thereof, and mixtures of these with sulfuric acid. In the present invention, the selection of the type of coagulant is very important.

In other words, by selecting a special and novel coagulant, a unique fiber structure expressed by negative TRIv can be developed, resulting in both excellent strength and good processability. On the other hand, when conventionally used coagulants such as water, methanol, ethylene glycol, and other hydrogen-bonding coagulants are used, the fibers have O or positive TRh, resulting in poor machinability. .

In the method of the present invention, the coagulant may contain up to about 5% by weight of water and other components (eg, hydrogen-bonding organic solvents).

In the present invention, the temperature of the coagulation bath is not particularly limited, and is usually used at about -30 to +50°C.

The temperature is preferably -10 to +20°C from the economical point of view of evaporation, cold storage energy, etc. in industrial implementation.

The dope stream extruded into the coagulation bath undergoes coagulation in the coagulation bath, and then the coagulated thread is removed from the coagulation bath by at least 1.
It is necessary to draw at a speed that produces a draft of 5. Here, "draft" is the value obtained by dividing the linear velocity of the coagulated filament when it is drawn out from the coagulation bath by the linear velocity of the dope passing through the spinneret. This is because if the draft is less than 1.5, the strength of the fibers is unsatisfactory. The upper limit of the draft is not specified, but is usually 15 or less. Draft is 3~
It is preferable to select it within the range of 10 from the viewpoint of fiber strength.

The coagulated filament drawn out from the coagulation bath passes through a step of removing sulfuric acid and the like. If a large amount of sulfuric acid or the like remains in the yarn, the performance of the fiber will be impaired. Preferably, the remaining sulfuric acid, etc.
000 ppm or less, more preferably 500 ppm or less. Removal of sulfuric acid and the like is usually carried out by washing the yarn with a coagulant. However, if desired, the coagulated filament may be washed with water or an alkaline aqueous solution, provided that the content of sulfuric acid to polymer in the coagulated filament is approximately 50% or less.

The coagulant must then be removed from the coagulated filament from which the sulfuric acid, etc. has been completely or almost completely removed. For this purpose, a method is usually used in which an organic solvent as a coagulant is evaporated. However, if necessary and possible,
It can also be carried out by once replacing the coagulant in the coagulated filament with water and then evaporating the water (that is, drying).

Various methods are possible for the process of removing sulfuric acid, etc. or coagulants, such as a method of processing the thread running between two or more rollers, a method of processing the thread on rollers, a method of processing the thread by winding it around a bobbin or a thread. , a method of depositing on a net, or a combination of these methods.

The fibers may be provided with an oil agent or the like in a desired step.

The washed and dried fibers may also be heat treated to modify their performance, if desired. The heat treatment is performed under relaxation or under tension (e.g. 1-15 g/d) for about 150 g/d.
It can be carried out at ~600°C. Preferably, it is carried out in an inert atmosphere such as nitrogen.

Heat treatment will generally result in crystal growth and improved chemical resistance. Furthermore, since heat treatment under tension further advances molecular chain orientation, an increase in modulus can generally be expected.

(5) Effects of the Invention In addition to the high strength, high modulus, and high heat resistance of conventional PPTA fibers, the fiber of the present invention has excellent cutting workability. These characteristics of the fibers of the present invention can be found in the unique orientation of the PPTA crystal axis, which gives rise to the practical feature that the fiber/woven fabric composite material is extremely easy to cut. The fibers of the present invention also have the characteristics of being difficult to fibrillate and having a high modulus as spun (ie, without heat treatment). Furthermore, the fibers can be expected to have excellent dimensional stability in the radial direction, and therefore are particularly preferably used as reinforcing fibers for composite materials used in environments with large changes in temperature and humidity.

Another feature of the fibers of the present invention is that they have significantly improved resistance to compressive forces compared to conventional PPTA fibers, making them suitable for use in areas subject to compressive and bending forces. be. Such favorable compressive properties are believed to be due to the fact that the fibers of the present invention have a unique orientation structure of crystalline axes that is not found in conventional PPTA fibers.

The fibers of the present invention are useful as reinforcing materials for rubber such as tire cords and various belts, and reinforcing materials for plastics by utilizing the above-mentioned properties. When the fibers of the present invention are used for reinforcing these rubbers and plastics,
Although the fibers of the present invention are usually used in the form of multifilaments, they are not limited thereto, and can be used in the form of monofilaments, roving yarns, staples, chopped strands, etc., such as robes, woven fabrics, plastics, etc. It can also be used as a reinforcing material for metals, cement, ceramics, etc., and as cotton.

(6) Examples Examples are given below to specifically explain the present invention. In the Examples, each measurement was performed by the following method. The strength, elongation, and modulus of single fibers were measured according to the method disclosed in Japanese Patent Application Laid-Open No. 47-39458, and the gradient TR1v of the refractive index due to polarized light vibrating perpendicularly to the length direction of the fiber was determined as described above. I did it the way I did.

The density of PPTA fibers was determined by using toluene and carbon tetrachloride.
Measurements were made using a density gradient tube at 5°C. Knife cut strength was used as a method to evaluate the cutting workability of fibers. Knife cut strength was evaluated by setting a cutting knife on the fixed grip side of the tensile testing machine and setting both ends of the single fiber on the movable grip side, and measuring the cutting strength when cutting the folded portion of the single fiber with the knife. The measurement length of the single fiber at this time was 5 cm, and the other conditions were the same as when measuring the single fiber strength.

The resistance of a fiber to compressive stress is expressed as the ratio of the residual tensile strength to the original tensile strength after compressive force is applied to the fiber. The compressive force was applied using the shrinkage force when preparing the nylon 6 film by a wet method. That is, nylon 6
A 15% formic acid dope was prepared, and a film was cast on a glass plate on which the PPT eight filament to be tested was placed.The film was coagulated in water, washed, and dried at 105°C for 1 hour. The nylon 6 film was shrunk through coagulation and drying, so that compressive force was applied to the PPTA fibers held within the film. The dried sample was placed in formic acid and nylon 6
was almost completely dissolved and removed, then washed with water and dried, and this sample was subjected to a tensile test. (The tensile test was performed using the above-mentioned ti
l Same as fiber test method. ) Example 1 According to the reference example of JP-A-55-122012, a logarithmic viscosity of 5.80 PPTA was obtained.

PPTA in 99.8% sulfuric acid with polymer concentration of 18%
The mixture was dissolved at 80° C. and defoamed under reduced pressure for about 2 hours. While filtering the dope kept at about 80°C,
Extruded from a spinneret with 50 mm diameter pores, approx.
After running the dragon in the air, it was introduced into a coagulation bath maintained at about 10°C. As coagulation baths, (A) dioxane (solubility parameter 10.0) and (B) pyridine (solubility parameter 10.6) were used. The coagulated thread was drawn out at 100 m/min while traveling approximately 60 cm in the coagulation bath. At this time, a calculated draft of approximately 6.5 was required.

The fibers taken out from the coagulation bath were once wound onto a stainless steel bobbin, immersed overnight in a container containing the same organic solvent as the coagulation bath to advance deoxidation, and then washed with water day and night. The fibers were further dried at about 100°C.

The properties of the obtained fibers are described below.

(A) Dioxane coagulated fiber; TRIv--0,012
, density -1.43g/c+d, single fiber denier -1.2
, single fiber strength = 28.2 g/denier, single fiber elongation = 3
．． 0%, single fiber modulus = 833 g/denier, knife cut strength = 4.7 g/denier, compression resistance -〇, 78° (B) Pyridine coagulated fiber, TRIv--
0,021, density = 1.41 g/cJ, single fiber denier -1,2, single fiber strength = 30.1 g/denier, single fiber elongation -5,0%, single fiber modulus -725 g/denier, knife cut Strength = 6.6 g/denier, compression resistance -〇, 70° These fibers have lower knife cut strength and superior compression resistance than the fibers of the following comparative examples.

Comparative Example Using the dope and spinning apparatus and conditions of Example 1, the coagulation baths were (A) water and (B) methanol.

The properties of the obtained fibers were as follows.

(A) Water-coagulated fiber, TRIV= +0.057,
Density=1.44g/c+J, IL fiber strength=33.
3g/denier, single fiber elongation = 5.5%, single fiber modulus = 529g/denier, knife cut strength = 1
0.7 g/denier, compression resistance = 0.57° (B) Methanol coagulated fiber, TRIV = +0.0
38, Density=゛1.42g/cd, $Fiber strength-28
, 4g/denier, single fiber elongation = 5.2%, single fiber modulus -560g/denier, knife cut strength = 8
．． 1 g/denier, compression resistance = 0.60° Example 2 The fiber of (A) of Example 1 was subjected to tension heat treatment. Heat treatment is
4g in a tubular heat treatment machine in a nitrogen atmosphere at approximately 300℃
/denier tension was applied for 5 seconds.

The obtained fibers had TRIv--0,008, density-1,
45 g/cl, single fiber strength -27,6 g/denier, single fiber elongation -2,10; o, jji fiber modulus = 1
060g/denier, knife cut strength = 5.2g
/denier, compression resistance = 0.68.

Example 3 PPTA with a logarithmic viscosity of 6.2 was dissolved in 99.6% sulfuric acid with a logarithmic viscosity of 19.3
Dissolved in % of the world. The dope, which had been degassed and filtered under reduced pressure, was placed in a spinneret (0.07 mm diameter, 50° C.) maintained at approximately 85°C.
5℃ through the air gap of about 10 cranes.
of tetrahydrofuran (solubility parameter = 9.5). The fibers run through the approximately 301 tetrahydrofuran bath were taken out with a draft of 4.0, and transferred onto a stainless steel wire gauze via rollers. next,
The sulfuric acid was completely removed by washing with water on a wire mesh. The fibers were air-dried at room temperature while placed on a wire mesh to obtain PPTA fibers. In addition, when the coagulated filament was sampled before being transferred to a wire gauze and the sulfuric acid content was measured, the sulfuric acid/polymer ratio was 0.29.

The properties of the obtained fibers are: TRIv = -0,025, density = 1.45 g/cJ, single fiber denier = 2.1,
Single fiber strength = 29.4 g/denier, single fiber elongation -6,
1%, single fiber modulus - 640 g/denier, knife cut strength = 5.4 g/denier, compression resistance - 0
．． It was 72.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the orientation characteristics of PPTA fibers, A1 and B indicate the orientation direction of the crystal axis in the fiber cross section, A1 is a conventionally known PPTA fiber, B,
indicates the fiber of the present invention. A2 and B2 indicate molecular chain orientation in the fiber longitudinal section. Figure 2 is a schematic diagram of interference fringes observed when a PPTA fiber is observed from the side with an interference microscope using polarized light vibrating in the direction perpendicular to the fiber axis; (B) is the case of the fiber of the present invention (Example 1) (refractive index 1.61.2).
(when using immersion liquid). d: Displacement of interference fringes due to fiber, distance between parallel interference fringes of D two-bank ground, r: radius of cross section of fiber. (A) in FIG. 3 is a schematic diagram of the cross section of the fiber, and (B)
1 shows interference fringes observed when the fiber of the present invention is observed from the lateral direction using an interference microscope using polarized light vibrating in the direction perpendicular to the fiber axis. d: Displacement of interference fringes due to fibers, D: Distance between parallel interference fringes in the background, r: Radius of fiber cross section, ro: Center of fiber cross section, rG: Outer periphery of fiber, S: Arbitrary position within fiber cross section Point, S', S': outer circumference of fiber corresponding to S, t'
Thickness of fiber cross section at s. (A+) (B+) (A2) (B2) Figure 1 (A) (B) Figure 2

Claims (1)

[Scope of Claims] 1. A fiber consisting essentially of poly(P-phenylene terephthalamide) having a single fiber strength of at least 20 g/denier, the refractive index of the fiber with polarized light vibrating perpendicular to the fiber axis. The gradient (TRI_v) of -0.2 to -
A fiber characterized in that it is 0.005. 2. Fiber according to claim 1, characterized in that it has a density of at least 1.40 g/cm^3. 3. Extruding a dope in which poly(P-phenylene terephthalamide) is dissolved in sulfuric acid or a sulfuric acid-based solvent to a polymer concentration of at least 15% by weight through a spinneret into a gas and then into a coagulation bath; In a method for producing poly(P-phenylene terephthalamide) fibers in which a coagulated thread is drawn out of a coagulation bath and a coagulant is removed, the coagulant contains hydrogen atoms that are compatible with sulfuric acid and have the ability to form hydrogen bonds. using one or more organic solvents having a solubility parameter of 11 or less, or a mixture thereof with sulfuric acid, and at a rate such that a draft of at least 1.5 is imparted. A method for producing poly(P-phenylene terephthalamide) fiber, which comprises drawing a coagulated filament from a coagulation bath.