JP2006063265A - Resin composition and blend fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition suitable for producing an ultrafine carbon fiber in high productivity; and to provide a blend fiber. <P>SOLUTION: The resin composition comprises 5-40 wt.% carbon fiber precursor and 95-60 wt.% polyester, and has ≤300 Pa sec melt viscosity measured at a temperature 50°C higher than the melting point of the polyester at 1216 sec<SP>-1</SP>shear rate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resin composition and a blended fiber useful for producing fine carbon fibers, a method for producing the blended fiber, and a method for producing a carbon fiber using the blended fiber.

  Since the characteristic value typified by the strength of the carbon fiber greatly depends on the number of defects in the fiber, reducing the fineness and reducing the number of defects greatly improves the performance of the carbon fiber. Carbon nanotubes that have become a hot topic in recent years are materials that can be called ideal carbon fibers formed from almost perfect graphite sheets, and their physical properties are much higher than those of ordinary carbon fibers. However, since carbon nanotubes are manufactured by a bottom-up method in which carbon atoms are stacked one by one, the productivity is very low and the price is high. For this reason, although it has excellent performance, it has not been widely used. Therefore, many attempts have been made to improve the production method of a normal carbon fiber with high productivity to produce carbon fibers that are as thin as possible, that is, carbon nanofibers, and obtain performance close to that of carbon nanotubes.

  In recent years, a method has been developed in which a carbon fiber precursor and a substance that decomposes and burns down upon firing are prepared to produce a blended fiber, which is then fired to obtain fine carbon fibers. For example, Patent Literature 1 and Patent Literature 2 describe a method of obtaining fine carbon fibers by using a phenol resin as a carbon precursor and performing blend spinning with polyethylene (PE) or polypropylene (PP). Patent Document 3 discloses a method for producing a carbon precursor fiber in which melt-forming acrylonitrile-based polymer is used as a carbon precursor, and acid-modified PE or methyl methacrylate (PMMA) is used as a sea part and melt-spun using a spinneret device. Is described.

    In such a method using a blended fiber, in order to obtain a fine carbon fiber, it is not sufficient to finely mix the carbon precursor and other components, and the mixed resin has a large draw ratio. It needs to be extended. As a method for drawing a fiber in melt spinning, a method for increasing a draft during spinning and a method for drawing a once wound fiber are known. Here, in the method of increasing the draft at the time of spinning, since the stretching is performed in a state where the resin immediately after discharge is low, the stretching stress is low, and the action of stretching the internal carbonized resin is weak, which is proportional to the increase in the draft. The drawing effect cannot be obtained. On the other hand, in the method of drawing the fiber once wound up, the drawing is performed at a low temperature of not less than the glass transition and not more than the melting point. Therefore, the drawing stress is high and the effect of drawing the carbonized resin inside is high, but the draw ratio itself is low. In order to obtain finer carbon fibers, it is essential to produce fibers by combining the two in a balanced manner.

However, PE described in Patent Document 1 has a very high viscosity at the time of melting, and if the draft at the time of melt spinning is set high, yarn breakage frequently occurs, so it was impossible to set the draft high. Furthermore, since PE has a glass transition temperature lower than room temperature and a high crystallization rate, the fiber obtained by melt spinning is highly crystallized, and it is difficult to stretch the fiber once wound. In addition, PP described in Patent Document 2 has better spinnability than PE and can be set to a high draft during melt spinning. However, like PE, the glass transition temperature is below room temperature, and PE and Similarly, it was difficult to draw the fiber once wound. On the other hand, amorphous polyolefins such as PMMA described in Patent Document 3 have insufficient fiber flexibility, and have poor yarn-making properties and cannot be stretched. As described above, it has been difficult to achieve both the spinning performance and the stretchability by the conventional techniques, and it has been difficult to efficiently obtain fine carbon fibers.
JP 2001-73226 A JP 2003-20517 A JP 2004-43994 A

  An object of the present invention is to provide a resin composition and a blended fiber that are suitable for producing fine carbon fibers and have high productivity.

The above object consists of 5 to 50% by weight of a carbon fiber precursor and 95 to 50% by weight of polyester, and has a melt viscosity of 300 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester. This is solved by the resin composition characterized in that.

  By mixing the carbon fiber precursor with a polyester excellent in spinning / drawing property, the carbon precursor in the fiber can be efficiently stretched, and fine carbon fibers can be produced. At the same time, since melt spinning and drawing at high speeds are possible, production efficiency is greatly improved, and manufacturing costs can be reduced. Furthermore, since the polyester-based resin exhibits high thermal stability, it is possible to increase the temperature at the time of performing the treatment for imparting thermal stability to the carbon fiber precursor, and it is possible to improve productivity and firing. The retainability of the initial fiber form is high, and it becomes possible to prevent fusion between fine carbon fibers.

  In the resin composition of the present invention, it is important that a carbon fiber precursor and polyester are mixed. Polyester is a resin excellent in spinning and drawing properties, and by dispersing a carbon precursor therein, it is possible to efficiently produce a blended fiber as a raw material for fine carbon fibers.

  In order to obtain a form in which the carbon precursor is dispersed in the polyester as described above, the ratio between the two is important. The weight of the carbon precursor is 5 to 50 with the total weight of the resin composition being 100% by weight. It is important that the polyester is 95-50% by weight. A lower polyester fraction is preferable because the yield of carbon fibers during firing is improved, but increasing the carbon precursor fraction adversely affects spinnability, so the weight of the carbon precursor is 10-30%. Is more preferable, and it is further more preferable in it being 15 to 20%.

  The carbon precursor referred to in the present invention refers to a substance that forms carbon fibers made of only carbon by performing a high-temperature heat treatment called firing after fiberization. Here, in the resin composition of the present invention, fiberization is performed by a highly productive melt spinning method, and therefore, the carbon precursor must be plasticized by heat so that it can be molded. As such a substance, 1 type, or 2 or more types of mixtures chosen from a polyimide, an acrylonitrile-type resin, a phenol resin, a cellulose derivative, a pitch, and a copolymer which has them as a main component can be used. Among these, acrylonitrile-based resins are preferable because of excellent spinnability. The method for imparting melt shapeability to the acrylonitrile resin is not particularly limited, and any method such as a method of adding water or a method of copolymerizing components other than acrylonitrile can be employed.

The polyester referred to in the present invention refers to a resin mainly composed of ester bonds, and preferred examples include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, and polylactic acid. In particular, since it is necessary to remove the polyester at the time of carbon fiber production, an aliphatic polyester that is completely decomposed by heat is preferable, and polylactic acid is most preferable. These polyesters may be copolymerized with other components within a range not impairing the gist of the present invention, and may contain a small amount of additives such as an antioxidant and a terminal group blocking agent.
Since these polyesters are excellent in yarn production and can be spun at a high draft, it is possible to set a high winding speed during melt spinning. For example, polyethylene terephthalate is industrially produced at a speed of 7,000 m / min or higher. Since spinning at such a high draft is possible, the carbon precursor inside the fiber can be stretched and refined, and high productivity can be secured. In addition, since polyester has a glass transition point higher than room temperature, it is possible to obtain a fiber having a low crystallinity and excellent stretchability even when taken with a relatively high draft by quenching during melt spinning. Further stretching can be performed. This stretching makes it possible to further stretch the carbon precursor inside the fiber, and to obtain a finer carbon fiber. Furthermore, crystallization can be promoted by heat-treating the drawn fiber, and the heat resistance of the fiber can be improved. For this reason, the deformation | transformation in the process of carbonizing a carbon precursor reduces, The quality of the carbon fiber obtained improves, Since processing temperature can be set high, productivity can also be improved. For this reason, it is preferable that melting | fusing point of polyester is 150 degreeC or more.

In addition, it is important that the resin composition of the present invention has a melt viscosity of 300 Pa · sec or less when measured at a shear rate of 1216 sec ⁻¹ at a temperature 50 ° C. higher than the melting point of the polyester in the resin composition. An incompatible polymer alloy such as the resin composition of the present invention is likely to generate an unstable flow state at the time of molding, and the productivity deteriorates particularly when molding with a large free surface such as melt spinning. However, it is possible to stabilize the flow state and improve productivity by keeping the melt viscosity at the molding temperature low. Therefore, the melt viscosity when measured at a shear rate of 1216 sec ⁻¹ at a temperature 50 ° C. higher than the melting point of the resin composition of the present invention is preferably 250 Pa · sec or less, and more preferably 200 Pa · sec or less.

Furthermore, the viscosity of the polyester having a high mixing ratio is more important for the molding stability of the resin composition. The polyester component alone constituting the resin composition is a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester. The melt viscosity is preferably 200 Pa · sec or less, more preferably 100 Pa · sec or less, as measured by.

  Here, the melting point in the present invention is an endotherm observed when a resin to be measured is measured at a temperature rising condition of 16 ° C./min from room temperature in a differential calorimetry performed by a differential scanning calorimeter (DSC manufactured by Perkin Elmer). Refers to peak temperature. Here, for a resin that does not show crystallinity and does not show a clear endothermic peak in measurement with a differential scanning calorimeter, the softening point is used instead of the melting point. The melt viscosity is a value measured with a capillary rheometer (Toyo Seiki Seisakusho Co., Ltd. Capillograph Type 1B).

  In addition to the above carbon precursor and polyester, the resin composition of the present invention can be mixed with other components within a range that does not impair the spirit of the invention. An agent or the like may be added.

  By making the said resin composition into a fiber form, it becomes a blend fiber suitable for manufacture of a fine carbon fiber. It is important that the blend fiber is a sea-island type blend fiber in which the carbon precursor is an island component and polyester is a sea component. Because of this structure, by removing the polyester component before or during firing, it becomes possible to take out fine fibers consisting of the carbon precursor in the original blend fiber, and by further firing It becomes possible to produce fine carbon fibers.

  In order to obtain fine carbon fibers after firing, it is necessary to refine the carbon precursor in the blend fiber, and the average of island components formed by the carbon precursor in the cross section perpendicular to the fiber axis of the blend fiber The diameter is preferably 500 nm or less. The diameter of the island component in the cross section can be measured by staining a thin piece sample cut in the direction perpendicular to the fiber axis as necessary and observing with a transmission electron microscope (TEM). An average diameter can be obtained by performing image processing on a TEM photograph containing 10 or more areas, calculating the diameter of each island component, and taking the average value of the radii of the obtained island components. In order to obtain finer carbon fibers, the diameter of the island component is preferably small, and more preferably 200 nm or less. However, considering the handleability and productivity during firing, the island component preferably has a diameter of 1 nm or more.

  Such a blended fiber can be prepared by mixing 5-50% by weight of a carbon precursor and 95-50% by weight of polyester and melt spinning. Mixing and melt spinning of the carbon precursor and the polyester may be performed separately or continuously, but it is important that the carbon precursor is sufficiently kneaded so that the carbon precursor is uniformly dispersed in the polyester. Mixing may be performed using a static kneading apparatus or a dynamic kneading apparatus, but in order to perform sufficient kneading, a stationary kneader having a dividing ability of 100,000 or more is preferable. If it is a dynamic kneading machine, a twin-screw kneading extruder is preferable.

  As a spinning method, it is important to use a melt spinning method. The melt spinning method can set the winding speed higher than that of the solution spinning method and is excellent in productivity, and it does not require recovery of the solvent, so there is less equipment burden and the cost can be kept low. is there. Moreover, since the melt of the resin used for melt spinning has a higher viscosity than the resin solution used for solution spinning, the sea-island structure created by mixing is stable. Furthermore, in melt spinning, the structure is fixed by cooling the spinning line, and in solution spinning, the solvent is dispersed. However, since the spinning line in melt spinning proceeds much faster, the structure is fixed before the sea-island structure is disturbed. It is possible to make a blend fiber having a homogeneous sea-island structure.

  As the melt spinning apparatus, a known spinning apparatus such as an extruder type or a pressure melter type can be used. However, if the spinning apparatus has a high kneading capacity, mixing and melt spinning can be carried out continuously to improve productivity. It is preferable because it is excellent. The spinning conditions can be arbitrarily set so that the spinning property is good. However, since the spinning is a melt spinning of a mixture of a plurality of resins, care must be taken in selecting the die and setting the cooling conditions. Specifically, when spinning the mixture, a ballast effect that thickens the spinning line immediately after discharge is likely to occur, and this may cause a decrease in yarn production. Therefore, it is necessary to select a die having a large discharge port diameter as necessary. There is. At this time, if the discharge pressure becomes extremely low, the stability of discharge becomes low. Therefore, it is preferable to use a die having a throttle portion provided in the middle of the discharge hole. In addition, it is also important to shorten the time from the discharge to the start of cooling because the squeezing phenomenon in which the fibers after discharge are periodically thickened tends to occur during spinning of the mixture.

  Setting the winding speed at the time of melt spinning as high as possible within the range where yarn breakage does not occur frequently leads to improvement in productivity.However, since the resin composition of the present invention is based on polyester with good spinnability, the draft is increased. However, it is stable and can be wound at a high speed of 5,000 m / min or more. By winding up with such a high draft, it is possible to stretch the original sea-island structure and transform the carbon precursor, which is a sea component, into a thin and long fiber. However, since deformation by melt spinning is performed at a very high temperature immediately after discharge and concentrated at a low viscosity, the effect of stretching the carbon precursor inside the fiber tends to be saturated. On the other hand, if the draft is excessively large, orientational crystallization occurs on the spinning line, and the drawability of the wound fiber decreases. For this reason, the preferable winding speed is 500 m / min to 8,000 m / min, more preferably 1,000 m / min to 5,000 m / min, and 2,000 m / min to 4,000 m / min. And more preferred.

    Further, the obtained blended fiber is preferably stretched. By stretching the obtained blended fiber, it is possible to further stretch and refine the carbon precursor inside the fiber. Since the deformation during stretching is performed at a lower temperature than the deformation during melt spinning, the stress acting on the internal carbon precursor is large, and the relaxation behavior due to interfacial tension is small, so the carbon precursor is efficiently refined. It is possible. For this reason, it is preferable to make the stretching temperature as low as possible, but unevenness is likely to occur when stretching is performed at a temperature lower than the glass transition temperature. Therefore, the temperature is 10 to 20 ° C. higher than the glass transition temperature of the higher polyester and carbon precursor. It is preferable to do. Here, the higher the draw ratio, the better because the finer progresses, but it is necessary to select an appropriate value in relation to the elongation described later.

By stretching the obtained blended fiber, it is possible to refine the carbon precursor in the blended fiber and simultaneously improve the strength of the blended fiber. If the strength of the blended fiber is high, deformation due to external force can be reduced, so that the handleability and processability of the yarn bundle are improved. For this reason, the strength of the blended fiber is preferably 1 cN / dTex or more, and more preferably 2 cN / dTex or more. However, if the elongation of the fiber after drawing becomes too small, it causes thread breakage and the productivity is lowered. Therefore, the elongation of the drawn yarn is preferably 20% or more.
The blended fiber is preferably subjected to heat treatment in addition to stretching. By performing the heat treatment, crystallization of the polyester can be promoted, and the heat resistance of the blended fiber can be improved. Thus, by improving heat resistance, the deformation | transformation of the fiber in the process of subsequent carbonization can be suppressed and the quality of the carbon fiber obtained can be improved. At the same time, it is possible to increase the processing temperature in the subsequent process, and it is possible to improve productivity. The heat treatment is preferably performed at a temperature between the glass transition temperature and the melting point, and is preferably performed between (glass transition temperature + 20 ° C.) and (melting point−30 ° C.) of the polyester.

  Using the blended fiber thus obtained, a process for imparting thermal stability to the carbon precursor in the blended fiber, a process for removing the polyester in the blended fiber, and a process for producing carbon fiber by firing By performing this, fine carbon fibers can be produced.

  The step of imparting thermal stability by crosslinking the carbon precursor in the blended fiber is a step of imparting thermal stability so that the shape of the carbon precursor that had thermoplasticity during melt spinning does not change during firing. It is necessary to perform a treatment according to the carbon precursor. For example, when the carbon precursor is pitch, it is possible to promote bonding between benzene sheets by heating in the presence of a small amount of oxygen and to impart thermal stability. Thermal stability can be imparted by a crosslinking reaction with aldehydes in the presence of a catalyst. In the case of an acrylonitrile-based resin, heat treatment is performed near the melting point, whereby a cyclization reaction by an acrylonitrile group proceeds and thermal stability is imparted.

  The polyester in the blend fiber can be removed by hydrolysis with alkali or the like, or thermal decomposition with heat. When hydrolyzing with alkali, the polyester removal treatment may be performed before imparting thermal stability to the carbon precursor or after imparting thermal stability to the carbon precursor. In other words, the blended fiber becomes an aggregate of fine carbon precursor fibers, and the handleability is reduced, and the finer the carbon precursor fibers are, the more easily they are fused to each other. It is preferable to carry out after imparting stability. When removing polyester by thermal decomposition by heat, since the thermal decomposition temperature of polyester is generally higher than the softening point of the carbon precursor, it is necessary to carry out a treatment for imparting thermal stability to the carbon precursor in advance. is there. In addition, when removing polyester by thermal decomposition due to heat, since thermal decomposition proceeds simultaneously with baking during the heat treatment in the next baking step, it is possible to perform the polyester removal treatment and baking simultaneously, thereby improving productivity. preferable. However, since an aromatic polyester having a benzene ring in the molecular chain is not completely thermally decomposed in an inert atmosphere, it is impossible to simultaneously remove and bake the polyester. In this case, it is preferable that the polyester is decomposed and fired continuously by carrying out the main baking after thermally decomposing the polyester in an atmosphere containing a small amount of oxygen at a lower temperature than the normal baking.

  In the step of obtaining carbon fibers by firing, elements other than carbon inside the carbonized resin are removed to produce fibers made of pure carbon. Firing may be performed according to a known method, and it is preferable to perform heat treatment at 600 to 1200 ° C. under an inert gas such as nitrogen or argon.

  The carbon fiber obtained in this way is characterized by being extremely thin reflecting the shape of the carbonized resin in the original blend fiber, and can be used for high-performance electrodes and adsorbents by utilizing a large surface area. Because of its excellent mechanical properties, it is also useful as a resin additive and a reinforcing material for composite materials.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, the various measured values in each Example are the values measured by the following method.
A. Average diameter of island component in blended fiber After impregnating the blended fiber with epoxy resin and dyeing with RuO _4, an ultrathin section with a plane perpendicular to the fiber axis was prepared using a microtome, and a transmission electron microscope (( Hitachi, Ltd., H-7100FA) was used to observe the center of the fiber at a magnification of 40,000 times, and the resulting image was subjected to circular figure separation with image processing software (Mitani Corporation, Winroof). After measuring the area of the component and the circle-converted diameter, it was determined using the following formula.

B. Melting point Measurement was carried out using a differential scanning calorimeter (DSC, manufactured by Perkin Elmer Co., Ltd.) under a temperature rising condition from room temperature to 16 ° C./min, and the observed endothermic peak temperature was taken as the melting point.
C. Melt Viscosity Using a capillary rheometer (Capillograph Type 1B, manufactured by Toyo Seiki Seisakusho Co., Ltd.), a die having a pore diameter of 1 mmφ and L / D = 10 was measured at a shear rate of 1216 sec ⁻¹ .
D. High Elongation Tensile Tester (Orientec Co., Ltd. UTM-III) Test length was 20 cm / min and tensile rate was 20 cm / min to obtain strength and elongation.

Example 1
20% by weight of thermoplastic polyacrylonitrile resin (manufactured by Mitsui Chemicals, Valex # 3000) and 80% by weight of polylactic acid (manufactured by Cargill Dow Polymer LLC, 6250D, melting point 170 ° C., melt viscosity 83 ° C. at 220 ° C.) 2 Using a shaft kneading extruder (Technobel Co., Ltd., KZW15TWIN-30MG-FSS), kneading was performed at a set temperature of 190 ° C. with a screw rotation speed of 250 rpm and a processing speed of 4 kg / h to prepare a resin composition. The stability and spinnability of the kneaded gut were good, and no gut breakage occurred within 1 hour of trial production time. The melt viscosity at 220 ° C. of the obtained resin composition was 164 Pa · sec.

Example 2
A resin composition was prepared in the same manner as in Example 1 except that the mixing ratio was changed to 40% by weight of thermoplastic polyacrylonitrile resin and 60% by weight of polylactic acid. The stability and spinnability of the kneaded gut were good, and no gut breakage occurred within 1 hour of trial production time. The melt viscosity at 220 ° C. of the obtained resin composition was 246 Pa · sec.

Example 3
A resin composition was prepared in the same manner as in Example 1 except that polylactic acid was changed to 6200D (melting point: 170 ° C., melt viscosity: 155 Pa · sec) manufactured by Cargill Dow Polymer LLC. The stability of the kneaded gut was somewhat low, and one piece of gut was generated within one hour of the trial production time. The melt viscosity at 220 ° C. of the obtained resin composition was 222 Pa · sec.

Comparative Example 1
A resin composition was prepared in the same manner as in Example 1 except that the mixing ratio was changed to 60% by weight of thermoplastic polyacrylonitrile resin and 40% by weight of polylactic acid. The stability of the kneaded gut was extremely low, and 12 pieces of gut breakage occurred within one hour of the trial production time. The melt viscosity at 220 ° C. of the obtained resin composition was 327 Pa · sec.

Comparative Example 2
20% by weight of the thermoplastic polyacrylonitrile resin used in Example 1 and 80% by weight of a methacrylic resin (Sumitomo Chemical Co., Ltd., Sumipex LG35) were kneaded in the same manner as in Example 1 to prepare a resin composition. The stability of the kneaded gut was somewhat low, and three gut breaks occurred within one hour of the trial production time.

Comparative Example 3
A twin-screw kneading extruder similar to that used in Example 1 was prepared by using 20% by weight of novolak type phenolic resin (Sumitomo Bakelite Co., Ltd., PR-50731) and 80% by weight of low density polyethylene (Sumitomo Mitsui Polyolefin Co., Ltd., Mirason FL60). The resulting mixture was kneaded at a set temperature of 120 ° C. and a screw rotation speed of 300 rpm and a processing speed of 4 kg / h to prepare a resin composition. The stability of the kneaded gut was stable, and no gut breakage occurred within one hour of trial production time.

Example 4
The resin composition produced in Example 1 was put into a pressure melter type melt spinning apparatus, set to a melter temperature of 205 ° C. and a spin block temperature of 195 ° C., and using a die with a hole diameter of 0.23 mm, the die surface depth was 5 cm. It was set and melt spinning was performed at a winding speed of 1200 m / min to produce a blend fiber of 60 dTex, 6 filaments. Furthermore, the drawn fiber was stretched 2.6 times at a stretching speed of 600 m / min using a stretching machine in which the first heating roller (1HR) was set to 90 ° C. and the second heating roller (2HR) was set to 100 ° C. went. There was no yarn breakage or fluffing during drawing, and the drawn yarn could be stably produced. When the cross section of the obtained fiber was observed, it was a sea-island type mixed fiber in which the thermoplastic acrylonitrile resin was uniformly dispersed as an island component. The result of cross-sectional TEM observation of this fiber is shown in FIG. When the diameter of the island component was measured by image processing of the cross-sectional photograph, the average diameter calculated by Equation 1 was 140 nm. The blend fiber had a strength of 2.9 cN / dTex and an elongation of 54%.

Example 5
Melt spinning was performed with the same settings as in Example 4 except that the resin composition was changed to that prepared in Example 2. The obtained fiber was stretched 1.8 times under the same conditions as in Example 4. At this time, yarn breakage did not occur, but some fluff was observed in the drawn yarn. When the cross section of this fiber was observed, it was a sea-island type mixed fiber in which the thermoplastic acrylonitrile resin was dispersed almost uniformly as an island component. The result of cross-sectional TEM observation of this fiber is shown in FIG. When the diameter of the island component was measured by image processing of the cross-sectional photograph, the average diameter calculated by Equation 1 was 174 nm. The blend fiber had a strength of 1.8 cN / dTex and an elongation of 21%.

Example 6
Melt spinning was performed with the same settings as in Example 4 except that the resin composition was changed to that prepared in Example 3. As a result, yarn breakage was observed, and when the spinning speed was lowered to 900 m / min, fibers could be obtained without yarn breakage. This fiber was stretched 2.4 times under the same conditions as in Example 4. When the cross section of this fiber was observed, it was a sea-island type mixed fiber in which the thermoplastic acrylonitrile resin was dispersed almost uniformly as an island component. The result of cross-sectional TEM observation of this fiber is shown in FIG. When the diameter of the island component was measured by image processing of the cross-sectional photograph, the average diameter calculated by Equation 1 was 132 nm. The blend fiber had a strength of 3.5 cN / dTex and an elongation of 49%.

Example 7
A blend fiber was prepared by melt spinning in the same manner as in Example 4 except that the winding speed was changed to 3,000 m / min. Subsequently, the obtained drawn yarn was drawn 1.5 times under the same conditions as in Example 4 to produce a drawn yarn. When the cross section of the obtained fiber was observed, it was a sea-island type mixed fiber in which the thermoplastic acrylonitrile resin was uniformly dispersed as an island component. When the cross-sectional photograph of this fiber was image-processed and the diameter of the island component was measured, the average diameter calculated by Formula 1 was 129 nm. The blend fiber had a strength of 2.4 cN / dTex and an elongation of 38%.

Comparative Example 4
The resin composition produced in Comparative Example 1 was put into the same spinning machine as in Example 4, and melt spinning was performed using a 0.3 mmφ die at a melter temperature of 215 ° C. and a spin block temperature of 215 ° C., and 60 dTex, A 6-filament blend fiber was prepared. As for spinning, when the winding speed was 900 m / min, the yarn breakage was severe and spinning was impossible, and it was finally possible to reduce the winding speed to a winding speed of 600 m / min. When the cross section of the obtained fiber was observed, it was found that the thermoplastic acrylonitrile resin was a sea-island type blend fiber.

Comparative Example 5
The resin composition prepared in Comparative Example 2 was put into the same spinning machine as in Example 4, and melt spinning was performed using a 0.6 mmφ die with a melter temperature of 220 ° C. and a spin block temperature of 230 ° C., and 60 dTex, A 6-filament blend fiber was prepared. As for spinning, when the winding speed was 900 m / min, the yarn breakage was severe and spinning was impossible, and it was finally possible to perform spinning by lowering the winding speed to a winding speed of 500 m / min. Further, the obtained fiber was very brittle and could not be drawn. When the cross section of this fiber was observed, it was found that the thermoplastic acrylonitrile resin was a sea-island type blend fiber having an island component, but the island component had a very large diameter variation. The result of cross-sectional TEM observation of this fiber is shown in FIG. When the diameter of the island component was measured by image processing of the fiber cross-sectional photograph, the average diameter calculated by Equation 1 was 270 nm. Moreover, since it was very brittle, it was impossible to measure the strength.

Comparative Example 6
The resin composition produced in Comparative Example 3 was put into the same spinning machine as in Example 4, and melt spinning was performed using a 0.6 mmφ die with a melter temperature of 190 ° C. and a spin block temperature of 190 ° C., and 60 dTex, A 6-filament blend fiber was prepared. As for spinning, yarn breakage was severe even at a winding speed of 600 m / min, and spinning was impossible. Spinning was finally possible by lowering the winding speed to a winding speed of 100 m / min. Stretching of the obtained fiber was attempted, but at a stretching speed of 600 m / min, yarn breakage occurred frequently, and stable stretching was impossible. When the cross section of this fiber was observed, it was found that the phenolic resin was a sea-island blend fiber having an island component, and the average diameter of the island component was 1.5 μm.

Example 8
The blended fiber obtained in Example 4 is heat treated at 240 ° C. for 45 minutes in a nitrogen atmosphere to make it infusible, and then subjected to heat treatment at 600 ° C. for 1 hour in a nitrogen atmosphere to produce carbon fibers. did. When the produced carbon fiber was observed with an electron microscope, a carbon fiber having a diameter of 80 to 150 nm was observed.

Cross-sectional TEM photograph of the fiber of Example 4 (40,000 times) Cross-sectional TEM photograph of the fiber of Example 5 (40,000 times) Cross-sectional TEM photograph of the fiber of Example 6 (40,000 times) Cross-sectional TEM photograph of the fiber of Comparative Example 5 (40,000 times)

Claims (16)

It consists of 5 to 50% by weight of a carbon fiber precursor and 95 to 50% by weight of polyester, and has a melt viscosity of 300 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester. Resin composition. 2. The resin composition according to claim 1, wherein the carbon fiber precursor is an acrylonitrile-based resin having melt shapeability.   The resin composition according to claim 1, wherein the polyester is an aliphatic polyester. The resin composition according to any one of claims 1 to 3, wherein the polyester is a polyester having a melt viscosity of 200 Pa · sec or less measured at a shear rate of 1216 sec ^{-1 at a} temperature 50 ° C higher than the melting point. Resin which is a mixture of 5 to 50% by weight of a carbon fiber precursor and 95 to 50% by weight of a polyester and has a melt viscosity of 300 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester A blended fiber comprising a composition, wherein the carbon fiber precursor forms an island and the polyester forms a sea.   6. The blend fiber according to claim 5, wherein the average diameter of the island component in the fiber cross section is 500 nm or less.   The blend fiber according to any one of claims 5 and 6, wherein the carbon fiber precursor is an acrylonitrile-based resin having melt shapeability.   The blended fiber according to claim 5 or 6, wherein the polyester is an aliphatic polyester. The blend fiber according to any one of claims 5 to 8, wherein the polyester is a polyester having a melt viscosity of 200 Pa · sec or less measured at a shear rate of 1216 sec ^{-1 at a} temperature 50 ° C higher than the melting point. A resin obtained by mixing 5 to 50% by weight of a carbon fiber precursor and 95 to 50% by weight of a polyester and having a melt viscosity of 200 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester. A method for producing a blended fiber, comprising melt-spinning the composition. A resin obtained by mixing 5 to 50% by weight of a carbon fiber precursor and 95 to 50% by weight of a polyester and having a melt viscosity of 200 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point of the polyester. A method for producing a blended fiber, wherein the composition is melt-spun and then drawn.   The method for producing a blended fiber according to any one of claims 10 and 11, wherein the carbon fiber precursor is an acrylonitrile-based resin having melt shapeability.   12. The method for producing a blended fiber according to claim 10, wherein the polyester is an aliphatic polyester. 14. The production of a blend fiber according to claim 10, wherein the polyester is a polyester having a melt viscosity of 200 Pa · sec or less measured at a shear rate of 1216 sec ^{−1 at a} temperature 50 ° C. higher than the melting point. Method.   Using the blended fiber according to any one of claims 5 to 9, crosslinking a carbon fiber precursor in the fiber to impart thermal stability, removing the polyester in the fiber, A method for producing carbon fiber, comprising a step of firing carbon to produce carbon fiber.   The method for producing a carbon fiber according to claim 15, wherein the step of removing the polyester in the fiber and the step of firing the fiber to produce carbon fiber are performed simultaneously.