JP2015183166A - Acrylonitrile-based copolymer, acrylonitrile-based carbon fiber precursor fiber and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of improving a carbonization yield without damaging productivity and process properties in a carbon fiber production process.SOLUTION: Provided is an acrylonitrile-based copolymer in which the copolymerization ratio of acrylonitrile is 95 to 99.5 mol% or higher, and the copolymerization ratio of styrene is 0.5 to 1.5 mol%. Also provided is a method for producing a polyacrylonitrile-based carbon fiber precursor fiber comprising: a spinning step where the copolymer is spun by a wet spinning method or a dry-wet typ spinning method; a dry heat treatment step where the fiber obtained in the spinning step is subjected to dry heat treatment; and a drawing step where the fiber obtained by the dry heat treatment step is drawn. Also provided is a method for producing carbon fiber comprising: a flame-resistance imparting step where the polyacrylonitrile-based carbon fiber precursor fiber is imparted with flame resistance in the air at 200 to 300°C; a pre-carbonization step where teh fiber obtained in the flame-resistance imparting step is carbonized in an inert atmosphere heated at 900 to 3,000°C.

Description

  The present invention relates to a method for efficiently producing carbon fibers without reducing the carbonization yield.

  Carbon fiber is increasingly used as a reinforced fiber for composite materials due to increasing environmental problems, and its use is expanding in various fields. 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 at 200 to 300 ° C., under an inert atmosphere at 300 to 3000 ° C. It is manufactured industrially through a carbonization step that is carbonized in the process.

  When the flame-resistant fiber of the carbon fiber precursor is carbonized, nitrogen atoms, oxygen atoms, hydrogen atoms and some of the carbon atoms contained in the flame-resistant fiber are thermally decomposed and discharged as a large amount of gas components. The yield obtained is about 50% with respect to the polyacrylonitrile fiber. Since a low carbonization yield greatly affects the production cost of carbon fiber, it is important to improve the carbonization yield.

  Several methods have been proposed as methods for improving the carbonization yield. Patent Documents 1 to 5 propose a method of improving the carbonization yield by heat-treating the flame-resistant fiber at a relatively low temperature of about 400 ° C. in an inert atmosphere. In this method, carbon fibers having a high carbonization yield can be obtained continuously in the carbon fiber production process, but equipment for performing the heat treatment is newly required, and the equipment cost is increased.

  Patent Documents 6 to 9 propose methods for increasing the carbonization yield by chemical action. In this method, polyacrylonitrile fibers are treated with chemicals such as gases (sulfur compounds and iodine) and oxidizing agents that are not used in the normal carbon fiber manufacturing process, so the treatment is performed in a sealed reaction vessel. There have been problems as industrially applied technologies, such as the inability to perform continuous treatment and the need for new equipment for treating exhaust gas and waste.

JP 51-75124 A JP 58-174630 A JP 58-214535 A JP 2012-117161 A JP 2013-23801 A JP 58-109625 A JP 2002-160912 A JP 2001-2448025 A JP 2005-113305 A

  An object of the present invention is to provide a method for improving carbonization yield without impairing productivity and processability in a carbon fiber production process.

  In order to achieve the above object, the polyacrylonitrile copolymer used in the present invention comprises an acrylonitrile copolymer having an acrylonitrile copolymer ratio of 95 to 99.5 mol% and a styrene copolymer ratio of 0.5 to 1.5 mol%. It is a polymer.

  In the present invention, a method for producing a polyacrylonitrile-based carbon fiber precursor fiber from an acrylonitrile-based copolymer includes a spinning process in which spinning is performed by discharging from a spinneret by a wet spinning method or a dry-wet spinning method, and the spinning step. It is characterized by comprising a drying heat treatment step for drying and heat treating the obtained fiber, and a step for stretching the fiber obtained in the drying heat treatment step.

  Furthermore, in the present invention, a method for producing carbon fiber from a polyacrylonitrile-based carbon fiber precursor fiber includes a flameproofing step in which flameproofing is performed in air at 200 to 300 ° C., and a fiber obtained in the flameproofing step. A pre-carbonization step of pre-carbonizing in an inert atmosphere of ˜900 ° C., and a carbonization step of carbonizing the fiber obtained in the pre-carbonization step in an inert atmosphere of 900-3,000 ° C. And

  By using the present invention, the carbonization yield can be improved without impairing the productivity and processability in the carbon fiber production process.

  The present inventors have found that the carbon fiber carbonization yield can be achieved by copolymerizing a specific amount of styrene with acrylonitrile in order to improve the carbonization yield without impairing productivity and processability. Reached.

  That is, the feature of the present invention is that the range of styrene copolymerized with acrylonitrile is 0.5 to 1.5 mol%, preferably 0.7 to 1.3 mol%. When the copolymerization ratio of styrene is less than 0.5 mol%, the effect of improving the carbon fiber carbonization yield is reduced. When the copolymerization ratio is more than 1.5 mol%, the copolymerized styrene itself is thermally decomposed and carbonized. On the contrary, the yield decreases.

  Moreover, in this invention, the copolymerization ratio of acrylonitrile in an acrylonitrile copolymer is 95-99.5 mol%, and 97 mol% or more is preferable. If it is less than 95 mol%, yarn breakage tends to occur in the spinning process, and single fibers easily adhere to each other in the flameproofing process.

  The acrylonitrile-based copolymer in the present invention may be copolymerized with a copolymer component other than styrene for the purpose of improving yarn production and promoting flame resistance, and is a flame resistance promoting component copolymerized for the purpose of promoting flame resistance. Specific examples include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide. Further, for the purpose of preventing adhesion between single fibers, 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 in the flameproofing promoting component is more preferably two or more than one, and from that viewpoint, as the flameproofing promoting component that is a copolymer component, Acrylic acid, methacrylic acid, 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.

  The acrylonitrile-based copolymer in the present invention can be obtained by a known polymerization method such as solution polymerization, suspension polymerization, and emulsion polymerization, but for the purpose of improving the stability during yarn drawing and stretching, solution polymerization is used. Is preferred. In solution polymerization, it is not necessary to isolate the acrylonitrile copolymer from the start to the end of polymerization, or until the spinning solution becomes a spinning solution, and the acrylonitrile copolymer in the solvent in the state of the acrylonitrile copolymer solution. Since the entangled state of the molecular chain of the coalescence becomes uniform, it is preferable compared to other polymerization methods.

  The acrylonitrile-based copolymer in the present invention can be obtained by a known polymerization method such as radical polymerization or anionic polymerization, but radical polymerization is preferably used from an industrial viewpoint.

  The solvent used in the acrylonitrile-based copolymer solution of the present invention is not particularly limited as long as it can dissolve the acrylonitrile-based copolymer, but dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and the like can be preferably exemplified. Among these, dimethyl sulfoxide is more preferably used from the viewpoint of solubility. When using solution polymerization, it is preferable that the solvent used for polymerization and the solvent used for spinning be the same, because the step of separating and re-dissolving the obtained acrylonitrile copolymer is unnecessary.

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

  In the present invention, the polyacrylonitrile-based carbon fiber precursor fiber is subjected to a spinning process in which the acrylonitrile-based copolymer solution of the present invention is spun by spinning from a spinneret by a wet spinning method or a dry-wet spinning method. The fiber obtained in the spinning process can be manufactured by performing a dry heat treatment process in which the fiber obtained in the dry heat treatment process is subjected to a dry heat treatment process and then drawing the fiber obtained in the dry heat treatment process.

  The spinning solution is discharged from the spinneret by a wet spinning method or a dry-wet spinning method, introduced into a coagulation bath, and solidified to form a polyacrylonitrile-based carbon fiber precursor fiber. For the purpose of improving the denseness of the resulting polyacrylonitrile-based carbon fiber precursor fiber and enhancing the mechanical properties of the resulting carbon fiber, the spinning dope is more effective than the wet spinning method in which the spinning dope is directly discharged into a coagulation bath. It is more preferable to use a dry-wet spinning method that is once discharged into the air and then introduced into the coagulation bath.

  In the present invention, the coagulation bath used in the spinning step preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning dope and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the acrylonitrile copolymer 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.

  After a fiber bundle consisting of a large number of filaments spun from the spinneret is introduced into a coagulation bath to coagulate each filament, an in-bath drawing process, a water washing process, an oil agent application process, a drying heat treatment process, and a drawing process Through this, a polyacrylonitrile-based precursor fiber for carbon fiber production is obtained.

  However, the fiber bundle derived from the coagulation bath may be directly introduced into the in-bath drawing step by omitting the washing step, or may be introduced into the in-bath drawing step after removing the solvent in the washing step. . Such stretching in the bath is usually preferably performed in one or more stretching baths maintained at a temperature of 30 to 98 ° C. The draw ratio is preferably 2 to 6 times.

  For the purpose of preventing adhesion between single fibers after the stretching step in the bath, it is preferable to apply an oil agent made of silicone or the like to the fiber bundle. As such a silicone oil agent, it is preferable to use a modified silicone. As the silicone oil agent, an oil agent containing amino-modified silicone having high heat resistance can be used.

  The temperature of the drying heat treatment is preferably 100 to 200 ° C., and the stretching after the drying heat treatment is performed by stretching the fiber bundle 2 to 6 times in a pressurized steam. In the present invention, the single fiber fineness of the polyacrylonitrile-based carbon fiber precursor fiber is preferably 0.5 to 1.5 dtex. If the single fiber fineness is less than 0.5 dtex, the operability may be reduced due to a decrease in spinnability in the spinning process, or the productivity per number of discharge holes may be reduced, leading to a significant increase in cost. On the other hand, when the single fiber fineness exceeds 1.5 dtex, the difference between the inner and outer structures of each filament forming the obtained flame-resistant fiber bundle becomes remarkable, and the tensile strength and strand tensile elastic modulus of the obtained carbon fiber decrease. There is.

  The number of filaments forming the polyacrylonitrile-based carbon fiber precursor fiber bundle is preferably 1,000 to 3,000,000, more preferably 6,000 to 3,000,000, and still more preferably 12,000 to 2. 500,000, most preferably 24,000 to 2,000,000. 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 carbon fiber precursor fiber bundle is uniformly flameproofed. There are things that cannot be done.

Next, the manufacturing method of the carbon fiber of this invention is demonstrated. In the present invention, the polyacrylonitrile-based carbon fiber precursor fiber is subjected to a flameproofing process for flameproofing in air at 200 to 300 ° C, and the fiber obtained in the flameproofing process is subjected to an inert atmosphere at a temperature of 300 to 900 ° C. It can manufacture by performing the pre-carbonization process which pre-carbonizes in, and passing through the carbonization process which carbonizes the fiber obtained at the pre-carbonization process in 900-3000 degreeC inert atmosphere.
The preliminary carbonization step and the carbonization step are performed in an inert atmosphere, and examples of the inert gas used include nitrogen, argon, and xenon. Nitrogen is preferably used from an economical viewpoint.

  The obtained carbon fiber may be subjected to electrolytic treatment in order to modify its surface. Examples of the electrolytic solution used for the electrolytic treatment include acidic solutions such as sulfuric acid, nitric acid and hydrochloric acid, and aqueous solutions of alkalis or salts thereof such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate. Can be used. The amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the applied carbon fiber.

  By such electrolytic treatment, in the obtained composite material, the adhesion between the carbon fiber and the matrix resin can be optimized, the brittle breakage of the composite material due to too strong adhesion, the problem that the tensile strength in the fiber direction decreases, Although the tensile strength in the fiber direction is high, the problem that the adhesive property with the resin is inferior and the strength property in the non-fiber direction is not solved is solved, and in the resulting composite material, both the fiber direction and the non-fiber direction are solved. A balanced strength characteristic is 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.

<Measurement method of carbonization yield>
The carbonization yield was obtained from the following formula (1) using the stretch ratio of the firing step from the total fineness of the carbon fiber precursor fiber bundle and the total fineness of the carbon fiber bundle.
Carbonization yield (%) = (total fineness of carbon fiber bundle) / (total fineness of carbon fiber precursor fiber bundle × stretch ratio of flameproofing process × stretch ratio of preliminary carbonization process × stretch ratio of carbonization process) × 100 · ..Formula (1)

(Reference example)
Itaconic acid 0.5 mol% was added to 99.5 mol% of acrylonitrile as a flameproofing promoting component, and polymerization was carried out by a solution polymerization method in a nitrogen atmosphere using dimethylsulfoxide as a solvent to obtain an acrylonitrile copolymer solution.

  The spinning dope was discharged into the air once using a spinneret with a hole number of 3,000, passed through a space of about 4 mm, and then introduced into a coagulation bath consisting of an aqueous solution of 35% dimethyl sulfoxide controlled at 3 ° C. Coagulated yarn was obtained by the dry and wet spinning method. After the coagulated yarn was washed with water, it was stretched 3 times using a warm water tank to obtain a water bath stretched yarn. Further, after applying an amino-modified silicone-based silicone oil, a dry densification treatment was performed on the water bath drawn yarn using a 160 ° C. heating roller. The dried densified yarn is stretched 5 times in pressurized steam to obtain a yarn drawing total draw ratio of 13 times, a single fiber fineness of 1.1 dtex, and a single fiber of 3,000 acrylonitrile copolymer fibers. It was.

  Next, the obtained acrylic fiber was flameproofed in air with a temperature gradient of 220 to 270 ° C. to obtain a flameproof fiber bundle. The obtained flame-resistant fiber bundle was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300 to 900 ° C. to obtain a pre-carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized at a maximum temperature of 1500 ° C. in a nitrogen atmosphere. The total draw ratio during firing was 0.95. Subsequently, an electrolytic surface treatment was performed using a dilute sulfuric acid aqueous solution as an electrolytic solution, and after drying, a sizing agent was applied to obtain carbon fibers.

  The carbonization yield of the obtained carbon fiber was measured and found to be 49.8%. The results are shown in Table 1.

Example 1
Carbon fibers were produced in the same manner as in the Reference Example except that 98.5 mol% of acrylonitrile (AN) and 1.0 mol% of styrene (ST) were used as the acrylonitrile-based copolymer raw material. The carbonization yield of the obtained carbon fiber was measured and found to be 54.6%. The results are shown in Table 1.

(Example 2)
Carbon fibers were produced in the same manner as in the Reference Example, except that AN 98.8 mol% and ST 0.7 mol% were used as the acrylonitrile copolymer raw material. The carbonization yield of the obtained carbon fiber was measured and found to be 53.8%. The results are shown in Table 1.

(Example 3)
Carbon fibers were produced in the same manner as in the Reference Example except that AN 98.0 mol% and ST 1.5 mol% were used as acrylonitrile-based copolymer raw materials. The carbonization yield of the obtained carbon fiber was measured and found to be 53.1%. The results are shown in Table 1.

(Comparative Example 1)
A carbon fiber was produced in the same manner as in the Reference Example, except that AN 97.8 mol% and ST 1.7 mol% were used as the acrylonitrile copolymer raw material. When the carbonization yield of the obtained carbon fiber was measured, it was 49.6%, and the carbonization yield was not improved. The results are shown in Table 1.

(Comparative Example 2)
Carbon fibers were produced in the same manner as in the Reference Example, except that AN 99.2 mol% and ST 0.3 mol% were used as the acrylonitrile copolymer raw material. When the carbonization yield of the obtained carbon fiber was measured, it was 49.6%, and the carbonization yield was not improved. The results are shown in Table 1.

(Comparative Example 3)
Carbon fibers were produced in the same manner as in the Reference Example, except that AN 97.5 mol% and ST 2.0 mol% were used as the acrylonitrile copolymer raw material. When the carbonization yield of the obtained carbon fiber was measured, it was 47.8%, and the carbonization yield was lowered. The results are shown in Table 1.

(Comparative Example 4)
Carbon fibers were produced in the same manner as in the Reference Example except that AN 95.5 mol% and ST 4.0 mol% were used as the acrylonitrile copolymer raw material. When the carbonization yield of the obtained carbon fiber was measured, it was 42.7%, and the carbonization yield was greatly reduced. The results are shown in Table 1.

Claims (3)

An acrylonitrile copolymer having a copolymerization ratio of acrylonitrile of 95 to 99.5 mol% and a copolymerization ratio of styrene of 0.5 to 1.5 mol%. A spinning step of spinning the acrylonitrile-based copolymer according to claim 1 by a wet spinning method or a dry-wet spinning method, a drying heat treatment step of drying and heat-treating fibers obtained in the spinning step, and a drying heat treatment step. A method for producing a polyacrylonitrile-based carbon fiber precursor fiber comprising a drawing step of drawing the obtained fiber. A flameproofing step for flameproofing the polyacrylonitrile-based carbon fiber precursor fiber according to claim 2 in air at 200 to 300 ° C, and an inert atmosphere at 300 to 900 ° C for the fiber obtained in the flameproofing step The carbon fiber manufacturing method provided with the pre-carbonization process which pre-carbonizes inside, and the carbonization process which carbonizes the fiber obtained by this pre-carbonization process in 900-3,000 degreeC inert atmosphere.