JP2002004175A - Pan based precursor for carbon fiber and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PAN based precursor for a graphite fiber having an excellent adhesion with a matrix resin and a high compression strength at 0 deg. (flexural strength practically) by suppressing crystallization of the surface, and to provide a method of manufacturing it. SOLUTION: This PAN based precursor for carbon fiber includes sugars as a character. This method of manufacturing the PAN based precursor for carbon fiber imparts sugars to a water swollen fiber and then dries and densifies in manufacturing the precursor for carbon fiber by wet spinning or dry/wet spinning a PAN based copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PAN system for providing a graphitized fiber which has excellent adhesion to a matrix resin and high bending strength (related to 0 ° compression strength) which is a practical property of a composite. The present invention relates to a precursor and a method for manufacturing the precursor.

[0002]

2. Description of the Related Art Carbon fibers have been developed for various uses by taking advantage of their high specific strength and high specific elastic modulus.
In particular, carbon fibers starting from a PAN (polyacrylonitrile, hereinafter simply referred to as PAN) -based precursor are widely used because of their high specific strength and excellent workability. Carbon fibers are generally used as a composite material having a thermosetting resin or a thermoplastic resin as a matrix. In order to effectively utilize the strength and elastic modulus of the carbon fiber in the composite material, it is necessary that the carbon fiber and the matrix resin are firmly bonded. To this end, it is common to apply an oxidation treatment as a finish of the carbon fiber manufacturing process to impart a functional group to the carbon fiber surface. However,
When the carbonization temperature is increased to increase the elastic modulus, a phenomenon that the adhesion between the carbon fiber and the resin deteriorates is recognized. This is because, as the carbonization (graphitization) temperature is increased, the graphite structure of the carbon fiber is less likely to be oxidized because it approaches a perfect crystal, and therefore it is difficult to provide a sufficient functional group for bonding with the resin. Presumed. For this reason, a carbon fiber having a higher elastic modulus requires a stronger oxidation treatment, but there has been a problem that a sufficient adhesive force with a resin cannot be obtained by the oxidation treatment alone. There is also a problem that the 0 ° compressive strength decreases as the carbonization (graphitization) temperature is increased and the elastic modulus is increased.

[0003] The crystallinity of the carbon fiber is not always uniform in the radial direction of the cross section of the single fiber.
The surface layer portion is often higher, and there has been a problem that a decrease in strength due to defects on the fiber surface is further promoted. This is presumed to be due to the fact that oxygen diffuses from the fiber surface in the step of making the precursor flame-resistant in heated air, so that the surface layer has a higher degree of perfection as a flame-resistant structure.

[0004] As a means for solving the above problems, reducing the crystallinity of the surface of the fiber contributing to the adhesion to the matrix resin, facilitating the oxidation treatment, and improving the strength of the carbon fiber, the fiber of the PAN-based precursor is used. It has been proposed that a flame retardant element such as boron be present in the surface layer (JP-A-10-8843).

[0005] However, elements such as boron have a high carbonization temperature and exhibit a catalytic action to promote graphitization in a graphitized region of 2000 ° C. or higher. Was higher.

[0006]

SUMMARY OF THE INVENTION In view of the background of the prior art, the present invention suppresses the crystallinity of the surface layer, has good adhesion to the matrix resin, and has a 0 ° compressive strength (as a practical characteristic). Is to provide a PAN-based precursor for carbon fiber and a method for producing the same to provide a graphitized fiber having high bending strength.

[0007]

The present invention employs the following means in order to solve the above-mentioned problems. That is,
The PAN precursor for carbon fiber of the present invention is characterized by containing a saccharide.

The method for producing a PAN-based precursor for carbon fiber of the present invention is characterized in that the PAN-based copolymer is wet-spun and dry-wet-spun to produce a precursor for carbon fiber.
The method is characterized in that after the swelling is given to the water-swelled fiber, the fiber is dried and densified.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies from the above-mentioned viewpoints. The PAN-based precursor contained saccharides in the surface layer thereof and was calcined. As a result, the graphite structure of the surface layer of the carbon fiber was obtained. It has been found that the amorphous portion can be increased, the average crystallinity of the surface layer portion can be suppressed, and the above problem can be solved at once.

[0010] The PAN precursor for carbon fiber of the present invention contains a saccharide at least on its surface. As such a saccharide, for example, arabinose, xylose, glucose, fructose, mannose, galactose, sucrose, lactose, maltose, raffinose, starch, cellulose and its water-soluble cellulose, glycogen and the like are preferably used.

The appropriate content of the saccharide varies depending on the saccharide used, and is therefore difficult to say, but is generally about 0.5 to 10% by weight, more preferably about 0.5 to 5% by weight per fiber weight. It is good. 0.5% by weight
If it is less than 1, the effect of suppressing the crystallinity of the surface layer portion is insufficient, and 1
If it exceeds 0% by weight, the average crystallinity is greatly reduced,
The decrease in the elastic modulus of the carbon fiber is undesirably large.

In order to more effectively exert the effect of containing such saccharides, it is more preferable that the saccharides are contained mainly in the surface layer in the cross-sectional radial direction.

The method for producing a PAN-based precursor for carbon fiber according to the present invention is characterized in that when a PAN-based copolymer is produced by spinning a PAN-based copolymer by a wet or dry-wet method, the water-swelling degree fiber before drying and densification is produced. It is important to provide a water-soluble saccharide to the mixture and then dry-densify it.

As a method for spinning the PAN polymer, either a wet method or a dry-wet method is used. In order to include the saccharide in the surface layer of the fiber, it is preferable to add the saccharide to the water-swelled fiber having a degree of swelling of 50 to 300% before dry densification. If the degree of swelling is less than 50%, saccharides hardly penetrate from the surface layer of the fiber, and if it exceeds 300%, it penetrates into the inner layer of the fiber, which is not preferable.
Even though the degree of swelling is the same, the diameter and number of voids are different, so the degree of swelling is not particularly limited.

Further, as such saccharides, water-soluble saccharides are preferably used. That is, a water-insoluble substance is not preferable because it is difficult to impregnate the fiber surface layer. In addition, the saccharides contained in the precursor are preferably baked in a conventional manner, converted into carbon fibers, remain as carbides, form even a small amount of graphite crystal structure, and are preferably involved in the orientation thereof. Preferably, the carbonization residual ratio is at least 5% or more. From such a viewpoint, among sugars, water-soluble cellulose, for example, starch, glycogen, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose and the like are particularly preferably used.

The method for producing the PAN precursor for carbon fiber of the present invention will be described in more detail.

The PAN copolymer composition is not particularly limited, but preferably contains acrylonitrile preferably at least 90% by weight, more preferably at least 95% by weight.

The solvent for the copolymer is not particularly restricted but includes, for example, inorganic salts such as zinc chloride and sodium thiocyanate, and organic solvents such as dimethylsulfoxide, dimethylformamide, dimethylacetamide and N-methylpyrrolidone. A system can be used.

The spinning dope obtained by dissolving the copolymer in a solvent is spun into fibers by wet or dry-wet spinning according to a conventional method. Next, after water-washing, bath stretching, or water-washing after bath stretching is performed to obtain a water-swelled fiber having a degree of swelling of 50 to 300%. Factors that determine the degree of swelling include the hydrophilicity of the copolymer, the concentration of the spinning dope, the type of solvent, the solvent concentration of the coagulation bath, the coagulation bath temperature, the bath stretching temperature, and the bath stretching ratio. The degree of swelling of the fiber is 5 as long as it is not damaged.
These factors are set appropriately so as to be 0 to 300%.

Next, an aqueous solution of a saccharide is applied to the swollen fibers. The application method is not particularly limited. For example, a dipping method, a spraying method, a touch roll method, a guide supply method and the like are employed, but a dipping method which is easy to process is preferably used. The concentration of the processing solution is such that the final precursor preferably contains 0.5 to 10% by weight of saccharide, more preferably 0.5 to 5% by weight.
It is set so as to contain the weight%. Also, at the same time as sugars,
An oil agent for preventing adhesion between single fibers can be provided. Alternatively, after providing the saccharide, an oil agent for preventing adhesion between the single fibers can be provided. The oil agent for preventing the adhesion between the single fibers is not particularly limited, but a silicone compound modified with various functional groups is preferably used.

The swelled fiber to which the saccharide is added is then dried and densified according to a conventional method.
0 ° C. is preferred. If the drying temperature is lower than 130 ° C., the evaporation of water is slow, the saccharides diffuse to the inner layer of the single fiber, and the elasticity of the fiber as a whole decreases, which is not preferable from the viewpoint of the effect of the present invention. On the other hand, if the drying temperature is higher than 200 ° C., the adhesion between the single fibers tends to occur, which is not preferable.

After drying and densification, if necessary, the film is stretched in a heating medium such as pressurized steam to adjust the orientation. If necessary, a heat treatment at 130 to 200 ° C. is performed. Provided as a precursor for fibers.

The production of carbon fiber from the PAN precursor for carbon fiber of the present invention is not particularly limited, and it is carried out in accordance with a conventional method by flame resistance, carbonization and, if necessary, further graphitization at a higher temperature. , A surface electrolytic treatment is performed, and a surface treating agent is further applied to obtain a desired carbon fiber.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. <Measurement of strand strength and elastic modulus> After impregnating a carbon fiber bundle with a resin having the following composition and curing it at 130 ° C. for 35 minutes,
A tensile test was performed according to JIS R-7601.

* Resin composition ・ Epoxy resin ERL-4221 100 parts (manufactured by Union Carbide Co.) ・ Boron trifluoride monoethylamine (BF3 ・ MEA) 3 parts ・ Acetone 4 parts <Mold method composite ILSS (interlaminar shear strength) Measurement of bending strength> The carbon fiber wound around the metal frame was put into a concave mold having a groove width of 6 mm for engaging and recessing so that the volume content (Vf) of the carbon fiber became 60%, and the resin was poured. Then, heat and vacuum degas. After defoaming, set it on a press, engage a 2.5 mm-thick spacer, engage the concave and convex molds, and heat while pressing to cure the resin, and form a 6 mm wide, 2.5 mm thick test specimen. create. The measurement is converted to Vf = 60% using an Instron tester.

Resin: Ep828 (manufactured by Petrochemicals Co., Ltd.) 100 parts Boron trifluoride monoethylamine 3 parts Molding conditions: Demolding: molding under vacuum (10 mmHg or less) at 80 ° C. for 4 hours; pressing pressure of 4.9 MPa; 170 ° C x 1 hour After cure; After removing the test piece from the mold, 1
70 ° C. × 2 hours Measurement: ILSS: Cut the length of the test piece to 18 mm, measure n = 6 using a three-point bending jig with the supporting span being four times the thickness of the test piece, and determine the average value.

Bending strength: The length of the test piece was cut to 90 mm, and the supporting span was set to 24 by using a three-point bending jig.
Measure n = 5 as a factor and determine the average value. (Example 1) Ammonia gas was blown into a 20 wt% DMSO solution of a copolymer having an intrinsic viscosity of 1.7 and a copolymer composition of acrylonitrile 99.0 wt% and itaconic acid 1.0 wt% to adjust the pH to 8.0. This was used as a spinning solution. The spinning stock solution was passed through a 3000-hole die to a DMSO concentration of 6
0 wt%, guided into an aqueous coagulation bath at a temperature of 60 ° C, 10 m /
Withdrawn at a speed of minutes.

Then, after washing in a 6-stage hot water bath at 55 to 75 ° C. while maintaining a total draw ratio of 1.15 times,
The film was stretched 3.91 times in a hot water bath to obtain a water-swelled fiber having a swelling degree of 200%.

Next, as the saccharide, methylcellulose having an aqueous solution having a concentration of 2 wt% and having a viscosity of 25 cP at 20 ° C. is used. The aqueous swelling fiber is dipped while maintaining the aqueous solution at 45 ° C. After removing the adhering liquid, the mixture was passed through a water-dispersed solution of amino-modified silicone having an oil viscosity of 3000 cSt, then passed again through a nip roll, and dried and densified by a heating roller having a surface temperature of 150 ° C.

Then, in a steam pressurized at 145 ° C.
After stretching 89 times, the sheet was dried and heat-treated with a heating roller having a surface temperature of 170 ° C. to wind a precursor having a single fiber fineness of 0.8 dtex.

The precursor was heated at 245 ° C. and then at 255
The fiber was passed through heated air at a drawing temperature of 1.0 ° C. at a draw ratio of 1.0, and heated until the fiber specific gravity reached 1.34 to obtain an oxidized fiber.

Next, the maximum temperature is 750 ° C. in a nitrogen atmosphere.
Through a carbonization furnace having a maximum temperature of 1700 ° C. in a nitrogen atmosphere at a stretching ratio of 0.97, and then a graphitization furnace having a maximum temperature of 2300 ° C. in a nitrogen atmosphere. The fiber was passed at a draw ratio of 1.03 to obtain a graphitized fiber.

Next, a surface electrolytic treatment of 40 coulomb / g was performed using dilute sulfuric acid as an electrolytic solution, washed with water and dried to obtain a graphitized fiber.

The strength and elastic modulus of the resin-impregnated strand were evaluated to be 4.55 GPa and 410 GPa, respectively. Also, as a result of measuring ILSS (interlaminar shear strength) and bending strength of the mold method composite, each was 72.1MP.
a, which was as high as 1840 MPa. (Comparative Example 1) Graphitized fibers were obtained in the same manner as in Example 1 except that no saccharide was added. As a result of evaluating the strength and elastic modulus of the resin-impregnated strand, 4.55 GPa and 415 GPa were obtained, respectively.
GPa. Also, mold method composite ILSS
As a result of measuring (interlayer shear strength) and bending strength, they were 65.3 MPa and 1680 MPa, respectively. (Example 2) As a saccharide, an aqueous solution having a concentration of 2 wt%
Graphitized fibers were obtained in the same manner as in Example 1 except that hydroxyethyl cellulose having a viscosity of 200 cP at 20 ° C. was used, and the aqueous swelling fibers were dipped while maintaining the aqueous solution at 80 ° C. As a result of evaluating the strength and elastic modulus of the resin-impregnated strand, 4.52 GPa and 413 GP respectively were obtained.
a. In addition, as a result of measuring the ILSS (interlaminar shear strength) and the bending strength of the mold method composite, each was 7
It was as high as 2.5 MPa and 1860 MPa. (Example 3) Glycogen is used as a saccharide and its 2w
Graphitized fibers were obtained in the same manner as in Example 1 except that the water-swelled fibers were dipped while maintaining the t% aqueous solution at 80 ° C. As a result of evaluating the strength and elastic modulus of the resin-impregnated strand, they were 4.45 GPa and 410 GPa, respectively.
Also, as a result of measuring ILSS (interlaminar shear strength) and bending strength of the mold method composite, each was 71.5MP.
a, which was as high as 1820 MPa

[0035]

According to the present invention, it is possible to stably provide a graphitized fiber having excellent adhesion to a resin and excellent bending strength of a composite.

Continued on the front page F-term (reference) 4L033 AA05 AB01 AC15 CA02 CA05 4L035 BB03 BB04 BB06 BB11 BB15 BB17 BB59 BB60 BB66 BB69 BB80 BB82 BB85 BB89 BB91 DD13 FF01 HH10 MB04 4L037 AT02 CS03 PA04 PF31 PF91 PF91 PS10 PS17

Claims (3)

[Claims] 1. A PAN precursor for carbon fiber, wherein the PAN precursor for carbon fiber contains a saccharide at least on the surface. 2. A PAN for carbon fiber, wherein a PAN copolymer is wet-dried and dry-wet-spun to produce a precursor for carbon fiber, wherein saccharides are imparted to water-swelled fiber and then dried and densified. Manufacturing method of precursor. 3. The method for producing a PAN precursor for carbon fibers according to claim 2, wherein said saccharide is a water-soluble saccharide.