JP6048395B2 - Polyacrylonitrile-based polymer, carbon fiber precursor fiber, and method for producing carbon fiber - Google Patents

Description

  The present invention relates to a polyacrylonitrile polymer suitable for increasing the yarn density in the flameproofing process, a carbon fiber precursor fiber using the polyacrylonitrile polymer, and a method for producing the carbon fiber.

  Since carbon fiber has higher specific strength and specific modulus than other fibers, it can be used as a reinforcing fiber for composite materials in addition to conventional sports applications, aerospace applications, automobiles, civil engineering / architecture, pressure vessels and Widely deployed in general industrial applications such as windmill blades, there is a strong demand for further improvement in productivity.

  Among the carbon fibers, the most widely used polyacrylonitrile (hereinafter sometimes abbreviated as PAN) carbon fiber is a wet spinning, dry spinning or spinning solution composed of a PAN polymer as its precursor. After carbon fiber precursor fiber (hereinafter sometimes abbreviated as precursor fiber) is obtained by dry and wet spinning, it is heated in an oxidizing atmosphere at a temperature of 180 to 400 ° C. to convert it into flame resistant fiber. However, it is produced industrially by heating and carbonizing in an inert atmosphere at a temperature of at least 1000 ° C.

  In order to control equipment costs by reducing carbon fiber productivity and equipment size, there is a method to increase the density of fibers fired at one time, but in a flameproofing process where an exothermic reaction proceeds, within a limited space If the density of the existing fiber is too high, there is a problem that yarn breakage or ignition occurs. Various proposals have been made to date regarding methods for removing heat from a yarn bundle that is being flame-resistant. For example, a method for increasing the heat removal efficiency using a fluidized bed (see Patent Document 1), a method for controlling the temperature of the yarn using a cooling roller (see Patent Document 2), and flame resistance in an atmosphere containing vaporized organic compounds. And the like (see Patent Document 3).

Japanese Unexamined Patent Publication No. 03-33220 Japanese Patent Laid-Open No. 04-108117 Japanese Patent Laid-Open No. 2001-248025

  However, in the method using the fluidized bed, there are problems that particles leak out of the furnace and that the cost is higher than the conventional method in terms of equipment. Further, in the method using a cooling roller, it is necessary to increase the number of rollers in order to increase the heat removal efficiency, and there is a problem that the cost is increased accordingly. Furthermore, in the method of making flame resistant in an atmosphere containing an organic compound vapor, there is a problem that handling is difficult due to the flammability of the organic compound vapor and the effect on the human body.

  In view of the above problems, a manufacturing method is used in which the treatment is performed for a long time under precise temperature control with a substantially limited number of yarns in the flameproofing step. This restriction in the flameproofing process has been one of the major obstacles to the improvement of carbon fiber productivity.

  Then, this invention makes it a subject to provide the polyacrylonitrile-type polymer required for manufacture of the carbon fiber precursor fiber which can be flame-resistant with high density, without requiring a new installation.

The present invention for solving this problem has the following configuration. That is, the polyacrylonitrile polymer of the present invention comprises 1 to 30 mol% of a vinyl monomer having a leaving group and a nitrile group as a copolymerization component, 0.1 to 1 mol% of a flameproofing acceleration component , and acrylonitrile. It is obtained by polymerizing the acrylonitrile-based monomer composition to be contained .

  According to a preferred embodiment of the polyacrylonitrile-based polymer of the present invention, when the polyacrylonitrile-based polymer is heated in an air atmosphere for 100 minutes, the temperature at which the nitrile group residual ratio after heating is 35% is Tc ° C. The heat generation rate at Tc ° C. measured at 10 ° C./min in air by a differential scanning calorimeter is 1.4 J / g / s or less.

Polyacrylonitrile-based polymer of the present invention, a vinyl monomer having a leaving group and a nitrile group, at least one compound selected from the group consisting of compounds represented by the following formula (1) or formula (2) Although used, it is essential that the compound used in the present invention is at least one selected from the group consisting of 2-ethoxyacrylonitrile, 3-ethoxyacrylonitrile, and 2-acetoxyacrylonitrile. Furthermore, the flameproofing promoting component used in the present invention is at least one selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide. Is essential .

(In the formula (1), X is selected from OR ₁ , OCOR ₁ , SO ₃ R ₁ , NR ₁ R ₂ , Cl, Br, and I. Here, R ₁ and R ₂ are hydrogen or an alkyl group. Represents.)

(In the formula (2), X is selected from OR ₁ , OCOR ₁ , SO ₃ R ₁ , NR ₁ R ₂ , Cl, Br, and I. Here, R ₁ and R ₂ are hydrogen or an alkyl group. Represents.)
The method for producing a carbon fiber precursor fiber of the present invention is a method for producing a carbon fiber precursor fiber in which the polyacrylonitrile-based polymer is spun by a wet spinning method or a dry and wet spinning method.

  The carbon fiber production method of the present invention comprises a flameproofing step of flameproofing the carbon fiber precursor fiber in air at a temperature of 180 to 300 ° C., and a fiber obtained in the flameproofing step of 300 to 800. A carbon fiber obtained by sequentially preliminarily carbonizing in an inert atmosphere at a temperature of ° C and a carbonizing step of carbonizing the fiber obtained in the preliminary carbonization process in an inert atmosphere at a temperature of 1000 to 3000 ° C. It is a manufacturing method.

  According to the present invention, it is possible to increase the yarn density while suppressing yarn breakage in the flameproofing step of the carbon fiber precursor fiber, and therefore it is possible to improve the productivity of the carbon fiber.

  The inventors of the present invention have made extensive studies in order to produce carbon fiber carbon fiber precursor fibers capable of increasing the yarn density while suppressing yarn breakage in the flameproofing process. Reached.

Polyacrylonitrile-based polymer of the present invention, 1 to 30 mol% of a vinyl monomer having a leaving group and a nitrile group as a copolymerization component, flame accelerating component 0.1 to 1 mol%, and acrylonitrile containing acrylonitrile It is obtained by polymerizing a monomer composition .

  In the present invention, if the content of the vinyl monomer having a leaving group and a nitrile group is less than 1 mol%, it is difficult to sufficiently suppress the amount of heat generated in the flameproofing step, and the effects of the present invention cannot be obtained. There is. In addition, when the content of the vinyl monomer having a leaving group and a nitrile group exceeds 30 mol%, molecular breakage due to thermal decomposition at the copolymerization portion becomes remarkable, and the tensile strength of the resulting carbon fiber is greatly reduced. In addition, there is a concern that the fiber is melted and bonded in the flameproofing process. From this viewpoint, in the present invention, the content of the vinyl monomer having a leaving group and a nitrile group is 1 to 30 mol%. Preferably, it is 3-20 mol%.

If the content of the flameproofing promoting component is less than 0.1 mol%, the reaction in the flameproofing process cannot sufficiently proceed, and the yield in the carbonization process may be reduced. Moreover, when the content of the flameproofing promoting component exceeds 1 mol%, there is a concern that the reaction in the flameproofing process proceeds rapidly and it becomes difficult to sufficiently suppress the heat generation in the flameproofing process. From this viewpoint, in the present invention, the content of the flame resistance promoting component is 0.1 to 1 mol%. Preferably, it is 0.3-0.8 mol%. In the present invention, as flame accelerating component, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, at least one selected from the group consisting of mesaconic acid, acrylamide and methacrylamide are It must be used . In the present invention, the number of amide groups and carboxyl groups contained in the acrylonitrile monomer, than one even better that is two or more, from that point of view, copolymerizable component for promoting oxidization As acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid , itaconic acid and methacrylic acid are preferable.

  According to a preferred embodiment of the polyacrylonitrile-based polymer of the present invention, when the polyacrylonitrile-based polymer is heated in an air atmosphere for 100 minutes, the temperature at which the nitrile group residual ratio after heating is 35% is Tc ° C. A polyacrylonitrile-based polymer having an exothermic rate at Tc ° C. of 1.4 J / g / s or less measured by a differential scanning calorimeter in air at a heating rate of 10 ° C./min.

  The “nitrile group residual ratio” mentioned here is a parameter representing the progress of the flameproofing reaction, and can be determined by the following method. In the infrared absorption spectrum measurement of polyacrylonitrile-based polymer, the absorbance of the absorption due to the carbon-nitrogen triple bond of the nitrile group after heating is Da, and the absorbance of the absorption due to the carbon-nitrogen triple bond of the nitrile group before heating is Is Db, the nitrile group residual ratio X can be obtained by the following formula (3).

  X = Da / Db × 100 (3).

  In this invention, if the said heat_generation | fever rate is 1.4 J / g / s or less, flame resistance can be performed in a high-density state and the productivity of carbon fiber can be improved. When high-density flame resistance is achieved using a precursor larger than 1.4 J / g / s, heat generation and heat storage increase, and there is a risk of thread breakage and ignition, and exposure to excessive temperatures in an oxidized state. Therefore, there is a possibility of causing defects that deteriorate the mechanical properties.

Polyacrylonitrile-based polymer of the present invention, a vinyl monomer having a leaving group and a nitrile group, at least one compound selected from the group consisting of compounds represented by the following formula (1) or formula (2) Although used, it is essential that the compound used in the present invention is at least one selected from the group consisting of 2-ethoxyacrylonitrile, 3-ethoxyacrylonitrile, and 2-acetoxyacrylonitrile. Furthermore, the flameproofing promoting component used in the present invention is at least one selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide. Is essential .

(In the formula (1), X is selected from OR ₁ , OCOR ₁ , SO ₃ R ₁ , NR ₁ R ₂ , Cl, Br, and I. Here, R ₁ and R ₂ are hydrogen or an alkyl group. Represents.)

(In the formula (2), X is selected from OR ₁ , OCOR ₁ , SO ₃ R ₁ , NR ₁ R ₂ , Cl, Br, and I. Here, R ₁ and R ₂ are hydrogen or an alkyl group. Represents.)
As a method for producing the polyacrylonitrile-based polymer of the present invention, known polymerization methods such as solution polymerization, suspension polymerization, and emulsion polymerization can be selected. From the viewpoint of uniformly polymerizing the copolymer component, It is preferred to use solution polymerization. As the solution in the case of solution polymerization, an organic solvent in which polyacrylonitrile is soluble such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide is generally used.

  Next, the manufacturing method of the carbon fiber precursor fiber of this invention is demonstrated.

  The above-mentioned polyacrylonitrile-based polymer is used for the carbon fiber precursor fiber of the present invention. Usually, such a polymer is dissolved in a polyacrylonitrile-soluble solvent such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide to obtain a spinning dope. When using solution polymerization, it is preferable that the solvent used for the polymerization and the solvent used for the spinning dope are the same because the step of re-dissolution is unnecessary. The concentration of the polymer in the spinning dope is preferably 10 to 40% by mass from the viewpoint of stock solution stability.

  In the present invention, the spinning dope is spun from a die by a wet spinning method or a dry and wet spinning method and introduced into a coagulation bath to coagulate the fibers. In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide used as a solvent in 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 in the spinning dope can be used. Specifically, it is preferable to use water.

  The spun fiber is usually stretched in the bath at a stretching temperature of 30 to 98 ° C. by about 2 to 6 times after the solvent is removed in the water washing step, but the present invention is not limited to this. The water washing process may be omitted, and after spinning, the film may be stretched in a bath and then washed with water.

  It is preferable to apply an oil agent from the meaning of preventing adhesion between single fibers after the stretching step in the bath. The drying step is performed by drying the yarn after stretching in a bath with a hot drum or the like, and the drying temperature, time, and the like can be appropriately selected. Further, if necessary, the dried and densified yarn is also subjected to pressure steam drawing.

  The obtained carbon fiber precursor fiber is usually in the form of a continuous multifilament (bundle), and the number of filaments is preferably 1,000 to 3,000,000.

  Next, the manufacturing method of the carbon fiber of this invention is demonstrated.

  The carbon fiber precursor fiber produced by the above-described method is subjected to a flame resistance treatment in air at a temperature of 180 to 300 ° C., preferably while stretching at a stretch ratio of 0.8 to 2.5, and then 300 to 800. In an inert atmosphere at a temperature of ° C., pre-carbonization treatment is preferably performed while stretching at a stretch ratio of 0.9 to 1.5, and in an inert atmosphere at a maximum temperature of 1000 to 3000 ° C., the stretch ratio is preferably 0.1. Carbon fiber is produced by carbonizing while stretching at 9 to 1.1. Nitrogen, argon, xenon, etc. can be illustrated as gas used for an inert atmosphere, and nitrogen is preferably used from an economical viewpoint.

  The carbon fiber produced in this way can increase the yarn density in the flameproofing process without the need for new equipment, so it can be used for sports, aerospace, automobiles, civil engineering / architecture, pressure vessels and windmills. Carbon fibers suitable for general industrial applications such as blades can be produced with high productivity.

  Hereinafter, the present invention will be described more specifically with reference to examples. The measurement method used in this example will be described next.

<Measurement of nitrile group residual ratio and determination of Tc>
The nitrile group residual ratio X was measured as follows. First, a polyacrylonitrile-based polymer solution is cast on a glass plate and applied so as to have a constant thickness. Next, the glass plate coated with the polymer solution is dried in air at 120 ° C. using a hot air dryer or the like, and the solvent is evaporated to form a film having a thickness of 20 to 40 μm.

  The obtained film is heat-treated at a specific temperature (180 to 250 ° C., in increments of 5 ° C.) for 100 minutes using a hot air dryer or the like in an air atmosphere to perform a flame resistance treatment. The film before and after the flameproofing treatment thus obtained is freeze-pulverized to obtain a powder sample. Measurement is performed using a tablet obtained by grinding and mixing 2 mg of each powder sample and 300 mg of potassium bromide in a mortar with a tablet molding machine and using an FT-IR measuring instrument (manufactured by Shimadzu Corporation). The absorbance of the sample due to the carbon-nitrogen triple bond of the nitrile group of the sample before the flameproofing treatment is expressed as Db, and the absorbance of the sample due to the carbon-nitrogen triple bond of the nitrile group of the sample after the flameproofing treatment is expressed by the formula ( The nitrile group residual ratio X was determined using 3). Moreover, the temperature at which the nitrile group residual ratio thus determined was 35% was determined as Tc.

  X = Da / Db × 100 (3).

<Measurement of calorific value of polyacrylonitrile-based polymer>
The calorific value of the polyacrylonitrile polymer was measured as follows. The polyacrylonitrile-based polymer solution was desolvated in hot hot water and then freeze-pulverized, and 1 mg was placed in a sample pan. Then, it measured from room temperature to 400 degreeC on the conditions of the temperature increase rate of 10 degree-C / min and the air supply amount of 100 mL / min using DSC3100SA by Bruker AXS.

<Flame resistance test at Tc + 20 ° C>
Combining carbon fiber precursor fibers with a single fiber fineness of 1.0 dtex and filament number of 6000 to make the number of filaments 24,000, and then passing through a flameproofing furnace with the furnace temperature set at Tc + 20 ° C. Tested. Evaluation was made as ○ for those that could pass without causing thread breakage or fluff generation, and × for those that had thread breakage or fluff generation.

(Examples 1-7, Comparative Examples 1-5)
Polyacrylonitrile having a concentration of 20% by mass is obtained by radical polymerization of acrylonitrile and a copolymer component having the copolymer composition shown in Table 1 with azobisisobutyronitrile as an initiator by a solution polymerization method using dimethyl sulfoxide as a solvent. A system polymer solution was obtained.

  The obtained polyacrylonitrile-based polymer solution was made into a coagulated yarn by a wet spinning method using a spinneret having a single-hole diameter of 0.15 mm and a hole number of 6000 at a temperature of 40 ° C. The coagulated yarn thus obtained was washed with water by a conventional method, then stretched 3 times in warm water at 90 ° C., and further a silicone oil was added to obtain a stretched yarn in bath. The drawn yarn in the bath is subjected to a drying heat treatment using a roller heated to a temperature of 180 ° C., and then drawn five times in a pressurized steam, so that the single fiber fineness is 1.0 dtex and the number of filaments is 6000. Carbon fiber precursor fiber was obtained.

  The results of flame resistance at Tc + 20 ° C. are as shown in Table 1. Neither yarn breakage nor fluff generation was observed in the range of the examples.

Claims (4)

1-30 mol% of a vinyl monomer having at least one leaving group selected from the group consisting of 2-ethoxyacrylonitrile, 3-ethoxyacrylonitrile, and 2-acetoxyacrylonitrile and a nitrile group as a copolymerization component , acrylic acid 0.1 to 1 mol% of at least one flameproofing promoting component selected from the group consisting of methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide , and A polyacrylonitrile polymer obtained by polymerizing an acrylonitrile monomer composition containing acrylonitrile. When the polyacrylonitrile-based polymer is heated for 100 minutes in an air atmosphere, the temperature at which the residual ratio of the nitrile group after heating is 35% is Tc ° C. The polyacrylonitrile-based polymer according to claim 1, wherein the heat generation rate at Tc ° C measured as / min is 1.4 J / g / s or less. A method for producing a carbon fiber precursor fiber, wherein the polyacrylonitrile-based polymer according to claim 1 or 2 is spun by a wet spinning method or a dry-wet spinning method. A carbon fiber precursor fiber produced by the method for producing a carbon fiber precursor fiber according to claim 3 is obtained by a flame resistance process for flame resistance in air at a temperature of 180 to 300 ° C., and the flame resistance process. A preliminary carbonization step of pre-carbonizing the obtained fiber in an inert atmosphere at a temperature of 300 to 800 ° C., and a carbonization step of carbonizing the fiber obtained in the preliminary carbonization step in an inert atmosphere at a temperature of 1000 to 3000 ° C. The manufacturing method of the carbon fiber which obtains a carbon fiber sequentially through.