Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
1999-01-08
2001-02-27
Krynski, William (Department: 1774)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S367000, C423S447100, C423S447300
Reexamination Certificate
active
06194071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carbon fiber ball which is suitably used in the manufacture of composite materials containing carbon fibers and resin compounds containing carbon fibers, as well as a process for preparing the carbon fiber ball.
2. Background of the Invention
For the purpose of improving mechanical properties, electric characteristics, sliding performance, and other characteristics of a resin, carbon fibers are added to and compounded with the resin, and the thus-obtained composite materials have found wide utility. One known method for manufacturing such composite materials involves the continuous supply of a resin and short carbon fibers having a length of about 3-10 mm to a molding machine such as an extruder so as to attain uniform dispersion of the short carbon fibers in the resin matrix inside the molding machine, to thereby form a composite material in a continuous manner. Short carbon fibers interlaced in a complicated manner, such as pitch short carbon fibers manufactured by centrifugal spinning, are difficult to supply in quantity to a molding machine, such as an extruder, because their small bulk density prevents them from satisfactorily affording into an extruder from a hopper or from a supply means attached to a hopper. In such a case, there is employed a method in which a master batch is manufactured in advance by mixing a resin and short carbon fibers by use of a batch-type kneader, and the thus-obtained master batch is mixed with a resin to be molded. This method requires an extra step of manufacturing a master batch, and also has a drawback that continuous manufacturing cannot be performed.
In order to solve this problem, there is proposed a method in which short fibers are introduced into a swirling air stream so as to bring them to closely aggregate into a spherical shape having a diameter of 10 mm or less and a bulk density of 0.04-0.15 g/cm
3
; the resultant fibrous balls are mixed with a thermoplastic resin (powder or pellets); and then the mixture is kneaded at a temperature of not lower than the melting point of the thermoplastic resin (see Japanese Patent Application Laid-Open (kokai) No. 63-27207). However, this method is disadvantageous in that closely aggregated carbon fibers are interlaced in a complicated manner, to thereby prevent their uniform dispersion in the resin matrix during kneading.
Accordingly, the present invention is directed to a carbon fiber ball which permits a quantitative and stable supply of carbon fibers to an extruder or the like and enables the carbon fibers to be uniformly dispersed in the matrix of the resin with ease, as well as to a method of manufacturing the fiber ball.
SUMMARY OF THE INVENTION
The inventors of the present invention have conducted careful studies so as to attain uniform dispersion of short carbon fibers in the matrix of a resin by use of an extruder, and have found that the above-mentioned problem is satisfactorily solved by impregnating the short carbon fibers with a binder. The present invention was accomplished based on this finding.
According to a first aspect of the present invention, there is provided a carbon fiber ball comprising short carbon fibers and a binder, wherein the carbon fiber ball has a bulk density of 0.05-0.15 g/cm
3
. According to a second aspect of the present invention, there is provided a carbon fiber ball comprising short carbon fibers, a resin powder, and a binder, wherein the carbon fiber ball has a bulk density of 0.05-0.15 g/cm
3
.
The carbon fiber balls according to the first or second aspect of the present invention smoothly leave a hopper—or a supply means attached to the hopper—to enter an extruder with ease, because they have a generally spherical shape and a large bulk density, and therefore allow a quantitative and stable supply of the carbon fibers to an extruder or the like. In addition, the binder binds a short carbon fibers to another short carbon fibers or to resin powder so as to prevent breaking up of the carbon fiber ball, or to prevent detachment of the carbon fibers and resin powder from the carbon fiber balls. Moreover, the binder serves as a lubricant and improves sliding between short carbon fibers, to thereby cause the uniform dispersion of short carbon fibers in the resin matrix with ease in the process of dispersing the short carbon fibers in the resin matrix by kneading the carbon fiber balls and resin by use of an extruder or the like.
The resin powder of the second aspect of the present invention is present within and/or outside generally spherical balls formed of short carbon fibers interlaced with one another and increases the bulk density of the carbon fiber ball. In addition, the resin powder facilitates uniform dispersal of the short carbon fibers in the resin matrix when the carbon fiber balls and resin are kneaded.
The carbon fiber ball of the first aspect of the present invention may be manufactured by a process comprising the steps of filling a mixer with short carbon fibers, the mixer having a hollow cylindrical container which is disposed substantially horizontally and a plurality of flat blades and a plurality of rake-shaped vanes disposed therein for rotating about a horizontal axis of the cylindrical container as a common axis of rotation; rotating the flat and rake-shaped vanes simultaneously; adding a binder to the contents of the mixer; and then rotating the flat blades to form the carbon fiber ball. In the meantime, the carbon fiber ball of the second aspect of the present invention may be manufactured by a process comprising the steps of filling a mixer with short carbon fibers, the mixer having a hollow cylindrical container which is disposed substantially horizontally and a plurality of flat blades and a plurality of rake-shaped vanes disposed therein for rotating about a horizontal axis of the cylindrical container as a common axis of rotation; rotating the flat and rake-shaped vanes simultaneously; adding a binder to the contents of the mixer; rotating the flat blades; further adding a resin powder to the contents of the mixer; and rotating the flat blades to form the carbon fiber ball.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The carbon fiber ball of the first aspect of the present invention comprises short carbon fibers and a binder and has a bulk density of 0.05-0.15 g/cm
3
. The carbon fiber ball of the second aspect of the present invention comprises short carbon fibers, a resin powder, and a binder, and has a bulk density of 0.05-0.15 g/cm
3
. The carbon fiber ball of the first or second aspect of the present invention preferably has a diameter of 3-15 mm. Carbon fiber balls larger or smaller than the above size are poorly forwarded into an extruder from a hopper or from a supply means attached to a hopper, and make a quantitative, continuous supply of short carbon fibers difficult. The carbon fiber ball preferably has a diameter of 3-15 mm, more preferably 5-13 mm, and still more preferably 7-10 mm. At least 80% by weight carbon fiber balls should fall within the above-mentioned range of diameters of the fiber carbon ball, wherein the diameter of an individual carbon fiber ball refers to the largest value among those measured in various directions.
The short carbon fibers preferably have a length of 130 mm, more preferably 2-20 mm, and still more preferably 310 mm. Short carbon fibers having a length of 1 mm or less have insufficient interlacing of carbon fibers, and therefore easily break up and encounter difficulty in maintaining their shape. Carbon fibers having a length of 30 mm or more are difficult to form in a spherical shape.
No limitation is imposed on the diameter of the short carbon fiber, but short carbon fibers having a diameter of 5-30 &mgr;m are generally used.
With pitch-derived carbon fibers which are manufactured by centrifugal spinning, or with vapor-phase epitaxial carbon fibers manufactured by vapor phase epitaxy, it is difficult to increase the bulk density by aligning these fibers in one direction and causing them t
Palmarole Gerard
Shibuya Yukihiro
Takano Katsuto
Gray J. M.
Krynski William
Kureha Chemical Industries Co., Ltd.
Nixon & Vanderhye P.C.
LandOfFree
Carbon fiber ball and a process for manufacturing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Carbon fiber ball and a process for manufacturing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carbon fiber ball and a process for manufacturing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566860