Method for manufacturing fiber assembly and method for manufacturing prepreg sheet

Abstract

A method for producing a fiber assembly, the method comprising a process in which a plurality of fibers and a fiber treatment agent are put into a stirring tank, and a mixture of the fibers and the fiber treatment agent is granulated by being stirred by means of a mixing blade. With respect to this method for producing a fiber assembly, the fibers include carbon fibers and the granulation is carried out so that the fibers are aligned. A method for producing a fiber assembly, wherein a plurality of fibers including carbon fibers and a liquid are put into a stirring tank, and a mixture of the fibers and the liquid is stirred by means of a mixing blade, thereby directly obtaining a prolate spheroidal or strand-like fiber assembly.

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 being mixed and dispersed in a matrix such as a resin to improve mechanical or electrical properties such as high strength, high rigidity, low specific gravity, high electrical conductivity, and high abrasion resistance.

[0003] Generally, when a fiber-reinforced resin composition is obtained by mixing and dispersing carbon fibers in various resins, 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 steps.

[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 these required properties, there have been disclosed carbon fiber aggregates that have a predetermined average particle size and are surface-coated with an emulsion-based sizing agent whose main component is an epoxy compound, and carbon fiber chopped strands that are bundled with a predetermined sizing agent, have a predetermined density, and have a circular or elliptical cross section (for example, Patent Document 1).

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

[0007] Furthermore, as a method for efficiently producing an entangled body made of short carbon fibers, a method for producing a carbon fiber entangled body by a stirring granulation method in which curved carbon fibers and flexible spheres are stirred together has been disclosed (for example, Patent Document 3).

[0008] [Patent Document 1] Japanese Patent Application Publication No. 4-170435 [Patent Document 2] Japanese Patent Publication No. 2020-196882 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-220066 Summary of the Invention

[0009] An object of the present invention is to provide a method for producing a fiber assembly that can produce 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 the fibers and the fiber treating agent.

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

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

[0012] [1] A method for manufacturing a fiber aggregate, comprising: putting a plurality of fibers and a fiber treatment agent into an agitation tank; and agitating and granulating the mixture of the fibers and the fiber treatment agent with an agitator 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 according to [1], wherein the plurality of dried, cotton-like fibers are introduced into the stirring tank. [3] A method for producing a fiber aggregate according to [1] or [2], in which a stirring blade that rotates horizontally and an auxiliary stirring blade that rotates vertically are placed in a stirring tank, and stirring is carried out using the stirring blade that rotates horizontally and the auxiliary stirring blade that rotates vertically. [4] The method for producing a fiber aggregate according to any one of [1] to [3], wherein the plurality of carbon fibers are stirred and defibrated in the stirring tank by 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 rotates. [6] A 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 that can rotate around its 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] A method for producing a fiber aggregate according to any one of [5] to [8], wherein the stirring is performed so that the rotation direction of the stirring blade is opposite to the rotation direction of the stirring tank, and then the stirring is performed 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 assembly according to [5] or [9], which comprises 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 surface tension of the fiber treatment agent at 23°C is 120 mN / m or less.

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

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

[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 epoxy resins, unsaturated polyester resins, vinyl ester resins, polyurethane resins, and polyamide resins.

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

[20] , wherein the positions of the tips of the fibers constituting the fiber assembly are not uniform.

[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 a spheroid shape or a strand shape.

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

[23] , 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 introduced 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 granulation is carried out 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 surface tension of the fiber treatment agent at 23°C is 15 mN / m or more.

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

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

[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] , wherein

[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 manufacturing a fiber aggregate, in which a plurality of fibers and a fiber treatment agent containing a liquid are placed in a stirring tank, and the mixture of fibers and fiber treatment agent is stirred with a stirring 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 according to

[32] or

[33] , wherein the plurality of dried, cotton-like fibers are introduced into the stirring tank.

[35] A method for producing a fiber aggregate in which carbon fibers are oriented in a uniform manner, comprising: introducing a plurality of flocculent carbon fibers, a resin, and water into a stirring tank; and stirring and granulating the plurality of carbon fibers, the resin, and the water using a stirring blade disposed in the stirring tank.

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

[35] , which comprises adding a raw material containing the plurality of flocculent carbon fibers and a resin carbide.

[37] A method for producing a fiber aggregate in which carbon fibers are spun together according to

[35] or

[36] , which comprises adding a raw material containing the plurality of flocculent carbon fibers and 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 consisting of multiple carbon fibers and an organic binder, with 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 the tips of the multiple fibers constituting the carbon fiber aggregate are irregular.

[42] The carbon fiber aggregate according to

[40] or

[41] , wherein the length of the major axis of the carbon fiber aggregate is longer than the 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 epoxy resins, unsaturated polyester resins, vinyl ester resins, polyurethane resins, and polyamide resins.

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

[0014] [1a] A method for producing a fiber aggregate, comprising: charging 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 stirring blade is inclined in the direction of rotation, and the angle between the rear surface of the stirring blade in the direction of rotation and the bottom surface of the stirring vessel is 1 to 60°. [3a] The method for producing a fiber aggregate according to [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, in which fibers and a fiber processing agent are granulated by stirring them using a Henschel mixer. [6a] A method for producing a fiber aggregate, in which fibers and a fiber processing agent are granulated by stirring them using a granulator. [7a] The method for producing a fiber assembly according to any one of [1a] to [6a], wherein the surface tension of the fiber treatment agent at 23°C is 120 mN / m or less. [8a] The method for producing a fiber assembly according to any one of [1a] to [7a], wherein the viscosity of the fiber treatment agent at 23°C is 10 Pa·s or less. [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 5 to 120 parts by mass of the fiber treating agent is added 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 include 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 assembly according to any one of [1a] to [10a], wherein the fibers include 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] The method for producing a fiber assembly according to any one of [1a] to [17a], wherein the fiber treating agent is a liquid, and the method comprises a step of evaporating the liquid contained in the fiber treating agent. [19a] The method for producing a fiber assembly according to any one of [1a] to [18a], wherein the fiber assembly has a spheroid shape or a strand shape. [20a] The method for producing a fiber assembly 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: charging fibers and a liquid fiber treatment agent into a stirring tank; and granulating the mixture of fibers and 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 5 to 120 parts by mass of the fiber treating agent is added 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 a 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], which 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 viscosity of the fiber treatment agent at 23°C is 10 Pa·s or less. [4b] The method for producing a fiber aggregate according to any one of [1b] to [3b], wherein the tumbling 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 assembly 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], which comprises a side wall to which the tumbling tank is fixed and a rotary container that rotates horizontally within the side wall. [8b] The method for producing a fiber assembly according to [7b], wherein the peripheral speed of the rotating container 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 include 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 assembly according to any one of [1b] to [10b], wherein the fibers include 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] The method for producing a fiber assembly according to any one of [1b] to [17b], wherein the fiber treatment agent is a liquid, and the method includes 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 a spheroid shape or a strand shape. [20b] The method for producing a fiber assembly 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], which 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 according to [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 according to [1c] or [2c], wherein the operation of applying the strain rate is an operation of applying an airflow shear rate by blowing a gas into a container containing fibers and a 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 assembly 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: moving an agitator blade to bring the fibers and a fiber processing agent into contact with each other, thereby applying a shear rate to the fibers, 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 processing agent to impart a vibration speed to the container, thereby forming liquid bridges between the fibers and growing particles to form granules. [15c] A method for producing a fiber aggregate, comprising: rotating a container containing fibers and a fiber processing agent to impart a rotational speed thereto, thereby forming liquid bridges between the fibers and growing particles to form granules. [16c] A method for producing a fiber aggregate, comprising blowing gas into a vessel containing fibers and a fiber processing agent to impart an airflow shear velocity, thereby forming liquid bridges between the fibers and growing particles to form granules.

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

[0020] [1d] A fiber bundle containing a plurality of carbon fibers and a resin or a solvent, wherein the fiber bundle has an ellipsoidal shape 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 resulting image 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 its major axis length is defined as A. The binary image is approximated to an ellipse, and the major axis length of the 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] The 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 one of [1d] to [5d], wherein the fiber bundle has the major axis, minor axis 1 and minor axis 2, and the length B of the minor axis 1 is longer than the length C of the 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] The 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], wherein 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 contains at least one selected from an epoxy resin, a urethane resin, and a polyamide resin. [15d] A fiber assembly consisting of fiber bundles 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 specified by the following condition (1) of 0.75 to 0.93, and the number ratio of the fiber bundles W is 50% or more: 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 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 its major axis length is defined as A. The binary image is approximated as an ellipse, and the major axis length of the ellipse is defined 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. [Effects of the Invention]

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

[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 using a feeder with improved handling and workability. [Brief explanation of the drawings]

[0023] [Figure 1] Figure 1 shows an embodiment of an agitator blade for a stirring vessel used in the first embodiment of the fiber assembly manufacturing method of the present invention, where Fig. 1a is a horizontal cross-sectional view of the stirring vessel, and Fig. 1b is a cross-sectional view taken along line bb in Fig. 1a. [Figure 2] 2A and 2B are schematic diagrams showing an embodiment of a pan granulator used in the second embodiment of the method for producing a fiber aggregate of the present invention, where Fig. 2A is a side view and Fig. 2B is a view showing the internal structure of the granulator. [Figure 3A] FIG. 3A is a cross-sectional view showing a fixed side wall and a rotary 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 agitation granulator used in the method for producing a fiber aggregate according to the first aspect of the present invention. [Figure 4] Figure 4 is a photograph showing an example of the shape of recycled fibers. [Figure 5] FIG. 5 is a photograph showing an example of the morphology of virgin fibers. [Figure 6] Fig. 6a to 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 INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described in detail.

[0025] [First to third aspects of the present invention] A 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 fibers and the fiber treatment agent with a stirring blade to granulate the fibers so that the fibers are aligned, thereby producing a fiber aggregate. According to this aspect, even when using raw fiber having a long fiber length, a fiber aggregate with aligned fibers can be obtained. An example of a fiber aggregate is a self-organized carbon fiber bundle. Granulation can aggregate a plurality of fibers to form a single granular unit. In the first embodiment of the present invention, a Henschel mixer or a granulator can be used as the agitation 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. 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 force by stirring to the mixture of fibers and fiber treating agent, the fiber treating agent can be efficiently attached to the fiber surface, and 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. 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 the mixture of fibers and fiber treatment agent, the fiber treatment agent can be efficiently attached 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, thereby forming liquid bridges between the fibers and growing particles to form granules. This method for producing a fiber assembly also involves the following steps 1 to 4. 1. 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 crosslinking, and self-assembled 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 step divided by the characteristic length. Strain rate [1 / s] = Maximum speed [m / s] / Characteristic length [m] Here, the representative length is 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 ​​the container [m 2 ] The average cross-sectional area is the container 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, in which granulation is performed by rotating the agitator blades, the maximum speed is the peripheral speed of the agitator blades. In the case of rolling granulation, in which granulation is performed by rotating the 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 determined 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] <Strain amount> The amount of strain is obtained by multiplying the strain rate by the processing time, and this amount of strain is also a guide for granulation. Strain amount [-] = strain rate × processing time [s]

[0032] <Liquid crosslinking> This refers to the presence of a liquid in a narrow gap at the contact point between powder particles and a solid surface, or between particles. Negative pressure due to capillary forces is applied to the liquid bridges formed between particles, resulting in an attractive force (liquid bridge force) between the particles, immobilizing them. In this invention, liquid bridges refer to liquid bridges that occur in the gaps between fibers. When fibers come into contact so that they cross, the liquid bridge force acts at a point and is weak, whereas when fibers come into contact in parallel, the liquid bridge force acts in a line and is strong. Because liquid bridges that occur in fibers occur continuously in the fiber length direction, even when the fibers are not parallel to each other, the surface tension of the liquid can be expected to cause the fibers to change their angle and orient in the same direction to minimize the surface area of ​​the liquid.

[0033] <Self-assembled carbon fiber bundles (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. Prior to forming the SACFB, all of the short carbon fibers may be monofilaments. That is, the SACFB can 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 consisting of a small number of filaments, for example, less than 100. 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 tips of the carbon fibers constituting the bundle are not aligned, as illustrated in FIGS. 6(a) to 6(d).

[0034] <Mixing tank and mixing conditions> An agitation 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 below with reference to FIG.

[0035] As shown in Fig. 1a, the agitation granulator used in the first embodiment of the method for producing a fiber aggregate of the present invention preferably has a rotating shaft 2 on the central axis of a cylindrical agitation vessel 1 with a bottom, and multiple propeller-shaped agitation blades (three in Fig. 1a) extending radially at equal intervals from the rotating shaft 2. Disc-shaped agitation blades perpendicular to the rotating shaft may also be used. Discs with undulations and protrusions may also be used.

[0036] As shown in Fig. 1b, the agitator blade 3 is inclined in the rotation direction relative to the bottom surface 1A of the agitator vessel 1. The angle θ between the rear surface 3A in the rotation direction R and the bottom surface 1A of the agitator vessel 1 (hereinafter sometimes simply referred to as the "inclination angle") is preferably in the range of 1 to 60°. If the inclination angle θ of the agitator blade 3 is 1° or more, it is possible to agitate the fiber mixture particles while circulating them within the agitator vessel. If the inclination angle θ of the agitator blade 3 is 60° or less, it is possible to reduce resistance to the agitator blade and adjust the rotation speed within a range that does not place a load on the device. The inclination 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 longitudinal direction. The impeller is not limited to being bent in this way, and may be a straight plate-like impeller. The impeller may also be bent in an arc shape.

[0038] Some agitation granulators are provided with auxiliary agitation blades (choppers) on the wall of the agitation vessel for auxiliary agitation. Either type of agitation granulator can be used in the first aspect 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 agitator granulator are preferably such that the peripheral speed (hereinafter simply referred to as "peripheral speed") of the tip of the agitator blade (part 3a in Fig. 1a) is in the range of 1 to 20 m / s. If the peripheral speed is 1 m / s or more, it is possible to circulate and agitate the fiber mixture granules in the agitator tank. If the peripheral speed is 20 m / s or less, it is possible to make the particle shape of the fiber aggregate uniform. The peripheral speed of the agitator blade is more preferably 4 to 12 m / s, and even more preferably 4 to 8 m / s. The peripheral speed of the chopper is preferably in the range of 5 to 30 m / s.

[0041] There is no particular limitation on the stirring time in the stirring granulator, and stirring may be carried out for a period of time sufficient to obtain the desired fiber aggregate. The temperature at which the mixture is stirred is not particularly limited, and room temperature is acceptable. The fiber treatment agent is liquid when granulated, and the type of fiber treatment agent, stirring time, stirring temperature, etc. can be adjusted so that the fiber treatment agent becomes solid when the particle state (granulated state) is maintained as a fiber aggregate. The mixing conditions are adjusted so that a fiber aggregate in a pulled-together state is obtained, rather than spherical carbon fiber balls made from crimped fibers. Carbon fiber balls are likely to form when the fiber processing agent, especially liquid, is not included at all or a large amount is added and the fibers are stirred to obtain an aggregate, or when the average fiber length of the raw material is 1 mm or less.

[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 agitator granulators include batch agitator granulators such as the SP Granulator (Dalton), High Speed ​​Mixer (Earth Technica), Vertical Granulator (Powrex), Lödige Mixer (Matsubo), Super Mixer (Kawata), Power Kneader (Fuji Paudal), Henschel Mixer (Mitsui Miike), Universal Mixer Agitator (Shinagawa Kogyosho), Spartan Reuser (Fuji Paudal), and Bytemix (Hosokawa Micron), as well as continuous agitator granulators such as Flexomix (Hosokawa Micron) and Modulomix (Hosokawa Micron). Examples of combined agitation 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 a vertically rotating auxiliary mixing blade (chopper), and mixing with the horizontally rotating mixing blade and the vertically rotating auxiliary mixing blade enables efficient mixing and granulation. The vertically rotating auxiliary mixing blade has the role of crushing granules that have become too large and making the size of the fiber aggregate uniform.

[0044] The raw material before being fed into the agitation granulator may be a raw material that has not undergone wet mixing. That is, instead of wet fiber aggregates, a plurality of dry fibers may be fed directly into the agitation tank as the raw material and agitated. There are no particular restrictions on the timing of completion of granulation, but it is preferable that the fiber aggregate has been 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 aspect of the present invention, after the stirring and granulation as described above, it is preferable to carry out a drying step in which the liquid derived from the fiber processing 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 can 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, a flash dryer, an infrared dryer, a microwave dryer, a vacuum dryer, etc. Natural drying may also be used.

[0047] <Classification process> The uniformity of multiple fiber aggregates can be improved by classifying the multiple 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 interior space of the container. When the container is cylindrical, it is arranged so that the opening of the cylinder faces vertically. The sieve mesh is placed 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 move toward the outer periphery, causing large fiber aggregates to be discharged from above the sieve mesh and small fiber aggregates to fall below the sieve mesh and be classified. When the container is trough-shaped, the sieve 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 within 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, while small fiber aggregates fall through the mesh below the sieve. A classified fiber aggregate is obtained by collecting the fiber aggregate above and the fiber aggregate below the sieve separately. The mesh shape and opening of the sieve are adjusted so that the fiber aggregate can be sieved into the 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 be applied to the raw fiber to improve the uniformity of the fiber before use.

[0048] <Rolling tank> The tumbling 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 diagram showing the internal structure of the granulator. FIG. 3A is a cross-sectional view showing a fixed side wall and a rotary container of a tumbling tank used in a second embodiment of the method for producing a fiber aggregate. FIG. 3B is a perspective view showing the inside of an embodiment of a tumbling agitation granulator used in the method for producing a fiber aggregate according to the second aspect of the present invention.

[0050] The pan granulator of Figure 2 is configured so that granulation pan 11 rolls on 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 pressure angle adjustment device. An arm 21 having a spray 22 and a scraper 23 is provided in 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 centrifugal force moves the fiber mixture upward and crushes it 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, causing the fiber mixture to move upward, and crushing and granulation by sliding down are efficiently carried out, thereby increasing productivity.

[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 greater than the lower limit, the fiber mixture moves in the circumferential direction and collides with the wall surface due to centrifugal force, resulting in continuous crushing and granulation, making it possible to obtain a fiber aggregate with a uniform shape. If the peripheral speed of the rotating container is equal to or less than the upper limit, the centrifugal force acts appropriately, achieving a balance with the gravity acting on the fiber mixture, resulting in efficient crushing and granulation, thereby increasing productivity.

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

[0054] <Rolling Agitation Granulator> The tumbling agitator granulator will be described with reference to FIG. 3B. As shown in FIG. 3B, one embodiment of the tumbling agitator granulator includes a rotatable container 40 containing raw fibers and a fiber treatment agent, and a rotating shaft 42 disposed inside the container 40 and parallel to the central axis 41 of the container 40 at a position eccentric to the central axis 41. The rotating shaft 42 is preferably rotatable in the direction opposite to the rotation direction of the container 40. Rotating in the opposite direction increases the impact force between the agitator blade and the fiber aggregate, allowing for strong shearing to align the fibers in a short period of time. The rotating shaft 42 may also rotate in the same direction as the container 40. When the agitator blade rotates in the opposite direction to the rotation direction of the container, the number of filaments contained in the fiber aggregate tends to be small, and the distribution of the number and shape of the filaments contained in the fiber aggregate tends to be uniform. When the agitator blade rotates in the same direction as the rotation direction of the container, the number of filaments contained in each fiber aggregate tends to be large, and the fibers tend to be easily aggregated. It is believed that stirring with the impeller rotating in the opposite direction to the container's rotation, followed by stirring with the impeller rotating in the same direction as the container's rotation, promotes liquid bridging between fiber aggregates with a small number of filaments and a uniform distribution. This results in a uniform fiber aggregate with high bulk density. The rotating shaft 42 extends near the bottom plate 43 of the container 40 and has an impeller 44 that moves within the area of ​​the mixture of fibers and fiber treatment agent. The mixture is circulated by the rotation of the container 40, and the rotation of the impeller 44 applies shear to the mixture, aligning the fibers. The blades of the impeller 44 can be similar to those described for the agitator granulator. A scraper 45 is provided on the side of the container 40. Scrapers may be provided on the side, bottom, or both of the interior of the container 40. The scraper 45 can scrape off adhering raw materials.

[0055] Regarding the rotation conditions of the tumbling agitation granulator, the peripheral speed of the vessel 40 (vessel peripheral speed) can be set in the range of 0.4 to 1.2 m / s. If the peripheral speed is 0.4 m / s or higher, the fiber mixture granules can be circulated and agitated within the agitation tank. On the other hand, if the peripheral speed is 1.2 m / s or lower, the fiber mixture granules can be efficiently brought into contact with the agitation blades and scraper, thereby shortening the processing time. The peripheral speed can be set to 0.5 to 1.0 m / s or 0.7 to 0.9 m / s. The peripheral speed of the agitation blade tips (tip peripheral speed) of the agitation blades 44 is preferably set in the range of 1 to 30 m / s. If the tip peripheral speed is 1 m / s or higher, the fibers can be aligned in a short time, increasing the density of the fiber aggregate. On the other hand, if the tip peripheral speed is 30 m / s or lower, the particle shape of the fiber aggregate can be made uniform. The peripheral speed of the agitation blades 44 can be set to 10 to 20 m / s or 1 to 8 m / s.

[0056] The rolling agitation granulator may be any granulator having a container and a stirring blade that can be rotated by a rotating shaft, and examples of the stirring 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 barrel type 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 fiber treatment agent is preferably 1 [1 / s] or more and 700 [1 / s] or less. If the strain rate is above the lower limit, the fibers are easily oriented. If the strain rate is below the upper limit, uniform particles (fiber bundles) are obtained. The strain rate is particularly preferably 10 to 500 [1 / s], and especially 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 / 5 or less of the vessel height, and more particularly preferably 1 / 5 or more and 4 / 5 of the vessel height.

[0059] The amount of strain applied to the fibers and 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 especially preferably 5,000 to 20,000 [-].

[0060] The procedure 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 stirring blades to bring them into contact with each other (agitation granulation) Specifically, one example is a method in which fibers and a fiber processing agent are placed in an agitation tank 1 of an agitation granulator having agitation blades 3 as shown in FIG. 1 and then agitated.

[0062] The stirring granulator is as explained in the method for producing a fiber aggregate according to the first embodiment of the present invention, and its preferred embodiments and stirring conditions 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 [m] of the stirring blade and the raw material loading in the stirring tank 3. Strain rate [ / s] = peripheral speed of mixing blade [m / s] / charge height [m]

[0064] (2) Vibrating the container containing the fiber and fiber treatment agent to increase the vibration speed (granulation by vibration) Specifically, the fibers and fiber treatment agent are placed in a sealable container. Any sealable container can be used, but a cylindrical container with a screw-on lid is suitable. The sealed container is placed in a sieve shaker or similar device and vibrated for a certain period of time. Using the amplitude A and period T of the vibration, and assuming simple harmonic motion, the velocity (v) is calculated using the following formula. 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 vibration by the charge height. Strain rate [ / s] = Maximum speed generated by vibration [m / s] / Feeding height [m] The amplitude and period may be measured by any method, including using the settings of the shaker itself, or by capturing the vibrations themselves with a video camera and processing the images to determine the amplitude and period.

[0065] (3) Rotating a container containing fibers and a fiber processing agent to provide a rotational speed (rolling granulation) Specifically, there is mentioned a method using the pan granulator shown in FIG. 2, which was mentioned in the description of the method for producing the fiber aggregate according to the second embodiment of the present invention. In such rolling granulation, the strain rate corresponds to the value obtained by dividing the peripheral speed [m / s] of the outer periphery of the pan by the outer periphery length of the pan. Strain rate [ / s] = peripheral speed of pan [m / s] / peripheral length of pan [m]

[0066] (4) An operation of applying an airflow shear rate by blowing gas into a vessel containing fibers and a fiber processing agent (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 a granulation liquid onto the particles to grow them into granules through aggregation or coating.

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

[0068] <Fiber> 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 also contain inorganic fibers or organic fibers other than carbon 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 wire.

[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 plant 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 fiber, since it is particularly useful for producing a fiber-reinforced resin composition and can provide a fiber-reinforced resin composition with high specific strength and specific modulus. The proportion of carbon fiber in the raw fiber material is preferably 70 mass % or more, and particularly 90 to 100 mass %.

[0075] The raw material fibers are not limited to virgin fibers, but may also be recycled fibers. According to the first aspect, a carbon fiber aggregate having a high bulk density can be produced from recycled fibers, 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, a subcritical fluid, or a supercritical fluid, and fibers obtained by cutting scraps of a fiber substrate. The matrix can be completely removed from recycled fibers until the fibers become flocculent. If any resin residue remains, it may be removed by heat treatment in an oxidizing atmosphere.

[0076] The raw fiber is an aggregate of multiple discontinuous fibers (short fibers), and may be cotton-like or pulled together. If the monofilaments are aggregated to the extent that they do not scatter, the conversion efficiency into a fiber aggregate 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 extracted from a prepreg, a molded product, etc. For example, recycled fibers obtained by decomposing the matrix with heat are in a dry, cotton-like 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 fiber morphology from the fiber recycling process. This is because the rotation of the agitator blades can remove entanglements between 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 fiber. Virgin fiber is a mass of fiber bundles in which the fibers are aligned.

[0078] The raw fibers may be defibrated before being stirred in an agitator granulator or the like. For example, before adding the fiber treatment agent to the agitator tank, the raw fibers are defibrated by stirring the liquid-free fibers in the agitator tank with an agitator blade. The rotation of the agitator blade loosens the fibers bonded together by deposits such as resin carbide into smaller fibers, making it easier to align the fibers by stirring with the agitator blade after adding the fiber treatment agent. At the same time, the uniformity of the fiber aggregate can be improved.

[0079] The raw material fibers 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 limitation on the fiber diameter of raw fiber such as carbon fiber. The fiber diameter of raw fiber is a normal fiber diameter, for example, in the range of 5 μm to 20 μm. The bulk density of 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, the fibers can be easily converted into a fiber aggregate having a bulk density greater than that of the raw material fibers.

[0081] The average fiber length of raw material fibers such as carbon fibers is preferably 1 to 100 mm, and particularly preferably 2 to 50 mm. When used in a fiber-reinforced resin composition (pellets) to be used in extrusion molding, the average fiber length of raw material fibers is preferably 2 to 12 mm. When used in a fiber-reinforced resin material (prepreg) to be used in press molding, the average fiber length of raw material fibers is preferably 12 to 50 mm, and more preferably 12 to 30 mm from the viewpoint of facilitating uniform deposition of the fiber aggregate by scattering during prepreg production. When the fiber length of the raw material fibers is equal to or greater than the above lower limit, the strength of the fiber-reinforced resin composition can be sufficiently increased and fiber orientation can be highly controlled. When the average fiber length of raw material fibers is equal to or less than the above upper limit, entanglement in the equipment during fiber aggregate production can be suppressed, thereby increasing production efficiency and enabling uniform control of the particle shape of the fiber aggregate. 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 a 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 a liquid at room temperature from the viewpoint of being able to form liquid bridges between fibers at room temperature.

[0083] Examples of organic compounds include the following: Natural compounds such as starch, cyclodextrin, amino acids, peptides, proteins, natural rubber, soybean oil, and palm oil; Thermoplastic resins such as 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, 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, as well as 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(dioctylpyrophosphate) titanate, tetraisopropyl bis(dioctylphosphite) titanate, tetraoctyl bis(ditridecylphosphite) titanate, bis(dioctylbirophosphate)oxyacetate titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctylphosphate) titanate, isopropyl tricumylphenyl 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 granulation accelerators 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 resin, and polyurethane.

[0087] The fiber treatment agent preferably contains one or more selected from solvents, clay minerals, resins, and surfactants, which form liquid bridges between fibers to facilitate fiber orientation and improve the bulk density and uniform particle shape of the fiber assembly. From the standpoint of safety, the fiber treatment agent is preferably water, a water-in-water solution containing an organic compound, a water-in-water mechanical dispersion containing an organic compound, or a water-in-water dispersion containing an organic compound with 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 liquid crosslinks, water is preferred.

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

[0090] Examples of resins include ABS resin, vinylidene chloride latex, vinyl chloride resin, butadiene resin, fluororesin, polyacetal, polyamide resins such as nylon 6 and nylon 66, polyesters such as polyacrylate, polyetherimide, polyetheretherketone, 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; thermosetting resins such as epoxy resin, xylene resin, vinyl ester resin, phenolic resin, unsaturated polyester resin, furan resin, polyimide, polyurethane, melamine resin, and urea resin; and synthetic rubbers such as styrene-butadiene latex, butadiene latex, neoprene-butadiene latex, chloroprene rubber, urethane rubber, silicone rubber, fluororubber, and acrylic rubber. From the perspective of maintaining the shape of the fiber bundle, the resin preferably includes at least one selected from epoxy resin, urethane resin, and polyamide resin.

[0091] Examples of surfactants 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 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 within the above range at the stirring temperature can be used. If the surface tension of the fiber treatment agent is equal to or greater than the lower limit, an appropriate negative capillary pressure is applied to the liquid bridges connecting the fibers, causing the fibers to adhere to each other and become oriented, resulting in a dense fiber aggregate.If the surface tension is equal to or less than the upper limit, the fiber treatment agent will adequately wet the fiber surfaces, causing efficient liquid bridges to form, 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 using a B-type rotational viscometer. When granulating by heating, a fiber treatment agent having a viscosity tension in the above range at the temperature during stirring can be used. When the viscosity of the fiber treatment agent is equal to or less than the upper limit, friction between the fibers is appropriately generated, thereby obtaining a uniform fiber aggregate with a regular shape. Furthermore, the fiber treatment agent wets and spreads over the fiber surface, efficiently generating liquid bridges and providing an excellent fiber granulation effect.

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

[0096] Such a fiber treatment agent is preferably used in an amount of 5 to 120 parts by mass per 100 parts by mass of fibers. When the amount of fiber treatment agent used is equal to or greater than the lower limit, an appropriate amount of liquid bridges are generated between fibers, promoting the flow and adsorption of fibers and enabling proper orientation, resulting in a dense fiber aggregate. When the amount of fiber treatment agent used is equal to or less than the upper limit, the liquid bridges between 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 fiber treatment agent per 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, and more preferably 10 to 40 parts by mass, of fiber treatment agent per 100 parts by mass of fibers, from the viewpoints of facilitating drying and adjusting the fiber aggregate to a size suitable for pelletization. When the average fiber length of the raw material fibers is 12 to 50 mm, from the viewpoint of facilitating drying and 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 fibers.

[0097] The fiber treating agent may be charged into the stirring granulator together with the fibers in its entirety all 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 processing agent, it is possible to produce a fiber aggregate with high bulk density 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, and 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] There are no particular restrictions on the shape of the resulting fiber aggregate, but for use as a reinforcing fiber, it is preferably in the form of an elongated spheroid or strand. An example of a long spheroid shape is an ellipsoid, but the diameter of the thickest part can be 0.1 mm to 10 mm, the length of the major axis can be 3 mm to 150 mm, which is longer than the average fiber length of the fibers in the fiber assembly, and the cross-sectional shape can be circular, elliptical, or the like. When used as a pellet, the shape of the fiber assembly is preferably a long spheroid from the viewpoint of feed efficiency into a kneader, the diameter of the thickest part can be 2 mm to 7 mm, the length of the major axis can be longer than the average fiber length of the fibers in the fiber assembly, and the ratio (major axis length / average fiber length) is preferably 1.1 to 5.0 times and 3 mm to 18 mm. When used as a prepreg, the shape of the fiber assembly is preferably a strand from the viewpoint of scattering and facilitating uniform deposition of the fiber assembly, the diameter of the thickest part can be 2 mm to 10 mm, and the bundle length can be 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 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 in molded products with a 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 can be set to 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 pellet production, the fiber content in the fiber assembly can be, for example, 80 to 99% by mass. When the fiber assembly is directly placed in 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 a resin is contained in the fiber assembly, it is more preferable that the resin be contained in an amount of 0.1 to 20 parts by mass, and 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 aggregates produced by the above-described method for producing a fiber aggregate.

[0107] An example of a prepreg that can be produced using 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: Liquid thermosetting of the first protective film tree Depositing a plurality of short carbon fiber bundles comprising SACFB onto the surface to which the resin composition has been applied to form a carbon fiber mat. 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 multilayer 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 scattering, a plurality of short carbon fiber bundles containing SACFB on the surface of the first protective film to 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 carrier films 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 Figure 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 on 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 CFRP products using prepregs made with SACFB, the preferred molding method is press molding, but this is not limited to this. As this molding method, molding methods other than press molding, such as autoclave molding, can also be used.

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

[0116] A fiber bundle according to a fourth aspect of the present invention (hereinafter sometimes referred to as "fiber bundle W") contains a plurality of carbon fibers and a resin or a solvent, and 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 side opposite the vertical plate, and the resulting image 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 its major axis length is defined as A. The binary image is approximated to an ellipse, and the major axis length of the ellipse is defined 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 approaches an ellipse or a circle. As the value of A' / A decreases, the cross-sectional shape tends to resemble a shape with a corner or protruding fibers at the tip 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 easily against each other, preventing the formation of bridges in the feeder, particularly in the hopper, where fiber bundles support each other and prevent them from falling, for feeding the fiber bundles into the kneader. If A' / A is 0.93 or less, the fiber bundles are oriented in the flow direction and flow easily within the feeder. The fiber bundles are arranged so that there are fewer gaps within the feeder, allowing a constant amount to 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 the mechanical properties of the resin molded product, the major axis length A of the fiber bundle W is preferably 3 mm or more, more preferably 4 mm or more. From the viewpoint of preventing the occurrence of bridges, the major axis length A can be 30 mm or less, or 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 the 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, by the following method.

[0120] The fiber bundle is photographed at 20x magnification using a VHX-6000 digital microscope and ring light. The fiber bundle is placed naturally on a horizontally held white plate and photographed in a stable position from the vertical direction opposite the white plate. Image analysis is performed using software (ImageJ) and Otsu's binarization process (Make Binary) to obtain a binary image. This binary image is then contour extracted (Analyze Particles, Outlines) to obtain the outline of a single fiber bundle. The Feret's diameter is calculated from the obtained outline. The outline is approximated to an ellipse using the least squares method (Analyze Particles, Ellipses) to obtain the length A' of the major axis of the resulting 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 pellet production, 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, which 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 or more and 800,000 or less. The fiber bundle W can have an ellipsoidal shape by having a larger number of filaments at the center of the long axis than at the ends of the long axis. The fibers in the fiber bundle W are pulled together to form the fiber bundle. It is preferable that the fibers present on the surface of the fiber bundle are 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 clogging in a narrowed portion of the feeder, for example, a hopper, 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 preferably 3.0 times or less, and 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 controlling the supply amount, 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, 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, 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] In order to improve the feeding efficiency, the fiber aggregate preferably contains fiber bundles W in a proportion of 45% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 80% or more. The proportion may 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 extracted bundles. 3 ~450cm 3The fiber bundles are scooped into a measuring container, arranged on a white plate so that they do not overlap, and the arranged fiber bundles are photographed with a digital camera. The image obtained can be used to determine the 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 have 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 a cotton made of short fibers with a liquid, causing the short fibers to spontaneously bundle. Specifically, it can be produced by granulation such as rolling granulation, stirring granulation, and fluidized bed granulation. For example, A' / A can be adjusted to a specific range by charging a cotton made of short carbon fibers and a liquid into an agitator and stirring at a rotation speed of 120 to 470 rpm for the stirring blades (agitator) and a rotation speed of 2000 to 3000 rpm for the chopper. The liquid is preferably used in an amount of 5 to 120 parts by mass, more preferably 20 to 80 parts by mass, per 100 parts by mass of the fibers. The resins and solvents mentioned above can be used as 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, which has been 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 agitator granulator, it is preferable that the peripheral speed (hereinafter simply referred to as "peripheral speed") of the tip of the agitator blade (part 3a in Fig. 1a) is in the range of 1 to 20 m / s. If the peripheral speed is 1 m / s or more, it is possible to agitate the fiber mixture granules while circulating them in the agitator tank. If the peripheral speed is 20 m / s or less, it is possible to make the particle shape of the fiber aggregate uniform. The peripheral speed of the agitator blade is more preferably 4 to 12 m / s, and even more preferably 4 to 8 m / s. 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 A' / A tends to decrease as the rotation speed of the impeller and chopper increases. [Example]

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

[0131] [Agitation Granulator] In the following Examples 1 to 4, the agitation granulator has three agitation blades extending radially from a central rotation shaft as shown in Figure 1. The inclination angles θ of the agitation 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 single fiber aggregate was immersed in ethanol to disintegrate it into single fibers, transferred to filter paper, and dried. Images were taken with a digital microscope (Keyence: HX-6000-2), and the fiber length was measured using the built-in software. 100 fibers were counted for each sample, 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 (weighted average fiber length L = Σl 2 / Σl)

[0136] <Bulk density> 100 mL of multiple fiber aggregates was placed in a φ50 mm container, and the container was tapped 10 times from a height of 3 cm to deposit the fiber aggregate. The bulk density was calculated from the volume and weight. Measurements were performed in accordance with JIS Z 2512 and JIS R 1628.

[0137] <Long axis ratio A' / A> The fiber bundle obtained as a fiber assembly was placed on a horizontally held white plate and photographed at 20x magnification using a VHX-6000 digital microscope and ring light from the vertical direction opposite the white plate. The photographed image of the fiber bundle in Example 1 is shown in Figure 9. The photographed image of the fiber bundle in Comparative Example 1 is shown in Figure 12. The photographed image was subjected to Otsu's binarization (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 Figure 10. The Feret's diameter was calculated from the obtained contour and defined as the major axis length A. The contour was approximated to an ellipse using the least squares method (Analyze Particles, Ellipses) to obtain the major axis length A' of the resulting ellipse. A' was divided by A to obtain the major axis ratio A' / A. The approximate ellipse in Example 1 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, which was 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, which was designated as C.

[0139] <Area ratio S' / S> The fiber bundle obtained as a fiber assembly was placed on a horizontally held white plate and photographed at 20x magnification using a VHX-6000 digital microscope and ring light from the vertical direction opposite the white plate. The photographed image of the fiber bundle in Example 1 is shown in Figure 9. The photographed image of the fiber bundle in Comparative Example 1 is shown in Figure 12. The photographed image was subjected to Otsu's binarization (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 Figure 10. The Feret's diameter was calculated from the obtained contour and defined as the major axis length A. The point bisecting the major axis was defined as F, the intersections of the perpendicular line to the major axis at F and the contour were defined as Y and Y', and the line connecting Y and Y' was defined as the minor axis B. The area was calculated from the equation (S = π × A / 2 × B / 2). The contour was approximated by an ellipse using the least squares method (select Analyze Particles, Ellipses), and the area of ​​the ellipse was defined as S'. S' was divided by S to obtain the area ratio S' / S.

[0140] <Angle of repose> 200g of fiber bundle was allowed to fall naturally 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 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 ratio was calculated by dividing the number of fiber bundles with an A' / A ratio of 0.75 to 0.93 by 111. A' / A was calculated in the same way as for the <long axis ratio A' / A>, except that a digital camera was used instead of a digital microscope.

[0142] <Weight distribution of carbon fiber aggregates> 300 fiber bundles were randomly selected from multiple fiber bundles and the weight of each was measured. The number average and weight average were calculated from the measurement results of the 300 bundles. The weight average was divided by the number average to determine 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 using a planetary mixer and a homomixer at 80 to 100°C. The temperature was then lowered to 80°C while maintaining the kneading, and an aqueous solution of component (D) below was added in small amounts. During this process, the viscosity of the contents gradually increased. After the entire 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 mixture passed the phase inversion point, and the amount of water added was increased. Finally, aqueous dispersion 1 with an active ingredient content of approximately 40% by mass was obtained. (A) One-terminal acrylic-modified bisphenol A epoxy resin (35 parts by mass) (EP828 base, 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 adduct of bisphenol A (20 parts by mass) (D) Newcol 723SF (15 parts by mass) 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 this carbon fiber was placed in an agitator granulator (trade name: SP Granulator SPG25T, manufactured by Dalton, device volume: 25 liters, agitator blade inclination angle θ: 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 (a fiber treatment agent) and 60 g of dispersion 1 (solid content concentration: 40% by mass) was placed in the agitator granulator and granulated by agitation for 6 minutes at a blade speed of 400 rpm (agitator blade peripheral speed: 8 m / s) and a chopper speed of 3000 rpm. The granules were dried for 2 hours in a box dryer at 120°C to obtain carbon fiber aggregates with a short diameter 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 material was 0.28 m, the strain rate was 30 [1 / s], and the strain amount was 10,600.

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

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

[0147] 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. When measured four times every 36 seconds, the average discharge amount was 1.74 g with a standard deviation of 0.09 g. The proportion of fiber bundles with an A' / A ratio 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 below.

[0148] [Example 2] In the method for producing the carbon fiber aggregate of Example 1, the recycled carbon fiber was replaced with virgin carbon fiber (trade name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm). 3 Carbon fiber aggregates having an elongated spheroid shape with a minor axis of 1.5 mm and a major axis of 12 mm were obtained in the same manner as in Example 1, except that the amount of water used in the fiber treatment agent was changed to 180 g instead of the above. 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 stirring blade was 8.3 m / s, the height of the raw material 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 longitudinal ratio (A' / A) of this fiber assembly was 0.80, the area ratio (S' / S) was 0.78, and the particle density was 0.83 g / cm 3 The angle of repose was 50°.

[0150] This fiber aggregate was placed 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. When measured four times every 36 seconds, the average discharge amount 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 waste 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 fiber was replaced with virgin carbon fiber (trade name: Pyrofil Chopped Fiber TR03CM, manufactured by Mitsubishi Chemical Corporation, cut length 3.1 mm, bulk density 0.706 g / cm3 Ellipsoidal carbon fiber aggregates were obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with 250 g of Dispersion 2 (anionic polyamide solution, solids concentration 40 mass%) instead of 3000 g of Dispersion 1, and the amount of water used was 200 g. The surface tension of the fiber treatment agent (a 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 aggregates were evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregates were harder than the carbon fiber aggregates of Example 1 and tended to retain their shape more easily.

[0152] [Example 4] The granulation equipment was replaced with a stirring granulator (product name: Henschel Mixer FM10B, manufactured by Mitsui Miike Machinery Works, Ltd., equipment volume: 9 liters, stirring blade inclination angle θ: 30°), and recycled carbon fiber (average fiber length 2.5 mm, bulk density 0.03 g / cm 3 200 g of the dispersion liquid 1 (polyester emulsion, solids concentration 40% by mass), which was a fiber treatment agent, was mixed with 140 g of water and 20 g of dispersion liquid 1 (polyester emulsion, solids concentration 40% by mass), 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 Machinery Works, 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) was used. 3 200 g of the fiber-treating agent and 40 g of water were 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 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.

[0154] [Example 6] The granulation equipment was replaced with a rolling agitator 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 Corporation, cut length 3.1 mm, bulk density 0.706 g / cm) was used. 3 6000 g of the fiber treatment agent, a mixture of 200 g of water and 700 g of dispersion 2 (anionic polyamide solution, solids concentration 40% by mass), was 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) for the mixing pan 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 for 2 hours in a box dryer at 120°C to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregates were evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregates were harder than the carbon fiber aggregates of Example 1 and tended to retain their shape more easily.

[0155] [Example 7] 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 recycled carbon fiber (average fiber length 6.0 mm, bulk density 0.15 g / cm) was used. 3 6000 g of the dispersion liquid 2 (anionic polyamide solution, solids concentration 40% by mass) and a liquid mixture of 350 g of water and 700 g of dispersion liquid 2 (anionic polyamide solution, solids concentration 40% by mass), which was used as a fiber treatment agent, were added and 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 / s). The rotation speed of the stirring rotor was 1120 rpm (circumferential speed of the stirring blade: 16 m / s) for the first 3 minutes and 140 rpm (circumferential speed of the stirring blade: 2 m / s) for the next 3 minutes. The rotation direction of the stirring rotor was opposite to that of the mixing pan. The granules were dried in a box dryer at 120°C for 2 hours to obtain ellipsoidal carbon fiber aggregates. The obtained carbon fiber aggregates were evaluated in the same manner as in Example 1, and the results are shown in Table 1. The obtained carbon fiber aggregates were harder than the carbon fiber aggregates of Example 1 and tended to retain their 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, opening 4.3 mm), and vibrated at an amplitude of 35 Hz. The fraction that passed through the sieve mesh was collected, and ellipsoidal carbon fiber aggregates were obtained. 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 equipment was replaced with a rolling granulator (pan type, rotating container inner dimensions φ240 × 75 mm), and virgin carbon fiber (trade 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 aggregates and 10 g of water (a fiber treatment agent) were added, and the mixture was rolled at an inclination angle of 45° and a rotation speed of 60 rpm (side wall peripheral speed of 0.75 m / s) for 6 minutes to form granules. The granules were 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.

[0158] [Experimental Example 2] The granulation equipment was replaced with a vibration granulator (cylindrical sealed container, container inner dimensions φ80 × 200 mm), and virgin carbon fiber (trade 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 (a fiber treatment agent) 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 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 Corporation, cut length 3.1 mm, bulk density 0.706 g / cm) was used. 3 100 g of the carbon fiber aggregate was mixed with 1000 g of water (a fiber treatment agent) and 10 g of polyacrylamide (trade 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 Figure 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 granulation equipment 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, a mixture of 37.5 g of water and 2.5 g of dispersion 1 (polyester emulsion, solids concentration 40 mass%), was added to the container, and the container was rolled at an inclination angle of 45° and a rotation speed of 60 rpm (side wall peripheral speed 0.75 m / s) for 6 minutes 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 Figure 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 granulation equipment 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 dispersion liquid 1 (polyester emulsion, solids concentration 40% by mass), 37.5 g of water as a fiber treatment agent, and 2.5 g of dispersion liquid 1 (polyester emulsion, solids concentration 40% by mass) were mixed and 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 amorphous 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 were superior to the methods of Experimental Examples 3 to 5 in that ellipsoidal carbon fiber aggregates could be obtained efficiently in a short time.

[0164] [Example 9] Virgin carbon fiber (cut product of Mitsubishi Chemical Corporation's TR50S15L, fiber length 25 mm) was used as the carbon fiber. First, 1000 g of this carbon fiber was placed in an agitator granulator (trade name: SP Granulator SPG25T, Dalton Corporation, device volume: 25 liters, agitator blade inclination angle θ: 30°) and agitated for 1 minute to defibrate. Next, 400 g of water, a fiber treatment agent, was placed in the agitator granulator and agitated for 7 minutes to granulate. The peripheral speed of the agitator blade tip 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 vibrating 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] Strand-shaped carbon fiber aggregates were obtained in the same manner as in Example 9, except that in the manufacturing method of the carbon fiber aggregate of Example 9, 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 in the manufacturing method of the carbon fiber aggregate of Example 9, 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 content concentration 40 mass%). The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

[0167] [Example 12] The granulator was replaced with a rolling agitator granulator (product name: Intensive Mixer R05T, manufactured by Eirich Co., Ltd., device volume: 40 L, rotor type: star type). 3000 g of recycled carbon fiber (fiber-like carbon fiber obtained by pyrolysis of SMC consisting of Mitsubishi Chemical Corporation's TR50S15L short carbon fiber and vinyl ester resin, fiber length: 25 mm) was added, and a liquid mixture of 1950 g of water (a fiber treatment agent) and 450 g of dispersion 1 (polyester emulsion, solids concentration: 40% by mass) was added and stirred for 9 minutes to granulate. The mixing pan rotation speed was 29 rpm (rotating vessel peripheral speed: 0.8 m / s). The agitator rotor rotation speed was 1120 rpm (agitator blade peripheral speed: 16 m / s) for the first 6 minutes and 140 rpm (agitator blade peripheral speed: 2 m / s) for the next 3 minutes. The rotation direction of the stirring rotor was opposite to that of the mixing pan for the first 6 minutes, and then in the same direction as that of the mixing pan for the next 3 minutes. The granules were dried in a box dryer at 120°C for 2 hours to obtain strand-like carbon fiber aggregates. 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 the same direction as that of the mixing pan for the next 6 minutes, had a larger bulk density and a larger weight distribution value than the carbon fiber aggregate of Example 12.

[0169] [Experimental Example 6] The granulation equipment was replaced with a rolling granulator (pan type, rotating container internal dimensions φ240 × 75 mm), and 50 g of recycled carbon fiber (cotton-like carbon fiber obtained by pyrolyzing SMC composed of Mitsubishi Chemical Corporation's TR50S15L short carbon fiber and vinyl ester resin, fiber length 25 mm) and a liquid mixture of 37.5 g of water and 2.5 g of dispersion 1 (polyester emulsion, solids concentration 40 mass%) as a fiber treatment agent were added, and the mixture was 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 granules were dried for 2 hours in a box dryer at 120 ° C to obtain amorphous carbon fiber aggregates. The evaluation results of the obtained carbon fiber aggregate are shown in Table 2.

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

[0171] [Table 2]

[0172] From the above results, it is clear 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 exhibits 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. The fibers are less likely to be 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, allowing the original effects of the fibers used in producing the fiber aggregate to be effectively exerted. The high bulk density of the fiber aggregate 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 Applications No. 2021-101844, No. 2021-101845, and 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 axes 3 Mixing blades 11 Granulated Bread 12 Rolling shaft 21 Arm 22 Spray 23 Scraper 40 containers 44 Mixing blade 45 Scraper

Claims

1. A method for producing a fiber aggregate, comprising: charging a plurality of fibers and a fiber treatment agent into an agitation tank; and agitating and granulating the mixture of the fibers and the fiber treatment agent with an agitation blade, The method includes: introducing the plurality of flocculent fibers into the stirring tank; and granulating the fibers so that the fibers are aligned; the fibers include carbon fibers and have an average fiber length of 2 to 12 mm; The bulk density of the fiber assembly is 0.3 g / cm ３ This is the method for producing a fiber assembly.

2. The method for producing a fiber assembly according to claim 1, wherein the fiber assembly is made of fiber bundles, and the fibers present on the surface of the fiber bundles are oriented in a curved manner along the contour of an ellipsoid.

3. The method for producing a fiber assembly according to claim 1 , wherein the plurality of fibers have been heat-treated in an oxidizing atmosphere to remove resin residue.

4. The method for producing a fiber aggregate according to claim 1 , wherein the stirring tank is provided with a scraper and rotates.

5. The method for producing a fiber aggregate according to claim 4, wherein the stirring is performed by rotating the stirring blades in the opposite direction to the rotation direction of the stirring tank, and then the stirring is performed by rotating the stirring blades in the same direction as the rotation direction of the stirring tank.

6. The method for producing a fiber aggregate according to claim 4, further comprising rotating the stirring tank at a peripheral speed of 1.2 m / sec or less.

7. The method for producing a fiber assembly according to any one of claims 1 to 6, wherein the surface tension of the fiber treatment agent at 23°C is 120 mN / m or less.

8. The method for producing a fiber assembly according to any one of claims 1 to 6, wherein the fiber treatment agent has a viscosity of 10 Pa·s or less at 23°C.

9. The method for producing a fiber assembly according to any one of claims 1 to 6, wherein the positions of tips of the plurality of fibers constituting the fiber assembly are irregular.

10. The method for producing a fiber assembly according to any one of claims 1 to 6, 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.

11. The method for producing a fiber assembly according to any one of claims 1 to 6, wherein the fiber assembly has a spheroid shape or a strand shape.

12. The method for producing a fiber aggregate according to any one of claims 1 to 6, 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.

13. 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 claims 1 to 6.

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