JP2011213797A - Hybrid carbon fiber reinforced thermoplastic resin composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hybrid carbon fiber reinforced thermoplastic resin composite material which exhibits high strength not achieved by single carbon fiber reinforcement with respect to flexural strength in both 0° and 90° directions, and which is suitable for a structural material.SOLUTION: The hybrid carbon fiber reinforced thermoplastic resin composite material comprises based onf 100 pts.mass of a thermoplastic resin (A), 80-250 pts.mass of long carbon fibers (B) having a fiber diameter of 3-25 μm and a length of ≥20 mm, and 0.1-10 pts.mass of fine carbon fibers (C) having a fiber diameter of 0.5-20 nm and a length of 100-5,000 nm. In the hybrid carbon fiber reinforced thermoplastic resin composite material, it is preferable that the thermoplastic resin (A) is a polyamide resin and/or an acid modified polypropylene resin. In the hybrid carbon fiber reinforced thermoplastic resin composite material, it is more preferable that the fine carbon fibers (C) are carbon nanotubes and/or carbon nanofibers.

Description

    The present invention relates to a hybrid carbon fiber reinforced thermoplastic resin composite material comprising carbon long fibers and carbon fine fibers. More specifically, the present invention relates to a hybrid carbon fiber reinforced thermoplastic resin composite material in which the mechanical strength in the axial direction and the transverse direction of carbon long fibers is remarkably improved by the synergistic effect of carbon long fibers and carbon fine fibers.

Conventionally, a long glass fiber reinforced polypropylene composite material has been known (see, for example, Non-Patent Document 1). However, such a conventional technique has low adhesiveness between glass fiber and polypropylene, has a low reinforcing effect on the strength and elastic modulus of glass fiber, and is unsatisfactory in practical performance as a structural material.
Regarding the adhesion between glass fiber and polypropylene, it is effective to modify propylene with a polar functional group such as maleic anhydride, as disclosed in JP-A Nos. 05-001184 (Patent Document 1) and JP-A No. 06-279615 (Patent Document 2). ). Furthermore, JP 2005-170691 (Patent Document 3) discloses the use of glass fibers treated with a sizing agent containing a special coupling agent. However, the reliability of the high strength and physical properties required for a high-strength structural member such as a safety part has not been achieved. Further, regarding carbon fiber reinforced polypropylene using carbon fiber having higher strength and elastic modulus than glass fiber, a composition having improved adhesiveness using a maleic anhydride-modified polyolefin copolymer is disclosed in JP-A-2005-256206 ( It is disclosed in Patent Document 4). However, the adhesion between the carbon fiber and the polypropylene is still low, and the high strength of the carbon fiber is not reflected in the composite material, and the demand as a structural material has not been achieved.
Moreover, the glass long fiber reinforced polyamide resin composite material which applied the electric wire coating method was known (for example, refer nonpatent literature 2). However, such a conventional technique is not satisfactory in practical performance as a structural material because glass fiber breakage is remarkable in the compounding process and injection molding process, and the reinforcing effect on the strength and elastic modulus of the glass fiber is lowered.

Japanese Patent Laid-Open No. 05-001184 Japanese Patent Laid-Open No. 06-279615 JP 2005-170691 A JP-A-2005-256206 JP 2006-117756 A JP 2003-135976 A JP 2002-105329 A JP 2005-200620 A JP 2009-138032 A JP 2002-97375 A JP 2003-286350 A

Plastics, Vol. 36 (7), p103 (1985) Composites, July, 150 (1973)

On the other hand, research for blending carbon fibers and fine carbon fibers has been underway in order to reduce volume resistivity and to provide conductivity and electromagnetic shielding properties. Japanese Unexamined Patent Application Publication No. 2006-117756 (Patent Document 5) discloses a polyamide composite material containing carbon nanotubes. JP-A-2003-135976 (Patent Document 6) describes that the volume resistivity is stabilized by containing fine carbon fibers such as carbon nanotubes in the thermoplastic resin, and the pitch-based carbon fiber milled is mixed with carbon nanotubes. Japanese Patent Application Laid-Open No. 2002-105329 (Patent Document 7) and the effect of combining ketjen black and carbon nanotubes with vapor grown carbon fiber are disclosed in Japanese Patent Application Laid-Open No. 2005-200620 (Patent Document 8). Yes. Further, JP 2009-138032 (Patent Document 9) discloses that a carbon nanotube and a conductive polymer are used in combination. Moreover, by combining carbon nanotubes and conductive carbon fibers in a thermoplastic resin, the conductivity and gas barrier properties are improved, and a resin composition suitable for a fuel cell separator is provided. -97375 (Patent Document 10). JP-A-2003-286350 (Patent Document 11) discloses a relatively low blending amount of carbon fiber for the purpose of stepwise diluted carbon nanotubes and injection molding. However, the combined use of carbon nanotubes is aimed at exhibiting electrical conductivity, and for reinforcement, only the reinforcing effect by carbon fiber is expected, and the amount of carbon fiber satisfying the required strength was blended.
Improvements in elastic modulus and strength due to the incorporation of carbon nanotubes have been disclosed for transparent film molded products that are difficult to reinforce carbon fibers, but the effect is much smaller than the reinforcement effect of carbon long fibers, and structural materials The intended composite material was totally unexpected and had not been applied.
A structural material made of carbon fiber reinforced resin is very strong when subjected to a tensile load in the length direction of the carbon fiber, but is very weak when subjected to a load in a direction transverse to the fiber axis or a bending load. This strength was not improved by increasing the amount of carbon fiber, but rather a negative effect.
There was a strong demand from designers to improve the strength when subjected to bending load or lateral load with respect to the axial direction of the fiber, which cannot be improved by increasing the amount of carbon fiber.

The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a composite material suitable for a structural material having improved strength when subjected to a bending load or a load lateral to the axial direction of the fiber.

As a result of intensive studies, the present inventors have found that the above problems can be solved by the following means, and have reached the present invention.
That is, this invention consists of the following structures.
1. 80 to 250 parts by mass of carbon fiber (B) having a fiber diameter of 3 to 25 μm and a length of 20 mm or more, and a fiber diameter of 0.5 to 20 nm and a length of 100 to 5000 nm with respect to 100 parts by mass of the thermoplastic resin (A). It is a hybrid carbon fiber reinforced thermoplastic resin composite material characterized by containing 0.1 to 10 parts by mass of carbon fine fiber (C).
2. Moreover, it is a hybrid carbon fiber reinforced thermoplastic resin composite material in which the thermoplastic resin (A) is preferably a polyamide resin and / or an acid-modified polypropylene resin.
3. In addition, in the hybrid carbon fiber reinforced thermoplastic resin composite material, the carbon fine fiber (C) is a carbon nanotube and / or a carbon nanofiber.
4). 1. A carbon fiber reinforced thermoplastic resin composite material for stamping molding, ~ 3. Any of the hybrid carbon fiber reinforced thermoplastic resin composite materials.

    The present invention is a hybrid carbon fiber reinforced thermoplastic composite material that has a very high bending strength that cannot be achieved only by an increase in the amount of carbon fiber and a strength that is extremely high when subjected to a load transverse to the axial direction of the carbon fiber. It is. A molded part obtained by molding a prepreg of a carbon fiber reinforced thermoplastic resin composite material obtained by the present invention is used for a frame part of an automobile, a structural member of a mechanical instrument, a sports instrument or the like. The reason why the present invention provides a prepreg having high bending strength and high strength in the transverse direction with respect to the fiber axis is not yet clear, but increases the compression modulus of the thermoplastic resin in which the fine carbon fibers form the matrix. Therefore, when subjected to bending stress, by suppressing the deformation on the compression side and suppressing the buckling of the carbon fiber, the high tensile strength of the carbon fiber is made effective by preventing the compression failure mode, and fine It is considered that the carbon fiber has low orientation with respect to the axial direction of the carbon fiber and has a reinforcing action in the lateral direction with respect to the axial direction where the reinforcing effect of the carbon fiber cannot be expected.

The present invention is described in detail below.
In the present invention, the fiber diameter is 3 to 25 μm, the carbon long fiber (B) is 80 to 250 parts by mass and the fiber diameter is 0.5 to 20 nm, and the length is 100 to 100 parts by mass of the thermoplastic resin (A). A hybrid carbon fiber reinforced thermoplastic resin composite material comprising 0.1 to 10 parts by mass of carbon fine fibers (C) having a thickness of 100 to 5000 nm.
Moreover, it is a hybrid carbon fiber reinforced thermoplastic resin composite material in which the thermoplastic resin (A) is preferably a polyamide resin and / or an acid-modified polypropylene resin.
Furthermore, it is a hybrid carbon fiber reinforced thermoplastic resin composite material in which the carbon fine fibers (C) are preferably carbon nanotubes and / or carbon nanofibers.
Furthermore, it is a hybrid carbon fiber reinforced thermoplastic resin composite material that is preferably a stamped molded hybrid carbon fiber reinforced thermoplastic resin composite material.

In the present invention, carbon long fibers or continuous fibers having a weight average fiber length of 20 mm or more, preferably 30 mm or more, more preferably 33 mm or more, and further preferably 100 mm or more are used. When the weight average fiber length is less than 20 mm, the strength as a structural material is not achieved, which is not preferable. The preferred fiber length is fundamentally different between the composite material for the structural material and the composite material for the purpose of imparting electrical conductivity. In the case of the composite material for structural material which is the object of the present invention, a fiber length capable of transmitting stress even under high stress or high strain is required. The objective cannot be achieved when the fibers are entangled or in contact. In terms of mechanical properties, continuous fibers are preferable, but fluidity in the mold during stamping molding is required, so as a prepreg, it was cut to a length that satisfies the fluidity while maintaining a sufficient aspect ratio for reinforcement. Things are sometimes used. Although it does not restrict | limit especially in a manufacturing method as carbon fiber, After processing fibers, such as a polyacrylonitrile fiber and a cellulose fiber, in air at 200-300 degreeC, it is baked at 1000-3000 degreeC or more in inert gas. Carbon fibers produced by carbonization and having a tensile strength of 20 t / cm ² or more and a tensile modulus of 200 GPa or more are preferred. The diameter of the single fiber used in the present invention is not particularly limited, but is preferably 3 to 25 μm from the composite production line process; particularly preferably 4 to 15 μm. If it is less than 3 μm, impregnation and defoaming are difficult, and if it exceeds 25 μm, the specific surface area becomes small and the effect of compositing becomes unfavorable. The carbon fiber used in the present invention is preferably treated for improving adhesion by wet oxidation with air or nitric acid, dry oxidation, heat cleaning, whiskerizing, or the like. Moreover, it is preferable that the carbon fiber used for composite material manufacture of this invention is bundled by the bundling agent which softens at 100 degrees C or less from the handleability of a work process. Although there is no restriction | limiting in particular in the number of focusing filaments, 1000-30000 filaments, Preferably 3000-25000 filaments are preferable.
The carbon long fiber or continuous fiber is contained in an amount of 80 to 250 parts by mass, preferably 90 to 200 parts by mass, per 100 parts by mass of the thermoplastic resin. If it is less than 80 parts by mass, the strength and elastic modulus as a structural material are low and not preferable, and if it exceeds 250 parts by mass, it is difficult to impregnate carbon fiber with a thermoplastic resin, and the generation of fluff and void ratio during impregnation is high. It is not preferable.

The carbon fine fiber used in the present invention is called carbon nanotube or carbon nanofiber, and the carbon layer is a single layer with a carbon hexagonal mesh surface closed in a cylindrical shape or a cylindrical carbon layer is nested. There is a multi-layered one that is not limited to any one. Multi-walled carbon nanotubes with high bending strength that are difficult to break due to shear pressure during impregnation are preferred. The single fiber diameter is 0.5 to 20 nm, preferably 5 to 15 nm, and the length is 100 to 5000 nm, preferably 150 to 3000 nm. When the single fiber diameter is less than 0.5 nm, it is difficult to disperse in the thermoplastic resin, and the carbon fiber is easily broken by the shear stress during impregnation, which is not preferable. On the other hand, if it exceeds 20 nm, the fine dispersion effect characteristic of fine fibers cannot be obtained, and the hybrid reinforcing effect with carbon fibers cannot be obtained, which is not preferable. If the length is less than 100 nm, the reinforcing effect is small and is not preferred for the present invention. If the length is more than 5000 nm, it is difficult to disperse in the resin. The aspect ratio (L / D) obtained by dividing the length (L) by the single fiber diameter (D) is preferably 10 or more, more preferably 50 or more, and particularly preferably 100 or more.
The method for producing carbon nanotubes and carbon nanofibers used in the present invention is not limited, but a method of arc discharge between the carbon electrodes and growing on the cathode surface of the discharge electrode, or irradiating the silicon carbide with a laser beam, It is produced by a method of heating and sublimation, a method of carbonizing a hydrocarbon in a gas phase under a reducing atmosphere using a transition metal catalyst, and the like. The shape and size of the carbon nanotube obtained by the manufacturing method are different. In the carbon nanotube, the graphite layer is substantially parallel to the fiber axis. On the other hand, fine carbon fibers produced by the vapor phase method are not hollow depending on the production method, have a structure in which the graphite layer is inclined with respect to the fiber axis, and are substantially perpendicular to the fiber axis. There are some things that are unclear, and these are called nanofibers. In the present invention, a graphite layer having a substantially right angle or an unclear graphite layer is not preferable because the reinforcing effect is small.
The composite material of the present invention contains 0.1 to 10 parts by mass, preferably 1 to 7 parts by mass of the carbon fine fiber (C) with respect to 100 parts by mass of the thermoplastic resin (A). If it is less than 0.1 parts by mass, the effect of hybridizing carbon fine fibers cannot be exhibited, which is not preferable. On the other hand, if it exceeds 10 parts by mass, the melt viscosity of the resin increases and the impregnation property of the carbon fibers decreases, which is not preferable. The difference between the case where the carbon fiber of the equal mass part is increased and the case where the carbon fine fiber is hybrid is that the carbon fiber (B) is 60 parts by mass, particularly 100 parts by mass with respect to 100 parts by mass of the thermoplastic resin (A). It is remarkable in the composite material contained exceeding. When the carbon fiber content exceeds this, the bending strength in the transverse direction of the carbon fiber content with respect to the length direction of the carbon fiber (hereinafter referred to as 90 ° bending strength) decreases, but the carbon fine fiber is hybridized. In this case, there is a big difference that the 90-degree bending strength increases. In addition, when the carbon fiber content increase is replaced with carbon fine fiber with respect to the increase in the bending strength in the length direction of the carbon fiber (hereinafter referred to as 0 degree bending strength) with respect to the increase in carbon fiber content, Its intensity increment is more than twice. The 0 degree bending strength of the composite material containing 5 parts by mass of carbon fine fiber is 1/2 with respect to the 0 degree bending strength of the composite material containing 5 parts by mass of carbon fiber in 100 parts by mass of the thermoplastic resin (A). Because of the following, the hybrid effect of carbon fiber and fine carbon fiber is a surprising synergistic effect that is not expected at all. The reason for this effect is not well understood, but long carbon fibers are effective for strengthening the tension side, and fine carbon fibers that fill the gap between the carbon fibers are effective for strengthening the buckling on the compression side. It is considered that a synergistic effect was exhibited in the bending strength in which the tensile deformation mode and the compression deformation mode were combined.
According to the present invention, the 0-degree bending strength is 1000 MPa, and the 90-degree bending strength is more than 95 MPa, preferably more than 100 MPa.

The thermoplastic resin used in the present invention is not particularly limited. Examples include polyamide resin, saturated polyester resin, polycarbonate resin, polyolefin resin, polyphenylene sulfide resin, polyoxymethylene resin, polyphenylene ether resin, polystyrene resin, ABS resin, AS resin, and the like. Among these, those containing a functional group having an affinity for carbon fiber or fine carbon fiber are preferable because they have high adhesion to the fiber and can exert a reinforcing effect. Of these, polypropylene resins and / or polyamide resins are preferred, and acid-modified polypropylene resins are particularly preferred among polypropylene resins.
The weight average molecular weight of the acid-modified polypropylene preferably used in the present invention is 80,000 to 200,000, preferably 90,000 to 180,000. When the weight average molecular weight exceeds 200,000, the melt viscosity becomes high, and when the prepreg is produced, the impregnation property is low and voids are easily contained, and the present invention is not achieved. If the weight average molecular weight is less than 80,000, the strength and elongation are low, and the strength and elongation of the molded product obtained from the prepreg is low, which is not preferable. As a polymerization catalyst, a metallocene catalyst is preferable to a Ziegler-Natta catalyst. Acid modification can be obtained by grafting an unsaturated acid or an unsaturated acid anhydride with a radical derived from an organic peroxide. Of the organic peroxides, dialkyl peroxides are preferred to peroxydicarbonates and peroxyketals. The polydispersity index (ratio of the weight average molecular weight to the number average molecular weight) of the acid-modified polypropylene used in the present invention is 1.5 to 7, preferably 1.6 to 6, particularly preferably 1.7 to 5. is there. In order to obtain an acid-modified polypropylene having a polydispersity index of less than 1.5, a fractionation treatment is required, resulting in an increase in cost. On the other hand, when it exceeds 7, even if the weight average molecular weight is in the range of 80,000 to 200,000, the mixed low molecular weight polypropylene lowers the strength and elongation, which is not preferable. On the other hand, the mixed high molecular weight component is not preferable because it impregnates and impairs. Since the polydispersity index is small, it is considered that even in a relatively low weight average molecular weight product, the low molecular weight component is very small and the high elongation of acid-modified polypropylene is high. It was found that the impregnation properties during prepreg production depended strongly on the weight average molecular weight, while the mechanical properties depended on the low component. By controlling the molecular weight distribution very narrowly, it is possible to achieve both a low weight average molecular weight and a low low molecular weight component.
The weight average molecular weight and the distribution thereof are measured by a gel permeation chromatography method using a 140 ° C. high temperature column for a 1,2,4-trichlorobenzene solution at 140 ° C. according to JIS K7252.

Acid-modified polypropylene used in the present invention, it is necessary to have a reinforcement and high adhesive strength, in an infrared absorption Superutoru, absorbance area of 1790 cm ^-1 and 1710 cm ^-1 relative to the absorbance area of 840 cm ^-1 Is modified with an acid that has a ratio of 0.1 to 1.2, preferably 0.2 to 1.0. When the acid anhydride modification degree is less than 0.1%, the strength of the molded product obtained by molding the prepreg is low, which is not preferable. On the other hand, if it exceeds 1.2, thermal decomposition and thermal discoloration occur, which is not preferable. Examples of the acid component include anhydrides such as maleic acid, itaconic acid, succinic acid, and adipic acid, acrylic acid, and methacrylic acid. Of these, maleic acid and itaconic acid anhydride are preferred because they are easily modified. 840 cm ⁻¹ is infrared absorption derived from polypropylene, and is a thickness correction coefficient of the measured test piece. In addition, 1790 cm ⁻¹ and 1710 cm ⁻¹ are absorptions derived from carboxylic anhydride and carboxylic acid, respectively, and the effects are arranged by the total degree of modification since the water absorption and dehydration states are transferred.

  The polypropylene (A) used in the present invention is a homo-type polypropylene having 95% by mole or more of propylene repeating units having almost no branched structure due to impregnation properties at the time of prepreg production and having a high elastic modulus in terms of physical properties. Isotactic or syndiotactic high stereoregularity fractions are preferred. Those having a high isotactic fraction are particularly preferred. In addition, the polymerization catalyst for polypropylene used in the present invention is not particularly limited, but a metallocene catalyst that can provide a polypropylene having a stereoregularity and a sharp molecular weight distribution is preferable.

The acid-modified polypropylene resin and composition of the present invention are not limited in starting materials and production conditions, but with respect to 100 parts by mass of polypropylene (A) having a melt flow rate of 0.1 to 4 dg / min, maleic anhydride A preferred embodiment is obtained by melt-kneading 0.05 to 3 parts by mass of an organic peroxide having a temperature of from 0 to 5 parts by mass and a half-life of 1 minute at 170 to 185 ° C.
The method of acid-modifying a polypropylene (A) by reacting an unsaturated dicarboxylic acid compound and an organic peroxide is industrially preferable, but when modified by this method, the molecular chain of the polypropylene (A) is cleaved by radicals. Accompanied by side reactions. To control this reaction, the radical generation characteristics of the organic peroxide must be matched. An organic peroxide having a half-life of 1 minute at 170 to 185 ° C, preferably 172 to 183 ° C is preferred. When the temperature is less than 170 ° C., radical generation starts from a state in which only a low molecular weight polypropylene is melted, so that a low amount of polypropylene is likely to be generated, and the polydispersity index becomes high. On the other hand, when the temperature exceeds 185 ° C., when the modification reaction is carried out with an extruder having a residence time of 2 minutes or less, a high temperature of 230 ° C. or more is required, which is likely to be accompanied by thermal decomposition and thermal discoloration, which is not preferable from the viewpoint of quality stability. Examples of the organic peroxide having a half-life of 1 minute at 170 to 185 ° C include methyl ethyl ketone peroxide (182 ° C), t-butyl hydroperoxide (179 ° C), and dicumyl peroxide (172 ° C). 2,5-dimethyl-2,5-di (t-butylperoxide) hexane (180 ° C.), n-butyl 4,4-di (t-butylperoxy) valerate (173 ° C.) and the like. Among these, t-butyl hydroperoxide (179 ° C.), dicumyl peroxide (172 ° C.), 2,5 dimethyl 2,5 di (t-butyl peroxide) hexane (180 ° C.) has an active oxygen content. Highly preferred. When 0.01 to 5 parts by mass of maleic anhydride is graft-modified with respect to 100 parts by mass of polypropylene, the organic peroxide is 0.05 to 3 parts by mass, preferably 0.1 ~ 1 part by mass is used.
If it is less than 0.05 parts by mass, the reaction tends to be insufficient, which is not preferable. When the amount exceeds 3 parts by mass, the low molecular weight polypropylene is not preferable because radical action is likely to occur.

The polyamide resin preferably used in the present invention is not particularly limited, but is preferably a polyamide resin having a melting point of 100 ° C. or higher and a flexural modulus of 2 GPa or higher because it is combined and used as a structural material. Examples thereof include aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 12, polyamide 11, polyamide 610, and polyamide 46, polyamide MXD6, polyamide 9T, polyamide 6T, polyamide 4T, copolymers thereof, and polymer alloys. In order to exert the effects of the present invention, a polyamide copolymer having a main polyamide of less than 70 mol% is not preferable because of a slow crystallization rate, a low melting point, low heat resistance and low rigidity.
The molecular weight of the polyamide resin used in the present invention is not particularly limited, but the relative viscosity at a concentration of 0.05 g / l of 98% by mass sulfuric acid measured at 25 ° C. is 1.8 to 2.8, more preferably 1.9. It is in the range of ~ 2.6. Slightly low molecular weight is preferable from the viewpoint of impregnation into carbon fiber. If the relative viscosity is less than 1.8, the resin is brittle and the effects of the present invention are hardly exhibited. On the other hand, if it exceeds 2.8, the melt viscosity becomes high and the impregnation property to the carbon fiber is lowered, which is not preferable.

The composite material of the present invention is used by stamping as a prepreg. The prepreg referred to in the present invention is a plate-shaped, sheet-shaped, or tape-shaped preformed material obtained by impregnating a reinforcing fiber with a resin in advance. The prepreg as the preform is further stamped to obtain a molded product having a practical shape. Preparation of prepreg and stamping molding are melt processing, and are generally used by heating to a high temperature of 20 to 100 ° C., preferably 30 to 80 ° C. from the melting point.

In addition to the above essential components, the composite material of the present invention has a crystal nucleating agent / mold releasing agent, a lubricant, an antioxidant, a flame retardant, a light resistance agent, a weather resistance, for the purpose of improving physical properties, moldability, and durability. Agents, antioxidants, etc. can be blended.
The method for producing the composite material of the present invention is not particularly limited. Preferably, the carbon fiber is impregnated after finely dispersing the fine carbon fiber (C) in the thermoplastic resin (A). As a method of finely dispersing fine carbon fibers in a thermoplastic resin, a thermoplastic resin (A) and fine carbon fibers (C) are premixed in a predetermined ratio into a hopper of a screw type extruder whose temperature is controlled to be higher than the melting point of the resin. And supply. A method of pelletizing the melt-kneaded strand after water cooling, or a method of supplying the thermoplastic resin (A) to the upstream hopper, supplying fine carbon fibers from the downstream side feeder, and pelletizing the melt-kneaded strand after water cooling Etc. Also, melt and knead high-concentration fine carbon fiber in a thermoplastic resin in advance, blend the thermoplastic resin into the obtained master batch of fine carbon fiber, melt-knead to dilute the fine carbon fiber. Also, a pellet containing a predetermined concentration of fine carbon fibers is used. Conversely, a method of concentrating the fine carbon fibers to a higher concentration by further melting and kneading the fine carbon fibers to a thermoplastic resin pellet obtained by melting and kneading the low concentration fine carbon is also used. .
In the case of the dilution method or the concentration method, the first-stage thermoplastic resin and the second-stage and subsequent thermoplastic resins are not limited to the same resin or different resins. However, it is preferable that the first-stage thermoplastic resin and the second-stage thermoplastic resin have good compatibility and nano-dispersibility. The first-stage thermoplastic resin has a lower viscosity than the second-stage thermoplastic resin in terms of finely dispersing fine carbon fibers.
A carbon fiber-containing thermoplastic resin containing fine carbon fibers is melted and impregnated in a die or between rolls to produce a prepreg made of the composite material of the present invention.

In the composite material prepreg of the present invention, the resin is heated and melted by infrared heating or high-frequency heating, supplied to a mold of a compression molding machine, demolded after shaping cooling, and a structural material part is formed.
Molded parts obtained from the composite material of the present invention include automobile frames, bumper face bar support materials, chassis shells, seat frames, suspension support parts, sunroof frames, bumper beams, two-wheeled vehicle frames, farm equipment frames, OA. Used for parts that require high strength and rigidity, such as equipment frames and machine parts.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples.
Examples 1-8
Polypropylene, polyamide resin, maleic anhydride, organic peroxide, fine carbon fiber, fine carbon fiber masterbatch are blended in the parts by mass shown in Table 1, and in the case of polypropylene, the cylinder temperature is 200 ° C., and the polyamide resin In this case, it was put into a hopper of a screw type twin screw extruder (PCM30 manufactured by Ikekai Tekko Co., Ltd.) whose temperature was adjusted to 270 ° C. It was melt-kneaded at a screw speed of 100 rpm, cooled with water, and pelletized.
The resulting pellets of the fine carbon fiber-containing thermoplastic resin were dried at 80 ° C. for 1 hour, then placed in an aluminum laminated moisture-proof bag and stored in an absolutely dry state.
The fine carbon fiber-containing thermoplastic resin pellets were put into a hopper of a screw type extruder, and the plasticized resin was weighed by a gear pump and supplied to an impregnation table of an impregnation apparatus. On the other hand, the carbon fiber roving was expanded and opened at a constant speed and supplied to the die head of the extruder, and the amount of the thermoplastic resin supplied from the extruder was adjusted so that the mixing ratio shown in Table 2 was obtained. A tape-shaped prepreg impregnated and coated from a die having a width of 10 mm and a height of 0.2 mm was immersed in a water bath and solidified, and then wound on a basket.
The tape-shaped prepreg was fixed on a metal frame having an inner dimension of 200 mm × 150 mm by stacking 12 layers so that the fiber axes were parallel. After preheating to 200 ° C. to 260 ° C. with an IR heater, it was set in a 200 mm × 150 mm mold whose temperature was adjusted to a surface temperature of 120 to 180 ° C. and compressed and held at 30 MPa for 5 minutes. Thereafter, the mold was opened and the molded product was taken out.

Evaluation and analysis were performed by the following methods.
-Dimensional measurement of fine carbon fiber 0.5 mm in width and 3 mm in length were sampled from the lateral side surface of the prepreg tape having a thickness of about 2 mm obtained by the present invention. From this, an ultra-thin section having a thickness of 50 to 200 nm, preferably 80 to 150 nm, was obtained using an ultramicrotome. The ultrathin slice was observed at 5 to 500,000 times using a transmission electron microscope (Hitachi High Technology) to obtain a transmission image photograph. Transmission images were obtained by changing the field of view so that there were about 30 fine fibers. For all the fine carbon fibers in the limited field of view of this transmission image photograph, the fiber diameter and length are measured, and the average fiber length of the weight average in the composite material is calculated on the assumption that the diameter is uniform in the length direction. Asked.
Strictly speaking, in a transmission type photograph, it is a projection image onto a plane in an ultrathin slice, which is the projection length and fiber diameter, and is actually observed as a smaller dimension. The projected dimension obtained in the range of 50 to 200 nm was defined as the dimension of the fine carbon fiber.
-Fiber diameter measurement of carbon long fiber About 2 mm thick prepreg tape obtained according to the present invention, it was embedded with an epoxy resin, and a microtome was used to cut out a thin piece from the cross section of the molded product, and a scanning electron microscope Using S3500N type (Hitachi High Technology Co., Ltd.), the fiber diameter was measured by changing the field of view at 1000 times and observing 10 pieces under vacuum. Their average diameter was determined.
-Carbon long fiber length About 100 mm of the prepreg tape obtained by this invention, it observed by 50 time using the Keyence microscope, the length of the single fiber of 30 carbon fibers was measured, and a weight average Asked. When pills and single yarn breakage were not observed, the length of the prepreg tape was 100 mm.
・ Content of fine carbon fiber (A _N )
The fine carbon fiber content (A _N ) was calculated from the respective charged masses when the fine carbon fibers and the thermoplastic resin were melt-kneaded according to the equation (1).
A _N = W _N / (W _N + W _T ) (1)
Here, WN: mass of charged fine carbon fiber, WT: mass of charged thermoplastic resin / carbon fiber amount About prepreg tape, heating at 550 ° C. for 5 hours, and obtaining the thermoplastic resin fraction from the mass reduction rate, From the obtained thermoplastic resin fraction, the fine carbon fiber-containing thermoplastic resin fraction obtained in (4) was calculated, and the fine carbon fiber fraction was subtracted from the whole by the formula (2) to obtain the carbon fiber amount.

C = 1- (1 + A _N ) B (2)
Here, C: carbon fiber fraction, B: thermoplastic resin fraction,
A _N : Fine carbon fiber content in the fine carbon fiber-containing thermoplastic resin (5) Evaluation of physical properties From the obtained flat plate-shaped product having a thickness of about 2 mm, the length direction of the carbon fiber (0 degree) and perpendicular thereto For each direction (90 degrees), 5 test pieces each having a size of 15 mm × 100 mm were cut. This is stored in a desiccator for 48 hours at 23 ° C. and then bent in accordance with ISO178 using a three-point bending tester (Tensilon 4L type manufactured by Orientec Corp.) with a span length of 80 mm and a crosshead speed of 1 mm / min. The strength was measured.

Comparative Examples 1-7
Except for changing the types and blending ratios of carbon long fibers, fine carbon fibers, and thermoplastic resins as shown in Table 3, a prepreg was prepared in the same manner as in the examples, and then a flat plate was formed by stamping. A test piece was cut from the flat plate. About the obtained test piece, 0 degree | times bending strength and 90 degree | times bending strength were measured just like the Example. The obtained test data is shown in Table 3 together.
Raw materials used in the experiment and symbol PP1: unmodified polypropylene (manufactured by Prime Polymer, E111G, MFR 0.5 dg / min)
PP2: unmodified polypropylene (manufactured by Prime Polymer, J136, MFR 20 dg / min)
PA6: Polyamide 6 (T802 manufactured by Toyobo Co., Ltd., relative viscosity 2.5)
MAH: Powdered maleic anhydride (manufactured by NOF Corporation)
25B: organic peroxide 2,5 dimethyl 2,5 di (t-butyl peroxide) hexane (180 ° C.) (manufactured by NOF Corporation, Perhexa 25B) 1 minute half-life temperature 179.8 ° C.
CF: Carbon fiber manufactured by Toho Tenax Co., Ltd., IMS 40 (single fiber diameter 6.4 μm, 6000 filaments)
CNT1: multi-walled carbon nanotube (VGCF manufactured by Showa Denko KK, single fiber type 18 nm, length 2800 nm)
CNTM: 20% carbon nanotube / polypropylene masterbatch (FIBRIL MB3020-01 manufactured by Hyperion Catalysis international, Inc.)

  A stamping molded product obtained from the composite material of the present invention having a synergistic reinforcing effect by a hybrid of carbon long fibers and fine carbon fibers has a very high 0-degree bending strength and 90-degree direction which cannot be obtained by single reinforcement of carbon fibers. Has bending strength. This composite material enables the structural member to be made of resin, and is expected to make a significant contribution to the industry in terms of weight reduction and energy saving.

Claims (4)

  80 to 250 parts by mass of carbon fiber (B) having a fiber diameter of 3 to 25 μm and a length of 20 mm or more, and a fiber diameter of 0.5 to 20 nm and a length of 100 to 5000 nm with respect to 100 parts by mass of the thermoplastic resin (A). Carbon fiber (C) 0.1 to 10 parts by mass of hybrid carbon fiber reinforced thermoplastic resin composite material characterized by containing The hybrid carbon fiber reinforced thermoplastic resin composite material according to claim 1, wherein the thermoplastic resin (A) is a polyamide resin and / or an acid-modified polypropylene resin. The hybrid carbon fiber reinforced thermoplastic resin composite material according to claim 1 or 2, wherein the carbon fine fiber (C) is a carbon nanotube and / or a carbon nanofiber.   The hybrid carbon fiber reinforced thermoplastic resin composite material according to any one of claims 1 to 3, which is a hybrid carbon fiber reinforced thermoplastic resin composite material for stamping molding.