Pre-impregnated materials (prepregs) are reinforcement fibres or fabrics into which a pre-catalysed resin system has been impregnated by a machine. The resin systems in these materials react very slowly at room temperature, giving rise to working times of many days or months. Prepreg resins can only be fully cured by heating them to the prescribed cure temperature. The accuracy of the machinery used to combine the fabric or fibre with the resin ensures that laminates produced from prepregs have more consistent and higher fibre contents than can be achieved by wet lay-up techniques. This allows the use of very tough, strong resin systems that would be too high in viscosity to be impregnated by hand.
SPRINT™ materials consist of a layer of fibre reinforcement either side of a pre-cast, pre-catalysed resin film with a very lightweight tack film on one face. The material therefore has the appearance of dry reinforcement, which has resin concealed at its centre. SPRINT™ materials are produced by a process that differs from conventional prepreg so that the fibres in the reinforcements remain dry and un-impregnated by the resin. SPRINT™ materials are laid up in a mould and vacuum bagged as for conventional prepreg. However, when the vacuum is applied, the air transport properties of the dry reinforcement enable air trapped in the fibre bundles and between layers to be easily removed. When the temperature is then raised for the cure, the resin film softens and flows into the air-free reinforcement. The void content of the resultant laminate is extremely low (typically 0-0.5%).