JP2014167039A - Polyacrylonitrile-based polymer, carbon fiber precursor fiber, method for producing the same, and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyacrylonitrile-based polymer required for producing carbon fiber precursor fibers with high productivity, which have a catalytic metal uniformly dispersed therein at a high concentration and are capable of causing a catalyst graphitization reaction.SOLUTION: The polyacrylonitrile-based polymer contains as copolymerization components at least acrylonitrile (a) and a salt (b) which comprises an organic acid having a group VIII metal and a vinyl group and an organic acid having no vinyl group.

Description

  The present invention relates to a polyacrylonitrile polymer suitable for the production of highly crystalline carbon fibers, a carbon fiber precursor fiber using the polyacrylonitrile polymer, a method for producing the same, and a method for producing carbon fibers. is there.

  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 It is widely deployed in general industrial applications such as windmill blades, and there is a strong demand for both higher productivity and higher elastic modulus.

  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 may be abbreviated as precursor fiber) is obtained by dry and wet spinning, it is heated in an oxidizing atmosphere at a temperature of 200 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 obtain a carbon fiber having a high elastic modulus, there is a method of increasing the degree of orientation of the carbon fiber or increasing the crystallinity. As a method for controlling the degree of orientation of the carbon fiber to be high, it is often performed to increase the tension of the fiber bundle or set the draw ratio to a high value in each of the manufacturing processes described above. There are many cases. Moreover, as a general method for increasing the crystallinity of the carbon fiber, there is a method for increasing the temperature of the carbonization step, but it is difficult to achieve a balance with the productivity of the carbon fiber. As a method for improving crystallinity without raising the carbonization temperature, there is a technique called catalytic graphitization. By using the catalyst metal, the activation energy of the carbonization reaction is reduced, and even when carbonized at a low temperature, it is possible to form a carbon structure similar to a carbon fiber carbonized at a high temperature.

  Up to now, as a method of obtaining carbon fiber with high elastic modulus using catalytic graphitization, a method of adding catalyst metal powder, salt or complex to spinning solution or carbon fiber precursor fiber made of PAN polymer (patent) Documents 1 and 2) are known. However, when a catalyst metal is added to the surface of the carbon fiber precursor fiber, only the surface of the carbon fiber is highly crystallized, and an improvement in the elastic modulus is not recognized. In addition, when metal powder is added to the spinning solution, it is difficult to disperse uniformly and the strength is significantly reduced. When a metal salt or complex is added, the catalyst metal is eluted in the spinning process. There's a problem.

  As a method for solving this problem, the inventors proposed using a polyacrylonitrile-based polymer containing a salt of a group VIII metal and an organic acid having a vinyl group as a copolymerization component (Japanese Patent Application No. 2012-168130). . However, such a polymer has low stretchability at the time of spinning, and has a problem in improving productivity.

Japanese Patent No. 734856 Japanese Patent No. 826096

  An object of the present invention is to provide a polyacrylonitrile-based polymer that can improve stretchability during spinning while containing a salt having a Group VIII metal as a copolymerization component.

  The present invention for solving this problem has the following configuration. That is, the polyacrylonitrile-based polymer of the present invention is a copolymer of at least acrylonitrile (a) and a salt (b) comprising a Group VIII metal, an organic acid having a vinyl group and an organic acid not having a vinyl group. It is a polyacrylonitrile polymer contained as a component.

  According to a preferred embodiment of the polyacrylonitrile-based polymer of the present invention, the polyacrylonitrile-based polymer further contains a Group VIII metal and a salt (c) of an organic acid having a vinyl group as a copolymerization component.

  According to a preferred aspect of the polyacrylonitrile polymer of the present invention, the Group VIII metal contained in the polyacrylonitrile polymer is at least one metal selected from the group consisting of iron, cobalt, and nickel.

  The carbon fiber precursor fiber of the present invention can be produced by spinning the polyacrylonitrile-based polymer by a wet or dry wet spinning method.

  According to a preferred embodiment of the carbon fiber precursor fiber of the present invention, the content of the Group VIII metal contained in the carbon fiber precursor fiber is relative to the number of moles of all monomers of the polymer constituting the carbon fiber precursor fiber. And 0.1 mol% or more.

  Moreover, the carbon fiber of the present invention comprises a flameproofing step in which the carbon fiber precursor fiber is flameproofed in air at a temperature of 200 to 300 ° C, and a fiber obtained in the flameproofing step is heated to 300 to 800 ° C. A pre-carbonization step of pre-carbonizing in an inert atmosphere at a temperature and a carbonization step of carbonizing the fiber obtained in the pre-carbonization step in an inert atmosphere at a temperature of 1000 to 2000 ° C. it can.

  According to the present invention, at least acrylonitrile (a) and a polyacrylonitrile containing a group (VIII) metal, a salt (b) comprising an organic acid having a vinyl group and an organic acid not having a vinyl group, as a copolymerization component By using the system polymer, it is possible to produce a carbon fiber precursor fiber in which the catalytic metal is uniformly dispersed at a high concentration and capable of causing the catalytic graphitization reaction with high productivity.

  The present inventors have conducted extensive studies to produce a carbon fiber precursor fiber capable of causing catalytic graphitization reaction in which the catalyst metal is dispersed uniformly and at a high concentration. The invention has been reached.

  The polyacrylonitrile copolymer in the present invention (hereinafter sometimes simply referred to as a PAN copolymer) includes at least acrylonitrile (a), a Group VIII metal, an organic acid having a vinyl group, and vinyl. It is a polyacrylonitrile-based polymer containing a salt (b) composed of an organic acid having no group as a copolymerization component.

Although the mechanism for improving the stretchability at the time of producing the carbon fiber precursor fiber when the polyacrylonitrile-based polymer of the present invention is used is not necessarily clarified, the following mechanism is conceivable. A salt of a Group VIII metal and an organic acid having a vinyl group and not having an organic acid having no vinyl group (hereinafter simply referred to as a salt of an organic acid having a Group VIII metal and a vinyl group (c)) Is composed of two organic acid molecules having one group VIII metal atom and a vinyl group. Therefore, a polyacrylonitrile polymer containing a salt of a Group VIII metal and an organic acid having a vinyl group as a copolymerization component produces a crosslinked structure through an ionic bond between the Group VIII metal and an organic acid having a vinyl group. In addition, the drawability at the time of spinning may be lowered. On the other hand, in the polyacrylonitrile-based polymer containing a group (VIII) metal and a salt (b) composed of an organic acid having a vinyl group and an organic acid not having a vinyl group, a group VIII metal and Since it is difficult to generate a cross-linked structure via an ionic bond of an organic acid having a vinyl group, the distance between the polyacrylonitrile polymers can be increased, and the stretchability can be improved.
However, in the polyacrylonitrile-based polymer of the present invention, the above-mentioned Group VIII metal and organic acid salt (c) having a vinyl group may be used as a copolymerization component within the range not impairing the object of the present invention. There is no. In order to suppress a decrease in stretchability, a salt (b) comprising a Group VIII metal and an organic acid having a vinyl group and an organic acid not having a vinyl group in the copolymerization component, a Group VIII metal and a vinyl group It is preferable that the mass ratio ((b) / (c)) of the salt (c) of the organic acid having a ratio of 0.3 or more. More preferably, it is 1 or more. When (b) / (c) is 0.3 or more, the distance between the polyacrylonitrile polymers is easily separated, and when (b) / (c) is 1 or more, the distance is further easily separated. Can be greatly improved.

  The Group VIII metal is preferably at least one metal selected from the group consisting of iron, cobalt, and nickel. Among catalyst metals used for catalytic graphitization, iron, cobalt, and nickel can exhibit a catalytic graphitization effect from a low carbonization temperature, and thus facilitate high crystallization of carbon fibers.

  As the organic acid having a vinyl group used as a copolymerization component of the polyacrylonitrile-based copolymer of the present invention, acrylic acid, methacrylic acid, allyl sulfonic acid, methallyl sulfonic acid, and the like can be used. Examples of organic acids that do not have are saturated fatty acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, hydroxy acids such as lactic acid, malic acid, citric acid, benzoic acid, salicylic acid, gallic acid, etc. Aromatic carboxylic acid or sulfonic acid such as methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, or the like can be used.

  In addition, as other vinyl compounds copolymerizable with acrylonitrile, from the viewpoint of promoting flame resistance, for example, acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof Allyl sulfonic acid, methallyl sulfonic acid and alkali metal salts or alkyl esters thereof can be used.

  As a method for producing the polyacrylonitrile-based polymer of the present invention, a known polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization can be selected, but 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.

  In addition, when the polyacrylonitrile polymer of the present invention is produced by the above-described solution polymerization, if the content of the Group VIII metal is excessively increased, the viscosity may increase and stirring may be difficult. Even in such a case, it is possible to continue the polymerization by reducing the viscosity by adding a compound that becomes a ligand of the Group VIII metal. Known compounds such as acetylacetone can be used as the compound that becomes the ligand of the Group VIII metal. The mechanism by which the viscosity is reduced by adding a Group VIII metal ligand has not been clarified, but the addition of the ligand weakens the interaction between the Group VIII metal and the polyacrylonitrile polymer. It is presumed that the viscosity will decrease.

  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. From the viewpoint of improving the denseness of the obtained carbon fiber precursor fiber, the dry and wet spinning method is more preferable. 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. As the component of the oil agent, for example, an oil agent containing a modified silicone such as amino-modified silicone is preferable from the viewpoint of heat resistance. 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. Finally, the dried and densified yarn is also subjected to pressurized steam stretching.

  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, more preferably 6,000 to 36,000. 000. The fineness of the single fiber is preferably 0.5 to 1.5 dtex.

  The content of the Group VIII metal in the carbon fiber precursor fiber of the present invention is 0.1 mol% or more with respect to the number of moles of all monomers of the polymer constituting the carbon fiber precursor fiber according to the present invention. Preferably there is. The total monomer of the polymer constituting the carbon fiber precursor fiber is an organic acid having acrylonitrile, a Group VIII metal and a vinyl group used as a copolymerization component of the polymer constituting the carbon fiber precursor fiber of the present invention. And a salt (b) composed of an organic acid not having a vinyl group, a salt (c) composed of a Group VIII metal and an organic acid having a vinyl group, and other vinyl compounds copolymerizable with acrylonitrile. is there.

  When the content of the Group VIII metal used in the present invention is less than 0.1 mol% with respect to the number of moles of all monomers of the polymer constituting the carbon fiber precursor fiber, the catalyst graphitizing effect is hardly exhibited. Thus, the effects of the present invention may not be obtained. In addition, when the content of the Group VIII metal is 10 mol% or more with respect to the number of moles of all monomers of the polymer constituting the carbon fiber precursor fiber, molecular breakage due to thermal decomposition at the copolymerized portion becomes remarkable. From this point of view, there is a concern that the tensile strength of the resulting carbon fiber will be significantly reduced, so that the content of the Group VIII metal is 0 with respect to the number of moles of monomers constituting the carbon fiber precursor fiber. More preferably, it is 1-10 mol%. More preferably, it is 0.2-3 mol%.

  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 200 to 300 ° C., preferably with a draw 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 2000 ° 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.

  Carbon fibers produced in this way have high crystallinity by catalytic graphitization without raising the carbonization temperature, and are used in sports applications, aerospace applications, automobiles, civil engineering / architecture, pressure vessels, windmill blades, etc. Carbon fibers suitable for general industrial applications 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.

<Group VIII metal content in carbon fiber precursor fiber and polyacrylonitrile polymer solution>
The Group VIII metal content of the carbon fiber precursor fiber was measured with a fluorescent X-ray analyzer. As the fluorescent X-ray analyzer, a fluorescent X-ray apparatus VENUS200 manufactured by Nippon Philips Co., Ltd. was used. The primary X-ray source was Sc, and the measurement conditions were a reduced pressure and an atmospheric pressure of 4 to 8 Pa, a temperature of 37 ° C., and a measurement time of 25 seconds. The polyacrylonitrile-based polymer and carbon fiber precursor fiber, which are measurement samples, were wound around a Teflon (registered trademark) plate having a length of 30 mm, a width of 30 mm, and a thickness of 2 mm without any gaps. At this time, the carbon fiber precursor fiber was sampled to a length of 60 cm.

  From the fluorescence X-ray intensity of the Group VIII metal of the obtained carbon fiber precursor fiber, the content of the Group VIII metal was determined for each using a calibration curve. Further, the Group VIII metal content in the polyacrylonitrile-based polymer solution was obtained by calculation from the number of moles of the added Group VIII metal and the number of moles of monomers constituting the polyacrylonitrile-based polymer.

<Measurement of pressure steam drawing limit magnification of carbon fiber precursor fiber>
The speed before stretched with steam is increased to 30 m / min, the speed on the take-up side is increased from 60 m / min to a speed of about 2 m / sec, the speed on the take-up side when the yarn is broken is read, and this speed is The value divided by the speed was determined as the stretching limit magnification. Further, the test was performed while changing the supplied steam pressure by 0.05 GPa, the peak value of the stretch limit magnification was determined, and the stretchability was evaluated using the value. Measurement was performed at n = 2, and the average value was used.
(Examples 1 to 5, Comparative Examples 1 and 2)
A copolymer component composed of acrylonitrile and the copolymer composition shown in Table 1 (the rest is acrylonitrile) is radically polymerized using azobisisobutyronitrile as an initiator by a solution polymerization method using dimethyl sulfoxide as a solvent. A solution of a mass% polyacrylonitrile-based polymer was obtained. The cobalt acrylate shown in the copolymerization component column of Table 1 refers to a salt composed of acrylic acid and cobalt, and acrylic acid / cobalt acetate refers to a salt composed of acrylic acid, acetic acid and cobalt. When the viscosity increased during the polymerization and stirring became difficult, acetylacetone was added to lower the viscosity and the polymerization was continued.
The obtained polyacrylonitrile-based polymer solution was discharged into the air once at a temperature of 40 ° C. using a spinneret having a single hole diameter of 0.15 mm and a hole number of 6000, and passed through a space of about 2 mm. A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath composed of an aqueous solution of 40% by mass dimethyl sulfoxide controlled at a temperature of 10 ° 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 an amino-modified silicone silicone oil was added to obtain a stretched yarn in the bath. This stretched yarn in the bath was subjected to a drying heat treatment using a roller heated to a temperature of 180 ° C., and then the pressure water vapor stretching limit magnification was measured.
In any of the examples, the limit ratio of stretched steam with water vapor was higher than that of the comparative example, and it was confirmed that the stretchability was improved.

Claims (6)

A polyacrylonitrile-based polymer containing at least acrylonitrile (a) and a salt (b) comprising a Group VIII metal, an organic acid having a vinyl group and an organic acid not having a vinyl group as a copolymerization component. Furthermore, the polyacrylonitrile-type polymer of Claim 1 which contains the salt (c) of the organic acid which has a Group VIII metal and a vinyl group as a copolymerization component. The polyacrylonitrile-based polymer according to claim 1 or 2, wherein the Group VIII metal is at least one metal selected from the group consisting of iron, cobalt, and nickel. The manufacturing method of the carbon fiber precursor fiber which spins the polyacrylonitrile-type polymer in any one of Claims 1-3 by the wet or dry wet spinning method. The carbon fiber precursor fiber obtained by the method according to claim 4, wherein the content of the Group VIII metal is 0 with respect to the number of moles of all monomers of the polymer constituting the carbon fiber precursor fiber. The carbon fiber precursor fiber which is 1 mol% or more. A flameproofing step of flameproofing the carbon fiber precursor fiber produced by the method according to claim 4 or the carbon fiber precursor fiber according to claim 5 in air at a temperature of 200 to 300 ° C, and A preliminary carbonization step of precarbonizing the fiber obtained in the flameproofing step in an inert atmosphere at a temperature of 300 to 800 ° C, and an inert atmosphere of the fiber obtained in the preliminary carbonization step at a temperature of 1000 to 2000 ° C The manufacturing method of the carbon fiber which obtains carbon fiber through the carbonization process which carbonizes inside sequentially.