JP2002194626A - Carbon fiber, carbon fiber-reinforced composite material, and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber which has a high tensile strength and a high compression strength and can be produced in an excellent cost performance. SOLUTION: This carbon fiber having a tortional modulus of elasticity of >=17 GPa can be produced at an excellent cost performance by controlling a total time required for a flame-resisting treatment process to 70 to 120 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon fiber having both excellent tensile strength and compressive strength and excellent cost performance, and a method for producing the same.

[0002]

2. Description of the Related Art Since carbon fibers are lightweight and have excellent mechanical properties such as high specific strength and specific elastic modulus as compared with other fibers, they are used as a reinforcing material when producing a composite material together with a resin or the like. It is widely used industrially. The superiority of the carbon fiber reinforced composite material obtained in this way has been increasing more and more in recent years, and particularly in sports and aerospace applications, there is a demand for higher performance of carbon fiber and carbon fiber reinforced composite material.

[0003] In order to achieve such high performance, there has conventionally been a demand for improvement in tensile properties, and the tensile strength of carbon fibers has been greatly improved in recent years in response to the demand. However, since the compressive strength has hardly been improved, practical characteristics such as bending strength sometimes peaked out due to the compressive strength.

For example, JP-A-58-214527 and JP-A-61-225330 disclose a method of subjecting a carbon fiber to a post-treatment such as a gas phase treatment, a liquid phase treatment, and an electrolytic oxidation treatment. There has been proposed a method of forcibly removing surface defects by etching a portion.

However, according to these methods, although the tensile strength of the obtained carbon fiber is improved, it is thought that the improvement of the compressive strength is hardly expected. Furthermore, since the post-treatment is performed, the operation and the steps may be complicated, and the manufacturing cost may be increased. Therefore, it may be difficult to adopt the method as an actual production technique. There is a great demand for higher performance and lower price of carbon fiber, and carbon fiber is not acceptable to the market unless it is high in cost performance.

Japanese Patent Application Laid-Open No. 2000-160436 proposes a carbon fiber having a surface area ratio of 1.02 to 1.09. Adhesion may decrease, and composite material performance may decrease. Further, when a precursor is manufactured by the method described in the publication, productivity may be insufficient and manufacturing cost may increase.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to improve the single fiber compressive strength of carbon fiber, which is an important factor controlling the compressive strength of a carbon fiber reinforced composite material. And

[0008] That is, an object of the present invention is to provide a carbon fiber having an excellent torsional elasticity as an index of single fiber compressive strength. Another object of the present invention is to provide a method for producing a carbon fiber having a high torsional modulus of elasticity that is excellent in cost performance.

[0009]

According to the present invention, there is provided a carbon fiber having a torsional elasticity of 17 GPa or more.

[0010] Such a carbon fiber having a high torsional modulus of elasticity can be manufactured with excellent cost performance by setting the total time required for the oxidizing treatment step to be 70 minutes or more and less than 120 minutes.

Since the carbon fiber obtained in this way is excellent in both tensile strength and compressive strength, the use of such a carbon fiber makes it possible to realize a carbon fiber reinforced composite material having excellent strength properties.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have developed a carbon fiber oxidizing treatment capable of improving the torsional modulus of elasticity in addition to the tensile strength characteristic represented by the 0 ° tensile strength of carbon fiber (hereinafter simply referred to as strength). The present inventors have found the conditions and reached the present invention.

The surface area ratio of the carbon fiber thus obtained is preferably 1.10 or more and less than 1.30 from the viewpoint of the adhesion to the matrix.

Further, from the viewpoint of realizing a sufficient tensile strength, the average single fiber strength is preferably 4.7 GPa or more, and the resin-impregnated strand tensile strength is preferably 5 GPa or more.

Further, from the viewpoint of realizing sufficient tensile strength and excellent cost performance, the crystal size Lc of the carbon network plane is preferably from 1.4 nm to 2.0 nm,
The degree of orientation π _{002 in the} fiber axis direction is preferably 79% or more.

The carbon fiber having the above-mentioned properties can be suitably obtained by firing an acrylic carbon fiber precursor (hereinafter simply referred to as a precursor). As the spinning method, a wet spinning method is preferable. The term “calcination” refers to a series of processes in which the precursor obtained in the spinning process is preliminarily carbonized and carbonized subsequent to flame resistance to obtain carbon fibers as a final product.

Hereinafter, the method for producing a carbon fiber of the present invention will be described by taking as an example a method for producing a precursor by a wet spinning method.

As a precursor raw material, a polymer containing acrylonitrile at 85% by mass or more and a polymerizable unsaturated monomer copolymerizable with acrylonitrile at 15% by mass or less is suitably used. Specific examples of the polymerizable unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, and acrylic acid, methacrylic acid, itaconic acid, and their ammonium salts, and acrylic acid, methacrylic acid. Examples include acids, itaconic acids and their alkyl esters, and acrylamide, methacrylamide and their derivatives, and allylsulfonic acid, methallylsulfonic acid and their salts, and alkyl esters.

As a polymerization method for obtaining the polymer, a suspension polymerization method, a solution polymerization method, an emulsion polymerization method and the like can be employed.

The obtained polymer is dissolved in a solvent to prepare a polymer solution as a spinning dope. As the solvent used for the polymer solution, an organic or inorganic solvent can be used,
In the case of a wet spinning method in which a spinning dope is spun directly into a coagulation bath via a spinneret, an organic solvent is preferred. Specifically, dimethyl sulfoxide, dimethylformamide, dimethylacetamide and the like can be mentioned. When a concentrated aqueous solution of an inorganic salt such as an aqueous solution of nitric acid, rodan soda, and zinc chloride is used as an inorganic solvent, a carbon fiber having a desired surface morphology may not be obtained.

After spinning in a coagulation bath, the yarn may be stretched directly in a stretching bath without washing with water, or may be stretched in a stretching bath after the solvent is removed by washing with water. The stretching bath is usually
It is made of hot water whose temperature is controlled at 50 to 98 ° C., and is set so that the concentration of the solvent ranges from 0% by mass to the concentration of the coagulation bath.

The stretching ratio is preferably set based on a conventional method without lowering the productivity or increasing the production cost.

Further, in the precursor according to the present invention, it is preferable to apply a silicone oil agent to the yarn prior to dry densification.

The amount of the silicone oil adhering to the yarn is preferably 0.2 to 2% by mass based on the dry mass of the yarn.

The method of applying the oil agent to the yarn includes a dipping method,
Kiss roller method, guide lubrication method, method using driven / non-driven rollers in oil bath, method of applying a running yarn to fixed / non-fixed guide bar, applying yarn, running yarn in oil sprayed upward A variety of methods, such as a method of applying by applying oil, a method of applying the oil by dripping the oil onto the running yarn from above, a method of applying the yarn by running the yarn in a space where the oil solution is sprayed, or a method of combining a plurality of them. There is a grant method,
These methods can be appropriately selected according to the type and use of the yarn.

If the amount of the silicone oil is too large, the resulting carbon fiber may not have sufficient resin adhesiveness. Therefore, the amount of the silicone oil to be applied is kept to the minimum necessary. It is preferable to take care to give the yarn uniformly to the yarn.

Next, the drawn yarn in the bath is dried and densified by drying with a hot drum or the like. Here, the drying temperature, required time, and the like can be appropriately selected.

It is preferable that the yarn after drying and densification is stretched in a higher temperature environment, for example, by stretching in a pressurized steam.

Since the stretching ratio before the drying and densification is reduced as compared with the conventional method, the stretching ratio before the drying and densification is preferably as high as possible from the viewpoint of processability. Therefore, the stretching ratio is preferably 3 times or more.

From the viewpoint of improving the strength of the carbon fiber, it is preferable that the precursor does not cause firing unevenness in the subsequent flameproofing step. The single fiber fineness of the precursor is preferably 1.5 d (d: denier) or less.

Through the above-described production process, a precursor having a predetermined fineness and orientation can be obtained, and carbon fibers having desired characteristics can be obtained after firing.

The oxidizing conditions for obtaining the carbon fiber of the present invention are as follows.
Tension or stretching conditions are preferably employed. It is preferable that the total time required for the flame-proofing step is 70 minutes or more and less than 120 minutes.

In the present invention, the density of the oxidized fiber is preferably 1.25 g / cm ³ or more, more preferably 1.
It is good to be flame resistant until it becomes ³ g / cm ³ or more.
It is preferably at most 6 g / cm ³ . In addition, to achieve sufficient tensile strength and excellent cost performance,
It is preferably from 1.36 g / cm ^{3 to} less than 1.40 g / cm ³ .

As the atmosphere in the flame-proofing step, any of oxidizing atmospheres such as air, oxygen, nitrogen dioxide, and hydrogen chloride can be adopted, but an air atmosphere is preferred because it is low in cost.

The yarn which has been subjected to flame resistance is carbonized in an inert atmosphere by a conventional method. The atmosphere temperature here is preferably 1000 ° C. or higher, and more preferably 1200 ° C. or higher, from the viewpoint of improving the performance of the obtained carbon fiber. Further, if necessary, it can be carbonized at 2000 ° C. or higher to obtain graphitized fibers, but the strength may be reduced. In addition, in order to obtain a carbon fiber having a high density with few defects inside the carbon fiber such as voids, the temperature is set at 350 to 500 ° C. and 1000 ° C.
The heating rate at a temperature of from 1200 ° C. to 1200 ° C. is preferably 500 ° C./min or less, preferably 300 ° C./min or less, more preferably 1 ° C./min or less.
50 ° C./min or less is good. If the heating rate is 10 ° C./min or less, the productivity will decrease. Further, in order to improve the compactness of the carbon fiber, 1% at 350 to 500 ° C.
Above, preferably 5% or more. In addition, 1
Stretching exceeding 0% is not preferable because fluff is likely to occur. It is preferable from the viewpoint of improving the physical properties and processability of the carbon fiber that carbonization is performed separately in a plurality of furnaces in a low-temperature portion of 600 to 1000 ° C. and in a temperature range higher than 600 ° C. where decomposition products are relatively large.

The carbon fiber thus obtained is subjected to an electrolytic oxidation treatment in an electrolytic solution or an oxidation treatment in a gas phase or a liquid phase, so that the affinity between the carbon fiber and the matrix resin in the composite material and the resin adhesiveness can be improved. Can be improved.

In particular, the oxidation treatment can be performed in a short time,
The electrolytic oxidation treatment is preferred because the oxidation treatment is easily controlled. As the electrolytic solution for the electrolytic oxidation treatment, any of an acidic solution and an alkaline solution can be adopted. Specific examples of the electrolyte dissolved in the acidic electrolyte include inorganic acids such as sulfuric acid and nitric acid, organic acids such as acetic acid and butyric acid, and salts such as ammonium sulfate and ammonium hydrogen sulfate. Among them, sulfuric acid and nitric acid showing strong acidity are preferable, and ammonium nitrate and the like can be used. Specific examples of the electrolyte dissolved in the alkaline electrolyte include hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, inorganic salts such as sodium carbonate and sodium hydrogen carbonate, and organic salts such as sodium acetate and sodium benzoate. Further, these potassium salts, barium salts or other metal salts, and ammonium salts, and organic compounds such as tetraethylammonium hydroxide or hydrazine, but from the viewpoint of preventing curing failure of the resin,
Ammonium carbonate, ammonium hydrogen carbonate, and tetraalkylammonium hydroxides containing no alkali metal can be preferably used.

The amount of electricity supplied can be optimized according to the degree of carbonization of the carbon fibers. From the viewpoint of appropriately suppressing the decrease in the crystallinity of the surface layer, the amount of electricity is 3 to 500 coulomb /
g, more preferably in the range of 5 to 200 coulombs / g.

After the electrolytic oxidation treatment, the yarn is preferably washed with water and dried. At the time of drying, if the temperature is too high, the functional group present on the outermost surface of the carbon fiber is easily lost by thermal decomposition, so it is desirable to set the drying temperature as low as possible,
It is preferable to dry at 200 ° C. or less.

Further, if necessary, a sizing agent can be provided by a conventional method.

The carbon fiber according to the present invention preferably has a tensile modulus in the resin impregnated strand of 200 GPa or more, preferably 220 GPa or more, more preferably 24 GPa or more.
Those having 0 GPa or more are good. If necessary, carbon fibers having a higher tensile modulus can be used. When the tensile modulus is less than 200 GPa, when the composite material is used,
Desired characteristics may not be obtained in some cases, which is not preferable.

The carbon fiber obtained by such a method can be combined with a matrix by a conventional method to prepare a prepreg as an intermediate substrate or a composite material as a final product. As the resin used as the matrix,
Epoxy resins, phenolic resins, polyester resins, vinyl ester resins, bismaleimide resins, polyimide resins, polycarbonate resins, polyamide resins, polypropylene resins, ABS resins, and the like. Further, in addition to the resin, cement, metal, ceramics and the like can be used for the matrix.

The prepreg can be used as a resin-impregnated sheet in which carbon fibers are aligned in one direction, that is, as a one-way prepreg, or can be used as a woven prepreg in which carbon fibers are woven beforehand and then impregnated with resin. .

The composite material can be produced by laminating and curing these prepregs in an arbitrary direction, or by a filament winding method in which the resin is directly impregnated and wound. In addition, the composite material
Cut carbon fiber into chopped fiber in advance, extrude while kneading with resin, pull out long fiber together with resin, sheet molding compound (SM
It can also be manufactured by a method such as a hand lay-up method, a press molding method, an autoclave method, a pultrusion method, etc. after once processing into a chopped fiber or the like method.

The composite materials include primary and secondary structural materials for aircraft, sports equipment such as golf shafts, fishing rods, snowboards, ski poles, marine equipment such as yacht masts, hulls for boats, flywheels, CNG tanks, and windmills. Can be used as general materials for energy related industries such as turbine blades, repair / reinforcement materials for roads and bridge piers, and building materials such as curtain walls.
It can be suitably used for G tanks and the like, taking advantage of the composite material according to the present invention having a high degree of fracture resistance and repeated fatigue resistance.

[0046]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In addition, each physical property value was measured by the method shown below.

<Surface area ratio> The carbon fiber to be measured was
m and fixed on a substrate (slide glass) using a carbon paste. The central portion of the fixed carbon fiber single yarn is measured using an atomic force microscope (AFM, SPI3700 / SPA-300 manufactured by Seiko Instruments Inc.) under the following conditions to obtain an image of a three-dimensional surface shape; scanning Mode: Tapping mode Probe: Olympus Optical Kogyo Co., Ltd. Si cantilever-integrated probe SN-DF20 Scanning range: 2.5 μm × 2.5 μm Scanning speed: 0.5 Hz Number of pixels: 256 × 256 Measurement environment: room temperature and in air.

An image obtained by observing each single yarn one by one is subjected to a Tilt process and a Highpass filter to obtain an inverse Fourier transform image, and a surface area ratio is calculated in a cross section mode. Note that the projected area is an approximate projected area on a cubic surface in consideration of the curvature of the fiber cross section. The surface area ratio is determined from the relationship of surface area ratio = actual surface area / projected area. For each sample, measurement is performed at five locations selected arbitrarily, and the arithmetic mean value at three locations excluding the maximum value and the minimum value is defined as the final surface area ratio.

<Average Single Fiber Strength> JIS R 7601
The average single fiber strength is measured according to.

<Strength of resin-impregnated strand and elastic modulus of resin-impregnated strand> 120 g (100 g) of ERL-4221 manufactured by Union Carbide Co., Ltd. was added to the carbon fibers to be measured.
Parts by mass), Kayahard (MCD) 10 manufactured by Nippon Kayaku Co., Ltd.
Impregnated with a resin composition obtained by mixing 8 g (90 parts by mass), 3.6 g (3 parts by mass) of N, N benzyldimethylamine and 60 g (50 parts by mass) of acetone, and then at 130 ° C.
Heat and cure for 120 minutes to obtain a resin-impregnated strand. Using the obtained resin-impregnated strand, a tensile strength and a tensile modulus are determined by a resin-impregnated strand test method (according to JIS R 7601), and these are defined as a resin-impregnated strand strength and a resin-impregnated strand elastic modulus, respectively.

<Carbon network face crystal size Lc> The fiber bundle is cut into a length of 50 mm, 30 mg is precisely weighed and sampled, and the sample fiber axes are aligned so as to be exactly parallel. It is used to prepare a fiber sample bundle having a width of 1 mm and a uniform thickness. After being impregnated with a vinyl acetate / methanol solution so as not to lose its shape, it is fixed to a wide-angle X-ray diffraction sample table. As an X-ray source, using an X-ray generator manufactured by Rigaku Denki Co., Ltd., a CuKα ray (Ni
Filter). Using a goniometer manufactured by Rigaku Denki Co., Ltd., the surface index of graphite (00
A diffraction peak near 2θ = 26 ° corresponding to 2) is detected by a scintillation counter.

From the half width of the diffraction peak corresponding to (002), the carbon network face crystal size Lc is obtained by using the following equation; Lc = Kλ / (β ₀₂ cos θ) where K is the Scherrer constant (0.9) , Λ is the wavelength of the used X-ray (here, CuKα ray is used, and 0.154
18 nm), and θ is the Bragg diffraction angle. Β ₀₂ is the true half-width, which is determined by the following equation: β ₀₂ = β _E2 −β ₁₂ where β _E2 is the apparent half-width and β ₁₂ is the device constant, here 1.05 × 10 ^-2 rad.

<Degree of orientation π _{002 in} fiber axis direction> A sample was prepared in the same manner as in the case of the carbon network face crystal size Lc, and a profile in the meridian direction including the highest intensity of (002) diffraction obtained by the same analysis method. From the half width (H °) of the spread of
The degree of crystal orientation π ₀₀₂ (%) in the fiber axis direction is determined using the following equation; π ₀₀₂ = [(180−H) / 180] × 100.

<Torsion Modulus Gf> As shown in FIG. 1, one end of a single fiber (10) having a length of 10 cm is inserted into a fine hole provided at the center of a 0.5 g glass weight (20). The other end is adhered to the cushion paper (30) with an instant adhesive, fixed with a clip and suspended. afterwards,
Rotate the weight + 10 ° to twist the fiber and release it.
The fiber turns around and stops at -10 [deg.] In the opposite direction, and then turns back to +10 [deg.] And stops. -10 ° to +10
The time of one cycle up to ° is measured for five consecutive cycles,
Find the average value. This was measured for five single fibers,
The average value T (second) is obtained, and the torsional elastic modulus Gf (GPa) is obtained by the following equation; Gf = 125πLI / (d ⁴ T ² ) × 10 ⁻⁵ I = MD ² / (8 g) where L is Fiber length (mm), d is single yarn diameter (m
m), M is the mass of the weight (g), D is the diameter of the weight (m
m) and g are gravitational acceleration (m / sec ² ), and I is moment (twist).

<Density after Oxidation Treatment> JIS R 76
In accordance with No. 01, the density after the oxidation treatment is measured.

Example 1 An acrylic copolymer composed of 96% by mass of acrylonitrile units, 1% by mass of methacrylic acid units and 3% by mass of acrylamide units and having an intrinsic viscosity [η] of 1.7 was obtained by a suspension polymerization method. Manufactured. The obtained acrylic copolymer was dissolved in dimethylacetamide to prepare a spinning stock solution (polymer concentration: 21% by mass, stock solution temperature: 60 ° C). This spinning dope was used in a 0.075 mm diameter, 3 holes.
Using a 2,000 nozzle, the mixture was discharged into an aqueous dimethylacetamide solution having a temperature of 38 ° C. and a concentration of 67% by mass to form a coagulated yarn.

The coagulated yarn obtained by the above wet spinning method is stretched 1.5 times in the air, and then 4.0 mm in warm water.
The film was stretched twice, washed and desolvated. Thereafter, the coagulated yarn is immersed in a 1.0% by mass silicone oil solution, and
Drying and densification were performed with a heating roller at 75 ° C.

Subsequently, the total draw ratio was 1 in pressurized steam.
The film was stretched three times to obtain a precursor made of an acrylic fiber having a single yarn fineness of 1.2 dtex and a total fineness of 3600 dtex.

The precursor obtained as described above is
While heating in air from 220 ° C. to 270 ° C. in 90 minutes, it was heated at a draw ratio of 1.0 to convert it to oxidized fiber.
At this time, the density of the oxidized fiber was 1.38 g / cm ³ .

Further, the oxidized fiber is heated from 300 ° C. to 700 ° C.
Preliminarily carbonized at a draw ratio of 1.05 in an inert atmosphere while raising the temperature for 1.5 minutes. The heating rate at this time is 267 ° C
/ Min. After preliminary carbonization, carbonization was performed in an inert atmosphere while the temperature was raised from 1100 ° C. to 1300 ° C. in 1.5 minutes. The heating rate at this time was 133 ° C./min.
The stretching ratio of the combined pre-carbonization and carbonization was 1.0.

Thereafter, in an aqueous solution of ammonium nitrate,
An electrolytic oxidation treatment of 30 coulomb / g-CF was performed to obtain a carbon fiber.

The surface ratio of the obtained carbon fibers was 1.13,
The average single fiber strength is 5.1 GPa, the resin-impregnated strand tensile strength is 5.4 GPa, and the resin-impregnated strand elastic modulus is 2
50 GPa, carbon network face crystal size Lc is 1.5 nm, orientation degree π _{002 in the} fiber axis direction is 81%, and torsional elasticity is 20.
GPa.

The quality of the obtained carbon fiber was very good, and it was found that the carbon fiber had high performance.

[0064]

According to the carbon fiber of the present invention,
A carbon fiber reinforced composite material that is lightweight, has high performance, and is excellent in cost performance can be obtained. Accordingly, the obtained composite material can be suitably used for energy-related applications such as a flywheel rotor, a CNG tank, and a primary structural material of an aircraft.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view for explaining an apparatus for measuring a torsional elastic modulus.

[Explanation of symbols]

 10 fiber 20 weight 30 cushion paper

Continued on front page F-term (reference) 4F072 AA02 AA04 AA07 AA08 AB10 AB22 AB34 AD02 AD03 AD04 AD05 AD08 AD13 AD23 AD37 AD41 AD45 AL02 AL04 AL05 AL07 4J002 AA001 BB121 BH021 BN151 CC031 CD001 CF001 CG001 CL001 CM041 DA016 FA046 GC00 001 001 BB11 BB15 BB17 BB60 BB66 BB69 BB72 BB77 BB85 BB89 BB91 FF01 GG01 HH10 MB03 MB09 MB19 4L037 AT02 CS03 FA05 FA06 FA07 FA08 FA12 PA57 PA61 PC10 PC11 PC13 PF44 PS00 PS02 PS12 PS17 UA10 UA12 UA20

Claims (8)

[Claims] 1. A carbon fiber having a torsional elasticity of 17 GPa or more. 2. The carbon fiber according to claim 1, wherein the surface area ratio is not less than 1.10 and less than 1.30. 3. The carbon fiber according to claim 1, wherein the average single fiber strength is 4.7 GPa or more, and the resin-impregnated strand tensile strength is 5 GPa or more. 4. A carbon network face crystal size Lc of 1.4 to 2.
4. The carbon fiber according to claim 1, wherein the carbon fiber has a degree of orientation π ₀₀₂ of 79% or more in the fiber axis direction. 5. The density after the oxidation treatment is 1.36 g / cm.
Carbon fiber according to any one of claims 1 to 4, characterized in that less than ³ or more 1.40 g / cm ^3. 6. The carbon fiber according to claim 1, wherein an acrylic fiber obtained by a wet spinning method is used as a precursor. 7. A carbon fiber reinforced composite material using the carbon fiber according to any one of claims 1 to 6. 8. The total time required for the oxidation treatment step is 70.
The method for producing carbon fiber according to any one of claims 1 to 6, wherein the heating time is not less than 120 minutes and not more than 120 minutes.