JPH08296124A - Non-circular cross section carbon fiber and carbon fiber-reinforced composite material - Google Patents

Abstract

PURPOSE: To obtain a non-circular cross section carbon fiber capable of improving the fundamental characteristics of its compressed system and capable of providing a composite material suitable as a structural material. CONSTITUTION: This carbon fiber has a non-circular cross section and the cross- sectional shape is a non-circular shape having at least a symmetric surface passing through the center of the figure, has a rotation symmetric angle θdefined θ=360 deg./n (n is an integer of 1-10), and has a base weight of >=0.1mg/m per a single fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber for molding a fiber-reinforced composite material and a composite material using the fiber. More specifically, the present invention relates to a carbon fiber which provides a composite material having excellent compression system mechanical properties and suitable as a structural material, and a composite material using the carbon fiber.

[0002]

2. Description of the Related Art Carbon fibers have excellent specific strength and specific elastic modulus as compared with other fibers, and therefore, due to their excellent mechanical properties, they are industrially widely used as reinforcing fibers for composite materials with resins. It's being used. In recent years, the superiority of carbon fiber composite materials has increased more and more, and especially for sports and aerospace applications, there is a strong demand for higher performance of the carbon fiber composite materials. The characteristics of the composite material are largely due to the characteristics of the carbon fiber itself, and this requirement is, in the first place, a demand for higher performance of the carbon fiber itself. In response to the demand for higher performance of this carbon fiber, long-term progress has been made so far in terms of tensile properties such as tensile strength and tensile elastic modulus. On the other hand, however, the improvement of the compression characteristic value has not been followed, and no satisfactory improvement has been observed in the characteristics of the composite material, particularly in the practical characteristics such as compression characteristics and bending characteristics.

Conventionally, as a measure for improving the basic characteristics of this composite material, a method of improving the surface characteristics of the carbon fiber by electrolytic surface treatment, a method of improving the characteristics of the matrix resin to be applied, and the carbon fiber constituting the composite material family. Many proposals have been made, such as a method for devising the arrangement of. The reality is that the results are not always satisfactory.

Under such conventional technical background, various investigations have been made on measures for improving the basic characteristics of the composite material of carbon fiber and resin, and as a result, JP-A-3-9791.
8, 3-185121, 4-202815, it was reported that it is very effective to make the fiber cross-section non-circular in addition to the improvement of the internal structure of the carbon fiber itself. .

However, the above-mentioned non-circular cross-section yarns may have poor yarn-forming properties, particularly drawability, and as a result, the yarn-forming ability may be reduced. With respect to this problem, the present inventors have found that the carbon fiber obtained has a high compressive strength when the single yarn fineness is increased to suppress the decrease in performance, and the present invention has been achieved.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a carbon fiber having a high compressive strength which could not be achieved by the above-mentioned prior art, and a composite material using such a carbon fiber.

[0007]

The carbon fiber of the present invention has the following constitution in order to achieve the above object. That is,
The fiber cross-sectional shape is a non-circular shape having at least one plane of symmetry passing through its centroid and having a rotational symmetry angle θ defined by θ = 360 ° / n (n is an integer from 1 to 10). And, the basis weight per single fiber is 0.1 mg
It is a non-circular cross-section carbon fiber characterized by being / m or more.

The carbon fiber reinforced composite material of the present invention is
In order to achieve the above-mentioned subject, it has the following composition. That is, it is a carbon fiber reinforced composite material characterized by comprising the above carbon fiber and a resin. Hereinafter, the present invention will be described in detail.

The carbon fiber of the present invention has a non-circular cross section with a constant symmetry. The non-circular shape having the certain symmetry means that there is at least one symmetry plane passing through the centroid and the rotational symmetry angle defined by θ = 360 ° / n (n is an integer from 1 to 10). It is specified by θ.

The non-circular cross section of the carbon fiber increases the contact area with the matrix resin to increase the adhesive force when it is used in the composite material, and is more uniform to the matrix resin than the circular cross section. Therefore, the basic properties of the composite material can be significantly improved by increasing the dispersibility.

Further, since the carbon fiber having a non-circular cross section has a larger second moment of area than the carbon fiber having a circular cross section, the bending rigidity of the composite material can be improved. Moreover, since the non-circular cross-sectional shape is symmetric, it is possible to make the stress distribution in the cross-sectional direction uniform with respect to the strain in the longitudinal direction (fiber longitudinal direction) of the composite material.

Further, the carbon fiber having a non-circular cross section of the present invention has a basis weight of 0.1 mg / m 2 or more per single fiber. That is, since the single yarn diameter is large, the bending is small, and the alignment is improved, the tensile properties and compression properties of the composite material are further improved. In order to improve the basic characteristics, the weight per single fiber is preferably 0.125 mg or more,
0.15 mg or more is more preferable, and 0.20 mg or more is further preferable. The upper limit is not particularly limited,
In order to obtain a carbon fiber having a large basis weight, it is preferable to use a precursor having a large single yarn fineness, and in this case, there is a problem that burn marks are likely to occur during flame resistance. Therefore, the basis weight per single fiber is practically 0.50 mg or less.

The unit weight per single fiber referred to in the present invention is, for example, 100 to 1,000,000 filaments.
It is an average value of the numerical values obtained by measuring the mass of 1 m of the carbon fiber bundle of the book twice and dividing it by the number of filaments. Since carbon fibers usually have a moisture content of 0.1% or less, the adsorbed moisture content can be ignored, but the firing temperature is low and the moisture content is 0.1%.
If it exceeds, the mass is measured after drying at 120 ° C. for 2 hours.

By summing up these actions,
The excellent mechanical properties of the carbon fiber are effectively reflected in the composite material.

Further, the effect of reflecting the carbon fiber on the composite material is further improved by the fact that the internal structure of the carbon fiber is a uniform crystal structure having no lamellar structure (non-lamellar structure). Since the surface smoothness S of the fiber surface is 1.16 or less and has a high degree of smoothness without fine irregularities, stress at the interface between the matrix resin and the carbon fiber is not locally concentrated in the composite material. It can be further increased.

In the present invention, the fact that the fiber cross section is rotationally symmetric means that exactly the same figure is repeated when rotated by an angle θ around the centroid, and the rotational angle at that time is called rotational symmetry angle. In addition, the symmetry plane means a boundary plane in which the left and right figures are self-identical when performing a mirroring operation on the fiber cross section.

In a regular polygonal or regular multilobal fiber cross section, n defining the rotational symmetry angle θ is the same as the number of symmetry planes. That is, in a regular trilobal cross section in which the equilateral triangular cross section 1 in FIG. 1 and the fiber cross section in FIG. 2 have a concave portion toward the center, the number of n of the rotational symmetry angle θ is 3, and the number of symmetry planes is also. It is 3. Further, in the regular quadrilateral section of FIG. 3, the rotational symmetry angle θ has a value of n, and the number of symmetry planes is also 4.

On the other hand, in the case of a non-regular polygonal or non-regular multilobal fiber cross section, the number n of symmetry planes defining the rotational symmetry angle θ and the number of planes of symmetry vary depending on the deformed shape. Becomes a number.
For example, in an isosceles triangle, a vertically elongated pentagon, a heart shape, and a modified trilobal cross section in FIG. 5, n defining the rotational symmetry angle θ is 1 and the number of symmetry planes is 1. Further, in a rectangle, a vertically long hexagon, a dogbone type, a Mayu type, an H-shaped section of FIG. 4 and a modified four-leaf section of FIG. 6, n that defines the rotational symmetry angle θ is 2, and the number of symmetry planes is It is 2.

In the present invention, the upper limit of n defining the rotational symmetry angle θ is 10, but it is more preferable to set the upper limit to 5. This is because when n exceeds 10, the fiber cross section becomes close to a circular shape, and the effect of the non-circular cross section according to the present invention is reduced.

In addition to the above-mentioned symmetry, the non-circular cross section of the carbon fiber is a non-circular cross section having a concave portion toward the center of the cross section of the fiber, and the degree of deformation thereof is also within a certain range. Is preferred. For example, if the shape is an extremely flat shape such as an elongated flat cross section, the carbon fiber will not be uniformly dispersed in the composite material, and the basic characteristics of the composite material will be reduced. When the ratio (R / r) of the circumscribed circle radius R and the inscribed circle radius r of the cross-sectional figure of the trilobal section 7 of the carbon fiber shown in FIG. 7 is defined as the degree of deformation D, the degree of deformation D is It is preferably 1.1 to 7.0, more preferably 1.3 to 6.0, and further preferably 1.5 to 5.0.

As described above, the carbon fiber of the present invention is unique in that it has a uniform crystal structure without an lamella structure in order to improve the basic properties of the composite material. Is preferable from the viewpoint of improving the compressive strength. As shown in FIGS. 8 and 9, the lamella structure means a leaf-shaped (leaf-shaped) oriented structure a radially extending in the cross section of the carbon fiber F.
I mean. The presence or absence of the lamella structure a can be easily confirmed by observing the cross section (fracture surface) of the carbon fiber with a scanning electron microscope (SEM). Generation of such a lamella structure can be eliminated by producing carbon fiber using the precursor obtained by dry-wet spinning of a PAN polymer, for example.

Further, in the present invention, the surface smoothness S is 1.16 or less, and the fiber surface does not have fine irregularities,
It is preferable to have extremely high smoothness. If fine irregularities are present on the surface of the carbon fiber, stress is likely to be concentrated on the irregularities and serve as a starting point of fracture, which causes a decrease in compressive strength and bending strength particularly when the composite material is formed.

The surface smoothness S is measured as follows.
The cross section of the carbon fiber was magnified 7500 times by SEM and further magnified 4 times, that is, the magnified picture of 30,000 times, and the circumference L of the cross section and the circumscribed circumference L ₀ obtained by the image analyzer were obtained. Is defined as the square of L / L ₀ . That is, it is a value obtained as (L / L ₀ ) ² .

Such a surface smoothness S of 1.16 or less can be easily achieved by using, for example, a precursor obtained by dry-wet spinning a PAN polymer. Such a high degree of surface smoothness may also be obtained by dry spinning or melt spinning, but in the precursor by the former method, since the volumetric shrinkage due to evaporation of the spinning dope solvent is large, the spinning nozzle with a non-circular fiber cross-sectional shape is used. However, it is difficult to control the fiber cross-sectional shape within the range of the preferable degree of deformation D described above. Also,
It is difficult to obtain good carbon fibers by melt spinning.

As shown in FIGS. 10 to 12, the cross-sectional shape of the carbon fiber of the present invention has a multi-lobed shape, and has a bulge once from the root of each leaf to the tip, It is preferable that a plurality of circles are joined to each other and the deformation degree D of the fiber cross section is in the range of 1.5 to 3.0. When the degree of deformation D of the fiber cross section is less than 1.5, each root practically ceases to have a bulge from the root to the tip, and when it exceeds 3.0, the leaves are baked during the carbon fiber manufacturing process. There is a case that it is damaged and fluffing increases.

Although it is not clear why the carbon fiber having such a shape has a great effect of improving the composite characteristics, it is considered as follows. Various factors are assumed to control the lateral properties of the carbon fiber reinforced composite material, but the physical shape and the surface area thereof are important factors as physical factors. As described above, the cross section of the carbon fiber is multi-lobed, and if each leaf has a bulge from the root to the tip, the surface area is large and there is a kind of space between the leaves. Since it exerts a so-called anchor effect that works like an anchor, it is considered that the adhesive force with the matrix resin and the compressive strength after impact are improved.

In addition, since the distance from the surface of the single fiber to the center is shorter than that of the ordinary cross-section yarn, oxygen permeation to the center is easy, and more uniform firing is possible, and the strength of the carbon fiber is increased. It is considered that, as the elastic modulus is improved, the resistance against bending deformation is increased and the compressive strength and bending strength are improved.

Further, with such a shape, it is easy to obtain a carbon fiber having a large single fiber fineness, and these characteristics are further improved by improving the alignment.

As for the mechanical properties of the carbon fiber according to the present invention as described above, the tensile strength of the resin-impregnated strand is usually 300 kgf / mm ² or more. Preferably 350 kgf / mm ² or more, more preferably 400 kgf / mm ² or more, more preferably 50
It is preferably 0 kgf / mm ² or more. The tensile modulus of the carbon fiber is usually 20 × 10 ³ kgf / mm ² or more, preferably 22 × 10 ³ kgf / mm ² or more, more preferably 24 × 10 ³ kgf / mm ² or more, further preferably 28 ×. 10 ³ kgf / mm ² or more is desirable. The above strand strength or elastic modulus is 300 kgf / m, respectively
When the carbon fiber is less than m ² or less, or less than 20 × 10 ³ kgf / mm ² , the desired properties as a structural material may not be obtained when it is made into a composite.

The carbon fiber of the present invention may be any of acrylic type, pitch type, rayon type and the like, but an example of the method for producing the carbon fiber of the present invention will be described in the case of acrylic type.

The polyacrylonitrile constituting the precursor of acrylic carbon fiber is preferably a polymer containing 85% or more of acrylonitrile and 15% or less of a polymerizable unsaturated monomer copolymerizable with acrylonitrile. Examples of the polymerizable unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and alkyl esters, acrylamide, methacrylamide and their derivatives, allylsulfonic acid, methallylsulfonic acid and Examples thereof include salts or alkyl esters thereof. Also,
It is preferable to copolymerize a polymerizable unsaturated monomer that accelerates the flameproofing reaction, such as unsaturated carboxylic acid. The copolymerization amount is preferably 0.1 to 10% by weight, and 0.3 to 5
It is more preferably in the range of 0.5% by weight and even more preferably in the range of 0.5 to 3% by weight. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid,
Mesaconic acid etc. can be mentioned. Further, in order to improve the oxygen permeability to the inside of the single yarn and fire the precursor having a large fineness, it is preferable to copolymerize at least one selected from alkyl esters of unsaturated carboxylic acids and vinyl acetate. . The copolymerization amount is preferably 0.1 to 10% by weight, more preferably 0.3 to 5% by weight, and further preferably 0.5 to 3% by weight. Specific examples of the alkyl ester of unsaturated carboxylic acid include methyl acrylate, methyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, and secondary butyl methacrylate. Among them, acrylic acid, Propyl, butyl, isobutyl and secondary butyl esters of methacrylic acid are preferred. .

As the polymerization method, suspension polymerization, solution polymerization,
A conventionally known method such as emulsion polymerization can be adopted.
As the degree of polymerization, the intrinsic viscosity ([η]) is preferably 1.
It is 0 or more, more preferably 1.35 or more, and further preferably 1.7 or more. From the viewpoint of spinning stability, [η] is generally 5.0 or less.

As the solvent in the case of solution spinning, known organic and inorganic solvents can be used, and specifically, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, an aqueous solution of rhodanese and an aqueous solution of zinc chloride are used as the solvent. The polymer solution to be used is the spinning dope.

The polymer can be made into a precursor by a known method. The spinning may be carried out by a wet spinning method in which it is directly spun into a coagulation bath, a dry-wet spinning method in which it is once spun into air and then solidified in a bath, or a dry spinning method or melt spinning, but for the reasons described above. Dry-wet spinning is preferred. The spinneret discharge holes used for spinning must be non-circular with the same symmetry as the cross-section of the resulting carbon fiber. The non-circular shape is θ = 360 ° / n (n
Is an integer from 1 to 10)
And have at least one plane of symmetry passing through the centroid. In the present invention, it is not preferable that the material is discharged from an ordinary circular hole and has a non-circular cross section depending on the solidification conditions because it is difficult to control the cross-sectional shape.

In the case of the spinning method using a solvent and a plasticizer, the spun yarn may be drawn directly in the bath, or may be drawn in the bath after washing with water to remove the solvent and the plasticizer.
The stretching conditions in the bath are usually about 2 to 6 times in a stretching bath at 50 to 98 ° C. Dry densification is achieved by drying the yarn after drawing in the bath with a hot drum or the like. The drying temperature, time, etc. can be appropriately selected.
If necessary, the dried and densified yarn may be stretched at a higher temperature (for example, in pressure steam),
By these, a precursor having a predetermined denier and orientation can be obtained. Further, it is preferable to add a silicone oil agent for the purpose of imparting heat resistance, prior to drying and densifying.

In order to obtain the carbon fiber having a large single yarn fineness of the present invention, it is preferable to use a precursor having a large single yarn fineness. However, if the fineness is too large, it becomes difficult to uniformly fire the inner and outer layers of the single yarn.
5.0 denier is preferable, 1.5 to 4.5 denier is more preferable, and 2.0 to 4.0 denier is further preferable.

By firing such a precursor, a high performance carbon fiber can be obtained. As the flameproofing condition, a conventionally known method can be adopted, and tension or stretching conditions are preferably used in the range of 200 to 300 ° C. in an oxidizing atmosphere, and the density is preferably 1.25.
The heat treatment is performed until it reaches g / cm ³ or more, more preferably 1.30 g / cm ³ . This density is 1.60 g /
It is general to keep it to be not more than cm ³ , and if it is more than this, the physical properties may deteriorate. As the atmosphere, generally known air, oxygen, nitrogen dioxide, hydrogen chloride and the like oxidizing atmosphere can be used, but from the viewpoint of economy, air is preferable.

The yarn that has been flame-proofed is carbonized in an inert atmosphere by a conventionally known method. The carbonization temperature is preferably 1000 ° C. or higher in view of the physical properties of the resulting carbon fiber, and graphitization can be carried out at a temperature of 2000 ° C. or higher if necessary. Also, 350 to 500 ° C and 1
The heating rate at 000 to 1200 ° C. is preferably 50.
It is 0 ° C./min or less, more preferably 300 ° C./min or less, still more preferably 150 ° C./min or less. This makes it possible to obtain a dense carbon fiber having few internal defects such as voids. If the rate of temperature increase is 10 ° C./minute or less, the productivity may decrease. Also, 350 to 50
At 0 ° C. or 2300 ° C. or higher, preferably 1% or more, more preferably 5% or more, further preferably 10%
Performing the above stretching is important for improving the denseness. It should be noted that the stretching exceeding 40% may easily cause fuzz.

The carbon fiber having a non-circular cross section obtained in this manner is subjected to electrolytic oxidation treatment in an electrolytic cell made of an aqueous solution of sulfuric acid or nitric acid, or to an oxidation treatment in a gas phase or a liquid phase. It is preferable because the affinity and adhesiveness between the carbon fiber and the matrix resin in the composite material described later can be improved.

For the surface treatment, various surface treatment methods such as vapor phase oxidation and electrolytic oxidation have been studied, but electrolytic oxidation is preferable because it can be oxidized in a short time and the degree of oxidation can be easily controlled. As the electrolytic solution for the electrolytic treatment, either acidic or alkaline can be adopted, and the acidic electrolyte may be any that exhibits acidity in an aqueous solution, and specifically, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, carbonic acid, etc. Examples thereof include inorganic acids, organic acids such as acetic acid, butyric acid, oxalic acid, acrylic acid and maleic acid, and salts such as ammonium sulfate and ammonium hydrogensulfate. Sulfuric acid and nitric acid which show strong acidity are preferable. Any alkaline electrolyte may be used as long as it shows alkalinity in an aqueous solution. Specifically, hydroxides such as sodium hydroxide, potassium hydroxide and barium hydroxide, and inorganic salts such as ammonia, sodium carbonate and sodium hydrogen carbonate. , Sodium acetate, organic salts such as sodium benzoate, further potassium salts thereof, barium salts or other metal salts, and ammonium salts, organic compounds such as tetraethylammonium hydroxide or hydrazine, but preferably resin curing Preference is given to ammonium carbonate, ammonium hydrogencarbonate, tetraalkylammonium hydroxides, etc. which do not contain any disturbing alkali metals.

The concentration of the electrolytic solution is 0.01 to 5 mol / l, preferably 0.1 to 1 mol / l. That is, the higher the concentration, the lower the electrolytic treatment voltage, but the handleability and odor become stronger and the environment worsens, so it is preferable to optimize from these.

The temperature of the electrolytic solution is 0 to 100 ° C, preferably 10 to 40 ° C. In other words, when the temperature is high, the odor becomes strong and the environment deteriorates, so low temperature is preferable,
It is preferable to optimize in consideration of the operating cost.

The amount of electricity is preferably optimized in accordance with the carbonization degree of the carbon fiber to be treated, and a high elastic modulus yarn requires a larger amount of electricity. From the viewpoint of promoting the decrease of the crystallinity of the surface layer and improving the productivity, while preventing the decrease of the strength of the carbon fiber substrate, the electrolytic treatment is preferably repeated a plurality of times with a small amount of electricity. Specifically, the amount of electricity supplied per electrolytic cell is preferably 5 coulomb / g · tank (1 g of carbon fiber, the amount of electricity per tank) or more and 100 coulomb / g · tank or less, more preferably 10 coulomb. / G / tank or more, 80
Coulomb / g · tank or less, more preferably 20 coulomb / g · tank or more and 60 coulomb / g · tank or less. Further, from the viewpoint of controlling the deterioration of the crystallinity of the surface layer within an appropriate range, it is preferable that the total amount of electricity in the energization treatment is in the range of 5 to 1000 coulombs / g, further preferably 10 to 500 coulombs / g.

The number of tanks is preferably 2 or more, more preferably 4 or more. From the viewpoint of equipment cost, 10 or less tanks are preferable, and it is preferable to optimize the amount of electricity, voltage, current density and the like.

From the viewpoint of effectively oxidizing the surface of the carbon fiber and not impairing the safety, the current density is 1.5 amperes / m ² per 1 m ² of the surface area of the carbon fiber in the electrolytic treatment liquid.
^{It is 2} or more and 1000 amps / m ² or less, preferably 3 amps / m ² or more and 500 amps / m ² or less. The processing time is preferably several seconds to ten and several minutes, more preferably about 10 seconds to 2 minutes.

From the viewpoint of safety, the electrolysis voltage is 25 V or less,
Furthermore, 0.5-20V is preferable. The electrolytic treatment method may be either a batch method or a continuous method, but a continuous method is preferable because it has good productivity and small variations. As the energization method, either direct energization in which the carbon fiber is brought into direct contact with the electrode roller to energize it, or indirect energization in which the carbon fiber and the electrode are energized via an electrolytic solution or the like, it is possible to employ electrolysis Indirect energization that suppresses fuzzing during processing, electric sparks, etc. is preferred.

In the electrolytic treatment method, the required number of electrolytic cells may be arranged and passed once, or may be passed through one electrolytic cell a required number of times. The anode length of the electrolytic cell is preferably 5 to 100 mm,
Cathode length is 300-1000 mm, further 350-90
0 mm is preferable.

After electrolytic treatment or cleaning treatment,
It is preferable to wash with water and dry. In this case, if the drying temperature is too high, the functional groups existing on the re-surface of the carbon fiber are likely to disappear by thermal decomposition. Therefore, it is desirable to dry at a temperature as low as possible. Specifically, the drying temperature is 250.
It is preferable to dry at a temperature of not higher than 0 ° C, more preferably not higher than 210 ° C.

Furthermore, sizing can be performed by a conventionally known technique, if necessary.

Next, a carbon fiber composite material using the carbon fiber having a non-circular cross section will be described. The carbon fiber obtained by the production method example of the present invention is a non-circular shape having a symmetric cross-sectional shape of the fiber, and a substantially uniform crystal having no lamellar structure in the cross-section of the fiber. It has a structure. Furthermore, the strength and elastic modulus of the carbon fiber are such that the tensile strength in the resin-impregnated strand form is 300k.
gf / mm ² or more, tensile elastic modulus 20 × 10 ³ kgf / m
It has excellent characteristics of m ² or more. Therefore, by using this carbon fiber as a composite material, ILSS of the composite material,
Basic properties such as compressive strength and bending strength can be improved.

The matrix resin used in the carbon fiber composite material of the present invention may be either a thermosetting resin or a thermoplastic resin, and examples thereof include epoxy resin, phenol resin, polyimide resin polyester resin, polyamide resin and the like. To be

The carbon fiber composite material of the present invention can be manufactured by a hand lay-up method, a press molding method or an autoclave method after being once processed into a prepreg, a sheet molding compound (SMC), chopped fiber or the like. It can also be molded by a pull-through method, a filament winding method, or the like.

[0053]

EXAMPLES The present invention will be described in more detail below with reference to examples.

The tensile strength and elastic modulus in the present invention were determined by the resin-impregnated strand method.

(Tensile strength, elastic modulus) "Bakelite" E
RL-4221 (registered trademark, manufactured by Union Carbide Co., Ltd.) / Boron trifluoride monoethylamine (BF ₃
MEA) / acetone = 100/3/4 parts impregnated into carbon fiber, and the resin-impregnated strand obtained is 30 at 130 ° C.
It was cured by heating for a minute, and measured according to the resin-impregnated strand test method defined in JIS-R-7601.

(Composite 0 ° compressive strength) Carbon fibers are aligned in one direction, sandwiched from both sides with a resin film coated with # 3620 resin manufactured by Toray Industries, Inc., and then the carbon fibers are impregnated with a pressure roller. , Create a prepreg sheet. The sheets were laminated with the fiber axes aligned, and the temperature was 180 ° C and the pressure was 6 kgf / cm using an autoclave.
^The resin is cured by treating with ² for 2 hours to prepare a flat plate having a thickness of about 1 mm. This flat plate is cut with a diamond cutter to prepare a test piece having a length of 80 mm in the fiber axis direction and a width of 12 mm in the direction perpendicular to the fiber axis. A composite tab made of carbon fiber and an epoxy resin and having a thickness of about 1 mm is adhered to both sides of both ends of the test piece, leaving 5 mm in the center, to obtain a test piece for measuring the compressive strength. The rest is ASTM-D
It measured according to the test method prescribed | regulated to 695.

Example 1 By a solution polymerization method using dimethyl sulfoxide as a solvent,
[Η] consisting of 96% by weight of acrylonitrile, 1% by weight of itaconic acid and 3% by weight of isobutyl methacrylate had a [η] of 1.
70, a spinning dope having a polymer concentration of 20% was obtained. Figure 1
After being discharged into the air through a spinneret for 3000 filaments having 3 spinning holes and running in a space of about 3 mm, it was coagulated in a 30% aqueous solution of dimethyl sulfoxide at 10 ° C., and the coagulated yarn was washed with water. Bath stretch up to 4 times,
After applying a process oil agent consisting of an amino-modified silicone oil agent (amino-modified amount 0.8%), it was dried and densified. further,
Single yarn fineness 2.0 by drawing up to 2.5 times in pressurized steam
d, a precursor having a total fineness of 6000D was obtained.

The obtained precursor is 240 to 280 ° C.
In air, heating at a draw ratio of 1.05 and a density of 1.37 g
A flameproofed yarn of / cm ³ was obtained. Then, in a nitrogen atmosphere, 35
The rate of temperature increase in the temperature range of 0 to 500 ° C. was set to 200 ° C./min, and the film was stretched at 2% and then fired to 1400 ° C. The cross-sectional shape of the carbon fiber at this time is shown in FIG.
What was shown in 0 was obtained.

Subsequently, an aqueous solution of sulfuric acid having a concentration of 0.1 mol / l was used as an electrolytic solution, electrolytic treatment was performed at 10 coulomb / g, and washing with water
It was dried in heated air at 150 ° C. Table 1 shows the physical properties of the carbon fiber thus obtained.

Comparative Example 1 The precursor has a single yarn fineness of 1.0 d and a total fineness of 3000.
A carbon fiber was obtained in the same manner as in Example 1 except that the carbon fiber was D.
The physical properties are shown in Table 1.

Example 2 A carbon fiber was obtained in the same manner as in Example 1 except that the polymer composition was 99% by weight of acrylonitrile and 1% by weight of itaconic acid. The physical properties are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that a precursor having a circular cross section was obtained using a die having circular holes. However, the carbon fiber could not be obtained due to yarn breakage during carbonization.

Example 3 A carbon fiber was obtained in the same manner as in Example 1 except that the polymer composition was 95% by weight of acrylonitrile, 1% by weight of itaconic acid and 4% by weight of methyl acrylate. Table 1 for physical properties
Shown in

Example 4 A carbon fiber was obtained in the same manner as in Example 1 except that the carbon fiber was fired up to 1700 ° C. The physical properties are shown in Table 1.

Example 5 A carbon fiber was obtained in the same manner as in Example 1 except that the polymer composition consisted of 99% by weight of acrylonitrile and 1% by weight of itaconic acid, and the composition was fired up to 1700 ° C. The physical properties are shown in Table 1.

Example 6 A carbon fiber was obtained in the same manner as in Example 1 except that the carbon fiber was fired up to 2000 ° C. The physical properties are shown in Table 1.

Example 7 A carbon fiber was obtained in the same manner as in Example 1 except that the polymer composition consisted of 99% by weight of acrylonitrile and 1% by weight of itaconic acid, and the composition was fired up to 2000 ° C. The physical properties are shown in Table 1.

[0068]

[Table 1]

[0069]

As described above, in the carbon fiber and the carbon fiber reinforced composite material of the present invention, the carbon fiber having a specific non-circular cross section can improve the basic characteristics of the compression system. A composite material suitable as a structural material can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of the shape of a single fiber cross section of a carbon fiber of the present invention.

FIG. 2 is a schematic view showing an example of the shape of a single fiber cross section of the carbon fiber of the present invention.

FIG. 3 is a schematic view showing a shape example of a single fiber cross section of the carbon fiber of the present invention.

FIG. 4 is a schematic view showing a shape example of a single fiber transverse section of the carbon fiber of the present invention.

FIG. 5 is a schematic view showing a shape example of a single fiber cross section of the carbon fiber of the present invention.

FIG. 6 is a schematic view showing a shape example of a single fiber transverse section of the carbon fiber of the present invention.

FIG. 7 is a schematic diagram for explaining the definition of the degree of deformation D of a carbon fiber cross section.

FIG. 8 is a schematic view showing an example of a lamella structure in a cross section of carbon fiber.

FIG. 9 is a schematic view showing an example of a lamella structure in a cross section of carbon fiber.

FIG. 10 is a schematic view showing an example of the shape of a single fiber transverse section of the carbon fiber of the present invention.

FIG. 11 is a schematic view showing a shape example of a single fiber cross section of the carbon fiber of the present invention.

FIG. 12 is a schematic view showing an example of the shape of a single fiber cross section of the carbon fiber of the present invention.

FIG. 13 is a schematic plan view showing the shape of the spinning holes of the spinneret used in Example 1.

FIG. 14 is a schematic plan view showing the shape of a spinning hole of a spinneret used in Comparative Example 2.

FIG. 15 is a cross-sectional view of a single fiber spun from the spinning hole having the shape shown in FIG.

[Explanation of symbols]

 F: Carbon fiber a: Lamellar structure R: Circumscribed circle radius r: Inscribed circle radius

Claims (5)

[Claims] 1. The fiber cross-sectional shape has at least one plane of symmetry passing through its centroid, and has a rotational symmetry angle θ defined by θ = 360 ° / n (n is an integer from 1 to 10). A non-circular cross-section carbon fiber having a non-circular shape and a basis weight per single fiber of 0.1 mg / m 2 or more. 2. The non-circular shape according to claim 1, wherein the internal structure is a non-lamellar structure having a substantially uniform crystal structure, and the surface smoothness S of the fiber surface is 1.16 or less. Cross section carbon fiber. 3. A single fiber has a non-circular cross section having a concave portion toward the center side of the fiber cross section, and the ratio R of the circumscribed circle radius R and the inscribed circle radius r in the cross section. The degree of deformation D defined by / r is 1.1 to 7.0, and the carbon fiber having a non-circular cross section according to claim 1 or 2. 4. The monofilament has a cross-sectional shape of 3 to 5 leaves, and each leaf has a bulge from its root to its tip, and a plurality of circles are substantially joined. The carbon fiber having a non-circular cross section according to claim 3, wherein the carbon fiber has a shape and a deformation degree D of 1.5 to 3. 5. A carbon fiber reinforced composite material comprising the carbon fiber having a non-circular cross section according to any one of claims 1 to 4 and a resin.