JP2007182645A - Method for producing acrylic fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an acrylic fiber having good appearance quality in high productivity when producing the acrylic fiber. <P>SOLUTION: The method for producing the acrylic fiber comprising extruding a spinning stock solution comprising a polyacrylonitrile-based polymer from a spinneret, coagulating the extruded solution in a coagulation bath, and subjecting the obtained yarn to a pressurized steam drawing step involves extruding the spinning stock solution while regulating the back pressure of the spinneret at the extrusion of the spinning stock solution so as to be 20-200 kgf/cm<SP>2</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an acrylic fiber, and particularly relates to a method for producing an acrylic fiber capable of obtaining an acrylic fiber having a good quality with high productivity.

  Acrylic fibers are being used for slate reinforcement as an asbestos substitute material in addition to applications for clothing and construction. Acrylic fibers are also suitably used as carbon fiber precursor fibers, and in order to further increase the amount used, it is important to reduce manufacturing costs and provide inexpensive acrylic fibers. It is.

  As a means to reduce the production cost of acrylic fiber, aiming to improve equipment productivity, that is, to increase the production amount per unit equipment, thickening the yarn to be processed or processing yarn There are means such as higher density that narrows the occupation width of the device per strip. However, with these means, the thermal conductivity and liquid permeability to the inside of the yarn are reduced by thickening and increasing the density of the yarn. Thread breakage may occur and process passability may decrease.

  Another means for reducing the production cost of acrylic fibers is to increase the amount of the spinning dope discharged from the die and increase the speed of the process without increasing the thickness and density. Can be mentioned. As for speeding up, there is a method of increasing the speed at which the acrylic fiber is taken out from the coagulation bath, but it is difficult to increase the speed greatly because the operation beyond the spinnability limit cannot be performed. Therefore, without changing the speed at which the discharged yarn is taken out from the coagulation bath, a method of gradually increasing the speed by in-air stretching, in-bath stretching or pressurized steam stretching to increase the final winding speed is mainly adopted. There has been proposed a method for improving stretchability by further improving the stretching process and reducing manufacturing cost.

  Specifically, a method for improving stretchability by air stretching after solidification has been proposed (see Patent Document 1). By using aerial drawing, the solvent of the spinning dope is prevented from abruptly detaching and separating, and the cross-sectional shape during coagulation is maintained by drawing uniformly, and the remaining solvent of the spinning dope is plasticized. It works as an agent and enables effective stretching. However, as described in the example of Patent Document 1, the effect of air stretching has only about twice the stretchability, and the effect of reducing the manufacturing cost by air stretching is small. In addition, since the densification by stretching proceeds while the solvent remains in the fiber, it is necessary to lengthen the washing process or use a surfactant or a solvent in order to sufficiently remove and separate the solvent. Further, the process becomes complicated, which is not preferable, and if the fiber is further stretched with the solvent remaining, adhesion between single fibers is likely to occur and the strength may be reduced.

  Separately, a multi-stage stretching method has been proposed as a method for stably and effectively performing hot water stretching in stretching in a bath after solidification (see Patent Document 2). However, when this proposed method is used for thick yarns with thick yarns, the effect of improving stretchability is not sufficient due to the low permeability of hot water into the yarns.

  Furthermore, it is possible to stretch at a higher temperature than in-bath stretching, and pressure steam stretching has been conventionally used as a higher stretching method (see Patent Document 3). Further, as a method for further improving the stretchability in the pressurized steam stretching, a method of optimizing the wetness of steam and appropriately wetting the yarn to give a plasticizing effect has been proposed (see Patent Document 4). However, even in this proposed method, the effect of improving stretchability is small for thick yarns and high-density yarns for the same reason as in Patent Document 2, and the wetness is optimized even for thin yarns. However, it was difficult to perform a high stretching process stably.

The method of improving the stretching process by improving the stretching process as described above is difficult to stabilize the process, and it is inevitable that the process is complicated, and as a result, the stretch potential of the fiber itself does not change. The big effect cannot be expected.
JP-A 63-275713 Japanese Patent Laid-Open No. 50-154531 Japanese Examined Patent Publication No. 60-39663 JP 58-214521 A

  In view of the current situation, an object of the present invention is to provide a production method for obtaining acrylic fibers having high productivity and good quality when producing acrylic fibers.

In order to achieve the above-mentioned object of the present invention, the acrylic fiber manufacturing method of the present invention has the following configuration. That is, the acrylic fiber production method of the present invention is a method for producing an acrylic fiber that is subjected to a pressurized steam stretching step by discharging a spinning stock solution comprising a polyacrylonitrile-based polymer from a die and coagulating it in a coagulation bath. This is a method for producing an acrylic fiber that discharges by controlling the pressure on the back surface of the die at the time of discharging the spinning dope in a range of ²⁰ to 200 kgf / cm ² .

  According to a preferred embodiment of the method for producing acrylic fiber of the present invention, the intrinsic viscosity of the polyacrylonitrile polymer is in the range of 1.5 to 5, and the concentration of the polyacrylonitrile polymer in the spinning dope is 12 to 30. It is preferably in the range of% by weight, and the viscosity at the time of discharging the spinning dope is preferably in the range of 200 to 2,500 poise.

  Further, the carbon fiber production method of the present invention is made flame-resistant at a temperature in the range of 200 to 300 ° C. in the air, and subsequently 300 to 2,000 ° C. in an inert atmosphere. It is the manufacturing method of the carbon fiber which carbonizes at the temperature of the range of this.

  According to the present invention, high-stretching treatment can be stably realized in the stretching treatment after solidification, and acrylic fibers having high quality and good quality can be obtained. Thereby, the manufacturing cost of acrylic fiber can be reduced.

  The inventors of the present invention have earnestly pursued the purpose of obtaining acrylic fibers having high productivity and good quality by reducing the production cost by performing a high drawing process in the production process of acrylic fibers. As a result of repeated studies, it has been found that the discharge conditions when discharging the spinning dope from the die affect the fiber structure after coagulation, and that the fiber structure affects the stretchability in the pressurized steam drawing process following the coagulation, The present invention has been reached.

  Hereinafter, the manufacturing method of the acrylic fiber of this invention is demonstrated in detail.

In the present invention, a spinning stock solution composed of a polyacrylonitrile-based polymer is discharged from a die, solidified in a coagulation bath, and an acrylic fiber is produced through a pressurized steam drawing process. In the present invention, the back pressure of the base when discharging the spinning dope is in the range of ^{20 to} 200 kgf / cm ² , preferably in the range of 25 to 180 kgf / cm ² , and more preferably in the range of 30 to 160 kgf / cm ^2. . Here, the back pressure of the base is determined by the following equation.

Base back pressure (kgf / cm ² ) = 1.28 × v × L × η / (π × g × d × D ⁴ )
・ Π: Circumference ratio ・ g: Gravitational acceleration = 9.8 (m / sec ² )
V: Spinning stock solution discharge rate from a single hole in the die (cm ³ / sec)
L: Thickness of the base discharge part (mm)
D: Hole diameter of the base (mm)
・ Η: Viscosity at the time of discharging the spinning dope
D: Specific gravity of the spinning dope = 1.1
By restricting and controlling the pressure on the back surface of the die within the above range, high-stretching can be stably achieved when the steam solidified in the coagulation bath is subjected to pressurized steam stretching. The reason for this is not clear, but the degree of entanglement between the polyacrylonitrile molecules in the spinning dope can be controlled by the pressure on the back of the die. It is considered that the molecules are in a state of being highly stretchable. That is, when the back pressure of the base is too low, the degree of entanglement between the polyacrylonitrile molecules is too small, so that the entanglement is released by a little stretching and high stretching cannot be performed. Conversely, the back pressure of the base is too high. In this case, since the degree of entanglement between the polyacrylonitrile molecules is too large, the entanglement cannot be sufficiently extended, so that it is considered that the stretchability cannot be improved. Also, from the viewpoint of process stability, if the back pressure of the base is too small, the discharge of the spinning stock solution may not be stable, and stable operation may not be possible, while if the back pressure of the base is too high, Since it is necessary to increase the pressure resistance of the base and piping, the manufacturing cost increases.

  In the present invention, the intrinsic viscosity of the polyacrylonitrile polymer is preferably in the range of 1.5 to 5, more preferably in the range of 1.7 to 4.5, and still more preferably in the range of 2 to 4. It is. The higher the intrinsic viscosity, the higher the physical properties of the acrylic fiber. In addition, when the obtained acrylic fiber is used as a carbon fiber precursor fiber, the higher the intrinsic viscosity, that is, the higher the molecular weight, the stronger the connection between the molecules, and the higher the tension can be achieved by carbonization treatment. A carbon fiber having a high elastic modulus can be obtained. If the intrinsic viscosity of the polyacrylonitrile polymer is lower than the above range, the physical properties of the acrylic fiber may be lowered. Moreover, when the obtained acrylic fiber is used as a carbon fiber precursor fiber, the carbon fiber may not be able to be stretched at high tension, and the resulting carbon fiber may have low physical properties. On the other hand, when the intrinsic viscosity of the polyacrylonitrile-based polymer is higher than the above range, gelation of the spinning dope becomes remarkable and stable spinning becomes difficult.

  In the present invention, the concentration of the polyacrylonitrile polymer in the spinning dope is preferably in the range of 12 to 30% by weight, more preferably in the range of 14 to 28% by weight, still more preferably 16 to 26% by weight. Range. If the concentration of polyacrylonitrile polymer in the spinning dope is lower than this range, the solvent to be detached or separated when the spinning dope is coagulated in a coagulation bath increases, and the fibers cannot be sufficiently densified. Fiber strength may be reduced. Moreover, when the acrylic fiber which is not sufficiently densified is used as a carbon fiber precursor fiber, the tensile strength of the obtained carbon fiber may be lowered. On the other hand, if the concentration of the polyacrylonitrile polymer in the spinning dope is higher than this range, gelation of the spinning dope becomes remarkable and spinning may not be stable.

  In the present invention, the discharge viscosity of the spinning dope is preferably in the range of 200 to 2,500 poise, more preferably in the range of 230 to 2,200 poise, and still more preferably in the range of 250 to 2,000 poise. . Here, the discharge viscosity of the spinning dope refers to the viscosity of the spinning dope measured at the temperature of the nozzle itself that discharges the spinning dope as the temperature of the spinning dope at the time of discharge. The discharge viscosity of the spinning dope is a factor related to the back pressure of the die, and the discharge viscosity in such a range is preferable for setting the back pressure of the die to the above range, and if the discharge viscosity is too low, spinning is possible. On the contrary, when the viscosity at the time of discharge is too high, the spinning dope becomes easy to gel and stable spinning becomes difficult.

  Next, the manufacturing method of the acrylic fiber of this invention is demonstrated in detail later on in order.

  In the present invention, the acrylic fiber is obtained by discharging and spinning a polyacrylonitrile polymer from a die. The polyacrylonitrile-based polymer is obtained by polymerizing acrylonitrile with preferably 98 mol% or more, more preferably 99 mol% or more and the copolymerization component preferably less than 2 mol%, more preferably less than 1 mol%. is there. When there are too many copolymer components, plasticity will become high, and since it is plasticized too much in the extending process after coagulation | solidification, stretchability may not improve.

  The copolymerization component is not particularly limited, but when the obtained acrylic fiber is used as a carbon fiber precursor fiber, a component having a flame resistance promoting action is used for the purpose of promptly promoting the flame resistance reaction. It is preferable to copolymerize 0.1 mol% or more. On the other hand, as the amount of copolymerization of the component having the flameproofing promoting action increases, the rate of heat generation in the flameproofing reaction increases and the risk of runaway reaction may occur, so the copolymerization amount of such component exceeds 1 mol%. It is preferable to set it to a range that does not exist. Examples of the component having a flame resistance promoting action include those having at least one carboxyl group or amide group.

  Specific examples of the copolymer component include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide, and methacrylamide. Since the carboxyl group has a higher flame resistance promoting effect than the amide group, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, and the like can be mentioned.

  As a polymerization method of the polyacrylonitrile-based polymer, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, and the like can be applied, but a solution polymerization method using an organic solvent capable of uniformly dissolving the polymerization raw material is preferable. Used. Specific examples of the organic solvent used in the solution polymerization method include dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, and dimethyl sulfoxide is most preferable from the viewpoint of solubility.

  Acrylic fibers can be obtained by spinning a polyacrylonitrile polymer. At the time of spinning, the polyacrylonitrile-based polymer such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide is dissolved in a soluble solvent to obtain a spinning dope. In particular, when a solution polymerization method is used, if the solvent used for the polymerization and the solvent used for the spinning dope are the same, the step of separating the resulting polyacrylonitrile-based polymer and re-dissolving in the solvent is performed. This is a preferred embodiment because it is unnecessary. The concentration of the polyacrylonitrile polymer in the spinning dope is as described above.

  Prior to spinning the spinning dope, it is preferable to pass the spinning dope through a filter having an opening of 1 μm or less to remove the polymer raw material and impurities mixed in each step. Thereby, when the obtained acrylic fiber is used as a precursor fiber of carbon fiber, the obtained carbon fiber has high tensile strength.

  As the spinning method, a wet spinning method or a dry-wet spinning method is preferably used because of its high productivity. Among these, the dry and wet spinning method in which the spinning solution is discharged from the die and introduced into the coagulation bath through a space of 1 to 4 mm to coagulate the fibers can improve the denseness of the fibers, and is more preferable in the present invention. Can be used.

  The shape of the die used in the present invention is such that the hole diameter D is in the range of 0.05 to 0.18 mm, the thickness L of the discharge part is in the range of 0.1 to 0.5 mm, and the L / D is 1.5. Is preferably in the range of ˜4, more preferably, the pore diameter D is in the range of 0.08 to 0.15 mm, the discharge portion thickness L is in the range of 0.16 to 0.45 mm, and L / D is It is a range of 2-3. The shape of the die is preferably in the above range in order to make the pressure on the back surface of the die within a desired range and from the viewpoint of spinnability in spinning and stability during discharge.

  In the present invention, in order to make the viscosity at the time of discharging the spinning dope within the above range, it is preferable to control the temperature at the time of discharging the spinning dope. As described above, the temperature at which the spinning dope is discharged is regarded as the temperature of the die itself that discharges the spinning dope. By controlling the temperature of the die, the temperature at which the spinning dope is discharged can be controlled, and the viscosity at the time of discharging. Can be controlled. The temperature is preferably in the range of 10 to 85 ° C, more preferably in the range of 15 to 80 ° C. If the temperature of the spinning dope is too low, condensation may occur on the discharge surface of the die when discharging from the die, and if the temperature of the spinning dope is too high, gelation becomes prominent and stable spinning is achieved. May be difficult.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning dope and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the polyacrylonitrile-based polymer and is compatible with the solvent used in the spinning dope can be used. Specifically, it is preferable to use water.

  In the present invention, after the discharged yarn material is introduced into a coagulation bath and solidified, an acrylic fiber is obtained through a pressure steam drawing process, but if necessary, a water washing step, a drawing step in the bath, An oil agent application step and a drying heat treatment step can be appropriately incorporated.

  The water washing step is preferably incorporated immediately after being taken out from the coagulation bath as a means for removing the solvent remaining from the spinning dope and the water and solvent taken out from the coagulation bath from the coagulated fiber.

  The stretching process in the bath is generally a method in which the yarn is stretched by passing it through hot water adjusted to a temperature preferably in the range of 30 to 98 ° C. In this process, a single or a plurality of stretching baths are used. This step may be combined with the water washing step or after the water washing step.

  The oil agent application step is suitable for improving process passability and handling properties. Further, when the obtained acrylic fiber is used as a carbon fiber precursor fiber, the single fibers may adhere to each other at the initial stage of the flameproofing treatment and carbonization treatment. For the purpose of preventing the adhesion, silicone and the like It is preferable to apply an oil consisting of As such silicone, modified silicone is preferably used, and amino-modified silicone having high heat resistance is preferably used.

  The drying heat treatment process is a process of drying water or the like in the washing process or the stretching process in the bath, and may be either a contact system or a non-contact system as long as it can be efficiently dried in a short time, and the single fibers do not adhere to each other, and It is preferable to carry out at the temperature of the range of 120-190 degreeC from a viewpoint of drying efficiency.

  The pressurized steam stretching is preferably carried out at a temperature in the range of 120 to 190 ° C. from the viewpoint of stretchability in which single fibers do not adhere to each other.

  The single fiber fineness of the acrylic fiber of the present invention is preferably in the range of 0.3 to 1.3 dtex, more preferably in the range of 0.5 to 1.0 dtex. If the single fiber fineness is too small, the spinnability may be reduced. Conversely, if the single fiber fineness is too large, flame resistance can sufficiently progress to the inside of the single fiber when used as a precursor fiber of carbon fiber. In addition, the process passability in the subsequent carbonization treatment may be reduced.

  Acrylic fiber obtained by the above method is flame resistant at a temperature in the range of 200 to 300 ° C. in the air, and then carbonized at a temperature in the range of 300 to 2,000 ° C. in an inert atmosphere. Carbon fibers having various physical properties can be produced.

  When the acrylic fiber obtained by the method for producing an acrylic fiber of the present invention is used as a carbon fiber precursor fiber, the total number of filaments of the acrylic fiber bundle is in the range of 10,000 to 100,000. Preferably there is. When the number of filaments is out of the range, productivity may be reduced, or uniform processing may not be performed in flame resistance or carbonization.

  The flameproofing time can be appropriately selected according to the treatment temperature, but the specific gravity of the resulting flameproofed fiber is preferably in the range of 1.3 to 1.5, more preferably 1.32 Setting to be in the range of 1.47 is a preferred embodiment for the purpose of improving the process passability in the subsequent carbonization treatment and the physical properties of the resulting carbon fiber.

  Subsequent to the flameproofing treatment, carbon fiber is obtained by carbonizing in an inert atmosphere. As an inert atmosphere, nitrogen, argon, xenon etc. can be illustrated preferably, for example, and nitrogen is preferably used from an economical viewpoint.

  The carbonization treatment is preferably performed separately because different reactions occur in the temperature range of 300 to 800 ° C. and in the temperature range of 800 to 2,000 ° C., and the maximum treatment temperature is 1,200 to 2 , Preferably in the range of 1,000 ° C. In the low temperature region of carbonization, it is preferable to set the temperature and time so that the specific gravity of the treated fiber is preferably 1.5 to 1.7 from the subsequent carbonization treatment passability in the high temperature region. It is. The treatment time of the carbonization treatment in the high temperature region can be appropriately selected according to the treatment temperature, but it is more preferred that the specific gravity of the obtained carbon fiber is preferably in the range of 1.76 to 1.87. It sets so that it may become 1.77-1.86. When the specific gravity is too small, the carbonization treatment is insufficient, so that the physical properties expressed in the obtained carbon fiber may be low. Conversely, when the specific gravity is too large, brittleness becomes remarkable. It may be weakened by rubbing, and the quality and processability may deteriorate.

  The obtained carbon fiber can be electrolytically treated for surface modification. Examples of the electrolytic solution used for the electrolytic treatment include acidic solutions such as sulfuric acid, nitric acid and hydrochloric acid, alkalis such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or salts thereof. Can be used as an aqueous solution. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied. By such electrolytic treatment, in the composite material obtained using carbon fiber, the adhesion between the carbon fiber and the matrix can be optimized, and the brittle fracture of the composite material due to excessive adhesion or the tensile in the fiber direction The problem that strength is reduced and the tensile strength in the fiber direction is high, but the problem of poor adhesion to the resin and the absence of strength properties in the non-fiber direction are solved. In the resulting composite material, the fiber direction and non-fiber Strength characteristics balanced in both directions are developed.

  Thus, according to the present invention, it is possible to obtain acrylic fibers having high productivity and good quality, and as a result, the production cost of the acrylic fibers can be reduced, and the acrylic fibers are used as a precursor. Since the manufacturing cost can be reduced also in the carbon fiber used as the fiber, the carbon fiber can be suitably developed for general industrial uses such as automobile use and reinforcement.

  Next, the manufacturing method of the acrylic fiber of this invention is demonstrated more concretely using an Example. The measuring methods of various physical property values used in this example are collectively described below. Tables 1 and 2 collectively show the experimental conditions and measurement results used in the examples and comparative examples.

<Viscosity when spinning stock solution is discharged>
The temperature of the die is measured, and the viscosity at this temperature is measured with a B-type viscometer using a separately prepared spinning stock solution. In this example, a B8L type viscometer manufactured by Tokyo Keiki Co., Ltd. was used as the B type viscometer, rotor No. 4 was used, the spinning stock solution viscosity was in the range of 0 to 1,000 poise, the rotor rotation speed was 6 rpm, and the spinning stock solution viscosity was The range of 1,000 to 10,000 poise was measured at a rotor rotational speed of 0.6 rpm.

<Intrinsic viscosity of polyacrylonitrile-based polymer>
150 mg of a polyacrylonitrile polymer dried by heat treatment at 120 ° C. for 2 hours and maintained at a temperature of 25 ° C. is dissolved in 50 ml of dimethylformamide containing 0.1 mol / liter of sodium thiocyanate. The obtained solution was temperature-controlled in a hot water bath at a temperature of 25 ° C., and the Ostwald viscometer that was previously adjusted to a temperature of 25 ° C. was used to set the drop time between the marked lines with an accuracy of 1/100 second. Measure and let the time be t (seconds). Similarly, dimethylformamide added with 0.1 mol / liter of sodium thiocyanate in which the polyacrylonitrile-based polymer is not dissolved is also measured, and the dropping time is defined as t0 (seconds). The intrinsic viscosity [η] is calculated using the following formula.
[Η] = {(1 + 1.32 × ηsp) ^ (1/2) −1} /0.198
(However, ηsp = (t / t0) −1).

<Drawing limit magnification in pressurized steam stretching and determination of stretch ratio capable of long-term operation>
When the speed used for pressurized steam stretching is kept constant, the steam pressure is changed and the steam temperature is changed in increments of 10 ° C from 120 ° C to 190 ° C. The drawing-side speed is read, and the value obtained by dividing the speed by the speed used for the pressurized steam stretching is defined as the stretching limit magnification at that temperature. Here, the fluff means a piece of single fiber of 5 mm or more protruding from a bundle of running acrylic fibers. And let the value of the highest draw ratio in the draw limit magnification in each temperature be the draw limit ratio in pressurization steam drawing, and let it be an index of the extensibility in pressurization steam extension of the fiber. The larger the stretching limit magnification, the higher the final winding speed, and the manufacturing cost can be reduced.

  Count the fluff on the take-up side of the pressurized steam drawing and find the draw ratio that can be operated for a long time. The measuring time is the time for which the acrylic fiber 10,000 m travels, and may be measured continuously or intermittently. The draw ratio when no fluff is generated is determined to be a draw ratio that can be operated for a long time.

<Fiber specific gravity>
The method described in JIS R7601 (1986) is followed. In the case of a flame-resistant fiber, ethanol is used, and in the case of a fiber or carbon fiber after carbonization treatment in a low temperature region, ortho-dichlorobenzene is used as a reagent. 1.0 to 1.5 g of fiber was collected and dried at 120 ° C. for 2 hours. After measuring the absolute dry mass W1 (g), the reagent having a known specific gravity (specific gravity ρ) was impregnated, and the fiber mass W2 (g) in the reagent was measured. The following formula, fiber specific gravity = (W1 × ρ) / The fiber specific gravity is obtained from (W1-W2). In this example, Wako Pure Chemical Industries, Ltd. special grades were used for ethanol and orthodichlorobenzene.

<Determination of stretch limit tension in carbonization and carbonization tension that can be operated for a long time>
Measurement is performed at a desired processing temperature on the processing outlet side in a high temperature region of 800 ° C. or higher of carbonization processing. A value obtained by measuring the tension expressed when the rate of carbonization treatment is kept constant and changing the take-off rate, and dividing the measured tension (g) by the total fineness (dtex) of the carbon fiber bundle after carbonization treatment. Is the tension (g / dtex) in carbonization. The maximum carbonization treatment tension that appears when the pulling speed is changed is defined as the stretching limit tension in the carbonization treatment, and is an index of the stretchability in the carbonization treatment. Larger values indicate that carbonization treatment with higher tension is possible, which is suitable for producing carbon fibers having a high tensile elastic modulus.

  The fluff is counted on the take-off side of the carbonization treatment, and the carbonization treatment tension that can be operated for a long time is obtained. The measurement time is the time for which the carbon fiber of 1,000 m travels, and it may be measured continuously or intermittently. The tension in the carbonization treatment when the fluff is 5 pieces / m or less is determined as the carbonization treatment tension capable of operating for a long time. A carbon fiber having a higher tensile elastic modulus can be obtained as the carbonization treatment tension increases.

<Tensile strength and tensile modulus of carbon fiber>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The resin impregnated strand of carbon fiber to be measured was 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 weights). Part) is impregnated into carbon fiber and cured at a temperature of 130 ° C. for 30 minutes. The number of strands to be measured is six, and the average value of each measurement result is the tensile modulus and tensile strength. In this example, “Bakelite (registered trademark)” ERL 4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate.

[Example 1]
A copolymer obtained by copolymerizing 99.5 mol% of acrylonitrile and 0.5 mol% of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to obtain a polyacrylonitrile-based polymer having an intrinsic viscosity of 2.7. Obtained. The amount of dimethyl sulfoxide was adjusted so that the resulting polyacrylonitrile-based polymer had a concentration of 17% by weight to obtain a spinning dope. Subsequently, ammonia gas was blown to pH 8.5 to neutralize itaconic acid, and the hydrophilicity of the spinning dope was improved by introducing ammonium groups into the polymer component. The diameter of the hole D is 0.1 mm, the thickness L of the discharge part is 0.25 mm, the L / D is 2.5, and a pipe having a shape of 4,000 holes is used. A temperature of 65 ° C. was set, and a spinning stock solution having a temperature of 65 ° C. was discharged into the air. The discharging viscosity of the spinning dope was 800 poise, the amount of spinning dope discharged from the single hole of the die was 0.00156 cm ³ / sec, and the back pressure of the die was 118 kg / cm ² . After passing through a space of a distance of about 3 mm, it was coagulated by dry and wet spinning introduced into a coagulation bath consisting of a 35% by weight dimethyl sulfoxide aqueous solution adjusted to a temperature of 3 ° C. The coagulated yarn was washed with water and then stretched 3 times in a bath using warm water at a temperature of 60 ° C. to give an amino-modified silicone silicone oil. Subsequently, a drying heat treatment was performed using a roller heated to a temperature of 170 ° C., and a pressure steam stretching process was performed. The stretching limit magnification in the pressure steam stretching was 8 times. Moreover, since the draw ratio at which the operation can be performed for a long time was 6 times, the acrylic fiber was drawn at such a magnification, the total draw ratio was 18 times, the single fiber fineness was 0.7 dtex, and the number of filaments was 4. 1,000 acrylonitrile fiber bundles were obtained.

  Six obtained acrylonitrile fiber bundles were combined and the number of filaments was set to 24,000, followed by flameproofing treatment in air at a temperature range of 230 to 260 ° C., and flameproofing fiber having a specific gravity of 1.37. Got. The obtained flame-resistant fiber was subsequently carbonized at a temperature rising rate of 100 ° C./min in a temperature range of 300 to 800 ° C. in a nitrogen atmosphere to obtain a fiber having a specific gravity of 1.6, and subsequently 800 to 800 nm in a nitrogen atmosphere. Carbonization was performed in a temperature region of 1,600 ° C. At this time, the stretching limit tension in the carbonization treatment was 1.9 g / dtex. Moreover, since the carbonization treatment tension capable of operating for a long time was 1.55 g / dtex, the carbonization treatment was performed with such a tension to obtain carbon fibers having a specific gravity of 1.82. The obtained carbon fiber is subjected to a surface treatment that gives an electric charge of 40 coulombs / g by an anodic charge treatment in an aqueous sulfuric acid solution, washed with water, then applied with a sizing agent, and dried to obtain a surface-treated carbon fiber. Got a bunch. The surface-treated carbon fiber bundle thus obtained was measured for tensile strength and tensile elastic modulus.

[Example 2]
Using a spinning dope having the same characteristics as in Example 1, the shape of the die has a hole diameter D of 0.13 mm, a discharge portion thickness L of 0.26 mm, L / D of 2, a number of holes of 4, 000, the temperature of the pipe and the base was set to 30 ° C., and the spinning dope at a temperature of 30 ° C. was discharged into the air. The spinning stock solution had a discharge viscosity of 2,500 poise, the spinning stock solution discharge rate from the single die hole was 0.00156 cm ³ / sec, and the spinneret back pressure was 134 kg / cm ² . In the same manner as in Example 1, ejection, coagulation, washing with water, stretching in a bath, application of an oil agent, and drying heat treatment were performed, and subjected to pressurized steam stretching. The drawing limit magnification in the pressure steam drawing was 7.5 times. In addition, since the draw ratio capable of operating for a long time was 5.5 times, the acrylic fiber was drawn at such a magnification, the total draw ratio was 16.5 times, and the single fiber fineness was 0.7 dtex, An acrylonitrile fiber bundle having 4,000 filaments was obtained. Six obtained acrylonitrile fiber bundles were combined and subjected to flameproofing treatment and carbonization treatment in the same manner as in Example 1. At this time, the stretching limit tension in the carbonization treatment was 1.88 g / dtex. Moreover, since the carbonization treatment tension | tensile_strength which can be operated for a long time was 1.53 g / dtex, it carbonized with this tension | tensile_strength and obtained carbon fiber with a specific gravity of 1.81. The obtained carbon fiber was subjected to a surface treatment in the same manner as in Example 1, and the tensile strength and tensile elastic modulus of the surface-treated carbon fiber bundle were measured.

[Example 3]
The intrinsic viscosity of the polyacrylonitrile-based polymer is 1.6, the concentration of the polyacrylonitrile-based polymer in the spinning dope is changed to 22% by weight, a die having the same shape as in Example 1 is used, and the temperature of the pipe and the die is 30. The spinning dope at a temperature of 30 ° C. was discharged into the air. The spinning stock solution had a discharge viscosity of 750 poise, the spinning stock solution discharge rate from the single hole of the base was 0.00121 cm ³ / sec, and the back surface pressure of the base was 85 kg / cm ² . In the same manner as in Example 1, coagulation, washing with water, stretching in a bath, application of an oil agent, and drying heat treatment were performed and subjected to pressurized steam stretching. The stretching limit magnification in the pressure steam stretching was 8.2 times. Moreover, since the draw ratio at which the operation can be performed for a long time was 6 times, the acrylic fiber was drawn at such a magnification, the total draw ratio was 18 times, the single fiber fineness was 0.7 dtex, and the number of filaments was 4. 1,000 acrylonitrile fiber bundles were obtained. Six obtained acrylonitrile fiber bundles were combined and subjected to flameproofing treatment and carbonization treatment in the same manner as in Example 1. At this time, the stretch limit tension in the carbonization treatment was 1.2 g / dtex. Moreover, since the carbonization treatment tension which can be operated for a long time was 0.83 g / dtex, carbonization treatment was performed with such a tension to obtain carbon fibers having a specific gravity of 1.82. The obtained carbon fiber was subjected to a surface treatment in the same manner as in Example 1, and the tensile strength and tensile elastic modulus of the surface-treated carbon fiber bundle were measured.

[Comparative Example 1]
A base having the same shape as the spinning stock solution having the same characteristics as in Example 1 was used, the piping and the base temperature were set to 30 ° C., and the spinning stock solution having a temperature of 30 ° C. was discharged into the air. The spinning stock solution had a discharge viscosity of 2,500 poise, the spinning stock solution discharge rate from the single die hole was 0.00156 cm ³ / sec, and the die back pressure was 369 kg / cm ² . In the same manner as in Example 1, ejection, coagulation, washing with water, stretching in a bath, application of an oil agent, and drying heat treatment were performed, and subjected to pressurized steam stretching. The stretching limit magnification in the pressure steam stretching was 3.8 times. Moreover, since the draw ratio that can be operated for a long time was 2.5 times, the acrylic fiber was drawn at such a magnification, the total draw ratio was 7.5 times, and the single fiber fineness was 0.7 dtex, An acrylonitrile fiber bundle having 4,000 filaments was obtained. Six obtained acrylonitrile fiber bundles were combined and subjected to flameproofing treatment and carbonization treatment in the same manner as in Example 1. At this time, the stretching limit tension in the carbonization treatment was 1.85 g / dtex. Moreover, since the carbonization treatment tension | tensile_strength which can be operated for a long time was 1.48 g / dtex, it carbonized with this tension | tensile_strength and obtained carbon fiber with a specific gravity of 1.81. The obtained carbon fiber was subjected to a surface treatment in the same manner as in Example 1, and the tensile strength and tensile elastic modulus of the surface-treated carbon fiber bundle were measured.

[Comparative Example 2]
A base having the same shape as the spinning stock solution having the same characteristics as in Example 1 was used, the pipe and the base temperature were set to 90 ° C., and the spinning stock solution having a temperature of 90 ° C. was discharged into the air. The spinning stock solution had a discharge viscosity of 100 poise, the spinning stock solution discharge rate from the single die hole was 0.00156 cm ³ / sec, and the spine back pressure was 15 kg / cm ² . Although discharging and coagulation were performed in the same manner as in Example 1, it was not possible to stably discharge and acrylic fibers could not be obtained.

[Comparative Example 3]
Using a spinning stock solution having the same characteristics as in Example 1, the shape of the die has a hole diameter D of 0.07 mm, a discharge portion thickness L of 0.21 mm, L / D of 3, a number of holes of 4, The nozzle and the nozzle temperature were set to 65 ° C., and the spinning dope at a temperature of 65 ° C. was discharged into the air. The spinning viscosity of the spinning solution was 800 poise, the amount of spinning solution discharged from the single hole of the die was 0.00156 cm ³ / sec, and the pressure on the back surface of the die was 413 kg / cm ² . In the same manner as in Example 1, ejection, coagulation, washing with water, stretching in a bath, application of an oil agent, and drying heat treatment were performed, and subjected to pressurized steam stretching. The stretching limit magnification in the pressure steam stretching was 3.5 times. Moreover, since the draw ratio that can be operated for a long time was 2.3 times, the acrylic fiber was drawn at such a magnification, the total draw ratio was 6.9 times, and the single fiber fineness was 0.7 dtex, An acrylonitrile fiber bundle having 4,000 filaments was obtained. Six obtained acrylonitrile fiber bundles were combined and subjected to flameproofing treatment and carbonization treatment in the same manner as in Example 1. At this time, the stretching limit tension in carbonization was 1.8 g / dtex. Moreover, since the carbonization treatment tension | tensile_strength which can be operated for a long time was 1.45 g / dtex, it carbonized with this tension | tensile_strength and obtained carbon fiber with a specific gravity of 1.81. The obtained carbon fiber was subjected to a surface treatment in the same manner as in Example 1, and the tensile strength and tensile elastic modulus of the surface-treated carbon fiber bundle were measured.

  The acrylic fiber obtained by the present invention is inexpensive due to a reduction in production cost and has a good quality, so that it can be used in a wide range of applications. Moreover, also in the carbon fiber which uses the acrylic fiber obtained by this invention as a precursor fiber, a manufacturing cost can be reduced and it can use suitably for general industrial uses like a motor vehicle use or a reinforcing material.

Claims (4)

In a method for producing acrylic fiber, a spinning stock solution made of a polyacrylonitrile-based polymer is discharged from a die, solidified in a coagulation bath, and subjected to a pressurized steam drawing process. A method for producing an acrylic fiber that is controlled and discharged in a cm ² range.   The method for producing an acrylic fiber according to claim 1, wherein the intrinsic viscosity of the polyacrylonitrile polymer is in the range of 1.5 to 5 and the concentration of the polyacrylonitrile polymer in the spinning dope is in the range of 12 to 30% by weight.   The method for producing an acrylic fiber according to claim 1 or 2, wherein the spinning viscosity of the spinning dope is in the range of 200 to 2,500 poise.   The acrylic fiber produced by the method for producing an acrylic fiber according to any one of claims 1 to 3 is flame-resistant at a temperature in the range of 200 to 300 ° C in air, and subsequently 300 to 2 in an inert atmosphere. A method for producing carbon fiber, which is carbonized at a temperature in the range of 1,000 ° C.