JP2013203836A - Carbon fiber composite molded article, carbon fiber sandwich material, and automotive floor pan containing the carbon fiber composite molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber-reinforced composite material containing a thermoplastic resin as a matrix.SOLUTION: A carbon fiber composite molded article comprises a random layer and a one direction material layer, wherein the random layer comprises a composite material in which the composite material is constituted of PAN carbon fibers having a fiber length of >5 mm and ≤100 mm and a single fiber fineness of 1.0 to 2.4 dtex, and a thermoplastic resin, wherein the carbon fibers are paralleled in one direction, and fiber bundles having ≥the critical number of yarns defined in formula (1): critical yarn number =72/F(F is a single fiber fineness (dtex) of the carbon fibers) and fiber bundles in a yarn state or <the critical number thereof are simultaneously present; and the one direction material layer comprises a one direction material in which the carbon fibers are arranged in one direction, and the thermoplastic resin.

Description

  The present invention relates to a carbon fiber reinforced composite material using a thermoplastic resin as a matrix, wherein the carbon fiber that is substantially two-dimensionally oriented randomly and satisfies a specific opening state is present in the thermoplastic resin. The present invention relates to a molded body having a random layer, a unidirectional material layer composed of a unidirectional material in which carbon fibers are aligned in one direction, and a thermoplastic resin, and a sandwich material including the same. An object of the present invention is to provide a carbon fiber composite material that is excellent in mechanical properties and, in particular, has an excellent reinforcing function due to the composite of carbon fibers.

  As a fiber-reinforced composite material using carbon fiber, aramid fiber, glass fiber, or the like as a reinforcing fiber, an isotropic random mat is used because of formability and simplicity of the process. In recent years, as a means for improving the mechanical properties of a composite material using a random mat, a method using a chopped fiber bundle in which a fiber bundle is cut obliquely and its cross-sectional area is changed has been proposed (Patent Documents 1 and 2). ), But only proposals for composite materials with a thermosetting resin matrix.

Moreover, although the technique of injection-molding the long fiber pellet containing a reinforced fiber is also proposed about the composite material which uses a thermoplastic resin as a matrix (patent document 3), although it is a long fiber pellet, the length of a pellet has a restriction | limiting, Furthermore, there existed a subject that the reinforcing fiber was cut in the thermoplastic resin by kneading and the length of the reinforcing fiber could not be maintained. Further, such a molding method by injection molding has a problem that the reinforcing fibers are oriented and an isotropic product cannot be obtained.
Thus, the conventional composite material obtained by random mat or injection molding has a problem of low rigidity, and a carbon fiber composite molded body having excellent torsional rigidity is required. On the other hand, Patent Document 4 specifies a relationship between the average number of fibers and the carbon fiber diameter, and shows a highly rigid carbon fiber composite molded body. However, the direct influence of the carbon fiber diameter or fineness is clearly shown. It has not been.

JP 2009-114611 A JP 2009-114612 A Japanese Patent Laid-Open No. 9-286036 JP 2011-241338 A

  The present invention relates to a carbon fiber composite molded body composed of a PAN carbon fiber having a single fiber fineness of 1.0 to 2.4 dtex and a thermoplastic resin, a carbon fiber composite molded body having excellent rigidity, and a three-dimensional shape. An object of the present invention is to provide a carbon fiber composite molded body and a carbon fiber sandwich material containing the same.

  In response to the above problem, the carbon fiber is aligned in one direction with a random layer made of a composite material in which carbon fibers that are oriented in a two-dimensional random manner and satisfy a specific opening state are present in the thermoplastic resin. The present inventors have found that a carbon fiber composite material having excellent rigidity can be provided by forming a molded body having a unidirectional material layer composed of a unidirectional material and a thermoplastic resin.

That is, the present invention is composed of a carbon fiber having a fiber length of more than 5 mm and not more than 100 mm and a thermoplastic resin, and the carbon fibers are substantially two-dimensionally randomly oriented, and the number of critical single yarns or more defined by the formula (1) A unidirectional material in which carbon fibers are aligned in one direction, and a random layer made of a composite material characterized by the fact that there are simultaneously a fiber bundle and a fiber bundle composed of a single yarn state or less than the critical number of single yarns. And a unidirectional material layer made of a thermoplastic resin.
Critical number of single yarns = 72 / F ^0.5 (1)

  The composite molded body of the present invention exhibits high mechanical strength, and can be used for various components such as automobile inner and outer plates, components, various electric products, machine frames and casings, and the like. With the composite molded body of the present invention, it is possible to obtain a molded product having particularly excellent rigidity, so that it can be used as an automobile component member having an open section structure or a closed section structure, and in particular, a side member, a cross member, a side pillar, and a floor pan. Is also applicable.

[Carbon fiber composite molded body]
The composite molded body of the present invention is composed of a PAN carbon fiber having a fiber length of more than 5 mm and not more than 100 mm and having a single fiber fineness of 1.0 to 2.4 dtex and a thermoplastic resin, and the carbon fibers are oriented substantially two-dimensionally randomly. A composite material characterized in that a fiber bundle (A) having a number of critical single yarns or more defined by the formula (1) and a fiber bundle having a single yarn state or less than the critical number of single yarns exist simultaneously. And a unidirectional material layer composed of a unidirectional material in which carbon fibers are aligned in one direction and a thermoplastic resin.
Critical number of single yarns = 72 / F ^0.5 (1)
(Where F is the single fiber fineness (dtex) of the carbon fiber)

In particular, for the carbon fiber bundle (A) composed of the critical single yarn number or more defined by the formula (1), the ratio of the carbon fiber bundle (A) to the total amount of the fiber is 30 Vol% or more and less than 90 Vol%, and the carbon fiber When a composite material characterized in that the average number of fibers (N) in the bundle (A) satisfies the following formula (2) is used, a composite molded body exhibiting higher mechanical properties can be obtained.
Critical number of single yarns = 72 / F ^0.5 (1)
840 / F <N <2800 / F (2)
(Where F is the single fiber fineness (dtex) of the carbon fiber)

  Here, “substantially two-dimensional random” means that carbon fibers constituting the composite material are measured in two directions in which the main orientation direction of the fiber axis is in the contact surface of the composite material and perpendicular to each other in the plane. It means that the ratio obtained by dividing the larger value of the tensile modulus of elasticity by the smaller value does not exceed 2.

[Random layer]
The random layer constituting the composite molded body of the present invention is composed of a PAN carbon fiber having a fiber length of more than 5 mm and not more than 100 mm and a single fiber fineness of 1.0 to 2.4 dtex and a thermoplastic resin. The fiber bundle is oriented substantially two-dimensionally randomly, and there are simultaneously a fiber bundle having the number of critical single yarns defined by the formula (1) or more and a fiber bundle composed of a single yarn state or less than the critical single yarn number. It consists of a characteristic composite material.
Critical number of single yarns = 72 / F ^0.5 (1)

When it is necessary to obtain higher mechanical properties, the fiber length is preferably more than 10 mm. Moreover, about the carbon fiber bundle (A) comprised by the critical single yarn number or more defined by Formula (1), the ratio of the carbon fiber bundle (A) with respect to the fiber whole quantity is 30 Vol% or more and less than 90 Vol%, and a carbon fiber bundle It is preferable that the average number of fibers (N) in (A) satisfy the following formula (2).
840 / F <N <2800 / F (2)
(Where F is the single fiber fineness (dtex) of the carbon fiber)

  The composite molded body of the present invention comprises a random layer containing carbon fibers having an average fiber length of more than 5 mm and not more than 100 mm, the degree of opening being controlled in the thermoplastic resin matrix, and the carbon fibers being oriented substantially two-dimensionally randomly. Since it is a base material, it is characterized by excellent torsional rigidity. In order to improve torsional rigidity when using a unidirectional material of continuous fibers as a base material, it is effective to laminate 45 degrees as the direction of continuous fibers, but it is productivity to laminate continuous fibers in the 45 degrees direction. However, in the present invention, the torsional rigidity can be borne by a random layer that can be produced by an industrially advantageous method as described later.

[Random layer carbon fiber]
The carbon fibers constituting the random layer are discontinuous and have an average fiber length of more than 5 mm and not more than 100 mm. The random layer is characterized in that the reinforcing function can be expressed by including carbon fibers that are long to some extent, preferably the average fiber length of the carbon fibers is 10 mm or more and 100 mm or less, more preferably 15 mm or more and 80 mm or less, and further 20 mm or more. 60 mm or less is preferable. Since the matrix resin is a thermoplastic resin, a composite material can be obtained without being melt-kneaded by a preferable manufacturing method described later, and thus the length of the carbon fiber used can be maintained in the composite material. A carbon fiber having a sharp fiber length distribution can be obtained, and the presence of carbon fibers having a uniform fiber length can preferably provide a layer made of a composite material having uniform physical properties.

  The single fiber fineness of the PAN-based carbon fiber constituting the random layer is preferably 1.0 to 2.4 dtex. This is because the mechanical properties are good when it is 1.0 dtex or more, and when it is 2.4 dtex or less, the production during carbon fiber production is excellent. It is preferable to use a carbon fiber to which a sizing agent is attached, and the sizing agent is preferably more than 0.1 parts by weight and 10 parts by weight or less with respect to 100 parts by weight of the carbon fibers.

  Moreover, as a reinforced fiber used for this invention, it is preferable that cross-sectional shape is 0.70 or more and 0.90 or less roundness. Furthermore, the cross-sectional shape is preferably an empty bean type. Even if the fineness of the single fiber is increased, the roundness is larger than 0.90 by making the cross-sectional shape into a relatively simple shape round bean type with a roundness of 0.70 or more and 0.90 or less. The strand strength can be maintained at a higher value than the reinforcing fiber having a close sectional shape. Further, since the single fibers can be densely packed, the fiber content in the prepreg is improved, and the mechanical properties of the composite material can be improved.

<Diameter and roundness of carbon fiber bundle>
(1) Preparation of sample A carbon fiber bundle cut to a length of 5 cm is embedded in an epoxy resin (Epomount main agent: Epomount curing agent = 100: 9 (mass ratio)), cut to 2 cm, and the cross section is exposed. And mirror-finished.
(2) Etching treatment of observation surface Further, in order to clarify the outer shape of the fiber, the cross section of the sample was etched by the following method.
-Equipment used: Plasma etching equipment (manufactured by JEOL Ltd., product name: P-170)
Processing conditions: atmospheric gas: Ar / O ₂ = 75/25, plasma output: 50 W, vacuum: about 120 Pa, processing time: 5 min
(3) SEM observation The cross section of the sample obtained by said (1) and (2) was observed using SEM (the product name: FEI-XL20 by PHILIPS), and five or more fibers were displayed on the screen. We arbitrarily photographed five photographs showing the cross section.
(4) Measurement of single fiber diameter of carbon fiber bundle For each sample, 20 pieces are arbitrarily selected from 5 SEM photographs, but 3 or more single fiber sections are selected from one photograph, and image analysis software The outer shape of the cross section of the fiber was traced using a product name “Image-Pro PLUS” manufactured by Parr Co., Ltd., and the major axis (maximum ferret diameter) d of the cross section was measured. The average of the major axis d of all selected single fiber cross sections was defined as the diameter Di of the single fiber of the carbon fiber bundle.
(5) Roundness measurement The outer shape of the fiber cross-section was traced using image analysis software (product name: Image-Pro PLUS, manufactured by Nippon Roper Co., Ltd.), and the circumference L and area S were measured. For each sample, 20 pieces were arbitrarily selected from five photographs, but three or more fiber cross sections were selected from one photograph, measured, average values of L and S were obtained, and roundness was calculated by the following equation. .
Roundness = 4πS / L ² (3)

[Opening degree]
Generally, carbon fiber is a fiber bundle in which thousands to tens of thousands of filaments are gathered. In particular, when a thin-walled composite is obtained, if carbon fibers are used in the form of fiber bundles, the entangled portion of the fibers becomes locally thick, and a thin-walled one cannot be obtained. Therefore, it is important to open and use the carbon fiber, but in the random layer, the degree of opening of the carbon fiber in the thermoplastic resin matrix is controlled, and a carbon fiber bundle made of carbon fibers of a specific number or more. And other open carbon fibers.

When it is necessary to obtain higher mechanical properties, the degree of opening of the carbon fibers in the thermoplastic resin matrix is controlled, and a carbon fiber bundle composed of carbon fibers of a specific number or more and other opened carbons. It is desirable to use a random layer containing fibers at a specific ratio. That is,
In the random layer, the formula (1)
Critical number of single yarns = 72 / F ^0.5 (1)
(Where F is the single fiber fineness (dtex) of the carbon fiber)
With respect to the carbon fiber bundle (A) composed of the number of critical single yarns or more defined in, it is preferable for the purpose of obtaining excellent mechanical properties that the ratio to the total amount of fibers is 30 Vol% or more and less than 90 Vol%. In the composite molded body, there is a fiber bundle composed of a single yarn state or less than the critical single yarn number as carbon fibers other than the carbon fiber bundle (A). The ratio of the carbon fiber bundle (A) when obtaining a molded article having excellent mechanical properties is more preferably 40 Vol% or more and less than 80 Vol%.

  On the other hand, for the purpose of obtaining a composite molded body that can be thinned and has excellent surface quality, the ratio of the carbon fiber bundle (A) composed of the number of critical single yarns or more to the total amount of fibers is more than 0 vol% and less than 30 vol% It is preferable that When the proportion of the carbon fiber bundle (A) is 90 Vol% or more, the entangled portion of the fiber is locally thick, and a thin product cannot be obtained, which is not suitable for the purpose of the present invention.

Furthermore, when it is going to obtain the compact | molding | casting excellent in mechanical physical property, about the random layer, the average fiber number (N) in the carbon fiber bundle (A) comprised by more than a critical single yarn number is following formula (2).
840 / F <N <2800 / F (2)
(Where F is the single fiber fineness (dtex) of the carbon fiber)
It is preferable to satisfy.

  When the average number of fibers (N) in the carbon fiber bundle (A) is 840 / F or less, it is difficult to obtain a high fiber volume content (Vf). Further, when the average number of fibers (N) in the carbon fiber bundle (A) is 2800 / F or more, a locally thick portion is generated, which tends to cause voids.

On the other hand, when the average number of fibers (N) in the carbon fiber bundle (A) satisfies the following formula (4), a composite molded body that can be made thinner and has excellent surface quality is obtained.
140 / F <N <350 / F (4)
(Where F is the single fiber fineness (dtex) of the carbon fiber)

  In such a composite material in which carbon fiber bundles (A) equal to or higher than the critical single yarn defined by the formula (1) and carbon fibers (B) having a single yarn state or less than the critical single yarn number are present simultaneously, It is possible to provide a composite molded body with good fiber filling efficiency, less variation in density, and excellent mechanical strength.

  In addition, the amount of carbon fibers in the composite molded body, that is, the fiber volume, is obtained by coexisting carbon fiber bundles composed of carbon fibers of a specific number or more and other opened carbon fibers in a specific ratio. It is possible to increase the content (Vf).

  Specifically, when the single fiber fineness of the carbon fibers constituting the composite molded body is 1.0 to 2.4 dtex, the critical single yarn number is 45 to 65, and the ratio of carbon fiber bundles more than the critical single yarn number to the total fiber amount Is 30 vol% or more and less than 90 vol%.

  The composite molded body of the present invention can have various thicknesses, but a thin molded product having a thickness of about 0.2 to 1.0 mm can be suitably obtained. That is, according to the present invention, a composite molded body having various thicknesses can be provided. In particular, a thin molded article can be suitably obtained, and a skin of a sandwich member can also be provided.

[Thermoplastic resin in random layer]
The abundance of the thermoplastic resin in the random layer is preferably 50 to 1000 parts by weight with respect to 100 parts by weight of the carbon fibers. More preferably, it is 50 to 500 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the carbon fiber, and more preferably 50 to 100 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the carbon fiber.

  Examples of the thermoplastic resin include vinyl chloride resin, vinylidene chloride resin, vinyl acetate resin, polyvinyl alcohol resin, polystyrene resin, acrylonitrile-styrene resin (AS resin), acrylonitrile-butadiene-styrene resin (ABS resin), acrylic resin, Methacrylic resin, polyethylene resin, polypropylene resin, polyamide 6 resin, polyamide 11 resin, polyamide 12 resin, polyamide 46 resin, polyamide 66 resin, polyamide 610 resin, polyacetal resin, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, boribylene Terephthalate resin, polyarylate resin, polyphenylene ether resin, polyphenylene sulfide resin, polysulfone resin, polyethersulfur Down resin, polyether ether ketone resins, and mixtures thereof, and the like.

[Other agents]
In the random layer, various fibrous or non-fibrous fillers such as glass fibers and organic fibers, flame retardants, UV-resistant agents, pigments, mold release agents, softeners, plasticizers, as long as the object of the present invention is not impaired. A surfactant additive may be included.

[Development of reinforcing function by carbon fiber]
The random layer composite material is capable of developing strength of 60 to 80% with respect to the theoretical value of the strength of the composite material in which carbon fibers are randomly included in two-dimensional pseudo-isotropic. The reason why it is possible to achieve such a strength expression rate is that, as described above, it is effective in a composite material by coexisting a carbon fiber bundle composed of carbon fibers of a specific number or more and other opened carbon fibers. This is probably due to the presence of carbon fiber.

[Unidirectional material layer]
The unidirectional material layer constituting the carbon fiber composite molded body of the present invention comprises a unidirectional material in which continuous fibers of carbon fibers are aligned in one direction and a thermoplastic resin. The unidirectional material of carbon fiber is obtained by aligning carbon fibers having a continuous length in one direction. The unidirectional material may be a laminate of a plurality of unidirectional materials, and a bundle of fiber reinforcements aligned in one direction and laminated at different angles (multiaxial fabric base material) Nylon yarn, polyester yarn, glass fiber yarn, and other stitch yarns that pass through the laminate in the thickness direction and are stitched by reciprocating between the front and back surfaces of the laminate along the surface direction. A shaft fabric may be used.

  The amount of the thermoplastic resin in the unidirectional material layer is preferably 30 to 200 parts by weight with respect to 100 parts by weight of the carbon fiber. The abundance of the thermoplastic resin is more preferably 40 to 100 parts by weight with respect to 100 parts by weight of the carbon fibers.

  The thermoplastic resin constituting the unidirectional material layer may be the same as or different from the matrix in the random layer. Specific examples of the thermoplastic resin are the same as those described in the section of the random layer. The unidirectional material layer is preferably formed by impregnating or semi-impregnating a thermoplastic resin with a unidirectional material in which carbon fibers are aligned in one direction. Here, the degree of impregnation or semi-impregnation can be appropriately adjusted in the press step of the production method described later.

[Laminate]
In the carbon fiber composite molded body of the present invention, the unidirectional material layer in which the carbon fibers are aligned in one direction is preferably present in an amount of 5 to 100% with respect to the total volume of the random layer, An area ratio and a lamination | stacking site | part can be suitably selected according to various uses.
The unidirectional material layer is preferably arranged so as to effectively develop desired torsional rigidity and bending rigidity. It is also preferable to arrange the unidirectional material layer so as to interweave two axes within a range of 30 to 120 degrees, for example.

  As the random layer and the unidirectional material layer, those having a desired thickness can be used. The thickness of the random layer is not particularly limited, but is preferably 0.1 to 5 mm. The thickness of the unidirectional material layer is not particularly limited, but is preferably 0.1 to 5 mm.

  It is also possible to obtain a molded body having a desired shape such as a three-dimensional shape by selecting the shape of the mold. The composite molded body of the present invention has a short resin moving distance in the pressing step and can be impregnated with the resin in a relatively short time, and can provide a molded product that is thin, excellent in physical properties, and excellent in surface quality. In addition, since the carbon fiber isotropically exists in the molded body, a homogeneous molded product with less warpage can be easily obtained even if the fiber is reinforced in one direction. It is also possible to obtain a composite molded body by attaching a random layer to the surface layer of a member having an open cross-sectional shape or a closed cross-sectional shape obtained by pultrusion molding or the like, for example, by a tape layup method or the like.

  The carbon fiber composite molded body of the present invention may have a multilayer structure further having layers other than the random layer and the unidirectional material layer. Since the carbon fiber composite molded body of the present invention can be obtained as a thin layer as a random layer, it can be preferably used as the skin of a sandwich member. Although there is no limitation in particular as a core material at this time, the foam of resin, the nonwoven fabric of glass fiber, or an organic fiber can be used.

[Sandwich material]
As a laminated structure, a sandwich material using a plurality of random layers and unidirectional material layers is also preferable. That is, the present invention includes a sandwich material having a random layer as a skin layer and a unidirectional material layer as a core material, and a sandwich material having a random layer as a core material and a unidirectional material layer as a skin layer. In the case of a sandwich material having a random layer as a skin layer, it is excellent in design and the like, and is excellent in prevention of cracks due to impact load. Therefore, it is particularly suitable for use in structural members of vehicles such as automobiles and railways.

  In the case of a sandwich material having a random layer as a core material, it is easy to achieve both mechanical properties, particularly strength and rigidity, and therefore, it is particularly suitable for use in structural members such as buildings. Also when it is set as such a sandwich material, the ratio of the unidirectional material layer with respect to the total volume of a random layer can be preferably selected from the range of 5 to 100% according to various uses.

[Production method of random layer]
Hereinafter, a method for preferably obtaining the random layer will be described. A random layer can be preferably manufactured by performing the process 5 further by the following processes 1-4.
1. Cutting carbon fiber,
2. A process of opening the fiber bundle to some extent by introducing the cut carbon fiber into the tube and blowing air onto the carbon fiber,
3. A spreading process of spreading the opened carbon fiber and simultaneously sucking the carbon fiber and the thermoplastic resin by sucking together with the fibrous or powdered thermoplastic resin,
4). A step of fixing a coated carbon fiber and a thermoplastic resin to obtain a random mat.
5. A step of press-molding the obtained random mat.

[Cut process]
The process of cutting carbon fiber will be described. The carbon fiber cutting method is preferably a step of cutting carbon fiber using a knife such as a rotary cutter. As the rotary cutter, it is preferable to use a splitting cutter that splits and cuts a fiber bundle into about 1/2 to 1/20. The rotary splitting cutter has a plurality of blades arranged at equal intervals and spirally along the main body. As with conventional cutters, it is difficult to obtain a composite molded article that is thin and excellent in physical properties by cutting and applying the fiber bundle as it is. By cutting the fiber bundle while dividing it into finer bundles, the homogeneity of the random mat obtained in step 4 can be improved, and a thin random mat can be obtained, and a composite material can be suitably obtained. The knife angle for continuously cutting the carbon fiber is not particularly limited, and a 90-degree blade or an angle with respect to a general fiber may be used.

[Opening process]
Next, the cut carbon fiber is introduced into the tube, and air is blown onto the fiber to open the fiber bundle apart. More specifically, it is a step of opening the fiber bundles apart by continuously introducing the cut carbon fibers into the pipe and blowing the pressure air directly onto the fibers. The degree of opening can be appropriately controlled by air pressure or the like.

  A preferred method for opening the carbon fiber is a method in which compressed air is blown directly onto the carbon fiber. Specifically, carbon fibers can be opened by blowing air from a compressed air blowing hole, preferably at a wind speed of 5 to 500 m / sec. Preferably, the fiber bundle has an arbitrary degree of opening by opening several holes of about Φ1 mm in the tube through which the carbon fiber passes, applying a pressure of about 0.01 to 0.80 MPa from the outside, and blowing compressed air directly onto the fiber bundle. Can be opened.

[Coating process]
Next, the spread carbon fiber is diffused, and at the same time, it is sucked together with the fibrous or powdery thermoplastic resin, and the coating process is performed to simultaneously spray the carbon fiber and the thermoplastic resin. The composite molded body of the present invention can be suitably obtained by simultaneously applying the opened carbon fiber and the fibrous or powdery thermoplastic resin on the sheet.

  In the coating step, the amount of the thermoplastic resin supplied is preferably 50 to 1000 parts by weight with respect to 100 parts by weight of the carbon fiber. More preferably, it is 50 to 400 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the carbon fiber, and further preferably 50 to 100 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the carbon fiber.

In the coating step, a desired thickness can be obtained by appropriately selecting the supply amounts of the carbon fiber and the thermoplastic resin. Here, it is preferable that the carbon fiber and the fibrous or powdery thermoplastic resin are dispersed so as to be two-dimensionally oriented. In order to apply the opened carbon fiber while being two-dimensionally oriented, an application method and a fixing method described below are important. In the carbon fiber coating method, it is preferable to use a tapered tube having a conical shape. In a tube such as a cone, air diffuses and the flow velocity in the tube is reduced. At this time, a rotational force is applied to the carbon fiber. The carbon fibers opened using this venturi effect can be preferably diffused and dispersed.
It is preferable to apply on a breathable sheet provided at the lower part of the opening device. Also for the following fixing step, it is preferable to spray on a movable breathable sheet having a suction mechanism.

[Fixing process]
Next, the applied carbon fiber and the thermoplastic resin are fixed to obtain a random mat. Specifically, the applied carbon fiber and thermoplastic resin are sucked from the lower part of the breathable sheet to fix the carbon fiber to obtain a random mat. The thermoplastic resin sprayed simultaneously with the carbon fiber is mixed, and if it is in the form of a fiber, it is fixed with the carbon fiber even if it is in powder form by air suction.

  Specifically, a random mat with a high two-dimensional orientation can be obtained by suction from the lower part through a breathable sheet. Also, the powdered or short fiber thermoplastic resin is sucked using the generated negative pressure, and can be easily mixed with the carbon fiber by the diffusion flow generated in the tube. In the obtained random mat, the presence of the thermoplastic resin in the vicinity of the carbon fiber enables the resin to be impregnated in a relatively short time because the resin moving distance is short in the following hot pressing step. A random mat may be obtained as a random layer and subjected to a lamination step with a unidirectional material layer described below. In the press for laminating with the unidirectional material layer, the resin travel distance is short, the resin can be impregnated in a relatively short time, and the unidirectional material layer can be firmly laminated.

[press]
Next, a molded plate obtained by subjecting the obtained random mat to a pressing process may be used as a random layer and subjected to a carbon fiber composite molded body laminating process described later. At this time, a plurality of random mats can be stacked to have a desired thickness. There are no particular restrictions on the method and conditions for press molding, but it is preferable to perform hot pressing under the conditions of not lower than the melting point of the matrix thermoplastic resin and not lower than the melting point plus 80 ° C. or the decomposition temperature. The press pressure and press time can also be appropriately selected.

[Method for producing unidirectional material layer]
The method for producing a unidirectional material layer composed of a unidirectional material of carbon fiber and a thermoplastic resin is not particularly limited, and can be obtained by, for example, a pultrusion method. In the case of the pultrusion method, a carbon fiber impregnated with a thermoplastic resin is preferably obtained. When a layer impregnated with a thermoplastic resin is suppressed, that is, a semi-impregnated layer, for example, a method of aligning carbon fibers in one direction on a sheet made of a thermoplastic resin and heating while pressing if necessary is preferable. Can be obtained.

[Method for producing carbon fiber composite molded body]
The carbon fiber composite molded body can be manufactured by laminating a random layer and a unidirectional material layer, and molding them by various methods. As a specific method for obtaining a three-dimensional carbon fiber composite molded body, a method of obtaining a plate-like product obtained by laminating a random layer and a unidirectional material layer and press-molding it is preferably mentioned.

  In this method, as described in the above section for the production method of the random layer, a random mat or a plate-like material obtained by subjecting the random mat to press molding is used as a random layer, and a plate in which a unidirectional material layer is laminated. A preferred method is to obtain a product and shape it into various shapes by, for example, press molding. Here, it is preferable to perform press molding by adjusting the degree of impregnation or semi-impregnation of the random layer and the unidirectional material layer.

  Particularly in the case of a three-dimensional shape, a method in which a random layer and a unidirectional material layer are combined and pressed in a mold is also preferred. In this method, a unidirectional material layer is arranged at a desired position in the mold, and the random mat described in the above-mentioned method for producing a random layer is set on the three-dimensional mold so as to follow the random mat. A method of pressing is preferred. Although depending on the shaping shape, in the case of a complicated shape, it is preferable to use a semi-impregnated unidirectional material layer.

[Production method of sandwich material]
The sandwich material can be appropriately manufactured by combining a random layer and a unidirectional material layer in the same manner as the above-described method for manufacturing a carbon fiber composite molded body.

Examples are shown below, but the present invention is not limited thereto.
[Analysis of carbon fiber bundles in random layers]
The degree of opening of the carbon fiber bundle in the random layer was determined by the following procedure.
1) A random layer is cut out to 100 mm × 100 mm, and after measuring the thickness (Ta), the resin is removed in a furnace for about 500 ° C. × 1 hour.
2) Remove all fiber bundles with tweezers from the composite material from which the resin has been removed.
3) For all fiber bundles, the length (Li) and weight (Wi) of each fiber bundle are measured, and the number of fiber bundles (I) is recorded. When the fiber bundle is so small that it cannot be taken out by tweezers, the weight is finally measured together (Wk). At this time, a balance capable of measuring up to 1/1000 g is used. In addition, when the fiber length is short, the weight of the fiber bundle is small and measurement becomes difficult. In such a case, the fibers are classified at intervals of about 0.2 mm, and a plurality of classified fiber bundles are provided. The weight was measured collectively and the average value was used.
4) After measurement for all classifications, perform the following calculations. From the single fiber fineness (F) of the carbon fiber used, the number of fibers (Ni) of the classified fiber bundle group is obtained by the following equation.
Ni = Wi / (Li × F).
The average number of fibers (N) in the carbon fiber bundle (A) is obtained by the following formula.
N = ΣNi / I
Further, the volume (Vi) of each fiber bundle and the ratio (VR) of the carbon fiber bundle (A) to the whole fiber are obtained by the following formula using the fiber specific gravity (ρ) of the carbon fiber used.
Vi = Wi / ρ
VR = ΣVi / Va × 100
Here, Va is the volume of the cut-out layer, Va = 100 × 100 × Ta

[Method of measuring bending stiffness of molded products]
The bending stiffness in the following examples was evaluated by three-point bending with a central load. The molded product was placed on a fulcrum of r = 2 mm where the distance between the fulcrums was 500 mm, and the center deflection when a load of 50 kg was applied to the central part between the fulcrums with an indenter of r = 5 mm was measured.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples. The following carbon fibers were used in Examples and Comparative Examples.
(Carbon fiber)
PAN-based carbon fiber 1 (single fiber fineness 1.2 dtex, strength 4218 MPa, elastic modulus 236 GPa, roundness: 0.80)
PAN-based carbon fiber 2 (single fiber fineness 2.4 dtex, strength 3477 MPa, elastic modulus 2340 Pa, roundness: 0.80)
PAN-based carbon fiber 3 (TR50S manufactured by Mitsubishi Rayon Co., Ltd.) (single fiber fineness 0.7 dtex, strength 4900 MPa, elastic modulus 240 GPa, roundness: 0.95)

[Unidirectional material outer layer compact]
Example 1
A PAN-based carbon fiber 1 was used, and a rotary cutter that used a cemented carbide to form a knife was used as the cutting device. The angle of the knife was 90 degrees with the circumferential direction, and a knife with a blade width of 1 mm was used. The knives were arranged at a pitch of 16 mm in the circumferential direction, and adjacent knives were arranged so as to be offset from each other by 1 mm in the circumferential direction. A tube having small holes was prepared as a fiber opening device, and compressed air was supplied using a compressor. At this time, the wind speed from the small hole was 100 m / sec. This pipe was placed directly under the rotary cutter, and a tapered pipe was welded to the lower part thereof. A matrix resin is supplied from the side surface of the taper tube, and a polycarbonate resin (trade name: “Panlite” (registered trademark) L-1225L pellet) manufactured by Teijin Kasei Co., Ltd.) is frozen and pulverized as the matrix resin. And powder classified at 30 mesh. At this time, the average particle diameter was about 1 mm. Next, a table movable in the XY directions was installed at the lower part of the taper tube outlet, and suction was performed from the lower part of the table with a blower. The carbon fiber supply rate was set to 150 g / min and the matrix resin supply rate was set to 125 g / min. When the apparatus was operated, carbon fiber having an average fiber length of 16 mm and polycarbonate were mixed, and the thickness was 0.5 mm. A random mat of a degree was obtained.

  Next, on a sheet in which continuous fibers of the PAN-based carbon fiber 1 are aligned in one direction, a polycarbonate resin film, a Panlite (registered trademark) sheet (with 100 parts by volume of polycarbonate resin with respect to 100 parts by volume of carbon fiber) D-50, 50 [mu] th thick) was placed and bonded together with a 300 [deg.] C. heating roller.

  Two sheets of the obtained unidirectional material were laminated in the center of the mold, and then the obtained random mat was cut into a size of 30 cm wide × 50 cm long, and four layers were laminated and molded. . This was heated at 2.0 MPa for 5 minutes in a press apparatus heated to 300 ° C., and formed into the shape shown in FIG.

  Two sets of molded bodies were used and bonded in plane symmetry to obtain a prism. The three-point bending of this prism was measured. About the random layer of the obtained molded body, the number of critical single yarns defined by the formula (1), the average number of fibers (N) in the carbon fiber bundle (A) composed of the number of critical single yarns or more, the number of critical single yarns or more The ratio of the carbon fiber bundle (A) to be constructed is shown in Table 1. When a bending test was performed on the molded body, it was 1.9 mm at the center deflection.

[Example 2]
For the random layer of the molded body obtained using the PAN-based carbon fiber 2 in the same manner as in Example 1, the critical single yarn number defined by the formula (1) is a carbon fiber bundle composed of at least the critical single yarn number ( The ratio of the carbon fiber bundle (A) composed of the average number of fibers (N) in A) and the number of critical single yarns or more is shown in Table 1.
When the bending test of the molded body was performed, it was 2.0 mm at the center deflection.

[Comparative Example 1]
About the random layer of the molded body obtained by using the PAN-based carbon fiber 3 in the same manner as in Example 1, the number of critical single yarns defined by the formula (1), a carbon fiber bundle (A Table 1 shows the ratio of the carbon fiber bundle (A) composed of the average number of fibers (N) and the number of critical single yarns or more.
When the bending test of the molded body was carried out, it was 2.3 mm at the center deflection.

[Random core sand UD skin molding]
(Example 3)
A PAN-based carbon fiber 1 was used, and a rotary cutter that used a cemented carbide to form a knife was used as the cutting device. The angle of the knife was 90 degrees with the circumferential direction, and a knife with a blade width of 1 mm was used. The knives were arranged at a pitch of 16 mm in the circumferential direction, and adjacent knives were arranged so as to be offset from each other by 1 mm in the circumferential direction. A tube having small holes was prepared as a fiber opening device, and compressed air was supplied using a compressor. At this time, the wind speed from the small hole was 100 m / sec. This pipe was placed directly under the rotary cutter, and a tapered pipe was welded to the lower part thereof. A matrix resin is supplied from the side of the taper tube, and a polycarbonate resin (product name: “Panlite” (registered trademark) L-1225L pellet) manufactured by Teijin Chemicals Ltd.) is frozen and pulverized as the matrix resin. And powder classified at 30 mesh. At this time, the average particle diameter was about 1 mm. Next, a table movable in the XY directions was installed at the lower part of the taper tube outlet, and suction was performed from the lower part of the table with a blower. The carbon fiber supply rate was set to 150 g / min and the matrix resin supply rate was set to 125 g / min. When the apparatus was operated, carbon fiber having an average fiber length of 16 mm and polycarbonate were mixed, and the thickness was 0.5 mm. A random mat of a degree was obtained. Next, the obtained random mat was heated at 2.0 MPa for 5 minutes with a press apparatus heated to 300 ° C. to obtain a molded plate of t = 0.2 mm.

  A unidirectional material composed of PAN-based carbon fiber 1 and 100% by volume of carbon fiber 100% by volume, polycarbonate “Panlite” (registered trademark) L-1225L, 100% by volume, and pultrusion molding. A unidirectional material was obtained by forming a plate having a thickness of 25 mm and a thickness of 0.1 mm.

  The produced random-layer shaped plate was cut into a size of 30 cm wide × 50 cm long, and a stack of 6 layers of unidirectional materials arranged in parallel on top and bottom of a stack of 4 layers was heated to 300 ° C. The sandwich was heated at 2.0 MPa for 5 minutes with a press machine to obtain a sandwich plate with t = 1.0 mm. The obtained sandwich plate was heated to 300 ° C. using a heater and then formed into the shape shown in FIG. 5 with a cold press.

  Two sets of these were used and bonded in plane symmetry to obtain a prism. When the three-point bending of this prism was measured, it was 2.2 mm at the center deflection.

  About the random layer of the obtained sandwich plate, the number of critical single yarns defined by the formula (1) is the average number of fibers (N) in the carbon fiber bundle (A) composed of the number of critical single yarns or more, the number of critical single yarns or more The ratio of the carbon fiber bundle (A) composed of is shown in Table 1. Two sets of these were used and bonded in plane symmetry to obtain a prism. When the bending test of the three-point molded body of this prism was carried out, it was 2.0 mm at the center deflection.

Example 4
About the random layer of the sandwich plate produced in the same manner as in Example 3 using the PAN-based carbon fiber 2, the number of critical single yarns defined by the formula (1), a carbon fiber bundle (A Table 1 shows the ratio of the carbon fiber bundle (A) composed of the average number of fibers (N) and the number of critical single yarns or more. When a bending test was performed on the molded body, it was 1.9 mm at the center deflection.

(Comparative Example 2)
About the random layer of the sandwich plate produced in the same manner as in Example 3 using the PAN-based carbon fiber 3, the number of critical single yarns defined by the formula (1), the carbon fiber bundle (A Table 1 shows the ratio of the carbon fiber bundle (A) composed of the average number of fibers (N) and the number of critical single yarns or more. When the bending test of the molded body was carried out, it was 2.2 mm at the center deflection.

Claims (12)

It is composed of a PAN carbon fiber having a fiber length of more than 5 mm and not more than 100 mm and having a single fiber fineness of 1.0 to 2.4 dtex and a thermoplastic resin, and the carbon fibers are substantially two-dimensionally oriented, and the formula (1) A random layer made of a composite material characterized by the simultaneous existence of a fiber bundle having a number of critical single yarns or more as defined in 1 and a fiber bundle composed of a single yarn state or less than the critical number of single yarns, and carbon fiber in one direction A carbon fiber composite molded body having a unidirectional material and a unidirectional material layer made of a thermoplastic resin.
Critical number of single yarns = 72 / F ^0.5 (1)
(Where F is the single fiber fineness (dtex) of the carbon fiber)   The carbon fiber composite molded body according to claim 1, wherein the shape of a cross section perpendicular to the fiber axis of a single fiber contained in the PAN carbon fiber is not less than 0.70 and not more than 0.90.   The carbon fiber composite molded body according to claim 1 or 2, wherein the unidirectional material layer is present in an amount of 5 to 100% with respect to the total volume of the random layer.   The carbon fiber composite molded body according to any one of claims 1 to 3, wherein an amount of the thermoplastic resin in the random layer is 50 to 1000 parts by weight with respect to 100 parts by weight of the carbon fiber.   The carbon fiber composite molded body according to any one of claims 1 to 3, wherein an abundance of the thermoplastic resin in the unidirectional material layer is 30 to 200 parts by weight with respect to 100 parts by weight of the carbon fibers. In the random layer, for the carbon fiber bundle (A) composed of the critical single yarn number or more defined by the formula (1), the ratio of the carbon fiber bundle (A) to the total amount of the fiber is 30 Vol% or more and less than 90 Vol%, And the average fiber number (N) in a carbon fiber bundle (A) satisfy | fills following formula (2), The carbon fiber composite molded object in any one of Claims 1-5 characterized by the above-mentioned.
840 / F <N <2800 / F (2)
(Where F is the single fiber fineness (dtex) of the carbon fiber)   The carbon fiber composite molding according to any one of claims 1 to 6, wherein the unidirectional material layer is obtained by impregnating or semi-impregnating a thermoplastic resin with a unidirectional material in which continuous fibers of carbon fibers are aligned in one direction. body.   The carbon fiber composite molded article according to any one of claims 1 to 7, which is a three-dimensional shape obtained by obtaining a plate-like product obtained by laminating the random layer and the unidirectional material layer and press-molding it.   The carbon fiber composite molded body according to any one of claims 1 to 7, which is a three-dimensional shape obtained by combining the random layer and the unidirectional material layer and pressing in a mold.   A carbon fiber sandwich material comprising the carbon fiber composite molded body according to any one of claims 1 to 9, wherein the random layer is a skin layer, and the unidirectional material layer is a core material.   A carbon fiber sandwich material comprising the carbon fiber composite molded body according to claim 1, wherein the random layer is a core material and the unidirectional material layer is a skin layer.   The carbon fiber composite molded article according to any one of claims 1 to 9, wherein the random layer is used over the entire surface, and a unidirectional material layer is partially used for a cross member or a side member, or both. Including car floor pans.