Method of producing fiber assembly and method of producing prepreg sheet
A method for producing a fiber assembly, including: putting a plurality of fibers and a fiber treatment agent into a stirring tank; and stirring a mixture of the fibers and the fiber treatment agent with a stirring blade to granulate the mixture, wherein the fibers include carbon fibers, and the mixture is granulated such that the fibers are aligned. A method for producing a fiber assembly, wherein a plurality of fibers containing carbon fibers and a liquid are put into a stirring tank and the mixture of the fibers and the liquid is stirred with a stirring blade, thereby obtaining a fiber assembly which has a spheroidal shape or a strand shape.
1 . A method of producing a fiber assembly, comprising:
heat treating a plurality of fibers in a cotton form in an oxidizing atmosphere to remove resin residue included in the plurality of fibers,
putting the plurality of fibers and a fiber treatment agent into a stirring tank; and
stirring a mixture of the plurality of fibers and the fiber treatment agent with a stirring blade to granulate the mixture so that the plurality of fibers are aligned;
wherein the plurality of fibers includes carbon fibers,
the plurality of fibers has an average fiber length of 2 to 12 mm, and
the fiber assembly has a bulk density of 0.3 g/cm 3 or more.
2 . The method of producing a fiber assembly according to claim 1 , wherein the fiber assembly is composed of a fiber bundle, and the plurality of fibers presents on the surface of the fiber bundle are curved and oriented along an outline of an ellipsoid.
3 . The method of producing a fiber assembly according to claim 1 ,
wherein the stirring tank includes a scraper and is made to rotate.
4 . The method of producing a fiber assembly according to claim 3 ,
wherein the stirring is carried out such that a rotation direction of the stirring blade is the same as a rotation direction of the stirring tank after the stirring is carried out such that the rotation direction of the stirring blade is opposite to the rotation direction of the stirring tank.
5 . The method of producing a fiber assembly according to claim 3 , further comprising:
rotating the stirring tank at a peripheral speed of 1.2 m/sec or less.
6 . The method of producing a fiber assembly according to claim 1 ,
wherein the fiber treatment agent has a surface tension of 120 mN/m or less at 23° C.
7 . The method of producing a fiber assembly according to claim 1 ,
wherein the fiber treatment agent has a viscosity of 10 Pa's or less at 23° C.
8 . The method of producing a fiber assembly according to claim 1 ,
wherein positions of tips of the plurality of fibers constituting the fiber assembly are not aligned.
9 . The method of producing a fiber assembly according to claim 1 ,
wherein a length of a major axis of the fiber assembly is greater than an average fiber length of the plurality of fibers contained in the fiber assembly.
10 . The method of producing a fiber assembly according to claim 1 ,
wherein the fiber assembly has a prolate spheroidal shape or a strand shape.
11 . The method of producing a fiber assembly according to claim 1 ,
wherein a ratio (Y/X) of an average fiber length Y of the plurality of fibers in the fiber assembly to an average fiber length X of the plurality of fibers before being put into the stirring tank is 0.55 or greater.
12 . A method of producing a prepreg sheet, comprising:
accumulating a plurality of fiber assemblies obtained by the method of producing a fiber assembly according to claim 1 .
13 . The method according to claim 1 , wherein the fiber assembly consists of a plurality of carbon fibers and an organic binder;
wherein the carbon fibers are recycled fibers,
the fibers have an average fiber length of 2 to 12 mm,
the carbon fiber assembly has a bulk density of 0.3 g/cm 3 or more, and
the carbon fiber assembly has a prolate spherical shape with a major axis length of 3 mm to 18 mm.
14 . The method according to claim 13 , wherein the fiber assembly is composed of a fiber bundle, and the fibers present on the surface of the fiber bundle are curved and oriented along an outline of an ellipsoid.