Process of debundling carbon fiber tow and molding compositions containing such fibers
A process for debundling a carbon fiber tow into dispersed chopped carbon fibers suitable for usage in molding composition formulations is provided. A carbon fiber tow is fed into a die having fluid flow openings, through which a fluid impinges upon the side of the tow to expand the tow cross sectional area. The expanded cross sectional area tow extends from the die into the path of a conventional fiber chopping apparatus to form chopped carbon fibers, or through contacting tines of a mechanical debundler. Through adjustment of the relative position of fluid flow openings relative to a die bore through which fiber tow passes, the nature of the fluid impinging on the tow, the shape of the bore, in combinations thereof, an improved chopped carbon fiber dispersion is achieved. The chopped carbon fiber obtained is then available to be dispersed in molding composition formulations prior to formulation cure.
1. A process for debundling carbon fiber tow into chopped carbon fibers comprising:
feeding the carbon fiber tow defined by a bundle cross sectional area and a tow surface into a die having a bore, the die having an entrance opening, at least two fluid flow openings and a separate exit opening in a terminal face of the die, where the bore is sized larger than the bundle cross sectional area with the proviso that if the at least two fluid flow openings are two openings, that the two openings are not diametrically positioned through a circular cross sectional bore, and where the carbon fiber tow moves linearly through the die from the entrance opening to the exit opening;
impinging on the carbon fiber tow within the bore through a first opening of the at least two fluid flow openings with a fluid at a flow rate to expand carbon fiber tow to an expanded cross sectional area greater than the bundle cross sectional area within said bore;
exiting the expanded cross sectional area carbon fiber tow from the exit opening in the terminal die face of the die; and
chopping the expanded cross sectional area carbon fiber tow upon exiting said die to form the chopped carbon fiber.
2. The process of claim 1 wherein the carbon fiber tow has at least 1,000 carbon fibers therein.
3. The process of claim 1 wherein chopping occurs proximal to the terminal face of said die.
4. The process of claim 1 wherein the bore is a cross sectional shape of triangular, circular, oval, or polygonal.
5. The process of claim 1 wherein the at least two fluid flow openings are laterally displaced along a length of the bore.
6. The process of claim 1 wherein at least one of the fluid flow openings defines a fluid exhaust.
7. The process claim 1 wherein the fluid is air.
8. The process of claim 1 wherein the fluid is gaseous and further comprises particulate.
9. The process of claim 1 wherein the fluid is gaseous and further comprises radicals.
10. The process of claim 1 wherein the fluid is gaseous and further comprises a coupling agent.
11. The process of claim 1 further comprising dispersing the chopped carbon fiber in a molding composition prepolymer formulation.
12. The process of claim 11 wherein said molding composition prepolymer comprises polar monomers.
13. The process of claim 12 wherein said polar monomers comprise a majority by weight of said molding composition absent fiber and fillers.
14. The process of claim 1 further comprising contacting said tow with a plurality of rotating tines.
15. A process for debundling carbon fiber tow into chopped carbon fibers comprising:
feeding the carbon fiber tow defined by a bundle cross sectional area and a tow surface into a die having a bore, the die having at least two fluid flow openings, where the bore is sized larger than the bundle cross sectional area with the proviso that if the at least two fluid flow openings are two openings, that the two openings are not diametrically positioned through a circular cross sectional bore;
impinging on the carbon fiber tow through a first opening of the at least two fluid flow openings with a fluid at a flow rate to expand carbon fiber tow to an expanded cross sectional area greater than the bundle cross sectional area within said bore; and
chopping the expanded cross sectional area carbon fiber tow upon exiting said die to form the chopped carbon fiber contacting said tow with a plurality of rotating tines while simultaneously exposing said tow to at least one of heat or plasma.
16. The process of claim 15 comprising contacting said tow with a plurality of rotating tines while simultaneously exposing said tow to at least one of heat or plasma wherein heat is applied under an inert or reducing environment.
17. A process for debundling carbon fiber tow into chopped carbon fibers comprising:
feeding a continuous carbon fiber tow defined by a bundle cross sectional area and a tow surface into a mechanical debundler comprising: a feed area that accepts said continuous tow between two opposing rollers with tines, where a first roller of said two opposing rollers spins clockwise and a second roller of said two opposing rollers spins counter clockwise so as to pull the continuous tow inward towards a single lower tined roller that rotates faster than the upper two rollers;
expanding said continuous tow to about 5 times in loft.
18. The process of claim 17 further comprising chopping the expanded cross sectional area carbon fiber tow upon exiting said mechanical debundler to form the chopped carbon fiber.
19. The process of claim 17 further comprising applying at least one of blowing air, heat or plasma to said tow in a region between said lower tined roller and the upper two rollers.