Method for manufacturing fiber assembly and method for manufacturing prepreg sheet

Abstract

To provide a fiber assembly having high bulk density in which fibers are uniformly aligned while maintaining a length without cutting off fibers.SOLUTION: A fiber assembly that is made of a plurality of carbon fibers and a fiber bundle containing resin or solvent, and has the bulk density of 0.3 g / cm3 or more, where the fiber bundle includes a fiber bundle W1, the fiber bundle W1 is in an oval shape, fibers present on the surface of the fiber bundle are oriented along an oval outline in a bent manner, the average fiber length of fibers in the fiber bundle is 2 to 12 mm, and A' / A specified by the following condition (1) is 0.75 to 0.93. Condition (1): an image, which is obtained by imaging from a vertical direction on the opposite side of the plate by using a fiber bundle placed on a white plate as a reference, is binarized by using an image analysis software to obtain a binary image. An outline is extracted from the binary image to obtain an outline of the fiber bundle. Feret's diameter is calculated from the obtained outline to use the diameter as a long axis length A. The long axis length of an oval obtained by elliptically approximating the binary image is A'.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a fiber assembly and a method for producing a prepreg sheet. [Background technology]

[0002] Carbon fibers have been used in a variety of applications as an industrially important material by mixing and dispersing them in matrices such as resins to improve mechanical and electrical properties such as high strength, high rigidity, low specific gravity, high electrical conductivity, and high abrasion resistance.

[0003] In general, when carbon fibers are mixed and dispersed in various resins to obtain a fiber-reinforced resin composition, a carbon fiber aggregate obtained by granulating a plurality of carbon fibers in advance with a sizing agent or the like is used in order to facilitate handling of the carbon fibers and improve workability in the mixing and dispersion process.

[0004] The carbon fiber aggregate is required to have excellent workability when producing a fiber-reinforced resin composition, stable supplyability through a feeder, excellent fiber dispersion in the matrix, and excellent effects of improving the physical properties of the resulting resin composition.

[0005] As carbon fiber aggregates that satisfy such required characteristics, there have been disclosed carbon fiber aggregates having a specified average particle size and surface-coated with an emulsion-based sizing agent mainly composed of an epoxy compound, and carbon fiber chopped strands that are bundled with a specified sizing agent, have a specified density, and have a circular or elliptical cross section (e.g., Patent Document 1).

[0006] Furthermore, as a carbon fiber aggregate that can be quantitatively and stably supplied to an extruder or the like from recycled carbon fibers using a feeder and that can easily and uniformly disperse the carbon fibers in a resin matrix using an extruder or the like, a carbon fiber aggregate that is made of carbon fibers and an epoxy resin-based sizing agent and has a predetermined bulk density, etc., and is produced by a wet extrusion granulation method has been disclosed (for example, Patent Document 2).

[0007] In addition, as a method for efficiently producing an entangled body made of short carbon fibers, a method for producing a carbon fiber entangled body by an agitation granulation method in which curved carbon fibers and flexible spheres are agitated together has been disclosed (for example, Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Unexamined Patent Publication No. 4-170435 [Patent Document 2] JP 2020-196882 A [Patent Document 3] JP 2000-220066 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for producing a fiber assembly capable of producing a fiber assembly having a high bulk density in which the fibers are aligned while maintaining their length, without cutting the fibers. Another object of the present invention is to provide a method for producing a prepreg sheet using this fiber assembly. [Means for solving the problem]

[0010] The present inventors have found that the above problems can be solved by using a stirring tank to stir and granulate fibers and a fiber treating agent.

[0011] That is, the present invention includes the following aspects [1] to

[45] . The following aspects [1] to

[45] may be referred to as the "first aspect of the present invention".

[0012] [1] A method for producing a fiber aggregate, comprising: putting a plurality of fibers and a fiber treatment agent into a stirring tank; stirring and granulating the mixture of the fibers and the fiber treatment agent with a stirring blade; wherein the fibers include carbon fibers, and the fibers are granulated so as to be aligned. [2] The method for producing a fiber aggregate described in [1], wherein the plurality of dried, cotton-like fibers are put into the stirring tank. [3] A method for producing a fiber aggregate according to [1] or [2], in which a stirring blade rotating horizontally and an auxiliary stirring blade rotating vertically are placed in a stirring tank, and stirring is carried out using the stirring blade rotating horizontally and the auxiliary stirring blade rotating vertically. [4] The method for producing a fiber aggregate according to any one of [1] to [3], further comprising agitating and defibrating the carbon fibers in the stirring tank with the stirring blades before the fiber treatment agent is added to the stirring tank. [5] The method for producing a fiber aggregate according to any one of [1] to [4], wherein the stirring tank is provided with a scraper and rotated. [6] The method for producing a fiber aggregate according to any one of [1] to [5], wherein the agitator blade is inclined in the direction of rotation, and the angle between the rear surface of the agitator blade in the direction of rotation and the bottom surface of the agitator tank is 1 to 60°. [7] The method for producing a fiber aggregate according to any one of [1] to [6], wherein the stirring tank is provided with a rotating shaft capable of rotating about an axis, and the plurality of stirring blades extend radially from the rotating shaft. [8] A method for producing a fiber assembly according to any one of [1] to [7], comprising rotating the stirring blade so that the peripheral speed of the tip of the stirring blade is 1 to 20 m / sec. [9] The method for producing a fiber aggregate according to any one of [5] to [8], comprising stirring the mixture so that the rotation direction of the stirring blade is opposite to the rotation direction of the stirring tank, and then stirring the mixture so that the rotation direction of the stirring blade is the same as the rotation direction of the stirring tank.

[10] A method for producing a fiber aggregate according to [5] or [9], comprising rotating the stirring tank at a peripheral speed of 1.2 m / sec or less.

[11] The method for producing a fiber assembly according to any one of [1] to

[10] , wherein the fiber treatment agent has a surface tension of 120 mN / m or less at 23° C.

[12] The method for producing a fiber assembly according to any one of [1] to

[11] , wherein the fiber treatment agent has a viscosity of 10 Pa·s or less at 23° C.

[13] The method for producing a fiber assembly according to any one of [1] to

[12] , wherein the fiber treatment agent contains water.

[14] The method for producing a fiber assembly according to any one of [1] to

[13] , wherein the fiber treatment agent contains one or more resins selected from an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a polyurethane resin, and a polyamide resin.

[15] The method for producing a fiber assembly according to any one of [1] to

[14] , wherein the fiber treating agent is added in an amount of 10 to 40 parts by mass per 100 parts by mass of the fibers.

[16] The method for producing a fiber assembly according to any one of [1] to

[15] , wherein the fiber treatment agent is a liquid, and the method comprises a step of evaporating the liquid contained in the fiber treatment agent.

[17] The method for producing a fiber assembly according to any one of [1] to

[16] , wherein the fibers further contain glass fibers.

[18] The method for producing a fiber assembly according to any one of [1] to

[17] , wherein the fibers further contain organic fibers.

[19] The method for producing a fiber assembly according to any one of [1] to

[18] , wherein the fibers have an average fiber length of 12 to 50 mm.

[20] The method for producing a fiber assembly according to any one of [1] to

[19] , wherein the fibers have an average fiber length of 2 to 12 mm.

[21] The positions of the tips of the multiple fibers constituting the fiber assembly are irregular.

[20] A method for producing a fiber assembly according to any one of the above items.

[22] The method for producing a fiber assembly according to any one of [1] to

[21] , wherein the length of the major axis of the fiber assembly is longer than the average fiber length of the fibers contained in the fiber assembly.

[23] The method for producing a fiber assembly according to any one of [1] to

[22] , wherein the fiber assembly has an elongated spheroid shape or a strand shape.

[24] The method for producing a fiber aggregate according to any one of [1] to

[23] , wherein a ratio (Y / X) of an average fiber length Y of the fibers in the fiber aggregate to an average fiber length X of the fibers before being charged into the stirring tank is 0.55 or more.

[25] The method for producing a fiber assembly according to any one of [1] to

[24] , wherein the fiber assembly is granulated by stirring using a Henschel mixer.

[26] The method for producing a fiber assembly according to any one of [1] to

[24] , wherein the mixture is granulated by stirring using a granulator.

[27] The method for producing a fiber assembly according to any one of [1] to

[26] , wherein the fiber treatment agent has a surface tension of 15 mN / m or more at 23°C.

[28] The method for producing a fiber assembly according to any one of [1] to

[27] , wherein the fiber treatment agent has a viscosity of 0.0001 Pa·s or more at 23° C.

[29] The method for producing a fiber assembly according to any one of [1] to

[28] , wherein the number of filaments in the fiber assembly is 8,000 or more and 800,000 or less.

[30] The bulk density of the fiber is 0.01 to 0.040 g / cm 3 The method for producing a fiber assembly according to any one of [1] to

[29] ,

[31] The method for producing a fiber assembly according to any one of [1] to

[30] , wherein a strain rate applied to the fibers and the fiber treatment agent is 1 [1 / s] or more and 700 [1 / s] or less.

[32] A method for producing a fiber aggregate, comprising: introducing a plurality of fibers and a fiber treatment agent containing a liquid into a mixing tank; stirring the mixture of the fibers and the fiber treatment agent with a mixing blade to cause liquid bridging, thereby directly obtaining a fiber aggregate in which the fibers are aligned.

[33] The method for producing a fiber assembly according to

[32] , wherein the fibers include carbon fibers.

[34] The method for producing a fiber aggregate described in

[32] or

[33] , further comprising feeding the plurality of dried, cotton-like fibers into the stirring tank.

[35] A method for producing a fiber aggregate in which carbon fibers are aligned, comprising: introducing multiple cotton-like carbon fibers, resin, and water into a stirring tank; and stirring and granulating the multiple carbon fibers, the resin, and the water using a stirring blade placed in the stirring tank.

[36] A method for producing a fiber aggregate in which carbon fibers are aligned, as described in

[35] , comprising inputting a raw material containing the plurality of cotton-like carbon fibers and further a resin carbide.

[37] A method for producing a fiber aggregate having aligned carbon fibers according to

[35] or

[36] , comprising feeding a raw material containing the plurality of cotton-like carbon fibers and further glass fibers.

[38] A method for producing a prepreg sheet, comprising stacking a plurality of fiber assemblies obtained by the method for producing a fiber assembly according to any one of [1] to

[37] .

[39] A method for producing pellets, comprising kneading a fiber aggregate obtained by the method for producing a fiber aggregate according to any one of [1] to

[37] with a resin.

[40] A composite material comprising multiple carbon fibers and an organic binder, and having a bulk density of 0.1 to 0.29 g / cm 3 or a carbon fiber aggregate having an angle of repose of 60° or less and an elongated spheroid shape with a major axis length of 3 mm to 18 mm.

[41] The carbon fiber aggregate according to

[40] , wherein the positions of tips of the multiple fibers constituting the carbon fiber aggregate are not uniform.

[42] The carbon fiber aggregate according to

[40] or

[41] , wherein the length of a major axis of the carbon fiber aggregate is longer than an average fiber length of the fibers contained in the carbon fiber aggregate.

[43] The carbon fiber aggregate according to any one of

[40] to

[42] , wherein the carbon fiber aggregate contains a resin carbide.

[44] The carbon fiber aggregate according to any one of

[40] to

[43] , wherein the carbon fiber aggregate contains glass fibers.

[45] The carbon fiber aggregate according to any one of

[40] to

[44] , wherein the organic binder contains one or more resins selected from an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a polyurethane resin, and a polyamide resin.

[0013] The present invention also includes the following aspects [1a] to [25a]. The following aspects [1a] to [25a] may be referred to as "I of the first aspect of the present invention."

[0014] [1a] A method for producing a fiber aggregate, comprising: introducing fibers and a fiber treatment agent into a stirring tank; and granulating the mixture of fibers and the fiber treatment agent by stirring with a stirring blade. [2a] The method for producing a fiber aggregate according to [1a], wherein the agitator blade is inclined in the direction of rotation, and the angle between the rear surface of the agitator blade in the direction of rotation and the bottom surface of the agitator tank is 1 to 60°. [3a] The method for producing a fiber aggregate described in [1a] or [2a], wherein the plurality of stirring blades extend radially from a rotation shaft in the stirring tank. [4a] The method for producing a fiber assembly according to any one of [1a] to [3a], wherein the peripheral speed of the tip of the stirring blade is 1 to 20 m / sec. [5a] A method for producing a fiber aggregate, comprising granulating fibers and a fiber processing agent by stirring them using a Henschel mixer. [6a] A method for producing a fiber aggregate, comprising granulating fibers and a fiber treating agent using a granulator. [7a] The method for producing a fiber assembly according to any one of [1a] to [6a], wherein the fiber treatment agent has a surface tension of 120 mN / m or less at 23° C. [8a] The method for producing a fiber assembly according to any one of [1a] to [7a], wherein the fiber treatment agent has a viscosity of 10 Pa·s or less at 23° C. [9a] The method for producing a fiber assembly according to any one of [1a] to [8a], wherein the fibers have an average fiber length of 1 to 100 mm. [10a] The method for producing a fiber assembly according to any one of [1a] to [9a], wherein the fiber treating agent is added in an amount of 5 to 120 parts by mass per 100 parts by mass of the fibers. [11a] The method for producing a fiber assembly according to any one of [1a] to [10a], wherein the fibers contain carbon fibers. [12a] The method for producing a fiber assembly according to any one of [1a] to [10a], wherein the fibers contain glass fibers. [13a] The method for producing a fiber assembly according to any one of [1a] to [10a], wherein the fibers include organic fibers. [14a] The method for producing a fiber assembly according to any one of [1a] to [10a], wherein the fibers contain carbon fibers and organic fibers. [15a] The method for producing a fiber aggregate according to any one of [1a] to [10a], wherein the fibers contain carbon fibers and glass fibers. [16a] The method for producing a fiber assembly according to any one of [1a] to [15a], wherein the fiber treatment agent contains at least one selected from a solvent, a clay mineral, a polymer, and a surfactant. [17a] The method for producing a fiber aggregate according to any one of [1a] to [16a], wherein the ratio (Y / X) of the average fiber length Y of the fibers in the fiber aggregate to the average fiber length X of the fibers before being charged into the stirring tank is 0.55 or more. [18a] A method for producing a fiber assembly according to any one of [1a] to [17a], wherein the fiber treatment agent is a liquid, the method comprising a step of evaporating the liquid contained in the fiber treatment agent. [19a] The method for producing a fiber assembly according to any one of [1a] to [18a], wherein the fiber assembly has an elongated spheroid shape or a strand shape. [20a] The method for producing a fiber aggregate according to any one of [1a] to [19a], wherein the fibers are granulated so as to be aligned. [21a] A method for producing a fiber aggregate, comprising: introducing fibers and a liquid fiber treatment agent into a stirring tank; and granulating the mixture of fibers and the fiber treatment agent by stirring with a stirring blade. [22a] The method for producing a fiber assembly according to [21a], wherein the fibers have an average fiber length of 1 to 100 mm. [23a] The method for producing a fiber assembly according to [21a] or [22a], wherein the fiber treating agent is added in an amount of 5 to 120 parts by mass per 100 parts by mass of the fibers. [24a] The method for producing a fiber assembly according to any one of [21a] to [23a], wherein the fiber assembly has an elongated spheroid shape or a strand shape. [25a] The method for producing a fiber aggregate according to any one of [21a] to [24a], wherein the ratio (Y / X) of the average fiber length Y of the fibers in the fiber aggregate to the average fiber length X of the fibers before being charged into the stirring tank is 0.55 or more.

[0015] The present invention also includes the following aspects [1b] to [20b]. The following aspects [1b] to [20b] may be referred to as the "second aspect of the present invention."

[0016] [1b] A method for producing a fiber aggregate, comprising: putting fibers and a fiber processing agent into a tumbling drum and granulating the fibers by rotating the tumbling drum. [2b] The method for producing a fiber assembly according to [1b], wherein the surface tension of the fiber treatment agent at 23°C is 120 mN / m or less. [3b] The method for producing a fiber assembly according to [1b] or [2b], wherein the fiber treatment agent has a viscosity of 10 Pa·s or less at 23°C. [4b] The method for producing a fiber aggregate according to any one of [1b] to [3b], wherein the rolling tank is a pan-type rotating body. [5b] The method for producing a fiber aggregate according to any one of [1b] to [3b], wherein the tumbling tank is a drum-shaped rotating body. [6b] The method for producing a fiber aggregate according to [4b] or [5b], wherein the moving speed of the cylindrical side wall of the rotor is 0.20 to 1.60 m / s. [7b] The method for producing a fiber aggregate according to any one of [1b] to [3b], further comprising a side wall to which the tumbling tank is fixed and a rotating container that rotates horizontally within the side wall. [8b] The method for producing a fiber aggregate according to [7b], wherein the peripheral speed of the rotating vessel is 1 to 20 m / s. [9b] The method for producing a fiber assembly according to any one of [1b] to [8b], wherein the fibers have an average fiber length of 1 to 100 mm. [10b] The method for producing a fiber assembly according to any one of [1b] to [9b], wherein the fiber treating agent is used in an amount of 5 to 120 parts by mass per 100 parts by mass of the fibers. [11b] The method for producing a fiber assembly according to any one of [1b] to [10b], wherein the fibers contain carbon fibers. [12b] The method for producing a fiber assembly according to any one of [1b] to [10b], wherein the fibers contain glass fibers. [13b] The method for producing a fiber assembly according to any one of [1b] to [10b], wherein the fibers include organic fibers. [14b] The method for producing a fiber assembly according to any one of [1b] to [10b], wherein the fibers contain carbon fibers and organic fibers. [15b] The method for producing a fiber aggregate according to any one of [1b] to [10b], wherein the fibers contain carbon fibers and glass fibers. [16b] The method for producing a fiber assembly according to any one of [1b] to [15b], wherein the fiber treatment agent contains at least one selected from a solvent, a clay mineral, a polymer, and a surfactant. [17b] The method for producing a fiber aggregate according to any one of [1b] to [16b], wherein the ratio (Y / X) of the average fiber length Y of the fibers in the fiber aggregate to the average fiber length X of the fibers before being charged into the stirring tank is 0.55 or more. [18b] A method for producing a fiber aggregate according to any one of [1b] to [17b], wherein the fiber treatment agent is a liquid, the method comprising a step of evaporating the liquid contained in the fiber treatment agent. [19b] The method for producing a fiber assembly according to any one of [1b] to [18b], wherein the fiber assembly has an elongated spheroid shape or a strand shape. [20b] The method for producing a fiber aggregate according to any one of [1b] to [19b], wherein the fibers are granulated so as to be aligned.

[0017] The present invention also includes the following aspects [1c] to [16c]. The following aspects [1c] to [16c] may be referred to as the "third aspect of the present invention."

[0018] [1c] A method for producing a fiber assembly, comprising: granulating the fibers by liquid bridging the fibers together while applying a strain rate to the fibers and the fiber treatment agent, thereby growing particles. [2c] The method for producing a fiber assembly according to [1c], wherein the strain rate is 1 [1 / s] or more and 700 [1 / s] or less. [3c] The method for producing a fiber aggregate according to [1c] or [2c], wherein the operation of applying the strain rate is an operation of applying a shear rate by moving an agitator blade to bring the fibers and the fiber treatment agent into contact with each other. [4c] The method for producing a fiber aggregate according to [1c] or [2c], wherein the operation of applying the strain rate is an operation of applying a vibration rate by vibrating a container containing the fibers and the fiber treatment agent. [5c] The method for producing a fiber aggregate described in [1c] or [2c], wherein the operation of applying the strain rate is an operation of applying a rotational speed by rotating a container containing the fibers and the fiber treatment agent. [6c] The method for producing a fiber aggregate described in [1c] or [2c], wherein the operation of applying the strain rate is an operation of applying an air flow shear rate by blowing a gas into a container containing the fibers and the fiber treatment agent. [7c] The method for producing a fiber assembly according to any one of [1c] to [6c], wherein the fiber treating agent is used in an amount of 5 to 120 parts by mass per 100 parts by mass of the total amount of the fibers. [8c] The method for producing a fiber assembly according to any one of [1c] to [7c], wherein the fibers have an average fiber length of 1 to 100 mm. [9c] The method for producing a fiber assembly according to any one of [1c] to [8c], wherein the fiber treatment agent contains at least one selected from a solvent, a clay mineral, a polymer, and a surfactant. [10c] The method for producing a fiber assembly according to any one of [1c] to [9c], wherein the fibers include at least one type of fiber selected from the group consisting of carbon fibers, glass fibers, and organic fibers. [11c] The method for producing a fiber assembly according to any one of [1c] to [10c], wherein the fiber assembly has an elongated spheroid shape or a strand shape. [12c] The method for producing a fiber aggregate according to any one of [1c] to [11c], wherein the fibers are granulated so as to be aligned. [13c] A method for producing a fiber aggregate, comprising: bringing fibers and a fiber treating agent into contact with each other by moving an agitator blade to impart a shear rate thereto, thereby forming liquid bridges between the fibers and growing particles, thereby granulating the fibers. [14c] A method for producing a fiber aggregate, comprising: vibrating a container containing fibers and a fiber treatment agent to impart a vibration speed thereto, thereby forming liquid bridges between the fibers and growing particles, thereby granulating the fibers. [15c] A method for producing a fiber aggregate, comprising: granulating the fibers by forming liquid bridges between the fibers while rotating a container containing fibers and a fiber treating agent to give the container a rotational speed, thereby causing particles to grow. [16c] A method for producing a fiber aggregate, comprising: blowing gas into a vessel containing fibers and a fiber treatment agent to impart an airflow shear velocity thereto, thereby forming liquid bridges between the fibers and causing the fibers to grow into particles, thereby granulating the fibers.

[0019] The present invention also includes the following aspects [1d] to [17d]. The following aspects [1d] to [17d] may be referred to as the "fourth aspect of the present invention."

[0020] [1d] A fiber bundle comprising a plurality of carbon fibers and a resin or a solvent, the fiber bundle having an ellipsoidal shape and an A' / A ratio specified by the following condition (1) of 0.75 to 0.93. Condition (1): The image obtained by photographing a fiber bundle placed on a white plate from the vertical direction opposite the plate is binarized using image analysis software to obtain a binary image. The outline of the fiber bundle is obtained by extracting the outline of the binary image. The Feret diameter is calculated from the obtained outline and the major axis length is defined as A. The major axis length of the ellipse obtained by approximating the binary image to an ellipse is defined as A'. [2d] The fiber bundle according to [1d], wherein the major axis length A of the fiber bundle is 3 to 30 mm. [3d] A fiber bundle according to [1d] or [2d], wherein the average fiber length of the fibers in the fiber bundle is shorter than the major axis. [4d] The fiber bundle according to any one of [1d] to [3d], wherein the average fiber length of the fibers in the fiber bundle is 2 to 12 mm. [5d] The fiber bundle according to any one of [1d] to [4d], wherein the fibers present on the surface of the fiber bundle are oriented in a curved manner along the contour of an ellipsoid. [6d] The fiber bundle according to any of [1d] to [5d], wherein the fiber bundle has the major axis, minor axis 1 and minor axis 2, and length B of minor axis 1 is longer than length C of minor axis 2. [7d] The fiber bundle according to any one of [1d] to [6d], wherein B is 1 to 9 mm and C is 0.5 to 6 mm. [8d] The fiber bundle according to any one of [1d] to [7d], wherein the ratio of the major axis to the minor axis 1 (B / A) is 2 to 12, and the ratio of the major axis to the minor axis 2 (C / A) is 1 to 6. [9d] A fiber bundle according to any one of [1d] to [8d], wherein B is 1.5 times or more of C. [10d] The particle density of the fiber bundle represented by the following formula (2) is 0.3 to 1.8 g / cm 3 The fiber bundle according to any one of [1d] to [9d], Particle density=G / (4πabc / 3)...Equation (2) (In formula (2), G represents the mass of the fiber bundle, a represents A / 2, b represents B / 2, and c represents C / 2.) [11d] The fiber bundle according to any one of [1d] to [10d], wherein the fiber bundle contains a resin carbonized material. [12d] The fiber bundle according to any one of [1d] to [11d], wherein the fiber bundle contains glass fibers. [13d] The fiber bundle according to any one of [1d] to [12d], wherein the fibers contain a resin. [14d] The fiber bundle according to [13d], wherein the resin includes at least one selected from an epoxy resin, a urethane resin, and a polyamide resin. [15d] A fiber assembly comprising a fiber bundle containing a plurality of fibers and a resin or a solvent, wherein the fiber bundles W have an ellipsoidal shape and an A / A' ratio of 0.75 to 0.93 as specified by the following condition (1) account for 50% or more of the fiber bundles: Condition (1): A fiber bundle placed on a white plate is photographed from the vertical direction opposite the plate, using the fiber bundle as a reference, and the resulting image is binarized using image analysis software to obtain a binary image. The binary image is contour-extracted to obtain the outline of the fiber bundle. The Feret diameter is calculated from the obtained outline, and the major axis length is designated as A. The binary image is approximated to an ellipse, and the major axis length of the ellipse is designated as A'. [16d] Bulk density is 0.1 to 0.8 g / cm 3 The fiber assembly according to [15d], [17d] A fiber assembly according to [15d] or [16d], having an angle of repose of 60° or less. Effect of the Invention

[0021] According to a preferred embodiment of the present invention, a fiber aggregate having a high bulk density can be obtained in which the fibers are aligned while maintaining their length without cutting the fibers. Moreover, even recycled fibers having a low bulk density can be made into a highly oriented dense fiber aggregate. Therefore, efficient feeding is possible in equipment using various feeders such as fiber-reinforced resin pellets without causing bridging between fibers.

[0022] Using the fiber aggregate produced by the present invention, for example a carbon fiber aggregate, a fiber reinforced resin composition and a prepreg sheet that exhibit the inherent property improving effect of carbon fiber can be produced by carrying out a fixed amount and stable supply with a feeder under improved handling and workability. [Brief description of the drawings]

[0023] [Figure 1] Fig. 1 shows an embodiment of an agitating blade of an agitating vessel used in the first embodiment of the fiber aggregate manufacturing method of the present invention, Fig. 1a is a horizontal cross-sectional view of the agitating vessel, and Fig. 1b is a cross-sectional view taken along line bb in Fig. 1a. [Diagram 2] Fig. 2 is a schematic diagram showing an embodiment of a pan granulator used in the method for producing a fiber aggregate according to the second aspect of the present invention, Fig. 2a is a side view, and Fig. 2b is a view showing the internal structure of the granulator pan. [Figure 3A] FIG. 3A is a cross-sectional view showing a fixed side wall and a rotating container of a tumbling tank used in a method for producing a fiber aggregate according to a second embodiment of the present invention. [Figure 3B] FIG. 3B is a perspective view showing the inside of an embodiment of a tumbling stirring granulator used in the method for producing a fiber aggregate according to the first aspect of the present invention. [Figure 4] FIG. 4 is a photograph showing an example of the morphology of recycled fibers. [Diagram 5] FIG. 5 is a photograph showing an example of the morphology of virgin fibers. [Figure 6] Figures 6a–6d are enlarged photographs showing the ends of the SACFB, respectively. [Figure 7]FIG. 7 is an enlarged photograph showing the end of a chopped carbon fiber bundle. [Figure 8] FIG. 8 is a conceptual diagram of a sheet prepreg manufacturing device. [Figure 9] FIG. 9 is an image of the fiber bundle obtained in Example 1. [Figure 10] FIG. 10 is a diagram showing the outline of the fiber bundle obtained in Example 1. [Figure 11] FIG. 11 is a diagram showing an approximate ellipse of the fiber bundle obtained in Example 1. [Figure 12] FIG. 12 is an image of the fiber bundle obtained in Experimental Example 3. [Figure 13] FIG. 13 is an image of the fiber bundle obtained in Experimental Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments.

[0025] [First to third aspects of the present invention] The method for producing a fiber aggregate according to the first aspect of the present invention is a method for producing a fiber aggregate by using at least carbon fibers as fibers, charging a plurality of fibers and a fiber treatment agent into a stirring tank, and stirring the mixture of the fibers and the fiber treatment agent with a stirring blade to granulate the fibers so that the fibers are aligned. According to this aspect, even when raw material fibers having a long fiber length are used, a fiber aggregate in which the fibers are aligned can be obtained. One example of a fiber aggregate is a self-organized carbon fiber bundle. By granulation, a plurality of fibers can be aggregated to form one granular unit. In the first embodiment of the present invention, a Henschel mixer or a granulator can be used as the stirring granulator.

[0026] The method for producing a fiber assembly according to I of the first aspect of the present invention includes the following steps 1 to 4. 1. The process of wetting the fibers with a fiber treatment agent 2. The process of bringing wet fibers into contact with each other 3. A process in which liquid bridges are formed between fibers oriented in the same direction 4. The process of growing fiber bundles by repeating steps 1. to 3. By applying a stirring force to the mixture of the fibers and the fiber treating agent, the fiber treating agent can be efficiently attached to the fiber surfaces, and the contact and orientation of the fibers can be promoted.

[0027] The method for producing a fiber aggregate according to the second aspect of the present invention is a method for producing a fiber aggregate by putting fibers and a fiber treating agent into a tumbling drum and granulating the fibers by rotating the tumbling drum. This method for producing a fiber assembly also involves the following steps 1 to 4. 1. The process of wetting the fibers with a fiber treatment agent 2. The process of bringing wet fibers into contact with each other 3. A process in which liquid bridges are formed between fibers oriented in the same direction 4. The process of growing fiber bundles by repeating steps 1. to 3. By applying centrifugal force due to rotation and collision force due to sliding to a mixture of fibers and fiber treatment agent, the fiber treatment agent can be efficiently adhered to the fiber surface and contact and orientation of the fibers can be promoted.

[0028] The method for producing a fiber aggregate according to the third aspect of the present invention is a method for producing a fiber aggregate by applying a strain rate to the fibers and the fiber treatment agent while liquid bridging the fibers together to grow particles, thereby granulating the fibers. This method for producing a fiber assembly also involves the following steps 1 to 4. 1. The process of wetting the fibers with a fiber treatment agent 2. The process of bringing wet fibers into contact with each other 3. A process in which strong liquid bridges are formed between fibers oriented in the same direction 4. The process of growing fiber bundles by repeating steps 1. to 3. In this case, by applying a strain rate, the fiber treatment agent can be efficiently attached to the fiber surface, and contact and orientation of the fibers can be promoted.

[0029] In the present invention, the definitions of strain rate, liquid cross-linking, and self-organized carbon fiber bundles are as follows.

[0030] <Strain rate> The strain rate in the present invention is defined as the maximum speed at which the fibers move per unit time in the granulation process divided by the characteristic length. Strain rate [1 / s] = maximum speed [m / s] / characteristic length [m] The characteristic length here refers to the height at which the fibers are charged into the container, and is calculated as the weight of the charged fibers divided by the bulk density of the fibers and then divided by the average cross-sectional area of ​​the container. Feeding height [m] = fiber weight [kg] / fiber bulk density [kg / m 3 ] / average cross-sectional area of ​​container [m 2 ] The average cross-sectional area is the container's internal volume [m 3 ] divided by the height of the inner surface of the container along the axis of rotation or vibration. For example, in the case of agitation granulation, where granulation is performed by rotating the agitator blade, the maximum speed is the peripheral speed of the agitator blade. In the case of rolling granulation, where granulation is performed by rotating a container, the maximum speed is the peripheral speed of the container. In the case of granulation by vibration, the maximum speed is the speed calculated from the amplitude and period of the vibration. In the case of granulation in a fluidized bed, the maximum speed is the blowing speed of the air current. If the object is moving, the maximum speed can also be found by filming the movement with a video camera and deriving the distance that a set reference point moves per unit time using image processing.

[0031] <Amount of strain> The amount of strain is obtained by multiplying the strain rate by the processing time. This amount of strain is also a measure of granulation. Strain amount [-] = strain rate × processing time [s]

[0032] <Liquid crosslinking> It means that a liquid exists in a narrow gap between powder particles and a solid surface, or between particles. The liquid bridge formed between particles is subjected to negative pressure due to capillary force, so that the particles are immobilized by the attraction (liquid bridge force). In the present invention, the liquid bridge refers to a liquid bridge formed in the gap between fibers. When the fibers are in contact with each other so as to cross, the liquid bridge force acts at a point, so it is weak, and when the fibers are in contact in parallel, the liquid bridge force acts in a line, so it is strong. Since the liquid bridge formed in the fiber occurs continuously in the length direction of the fiber, even if the fibers are not parallel to each other, the surface tension of the liquid can be expected to cause the fibers themselves to change their angle and orient in the same direction so that the surface area of ​​the liquid is minimized.

[0033] <Self-assembled carbon fiber bundle (SACFB)> The SACFB is one embodiment of a fiber assembly, and is formed through a process in which a plurality of short carbon fibers are assembled to form a bundle. In a stage before forming the SACFB, all of the plurality of short carbon fibers may be monofilaments. That is, the SACFB may be formed by aggregating a plurality of carbon fiber filaments to form a bundle. In another example, the SACFB may be formed by aggregating a plurality of fine carbon fiber bundles, each of which is composed of a small number of filaments, for example, less than 100 filaments. Alternatively, the SACFB may be formed by aggregating a plurality of carbon fiber monofilaments and a plurality of fine carbon fiber bundles. At the end of the SACFB, the positions of the tips of the plurality of carbon fibers constituting the bundle are not uniform, as exemplified in Figs. 6(a) to (d).

[0034] <Mixing tank and mixing conditions> Hereinafter, a stirring granulator that can be suitably used in the method for producing a fiber aggregate according to the first embodiment of the present invention will be described with reference to FIG.

[0035] As shown in Fig. 1a, the agitation granulator used in the fiber aggregate manufacturing method according to the first embodiment of the present invention preferably has a rotating shaft 2 on the central axis of a cylindrical stirring tank 1 with a bottom, and multiple propeller-shaped agitation blades (three in Fig. 1a) extend radially at equal intervals from the rotating shaft 2. The agitation blades may be disk-shaped and perpendicular to the rotating shaft. They may also be disks with undulations and protrusions.

[0036] As shown in FIG. 1b, the stirring blade 3 is provided inclined in the rotation direction with respect to the bottom surface 1A of the stirring tank 1. The included angle θ between the surface 3A, which is the rear surface with respect to the rotation direction R, and the bottom surface 1A of the stirring tank 1 (hereinafter, sometimes simply referred to as the "tilt angle") is preferably in the range of 1 to 60°. If the tilt angle θ of the stirring blade 3 is 1° or more, it is possible to stir the fiber mixture particles while circulating them in the stirring tank. If the tilt angle θ of the stirring blade 3 is 60° or less, it is possible to adjust the rotation speed within a range where the resistance to the stirring blade is suppressed and the load on the device is not applied. The tilt angle θ is more preferably 10 to 50°, and even more preferably 20 to 40°.

[0037] In Fig. 1a, the impeller 3 is bent at an angle α in the middle of its length. The impeller is not limited to be bent in this way, and may be a straight plate-like impeller. The impeller may be bent in an arc shape.

[0038] Some stirring granulators are provided with auxiliary stirring blades (choppers) on the wall of the stirring vessel for auxiliary stirring. Either type of stirring granulator can be used in the first embodiment of the present invention.

[0039] The stirring tank of the stirring granulator may be provided with a scraper on the bottom or side. By providing the scraper on the stirring tank, the granulation efficiency can be improved.

[0040] The rotation direction conditions of the stirring granulator are preferably such that the peripheral speed (hereinafter simply referred to as "peripheral speed") of the tip of the stirring blade (part 3a in Fig. 1a) is in the range of 1 to 20 m / sec. If the peripheral speed is 1 m / sec or more, it is possible to stir the fiber mixture granules while circulating them in the stirring tank. If the peripheral speed is 20 m / sec or less, it is possible to make the particle shape of the fiber aggregate uniform. The peripheral speed of the stirring blade is more preferably 4 to 12 m / sec, and even more preferably 4 to 8 m / sec. The peripheral speed of the chopper is preferably in the range of 5 to 30 m / sec.

[0041] There is no particular limitation on the stirring time in the stirring granulator, and stirring may be performed for a period of time sufficient to obtain a desired fiber aggregate. The temperature during stirring is not particularly limited and may be room temperature. Temperature rise of the container and mixture due to stirring is permitted. The fiber treatment agent is liquid when granulated, and the type of fiber treatment agent, mixing time, mixing temperature, etc. can be adjusted so that the fiber treatment agent becomes solid when the particulate state (granulated state) is maintained as a fiber aggregate. The mixing conditions are adjusted so that a fiber aggregate in an aligned state is obtained, rather than spherical carbon fiber balls made of crimped fibers. When the fiber processing agent, especially when no liquid is added at all or a large amount is added to the fiber and the aggregate is obtained by stirring the fibers, or when the average fiber length of the raw material is 1 mm or less, carbon fiber balls are likely to be obtained.

[0042] The stirring granulator may be any granulator having a cylindrical container and stirring blades that can be rotated by a rotating shaft. Examples of the stirring blade include a paddle type, a propeller type, a turbine type, an anchor type, and a ribbon type. Examples of stirring granulators include batch-type stirring granulators such as SP Granulator (Dalton), High Speed ​​Mixer (Earth Technica), Vertical Granulator (Powrex), Loedige Mixer (Matsubo), Super Mixer (Kawata), Power Kneader (Fuji Paudal), Henschel Mixer (Mitsui Miike), Universal Mixer Mixer (Shinagawa Kogyosho), Spartan Reuser (Fuji Paudal), and Byte Mix (Hosokawa Micron), as well as continuous stirring granulators such as Flexomix (Hosokawa Micron) and Modulomix (Hosokawa Micron). Examples of combined agitator granulators and fluidized bed granulators include the Multiplex Granulator (Powrex), Spiracoater (Powrex), Spiraflow (Freund Industries), and New Marmerizer (Fuji Paudal).

[0043] The mixing vessel has a mixing blade (agitator) that rotates horizontally and an auxiliary mixing blade (chopper) that rotates vertically, and efficient mixing and granulation can be achieved by mixing with the horizontally rotating mixing blade and the vertically rotating auxiliary mixing blade. The vertically rotating auxiliary mixing blade has the role of crushing granulated material that has become too large and making the size of the fiber aggregate uniform.

[0044] The raw material before being fed into the stirring granulator may be a raw material that has not been wet mixed. In other words, instead of a wet fiber aggregate, a plurality of dry fibers may be fed directly into the stirring tank as the raw material and stirred. There is no particular restriction on the time when the granulation is completed, but it is preferable that the fiber aggregate is formed to an extent that the particle size distribution can be specified.

[0045] <Drying process> In the method for producing a fiber aggregate according to the first embodiment of the present invention, after stirring and granulating as described above, it is preferable to carry out a drying step in which the liquid derived from the fiber treating agent contained in the obtained granules is evaporated. The conditions for the drying process vary depending on the type of fiber treatment agent used. Drying may be carried out using a dryer at 50 to 150° C. for about 1 to 5 hours.

[0046] Examples of drying equipment include a box dryer, a belt conveyor dryer, a tunnel dryer, a fixed tank agitator dryer, a drum rotary dryer, a rotary kiln, a fluidized bed dryer, an agitator hot air dryer, an airflow dryer, an infrared dryer, a microwave dryer, a vacuum dryer, etc. Natural drying may also be used.

[0047] <Classification process> A plurality of fiber aggregates can be classified to improve the uniformity of the plurality of fiber aggregates. The sieve used for classification can be configured to include a vibration mechanism, a container connected to the vibration mechanism, and a sieve mesh that divides the internal space of the container. When the container is cylindrical, the container is arranged so that the opening of the cylinder faces vertically. The sieve mesh is arranged at the opening at one end of the container, and the fiber aggregate is supplied onto the sieve mesh. The container is vibrated so that the fiber aggregates are directed toward the outer periphery, and large fiber aggregates are discharged from above the sieve mesh, and small fiber aggregates are dropped below the sieve mesh for classification. When the container is trough-shaped, the sieve screen is arranged to divide the internal space of the container in the longitudinal direction. The fiber aggregate is supplied from one longitudinal end of the inclined container, and the fiber aggregate moves vertically from top to bottom inside the container and is discharged from the other end of the container. Due to the vibration of the container, large fiber aggregates remain on the sieve screen, while small fiber aggregates fall through the meshes to the bottom of the sieve screen. A classified fiber aggregate is obtained by collecting the fiber aggregate above the sieve screen and the fiber aggregate below the sieve screen separately. The mesh shape and opening of the sieve are adjusted so that the fiber aggregate can be sieved into a desired size. When the fiber aggregate has an ellipsoidal shape, the mesh shape is preferably rectangular or rhombic. The mesh shape may also be square or circular. For example, the sieve may be a vibrating sieve (Dalton) or a finger screen (Taiyo Machinery). A classification process may also be applied to the raw fiber to increase the uniformity of the fiber before use.

[0048] <Rolling tank> The rolling tank used in the second embodiment of the present invention may be a pan-type rotating body or a drum-type rotating body.

[0049] 2A and 2B are schematic diagrams showing an embodiment of a pan granulator used in the method for producing a fiber aggregate according to the second aspect of the present invention, in which Fig. 2A is a side view of the pan granulator, and Fig. 2B is a view showing the internal structure of the granulator. FIG. 3A is a cross-sectional view showing a fixed side wall and a rotating container of a tumbling tank used in a second embodiment of a method for producing a fiber aggregate. FIG. 3B is a perspective view showing the inside of an embodiment of a tumbling stirring granulator used in the method for producing a fiber aggregate according to the second aspect of the present invention.

[0050] The pan granulator in Fig. 2 is configured such that a granulation pan 11 rolls on a rolling shaft 12. Reference numeral 13 denotes a motor, 14 denotes a reducer, 15 denotes a pan support, 16 denotes a machine base, and 17 denotes a depression angle adjustment device. An arm 21 having a spray 22 and a scraper 23 is provided within the granulating pan.

[0051] The moving speed of the cylindrical side wall of such a rotor is preferably 0.20 to 1.60 m / s, and more preferably 0.50 to 1.00 m / s. If the moving speed of the cylindrical side wall is equal to or higher than the lower limit, the fiber mixture is moved upward by centrifugal force and crushed by the impact of sliding down, making it possible to make the shape of the fiber aggregate uniform. If the moving speed of the cylindrical side wall is equal to or lower than the upper limit, the centrifugal force acts appropriately, the fiber mixture is moved upward, and crushing and granulation by sliding down are efficiently performed, so that productivity can be increased.

[0052] As shown in FIG. 3A, the tumbling tank preferably has a fixed side wall 31 and a rotating container 32 that rotates horizontally within the side wall. In this case, the peripheral speed of the rotating container is preferably 1 to 20 m / s, more preferably 5 to 10 m / s. If the peripheral speed of the rotating container is equal to or higher than the lower limit, the fiber mixture moves in the circumferential direction and collides with the wall surface due to centrifugal force continuously, and the shape of the fiber aggregate can be made uniform through crushing and granulation. If the peripheral speed of the rotating container is equal to or lower than the upper limit, the centrifugal force works appropriately to balance with the gravity acting on the fiber mixture, and crushing and granulation are efficiently performed, thereby increasing productivity.

[0053] The rolling granulator may be any granulator having a rotatable container, and a cylindrical container may be used. The rotatable container is provided with the stirring blades described above, and serves as both a rolling tank and a stirring tank, and can be used for stirring granulation as an embodiment of the rolling stirring granulator described below. Cylindrical containers include pan types such as regular pans, multi-tier pans, irregular pans, parabolic pans, double pans, and truncated conical pans, as well as drum pans. Examples of rolling granulators include pan-type granulators (Nihon Spindle), Spiracoaters (Okada Seiko), Spiral Flow (Freund Corporation), and New Marmerizers (Fuji Paudal).

[0054] <Rolling agitation granulator> The rolling agitation granulator will be described with reference to FIG. 3B. As shown in FIG. 3B, one embodiment of the rolling agitation granulator includes a rotatable container 40 that stores raw fibers and a fiber treatment agent therein, and a rotating shaft 42 that is disposed inside the container 40 and eccentric to the central axis 41 of the container 40 and parallel to the central axis 41. The rotating shaft 42 is preferably rotatable in the opposite direction to the rotation direction of the container 40. By rotating in the opposite direction, the impact force between the agitation blade and the fiber aggregate increases, and it is possible to align the fibers in a short time by strong shearing. The rotating shaft 42 may rotate in the same direction as the container 40. When the rotation direction of the agitation blade is opposite to the rotation direction of the container, the number of filaments contained in the fiber aggregate tends to be small, and the number and shape of the filaments contained in the fiber aggregate tend to be uniform. When the rotation direction is the same as the rotation direction of the container, the number of filaments contained in one fiber aggregate tends to be large, and the fibers tend to be easily bundled. It is believed that when the stirring is performed so that the direction of rotation of the stirring blade is opposite to the direction of rotation of the container, and then the stirring is performed so that the direction of rotation of the stirring blade is the same as the direction of rotation of the container, liquid bridging between fiber aggregates with a small number of filaments and uniform distribution advances. This allows for a fiber aggregate with a uniform and high bulk density to be obtained. The rotating shaft 42 has a stirring blade 44 that extends to the vicinity of the bottom plate 43 of the container 40 and moves within the area of ​​the mixture of the fibers and the fiber treatment agent. The mixture is circulated by the rotation of the container 40, and the mixture is sheared by the rotation of the stirring blade 44, so that the fibers can be aligned. The blades of the stirring blade 44 can be the same as those described for the stirring granulator. The side of the container 40 is equipped with a scraper 45. A scraper may be provided on the side, bottom, or both of the inside of the container 40. The scraper 45 can scrape off the adhering raw material.

[0055] Regarding the rotation conditions of the rolling stirring granulator, the circumferential speed of the vessel 40 (vessel circumferential speed) can be in the range of 0.4 to 1.2 m / sec. If the circumferential speed is 0.4 m / sec or more, the fiber-mixed granules can be stirred while circulating in the stirring tank. On the other hand, if the circumferential speed is 1.2 m / sec or less, the fiber-mixed granules can be efficiently brought into contact with the stirring blade or scraper, and the processing time can be shortened. The circumferential speed can be 0.5 to 1.0 m / sec or 0.7 to 0.9 m / sec. It is preferable that the circumferential speed of the stirring blade tip (tip circumferential speed) of the stirring blade 44 is in the range of 1 to 30 m / sec. If the tip circumferential speed is 1 m / sec or more, it is possible to align the fibers in a short time and increase the density of the fiber aggregate. On the other hand, if the tip circumferential speed is 30 m / sec or less, it is possible to make the particle shape of the fiber aggregate uniform. The circumferential speed of the stirring blade 44 can be 10 to 20 m / sec or 1 to 8 m / sec.

[0056] The rolling agitation granulator may be any granulator having a container and an agitation blade that can be rotated by a rotating shaft, and examples of the agitation blade include paddle type, propeller type, turbine type, anchor type, ribbon type, etc. Examples of the rolling agitation granulator include an intensive mixer (Eirich) and a tilting-body rolling agitation granulator (Kitagawa).

[0057] <Strain rate> In the method for producing a fiber aggregate according to the third aspect of the present invention, the strain rate applied to the fibers and the fiber treatment agent is preferably 1 [1 / s] or more and 700 [1 / s] or less. If the strain rate is equal to or more than the lower limit, the fibers are easily oriented. If the strain rate is equal to or less than the upper limit, uniform particles (fiber bundles) are obtained. The strain rate is preferably 10 to 500 [1 / s], more preferably 20 to 200 [1 / s].

[0058] The charge height when the fibers are charged into the vessel is preferably 1 / 50 or more and 2 times or less of the vessel height. If the charge height is above the lower limit, the fibers are easily oriented. If the charge height is below the upper limit, uniform particles (fiber bundles) are obtained. The charge height is particularly preferably 1 / 10 or more and 1 / 2 or less of the vessel height, more particularly preferably 1 / 5 or more and 4 / 5 of the vessel height.

[0059] The amount of strain applied to the fibers and the fiber treatment agent is preferably 5,000[-] or more and 230,000[-] or less. If the amount of strain is above the lower limit, the fibers are easily oriented. If the amount of strain is below the upper limit, uniform particles (fiber bundles) are obtained. The amount of strain is particularly preferably 5,000 to 100,000[-], and more preferably 5,000 to 20,000[-].

[0060] The operation for applying a strain rate to the fiber and the fiber treatment agent is not particularly limited, but specific examples include the following methods.

[0061] (1) An operation of applying a shear rate to the fibers and the fiber treatment agent by moving the agitating blades to bring them into contact with each other (agitation granulation) Specifically, one example of the method is to feed the fibers and the fiber processing agent into an agitation tank 1 of an agitation granulator having an agitation blade 3 as shown in FIG. 1, and then agitate the fibers and the fiber processing agent.

[0062] The stirring granulator is as explained in the above-mentioned first embodiment of the method for producing a fiber aggregate of the present invention, and the preferred embodiment and stirring conditions thereof are also as explained above.

[0063] When performing stirring granulation, the strain rate is calculated by dividing the peripheral speed of the outermost diameter of the stirring blade (the peripheral speed of the tip 3a of the stirring blade 3) [m / s] by the height of the stirring blade and the raw material in the stirring tank 3 [m]. Strain rate [ / s] = circumferential speed of impeller [m / s] / feed height [m]

[0064] (2) The operation of vibrating a container containing fibers and a fiber processing agent to impart a vibration speed (granulation by vibration) Specifically, the fibers and the fiber treatment agent are placed in a sealable container. Any type of sealable container can be used, but a cylindrical container with a screw-on lid can be used. The sealed container is placed in a sieve shaker or similar device and subjected to vibration for a certain period of time. Using the amplitude A and period T of the vibration at this time, the velocity (v) is calculated using the following formula, assuming simple harmonic motion. t is the elapsed time, and the maximum velocity can be obtained at t=0, T / 2, etc. v = (2π / T) Acos(2πt / T) When granulation is performed by vibration, the strain rate is calculated by dividing the maximum velocity (v) [m / s] generated by the vibration by the feed height. Strain rate [ / s] = maximum speed caused by vibration [m / s] / feed height [m] The amplitude and period may be measured by any method, including using the settings of the shaker itself, or by capturing the vibration itself with a video camera and determining the amplitude and period through image processing.

[0065] (3) Rotating a container containing fibers and a fiber processing agent to give the fibers a rotational speed (rolling granulation) Specifically, there may be mentioned a method using the pan granulator shown in FIG. 2, which was mentioned in the explanation of the method for producing the fiber aggregate according to the second embodiment of the present invention. In this type of rolling granulation, the strain rate corresponds to the peripheral speed [m / s] of the pan divided by the peripheral length of the pan. Strain rate [ / s] = circumferential speed of pan [m / s] / pan circumference [m]

[0066] (4) An operation of blowing gas into a vessel containing fibers and a fiber processing agent to impart an airflow shear velocity (fluidized bed granulation) Specifically, the fluidized bed granulation method involves pumping gas into the bottom of a granulation chamber to lift the raw powder particles into the air, forming a layer in which the particles become fluidized, and then spraying the granulation liquid onto the particles to grow them into granules through aggregation or coating.

[0067] In such a fluidized bed granulation, the airflow velocity is the maximum velocity, which is divided by the feed height to define the strain rate. Strain rate [ / s] = blowing speed [m / s] / feed height [m]

[0068] <Textile> The fibers used in the production of the fiber aggregate (hereinafter, sometimes referred to as "raw fibers") contain carbon fibers. As long as the raw fibers contain carbon fibers, they may further contain inorganic fibers other than carbon fibers or organic fibers.

[0069] Examples of inorganic fibers other than carbon fibers include glass fibers, carbon fibers, boron fibers, silicon carbide fibers, silicon nitride fibers, alumina fibers, stainless steel fibers, and piano wires.

[0070] The organic fibers include chemical fibers and natural fibers.

[0071] Examples of chemical fibers include polyester fibers such as polyethylene terephthalate (PET) fibers, polybutylene terephthalate fibers, polytrimethylene terephthalate fibers, and polylactic acid fibers; polyamide fibers such as nylon 6 fibers and nylon 66 fibers; polyacrylic fibers; polyolefin fibers such as polypropylene fibers; polyphenylene sulfide fibers; and polycarbonate fibers.

[0072] Examples of natural fibers include vegetable fibers such as cotton, hemp, kenaf, bamboo cotton, bamboo rayon, and rayon, and animal fibers such as wool and silk.

[0073] These fibers may be used alone or in combination of two or more.

[0074] Among these fibers, it is preferable to use at least carbon fibers, since they are particularly useful for producing a fiber-reinforced resin composition and can provide a fiber-reinforced resin composition having high specific strength and specific elastic modulus. The proportion of carbon fibers in the raw fiber material is preferably 70 mass% or more, and more preferably 90 to 100 mass%.

[0075] The raw fiber is not limited to virgin fiber, but may be recycled fiber. In particular, according to the first aspect, a carbon fiber aggregate having a high bulk density can be produced from recycled fiber, in which the fibers are aligned while maintaining their length without cutting the fibers. Examples of recycled fibers include fibers obtained by decomposing the matrix using heat, subcritical fluid, or supercritical fluid, and fibers obtained by cutting the end material of a fiber substrate. The matrix can be completely removed from recycled fibers until the fibers become cotton-like. If there is any resin residue that cannot be completely removed, it may be removed by heat treatment in an oxidizing atmosphere.

[0076] The raw fiber is an assembly of multiple discontinuous fibers (short fibers), and may be cotton-like or aligned. If the monofilaments are assembled to a degree that they do not scatter, the conversion efficiency to a fiber assembly is high. The discontinuous fiber may be obtained by cutting a bundle of continuous fibers, or fibers in a discontinuous form may be used. The continuous fiber may be a tow, or may be taken out from a prepreg, a molded product, or the like. For example, recycled fibers obtained by decomposing the matrix with heat are in a dry, cotton-like fiber state immediately after heating. By using agitation granulation, it is possible to obtain a fiber aggregate in which the fibers are aligned without changing the form of the fibers from the fiber recycling process. This is because the rotation of the agitator blades can remove tangles between the fibers and adhesions such as resin carbonized matter.

[0077] Figure 4 shows an example of the morphology of recycled fibers. Recycled fibers are clumps of fibers that are randomly layered. Figure 5 shows an example of the morphology of virgin fibers. Virgin fibers are a mass of aligned fiber bundles.

[0078] The raw fibers may be defibrated before being stirred in a stirring granulator or the like. For example, before the fiber treatment agent is added to the stirring tank, the raw fibers are defibrated by stirring the fibers without liquid in the stirring tank with a stirring blade. The rotation of the stirring blade loosens the fibers bonded together with adhesions such as resin carbonized material into smaller units of fiber, which makes it easier to align the fibers by stirring with the stirring blade after the fiber treatment agent is added. At the same time, the uniformity of the fiber aggregate can be improved.

[0079] The raw fiber may have a sizing agent or FRP matrix resin attached thereto. The amount of resin residue in raw fiber such as carbon fiber is, for example, in the range of 0.01 to 10%.

[0080] There is no particular restriction on the fiber diameter of the raw fiber such as carbon fiber. The fiber diameter of the raw fiber is a normal fiber diameter, for example, in the range of 5 μm to 20 μm. The bulk density of the raw fiber is, for example, 0.01 to 0.90 g / cm 3 The bulk density of the raw fiber is in the range of 0.01 to 0.040 g / cm 3 Within this range, it is easy to convert the raw fiber into a fiber aggregate having a bulk density greater than that of the raw fiber.

[0081] The average fiber length of the raw fiber such as carbon fiber is preferably 1 to 100 mm, particularly preferably 2 to 50 mm. When used in a fiber-reinforced resin composition (pellets) used in extrusion molding, the average fiber length of the raw fiber is preferably 2 to 12 mm. When used in a fiber-reinforced resin material (prepreg) used in press molding, the average fiber length of the raw fiber is preferably 12 to 50 mm, and more preferably 12 to 30 mm from the viewpoint of easily scattering and uniformly depositing the fiber aggregate during prepreg production. If the fiber length of the raw fiber is not less than the above lower limit, the strength of the fiber-reinforced resin composition can be sufficiently increased and the fiber orientation can be highly controlled. If the average fiber length of the raw fiber is not more than the above upper limit, the production efficiency can be improved by suppressing entanglement in the device when producing the fiber aggregate, and the particle shape of the fiber aggregate can be uniformly controlled. The average fiber length is preferably a weighted average fiber length. The average fiber length can be measured by the method described in the Examples section below. The fiber length can also be calculated by binarizing an image taken by microscopic observation using image processing software such as ImageJ.

[0082] <Textile treatment agent> The fiber treatment agent is not particularly limited as long as it can granulate fibers to form a fiber aggregate. The fiber treatment agent may be liquid. Examples of the fiber treatment agent that can be used include a solvent, a solvent in which an organic compound is dissolved, a solvent in which an organic compound is mechanically dispersed, a solvent in which an organic compound is dispersed with a surfactant, and a solvent in which the viscosity is reduced by heating. The fiber treatment agent is preferably liquid at room temperature from the viewpoint of forming liquid bridges between fibers at room temperature.

[0083] Examples of the organic compounds include the following: Natural compounds such as starch, cyclodextrin, amino acids, peptides, proteins, natural rubber, soybean oil, and coconut oil; ABS resin, vinylidene chloride latex, vinyl chloride resin, butadiene resin, fluororesin, polyacetal, polyamides such as nylon 6 and nylon 66, polyesters such as polyacrylate, polyetherimide, polyether ether ketone, polyethylene, polyethylene oxide, polyethylene terephthalate, and polybutylene terephthalate, thermoplastic resins such as polycarbonate, polystyrene, polysulfone, polyvinyl ether, polyphenylene oxide, polyphenylene sulfide, polypropylene, and methacrylic resin, precursors and monomers of these resins, and modified products of these resins; Thermosetting resins such as epoxy resins, xylene resins, vinyl ester resins, phenolic resins, unsaturated polyester resins, furan resins, polyimides, polyurethanes, melamine resins, and urea resins, precursors and monomers of these resins, and modified products of these resins; Synthetic rubbers such as styrene-butadiene latex, butadiene latex, neoprene-butadiene latex, chloroprene rubber, urethane rubber, silicone rubber, fluororubber, acrylic rubber, etc.; silane coupling agents such as vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, tris-(2-methoxyethoxy)vinylsilane, γ-glycidoxypropyltrimethoxysilane, 3-(trimethoxysilyl)propyl methacrylate, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane; Titanium coupling agents such as isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, bis(dioctyl bilophosphate)oxyacetate titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate, and isopropyl tri(N-aminoethyl-aminoethyl) titanate:

[0084] Specific examples of fiber treatment agents include the following:

[0085] Examples of the solvent include organic solvents such as alcohols, ketones, and hydrocarbons, and water. Examples of the granulation accelerator include organic thickeners such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), xanthan gum, guar gum, starch, polyvinyl alcohol, polyacrylamide, polyethylene glycol, and polyethylene oxide; and inorganic thickeners such as smectite clay minerals such as montmorillonite, saponite, hectorite, bentonite, beidellite, nontronite, sauconite, stevenside, laponite, and synthetic smectite, and white carbon such as hydrated silica, anhydrous silica, and hydrated silicate.

[0086] Examples of sizing agents include polyvinyl alcohols (PVA) such as unsaponified polyvinyl acetate, partially saponified PVA, fully saponified PVA, and modified PVA (itaconic acid modified, phthalic acid modified, acrylic acid modified, etc.); copolymers of vinyl acetate with ethylene, maleic acid, crotonic acid, or acrylic acid; cellulose derivatives such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose; starch derivatives such as corn starch and soluble starch; acrylic polymers such as polyacrylic acid soda and polyacrylamide; rubber latex, epoxy resins, and polyurethanes.

[0087] The fiber treatment agent preferably contains one or more selected from a solvent, a clay mineral, a resin, and a surfactant, which forms a liquid bridge between fibers to facilitate fiber orientation, and improves the bulk density of the fiber assembly and uniforms the particle shape. From the standpoint of safety, the fiber treatment agent is preferably water, an organic compound dissolved in water, an organic compound mechanically dispersed in water, or an organic compound dispersed in water by a surfactant. As an embodiment of the resin, a polymer may be contained.

[0088] Examples of the solvent include organic solvents such as alcohols (e.g., methanol, ethanol, propanol, etc.), ketones (e.g., acetone, methyl ethyl ketone, etc.), hydrocarbons (e.g., hexane, cyclohexane, benzene, toluene, styrene, etc.), and water. From the viewpoint of forming a liquid crosslink, water is preferred.

[0089] Examples of clay minerals include montmorillonite, saponite, hectorite, bentonite, beidellite, nontronite, sauconite, stevenside, laponite, and synthetic smectite.

[0090] Examples of the resin include ABS resin, vinylidene chloride latex, vinyl chloride resin, butadiene resin, fluororesin, polyacetal, polyamide resin such as nylon 6 and nylon 66, polyester such as polyacrylate, polyetherimide, polyetheretherketone, polyethylene, polyethylene oxide, polyethylene terephthalate, and polybutylene terephthalate, thermoplastic resin such as polycarbonate, polystyrene, polysulfone, polyvinyl ether, polyphenylene oxide, polyphenylene sulfide, polypropylene, and methacrylic resin; thermosetting resin such as epoxy resin, xylene resin, vinyl ester resin, phenol resin, unsaturated polyester resin, furan resin, polyimide, polyurethane, melamine resin, and urea resin; synthetic rubber such as styrene-butadiene latex, butadiene latex, neoprene-butadiene latex, chloroprene rubber, urethane rubber, silicone rubber, fluororubber, and acrylic rubber; etc. From the viewpoint of maintaining the shape of the fiber bundle, it is preferable that the resin contains at least one selected from epoxy resin, urethane resin, and polyamide resin.

[0091] Examples of the surfactant include anionic surfactants such as alkyl ether carboxylates, cationic surfactants such as aliphatic quaternary ammonium salts and imidazolinium salts, amphoteric surfactants such as carboxyl betaine types, and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene glycerin fatty acid esters, and polyethylene glycol fatty acid esters.

[0092] The fiber treating agent preferably has either one or both of the following physical properties (1) and (2). (1) Surface tension at 23°C is 120 mN / m or less (2) Viscosity at 23°C is 10 Pa s or less

[0093] If the surface tension of the fiber treatment agent at 23°C is 120 mN / m or less, liquid bridges can be formed between fibers, facilitating fiber movement and enabling fiber orientation. The surface tension of the fiber treatment agent at 23°C can be 110 mN / m or less, 100 mN / m or less, 90 mN / m or less, 72 mN / m or less, 60 mN / m or less, 50 mN / m or less, or 40 mN / m or less. On the other hand, the surface tension of the fiber treatment agent at 23°C can be 10 mN / m or more, 15 mN / m or more, 20 mN / m or more, or 30 mN / m or more. Here, the surface tension at 23° C. is a value measured by the plate method (vertical plate method). When granulation is performed by heating, a fiber treatment agent having a surface tension in the above range at the stirring temperature can be used. If the surface tension of the fiber treatment agent is equal to or higher than the lower limit, an appropriate negative capillary pressure is applied to the liquid bridges connecting the fibers, and the fibers are adsorbed to each other and oriented, thereby obtaining a dense fiber aggregate. If the surface tension is equal to or lower than the upper limit, the fiber treatment agent adequately wets the fiber surfaces, and liquid bridges are efficiently generated, resulting in excellent fiber granulation efficiency.

[0094] If the viscosity of the fiber treatment agent at 23°C is 10 Pa·s or less, it is possible to make the particle shape of the fiber aggregate uniform. The viscosity of the fiber treatment agent at 23°C can be 8 Pa·s or less, 5 Pa·s or less, 2 Pa·s or less, or 0.5 Pa·s or less. On the other hand, the viscosity of the fiber treatment agent at 23°C can be 0.0001 Pa·s or more. Here, the viscosity at 23° C. is a value measured by a B-type rotational viscometer. When granulation is performed by heating, a fiber treatment agent having a viscosity tension in the above range at the stirring temperature can be used. If the viscosity of the fiber treatment agent is equal to or lower than the upper limit, friction between the fibers is appropriately generated, which allows a uniform fiber aggregate with a regular shape to be obtained. In addition, the fiber treatment agent spreads over the fiber surface, which allows liquid bridging to be efficiently generated, resulting in excellent fiber granulation effect.

[0095] The surface tension of the fiber treatment agent at 23° C. can be adjusted, for example, by mixing a surfactant or a solvent. The viscosity of the fiber treatment agent at 23° C. can be adjusted, for example, by mixing a granulation promoter or a solvent.

[0096] It is preferable to use 5 to 120 parts by mass of such a fiber treatment agent relative to 100 parts by mass of fibers. If the amount of the fiber treatment agent used is equal to or more than the lower limit, an appropriate amount of liquid bridges are generated between the fibers, which promotes the flow and adsorption of the fibers to allow proper orientation, and a dense fiber aggregate can be obtained. If the amount of the fiber treatment agent used is equal to or less than the upper limit, the liquid bridges between the fibers do not disappear, and a fiber aggregate that maintains its particle shape without becoming a slurry can be obtained. It is more preferable to use 20 to 80 parts by mass of the fiber treatment agent relative to 100 parts by mass of fibers. When the average fiber length of the raw material fibers is 2 to 12 mm, it is preferable to use 5 to 50 parts by mass of the fiber treatment agent relative to 100 parts by mass of fibers, and more preferably use 10 to 40 parts by mass, from the viewpoint of facilitating drying and adjusting the fiber aggregate to a size suitable for pelletization. When the average fiber length of the raw fiber is 12 to 50 mm, from the viewpoints of facilitating drying and of adjusting the fiber aggregate to a size suitable for the prepreg, it is preferable to use 20 to 120 parts by mass, and more preferably 30 to 80 parts by mass, of the fiber treatment agent per 100 parts by mass of the fiber.

[0097] The fiber treating agent may be charged together with the fibers into the stirring granulator in its entirety at once, or may be charged intermittently in portions, or may be charged continuously.

[0098] <Fiber assembly> According to the first aspect of the present invention, by granulating fibers and a fiber treatment agent, a fiber aggregate with high bulk density can be produced in which the fibers are aligned while maintaining their length without cutting the fibers.

[0099] The average fiber length of the fibers in the fiber assembly is preferably 1 to 100 mm, particularly preferably 2 to 50 mm. The average fiber length of the fibers in the fiber assembly is preferably 2 to 12 mm when used in a fiber reinforced resin composition (pellets) to be used in extrusion molding. The average fiber length of the fibers in the fiber assembly is preferably 12 to 50 mm when used in a fiber reinforced resin composition (prepreg) to be used in press molding.

[0100] Regarding the degree of fiber length maintenance, in order to improve the uniformity of the fiber aggregate, the ratio (Y / X) of the average fiber length Y of the fibers in the fiber aggregate to the average fiber length X of the raw material fibers before being charged into the stirring tank is preferably 0.55 or more, more preferably 0.70 or more, even more preferably 0.80 or more, and particularly preferably 0.90 or more. This ratio (Y / X) can be 1 or less.

[0101] The shape of the resulting fiber aggregate is not particularly limited, but for use as a reinforcing fiber, it is preferably in the form of an oval or strand. An example of an oval shape is an ellipsoid, but the diameter of the thickest part may be 0.1 mm to 10 mm, the length of the long axis may be 3 mm to 150 mm, longer than the average fiber length of the fibers in the fiber assembly, and the cross-sectional shape may be circular, oval, etc. When used for pellets, the shape of the fiber assembly is preferably an oval shape from the viewpoint of feeding efficiency to a kneader, the diameter of the thickest part may be 2 mm to 7 mm, the length of the long axis may be longer than the average fiber length of the fibers in the fiber assembly, and the ratio (long axis length / average fiber length) is preferably 1.1 to 5.0 times, 3 mm to 18 mm. When used for prepregs, the shape of the fiber assembly is preferably a strand shape from the viewpoint of scattering and uniformly depositing the fiber assembly, and the diameter of the thickest part may be 2 mm to 10 mm. The bundle length is longer than the average fiber length of the fibers in the fiber assembly, and the ratio (bundle length / average fiber length) is preferably 1.1 to 3.0 times and 12 mm to 150 mm.

[0102] The major axis of this fiber aggregate is preferably longer than the average fiber length of the fibers contained in the fiber aggregate.

[0103] The bulk density of the fiber assembly is, for example, 0.03 to 0.7 g / cm 3 Although it depends on the raw fiber used, from the viewpoint of the transport efficiency of the fiber aggregate, the bulk density is set to 0.1 g / cm 3 More than 0.2 g / cm is preferable. 3 The above is particularly preferred. For applications involving molded products with low fiber content, the bulk density is 0.1 g / cm 3 More than 0.3g / cm 3 Less than 0.1g / cm 3 More than 0.29g / cm 3 For molded products requiring strength, the bulk density is 0.3 g / cm 3 ~0.6g / cm 3 Since the amount that can be fed at one time can be increased, in either case, the bulk density is 0.15 g / cm 3 More than 0.2 g / cm is preferable. 3 The angle of repose of the fiber aggregate is preferably 60° or less, more preferably 50° or less. It can be 10° or more. The bulk density and angle of repose of the fiber assembly are measured by the method described in the Examples section below.

[0104] The fiber content in the fiber assembly can be, for example, 10 to 99% by mass. When used for producing pellets, the fiber content in the fiber assembly can be, for example, 80 to 99% by mass. When the fiber assembly is directly put into a molding die or the like for molding, the fiber content in the fiber assembly can be, for example, 10 to 70% by mass. When the fiber assembly contains a resin, it is more preferable that the resin is contained in an amount of 0.1 to 20 parts by mass, particularly 0.5 to 10 parts by mass, per 100 parts by mass of the fibers in the fiber assembly.

[0105] <Application> The fiber aggregate, particularly the carbon fiber aggregate, produced by the fiber aggregate production method of the first aspect of the present invention can be effectively used as a reinforcing fiber in fiber reinforced resin composition molding materials such as various prepregs (random, unidirectional), pellets, stampable sheets, etc.

[0106] <Prepreg sheet manufacturing method> The method for producing a prepreg sheet includes stacking a plurality of fiber assemblies produced by the above-mentioned method for producing a fiber assembly.

[0107] An example of a prepreg that can be produced using the SACFB as a fiber assembly is a sheet prepreg. In a preferred example, the sheet prepreg can be produced through the following first to fourth steps.

[0108] First step: applying a liquid thermosetting resin composition to the surface of each of the first protective film and the second protective film. Second step: forming a carbon fiber mat by depositing a plurality of short carbon fiber bundles including SACFB on the surface of the first protective film on which the liquid thermosetting resin composition has been applied. Third step: A step of forming a laminate by bonding the second protective film to the first protective film with the carbon fiber mat sandwiched therebetween so that the surfaces coated with the liquid thermosetting resin composition face each other. Fourth step: A step of impregnating the carbon fiber mat with the liquid thermosetting resin composition by pressing the laminate to obtain a sheet prepreg.

[0109] The first protective film and the second protective film are synthetic resin films, and the material thereof can be appropriately selected from polyolefins such as polyethylene and polypropylene, polyvinylidene chloride, vinyl chloride resins, polyamides, etc. The first protective film and the second protective film may be multi-layer films. The specifications of the first protective film and the second protective film may be the same or different.

[0110] In the second step, a carbon fiber mat is formed by depositing, for example by spreading, a plurality of short carbon fiber bundles containing SACFB on the surface of the first protective film on which the liquid thermosetting resin composition has been applied.

[0111] The amount of liquid thermosetting resin composition applied to the first protective film and the second protective film 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 taking into account the basis weight and fiber content of the sheet prepreg to be produced.

[0112] When a thickener is blended in the liquid thermosetting resin composition, the prepreg is aged after the fourth step until the viscosity of the liquid thermosetting resin composition becomes sufficiently high.

[0113] In the above procedure, the first protective film and the second protective film may be a carrier film unwound from a roll. In a preferred embodiment, a sheet prepreg manufacturing apparatus, the conceptual diagram of which is shown in FIG. 8, can be used to continuously manufacture long sheet prepregs. The sheet prepreg manufacturing apparatus shown in FIG. 8 has a section for applying a liquid thermosetting resin composition to a first protective film unwound from a roll, a section for scattering carbon fiber bundles onto the first protective film to deposit a carbon fiber mat, a section for applying a liquid thermosetting resin composition to a second protective film unwound from a roll, a section for bonding the second protective film to the first protective film to form a laminate, a section for pressurizing the laminate, and a section for winding up the laminate.

[0114] When manufacturing a CFRP product using a prepreg using SACFB, the molding method is preferably a press molding method, but is not limited thereto. As the molding method, a molding method other than the press molding method, such as an autoclave molding method, can also be used.

[0115] [Fourth aspect of the present invention] The fourth aspect of the present invention will now be described.

[0116] A fiber bundle according to a fourth aspect of the present invention (hereinafter, may be referred to as "fiber bundle W") contains a plurality of carbon fibers and a resin or a solvent, the fiber bundle has an ellipsoidal shape, and A' / A specified by the following condition (1) is 0.75 to 0.93. The fiber bundle according to the fourth aspect is one aspect of a fiber aggregate. Condition (1): A fiber bundle placed on a white plate is photographed from the opposite side of the vertical plate, and the image obtained is binarized using image analysis software to obtain a binary image. The binary image is contour-extracted to obtain the outline of the fiber bundle. The Feret diameter is calculated from the obtained outline, and the major axis length is designated as A. The binary image is approximated to an ellipse, and the major axis length of the ellipse is designated as A'.

[0117] As A' / A approaches 1, the cross-sectional shape of the fiber bundle when cut in the same direction as the long axis becomes closer to an ellipse or a circle. As the value of A' / A decreases, the cross-sectional shape tends to have a corner or a protruding fiber at the end of the long axis. If A' / A is 0.75 or more, when a large number of fiber bundles are present (multiple fiber aggregates), the fiber bundles tend to slide against each other, and bridges that support each other and hinder the fall of the fiber bundles, particularly in the hopper, in the feeder for feeding the fiber bundles into the kneader can be suppressed. If A' / A is 0.93 or less, the fiber bundles are oriented in the flow direction and easily flow in the feeder, and the fiber bundles are arranged so that there are fewer gaps in the feeder, so that a constant amount can be continuously supplied. A' / A can be, for example, 0.93 or less, 0.92 or less, or 0.91 or less. A' / A can be, for example, 0.75 or more, 0.80 or more, 0.81 or more, or 0.85 or more.

[0118] From the viewpoint of mechanical properties of the resin molded product, the major axis length A of the fiber bundle W is preferably 3 mm or more, and more preferably 4 mm or more. From the viewpoint of preventing bridge formation, the major axis length A can be 30 mm or less, and 25 mm or less.

[0119] The ratio (S' / S) of the area S' of a virtual ellipse determined from the major and minor axes of the contour to the area S of an ellipse obtained by elliptical approximation can be set to 0.70 to 1.06, or 0.80 to 0.92. Condition (1) can be implemented, for example, in the following manner.

[0120] The fiber bundle is photographed at 20x magnification using a VHX-6000 digital microscope and ring illumination. The fiber bundle is placed naturally on a white board held horizontally and photographed in a stable position from the vertical direction opposite the white board. For image analysis, a binary image is obtained using Otsu's binarization process (Make Binary) using software (ImageJ). The contour of this binary image is extracted (Analyze Particles, Outlines) to obtain the contour of one fiber bundle. The Feret's diameter is calculated from the obtained contour. The contour is approximated to an ellipse using the least squares method (Analyze Particles, Ellipses) to obtain the length A' of the major axis of the ellipse.

[0121] The average fiber length of the fibers in the fiber bundle W is preferably 1 to 100 mm, and particularly preferably 2 to 50 mm. When used for producing pellets, the average fiber length of the fibers in the fiber bundle W is preferably 2 to 12 mm. The average fiber length is preferably a weighted average fiber length, and can be measured by the method described in the Examples section below. The average fiber length of the fibers can be shorter than the major axis A, and can have a relationship of 0.2 x A to 0.8 x A mm.

[0122] The number of filaments contained in the fiber bundle W can be, for example, 8,000 to 800,000. The number of filaments at the center of the long axis of the fiber bundle W is greater than that at the end of the long axis, so that the fiber bundle W can have an ellipsoidal shape. The fibers in the fiber bundle W are pulled together to form a fiber bundle. The fibers present on the surface of the fiber bundle are preferably curved and oriented along the contour of the ellipsoid.

[0123] The ellipsoid has a major axis, a minor axis 1 and a minor axis 2, and in order to prevent the fiber bundle from being blocked in a narrowed portion of a hopper in a feeder, for example, it is preferable that the length B of the minor axis 1 is longer than the length C of the minor axis 2 and is close to the length C of the minor axis 2. From the viewpoint of preventing the occurrence of bridges, B is 3.0 times or less, preferably 2.0 times or less, and can be 1.1 times or more, for example, 1.5 times or more, of C. Specifically, the length B is preferably 1 mm or more, more preferably 2 mm or more, from the viewpoint of supply amount control, and is usually 9 mm or less, preferably 8 mm or less, more preferably 6 mm or less, from the viewpoint of preventing bridge formation. From the viewpoint of controlling the supply amount, C is preferably 0.5 mm or more, and more preferably 1 mm or more. From the viewpoint of preventing bridge formation, C is usually 6 mm or less, preferably 4 mm or less, and more preferably 3 mm or less.

[0124] The ratio of the major axis to the minor axis 1 (B / A) can be 2-12, and the ratio of the major axis to the minor axis 2 (C / A) can be 1-6.

[0125] The particle density of the fiber bundle, expressed by the following formula (2), is 0.3 to 1.8 g / cm 3 It can be said that: Particle density=G / (4πabc / 3)...Equation (2) (In formula (2), G represents the mass of the fiber bundle, a represents A / 2, b represents B / 2, and c represents C / 2.)

[0126] From the viewpoint of improving the feed efficiency, the fiber aggregate preferably has a number ratio of fiber bundles W of 45% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 80% or more. The number ratio can be less than 100%. The number ratio is calculated by extracting 100 to 10,000 fiber bundles from the fiber assembly and dividing the number of fiber bundles W in the extracted fiber assembly by the number of bundles extracted. 3 ~450cm 3is scooped up into a measuring container, the scooped fiber bundles are arranged on a white board so as not to overlap, and the arranged multiple fiber bundles are photographed with a digital camera, and the image obtained can be used to determine A' / A of each fiber bundle using the image analysis method of condition (1). It is preferable to extract fiber bundles from an aggregate in which multiple fiber bundles are aggregated and from a fiber aggregate from which fine powder has been removed.

[0127] <Method of Manufacturing Fiber Bundle W> The fiber bundle W is obtained by mixing cotton made of short fibers with a liquid to spontaneously bundle the short fibers. Specifically, it can be produced by granulation such as rolling granulation, stirring granulation, and fluidized bed granulation. For example, A' / A can be set to a specific range by feeding cotton made of short carbon fibers and liquid into an agitator and stirring at a rotation speed of 120 to 470 rpm of the stirring blade (agitator) and a rotation speed of 2000 to 3000 rpm of the chopper. It is preferable to use 5 to 120 parts by mass of the liquid per 100 parts by mass of the fiber, and more preferably 20 to 80 parts by mass. The resin and solvent mentioned above can be used as the components constituting the liquid.

[0128] An example of a granulating agitator suitable for use in producing the fiber bundle W is the agitating granulator shown in Fig. 1 described above as the agitating granulator in the method for producing a fiber aggregate according to the first embodiment of the present invention. The specific agitating granulator and agitation conditions are also the same.

[0129] Regarding the rotation direction conditions of the stirring granulator, it is preferable that the peripheral speed (hereinafter simply referred to as "peripheral speed") of the stirring blade tip (part 3a in Fig. 1a) is in the range of 1 to 20 m / sec. If the peripheral speed is 1 m / sec or more, it is possible to stir the fiber mixture granules while circulating them in the stirring tank. If the peripheral speed is 20 m / sec or less, it is possible to make the particle shape of the fiber aggregate uniform. The peripheral speed of the stirring blade is more preferably 4 to 12 m / sec, and even more preferably 4 to 8 m / sec. The rotation speed of the impeller can be set to 30 to 1800 rpm. The rotation speed of the chopper can be set to 800 to 5000 rpm. As long as the fibers are not cut, the higher the rotation speed of the impeller and chopper, the smaller A' / A tends to be. EXAMPLES

[0130] The present invention will be described in more detail below using examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0131] [Mixing granulator] In the following Examples 1 to 4, the stirring granulator has three stirring blades extending radially from a central rotating shaft as shown in Fig. 1. The inclination angles θ of the stirring blades are as follows:

[0132] [Measurement and evaluation method] The various measurement and evaluation methods were as follows:

[0133] <Surface tension> The surface tension of the fiber treatment agent at 23° C. was measured using an automatic surface tensiometer (Kyowa Interface Science: CBVP-A3, plate method).

[0134] <Viscosity> The viscosity of the fiber treatment agent at 23° C. was measured using a B-type rotational viscometer (Brookfield: LVDV-1 Pri, spindle S61). The value measured at 50 rpm was used as the representative viscosity value.

[0135] <Average fiber length> A fiber aggregate was immersed in ethanol and disintegrated into single fibers, transferred onto filter paper and dried, and then photographed with a digital microscope (Keyence: HX-6000-2). The fiber length was measured using the built-in software. For each sample, 100 fibers were counted and the average fiber length (weighted average fiber length) was calculated. The weighted average fiber length was calculated by dividing the sum of the squares of the measured lengths by the sum of the measured lengths so that the length is weighted (weighted average fiber length L = Σl 2 / Σl)

[0136] <Bulk density> 100 mL of multiple fiber aggregates was placed in a φ50 mm container, tapped 10 times from a height of 3 cm to deposit the fiber aggregate, and the bulk density was calculated from the volume and weight. Measurements were performed in accordance with JIS Z2512 and JIS R1628.

[0137] <Long axis ratio A' / A> The fiber bundle obtained as a fiber assembly was placed on a white plate held horizontally, and photographed at a magnification of 20 times using a digital microscope VHX-6000 and a ring light from the vertical direction opposite to the white plate. The photographed image of the fiber bundle in Example 1 is shown in FIG. 9. The photographed image of the fiber bundle in Comparative Example 1 is shown in FIG. 12. The photographed image was subjected to Otsu's binarization processing (Make Binary) using ImageJ (Wayne Rasband) to obtain a binary image. The binary image was subjected to contour extraction (Analyze Particles, Outlines) to obtain the contour of one fiber bundle. The contour of the fiber bundle in Example 1 is shown in FIG. 10. The Feret's diameter was calculated from the obtained contour and set as the major axis length A. The contour was approximated to an ellipse by the least squares method (Analyze Particles, Ellipses) to obtain the major axis length A' of the obtained ellipse. A' was divided by A to obtain the major axis ratio A' / A. The approximate ellipse in the first embodiment is shown in FIG.

[0138] <BおよびC> The fiber bundle obtained as a fiber assembly was placed on a white plate held horizontally, and the length in the direction perpendicular to the long axis was measured with a vernier caliper and designated as B. The fiber bundle was placed on a white plate held horizontally, and the height in the vertical direction perpendicular to the long axis was measured with a height gauge and designated as C.

[0139] <Area ratio S' / S> The fiber bundle obtained as a fiber assembly was placed on a white plate held horizontally, and photographed at a magnification of 20 times using a digital microscope VHX-6000 and a ring light from the vertical direction opposite to the white plate. The photographed image of the fiber bundle in Example 1 is shown in FIG. 9. The photographed image of the fiber bundle in Comparative Example 1 is shown in FIG. 12. The photographed image was subjected to Otsu's binarization processing (Make Binary) using ImageJ (Wayne Rasband) to obtain a binary image. This binary image was subjected to contour extraction (Analyze Particles, Outlines) to obtain the contour of one fiber bundle. The contour of the fiber bundle in Example 1 is shown in FIG. 10. The Feret's diameter was obtained from the obtained contour, and the major axis length A was obtained. The point that bisects the major axis is F, the intersection points of the perpendicular line to the major axis at F and the contour are Y and Y', and the straight line connecting Y and Y' is the minor axis B, and the area obtained from the formula (S=π×A / 2×B / 2) was S. The area of ​​the ellipse obtained by approximating the contour to an ellipse using the least squares method (select Analyze Particles, Ellipses) was taken as S'. The area ratio S' / S was calculated by dividing S' by S.

[0140] <Angle of repose> 200g of fiber bundle was allowed to fall from a height of 100mm onto a horizontally held circular plate of φ95mm, and the pile height of the fiber bundle was measured after 10 seconds. The radius of the circular plate is R, the pile height is T, and the angle of repose is θ=tan -1 (T / R) was sought.

[0141] <Number ratio of fiber bundles W (0.75-0.93 number ratio)> 111 fiber bundles were randomly selected from multiple fiber bundles, and the number of fiber bundles with A' / A between 0.75 and 0.93 was divided by 111 to determine the number ratio. A' / A was calculated in the same manner as for <long axis ratio A' / A>, except that a digital camera was used instead of a digital microscope.

[0142] <Weight distribution of carbon fiber aggregates> Randomly extract 300 fiber bundles from multiple fiber bundles and measure the weight of each. Calculate the number average and weight average from the measurement results of 300 bundles. The weight average was divided by the number average to obtain the weight distribution of the carbon fiber aggregate.

[0143] [Production Example 1: Dispersion 1] The following types and amounts of components (A), (B), and (C) were kneaded and mixed with a planetary mixer and a homomixer at 80 to 100°C. After that, the temperature was lowered to 80°C while maintaining the kneading, and then an aqueous solution of the following component (D) was added little by little. In this process, the viscosity of the contents gradually increased. After all the aqueous solution of component (D) was added, the temperature was lowered to 60°C while thoroughly kneading for 10 minutes. Next, deionized water was added dropwise in small amounts until the phase inversion point was passed, and the amount of water added was increased. Finally, an aqueous dispersion 1 with an active ingredient content of about 40% by mass was obtained. (A) One-terminated acrylic-modified bisphenol A epoxy resin (35 parts by mass) (based on EP828 manufactured by Mitsubishi Chemical Corporation) (B) Aliphatic urethane acrylate oligomer (30 parts by mass) (CN-9788 manufactured by Sartomer Corporation) (C) Fumaric anhydride ester of ethylene oxide 2 moles of bisphenol A (20 parts by mass) (D) Newcol 723SF (15 parts by weight) manufactured by Nippon Nyukazai Co., Ltd.

[0144] [Example 1] The carbon fiber used was a cotton-like recycled carbon fiber (average fiber length 2.5 mm, bulk density 0.034 g / cm) obtained by pyrolysis. 3) was used. First, 1200 g of the carbon fiber was put into an agitator granulator (product name: SP Granulator SPG25T, Dalton, device volume: 25 liters, inclination angle θ of the agitator blade: 30°, agitator blade diameter: 396 mm) and agitated for 1 minute to defibrate. Next, a liquid (surface tension at 23°C: 39.5 mN / m, viscosity at 23°C: 0.0017 Pa·s) containing 900 g of water as a fiber treatment agent and 60 g of dispersion 1 (solid content concentration 40 mass%) was put into the agitator granulator and granulated by stirring for 6 minutes at a speed of 400 rpm (circumferential speed of the agitator blade: 8 m / sec) and 3000 rpm of the chopper. The granulated material was dried for 2 hours in a box dryer at 120°C to obtain a carbon fiber aggregate having a spheroid shape with a short axis of 1.5 mm and a long axis of 12 mm. The peripheral speed of the impeller was 8.3 m / s, the height of the raw materials was 0.28 m, the strain rate was 30 [1 / s], and the strain amount was 10,600.

[0145] For the obtained carbon fiber aggregate, the average fiber length and bulk density of the carbon fibers in the carbon fiber aggregate were measured by the above-mentioned methods. The results are shown in Table 1. In addition, the appearance of the carbon fiber aggregate was observed to check the state in which the carbon fibers were aligned. The results are shown in Table 1.

[0146] The fiber aggregate has a longitudinal ratio (A' / A) of 0.91, an area ratio (S' / S) of 0.92, and a particle density of 0.71 g / cm. 3 , and the angle of repose was 54°.

[0147] This fiber aggregate was fed into a screw feeder (manufactured by Labtech Engineering, single shaft, feeder diameter φ33, screw diameter φ25) with a hopper (inverted square pyramid shape, inlet length 120 mm, inlet width 200 mm, outlet length 120 mm, outlet width 35 mm, hopper angle 35°) and operated at 10 rpm. The discharge amount was measured four times every 36 seconds and was 1.74 g on average with a standard deviation of 0.09 g. The proportion of fiber bundles with A' / A in the range of 0.75 to 0.93 was 58%. The fiber assembly of Example 1 could be discharged more stably than the fiber assembly of Comparative Example 1 described later.

[0148] [Example 2] In the method for producing the carbon fiber aggregate of Example 1, the recycled carbon fibers were replaced with virgin carbon fibers (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm 3 The same procedure as in Example 1 was repeated, except that the amount of water used in the fiber treatment agent was changed to 180 g, to obtain carbon fiber aggregates in the shape of an elongated sphere having a minor axis of 1.5 mm and a major axis of 12 mm. The surface tension of the fiber treatment agent used in this example (a mixture of water and dispersion 1) at 23°C was 38.4 mN / m and the viscosity at 23°C was 0.0029 Pa·s. The peripheral speed of the impeller was 8.3 m / s, the height of the raw materials was 0.014 m, and the strain rate was 613 [1 / s]. The strain amount was 220,700. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0149] The fiber aggregate has a longitudinal ratio (A' / A) of 0.80, an area ratio (S' / S) of 0.78, and a particle density of 0.83 g / cm. 3 , the angle of repose was 50°.

[0150] This fiber aggregate was fed into a screw feeder (manufactured by Labtech Engineering, single-axis, feeder diameter φ33, screw diameter φ25) with a hopper (inverted square pyramid shape, inlet length 120 mm, inlet width 200 mm, outlet length 120 mm, outlet width 35 mm, hopper angle 35°) and operated at 10 rpm. The average discharge amount when measured four times every 36 seconds was 2.28 g, with a standard deviation of 2.48 g. The fiber assembly of Example 2 was able to discharge a larger amount of material than the fiber assembly of Comparative Example 1 described below.

[0151] [Example 3] In the method for producing the carbon fiber aggregate of Example 1, the recycled carbon fibers were replaced with virgin carbon fibers (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm3 An ellipsoidal carbon fiber aggregate was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with 3,000 g of Dispersion 2 (anionic polyamide solution, solid content concentration of 40 mass%), Dispersion 1 was replaced with 250 g of Dispersion 2 (anionic polyamide solution, solid content concentration of 40 mass%), and the amount of water used was 200 g. The surface tension of the fiber treatment agent (mixture of water and Dispersion 2) at 23°C was 59.0 mN / m, and the viscosity at 23°C was 0.0022 Pa s. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregate was harder than the carbon fiber aggregate of Example 1 and tended to retain its shape more easily.

[0152] [Example 4] The granulator was replaced with an agitator granulator (product name: Henschel Mixer FM10B, manufactured by Mitsui Miike Seisakusho Co., Ltd., device volume: 9 liters, inclination angle of the agitator blade θ: 30°), and recycled carbon fiber (average fiber length 2.5 mm, bulk density 0.03 g / cm 3 200g of the fiber treatment agent, a mixture of 140g of water and 20g of dispersion 1 (polyester emulsion, solids concentration 40% by mass), was added, and the mixture was stirred for 3 minutes at a stirring impeller speed of 1200 rpm (stirring impeller peripheral speed: 13 m / sec) to form granules. The granules were dried for 2 hours in a box dryer at 120°C to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0153] [Example 5] The granulation equipment was replaced with an agitation granulator (product name: Henschel Mixer FM10B, manufactured by Mitsui Miike Seisakusho Co., Ltd., device volume: 9 liters, inclination angle of the agitation blade θ: 30°), and virgin carbon fiber (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm 3 200 g of cellulose acetate and 40 g of water, which is a fiber treatment agent, were added and granulated by stirring for 3 minutes at a stirring impeller speed of 1200 rpm (circumferential speed of the stirring impeller: 13 m / sec). The granulated material was dried for 2 hours in a box dryer at 120°C to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0154] [Example 6] The granulation equipment was replaced with a rolling agitation granulator (product name: Intensive Mixer R05T, manufactured by Eirich Co., Ltd., equipment volume: 40 liters, rotor type: star type), and virgin carbon fiber (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Co., Ltd., cut length 3.1 mm, bulk density 0.706 g / cm 3 6000g of cellulose acetate ester, 200g of water as a fiber treatment agent, and 700g of dispersion 2 (anionic polyamide solution, solids concentration 40% by mass) were added, and the mixture was stirred for 3 minutes at a speed of 29 rpm (circumferential speed of the rotating container: 0.8 m / sec) and 560 rpm (circumferential speed of the stirring blade: 8 m / sec) for granulation. The stirring rotor rotated in the opposite direction to the mixing pan. The granulated material was dried in a box dryer at 120°C for 2 hours to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregate was harder than the carbon fiber aggregate of Example 1 and tended to retain its shape more easily.

[0155] [Example 7] The granulator was replaced with a rolling agitator granulator (product name: Intensive Mixer R05T, manufactured by Eirich Co., Ltd., device volume: 40 liters, rotor type: star type), and recycled carbon fiber (average fiber length 6.0 mm, bulk density 0.15 g / cm 3 6000g of cellulose acetate 200g, 350g of water as a fiber treatment agent, and 700g of dispersion 2 (anionic polyamide solution, solid content concentration 40% by mass) were added, and the mixture was stirred for 6 minutes to form granules. The rotation speed of the mixing pan was 29 rpm (circumferential speed of the rotating container: 0.8 m / sec). The rotation speed of the stirring rotor was 1120 rpm (circumferential speed of the stirring blade: 16 m / sec) for the first 3 minutes, and 140 rpm (circumferential speed of the stirring blade: 2 m / sec) for the next 3 minutes. The rotation direction of the stirring rotor was the opposite direction to that of the mixing pan. The granules were dried in a box dryer at 120°C for 2 hours to obtain an ellipsoidal carbon fiber aggregate. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregate was harder than the carbon fiber aggregate of Example 1 and tended to retain its shape more easily.

[0156] [Example 8] The carbon fiber aggregate obtained in Example 7 above was placed in a vibrating sieve (product name: Vibrating Sieve 401C, manufactured by Dalton, sieve mesh: 5 mesh, linearity 0.8 mm, mesh size 4.3 mm) and vibrated at an amplitude of 35 Hz. The fraction that passed through the sieve mesh was collected to obtain an ellipsoidal carbon fiber aggregate. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1. In the feed evaluation, the fiber aggregate of Example 8 was able to discharge a larger amount than the fiber aggregate of Example 7.

[0157] [Experimental Example 1] The granulation device was replaced with a rolling granulator (pan type, rotating container inner dimensions φ240 × 75 mm), and virgin carbon fiber (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm) was used. 3 50 g of a mixture of 10 g of water and 50 g of a fiber treatment agent were added, and the mixture was rolled for 6 minutes at an inclination angle of 45° and a rotation speed of 60 rpm (side wall peripheral speed 0.75 m / s) to form granules. The granules were dried for 2 hours in a box dryer at 120°C to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0158] [Experimental Example 2] The granulator was replaced with a vibration granulator (cylindrical sealed container, container inner dimensions φ80 × 200 mm), and virgin carbon fiber (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm) was used. 3 50 g of carbon fiber powder and 10 g of water, which is a fiber treatment agent, were added and granulated by manually vibrating (frequency 2 Hz, amplitude 200 mm) for 30 seconds. The granulated material was dried in a box dryer at 120°C for 2 hours to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0159] [Experimental Example 3] The granulation equipment was replaced with an extrusion granulator (product name: Pelleter Double EXDF (pre-extrusion type), manufactured by Dalton, screen diameter 6 mm), and virgin carbon fiber (product name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical, cut length 3.1 mm, bulk density 0.706 g / cm 3 100 g of the carbon fiber aggregate was mixed with 1000 g of water (a fiber treatment agent) and 10 g of polyacrylamide (product name: Acryprimer GA1055L, manufactured by Mitsubishi Chemical Corporation), and extruded at 200 kg / h to form granules. The granules were dried in a box dryer at 120°C for 2 hours to obtain irregular carbon fiber aggregates. The shape of the irregular carbon fiber aggregates is shown in FIG. 12. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0160] [Experimental Example 4] The granulator was replaced with a rolling granulator (pan type, rotating container inner dimensions φ240 × 75 mm), and recycled carbon fiber (average fiber length 2.5 mm, bulk density 0.03 g / cm 3 50 g of the fiber treatment agent, 37.5 g of water, and 2.5 g of dispersion 1 (polyester emulsion, solids concentration 40 mass%) were added, and the mixture was rolled for 6 minutes at an inclination angle of 45° and a rotation speed of 60 rpm (side wall surface peripheral speed 0.75 m / s) to form granules. The granules were dried for 2 hours in a box dryer at 120°C to obtain irregular carbon fiber aggregates. The shape of the irregular carbon fiber aggregates is shown in FIG. 13. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0161] [Experimental Example 5] The granulator was replaced with a vibration granulator (cylindrical sealed container, container inner dimensions φ80 × 200 mm) and recycled carbon fiber (average fiber length 2.5 mm, bulk density 0.03 g / cm 350 g of the fiber treatment agent, 37.5 g of water, and 2.5 g of dispersion 1 (polyester emulsion, solids concentration 40% by mass) were added, and the mixture was manually vibrated (frequency 2 Hz, amplitude 200 mm) for 30 seconds to form granules. The granules were dried in a box dryer at 120°C for 2 hours to obtain irregular carbon fiber aggregates. The obtained carbon fiber aggregate was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0162] [Table 1]

[0163] In the methods of Experimental Examples 3 to 5, ellipsoidal carbon fiber aggregates could not be obtained within a specific time. In the methods of Experimental Examples 3 to 5, for example, by extending the treatment time, ellipsoidal carbon fiber aggregates may be obtained. However, the methods of Examples 1 to 8 are superior to the methods of Experimental Examples 3 to 5 in that ellipsoidal carbon fiber aggregates can be obtained efficiently in a short time. This was the result.

[0164] [Example 9] As the carbon fiber, virgin carbon fiber (cut product of TR50S15L manufactured by Mitsubishi Chemical Corporation, fiber length 25 mm) was used. First, 1000 g of this carbon fiber was put into an agitation granulator (product name: SP Granulator SPG25T, manufactured by Dalton, device volume: 25 liters, inclination angle θ of the agitation blade: 30°) and agitated for 1 minute to defibrate. Next, 400 g of water, which is a fiber treatment agent, was put into the agitation granulator and agitated for 7 minutes to granulate. The peripheral speed of the tip of the agitation blade was 4 m / s for the first minute, 8 m / s for the next 3 minutes, and 4 m / s for the next 3 minutes. The granulated material was dried for 30 minutes in a vibration type hot air dryer at 110 ° C. to obtain a strand-shaped carbon fiber aggregate. The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0165] [Example 10] In the manufacturing method of the carbon fiber aggregate of Example 9 described above, a strand-shaped carbon fiber aggregate was obtained in the same manner as in Example 9, except that the fiber treatment agent was replaced with a mixed liquid of 375 g of water and 25 g of dispersion 1 (polyester emulsion, solid content concentration 40 mass%). The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0166] [Example 11] In the manufacturing method of the carbon fiber aggregate of Example 9 described above, a strand-like carbon fiber aggregate was obtained in the same manner as in Example 9, except that the virgin carbon fiber was replaced with 1000 g of recycled carbon fiber (cotton-like carbon fiber obtained by pyrolyzing SMC composed of short carbon fiber TR50S15L manufactured by Mitsubishi Chemical Corporation and vinyl ester resin, fiber length 25 mm) and the fiber treatment agent was replaced with a mixed liquid of 750 g of water and 50 g of dispersion 1 (polyester emulsion, solid concentration 40 mass%). The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0167] [Example 12] The granulation device was replaced with a rolling agitation granulator (product name: Intensive Mixer R05T, manufactured by Eirich Co., Ltd., device volume: 40 liters, rotor type: star type), and 3000 g of recycled carbon fiber (cotton-like carbon fiber obtained by pyrolyzing SMC consisting of short carbon fiber TR50S15L manufactured by Mitsubishi Chemical Co., Ltd. and vinyl ester resin, fiber length 25 mm) and a liquid mixed with 1950 g of water as a fiber treatment agent and 450 g of dispersion liquid 1 (polyester emulsion, solid content concentration 40 mass%) were added, and the mixture was agitated for 9 minutes to granulate. The rotation speed of the mixing pan was 29 rpm (circumferential speed of the rotating container: 0.8 m / s). The rotation speed of the agitation rotor was 1120 rpm (circumferential speed of the agitation blade: 16 m / s) for the first 6 minutes and 140 rpm (circumferential speed of the agitation blade: 2 m / s) for the next 3 minutes. The rotation direction of the stirring rotor was the opposite direction to the mixing pan for the first 6 minutes, and the same direction as the mixing pan for the next 3 minutes. The granules were dried in a box dryer at 120°C for 2 hours to obtain a strand-shaped carbon fiber aggregate. The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0168] [Modification of Example 12] The carbon fiber aggregate obtained in the same manner as in Example 12, except that the rotation direction of the stirring rotor was opposite to that of the mixing pan for the first 3 minutes and then in the same direction as that of the mixing pan for the next 6 minutes, had a higher bulk density and a higher weight distribution value than the carbon fiber aggregate of Example 12.

[0169] [Experimental Example 6] The granulation device was replaced with a rolling granulator (pan type, rotating container inner dimensions φ240×75 mm), and 50 g of recycled carbon fiber (cotton-like carbon fiber obtained by pyrolyzing SMC consisting of short carbon fiber TR50S15L manufactured by Mitsubishi Chemical Corporation and vinyl ester resin, fiber length 25 mm) and a liquid mixed with 37.5 g of water and 2.5 g of dispersion 1 (polyester emulsion, solid content concentration 40 mass%) as a fiber treatment agent were added, and granulated by rolling at an inclination angle of 45° and a rotation speed of 60 rpm (side wall surface peripheral speed 0.75 m / s) for 6 minutes. The granulated material was dried for 2 hours in a box dryer at 120 ° C. to obtain an irregular carbon fiber aggregate. The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0170] [Experimental Example 7] The granulation device was replaced with a vibration granulator (cylindrical sealed container, container inner dimensions φ80×200 mm), and 50 g of recycled carbon fiber (cotton-like carbon fiber obtained by pyrolyzing SMC consisting of short carbon fiber TR50S15L manufactured by Mitsubishi Chemical Corporation and vinyl ester resin, fiber length 25 mm) and a liquid mixed with 37.5 g of water and 2.5 g of dispersion 1 (polyester emulsion, solid content concentration 40 mass%) as a fiber treatment agent were added, and the mixture was manually vibrated for 30 seconds (frequency 2 Hz, amplitude 200 mm) to granulate. The granulated material was dried for 2 hours in a box dryer at 120 ° C. to obtain an irregular carbon fiber aggregate. The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0171] [Table 2]

[0172] From the above results, it is understood that, according to the examples, it is possible to produce a carbon fiber aggregate having a high bulk density in which the fibers are aligned while maintaining their length without cutting the fibers. The obtained fiber aggregate has the following effects. The fibers that make up the fiber aggregate are oriented in one direction, making it difficult to form bridges within the feeder. Since the fibers are not easily cut during the granulation process and the fiber length of the fibers in the fiber aggregate does not become excessively shorter than the fiber length of the fibers used, the inherent effects of the fibers used in the production of the fiber aggregate can be effectively exerted. The fiber aggregate has a high bulk density, which makes it easy to handle and efficient to mix.

[0173] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-101844, Japanese Patent Application No. 2021-101845, and Japanese Patent Application No. 2021-101846 filed on June 18, 2021, Japanese Patent Application No. 2021-174789 filed on October 26, 2021, and Japanese Patent Application No. 2021-189657 filed on November 22, 2021, and is incorporated by reference in its entirety. [Explanation of symbols]

[0174] 1 Mixing tank 2 Rotation Axis 3 Mixing blade 11 Granulated bread 12 Rolling shaft 21 Arm 22 Spray 23 Scraper 40 containers 44 Mixing blade 45 Scraper

Claims

1. A fiber bundle containing a plurality of carbon fibers and a resin or a solvent, and having a bulk density of 0.3 g / cm ３ The fiber assembly as described above, The fiber bundle includes a fiber bundle W1, The fiber bundle W1 has an ellipsoidal shape, fibers present on the surface of the fiber bundle are oriented in a curved manner along the contour of the ellipsoid, the average fiber length of the fibers in the fiber bundle is 2 to 12 mm, and A' / A specified by the following condition (1) is 0.75 to 0.

93. Condition (1): A fiber bundle placed on a white plate is photographed from the vertical direction opposite the plate, and the image obtained is binarized using image analysis software to obtain a binary image. The binary image is contour-extracted to obtain the contour of the fiber bundle. The Feret diameter is calculated from the contour and the major axis length is designated as A. The binary image is approximated to an ellipse, and the major axis length of the ellipse is designated as A'.

2. The fiber assembly according to claim 1, wherein the major axis length A of the fiber bundle is 3 to 30 mm.

3. The fiber assembly according to claim 1 , wherein the average fiber length of the fibers in the fiber bundle is shorter than the major axis of the fibers.

4. The fiber assembly according to claim 1 , wherein the fiber bundle has the major axis, a minor axis 1 and a minor axis 2 , and a length B of the minor axis 1 is longer than a length C of the minor axis 2 .

5. The fiber assembly according to claim 4, wherein the fiber bundle has B of 1 to 9 mm and C of 0.5 to 6 mm.

6. The fiber bundle according to claim 4, wherein the ratio (B / A) of the long axis to the short axis 1 of the fiber bundle is 2 to 12, and the ratio (C / A) of the long axis to the short axis 2 of the fiber bundle is 1 to 6.

7. The fiber assembly according to claim 4 , wherein B is 1.5 times or more as large as C.

8. The particle density of the fiber bundle represented by the following formula (2) is 0.3 to 1.8 g / cm ３ The fiber assembly according to claim 4, Particle density = G / (4πabc / 3)...Equation (2) (In formula (2), G represents the mass of the fiber bundle, a represents A / 2, b represents B / 2, and c represents C / 2.)

9. The fiber assembly according to any one of claims 1 to 8, wherein the number ratio of the fiber bundles W1 is 50% or more.

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