JPS63249716A - Production of fibrillated fiber and pulpy particle - Google Patents

Abstract

PURPOSE:To obtain the titled highly fibrillated yarn by a simple method, by extruding an optically anisotropic dope of para-orientated aromatic polyamide from a spinneret through a gas to a coagulating bath, releasing tension, impregnating the yarn with a blowing agent, drying and then expanding. CONSTITUTION:Para-orientated aromatic polyamide is dissolved in 97-101wt.% conc. sulfuric acid in >=14wt.% polymer concentration to give optically anisotropic dope, which is extruded from a spinneret to a gas, then to a coagulating solution, made into yarn and tension is released from the coagulated yarn in coagulation period and/or initial period of washing period wherein the amount of remaining sulfuric solvent is >=5wt.% based on dried yarn to give yarn having >=50wt.% water content. Then the yarn is impregnated with a solution of a blowing agent in a water-miscible solvent under release of tension to give >=0.5wt.% based on dried yarn weight of the blowing agent. The yarn is dried and heated to >=the decomposition temperature of the blowing agent to give the aimed yarn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing fibrillated fibers and gruppy particles having excellent heat resistance and mechanical properties. This invention relates to a method for industrially producing highly fibrillated fibers and matrix particles suitable for use as resin reinforcing materials, friction material 1 synthetic paper raw materials, etc.

[Conventional technology]

/IJ (p-phenylene terephthalamide>VC typified by matrix oriented aromatic polyamide is heat resistant.

It has excellent mechanical properties, electrical properties, etc., and is known to be useful as fibers, films, sheet-like materials, and lap-like particles.

For example, Japanese Patent Publication No. 50-8478 describes a fiber with high strength and high modulus obtained from an optically anisotropic solution of an aromatic polyamide. Fibrids obtained directly from anisotropic doping have also been described.

Furthermore, a method for obtaining 9-lupe-shaped particles is disclosed, in which a 9-belt-shaped material or monofilament is obtained from an optically anisotropic dope of a 2-oriented aromatic polyamide, and then the formed product is fibrillated by mechanical shearing force. has been done. However, the disclosure of this publication is.

It has been found that the degree of fibrillation is not necessarily at a satisfactory level even though it is limited to starting materials such as film-like materials or monofilaments, which have low density and are brittle and easily disintegrated. In addition, as disclosed in the answer to the patent opposition case against the application related to the publication, I4 fibers are made from optically anisotropic dope and then fibrillated by removing the multifilament from the optically anisotropic dope. It is also possible to produce fiber-shaped particles, but even in the fiber-shaped particles obtained by this method, there are many cases where the surface portion of the filament is only fluffy, probably due to mechanical shearing force, or there is no fibrillation. In order to improve the quality of the product, mechanical shearing force such as thorough beating or grinding must be applied to produce pulp-like particles with a small particle size, otherwise sufficient performance cannot be achieved.

[Problem that the invention seeks to solve]

In view of the above-mentioned current state of the prior art, the present invention is extremely useful for producing spherical particles, and as such.

Fibrillated fibers of oriented aromatic polyamide useful as reinforcing materials and highly fibrillated with suitable particle sizes! A method for manufacturing rug-shaped particles is provided.

[Means for solving problems]

In order to achieve the above object, the present invention provides an alternative to the conventional method of fibrillating fibers from the outside using mechanical shearing force.
As a result of extensive research into a method of uniformly fibrillating the entire fiber using crushing force from within the fiber, we found that
We discovered that highly fibrillated fibers and /4 loop-shaped particles can be obtained by impregnating the inside of fibers with a blowing agent and then using a chemical reaction to foam the blowing agent. Based on this, further research was conducted and the present invention was completed.

[Structure of the invention]

That is, 1 the present invention uses para-oriented aromatic polyamide at a concentration of 97%.
~101% by weight of concentrated sulfuric acid with at least 14% by weight of ? The optically anisotropic dope dissolved to a reamer concentration is extruded from a spinneret into a gas and then into a coagulation bath, and during coagulation and/or the remaining sulfuric acid solvent is reduced to 5% with respect to the dry fiber. At the initial stage of washing, the tension is substantially released from the coagulated thread, and a solution of the thread containing at least 50% by weight of water and a blowing agent dissolved in a water-miscible solvent is removed to substantially reduce the tension. The foaming agent is impregnated into the fibers in an amount of at least 0.5% by weight based on the weight of the dry fibers by contacting the fibers with a target, and then removed from the solution, and then while drying or once the foaming agent is impregnated into the fibers. A process for producing fibrillated fibers characterized by drying at a temperature below the decomposition temperature of the blowing agent and then heating to a temperature above the decomposition temperature of the blowing agent, and a method for producing fibrillated fibers comprising drying the fibrillated fiber at a temperature below the decomposition temperature of the blowing agent. Optically anisotropic Dogue dissolved in iso-sulfuric acid to a polymer concentration of at least 14% by weight is extruded from a spinneret into a gas and then into a coagulation bath, and during coagulation and/or the remaining sulfuric acid solvent is removed. Substantially relieves tension from the coagulated yarns at the initial stage of washing with a concentration of at least 5% by weight based on dry fibers;
A yarn containing water of 0% by weight or more and a solution of a blowing agent dissolved in a solvent miscible with water are brought into contact with each other under substantial release of tension to infuse the blowing agent into the fibers by the weight of the dry fibers. After impregnating the foaming agent to a concentration of at least 0.5% by weight based on the foaming agent, the foaming agent is taken out from the solution, cut into lengths of 30W or less, or before cutting, while drying or once the decomposition temperature of the foaming agent is reduced. This is a method for producing Al loop-like particles, which is characterized by drying at a temperature below and then heating to a temperature higher than the decomposition temperature of the blowing agent.

What is the Noyara-oriented aromatic polyamide referred to in the present invention?

The amide bond is at the para position of the aromatic ring or at a similar orientation position (4,4'-biphenylene, 1,5-naphthalene).

2.6-rifthalene, etc., consisting essentially of repeating units bonded in coaxial or parallel orientations in opposite directions, such as p'J (p-phenylenetele 7-thalamide). (Hereinafter referred to as PPTA (!: abbreviated),
Poly(p-benzamide), Isu(4,4'-benzanilidetele-7talamide), Poly(p-phenylene-4,4'-biphenylene dicarbonamide), Poly(p-7enylene-2, Examples include aromatic polyamides having a polypara-oriented structure or a structure close to a para-oriented structure, such as 6-naphthalene dicargenamide). These polyamides.

It is convenient to produce it from an aromatic diamine and an aromatic socargenic acid chloride by a conventionally known low temperature solution polymerization method. In particular, /su (p-phenylene teretal amyl) can be polymerized from simple monomers, is inexpensive, and is therefore preferred from an industrial standpoint.

In the present invention, the degree of polymerization of the /4-based aromatic polyamide is preferably 2.5 or more, more preferably 3.5 or more, since if it is too low, Yalp particles with good mechanical properties cannot be obtained. A polymer having a degree of polymerization that gives a logarithmic viscosity η1nh (a value measured at 30° C. by dissolving poly-f-0,5,9 in 100 ml of sulfuric acid) is selected.

In the present invention, optically anisotropic DOG, which is prepared by dissolving para-oriented aromatic polyamide in sulfuric acid, is used for fiber formation.

The concentration of sulfuric acid used in this case must be 97 to 101% by weight. If the concentration is less than 97% by weight, the ability to dissolve para-oriented aromatic polyamide decreases, making it difficult to obtain fibers with excellent physical properties. On the other hand, 101% by weight
The same applies to the above.

The solubility of the oriented aromatic polyamide is undesirable because it lowers its solvency.

Further, the polymer concentration in the dope needs to be 14% by weight or more. When the concentration is 14% by weight or less, it is difficult to form an optically anisotropic dope without blurring.

The viscosity of the dope increases, significantly reducing operability. On the other hand, if the concentration is too high, for example, 22 wt.% or more, the viscosity of the dope becomes too high, which necessitates setting the dope temperature high, which tends to cause difficulties in the spinning operation. Therefore, it should be chosen not to be too expensive. The polymer concentration of the spinning doug is most preferably between 16 and 20% by weight.

Optical anisotropy can be confirmed by placing a thin dope-stretched preparation on a slide glass between crossed nicols of a polarizing microscope, and the dark field of the crossed nicols changes to bright field. It can also be confirmed by the fact that it orients itself under shearing force during melting and reflects light diffusely, producing a metallic or pearl-like luster.

When preparing and using DOG, in the above polymer concentration range, the dope may solidify near room temperature, so it may be handled at a temperature from room temperature to about 80°C.

However, from the viewpoint of avoiding decomposition of the polymer as much as possible, it is preferable to select a temperature as low as possible as long as it does not solidify.

It is recognized that the nine-spinning dope prepared in this manner has optical anisotropy within the above polymer concentration and doping temperature ranges. The dope is once extruded into the air through a spinneret and then introduced into a coagulation bath.

Since the coagulating or coagulated yarn in the coagulation bath is hardly stretched, the discharged dope is drawn in the air directly below the nozzle and is stretched. In this stretching, if the stretching rate is low, the physical properties of the fiber, such as strength and initial modulus, cannot be sufficiently increased;
If the temperature is too high, the dope flow will be cut off between these points.

The stretching ratio is set between 4 and 15 times, preferably between 5 and 12 times. The length in the air where the dope is stretched, the distance from the surface of the spinning nozzle where the dope is discharged to the surface of the coagulation bath is usually in the range of about 1 to 50 yntx, preferably 3 to 20 intx. set, but is not limited to this. Specifically, it may be determined by taking into consideration the discharge speed of Dogue from the spinning nozzle, the above-mentioned draft rate, reducing the chance of filament fusion, and the like.

The pore diameter of the spinning nozzle used for discharging the dope is
It should be selected depending on the thickness of the fiber to be manufactured and the above draft rate setting, and is usually 0.05~
A range of 0.10 m is selected, but the range is not limited to this. Furthermore, the number of holes provided in the spinning nozzle is
It may be determined depending on the structure of the fiber to be manufactured, and is not particularly limited when carrying out the method of the present invention.

In the present invention, it is important to separate the spinning nozzle and the coagulation bath in order to obtain fibers with high density (fewer coids) and excellent mechanical properties.

In carrying out the invention, water or an aqueous sulfuric acid solution having a concentration of up to 70% is preferably used as the coagulating liquid. However, 1, for example, an aqueous solution of a salt such as ammonium chloride, calcium chloride, calcium carbonate, sodium chloride, sodium sulfate, etc., or a mixture thereof, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an organic solvent such as methanol, ethanol, ethylene glycol, etc. Alternatively, it may be an aqueous solution of these, and is not particularly limited.

The temperature of the coagulating liquid is generally kept at 15°C or lower, more preferably at 10°C or lower. This is because the lower the temperature of the coagulation bath, the less voids are generated inside and the density becomes larger.

This is because mechanical performance such as strength is also improved. Note that the lower limit of the coagulation bath temperature is not particularly limited, and is up to the melting point (freezing point) determined by the composition of the coagulation bath.

The fibers pulled out from the coagulation bath are substantially neutralized and washed with water or aqueous alkali to remove the solvent and coagulation bath liquid by a method similar to the conventional method.

In the method of the present invention, the tension acting on the fibers is released during the washing step in which the amount of rR remaining at the time of coagulation is large.

This is important in increasing the effect of impregnation despite the high density and therefore dense structure. The reason for this has not yet been elucidated in detail, but
It is presumed that there is a delicate relationship with the orientation of the molecular chains of the ripple-shaped fibers swollen with water, the formation of crystals, etc.

In the production of fibers, it is difficult to effectively release the tension from the yarn during coagulation under industrial production methods and conditions. It is preferable to wash with water under substantially no tension. For such a method, it is industrially convenient to transfer the yarn containing the residual solvent in the coagulation bath onto a net conveyor and wash it there under no tension. The time to release the tension from the coagulated filament is when the amount of residual solvent in the filament is at least 5% by weight relative to the dry fiber, more preferably at least 10% by weight. This is important in order to make the impregnation with the agent effective. On the other hand, if the tension is released only after coagulation and washing have proceeded until the residual solvent is less than 5% by weight, the impregnation will not be sufficient.

The coagulated fiber threads are taken out of the spinning bath in the coagulated state via a suitable device such as a take-off roll, and are shaken off by a transfer device onto a conveyor for processing.

The yarn pile deposited on the treatment conveyor moves with the conveyor and is led to a water washing step to remove the solvent from the yarn, and then impregnated with a blowing agent in an impregnation treatment step.

In the washing step, preferably the washing water is

The coagulation liquid contained in the yarn pile is supplied onto the yarn pile in a shower form from a perforated plate, in a mist form from a spray nozzle, or along a large number of brush-like fibers, and then flows through a processing conveyor. However, the method of supplying the washing water is not limited in carrying out the present invention, and is not limited to the above example.

The thread pile-like thread that has been washed with water must be kept in a water content of at least 50% by weight without being dried in a state where the tension is substantially released, and it must be brought into contact with a solution containing a blowing agent. No. If the moisture content is less than 50% by weight, the fiber is in a so-called half-dry state, and the rate of diffusion from the solution containing the impregnating agent into the interior of the fiber decreases significantly, making it impossible to impregnate a practical amount.

The method of impregnation is carried out by supplying a solution containing a foaming agent to the thread pile on the processing conveyor by spraying, showering, etc., by the same means as washing with water, or by immersing the whole conveyor in the processing liquid.

The blowing agent used in the present invention is not particularly limited, and can be heated, for example, with oxygen.

Any foaming agent that generates gas such as nitrogen or carbon dioxide may be used. Specifically, for example, inorganic foaming agents such as sodium bicarbonate and ammonium carbonate, and organic azo compounds that foam mainly with nitrogen gas as a main component.

Examples include nitroso compounds, sulfonyl hydrazide compounds, etc.; among these, azobisnitrile compounds (having 5 or less alkyl groups or cyclohexyl groups),
Sulfonyl hydrazide compound (R-5o2NH-NH2
) is particularly preferably used because it is easy to control foaming and easy to handle.

In the present invention, it is important that the blowing agent is used as a solution dissolved in a water-miscible solvent.

For solutions dissolved in water-immiscible solvents, the water content is reduced by 50%.
When it comes into contact with yarn containing more than % by weight, it may not be sufficiently diffused into the fibers, making it difficult to form a high degree of fibrillation, or it may take a long time for diffusion to become efficient. This is because processing cannot be performed. The term "solvent miscible with water" as used herein refers not only to water but also to a solvent that dissolves at least 5% by weight in water, such as methanol,
Alcohols such as ethanol, ethers, amide solvents such as dimethylformamide and N-methylpyrrolidone, dimethyl sulfoxide, and the like are used. In special cases, emulsifiers may also be used as solvents that are not themselves miscible with water.

It is also useful for the method of the present invention to use it as a dispersion with a surfactant or the like.

Such blowing agent solutions usually have a blowing agent concentration of 1.

It is used in an amount of 5 to 10% by weight, but is not limited thereto. In the impregnation treatment of the present invention, in some cases, when the yarn is brought into contact with the above-mentioned treatment liquid, the solubility of the blowing agent may decrease due to the moisture retained in the yarn, and a portion of the blowing agent may precipitate. Even in this case, the impregnation treatment can be carried out without any particular problem.

Other conditions for the impregnation treatment may be determined as appropriate depending on the amount of blowing agent impregnated into the fiber required, but the impregnation treatment temperature should be below the decomposition temperature of the blowing agent used. .

In the present invention, it is necessary that the amount of one blowing agent impregnated is at least 0.5% by weight based on the weight of the dried fibers. If it is less than 0.5% by weight, when it is heated and foamed later, it will not be possible to obtain a crushing force due to the generation of gas sufficient to cause fibrillation, resulting in incomplete fibrillation. Preferably, the impregnation is 1% by weight or more.

In the method of the invention, after the above-mentioned impregnation has been carried out.

It is removed from the impregnating solution, washed with water or the like to remove excess solution if necessary, and then dried. Drying is an important process to increase fiber density and refine the structure. usually.

・In the manufacturing process of matrix-oriented aromatic polyamide fibers, they are dried at a temperature of 120°C or higher, but in the present invention, they are dried at a temperature higher than the decomposition temperature of the impregnated blowing agent to cause fibrillation. In order to form fibrillated fibers, drying at a temperature below the decomposition temperature of the standing foaming agent and then heating at a temperature above the decomposition temperature is necessary. In a method in which undried fibers containing a blowing agent are dried and heated above the decomposition temperature of the blowing agent, the structure is densified by drying and the crushing force of the gas generated by the decomposition of the blowing agent causes the fibers to decompose. Splitting occurs in the fiber length direction, resulting in highly fibrillated fibers.

Even in some fibers that have been once dried at a temperature below the decomposition temperature of the blowing agent, fibrillated fibers similar to those described above can be obtained by subsequently heating the fiber to a temperature above the decomposition temperature of the blowing agent.

In the method of the present invention, the oriented aromatic polyamide has a structure that is highly oriented and is highly oriented in the fiber length direction during the fiberization process. It is believed that splitting occurs and highly fibrillated fibers are obtained.

In order to obtain all the pulp particles in the method of the present invention, 30 m
Cutting the undried fibers impregnated with a blowing agent into the following lengths and decomposing the blowing agent by the same means and method as described above, and cutting the fibrillated fibers described above into suitable lengths of 30 m or less. It is done by doing.

In the method of the present invention, it is also effective to heat the foaming agent to a temperature above its decomposition temperature by using a grinder such as a scraping roll or a grind mill refiner to heat the foaming agent using frictional heat to cause foaming and fibrillation. This is preferably applied.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
These examples do not limit the invention in any way.

In the examples, "%" and "part" unless otherwise specified.
represent weight percent and weight part, respectively. Furthermore, the main parameters used in the method of the present invention are measured as follows.

<Method for measuring intrinsic viscosity> Intrinsic viscosity (ηinh) is measured by a conventional method at 30°C using a solution of polymer or fiber dissolved in 98.5% by weight concentrated sulfuric acid at a concentration (C1 = 0.511/di). .

Reference Example (Method for producing poly-p-phenylene terephthalamide) Poly-IJ-p-7 2-2-2 terephthalamide (hereinafter referred to as "PPTA") was obtained by a low-temperature polymerization method. In the polymerization apparatus shown in Japanese Patent Publication No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48 parts of paraphenyl diamine was dissolved in 1000 parts of N-methylpyrrolidone.
．． 6 parts were dissolved. After cooling to 8°C, 91.4 parts of terephthalic acid dichloride was added at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese-like shape, so it was
The polymerization reaction product was discharged from the polymerization apparatus according to the method described in Japanese Patent No. 43986, and immediately transferred to a twin-screw closed kneader, and the polymerization reaction product was pulverized in the same kneader. next.

The finely pulverized product was transferred to a Hefsiel mixer, an approximately equal amount of water was added thereto, and the mixture was further pulverized, filtered, washed several times in hot water, and dried in hot air at 110°C.

95 parts of pale yellow PPTA with ηlnh of 560 was obtained.

Note that PPTA with different η1nh can be easily obtained by changing the ratio of N-methylpyrrolidone and monomers (claphenylenediamine and terephthalic acid dichloride), or the ratio between heptamers, etc.

Example 1 PPTA Q with intrinsic viscosity (171 nh %E 7.05
A polymer solution for spinning (hereinafter referred to as "dope") was prepared by dissolving the polymer in 99.7% concentrated sulfuric acid while maintaining the temperature at 80°C so that the polymer concentration was 18.7%. . It was confirmed by polarizing microscopy observation under crossed Nicols that this polymer solution exhibited optical anisotropy.

This dough f was left to stand under vacuum for 2 hours to defoam, and then used for spinning.

After passing the r-p through a gear pump and filtering it using a candle filter made of 8 layers of 300 mesh stainless wire mesh, it is passed through a spinning nozzle with a pore diameter of 07 m x φ and 100 holes into a coagulation bath through a spinning nozzle of 5 mm. I pushed it inside. A 10% aqueous sulfuric acid solution cooled to 1.5° C. was used as the coagulation liquid, and the yarn introduced into the coagulation bath was changed direction with a direction changing roll and then introduced into a Nelson roll. At this time, the amount of sulfuric acid remaining in the fiber was 16.2% by weight of the dry fiber.

The yarn taken up by the Nelson roll is then processed by the device disclosed in Japanese Patent Publication No. 55-9088, that is,
The yarn was transferred onto a reversing net using a pair of gear rolls (rolls in which gear-shaped rolls mesh with each other and the yarn is fed out between them), and then the yarn was reversed and placed on a processing net conveyor. The pile placed on the processing net conveyor is washed with water using a single shower.
In the impregnation treatment process with a water content of about 220% by weight, azobisisobutyronitrile e1 was added using the same shower method.
An acetone solution dissolved at a concentration of 2% was dropped onto the surface, and the surface was left in contact with the surface for 10 minutes to impregnate the surface, followed by washing with water to remove excess acetone solution. Then, it was dried through hot air drying at 80°C.

The material was passed through a hot air stove maintained at a temperature of 180° C. while controlling the speed so that the retention time was 5 minutes, and then wound up using a winding machine.

In addition, it was recognized from the absorption of the azo group of Fvr-IR that the fiber after drying contained 1.2% azobisisobutyronitrile. It was also observed with the naked eye that the obtained fibers had many finely split fibrils in each single filament. The physical properties of this fiber are fineness of 154 denier/1
00 filament, tensile strength of 19.7 II/d, elongation of 4.3%, and initial modulus of 485 N/d.

Example 2 The fibrillated fibers obtained in Example 1 were rolled back into a total shape and cut into a length of 4 m to obtain pulp particles.

The pulp-like Canadian hardness was 700, and the strength of the paper obtained by making the paper using a Tu-Standard paper machine was 0.7 U//llm2.

Example 3 Moisture content 220 using exactly the same equipment and method 1 conditions as Example 1
% water-washed yarn was produced, and then brought into contact with a 30% dimethyl sulfoxide solution of p-toluenesulfonyl hydrazide for 20 minutes, washed with water, and then cut into 5 mm lengths to obtain short fibers.

FT indicates that this short fiber contains approximately 2.4% p-toluenesulfonyl hydrazide based on the dry fiber weight.
-Recognized by IR absorption.

Next, this short fiber was placed in a heat furnace with an internal temperature of 160°C for 30 minutes.
It was put in for 0 minutes and then dried and heated.

It was observed that the obtained short fibers were fibrillated and intertwined with each other to form yalp-like particles.

This pulp-like particle had a Canadian water rating of 480, and was recognized to have excellent paper-making properties.

The tensile strength of the paper obtained by the Ta-Standard paper machine was 0.9 kg, /+m2.

Example 4 An impregnated washed thread was obtained using the same recipe as in Example 1 except that a 10% solution of azodicardenamide in N-methyl-2-pyrrolidone was used.The impregnated washed thread was then dried at 120°C. Azogical? Fibrillated fibers of polyparaphenylene terephthalamide were obtained by placing the fibers in a heat treatment furnace at 250°C for 5 minutes so that the temperature reached the decomposition temperature (200 to 210°C) of poly(paraphenylene terephthalamide) or higher.

Example 5 After air-drying the impregnated short fibers obtained in Example 3,
It was placed in a grind mill in which two polishing plates faced each other and rotated in reverse. At this time, the temperature inside is approximately 140℃ due to frictional heat.
heated to. After 20 minutes of treatment, fine, spiny-like particles with a length of less than 2 u were obtained due to scission.

〔Effect of the invention〕

According to the present invention, it is possible to obtain fibers and/f rug-like rice particles that are uniformly and highly fibrillated throughout the fibers by crushing force from inside the fibers, and it is also possible to obtain fibers and/or rug-like rice grains that are highly fibrillated throughout the fibers, and also to obtain large amounts of fibrillated rice particles by using methods using mechanical shearing force. Gurg-like particles can be easily obtained without requiring energy.

Furthermore, as a result of obtaining a matrix-oriented aromatic polyamide fiber in the form of fibrillated continuous filaments, it can be used as is as a reinforcing fiber with extremely high adhesive strength for reinforcing rubber or belts.

Claims (3)

[Claims] (1) An optically anisotropic dope prepared by dissolving a para-oriented aromatic polyamide in concentrated sulfuric acid with a concentration of 97 to 101% by weight to give a polymer concentration of at least 14% by weight is passed through a spinneret into a gas, and then into a coagulation bath. The tension is substantially released from the coagulated yarn during coagulation and/or at the initial stage of washing when the residual sulfuric acid solvent is 5% by weight or more based on the dry fiber, and is at least 50% by weight or more. A yarn containing moisture is obtained, and the yarn is contacted with a solution of a blowing agent in a water-miscible solvent under substantial release of tension to inject the blowing agent into the fibers of the yarn, forming a dry fiber. The blowing agent is impregnated to a concentration of at least 0.5% by weight based on the weight, removed from the solution, and then dried, or once dried at a temperature below the decomposition temperature of the blowing agent. A method for producing fibrillated fibers, which comprises heating to a temperature higher than the decomposition temperature of. (2) An optically anisotropic dope prepared by dissolving a para-oriented aromatic polyamide in concentrated sulfuric acid with a concentration of 97 to 101% by weight to give a polymer concentration of at least 14% by weight is passed through a spinneret into a gas, and then into a coagulation bath. The tension is substantially released from the coagulated yarn during coagulation and/or at the initial stage of washing when the residual sulfuric acid solvent is 5% by weight or more based on the dry fiber, and is at least 50% by weight or more. A yarn containing water of After impregnating the foaming agent with a concentration of at least 0.5% by weight, the blowing agent is taken out from the solution, cut into lengths of 30 mm or less, or before cutting, while drying, or once at the decomposition temperature of the blowing agent. A method for producing pulp-like particles, which comprises drying at a temperature below and then heating to a temperature equal to or higher than the decomposition temperature of the blowing agent. (3) The blowing agent is azodicarbonamide, azobisnitrile compound (▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ However, R and R' are an alkyl group or a cyclohexyl group having 5 or less carbon atoms),
Sulfonyl hydrazide compound (R-SO_2NH-NH
The manufacturing method according to claim 1 or 2, which is one or more selected from _2).