JP2005344254A - Carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substantially non-twisted carbon fiber which has both an improved tensile elastic modulus and an improved compression strength, highly harmonized physical values, and simultaneously an excellent fuzz grade, and to provide a method for producing the same. <P>SOLUTION: This substantially non-twisted carbon fiber is characterized by satisfying an expression (1): 230×10<SP>3</SP>≤E×C÷Lc≤400×10<SP>3</SP>[E(GPa) is a tensile elastic modulus; Lc is a crystal size; and C (MPa) is a compression strength of one direction composite made from the carbon fiber in the direction of 0°] or an expression (2): 1,150×10<SP>3</SP>≤E×F÷Lc≤1,800×10<SP>3</SP>[E(GPa) is a tensile elastic modulus; Lc (nm) is a crystal size; F(MPa) is a single fiber compression strength], and having an abraded fuzz rate of ≤10 fuzzes/m. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carbon fiber excellent in tensile modulus and compressive strength of a composite and excellent in quality and a method for producing the same.

  Since carbon fibers have a higher specific strength and specific modulus than other reinforcing fibers, they are widely used industrially as reinforcing fibers for composite materials in aerospace, sports and general industrial applications. In recent years, there has been an increasing demand for higher performance of carbon fiber reinforced composite materials (hereinafter referred to as composites). In general, the characteristics of composites largely depend on the performance of the carbon fiber itself, and the demand for higher performance of the composite means higher performance of the carbon fiber itself. Properties required for the composite include tensile properties such as tensile strength and compressive properties including compressive strength. The required properties differ depending on the application, but in particular, in applications that are used under complex stresses such as aircraft primary structural materials and golf club shafts, compressive force acts on one side of the composite and tensile force acts on the other side. In order to do so, the tensile and compression properties must be well balanced at a high level. Further, from the viewpoint of weight reduction, there is a demand for improving the rigidity of the composite by increasing the elastic modulus of the carbon fiber itself.

  In general, carbon fibers are known to have a trade-off relationship in that, when the firing temperature of carbon fibers is increased, the elastic modulus increases, but on the other hand, tensile strength and compressive strength are reduced. With respect to such a trade-off relationship, there are several proposals for two points of improving the compressive strength of the composite or improving the elastic modulus of the carbon fiber.

  For example, a technique for improving the compressive strength by specifying the relationship between the elastic modulus of carbon fiber and the crystal size and the microvoid diameter has been proposed (see Patent Document 1). However, in this technique, although an improvement in compressive strength is recognized, the absolute value is about 1350 MPa at the highest level, and it is not related to a so-called graphitized yarn having a crystal size exceeding 3 nm. Although an effect can be expected for weight reduction, sufficient compressive strength cannot be obtained due to its high crystallinity.

  Separately, it is known to improve the compressive strength by reducing the crystallinity of the carbon fiber. Conventionally, as means for reducing crystallinity, a technique for improving the compressive strength of a single fiber by injecting ions into the surface of the carbon fiber to lower the crystallinity of the carbon fiber surface layer is disclosed (Patent Document 2 and Patent). Reference 3). This technology can be applied to both carbonized yarn and graphitized yarn, and the effect of improving the compressive strength of single fibers is recognized. However, these documents do not mention the effect on composite properties, and the effect is unknown. It is. Furthermore, this technique requires special equipment for ion implantation and is unsuitable for mass production, and it is extremely difficult to industrially produce carbon fiber at low cost.

  Furthermore, low temperature carbonization is known as a method for refining the crystal size of carbon fibers. This is a method of reducing the crystal size by lowering the maximum carbonization temperature and obtaining high compressive strength (see Patent Document 4). By using this technique, special equipment such as the above-described ion implantation method is unnecessary, and there is an advantage that it is excellent in mass productivity, and at the same time, an improvement in compression characteristics of the composite can be expected. However, in this method, in order to lower the carbonization temperature, the elastic modulus of the carbon fiber is also reduced to a so-called ordinary elastic modulus level of 250 GPa, and sufficient rigidity cannot be obtained, so that the weight reduction of the composite product is limited. There is.

  On the other hand, in order to improve the elastic modulus of carbon fiber, a high-stretch firing technique that increases the stretch ratio in the flameproofing process and the carbonization process is known. For example, a method has been proposed in which the precursor, which is a precursor of carbon fiber, is subjected to fiber opening and twisting by air treatment, and the elastic modulus is improved by increasing the stretch ratio in the firing step (see Patent Document 5). However, as a result of investigations by the present inventors, in such a method, a large amount of fluff of carbon fibers is generated, the fluff quality of the running yarn is lowered, the product yield in the firing process is lowered, or the composite molding is performed. It turned out that there were problems such as causing problems of deteriorating quality.

Thus, the actual condition is that carbon fibers having high tensile elasticity modulus of carbon fibers and compressive strength of the composite and excellent carbon fiber fluff quality have not been obtained on an industrial scale.
JP 63-2111326 A Japanese Patent Laid-Open No. 3-180514 JP-A-9-170170 JP 2002-339170 A JP 58-214534 A

  The object of the present invention is to improve and improve both the tensile modulus and compressive strength, which have been difficult to improve at the same time by the conventional carbon fiber production method, and have highly harmonized physical property values. In addition, an object is to provide a substantially untwisted carbon fiber excellent in fluff quality and a method for producing the same.

  The present invention is intended to achieve the above object, and the carbon fiber of the present invention has a tensile elastic modulus E (GPa), crystal size Lc (nm), and compression of a unidirectional composite made from carbon fiber in the 0 ° direction. The following formula (1) is established between the strengths C (MPa), and the number of fuzzed fluffs measured by the fuzzing fluff evaluation method is 10 or less per 1 m. Fiber.

230 × 10 ³ ≦ E × C ÷ Lc ≦ 400 × 10 ³ (1)
Further, the carbon fiber of the present invention has the following formula (2) among the tensile elastic modulus E (GPa), the crystal size Lc (nm), and the single fiber compressive strength F (MPa), and the fuzzing fluff evaluation method It is a substantially untwisted carbon fiber characterized in that the number of rubbing fluffs measured in (1) is 10 or less per 1 m.

1150 × 10 ³ ≦ E × F ÷ Lc ≦ 1800 × 10 ³ (2)
The carbon fiber of the present invention has the following preferred embodiments.
(a) The tensile elasticity E (GPa) is in the range of 255 to 345 GPa, and the number of single fibers is at least 1,000.
(b) The crystal size Lc (nm) is in the range of 1.0 to 2.5.
(c) 0 degree compressive strength C (MPa) of the unidirectional composite produced from the said carbon fiber exists in the range of 1500-1800.
(d) The single fiber compressive strength F (MPa) of the carbon fiber is in the range of 6500 to 9000.
(e) The amount of the sizing agent attached to the carbon fiber weight is in the range of 0.1 to 1.0% by weight or less.
(f) The single fiber diameter R (μm) of the carbon fiber is in the range of 4 ≦ R ≦ 7.

  In the carbon fiber production method of the present invention, the carbonization step for carbonizing the carbon fiber is performed at a temperature in the range of 1000 to 1500 ° C. in an inert atmosphere, and the tension of the running yarn is 4.5 gf / It is a carbon fiber manufacturing method characterized by being performed at a high tension of tex or higher.

  In the carbon fiber production method of the present invention, 0.5 to 250 liters of water per kg is applied to the running yarn before the carbon fiber carbonization step and the electrolytic oxidation surface treatment step. In a preferred embodiment, the traveling yarn is impregnated with the electrolytic solution in a pre-impregnation tank installed immediately before the electrolytic oxidation surface treatment step.

  According to the present invention, it is possible to obtain a substantially untwisted carbon fiber excellent in both tensile modulus and compressive strength and at the same time excellent in fluff quality, so by using the carbon fiber of the present invention, A composite excellent in rigidity and compressive strength can be efficiently molded, and carbon fibers and prepregs excellent in quality can be provided.

  The carbon fiber according to the present invention has the following formula (1) between the tensile elastic modulus E (GPa), the crystal size Lc (nm), and the compressive strength C (GPa) in the 0 ° direction of the unidirectional composite produced from the carbon fiber. ) Or the following formula (2) holds between the tensile modulus E (GPa), the crystal size Lc (nm), and the single fiber compressive strength F (MPa), and the number of fuzzing fuzzes is 10 per m. It is a substantially untwisted carbon fiber characterized in that the number of carbon fibers is not more than one.

230 × 10 ³ ≦ E × C ÷ Lc ≦ 400 × 10 ³ (1)
1150 × 10 ³ ≦ E × F ÷ Lc ≦ 1800 × 10 ³ (2)
Here, the tensile elastic modulus E (GPa) can be obtained as follows. That is, a mixed resin of carbon fiber with 100 parts by weight of 3,4 epoxycyclohexylmethyl- (3,4-epoxy) cyclohexylcarboxylate, 3 parts by weight of boron trifluoride monoethylamine, and 4 parts by weight of acetone. After the mixed resin is cured by heating at a temperature of 130 ° C. for 35 minutes, a tensile test is performed using a tensile tester in accordance with the method defined in JIS R 7601 (1986). At this time, the sample length is 200 mm, and the tensile speed is 60 mm / min. And a tensile elasticity modulus is computed from the inclination of the load change in the range whose tensile elongation is 0.45-0.85%.

Further, the crystal size Lc (nm) can be obtained by a wide angle X-ray diffraction method. That is, a carbon fiber is cut into a length of 4 cm, and is solidified into a prismatic shape using a mold and an alcohol solution of collodion to obtain a sample. CuKα (Ni filter) is used as the X-ray source, and the output is 40 kV and 20 mA. Then, from the half width of the peak of the plane index (002) obtained by the transmission method, the crystal size is calculated using the Scherrer equation, that is, Lc (hkl) = K · λ / β _{0 ·} cos θ _B calculate. Here, Lc (hkl) is the average size of crystals in the direction perpendicular to the (hkl) plane, K is 1.0, λ is the wavelength of X-rays, and β ₀ is (β _E ² -β ₁ ² ) ^1/2 , θ _B is the Bragg angle, β _E is the apparent half width (measured value), and β ₁ is 1.05 × 10 ⁻² rad.

Further, the compressive strength C (GPa) in the 0 ° direction of the unidirectional composite can be obtained as follows. That is, first, a unidirectional prepreg having a basis weight of carbon fiber of 125 g / m ² and a content of 76% by weight is manufactured. As the resin, a mixed resin of 100 parts by weight of 3,4 epoxycyclohexylmethyl- (3,4-epoxy) cyclohexylcarboxylate, 3 parts by weight of boron trifluoride monoethylamine, and 4 parts by weight of acetone is used. . Next, this unidirectional prepreg is laminated so that the thickness of the carbon fiber is aligned, and the thickness is about 1 mm, and the resin is cured by heating and pressurizing in an autoclave at a temperature of 135 ° C. and a pressure of 290 MPa for 2 hours. Carbon fiber reinforced resin composite material (hereinafter referred to as CFRP). For this CFRP, the compressive strength in the 0 ° direction is measured in accordance with the method defined in JIS K 7076 (1991). At this time, the volume content (Vf) of carbon fiber is calculated from the thickness of CFRP, the weight of carbon fiber, the density of carbon fiber, and the number of laminated directional prepregs, and the compression strength in the 0 ° direction obtained above is calculated. , Converted to a value when the volume content of carbon fiber is 60%.

In the present invention, the number of fluffs representing the fluff quality of carbon fiber can be determined by the following method for evaluating fuzz. That is, a carbon fiber bobbin as an evaluation sample is left in a temperature control room controlled at a temperature of 23 ± 5 ° C. and a relative humidity of 60 ± 20% for 30 minutes or more. Next, using the fuzzing fluff apparatus in the temperature control room where the temperature and humidity conditions are set, according to the yarn path diagram shown in FIG. 1, carbon fiber is placed on the creel 1 with a built-in powder clutch, Make a yarn path. First, in order to generate rubbing fluff, carbon fibers are put on four of the rubbing pins 2 having a fixed surface with a diameter of 10 mm and mirror-finished, and then passed through the fluff counter 3. The fluff counter detects the number of fluff with a phototransistor while irradiating the running yarn from the lamp light and condensing the irradiated light with a lens. As detection accuracy, fluff having a yarn length of 2 mm or more and a carbon fiber single fiber diameter of 3 microns or more can be detected. The carbon fiber is wound around the drive roller 4 five times or more and wound around the winder 5 so as not to cause a slip during traveling. The yarn speed is set to 3 m / min, and the running of the carbon fiber is started on the yarn path via the roller 6 shown in FIG. After confirming that the yarn path is stable, the initial tension is adjusted with the powder clutch so that the tension of the carbon fiber during running measured between the fluff counting device 3 and the driving roller 4 becomes 6 gf / tex. Thereafter, the fluff counter is operated, and the evaluation of the rubbing fluff in the running state is repeated 3 times for 1 minute for each sample. The number of rubbing feathers X [pieces / m] is calculated from the following formula, where the number of rubbing feathers counted in one minute is X1, X2, and X3.
X = (X1 + X2 + X3) / 9
Moreover, the single fiber compressive strength F (MPa) can be calculated | required based on the following loop measurement methods. First, about 10 cm of carbon fiber monofilament 7 is placed on a slide glass, and 1 to 2 drops of glycerin are dropped at the center, and the preparation is placed on the loop in a state where a single fiber is twisted to form a loop. This is placed under a microscope to which a video camera is connected, and while constantly monitoring, holding both ends of the loop with fingers and applying a tensile strain 8 at a constant speed. The behavior until breaking is video-recorded, and the loop minor axis 9 (D) and major axis 10 (φ) shown in FIG. 2 are measured on the monitor while the playback screen is stopped. From the single fiber warp R and D, the following formula ε = 1.07 × R / D
2, the strain (ε) in the carbon fiber single fiber strained portion 11 in FIG. 2 is calculated, and a graph in which ε is taken on the horizontal axis and the ratio of the major axis to the minor axis (φ / D) is plotted on the vertical axis is plotted. FIG. 3 shows the plotted results.

  The loop major axis (φ) / loop minor axis (D) ratio shows a constant value (1.34) in a region where compression buckling does not occur, but increases rapidly when buckling starts. The strain at which the φ / D ratio suddenly increases is determined as the compression yield strain (εcf). Ten of these were measured to obtain an average value, and a value obtained by multiplying the average value by the tensile modulus E (MPa) was defined as a single fiber compressive strength F (MPa).

The carbon fiber of the present invention preferably has the following ranges for each parameter required by the above method. That is, the value (E × C / Lc) of the formula (1) consisting of the tensile elastic modulus E (GPa), the crystal size Lc (nm), and the compressive strength C (MPa) in the 0 ° direction is 230 × 10 ³ to It is in the range of 400 × 10 ³ GPa · MPa / nm, preferably in the range of 240 × 10 ^{3 to} 350 × 10 ³ GPa · MPa / nm, and more preferably in the range of 250 × 10 ^{3 to} 300 × 10 ³ GPa · nm. MPa / nm.

When this value is smaller than 230 × 10 ³ GPa · MPa / nm, the compression strength when the CFRP cylinder is formed becomes insufficient. Moreover, in order to make this value larger than 400 × 10 ³ GPa · MPa / nm, the production cost of the carbon fiber is significantly increased, and the use that can be developed is limited.

Further, the carbon fiber of the present invention has a value (E × F / Lc) of the formula (2) consisting of tensile elastic modulus E, composite compressive strength C (GPa) and single fiber compressive strength F (MPa) of 1150 × 10 ^{3 to} 1800 × 10 ³ GPa · MPa / nm, preferably 1250 × 10 ^{3 to} 1700 × 10 ³ GPa · MPa / nm, and more preferably 1350 × 10 ^{3 to} 1600 × 10 ^3. GPA · Mpa / nm.

When this value is smaller than 1150 × 10 ³ GPa · MPa / nm, the compressive strength of the composite is insufficient, and in order to make this value larger than 1800 × 10 ³ GPa · MPa / nm, the production cost of the carbon fiber is low. Significantly increased, limiting the applications that can be deployed.

  The carbon fiber of the present invention may be in the form of a bundle in which a plurality of single fibers are aggregated. In this case, the carbon fiber bundle in which the plurality of single fibers are aggregated is preferably substantially untwisted. Substantially no twist means that there are no more than 0.5 turns per meter even if there is a twist.

  The carbon fiber of the present invention preferably has a tensile modulus E (GPa) in the range of 255 to 345 GPa, and the tensile modulus E is more preferably in the range of 265 to 330 GPa. If the tensile modulus E is lower than 255 GPa, the rigidity of the CFRP cylinder is insufficient, and if the tensile modulus E exceeds 345 GPa, the compressive strength in the 0 ° direction of the composite decreases, and the CFRP The bending strength when it is made into a cylindrical body comes to be impaired.

  There are two factors that contribute to the tensile modulus E: carbonization temperature and carbonization tension. If any factor increases, the elastic modulus will improve. However, when the carbonization temperature is raised, the strength and compression characteristics are lowered, and when the carbonization tension is raised, there is a problem that the carbon fiber quality is lowered due to fuzzing.

  In the present invention, the composite 0 ° compressive strength C (MPa) of the carbon fiber is preferably in the range of 1500 to 1800 MPa, and more preferably 1550 to 1700 MPa. When the 0 ° compressive strength C is less than 1500 MPa, it is difficult to obtain a sufficient compressive strength when molded into CFRP, and when the 0 ° compressive strength C exceeds 1800 MPa, it is necessary in a state where the crystal size of the carbon fiber is miniaturized as much as possible. In order to secure the elastic modulus, it is necessary to significantly reduce the yarn speed, which greatly increases the production cost of the carbon fiber and restricts the applications that can be deployed.

  The 0 ° compressive strength C, which is a compression characteristic, depends on the carbon fiber carbonization degree, that is, the crystal size. In other words, if the carbonization temperature is increased to increase the degree of carbonization to increase the crystal size, the compressive strength decreases. For this reason, in order to express compressive strength at a high level, it is preferable to apply low temperature carbonization.

  In the carbon fiber bundle, a preferable range of the number of single fibers of the carbon fiber is 1000 to 48000, and a more preferable range is 6000 to 24000. Those having a number of single fibers of less than 1000 are too thin and inferior in handleability, and yarn breakage and fluff are likely to occur.

  The upper limit of the number of single fibers is not particularly limited, but if it is too thick, the uniformity of resin impregnation will be reduced when processed into a prepreg, resulting in voids when molded into CFRP, and the physical properties of the molded product will be reduced. Therefore, the number of single fibers is preferably 48,000 or less. In addition, when the number of single fibers is less than 1000, fluffing easily occurs due to rubbing with a roller in the firing step, and the quality may be lowered.

  The carbon fiber of the present invention preferably has a crystal size Lc (nm) in the range of 1.0 to 2.5. A more preferable range of the crystal size Lc is 1.5 to 2.0. If the crystal size Lc is smaller than 1.0 nm, the rigidity of the CFRP cylinder is insufficient and it is difficult to reduce the weight. If the crystal size Lc exceeds 2.5 nm, the compressive strength in the 0 ° direction of the composite will be insufficient.

  The crystal size Lc is determined uniformly by the carbonization temperature. Increasing the carbonization temperature also increases Lc. The carbonization temperature necessary for the crystal size obtained here is preferably 1000 to 1500 ° C.

  The carbon fiber of the present invention preferably has a single fiber diameter in the range of 4 to 7 μm. If the single fiber diameter is smaller than 4 μm, the weak yarn is liable to be broken during firing, and the quality of the carbon fiber is deteriorated and the process passability is lowered. On the other hand, if the single fiber diameter is larger than 7 μm, carbonization is not sufficiently performed to the inside of the single fiber, and the elastic modulus is lowered.

The fluff quality of the carbon fiber of the present invention is preferably 10 or less / m, more preferably 8 or less / m, and further preferably 5 or less / m, as the number of fluffs. If the abrasion fluff exceeds 10 pieces / m, the CF becomes fluffy when processed into a prepreg or composite molded product, and the product yield decreases or the productivity at the time of processing decreases, and the product quality deteriorates due to fuzz defects. become.
Reduction of fuzzing fluff means improvement in carbon fiber quality. Generally, the fuzz can be reduced by reducing the tension, but in order to secure the necessary elastic modulus by low-temperature carbonization, it is required to apply a certain amount of tension to the carbon fiber. In order to suppress scratching fluff under high tension, water is applied to the carbonized yarn (carbonized running yarn) with the most fluffing, and surface treatment liquid is pre-impregnated to internalize the fluff and suppress fluffing. The method of doing is mentioned. However, if the amount of water imparted to the carbonized yarn is small, fluffing occurs due to a decrease in convergence, and if it is too much, there is a risk of fluffing due to the impact on the carbonized yarn due to the flow of water itself. It is preferable to set it to -250 liters.

  Next, the manufacturing method of the carbon fiber of this invention is demonstrated.

  The carbon fiber prescribed | regulated to this invention can be manufactured as follows, for example. That is, after the polyacrylonitrile fiber is made flame resistant by heating at a temperature in the range of 200 to 300 ° C. in an oxidizing atmosphere (usually in air), the flame resistant fiber is inactivated prior to carbonization treatment. A so-called preliminary carbonization treatment is performed in which heating is performed at a temperature within a range of 300 to 1000 ° C. in an atmosphere (usually in a nitrogen atmosphere). After performing the preliminary carbonization treatment in this manner, the maximum temperature is in the range of 1000 to 1500 ° C. in an inert atmosphere (usually in a nitrogen atmosphere), and the running yarn tension is 4.5 gf / Carbon fibers can be produced by heating and carbonizing at tex or higher.

  With respect to the maximum carbonization temperature, a more preferable range is 1200 to 1450 ° C, and a further preferable range is 1250 to 1400 ° C. When the maximum carbonization temperature is 1000 ° C. or less, the tensile elastic modulus decreases, and when the maximum carbonization temperature exceeds 1500 ° C., the crystallization of carbon fibers is promoted and the compression strength when CFRP is obtained decreases. The tension of the running yarn is preferably 4.5 gf / tex or more, more preferably 5.0 gf / tex or more. If the tension of the running yarn is less than 4.5 gf / tex, it is difficult to obtain the necessary tensile elastic modulus, and if it is 7.0 gf / tex or more, fluff of carbon fiber is generated and not only the productivity is lowered due to winding around the roller. In addition, the quality of the carbon fiber is significantly lowered.

  In the present invention, in order to improve the compressive strength, the aim is to obtain high-quality carbon fibers by refining the crystal size by low-temperature carbonization. At the same time, in order to keep the tensile elastic modulus of the carbon fibers high, in the carbonization process It is necessary to increase the tension of the running yarn to the limit. When carbonized with high tension, productivity decreases due to winding of the carbonized yarn on the roller due to fluffing and deterioration of the fluff quality of the carbon fiber occurs. Therefore, the present inventors diligently studied, and by applying the following production technology, it is possible to produce carbon fibers with high productivity and high fluff quality by suppressing the occurrence of fluff even in high tension carbonization. It was.

  First, since the carbon fiber in a dry state obtained from the carbonization furnace is most likely to generate fluff, water, preferably pure water, may be imparted to the carbon fiber running on the roller to suppress the occurrence of fluff. preferable. This is considered to be because the convergence is improved by imparting water to the running carbon fiber, and fluffing and wrapping can be suppressed by making the fluff in the carbon fiber bundle. As a method for imparting water to the carbon fiber, methods such as a dripping method, a spray method, and a dip method are conceivable, but the method is not particularly limited to these methods.

  The amount of water to be applied is preferably 0.5 liter or more and 250 liters or less, more preferably 1 liter or more and 100 liters or less, and further preferably 2 liters or more and 50 liters or less, per 1 kg of the running carbon fiber. When the amount of water exceeds 250 liters, fluffing may occur due to the impact on the running yarn due to excessive supply, leading to an increase in cost associated with an increase in the amount of water used. In addition, when the amount of water is less than 0.5 liter, the effect of improving the convergence by applying water is insufficient, and the running yarn is taken up by the roller and winding may occur or the fluff quality may deteriorate.

  Furthermore, it is preferable to pre-impregnate the running yarn with an electrolyte as a carbonized yarn fluff suppression technique. This is aimed at suppressing the occurrence of fluff coming off from the running yarn due to the electrolyte flow in the surface treatment tank, and the suppression of splitting due to the single fiber entanglement of the adjacent running carbon fibers in the surface treatment tank. is there. Normally, when carbonized yarn travels in the surface treatment tank, the fluff existing in the carbon fiber bundle is pulled out or dropped by the flow of the electrolyte, resulting in poor separation due to fluffing or tangling between adjacent yarns. May occur. In order to prevent these problems, a pre-impregnation tank filled with a liquid is installed in front of the surface treatment tank, and the surface treatment tank is run in a state in which the carbon fiber is pre-impregnated with the liquid to improve the convergence of the running yarn. Is the method. The liquid used in the pre-impregnation tank here is not particularly limited, but it is preferable to use the electrolytic solution used in the surface treatment described later.

  As the surface treatment, an electrolytic oxidation surface treatment can be performed for the purpose of generating a functional group on the surface of the carbon fiber and enhancing the adhesion to the resin. The method includes liquid phase oxidation using a chemical solution, electrolytic oxidation in which carbon fiber is treated as an anode in an electrolytic solution, and vapor phase oxidation by plasma treatment in a phase state. As the surface treatment method, an electrolytic oxidation treatment method that is relatively easy to handle and is advantageous in terms of cost is preferably employed. As the electrolytic solution, either an acidic aqueous solution or an alkaline aqueous solution can be used. As the acidic aqueous solution, sulfuric acid or nitric acid exhibiting strong acidity is preferable, and as the alkaline aqueous solution, an aqueous solution of an inorganic alkali such as ammonium carbonate or ammonium hydrogen carbonate is preferable. Is preferably used.

After performing the electrolytic oxidation treatment by the surface treatment, a sizing agent can be applied to the carbon fiber and used for a molded product. The kind of the sizing agent here is not particularly limited, but a bisphenol A type epoxy resin mainly composed of an epoxy resin or an aliphatic compound having two or more epoxy groups at both ends having a linear structure is preferable. Used. The term “aliphatic compound” refers to an acyclic linear saturated hydrocarbon, a branched hydrocarbon, or a chain structure in which a carbon atom of the hydrocarbon is replaced with an oxygen atom. The epoxy group is preferably a highly reactive glycidyl group. Specific examples of the aliphatic compound having an epoxy group in the present invention include glycerin polyglycidyl ethers for glycidyl ether compounds and polyethylene glycol diglycidyl ethers for diglycidyl ether compounds.
A preferable range of the amount of the sizing agent attached to the carbon fiber is 0.1 to 1.0% by weight, and a more preferable range is 0.2 to 0.9% by weight. When the amount of sizing agent adhering exceeds 1.0% by weight, fluff and thread breakage are likely to occur when the carbon fiber is unwound from the package. In addition, when the sizing adhesion amount is less than 0.1% by weight, the carbon fiber at the time of thawing becomes easy to handle, and not only the handling property becomes difficult, but also high-order workability tends to deteriorate due to fuzzing. .

  The carbon fiber of the present invention is widely used industrially as a reinforcing fiber for composite materials in aerospace, sports and general industrial applications.

  Hereinafter, the present invention will be described in detail with reference to examples.

(Example 1)
An acrylonitrile fiber bundle having a single fiber fineness of 0.74 dtex and 12,000 single fibers was heated in an air atmosphere at a temperature of 240 ° C. for 90 minutes to obtain flame-resistant fibers, and then the highest in a nitrogen atmosphere. Pre-carbonization was performed at a temperature of 700 ° C. Subsequently, in a nitrogen atmosphere, the maximum temperature is 1300 ° C., the tension of the running yarn in the carbonization furnace is carbonized at 5.5 gf / tex, and subsequently the roller installed from the carbonization furnace outlet side to the surface treatment, 5 liters of pure water per 1 kg of running yarn is applied, passed through a pre-impregnation bath in which ammonium hydrogen carbonate is flowed immediately before the running yarn enters the surface treatment bath, and further subjected to electrolytic oxidation surface treatment using ammonium hydrogen carbonate as an electrolyte, Subsequently, a sizing agent containing glycerin polyglycidyl ether as a main component was adhered to 0.6% by weight to obtain a carbon fiber having a single fiber diameter of 5.5 μm. The carbon fiber and properties were as follows.

Tensile modulus (E): 295 GPa
Crystal size (Lc): 1.6 nm
Abrasion fluff: 2 / m
Compressive strength in 0 ° direction (C): 1580 MPa
Single fiber compressive strength (F): 7900 MPa
E × C / Lc: 291 × 10 ³ GPa · MPa / nm
E × F / Lc: 1457 × 10 ³ GPa · MPa / nm
Here, using the obtained carbon fiber, production of a unidirectional prepreg, production of a cylindrical molded product, and measurement of physical properties were performed based on the following methods. All physical properties were measured in an environment at a temperature of 23 ° C. and a relative humidity of 50%.

  A unidirectional prepreg was prepared as follows. The epoxy resin composition was applied onto release paper using a reverse roll coater to prepare a resin film. Next, two resin films were stacked on both sides of the carbon fiber on the carbon fiber aligned in one direction on the sheet, and heated and pressed to impregnate the resin to prepare a one-way prepreg. The carbon fiber weight fraction was 76% by weight. The unidirectional prepreg thus obtained was used for the reinforcing material I, straight material I and straight material II shown below.

  The carbon fiber used in the other unidirectional prepreg necessary for molding the following cylindrical molded product is characterized in that the angle material has a tensile modulus of 380 GPa, the crystal size is 3.9 nm, and the hoop material has a tensile modulus. The crystal size was 2.7 GPa at 295 GPa, and the reinforcing material II was a tensile elastic modulus of 245 GPa and the crystal size was 2.0 nm. The unidirectional prepreg manufacturing method is the same as that of the reinforcing material I, the straight material I, and the straight material II.

From these unidirectional prepregs, a cylindrical molded product was produced by the following procedures (a) to (e) using a stainless steel round bar having a diameter of 6.3 mm (length: 1000 mm).
(A) As the reinforcing material I, seven prepregs having a carbon fiber basis weight of 125 g / m ² are attached in the 0 ° direction with respect to the cylindrical axis direction.
(B) Next, as an angle material, ^two prepregs having a carbon fiber basis weight of 70 g / m ² are attached in a direction of ± 45 ° with respect to the cylindrical axis direction.
(C) As straight material I, one prepreg having a carbon fiber basis weight of 100 g / m ² is attached in a direction of 0 ° with respect to the cylindrical axis direction.
(D) As a hoop material, one prepreg having a carbon fiber basis weight of 55 g / m ² is attached in the ± 90 ° direction with respect to the cylindrical axis direction.
(E) As straight material II, ^two prepregs with a carbon fiber basis weight of 125 g / m2 are pasted in a direction of 0 ° with respect to the cylindrical axis direction.
(F) as a reinforcing material II, paste 6 sheets ± 45 ° direction prepreg of carbon fiber weight per unit area 100 g / ^{m 2} basis weight with respect to the cylindrical axis.
(G) Wrapping tape (heat-resistant film tape) is wound and heat-molded at a temperature of 130 ° C. for 2 hours in a curing furnace.
(H) After molding, the mandrel is extracted, and the wrapping tape is removed to obtain a cylindrical composite material.

  The bending fracture load of the cylinder was measured as follows. Using the above-obtained cylindrical composite material with an inner diameter of 6.3 mm, described in “Golf Club Shaft Certification Criteria and Method for Confirming Standards” (Product Safety Association, Approved by the Minister of International Trade and Industry, No. 2087, 1993) Based on the three-point bending test method, the bending fracture load was measured, the number of measurements was n = 6, and the average value was the bending fracture load. Here, the distance between fulcrums was 150 mm, and the test speed was 10 mm / min. The bending fracture load of this cylinder was 1800N.

(Example 2)
A carbon fiber and a cylindrical composite material were produced in the same manner as in Example 1 except that Example 1 and the pre-impregnation tank on the entrance side of the surface electrolytic treatment were not passed. The characteristics of this carbon fiber and the bending fracture load of the cylinder were as follows.

Tensile modulus (E): 292 GPa
Crystal size (Lc): 1.6 nm
Abrasion fluff: 4 / m
Compressive strength in 0 ° direction (C): 1560 MPa
Single fiber compressive strength (F): 7800 MPa
E × C / Lc: 285 × 10 ³ GPa · MPa / nm
E × F / Lc: 1424 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1770N
(Example 3)
In the same manner as in Example 1 except that 0.1 liter of pure water per kg of running yarn is applied to the roller installed in the surface treatment from the exit side of the carbonization furnace in Example 1, carbon fiber and a cylindrical composite material are provided. Produced. The characteristics of this carbon fiber and the bending fracture load of the cylinder were as follows.

Tensile modulus (E): 290 GPa
Crystal size (Lc): 1.7 nm
Abrasion fluff: 5 / m
Compressive strength in 0 ° direction (C): 1550 MPa
Single fiber compressive strength (F): 7700 MPa
E × C / Lc: 264 × 10 ³ GPa · MPa / nm
E × F / Lc: 1314 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1750N
(Comparative Example 1)
In Example 1, the carbonized fiber was carbonized at a maximum firing temperature of 1520 ° C. and the tension of the running yarn in the carbonization furnace was 4.4 gf / tex. After that, 4 liters of pure water is applied to 1 kg of carbon fiber running on the roller installed between the surface treatment from the carbonization furnace exit side, and after pre-impregnation with the electrolyte with the surface treatment, glycerin polyglycidyl A carbon fiber having a single fiber diameter of 5.4 μm was obtained by applying 0.5% by weight of a sizing agent mainly composed of ether. With respect to this carbon fiber, the characteristics and the like evaluated in the same manner as in Example 1 were slightly reduced in compression characteristics as follows. Moreover, the bending fracture load of the cylindrical composite material using this carbon fiber was 1700N.

Tensile elastic modulus (E): 296 GPa
Crystal size (Lc): 2.0 nm
Abrasion fluff: 5 / m
Compressive strength in 0 ° direction (C): 1520 MPa
Single fiber compressive strength (F): 7250 MPa
E × C / Lc: 225 × 10 ³ GPa · MPa / nm
E × F / Lc: 1073 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1700N
(Comparative Example 2)
Using acrylonitrile fiber having a single fiber fineness of 0.73 dtex and a single fiber number of 18000 as a raw material, it was subjected to flameproofing treatment in the same manner as in Example 1, and then pre-carbonized at a maximum temperature of 620 ° C. in a nitrogen atmosphere. After preliminary carbonization, the carbonized fiber is carbonized at a maximum firing temperature of 1800 ° C. and the tension of the running yarn in the carbonization furnace is 4.3 gf / tex. 4 liters of pure water per kg of carbon fiber traveling on the surface, and after electrolytic oxidation surface treatment using an aqueous sulfuric acid solution as an electrolytic solution without passing through a pre-impregnation tank installed on the surface treatment inlet side, A carbon fiber having a single fiber diameter of 5.6 μm was obtained by applying 1.0% by weight of a sizing agent mainly composed of a bisphenol A type epoxy resin. For this carbon fiber, the characteristics and the like evaluated in the same manner as in Example 1 and the bending fracture load of the cylinder were as follows, and both the fluff quality and the compression characteristics deteriorated.

Tensile modulus (E): 295 GPa
Crystal size (Lc): 2.4 nm
Abrasion fluff: 15 / m
Compressive strength in 0 ° direction (C): 1430 MPa
Single fiber compressive strength (F): 6700 MPa
E × C / Lc: 176 × 10 ³ GPa · MPa / nm
E × F / Lc: 824 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1500N
(Comparative Example 3)
Using acrylonitrile fiber having a single fiber fineness of 1.1 dtex and 12,000 single fibers as a raw material, it was subjected to a flameproofing treatment in the same manner as in Example 1, and then pre-carbonized at a maximum temperature of 650 ° C. in a nitrogen atmosphere. After preliminary carbonization, the maximum firing temperature of the carbonized fiber is carbonized at 1350 ° C., the tension of the running yarn in the carbonization furnace is 1.6 gf / tex, and on the roller installed between the surface treatment from the carbonization furnace exit side. 3 liters of pure water per 1 kg of carbon fiber traveling on the surface, pre-impregnated with a sulfuric acid aqueous solution in a pre-impregnation tank installed on the surface treatment inlet side, and subjected to electrolytic oxidation surface treatment using a sulfuric acid aqueous solution as an electrolytic solution Later, 0.9% by weight of a sizing agent mainly composed of a bisphenol A type epoxy resin was applied to obtain a carbon fiber having a single fiber diameter of 8.0 μm. About this carbon fiber, the characteristic etc. evaluated similarly to Example 1 and the bending fracture load of a cylinder are as follows, and the elasticity modulus did not reach a target.

Tensile elastic modulus (E): 233 GPa
Crystal size (Lc): 1.7 nm
Abrasion fluff: 2 / m
Compressive strength in 0 ° direction (C): 1580 MPa
Single fiber compressive strength (F): 7750 MPa
E × C / Lc: 217 × 10 ³ GPa · MPa / nm
E × F / Lc: 1062 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1700N
(Comparative Example 4)
Using acrylonitrile fiber having a single fiber fineness of 0.73 dtex and 12,000 single fibers as a raw material, it was subjected to a flame resistance treatment in the same manner as in Example 1, and then pre-carbonized at a maximum temperature of 720 ° C. in a nitrogen atmosphere. After preliminary carbonization, the carbonized fiber is carbonized at a maximum firing temperature of 2300 ° C. and the tension of the running yarn in the carbonization furnace is 2.7 gf / tex. 20 liters of pure water per 1 kg of carbon fiber traveling on the surface, pre-impregnated with an aqueous sulfuric acid solution in a pre-impregnation tank installed on the surface treatment inlet side, and subjected to electrolytic oxidation surface treatment using an aqueous sulfuric acid solution as an electrolytic solution Later, 1.5% by weight of a sizing agent mainly composed of a bisphenol A type epoxy resin was applied to obtain a carbon fiber having a single fiber diameter of 5.4 μm. For this carbon fiber, the characteristics and the like evaluated in the same manner as in Example 1 and the bending fracture load of the cylinder are as follows. As a result, the quality decreased, and the compression characteristics also deteriorated significantly.

Tensile modulus (E): 382 GPa
Crystal size (Lc): 3.9 nm
Abrasion fluff: 25 / m
Compressive strength in 0 ° direction (C): 1230 MPa
Single fiber compressive strength (F): 4300 MPa
E × C / Lc: 120 × 10 ³ GPa · MPa / nm
E × F / Lc: 421 × 10 ³ GPa · MPa / nm
Bending fracture load of cylinder: 1400N

  The carbon fiber of the present invention has a higher specific strength and specific modulus than other reinforcing fibers, and is widely used industrially as a reinforcing fiber for composite materials in aerospace, sports and general industrial applications. It is industrially useful.

FIG. 1 is a schematic diagram of a fuzzing fluff device for measuring the number of fuzzing fluffs representing the fluff quality of carbon fibers according to the present invention. FIG. 2 is a schematic diagram for measuring the carbon fiber single fiber compressive strength according to the present invention. FIG. 3 is a schematic view for calculating the carbon fiber single fiber compressive strength according to the present invention.

Explanation of symbols

1: Creel 2: Friction pin 3: Fluff counter 4: Drive roller 5: Winder 6: Roller 7: Carbon fiber monofilament 8: Tensile strain 9: Loop minor axis 10: Loop major axis 11: Strain calculation part

Claims (11)

The following formula (1) is established between the tensile elastic modulus E (GPa) of the carbon fiber, the crystal size Lc (nm), and the compressive strength C (MPa) in the 0 ° direction of the unidirectional composite produced from the carbon fiber, and A substantially untwisted carbon fiber, characterized in that the number of rubbing fluffs measured by the rubbing fluff evaluation method is 10 or less per 1 m.
230 × 10 ³ ≦ E × C ÷ Lc ≦ 400 × 10 ³ (1) The following formula (2) is established among the tensile elastic modulus E (GPa), the crystal size Lc (nm), and the single fiber compressive strength F (MPa) of the carbon fiber, and the fuzzed fluff measured by the fuzzy fluff evaluation method A substantially untwisted carbon fiber characterized in that the number is 10 or less per 1 m.
1150 × 10 ³ ≦ E × F ÷ Lc ≦ 1800 × 10 ³ (2)   The carbon fiber according to claim 1 or 2, wherein the tensile elasticity E (GPa) is in a range of 255 to 345 GPa and the number of single fibers is at least 1,000.   The carbon fiber according to claim 1 or 2, wherein the crystal size Lc (nm) is in the range of 1.0 to 2.5.   The carbon fiber according to claim 1, wherein the unidirectional composite produced from the carbon fiber has a 0 ° compressive strength C (MPa) in the range of 1500 to 1800. The carbon fiber according to claim 2, wherein the single fiber compressive strength F (MPa) of the carbon fiber is in the range of 6500 to 9000.   The carbon fiber according to claim 1 or 2, wherein the amount of the sizing agent attached to the carbon fiber weight is in the range of 0.1 to 1.0% by weight or less.   The carbon fiber according to claim 1 or 2, wherein a single fiber diameter R (µm) of the carbon fiber is within a range of 4≤R≤7.   The carbonization step for carbonizing the carbon fiber is performed in an inert atmosphere at a temperature in the range of 1000 to 1500 ° C., and the tension of the running yarn is high tension of 4.5 gf / tex or more. Carbon fiber manufacturing method.   10. The method for producing carbon fiber according to claim 9, wherein 0.5 to 250 liters of water per kg is applied to the running yarn before the carbon fiber carbonization step and the electrolytic oxidation surface treatment step. .   The method for producing carbon fiber according to claim 9 or 10, wherein the running yarn is impregnated with an electrolytic solution in a pre-impregnation tank installed immediately before the electrolytic surface oxidation treatment step.

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