Process for manufacturing a fiber reinforced composite article, the composite article obtained and the use thereof
A process for the preparation of a fiber reinforced composite article that facilitates manufacturing of composite articles with reduced cycle times, said composite articles exhibiting high fibre content, low void content and excellent visual and mechanical properties, and capable of use for the construction of mass transportation vehicles, in particular, in the automotive and aerospace industries.
1. A process for preparing a fiber reinforced composite article comprising the steps of:
a) providing a mold, comprising an upper die ( 11 ) and a lower die ( 12 ), the lower die ( 12 ) having a molding surface and vertically extending side walls ( 14 ), the upper die ( 11 ) having a complementary molding surface and vertically extending side walls ( 13 ) substantially aligned with the side walls of the lower die ( 12 ), so that the upper die ( 11 ) vertically moves into the lower die ( 12 ) to form a cavity ( 17 ) in a partially closed position and a completely closed position of the mold, wherein the cavity ( 17 ) in a partially closed position is sealed vacuum-tight by at least one seal ( 15 ) placed around the vertically extending side walls ( 13 ) of the upper die ( 11 ) or the vertically extending side walls ( 14 ) of the lower die ( 12 ) and perpendicular to the direction of movement of the upper die ( 11 ), and wherein the at least one seal ( 15 ) works as a resin retention seal which prevents the resin from leaking,
b) performing one of b1) applying a thermosetting resin composition onto a fibre reinforcement to form a treated fibre reinforcement, and placing the treated fibre reinforcement into the lower die ( 12 ) of the mold, or b2) placing a fibre reinforcement into the lower die ( 12 ) of the mold, and applying a thermosetting resin composition onto the fibre reinforcement while the mold is open,
c) moving the upper die ( 11 ) into the lower die ( 12 ) and partially closing the mold,
d) evacuating the mold in the partially closed position by means of a vacuum outlet to a pressure of from 0.1 to 100 mbar,
e) completely closing the mold and exerting a hydraulic pressure of from 2 to 100 bar onto the resin treated fibre reinforcement to complete impregnation of the fibre reinforcement,
f) curing the resin impregnated fibre reinforcement to form a cured fiber reinforced composite article, wherein the cured fibre reinforced composite article has a volume fraction of fibre of 50% to 70%, based on the total volume of fibre and resin in the composite article, and
g) demolding the cured fiber reinforced composite article
wherein the thermosetting resin composition is an epoxy resin composition comprising an epoxy resin, wherein the epoxy resin is the diglycidylether of bisphenol A or the diglycidylether of bisphenol F.
2. The process according to claim 1 , wherein the mold in the partially closed position in step d) is evacuated to a pressure of from 0.1 to 50 mbar.
3. The process according to claim 1 , wherein the hydraulic pressure exerted onto the resin treated fibre reinforcement in step e) is from 2 to 75 bar.
4. The process according to claim 1 , wherein curing of the resin impregnated fibre reinforcement in step f) is carried out under isothermal conditions at a temperature of from 50 to 200° C.
5. The process according to claim 1 , wherein at least two seals ( 15 ) and ( 15 b ) are placed around the vertically extending side walls ( 13 ) of the upper die ( 11 ) perpendicular to its direction of movement and are substantially aligned parallel to each other, in order to provide vacuum-tightness of the cavity ( 17 ) in partially closed and completely closed positions of the mold.
6. The process according to claim 1 , wherein the thermosetting resin composition is liquid at the molding temperature.
7. The process according to claim 6 , wherein the thermosetting resin composition has a viscosity of from 0.1 to 10,000 mPa·s at the molding temperature.
8. The process according to claim 1 , wherein the mold in the partially closed position in step d) is evacuated to a pressure of from 0.1 to 10 mbar.
9. The process according to claim 1 , wherein the hydraulic pressure exerted onto the resin treated reinforcement in step e) is from 10 to 50 bar.
10. The process according to claim 1 , wherein curing of the resin impregnated fibre reinforcement in step f) is carried out under isothermal conditions at a temperature of from 100 to 150° C.
11. The process according to claim 6 , wherein the thermosetting resin composition has a viscosity of from 0.1 to 100 mPa·s at the molding temperature.