JP2013233729A - Method for manufacturing joint member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a joint member having excellent joining strength by directly joining composite materials including carbon fibers and thermoplastic resin by a simple method without using a method for mechanical fastening or the like.SOLUTION: A method for manufacturing a joint member is characterized by including respective processes of: (i) preparing two or more composite materials which include carbon fibers of an average fiber length in a range of 10-100 mm and thermoplastic resin at a ratio of 30-200 pts.wt. of the thermoplastic resin to 100 pts.wt. of the carbon fibers; (ii) forming an energy director having a void on at least one of the composite materials; and (iii) overlapping a part to be joined which has the energy director to a part to be joined of the other composite material, and carrying out frictional press-bonding.

Description

  The present invention relates to a method for manufacturing a joining member. In particular, the present invention relates to a method for manufacturing a joining member obtained by joining a plurality of composite materials containing carbon fibers and a thermoplastic resin.

  In general, when joining resins, mechanical joining such as bolts / nuts and rivets, and joining methods using adhesives, welding, and the like are used. In general, mechanical joints with bolts and nuts increase in weight, and in the worst case, due to the decrease in fastening force due to the creep phenomenon of resin and stress concentration at the joint point, fractures occur one after another starting from the first stress concentration point. There are concerns going on. In joining with adhesives, it generally takes time to obtain practical strength, so it is necessary to consider the curing process, and it is necessary to secure an adhesive layer with a certain thickness to ensure strength, especially large members When joining these, a considerable amount of adhesive is required, and there is a concern about a significant increase in weight of the resulting member. Further, the strength of the adhesive alone is not always sufficient.

  In the case where the resin is thermoplastic, the strength of the resin itself can be obtained by melting the joint, and the weight is not increased by the joining, and the processing time is short, which is an extremely effective method. There is also a method of welding by adding heat such as a hot plate, heat rays, infrared rays, etc., but the mechanical vibration is applied to the bonding surface and the temperature is increased by the frictional heat, and the object to be bonded is fixed by melting and cooling. It is known that vibration welding and ultrasonic welding are highly useful and highly useful joining methods. In order to perform these weldings more efficiently, it is described that, as a trigger for welding, a rib-shaped protrusion is formed in Patent Document 1 and a conical energy director is formed in Patent Document 2. In welding, the energy director is a dense protrusion because the pressure-bonding force needs to be sufficiently transmitted to the joint surface via the director.

  On the other hand, when these vibration welding and ultrasonic welding are performed, if the rubbed resin is not melted, the resin waste spreads as burrs. Therefore, for example, as in Patent Document 3, a burr pool is set in advance so that burrs do not appear outside. It is written to be.

Japanese Patent Laid-Open No. 5-100364 JP-A-8-294972 JP-A-6-134866

  When composite materials containing carbon fiber and thermoplastic resin are joined together by mechanical fastening or the like, when the force applied to the joint is concentrated, the carbon fiber in the part is destroyed, and eventually the entire joint is destroyed. The original strength of the composite material is not utilized.

  Now, the two or more composite materials to be welded are pressed and adhered, and the adhesion surface is heated and melted by vibration or the like, and then fixed and bonded by cooling. When a composite material having an energy director that is a dense projection is used, the energy director surface is preferentially brought into contact. Therefore, the ultrasonic wave and vibration energy are concentrated to facilitate melting and efficient welding is performed.

  However, in a thermoplastic resin composite material including a filler such as carbon fiber, the filler does not basically melt, so that a large amount of waste containing the resin is generated on the energy director. As a result, since a large amount of insoluble debris is present at the bonding interface, the melting / fixing is hindered in the first place, and there is a problem that the expected bonding strength is not exhibited because efficient bonding cannot be performed.

  The object of the present invention is to provide a method for producing a joining member excellent in joining strength by directly joining composite materials containing carbon fiber and thermoplastic resin by a simple method without using a method such as mechanical fastening. There is to do.

  When joining the composite materials as described above, the inventors of the present invention are extremely useful for vibration welding and ultrasonic welding as described above, and by adding an energy director to the portion to be welded, the efficiency is improved. We focused on the fact that welding was achieved. And it discovered that a waste was accommodated in this space | gap by providing a space | gap in the front or back of energy director itself, and, therefore, joining was not inhibited and efficient welding could be performed.

That is, the present invention is as follows.
[1] (i) A plurality of composite materials containing carbon fiber and thermoplastic resin having an average fiber length of 10 to 100 mm in a proportion of 30 to 200 parts by weight with respect to 100 parts by weight of carbon fiber Prepare
(Ii) At least one composite material is provided with an energy director having voids and a bulk density of 0.4 g / cm ³ or more and 1.4 g / cm ³ or less,
(Iii) A method for manufacturing a bonding member, comprising: a step of overlapping and bonding a planned bonding portion having the energy director with a predetermined bonding portion of the other composite material.
[2] The method for manufacturing the joining member, wherein the bonding is performed by vibration welding or ultrasonic welding.
[3] The method for manufacturing the joining member, wherein the composite material is in a sheet form, and the carbon fibers are randomly arranged in an in-plane direction of the sheet.
[4] The composite material has a weight per unit area in the range of 25 to 4500 g / m ² , and the reinforcing fiber bundle composed of the number of critical single yarns defined by the following formula (1) is within the thermoplastic resin composite material. The manufacturing method of said joining member whose ratio with respect to the fiber whole quantity is 20% or more and less than 99% by volume ratio, and the average number of fibers (N) in a reinforcing fiber bundle satisfy | fills following formula (2).
Critical number of single yarns = 600 / D (1)
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
[5] The method for manufacturing a joining member described above, in which an adhesive or a joining component other than the joining member is not used.
[6] A joining member produced by the above-described method for producing a joining member, wherein the joint portion has a breaking strength of 15 MPa or more.

  According to the present invention, burrs generated during welding can be accommodated in the gap without hindering the welding. As a result, it is possible to provide a joining member with improved welding efficiency and greatly increased weld joint strength. Further, a joining member made of a composite material having a high joining strength can be obtained by a simple method without using a third dissimilar material such as an adhesive or a joining part.

It is an example of the perspective view of the energy director in this invention. It is an example of sectional drawing of the energy director in this invention. It is an example of sectional drawing of the energy director in this invention. It is the schematic of the joining piece produced in Example 1 of this invention.

Hereinafter, embodiments of the present invention will be described.
[Thermoplastic composite material]
The composite material used in the present invention is in the form of a sheet containing carbon fibers and a thermoplastic resin as a matrix. Here, the thickness is preferably in the range of, for example, 0.5 to 5 mm in consideration of moldability, particularly shapeability with a mold. In addition, two or more of such composite materials can be laminated and used. The carbon fiber has a fiber length in the range of 10 to 100 mm, preferably more than 10 mm and less than 50 mm.

  The composite material is preferably one in which carbon fibers are substantially two-dimensionally oriented in the composite material. Here, the orientation is substantially two-dimensionally random means that the carbon fibers are disordered in the in-plane direction of the composite material without being oriented in a specific direction such as one direction. Specifically, it means that they are arranged in the sheet surface without showing a specific directionality. Therefore, the composite material in the present invention is a substantially isotropic material having no in-plane anisotropy.

The composite material has a basis weight in the range of 25 to 4500 g / m ² , and the ratio of the reinforcing fiber bundle (A) composed of the number of critical single yarns defined by the following formula (1) to the total amount of carbon fibers is When the volume is 20% or more and less than 99% and the average number of fibers (N) in the reinforcing fiber bundle (A) satisfies the following formula (2), the balance between moldability and mechanical strength is good.
Critical number of single yarns = 600 / D (1)
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
Here, D is the average fiber diameter (μm) of the carbon fibers.

Preferably, the fiber bundle and the single yarn having a number less than the critical single yarn defined by the above formula (1) and the carbon fiber bundle (A) composed of the critical single yarn or more are simultaneously present, and the carbon fiber bundle (A ′) The ratio of the mat to the total amount of fibers is 50% or more and less than 90% by volume, and the average number of fibers (N) in the carbon fiber bundle (A ′) satisfies the following formula (3).
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² (3)
(Where D is the average fiber diameter (μm) of the carbon fiber)

As described above, in the plane of the composite material according to the present invention, the carbon fibers are not oriented in a specific direction and are dispersed and arranged in a random direction.
Thus, the composite material used in the present invention is an in-plane isotropic material. When a molded body is obtained from the composite material, the isotropy of the carbon fibers in the composite material is maintained in the molded body. By obtaining a molded body from the composite material by press molding or the like, and determining the ratio of the tensile elastic modulus in two directions orthogonal to each other, the isotropy of the composite material and the molded body therefrom can be quantitatively evaluated. It is assumed that it is isotropic when the ratio of the modulus of elasticity in the two directions in the molded body obtained from the composite material divided by the smaller one does not exceed 2. When the ratio does not exceed 1.3, the isotropic property is considered excellent.

The basis weight of the carbon fiber in the composite material used in the present invention is preferably in the range of 25 to 4500 g / m ² . The composite material is useful as a prepreg, and various basis weights can be selected in accordance with a desired molding. The carbon fibers constituting the composite material are discontinuous, and the reinforcing function can be expressed by including carbon fibers that are somewhat long. The fiber length is expressed by an average fiber length obtained by measuring the fiber length of carbon fibers in the obtained composite material. As a method for measuring the average fiber length, there is 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. The average fiber length of the carbon fibers is preferably more than 10 mm and 50 mm or less. The fiber length distribution may be single or a mixture of two or more. The carbon fiber constituting the composite material can provide a composite material having excellent strength while being lightweight.

The average fiber diameter of the carbon fibers is preferably 3 to 12 μm. The adhesion strength between the carbon fiber and the thermoplastic resin as the matrix is desirably 5 MPa or more in the strand tensile shear test. In addition to the selection of the matrix resin, this strength is a method of changing the surface oxygen concentration ratio (O / C) of the carbon fiber, or a method of increasing the adhesion strength between the fiber and the matrix resin by applying a sizing agent to the carbon fiber. And the like.
Note that the composite material used in the present invention may include glass fiber, aramid fiber, or the like for imparting impact resistance.

[Carbon fiber opening degree]
As described above, the composite material in the present invention preferably has the following formula (1):
Critical number of single yarns = 600 / D (1)
(Where D is the average fiber diameter (μm) of the carbon fiber)
In the carbon fiber bundle (A) composed of the number of critical single yarns or more defined in, the ratio of the mat to the total amount of fibers is 20 vol% or more and less than 99 vol%, and the mat contains carbon fibers other than the carbon fiber bundle (A). There are fiber bundles composed of a single yarn state or less than the critical number of single yarns.

Furthermore, the average fiber number (N) in the carbon fiber bundle (A) composed of the number of critical single yarns or more satisfies the following formula (2).
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Where D is the average fiber diameter (μm) of the carbon fiber)

  In order to make the average number of fibers (N) in the carbon fiber bundle (A) within the above range, the size of the fiber bundle to be subjected to the cutting process, for example, the width of the bundle and the number of fibers per width are adjusted in the preferred production method described later. You can control it. Specifically, there are a method of expanding the width of the fiber bundle by opening the fiber and using it for the cutting process, and a method of providing a slit process before the cutting process. Further, the fiber bundle may be slit simultaneously with the cutting.

  Specifically, when the average fiber diameter of the carbon fiber constituting the composite material is 5 to 7 μm, the critical single yarn number is 86 to 120, and when the average fiber diameter of the carbon fiber is 5 μm, the average fiber in the fiber bundle The number is in the range of more than 240 to less than 4000, but 300 to 2500 is particularly preferable. More preferably, it is 400-1600. When the average fiber diameter of the carbon fibers is 7 μm, the average number of fibers in the fiber bundle is in the range of more than 122 to less than 2040, and in particular, 150 to 1500 is preferable. More preferably, the number is 200 to 800.

When the average number of fibers (N) in the carbon fiber bundle (A) is 0.6 × 10 ⁴ / D ² or less, it is difficult to obtain a high fiber volume content (Vf). In addition, when the average number of fibers (N) in the carbon fiber bundle (A) is 1 × 10 ⁵ / D ² or more, a locally thick portion is generated, which tends to cause voids.

  Furthermore, as a form of the carbon fiber bundle (A), the ratio of the carbon fiber bundles having a thickness of 100 μm or more is preferably less than 3% of the total number of carbon fiber bundles (A). If the carbon fiber bundle having a thickness of 100 μm or more is less than 3%, it is preferable because the thermoplastic resin is easily impregnated into the fiber bundle. More preferably, the proportion of carbon fiber bundles having a thickness of 100 μm or more is less than 1%. In order to make the proportion of carbon fiber bundles having a thickness of 100 μm or more less than 3%, it is possible to control by widening the fibers used and using thin fibers.

[Matrix resin]
Although there is no limitation in particular as matrix resin contained in the composite material used for this invention, the following can be illustrated.
That is, as a kind of thermoplastic resin, 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, polybutylene naphthalate resin, boribylene terephthalate resin, polyarylate resin, polyphenylene ether resin, polyphenylenesulfur De resins, polysulfone resins, polyethersulfone resins, polyether ether ketone resins, such as polylactic acid resins.
These thermoplastic resins may be used alone or in combination of two or more.

The amount of the matrix resin is preferably 30 to 200 parts by weight with respect to 100 parts by weight of the carbon fiber. More preferably, it is 30 to 150 parts by weight of the matrix resin with respect to 100 parts by weight of the carbon fiber, and further preferably 35 to 100 parts by weight of the matrix resin with respect to 100 parts by weight of the carbon fiber.
Further, in the composite material used in the present invention, various fibrous or non-fibrous fillers, flame retardants, UV-resistant agents, pigments, mold release agents of organic fibers or inorganic fibers within the range not detracting from the object of the present invention. , Softeners, plasticizers, surfactant additives may be included.

[Energy Director]
The energy director used in the present invention is a protrusion formed on a plane on which a composite material is welded. The energy director can be applied simultaneously with the molding of the composite material, or by being separately bonded or adhered to the surface of the flat composite material, but is preferably provided at the same time as the molding. The shape of the energy director is a cylinder, a cone, a truncated cone, a prism, a pyramid, a truncated pyramid, etc., and the size may be arbitrarily set, but the height is preferably about 0.5 mm to 100 mm. In the case of a cone or a truncated cone, the base diameter is preferably 1 mm to 100 mm. In the case of a prism, a pyramid, or a truncated pyramid, the length is preferably 1 mm to 3000 mm, and the width is preferably 1 mm to 100 mm. The number of energy directors to be welded at one time (at a time) to any part to be bonded of another composite material may be arbitrarily set, but the total area of the roots of the energy directors to be welded at one time is approximately 0.8 mm ^2. ˜20 m ² is preferred.

  Since the composite material used in the present invention contains carbon fibers that do not melt, a large amount of carbon fiber waste is generated at the joint interface when vibration welding or ultrasonic welding described later is performed. Since the void portion is provided in the energy director applied to the thermoplastic composite material in the present invention, the waste generated by welding can be accommodated in the void portion. The air gap may be inside the energy director, but can be provided on the joining surface of the energy director, the opposite surface of the joining, or both for the sake of simplicity of manufacturing.

The porosity of the energy director is 15% by volume or more and 65% by volume or less, preferably 20% by volume or more, because the scraps are sufficiently stored and the rigidity of the energy director is not deformed by pressurization. is 60 volume% or less, more but preferably is preferably below 55 volume% to 25 volume%, the energy director 0.40 g / cm ³ or more 1.40 g / cm ³ when converted in the bulk density of less, preferably 0. 43 g / cm ³ or more 1.05 g / cm ³ or less, 0.47 g / cm ³ or more 0.84 g / cm ³ or less. The voids in the director may be continuous or may exist in the form of closed cells. The bulk density of the energy director can be calculated by actually measuring the volume and weight of the dotted line portion when there is a gap on the back side of the energy director as shown in FIG.

  As a material constituting this energy director, the thermoplastic resin constituting the composite material can be mentioned, but it is preferable to use the same thermoplastic resin used in the composite material in the following welding. is there. More preferably, it is the same material as the composite material.

[Welding method]
In the present invention, for example, two composite materials are prepared, and an energy director is provided in one composite material by the above-described method. Next, a part or the whole of the part provided with the energy director is used as a part to be joined, and this part to be bonded is overlapped with the part to be joined of the other composite material to be welded and bonded by pressure bonding. The other composite material may also be provided with an energy director. Also, for example, three composite materials are prepared, and one of the composite materials is provided with an energy director, two of which are to be joined, and the two joints are joined to the other two composite materials. It can also be overlapped and joined with the planned portion.

  As pressure-bonding conditions at the time of welding, it is preferable to apply a pressure of 0.01 to 2 MPa to the welding surface, more preferably 0.02 to 1.5 MPa, and even more preferably 0.05 to 1 MPa. If the pressure is less than 0.01 MPa, a good bonding force may not be obtained, and the composite material may spring back during heating and the shape may not be maintained, resulting in a decrease in material strength. On the other hand, when the pressure exceeds 2 MPa, the pressurized part may be crushed, making it difficult to maintain the shape or reducing the material strength.

  As the welding method, vibration welding or ultrasonic welding is preferable. Vibration welding is preferably about 100 to 300 Hz, and in the case of ultrasonic vibration, 10 to 50 kHz is preferable. The total number of vibrations is preferably 300 to 10,000 in the case of vibration welding, and preferably 10,000 to 150,000 in the case of ultrasonic vibration.

[Joint material]
The joining member in the present invention is obtained by combining and joining two or more thermoplastic composite materials by the above-described method, and the shape of the thermoplastic composite material to be used is adapted to its use and joining site. According to the present invention, the composite materials can be bonded together efficiently and with a strength of 15 MPa or more, and can be suitably used as a structural member. Examples of such a structural member include parts constituting a moving body such as an automobile. The bonding strength can be evaluated by a tensile test or the like.

That is, the present invention includes the following.
It is composed of a plurality of composite materials comprising carbon fiber having an average fiber length of 10 to 100 mm and thermoplastic resin in a proportion of 30 to 200 parts by weight of thermoplastic resin with respect to 100 parts by weight of carbon fiber. A joining member having a fracture strength of 15 MPa or more at the joining portion,
The composite material is (i) a sheet,
(Ii) The carbon fibers are randomly arranged in the in-plane direction,
(Iii) For carbon fiber bundles having a basis weight in the range of 25 to 4500 g / m ² and composed of the number of critical single yarns defined by the following formula (1), the ratio to the total amount of carbon fibers in the composite material is volume. The joining member which is 20% or more and less than 99% by a ratio, and the average number of fibers (N) in the carbon fiber bundle satisfies the following formula (2).
Critical number of single yarns = 600 / D (1)
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

[Reference example]
Carbon fiber “Tenax” (registered trademark) STS40-24KS (fiber diameter: 7 μm, fiber width: 10 mm, tensile strength: 4000 MPa) manufactured by Toho Tenax Co., Ltd. is used as the carbon fiber, and nylon 6 resin A1030 manufactured by Unitika is used as the matrix resin. A mat having carbon fibers oriented at random with a carbon fiber basis weight of 1800 g / m ² and a nylon resin basis weight of 1500 g / m ² was prepared. The mat was heated at 2.0 MPa for 5 minutes with a press apparatus heated to 260 ° C. to obtain a molded plate (composite material) with t = 2.3 mm.
About the obtained composite material, the number of critical single yarns defined by Formula (1) is 86, the average number of single yarns (N) in the carbon fiber bundle (A) composed of the number of critical single yarns or more is 420, The ratio of the carbon fiber bundle (A) constituted by the number of single yarns or more was 85 Vol%. The fiber volume content of the obtained composite material was 43 Vol%.

As a result of cutting out test pieces of 250 × 25 mm each from n = 5 from 0 ° and 90 ° directions according to JIS K 7164, the tensile modulus ratio Eδ = 1.02 and the tensile strength was 510 MPa. there were.
Moreover, the average fiber length of the carbon fibers of the obtained random mat was 12 mm, and a fiber bundle having a thickness of 100 μm or more was not observed. The adhesion strength between the used fiber and the matrix resin was measured and found to be 50 MPa.

[Example 1]
(A piece) The flat plate obtained in the reference example was directly cut into a length of 100 mm and a width of 25 mm.
(B piece) The flat plate obtained in the reference example was pressed at 260 ° C. and 2.5 MPa using a die engraved so as to form a 10φ energy director as shown in FIG. The center was cut into a length of 100 mm and a width of 25 mm so that the center was the center in the short direction and the intersection of 12.5 mm from the end in the long direction.
(Junction piece) The A piece and the B piece energy director side were set to overlap by 25 mm in length, and the horn of an ultrasonic welding machine 2000Xdt manufactured by Emerson was pressed with a force of 150 N. Next, 20 kHz ultrasonic vibration was welded for 3 seconds at an amplitude setting value of 80%, and cooled at room temperature for 10 seconds to take out the joined piece (see FIG. 4). Five such pieces were manufactured, and a tensile test was performed at 1 mm / min one by one using an Instron 5587 universal testing machine (tested in accordance with JIS K 7164) to determine the fracture strength of the joint. However, the average of the five measured values was 71.2 MPa. When the energy director part was cut out and the bulk density was measured, it was 0.92 g / cm ³ .

[Example 2]
The shape of the energy director of the B piece is as shown in FIG. Set the energy director side of the A piece and B piece so as to overlap each other by 25 mm, pressurize with a force of 110 N using a vibration welding machine M-107 manufactured by Emerson, and vibrate at 240 Hz with an amplitude of 1.5 mm. It was welded for 2 seconds, cooled at room temperature for 10 seconds, and the joined piece was taken out. Five such pieces were manufactured, and in the same manner as in Example 1, a tensile test was conducted at 1 mm / min for each of 5587 universal testing machines manufactured by Instron, and the fracture strength of the joint was determined. The average value was 68.7 MPa. When the energy director part was cut out and the bulk density was measured, it was 1.02 g / cm ³ .

[Example 3]
Except that the shape of the energy director of the B piece is 10φ shown in FIG. 2, five joining pieces were produced in the same manner as in Example 1, and one Instron 5587 universal testing machine was produced in the same manner as in Example 1. Tensile tests were performed at 1 mm / min at a time, and the fracture strength of the joint was determined. The average of the five measured values was 28.0 MPa.

[Comparative example]
Except for using B pieces and using two A pieces, five joining pieces were produced in the same manner as in Example 1, and in the same manner as in Example 1, one 5587 universal testing machine manufactured by Instron, 1 mm / When a tensile test was performed in minutes to determine the fracture strength of the joint, the average of the five measured values was 9.8 MPa.

Claims (7)

(I) preparing a plurality of composite materials containing carbon fiber and thermoplastic resin having an average fiber length of 10 to 100 mm in a proportion of 30 to 200 parts by weight with respect to 100 parts by weight of carbon fiber; ,
(Ii) At least one composite material is provided with an energy director having voids and a bulk density of 0.4 g / cm ³ or more and 1.4 g / cm ³ or less,
(Iii) A method for manufacturing a bonding member, comprising: a step of overlapping and bonding a planned bonding portion having the energy director with a predetermined bonding portion of the other composite material.   The manufacturing method of the joining member of Claim 1 crimped | bonded by vibration welding or ultrasonic welding.   The method for manufacturing a joining member according to claim 1 or 2, wherein the composite material is in a sheet form, and the carbon fibers are randomly arranged in an in-plane direction of the sheet. The composite material has a basis weight in the range of 25 to 4500 g / m ² , and the reinforcing fiber bundle composed of the number of critical single yarns defined by the following formula (1) is based on the total amount of fibers in the thermoplastic resin composite material. The manufacturing method of the joining member according to claim 3, wherein the ratio is 20% or more and less than 99% by volume, and the average number of fibers (N) in the reinforcing fiber bundle satisfies the following formula (2).
Critical number of single yarns = 600 / D (1)
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)   The manufacturing method of the joining member in any one of Claims 1-4 which does not use adhesive agents or joining components other than a joining member.   A joining member produced by the method for producing a joining member according to any one of claims 1 to 5, wherein the fracture strength of the joined portion is 15 MPa or more. A plurality of composite materials comprising carbon fiber having an average fiber length of 10 to 100 mm and thermoplastic resin in a proportion of 30 to 200 parts by weight with respect to 100 parts by weight of carbon fiber are joined. The fracture strength of the joined portion is 15 MPa or more, and the composite material is (i) sheet-like,
(Ii) The carbon fibers are randomly arranged in the in-plane direction of the sheet,
(Iii) For carbon fiber bundles having a basis weight in the range of 25 to 4500 g / m ² and composed of the number of critical single yarns defined by the following formula (1), the ratio to the total amount of carbon fibers in the composite material is volume. The joining member which is 20% or more and less than 99% by a ratio, and the average number of fibers (N) in the carbon fiber bundle satisfies the following formula (2).
Critical number of single yarns = 600 / D (1)
0.6 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)