JP2001288613A - Precursor for carbon fiber, method for producing the same precursor and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precursor for carbon fiber which has a high degree of orientation, a low degree of delustering and only a small amount of surface imperfection, and to provide carbon fiber having strength of >=4,900 MPa and an elongation of >=2.0% under a stabilized condition without breakage, cementing, or the like. SOLUTION: An acrylic precursor for producing carbon fiber having a delustering degree of <=18 and a content of fibers each having a ripple-like surface due to draw resonance of <=50% is obtained by the wet spinning of a spinning dope which is made of a copolymer comprising at least 90% of acrylonitrile and having an intrinsic viscosity [η] of 1.0-3.5 and an ratio (Mw/Mn) (wherein Mw is an weight average molecular weight; and Mn is an number average molecular weight) of <=2.5 and has a copolymer concentration of 6-13%, followed by washing wet-spun filaments with water, and then by drying and drawing them. A method for producing carbon fiber is to shrink the precursor in a shrinkage percentage of >=20% until the precursor rises in its fiber specific gravity up to 1.3-1.4, and than to draw the precursor by 2-10% at 300-700 deg.C in an inert atmosphere and further to treat it at 1,200-1,700 deg.C in such a way as to shrink by 2-7% when treating the precursor having those characteristics to impart to it flame resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an acrylic precursor for obtaining high-strength carbon fibers, a method for producing the same, and a method for producing carbon fibers.

[0002]

2. Description of the Related Art It is widely known that an acrylic precursor is used for the production of carbon fiber, and that carbon fiber can be obtained through oxidization treatment and carbonization treatment. Utilizing the characteristics of high specific strength and specific elastic modulus, it has been used for applications from sports and leisure goods to aerospace field and general industrial field.

In the production of high-performance carbon fibers, the properties of the precursor directly affect the performance of the target carbon fiber, so that the precursor has high performance, that is, improves the degree of orientation and denseness, and suppresses defects. And various proposals have hitherto been made.

In order to increase the degree of orientation of the precursor, it is necessary to increase the intrinsic viscosity [η] of the copolymer in the spinning dope to increase the draw ratio, and to improve the denseness, it is necessary to increase the draw ratio of the polymer in the spinning dope. It is known that in order to increase the concentration and further suppress defects, it is effective to enhance the filtration of the spinning solution and to purify the spinning process. For example, JP-A-63-295713 proposes that an X-ray orientation degree of 92% or more can be obtained at a weight average molecular weight of 500,000 or more (intrinsic viscosity [η] 4.2 or more). However, with this method, the degree of orientation is improved, but it is difficult to improve the denseness. In addition, the intrinsic viscosity is 0.9 to 1.5
Japanese Patent Application Laid-Open No. H11-12856 proposes a spinning method in which the concentration of the copolymer is increased to 22 to 35%, but when the concentration of the copolymer is increased by 20% or more, the viscosity of the spinning solution increases. In wet spinning, there is a problem that the spinning speed is significantly reduced.

[0005]

An object of the present invention is to solve the above-mentioned problems, that is, to produce high-performance carbon fibers, the orientation is high, the devitrification is low, and the number of defects is small. An object of the present invention is to provide an acrylic precursor.

[0006]

The present invention has the following construction.

According to the present invention, an acrylic polymer having an intrinsic viscosity [η] of 1.0 to 3.5, a ratio (Mw / Mn) of a weight average molecular weight Mw to a number average molecular weight Mn of 2.5 or less, is used. An undiluted spinning solution having a concentration of 6 to 13% is wet-spun, washed with water, dried and stretched, and has a devitrification degree of 18 or less and an X-ray orientation degree of 9
0% or more, pulsation rate 50% or less, moisture content 30-50%
When an acryl-based precursor for producing carbon fiber comprising: and a precursor having such properties are subjected to a flame-proof treatment, the fiber specific gravity increases by 20% until the fiber specific gravity increases to 1.3 to 1.4.
After giving the following shrinkage, 3
2-10% stretching at a temperature of 00-700 ° C, and 2-7% at a temperature of 1200-1700 ° C in an inert atmosphere
To obtain carbon fibers by performing shrinkage treatment. In this way, carbon fibers having a strength of 4900 MPa or more and an elongation of 2.0% or more can be industrially obtained under stable conditions without thread breakage and sticking.

According to the present invention, when the intrinsic viscosity [η] of the polymer is 1.0 to 3.5, the Mw / Mn is reduced to 2.5 or less so that the degree of orientation is 90% or more, and It is characterized in that a highly dense precursor represented by a devitrification degree of 18 or less can be obtained even if the coalescence concentration is as low as 6 to 13%. By using such an acrylic fiber as a precursor, the problem of obtaining carbon fibers having high strength and high elongation could be solved.

In the present invention, the acrylic polymer includes a compound having a carboxyl group such as acrylic acid, methacrylic acid and itaconic acid or salts thereof, and acrylic acid esters such as methyl acrylate and methyl methacrylate;
An acrylic copolymer comprising 1 to 10% by weight of a copolymer component having a neutral group such as methacrylic acid ester such as methyl methacrylate, vinyl acetate, styrene, and methacrylonitrile, and a balance of acrylonitrile; Acrylic precursors for fiber production are fibers made of these polymers. If the copolymer component exceeds 10% by weight,
This is not advisable because the heat resistance of the precursor decreases and the sticking of carbon fibers increases. Copolymers containing at least 90% acrylonitrile are prepared by known methods, for example by aqueous suspension polymerization, emulsion polymerization or solution polymerization in solvents.

As the spinning solvent for the acrylic copolymer, many organic solvents and inorganic salt solvents are used.
A method of directly obtaining a polymer solution by homogeneous solution polymerization in a zinc chloride aqueous solution is preferable because the molecular weight distribution can be narrowed. Here, the zinc chloride-based aqueous solution is a solution well-known as a solvent for producing acrylonitrile-based fibers, and is a salt solution of zinc chloride alone or a mixed salt thereof with a chloride such as sodium, potassium, magnesium, or the like. The zinc chloride-based aqueous solution of the solvent is preferably 56 to 65% and does not contain zinc oxide, and is preferably filtered with a filter having an opening of 0.6 μm or less before charging the polymerization vessel.

The intrinsic viscosity [η] of the polymer is required to be 1.0 or more. If the intrinsic viscosity [η] is less than 1.0, the stretchability decreases, it becomes difficult to obtain a fiber having a high degree of orientation, and the strength of the carbon fiber also decreases. . If the intrinsic viscosity [η] exceeds 3.5, there is a problem that the spinning speed decreases and the drawability decreases due to a sharp increase in the viscosity of the spinning dope. Therefore, the intrinsic viscosity [η] is 1.
0 to 3.5 is good. The preferred range is 1.5-2.5
It is.

In order to reduce the molecular weight distribution Mw / Mn to 2.5 or less, it is preferable to carry out continuous solution polymerization in an aqueous zinc chloride solution and stop the polymerization yield at about 95%. If the polymerization yield exceeds 95%, the molecular weight distribution becomes large, and Mw / Mn becomes 2.5
It is difficult to: Mw / Mn ratio of 2.5
When the molecular weight distribution exceeds (the molecular weight distribution increases), the drawability during spinning decreases, and the problem of increased fluff due to breakage of single yarns occurs. It is difficult to obtain a precursor with a high degree of orientation and less fluff. And high performance carbon fibers cannot be obtained.

When the intrinsic viscosity [η] is higher than 3.5, the orientation degree of 90% or more can be obtained even when the ratio of Mw / Mn is 2.5 or more. The productivity is significantly reduced due to the increase in viscosity. Therefore, [η] is 1.0
In the case of the polymer of ~ 3.5, Mw / Mn needs to be 2.5 or less.

The higher the polymer concentration of the spinning dope, the lower the amount of solvent and coagulant in the coagulation bath is reduced, which is advantageous for obtaining fibers having less voids and low devitrification. 1
If it exceeds 3%, the viscosity of the spinning dope increases sharply, and there are problems such as gelation of the spinning dope, a decrease in stretchability, and a decrease in spinning speed.

On the other hand, when the polymer concentration is less than 6%, voids are frequently generated, the devitrification is increased, the stretchability is lowered, and the mechanical properties of the carbon fiber are lowered, which is not preferable as a precursor. Therefore, by setting the polymer concentration of the spinning dope to 6 to 13%, spinning can be performed at a high spinning speed with high productivity.

As the spinning method of the acrylic precursor for producing carbon fibers, a dry spinning method, a dry-wet spinning method, a wet spinning method, or the like can be used, but a wet spinning method with high productivity is preferred. In the case of spinning using a zinc chloride-based solvent in the wet spinning method, it is effective to lower the temperature of the spinning solution discharged from the nozzle as much as possible to reduce voids in the coagulated yarn and reduce the devitrification degree. However, if it is too low, there is a problem that the viscosity of the spinning solution increases, the back pressure of the nozzle increases, the discharge speed decreases, and the productivity decreases. For this reason, the temperature at the time of discharging the spinning solution is preferably 20 to 50 ° C. For the coagulation bath, a solution prepared by diluting the same kind of solvent as the spinning solution with water is used, and conditions for lowering the coagulation speed are employed to reduce voids in the coagulated yarn. Specifically, temperature 0-10
A zinc chloride-based aqueous solution having a temperature of 20 ° C and a concentration of 20 to 30% is preferable.

Draft rate in the coagulation bath (discharge linear velocity S1
Of the take-up roller and the surface speed S2 of the take-off roller (S2 / S1)
In order to reduce voids in the coagulated yarn and reduce surface defects, it is better to be as small as possible.However, if too small, problems such as an increase in nozzle back pressure and swelling of the nozzle discharge surface may occur. Spinning at 15-40% is preferred. Since voids in the coagulated yarn greatly affect the denseness (devitrification) of the fibers in the subsequent step, it is necessary to reduce the voids as much as possible. The coagulated yarn is subsequently washed with water and stretched in a bath, and the washing and stretching in a bath are performed in multiple stages. Washing temperature is 1
At 0 to 95 ° C., stretching in the bath is performed 2 to 4 times, and in order to promote the desolvation of the fiber, the pH of the washing bath is adjusted by adding an acid such as hydrochloric acid or acetic acid so that the pH is 4 or less. Is preferred.

In the case of a precursor for carbon fiber, if there is adhesion or fusion of a single fiber, it causes sticking in the carbonization step.
Such adhesion and fusion in the spinning process must be prevented. To prevent the adhesion of single fibers, apply an oil agent to the fibers after the washing process, and use a suction drum type drier for 0 to 15%.
It is preferable to perform densification while applying shrinkage, and then perform stretching.

As the oil, a silicone compound, a higher alcohol, a higher fatty acid ester or the like can be used alone or in a mixture thereof. However, the amount of the oil should be minimized. The oil agent penetrates into the interior of the fiber to inhibit densification and remains as a defect in the fiber, which is not preferable. The attachment amount of the oil agent may be an amount capable of preventing the sticking of the carbon fibers, and is specifically about 0.01 to 1.0%. By shrinking the fibers during drying, the densification of the fibers progresses, and further, a difference between the single fibers due to a difference in shrinkage speed of the single fibers occurs, so that the adhesive yarn can be prevented.

The fiber after drying and densification is then
The stretching is performed 10 times, and this step is an important step for improving the degree of orientation of the precursor. When water vapor is used, water acts as a plasticizer for the acrylic fiber, and high drawing is possible. Fiber before drawing (fiber after drying and densification)
In the case of water repellency, since a plasticizing effect of water cannot be obtained, it is necessary to improve wettability to water.

When a silicone oil is applied to the fiber, the fiber generally becomes water repellent, so that a hydrophilic surfactant,
For example, the fibers are preferably made hydrophilic by using a combination of a polyethylene glycol derivative, a polyhydric alcohol derivative, a sulfonate, a phosphate, a carboxylate, and the like.

Further, in order to enhance the plasticizing effect of water, it is preferable to add 10 to 30% of water to the fiber before the steam drawing. Spraying, immersion, and roller transfer can be used to apply water, but the temperature of water is preferably 70 to 90 ° C.

In order to obtain a degree of orientation of the precursor of 90% or more, it is necessary to make the total draw ratio (the ratio S3 / S2 between the final roller speed S3 and the take-up roller speed S2) of the spinning process 10 times or more. If the total stretching ratio is less than 10 times, it is difficult to obtain an orientation degree of 90% or more. On the other hand, the higher the draw ratio, the higher the degree of orientation tends to be. However, when the fiber is stretched to the draw limit (maximum draw ratio), the fiber surface becomes pulsed, and when a precursor having a pulse rate exceeding 50% is used. The veins remain as surface defects of the carbon fibers even after firing, and high-strength carbon fibers cannot be obtained. Therefore, the stretching is preferably performed at 80 to 95% of the maximum stretching ratio, and the substantial upper limit of the total stretching ratio is 25 times. When the stretching ratio is 80% or less of the maximum stretching ratio, the degree of crystal orientation is 90%.
When the stretching is performed at 95% or more of the maximum stretching ratio, the degree of orientation is improved, but the yarn breakage at the time of stretching is increased, and not only the process becomes unstable, but also the pulsation ratio is increased. Is 5
It exceeds 0%, and the devitrification does not become 18 or less.

Since the devitrification degree is greatly affected by the temperature at the time of stretching, the saturated steam pressure of the stretching cylinder is 245 KP.
a (127 ° C.) or less. If the saturated vapor pressure exceeds 245 KPa, a devitrification degree of 18 or less cannot be obtained.

The fiber immediately after drawing has a distortion such as residual shrinkage because the fiber structure is not fixed. The present inventors have found that, as a method for stabilizing the fiber structure, water is applied to the fiber immediately after drawing to make the water content 30 to 50%. The fiber immediately after drawing is 5 at a temperature of 80 to 100 ° C.
Although water content of about 30% is contained, residual strain can be eliminated by applying water of 30 ° C. or lower to the water by a spray method, an immersion method, a roller transfer method, or the like.

Next, the precursor thus obtained is fired to obtain carbon fibers. The flameproofing process is performed in air 200 ~
It is preferable to raise the temperature stepwise at a temperature lower than the heat storage cutting temperature of the fiber in the range of 300 ° C. Further, in the flame-proofing step, it is preferable to give a shrinkage of 20% or less before the specific gravity rises to 1.3 to 1.4. In the precursor with a high degree of orientation, a high tension acts on the strand due to a strong shrinkage force in the initial stage of flame resistance (specific gravity is about 1.2). Therefore, by giving an appropriate shrinkage, the strand is prevented from fluffing and yarn breakage. This is very important.

The shrinkage is preferably 20% or less, and if it exceeds 20%, the degree of fiber orientation is reduced, and a high-performance carbon fiber cannot be obtained. A more preferred range is 3 to 15%. If the specific gravity of the oxidized fiber is low, the yield of carbon fiber decreases,
The stretchability in the first carbonization step is improved. Also, when the specific gravity of the oxidized fiber is high, the yield of carbon fiber is improved, but the drawability is reduced. Judging comprehensively from these, the preferable range of the specific gravity for flame resistance is 1.3 to 1.4. When carbonizing oxidized fiber having a specific gravity of 1.3 to 1.4, the carbonization step is preferably performed in two stages.

In the first carbonization furnace, 300
It is preferable to perform stretching at 2 to 10% at ~ 700 ° C. Here, thermal decomposition of the oxidized fiber occurs, so that the weight is reduced and the degree of orientation is reduced. The temperature of the first carbonization furnace is 300
When the temperature is lower than 700 ° C., the thermal decomposition reaction is too slow, and it takes a long time for carbonization, and there is a problem that the productivity is reduced.
Above, there is a problem that the thermal decomposition rate is too fast and the degree of orientation is significantly reduced. The preferred range is 400-650 ° C
It is. In order to suppress a decrease in the degree of orientation, it is effective to perform stretching by 2 to 10%. When the stretching ratio is 2% or less, it is insufficient to suppress the decrease in the degree of orientation, and when it exceeds 10%, the degree of orientation reaches saturation and no further improvement is observed.
The preferred range of the stretching ratio is 2 to 10%.

In the second carbonization furnace, 120 in an inert atmosphere.
The carbonization is completed while giving 2-7% shrinkage at 0-1700 ° C. If the temperature of the second carbonization furnace is less than 1200 ° C., it is difficult to obtain a carbon fiber strength of 4900 MPa, which is not preferable. If it exceeds 1700 ° C., the elastic modulus increases, but the strength tends to decrease, which is not preferable.
In the second carbonization furnace, if the shrinkage ratio is less than 2%, the stretchability is reduced, so that fluff due to breakage of single yarn increases, and if it exceeds 7%, the tension of the fiber decreases, causing slackness of the yarn in the furnace. In addition, the process passability becomes unstable, which is not preferable. According to the study of the present inventors, since the shrinkage rate in the second carbonization furnace hardly affects the strength of the carbon fiber, 2 to 7% is appropriate in terms of processability.

[0030]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

(Devitrification degree) A sample dried by a ventilation dryer at 75 ° C. for 24 hours is cut into a fiber length of 40 mm, 2 g is collected, and opened with a hand card. The opened sample is made into a disc shape with a diameter of 20 mm, and 490 KPa is applied with a hydraulic press.
Press for 30 seconds. A 20 mm disk-shaped fiber mass is placed in a measuring cell, filled with anisole, left standing for 10 minutes to remove bubbles, and the lightness (L value) is measured with a Hunter-type color difference meter (L1). On the other hand, the lightness (L2) of a standard cotton (completely devitrified cotton) is measured in the same manner using a Hunter-type color difference meter. The devitrification degree was determined from the following equation (1). (The lightness L2 of the standard cotton is 5.) Devitrification (L value) = L1−L2 (1)

(Molecular weight distribution Mw / Mn) Number average molecular weight M
n is a value measured by an osmotic pressure method, and a weight average molecular weight Mw is a value obtained by measuring the intrinsic viscosity [η] of the polymer using dimethylformamide (DMF) and calculating by the formula (2). [Η] = 2.83 × 10 −4 Mw 0.75 (2)

(Degree of Crystal Orientation by Wide-Angle X-Ray Diffraction) Using a Kα ray of Cu monochromated with a Ni filter as an X-ray source, a plane index (400) observed near 2θ = 17 °
From the half-value width H (°) of the peak obtained by scanning the peak in the circumferential direction. Degree of orientation (%) = {(180-H) / 180} × 100 (3)

(Pulsation rate) A sample dried by a ventilation dryer at 75 ° C for 24 hours was cut into a fiber length of about 10 mm, 100 single fibers were collected, and the surface of the fiber was observed with an optical microscope. Then, the number (n) of the pulsating fibers is counted. (Stripes are visible in the pulsating fibers.) Pulsating rate (%) = (n / 100) × 100 (4)

Example 1 Polymer composition obtained by solution polymerization in a 60% aqueous zinc chloride solution. Limit of 96.5% by weight of acrylonitrile, 2.5% by weight of methyl acrylate, 1% by weight of itaconic acid. Viscosity [η] 1.8, Mw / M
A stock solution for spinning with n = 2.0 and a copolymer concentration of 7.5% by weight was discharged and coagulated at a draft rate of 25% into a 25% aqueous zinc chloride solution at 6 ° C. using a nozzle having 12,000 holes. 10
The film was stretched three times in a multi-stage washing bath having a temperature gradient of ~ 90 ° C to obtain a gel yarn having a water content of 150%.

The gel yarn was passed through an oil bath containing 0.4 parts by weight of a mixture of 30 parts of an amino-modified silicone (viscosity: 2500 cst, amino equivalent 3000) and 70 parts of a phosphoric ester (diethanolaminostearylethoxyphosphate). Subsequently, it is dried and densified by applying a 7% shrinkage with a suction drum dryer at 80 ° C. to 140 ° C., and then stretched 4.5 times in saturated steam of 167 KPa, and sprayed with pure water at 15 ° C. To a water content of 37%, and stored in a can. Single fiber fineness 0.65 dtex,
An acrylic precursor for carbon fiber production having a devitrification degree of 15, an orientation degree of 91.2% and a pulsation rate of 0% was obtained.

This precursor was shrunk at a temperature of 240 to 250 ° C. by 10% while shrinking it by 10% to obtain an oxidized yarn having a fiber specific gravity of 1.35. Subsequently, it was stretched by 3% in a nitrogen atmosphere at 300 to 500 ° C. 5 in a nitrogen atmosphere at 1350 ° C
% Shrinkage to obtain a carbon fiber. The fiber diameter of the obtained carbon fiber is 5.2 μm, the tensile strength is 5600 MPa,
The elastic modulus was 245 GPa and the elongation was 2.2%.

(Examples 2 to 5, Comparative Examples 1 to 4) In solution polymerization in a 60% aqueous zinc chloride solution, polymerization conditions were changed to obtain various intrinsic viscosities [η] and molecular weight distributions (Mw / M
A spinning stock solution having n) was prepared, and spinning and carbonization were performed under the same conditions as in Example 1. The results are shown in Table 1.

Example 6 Polymer Composition Obtained by Solution Polymerization in 60% Aqueous Zinc Chloride Solution 95% by weight of acrylonitrile, 4% by weight of methyl acrylate, 1% by weight of itaconic acid Intrinsic viscosity [η] 1.4, Mw / Mn = 1.
9. A spinning dope having a copolymer concentration of 8.5% by weight was filled with 24 pores.
Using a 000 nozzle, the mixture was discharged into a 25% zinc chloride aqueous solution at 0 ° C. at a draft rate of 30%, solidified, washed with water and stretched to obtain a gel yarn having a water content of 130%.

The gel yarn was passed through an oil bath containing 1.5 parts by weight of a mixture of 75 parts of amino-modified silicone (viscosity: 3500 cst, amino equivalent: 2000) and 25 parts of sodium dioctyl sulfosuccinate. 1
Drying and densification are performed while applying 7% shrinkage in a suction drum dryer at 30 ° C., then stretched 5 times in saturated steam of 162 KPa, sprayed with pure water at 15 ° C. to a moisture content of 35%, Stored in Kens. Single fiber fineness 0.
An acrylic precursor for carbon fiber production having a dtex of 60 dtex, a degree of devitrification of 14, a degree of orientation of 91.5%, and a pulsating rate of 10% was obtained.

This precursor was shrunk by 10% at a temperature of 240 to 250 ° C. to give an oxidized yarn having a fiber specific gravity of 1.35, followed by drawing 8% in a nitrogen atmosphere at 300 to 500 ° C. 5.5% shrinkage was performed in a nitrogen atmosphere at 1100 to 1350 ° C to obtain carbon fibers. The fiber diameter of the obtained carbon fiber is 4.9 μm, and the tensile strength is 57.
It was 50 MPa, the elastic modulus was 250 GPa, and the elongation was 2.3%.

(Comparative Example 5) The stretching ratio of the first carbonization furnace was 1
%, And the contraction rate of the second carbonization furnace was 5%, to obtain carbon fibers in the same manner as in Example 6. The obtained carbon fiber has a strength of 4
630 MPa, which was unsatisfactory.

Example 7 Polymer composition obtained by solution polymerization in a 60% aqueous zinc chloride solution 97% by weight of acrylonitrile, 3% by weight of methyl acrylate, intrinsic viscosity [η] 1.5, Mw / Mn = 1.7, copolymer concentration 8.
A 0% by weight spinning solution was introduced into a 28% aqueous zinc chloride solution at 0 ° C. using a nozzle having 24,000 holes at a draft rate of 25%.
And solidified, washed with water and stretched, with a moisture content of 150%
Was obtained.

The gel yarn was passed through an oil bath containing 1.5 parts by weight of a mixture of 75 parts of an amino-modified silicone (viscosity: 3500 cst, amino equivalent: 2000) and 25 parts of sodium dioctyl sulfosuccinate. 1
Drying and densification are performed while applying 7% shrinkage with a 30 ° C. suction drum dryer, and then stretched 5 times in saturated steam of 162 KPa, and sprayed with pure water at 15 ° C. to a moisture content of 37%. Stored in Kens. Single fiber fineness 0.
An acrylic precursor for carbon fiber production having a dtex of 60 dtex, a degree of devitrification of 16, a degree of orientation of 91.2%, and a pulsation rate of 10% was obtained.

This precursor was shrunk by 10% at a temperature of 245 to 256 ° C. into a flame-resistant yarn having a fiber specific gravity of 1.35, and then stretched by 6% in a nitrogen atmosphere of 300 to 500 ° C. 6% shrinkage was performed in a nitrogen atmosphere at 1100 to 1350 ° C to obtain carbon fibers. The fiber diameter of the obtained carbon fiber is 5 μm, and the tensile strength is 5450MP.
a, the elastic modulus was 250 GPa, and the elongation was 2.2%.

(Comparative Example 6) As a result of setting the stretching ratio of the first carbonization furnace to 11% in Example 7, the yarn was cut, and carbon fibers could not be obtained.

Example 8 Polymer Composition Obtained by Solution Polymerization in 60% Aqueous Zinc Chloride Solution 99% by weight of acrylonitrile and 1% by weight of itaconic acid have intrinsic viscosity [η].
2.0, Mw / Mn = 2.0, and a copolymer concentration of 7.0% by weight were fed to a spinning dope using a nozzle having 24,000 holes.
The mixture was discharged and solidified in a zinc chloride aqueous solution at 22 ° C. and a draft rate of 24%, solidified, washed with water and stretched to obtain a gel yarn having a water content of 150%.

The gel yarn was passed through an oil bath containing 1.5 parts by weight of a mixture of 75 parts of amino-modified silicone (viscosity: 3500 cst, amino equivalent: 2000) and 25 parts of sodium dioctyl sulfosuccinate. 1
Drying and densification were carried out while applying a 7% shrinkage in a suction drum dryer at 30 ° C., then stretched 5 times in saturated steam at 162 KPa, and sprayed with pure water at 15 ° C. to a moisture content of 38%. Stored in Kens. Single fiber fineness 0.
An acrylic precursor for carbon fiber production having a dtex of 60 dtex, a degree of devitrification of 17, a degree of orientation of 91.0%, and a pulsating rate of 10% was obtained.

The precursor was shrunk by 10% at a temperature of 240 to 250 ° C. while shrinking by 10% to obtain an oxidized yarn having a fiber specific gravity of 1.35. Subsequently, it was stretched by 2% in a nitrogen atmosphere at 300 to 500 ° C. 5% shrinkage was performed in a nitrogen atmosphere at 1100 to 1350 ° C to obtain carbon fibers. The fiber diameter of the obtained carbon fiber is 5 μm, and the tensile strength is 5370MP.
a, the elastic modulus was 250 GPa, and the elongation was 2.2%.

(Comparative Example 7) The elongation ratio of the first carbonization furnace was 5
%, And the contraction rate of the second carbonization furnace was set to 8%. The yarn slackened in the second carbonization furnace, and the yarn was broken.

(Comparative Example 8) In Comparative Example 7, as a result of reducing the shrinkage of the second carbonization furnace by 1%, the yarn started to fluff.
Eventually, thread breakage occurred.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

According to the present invention, there is provided an acrylic precursor for producing carbon fiber having a high degree of orientation, a low degree of devitrification and a small number of surface defects, and is capable of producing a high-strength carbon fiber under stable conditions without thread breakage or sticking. Offering can be obtained efficiently.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinichi Muto 234 Kamitsukari, Nagaizumi-cho, Sunto-gun, Shizuoka Toho Rayon Co., Ltd. F-term (reference) 4L035 BB03 BB06 BB10 BB15 BB17 BB20 BB22 BB60 BB66 BB80 BB85 BB91 DD13 EE07 EE20 FF01 FF04 GG04 HH04 HH10 MB04 MB06 MB19 4L037 CS03 FA03 FA06 FA08 FA11 PA54 PA55 PA70 PC10 PC11 PC14 PF45 PF54 PS00 PS02 PS18 UA20

Claims (4)

[Claims] 1. An acrylic polymer having an intrinsic viscosity [η] of 1.
0 to 3.5, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 2.5 or less, the devitrification degree defined in the text is 18 or less, and the crystal orientation degree by wide-angle X-ray diffraction is 90. %
As described above, a precursor for carbon fiber production having a pulsation rate of 50% or less and a water content of 30 to 50%. 2. An acrylic polymer having an intrinsic viscosity [η] of 1.
0 to 3.5, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 2.5 or less, and the polymer concentration is 6 to 13.
%, Spinning, spin-drying, drying and densifying, and stretching in saturated steam at a pressure of 245 KPa or less to produce a precursor for carbon fiber production with a water content of 30 to 50%. 3. Use of the precursor obtained in claim 1 or 2 until the fiber specific gravity rises to 1.3 to 1.4.
After giving a shrinkage of 0% or less, 300-
A stretch of 2 to 10% is added at 700 ° C., and a shrinkage treatment of 2 to 7% is performed at a temperature of 1200 to 1700 ° C. in an inert atmosphere to obtain a tensile strength of 4900 MPa or more and an elongation of 2.0%.
A method for producing the above carbon fibers. 4. A carbon fiber having a tensile strength of not less than 4900 MPa and an elongation of not less than 2.0% obtained from claim 1, 2 or 3.