JP2002054022A - Acrylonitrile precursor fiber and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide wet-extruded acrylonitrile precursor fiber that is improved in the filament-bundling properties, thus complementarily is largely decreased in the finishing oil applied to the fiber surface and has the filament shape that can maintain the process passage in the firing process at a high level and provide a method of producing the same. SOLUTION: The objective acrylonitrile precursor fiber is produced by the wet process and has the following characteristics: The fiber has wrinkles in the fiber-axis direction, but the cross section of the fiber is substantially round, the depth of the wrinkles distributes in the range of one or more wrinkles inside the cross section, but the maximum value of the wrinkle depth is <=100 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic precursor fiber used for producing a carbon fiber used as a reinforcing fiber material in various composite materials.
The present invention relates to an acrylic precursor fiber that is manufactured using wet spinning and is then excellent in processability when converted into carbon fiber by firing, and has good bunching properties, and a method for manufacturing the same.

[0002]

2. Description of the Related Art High-performance composite materials using fiber-reinforced resin materials, particularly carbon fibers as reinforcing fiber materials, are fields where lightweight and excellent mechanical strength are desired, such as aerospace applications, sports and leisure applications. Has become widely used. Among the carbon fibers blended as a reinforcing fiber material in such various types of resin materials, an acrylic fiber is used as a precursor thereof, and the carbon fiber produced by firing it has its own mechanical properties, For example, it has excellent strength and elastic modulus, and is expected to be used more and more.
In other words, high-performance composite materials that utilize carbon fiber as a reinforcing fiber material in the above-mentioned state-of-the-art application fields and in very special applications have their technology diverted to general industrial applications, Accordingly, it is necessary to produce carbon fibers at a lower cost and with good reproducibility while maintaining high quality.

[0003] When producing carbon fibers, it is important to keep the convergence of the precursor fibers at a certain level or more in order to achieve low cost and high quality. If the convergence of the precursor fiber is poor, in the step of firing the precursor fiber, winding of the fiber around a roll is caused, and the supply of the fiber to be subjected to the firing step is interrupted. It causes trouble. Along with this, the cost increases due to a decrease in yield. Alternatively, after baking, fluff or the like may be generated in the carbon fiber, which may lower the quality of the generated carbon fiber itself.

In order to avoid these problems in the process,
Conventionally, a treatment has been performed in advance so that the precursor fibers have a bundle property. Conventionally, as a means that has been used for improving the convergence, it has been widely practiced to apply an oil agent to the surface of the precursor fiber and use the effect of the oil agent film to bundle the individual fibers together. , Has a certain effect. However, the oil agent applied to the surface of the precursor fiber is turned into tar in a firing furnace. If the amount of tar is large, the oil agent may be warped or cut. That is, it has adverse effects such as lowering the yield of the firing step and lowering the performance and quality of the obtained carbon fiber. Therefore, although the use of an oil agent is effective in improving the convergence of the precursor fiber, the amount of the oil agent coated on the fiber surface is preferably as small as possible. In other words, it is desired that the precursor fiber itself has a bunching property and the amount of the oil agent used to compensate for the bundle is smaller.

On the other hand, one of the factors governing the convergence of the precursor fiber itself is the surface morphology of the fiber. Compared with the acrylic fiber produced by the dry-wet spinning method, the acrylic fiber produced by the wet spinning method has a rough surface form with uneven wrinkles in the fiber axis direction. When large surface wrinkles are present, the convergence of the precursor fibers in the manufacturing process is reduced, and as a result, there is a problem that troubles such as winding around a roll are likely to occur.

[0006]

As described above, the use of carbon fiber reinforced composite materials has been expanded, and the use of carbon fiber as a reinforcing fiber material has been increased more than ever before.
It has become necessary to manufacture the semiconductor device at a lower cost and with good reproducibility while maintaining high quality. that time,
It is desirable to use acrylonitrile-based precursor fiber as a precursor fiber used for producing carbon fiber in order to maintain high quality of carbon fiber. In addition, in order to reduce costs, the wet spinning method, which has much higher productivity than the dry-wet spinning method, is adopted to prevent troubles such as winding around rolls in the baking process, etc. It is desired to produce an acrylonitrile-based precursor fiber that can be suppressed and achieve high productivity and yield. Specifically, in the acrylonitrile-based precursor fiber produced by the wet spinning method, which is excellent in production efficiency, the lack of convergence, which is mainly due to the surface wrinkles of the fiber surface derived from the production method itself, is considered. It is desired that the amount of the oil agent applied to the fiber surface can be reduced for the purpose of improving and compensating the above-mentioned poor convergence.

An object of the present invention is to solve the above-mentioned problems. An object of the present invention is to provide an acrylonitrile-based precursor fiber produced by the wet spinning method while taking advantage of the excellent production efficiency of the wet spinning method. Improving the poor convergence, a major drawback that has been left in the past, the spinning process itself,
For example, to enhance the processability in the fiber winding process and the like, and further, with the improvement of the convergence, significantly reduce the amount of oil applied to the fiber surface for the purpose of complementing it,
An object of the present invention is to provide an acrylonitrile-based precursor fiber formed by a wet spinning method and having a shape capable of maintaining a high process passability in a firing step, and a method for producing the same. More specifically, the method for producing acrylonitrile-based precursor fibers produced by the wet spinning method is improved, and the fiber surface wrinkles that have been a factor of poor convergence are also improved in shape, and the production thereof is improved. An object of the present invention is to provide a method for producing an acrylonitrile-based precursor fiber by a wet spinning method, which can be performed with high reproducibility.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies and studies to solve the above-mentioned problems. As a result, the acrylonitrile-based precursor fiber produced by the wet spinning method is caused by the production method. Then, wrinkles are formed in the direction of the fiber axis. If the wrinkles are too deep, they cause poor convergence, but if they are relatively shallow, the precursor fibers are fired. It has been found that the obtained carbon fiber is preferable because it improves the adhesion to the resin. Based on this finding, by controlling the depth of wrinkles formed in the fiber axis direction, it is possible to improve the convergence of the acrylonitrile-based precursor fiber itself, and a fiber surface having such wrinkles, When the coefficient of friction between the metal roller used in the firing step and the metal roller used in the firing step is in an appropriate range, it has been found that the width of the yarn of the fiber bundle is excessively widened, and the problem that the process passability is reduced can be avoided. . More specifically, the present inventors
Regarding the acrylonitrile-based precursor fiber produced by the wet spinning method, the wrinkle depth is set to 10 even at the maximum.
When the thickness is not more than 0 nm, it has been found that it does not cause poor convergence and that the process passability in the subsequent firing step can be maintained, and the present invention has been completed.

That is, the acrylonitrile-based precursor fiber of the present invention is an acrylonitrile-based precursor fiber produced by a wet spinning method, which has wrinkles in the fiber axis direction, but has a substantially cross-sectional shape. Indicates a circle,
The wrinkle depth, measured from the outer edge of the substantially circular fiber cross-section, has a distribution between one or more existing wrinkles in the cross-section, with a maximum wrinkle depth distribution of 100 nm.
An acrylonitrile precursor fiber characterized by the following.

The acrylonitrile-based precursor fiber of the present invention is an acrylonitrile-based precursor fiber obtained by coating the surface of the fiber having wrinkles in the fiber axis direction with an oil agent. Except for those remaining in the deep part of the wrinkles on the surface, in a fiber single yarn substantially completely removed with a solvent, when the fiber single yarn is brought into contact with a flat metal surface, a fiber having a wrinkle with respect to the fiber axis direction. It is preferable that the static friction coefficient between the surface and the metal surface is 0.35 or more, and the dynamic friction coefficient is 0.30 or more.

[0011] In addition, the method for producing acrylonitrile-based precursor fiber of the present invention is a method for producing acrylonitrile-based precursor fiber by a wet spinning method, wherein the acrylonitrile-based precursor fiber is discharged from a nozzle hole having a substantially circular opening. In order to make the coagulated yarn produced by coagulation a predetermined fiber diameter, a stretching step is provided,
After the drawing step, a process of coating the fiber surface with a predetermined amount of an oil agent is performed, and then a process of drying and densifying the fiber itself is provided,
The stretching step includes an aerial stretching step and a subsequent wet heat stretching step, and in the wet heat stretching step performed before the dry densification step, the wet heat stretching ratio is selected in a range not to reach 3.0 times. A method for producing an acrylonitrile-based precursor fiber, characterized in that:

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The characteristics of the acrylonitrile precursor fiber of the present invention and the advantages obtained due to the characteristics will be described in more detail below.

Since the acrylonitrile-based precursor fiber of the present invention is formed by using a wet spinning method, its surface has wrinkles extending in the fiber axis direction.
The obtained carbon fiber also has a shape in which the wrinkles are retained.
Further, when mixed with a resin as a reinforcing fiber, the enlargement of the surface area caused by the wrinkles is used to obtain good adhesion to the resin. Accordingly, it is desirable that the wrinkles in the fiber axis direction have a certain depth, from the viewpoint of adhesiveness with the resin, but if the wrinkles are too deep, the convergence of the fiber bundle is reduced, and It causes deterioration of the passability in the body fiber winding step and the subsequent baking step.

In the acrylonitrile-based precursor fiber of the present invention, the depth of the wrinkles is adjusted so that these contradictory constraints are harmonized and the advantage of having wrinkles is sufficiently exhibited while suppressing a decrease in processability. The maximum value (maximum depth of wrinkles) of the height distribution is set to be in a range of 100 nm or less. More preferably, the maximum wrinkle depth is selected in the range of 70 nm or less. On the other hand, when the depth of the wrinkles is as shallow as less than 30 nm, the function (advantage) of improving the adhesiveness with the resin is rapidly reduced. Therefore, the maximum depth of the wrinkles is at least 30 nm, preferably at least 30 nm in the range of 70 nm or less. Is more preferably selected to be 50 nm or more.

In the acrylonitrile-based precursor fiber of the present invention, a metal roll is used when winding or feeding the fiber in the spinning step and thereafter in the firing step for forming carbon fiber. When the width of the yarn of the precursor fiber is increased on the metal roll, the frequency of causing a decrease in the processability is high. In particular,
When the acrylonitrile-based precursor fiber has low bundle property of the fiber bundle, it becomes a major factor of deterioration in processability in the step of winding the precursor fiber and the subsequent firing step. In order to improve the convergence of the fiber bundle, a method of applying an oil agent to the fiber surface is used.However, if the intrinsic friction coefficient of the fiber is small, even if the oil agent is applied, the spread of the yarn width is sufficiently suppressed. Not be able to
As a result, it was found that the process passability was not improved.

In addition, it is possible to further improve the convergence of the fiber bundle by increasing the amount of the oil agent applied, but a large amount of the oil agent covering the fiber surface is tarified in a firing furnace.
Since this tar causes fluff, breakage of bundles, etc., and lowers the yield of the firing process, and causes the performance and quality of the carbon fiber to deteriorate, the characteristics of the obtained carbon fiber itself and the yield are adversely affected. It turned out that this was not an essential improvement.

Therefore, it is preferable to achieve a desired fiber bundle convergence without excessively increasing the amount of the oil agent applied to the fiber surface by setting the intrinsic friction coefficient of the fiber to a certain level or more. In the acrylonitrile-based precursor fiber produced by the wet spinning method, a step of applying an oil agent is provided in the spinning step, but the oil agent on the surface is removed by a solvent such as methyl ethyl ketone, and the oil agent is not adhered. When the intrinsic friction coefficient of the fiber is evaluated, the coefficient of static friction between the fiber and the metal is preferably 0.35 or more, and the dynamic friction coefficient is preferably 0.30 or more. In this case, it is more preferable that the acrylonitrile-based precursor fiber has a static friction coefficient between the fiber surface and the smooth metal surface of 0.36 or more and a dynamic friction coefficient of 0.30 or more in the fiber axis direction.

The values of the coefficient of static friction and the coefficient of kinetic friction are represented by values measured for a single fiber yarn in accordance with the method of evaluating the "coefficient of friction" described below. Generally, the static friction coefficient is higher than the dynamic friction coefficient,
In the present invention, the coefficient of static friction between the fiber and the metal is
It is desirable to select a value not exceeding 0.44. Naturally, it is desirable to select the coefficient of kinetic friction between the fiber and the metal so as not to exceed 0.44.

If the fiber surface shape as described above, specifically, wrinkles having an appropriate depth in the fiber axis direction is formed,
Even when using an acrylonitrile-based precursor fiber produced by a spinning method other than the wet spinning method, the properties of the obtained carbon fiber and the productivity thereof are substantially the same as those using the acrylonitrile-based precursor fiber of the present invention. It is. However, for example, it is difficult to produce a fiber having a wrinkle having a maximum depth of 30 nm or more by the dry-wet spinning method, and the carbon fiber obtained therefrom has an effective wrinkle capable of obtaining good adhesiveness with a resin. It is difficult to achieve a depth of 30 nm or more. In addition, the productivity of the acrylonitrile-based precursor fiber itself is generally much higher in the wet spinning method than in other dry-wet spinning methods, and the acrylonitrile-based precursor fiber produced by the wet spinning method is generally used. It is preferable that the fiber has the above-mentioned surface shape and friction coefficient.

In the acrylonitrile-based precursor fiber produced by the wet spinning method, the wrinkles formed in the fiber axis direction are such that a coagulated yarn produced by discharging and coagulating from a spinning dope initially has a predetermined fiber diameter. Therefore, by the process of stretching,
The depth will be different. The coagulated yarn is once drawn in the air, and then subjected to wet heat drawing in warm water, which also serves as removal of the solvent contained in the coagulated yarn, and then is subjected to dry densification, which is performed before this dry densification step. The depth of wrinkles formed on the surface of the obtained precursor fiber can be adjusted by the stretching ratio in the wet heat stretching. In the method for producing the acrylonitrile-based precursor fiber of the present invention, by selecting the wet heat draw ratio in a range not reaching 3.0 times, the maximum depth of wrinkles does not exceed 100 nm, but is at least 30 nm or more. A certain range of wrinkles is formed with good reproducibility. In particular, when the wet heat stretching ratio is selected to be 2.0 times or less, the maximum depth of wrinkles can be more reliably kept within a range not exceeding 100 nm.
On the other hand, when the wet heat drawing ratio is 3.0 times or more in wet spinning, the maximum depth of the wrinkles frequently increases to 100 nm or more, and as a result, it becomes difficult to achieve the desired fiber bundle convergence. As a result, the process passability cannot be increased.

When the precursor fiber whose surface shape is controlled in this way is used, the surface shape of the obtained carbon fiber inherits the surface of the precursor fiber almost as it is. In addition, the surface shape of the carbon fiber greatly affects the interfacial adhesion between the carbon fiber and the matrix resin constituting the carbon fiber composite material, and the flexural strength and tensile strength of the carbon fiber composite material depend on the degree of the interfacial adhesion. The balance of equal performance also changes.
That is, the performance itself of the carbon fiber composite material can be controlled. Specifically, by controlling the surface shape of the precursor fiber used in the production of the carbon fiber, the interfacial adhesion between the obtained carbon fiber and the matrix resin can be improved, and the surface of the precursor fiber used as a raw material can be improved. In addition, by avoiding unnecessary application of an excessive oil agent, generation of fluff, breakage of bundles, and the like can be suppressed, so that the carbon fiber composite material can have performance according to the purpose and application.

Further, the acrylonitrile precursor fiber of the present invention and a method for producing the same will be described in more detail.

The acrylonitrile precursor fiber of the present invention is produced by a wet spinning method using an acrylonitrile polymer as a raw material.

As the polymerization method of the acrylonitrile polymer used as a raw material, any of known polymerization methods such as solution polymerization and suspension polymerization can be employed. It is preferable to remove the unreacted monomer, polymerization catalyst residue, and other impurities from the polymerized copolymer as much as possible. Further, from the viewpoints of elongation in precursor fiber spinning and performance development of carbon fiber, the degree of polymerization of the copolymer is preferably such that the intrinsic viscosity [η] is 1.0 or more, particularly 1.4 or more. . However,
An intrinsic viscosity [η] in a range not exceeding 2.0 is used.

Next, the copolymer subjected to the above treatment is dissolved in a solvent to prepare a spinning dope. As the solvent, an organic solvent such as dimethylacetamide, dimethylsulfoxide, and dimethylformamide, and an aqueous solution of an inorganic compound such as zinc chloride and sodium thiocyanate can be used. Organic solvents are preferred because they do not contain metal in the fiber to be produced and the process is simplified. Among them, it is more preferable to use dimethylacetamide as the solvent in that the denseness of the coagulated yarn is high.

In order to obtain a dense coagulated yarn at the time of spinning, it is preferable to use a polymer solution having a polymer concentration of a certain level or more as a spinning solution. Specifically, the polymer concentration in the spinning dope is set to 17% or more, more preferably 19% or more. Although it depends on the degree of polymerization of the copolymer to be used, it is usually used to obtain appropriate viscosity and fluidity. The polymer concentration is preferably in the range not exceeding 25%.

In the spinning step, first, the spinning solution is discharged from a nozzle hole having a circular cross section into a coagulation bath to form a coagulated yarn. The coagulation bath has a substantially circular coagulated yarn cross-sectional shape,
In addition, it is necessary to set the conditions so that there is a sufficient margin for taking out the produced coagulated yarn. The concentration and temperature of the solvent contained in the coagulation bath are set so as to satisfy these requirements. A substantially circular shape has no noticeable constriction in the cross section, and the extended shape has a circular shape or a similar shape, for example, an elliptical shape having a ratio of major axis to minor axis of 1.2 or less, more preferably 1.1 or less. Including. When the precursor fiber having such a cross-sectional shape is used, flame resistance is uniform in the fiber cross-sectional direction and then carbonization is performed in the firing step, so that a higher-performance carbon fiber can be obtained.

For the coagulation bath, an aqueous solution containing a solvent used for the spinning solution is preferably used. The concentration of the contained solvent is adjusted so that the spinning dope discharged from the nozzle hole becomes a coagulated yarn having a desired fiber diameter. Depending on the type of solvent used, for example, when dimethylacetamide is used, its concentration is 50 to 80%, preferably 60 to 75%.
Select in the range.

The temperature of the coagulation bath is preferably lower from the viewpoint of the denseness of the coagulated yarn. However, taking into account that if the temperature of the coagulation bath is excessively lowered, the take-up speed of the coagulated yarn is reduced and the overall productivity is reduced.
° C or lower, more preferably in the range of 20 ° C or higher and 40 ° C or lower.

In producing the acrylonitrile-based precursor fiber of the present invention, a step of stretching the coagulated yarn to a desired fiber diameter is provided. First, the coagulated yarn to be withdrawn from the coagulation bath is
Preferably, the film is stretched in the air at a stretching ratio of 2.0 times or less, more preferably 1.3 times or less. As a matter of course, the stretching ratio in such aerial stretching is not less than 1.0 times.

Subsequent to the aerial drawing, while the solvent contained in the coagulated yarn is being washed in boiling water, a wet heat drawing is further performed. The stretching ratio of the wet heat stretching is selected in a range not to reach at most 3.0 times, more preferably in a range of 2 times or less. In addition, since this wet heat stretching also performs washing and removal of the contained solvent, a multi-stage stretching method of two or more stages can be used. As a matter of course, the stretching ratio in such wet heat stretching is not less than 1.0 times.

Further, it is effective that the stretching bath temperature used for the wet heat stretching is as high as possible within a range in which the single yarns do not fuse together. From this viewpoint, the temperature of the stretching bath is preferably set to a high temperature of 70 ° C. or higher. In the case of multi-stage stretching, it is preferable to set the final bath to a high temperature of 90 ° C. or higher.

After wet heat drawing and washing, the fiber surface is subjected to an oil treatment by a known method. The type of the oil agent is not particularly limited, but an amino silicon-based surfactant is preferably used. After this oil agent treatment, dry densification is performed. The temperature of this dry densification is chosen to be above the fiber glass transition temperature. The glass transition temperature may vary depending on the fact that the state of the fiber itself changes substantially from a water-containing state to a dry state, and a method using a heating roller having a temperature of about 100 to 200 ° C is preferable.

In the production method of the present invention, it is preferable to provide a post-stretching step of making the precursor fiber of the present invention a desired fiber diameter by performing drawing again after drying and densification. After this, various methods can be used as long as the dry state of the fiber itself is not significantly changed, such as dry heat drawing using a high-temperature heating roller or a hot platen pin, or steam drawing by pressurized steam. The stretching ratio in the post-stretching step itself is set to 1.1 times or more, more preferably 2.0 times or more, and further preferably 2.5 times or more.

That is, a pre-stretching step consisting of an aerial stretching and a wet heat stretching performed before the dry densification and a post-stretching step performed after the dry densification,
The stretching ratio in the post-stretching step is selected so as to achieve a predetermined stretching ratio.

On the other hand, if the total draw ratio of the pre-draw ratio and the post-draw ratio is too low, the orientation of the fibers will not be sufficient and the performance of the carbon fiber will be reduced. In this respect, the total stretching ratio is preferably from 7 to 20 times, more preferably from 10 to 15 times.

[0037]

The present invention will be described more specifically with reference to the following examples. The following embodiments are examples of the best mode of the present invention, but the present invention is not limited to these embodiments.

Further, “%” used for notation of the content rate and the concentration is used.
Represents weight%.

Various physical properties of the acrylonitrile-based precursor fiber used in describing the present invention, specifically, “wrinkle depth”, “static friction coefficient”, “dynamic friction coefficient”, and In the examples, an evaluation method will be described in advance with respect to an index indicating a characteristic used for the description, specifically, “thread width” and “firing property in a firing step”. In the examples, unless otherwise specified, various physical property values to be described,
The index represents a value measured and evaluated by the method described herein. Normally, a plurality of samples are evaluated and the average value is adopted.

(A) "Wrinkle depth" Place several fiber single yarns to be evaluated on a hemocover glass.
A sample in which both ends are fixed with an adhesive liquid (for example, a stationery correction liquid) is used as a sample, and an atomic force microscope (manufactured by Seiko Instruments, SPI3700 / SPA-300) is used in AFM mode using a silicon nitride cantilever. Perform the measurement. After measuring an arbitrary 3 μm range of each fiber single yarn and performing a two-dimensional Fourier transform on the obtained measurement image, the curvature of the fiber surface, that is, after cutting the corresponding low-frequency components such as gently uneven deformation, the reverse is performed. The conversion is performed, and only the steep wrinkle shape is displayed, excluding irregularities derived from the curvature of the fiber surface. The depth of the displayed wrinkles is measured for an arbitrary cross section of the planar image obtained by performing the above processing.
That is, in this method, the depth of the wrinkle is measured as the depth from the extension to the tip of the wrinkle, assuming the extension of a substantially circular cross section.

The deepest wrinkle among a plurality of wrinkles present on the surface of each fiber single yarn obtained by such a measuring method is defined as “the wrinkle having the maximum depth”. Further, the depth of the “wrinkle having the maximum depth” is defined as the maximum value of the wrinkle depth distribution (maximum wrinkle depth).

(B) "Coefficient of friction" First, the fiber bundle coated with the oil agent to be evaluated is subjected to Soxhlet extraction of the oil agent using a solvent (in this example, methyl ethyl ketone) to remove it. By this solvent extraction, almost all of the oil agent covering the fiber surface is removed except for those slightly remaining at the deep part of the wrinkles. In the following examples, it was confirmed that this removed about 90% of the oil agent. This oil agent removal treatment is performed, the fiber bundle is unraveled, and the collected fiber single yarn is subjected to JI
The coefficient of friction with respect to a flat metal surface is measured by the following method according to SL1015.

A single fiber of fiber collected from the fiber bundle subjected to the oil agent removal treatment is attached to a stainless steel cylindrical cylinder connected to a motor at a contact angle of π radian. A load (M) of 0.1 g is set at one end of the fiber single yarn, and a torsion balance meter is set at the other end. The cylindrical cylinder is rotated at a constant peripheral speed, the reading (T) of the torsion balance meter is measured, and the friction coefficient is calculated by the following equation. The measured value of the friction coefficient at a peripheral speed of 30 revolutions per minute is defined as the dynamic friction coefficient. On the other hand, a value at a peripheral speed of 0 is defined as a static friction coefficient.

[0044]

(Equation 1)

The coefficient of friction evaluated by the above measuring method is as follows:
This corresponds to the coefficient of friction in the fiber axis direction of each fiber single yarn.

(C) “Thread width” As for the acrylonitrile-based precursor fiber thus produced, the thread width of the formed fiber bundle is measured and used as an index of the convergence. Specifically, immediately after passing a series of spinning steps and passing through the final roller, the width of the manufactured fiber bundle in the direction perpendicular to the fiber axis is measured by directly applying a ruler to the yarn.

(D) “Firing process passing property” The acrylonitrile precursor fiber thus produced was visually observed in the firing process for the fiber bundle. ◎: There was no single fiber wrapping around the roll, and the operability was extremely good. ○: A single fiber wrapped around the roll was rare but the operability was good. △: A single fiber wrapped around the roll was slightly observed and the operability was slightly inferior. A rating was given on a scale.

(Examples 1, 2 and Comparative Example 1) An acrylic copolymer copolymerized with 96% of acrylonitrile, 1% of methacrylic acid, and 3% of acrylamide was dissolved in dimethylacetamide to obtain a spinning solution (polymer concentration: 21%). %, Stock solution temperature 6
0 ° C.). This spinning stock solution is 0.075 m in diameter.
m, using a base having 3000 holes, temperature 38 ° C, concentration 6
It was discharged into a 7% aqueous solution of dimethylacetamide to form a coagulated yarn. This coagulated yarn was first drawn in air, and then drawn in warm water. Table 1 shows the stretching ratios of the two stretching steps in Examples 1 and 2 and Comparative Example 1; the stretching ratio in air and the stretching ratio in warm water.

At the time of drawing in the warm water, the fiber itself was washed and desolvated at the same time. Thereafter, the fiber was immersed in a silicon-based oil solution and dried and densified with a 175 ° C. heating roller. As the silicon-based oil solution, an aqueous solution of an aminosilicon-based surfactant having the same concentration and 1.0% was used in all of Examples 1 and 2 and Comparative Example 1.

Subsequent to the drying and densification step, the film is stretched in pressurized steam so that the total stretching ratio becomes 13 times, and the single fiber fineness is 1.2 dtex and the total fineness is 360.
An acrylonitrile precursor fiber of 0 dtex was obtained. For the precursor fibers of Examples 1 and 2 and Comparative Example 1 produced under different drawing ratios in the hot water, the maximum value of the wrinkle depth distribution (maximum wrinkle depth), The coefficient of kinetic friction and the coefficient of static friction, the yarn width and the passing property in the firing step were evaluated. Table 2 also shows the evaluation results.

[0051]

[Table 1]

Example 3 Spinning was carried out under the same conditions as in the acrylonitrile-based precursor fiber of Example 1 except that the number of holes in the spinneret used for producing the coagulated yarn was 24,000, and the single fiber fineness was 1. 2dtex, total fineness is 28800d
An acrylonitrile precursor fiber of tex was obtained. Regarding the prepared precursor fiber of Example 3, the maximum value of the wrinkle depth distribution (maximum wrinkle depth), the coefficient of kinetic friction and the coefficient of static friction, the yarn width, and the passability of the firing step were also determined in accordance with the above evaluation method. ,evaluated. Table 2 also shows the evaluation results.

(Comparative Example 2) Spinning was performed under the same conditions as in the acrylonitrile precursor fiber of Comparative Example 1 except that the number of holes in the spinneret used for producing the coagulated yarn was 24,000, and the single fiber fineness was 1. 2dtex, total fineness is 28800d
An acrylonitrile precursor fiber of tex was obtained. Regarding the produced precursor fiber of Comparative Example 2, the maximum value of the wrinkle depth distribution (maximum wrinkle depth), the kinetic friction coefficient and the static friction coefficient, the yarn width, and the passing property in the firing step were also determined according to the evaluation method described above. ,evaluated. Table 2 also shows the evaluation results.

[0054]

[Table 2]

From the evaluation results shown in Table 2, although the wrinkles are formed in the fiber axis direction by the wet spinning method, the maximum value of the wrinkle depth distribution (maximum wrinkle depth) is 100 nm.
It can be seen that the three types of acrylonitrile-based precursor fibers of Examples 1 to 3 having the following ranges have excellent process passability in the firing process. On the other hand, the acrylonitrile-based precursor fibers of Comparative Examples 1 and 2, in which the maximum value of the wrinkle depth distribution (maximum wrinkle depth) significantly exceeds 100 nm, may have difficulty in processability in the firing step. I understand. The processability in this firing step is related to the convergence of the fiber itself. In the precursor fibers of Examples 1 and 2, the yarn width is 30 m.
m, and in the precursor fiber of Example 3, although the thread width has reached 40 mm, the maximum value of the wrinkle depth distribution (maximum wrinkle depth) itself is the same as that of Example 1. 1
Even when compared with the precursor fiber of the above, the processability in the firing step is in a good range. On the other hand, the precursor fiber of Comparative Example 1 is apparently the same as the yarn width of the precursor fiber of Example 3 as long as the yarn width is compared, but the maximum depth distribution of the wrinkles is 40 mm. The value (maximum depth of wrinkles) is 171 nm, which is about twice as large as 87 nm of the precursor fiber of Example 3, and this difference is reflected in the process passability in both firing steps.

In addition, the passability of the calcination step is determined by the coefficient of static friction between the fiber surface and the smooth metal surface except for the oil agent applied to the surface of the acrylonitrile precursor fiber. It can also be seen that it is related to the selection of the range of the dynamic friction coefficient. That is, three types of Examples 1 to 3 satisfying the condition that the static friction coefficient between the wrinkled fiber surface and the metal surface is 0.35 or more and the dynamic friction coefficient is 0.30 or more in the fiber axis direction. It can be seen that the acrylonitrile-based precursor fiber has excellent processability in the firing step. On the other hand, in the fiber axis direction, the acrylonitrile-based precursor of Comparative Examples 1 and 2, wherein the coefficient of static friction between the wrinkled fiber surface and the metal surface is less than 0.35 and the coefficient of kinetic friction is less than 0.30 It turns out that a body fiber has difficulty in the processability in a baking process.

As a matter of course, the static friction coefficient measured by the above-mentioned evaluation method becomes a value higher than the dynamic friction coefficient.
If both the static friction coefficient and the dynamic friction coefficient become excessively high, there is a concern that a problem may occur in the process. Therefore, even in a state in which the oil agent applied to the fiber surface is removed, the coefficient of static friction is kept within the range of 0.44 or less, and the coefficient of dynamic friction is kept within the range of 0.35 or less. It is more desirable to choose.

In addition, in order to reproducibly produce acrylonitrile-based precursor fibers produced by a wet spinning method, which are excellent in processability in the above-mentioned firing step, a nozzle hole having a substantially circular opening is required. In order to obtain a predetermined fiber diameter of the coagulated yarn produced by discharging and coagulating from the fiber, a drawing step is provided, and after the drawing step, a process of coating a predetermined amount of an oil agent on the fiber surface is performed. In the pre-stretching step, an aerial stretching step and a subsequent wet-heat stretching step are performed, and in the wet-heat stretching step performed before the dry densification step, the wet-heat stretching ratio is set to 3.0. It is concluded that it is desirable to select a range that does not reach double. More preferably, when the wet heat stretching ratio is selected to be 2.0 times or less, the depth of wrinkles generated in the fiber axis direction with high reproducibility is set to a suitable range, specifically, the maximum depth of wrinkles is set to 1
It is possible to keep the thickness below 00 nm.

[0059]

The acrylonitrile-based precursor fiber of the present invention is used as a raw material when a carbon fiber is produced by firing, and is an acrylonitrile-based precursor fiber produced by a wet spinning method. Although having a wrinkle in the fiber axis direction, the cross-sectional shape of the fiber is substantially circular,
The wrinkle depth, measured from the outer edge of the substantially circular fiber cross-section, has a distribution between one or more existing wrinkles in the cross-section, with a maximum wrinkle depth distribution of 100 nm.
Since it is the following, it is an acrylonitrile-based precursor fiber having good processability in a firing step and the like and excellent in convergence. In addition, such a wrinkle shape having an appropriate depth is retained even when baked into a carbon fiber, and when mixed with a matrix resin, a carbon fiber having an interfacial adhesion suitable for a high-performance composite material is obtained. . In addition, such an acrylonitrile-based precursor fiber having a wrinkle shape having an appropriate depth, when produced by a wet spinning method having high productivity, has a substantially circular coagulated yarn having a predetermined fiber diameter. Therefore, a stretching step is provided, after this stretching step, a process of coating a predetermined amount of an oil agent on the fiber surface is performed, and then, a step of drying and densifying the fiber itself is provided. In particular, in the wet heat stretching step carried out before the dry densification step, the wet heat stretching ratio is selected within a range not reaching 3.0 times, thereby producing a product with high reproducibility. be able to.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoko Izumi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Mitsuo Hamada 201-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Masako Iwamoto 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Technology Research Laboratory (72) Inventor Toru Manabe 20 Miyukicho, Otake City, Hiroshima Prefecture No. 1 Mitsubishi Rayon Co., Ltd. Central Research Laboratory F-term (reference) 4L035 BB03 BB06 BB11 BB15 BB17 BB60 BB66 BB69 BB82 BB85 BB93 DD06 EE20 FF01 MB03 MB09 MB19 4L037 CS03 PA57 PA68 PA69 PF45 PF52

Claims (3)

[Claims] 1. An acrylonitrile-based precursor fiber produced by a wet spinning method, which has wrinkles in the fiber axis direction, but has a substantially circular cross-sectional shape; The wrinkle depth measured from the outer edge of the fiber cross section has a distribution between one or more existing wrinkles in the cross section, and the maximum value of the wrinkle depth distribution is 100 nm.
An acrylonitrile-based precursor fiber, characterized in that: 2. An acrylonitrile-based precursor fiber in which an oil is coated on the surface of the fiber having wrinkles in the fiber axis direction, wherein the oil which is coated on the surface is left in a deep part of the wrinkles on the surface. Except for the fiber single yarn substantially completely removed with the solvent, when the fiber single yarn is brought into contact with a flat metal surface, with respect to the fiber axial direction, the static friction coefficient between the wrinkled fiber surface and the metal surface is reduced. 2. The acrylonitrile-based precursor fiber according to claim 1, wherein the acrylonitrile-based precursor fiber has a dynamic friction coefficient of 0.35 or more. 3. A method for producing acrylonitrile-based precursor fibers by a wet spinning method, wherein a coagulated yarn produced by discharging and coagulating from a nozzle hole having a substantially circular opening has a predetermined fiber diameter. In order to provide a stretching step, after the stretching step, a process of coating a predetermined amount of oil agent on the fiber surface, and then a dry densification step of the fiber itself is provided, the stretching step, the air stretching step and subsequent Producing an acrylonitrile-based precursor fiber, wherein the wet-heat stretching step is performed before the dry densification step, and the wet-heat stretching ratio is selected within a range not to reach 3.0 times. Method.