JP5722732B2 - Method for producing isotropic random mat for forming thermoplastic composite material - Google Patents

Description

  The present invention relates to a method for producing an isotropic random mat for producing a fiber-reinforced composite material using a thermoplastic resin as a matrix.

  Fiber reinforced composite materials using carbon fibers, aramid fibers, glass fibers, etc. as reinforcing fibers in order to reinforce resins, make use of their high specific strength and specific elastic modulus, structural materials such as aircraft and automobiles, fishing rods, It is widely used as a molding material for sports equipment such as tennis rackets and golf shafts or general industrial applications. Examples of the form of the reinforcing fiber used in these composite materials include a woven fabric made of continuous fibers, a UD sheet in which fibers are aligned in one direction, a random sheet made using cut fibers, and a nonwoven fabric.

  In general, a woven fabric, a UD sheet, etc. using continuous fibers are arranged so that the fiber arrangement direction of each layer has a constant crossing angle (for example, 0 / + 45 / -45 / 90) due to the anisotropy of continuous fibers. It is necessary to laminate the layers, and in addition to laminate the surface object to prevent warping of the molded product, and the mere lamination alone tends to cause problems such as delamination and delamination due to insufficient adhesion strength between layers. Since the process becomes complicated and a special operation is required at the time of lamination, it is one of the causes for raising the manufacturing cost of the fiber-reinforced composite material.

  On the other hand, an attempt has been made to obtain a relatively inexpensive fiber-reinforced composite material by using a random mat that is isotropic in advance. This random mat is made by spraying the cut reinforcing fiber alone with the thermosetting resin at the same time onto the mold (dry type), or adding the precut reinforcing fiber to the slurry containing the binder resin and making paper. It is manufactured by a method (wet method) or the like.

  Among them, the dry method can obtain a random mat relatively inexpensively because the apparatus is small. As this dry method, a continuous fiber is used, and a technique of spraying at the same time as cutting the fiber is often used, and most of them use a rotary cutter. However, in this method, when the interval between the cutter blades is widened in order to increase the fiber length of the cut fibers, the cutting frequency is lowered, so that the ejection of the fibers from the cutter becomes discontinuous. For this reason, local fiber texture spots are generated, and in particular, when a mat with a low fabric weight is created, the thickness spots become conspicuous, and the problem of poor surface design is inevitable.

  Another problem with fiber reinforced composite materials is that it takes a long time to form. Usually, a molded product of a fiber reinforced composite material is obtained by placing a material called a prepreg in which a reinforcing fiber base material is impregnated with a thermosetting resin in an autoclave and heating and pressing for 2 hours or more. In recent years, an RTM molding method in which a thermosetting resin is poured after a reinforcing fiber base not impregnated with a resin is set in a mold has been proposed, and the molding time has been greatly reduced by this method. However, even when the RTM molding method is used, it takes 10 minutes or more to mold one molded product.

  Therefore, a composite material using a thermoplastic resin as a matrix in place of a conventional thermosetting resin has attracted attention. However, the thermoplastic resin generally has a higher viscosity than the thermosetting resin, so that the time for impregnating the resin into the reinforcing fiber base becomes longer, resulting in a longer tact time until molding. It was.

  As a technique for solving these problems, a technique called thermoplastic stamping molding (TP-SMC) has been proposed. This is because a chopped fiber pre-impregnated with a thermoplastic resin is heated to a temperature equal to or higher than the melting point of the resin or a flowable temperature. The resin is flowed into a product shape and then cooled. In this method, by using fibers impregnated with a resin in advance, molding can be performed in a short time of about 1 minute.

  In addition, although the fiber bundle of chopped fiber and the manufacturing method of the molding material are disclosed in the following Patent Document 1 and Patent Document 2, this is a molding material called SMC or a stampable sheet. The material causes the fibers and the resin to flow in the mold for molding by thermoplastic stamping molding, so that it is difficult not only to produce a thin molded product but also to disturb the fiber orientation during molding and to control it. There was a problem such as.

  In addition, Patent Document 3 below proposes a method for making a prepreg by impregnating a resin after making a thin sheet from a reinforcing fiber by a papermaking method as a means for producing a thin-walled product without causing the fibers to flow. ing. However, in the papermaking method, the reinforcing fibers are homogeneously dispersed in the dispersion, so that all the reinforcing fibers in the prepreg are in the form of single yarn.

JP 2009-114611 A JP 2009-114612 A JP 2010-235777 A

  The present invention is intended to solve the problems of the conventional fiber reinforced composite material as described above, and its main purpose is to produce an isotropic fiber reinforced composite material comprising a reinforced fiber and a thermoplastic resin. An object of the present invention is to provide a method for producing a random mat with high productivity and low cost.

The above object is achieved by the following production methods [1] to [13] according to the present invention.
[1] Continuously cut to an average fiber length of 3 to 100 mm in a state where strands composed of a plurality of reinforcing fibers are continuously slit along the longitudinal direction to form a plurality of narrow strands having a width of 0.05 to 5 mm. Then, by blowing gas to the cut reinforcing fiber bundle, the fiber is opened, and the reinforcing fiber is deposited and fixed on a breathable support together with a granular or short fiber thermoplastic resin. And a method for producing an isotropic random mat for forming a thermoplastic composite material, comprising forming an isotropic random mat in which the thermoplastic resin is mixed.
[2] The reinforcing fiber strand is continuously slit along the longitudinal direction to form a plurality of narrow strands having a width of 0.05 to 5 mm, and each narrow strand is continuously formed to have an average fiber length of 3 to 100 mm. After cutting, gas is blown to the cut reinforcing fiber bundle, the reinforcing fiber bundle is opened with gas, and this is moved on the breathable support that moves together with the granular or short fiber thermoplastic resin. The isotropic random mat in which the reinforcing fibers and the thermoplastic resin are mixed is formed by depositing and fixing to the manufacturing method according to [1].
[3] The method according to [1] or [2], wherein the reinforcing fiber is a carbon fiber.
[4] When depositing and fixing the reinforcing fiber together with the thermoplastic resin on a breathable support, the reinforcing fiber bundle (A) composed of a critical single yarn or more defined by the following formula (1) The isotropic random mat in which reinforcing fiber bundles (B1) and / or reinforcing fiber single yarns (B2) having less than the number of yarns are present simultaneously, is described in any one of [1] to [3] above Production method.
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
[5] The method according to [4], wherein a ratio of the reinforcing fiber bundle (A) in the isotropic random mat to the total amount of fibers is 20 to 99 Vol%.
[6] The production method according to [4] or [5], wherein the average number of fibers (N) in the reinforcing fiber bundle (A) in the isotropic random mat satisfies the following formula (2).
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers.)
[7] The reinforcing fiber yarn pieces obtained by continuously slitting the thin reinforcing fiber strands cut to an average fiber length of 3 to 100 mm are moved in the transport path for sucking and transporting, or in the middle of the transport path or Gas is blown to the reinforcing fiber yarn pieces from the gas blowing nozzle disposed at the end portion to open the fiber, and a powdery or fibrous thermoplastic resin is supplied in the middle or at the end portion of the transport path. The isotropic random mat in which the reinforcing fiber and the thermoplastic resin are mixed is sprayed on a breathable support that continuously moves the reinforcing fiber and the thermoplastic resin simultaneously in a certain direction. It forms, The manufacturing method in any one of Claims 1-6 characterized by the above-mentioned.
[8] The transport route for sucking and transporting the cut reinforcing fiber yarn pieces is composed of a flexible tube, and further, a taper tube is continuously provided on the downstream side thereof, and the reinforcing fiber and the thermoplastic are provided in the building. Resin is diffused, The manufacturing method as described in said [7] characterized by the above-mentioned.
[9] The tip of the sprayed portion of the reinforcing fiber and the thermoplastic resin is reciprocated in a direction perpendicular to the moving direction of the breathable support that moves continuously, so that the reinforcing fiber and the above are supported on the support. The manufacturing method according to [7] or [8] above, wherein an isotropic random mat having a desired width mixed with a thermoplastic resin is formed.
[10] By changing the blowing pressure of the airflow to the cut reinforcing fiber yarn pieces, the ratio of the fiber reinforcing bundle (A) to the total amount of fibers of the random mat and the average number of fibers in the reinforcing fiber bundle (A) can be freely set. The manufacturing method according to any one of [7] to [9] above, wherein isotropic random mats having different physical properties are produced.
[11] The above [7], wherein a random mat in which the volume content of the reinforcing fibers is partially changed is produced by changing the amount of the thermoplastic resin supplied to the spraying portion over time. -[10] The manufacturing method in any one of.
[12] An isotropic property in which the material weight is continuously changed or the thickness of the material is slanted by changing the moving speed of the support and the reciprocating speed of the tip of the spraying part over time. The method according to any one of [7] to [11] above, wherein a random mat is produced.
[13] The length of the sprayed portion of the reinforcing fiber and the thermoplastic resin by reciprocating horizontally and vertically with respect to the running direction of the breathable support and continuously changing the reciprocating distance. The manufacturing method according to any one of [7] to [12], wherein an isotropic random mat whose width direction dimension is changed along the direction is produced.

  According to the method of the present invention, a substantially isotropic random mat that gives a fiber-reinforced composite material excellent in surface quality and physical properties at low cost can be efficiently produced at low cost. A good thermoplastic composite material can be produced by applying pressure. And this thermoplastic composite material can be shape | molded in a very short time, and the target fiber reinforced composite molded article can be obtained. Further, according to the method of the present invention, the resulting fiber-reinforced composite material can be thinned and isotropic, and by using this, a molded product excellent in both appearance and physical properties can be obtained. Can do. Therefore, the composite material manufactured by the method of the present invention includes, for example, inner plates, outer plates, constituent members, etc. of automobiles, railway vehicles, airplanes, etc., as well as frames and casings of various electric products, machines and devices. It is useful as a molding material.

Schematic showing an example of an apparatus for continuously performing the method of the present invention

<Reinforcing fiber>
The reinforcing fiber used in the method of the present invention is preferably at least one selected from the group consisting of carbon fiber, P-aramid fiber and glass fiber. These may be used alone or in combination of two or more. Among these, carbon fiber is particularly suitable because it can provide a composite material that is lightweight and excellent in strength. The carbon fiber may be PAN-based or pitch-based, but the average fiber diameter is preferably 3 to 12 μm, more preferably 5 to 7 μm. In most cases, those reinforcing fibers to which a sizing agent is attached are used. The adhesion amount of the sizing agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the reinforcing fiber.

  In the case of carbon fiber, as a wound body (package) in which substantially non-twisted strands (strands) in which 3000 to 60000 single yarns (single fibers) made of continuous fibers are bundled are wound around a bobbin. Supplied.

<Thermoplastic resin>
On the other hand, the thermoplastic resin used as the matrix resin in the method of the present invention is, for example, 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 Rufido resins, polysulfone resins, polyethersulfone resins, polyether ether ketone resins, polylactic acid resins, or a resin consisting of a copolymer thereof. These may be used alone or in combination of two or more.

  Among these thermoplastic resins, those having a melting point of 180 to 350 ° C. are preferable. These thermoplastic resins contain additives such as flame retardants, stabilizers, UV-resistant agents, antistatic agents, pigments, mold release agents, softeners, plasticizers, and surfactants as necessary. It does n’t matter,

  In the method of the present invention, the thermoplastic resin is used as a solid, and the form thereof may be either a granular form or a short fiber form, or both may be used in combination. In either case, the one having a form and size that is diffused in an air flow generated by gas blowing described later is used.

  When the thermoplastic resin is in the form of granules, spherical or strip-like particles are preferred. As a spherical example, a perfect circle or an ellipse rotating body or an egg-like shape is preferably mentioned. A preferable average particle diameter in the case of a sphere is 0.01 to 1000 μm, more preferably 0.1 to 900 μm. A particularly preferable average particle diameter is 1 to 800 μm. The particle size distribution is not particularly limited, but a sharp distribution is preferable for obtaining a thinner molded product, and can be adjusted to a desired particle size distribution by an operation such as classification. Examples of the strip shape include a columnar shape such as a pellet, a prismatic shape, a flake shape, and a flake shape. As the strip-like material, a material obtained by cutting a thermoplastic resin film into a strip or the like can be used. In this case, the granular material may have a certain aspect ratio, but the length of the longest part is the same as that of the short fiber described later, that is, the dimension of the longest part is 50 mm or less, preferably 10 mm or less. Is appropriate.

  Moreover, when a thermoplastic resin is a short fiber form, the thing of fineness 100-5000 dtex and the fineness of 1000-2000 dtex are more preferable, and average fiber length is 0.5-50 mm, More preferably, it is 1-10 mm.

  In the method of the present invention, as the above heat-composable resin, a granular material and a short fiber may be used in combination.

  In the production of the composite material of the present invention, in addition to the main raw materials described above, various fibrous or non-fibrous fillers, flame retardants, stabilizers, UV-resistant agents, Additives such as antistatic agents, pigments, mold release agents, softeners, plasticizers and surfactants can be used.

<Manufacture of isotropic random mats for composite materials>
Next, a preferred method for producing an isotropic random mat according to the present invention and a composite material using the same will be described in detail. The method of the present invention preferably includes the following steps (I) to (VI), and particularly good isotropic random mats and composite materials are produced by sequentially performing these steps. .

  In the random mat produced by the method of the present invention, the reinforcing fibers are not oriented in a specific direction and are distributed in a random direction in the plane. That is, the random mat according to the method of the present invention is an in-plane isotropic material. When the molded body is obtained from the random mat, the isotropy of the reinforcing fibers in the random mat is maintained in the molded body. By obtaining a molded body from a random mat and obtaining a ratio of tensile elastic moduli in two directions perpendicular to each other, the isotropy of the random mat and the molded body therefrom can be quantitatively evaluated. In-plane isotropic is assumed when the ratio of the modulus of elasticity in the two directions in the molded body obtained from the random mat divided by the smaller one does not exceed 2. In particular, when this ratio does not exceed 1.3, it is assumed that the isotropic property is excellent.

(I) Supplying step of reinforcing fiber strands In the method of the present invention, the reinforcing fibers are drawn from a plurality of reinforcing fiber wound bodies arranged in the creel part, respectively, and consist of a single yarn or this. It is used as a strand in which a plurality of wires are aligned. The strand width is preferably 10 to 50 mm (particularly 20 to 30 mm). For this reason, when the strand width of the reinforcing fiber to be supplied is small, the strand may be widened to the predetermined width in the strand supply step as necessary to form a thin wide strand. This widening operation can be performed, for example, by bringing the strand into contact with a widening roller or bar.

(II) Step of slitting the strand The continuous reinforcing fiber strand is continuously slit parallel to the longitudinal direction of the strand (that is, along the fiber length direction), so that the strand width is 0.05 to 5 mm, preferably Is made into a plurality of narrow strands of 0.1 to 1.0 mm.
Specifically, the wide strand continuously transferred from the previous process is continuously cut in the longitudinal direction by a longitudinal slit device (slitter) having a blade parallel to the fiber length direction, or the travel path of the wide strand One or a plurality of division guides can be provided in this, so that the strand can be divided into a plurality of pieces. In the method of the present invention, the wide strands to be supplied are slit as described above in order to make the fiber structure of the obtained random mat suitable, and the strand widths outside this range will be described later. It becomes difficult to form a random mat having a special fiber structure, and as a result, it is difficult to produce a good composite material that is the object of the present invention.

(III) Step of cutting reinforcing fiber Next, the narrow reinforcing fiber strand slit as described above is cut (cut) into an average fiber length of 3 to 100 mm, preferably 4 to 50 mm. If the average fiber length at this time is outside the above range, the linearity of the fibers cannot be maintained, and it is not preferable because sufficient strength cannot be expressed as a composite material after molding.

  Here, the “average fiber length” is obtained by a method of measuring the fiber length of 100 randomly extracted fibers up to 1 mm using calipers or the like, and obtaining the average. In the usual case, the average fiber length coincides with the cutting interval of the strand by the cutter.

  In the method of the present invention, a rotary cutter is preferable as an apparatus used when cutting reinforcing fibers into an average fiber length of 3 to 100 mm.

As the rotary cutter, it is preferable to use a rotary cutter provided with a spiral knife having a specific angle. In order to obtain a random mat for reinforcing a thermoplastic resin having excellent surface quality, the density of fibers is greatly affected. In a normal rotary cutter, the fiber cut is discontinuous, and when it is introduced into the mat as it is, the fiber weight is likely to be uneven. Therefore, by using a knife arranged at a specific angle and continuously cutting the fibers without interruption, it is possible to obtain a mat with small density spots. The knife angle for continuously cutting the reinforcing fiber is geometrically calculated by the width of the reinforcing fiber to be used and the fiber length after the cutting, and the relationship between them satisfies the condition of the following formula (a). It is preferable to satisfy.
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is an angle formed by the circumferential direction and the arrangement direction of the knife.)

  In this case, if a cutter having a knife crossing in the fiber direction and a knife parallel to the fiber length direction is used, the fiber bundle can be slit in the vertical direction and simultaneously cut to a specific fiber length. If used, slit process (II) and cut (III) can be carried out simultaneously.

(IV) Step of opening the cut reinforcing fiber In the next step, gas is blown onto a strand of reinforcing fiber cut to a predetermined fiber length (hereinafter sometimes referred to as “strand piece”). The fiber is spread so as to be divided into fiber bundles of a desired size (number of bundles).
In the opening process (IV) in the method of the present invention, the strand piece is introduced into a path made of a flexible tube such as a flexible tube or a hose, and air or the like is fed to the reinforcing fiber bundle piece passing through the path. It is a step of separating the strand pieces into a desired converging size and dispersing them in the gas by blowing the gas. About these degrees, it can control suitably by the pressure etc. of the gas to spray. In a preferred embodiment of the present invention, an air blowing nozzle is provided in the middle of the path or at the tip, and air is blown directly onto the strand piece at a wind speed of 5 to 500 m / sec from the compressed air blowing hole. The reinforcing fibers can be opened appropriately. Specifically, several holes with a diameter of about 1 mm are made in the path through which the reinforcing fiber pieces pass, and compressed air is blown directly from the holes to the strand pieces by applying a pressure of about 0.2 to 0.8 MPa from the outside. By using the gas blowing nozzle, it can be opened to a desired extent.

In this fiber opening process, all the fibers constituting the strand pieces are not separated and separated until they are completely formed into a single yarn, but a part is opened into a single yarn or a state close thereto. However, a considerable part is adjusted so that the single yarn becomes a bundle of fibers bundled with a certain number or more. That is, in the random mat described later, the degree of fiber-opening is such that the proportion of reinforcing fiber bundles (A) consisting of the number of critical single yarns defined by the following formula (1) is 20 to 99 Vol% of the total, preferably Is adjusted to be 30 to 90 Vol%, particularly preferably 30 to 80 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) composed of the number of critical single yarns or more is represented by the following formula (2). It is preferable to satisfy.
Critical number of single yarns = 600 / D (1)
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  Specifically, when the average fiber diameter of the carbon fibers constituting the random mat is 5 to 7 μm, the critical single yarn number is 86 to 120. When the average fiber diameter of the carbon fibers is 5 μm, the average number of fibers (N) in the fiber bundle is in the range of 280 to 2000, but 600 to 1600 is particularly preferable. When the average fiber diameter of the carbon fibers is 7 μm, the average number of fibers (N) in the fiber bundle is in the range of 142 to 1020, preferably 300 to 800.

  Therefore, in the fiber opening process, the reinforcing fiber bundle in which more than a specific number of reinforcing fibers are gathered at the stage of the random mat by controlling the degree of fiber opening while taking into account the conditions such as slits and cuts already described. (A) is included in the above ratio, and the rest is a mat that is a fiber bundle (B1) less than the critical number of single yarns and fibers (B2) completely separated up to single yarns.

(V) Step of forming random mat from reinforcing fiber and thermoplastic resin This step is to diffuse the cut and opened reinforcing fiber into the air, and at the same time, a granular or short fiber thermoplastic resin (Hereinafter collectively referred to as “thermoplastic resin particles etc.”), and the reinforcing fibers are sprinkled together with the thermoplastic resin particles etc. onto a breathable support provided below the opening device, In this process, a random mat is formed by depositing and fixing to a predetermined thickness in a state where reinforcing fibers and thermoplastic resin particles are mixed.

In this process, the reinforcing fibers opened with gas and the thermoplastic resin particles supplied from another route are sprayed onto the breathable support at the same time, and the breathable support is in a state where they are almost uniformly mixed. It is deposited on the body in a mat shape and fixed in that state. At this time, if the air-permeable support is constituted by a conveyor made of a net and is continuously moved in one direction and deposited thereon, a random mat can be continuously formed. Moreover, you may make it implement | achieve uniform deposition by moving a support body back and forth and right and left.

  Here, it is preferable that the reinforcing fibers and the thermoplastic resin particles are dispersed so as to be two-dimensionally oriented. In order to apply the opened reinforcing fibers while being two-dimensionally oriented, it is preferable to use a tapered tube having a conical shape or the like that is expanded downstream. In the tapered tube, the gas blown to the reinforcing fiber diffuses and the flow velocity in the tube is reduced, so that a rotational force is applied to the reinforcing fiber at this time. By utilizing this venturi effect, the opened reinforcing fibers can be evenly sprayed together with the thermoplastic resin particles and the like. In addition, for the fixing step described later, it is preferable to spray on a movable ventilation support (such as a net conveyor) having a suction mechanism below and deposit it in a random mat shape.

  In this step, the supply amount of the thermoplastic resin particles and the like is preferably 50 to 1000 parts by weight with respect to 100 parts by weight of the reinforcing fibers. More preferably, the thermoplastic resin particles and the like are 55 to 500 parts by weight with respect to 100 parts by weight of the reinforcing fiber, and still more preferably the thermoplastic resin particles and the like are 60 to 300 parts by weight.

  This random mat forming step includes a step of fixing reinforced fibers, thermoplastic resin particles, and the like. That is, this fixing step is a step of fixing the accumulated reinforcing fibers and thermoplastic resin particles. Preferably, the reinforcing fibers are fixed by sucking air from the lower part of the breathable support. The thermoplastic resin sprayed at the same time as the reinforcing fiber is also mixed, and if it is fibrous, it is fixed with the reinforcing fiber even if it is particulate by air suction.

  Thus, a mat having a high two-dimensional orientation can be obtained by suction from the lower part of the deposition surface. Further, the negative pressure generated here can be used to suck the thermoplastic resin particles and the like, and can be easily mixed with the reinforcing fiber by the diffusion flow generated in the pipe. In the random mat thus obtained, the thermoplastic resin particles and the like are uniformly present in the gaps and the vicinity of the reinforcing fibers constituting the random mat, so that the moving distance of the resin is short and relatively short in the heating and impregnation step described later. The resin can be impregnated into the random mat over time.

  In addition, in order to prevent this when a mesh of a sheet, a net, etc. constituting the breathable support is large and a part of the thermoplastic resin particles or the like does not remain in the mat through the support, It is also possible to set a non-woven fabric or the like on the surface and spray and fix reinforcing fibers and thermoplastic resin particles on the non-woven fabric. In this case, if the nonwoven fabric is made of the same resin as the thermoplastic resin particles or the like, it is not necessary to peel the nonwoven fabric from the deposited mat, and the nonwoven fabric constituting fiber becomes a matrix of the composite material by heating and pressurizing as it is in the next step. It can be used as part of a thermoplastic resin.

In the method of the present invention, after the reinforcing fiber strand is cut to a certain length, the strand piece and the reinforcing fiber separated into a single yarn state at the time of cutting are supplied to the transport path for sucking and transporting, and the middle or the end of the transport path Gas is blown to the reinforcing fibers from the gas blowing nozzle installed in the section, and the cut strand pieces are separated and opened into reinforcing fiber bundles of a desired size (thickness), and at the same time, the reinforcing fibers are made of thermoplastic resin particles. A random mat is formed by spraying and depositing on the surface of a breathable support (hereinafter sometimes referred to as “fixing net”) that moves continuously or intermittently in a certain direction. Can do. The transport route is preferably constituted by a flexible tube such as a flexible tube or a hose and a tapered tube continuously provided at the tip thereof. In this case, a gas blowing nozzle may be installed at the connection between the flexible tube and the taper tube. In this case, it is preferable to open a supply path for thermoplastic resin particles or the like on the inner wall of the taper tube.
In the method of the present invention, in order to obtain a desired random mat, the following methods can be employed, and two or more of these methods can be used in combination.

A) The fixing net is reciprocated horizontally in the direction orthogonal to the traveling direction of the fixing net that continuously travels in a fixed direction, for example, at the tip of the reinforcing fiber transport path (for example, the tip of the tapered tube). A method for producing a random mat on top.
B) By changing the gas blowing pressure over time or position, the ratio of the fiber reinforced bundle to the total amount of fibers in the random mat and the average number of fibers in the reinforced fiber bundle can be freely changed, and the physical properties are different. A method for producing a random mat.
C) When fixing the reinforcing fiber on the traveling fixing net, the thermoplastic resin particles and the like are simultaneously supplied to mix the fiber and the resin, and at that time, the supply amount of the thermoplastic resin is continuously increased. A method for producing a random mat in which the volume content of the reinforcing fiber is continuously changed by changing the volume of the reinforcing fiber.
D) When a random mat is produced on the fixing net by reciprocating the tip of the transport path of the reinforcing fiber horizontally in a direction perpendicular to the traveling direction of the fixing net, the traveling speed of the fixing net traveling and the A method of producing a random mat in which the material weight is continuously changed by changing the reciprocating speed of the spray nozzle, respectively, and the thickness of the material is inclined.
E) When making the random mat on the fixing net by reciprocating the tip of the transport path of the reinforcing fiber horizontally in the direction perpendicular to the traveling direction of the fixing net, the reciprocating distance of the spray nozzle is continuously set. The method of producing the random mat from which the width direction dimension differs by changing into.

  In the method of the present invention, at the time of forming the random mat, if necessary, the fibrous or non-fibrous filler and various additives can be sprinkled and deposited simultaneously with the reinforcing fiber and the thermoplastic resin. Further, a thermoplastic film may be laminated.

<Random mat obtained by the method of the present invention>
In the method of the present invention, an isotropic random mat is formed on the breathable support (fixing net) as described above. The random mat preferably has the following fiber configuration.

That is, the random mat in the present invention is composed of reinforcing fibers having a fiber length of 10 to 100 mm and a thermoplastic resin, and the reinforcing fibers are oriented substantially two-dimensionally at a basis weight of 25 to 3000 g / m ² . .

As described above, in this random mat, the reinforcing fiber bundle (A) composed of the number of critical single yarns defined by the following formula (1) is 20 to 99% by volume, particularly 30% with respect to the total amount of fibers of the mat. It is preferable that it exists in the ratio of -90Vol% or less, and average fiber number (N) in the said reinforced fiber bundle (A) satisfy | fills following formula (2).
Critical number of single yarns = 600 / D (1)
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  If the ratio of the reinforcing fiber bundle (A) to the total amount of fibers in the random mat is less than 20 Vol%, there is an advantage that a composite material having excellent surface quality can be obtained when the random mat is molded, but the fibers have excellent mechanical properties. It becomes difficult to obtain a reinforced composite material. When the ratio of the reinforcing fiber bundle (A) exceeds 99 Vol%, the entangled portion of the fibers becomes locally thick, and a thin-walled product cannot be obtained, which is not suitable for the purpose of the present invention. The ratio of the reinforcing fiber bundle (A) is more preferably 30 to 90 Vol%, and particularly preferably 30 to 80 Vol%. Specifically, when the average fiber diameter of the carbon fibers constituting the random mat is 5 to 7 μm, the number of critical single yarns is 86 to 120, and the carbon fiber strand pieces in which the larger number than the critical single yarns are converged and integrated. Corresponds to the reinforcing fiber bundle (A) mentioned here. Accordingly, in a suitable random mat, 20 to 99 Vol of reinforcing fibers constituting the reinforcing mat are reinforcing fiber bundles (A) in which the reinforcing fiber bundles are converged to a critical number of single yarns or more, and the remainder are reinforcing fiber bundles (B1) and / or Or it is comprised by the fiber group isolate | separated into single yarn (B2).

Furthermore, the average number of fibers (N) in the reinforcing fiber bundle (A) composed of the number of critical single yarns or more is represented by the following formula (2).
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
It is preferable to satisfy.

  For example, when the average fiber diameter of the carbon fibers is 5 μm, the average number of fibers (N) in the fiber bundle is in the range of 280 to 2000, and in particular, 600 to 1600 is preferable. When the average fiber diameter of the carbon fibers is 7 μm, the average number of fibers (N) in the fiber bundle is in the range of 142 to 1020, preferably 300 to 800. The average fiber length of the reinforcing fibers in the random mat is 5 to 100 mm or less, preferably 10 to 100 mm, more preferably 15 to 80 mm, and particularly preferably 20 to 60 mm. In the above-described reinforcing fiber cutting step, when the reinforcing fiber is cut to a fixed length, the average fiber length in the random mat is substantially equal to the cut fiber length.

When the average number of fibers (N) in the reinforcing fiber bundle (A) is 0.7 × 10 ⁴ / D ² or less, it is difficult to obtain a high fiber volume content (Vf). Further, when the average number of fibers (N) in the reinforcing fiber bundle (A) is 6 × 10 ⁴ / D ² or more, a locally thick portion is generated, which is likely to cause a void. When trying to obtain a thin composite material having a thickness of 1 mm or less, if fibers that are simply separated are used, the density is large and good physical properties cannot be obtained. When all the fibers are opened to the single yarn level, it becomes easy to obtain a thinner one, but the entanglement of fibers in the mat increases, and a fiber with a high fiber volume content cannot be obtained. Reinforcing fiber comprising a reinforcing fiber bundle (A) having a critical single yarn or more defined by the above formula (1), a reinforcing fiber bundle (B1) less than the number of critical single yarns, and / or a completely separated single yarn (B2) By using a random mat in which the group is present at the same rate as described above, it is possible to obtain a random mat that provides a composite material that is thin and has high physical properties. The random mat can have various thicknesses, and a thin molded product having a thickness of about 0.2 to 1 mm can be suitably obtained using the random mat as a preform. In addition, the average number of fibers and the ratio in the reinforcing fiber bundle (A) can be controlled by selecting conditions for the slit process, the cut process, and the fiber opening process.

  Thus, by using a random mat in which reinforcing fibers having different convergence states are mixed at a specific ratio, the surface properties, physical properties, moldability, and the like of the composite material are greatly improved.

  The thickness of the random mat is not particularly limited, and a random mat having a thickness of 1 to 100 mm can be obtained as desired. In order to exhibit the effect of the present invention that a thin composite material molded product can be obtained, the random mat is preferably 2 to 50 mm thick.

  In order to make the abundance of the reinforcing fiber bundle (A) in the random mat 20 to 99% by volume, it can be controlled by, for example, the pressure of air to be blown in the opening process. It can also be controlled by adjusting the size of the fiber bundle used in the cutting step, for example, the width of the bundle and the number of fibers per width. Specifically, a method of providing a slit process before the cutting process, including providing the strand in a state where the strand is widened to form a thin and wide strand, and the like. Further, there are a method of cutting a fiber bundle using a so-called splitting knife in which many short blades are arranged, and a method of slitting simultaneously with cutting.

The average number of fibers (N) in the reinforcing fiber bundle (A) composed of the number of critical single yarns or more is preferably less than 6 × 10 ⁴ / D ² , but the average number of fibers in the reinforcing fiber bundle (A) In order to make (N) within the above range, in the preferred production method described later, it is also possible to control by adjusting the size of the fiber bundle used in the cutting step, for example, the width of the bundle and the number of fibers per width. Specifically, there are a method for expanding the width of the fiber bundle by opening the fiber and using it for the cutting step, and a method for providing a slit step before the cutting step. The fiber bundle may be slit simultaneously with the cutting. Further, by controlling the pressure of the gas blown to the fiber bundle pieces in the fiber opening process, the degree of variation of the cut fiber bundle is adjusted, and the average number of fibers (N) in the reinforcing fiber bundle (A) is within a desired range. You can also

  In the method of the present invention, a random mat can be prepared according to the thickness of a composite material molded product for various purposes. In particular, a thin-walled one is used as a preform for a thin molded product such as a skin of a sandwich material. Useful.

(VI) Step of impregnating thermoplastic resin in random mat The random mat in the present invention contains a solid thermoplastic resin and becomes a preform for obtaining a fiber-reinforced composite material. In this random mat, the reinforcing fibers and solid thermoplastic resin particles are mixed without any spots. Specifically, since the solid thermoplastic resin is dispersed and present in the gaps or in the vicinity of the reinforcing fibers constituting the random mat, there is no need to flow the fibers and the resin again in the mold. By simply heating and pressing the mat through one or more pairs of heating rollers whose surface temperature is set to a temperature equal to or higher than the softening point of the thermoplastic resin, preferably the melting point, the thermoplastic resin softens or melts in the random mat. The resin is impregnated almost uniformly. Therefore, it becomes the target sheet-like composite material by cooling quickly after this heating and pressurization.
In addition, before implementing said heating and pressurization, a random mat can be continuously introduced into a heating chamber and preheated. In this case, the preheating temperature is preferably a temperature from the glass transition point to the melting point of the thermoplastic resin. By performing this preheating step, the thermoplastic resin particles and the like in the random mat are partially bonded to the reinforcing fibers and fixed in the mat.

  According to the study by the present inventors, it was confirmed that the bundled state of the reinforcing fibers in the obtained composite material is not different from the state in the random mat. In other words, a material that satisfies the conditions of the above formulas (1) and (2) in the random cut also satisfies the conditions of the above equations (1) and (2) in the composite material impregnated with the resin.

Next, FIG. 1 shows an example in which a composite material is efficiently manufactured by continuously performing the above steps. In FIG. 1, 11 is a creel of reinforcing fiber yarn, 12 is a widening device for reinforcing fiber strands arranged as necessary, 13 is a yarn guide, 14 is a cutting / opening device having a taber tube at the bottom, 15 is a thermoplastic resin supply unit, 16 is a movable breathable support (fixing net conveyor) installed below the opening device, 17 is a suction device installed below the breathable support, and 18 is a random mat preheater. Reference numeral 19 denotes a vertical slit device (slitter). Y represents a reinforcing fiber strand, and M represents a random mat.

  In this example, reinforcing fibers such as carbon fibers are drawn from the wound yarns arranged on the creel 11 at a predetermined speed and supplied to the widening device 12 as strip-like strands Y. With the widening device 12, the strand is expanded to a predetermined width and becomes a wide and thin belt-like strand. In addition, when the original strand has sufficient width and thinness to a slit, it is not necessary to widen. The belt-like strand is subsequently supplied to the next step through the yarn guide 13 and is slit along the length of the strand by the longitudinal slit device 19 to form a plurality of narrow strands. After that, it is introduced into the cutting / opening device 14, cut into a predetermined fiber length by a cutter installed in the device 14, and an air nozzle (in the vicinity of the entrance of the Taber tube in the lower conveying path in the device) (Not shown) gas is jetted toward the strand pieces in the tube, and the reinforcing fibers constituting the strands are scattered into the gas in a focused state of a desired size. At this time, the thermoplastic resin supply unit 15 simultaneously supplies the granular or short fiber thermoplastic resin into the tapered tube, and a conveyor having a breathable support, specifically a breathable net, together with the reinforcing fibers. 16. Then, the reinforcing fiber and the thermoplastic resin are fixed on the support in a mixed state by the suction device 17 disposed below the support to form a random mat.

  In the case of continuously producing a composite material from the random mat M, the random mat M is supplied to a heating and pressing apparatus (not shown) provided with a pair of heating rollers, and preferably above the softening point of the thermoplastic resin. Is heated and pressed at a temperature equal to or higher than the melting point to soften or melt the thermoplastic resin dispersed in the random mat and uniformly impregnate the random mat. At this time, prior to the heating and pressurization, if necessary, a random mat may be introduced into a preheating device equipped with a heating chamber and preheated to a temperature higher than the secondary transition point (Tg) of the thermoplastic resin. After heating and pressing, it is preferable to rapidly cool to near room temperature by contacting with a cooling roller (not shown) or the like. The composite material sheet thus continuously produced can be cut to a desired size by a cutting device (not shown) to obtain the target fiber-reinforced composite material C. In addition, when implementing shaping | molding following the manufacturing process of this composite material, you may make it supply a continuous-length composite material as it is to a shaping | molding process, without cutting.

<Fiber-reinforced composite material obtained from random mat>
From such a random mat according to the method of the present invention, a fiber-reinforced composite material composed of reinforcing fibers and a thermoplastic resin can be produced by a simple operation. As mentioned above, since the random mat in the present invention is present in a mixture of reinforcing fibers and granular and / or fibrous thermoplastic resin without unevenness, it is not necessary to flow the fibers and resin in the mold, There is an advantage that the thermoplastic resin can be easily impregnated. Therefore, also in the composite material obtained by the present invention, it is possible to maintain the isotropic strength of the reinforcing fibers in the random mat.

Such a suitable fiber-reinforced composite material is a composite material substantially composed of the above-mentioned reinforcing fibers having a fiber length and a thermoplastic resin, in which the reinforcing fibers are substantially two-dimensionally oriented, and has the following formula ( About the reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in 1), the ratio of the reinforcing fiber bundle (A) to the total amount of fibers is 20 to 99 Vol%, and the reinforcing fiber bundle (A) The average number of fibers (N) satisfies the following formula (2).
Critical number of single yarns = 600 / D (1)
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

<Use of fiber reinforced composite material>
The random mat obtained by the method of the present invention or the composite material obtained therefrom can be formed into a desired molded article by, for example, press molding or thermoforming. This composite material can be molded in a very short time (for example, within a few minutes) regardless of which molding method is used, and the resulting molded product is lightweight and has good physical properties. It is advantageous. Specifically, it is useful as a molding material for inner plates, outer plates, structural members, etc. of automobiles, railway vehicles, airplanes, etc., and various electrical products, machine frames and casings. By using the carbon fiber composite material produced by the method as a skeleton, the skeleton of an electric vehicle can be produced by press molding in a short time of about 1 minute or less.

  EXAMPLES The present invention will be described below with reference to examples, but the scope of the present invention is not limited thereto. In addition, each measured value in an Example is a value measured with the following method.

1) Analysis of reinforcing fiber bundle in random mat A random mat is cut out to about 100 mm × 100 mm. From the cut out mat, all the fiber bundles are taken out with tweezers, and the number (I) of bundles of reinforcing fiber bundles (A) and the length (Li) and weight (Wi) of the fiber bundles are measured and recorded. When the fiber bundle is so small that it cannot be taken out with tweezers, the weight is finally measured together (Wk). For measuring the weight, a balance capable of measuring up to 1/100 mg is used. The number of critical single yarns is calculated from the fiber diameter (D) of the reinforcing fibers used in the random mat, and is divided into a reinforcing fiber bundle (A) having a number of critical single yarns or more and the other. In addition, when two or more types of reinforcing fibers are used, it is divided for each type of fiber, and measurement and evaluation are performed for each.
The method for obtaining the average number of fibers (N) of the reinforcing fiber bundle (A) is as follows.
The number of fibers (Ni) in each reinforcing fiber bundle is obtained by the following equation from the fineness (F) of the reinforcing fibers used.
Ni = Wi / (Li × F)
The average number of fibers (N) in the reinforcing fiber bundle (A) is obtained from the number of bundles (I) of the reinforcing fiber bundle (A) by the following formula.
N = ΣNi / I
The ratio (VR) of the reinforcing fiber bundle (A) to the total amount of fibers of the mat can be obtained by the following equation using the density (ρ) of the reinforcing fibers.
VR = Σ (Wi / ρ) × 100 / ((Wk + ΣWi) / ρ)

2) Analysis of average fiber length of reinforcing fibers contained in random mat or composite material The length of 100 reinforcing fibers randomly extracted from random mat or composite material was measured and recorded to the 1 mm unit with calipers and loupes, From the measured lengths (Li) of all the reinforcing fibers, the average fiber length (La) is obtained by the following formula. In the case of a composite material, the reinforcing fiber is extracted after removing the resin in the furnace at about 500 ° C. for about 1 hour.
La = ΣLi / 100

3) Reinforcing fiber bundle analysis in composite material For a composite material, the resin is removed in a furnace at about 500 ° C. for about 1 hour, and then measured in the same manner as in the above random mat method.

4) Analysis of fiber orientation in composite material After forming the composite material, as a method of measuring the isotropy of the fiber, a tensile test based on an arbitrary direction of the forming plate and a direction orthogonal thereto is performed. It can be confirmed by measuring the tensile elastic modulus and measuring the ratio (Eδ) obtained by dividing the measured value of the tensile elastic modulus by the smaller one. The closer the modulus ratio is to 1, the better the material is. In the present invention, when the elastic modulus ratio is 1.3 or less, it is evaluated as isotropic.

[Example 1]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10 mm) manufactured by Toho Tenax Co., Ltd. was used as the reinforcing fiber. After slitting to a width of 0.8 mm using a vertical slitting device, the fiber length was cut to 20 mm. As a cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. At this time, the following formula (a)
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is the angle between the circumferential direction and the knife.)
In this case, θ was 68 degrees, and the pitch of the blades was cut so that 20 mm reinforcing fiber had a fiber length of 20 mm.

  The strand that passed through the cutter was introduced into a flexible transportation pipe arranged immediately below the rotary cutter, and subsequently introduced into a fiber opening device (gas blowing nozzle) continuously provided at the lower end of the transportation pipe. As this fiber opening device, nipples made of SUS304 having different diameters were welded to produce a double pipe. A small hole was provided in the inner tube of the double tube, and compressed air was supplied between the inner tube and the outer tube with a compressor. At this time, the wind speed from the small hole was 450 m / sec. A taper pipe whose diameter increases downward is welded to the lower end portion of the double pipe so that the reinforcing fibers cut in the taper pipe move downward along with the air flow.

  Matrix resin was supplied into the tube from the hole provided on the side surface of the tapered tube. As matrix resin, particles of nylon resin (polyamide 6 resin) “A1030” manufactured by Unitika Ltd. were used.

  Then, an air-permeable support body (hereinafter referred to as “fixing net”) that moves in a certain direction is installed below the outlet of the taper pipe, and suction is performed from below by a blower. The mixture of cut reinforcing fibers and nylon resin particles discharged along with the air flow from the tip of the taper tube is deposited in a band shape on the fixing net while reciprocating in the width direction of the fixing net moving at a constant speed. I let you.

At this time, the reinforcing fiber supply amount was set to 212 g / min, the matrix resin supply amount was set to 320 g / min, and the apparatus was operated. As a result, the reinforcing fibers and the thermoplastic resin were randomly mixed on the fixing net. A mat was formed. The basis weight of the reinforcing fibers of this random mat was 265 g / m ² .

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the above formula (1) was 86, and the reinforcing fiber bundle (A ), The ratio of the mat to the total amount of fibers was 35 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 240. Further, the nylon resin particles were uniformly dispersed in the reinforcing fiber with almost no spots.

Four of these random mats were stacked, put into a mold, heated at a temperature of 300 ° C., a pressure of 1.0 MPa, and a heating time of 3 minutes to obtain a molded plate having a thickness of 2.0 mm. An ultrasonic flaw detection test was performed on the obtained composite material molded plate. As a result, no unimpregnated portions and voids were confirmed.

  Further, when the tensile elastic modulus in the directions of 0 ° and 90 ° of the obtained molded plate was measured, the elastic modulus ratio (Eδ) was 1.03, there was almost no fiber orientation, and the isotropic property was maintained. A molded plate could be obtained. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

[Example 2]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10 mm) manufactured by Toho Tenax Co., Ltd. was used as the reinforcing fiber. After slitting to a width of 0.8 mm using a vertical slitting device, the fiber length was cut to 20 mm. As a cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. At this time, the following formula (a)
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is the angle between the circumferential direction and the knife.)
In this case, θ was 68 degrees, and the pitch of the blades was cut so that 20 mm reinforcing fiber had a fiber length of 20 mm.

  The strand that passed through the cutter was introduced into a flexible transport pipe arranged immediately below the rotary cutter, and subsequently introduced into a fiber opening device (gas blowing nozzle). As the opening device, the same one as in Example 1 is used, in which a small hole is provided in the inner tube of a double tube welded with a nipple made of SUS304 having a different diameter, and between the inner tube and the outer tube. Compressed air was sent to the air. At this time, the wind speed from the small hole was changed with time from 100 m / sec to 450 m / sec at a rate of 100 m / sec per minute. A taper pipe whose diameter increases downward is welded to the lower end of the double pipe.

  Matrix resin was supplied from the side surface of the tapered tube. Nylon resin “A1030” particles manufactured by Unitika Ltd. were used as the matrix resin. Then, a fixing net moving in a certain direction is installed below the outlet of the taper pipe, and suction is performed by a blower from below, and the flexible transport pipe and the taper pipe are placed on the fixing net of the fixing net. While reciprocating in the width direction, a band-like mat was deposited and fixed on the mixture of cut reinforcing fibers and nylon resin particles.

At this time, the reinforcing fiber supply amount was set to 212 g / min, the matrix resin supply amount was set to 320 g / min, and the apparatus was operated. As a result, the reinforcing fiber and the thermoplastic resin were mixed on the fixing net with a thickness of about 6 mm. A random mat was formed. The basis weight of the reinforcing fibers of this random mat was 265 g / m ² .

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the above formula (1) was 86, and the reinforcing fiber bundle (A ), The ratio of the mat to the total amount of fibers is 35 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) is 240. From the mat form, the ratio of the reinforcing fiber bundle (A) to the total amount of fibers of the mat is 80 Vol. %, And a reinforcing fiber bundle having an average number of fibers (N) in the reinforcing fiber bundle (A) of 1000 was obtained. Further, the nylon resin particles were uniformly dispersed in the reinforcing fiber with almost no spots.

  Four random mats are stacked, and a mold having a three-dimensional complex shape with a vertical surface is used. The material is charged to 70% of the projected area of the mold, and the temperature is 300 ° C., the pressure is 1.0 MPa, and the heating time is 3 minutes. When the reinforcing fiber bundle (A) was heated and pressed, the ratio of the mat to the total fiber amount was 80 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 1000. The material mainly flowed on the standing surface to obtain a molded product having a thickness of 2.0 mm, which completely followed the mold shape. An ultrasonic flaw detection test was performed on the obtained composite material molded article, and no unimpregnated portion or void was found.

  When the tensile modulus of elasticity of the resulting molded plate in the 0 degree and 90 degree directions was measured, the ratio of elastic modulus (Eδ) was 1.03, there was almost no fiber orientation, and the isotropic plate was maintained. Could get. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

[Example 3]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10 mm) manufactured by Toho Tenax Co., Ltd. was used as the reinforcing fiber. After slitting to a width of 0.8 mm using a vertical slitting device, the fiber length was cut to 20 mm. As a cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. At this time, the following formula (a)
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is the angle between the circumferential direction and the knife.)
In this case, θ was 68 degrees, and the pitch of the blades was cut so that 20 mm reinforcing fiber had a fiber length of 20 mm.

  The strand that passed through the cutter was introduced into a flexible transport pipe arranged directly under the rotary cutter, and subsequently introduced into a fiber opening device (gas blowing nozzle). As the opening device, the same one as in Example 1 is used, in which a small hole is provided in the inner tube of a double tube welded with a nipple made of SUS304 having a different diameter, and between the inner tube and the outer tube. Compressed air was sent to the air. At this time, the wind speed from the small hole was 450 m / sec. A taper pipe whose diameter increases downward is welded to the lower end of the double pipe.

  Matrix resin was supplied from the side surface of the tapered tube. Nylon resin “A1030” particles manufactured by Unitika Ltd. were used as the matrix resin. Then, a fixing net moving in a certain direction is installed below the outlet of the taper pipe, and suction is performed by a blower from below, and the flexible transport pipe and the taper pipe are placed on the fixing net of the fixing net. While reciprocating in the width direction, a band-like mat was deposited and fixed on the mixture of cut reinforcing fibers and nylon resin particles.

At this time, the supply amount of the reinforcing fiber was set to 212 g / min, the supply amount of the matrix resin was changed to 547 g / min for 1 minute, and then the supply amount of the matrix resin was changed to 320 g / min for 1 minute, and further 205 g / min. When the apparatus was operated for 1 minute after the change, the random mat in which the reinforcing fibers and the thermoplastic resin were mixed was formed on the support. The basis weight of the reinforcing fibers of this random mat was 265 g / m ² .

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the above formula (1) was 86, and the reinforcing fiber bundle (A ) Is a reinforcing fiber bundle in which the ratio of the mat to the total amount of fibers is 35 Vol%, the average number of fibers (N) in the reinforcing fiber bundle (A) is 240, and the ratio of the volume content of reinforcing fibers to the entire random mat is 20 Vol. From 1% to 40% by volume, a mat having a gradient change in the longitudinal direction of the mat was obtained. Further, the nylon resin particles were uniformly dispersed in the reinforcing fiber with almost no spots.

  Four random mats are stacked, and a mold having a three-dimensional complex shape with a vertical surface is used. The material is charged to 70% of the projected area of the mold, and the temperature is 300 ° C., the pressure is 1.0 MPa, and the heating time is 3 minutes. In the region where strength is required, the portion where the proportion of the reinforcing fiber is 40% by volume with respect to the entire random mat is allocated, and in the region where strength is not required, the proportion of the reinforcing fiber relative to the entire random mat is A molded product having a thickness of 2.0 mm was obtained, in which a portion of 20 Vol% was applied and the shape of the mold was completely followed. In this molded product, a molded product satisfying the required structural properties, particularly strength and rigidity, was obtained while reducing the amount of reinforcing fiber, which is generally expensive in material cost. When this composite material molded body was subjected to an ultrasonic flaw detection test, no unimpregnated portions and voids were found.

  The tensile elastic modulus in the 0 degree and 90 degree directions of the obtained molded product was measured in each region by dividing the volume content of the reinforcing fiber in each region from 20 Vol% to 40 Vol%. (Eδ) was 1.03 to 1.05, and there was almost no fiber orientation, and a molded product maintaining isotropy could be obtained. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

A press apparatus heated to 300 ° C. was heated at 1.0 MPa for 3 minutes to obtain a molded plate having a thickness of 0.6 mm. When the ultrasonic inspection test was performed about the obtained composite material, the unimpregnated part and the void were not confirmed.

[Example 4]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10 mm) manufactured by Toho Tenax Co., Ltd. was used as the reinforcing fiber. After slitting to a width of 0.8 mm using a vertical slitting device, the fiber length was cut to 20 mm. As a cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. At this time, the following formula (a)
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is the angle between the circumferential direction and the knife.)
In this case, θ was 68 degrees, and the pitch of the blades was cut so that 20 mm reinforcing fiber had a fiber length of 20 mm.

  The strand that passed through the cutter was introduced into a flexible transport pipe arranged directly under the rotary cutter, and subsequently introduced into a fiber opening device (gas blowing nozzle). As the opening device, the same one as in Example 1 is used, in which a small hole is provided in the inner tube of a double tube welded with a nipple made of SUS304 having a different diameter, and between the inner tube and the outer tube. Then, compressed air was supplied. At this time, the wind speed from the small hole was 450 m / sec. A tapered tube having a diameter increasing downward was welded to the lower end of the tube.

  Matrix resin was supplied from the side surface of the tapered tube. Nylon resin “A1030” particles manufactured by Unitika Ltd. were used as the matrix resin. Then, a fixing net moving in a certain direction is installed below the outlet of the taper pipe, and suction is performed by a blower from below, and the flexible transport pipe and the taper pipe are placed on the fixing net of the fixing net. While reciprocating in the width direction, a band-like mat was deposited and fixed on the mixture of cut reinforcing fibers and nylon resin particles.

At this time, the moving speed of the fixing net moving in a fixed direction is set to 0.8 m / min, the reinforcing fiber supply amount is set to 634 g / min, the matrix resin supply amount is set to 958 g / min, and the operation is performed for one minute. Thereafter, the moving speed of the fixing net was continuously changed to 1.0 m / min, the reinforcing fiber supply rate was set to 528 g / min, and the matrix resin supply rate was set to 798 g / min, and the system was operated for 1 minute. Furthermore, when the moving speed of the fixing net was changed to 1.5 m / min, the reinforcing fiber supply amount was set to 396 g / min, and the matrix resin supply amount was set to 599 g / min. A random mat in which the thermoplastic resin and the thermoplastic resin were mixed was formed. The weight of the reinforcing fiber of the random mat is 792 g / m ² when the moving speed of the fixing net is 0.8 m / min, 528 g / min when the moving speed is 1.0 m / min, and the moving speed is 1. At 5 m / min, it was 264 g / min.

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the above formula (1) was 86, and the reinforcing fiber bundle (A ), The ratio of the mat to the total amount of fibers was 35 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 240. Further, the nylon resin particles were uniformly dispersed in the reinforcing fiber with almost no spots.

  Four random mats are laminated so that the upstream side and the downstream side coincide with each other, and a three-dimensional complex mold having an inclined surface is used. The temperature is 300 ° C., the pressure is 1.0 MPa, and the heating time is 3 minutes. When heated and press-molded, a molded body that completely follows the mold shape and has a thickness continuously inclined from 2 mm to 6 mm was obtained. When this composite material molded body was subjected to an ultrasonic flaw detection test, no unimpregnated portions and voids were found.

  The tensile elastic modulus in the 0 degree and 90 degree directions of the obtained molded plate was measured in each region by dividing the volume content of reinforcing fibers in each region from 20 Vol% to 40 Vol%. The ratio (Eδ) was 1.02, and there was almost no fiber orientation, and a molded plate that maintained isotropy could be obtained. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

  This random mat was heated at 1.0 MPa for 3 minutes with a press apparatus heated to 300 ° C. to obtain a molded plate having a thickness of 0.6 mm. When the ultrasonic inspection test was performed about the obtained composite material, the unimpregnated part and the void were not confirmed.

[Example 5]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10 mm) manufactured by Toho Tenax Co., Ltd. was used as the reinforcing fiber. After slitting to a width of 0.8 mm using a vertical slitting device, the fiber length was cut to 20 mm. As a cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. At this time, the following formula (a)
Reinforcing fiber length (blade pitch) = reinforcing fiber strand width × tan (90−θ) (a)
(Here, θ is the angle between the circumferential direction and the knife.)
In this case, θ was 68 degrees, and the pitch of the blades was cut so that 20 mm reinforcing fiber had a fiber length of 20 mm.

  The strand that passed through the cutter was introduced into a flexible transport pipe arranged just below the rotary cutter, and then introduced into a fiber opening device (gas blowing nozzle). As in the case of Example 1, as the fiber opening device, a device in which a small hole is provided on the inner tube of a double tube welded with a nipple made of SUS304 having a different diameter, between the inner tube and the outer tube is used. In addition, compressed air was fed using a compressor. At this time, the wind speed from the small hole was 450 m / sec. A tapered tube having a diameter increasing downward is welded to the lower end of the double tube.

Matrix resin was supplied from the side surface of the tapered tube. Nylon resin “A1030” particles manufactured by Unitika Ltd. were used as the matrix resin. The reinforcing fiber supply amount is set to 137 g / min and the matrix resin supply amount is set to 207 g / min. A fixing net moving in a fixed direction is installed at the lower part of the taper tube outlet, and the blower is provided below the blower. Suction is performed on the fixing net, and the strip of reinforced fiber and nylon resin is deposited and fixed on the fixing net while reciprocating the flexible transport pipe and taper pipe in the width direction of the fixing net. It was. At that time, when the mat is formed by continuously changing the moving distance of the tapered tube from 1.0 m to 0.3 m in the width direction of the fixing net, the reinforcing fiber and the thermoplastic resin are not spotted on the fixing net. A mixed taper-shaped random mat was formed. The basis weight of the reinforcing fibers in this random mat was 265 g / m ² .

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the above formula (1) was 86, and the reinforcing fiber bundle (A ), The ratio of the mat to the total amount of fibers was 35 Vol%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 240. Further, the nylon particles were uniformly dispersed in the reinforcing fiber with almost no spots.

  When four random mats are stacked and a taper-shaped three-dimensional complex mold is used, press molding is performed by heating at a temperature of 300 ° C., a pressure of 1.0 MPa, and a heating time of 3 minutes. A molded body having a thickness of 2 mm following the above was obtained. When this molded body was obtained, the random mat itself was put into the mold in a form close to the final shape, so that no material end material was required, and production efficiency could be improved. Further, when an ultrasonic flaw detection test was performed on the obtained composite material molded body, no unimpregnated portion or void was confirmed.

  The tensile elastic modulus in the direction of 0 degree and 90 degrees of this molded body was measured in each region by dividing the volume content of the reinforcing fiber in each region from 20 Vol% to 40 Vol%. Eδ) was 1.04, and there was almost no fiber orientation, and a molded plate maintaining isotropy could be obtained. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

[Example 6]
As a reinforcing fiber, carbon fiber “Tenax” (registered trademark) IMS60-12K (average fiber diameter 5 μm, fiber width 6 mm) manufactured by Toho Tenax Co., Ltd. was used. Cut into. As the cutting device, a rotary cutter using a cemented carbide and a spiral knife arranged on the surface was used. This rotary cutter was provided with blades parallel to the fiber direction at intervals of 0.5 mm. At this time, θ in the above formula (a) was 17 degrees and the blade pitch was 20 mm. The cut reinforcing fiber was immediately introduced into a fiber opening device arranged immediately below the rotary cutter and opened by gas blowing. As a fiber opening device, a double tube having a small hole inside was used as in Example 1, and compressed air was supplied to this. The wind speed from the small hole was 150 m / sec. A tapered tube was welded to the lower end of the double tube.

And from the side surface of the taper tube, polyamide 66 fiber (“T5 nylon” fineness 1400 dtex made by Asahi Kasei Fiber) dry-cut to 2 mm was supplied as this matrix resin. A breathable table movable in the XY directions was installed at the lower part of the tapered tube outlet, and suction was performed from the lower part of the table with a blower. Then, the supply amount of the reinforcing fibers was set to 1000 g / min, the supply amount of the matrix resin was set to 3000 g / min, and the apparatus was operated. As a result, a random mat having a thickness of about 10 mm in which the reinforcing fibers and the polyamide short fibers were mixed was obtained. . The basis weight of the reinforcing fiber of this mat was 1000 g / m ² .

  When the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined for the obtained random mat, the critical single yarn number defined by the formula (1) was 120, and the mat of the reinforcing fiber bundle (A) The percentage of the total amount of reinforcing fibers was 86%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 900. The polyamide fiber was dispersed in the reinforcing fiber with almost no spots.

  The obtained random mat was heated and pressurized with a heating nip roller at 280 ° C. to melt the polyamide fibers in the mat and impregnated in the mat, and then cooled to obtain a composite material sheet.

  This was heated at 1.0 MPa for 3 minutes with a heated press molding apparatus to obtain a molded plate having a thickness of 3.2 mm. When an ultrasonic flaw detection test was performed on the obtained composite material molded plate, no unimpregnated portion or void was found.

  When the tensile modulus of elasticity of the resulting molded plate in the 0 degree and 90 degree directions was measured, the ratio of elastic modulus (Eδ) was 1.07, and there was almost no fiber orientation, and a material that maintained isotropy was obtained. I was able to get it. Furthermore, this molded plate was heated in a furnace at 500 ° C. for about 1 hour to remove the resin, and then the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) were examined. There was no difference from the measurement results.

11: Creel 12: Strand widening device 13: Yarn guide 14: Cutting / opening device 15: Thermoplastic resin supply unit 16: Breathable support (conveyor having a breathable net)
17: Suction device 18: Random mat preheating device 19: Vertical slit device Y: Reinforcing fiber strand M: Random mat

Claims (13)

In a state in which strands made of a plurality of reinforcing fibers are continuously slit along the longitudinal direction to form a plurality of narrow strands having a width of 0.05 to 5 mm , the fibers are continuously cut to an average fiber length of 3 to 100 mm and cut. The reinforced fiber bundle and the thermoplastic fiber are opened by blowing gas to the reinforced fiber bundle, and deposited and fixed on a breathable support together with a granular or short fiber thermoplastic resin . A method for producing a random mat for forming a thermoplastic composite material, comprising forming an isotropic random mat mixed with a resin.   The reinforcing fiber strand is continuously slit along its longitudinal direction to form a plurality of narrow strands having a width of 0.05 to 5 mm, and each narrow strand is continuously cut to an average fiber length of 3 to 100 mm. Gas is blown to the cut reinforcing fiber bundle, the reinforcing fiber bundle is opened by gas, and this is deposited and fixed on a moving air-permeable support together with a granular or short fiber thermoplastic resin. The manufacturing method according to claim 1, wherein an isotropic random mat in which the reinforcing fibers and the thermoplastic resin are mixed is formed.   The manufacturing method according to claim 1, wherein the reinforcing fiber is a carbon fiber. When depositing and fixing the reinforcing fiber together with the thermoplastic resin on a breathable support, the reinforcing fiber bundle (A) composed of the number of critical single yarns defined by the following formula (1) and less than the critical single yarn number The manufacturing method according to any one of claims 1 to 3, wherein an isotropic random mat in which the reinforcing fiber bundle (B1) and / or the reinforcing fiber single yarn (B2) is present at the same time is used.
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)   The manufacturing method according to claim 4, wherein a ratio of the reinforcing fiber bundle (A) in the isotropic random mat to the total amount of fibers is 20 Vol% or more and 99 Vol% or less. The manufacturing method according to claim 4 or 5, wherein an average number of fibers (N) in the reinforcing fiber bundle (A) in the isotropic random mat satisfies the following formula (2).
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers.) Reinforced fiber yarn pieces obtained by continuously slitting the thin reinforcing fiber strands cut to an average fiber length of 3 to 100 mm are moved in the transport route for sucking and transporting, and in the middle or at the end of the transport route. While blowing the gas to the reinforcing fiber yarn pieces from the arranged gas blowing nozzle to open the fiber, and supplying a granular or short fiber thermoplastic resin in the middle or at the end of the transport path, strengthening The fibers and the thermoplastic resin are simultaneously sprayed onto a breathable support that continuously moves in a certain direction, and an isotropic random mat in which the reinforcing fibers and the thermoplastic resin are mixed is formed on the support. The manufacturing method according to any one of claims 1 to 6, wherein:   The transport path for sucking and transporting the cut reinforcing fiber yarn pieces is constituted by a flexible pipe, and a tapered pipe is continuously provided at the tip thereof, and the reinforcing fiber and the thermoplastic resin are placed in the tapered pipe. The manufacturing method according to claim 7, wherein diffusion is performed.   Desirable that the reinforcing fiber and the thermoplastic resin are mixed on the support by reciprocating the tip of the blowing portion of the reinforcing fiber and the thermoplastic resin in a direction perpendicular to the moving direction of the breathable support. The manufacturing method according to claim 7, wherein an isotropic random mat having a width is formed.   By changing the blowing pressure of the airflow to the cut reinforcing fiber yarn pieces, the ratio of the fiber reinforced bundle (A) to the total amount of fibers in the random mat and the average number of fibers in the reinforcing fiber bundle (A) can be freely changed. An isotropic random mat having different physical properties is produced, and the manufacturing method according to any one of claims 7 to 9.   The random mat in which the volume content of the reinforcing fibers is partially changed is produced by changing the supply amount of the thermoplastic resin to the spraying portion with time. The manufacturing method in any one of.   By changing the moving speed of the support and the reciprocating speed of the tip of the spray part over time, an isotropic random mat with a continuously changing material weight or an inclined material thickness is produced. The manufacturing method according to claim 1, wherein the manufacturing method is performed. By reciprocating the tip of the blowing part of the reinforcing fiber and the thermoplastic resin in the horizontal and vertical directions with respect to the running direction of the breathable support and continuously changing the reciprocating distance in the longitudinal direction. The manufacturing method according to any one of claims 7 to 12, wherein an isotropic random mat whose width direction dimension is changed is produced.