JP2011213773A - Polyacrylonitrile-based polymer and carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer which ensures high polymerization stability and drawability after yarn-making without spoiling productivity and processability and a method for producing the same.SOLUTION: The method for producing the polymer comprises polymerizing an acrylonitrile-based polymer by heat treating a solution comprising acrylonitrile, a radical polymerization initiator, a polymerization inhibitor, a component copolymerizable with acrylonitrile and a solvent, wherein a weight ratio (B/A) between the radical polymerization initiator (A) and the polymerization inhibitor (B) satisfies 2≤(B/A)<210 and the polymerization inhibitor is used in an amount of 10-140 ppm relative to the total amount of the solution.

Description

  The present invention relates to a polymer excellent in polymerization stability and stretchability after spinning, and further to a polymer capable of obtaining high firing stretchability and a method for producing the same.

  Carbon fiber is increasingly used as a reinforced fiber for composite materials due to increasing environmental problems, and its importance has been increasing. In addition, there is a strong demand for higher performance. Conventionally, there has been a demand for improving single properties such as tensile properties, and various properties of carbon fibers have been improved in response to such requests. However, in recent years, it has been required to satisfy a plurality of characteristics simultaneously and at a high level. In particular, in carbon fibers applied to parts subjected to stress from various directions, such as aircraft structural members, simultaneously improving the tensile modulus and compressive strength is important for achieving further weight reduction. It has become a challenge.

  The most widely used polyacrylonitrile-based carbon fiber is a flame-proofing process in which a polyacrylonitrile-based precursor fiber bundle is converted to a flame-resistant fiber in an oxidizing atmosphere of 200 to 300 ° C., under an inert atmosphere of 300 to 3000 ° C. It is manufactured industrially through a carbonization step that is carbonized in the process. At this time, it is generally known that the tensile elastic modulus of carbon fibers can be increased as the maximum temperature in the carbonization process is increased. However, by increasing the maximum temperature of the carbonization step, the compressive strength of the resulting carbon fiber decreases with the growth of the graphite crystals. That is, as long as the carbonization temperature is adjusted using the same polyacrylonitrile-based precursor fiber bundle, the tensile elastic modulus and the compressive strength of the carbon fiber are in a trade-off relationship. Therefore, in applications that require compressive strength, a technique for increasing the tensile modulus other than the control of the carbonization temperature is required.

  In order to improve the tensile modulus of carbon fiber, it is known that it is effective to increase the degree of orientation of the obtained carbon fiber by stretching the fiber during firing. However, simply increasing the draw ratio inevitably leads to the occurrence of fluff and yarn breakage, and the operability and the quality of the resulting carbon fibers are unavoidable. Therefore, some proposals have been made so far.

  As a technique for stably performing stretching in carbonization that has been proposed so far, a technique for increasing the molecular weight of a polyacrylonitrile-based polymer to be used has been proposed. When polymerizing a polyacrylonitrile-based polymer, a technique for increasing the molecular weight by reducing the concentration of the polymerization initiator and decreasing the polymerization start point is disclosed in order to improve the molecular weight (Patent Document 1). Moreover, although it is not necessarily limited to a high molecular weight, it is said that the polymer may contain the polymerization inhibitor in this technique (patent document 2). Here, the meaning of the polymerization inhibitor in Patent Document 2 is as follows. In general, a polymerization inhibitor is added to radically polymerizable monomers such as acrylonitrile in order to ensure stability during storage. When radically polymerizing acrylonitrile or the like, usually, the monomer and the polymerization inhibitor are not separated by distillation or the like, and the polymerization is generally carried out in a system containing a polymerization inhibitor. Moreover, in order to prevent post-polymerization of the polymer after radical polymerization, it is common to add a polymerization inhibitor to the polymer after polymerization (for example, Patent Document 3). In such a case, the residual amount of the polymerization inhibitor is not clear, but even if a polymer containing the polymerization inhibitor is used for the carbon fiber, it disappears in the firing step and has no influence on the physical properties of the carbon fiber. .

  However, in the acrylic fiber bundles obtained by the techniques of Patent Document 1 and Patent Document 2, the molecular weight distribution may fluctuate unless the conditions during polymerization are strictly controlled. In some cases, the problem of fluctuations in the post-stretchability in the case may occur.

  As a technique for suppressing fluctuations in the molecular weight distribution, a technique for controlling the molecular weight distribution by controlling the radical concentration by intermittently adding a polymerization initiator that generates radicals has been proposed (Patent Document). 4).

International Publication No. 2007/069511 JP 2009-256816 A JP-A-1-168750 JP-A-11-172217

  However, since the technique of Patent Document 4 controls the radical concentration to introduce the polymerization initiator in several times, not only the process becomes complicated, but also the polymerization inhibitor in the monomer, It is necessary to control the amount of the polymerization initiator so as to cancel out the radical trap source whose amount fluctuates, such as the oxygen concentration, and the application to the techniques of Patent Documents 1 and 3 can be applied to the molecular weight or the The effective radical concentration in the polymerization system must be measured to control the amount of the polymerization initiator, which is substantially impossible. Therefore, the technique of controlling the amount of the polymerization initiator with respect to the radical trap source whose amount varies cannot be a technique for controlling the molecular weight at the initial stage of polymerization. The object of the present invention is to impair productivity and processability. It is an object of the present invention to provide a polyacrylonitrile-based polymer that can obtain high polymerization stability and post-filament stretchability, and furthermore, fired stretchability.

The present inventors have found that the dispersion of molecular weight can be reduced without impairing the process by imparting an excessive radical trapping capability from the radical trapping source such as oxygen or a polymerization inhibitor in the monomer, and the polymer produced thereby. It has been found that the acrylonitrile-based polymer can be post-stretched very stably in the yarn production process, and extremely high fired stretchability can be obtained in the subsequent carbonization process. The method for producing a polyacrylonitrile polymer for carbon fiber of the present invention for achieving the above object comprises a copolymerization component of acrylonitrile, a radical polymerization initiator, a polymerization inhibitor, acrylonitrile, and a solvent, and a radical polymerization initiator ( The weight ratio (B / A) between A) and the polymerization inhibitor (B) satisfies the formula (1),
2 ≦ (B / A) <210 Formula (1)
And a polymerization inhibitor is 8 ppm-140 ppm with respect to the total amount of solution, and the solution whose dissolved oxygen concentration is 1-10 ppm is heat-processed.
The polymerization inhibitor used in the present invention preferably contains at least one polycyclic aromatic structure or monocyclic aromatic structure. Specifically, hydroquinone, methylhydroquinone, hydroquinone monomethyl ether, 4- Contains one or more selected from methoxy-1-naphthol, p-hydroxydiphenylamine, N, N-diphenyldiamine, 2-tertiarybutylhydroquinone, 2,5-ditertiarybutylhydroquinone, t-butylcatechol, and nitronaphthol More preferably. The polyacrylonitrile polymer of the present invention has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) method of 500 to 700,000 and an intrinsic viscosity of 2.0 to 3.0. It is preferable that

  By applying the method for producing a polyacrylonitrile-based polymer of the present invention, a polymer having a stable molecular weight can be polymerized even in a polymerization system having few polymerization initiators that generate radicals. Although the polyacrylonitrile-based polymer is a high-molecular weight polyacrylonitrile-based polymer, stable post-drawability can be achieved in the post-yarn drawing step, so that in the post-yarn drawing step between polymerization batches. It is possible to obtain a polyacrylonitrile-based carbon fiber precursor fiber having almost no difference in post-stretchability and stable and good quality, and as a result, stably producing carbon fiber having excellent firing stretchability and excellent quality. Can do.

  The present inventors control the number of effective radicals generated at the initial stage of polymerization, and stabilize the molecular weight of the polymer to be produced, so that a polyacrylonitrile-based polymer having a stabilized molecular weight distribution at the end of polymerization can be obtained. It was found that the polyacrylonitrile-based polymer obtained by such a production method stably exhibits post-stretchability in the post-yarn-stretching step, and exhibits high stretchability in firing. Reached.

Hereinafter, the production method of the polyacrylonitrile polymer and the production method of the carbon fiber of the present invention will be described in detail.
The polyacrylonitrile-based polymer for carbon fiber of the present invention includes a copolymerization component of acrylonitrile, a radical polymerization initiator, a polymerization inhibitor, and acrylonitrile and a solvent, and includes a radical polymerization initiator (A) and a polymerization inhibitor (B). Weight ratio (B / A) satisfies formula (1) 2 ≦ (B / A) <210 formula (1)
And the polyacrylonitrile polymer which heat-processes the solution (it may be described as the polymerization undiluted solution in this invention) whose polymerization inhibitor is 8 ppm-140 ppm with respect to the total solution amount, and whose dissolved oxygen concentration is 1-10 ppm. There is a manufacturing method.

  The mechanism for obtaining a polyacrylonitrile-based polymer that can be stably stretched in the post-yarn-stretching step by polymerizing under conditions such as the specific polymerization inhibitor amount is not necessarily clear, but is considered as follows. ing. In the case where the amount of the polymerization inhibitor is less than a specific range, the polymerization initiator contained in the monomer and the amount of radical trapping action such as residual oxygen in the polymerization system varies from one polymerization batch to another, so that the polymerization initiator at the initial stage of polymerization In a system with a small amount, the generated radicals are offset, and the number of radicals that work effectively during the induction period, during which the polymer in the initial stage of polymerization is likely to vary, greatly varies the molecular weight of the polymer generated in the initial stage of polymerization. As described above, the molecular weight distribution at the end of the polymerization varies, and the post-drawing property is considered to be unstable in the post-yarn drawing drawing step. The molecular weight factor that fluctuates the post-drawing property in the post-yarn drawing step is that the number of radicals that work effectively as a result of radicals being trapped in the initial stage of polymerization is extremely reduced, and the polymerization starting point is reduced. It is considered that this further polymerized component inhibits stretching in the subsequent spinning process, thereby reducing post-stretchability. For this reason, the polymer of the present invention has an extremely large radical trapping ability compared to the radical inhibitory ability of the polymerization inhibitor contained in the monomer and the residual oxygen in the polymerization system by setting the amount of the polymerization inhibitor within a specific range. By adding, the number of radicals that work effectively in the initial stage of polymerization does not vary even if the amount of residual oxygen in the polymerization inhibitor or polymerization system contained in the monomer varies. As a result, the molecular weight distribution at the end of the polymerization is stabilized, and even if the polymerization batch changes, the molecular weight distribution becomes almost the same, and there is almost no difference between the polymerization batches in the subsequent spinning process, so stable post-drawability I think that expresses.

  Here, the definitions of the initial stage of polymerization and the induction period are as follows. The temperature at which radicals are generated varies depending on the type of radical polymerization initiator, but when a solution used for polymerization is heated and a specific temperature is reached, all radicals are not generated, but at a certain rate at each temperature of the superheating process. Radicals are generated, and there is a region where the radical concentration increases in the overheating process, and this is the induction period. In addition, the time at which radicals at the beginning of the induction period begin to occur is defined as the initial stage of polymerization.

  Here, polymerization means that monomers are connected starting from the generated radicals, and in a specific monomer amount, the smaller the number of radicals that are the starting point, the more monomers connected per one starting point. A polymer can be obtained. Therefore, a high molecular weight polymer is formed at the initial stage of polymerization.

The acrylonitrile used in the present invention is preferably one containing a polymerization inhibitor so that polymerization in a single storage state does not proceed, and more preferably stored in an inert gas.
The polymerization inhibitor used in the present invention preferably has a polycyclic aromatic structure or a monocyclic aromatic structure, preferably hydroquinone, methylhydroquinone, hydroquinone monomethyl ether, 4-methoxy-1-naphthol, p-hydroxydiphenylamine, N, More preferably, it contains one or more selected from N-diphenyldiamine, 2,5-ditertiarybutylhydroquinone, and nitronaphthol.

  Moreover, in this invention, it is essential that the sum with the polymerization inhibitor contained in acrylonitrile is 8 ppm-140 ppm with respect to the total solution weight. When the amount of the polymerization inhibitor is less than 8 ppm, sufficient polymerization stability cannot be obtained, and when it exceeds 140 ppm, the cost is increased due to the amount of the polymerization initiator and the polymerization inhibitor used, and the polymerization initiator is not balanced. This is because there is a problem that the degree of polymerization of the high molecular weight component in the obtained polymer is not sufficiently high. The amount and type of the polymerization inhibitor contained in acrylonitrile used in the present invention is not particularly limited, but it is preferably contained in an acrylonitrile weight ratio of 20 ppm to 40 ppm from the viewpoint of stability of acrylonitrile alone. The amount of the polymerization inhibitor contained in acrylonitrile is measured by the absorbance of acrylonitrile. The method for adjusting the amount of the polymerization inhibitor in the present invention is to measure the amount of the polymerization inhibitor contained in acrylonitrile, precisely weigh the added amount of the polymerization inhibitor so that it becomes 8 ppm to 140 ppm with respect to the total weight of the solution, A solution having a polymerization inhibitor of 8 ppm to 140 ppm with respect to the total weight of the solution is prepared by dissolving the inhibitor in a solvent and then mixing with acrylonitrile.

  The radical polymerization initiator used in the present invention is not particularly limited, but is preferably an oil-soluble azo compound, a water-soluble azo compound, a peroxide, etc., from the viewpoint of easy handling from a safety aspect and industrially efficient polymerization. Those having a radical generation temperature in the range of 30 to 150 ° C. are preferably used. Among them, an azo compound that does not have a concern of oxygen generation that inhibits polymerization at the time of decomposition is preferably used.

  The method for producing the polyacrylonitrile-based polymer of the present invention is a heat treatment in the air in the space-time in which the carbon fiber precursor fiber bundle obtained by spinning the polymer obtained by the present invention is flame-resistant. From the viewpoint of efficiently performing the process, it is essential that the copolymerization component is contained in the polymerization stock solution in the present invention. In general, from the standpoint of yarn-making property, if the amount of the copolymer component is small (as an extreme example, polyacrylonitrile alone) is not preferable because the plasticity is lowered and the yarn-drawing property is lowered. When the amount of the copolymer is large, the heat resistance is lowered, and fusion is likely to occur. A preferable amount of the copolymer component is 0.1 to 0.5 mol%. Further, from the viewpoint of efficiently performing heat treatment in air at the time of flame resistance, it is preferable to copolymerize at least 0.1 mol% or more of the flame resistance promoting component as a copolymer component. Preferred examples of the flame resistance promoting component include those having at least one carboxyl group or amide group. As the amount of copolymerization of the flameproofing promoting component is increased, the flameproofing reaction is promoted, flameproofing treatment can be performed in a short time, and this is a preferred embodiment for the purpose of increasing productivity. However, on the other hand, the greater the amount of copolymerization of the flameproofing promoting component, the lower the heat resistance, or the higher the heat generation rate and the risk of a runaway reaction, so that it does not exceed 0.5 mol%. It is preferable. Specific examples of the flame resistance promoting component which is a copolymer component are preferably exemplified by acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide. The For the purpose of preventing a decrease in heat resistance, it is preferable to use a small amount of a monomer having a high flame resistance promoting effect, and it is preferable to use a flame resistance promoting component having a carboxyl group rather than an amide group. Further, the number of amide groups and carboxyl groups contained is more preferably two or more than one, and from that viewpoint, as the flame resistance promoting component which is a copolymer component, acrylic acid, methacrylic acid are used. Itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid are preferred, itaconic acid, maleic acid and mesaconic acid are more preferred, and itaconic acid is most preferred. For the purpose of improving the spinning property of the polymer obtained by the present invention, a copolymer component other than the flame resistance promoting component such as acrylate or methacrylate may be copolymerized, but carbon obtained by spinning the polymer is used. For the purpose of preventing a decrease in heat resistance during the flameproofing process of the fiber precursor fiber bundle, it is preferable that the total amount of copolymer components other than acrylonitrile does not exceed 0.5 mol%.

  As a polymerization method for producing the polyacrylonitrile-based polymer used in the present invention, it is essential to use solution polymerization for the purpose of uniformly polymerizing the copolymer component. As the solution used in the solution polymerization, it is preferable to use a solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide. Among these, dimethyl sulfoxide is more preferably used from the viewpoint of solubility of the produced polyacrylonitrile-based polymer.

  Further, it is essential that the solution before heating used for obtaining the polyacrylonitrile-based polymer of the present invention has a dissolved oxygen concentration of 1 to 10 ppm. If the amount of oxygen contained in the solution is 10 ppm or more, the number of effective radicals cannot be controlled even in a polymerization system to which the polymerization inhibitor of the present invention is applied, and the molecular weight varies. As for the lower limit, it is industrially impossible to make the dissolved oxygen concentration contained in the solution 1 ppm or less. Therefore, the lower limit is set to the value shown on the left. It is set. By continuously supplying an inert gas substantially free of oxygen to the solution before heating and stirring in an atmosphere sealed with the inert gas, the oxygen in the solution can be adjusted to 1 to 10 ppm. The inert gas used is preferably nitrogen in terms of cost. The polyacrylonitrile-based polymer of the present invention can be obtained by heat-treating the solution. In the present invention, the polyacrylonitrile-based polymer means that at least acrylonitrile is the main constituent of the polymer skeleton, and the main constituent usually occupies 95 to 100 mol% of the polymer skeleton. Say.

  The polyacrylonitrile polymer obtained by the production method of the present invention has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) method of 500 to 700,000 and an intrinsic viscosity of 2.0 to 3. 0 is preferred. If the weight average molecular weight is 500,000 or less, the stretchability in firing is low, which is not preferable. A weight average molecular weight of 700,000 or more is not preferable because the viscosity is high when the polymer is dispersed in a solvent, and it is necessary to lower the concentration of the polymer for spinning, which increases production costs. The weight average molecular weight Mw can be controlled by a polymerization initiator that generates radicals, a monomer concentration, a chain transfer agent, and a polymerization time. Although it is possible to increase the weight average molecular weight Mw by reducing the amount of the polymerization initiator, it should be noted that if the polymerization initiator is decreased, the polymerization rate decreases when the same polymerization time is used.

  Hereinafter, a method for producing a polyacrylonitrile-based precursor fiber for carbon fiber obtained using the polyacrylonitrile-based polymer obtained by the production method of the present invention will be described in detail.

  The spinning dope used in the method for producing a polyacrylonitrile-based precursor fiber for carbon fiber is obtained by dissolving the polyacrylonitrile-based polymer of the present invention in a solvent in which polyacrylonitrile such as dimethylsulfoxide, dimethylformamide, and dimethylacetamide is soluble. Is. In the case of using solution polymerization, it is preferable that the solvent used for the polymerization and the spinning solvent are the same because the step of separating the obtained polyacrylonitrile-based polymer and re-dissolving in the spinning solvent becomes unnecessary. The polyacrylonitrile polymer used in the present invention is preferably a spinning dope having a concentration of 10 to less than 20% by weight. If the concentration of the spinning dope is less than 10% by weight, the yield of the polyacrylonitrile-based precursor fiber for carbon fiber production with respect to the spinning dope is poor and productivity is unfavorable. On the other hand, if the concentration of the spinning dope exceeds 20% by weight, the viscosity of the spinning dope becomes high, and the discharge pressure from the die becomes high in the spinning process, which is not preferable in terms of processability. Moreover, this density | concentration can be adjusted with the ratio of the solvent with respect to a polyacrylonitrile-type polymer.

  Such a method for producing a polyacrylonitrile-based precursor fiber for carbon fiber includes a spinning process in which the spinning solution is spun by spinning from a spinneret by a wet spinning method or a dry-wet spinning method, and the fiber obtained in the spinning step is bathed in a water bath. A water washing step for washing in, a water bath drawing step for drawing the fiber obtained in the water washing step in a water bath, a drying heat treatment step for drying and heat treating the fiber obtained in the water bath drawing step, and the drying heat treatment step. A production method comprising a steam stretching step of steam stretching the obtained fiber is preferably applied.

  In the spinning step in the method for producing the polyacrylonitrile-based precursor fiber for carbon fiber, in order to obtain high-strength carbon fiber, the polyacrylonitrile-based polymer raw material is passed through a filter having an opening of 1 μm or less before spinning the spinning raw solution. It is preferable to remove impurities mixed in each step. The spinning solution is spun from the die by a wet spinning method or a dry-wet spinning method, and introduced into a coagulation bath to coagulate the fibers. In order to increase the denseness of the obtained polyacrylonitrile-based precursor fiber for carbon fiber and to increase the mechanical properties of the obtained carbon fiber, it is preferable to use a dry and wet spinning method.

  In the method for producing a polyacrylonitrile-based precursor fiber for carbon fiber, the coagulation bath may contain a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning dope and a so-called coagulation promoting component. preferable. As the coagulation accelerating component, a component that does not dissolve the polyacrylonitrile-based polymer and is compatible with the solvent used for the spinning dope can be used. Specifically, it is preferable to use water as a coagulation promoting component. A polyacrylonitrile-based precursor fiber for carbon fiber production can be obtained through a washing step, a water bath drawing step, a drying heat treatment step, and a steam drawing step after a spinning step in which fiber yarns spun into a coagulation bath are introduced and solidified. .

  Such a method for producing a polyacrylonitrile-based precursor fiber for carbon fiber has a water bath stretching step of stretching the fiber obtained in the water washing step in a water bath after removing the solvent by the water washing step. Here, the water bath stretching step is a step of stretching the yarn after the water washing step at least 1.3 times in a water bath, and after pre-stretching in a water bath at 60 to 80 ° C., the maximum temperature 60 to 98. It is preferable to stretch in a water bath at ° C. Moreover, it is preferable to wash with water using the water bath which consists of several steps whose water bath temperature in a water-washing process is 10 thru | or 60 degreeC. Moreover, it is preferable that the draw ratio in extending | stretching in a water bath is 1.3-5 times, More preferably, it is 2-4 times.

  After the water bath stretching step, it is preferable to apply an oil agent made of silicone or the like to the yarn for the purpose of preventing adhesion between single fibers. As such a silicone oil agent, it is preferable to use a modified silicone, and one containing an amino-modified silicone having high heat resistance can be used.

  A polyacrylonitrile-based precursor fiber for carbon fiber is obtained by performing a drying heat treatment and steam stretching after the above-described washing step, water bath stretching step, and if necessary an oil agent application step.

  In the present invention, the drying heat treatment is preferably performed at a temperature of 160 to 200 ° C. for the purpose of increasing crystallinity in the fiber axis direction. In the drying heat treatment, the yarn may be brought into direct contact with the heated roller, or the heated atmosphere may be run in a non-contact manner, but from the viewpoint of drying efficiency, the yarn is brought into direct contact with the heated roller. It is preferable to dry the yarn until the moisture content in the yarn is 1% by weight, thereby densifying the fiber structure.

  In the present invention, the steam stretching is preferably performed at least 3 times, more preferably 4 times or more, and further preferably 5 times or more in the pressurized steam. The total draw ratio including the water washing step, the water bath drawing step and the steam drawing step is preferably 11 to 15 times from the viewpoint of increasing the crystallinity in the fiber axis direction. When the draw ratio is less than 11 times, the crystallinity in the fiber axis direction is low, and the strand tensile strength is difficult to be exhibited. When the draw ratio exceeds 15 times, the draw breakage becomes remarkable, and the resulting polyacrylonitrile precursor for carbon fiber is obtained. It shows a tendency for the quality of body fibers and carbon fibers to decrease.

In the present invention, the number of filaments per yarn of the polyacrylonitrile-based precursor fiber for carbon fiber is preferably 1,000 to 3,000,000, more preferably 6,000 to 3,000. 2,000, more preferably 12,000 to 2,500,000. The number of filaments is preferably 1,000 or more for the purpose of improving productivity. However, when the number exceeds 3,000,000, the inside of the polyacrylonitrile-based precursor fiber yarn for carbon fiber is evenly distributed. Flameproofing treatment may not be possible.
Next, the manufacturing method of the carbon fiber of this invention is demonstrated. The method for producing a carbon fiber of the present invention is obtained by subjecting the polyacrylonitrile-based precursor fiber obtained as described above to flame resistance and preliminary carbonization, and then carbonizing under a specific carbonization tension.
First, the flameproofing process will be described. The flame resistance is preferably performed at as high a temperature as possible without causing a runaway reaction. Specifically, it is preferably performed in air at 200 to 300 ° C.

  The stretch ratio when making flame resistant is preferably 0.80 to 1.20, more preferably 0.90 to 1.20, and still more preferably 0.85 to 1.10. When the draw ratio is less than 0.80, the degree of orientation of the obtained flame-resistant fiber becomes insufficient, and the strand tensile modulus of the obtained carbon fiber may be lowered. On the other hand, when the draw ratio exceeds 1.20, processability may be deteriorated due to generation of fluff and yarn breakage.

  The treatment time for flame resistance can be appropriately selected within a range of 10 to 100 minutes, but for the purpose of the subsequent preliminary carbonization process and the improvement of the mechanical properties of the resulting carbon fiber, the specific gravity of the flame resistant fiber obtained. Is preferably set in a range of 1.3 to 1.38.

  Next, the preliminary carbonization step and the carbonization step of the present invention will be described.

  In the carbon fiber production method of the present invention, the above-mentioned flameproof fiber is pre-carbonized in an inert atmosphere at a temperature of 300 to 800 ° C., and then carbonized in an inert atmosphere at a temperature of 1000 to 2000 ° C. can get. You may include the graphitization process performed in the inert atmosphere of the temperature of 2000-3000 degreeC as needed.

    In the present invention, the preliminary carbonization step, the carbonization step, and the graphitization step are performed in an inert atmosphere. Preferred examples of the inert gas used include nitrogen, argon, and xenon, from an economical viewpoint. Is preferably nitrogen.

  In the present invention, the pre-carbonization temperature is preferably 300 to 800 ° C., and the temperature increase rate in the pre-carbonization is preferably set to 500 ° C./min or less.

The draw ratio during the preliminary carbonization is preferably 1.00 to 1.30, more preferably 1.10 to 1.30, and even more preferably 1.10 to 1.20. . When the draw ratio is less than 1.00, the degree of orientation of the obtained preliminary carbonized fiber may be insufficient, and the strand tensile elastic modulus of the carbon fiber may decrease. On the other hand, when the draw ratio exceeds 1.30, the processability may be deteriorated due to the occurrence of fluff and yarn breakage.
In this invention, it is preferable that the temperature in a carbonization process is 1000-2000 degreeC, More preferably, it is 1300-1700 degreeC, More preferably, it is 1400-1650 degreeC. The higher the maximum temperature, the higher the tensile modulus, but the graphitization proceeds, the two-dimensionality of the carbon structure increases, and as a result, the amount of conduction electrons may increase, and consequently the compressive strength may decrease. Considering the balance between the two, the temperature in the carbonization process is set.
The carbon fiber of the present invention can be obtained by making the precursor fiber flame resistant and pre-carbonized and then carbonizing it under a specific range of tension conditions. The tension in the carbonization step of the carbon fiber of the present invention is preferably 2.2 to 17.5 mN / dTex, more preferably 3.5 to 16.5, and preferably 3.2 to 15.5. Further preferred. When the tension is less than 2.2 mN / dTex, the degree of orientation and denseness of the obtained carbon fiber may be insufficient, and the strand tensile elastic modulus may decrease. On the other hand, when the tension exceeds 17.5 mN / dTex, processability may be deteriorated due to generation of fluff or yarn breakage.

  Here, the tension in the carbonization step is the value obtained by dividing the tension (mN) measured with the roll on the exit side of the carbonization furnace by the fineness (dTex) at the time of absolutely dry of the polyacrylonitrile-based precursor fiber for carbon fiber production. To do. The tension in the carbonization process can be controlled by adjusting the weight by applying a pulley-like roll having a weight to the yarn between the fixed shafts by running the yarn on the fixed shaft having the roll. it can.

  The obtained carbon fiber can be electrolytically treated for surface modification. The electrolytic solution used for the electrolytic treatment includes an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, an alkali solution such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or a salt thereof as an aqueous solution. Can be used as 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 is high, the problem of poor adhesion to the resin and non-fibrous strength properties is solved, and the resulting composite material is balanced in both the fiber and non-fiber directions. Strength characteristics are developed.

  After the electrolytic treatment, a sizing treatment can be performed in order to give the obtained carbon fiber a focusing property. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the composite material. The drying of the applied sizing agent is not particularly limited, but if the yarn is brought into direct contact with a heated roller, the carbon fiber may deteriorate in quality because of its low elongation, so use a non-contact type hot air furnace. It is preferable.

  The carbon fiber obtained by the production method of the present invention has high compressive strength and tensile elastic modulus. Therefore, the carbon fiber of the present invention is an aircraft member, a pressure vessel member, an automobile member, a fishing rod and the like by various molding methods such as autoclave molding as a prepreg, resin transfer molding as a preform such as a woven fabric, and filament winding. It can be suitably used as a sports member such as a golf shaft.

  The measuring method of various physical property values described in this specification is as follows.

<Measurement of amount of acrylonitrile-containing polymerization inhibitor>
20 ml of acrylonitrile for polymerization is precisely weighed in a conical flask with a stopper, 10 ml of concentrated nitric acid is added, shaken for 1 minute, and allowed to stand for 2 minutes to obtain a sample solution. The sample solution is placed in a 10 ml quartz cell, the absorbance at a wavelength of 400 nm is measured with an absorptiometer, and the value on the calibration curve is read to determine the amount of polymerization inhibitor.
The amount of polymerization inhibitor contained in acrylonitrile is a polymerization inhibitor amount-absorbance calibration curve using at least four types of acrylonitrile with known amounts of polymerization inhibitors with different amounts of polymerization inhibitor.
The absorbance is measured using acrylonitrile having a known polymerization inhibitor amount and having a polymerization inhibitor weight ratio of 40 ppm, 100 ppm, 150 ppm, and 200 ppm. In the present invention, a self-recording spectrophotometer UV-240 manufactured by Shimadzu Corporation was used as an absorbance measurement apparatus.

<Weight average molecular weight (Mw)>
A sample solution is obtained by dissolving in dimethylformamide (0.01N-lithium bromide added) so that the concentration of the polymer is 0.1% by weight. For the obtained sample solution, a molecular weight distribution curve is obtained from the GPC curve measured under the following conditions (i) and (ii) using a GPC apparatus, and Mw is calculated. The measurement is performed three times under each condition, and the arithmetic average value is defined as Mw of the polymer. It should be noted that the data of the condition (ii) is adopted when the data is different between the conditions (i) and (ii).
Condition (i)
-Column: Column for polar organic solvent GPC-Flow rate: 0.8 ml / min
・ Temperature: 40 ℃
・ Sample filtration: Membrane filter (0.45μm cut)
・ Injection volume: 20 μl
-Detector: Differential refractive index detector condition (ii)
-Column: Column for polar organic solvent GPC-Flow rate: 0.5 ml / min
・ Temperature: 70 ℃
・ Sample filtration: Membrane filter (0.45μm cut)
・ Injection volume: 200 μl
-Detector: The differential refractive index detector Mw uses at least six types of monodisperse polystyrenes with different molecular weights and known molecular weights to prepare an elution time-molecular weight calibration curve, and at the corresponding elution time on the calibration curve. It is determined by reading the corresponding polystyrene equivalent molecular weight. The GPC apparatus and column to be used are not particularly limited as long as the above conditions are satisfied. In Examples and Comparative Examples described later, CLASS-LC2010 manufactured by Shimadzu Corporation is used as the GPC apparatus, and Tosoh Corporation is used as the column. TSK-GEL-α-M (× 2) manufactured by Wako Pure Chemical Industries, Ltd. as dimethylformamide and lithium bromide, 0.45 μ-FHLP FILTER manufactured by Millipore Corporation as a membrane filter, differential refractive index detector RID-10AV manufactured by Shimadzu Corporation as a monodisperse polystyrene for preparing a calibration curve was used with molecular weights of 184000, 427000, 791000, 1300000, 1810000, and 4240000, respectively. In addition, it superposed | polymerized 5 times in the same composition, Mw was calculated about each polymer, and the arithmetic average value was made into the weight average molecular weight Mw. In addition, the standard deviation was calculated, and the standard deviation / arithmetic mean × 100 was regarded as the variation (CV). <Criteria for Quality Grade of Carbon Fiber Precursor Fiber>
The inspection items were as follows: 3,000 fiber bundles were run at a speed of 1 m / min, and after running 15 m or more after starting, the number of fluff and pills was visually counted in the range of 300 m and evaluated in the following three stages. To do. The evaluation criteria are as follows. In addition, measurement shall be performed by selecting any one yarn.

Grade 1: Within 300 m of fiber, within 1 piece Grade 2: Within 300 m of fiber, within 2 to 15 grade 3: Over 16 pieces of fiber in 300 m <Intrinsic viscosity>
At a temperature of 60 ° C., 150 mg of a polyacrylonitrile-based polymer that has been heat-treated at 120 ° C. for 2 hours and dried is dissolved in 50 ml of dimethylformamide containing 0.1 mol / liter of sodium thiocyanate. About the obtained solution, the fall time between marked lines is measured with the accuracy of 1/100 second using an Ostwald viscometer in the temperature of 25 degreeC. Let the measured fall time be t (seconds). Similarly, measurement is also performed on dimethylformamide added with 0.1 mol / liter of sodium thiocyanate in which the polyacrylonitrile-based polymer is not dissolved, and the dropping time is defined as t ₀ (seconds). The intrinsic viscosity [η] was calculated using the following formula.
[η] = {(1 + 1.32 × ηsp) ^(1/2) −1} /0.198
ηsp = (t / t ₀ ) −1
The said measurement is performed 3 times and let the arithmetic mean be the intrinsic viscosity of the polyacrylonitrile-type polymer. In each of the examples and comparative examples, polymerization was carried out five times with the same composition, the intrinsic viscosity was measured for each polymer, and the arithmetic average was taken as the intrinsic viscosity [η].
In Examples and Comparative Examples described later, Wako Pure Chemicals special grades were used as the sodium thiocyanate and dimethylformamide.

<Dissolved oxygen concentration>
Using a model 410 manufactured by Hack Ultra Co., Ltd. as a dissolved oxygen analyzer, a sensor is installed at the bottom of the polymerization tank so that the sensor is filled with the solution used for polymerization, and a copolymerization component of acrylonitrile and acrylonitrile used for polymerization and The dissolved oxygen concentration of the solution to be subjected to polymerization is measured in real time when the solvent and the polymerization inhibitor are charged into the polymerization tank, and also measured in real time when the inert gas is replaced.

<Strand tensile modulus and strength of carbon fiber>
The strand tensile modulus and strength of the carbon fiber are determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The test piece is prepared by impregnating carbon fiber with the following resin composition and curing conditions of heat treatment at 130 ° C. for 35 minutes.
Resin composition: 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate (100 parts by weight) / 3 boron fluoride monoethylamine (3 parts by weight) / acetone (4 parts by weight)
The number of strands to be measured is six, and the arithmetic average value of each measurement result is the strand tensile modulus and strength of the carbon fiber.
In Examples and Comparative Examples described later, as the 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate, “BAKELITE (registered trademark)” ERL- manufactured by Union Carbide Co., Ltd. 4221 was used.

Examples 1 to 11 and Comparative Examples 1 to 6 described below were carried out using the conditions described in Table 1 in the method of implementation described in the following comprehensive examples.
Comprehensive example:
A monomer composed of 99.6 mol of acrylonitrile and 0.4 mol% of itaconic acid as a copolymer component, 20 wt% of dimethyl sulfoxide as a solvent, a polymerization inhibitor described in Table 1 in an amount shown in Table 1, and 2,2′- After charging azobisisobutyronitrile to be a polymerization initiator / polymerization inhibitor listed in Table 1, the inside of the polymerization tank was replaced with nitrogen while stirring the solution, and the dissolved oxygen concentration of the solution was When the concentration shown in Table 1 was reached, a polyacrylonitrile polymer was produced by a solution polymerization method by heating. Here, as acrylonitrile, a polymerization inhibitor containing 40 ppm of 4-methoxy-1-naphthol was used.

Ammonia gas was blown into the manufactured polyacrylonitrile polymer until the pH reached 8.5, and ammonium groups were introduced into the polyacrylonitrile copolymer while neutralizing itaconic acid to obtain a spinning dope. In addition, it superposed | polymerized 5 times in the same composition, the weight average molecular weight and the intrinsic viscosity were measured about each obtained spinning dope. The measurement results are shown in Table 1.
The obtained spinning dope was discharged at 40 ° C. using a spinneret having a diameter of 0.12 mm and a hole number of 3,000, and once discharged into the air, passed through a space of about 4 mm, and then controlled at 3 ° C. 35 A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath comprising an aqueous solution of% dimethyl sulfoxide.

After this coagulated yarn was washed with water by a conventional method, the water bath stretching process was performed using a two-warm warm water tank and stretched 3.5 times, and after addition of an amino-modified silicone silicone oil, 160 ° C. Then, a drying densification treatment was performed using a heating roller of No. 3, and then the resultant yarn was stretched 3.7 times in a pressurized steam, so that the total spinning ratio was 13 times, the single fiber fineness was 0.7 dtex, and the number of single fibers was 3 1,000 polyacrylonitrile-based precursor fibers were obtained. Next, four acrylic fibers obtained were combined, and the number of single fibers was 12,000. In air at a temperature of 240 to 260 ° C., a flameproofing treatment was performed while drawing at a draw ratio of 1.0. A flame-resistant fiber bundle having a specific gravity of 1.35 was obtained. The obtained flame-resistant fiber bundle is pre-carbonized while being stretched at a stretch ratio of 1.15 in a nitrogen atmosphere at a temperature of 300 to 800 ° C., and then tension is applied in a nitrogen atmosphere at a maximum temperature of 1,500 ° C. The maximum tension at which yarn breakage does not occur, that is, the carbonized stretch limit tension shown in Table 3, is found by increasing from 2.2 mN / dTex by 0.1 mN / dTex. A fiber bundle was obtained. About the obtained carbon fiber bundle, strand tensile strength (GPa) and strand tensile elasticity modulus (GPa) were measured. Each measurement result is shown in Table 1.
[Comparative Example 1] Polymerized yarn was produced under the conditions shown in Table 1. Since the amount of the polymerization inhibitor was less than the lower limit of the present invention, it was found that the obtained polymer had a large variation in weight average molecular weight and a poor precursor fiber quality grade. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.
[Comparative Example 2] Polymerized yarn was produced under the conditions shown in Table 1. Since the amount of the polymerization inhibitor was larger than the upper limit of the present invention, it was found that the obtained polymer had a low weight average molecular weight. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.
[Comparative Example 3] Polymerized yarn was produced under the conditions shown in Table 1. Since the ratio of polymerization initiator / polymerization inhibitor was less than the lower limit of the present invention, it was found that the obtained polymer had a low weight average molecular weight. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.
[Comparative Example 4] Polymerized yarn was produced under the conditions shown in Table 1. Since the ratio of the polymerization initiator / polymerization inhibitor was larger than the upper limit of the present invention, the obtained polymer was found to have a low weight average molecular weight and intrinsic viscosity. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.
[Comparative Example 5] Polymerized yarn was produced under the conditions shown in Table 1. Since the dissolved oxygen concentration was higher than the upper limit of the present invention, it was found that the obtained polymer had a large variation in weight average molecular weight and poor precursor fiber grade. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.
[Comparative Example 6] Polymerized yarn was produced under the conditions shown in Table 1. Since distilled water was used instead of the polymerization inhibitor, it was found that the obtained polymer had a large variation in weight average molecular weight and a poor precursor fiber quality grade. The obtained polyacrylonitrile-based precursor fiber was flame-resistant and pre-carbonized to produce a carbon fiber bundle. It was found that the carbonized stretch critical tension was low, and the obtained carbon fiber had a low strand tensile modulus.

It contains a copolymerization component of acrylonitrile, radical polymerization initiator, polymerization inhibitor, and acrylonitrile, and a solvent. The weight ratio of radical polymerization initiator and polymerization inhibitor is within a specific range, and the polymerization inhibitor is specified based on the total amount of the solution. It was found that the polymer obtained by polymerizing the acrylonitrile-based polymer by heat-treating the solution in the amount of 5% was stable in molecular weight, and stable post-stretching was possible in the post-yarn-stretching step. It was.

  According to the present invention, a polymer having a stable molecular weight can be polymerized even in a polymerization system with few polymerization initiators that generate radicals without impairing productivity and processability, and a high molecular weight polyacrylonitrile system Even with a polymer, stable post-drawability can be realized in the post-yarn drawing step, and a polymer with little difference in post-drawability in the post-yarn drawing step can be produced even if the polymerization batch changes. As a result, carbon fibers having excellent quality can be stably produced.

  The carbon fiber obtained by the present invention has high compressive strength and tensile elastic modulus. Therefore, the carbon fiber of the present invention is applicable to various molding methods such as an autoclave molding method using a prepreg, a resin transfer molding method using a preform such as a woven fabric, and a filament winding molding method. It is suitably used for the formation of sports members such as aircraft members, pressure vessel members, automobile members, fishing rods, and golf shafts.

Claims (5)

It contains a copolymerization component of acrylonitrile, a radical polymerization initiator, a polymerization inhibitor, and acrylonitrile and a solvent, and the weight ratio (B / A) of the radical polymerization initiator (A) to the polymerization inhibitor (B) is represented by the formula (1). Meet,
2 ≦ (B / A) <210 Formula (1)
And the manufacturing method of the polyacrylonitrile type polymer which heat-processes the solution whose polymerization inhibitor is 8 ppm-140 ppm with respect to the total solution amount, and whose dissolved oxygen concentration is 1-10 ppm. The method for producing a polyacrylonitrile-based polymer according to claim 1, wherein the polymerization inhibitor contains at least one polymerization inhibitor having a polycyclic aromatic structure and / or a monocyclic aromatic structure. Polymerization inhibitors are hydroquinone, methylhydroquinone, hydroquinone monomethyl ether, 4-methoxy-1-naphthol, p-hydroxydiphenylamine, N, N-diphenyldiamine, 2-tertiary butyl hydroquinone, 2,5-ditertiary butyl hydroquinone, The method for producing a polyacrylonitrile-based polymer according to claim 2, comprising at least one selected from t-butylcatechol and nitronaphthol. The weight-average molecular weight (Mw) measured by a gel permeation chromatograph (GPC) method is 500 to 700,000, and the intrinsic viscosity is 2.0 to 3.0. The production according to any one of claims 1 to 3. A polyacrylonitrile polymer obtained by the method. A method for producing carbon fibers, comprising spinning, flameproofing, and preliminary carbonizing the polyacrylonitrile-based polymer according to claim 4 and then carbonizing the carbonized tension at 2.2 mN / dTex to 17.5 mN / dTex.