JP2007162144A - Method for producing carbon fiber bundle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber bundles-producing method for stably feeding a carbon fiber having high tensile modulus in high quality. <P>SOLUTION: In the method for producing carbon fiber bundles by making adjacently traveling plurality of polyacrylonitrile-based fiber bundles nonflammable at 200-300°C in the air, subsequently carrying out primary carbonizing treatment of the treated fiber bundles at 300-800°C in an inert atmosphere and further carrying out secondary carbonizing treatment of the treated fiber bundles at 1,200-2,000 maximum treating temperature in an inert atmosphere, fiber bundles supplied for secondary carbonizing treatment have ≤4,000 dtex/mm total fineness per width, and tension of ≥500 mg/dtex is applied to the fiber bundles when carrying out secondary carbonizing treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon fiber bundle, and in particular, is a method for producing a carbon fiber bundle capable of obtaining a carbon fiber bundle having high performance and good quality.

  Carbon fibers are used in various applications because of their excellent mechanical and electrical properties. In recent years, in addition to conventional sports applications such as golf clubs and fishing rods and aircraft applications, development for so-called general industrial applications such as automobile members, CNG tanks, seismic reinforcement of buildings, and ship members has been progressing. Along with this, the level of required mechanical properties is also increasing. For example, in aircraft applications, many structural members are being replaced with carbon fiber reinforced plastics for weight reduction. However, as the use site becomes larger, rigidity is required as a structural member, and carbon having a higher tensile elastic modulus. There is a need for fiber.

As a method for obtaining a polyacrylonitrile-based carbon fiber, a primary carbonized fiber obtained by flame-proofing a polyacrylonitrile-based fiber at 200 to 300 ° C. in air and subsequently performing a primary carbonization treatment at 300 to 800 ° C. in an inert atmosphere, A method of secondary carbonization treatment at a maximum treatment temperature of 1,200 to 2,000 ° C. in an inert atmosphere is common.
In order to improve the tensile modulus of carbon fiber, there is a method to increase the maximum treatment temperature of the secondary carbonization treatment. However, although the tensile modulus is certainly improved, the tensile strength decreases at 1,500 ° C. Therefore, it is difficult to obtain a carbon fiber having a balance between elastic modulus and strength.

  Therefore, there has been proposed a method for improving the tensile elastic modulus without reducing the tensile strength by controlling the firing conditions in flame resistance and primary carbonization and performing high stretching under high tension in the subsequent secondary carbonization treatment. (See Patent Documents 1, 2, 3, and 4). However, in these methods, since the tension in the secondary carbonization treatment is high, the packing state between the fibers becomes denser than the treatment in the low tension, so that the decomposition gas generated from the fibers themselves is removed from the bundle. It becomes difficult to separate, and unevenness is likely to occur in the degree of secondary carbonization treatment between single fibers in the bundle. And the unevenness of the degree of the secondary carbonization treatment causes unevenness of tension between single fibers in the bundle, and fluff and thread breakage are likely to occur. That is, physical properties can be improved by these methods alone, but it cannot be said that the quality of the obtained carbon fibers has reached a sufficient level. In addition, winding of the fluff around the roller or thread breakage may cause a decrease in productivity.

As a method of producing high-quality carbon fibers with high productivity, in the primary carbonization treatment and the secondary carbonization treatment, the flatness of the treated fiber bundle is regulated, and a gap is not formed between adjacent fiber bundles. A method for supplying a large number of treated fibers into a furnace has been proposed (see Patent Document 5). The technique proposed in Patent Document 5 aims to obtain a carbon fiber having a low tensile elastic modulus such as 220 to 240 GPa at a low tension of 45 to 190 mg / dtex in the secondary carbonization treatment. Although effective when performing low-tension carbonization, when producing carbon fiber having a high tensile elastic modulus of 330 GPa or more, which is required for aircraft applications, etc., carbonization with higher tension is required. Necessary. In Patent Document 5, secondary carbonization treatment is performed without creating a gap between fiber bundles, and simply applying such a technique tends to cause fluff and thread breakage. There was a problem that could not be obtained.
Japanese Patent No. 1709121 Japanese Patent No. 1709122 Japanese Patent No. 1713506 Japanese Patent No. 2667663 JP 2003-55843 A

  In view of the present situation, the object of the present invention is to produce high-quality carbon fibers by suppressing the occurrence of fuzz and yarn breakage in producing high-performance carbon fibers having both excellent tensile modulus and tensile strength. It is in providing the manufacturing method of a fiber.

  In order to achieve the above-described object of the present invention, the carbon fiber bundle manufacturing method of the present invention has the following configuration. That is, a plurality of polyacrylonitrile fiber bundles that run adjacent to each other are made flame resistant at 200 to 300 ° C. in the air, and subsequently subjected to primary carbonization treatment at 300 to 800 ° C. in an inert atmosphere. In the active atmosphere, the carbon fiber bundle is subjected to secondary carbonization treatment at a maximum treatment temperature of 1,200 to 2,000 ° C., and the fiber bundle subjected to the secondary carbonization treatment has a total fineness of 4,000 dtex / It is a manufacturing method of a carbon fiber bundle which is not more than mm and gives a tension of 500 mg / dtex or more to the fiber bundle when performing the secondary carbonization treatment.

  According to a preferred aspect of the method for producing carbon fiber of the present invention, in performing the secondary carbonization treatment, in addition to setting the interval between adjacent fiber bundles to be 2 mm or more, the fiber bundle to be subjected to the secondary carbonization treatment, It is preferable that the weight loss rate when heat-treated at 1,000 ° C. for 2 minutes in a nitrogen atmosphere is 25% or less and the degree of crystal orientation is 78% or more.

  According to the present invention, high tension treatment in secondary carbonization treatment can be realized stably, whereby high-performance and high-quality carbon fibers can be produced.

  In order to improve the tensile elastic modulus of the carbon fiber, the present inventors have made extensive studies focusing on the behavior in the secondary carbonization treatment, how to perform high-stretching treatment without lowering the tensile strength and quality. As a result, in the secondary carbonization treatment under high tension, the decomposition gas generated from the fiber itself becomes difficult to separate from the fiber bundle due to the dense packing state due to the high tension, so that the single fibers in the bundle are Unevenness is likely to occur in the degree of secondary carbonization treatment, and unevenness in the degree of secondary carbonization treatment causes unevenness in tension between single fibers in the bundle, and fluff and thread breakage are likely to occur. The present invention was reached.

  Hereinafter, the present invention will be described in more detail.

  In the present invention, a plurality of polyacrylonitrile-based fiber bundles that run adjacent to each other are flame-resistant at 200 to 300 ° C. in the air while maintaining the state where the fiber bundles are adjacent to each other. Further, a secondary carbonization treatment is performed. Although the primary carbonization treatment and the secondary carbonization treatment are performed in an inert atmosphere, preferred examples of the gas to be used include nitrogen, argon, xenon, and nitrogen is preferably used from an economical viewpoint. The maximum temperature in the secondary carbonization treatment is 1,200 to 2,000 ° C, preferably 1,300 to 1,700 ° C. In general, the higher the maximum temperature for carbonization, the higher the tensile modulus of the carbon fiber obtained, but the tensile strength becomes maximum at around 1500 ° C. In addition, as the maximum carbonization temperature increases, the compressive strength decreases. On the other hand, when the maximum temperature is less than 1200 ° C., the moisture content of the carbon fiber increases, and thus there is a problem that the water absorption property of the composite that is a molded product is lowered.

  In the present invention, the fiber bundle after the primary carbonization treatment to be subjected to the secondary carbonization treatment has a total fineness of 4,000 dtex / mm or less, preferably 3,800 dtex / mm or less, more preferably 3,500 dtex / mm or less per width. To do. If the total fineness per width of the fiber bundle to be subjected to the secondary carbonization treatment is too large, the bundle thickness becomes too thick, and it becomes difficult to desorb the cracked gas bundle from the secondary carbonization treatment. Unevenness occurs in the degree of secondary carbonization treatment between fibers, the unevenness of the degree of secondary carbonization treatment causes unevenness of tension between single fibers in the bundle, and fluff and thread breakage may occur . The smaller the value of the total fineness per width of the fiber bundle to be subjected to the secondary carbonization treatment, the thinner the bundle thickness and the easier the decomposition gas is released, but when the bundle thickness becomes too thin, the single fibers are rubbed against a roller or the like. For this reason, wrapping may occur, and the process passability may decrease, so the lower limit is preferably set to about 500 dtex / mm.

  In the secondary carbonization treatment, the tension applied to the fiber bundle is 500 mg / dtex or more, preferably 700 mg / dtex or more, more preferably 900 mg / dtex or more. If the tension is too low, the orientation of the fibers is relaxed in the secondary carbonization treatment, even if a high-tension treatment is performed in the flame-proofing treatment leading to the secondary carbonization treatment, or the primary carbonization treatment. Carbon fiber cannot be obtained. In addition, the higher the tension, the higher the tensile modulus of the carbon fiber obtained, which is preferable, but there is a limit to the tension that can be applied to the treated fiber bundle, and the intrinsic viscosity and yarn-making conditions of the polyacrylonitrile-based polymer, flameproofing conditions, etc. The critical tension varies depending on the primary carbonization conditions. Therefore, the tension applied to the fiber bundle in the secondary carbonization treatment is preferably 90% or less of the critical tension for stable treatment.

When performing the secondary carbonization treatment, the interval between adjacent fiber bundles traveling is preferably 2 mm or more, preferably 4 mm or more. When the interval is less than 2 mm, it is difficult to desorb the cracked gas from the width direction of the bundle, the occurrence of fluff and yarn breakage increases, and high-quality carbon fibers may not be obtained. Since the distance between the bundles is too close, fluff and thread breakage may occur due to contact with the adjacent traveling fiber bundle. Moreover, since the productivity per machine width of a processing apparatus will fall if the space | interval between fiber bundles is too wide, it is preferable that the upper limit shall be about 10 mm.

In the present invention, the fiber bundle to be subjected to the secondary carbonization treatment may have a weight loss rate of 25% or less, preferably 20% or less when heat-treated at 1,000 ° C. for 2 minutes in a nitrogen atmosphere. If the weight loss rate is too large, the decomposition gas generated in the carbonization process increases, that is, the decomposition gas to be desorbed from the bundle increases, so that the desorption is difficult, and processing unevenness, fluff, and yarn breakage occur. It tends to happen. Further, when the weight loss rate is less than 10%, the degree of primary carbonization treatment is too deep, and high tension treatment in the secondary carbonization treatment may not be performed.

  In the present invention, the fiber bundle subjected to the secondary carbonization treatment has a crystal orientation of 78% or more, preferably 80% or more. If the degree of orientation is too small, it is difficult to obtain a carbon fiber having a high tensile elastic modulus, which is an object of the present invention, even if the secondary carbonization treatment is performed under the high tension that is the range of the present invention. Further, in order to increase the degree of orientation, it is possible to treat with higher tension in the flameproofing treatment and the primary carbonization treatment. However, if the tension is too high, yarn breakage occurs, so the upper limit of the degree of orientation is 87%. The degree is preferred.

  The carbon fiber production method of the present invention will be described in further detail in order.

  In the present invention, the polyacrylonitrile fiber bundle is obtained by spinning a polyacrylonitrile polymer. The polyacrylonitrile-based polymer is obtained by polymerizing acrylonitrile preferably at 98 mol% or more, more preferably 99 mol% or more, and a copolymer component preferably at less than 2 mol%, more preferably less than 1 mol%. If the polymerization amount of acrylonitrile is too small, the weight loss rate when heat-treated at 1,000 ° C. for 2 minutes in a nitrogen atmosphere may exceed 25%, and the amount of decomposition gas generated in the secondary carbonization treatment increases. In some cases, the increase in the copolymerization component may improve the plasticity of the molecule, so that orientation relaxation is likely to occur as the fiber, and the tensile modulus of the finally obtained carbon fiber may be reduced.

  As the copolymer component, it is preferable to copolymerize 0.1 mol% or more of a component having a flame resistance promoting action for the purpose of promptly promoting the flame resistance reaction. On the other hand, as the amount of copolymerization of the component having the flameproofing promoting action increases, the rate of heat generation in the flameproofing reaction increases and the risk of runaway reaction may occur, so the copolymerization amount of such component exceeds 1 mol%. It is preferable to set it to a range that does not exist. Examples of the component having flame resistance promoting action include those having at least one carboxyl group or amide group, and specific examples include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid. , Mesaconic acid, acrylamide, methacrylamide and the like. Since the carboxyl group has a higher flame resistance promoting effect than the amide group, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesanconic acid are more preferred.

As a polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and the like can be applied, but a solution polymerization method using an organic solvent capable of uniformly dissolving a polymerization raw material is preferably used, and a specific organic solvent is used. Examples thereof include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc. Among them, dimethyl sulfoxide is most preferable from the viewpoint of solubility.
The intrinsic viscosity of the polyacrylonitrile polymer is preferably 1.3 to 5, and more preferably 1.5 to 4. When the intrinsic viscosity is a low molecular weight of less than 1.3, the spinnability in spinning may be lowered. On the other hand, the higher the intrinsic viscosity, that is, the higher the molecular weight, the stronger the connection between the molecules, and the carbon fiber can be stretched at a high tension, so that a carbon fiber with a high tensile modulus can be obtained. In such a case, the gelation of the polymer becomes remarkable and stable spinning may be difficult.

  A precursor fiber for carbon fiber is obtained by spinning a polyacrylonitrile-based polymer by a wet or dry wet spinning method. In spinning, the polymer such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide or the like is dissolved in a soluble solvent to obtain a spinning dope. In particular, when the solution polymerization method is used, it is preferable that the solvent used for the polymerization is the same as the solvent used for the spinning dope because a step of separating the obtained polymer and re-dissolving in the solvent is unnecessary. The concentration of the polymer in the spinning dope is preferably 10 to 40% by weight from the viewpoint of stock solution stability. In order to obtain a high-strength carbon fiber, it is preferable to pass through a filter having an opening of 1 μm or less before spinning the spinning solution to remove the polymer raw material and impurities mixed in each step.

  The spinning solution is spun from the die by a wet or dry wet spinning method and introduced into a coagulation bath to coagulate the fibers. In order to increase the density of the obtained carbon fiber precursor fiber and to increase the mechanical properties of the obtained carbon fiber, it is more preferable to use a dry and wet spinning method.

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

  After introducing into a coagulation bath and coagulating the yarn, a polyacrylonitrile fiber bundle is obtained through a washing step, an in-bath drawing step, an oil agent application step, a drying heat treatment step, and a steam drawing step as necessary. However, the solidified yarn may be directly stretched in the bath without the water washing step, or may be stretched in the bath after the solvent is removed by the water washing step. Such stretching in the bath is usually preferably performed at a stretching ratio of 1 to 5 times in a single or a plurality of stretching baths whose temperature is adjusted to 30 to 98 ° C. After the stretching process in the bath, it is preferable to apply an oil agent made of silicone or the like to the yarn for the purpose of preventing adhesion between the single fibers. As such silicone, modified silicone is preferably used, and amino-modified silicone having high heat resistance is more preferably used. The drying heat treatment in the drying heat treatment step may be either a contact method or a non-contact method as long as it can be efficiently dried in a short time, and is preferably performed at 120 to 190 ° C. from the standpoint of drying efficiency without bonding single fibers. In the steam drawing step, it is preferable that the single fibers do not adhere to each other and from the viewpoint of stretchability, it is preferably performed at 120 to 190 ° C., and the draw ratio is 3 times or more from the viewpoint of productivity and mechanical properties of the obtained carbon fiber. It is good.

  In the present invention, in the polyacrylonitrile fiber bundle, the fineness of the single fiber constituting it may be 0.3 to 1.3 dtex, preferably 0.5 to 1.0 dtex. If the single fiber fineness is too small, the passability of the yarn-making process and the firing process may be reduced due to a decrease in spinnability and the occurrence of yarn breakage due to contact with rollers and guides, and the single fiber fineness is too large. In addition, the difference between the inner and outer structures of each single fiber after flame resistance increases, and the processability in the subsequent primary carbonization treatment may decrease, and the tensile strength and tensile modulus of the resulting carbon fiber may decrease.

  The polyacrylonitrile fiber bundle preferably has a number of filaments of 10,000 to 100,000. When the number of filaments deviates from the above range, productivity may be lowered, or uniform processing may not be performed in flame resistance, primary carbonization treatment, or secondary carbonization treatment.

  In the present invention, a plurality of polyacrylonitrile fiber bundles are run adjacent to each other, and flameproofing treatment, primary carbonization treatment, and secondary carbonization treatment are performed while maintaining the adjacent state. The higher the tension applied to the fiber bundle during the flameproofing treatment, the so-called flameproofing tension, the higher the degree of orientation as the fiber, and the higher the degree of orientation of the carbon fiber obtained by the subsequent primary carbonization and secondary carbonization treatment. Although it is preferable to improve the tensile elastic modulus, if the limit tension is exceeded, thread breakage occurs, and the quality and processability are deteriorated. Therefore, the flameproof tension is 0.6 × A to 0.9 × A, preferably 0.63 × A to 0.85 × A, with respect to the flameproof limit tension A (mg / dtex) measured by the method described later. It is better to be in the range. If the flameproof tension is too low, the target carbon fiber having a high tensile elastic modulus may not be obtained. On the other hand, if it is too high, the process is passed with a tension close to the stretching limit. The occurrence of thread breakage may increase.

  The flameproofing time can be appropriately selected according to the treatment temperature, but is set so that the specific gravity of the obtained flameproofing fiber is 1.3 to 1.5, preferably 1.32 to 1.47. It is preferable for the purpose of improving the process passability in the subsequent primary carbonization treatment and the mechanical properties of the resulting carbon fiber.

  A flame-resistant fiber bundle obtained by flame-proofing is subjected to primary carbonization under the above-described conditions. The higher the tension during the primary carbonization treatment, the higher the degree of orientation as the fiber, and the higher the degree of orientation of the carbon fiber obtained by the subsequent secondary carbonization treatment, which is preferable for improving the tensile elastic modulus of the carbon fiber. If the limit tension is exceeded, thread breakage will occur, degrading the quality and processability. Then, the tension | tensile_strength provided to a fiber bundle by a primary carbonization process is 0.65 * B-0.9 * B with respect to the primary carbonization draw limit tension B (mg / dtex) measured by the below-mentioned method, Preferably it is 0.67. It is good to carry out in the range of xB to 0.85xB. When the tension is too low, in the fiber bundle after the primary carbonization treatment, it is difficult to make the crystal orientation height within the above-described preferable range, and a carbon fiber bundle having a desired high tensile elastic modulus cannot be obtained. On the contrary, when the tension applied is too high, the process passes with a tension close to the stretching limit, so that the occurrence of fluff and yarn breakage may increase.

  The treatment time for primary carbonization can be appropriately selected according to the treatment temperature, but the specific gravity of the obtained fiber bundle after the primary carbonization treatment is 1.5 to 1.7, preferably 1.52 to 1.7. More preferably, it is important to set it as 1.55-1.7. When the specific gravity of the primary carbonized fiber is too small, the primary carbonization treatment is not sufficient, so that the weight loss rate when heat-treated at 1,000 ° C. for 1 minute in a nitrogen atmosphere is 20% or less, which is a preferred embodiment of the present invention. It is difficult to obtain a fiber bundle, and the amount of cracked gas generated in the subsequent secondary carbonization treatment increases, that is, the amount of cracked gas to be desorbed from the bundle increases. Thread breakage is likely to occur.

  In the present invention, the carbon fiber is manufactured by subjecting the fiber bundle after the primary carbonization treatment thus obtained to the secondary carbonization treatment under the conditions described above.

  In the present invention, it is necessary to control the total fineness per width of the fiber bundle to be provided in the above-described range when performing the secondary carbonization treatment in order to obtain a high-quality carbon fiber. The control means is not particularly limited as long as it is a method of reducing the thickness of the bundle and expanding the width of the bundle without damaging the fibers. For example, a method of sequentially contacting a plurality of rollers provided in multiple stages along the traveling direction of the fiber bundle traveling while applying a desired tension can be mentioned. In this method, the desired fineness per width can be controlled by appropriately changing the contact angle with a plurality of rollers. Further, in JP 2004-225183 A, when sequentially contacting a plurality of rollers provided in multiple stages along the traveling direction of a fiber bundle that travels in a state where a desired tension is applied, Means using a lateral vibration roller that vibrates and a vertical vibration roller that vibrates in the vertical direction of the traveling direction have been proposed, and such means can also be suitably used in the present invention. In addition, Japanese Patent No. 25555689 discloses that a curved surface body is brought into contact with a curved surface body having a convex surface on the fiber bundle side in a plane intersecting the traveling direction of the fiber bundle traveling in a state in which a desired tension is applied. Means to vibrate are proposed, and such means can also be suitably used in the present invention.

  The treatment time for the secondary carbonization treatment can be appropriately selected according to the treatment temperature, but the specific gravity of the obtained carbon fiber bundle is preferably 1.76 to 1.87, more preferably 1.79 to 1.86. Set to be. When the specific gravity is too small, the secondary carbonization treatment is insufficient, so that the target tensile elastic modulus may not be expressed in the obtained carbon fiber bundle. Conversely, when the specific gravity is too large, brittleness is remarkable. Therefore, it becomes weak against abrasion, and the quality and process passability may be lowered.

  The obtained carbon fiber bundle can be subjected to electrolytic treatment for surface modification. As an electrolytic solution used for the electrolytic treatment, an acidic solution such as sulfuric acid, nitric acid, hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate, ammonium bicarbonate or a salt thereof is used as an aqueous solution. be able to. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied. Such electrolytic treatment can optimize the adhesion between the carbon fiber and the matrix in the resulting composite material, causing a brittle breakage of the composite material due to excessive adhesion, a problem in which the tensile strength in the fiber direction decreases, the fiber direction Although the tensile strength at is high, the problem of poor adhesion to the resin and lack of strength properties in the non-fiber direction has been resolved, and the resulting composite material has a balanced strength in both the fiber and non-fiber directions. Characteristic comes to be expressed.

  Thus, according to the present invention, a carbon fiber bundle having a tensile elastic modulus of 330 GPa or more and a crystal orientation of 83 to 90% can be suitably obtained. Carbon fiber bundles having a tensile modulus that is too low are unsuitable for use in aerospace applications where high tensile modulus is required.

Next, the present invention will be described more specifically with reference to examples. In addition, the measuring method of the various characteristics used by this invention is described collectively below. The experimental conditions used in each example and comparative example and the measurement results obtained are summarized in Tables 1 and 2.
<Total fineness per width of fiber bundle>
First, the width of the fiber bundle is measured using an image sensor. The image sensor is installed above and below the traveling fiber bundle immediately before the side where the secondary carbonization treatment apparatus enters. The measurement starts reading the image sensor after the tension is stabilized. Reading was performed at intervals of 2 seconds for 1 minute, and the average value at the time of reading was used. In this example, Keyence Co., Ltd. (sensor head VG-035, controller VG-300) was used as the image sensor.

Then, the total fineness of the fiber bundle, which is the weight per unit length of the fiber bundle (g / 10000 m = dtex), is divided by the width of the fiber bundle obtained by the above method to obtain the total fineness per width.
<Each treatment tension>
Flame resistance tension, primary carbonization treatment tension, and secondary carbonization treatment tension are measured on the outlet side of each processing apparatus. The measured tension (mg) per treated fiber bundle is divided by the total fineness (dtex) of the treated fiber bundle to obtain the treated tension (mg / dtex).
<Weight loss rate of fiber>
The fiber used for measurement is freeze-ground in liquid nitrogen, and then passed through a sieve having an opening of 0.5 mm to obtain a powder. 5 mg of this powder is accurately weighed and placed in a platinum bread container. This is measured under the following conditions using a differential heat / thermogravimetric simultaneous measurement device (hereinafter referred to as TG-DTA device). First, the measurement part of the TG-DTA apparatus is replaced with a nitrogen atmosphere, the temperature is increased to 100 ° C. at a temperature increase rate of 50 ° C./min, held at 100 ° C. for 5 minutes, and then the temperature increase rate is 500 ° C./min. The temperature is raised to 1,000 ° C. and maintained at 1,000 ° C. for 2 minutes. Then, from the weight after being held at 100 ° C. for 5 minutes, the weight loss rate after being held at 1,000 ° C. for 2 minutes is read and used as the weight loss rate. In this example, Bruker TG-DTA2000SA was used as the TG-DTA apparatus.
<Fiber specific gravity>
The method described in JIS R7601 (1986) is followed. In the case of a flame resistant fiber, ethanol is used, and in the case of a fiber after carbonization or carbon fiber, orthodichlorobenzene is used as a reagent. 1.0 to 1.5 g of fiber was collected and dried at 120 ° C. for 2 hours. After measuring the absolute dry mass W1 (g), the reagent having a known specific gravity (specific gravity ρ) was impregnated, and the fiber mass W2 (g) in the reagent was measured. The following formula, fiber specific gravity = (W1 × ρ) / The fiber specific gravity is obtained from (W1-W2). In this example, special grades manufactured by Wako Pure Chemical Industries, Ltd. were used for ethanol and orthodichlorobenzene.
<Crystal orientation>
Using the measurement sample produced as follows, the X-ray diffraction method is obtained from the 002 diffraction line obtained under the following conditions by the following derivation method. In this example, measurement was performed by a transmission method using a 4036A type (tube) manufactured by Rigaku Corporation as an X-ray diffraction apparatus.
A. Preparation of measurement sample A test piece having a length of 4 cm is cut out from the carbon fiber to be measured, and is solidified using a mold and a collodion / alcohol solution to obtain a prismatic shape as a measurement sample.
B. X-ray diffraction measurement conditions X-ray source: CuKα (using Ni filter)
Output: 40 kV, 20 mA
C. Derivation of the degree of crystal orientation from the 002 diffraction line It is calculated from the half width of the intensity distribution obtained by scanning the peak of the (002) plane observed in the vicinity of 2θ = 26 ° using the following equation.
Crystal orientation degree = (180−H) / 180 × 100 (%)
Here, H is an apparent half width (deg) <tensile modulus and tensile strength>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The resin impregnated strand of carbon fiber to be measured was 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 weights). Part) is impregnated with carbon fiber or graphitized fiber and cured at 130 ° C. for 30 minutes. The number of strands to be measured is six, and the average value of each measurement result is the tensile modulus and tensile strength. In this example, “Bakelite (registered trademark)” ERL4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate.
<Intrinsic viscosity of polyacrylonitrile-based polymer>
150 mg of a polyacrylonitrile polymer dried by heat treatment at 120 ° C. for 2 hours is maintained at 25 ° C. and dissolved in 50 ml of dimethylformamide added with 0.1 mol / liter of sodium thiocyanate. The obtained solution was temperature-controlled in a hot water bath at 25 ° C., and the drop time between the marked lines was measured with an accuracy of 1/100 second using an Ostwald viscometer that was temperature-controlled at 25 ° C. in advance. Let time be t (seconds). Similarly, dimethylformamide added with 0.1 mol / liter of sodium thiocyanate in which the polyacrylonitrile-based polymer is not dissolved is also measured, and the dropping time is defined as t0 (seconds). The intrinsic viscosity [η] is calculated using the following formula.
[Η] = {(1 + 1.32 × ηsp) ^ (1/2) −1} /0.198
However,
ηsp = (t / t0) −1
<Measurement of limit tension>
For the flameproof limit tension, primary carbonization limit tension, and secondary carbonization limit tension, the speed at which the fiber bundles are drawn from the processing equipment is fixed at the processing temperature desired by each processing equipment, and the speed at which the fiber bundle is supplied to the processing equipment is changed. Measure the tension that develops when it reaches, and use the maximum tension as the limit tension of the fiber bundle.
<Fuzz number measurement>
The number of fluff generation in the secondary carbonization treatment is measured at the secondary carbonization equipment delivery side. Single fiber breaks of 5 mm or more protruding above and below the running carbon fiber bundle are counted as fluff. The measurement is performed over 100 m, and the number of fluffs is divided by 100 m to obtain the number of fluffs (pieces / m).
[Example 1]
A copolymer obtained by copolymerizing 99.5 mol% of acrylonitrile and 0.5 mol% of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent, and a spinning stock solution having a concentration of 22 wt% and an intrinsic viscosity of 2 was obtained. Obtained. After the polymerization, ammonia gas was blown to pH 8.5 to neutralize itaconic acid, and the hydrophilicity of the spinning dope was improved by introducing ammonium groups into the polymer component. The obtained spinning dope is set to 40 ° C., once discharged into the air using a spinneret having a single hole diameter of 0.15 mm and a hole number of 4,000, and after passing through a space of a distance of about 4 mm, 3 ° C. The solution was coagulated by dry and wet spinning introduced into a coagulation bath consisting of a 35% by weight dimethyl sulfoxide aqueous solution controlled in the above. The coagulated yarn was washed with water by a conventional method, and then stretched 3.25 times in warm water, and further an amino-modified silicone-based silicone oil was added to obtain a stretched yarn in the bath. The drawn yarn in the bath is subjected to a drying heat treatment using a roller heated to 170 ° C., and then drawn four times in a pressurized steam at 150 ° C., the total draw ratio is 13 times, and the single fiber fineness is 0.7 dtex. An acrylonitrile fiber bundle having a filament number of 4,000 was obtained.

  Six obtained acrylonitrile fiber bundles were combined to obtain a filament number of 24,000, and subjected to a flame resistance treatment in air at 230 to 260 ° C. under a tension of 230 mg / dtex. A fiber bundle was obtained. Here, the flameproof limit tension was 320 mg / dtex.

  The obtained flame-resistant fiber bundle was subsequently subjected to primary carbonization treatment for 6 minutes under a tension of 220 mg / dtex in a nitrogen atmosphere having a maximum temperature of 700 ° C. with a rate of temperature increase at 300 to 700 ° C. being 100 ° C./min. A fiber bundle having a specific gravity of 1.6 was obtained. Here, the primary carbonization treatment limit tension was 300 mg / dtex. The obtained fiber bundle after the primary carbonization treatment had a weight loss rate of 18% and a crystal orientation degree of 80.5% when it was heat-treated at 1,000 ° C. for 2 minutes in a nitrogen atmosphere.

  When the fiber bundle after the primary carbonization treatment thus obtained is subjected to the secondary carbonization treatment, the total fineness per width is controlled to 3,000 dtex / mm using a multi-stage roller, and the fiber bundle traveling adjacently A secondary carbonization treatment was performed with an interval of 3 mm. The secondary carbonization treatment was performed in a nitrogen atmosphere having a maximum temperature of 1500 ° C. at a temperature of 800 to 1500 ° C. under a tension of 1,200 mg / dtex to obtain a carbon fiber bundle having a specific gravity of 1.81. At this time, the number of fluffs in the secondary carbonization treatment was 6 / m.

The obtained carbon fiber is subjected to a surface treatment that gives an electric charge of 40 coulomb / g by an anodic charge treatment in an aqueous sulfuric acid solution, washed with water, applied with a sizing agent, and dried to obtain a surface-treated carbon fiber bundle. Got. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Examples 2 and 3]
A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the total fineness per width of the fiber bundle after the primary carbonization treatment used in the secondary carbonization treatment was changed as shown in Table 1. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Examples 4 and 5]
Surface treated carbon in the same manner as in Example 1 except that the tension in the secondary carbonization treatment and the total fineness per width of the primary carbonized fiber bundle used in the secondary carbonization treatment were changed as shown in Table 1, respectively. A fiber bundle was obtained. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Examples 6 and 7]
A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the treatment time of the primary carbonization treatment was changed to 4 minutes and 2 minutes, respectively. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Examples 8 and 9]
A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the tension in the flameproofing treatment and the tension in the primary carbonization treatment were changed as shown in Table 1. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Examples 10 and 11]
The single fiber fineness of the polyacrylonitrile fiber bundle and the number of filaments used for flame resistance were changed as shown in Table 1, and the total fineness per width of the fiber bundle after the primary carbonization treatment used for the secondary carbonization treatment is shown. A carbon fiber bundle subjected to surface treatment was obtained in the same manner as in Example 1 except that the change was made as shown in FIG. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Example 12]
When the fiber bundle after the primary carbonization treatment was subjected to the secondary carbonization treatment, a surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the interval between adjacent fiber bundles was changed to 1 mm. . The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Comparative Example 1]
A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the total fineness per width of the fiber bundle after the primary carbonization treatment used for the secondary carbonization treatment was changed as shown in Table 1. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2. The number of fluff in the secondary carbonization treatment was large, and the processability was also reduced.
[Comparative Examples 2 and 3]
The single fiber fineness and the number of filaments of the polyacrylonitrile fiber bundle were changed as shown in Table 1, and the total fineness per width of the fiber bundle after the primary carbonization treatment used for the secondary carbonization treatment was changed as shown in Table 1. A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are summarized in Table 2.
[Comparative Example 4]
A surface-treated carbon fiber bundle was obtained in the same manner as in Example 1 except that the tension in the secondary carbonization treatment was changed as shown in Table 1. The surface-treated carbon fiber bundle thus obtained was measured for tensile modulus and tensile strength. The properties of each fiber bundle are shown in Table 2.

  The carbon fiber bundle obtained by the present invention can be suitably used as a large member for aerospace applications and industrial material applications because of its high tensile elastic modulus and good quality. Moreover, it can be used suitably also as sports members, such as a fishing rod and a golf shaft.

Claims (5)

A plurality of polyacrylonitrile fiber bundles that run adjacent to each other are made flame resistant at 200 to 300 ° C. in the air, and subsequently subjected to primary carbonization treatment at 300 to 800 ° C. in an inert atmosphere, and further an inert atmosphere. Medium, a method for producing a carbon fiber bundle subjected to secondary carbonization treatment at a maximum treatment temperature of 1,200 to 2,000 ° C., and the fiber bundle subjected to the secondary carbonization treatment has a total fineness of 4,000 dtex / mm or less per width. A method for producing a carbon fiber bundle, wherein a tension of 500 mg / dtex or more is applied to the fiber bundle during the secondary carbonization treatment. The method for producing a carbon fiber bundle according to claim 1, wherein the interval between adjacently running fiber bundles is 2 mm or more when performing the secondary carbonization treatment. The method for producing carbon fiber according to claim 1 or 2, wherein the fiber bundle subjected to the secondary carbonization treatment has a weight loss rate of 25% or less when heat-treated at 1,000 ° C for 2 minutes in a nitrogen atmosphere. The method for producing a carbon fiber bundle according to any one of claims 1 to 3, wherein the fiber bundle subjected to the secondary carbonization treatment has a degree of crystal orientation of 78% or more. A carbon fiber bundle produced by the method according to any one of claims 1 to 4, having a tensile elastic modulus of 330 GPa or more and a crystal orientation of 83 to 90%.