EP3222772A1 - Kohlefaservliesstoff - Google Patents

Kohlefaservliesstoff Download PDF

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Publication number
EP3222772A1
EP3222772A1 EP17165911.3A EP17165911A EP3222772A1 EP 3222772 A1 EP3222772 A1 EP 3222772A1 EP 17165911 A EP17165911 A EP 17165911A EP 3222772 A1 EP3222772 A1 EP 3222772A1
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EP
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Prior art keywords
carbon fiber
nonwoven fabric
carbon
fibers
fiber nonwoven
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP17165911.3A
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English (en)
French (fr)
Inventor
Katsuhiro MIYOSHI
Takafumi Hashimoto
Yoshihiro Naruse
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Toray Industries Inc
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Toray Industries Inc
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Application filed by Toray Industries Inc filed Critical Toray Industries Inc
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    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
    • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
    • D06M13/11—Compounds containing epoxy groups or precursors thereof
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4209—Inorganic fibres
    • D04H1/4242—Carbon fibres
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M15/00—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment
    • D06M15/19—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment with synthetic macromolecular compounds
    • D06M15/37—Macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D06M15/53—Polyethers
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
    • D06M2101/40—Fibres of carbon

Definitions

  • the present invention relates to a carbon fiber nonwoven fabric, and specifically, to a carbon fiber nonwoven fabric which can satisfy both of high flowability and mechanical properties when a molded article of a carbon fiber composite material is made using the same.
  • a carbon fiber composite material comprising carbon fibers and a thermoplastic resin is used for manufacture of various molded articles, and various technologies, aiming high mechanical properties of a manufactured molded article and a good flowability at the time of the manufacture, have been proposed.
  • carbon fibers in the carbon fiber composite material as a formation of a nonwoven fabric, for example, in Patent document 1, a carbon fiber nonwoven fabric is proposed wherein the proportion of specified carbon fiber bundles in a carbon fiber nonwoven fabric relative to the whole amount of fibers is suppressed to be low, and the average number of fibers in the respective specified carbon fiber bundles is controlled in a specified range.
  • Patent document 2 a composite material is proposed wherein the proportion of specified carbon fiber bundles in a carbon fiber nonwoven fabric relative to the whole amount of fibers, similar to that described above, is set higher, and the average number of fibers in the respective specified carbon fiber bundles is controlled in another specified range.
  • a carbon fiber nonwoven fabric as described in Patent document 2 wherein the carbon fiber bundles are thick and the proportion of the bundles is many, although the flowability at the time of manufacturing a molded article of a carbon fiber composite material using the same is high and the moldability is excellent, the mechanical properties are low and the variations in the mechanical properties are great.
  • an object of the present invention is to provide a carbon fiber nonwoven fabric in which high flowability and mechanical properties can be both satisfied with small variability in mechanical properties when a carbon fiber composite material is molded, and which also has an excellent shaping property for a carbon fiber mat.
  • a carbon fiber nonwoven fabric according to the present invention has the following structures.
  • R 1 represents H, OH, the following chemical formula 6 or the following chemical formula 7
  • R 2 represents H or OH
  • m and n represent an integer of 1 to 49
  • m + n is in a range of 10 to 50.
  • standard deviation ⁇ of the number of carbon fibers range of the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers, range of the drape value (cm)/single fiber flexural stiffness (Pa• cm 4 ), range of the single fiber flexural stiffness of carbon fibers, etc.
  • a carbon fiber nonwoven fabric in the carbon fiber nonwoven fabric according to the present invention, can be provided wherein, when a carbon fiber composite material is molded using the same, high flowability and high mechanical properties can be both achieved, the variability in the mechanical properties is small, and the carbon fiber followability to a small portion is also excellent.
  • the carbon fibers used in the present invention are not particularly restricted, high-strength and high-elastic modulus carbon fibers can be used, and one kind of carbon fibers may be used or two or more kinds of carbon fibers may be used together.
  • PAN-based, pitch-based and rayon-based carbon fibers can be exemplified. From the viewpoint of the balance between the strength and the elastic modulus of a molded article to be obtained, PAN-based carbon fibers are more preferable.
  • the density of carbon fibers is preferably in a range of 1.65 to 1.95 g/cm 3 , and more preferably in a range of 1.70 to 1.85 g/cm 3 . If the density is too high, the lightness in weight of a carbon fiber-reinforced plastic obtained is poor, and if too low, there is a case where the mechanical properties of a carbon fiber-reinforced plastic obtained become low.
  • the carbon fibers are preferably formed as a bundle from the viewpoint of productivity, and it is preferred that the number of single fibers in the bundle is many.
  • the number of single fibers for the carbon fiber bundle can be employed within a range of 1,000 to 350,000, and in particular, it is preferably employed within a range of 10,000 to 100,000.
  • the single fiber flexural stiffness of carbon fibers is preferably in a range of 1.0 x 10 -11 to 2.8 x 10 -11 (Pa• cm 4 ), and more preferably in a range of 1.0 x 10 -11 to 1.5 x 10 -11 (Pa• cm 4 ).
  • the carbon fibers are surface treated.
  • the carbon fibers are sized with an aliphatic compound having a plurality of epoxy groups.
  • the aliphatic compound in the present invention means a noncyclic straight-chain saturated hydrocarbon, a branched-chain saturated hydrocarbon, a noncyclic straight-chain unsaturated hydrocarbon, a branched-chain unsaturated hydrocarbon, or a chain-structure compound substituting oxygen atom (O), nitrogen atom (NH, N), sulfur atom (SO 3 H, SH) or carbonyl atomic group (CO) for the carbon atom of the above-described hydrocarbons (CH 3 , CH 2 , CH, C).
  • the above-described compound having a plurality of epoxy groups is a compound having an epoxy group at each end of the longest atomic chain, in particular, a compound having an epoxy group only at each end of the longest atomic chain.
  • an atomic chain having the greatest total number of atoms among the total numbers of carbon atoms and heteroatoms (oxygen atom, nitrogen atom, etc.) forming respective chain structures which link between two epoxy groups is defined as the longest atomic chain
  • the total number of atoms forming the longest atomic chain is defined as a number of atoms of the longest atomic chain.
  • the number of atoms such as hydrogen linked to the atoms forming the longest atomic chain is not included to the total number.
  • a structure hard to become a crosslinking point is preferred in order to prevent that a density of crosslinking between molecules of a compound of a sizing agent becomes too great.
  • the number of epoxy groups in a compound of a sizing agent is less than 2, it cannot be done to effectively bridge between carbon fibers and a matrix resin. Therefore, the number of epoxy groups is necessary to be two or more in order to effectively bridge between carbon fibers and a matrix resin.
  • the number of epoxy groups is preferably 6 or less, more preferably 4 or less, and further preferably, it is 2. Furthermore, it is more preferred that these two epoxy groups are present at both ends of the longest atomic chain. Namely, by the presence of the epoxy groups at both ends of the longest atomic chain, because it is prevented that a local density of crosslinking increases, such a structure is preferred for a tensile strength of a composite.
  • a glycidyl group having a high reactivity is preferred.
  • the molecular weight of such an aliphatic compound is preferably 80 or more and 3,200 or less, more preferably 100 or more and 1,500 or less, and further preferably 200 or more and 1,000 or less, from the viewpoint of preventing deterioration of handling ability as a sizing agent caused by a condition that the resin viscosity is too low or too high.
  • the aliphatic compound having a plurality of epoxy groups in the present invention for example, as diglycidyl ether compounds, can be exemplified ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether group, propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether group, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ether group, etc.
  • diglycidyl ether compounds can be exemplified ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether group, propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether group, 1,4-butanediol diglycidyl ether, neopentyl
  • polyglycidyl ether compounds can be exemplified glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether group, sorbitol polyglycidyl ether group, arabitol polyglycidyl ether group, trimethylol propane polyglycidyl ether group, pentaerythritol polyglycidyl ether group, polyglycidyl ether group of aliphatic polyatomic alcohol, etc.
  • polyglycidyl ether compound having a glycidyl group high in reactivity.
  • polyethylene glycol diglycidyl ether group, polypropylene glycol diglycidyl ether group, alkane diol diglycidyl ether group, and compounds having the following structures are preferred.
  • G represents a glycidyl group
  • R 1 represents -CH 2 CH 2 -, -CH 2 CH 2 CH 2 - or -CH(CH 3 ) CH 2 -
  • R 2 represents -CH 2 -
  • at least two of R 3 , R 4 and R 5 represent -G and the other represents -H or -G
  • m represents an integer of 1 to 25
  • n represents an integer of 2 to 75
  • x, y and z represent zero or a positive integer
  • x + y + z is preferably in a range of 0 to 25. Further, a mixture of these compounds may be used.
  • the number of atoms of the longest atomic chain is 20 or more. Namely, if the number of atoms is less than 20, there is a possibility that the density of crosslinking in the sizing layer becomes high and therefore it is likely to become a structure low in toughness, and as a result, a tensile strength of a composite is hard to be exhibited.
  • the number of atoms of the longest atomic chain is greater, because the sizing layer is flexible and is likely to become a structure high in toughness, as a result, a tensile strength of a composite is liable to be increased, and in particular, because there is a feature that a tensile strength in case of a brittle resin is high, more preferably, the number of atoms of the longest atomic chain is 25 or more, and further preferably, 30 or more.
  • the number of atoms of the longest atomic chain is preferably 200 or less, more preferably 100 or less.
  • the epoxy group is sufficiently apart from the cyclic skeletal structure, concretely, if apart from by 6 or more in number of atoms, it can be used.
  • an aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more is used as the sizing agent.
  • the "number of atoms present between an epoxy group and an aromatic ring” means the total number of carbon atoms, heteroatoms (oxygen atom, nitrogen atom, etc.) and carbonyl atomic groups forming chain structures which link between the epoxy group and the aromatic ring.
  • the number of atoms present between an epoxy group and an aromatic ring is less than 6 as the sizing agent, because a rigid and three-dimensionally large compound is interposed at an interface between carbon fibers and a matrix resin, the reactivity with a surface functional group present on the outermost surfaces of carbon fibers is not improved, and as a result, improvement of the properties in the lateral direction of a composite material cannot be expected.
  • R 2 represents an alkylene group having a carbon number of 2 to 30, R 3 is -H or -CH 3 , m and n represent an integer of 2 to 48, and m + n is in a range of 4 to 50.
  • the molecular chain of the compound is straight chain like having a flexibility and the molecular weight thereof is small so as not to interpose a rigid and three-dimensionally large compound at an interface between carbon fibers and a matrix resin in a carbon fiber composite material, and therefore, each of the above-described m, n is 2 or more, preferably 3 or more, further preferably 5 or more, and the above-described m + n is 4 or more, preferably 6 or more, further preferably 10 or more.
  • each of m, n is less than 2 or m + n is less than 4
  • R 2 is -CH 2 CH 2 - or CH(CH 3 )CH 2 -.
  • the bisphenol A part or B part has an advantage for improving the compatibility with a matrix resin and an advantage for improving the fluff resistance.
  • the skeletal structure of the aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more may also be a condensed polycyclic aromatic compound.
  • a condensed polycyclic aromatic compound for example, naphthalene, anthracene, phenanthrene, chrysene, pyrene, naphthacene, triphenylene, 1,2-benzanthracene, benzopyrene, etc. can be exemplified.
  • naphthalene, anthracene, phenanthrene and pyrene, whose skeletal structures are small, are preferred.
  • the epoxy equivalent of the condensed polycyclic aromatic compound having a plurality of epoxy groups is preferably in a range of 150 to 350, more preferably in a range of 200 to 300, from the viewpoint of obtaining an advantage for improving the adhesive property sufficiently.
  • the molecular weight of the condensed polycyclic aromatic compound having a plurality of epoxy groups is preferably in a range of 400 to 800, more preferably in a range of 400 to 600, from the viewpoint of preventing deterioration of handling ability as a sizing agent caused by increase of the resin viscosity.
  • the other components such as a bisphenol-type epoxy compound having a small molecular weight such as "Epikote” 828 or “Epikote” 834, a straight-chain like low molecular weight epoxy compound, polyethylene glycol, polyurethane, a polyester, an emulsifier or a surfactant, may be added, for the purpose of adjustment of viscosity, improvement of abrasion resistance, improvement of fluff resistance, improvement of convergence of fibers, improvement of higher-order processability, etc.
  • a bisphenol-type epoxy compound having a small molecular weight such as "Epikote” 828 or "Epikote” 834
  • a straight-chain like low molecular weight epoxy compound such as "Epikote” 828 or "Epikote” 834
  • a straight-chain like low molecular weight epoxy compound such as "Epikote” 828 or "Epikote” 834
  • the adhesion amount of the sizing agent to carbon fibers is preferably 0.01 wt.% or more and 10 wt.% or less per unit weight of carbon fibers, more preferably 0.05 wt.% or more and 5 wt.% or less, further preferably 0.1 wt.% or more and 2 wt.% or less, from the viewpoint of making the width of improvement of adhesive property with a resin while preventing the sizing agent from being consumed excessively.
  • the sizing agent is uniformly coated. Namely, it is preferred that the thickness of the sizing agent layer is in a range of 20 to 200 angstroms and the maximum value of the thickness does not exceed two times of the minimum value. By such a uniform sizing agent layer, a coupling effect can be exhibited more effectively.
  • a sizing agent In a carbon fiber nonwoven fabric according to the third embodiment of the present invention, at least one kind of a specified compound selected from the aforementioned chemical formulae (III), (IV) and (V) (hereinafter, also referred to as merely "a sizing agent") is made adhere to the carbon fibers of the carbon fiber nonwoven fabric at an amount of 0.1 to 5.0 wt.% relative to the weight of the carbon fibers of 100 wt.%.
  • Polyethylene oxide part or polypropylene oxide part in such a compound gives a smoothness to carbon fibers, exhibits an effect for reducing a friction force, and when formed to a carbon fiber nonwoven fabric described later, a friction force caused by tangle of carbon fibers to each other can be reduced, thereby improving the flowability and the formability.
  • bisphenol A part has an effect for improving the compatibility with a matrix resin.
  • a treatment method can be employed wherein a liquid containing a sizing agent (sizing liquid) is made adhere after water wet carbon fiber bundles having a moisture content of approximately 20 to 80 wt.%, wetted with water in known surface treatment process and water washing process, are dried.
  • a liquid containing a sizing agent sizing liquid
  • the method for providing a sizing agent is not particularly limited, for example, there are a method for dipping carbon fibers in a sizing liquid via rollers, a method for bringing carbon fibers into contact with rollers adhered with a sizing liquid, a method for spraying an atomized sizing liquid, etc.
  • the method may be any of batch type and continuous type, continuous type good in productivity and small in unevenness is preferred.
  • it is preferred to control the concentration and temperature of the sizing liquid, yarn tension, etc., so that the adhesion amount of sizing agent effective component relative to carbon fibers becomes uniform. Further, it is more preferred to vibrate carbon fibers with a ultrasonic wave when the sizing agent is provided.
  • the drying temperature and the drying time should be adjusted depending upon the adhesion amount of the compound, the drying temperature is preferably 130°C or higher and 350°C or lower, and more preferably 180°C or higher and 250°C or lower, from the viewpoints of completely removing a solvent used for providing the sizing agent, shortening the time required for drying, on the other hand, preventing thermal deterioration of the sizing agent and preventing deterioration of the spreading property of carbon fiber bundles caused by the bundles being hardened.
  • the solvent used for the sizing agent although water, methanol, ethanol, dimethyl formamide, dimethyl acetamide, acetone, etc. can be exemplified, water is preferred from the viewpoints of easy handling ability and disaster prevention. Therefore, in case where a compound insoluble or slightly soluble in water is used as a sizing agent, it is preferred to use it after making it water dispersible by adding an emulsifier, a surfactant, etc.
  • anionic emulsifiers such as styrene-maleic anhydride copolymer, olefin-maleic anhydride copolymer, formalin condensate of naphthalene sulfonate and polyacrylic soda, cationic emulsifiers such as polyethylene imine and polyvinyl imidazoline, nonionic emulsifiers such as nonyl phenol ethylene oxide adduct, polyvinyl alcohol, copolymer of polyoxyethylene ether ester and sorbitan ester ethyl oxide adduct, and nonionic emulsifiers small in interaction with epoxy groups are preferred.
  • anionic emulsifiers such as styrene-maleic anhydride copolymer, olefin-maleic anhydride copolymer, formalin condensate of naphthalene sulfonate and polyacrylic soda
  • cationic emulsifiers such as
  • the adhesion amount of a sizing agent relative to the mass of only the carbon fibers is preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.05 mass% or more and 5 mass% or less, and further preferably 0.1 mass% or more and 2 mass% or less. If less than 0.01 mass%, the effect for improving the adhesive property is hardly exhibited. If more than 10 mass%, there is a possibility that the mechanical properties when the carbon fiber nonwoven fabric is made into a molded article of a carbon fiber composite material may be reduced.
  • the drape value/ single fiber flexural stiffness determined by dividing the drape value, that is an index representing the hardness of the carbon fiber bundle, with the single fiber flexural stiffness, is preferably in a range of 1.4 x 10 3 to 4.0 x 10 3 cm/(Pa• cm 4 ), and more preferably in a range of 1.5 x 10 3 to 3.0 x 10 3 cm/(Pa• cm 4 ).
  • the drape value/ single fiber flexural stiffness is less than 1.4 x 10 3 cm/(Pa• cm 4 )
  • the convergence of the fibers is poor, in the process for preparing the carbon fiber aggregates such as air laid or carding described later, the fibers are liable to be spread, there is a possibility that the moldability deteriorates when made into a carbon fiber composite material, and if it exceeds 4.0 x 10 3 cm/(Pa• cm 4 ), there is a possibility that the wettability with a matrix resin deteriorates and the mechanical properties are reduced when made into a carbon fiber composite material.
  • the carding mentioned in the present invention means an operation for arranging the direction of discontinuous fibers or spreading fibers by applying a force in an approximately same direction to the aggregates of discontinuous fibers with a comb-like member. Generally, it is performed using a carding machine equipped with a roll having many needle-like projections on the surface and/or a roll wound with a metallic wire having saw blade-like projections.
  • the time (residing time), during which carbon fibers reside in the carding machine, is preferred to be short, for the purpose of preventing the carbon fibers from being folded.
  • the surface speed of the doffer roll is preferably a high speed, for example, such as 10 m/min. or higher.
  • a carding machine 1 mainly comprises a cylinder roll 2, a take-in roll 3 provided at an upstream side and closely to the outer circumferential surface of the cylinder roll 2, a doffer roll 4 provided closely to the outer circumferential surface of the cylinder roll 2 at a downstream side which is a side opposite to the side of the take-in roll 3, a plurality of worker rolls 5 provided closely to the outer circumferential surface of the cylinder roll 2 between the take-in roll 3 and the doffer roll 4, stripper rolls 6 provided closely to the worker rolls 5, and a feed roll 7 provided closely to the take-in roll 3, and a belt conveyer 8.
  • Discontinuous carbon fiber bundles 9 are supplied to belt conveyer 8, and the carbon fiber bundles 9 are introduced onto the outer circumferential surface of cylinder roll 2 through the outer circumferential surface of feed roll 7 and then through the outer circumferential surface of take-in roll 3. Up to this stage, the carbon fiber bundles are spread and become floc-like aggregates of carbon fiber bundles. Although a part of the floc-like aggregates of carbon fiber bundles introduced onto the outer circumferential surface of cylinder roll 2 wind around the outer circumferential surfaces of worker rolls 5, these carbon fibers are stripped off by stripper rolls 6 and returned again onto the outer circumferential surface of the cylinder roll 2.
  • Air laid is a process for producing a nonwoven fabric sheet of short fibers, it is not particularly restricted, and a general one can be used.
  • general air laid processes can be exemplified Honshu Paper process, Kroyer process, Danweb process, J&J process, KC process, Scott process, etc.
  • air laid machine 11 has drums 12 rotated in directions reverse to each other, each formed in a cylinder shape and having small holes, and pin cylinders 13 provided in the respective drums 12.
  • Carbon fiber bundle single materials or carbon fiber bundles and thermoplastic resin fibers are air transported to drums 12 together with a large amount of air, they are spread by pin cylinders 13 in drums 12, discharged from the small holes, and they drop onto wires 14 running thereunder.
  • the air used for the air transportation is sucked into a suction box 15 provided under wires 14, and only spread carbon fiber bundle single materials or spread carbon fiber bundles and thermoplastic resin fibers are left on wires 14 to form a carbon fiber nonwoven fabric.
  • the carbon fiber nonwoven fabric indicated here means a fabric which is kept in form by tangle or friction of fibers to each other at a condition where discontinuous carbon fiber bundles are spread and oriented by the above-described carding or air laid, and can be exemplified a thin sheet-like web, a nonwoven fabric obtained by laminating webs, as needed, by tangle or adhesion, etc.
  • the carbon fiber nonwoven fabric is obtained preferably by air laid, and from the viewpoint of uniformity of nonwoven fabric, it is obtained preferably by carding.
  • the carbon fiber nonwoven fabric may be formed by only carbon fibers, thermoplastic resin fibers and/or thermoplastic resin particles can also be contained. It is preferred to add thermoplastic resin fibers because breakage of carbon fibers at the process of air laid or carding can be prevented. Because carbon fibers are rigid and fragile, they are hard to be tangled and liable to be broken. Therefore, there is a problem in the carbon fiber nonwoven fabric formed by only carbon fibers that during the production, the fabric is easily cut or the carbon fibers are liable to be fallen off.
  • thermoplastic resin fibers and/or thermoplastic resin particles In the air laid process, by containing thermoplastic resin fibers and/or thermoplastic resin particles, the handling ability of the carbon fiber nonwoven fabric can be improved by carrying out a method for thermally fusing them by pressing or heat treatment due to thermal calender rollers or thermal emboss rollers or a method for tangling the fibers by needle punch or water jet needle, etc., employed at a later step.
  • thermoplastic resin fibers which are flexible and hard to be broken and liable to be tangled, carbon fiber aggregates high in uniformity can be formed.
  • the content of carbon fibers in the carbon fiber aggregates is preferably in a range of 20 to 95 mass%, more preferably in a range of 50 to 95 mass%, and further preferably in a range of 70 to 95 mass%. If the rate of carbon fibers is low, it becomes difficult to obtain high mechanical properties when made into a carbon fiber composite material, and to the contrary, if the rate of thermoplastic resin fibers is too low, the above-described advantage for improving uniformity of the carbon fiber aggregates cannot be obtained.
  • a number average x of carbon fibers forming a carbon fiber bundle (1) in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is in a range of 90 to 1,000.
  • the number average x of carbon fibers forming the bundle is preferably in a range of 90 to 600, more preferably in a range of 90 to 500.
  • the number average x is preferably in a range of 300 to 1,000, more preferably in a range of 500 to 1,000. If the number average x of carbon fibers of the carbon fiber bundles is less than 90, the number of tangles of fibers to each other increases, and the flowability deteriorates. If more than 1,000, the mechanical properties and the followability of carbon fibers to small parts deteriorate, and the variability in mechanical properties becomes great.
  • a proportion of the carbon fiber bundles (1), in which the number of carbon fibers forming a carbon fiber bundle is 90 or more, relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric is 5 wt.% or more and 80 wt.% or less. From the viewpoint of improving the carbon fiber strength utilization factor and the surface appearance of a molded article, it is preferably 5 wt.% or more and 50 wt.% or less, further preferably 5 wt.% or more and 45 wt.% or less.
  • the content of carbon fibers when made into a carbon fiber composite material and obtaining a high elastic modulus it is preferably more than 30 wt.% and 80 wt.% or less, further preferably more than 35 wt.% and 80 wt.% or less.
  • the surface appearance of a molded article and the flowability it is preferably more than 30 wt.% and 50 wt.% or less. If the proportion of the carbon fiber bundles (1) is less than 5 wt.%, the number of tangles of fibers to each other increases, and the flowability deteriorates. If more than 80 wt.%, the mechanical properties and the followability of carbon fibers to small parts deteriorate, and the variability in mechanical properties becomes great.
  • a standard deviation ⁇ of the number x n of carbon fibers forming the above-described carbon fiber bundle (1) in the carbon fiber nonwoven fabric satisfies a range of 50 ⁇ ⁇ 500 and the carbon fiber bundles are distributed in the carbon fiber nonwoven fabric by being dispersed, a carbon fiber nonwoven fabric can be obtained in which high flowability and mechanical properties can be both satisfied, the variability in mechanical properties is small, and which is excellent also in followability of carbon fibers to small parts.
  • the above-described standard deviation ⁇ is preferably in a range of 100 ⁇ ⁇ 350, more preferably in a range of 150 ⁇ ⁇ 350, and further preferably in a range of 150 ⁇ ⁇ 300.
  • the fiber length of the thermoplastic resin fibers is not particularly limited as long as it is in a range capable of achieving the objective of the present invention such as keeping the form of the carbon fiber aggregate or preventing falling off of carbon fibers, and generally, thermoplastic resin fibers having a length of approximately 3 to 100 mm can be used. Where, it is also possible to decide the fiber length of thermoplastic resin fibers relatively in accordance with the fiber length of carbon fibers.
  • thermoplastic resin fibers for the purpose of enhancing the effect of tangle due to the thermoplastic resin fibers.
  • the degree of the crimp is not particularly limited as long as it is in a range capable of achieving the objective of the present invention, and generally, thermoplastic resin fibers having a number of crimps in a range of approximately 5 to 25 crests per 25 mm and a rate of crimp in a range of approximately 3 to 30% can be used.
  • thermoplastic resin particles are contained in the carbon fiber aggregates
  • a spherical shape a small piece-like shape, and columnar shape such as a pellet
  • the preferable average particle diameter is in a range of 0.01 to 1,000 ⁇ m.
  • thermoplastic resin fibers The material for the above-described thermoplastic resin fibers is not particularly restricted, and it can be appropriately selected from a range that does not greatly reduce the mechanical properties of a carbon fiber composite material.
  • fibers can be used which are prepared by spinning a resin such as a polyolefin-group resin such as polyethylene or polypropylene, a polyamide-group resin such as nylon 6 or nylon 6,6, a polyester-group resin such as polyethylene terephthalate or polybutylene terephthalate, a polyetherketone, a polyethersulfone or an aromatic polyamide. It is preferred that such a material for thermoplastic resin fibers is appropriately selected in accordance with the combination with a matrix resin.
  • thermoplastic resin fibers prepared using the same resin as a matrix resin a resin having a compatibility with a matrix resin or a resin having a high adhesive property with a matrix resin is preferred, because the mechanical properties of a carbon fiber-reinforced plastic are not lowered.
  • the thermoplastic resin fibers are preferred to be composed of at least one kind of fibers selected from the group consisting of polyamide fibers, polyphenylene sulfide fibers, polypropylene fibers, polyetheretherketone fibers and phenoxy resin fibers.
  • a method may be employed wherein carbon fiber nonwoven fabric containing thermoplastic resin fibers is prepared and the thermoplastic resin fibers contained in the carbon fiber nonwoven fabric are used as the matrix resin as they are, or a method may also be employed wherein carbon fiber nonwoven fabric not containing thermoplastic resin fibers is used as a raw material, and a matrix resin is impregnated at an arbitrary stage for producing a carbon fiber composite material. Further, even in case where the carbon fiber nonwoven fabric containing thermoplastic resin fibers is used as the raw material, a matrix resin can be impregnated at an arbitrary stage for producing a carbon fiber composite material.
  • a resin forming thermoplastic resin fibers and a matrix resin may be an identical resin, or may be resins different from each other. In case where the resin forming thermoplastic resin fibers and the matrix resin are different from each other, it is preferred that both resins have a compatibility or a high affinity.
  • thermoplastic resin as a matrix resin is impregnated into the above-described carbon fiber nonwoven fabric, and the impregnation step for manufacturing the carbon fiber composite material can be carried out using a press machine having a heating function.
  • the press machine is not particularly restricted as long as it can realize temperature and pressure required for the impregnation of the matrix resin, a usual press machine having a plane-like platen moved vertically, or a so-called double belt press machine having a mechanism for running a pair of endless steel belts can be used.
  • the matrix resin is prepared in a sheet-like form such as a film, a nonwoven fabric or a woven fabric, it is laminated with the carbon fiber nonwoven fabric, and at that condition, the matrix resin can be melted and impregnated using the above-described press machine and the like.
  • a method can also be employed wherein discontinuous fibers are prepared using a matrix resin, by mixing them and inorganic fibers at a step for making a carbon fiber nonwoven fabric, a carbon fiber nonwoven fabric containing the matrix resin and the inorganic fibers is prepared, and this carbon fiber nonwoven fabric is heated and pressed using the press machine and the like.
  • a sample with a size of 100 mm x 100 mm was cut out from a carbon fiber nonwoven fabric, and thereafter, the sample was heated in an electric furnace heated at 500°C for about one hour to burn off organic substances such as thermoplastic resin fibers.
  • F is a fineness of carbon fibers
  • x n is a number of single fibers forming the carbon fiber bundle.
  • the determination is carried out at a condition where carbon fiber bundles, in each of which the number of single fibers of carbon fibers forming the carbon fiber bundle x n is 90 or more, are referred to as carbon fiber bundles (1), the total weight is referred to as M 1 and the total number of bundles is referred to as N. Further, the determination is carried out at a condition where carbon fiber bundles, in each of which the number of single fibers of carbon fibers forming the bundle is less than 90, are referred to as fiber bundles (2), and the total weight of the carbon fiber bundles (2) is referred to as M 2 .
  • the weight thereof was determined in the lump at the last. Further, in case where the fiber length is small and the determination of weight becomes difficult, the fiber lengths may be classified at an interval of about 0.2 mm and the weights of a plurality of classified bundles may be determined in the lump, and an average value thereof may be used.
  • N is the total number of bundles of the carbon fiber bundles (1).
  • the proportion of carbon fiber bundles (1) relative to the total weight of carbon fiber bundles is determined by the following equation: M 1 / M 1 + M 2 ⁇ 100
  • Vf content of carbon fibers in carbon fiber composite material
  • a sample of about 2g was cut out from a molded article of a carbon fiber composite material, and the mass thereof was determined. Thereafter, the sample was heated in an electric furnace heated at 500°C for one hour and organic substances such as a matrix resin were burnt off. After cooled down to a room temperature, the mass of the residual carbon fibers was determined. The rate of the mass of the carbon fibers to the mass of the sample before being burnt off with organic substances such as a matrix resin was determined, and it was defined as the content of carbon fibers.
  • a flexural strength was determined based on JIS-K7171.
  • Fiber strength utilization factor Flexural strength / Vf
  • the cross section of a fiber was supposed as a true circle, the geometrical moment of inertia was determined from the fiber diameter D, and the flexural stiffness was determined from the single fiber tensile elastic modulus and the geometrical moment of inertia.
  • Drape value/single fiber flexural stiffness
  • a carbon fiber bundle 21 drawn out from a bobbin without applying a tension is cut at a length of 40 cm, one end thereof is fixed by a fixing tape 22, a weight 23 of 100g is hung at the other end thereof, and after the twist and the bending are corrected, it is left in a measurement-temperature atmosphere for 30 minutes. Next, the weight 23 is removed, as shown in Fig.
  • the carbon fiber bundle 25 is placed on a horizontal and rectangular table 24 having a corner of 90° so as to protrude from the table by 25 cm, and after the part of carbon fibers on the table is fixed by a fixing tape 26 while the carbon fiber bundle with 40 cm is supported so as not to be broken, the support for the part protruding from the table is removed and the part is hung down, and after 2 seconds, the length of a horizontal distance L from the beginning point is measured, and the average value of "n" number of 3 times is defined as a drape value.
  • a friction device was used wherein 5 stainless rods each having a diameter of 10 mm (chrome plating, surface roughness: 1 to 1.5s) were arranged in parallel to each other at an interval of 50 mm at a zigzag arrangement style so that a carbon fiber yarn could pass through the surfaces of the rods with a contact angle of 120° per each rod surface.
  • a sizing agent prepared by preparing a mother liquor of the sizing agent by diluting glycerol triglycidyl ether with dimethyl formamide (hereinafter, abbreviated as DMF) so that the resin component became 1 wt.%, was provided to the carbon fibers by dipping method, and drying was carried out at 230°C.
  • the adhesion amount was 0.4 wt.%.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to glycerol diglycidyl ether.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to diglycerol polyglycidyl ether.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to diethylene glycol diglycidyl ether.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to bisphenol A type diglycidyl ether having an aromatic ring; "Epikote” 828 (epoxy compound having an aromatic ring) supplied by Yuka Shell Epoxy Kabushiki Kaisha.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to phenol novolak type glycidyl ether; "Epikote” 154 (epoxy compound having an aromatic ring) supplied by Yuka Shell Epoxy Kabushiki Kaisha.
  • the carbon fiber bundle (A) was cut at a fiber length of 15 mm, the cut carbon fiber bundles (A) and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 51 mm, number of crimps: 12 crests per 25 mm, rate of crimp: 15%) were mixed at a mass ratio of 90:10, and the mixture was introduced into a carding machine.
  • the web having come out was cross wrapped to form a sheet-like carbon fiber nonwoven fabric comprising carbon fiber bundles (A) and nylon 6 fibers and having an areal weight of 100 g/cm 2 .
  • the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 18 wt.%, the number average x of carbon fibers forming the bundle was 160, and the standard deviation ⁇ was 70.
  • CM1001 nylon resin film
  • Example 2 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 40 wt.%, the number average x of carbon fibers forming the bundle was 320, and the standard deviation ⁇ was 200.
  • the flexural strengths in 0° and 90° directions and the flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 480 MPa, the fiber strength utilization factor was 16.0 MPa/%, the CV value was less than 5%, and the flowability was 290%.
  • Example 3 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 62 wt.%, the number average x of carbon fibers forming the bundle was 615, and the standard deviation ⁇ was 320.
  • the flexural strengths in 0° and 90° directions and the flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 463 MPa, the fiber strength utilization factor was 15.4 MPa/%, the CV value was less than 5%, and the flowability was 313%.
  • Comparative Example 3 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 84 wt.%, the number average x of carbon fibers forming the bundle was 1,100, and the standard deviation ⁇ was 630.
  • the average value of the flexural strengths in 0° and 90° directions was 300 MPa
  • the fiber strength utilization factor was 10.0 MPa/%
  • the CV value was not less than 5%
  • the flowability was 320%, and although the flowability was excellent, the flexural strength and the fiber strength utilization factor were low, the mechanical properties were poor and the variability thereof was great.
  • a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -CH 3 , m to 2 and n to 2 and preparing a water emulsion in which the resin component of the sizing agent was 1 wt.%, was provided to the carbon fibers by dipping method, and drying was carried out at 180°C.
  • the adhesion amount was 0.8 wt.%.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -CH 3 , m to 5 and n to 5.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -CH 3 , m to 10 and n to 10.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -H, m to 15 and n to 15.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -CH 3 , m to 30 and n to 30.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -OH, R 3 to - CH 3 , m to 15 and n to 15.
  • the carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R 2 in the aforementioned chemical formula [I] to -CH 2 CH 2 -, R 3 to -CH 3 , m to 1 and n to 1.
  • the carbon fiber bundle (A1) was cut at a fiber length of 15 mm, the cut carbon fiber bundles (A1) and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 51 mm, number of crimps: 12 crests per 25 mm, rate of crimp: 15%) were mixed at a mass ratio of 90:10, and the mixture was introduced into a carding machine.
  • the web having come out was cross wrapped to form a sheet-like carbon fiber nonwoven fabric comprising carbon fiber bundles (A1) and nylon 6 fibers and having an areal weight of 100 g/cm 2 .
  • the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 18 wt.%, the number average x of carbon fibers forming the bundle was 160, and the standard deviation ⁇ was 70.
  • CM1001 nylon resin film
  • Example 9 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 40 wt.%, the number average x of carbon fibers forming the bundle was 320, and the standard deviation ⁇ was 200.
  • the flexural strengths in 0° and 90° directions and the flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 461 MPa, the fiber strength utilization factor was 15.4 MPa/%, the CV value was less than 5%, and the flowability was 297%.
  • Example 10 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 62 wt.%, the number average x of carbon fibers forming the bundle was 615, and the standard deviation ⁇ was 320.
  • the flexural strengths in 0° and 90° directions and the flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 449 MPa, the fiber strength utilization factor was 15.0 MPa/%, the CV value was less than 5%, and the flowability was 318%.
  • Comparative Example 6 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 84 wt.%, the number average x of carbon fibers forming the bundle was 1,100, and the standard deviation ⁇ was 630.
  • the average value of the flexural strengths in 0° and 90° directions was 300 MPa
  • the fiber strength utilization factor was 10.0 MPa/%
  • the CV value was not less than 5%
  • the flowability was 332%, and although the flowability was excellent, the flexural strength and the fiber strength utilization factor were low, the mechanical properties were poor and the variability thereof was great.
  • a continuous carbon fiber bundle having a fiber diameter of 7 ⁇ m, a tensile elastic modulus of 230 GPa, a single fiber flexural stiffness of 2.71 x 10 -11 Pa• m 4 and a number of filaments of 24,000 was dipped in this sizing agent emulsion through dip rollers, it was dried at 150°C for 1 minute using a hot air circulation type drier.
  • the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.8 wt.%, the coefficient of friction was 0.22 and the drape value was 5.3 cm.
  • the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.9 wt.%, the coefficient of friction was 0.23 and the drape value was 5.5 cm.
  • the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.6 wt.%, the coefficient of friction was 0.21 and the drape value was 5.0 cm.
  • dimethyl formamide solution containing 30 wt.% of bisphenol A diglycidyl ether type liquid epoxy resin having an epoxy equivalent of 225 to 280 and an average molecular weight of about 470 (“Epikote” 843, supplied by Shell Chemicals Ltd.) was added at a rate of 4:1, then, water was added and an emulsion of 1 wt.% thereof was prepared as a sizing agent.
  • the other conditions were similar to those for the carbon fiber bundle (A2).
  • the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.8 wt.%, the coefficient of friction was 0.34 and the drape value was 10.5 cm.
  • the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.7 wt.%, the coefficient of friction was 0.35 and the drape value was 6.2 cm.
  • the carbon fiber bundle (A2) was cut at a fiber length of 6 mm, the cut carbon fiber bundles and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and the mixture was introduced into an air laid machine.
  • the web having come out was heat treated to form a sheet-like carbon fiber nonwoven fabric comprising the carbon fibers and the nylon 6 fibers and having an areal weight of 200 g/cm 2 .
  • the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers was 13 wt.%, the number average x of carbon fibers forming the bundle was 160, and the standard deviation ⁇ was 70.
  • CM1001 nylon resin melt blow nonwoven fabric
  • the average value of the flexural strengths in 0° and 90° directions was 470 MPa
  • the fiber strength utilization factor was 15.7 MPa/%
  • the CV value was less than 5%.
  • a Flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (D2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 23 wt.%, the number average x of carbon fibers forming the bundle was 250, and the standard deviation ⁇ was 200.
  • the conditions and the results of the determinations and the evaluations are shown in Table 7.
  • the obtained carbon fiber nonwoven fabric is poor in flowability.
  • a Flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (E2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 22 wt.%, the number average x of carbon fibers forming the bundle was 260, and the standard deviation ⁇ was 210.
  • the conditions and the results of the determinations and the evaluations are shown together in Table 7.
  • the obtained carbon fiber nonwoven fabric is poor in flowability.
  • a Flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (A2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 80 wt.%, the number average x of carbon fibers forming the bundle was 1,200, and the standard deviation ⁇ was 630.
  • the conditions and the results of the determinations and the evaluations are shown together in Table 7. Although the obtained carbon fiber nonwoven fabric is good in flowability, the fiber strength utilization factor is low and the variability in properties is great.
  • the carbon fiber nonwoven fabric according to the present invention can be applied to manufacture of any carbon fiber reinforced molded article required with both of high flowability and mechanical properties and small variability in mechanical properties , which has not been achieved by conventional technologies.

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