Sheet molding compound, method for manufacturing same, and carbon fiber reinforced plastic

Abstract

The present invention provides a method for manufacturing an SMC capable of obtaining a high-quality SMC and carbon fiber reinforced plastic by using carbon fiber bundles of different forms, and a high-quality SMC. The present invention provides a method for manufacturing a sheet molding compound including a step for forming a carbon fiber mat by depositing chopped carbon fiber bundles and carbon fiber assemblies excluding the chopped carbon fiber bundles onto a carrier film traveling below a rotary body that has an axis of rotation substantially horizontal in a direction orthogonal to the axis of rotation of the rotary body, wherein the chopped carbon fiber bundles and the carbon fiber assemblies are separately supplied to the rotary body in a manner not contacting each other. The present invention also provides a sheet molding compound containing a matrix resin, chopped carbon fiber bundles, and a carbon fiber assemblies excluding the chopped carbon fiber bundles, wherein the content ratio of the chopped carbon fiber bundles is different in the thickness direction.

Description

Sheet molding compound, method for manufacturing the same, and carbon fiber reinforced composite material

[0001] This invention relates primarily to sheet molding compounds, methods for manufacturing the same, and carbon fiber reinforced composite materials. This application claims priority based on Japanese Patent Application No. 2025-029779, filed in Japan on 27 February 2025, and Japanese Patent Application No. 2025-058189, filed in Japan on 31 March 2025, the contents of which are incorporated herein by reference.

[0002] Carbon fiber reinforced plastics (CFRPs), obtained by impregnating carbon fiber (CF) with a matrix resin, are widely used in aerospace, sports and leisure, and other applications due to their excellent mechanical properties. However, since the production of carbon fiber consumes a large amount of energy, methods of recovering the carbon fiber contained in carbon fiber reinforced plastics and using it as recycled CF have attracted attention in recent years from the perspective of reducing environmental impact.

[0003] Sheet molding compound (SMC) is a type of intermediate material in which a fiber reinforcement containing carbon fibers is impregnated with a resin composition. As a fiber reinforcement used in SMC, a carbon fiber mat is known, which is formed by cutting continuous carbon fiber bundles to make chopped carbon fiber bundles and scattering them on a carrier film (for example, Patent Document 1). In SMC manufacturing, virgin CF is usually used in the form of chopped carbon fiber bundles. Patent Document 2 proposes a method for producing self-assembled carbon fiber bundles in order to make recycled CF obtained in a cotton-like form easier to use as a fiber reinforcement.

[0004] Patent Document 3 discloses a technique for forming a carbon fiber mat by quantitatively feeding recycled CF using a spiked lattice belt. Patent Document 4 discloses a technique for using virgin CF and recycled CF mixed in water.

[0005] Japanese Patent Publication No. 1-163218, International Publication No. 2022 / 265099, International Publication No. 2024 / 128010, International Publication No. 2020 / 040289

[0006] Generally, carbon fiber bundles produced from recycled carbon fiber (CF) are thicker than chopped carbon fiber bundles. When using carbon fiber bundles of different shapes, conventional techniques using spiked lattice belts, such as those described in Patent Document 3, make it difficult to uniformly distribute these differently shaped carbon fiber bundles across the entire carbon fiber mat, leading to a decrease in quality. Furthermore, Patent Document 4 does not address the uniformity of the mixture of virgin CF and recycled CF.

[0007] One of the objectives of the present invention is to provide a method for producing SMC and carbon fiber reinforced composite materials that can be obtained using carbon fiber bundles of different morphologies and that are of good quality, as well as to provide SMC and carbon fiber reinforced composite materials of good quality.

[0008] The present invention includes the following embodiments. The following [1] to

[27] may be referred to as "the first embodiment of the present invention." [1]: A method for manufacturing a sheet molding compound, comprising depositing chopped carbon fiber bundles and carbon fiber assemblies excluding the chopped carbon fiber bundles onto a carrier film that runs below a rotating body having a substantially horizontal axis of rotation in a direction perpendicular to the axis of rotation of the rotating body to form a carbon fiber mat, wherein the chopped carbon fiber bundles and the carbon fiber assemblies are supplied separately to the rotating body in such a manner that they do not come into contact with each other. [2]: The method for manufacturing a sheet molding compound according to [1], wherein the chopped carbon fiber bundles and the carbon fiber assemblies are supplied to the rotating body from separate paths and brought into contact with the rotating body. [3]: The method for manufacturing a sheet molding compound according to [1] or [2], wherein the chopped carbon fiber bundles and the carbon fiber assemblies come into contact with the rotating body at different positions in the direction of travel of the carrier film. [4]: The method for manufacturing a sheet molding compound according to [3], wherein the rotating bodies consist of a first rotating body and a second rotating body arranged such that their respective axes of rotation are parallel to each other, and either the chopped carbon fiber bundle or the carbon fiber aggregate falls to contact the first rotating body and the second rotating body at a position away from the center between the axes of rotation of the first rotating body and the second rotating body in the direction of travel of the carrier film. [5]: The method for manufacturing a sheet molding compound according to [4], wherein the first rotating body is rotationally driven to move from top to bottom on the side facing the second rotating body, and the second rotating body is rotationally driven to move from top to bottom on the side facing the first rotating body. [6]: The method for manufacturing a sheet molding compound according to [3], wherein there is one rotating body, and either the chopped carbon fiber bundle or the carbon fiber aggregate falls to contact the rotating body at a position away from the axis of rotation in the direction of travel on the carrier film. [7]: A method for manufacturing a sheet molding compound according to any one of [1] to [6], wherein the rotating body has a roll body having n rotational symmetry about the axis of rotation (wherein n is an integer of 1 or more and is finite).[8]: A method for manufacturing a sheet molding compound according to any one of [1] to [7], wherein the rotation speed of the rotating body is 100 rpm or more. [9]: A method for manufacturing a sheet molding compound according to any one of [1] to [8], wherein the rotation speed of the rotating body is 2000 rpm or less.

[10] : A method for manufacturing a sheet molding compound according to any one of [1] to [9], wherein the average bundle thickness of the chopped carbon fiber bundles is less than 0.3 mm, and the average maximum length in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate is 0.3 mm or more.

[11] : A method for manufacturing a sheet molding compound according to any one of [1] to

[10] , wherein the carbon fiber aggregate contains recycled carbon fibers.

[12] : The bulk density of the carbon fiber aggregate is 0.01 to 0.40 g / cm³. ３A method for producing a sheet molding compound according to any one of [1] to

[11] , which is produced from recycled carbon fibers.

[13] : A sheet molding compound comprising a matrix resin, chopped carbon fiber bundles, and a carbon fiber aggregate excluding the chopped carbon fiber bundles, wherein the content of the chopped carbon fiber bundles differs in the thickness direction of the sheet molding compound.

[14] : The sheet molding compound according to

[13] , wherein when the sheet molding compound is divided into three equal parts in the thickness direction and the layers from one side are designated as the first layer, second layer, and third layer, the difference between the content of the chopped carbon fiber bundles in the first layer and the content of the chopped carbon fiber bundles in the third layer is 1% by weight or more.

[15] : The sheet molding compound according to

[13] or

[14] , wherein the proportion of the chopped carbon fiber bundles on either one surface in the thickness direction of the sheet molding compound is 25% by weight or more relative to the total amount of the chopped carbon fiber bundles and the carbon fiber aggregate on that surface.

[16] : The sheet molding compound according to any one of

[13] to

[15] , wherein the average bundle thickness of the chopped carbon fiber bundles is less than 0.3 mm, and the average maximum length in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate is 0.3 mm or more.

[17] : The sheet molding compound according to any one of

[13] to

[16] , wherein the length in the longitudinal direction of the chopped carbon fiber bundles has less variation than the length in the longitudinal direction of the carbon fiber aggregate.

[18] : The sheet molding compound according to any one of

[13] to

[17] , wherein the content of the chopped carbon fiber bundles in the sheet molding compound is 10 to 90% by weight with respect to the total fiber weight in the sheet molding compound.

[19] : The sheet molding compound according to any one of

[13] to

[18] , wherein the average length in the longitudinal direction of the chopped carbon fiber bundles is 10 to 80 mm and the average width is 1.0 mm or more.

[20] : The sheet molding compound according to any one of

[13] to

[19] , wherein the shape of the chopped carbon fiber bundle when viewed from the thickness direction is substantially rectangular, with an angle of 85 to 95° between the longitudinal end of the chopped carbon fiber bundle and the longitudinal direction of the chopped carbon fiber bundle.

[21] : The sheet molding compound according to any one of

[13] to

[20] , wherein the average length in the longitudinal direction of the carbon fiber aggregate is 10 to 80 mm, and the average maximum length in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate is 0.3 mm or more.

[22] : The sheet molding compound according to any one of

[13] to

[21] , wherein the shape of the carbon fiber aggregate is spindle-shaped, elongated spherical, or strand-shaped.

[23] : The sheet molding compound according to any one of

[13] to

[22] , wherein the carbon fiber aggregate contains recycled carbon fibers with a residual carbon component of 5% by weight or less.

[24] : The sheet molding compound according to any one of

[13] to

[23] , wherein the carbon fiber aggregate comprises an organic binder.

[25] : The sheet molding compound according to any one of

[13] to

[24] , wherein τA is the average value of the interfacial shear strength between the matrix resin and the carbon fibers contained in the chopped carbon fiber bundle, and τA = 15 to 230 MPa.

[26] : The sheet molding compound according to any one of

[13] to

[25] , wherein τB is the average value of the interfacial shear strength between the matrix resin and the carbon fibers contained in the carbon fiber aggregate, and τB = 15 to 150 MPa.

[27] : A carbon fiber reinforced composite material which is a sheet molding compound manufactured by the method of any one of [1] to

[12] , or a molded product of the sheet molding compound according to any one of claims

[13] to

[26] .

[0009] The present invention also includes the following embodiments. The following [1a] to [12a] may be referred to as "the second embodiment of the present invention." [1a]: A sheet molding compound comprising at least two types of fiber bundles with different cross-sectional shapes and a matrix resin, wherein the fiber bundles include a fiber bundle X whose cross-sectional shape at the position with the largest area among the cross-sections perpendicular to the longitudinal direction is substantially rectangular, and a fiber bundle Y whose cross-sectional shape at the position with the largest area among the cross-sections perpendicular to the longitudinal direction is substantially elliptical, wherein the substantially rectangular cross-sectional shape of the fiber bundle X has a contour with a long side and a short side, and the angle between adjacent sides is 70 to 110°, and the substantially elliptical cross-sectional shape of the fiber bundle Y has a major axis and a minor axis, the length of the minor axis is 0.2 mm or more, the contour is composed of an outwardly convex curve, and the overlap rate with a perfect ellipse having the same major axis and minor axis is 80% or more. [2a]: The sheet molding compound according to [1a], wherein the average value LcX of the critical fiber length of the fiber bundle X, calculated by the following formulas (1) to (3), is 4 to 29 mm, and the average value LcY of the critical fiber length of the fiber bundle Y is 11 to 66 mm. (In formulas (1) to (3) above, SX is the average value of the cross-sectional area of ​​the substantially rectangular cross-section of the fiber bundle X (mm²) ２ ), SY is the average value of the cross-sectional area of ​​the substantially elliptical cross-section of the fiber bundle Y (mm²). ２ ), a is the average value (mm) of the short side length of the substantially rectangular cross-section of the fiber bundle X, b is the average value (mm) of the long side length of the substantially rectangular cross-section of the fiber bundle X, c is the average value (mm) of the major axis length of the substantially elliptical cross-section of the fiber bundle Y, d is the average value (mm) of the minor axis length of the substantially elliptical cross-section of the fiber bundle Y, and E is the average value (mm) of the outer circumference length of the substantially elliptical cross-section of the fiber bundle Y. τX is the average value (MPa) of the interfacial shear strength between the matrix resin and the fibers contained in the fiber bundle X, τY is the average value (MPa) of the interfacial shear strength between the matrix resin and the fibers contained in the fiber bundle Y, σ ｆＸ This is the average value (MPa) of the tensile strength of the fibers contained in the fiber bundle X, σ ｆＹ(This indicates the average value (MPa) of the tensile strength of the fibers contained in the fiber bundle Y.) [3a]: The sheet molding compound according to [1a] or [2a], wherein Vf is 60% or less when Vf is the volume content of the fiber bundle. [4a]: The sheet molding compound according to any one of [1a] to [3a], wherein the content ratio of the fiber bundle X to the total amount of the fiber bundle is 20% by volume or more. [5a]: The sheet molding compound according to any one of [1a] to [4a], wherein the content ratio of the fiber bundle Y to the total amount of the fiber bundle is 10% by volume or more. [6a]: The sheet molding compound according to any one of [1a] to [5a], wherein LaX is 10 mm or more when LaX is the average value of the length of the fibers contained in the fiber bundle X. [7a]: The sheet molding compound according to any one of [1a] to [6a], wherein LaY is 10 to 50 mm, when LaY is the average value of the length of the fibers contained in the fiber bundle Y. [8a]: The sheet molding compound according to [2a], where in formulas (1) and (2), τX is 15 to 230 MPa and τY is 15 to 150 MPa. [9a]: The sheet molding compound according to any one of [1a] to [8a], wherein the number of filaments in the fiber bundle X is 3,000 to 15,000. [10a]: The sheet molding compound according to any one of [1a] to [9a], wherein L is the average value of the length in the longitudinal direction of the fiber bundle Y, and R is the average value of the maximum length in the direction perpendicular to the longitudinal direction of the fiber bundle Y, when L / R is 12 to 48. [11a]: A sheet molding compound according to any one of [1a] to [10a], wherein the fiber bundle Y contains regenerated fibers. [12a]: A carbon fiber reinforced composite material which is a molded product of the sheet molding compound according to any one of [1a] to [11a].

[0010] According to the present invention, a method for producing SMC and carbon fiber reinforced composite materials of good quality can be obtained using carbon fiber bundles of different morphologies, and SMC and carbon fiber reinforced composite materials of good quality are provided.

[0011] Figure 1 is a schematic diagram of an SMC manufacturing apparatus. Figure 2 is a schematic diagram of a spiked lattice belt. Figure 3 is a schematic enlarged view of the section in the SMC manufacturing apparatus where fiber bundles are supplied to the rotating body. Figure 4 is a schematic diagram of a pin roll (rotating body). Figure 5 is a schematic diagram showing the positional relationship of two pin rolls (rotating bodies). Figure 6 is a schematic diagram of a cage roll (rotating body). Figure 7 is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 8A is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 8B is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 8C is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 9 is a schematic enlarged view of the section in the SMC manufacturing apparatus where fiber bundles are supplied to the rotating body. Figure 10A is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 10B is a schematic diagram illustrating the contact position of the fiber bundles to the rotating body. Figure 10C is a schematic diagram illustrating the contact position of the fiber bundle with the rotating body.

[0012] The present invention will be described in detail below. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits, and "A~B" means that it is A or greater and B or less. The numerical ranges of content, various physical properties, and property values ​​disclosed herein can be changed to new numerical ranges by arbitrarily combining their lower and upper limits.

[0013] Hereinafter, several embodiments of the present invention will be described with reference to the drawings as appropriate. The dimensional ratios in the drawings are for illustrative purposes only and may differ from those in reality. Also, identical components in the drawings are indicated by the same reference numerals, and descriptions of redundant components may be omitted. In this specification, "T direction" means a direction that is horizontal and perpendicular to the M direction. "M direction" is the direction in which the carrier film travels during the manufacturing of SMC. For example, in Figure 1, the T direction is perpendicular to the plane of the paper.

[0014] 1. Method for Manufacturing SMC One embodiment of the first aspect of the present invention relates to a method for manufacturing SMC. The method for manufacturing SMC according to one embodiment of the first aspect of the present invention includes depositing chopped carbon fiber bundles and carbon fiber assemblies excluding the chopped carbon fiber bundles onto a carrier film that runs below a rotating body whose axis of rotation is substantially horizontal, in a direction perpendicular to the axis of rotation of the rotating body, to form a carbon fiber mat. Hereinafter, the chopped carbon fiber bundles used in the method for manufacturing SMC according to the first aspect will also be referred to as "chopped carbon fiber bundles A," and the carbon fiber assemblies excluding the chopped carbon fiber bundles will also be referred to as "carbon fiber assemblies B." Furthermore, in the method for manufacturing SMC according to one embodiment of the first aspect of the present invention, the chopped carbon fiber bundles A and carbon fiber assemblies B are supplied separately to the rotating body in a manner that they do not come into contact with each other. The rotation axis of the rotating body being substantially horizontal means that the inclination of the rotation axis of the rotating body with respect to the horizontal is 5° or less, and it is particularly preferable that the rotation axis of the rotating body is horizontal.

[0015] Chopped carbon fiber bundle A is typically a carbon fiber bundle in which a continuous carbon fiber bundle has been cut to a predetermined length. The variation in fiber length of the short carbon fibers constituting chopped carbon fiber bundle A has a coefficient of variation (CV) of less than 15%, as measured in accordance with JIS L1019:2006 Section 7.2.2 (fibrograph method). The shape of chopped carbon fiber bundle A is usually flattened and approximately rectangular when viewed from the thickness direction. Carbon fiber aggregate B refers to carbon fiber bundles other than chopped carbon fiber bundle A. The variation in fiber length of the short carbon fibers constituting carbon fiber aggregate B has a coefficient of variation (CV) of 15% or more, as measured in accordance with JIS L1019:2006 Section 7.2.2 (fibrograph method). The shape of carbon fiber aggregate B is usually spindle-shaped, elongated spherical, strand-shaped, or a mass-like structure in which carbon fibers are irregularly assembled. Note that "strand-like" includes needle-like and wire-like structures. The variation in the longitudinal length of chopped carbon fiber bundle A is smaller than the variation in the longitudinal length of carbon fiber assembly B. The variation in the longitudinal length of chopped carbon fiber bundle A and carbon fiber assembly B can be calculated by calculating the coefficient of variation (CV) from the measurement results of their respective longitudinal lengths obtained by image analysis, which is described in the examples below.

[0016] 1.1. An example of an SMC manufacturing apparatus that can be preferably used in an SMC manufacturing method according to one embodiment of the first aspect of the SMC manufacturing apparatus is shown in Figure 1. The SMC manufacturing apparatus 100 shown in Figure 1 comprises a first fiber bundle supply unit 110 for supplying carbon fiber aggregates B, a second fiber bundle supply unit 120 for supplying chopped carbon fiber bundles A, a dispersion unit 130, and an impregnation unit 140.

[0017] The first fiber bundle supply unit 110 includes a first belt conveyor 1, a scraping roller 2, and a second belt conveyor 3.

[0018] The first belt conveyor 1 is an example of a belt conveyor with an upward sloping section, and has only an upward sloping section. In a modified example, the first belt conveyor 1 may have a horizontal section on either the upstream side or the downstream side of the upward sloping section, or both.

[0019] The width direction of the conveyor belt 11 of the first belt conveyor 1 is parallel to the T direction. The conveying surface 11a of the conveyor belt 11, that is, the surface on which the carbon fiber aggregate B is placed, is an uneven surface. This is to prevent the carbon fiber aggregate B to be conveyed from sliding off the conveying surface 11a of the conveyor belt 11 in the upward sloping section of the first belt conveyor 1.

[0020] The conveying surface 11a of the conveyor belt 11 may be, for example, an uneven surface having a recess with a bottom and a protrusion protruding from the bottom. In this case, the proportion occupied by the protrusion when the uneven surface is viewed from above is preferably 50% or less in area, and more preferably 10% or less. In one example, the protrusion on such an uneven surface may be a wall perpendicular to the bottom of the recess. Such a wall may be parallel to the width direction of the conveyor belt. In another example, the protrusion on such an uneven surface may be columnar. The columnar protrusion may be perpendicular to the bottom of the recess, or it may be inclined toward the direction in which the conveyor belt 11 travels.

[0021] In a preferred example, the conveyor belt 11 may be a spiked lattice belt. In other words, the first belt conveyor 1 may be a spiked lattice conveyor. Figure 2 is a view of a typical spiked lattice belt from the width direction. In a spiked lattice belt, the slat width is preferably 5 to 30 mm, and the spike length is preferably 5 to 20 mm. In a spiked lattice belt, the surface with spikes is the conveying surface.

[0022] The scraping roller 2 is an example of a scraping means for scraping off a portion of the carbon fiber aggregate B being conveyed by the first belt conveyor 1, and is optionally installed in the middle or at the top of the upward sloping section of the first belt conveyor 1. The scraping roller 2 has a rotation axis parallel to the T direction and a cylindrical portion with the rotation axis as its central axis, and a plurality of blades are arranged on the outer circumferential surface of the cylindrical portion, each parallel to the rotation axis.

[0023] While it is preferable, it is not essential that the conveying path of the second belt conveyor 3 be horizontal. Even if the second belt conveyor 3 has a slope, it is acceptable as long as the slope is not so steep that the carbon fiber aggregate B on the conveyor belt moves due to gravity. The width direction of the second belt conveyor 3 is parallel to the T direction. The discharge end 3E of the second belt conveyor 3 is positioned above the first carrier film 12, whose width direction is parallel to the T direction.

[0024] The carbon fiber aggregate B falling from the discharge end 1E of the first belt conveyor 1 falls onto the second belt conveyor 3 and is transported toward its discharge end 3E. The belt travel speed v2 of the second belt conveyor 3 is preferably equal to or less than the belt travel speed v1 of the first belt conveyor 1, and more preferably lower than the belt travel speed v1 of the first belt conveyor 1. The travel speed v3 of the first carrier film 12 is preferably equal to or less than the belt travel speed v2 of the second belt conveyor 3, and more preferably lower than the belt travel speed v2 of the second belt conveyor 3.

[0025] The second fiber bundle supply unit 120 includes a chopper 4 positioned above the first carrier film 12. The chopper 4 can be a type of chopper conventionally used in SMC manufacturing equipment, that is, a chopper equipped with a cutter roll 14, a receiving roll 15, and a guide roll 16, each having a rotation axis parallel to the T direction. The receiving roll 15 is typically made of rubber.

[0026] During the manufacturing of SMC, the continuous carbon fiber bundles C supplied in the second fiber bundle supply unit 120 are cut at predetermined intervals by the chopper 4 to become chopped carbon fiber bundles A. The chopper 4 may cut the continuous carbon fiber bundles C such that, when viewed from the thickness direction of the continuous carbon fiber bundles C, the angle between the longitudinal direction of the continuous carbon fiber bundles C and the cut surface is 85 to 95°.

[0027] In the example of the distribution unit 130 shown in Figures 1 and 3, a pair of rotating bodies, namely a first rotating body 17 and a second rotating body 18, are arranged side by side. The first rotating body 17 and the second rotating body 18 of the distribution unit 130 are located below the chopper 4. Both the first rotating body 17 and the second rotating body 18 have axes of rotation parallel to the T direction and are both driven by a drive mechanism (not shown). The rotational speeds of the first rotating body 17 and the second rotating body 18 may be independently controllable. Below the first rotating body 17 and the second rotating body 18 of the distribution unit 130, the first carrier film 12 travels in a direction perpendicular to their axes of rotation.

[0028] As shown in Figure 4, the first rotating body 17 has a roll body 19 and a shaft 20 that passes through the roll body 19 in the axial direction. The roll body 19 is of the pin roll type and has a cylinder 19a and a plurality of pins 19b arranged on the circumferential surface of the cylinder 19a. Both the roll body 19 and the shaft 20 have high rigidity and are made of a metallic material such as stainless steel. When the first rotating body 17 is rotated, the pins 19b move in the circumferential direction, so that the chopped carbon fiber bundle A and the carbon fiber aggregate B can be struck by the sides of the pins 19b.

[0029] A preferred embodiment of the pin roll type roll body 19 is as follows. The diameter of the cylinder 19a is not limited, but for example it may be 30 to 300 mm, or 60 to 150 mm. The larger the diameter of the cylinder 19a, the higher the peripheral speed at which the entire pin 19b moves when the first rotating body 17 is rotated, thus increasing the ability to disperse the chopped carbon fiber bundle A and the carbon fiber aggregate B.

[0030] The pin 19b extends perpendicularly to the axis of rotation (central axis) of the first rotating body 17 and, although not limited, has a cylindrical shape, for example. The boundary between the end face and the circumferential face of the pin 19b may be chamfered. The diameter of the pin 19b is, although not limited, for example, 1 to 15 mm, may be 1 to 10 mm, and preferably 1 to 5 mm. The length of the pin 19b, that is, the distance from the tip to the base of the pin, is, although not limited, for example, 10 to 150 mm, may be 10 to 100 mm, or may be 10 to 50 mm. It is preferable that all of the multiple pins 19b have the same shape and dimensions as each other.

[0031] The arrangement of the pins 19b on the circumferential surface of the cylinder 19a is preferably periodic in both the axial and circumferential directions. The period of the arrangement of the pins 19b on the circumferential surface of the cylinder 19a may be, for example, 5 mm or more and less than 20 mm, 20 mm or more and less than 40 mm, or 40 mm or more and less than 60 mm in the axial direction. In the example of Figure 4, the arrangement of the pins 19b on the circumferential surface of the cylinder 19a has a period of 90° in the circumferential direction, but periods other than 90° can also be adopted, such as 5°, 10°, 15°, 20°, 24°, 30°, 45°, 60°, 72°, 120°, 180°, etc.

[0032] In this specification, the maximum radius of a pin roll is defined as the distance from its axis of rotation to the tip of the longest pin. In the first rotating body 17, the radius of the cylinder 19a is preferably at least half, and more preferably at least 75%, of the maximum radius of the pin roll body 19. This is because a higher ratio of the cylinder radius to the maximum radius of the pin roll results in a smaller difference between the peripheral speed at the tip of the pin and the peripheral speed at the base of the pin when the pin roll is rotating.

[0033] In one example, the shaft 20 may also serve as the cylinder. However, this configuration is disadvantageous because, when the first rotating body 17 is rotated to optimize the peripheral speed at the tip of the pin 19b, fiber dust tends to adhere to areas with low peripheral speeds, such as the surface of the shaft 20 and near the base of the pin 19b.

[0034] Everything described above regarding the first rotating body 17 also applies to the second rotating body 18. The second rotating body 18 may comprise a pin roll type roll body 21 having a cylinder 21a and a plurality of pins 21b arranged on the circumferential surface of the cylinder 21a. Although not limited, in order to reduce the design, manufacturing, and maintenance costs of the distribution section 130, it is preferable to match the design and specifications of the first rotating body 17 and the second rotating body 18 in as many items as possible, including the axial length, maximum radius, cylinder diameter, pin shape, dimensions, number and arrangement, and the materials of the cylinder and pins.

[0035] During the production of SMC, chopped carbon fiber bundles A falling from chopper 4 and carbon fiber aggregates B falling from the discharge end 3E of the second belt conveyor 3 come into contact with the first rotating body 17 and the second rotating body 18, pass between the first rotating body 17 and the second rotating body 18, and accumulate on the first carrier film 12 being conveyed below to form a carbon fiber mat M. The surface of the conveyed first carrier film 12 is kept horizontal. This is to prevent the accumulated carbon fiber mat M from moving on the surface of the first carrier film 12 due to gravity.

[0036] When a larger amount of chopped carbon fiber bundles A and carbon fiber aggregates B pass between the first rotating body 17 and the second rotating body 18, they are struck by the pins of the pin roll. As shown in FIG. 5, the maximum radius r of the first rotating body 17 Ｍ１ and the maximum radius r of the second rotating body 18 Ｍ２ preferably has a sum greater than the distance d1 between the rotation axes of the two pin rolls. The maximum radius r of the first rotating body 17 Ｍ１ plus the cylinder radius r of the second rotating body 18 Ｃ２ , and the cylinder radius r of the first rotating body 17 Ｃ１ plus the maximum radius r of the second rotating body 18 Ｍ２ both have a sum smaller than the distance d1 between the rotation axes of the two pin rollers.

[0037] In one example, the maximum radius r of the first rotating body 17 in the dispersing section 130 Ｍ１ and the maximum radius r of the second rotating body 18 Ｍ２ may have a sum equal to the distance d1 between the rotation axes of the two pin rolls. In another example, the maximum radius r of the first rotating body 17 in the dispersing section 130 Ｍ１ and the maximum radius r of the second rotating body 18 Ｍ２ may have a sum slightly smaller than the distance d1 between the rotation axes of the two pin rolls. The difference {d1 - (r Ｍ１ + r Ｍ２ )} is preferably 10 mm or less, more preferably 5 mm or less.

[0038] The number of rotating bodies used in the dispersing section is not limited to two. In one example, the number of rotating bodies used in the dispersing section may be one, or may be three or more. For example, as in the example shown in FIG. 9, the dispersing section 130 may have only the first rotating body 17 as its rotating body. In one example, in addition to or instead of a pin roll, a type of rotating body other than a pin roll may be used.

[0039] The rotating body requires an element that moves circumferentially when rotated, similar to a pin in a pin roll, to strike the chopped carbon fiber bundle A and the carbon fiber assembly B. To satisfy this requirement, the rotating body should have n rotational symmetry about the axis of rotation. Here, n is a finite integer greater than or equal to 1, preferably 72 or less. n may also be 45 or less, 36 or less, or 24 or less. n may also be 1 to 72, 1 to 45, 1 to 36, 1 to 24, 2 to 16, 2 to 10, 3 to 8, or 4 to 6.

[0040] For example, the first rotating body 17 shown in Figure 4 has four-fold rotational symmetry about the axis of rotation.

[0041] The cage roll 22 shown in Figure 6 is an example of a rotating body of a type other than a pin roll. The cage roll 22 has a structure in which multiple rods 22b are stretched between a pair of discs 22a that share a rotation axis, and a shaft 22c passes through the center of each disc 22a.

[0042] In the example shown in Figure 6, the six rods 22b are arranged at equal intervals in the circumferential direction on a cylindrical surface centered on the axis of rotation, so the cage roll 22 has six-fold rotational symmetry around the axis of rotation. The material of the rods 22b is preferably metal, but is not limited to that. When the cage roll 22 is rotated, the rods 22b move in the circumferential direction and strike the chopped carbon fiber bundle A and the carbon fiber aggregate B. In modified examples, the rods 22b of the cage roll 22 may be replaced with rods with a non-round cross-section, such as square bars or flat bars, or with tensioned wires.

[0043] In one example of a cage roll, multiple rods may be arranged at equal intervals in the circumferential direction on each of several concentric cylindrical surfaces centered on the axis of rotation. The number of rods arranged on each cylindrical surface is not particularly limited, but could be, for example, 3 to 8. In one example of a cage roll, a structure may have a configuration in which multiple structural units, each having multiple rods stretched between a pair of discs sharing a rotation axis, are arranged in the longitudinal direction of the shaft. In this case, one disc may be shared between adjacent structural units.

[0044] The impregnation unit 140 comprises a first coating machine 5a, a second coating machine 5b, a laminating machine 6, and an impregnation machine 7. The first coating machine 5a is provided for applying resin paste P1 to the upper surface of the first carrier film 12 before the carbon fiber mat M is formed. The second coating machine 5b is provided for applying resin paste P2 to the second carrier film 13.

[0045] The lamination machine 6 is located upstream of the impregnation machine 7 and is provided to gradually bring the first carrier film 12 and the second carrier film 13 closer together and laminate them to form a laminate 40.

[0046] The impregnation machine 7 is equipped with two upper and lower belt conveyors to transport the laminate 40 by sandwiching it between the two conveyor belts, and is also equipped with a roll to pressurize the laminate 40 together with the conveyor belts.

[0047] 1.2. Continuous carbon fiber bundle The number of filaments in a continuous carbon fiber bundle C, that is, the number of carbon fiber filaments constituting the continuous carbon fiber bundle C, is preferably in the range of 3K to 100K. Here, K means 1000, so 3K is 3000 and 100K is 100000. The number of filaments in a continuous carbon fiber bundle C may be, for example, 12K, 15K, 20K, 24K, 48K, 50K, 60K, etc. The lower and upper limits of the number of filaments in a continuous carbon fiber bundle C can be arbitrarily combined, for example, 3K to 60K, 3K to 50K, 3K to 48K, 12K to 24K, 12K to 20K, or 15K to 20K. Typically, virgin carbon fiber (virgin CF) is used in the continuous carbon fiber bundle C, but it is not limited to that. The continuous carbon fiber bundle C may be partially split into multiple sub-bundles beforehand.

[0048] 1.3. Carbon Fiber Aggregates Carbon fiber aggregate B is typically a granulated material containing short carbon fibers and an organic binder, but is not limited to this. However, short carbon fibers refer to carbon fibers with a number-average fiber length of 200 mm or less. In carbon fiber aggregate B, the positions of the tips of each short carbon fiber may be uneven. When carbon fiber aggregate B is a granulated material, the positions of the tips of each short carbon fiber are usually uneven.

[0049] The shape of carbon fiber aggregate B may be spindle-shaped, elongated spherical, or strand-shaped. It may have a single shape or a mixture of multiple shapes. Furthermore, carbon fiber aggregate B has a substantially elliptical cross-section. The cross-section of carbon fiber aggregate B refers to the plane at the position with the largest area among the planes perpendicular to the longitudinal direction of carbon fiber aggregate B.

[0050] The number of filaments in carbon fiber aggregate B, i.e., the number of short carbon fibers, is preferably 500 or more on average, more preferably 1K or more, even more preferably 3K or more, preferably 200K or less, more preferably 100K or less, and even more preferably 30K or less. The lower and upper limits of the number of filaments in carbon fiber aggregate B can be arbitrarily combined, for example, 500 to 200K, 1K to 100K, or 3K to 30K.

[0051] The short carbon fibers constituting carbon fiber aggregate B are preferably recycled carbon fibers (recycled CF), but are not limited to them, and virgin CF may also be used. Recycled CF can be recovered, for example, from used CFRP or manufacturing scraps. Methods for recovering recycled CF are broadly classified into thermal decomposition and chemical decomposition, and either method may be used. Recycled CF may be thermally degraded during the recovery process. Recycled CF and virgin CF may be used in combination as the short carbon fibers constituting carbon fiber aggregate B. Virgin CF may be, for example, carbon fibers obtained by unbundling chopped carbon fiber bundles.

[0052] The number-average fiber length of the short carbon fibers constituting carbon fiber aggregate B is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more. If the number-average fiber length of the short carbon fibers is equal to or greater than the lower limit, the shape of carbon fiber aggregate B will be stable. The number-average fiber length of the short carbon fibers is preferably 150 mm or less, more preferably 100 mm or less, and even more preferably 80 mm or less. If the number-average fiber length of the short carbon fibers is equal to or less than the upper limit, entanglement between filaments will be less likely to occur, and the flow of filaments during molded body production will be easier, resulting in good mechanical properties and moldability. The lower and upper limits of the number-average fiber length of the short carbon fibers can be arbitrarily combined, for example, 5 to 150 mm, 10 to 100 mm, 10 to 80 mm, or 15 to 80 mm.

[0053] The fiber diameter of the short carbon fibers constituting the carbon fiber aggregate B is preferably 3 μm or more on a number average, more preferably 5 μm or more, preferably 20 μm or less, and more preferably 10 μm or less. The lower and upper limits of the fiber diameter of the short carbon fibers can be arbitrarily combined, for example, 3 to 20 μm or 5 to 10 μm.

[0054] Short carbon fibers can be obtained, for example, by cutting cotton-like carbon fibers. Cotton-like carbon fibers include, for example, recycled CF obtained by regenerating carbon fibers using a thermal decomposition method, specifically those with a bulk density of 0.01 to 0.40 g / cm³. ３ Recycled CF is preferred. The bulk density of recycled CF is 0.02 g / cm³. ３ The above is more preferable, 0.03 g / cm³ ３ The above is even more preferable, and also 0.25 g / cm³. ３ The following is more preferable: 0.15 g / cm³ ３ The following is even more preferable: The lower and upper limits of the bulk density of recycled CF can be arbitrarily combined, for example, 0.02 to 0.25 g / cm³. ３ , or 0.03-0.15 g / cm³ ３This is acceptable. The bulk density of recycled CF is measured by the following method: Fill a 2L disposable polypropylene cup (opening diameter 15.5cm, depth 18.5cm) with measuring marks with cotton-like recycled CF up to the top of the container without applying external pressure. When the volume readable from the measuring marks on the disposable cup reaches 2L, measure the weight. The measured weight of the recycled CF (in g) is divided into 2000 units (in cm³). ３ The bulk density of recycled CF is taken as the value obtained by dividing by ( ).

[0055] For example, cotton-like carbon fibers can be obtained by completely thermally decomposing sizing agents and matrix resins by dry distillation of resin-free CF tow or fabric scraps, prepreg manufacturing scraps, or used CFRP products at a temperature of preferably 600°C or higher, and then heating them in an oxidizing atmosphere at, for example, 550°C or higher, preferably 600°C or higher. They can also be obtained by regenerating carbon fibers using chemical decomposition methods. Examples include atmospheric pressure dissolution, supercritical fluid method, semiconductor thermal activation method, and electrolytic oxidation method. However, the supercritical fluid method is a method of decomposing the matrix resin using a subcritical or supercritical fluid. Sizing agents and matrix resins must be sufficiently removed in order to obtain cotton-like carbon fibers. Resin residues (residual carbon) that cannot be completely removed by chemical decomposition may be removed by heat treatment in an oxidizing atmosphere. Short carbon fibers can also be obtained, for example, by cutting long carbon fibers in tow shape of different lengths.

[0056] For the short carbon fibers, recycled carbon fiber (CF) containing residual carbon components such as sizing agents and resin residues can also be used. The content of residual carbon components in the recycled CF is preferably 5% by weight or less, and more preferably 3% by weight or less, relative to the total weight of the recycled CF. If the content of residual carbon components is below the above upper limit, the formation of carbon fiber aggregate B becomes easier. Furthermore, the content of residual carbon components is preferably 0.01% by weight or more, and more preferably 0.1% by weight or more. The lower and upper limits of the content of residual carbon components can be arbitrarily combined, for example, 0.01 to 5% by weight, or 0.1 to 3% by weight.

[0057] The organic binder is not particularly limited and includes, for example, resins commonly used for sizing in carbon fiber bundles. Specifically, examples include epoxy resins, unsaturated polyester resins, epoxy acrylate resins, polyurethane resins, and polyamide resins. One type of organic binder may be used alone, or two or more types may be used in combination.

[0058] The content of the organic binder in carbon fiber aggregate B is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and even more preferably 1 part by weight or more, per 100 parts by weight of short carbon fibers. It is preferable that the organic binder content is above the lower limit because it results in good convergence of carbon fiber aggregate B. The organic binder content in carbon fiber aggregate B is preferably 40 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of short carbon fibers. If the organic binder content is below the upper limit, the resin impregnation properties in the production of SMC are good, and the mechanical properties of the resulting CFRP are also excellent. The lower and upper limits of the organic binder content can be arbitrarily combined, for example, 0.1 to 40 parts by weight, 0.5 to 20 parts by weight, or 1 to 10 parts by weight.

[0059] Carbon fiber aggregate B may contain components other than short carbon fibers and organic binders. Examples of other components include resin additives such as stabilizers, release agents, pigments, dyes, UV absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents. These other components may be used individually or in combination of two or more.

[0060] Carbon fiber aggregate B is obtained, for example, by granulating a mixture of short carbon fibers and a binder liquid. The binder liquid can be, for example, a mixture of the above-mentioned organic binder with a liquid such as water. The granulation method of the mixture is not particularly limited; for example, stirring granulation can be employed. It is preferable to dry the obtained carbon fiber aggregate B to evaporate any contained solvents such as water. This allows the organic binder to adhere sufficiently to the carbon fibers, and the shape of the carbon fiber aggregate B can be easily maintained.

[0061] 1.4. Manufacturing Method The manufacturing method of SMC according to one embodiment of the first aspect of the manufacturing method will be explained as follows, using the case where the SMC manufacturing apparatus 100 is used as an example.

[0062] As shown in Figure 1, first, a continuous carbon fiber bundle C is drawn from a pre-prepared fiber package. The continuous carbon fiber bundle C may be drawn outwards from a bobbin package attached to a creel, or it may be drawn inwards from a package from which the bobbin has been removed. Multiple continuous carbon fiber bundles C are aligned parallel to each other and supplied to a chopper 4 from a direction perpendicular to the T direction, where the continuous carbon fiber bundles C are cut to a predetermined length to produce chopped carbon fiber bundles A. The predetermined length is typically in the range of 10 to 80 mm and may be 0.5 inches (approximately 1.3 cm), 1 inch (approximately 2.5 cm), 2 inches (approximately 5.1 cm), etc., but is not limited to these.

[0063] The chopped carbon fiber bundle A falls toward the dispersion section 130 located below the chopper 4 and is dispersed by the first rotating body 17 and the second rotating body 18 as it is deposited onto the first carrier film 12 that travels downwards.

[0064] Furthermore, carbon fiber assemblies B are supplied to the lower part of the first belt conveyor 1 and transported by the first belt conveyor 1 toward the discharge end 1E, which is the end of its upward slope. The steepness of the upward slope limits the amount of carbon fiber assemblies B that reach the discharge end 1E of the first belt conveyor 1 per unit time. Because there is an upper limit to the amount of carbon fiber assemblies B that can reach the discharge end 1E of the first belt conveyor 1, the amount of carbon fiber assemblies B discharged from the discharge end 1E of the first belt conveyor 1 per unit time remains constant. In other words, it becomes possible to supply a fixed amount of carbon fiber assemblies B to the downstream side of the first belt conveyor 1.

[0065] By rotating the optionally positioned scraping roller 2, the variation in the amount of carbon fiber aggregate B reaching the discharge end 1E of the first belt conveyor 1 per unit time can be further reduced. This is because when the height of the carbon fiber aggregate B on the first belt conveyor 1 exceeds the distance between the scraping roller 2 and the first belt conveyor 1, a portion of the carbon fiber aggregate B is scraped off by the scraping roller 2.

[0066] When the belt travel speed v2 of the second belt conveyor 3 is lower than the belt travel speed v1 of the first belt conveyor 1, the variation in the amount of carbon fiber aggregate B transported by the second belt conveyor 3 per unit time may be smaller than the variation in the amount of carbon fiber aggregate B discharged from the first belt conveyor 1 per unit time.

[0067] The carbon fiber aggregate B that falls from the discharge end 1E of the first belt conveyor 1 is transported toward the discharge end 3E by the second belt conveyor 3. The carbon fiber aggregate B falls toward the dispersion section 130 from the discharge end 3E of the second belt conveyor 3 and is dispersed by the first rotating body 17 and the second rotating body 18 as it accumulates on the first carrier film 12 that runs below. The chopped carbon fiber bundles A and carbon fiber aggregate B accumulated on the first carrier film 12 form a carbon fiber mat M on the first carrier film 12.

[0068] As shown in Figure 1, in this example, both the chopped carbon fiber bundle A and the carbon fiber aggregate B are in contact with the first rotating body 17 and the second rotating body 18. This allows the chopped carbon fiber bundle A and the carbon fiber aggregate B to be uniformly dispersed in the M and T directions, respectively, to form a carbon fiber mat M. This results in an SMC with high bulk density, excellent tackiness, and easy handling, as the carbon fibers do not easily adhere to the carrier film when the carrier film is peeled off. Furthermore, by using this SMC, a CFRP with high bending strength and a good appearance can be obtained.

[0069] Rotating both the first rotating body 17 and the second rotating body 18 is advantageous in preventing the chopped carbon fiber bundles A and carbon fiber assemblies B from becoming jammed between these two pin rolls. Preferably, as shown in Figure 3, the first rotating body 17 rotates such that the pins 19b move from top to bottom on the side facing the second rotating body 18, and the second rotating body 18 rotates such that the pins 21b move from top to bottom on the side facing the first rotating body 17.

[0070] One reason for rotating the first rotating body 17 and the second rotating body 18 such that the pins move from top to bottom on the side facing the other rotating body is to avoid applying strong shear forces to the chopped carbon fiber bundles A and carbon fiber aggregates B that pass between these two rotating bodies. Strong shear forces can cause fraying and a decrease in straightness of the carbon fiber bundles. To achieve this objective more effectively, it is preferable to make the peripheral speed at the pin tip equal between the first rotating body 17 and the second rotating body 18.

[0071] In a preferred example, the peripheral speed at the pin tips of the first rotating body 17 and the second rotating body 18 is set so that fiber bundles with fewer than 0.5K filaments are generated as little as possible, and if they are generated, their content in the carbon fiber mat M is less than 1% by weight. For example, if a continuous carbon fiber bundle C is partially split into multiple sub-bundles, and the number of filaments in each sub-bundle is less than 2K, the peripheral speed at the pin tips of the first rotating body 17 and the second rotating body 18 can be set so that fiber bundles with fewer than 0.2K filaments are generated as little as possible, and if they are generated, their content in the carbon fiber mat M is less than 1% by weight.

[0072] The rotational speed of the first rotating body 17 is preferably 100 rpm or more, more preferably 200 rpm or more, and even more preferably 300 rpm or more. If the rotational speed of the first rotating body 17 is above the lower limit, the chopped carbon fiber bundles A are easily loosened appropriately, and the number of filaments in the fiber bundles decreases, making it easier to obtain SMC with high bulk density and a molded article with high bending strength. The rotational speed of the first rotating body 17 is preferably 2000 rpm or less, more preferably 1500 rpm or less, and even more preferably 1200 rpm or less. If the rotational speed of the first rotating body 17 is below the upper limit, it is easier to control the content of chopped carbon fiber bundles A and carbon fiber aggregates B in the thickness direction of the carbon fiber mat M. The lower and upper limits of the rotational speed of the first rotating body 17 can be arbitrarily combined and may be, for example, 100 to 2000 rpm, 200 to 1500 rpm, or 300 to 1200 rpm. The preferred range of rotational speeds for the second rotating body 18 is the same as that for the first rotating body 17.

[0073] In the example shown in Figure 1, chopped carbon fiber bundles A and carbon fiber aggregates B are supplied to the first rotating body 17 and the second rotating body 18 in such a manner that they do not come into contact with each other. More specifically, the second fiber bundle supply unit 120 supplies chopped carbon fiber bundles A to the first rotating body 17 and the second rotating body 18 from directly above, while the first fiber bundle supply unit 110 supplies carbon fiber aggregates B from the side between the second fiber bundle supply unit 120 and the rotating bodies 17 and 18 in the height direction. In this example, the position of the discharge end 3E of the second belt conveyor 3 in the M direction is shifted downstream of the midpoint between the nearest contact points on the circumferences of the two rolls on the straight line connecting the rotation center of the cutter roll 14 and the rotation center of the receiving roll 15, i.e., towards the bonding machine 6. As a result, carbon fiber aggregates B fall downstream of chopped carbon fiber bundles A, and chopped carbon fiber bundles A and carbon fiber aggregates B do not come into contact with each other until they come into contact with the first rotating body 17 and the second rotating body 18.

[0074] As shown in Figure 1, in a preferred example, chopped carbon fiber bundles A and carbon fiber assemblies B are supplied to the first rotating body 17 and the second rotating body 18 from separate routes and brought into contact with the first rotating body 17 and the second rotating body 18. This makes it easy to stably supply chopped carbon fiber bundles A and carbon fiber assemblies B to the first rotating body 17 and the second rotating body 18, respectively. As a result, it becomes easy to uniformly distribute chopped carbon fiber bundles A and carbon fiber assemblies B in the M and T directions to form a carbon fiber mat M. Furthermore, it becomes easy to control the content of chopped carbon fiber bundles A and carbon fiber assemblies B in the carbon fiber mat M.

[0075] Typically, in the M direction, i.e., the direction of travel of the first carrier film 12, the chopped carbon fiber bundles A and carbon fiber aggregates B are brought into contact with the first rotating body 17 and the second rotating body 18 at different positions. By adjusting the respective contact positions of the chopped carbon fiber bundles A and carbon fiber aggregates B with respect to the rotating bodies 17 and 18, the content of chopped carbon fiber bundles A and carbon fiber aggregates B in the thickness direction of the carbon fiber mat M can be controlled.

[0076] In the example shown in Figure 1, the contact position of the chopped carbon fiber bundle A with the rotating bodies 17 and 18 is the position where the rotating bodies 17 and 18 contact a straight line extending vertically downward from the midpoint between the nearest contact points on the circumferences of both rolls, which lies on the straight line connecting the rotation center of the cutter roll 14 and the rotation center of the receiving roll 15 in the chopper 4. For example, the contact position of the chopped carbon fiber bundle A with respect to the first rotating body 17 and the second rotating body 18 can be adjusted by adjusting the position in the M direction of the midpoint between the nearest contact points of the cutter roll 14 and the receiving roll 15 in the chopper 4.

[0077] In the example shown in Figure 1, the contact position of the carbon fiber aggregate B with the rotating bodies 17 and 18 is the position where the rotating bodies 17 and 18 come into contact with a straight line extending vertically downward from the discharge end 3E of the second belt conveyor 3. For example, the contact position of the carbon fiber aggregate B with respect to the first rotating body 17 and the second rotating body 18 can be adjusted by adjusting the position of the discharge end 3E of the second belt conveyor 3 in the M direction.

[0078] In a preferred example, the contact positions of the chopped carbon fiber bundles A and carbon fiber assemblies B with respect to the rotating bodies 17 and 18 are adjusted in the M direction to be within the range from the rotation axis (central axis) of the first rotating body 17 to the rotation axis (central axis) of the second rotating body 18. This makes it easy to control the content of chopped carbon fiber bundles A and carbon fiber assemblies B in the thickness direction of the carbon fiber mat M while uniformly distributing the chopped carbon fiber bundles A and carbon fiber assemblies B in the M and T directions.

[0079] In another preferred example, within the range from the axis of rotation of the first rotating body 17 to the axis of rotation of the second rotating body 18 in the M direction, the contact position of either the chopped carbon fiber bundle A or the carbon fiber aggregate B with the rotating bodies 17 and 18 is set to a position away from the center between the axes of rotation of the rotating bodies 17 and 18, while the other contact position is set to the center between the axes of rotation of the rotating bodies 17 and 18. This makes it easy to make the content of the chopped carbon fiber bundle A and the carbon fiber aggregate B different in the thickness direction of the carbon fiber mat M.

[0080] In one example, as shown in Figures 3 and 7, the contact position of the carbon fiber assembly B with the rotating bodies 17 and 18 can be set to the position of the rotation axis of the second rotating body 18 in the M direction, and the contact position of the chopped carbon fiber bundle A with the rotating bodies 17 and 18 can be set to the center position between the rotation axes of the rotating bodies 17 and 18.

[0081] The closer the contact position of the chopped carbon fiber bundles A with the rotating bodies 17 and 18 is to the rotation axis of the upstream first rotating body 17, the higher the content of the chopped carbon fiber bundles A tends to be in the lower layer of the carbon fiber mat M formed on the first carrier film. On the other hand, within the range from the rotation axis of the first rotating body 17 to the rotation axis of the second rotating body 18 in the M direction, the closer the contact position of the carbon fiber aggregates B is to the rotation axis of the downstream second rotating body 18, and the higher the rotation speed of the second rotating body 18, the higher the content of the carbon fiber aggregates B tends to be in the upper layer of the carbon fiber mat M formed on the first carrier film.

[0082] In another example, as shown in Figure 8A, the contact positions of the chopped carbon fiber bundles A with the rotating bodies 17 and 18, and the contact positions of the carbon fiber assemblies B with the rotating bodies 17 and 18, may both be set downstream of the center between the rotation axes of the rotating bodies 17 and 18 in the M direction, i.e., on the rotation axis side of the second rotating body 18. However, even in this case, adjustments are made so that the falling chopped carbon fiber bundles A and carbon fiber assemblies B do not come into contact with each other until they come into contact with the second rotating body 18.

[0083] In another example, as shown in Figure 8B, both the contact position of the chopped carbon fiber bundle A with the rotating bodies 17 and 18, and the contact position of the carbon fiber assembly B with the rotating bodies 17 and 18, may be set upstream of the center between the rotation axes of the rotating bodies 17 and 18 in the M direction, i.e., on the rotation axis side of the first rotating body 17. However, even in this case, adjustments are made so that the falling chopped carbon fiber bundle A and carbon fiber assembly B do not come into contact with each other until they come into contact with the first rotating body 17.

[0084] In another example, as shown in Figure 8C, the contact position of the chopped carbon fiber bundle A with the rotating bodies 17 and 18 may be the position of the rotation axis of the first rotating body 17, and the contact position of the carbon fiber assembly B with the rotating bodies 17 and 18 may be the position of the rotation axis of the second rotating body 18. In each example, the contact positions of the chopped carbon fiber bundle A and the carbon fiber assembly B can be swapped.

[0085] As shown in the example in Figure 9, if the only rotating body in the dispersion unit 130 is the first rotating body 17, then within the range in which both the chopped carbon fiber bundle A and the carbon fiber aggregate B contact the first rotating body 17, the contact position of either the chopped carbon fiber bundle A or the carbon fiber aggregate B can be set to a position away from the rotation axis of the first rotating body 17, and the other can be set to the position of the rotation axis of the first rotating body 17. Even if the only rotating body in the dispersion unit 130 is the first rotating body 17, adjustments are made so that the falling chopped carbon fiber bundle A and the carbon fiber aggregate B do not come into contact with each other until they come into contact with the first rotating body 17.

[0086] In one example, as shown in Figure 10A, the contact position of the chopped carbon fiber bundle A with respect to the first rotating body 17 may be set to the position of the rotation axis of the first rotating body 17, and the contact position of the carbon fiber assembly B with respect to the first rotating body 17 may be set to a position away from the rotation axis of the first rotating body 17 in the direction of rotation. Similarly, as shown in Figure 10B, when the rotation direction of the first rotating body 17 is reversed, the contact position of the chopped carbon fiber bundle A with respect to the first rotating body 17 may be set to the position of the rotation axis of the first rotating body 17, and the contact position of the carbon fiber assembly B with respect to the first rotating body 17 may be set to a position away from the rotation axis of the first rotating body 17 in the direction of rotation. As shown in Figure 10C, the contact positions of both the chopped carbon fiber bundle A and the carbon fiber assembly B with respect to the first rotating body 17 may be set to contact the first rotating body 17 on both sides of the position of the rotation axis of the first rotating body 17. In each example, the contact positions of the chopped carbon fiber bundle A and the carbon fiber assembly B can be swapped.

[0087] Before depositing the carbon fiber mat M, a resin paste P1 is applied to one side of the first carrier film 12 drawn from the roll using a first coating machine 5a to form a first resin paste layer 31. The resin paste P1 is a thermosetting resin composition, and its base resin is not limited to, but may include, for example, vinyl ester resin (also called epoxy acrylate resin), unsaturated polyester resin, epoxy resin, polyimide resin, maleimide resin, or phenolic resin. A mixed resin of vinyl ester resin and unsaturated polyester resin may also be used as the base resin. The resin paste P1 may contain, as needed, a curing agent, polymerization inhibitor, thickener, reactive diluent, low shrinkage agent, flame retardant, antibacterial agent, etc.

[0088] Using the second coating machine 5b, a resin paste P2 having the same composition as resin paste P1 is applied to one side of the second carrier film 13 to form a second resin paste layer 32. The second carrier film 13 is placed with the side of the second resin paste layer 32 facing downwards, and is then placed on top of the first carrier film 12, which has a carbon fiber mat M on its upper surface. The resulting laminate 40 is then pressurized by the impregnation machine 7, impregnating the carbon fiber mat M with resin pastes P1 and P2, resulting in a resin-impregnated carbon fiber mat. The resin-impregnated carbon fiber mat is wound onto a bobbin while sandwiched between the first carrier film 12 and the second carrier film 13. The resin-impregnated carbon fiber mat wound onto the bobbin is thickened as needed and then shipped as SMC.

[0089] 2. Sheet Molding Compound Another embodiment according to the first aspect of the present invention relates to SMC. The SMC of one embodiment according to the first aspect of the present invention is an SMC containing a matrix resin, chopped carbon fiber bundles A and carbon fiber aggregates B, wherein the content of chopped carbon fiber bundles A differs in the thickness direction of the SMC.

[0090] 2.1. Chopped carbon fiber bundles The shape of a chopped carbon fiber bundle A, when viewed from the thickness direction, is typically a roughly rectangular shape, where the angle between the longitudinal end of the chopped carbon fiber bundle A and the longitudinal direction of the chopped carbon fiber bundle A is 85 to 95°.

[0091] The number of filaments in the chopped carbon fiber bundle A is preferably 500 or more on average, more preferably 1K or more, even more preferably 3K or more, preferably 200K or less, more preferably 100K or less, and even more preferably 50K or less. The lower and upper limits of the number of filaments in the chopped carbon fiber bundle A can be arbitrarily combined and may be, for example, 500 to 200K, 1K to 100K, or 3K to 50K.

[0092] The average thickness of the chopped carbon fiber bundle A is preferably less than 0.3 mm, and may be 0.25 mm or less, or 0.2 mm or less. The average thickness of the chopped carbon fiber bundle A may also be 0.01 mm or more, 0.03 mm or more, or 0.05 mm or more. The lower and upper limits of the average thickness of the chopped carbon fiber bundle A can be any combination, for example, 0.01 mm or more and less than 0.3 mm, 0.03 to 0.25 mm, or 0.05 to 0.2 mm.

[0093] The average length in the longitudinal direction of the chopped carbon fiber bundle A is preferably 10 mm or more, but may be 13 mm or more, 15 mm or more, or 20 mm or more, and preferably 80 mm or less, more preferably 60 mm or less, even more preferably 50 mm or less, and may be 40 mm or less. The lower and upper limits of the average length in the longitudinal direction of the chopped carbon fiber bundle A can be any combination, for example, 10 to 80 mm, 13 to 60 mm, 15 to 50 mm, or 20 to 40 mm.

[0094] The average width of the chopped carbon fiber bundle A is preferably 1.0 mm or more, and may be 1.2 mm or more, 1.5 mm or more, or 2.0 mm or more. It is also preferably 20 mm or less, more preferably 15 mm or less, even more preferably 12 mm or less, and may be 10 mm or less. The lower and upper limits of the average width of the chopped carbon fiber bundle A can be any combination, for example, 1.0 to 20 mm, 1.2 to 15 mm, 1.5 to 12 mm, or 2.0 to 10 mm.

[0095] When τA is defined as the average value of the interfacial shear strength between the matrix resin and the carbon fibers contained in the chopped carbon fiber bundle A, it is preferable that τA = 15 to 230 MPa from the viewpoint of strength as a carbon fiber reinforced composite material. τA can be determined by the microdroplet method. The microdroplet method is carried out as follows: A bisphenol A type epoxy resin is used as the matrix resin, and the epoxy prepolymer and tetraethylenepentamine are mixed in a ratio of [moles of epoxy groups] : [moles of active hydrogen of amine groups] = 1:1. The resulting mixture is attached to filaments uniformly sampled from the chopped carbon fiber bundle A, and resin balls are produced by curing the mixture at 100°C for 2 hours. From the obtained resin balls, those with a length of approximately 40 to 80 μm are set in a metal vise, and a pulping test is performed at a pulping speed of 0.12 mm / min. More than 30 data points are obtained for each sample, and the average value is taken as the interfacial shear strength τA. τA may be 20 MPa or higher, or 30 MPa or higher. Furthermore, τA may be, for example, 200 MPa or less, or 150 MPa or less. The lower and upper limits of τA can be arbitrarily combined, for example, 20 to 200 MPa, or 30 to 150 MPa.

[0096] 2.2. Carbon Fiber Assembly B The shape of the carbon fiber assembly B may be spindle-shaped, elongated spherical, strand-shaped, or a mass-shaped structure in which carbon fibers are irregularly assembled. It may be a single shape or a mixture of multiple shapes. From the viewpoint of stably producing SMC, the shape of the carbon fiber assembly B is usually preferably spindle-shaped, elongated spherical, or strand-shaped (including needle-shaped and wire-shaped). Furthermore, it is preferable that the carbon fiber assembly B has a substantially elliptical cross-section.

[0097] The number of filaments in carbon fiber aggregate B, i.e., the number of short carbon fibers, is preferably 500 or more on average, more preferably 1K or more, even more preferably 3K or more, preferably 200K or less, more preferably 100K or less, and even more preferably 30K or less. The lower and upper limits of the number of filaments in carbon fiber aggregate B can be arbitrarily combined, for example, 500 to 200K, 1K to 100K, or 3K to 30K.

[0098] The average length in the longitudinal direction of the carbon fiber aggregate B is preferably 10 mm or more, but may be 13 mm or more, 15 mm or more, or 20 mm or more, and preferably 80 mm or less, more preferably 70 mm or less, even more preferably 60 mm or less, and may be 50 mm or less. The lower and upper limits of the average length in the longitudinal direction of the carbon fiber aggregate B can be any combination, for example, 10 to 80 mm, 13 to 70 mm, 15 to 60 mm, or 20 to 50 mm.

[0099] The average value of the maximum length (hereinafter also referred to as "maximum width") in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate B is preferably 0.3 mm or more, but may be 0.4 mm or more, or 0.5 mm or more. The average value of the maximum width of the carbon fiber aggregate B may be 4.0 mm or less, 3.0 mm or less, or 2.0 mm or less. The lower and upper limits of the average value of the maximum width of the carbon fiber aggregate B can be arbitrarily combined and may be, for example, 0.3 to 4.0 mm, 0.4 to 3.0 mm, or 0.5 to 2.0 mm.

[0100] When τB is defined as the average interfacial shear strength between the matrix resin and the carbon fibers contained in the carbon fiber aggregate B, it is preferable that τB = 15 to 150 MPa from the viewpoint of strength as a carbon fiber reinforced composite material. τB can be determined in the same way as τA by changing the fiber bundle from which the filaments are sampled in the microdroplet method described above to the carbon fiber aggregate B. τB may be 17 MPa or higher, or 20 MPa or higher. Alternatively, τB may be, for example, 100 MPa or lower, or 80 MPa or lower. The lower and upper limits of τB can be arbitrarily combined, for example, 17 to 100 MPa or 20 to 80 MPa.

[0101] The short carbon fibers constituting carbon fiber aggregate B are as described in "1.3. Carbon Fiber Aggregates" above.

[0102] 2.3. Fiber Content The fiber content of SMC may be 20% to less than 30% by weight, 30% to less than 40% by weight, 40% to less than 50% by weight, 50% to less than 60% by weight, 60% to less than 70% by weight, 70% to less than 80% by weight, or 80% to less than 90% by weight, relative to the total weight of SMC. The higher the fiber content, the better the mechanical properties of the CFRP obtained from SMC. The lower the fiber content, the easier it is to flow during pressure molding, thus increasing the freedom of design in the shape of CFRP products molded from SMC.

[0103] The content of chopped carbon fiber bundles A in SMC is preferably 10% by weight or more, more preferably 15% by weight or more, even more preferably 20% by weight or more, and may be 25% by weight or more, relative to the total fiber weight in SMC, i.e., the total weight of chopped carbon fiber bundles A and carbon fiber aggregate B. If the content of chopped carbon fiber bundles A is above the lower limit, an SMC with high bulk density, excellent tackiness, and excellent handling properties, where carbon fibers do not easily adhere to the carrier film when the carrier film is peeled off, can be obtained. Furthermore, by using the above SMC, a CFRP with high bending strength and good appearance can be obtained. The content of chopped carbon fiber bundles A in SMC is preferably 90% by weight or less, more preferably 80% by weight or less, even more preferably 70% by weight or less, and may be 60% by weight or less, relative to the total fiber weight in SMC. If the content of chopped carbon fiber bundles A is below the upper limit, there is a tendency for the fiber filling properties into fine three-dimensional shapes such as ribs to be higher during pressure molding. Furthermore, the sustainability rate can be improved by increasing the use of recycled carbon fibers. The lower and upper limits of the chopped carbon fiber bundle A content can be arbitrarily combined and may be, for example, 10-90% by weight, 15-80% by weight, 20-70% by weight, or 25-60% by weight.

[0104] The content of chopped carbon fiber bundles A varies in the thickness direction of SMC. For example, when SMC is divided into three equal parts in the thickness direction, and these are designated as the first layer, second layer, and third layer from one side, the difference between the content of chopped carbon fiber bundles A in the first layer and the content of chopped carbon fiber bundles A in the third layer may be 1% by weight or more, 1 to 10% by weight, 10 to 20% by weight, 20 to 35% by weight, 35 to 50% by weight, or 50 to 65% by weight.

[0105] In a preferred example, the proportion of chopped carbon fiber bundles A on either one surface in the thickness direction of the SMC is preferably 25% by weight or more, more preferably 30% by weight or more, even more preferably 35% by weight or more, and also preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less, relative to the total amount of chopped carbon fiber bundles A and carbon fiber aggregates B on that surface. In CFRP obtained using SMC, the bending strength tends to increase as the proportion of chopped carbon fiber bundles A increases; therefore, a surface with a proportion of chopped carbon fiber bundles A of 25% by weight or more is particularly useful as the surface of a member requiring high bending strength. The lower and upper limits of the proportion of chopped carbon fiber bundles A can be arbitrarily combined and may be, for example, 25 to 90% by weight, 30 to 80% by weight, or 35 to 70% by weight. The proportion of chopped carbon fiber bundles A on either one surface of the SMC can be measured by the following method. First, the resin components are removed from the SMC by thermal decomposition or dissolution, and carbon fibers equivalent to one-third of the weight of the resulting carbon fiber mat are evenly recovered from the target surface. Next, chopped carbon fiber bundles A are selected by visual inspection of their shape, and their weight is measured. The proportion of chopped carbon fiber bundles A is calculated from the percentage of all recovered carbon fibers.

[0106] 2.4. Other Physical Properties The basis weight of SMC can be designed as appropriate depending on the application. For example, the basis weight of SMC is 300 g / m². ２ More than 500g / m ２ Less than 500g / m² ２ More than 1000g / m ２ Less than 1000 g / m² ２ More than 2000g / m ２Less than 2000 g / m² ２ More than 4000g / m ２ Less than 4000 g / m² ２ More than 6000g / m ２ Less than 6000 g / m² ２ More than 8000g / m ２ Less than 8000 g / m² ２ More than 10000g / m ２ It may be less than.

[0107] The thickness of the SMC can be designed to be, for example, 0.5 mm or more but less than 1.5 mm, 1.5 mm or more but less than 3 mm, or 3 mm or more but 6 mm or less, but is not limited to these.

[0108] 3. Carbon Fiber Reinforced Composite Material (CFRP) One embodiment according to the first aspect of the present invention relates to a carbon fiber reinforced composite material. The fiber reinforced composite material according to the first aspect of the present invention is an SMC manufactured by the manufacturing method according to the first aspect, or a molded product of an SMC according to the first aspect.

[0109] 4. Method for Manufacturing CFRP One embodiment of the first aspect of the present invention relates to a method for manufacturing CFRP. When manufacturing CFRP products from SMC, press molding is preferably used as the molding method, but is not limited to this. For example, molding methods other than press molding, such as autoclave molding, can also be used. The applications of CFRP products that can be manufactured using SMC according to the first aspect are diverse, including parts used in aircraft, unmanned aerial vehicles, automobiles, ships and various other transportation equipment, as well as sporting goods, leisure goods, etc.

[0110] 5. Sheet Molding Compound One embodiment according to a second aspect of the present invention relates to SMC. The SMC of one embodiment according to a second aspect of the present invention includes at least two types of fiber bundles with different cross-sectional shapes and a matrix resin. The fiber bundles included in the SMC according to the second aspect include a fiber bundle X whose cross-sectional shape at the position with the largest area among the cross-sections perpendicular to the longitudinal direction is substantially rectangular, and a fiber bundle Y whose cross-sectional shape at the position with the largest area among the cross-sections perpendicular to the longitudinal direction is substantially elliptical.

[0111] The roughly rectangular cross-sectional shape of fiber bundle X has a contour with a long side and a short side, and the angle between adjacent sides is 70 to 110°. The contour of the roughly rectangular cross-section of fiber bundle X may have rounded corners. The roughly elliptical cross-sectional shape of fiber bundle Y has a long axis and a short axis, with the length of the short axis being 0.2 mm or more, the contour is composed of an outwardly convex curve, and the overlap rate with a perfect ellipse having the same long axis and short axis is 80% or more.

[0112] The overlap rate is calculated using the following formula: Overlap rate (%) = (SY / S) × 100 where SY is the cross-sectional area (mm²) of the position with the largest area among the cross-sections perpendicular to the longitudinal direction of the fiber bundle Y. ２ ) is the area of ​​the union of the approximately elliptical cross-section of fiber bundle Y and the true ellipse when the approximately elliptical cross-section of fiber bundle Y is superimposed on the true ellipse where the major and minor axes coincide. In other words, S is the sum of the area of ​​the overlapping portion of the approximately elliptical cross-section of fiber bundle Y and the true ellipse, the area of ​​the portion of the approximately elliptical cross-section of fiber bundle Y that does not overlap with the true ellipse, and the area of ​​the portion of the true ellipse that does not overlap with the approximately elliptical cross-section of fiber bundle Y.

[0113] The SMC in one embodiment according to the second aspect includes at least two types of fiber bundles with different cross-sectional shapes, more specifically fiber bundle X and fiber bundle Y, and therefore exhibits good handling when scattering the fiber bundles in "6. Method for Manufacturing Sheet Molding Compound" described later. Furthermore, when press molding the SMC, the flow rate can be appropriately adjusted, the occurrence of defects such as sink marks and voids is suppressed, and a fiber-reinforced composite material with excellent mechanical strength can be obtained.

[0114] 5.1. Critical Fiber Length of Fiber Bundles In one embodiment of the SMC according to the second aspect, the average value LcX of the critical fiber length of fiber bundle X is preferably 4 to 29 mm, and the average value LcY of the critical fiber length of fiber bundle Y is more preferably 11 to 66 mm. This results in an SMC with excellent handling and moldability, and the fiber-reinforced composite material obtained using this SMC exhibits excellent mechanical strength. The methods for calculating LcX and LcY will be described later.

[0115] LcX is preferably 4 mm or more, more preferably 13 mm or more, even more preferably 15 mm or more, and preferably 29 mm or less, more preferably 25 mm or less, and even more preferably 20 mm or less. The lower and upper limits of LcX can be any combination, for example, 4 to 29 mm, 13 to 25 mm, or 15 to 20 mm.

[0116] LcY is preferably 11 mm or more, more preferably 15 mm, even more preferably 19 mm, and preferably 66 mm or less, more preferably 44 mm or less, and even more preferably 33 mm or less. The lower and upper limits of LcY can be any combination, for example, 11 to 66 mm, 15 to 44 mm, or 19 to 33 mm.

[0117] LcX and LcY are values ​​calculated by the following formulas (1) to (3).

[0118]

[0119] In equations (1) to (3), SX is the average value of the cross-sectional area (mm²) of the approximately rectangular cross-section at the position with the largest area among the cross-sections perpendicular to the longitudinal direction of the fiber bundle X. ２ ), SY is the average value of the cross-sectional area (mm²) of the approximately elliptical cross-section at the position with the largest area among the cross-sections perpendicular to the longitudinal direction of the fiber bundle Y. ２ τX is the average value (mm) of the short side length of the approximately rectangular cross section at the position with the largest area among the cross sections perpendicular to the longitudinal direction of fiber bundle X, and b is the average value (mm) of the long side length of the said cross section of fiber bundle X. c is the average value (mm) of the major axis length of the approximately elliptical cross section at the position with the largest area among the cross sections perpendicular to the longitudinal direction of fiber bundle Y, and d is the average value (mm) of the minor axis length of the said cross section of fiber bundle Y. E is the average value (mm) of the outer circumference length of the approximately elliptical cross section at the position with the largest area among the cross sections perpendicular to the longitudinal direction of fiber bundle Y. τX is the average value (MPa) of the interfacial shear strength between the matrix resin and the fibers contained in fiber bundle X, and τY is the average value (MPa) of the interfacial shear strength between the matrix resin and the fibers contained in fiber bundle Y. σ ｆＸ This is the average tensile strength (MPa) of the fibers contained in fiber bundle X, σ ｆＹThis represents the average tensile strength (MPa) of the fibers contained in fiber bundle Y. The method for adjusting LcX is not particularly limited; for example, it can be done by changing a and b. Reducing the difference between a and b tends to increase LcX. Increasing the difference between a and b tends to decrease LcX. The method for adjusting LcY is not particularly limited; for example, it can be done by changing c and d. Reducing the difference between c and d tends to increase LcY. Increasing the difference between c and d tends to decrease LcY.

[0120] SX, a, and b can be determined by the following method: Fix the fiber bundle X with embedding resin, and prepare an observation sample by scraping off the embedded resin together with the fiber bundle X at the position with the largest area among the cross-sections perpendicular to the longitudinal direction. Using a microscope, acquire a cross-sectional image of the fiber bundle X in the observation sample, and measure SX, a, and b by image analysis. Perform the measurement on 30 or more observation samples and calculate the average value. SY, c, d, and E can be determined by the following method: Change the fiber bundle to be sampled to fiber bundle Y, acquire a cross-sectional image in the same way, and measure SY, c, d, and E by image analysis. Perform the measurement on 30 or more observation samples and calculate the average value.

[0121] SX is, for example, 0.01 mm ２ Above, 0.1 mm ２ or greater than 1.0 mm ２ The above is sufficient, and also 40 mm ２ Below, 20mm ２ The following, or 10 mm ２ The following is acceptable: The lower and upper limits of SX can be combined arbitrarily, for example, 0.01 to 40 mm. ２ , 0.1 to 20 mm ２ , or 1.0-10 mm ２ That's fine.

[0122] a may be, for example, 0.01 mm or more, 0.05 mm or more, or 0.1 mm or more, and may also be 2.0 mm or less, 1.5 mm or less, or 1.0 mm or less. The lower and upper limits of a can be any combination, for example, 0.01 to 2.0 mm, 0.05 to 1.5 mm, or 0.1 to 1.0 mm.

[0123] b may be, for example, 1.0 mm or more, 2.0 mm or more, or 3.0 mm or more, and may also be 20 mm or less, 15 mm or less, or 10 mm or less. The lower and upper limits of b can be any combination, for example, 1.0 to 20 mm, 2.0 to 15 mm, or 3.0 to 10 mm.

[0124] SY is, for example, 0.01 mm ２ Above, 0.05 mm ２ or greater than 0.1 mm ２ The above is sufficient, and also 7.0 mm ２ Below, 5.0mm ２ The following, or 3.0 mm ２ The following is acceptable: The lower and upper limits of SY can be combined arbitrarily, for example, 0.01 to 7.0 mm. ２ ,0.05~5.0mm ２ , or 0.1 to 3.0 mm ２ That's fine.

[0125] c may be, for example, 0.01 mm or more, 0.03 mm or more, or 0.05 mm or more, and may also be 5.0 mm or less, 4.0 mm or less, or 3.0 mm or less. The lower and upper limits of c can be any combination, for example, 0.01 to 5.0 mm, 0.03 to 4.0 mm, or 0.05 to 3.0 mm.

[0126] d may be, for example, 0.01 mm or more, 0.03 mm or more, or 0.05 mm or more, and may also be 5.0 mm or less, 4.0 mm or less, or 3.0 mm or less. The lower and upper limits of d can be any combination, for example, 0.01 to 5.0 mm, 0.03 to 4.0 mm, or 0.05 to 3.0 mm.

[0127] E may be, for example, 0.06 mm or more, 0.19 mm or more, or 0.31 mm or more, and may also be 31.42 mm or less, 25.13 mm or less, or 18.85 mm or less. The lower and upper limits of E can be any combination, for example, 0.06 to 31.42 mm, 0.19 to 25.13 mm, or 0.31 to 18.85 mm.

[0128] τX and τY can be determined by the microdroplet method. The microdroplet method is performed as follows: A bisphenol A type epoxy resin is used as the matrix resin, and the epoxy prepolymer and tetraethylenepentamine are mixed in a ratio of [moles of epoxy groups] : [moles of active hydrogen of amine groups] = 1:1. The resulting mixture is attached to filaments sampled uniformly from fiber bundle X, and a resin ball is produced by curing reaction at 100°C for 2 hours. From the obtained resin balls, those with a length of approximately 40 to 80 μm are set in a metal vise, and a pulping test is performed at a pulping speed of 0.12 mm / min. More than 30 data points are obtained for each sample, and the average value is taken as the interfacial shear strength τX. τY can be similarly determined by changing the fiber bundle from which the filaments are sampled to fiber bundle Y.

[0129] τX may be, for example, 15 MPa or more, 20 MPa or more, or 30 MPa or more. Also, τX may be, for example, 230 MPa or less, 200 MPa or less, or 150 MPa or less. The lower and upper limits of τX can be arbitrarily combined, for example, 15 to 230 MPa, 20 to 200 MPa, or 30 to 150 MPa.

[0130] τY may be, for example, 15 MPa or more, 17 MPa or more, or 20 MPa or more. Also, τY may be, for example, 150 MPa or less, 100 MPa or less, or 80 MPa or less. The lower and upper limits of τY can be arbitrarily combined, for example, 15 to 150 MPa, 17 to 100 MPa, or 20 to 80 MPa.

[0131] σ ｆＸ and σ ｆＹThe tensile strength can be determined according to the following procedure based on JIS R7606 (2000). First, filaments are sampled evenly from the fiber bundle X. The sampled filaments are fixed to a test specimen holder using adhesive. The test specimen holder is attached to a tensile testing machine, and the maximum load is measured by tensile testing at a strain rate of 1 to 5 mm / min with 20 samples. The arithmetic mean of the tensile strength calculated from the following formula is σ ｆＸ The formula is: Tensile strength (MPa) = Maximum load (N) / Cross-sectional area of ​​the filament (mm²). ２ However, the cross-sectional area of ​​the filament is calculated by multiplying the mass per unit length of the fiber bundle (g / m) by its density (g / m). ３ This is the value obtained by dividing by ( ) and then by the number of filaments. σ ｆＹ This can be similarly determined by denoting the fiber bundle to be sampled as fiber bundle Y.

[0132] σ ｆＸ For example, it may be 1000 MPa or more, 2000 MPa or more, or 3000 MPa or more, and it may also be 9000 MPa or less, 8000 MPa or less, or 7000 MPa or less. ｆＸ If the value is above the aforementioned lower limit, the tensile strength of the SMC and fiber-reinforced composite material tends to be at a practically sufficient level. ｆＸ If it is below the upper limit, the excessive increase in the value of LcX tends to be suppressed and it can be easily adjusted to the preferred range. ｆＸ The lower and upper limits can be combined in any way, for example, 1000 to 9000 MPa, 2000 to 8000 MPa, or 3000 to 7000 MPa.

[0133] σ ｆＹ For example, it may be 500 MPa or more, 700 MPa or more, or 1000 MPa or more, and it may also be 5000 MPa or less, 4500 MPa or less, or 4000 MPa or less. ｆＹ If the value is above the aforementioned lower limit, the tensile strength of the SMC and fiber-reinforced composite material tends to be at a practically sufficient level. ｆＹ If it is below the upper limit, the excessive increase in the value of LcY tends to be suppressed and it can be easily adjusted to the preferred range. ｆＹThe lower and upper limits can be combined in any way, for example, 500 to 5000 MPa, 700 to 4500 MPa, or 1000 to 4000 MPa.

[0134] 5.2. Fiber Bundle Content The content ratio of fiber bundle X to the total amount of fiber bundles contained in SMC is preferably 20 volume% or more, more preferably 25 volume% or more, and even more preferably 30 volume% or more. If the content ratio of fiber bundle X is above the lower limit, SMC will exhibit better handling properties during manufacturing, and the fiber-reinforced composite material obtained using SMC will tend to have superior mechanical strength. The content ratio of fiber bundle X to the total amount of fiber bundles contained in SMC is preferably 90 volume% or less, more preferably 85 volume% or less, and even more preferably 80 volume% or less. If the content ratio of fiber bundle X is below the upper limit, it will be easier to appropriately adjust the flow rate when press-molding SMC, and the occurrence of defects such as sink marks and voids will tend to be suppressed. The lower and upper limits of the content ratio of fiber bundle X can be arbitrarily combined, for example, 20 to 90 volume%, 25 to 85 volume%, or 30 to 80 volume%.

[0135] The content ratio of fiber bundle Y to the total amount of fiber bundles contained in SMC is preferably 10 volume% or more, more preferably 15 volume% or more, and even more preferably 20 volume% or more. If the content ratio of fiber bundle Y is above the lower limit, it is easier to appropriately adjust the flow rate when press molding SMC, and the occurrence of defects such as sink marks and voids tends to be suppressed. The content ratio of fiber bundle Y to the total amount of fiber bundles contained in SMC is preferably 80 volume% or less, more preferably 75 volume% or less, and even more preferably 70 volume% or less. If the content ratio of fiber bundle Y is below the upper limit, it tends to show better handling properties in the manufacture of SMC. The lower and upper limits of the content ratio of fiber bundle Y can be arbitrarily combined, for example, 10 to 80 volume%, 15 to 75 volume%, or 20 to 70 volume%.

[0136] 5.3. Other Characteristics of Fiber Bundles Examples of fibers constituting a fiber bundle include carbon fibers, glass fibers, and aramid fibers. Among these, carbon fibers are most preferred because they have a low specific gravity and high strength. It is preferable that both fiber bundle X and fiber bundle Y are composed of carbon fibers.

[0137] The carbon fibers may be PAN-based carbon fibers or pitch-based carbon fibers. The carbon fibers may be virgin carbon fibers or recycled carbon fibers recovered from used CFRP or manufacturing scraps. Methods for recovering carbon fibers as recycled carbon fibers are broadly classified into thermal decomposition and chemical decomposition, and either method may be used. The recycled carbon fibers may be thermally degraded during the recovery process.

[0138] The fiber bundle X preferably contains fibers that have not been thermally degraded, typically virgin fibers, more preferably virgin carbon fibers, and even more preferably consists solely of virgin carbon fibers. A preferred example of the fiber bundle X is a chopped carbon fiber bundle in which long continuous carbon fibers are cut to a predetermined length, but is not limited to this.

[0139] The fiber bundle Y preferably contains recycled fibers, more preferably recycled carbon fibers, and even more preferably consists solely of recycled carbon fibers. This improves the use of sustainable materials in SMC and fiber-reinforced composite materials, thereby enhancing social sustainability. Recycled fibers are typically fibers recovered by removing the matrix resin from scraps or waste materials of fiber-reinforced composite materials through thermal or chemical decomposition. The fiber bundle Y may consist solely of virgin carbon fibers, or it may contain both virgin carbon fibers and recycled carbon fibers. The recycled fiber content in the fiber bundle Y is preferably 50% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 100%.

[0140] When LaX is the average length of the fibers contained in the fiber bundle X, LaX is preferably 10 mm or more, more preferably 15 mm or more, and even more preferably 20 mm or more. If LaX is above the lower limit, the handling properties of the SMC improve, and it tends to be easier to obtain a fiber-reinforced composite material with excellent mechanical strength. Furthermore, LaX is preferably 50 mm or less, and more preferably 37.7 mm or less. If LaX is below the upper limit, the moldability of the SMC tends to improve. The lower and upper limits of LaX can be arbitrarily combined, for example, 10 to 50 mm, 15 to 50 mm, or 20 to 37.7 mm.

[0141] When LaY is the average length of the fibers contained in the fiber bundle Y, LaY is preferably 10 to 50 mm. This improves the moldability of SMC and tends to make it easier to obtain fiber-reinforced composite materials with excellent mechanical strength. LaY is more preferably 15 mm or more, even more preferably 20 mm or more, even more preferably 45 mm or less, and even more preferably 40 mm. The lower and upper limits of LaY can be arbitrarily combined, for example, 15 to 45 mm or 20 to 40 mm.

[0142] When L is the average length of the fiber bundle Y in the longitudinal direction, and R is the average maximum length in the direction perpendicular to the longitudinal direction of the fiber bundle Y, L / R is preferably 12 to 48. If L / R is within the above range, it tends to be easier to obtain a fiber-reinforced composite material with excellent mechanical strength without hindering the fluidity when press-molding SMC. L / R is more preferably 14 or more, even more preferably 16 or more, even more preferably 38 or less, and even more preferably 34 or less. The lower and upper limits of L / R can be arbitrarily combined, for example, 14 to 38 or 16 to 34.

[0143] 5.4. Matrix Resin The matrix resin may be a thermosetting resin or a thermoplastic resin. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, and cyanate resins. Examples of thermoplastic resins include polyamide resins, polyacetal resins, polyacrylate resins, polysulfone resins, ABS resins, acrylic resins, polyester resins such as polybutylene terephthalate and polyethylene terephthalate, polyolefin resins such as polyethylene and polypropylene, polyphenylene sulfide, polyether ether ketone, liquid crystal polymers, polyvinyl chloride, fluorine-based resins such as polytetrafluoroethylene, and silicones. These may be used individually or in combination of two or more.

[0144] When a thermosetting resin is used as the matrix resin, it is possible to obtain a material that exhibits tackiness and drape at room temperature when molded, resulting in excellent handling properties. Furthermore, when used as a fiber-reinforced composite material, it is easy to obtain one with excellent mechanical properties. In particular, epoxy resins, unsaturated polyester resins, and vinyl ester resins are suitable as SMCs.

[0145] 5.5. Physical Properties of Sheet Molding Compounds When Vf is the volume content of fiber bundles in the SMC according to the second embodiment, Vf is preferably 60% or less, preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more. If Vf is within the above range, it is easy to achieve both the moldability of the SMC and the mechanical strength of the resulting fiber-reinforced composite material. The lower and upper limits of Vf can be arbitrarily combined, for example, 30-60%, 35-60%, or 40-60%.

[0146] The basis weight of the SMC according to the second embodiment can be appropriately designed depending on the application. For example, the basis weight of the SMC is 300 g / m². ２ More than 500g / m ２ Less than 500g / m² ２ More than 1000g / m ２ Less than 1000 g / m²２ 2000 g / m or more ２ less than 2000 g / m, 2000 g / m ２ 4000 g / m or more and less than 4000 g / m ２ less than 4000 g / m, 4000 g / m ２ 6000 g / m or more and less than 6000 g / m ２ less than 6000 g / m, 6000 g / m ２ 8000 g / m or more and less than 8000 g / m ２ less than, or 8000 g / m ２ 10000 g / m or more and less than 10000 g / m ２ can be less than the above value.

[0147] The thickness of the SMC according to the second aspect can be designed to, for example, 0.5 mm or more and less than 1.5 mm, 1.5 mm or more and less than 3 mm, or 3 mm or more and 5 mm or less, but is not limited thereto.

[0148] 6. Method for Producing Sheet Molding Compound The SMC of one embodiment according to the second aspect can be produced, for example, by a method of producing at least two types of fiber bundles having different cross-sectional shapes and impregnating these fiber bundles with a matrix resin.

[0149] 6.1. Production of Fiber Bundles The at least two types of fiber bundles having different cross-sectional shapes comprise a fiber bundle X having a substantially rectangular cross-section and a fiber bundle Y having a substantially elliptical cross-section. Note that the fiber bundle used for the SMC may further contain fiber bundles other than the fiber bundle X and the fiber bundle Y.

[0150] 6.1.1. Fiber Bundle X A fiber bundle X can be manufactured, for example, by cutting a continuous carbon fiber bundle to a predetermined length. The number of filaments in the continuous carbon fiber bundle is preferably in the range of 3K to 100K. Here, K means 1000, so 3K is 3000 and 100K is 100000. The number of filaments in the continuous carbon fiber bundle may be, for example, 12K, 15K, 20K, 24K, 48K, 50K, 60K, etc. Using a continuous carbon fiber bundle with a large number of filaments tends to increase the difference between a and b in fiber bundle X. Typically, virgin carbon fiber (virgin CF) is used for the continuous carbon fiber bundle, but it is not limited to this. The continuous carbon fiber bundle may also be partially split into multiple sub-bundles beforehand. This tends to reduce the difference between a and b in fiber bundle X. Alternatively, after cutting the continuous carbon fiber bundle to a predetermined length, it may be brought into contact with a rotating body. As a result, the difference between a and b in fiber bundle X tends to decrease.

[0151] The number of filaments in fiber bundle X is preferably 3K to 15K on average. If the number of filaments in fiber bundle X is within the above range, uneven distribution of fiber bundle X is less likely to occur during SMC manufacturing, and it is easier to uniformly distribute fiber bundle X. The number of filaments in fiber bundle X is more preferably 4K or more on average, even more preferably 5K or more, even more preferably 14K or less, and even more preferably 13K or less. The lower and upper limits of the number of filaments in fiber bundle X can be arbitrarily combined, for example, 4K to 14K or 5K to 13K. Note that the number of filaments in fiber bundle X refers to the number of fiber filaments that make up fiber bundle X.

[0152] 6.1.2. Fiber Bundle Y A fiber bundle Y can be produced, for example, by granulating short fibers, typically short carbon fibers, with an organic binder. However, short fibers refer to fibers with a number-average fiber length of 200 mm or less. In a fiber bundle Y, the positions of the tips of each short fiber may be uneven. When a fiber bundle Y is a granulated product, the positions of the tips of each short fiber are usually uneven.

[0153] The shape of the fiber bundle Y may be spindle-shaped, elongated spherical, or strand-shaped. It may be a single shape or a mixture of multiple shapes. The number of filaments in the fiber bundle Y is preferably 3K to 15K on average. If the number of filaments in the fiber bundle Y is within this range, uneven distribution of the fiber bundle Y is less likely to occur during SMC manufacturing, and the fiber bundle Y can be easily dispersed uniformly. The number of filaments in the fiber bundle Y is more preferably 4K or more on average, even more preferably 5K or more, even more preferably 14K or less, and even more preferably 13K or less. The lower and upper limits of the number of filaments in the fiber bundle Y can be arbitrarily combined, for example, 4K to 14K or 5K to 13K. Note that the number of filaments in the fiber bundle Y refers to the number of fiber filaments constituting the fiber bundle Y.

[0154] The short carbon fibers and organic binder that constitute fiber bundle Y are as described in "1.3. Carbon Fiber Assembly" above.

[0155] The fiber bundle Y may contain components other than short fibers and organic binders. Examples of other components include resin additives such as stabilizers, release agents, pigments, dyes, UV absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents. These other components may be used individually or in combination of two or more.

[0156] The fiber bundle Y is obtained, for example, by granulating a mixture of short fibers and a binder liquid. The binder liquid can be, for example, a mixture of the above-mentioned organic binder with a liquid such as water. The granulation method for the mixture is not particularly limited; for example, agitation granulation can be employed. It is preferable to dry the obtained fiber bundle Y to evaporate any contained solvents such as water. This allows the organic binder to adhere sufficiently to the short fibers, easily maintaining the shape of the fiber bundle Y. In granulation, increasing the agitation granulation time or decreasing the weight of the binder liquid relative to the weight of the short fibers tends to reduce the difference between c and d. Conversely, increasing the stirring speed or increasing the weight of the binder liquid relative to the weight of the short fibers tends to increase the difference between c and d.

[0157] 6.2. Impregnation of Matrix Resin SMC can be manufactured, for example, by following the following first to fourth steps: First step: Applying matrix resin to the surfaces of the first protective film and the second protective film. Second step: Depositing fiber bundles having at least two different cross-sections on the matrix resin-coated surface of the first protective film to form a carbon fiber mat. Third step: Laminating the second protective film to the first protective film with the carbon fiber mat in between, so that the matrix resin-coated surfaces face each other, to form a laminate. Fourth step: Impregnating the laminate with matrix resin by pressurizing it to obtain SMC.

[0158] In the first step, the first protective film and the second protective film are synthetic resin films, and their materials can be appropriately selected from polyolefins such as polyethylene and polypropylene, polyvinylidene chloride, vinyl chloride resin, polyamide, etc. The first protective film and the second protective film may also be multilayer films. The specifications of the first protective film and the second protective film may be the same or different. The first protective film and the second protective film may also be carrier films unwound from a roll.

[0159] In the second step, a carbon fiber mat is formed by depositing fiber bundles containing fiber bundles X and fiber bundle Y onto the surface of the first protective film coated with the matrix resin, for example, by scattering. Fiber bundles obtained by mixing fiber bundles X and fiber bundle Y in advance may be scattered, or fiber bundles X and fiber bundle Y may be scattered separately.

[0160] The amount of matrix resin applied to the first and second protective films in the first step, and the basis weight of the carbon fiber mat formed on the first protective film in the second step, are adjusted considering the basis weight and fiber content of the SMC to be manufactured.

[0161] If a thickening agent is added to the matrix resin, the SMC is aged after the fourth step until the viscosity of the matrix resin becomes sufficiently high. For example, after impregnating with the matrix resin, the SMC is kept at room temperature to 60°C for several hours to several tens of days, or at a temperature of 60 to 80°C for several seconds to several tens of minutes.

[0162] 7. Fiber-reinforced composite material One embodiment according to a second aspect of the present invention relates to a fiber-reinforced composite material. The fiber-reinforced composite material according to the second aspect of the present invention is a molded product of SMC according to the second aspect of the present invention and exhibits excellent mechanical strength.

[0163] 8. The fiber-reinforced composite material according to one embodiment of the second aspect of the method for manufacturing fiber-reinforced composite materials can be manufactured by molding the SMC according to one embodiment of the second aspect and curing the matrix resin. When manufacturing the fiber-reinforced composite material from SMC, a press molding method is preferably used, but is not limited to this method. For example, a molding method other than press molding, such as autoclave molding, can also be used.

[0164] An example of a method for manufacturing fiber-reinforced composite materials is described in detail below. For example, one sheet of SMC or multiple sheets of SMC stacked together are set between a pair of molds. The SMC is heated and compressed at 120 to 230°C for 2 to 60 minutes to cure the matrix resin and obtain a molded fiber-reinforced composite material. A honeycomb structure such as corrugated cardboard may be used as the core material, and SMC may be arranged on both sides or one side thereof.

[0165] 9. Experimental Results The results of experiments conducted by the inventors are described below. The present invention is not limited in any way by these experimental results.

[0166] [Average Length and Width of Chopped Carbon Fiber Bundles A] The average length and width of the chopped carbon fiber bundles A in the longitudinal direction were measured as follows: Chopped carbon fiber bundles A were randomly selected and arranged on a white sheet of paper with a metal ruler placed on top, without overlapping. After arranging the chopped carbon fiber bundles A on one side of the white sheet of paper, the sheet was placed on a spotlight and photographed to create an image. The contrast of this image was adjusted using the image processing software "ImageJ," and after image processing, the average length of the chopped carbon fiber bundles A in the longitudinal direction was measured by determining the maximum ferret diameter based on the length of the metal ruler. The average width of the chopped carbon fiber bundles A in the direction perpendicular to the longitudinal direction was determined by drawing parallel lines parallel to the longitudinal direction in the central part of the chopped carbon fiber bundle A, touching the side edges on both sides of that part, and measuring the distance between these parallel lines. The number of chopped carbon fiber bundles A measured was increased by continuing the above photography, image processing, and measurement until the total number of evaluated bundles reached 300 or more.

[0167] [Average Length and Maximum Width of Carbon Fiber Assembly B] The average length and maximum width of carbon fiber assembly B in the longitudinal direction were measured as follows: Carbon fiber assembly B was randomly selected and arranged on a white sheet of paper with a metal ruler placed on it, without overlapping. After arranging carbon fiber assembly B on one side of the white sheet of paper, it was placed on a spotlight and photographed to create an image. This image was processed by adjusting the contrast using the image processing software "ImageJ," and then the average length in the longitudinal direction of carbon fiber assembly B was measured by measuring the maximum ferret diameter based on the length of the metal ruler. In addition, the average maximum length (maximum width) in the direction perpendicular to the longitudinal direction of carbon fiber assembly B was determined by drawing parallel lines parallel to the longitudinal direction, touching the side edges on both sides of the widest part of carbon fiber assembly B, and measuring the distance between these parallel lines. The number of carbon fiber assembly B measured was increased by continuing the above photography, image processing, and measurement until the total number of evaluated units reached 300 or more.

[0168] [Residual Carbon Content] The residual carbon content of the recycled carbon fibers was measured as follows: Recycled carbon fibers were randomly selected and crushed in a mortar. 4 mg of recycled carbon fibers were then subjected to thermogravimetric analysis using a thermogravimetric analyzer (TA Instruments, TGA550) at an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording rate of 1 / 6 s. The analysis consisted of heating from room temperature to 100°C, holding at 100°C for 30 minutes, heating from 100°C to 400°C, and holding at 400°C for 480 minutes. The inflection point of the slope was identified on a graph plotting the weight loss rate against time. The residual carbon content was determined by subtracting the weight loss rate immediately after holding at 100°C from the weight loss rate at that inflection point.

[0169] [Content of Chopped Carbon Fiber Bundles A in Each Layer] For the carbon fiber mat formed in each example, the content of chopped carbon fiber bundles A was measured in the first, second, and third layers when the thickness direction was divided into three equal parts, as follows. However, the third layer is defined as the first carrier film side during manufacturing in SMC. A 10 cm square measurement sample was cut from the center in the width direction of the prepared carbon fiber mat, and its weight was measured. Then, chopped carbon fiber bundles A and carbon fiber aggregates B were evenly collected from the carbon fiber mat using tweezers, amounting to approximately 1 / 3 of the mat's weight, and the first, second, and third layers were separated. Chopped carbon fiber bundles A were visually selected from the separated chopped carbon fiber bundles A and carbon fiber aggregates B based on their shape, and their weight was measured. The proportion of chopped carbon fiber bundles A in the total weight of each layer was calculated and used as the content. Three or more of the aforementioned 10 cm square measurement samples were cut from the longitudinal direction of the carbon fiber mat and measured in the same manner, and the average value was adopted.

[0170] [Bulk Density] For the carbon fiber mat formed in each example, the bulk density of the first, second, and third layers, obtained by dividing the thickness direction into three equal parts, was measured as follows. However, the third layer is defined as the first carrier film side during manufacturing in SMC. Using each layer divided according to the [Content of Chopped Carbon Fiber Bundles A in Each Layer] above, chopped carbon fiber bundles A and carbon fiber aggregates B were dropped into a 2L disposable polypropylene cup with measuring marks (opening diameter 15.5 cm, depth 18.5 cm). The weight was measured when the volume read from the measuring marks on the disposable cup reached 2L. The measured weights of chopped carbon fiber bundles A and carbon fiber aggregates B (unit: g) were measured in a volume of 2000 (unit: cm³). ３ The value obtained by dividing by ) is the loose bulk density (unit: g / cm³). ３ The measurements were taken five times, and the average value was used as the loosened bulk density. When the content of chopped carbon fiber bundles A in each layer was between 0% and 75%, and the volume did not reach 2L, the loosened bulk density was measured when chopped carbon fiber bundles A and carbon fiber aggregates B were mixed in arbitrary proportions, a calibration curve was obtained, and the bulk density was calculated from the content of each layer.

[0171] [Fiber Content] Two sheets of SMC were stacked and press-molded at a temperature of 140°C, a pressure of 8 MPa, and a pressurizing time of 3 minutes to produce a CFRP plate with dimensions of 300 mm in length and width and a thickness of 2 mm. Five test pieces, each 25 mm wide and 120 mm long, were cut from the molded CFRP. The length, width, and thickness of each test piece were measured at three or more points, and the dimensions were obtained from the average values. The density of each test piece was obtained using the Archimedes method. The fiber content of each test piece was calculated from the above dimensions and density, and the average value of the five test pieces was adopted.

[0172] [Bundle Adhesion Amount] As an indicator of the handling ease of SMC, the amount of bundles (carbon fiber bundles) adhering to the SMC was measured as follows. After cutting the prepared SMC into a square with sides of 250 mm, the polyethylene film on both surfaces was peeled off and their weights were measured. The amount of bundles adhering to a 250 mm square polyethylene film (g) was calculated by subtracting the weight of two 250 mm square polyethylene films from the measured weights.

[0173] [Drape Evaluation] The fabricated SMC was cut into 60 mm x 250 mm strips, and the polyethylene film was removed. The SMC was then moved out of the plane from the edge of a horizontal surface at a height of 300 mm or more at a speed of 10 mm / second or less along the longitudinal direction of the SMC. The presence or absence of breakage due to the weight of the portion of the SMC that moved out of the plane was checked. If the SMC did not break even after being moved 24 cm out of the plane, it was evaluated as "A", and if it broke, it was evaluated as "B".

[0174] [Tackiness] The tackiness of SMC was evaluated according to the following criteria: A: When SMC was touched by hand, it had a moderate tackiness, making lamination work easy. B: When SMC was touched by hand, the tackiness was somewhat weak, but lamination work was still possible. C: When SMC was touched by hand, the tackiness was very weak, making lamination work impossible.

[0175] [Sustainability Rate] The carbon fiber aggregate B was calculated from the content of chopped carbon fiber bundles A in each layer, and the content of carbon fiber aggregate B was obtained. The sustainability rate was calculated as the ratio of recycled carbon fibers contained in carbon fiber aggregate B to the total weight of SMC.

[0176] [Bending Properties of CFRP] Two sheets of SMC were stacked and press-molded at a temperature of 140°C, a pressure of 8 MPa, and a pressurizing time of 3 minutes to produce a plate-shaped CFRP with dimensions of 300 mm in length and width and a thickness of 2 mm. Five test pieces, 25 mm wide and 120 mm long, were cut from the molded CFRP. A three-point bending test was performed on each test piece using a universal testing machine (Instron 4465) under the conditions of crosshead speed: 5 mm / min, span distance: 32 mm, nose radius R5, and support radius R3.2 to measure bending strength and bending modulus. The mean and standard deviation were obtained from the measurement results of the five test pieces. The CV value was calculated by dividing the obtained standard deviation by the mean. Bending strength and flexural modulus were measured when the CFRP was bent towards the surface side (second carrier film side, upper side when forming the carbon fiber mat) and when it was bent towards the back side (first carrier film side, lower side when forming the carbon fiber mat). In Table 2, the bending strength and flexural modulus when the CFRP was bent towards the surface side are shown in the "Surface Bending" column, and the bending strength and flexural modulus when the CFRP was bent towards the back side are shown in the "Back Bending" column.

[0177] [Appearance of CFRP] Two sheets of SMC were stacked and press-molded at a temperature of 140°C, a pressure of 8 MPa, and a pressurizing time of 3 minutes to produce a plate-shaped CFRP with dimensions of 30 cm in length and width and a thickness of 2 mm. The surface of the obtained CFRP was evaluated as "A" if it was smooth with no voids or bulges, and as "B" if voids or bulges were present.

[0178] [Moldability] When molding CFRP with a rib shape of approximately 2 mm, if the rib shape is filled with fibers and the surface near the rib is smooth, it is evaluated as "A", and if sink marks or dents occur near the rib shape, it is evaluated as "B".

[0179] [Uniformity] In the measurement of the bending properties of CFRP described above, a value of CV for bending strength when bent toward the surface is 20% or less, and a value of CV for bending modulus is 15% or less was evaluated as "A", and all other cases were evaluated as "B".

[0180] [Example 1] (1) Preparation of continuous carbon fiber bundle C A flat continuous carbon fiber bundle (TR50S15L manufactured by Mitsubishi Chemical Corporation) with 15K filaments, an average width of 7.5 mm, and an average bundle thickness of 0.14 mm was prepared as the continuous carbon fiber bundle C.

[0181] (2) Preparation of carbon fiber aggregate B As short carbon fibers, discontinuous recycled carbon fibers with a residual carbon content of 1.6 wt% were prepared by cutting them at 12 mm intervals in the longitudinal and transverse directions on a plane using a guillotine cutter. As an organic binder, a binder solution was prepared by mixing a water-based urethane resin with water and mixed with the short carbon fibers. A rolling granulator was used to mix the short carbon fibers and the binder solution. A 75 L incentive mixer (manufactured by Nippon Eirich Co., Ltd.) was used as the rolling granulator, and first the binder solution was added while mixing for 1 minute at a rotor speed of 150 rpm and a pan speed of 49 rpm. Subsequently, granulation was performed for 2.5 minutes at a rotor speed of 850 rpm and a pan speed of 49 rpm. Then, carbon fiber aggregate B was obtained by drying at 110°C for 3 hours using a vertical dryer, with an average length of 21.5 mm in the longitudinal direction of the fiber bundles and an average maximum width of 1.4 mm.

[0182] (3) SMC was manufactured using the continuous carbon fiber bundle C and carbon fiber aggregate B prepared for SMC production, with the SMC manufacturing apparatus 100 illustrated in Figure 1. As resin pastes P1 and P2, liquid thermosetting resin compositions containing vinyl ester resin, unsaturated polyester resin, styrene, polyisocyanate, and a radical polymerization initiator were used. In the chopper 4, the continuous carbon fiber bundle C was cut to a chopped carbon fiber bundle A with an average length of 25.4 mm in the longitudinal direction. The contact position of the carbon fiber aggregate B with the rotating bodies 17 and 18 was the position of the rotation axis of the second rotating body 18 in the M direction, and the contact position of the chopped carbon fiber bundle A with the rotating bodies 17 and 18 was the position of the center between the rotation axes of the rotating bodies 17 and 18. The first rotating body 17 and the second rotating body 18 were rotated so that the pins moved from top to bottom on the side facing the other rotating body, with a rotation speed of 300 rpm.

[0183] [Examples 2 and 3] SMC was manufactured in the same manner as in Example 1, except that the average length in the longitudinal direction, average bundle thickness, and average width of the chopped carbon fiber bundle A, the average length in the longitudinal direction, and the average maximum width of the carbon fiber assembly B were changed as shown in Table 1, and the rotational speeds of the first rotating body 17 and the second rotating body 18 were changed as shown in Table 1.

[0184] [Comparative Example 1] Instead of using chopped carbon fiber bundle A, only carbon fiber aggregate B with the average longitudinal length and average maximum width shown in Table 1 was used, and an SMC manufacturing apparatus similar to the SMC manufacturing apparatus 100 was used, except that it did not have a second fiber bundle supply unit, and SMC was manufactured in the same manner as in Example 1.

[0185] [Comparative Example 2] Using only continuous carbon fiber bundles C without using carbon fiber aggregate B, and with the average length, average bundle thickness, and average width of the chopped carbon fiber bundles A as shown in Table 1, an SMC manufacturing apparatus similar to that of the SMC manufacturing apparatus 100 was used, except that it lacked a second fiber bundle supply unit and a rotating body, and SMC was manufactured in the same manner as in Example 1.

[0186] [Comparative Example 3] The average length, average bundle thickness, and average width of the chopped carbon fiber bundle A were as shown in Table 1. 1 kg of the chopped carbon fiber bundle A and 1 kg of carbon fiber aggregate B, which had the average length and maximum width as shown in Table 1, were placed in a 30 L plastic bag, filled with air, sealed, and mixed by shaking up and down and left and right for 3 minutes. The same process was repeated 5 times to obtain 10 kg of mixture. Using the obtained mixture of chopped carbon fiber bundle A and carbon fiber aggregate B, SMC was manufactured using the SMC manufacturing apparatus 100 illustrated in Figure 1. The resin pastes P1 and P2 were the same as in Example 1. The mixture of chopped carbon fiber bundle A and carbon fiber aggregate B was supplied from the first fiber bundle supply unit 110, and the contact position of the mixture with the rotating bodies 17 and 18 was the position of the rotation axis of the second rotating body 18 in the M direction. The first rotating body 17 and the second rotating body 18 were each rotated so that the pins moved from top to bottom on the side facing the other rotating body, and the rotational speed was set to 900 rpm.

[0187] The results of the measurements and evaluations of the SMC obtained in each example and the CFRP molded using SMC are shown in Tables 1 and 2.

[0188]

[0189]

[0190] As shown in Tables 1 and 2, in Examples 1 to 3, where a carbon fiber mat was formed by contacting chopped carbon fiber bundles A and carbon fiber aggregates B with a rotating body, the SMC had excellent handling properties, the CFRP had high bending strength, good appearance, and excellent moldability. In addition, the CV values ​​of bending strength and flexural modulus were small, and the uniformity was excellent. On the other hand, in Comparative Example 1, where a carbon fiber mat was formed using only carbon fiber aggregates B, the SMC was poorly handled, the CFRP had low bending strength, and the appearance was poor. In Comparative Example 2, where a carbon fiber mat was formed using only chopped carbon fiber bundles A, the sustainability rate was low and the moldability was insufficient. In Comparative Example 3, where a carbon fiber mat was formed by contacting a mixture of chopped carbon fiber bundles A and carbon fiber aggregates B with a rotating body, the CV values ​​of bending strength and flexural modulus were large, and the uniformity was insufficient.

[0191] <Raw Materials> As short carbon fibers constituting fiber bundle Y, fibers Y1 to Y3 manufactured by the following procedure were used. ・Fiber Y1: SMC containing a chopped carbon fiber bundle with 15K filaments and a fiber length of 25.4 mm was prepared, heated at 700°C for 0.5 hours under a nitrogen gas atmosphere, and then further heat-treated at 600°C for 1 hour under an oxygen gas-containing atmosphere to thermally decompose the matrix resin. The resulting cotton-like carbon fibers (length 25.4 mm) were designated as fiber Y1. ・Fiber Y2: The cotton-like carbon fibers obtained by cutting fiber Y1 to a length of 15 mm were designated as fiber Y2. ・Fiber Y3: SMC containing a chopped carbon fiber bundle with 15K filaments and a fiber length of 50 mm was prepared, heated at 700°C for 0.5 hours under a nitrogen gas atmosphere, and then further heat-treated at 600°C for 2 hours under an oxygen gas-containing atmosphere to thermally decompose the matrix resin. The resulting cotton-like carbon fibers (length 50 mm) were designated as fiber Y3. Fiber Y4: Fiber Y4 was obtained by cutting fiber Y3 to a length of 15 mm and obtaining cotton-like carbon fibers.

[0192] <Evaluation of SMC Handling Ease> The fabricated SMC was cut into strips measuring 60 mm x 250 mm, and the polyethylene film was removed to obtain evaluation SMCs. The evaluation SMCs were moved out of the plane from the edge of a horizontal surface at a height of 300 mm or more at a speed of 10 mm / second or less in the longitudinal direction of the evaluation SMC. Then, it was checked whether the portion of the evaluation SMC that moved out of the plane broke due to its own weight. If the evaluation SMC did not break even after being moved 24 cm out of the plane, it was evaluated as "A (good)", and if it broke, it was evaluated as "B (poor)".

[0193] <Evaluation of SMC moldability> Using the fabricated SMC, CFRP with a rib shape of approximately 2 mm was molded. At this time, if the fibers were filled into the rib shape and the surface near the rib shape was smooth, it was evaluated as "A (good)", and if sink marks or dents occurred near the rib shape, it was evaluated as "B (poor)".

[0194] <Evaluation of Mechanical Strength of Fiber-Reinforced Composite Materials> The tensile strength σc was evaluated as the mechanical strength of fiber-reinforced composite materials. The tensile strength σc was calculated from the following equations (4) to (7) based on a modified formula of the Kelly model (Rak-Sam Choi, Kiyoshi Takahashi, Journal of the Japan Society for Composite Materials, 17, 5, 213-218 (1991)).

[0195] - If LaX ≤ LcX and LaY ≤ LcY:

[0196]

[0197] - If LcX < LaX and LcY < LaY:

[0198]

[0199] - If LaX ≤ LcX and LcY < LaY:

[0200]

[0201] - If LcX < LaX and LaY ≤ LcY:

[0202]

[0203] However, LaX represents the average length (mm) of the fibers contained in fiber bundle X, and LaY represents the average length (mm) of the fibers contained in fiber bundle Y. LcX and LcY represent the values ​​calculated by equations (1) and (2) above, respectively. σ ｆＸ This is the average tensile strength (MPa) of the fibers contained in fiber bundle X, σ ｆＹ VfX represents the average tensile strength (MPa) of the fibers contained in fiber bundle Y. VfX represents the volume content of fiber bundle X in SMC, VfY represents the volume content of fiber bundle Y in SMC, and Vf represents the volume content of fiber bundles in SMC. σ ｍ This is the tensile strength of the matrix resin.

[0204] [Examples 1a-2a, 5a] (Production of fiber bundles) A ​​continuous carbon fiber bundle with 15K filaments (TR50S15L, manufactured by Mitsubishi Chemical Corporation) was cut to a length of 25.4 mm using a chopper to obtain a fiber bundle X having a roughly rectangular cross-section (angle between adjacent sides: 102°). LaX, SX, a, b, τX, σ of the obtained fiber bundle X. ｆＸand LcX are shown in Table 3. Further, as the organic binder-containing liquid, Fine Surf NDB-800 (manufactured by Aoki Oil Industrial Co., Ltd.) was added as an additive in an amount of 0.2% by weight to an aqueous dispersion prepared by adjusting the solid content of Hydran N320 (manufactured by DIC Corporation) to 6 parts by weight based on 100 parts by weight of recycled CF, thereby preparing the organic binder-containing liquid. Using a 25 L SP Granulator (manufactured by Dalton Co., Ltd.) as a stirring granulator, 600 g of the short carbon fibers shown in Table 3 and 270 g of the organic binder-containing liquid were mixed and granulated. More specifically, the organic binder-containing liquid was charged into the stirring granulator at an injection pressure of 0.1 to 0.4 MPa using a pressure spray bottle, while the short carbon fibers were mixed for 1 minute at an agitator rotation speed of 118 rpm and a chopper rotation speed of 1500 rpm. Subsequently, mixing was further performed for 5 minutes at an agitator rotation speed of 470 rpm and a chopper rotation speed of 3000 rpm. The same operation was repeated 10 times to obtain 870 g of a granulated product. Next, the granulated product was dried at 120°C using a vertical dryer to obtain a fiber bundle Y having a substantially elliptical cross-section (overlap ratio to a true ellipse: 94%). The number-average number of filaments in the fiber bundle Y was 3.1 K. LaY, SY, c, d, E, τY, σ of the obtained fiber bundle Y ｆＹ and LcY are shown in Table 3. The obtained fiber bundle X and fiber bundle Y were mixed at the fiber content shown in Table 4 to obtain a fiber bundle.

[0205] (Impregnation with matrix resin) A resin paste containing vinyl ester resin, unsaturated polyester resin, styrene, polyisocyanate, and a radical polymerization initiator as the matrix resin was applied to one side of each of two polyethylene films A and B. Next, a fiber bundle mixed with fiber bundles X and Y was scattered on another polyethylene film C to form a carbon fiber mat. Then, polyethylene film A, with the resin paste applied to one side, was placed on top of the carbon fiber mat with the resin paste side facing downwards. Then, the polyethylene film was inverted so that polyethylene film C was on top and polyethylene film A was on the bottom. Subsequently, polyethylene film C was removed, and polyethylene film B, with the resin paste applied to one side, was placed on top of the carbon fiber mat with the resin paste side facing downwards. This resulted in a laminate in which the two polyethylene films A and B, with the resin paste applied, were bonded together with the carbon fiber mat in between, so that the resin paste sides faced each other. Next, the carbon fiber mat was impregnated with the resin paste by applying pressure to this laminate using a roll. Afterward, the resin paste was left at 23°C for 7 days to thicken, resulting in a basis weight of 2000 g / m². ２ SMC was obtained. The Vf of the obtained SMC is shown in Table 4. The results of the evaluation of the handling properties and moldability of the obtained SMC, and the results of the evaluation of the tensile strength of the fiber-reinforced composite material are shown in Table 4.

[0206] [Examples 3a to 4a] τX, σ shown in Table 3 ｆＸ SMC was obtained in the same manner as in Example 1a, except that a fiber bundle X having LcX was used. The Vf of the obtained SMC is shown in Table 4. The results of evaluating the tensile strength of the fiber-reinforced composite material are also shown in Table 4.

[0207] [Comparative Example 1a] Fiber bundle X was obtained in the same manner as in Example 1a. LaX, SX, a, b, τX, σ of the obtained fiber bundle X ｆＸTable 3 shows the values ​​of LcX. SMC was obtained in the same manner as in Example 1a, except that only the obtained fiber bundle X was used as the fiber bundle. Table 4 shows the Vf of the obtained SMC. Table 4 shows the results of the evaluation of the handling properties and moldability of the obtained SMC, and the results of the evaluation of the tensile strength of the fiber-reinforced composite material.

[0208] [Comparative Example 2a] Fiber bundle Y was obtained in the same manner as in Example 1a. LaY, SY, c, d, E, τY, σ of the fiber bundle Y ｆＹ Table 3 shows LcY. SMC was obtained in the same manner as in Example 1a, except that only the obtained fiber bundle Y was used as the fiber bundle. Table 4 shows the Vf of the SMC. Table 4 shows the results of the evaluation of the handling properties and moldability of the obtained SMC, and the results of the evaluation of the tensile strength of the fiber-reinforced composite material.

[0209]

[0210]

[0211] As shown in Tables 3 and 4, Examples 1a to 5a, which used fiber bundles containing fiber bundles X and Y, yielded SMC with excellent handling and moldability. On the other hand, Comparative Example 1a, which used only fiber bundle X, had poor moldability, and Comparative Example 2a, which used only fiber bundle Y, had poor handling.

[0212] 100 SMC manufacturing equipment 110 First fiber bundle supply unit 120 Second fiber bundle supply unit 130 Dispersion unit 140 Impregnation unit 1 First belt conveyor 2 Scraping roller 3 Second belt conveyor 4 Chopper 5a First coating machine 5b Second coating machine 6 Lamination machine 7 Impregnation machine 11 Conveyor belt 12 First carrier film 13 Second carrier film 14 Cutter roll 15 Receiving roll 16 Guide roll 17 First rotating body 18 Second rotating body 19 Roll body 19a Cylinder 19b Pin 20 Shaft 21 Roll body 21a Cylinder 21b Pin 31 First resin paste layer 32 Second resin paste layer 40 Laminate A Chopped carbon fiber bundle B Carbon fiber aggregate C Continuous carbon fiber bundle

Claims

1. A method for manufacturing a sheet molding compound, comprising depositing chopped carbon fiber bundles and carbon fiber assemblies excluding the chopped carbon fiber bundles onto a carrier film that runs below a rotating body having a substantially horizontal axis of rotation in a direction perpendicular to the axis of rotation of the rotating body to form a carbon fiber mat, wherein the chopped carbon fiber bundles and the carbon fiber assemblies are supplied separately to the rotating body in such a manner that they do not come into contact with each other.

2. The method for manufacturing a sheet molding compound according to claim 1, wherein the chopped carbon fiber bundle and the carbon fiber aggregate are supplied to the rotating body from separate paths and brought into contact with the rotating body.

3. The method for manufacturing a sheet molding compound according to claim 1, wherein, in the direction of travel of the carrier film, the chopped carbon fiber bundle and the carbon fiber aggregate are in contact with the rotating body at different positions.

4. The method for manufacturing a sheet molding compound according to claim 3, wherein the rotating bodies consist of a first rotating body and a second rotating body arranged such that their respective axes of rotation are parallel to each other, and either the chopped carbon fiber bundle or the carbon fiber assembly falls into contact with the first rotating body and the second rotating body at a position away from the center between the axes of rotation of the first rotating body and the second rotating body in the direction of travel of the carrier film.

5. The method for manufacturing a sheet molding compound according to claim 4, wherein the first rotating body is rotationally driven to move from top to bottom on the side facing the second rotating body, and the second rotating body is rotationally driven to move from top to bottom on the side facing the first rotating body.

6. The method for manufacturing a sheet molding compound according to claim 3, wherein there is one rotating body, and either the chopped carbon fiber bundle or the carbon fiber aggregate falls to a position away from the axis of rotation in the traveling direction on the carrier film and contacts the rotating body.

7. The method for manufacturing a sheet molding compound according to claim 1, wherein the rotating body has a roll body having n rotational symmetry about the axis of rotation (where n is a finite integer of 1 or more).

8. The method for manufacturing a sheet molding compound according to claim 1, wherein the rotational speed of the rotating body is 100 rpm or more.

9. The method for manufacturing a sheet molding compound according to claim 1, wherein the rotational speed of the rotating body is 2000 rpm or less.

10. The method for manufacturing a sheet molding compound according to claim 1, wherein the average bundle thickness of the chopped carbon fiber bundles is less than 0.3 mm, and the average maximum length in the direction perpendicular to the longitudinal direction of the carbon fiber assembly is 0.3 mm or more.

11. The method for producing a sheet molding compound according to claim 1, wherein the carbon fiber aggregate includes recycled carbon fibers.

12. The carbon fiber aggregate has a bulk density of 0.01 to 0.40 g / cm³. ３ A method for producing the sheet molding compound according to claim 1, which is manufactured from recycled carbon fiber.

13. A sheet molding compound comprising a matrix resin, chopped carbon fiber bundles, and a carbon fiber aggregate excluding the chopped carbon fiber bundles, wherein the content of the chopped carbon fiber bundles differs in the thickness direction of the sheet molding compound.

14. The sheet molding compound according to claim 13, wherein when the sheet molding compound is divided into three equal parts in the thickness direction and the layers are designated as a first layer, a second layer, and a third layer from one side, the difference between the content of the chopped carbon fiber bundles in the first layer and the content of the chopped carbon fiber bundles in the third layer is 1% by weight or more.

15. The sheet molding compound according to claim 13, wherein the proportion of the chopped carbon fiber bundles on either one surface in the thickness direction of the sheet molding compound is 25% by weight or more relative to the total amount of the chopped carbon fiber bundles and the carbon fiber aggregates on that surface.

16. The sheet molding compound according to claim 13, wherein the average bundle thickness of the chopped carbon fiber bundles is less than 0.3 mm, and the average maximum length in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate is 0.3 mm or more.

17. The sheet molding compound according to claim 13, wherein the length of the chopped carbon fiber bundles in the longitudinal direction has less variation than the length of the carbon fiber aggregate in the longitudinal direction.

18. The sheet molding compound according to claim 13, wherein the content of the chopped carbon fiber bundle in the sheet molding compound is 10 to 90% by weight with respect to the total fiber weight in the sheet molding compound.

19. The sheet molding compound according to claim 13, wherein the average length in the longitudinal direction of the chopped carbon fiber bundle is 10 to 80 mm and the average width is 1.0 mm or more.

20. The sheet molding compound according to claim 13, wherein the shape of the chopped carbon fiber bundle when viewed from the thickness direction is a substantially rectangular shape in which the angle between the longitudinal end of the chopped carbon fiber bundle and the longitudinal direction of the chopped carbon fiber bundle is 85 to 95°.

21. The sheet molding compound according to claim 13, wherein the average length in the longitudinal direction of the carbon fiber aggregate is 10 to 80 mm, and the average of the maximum lengths in the direction perpendicular to the longitudinal direction of the carbon fiber aggregate is 0.3 mm or more.

22. The sheet molding compound according to claim 13, wherein the shape of the carbon fiber aggregate is spindle-shaped, elongated spherical, or strand-shaped.

23. The sheet molding compound according to claim 13, wherein the carbon fiber aggregate contains recycled carbon fibers with a residual carbon component of 5% by weight or less.

24. The sheet molding compound according to claim 13, wherein the carbon fiber aggregate comprises an organic binder.

25. The sheet molding compound according to claim 13, wherein when τA is the average value of the interfacial shear strength between the matrix resin and the carbon fibers contained in the chopped carbon fiber bundle, τA = 15 to 230 MPa.

26. The sheet molding compound according to claim 13, wherein when the average value of the interfacial shear strength between the matrix resin and the carbon fibers contained in the carbon fiber aggregate is denoted as τB, τB = 15 to 150 MPa.

27. A carbon fiber reinforced composite material which is a sheet molding compound manufactured by the method described in any one of claims 1 to 12, or a molded product of the sheet molding compound described in any one of claims 13 to 26.

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