Epoxy Pre-Preg

The process of mechanically applying a resin system, usually epoxy based, to a fabric, (typically carbon fiber or Kevlar based); in an exact ratio of resin to fiber content is commonly known as Pre-Preg, short for pre-impregnation. The resin system is applied in what is known as a B-Staged state, meaning that the base resin and catalyst are pre mixed before being applied to the fabric and will not cure until subjected to heat.. The product is then frozen and shipped by refrigerated truck to the end user. The exact resin to fiber ratio that is attainable from this process is one of its major benefits. The resin to fiber ratio of a laminate has a major impact on the ultimate strength developed. In a marine application 40% resin to 60% fiber is near ideal. That will give you near perfect mechanical properties. The manufacturer, when ready to create a part, has only to thaw the pre-preg product, which is only an overnight process. At that point if the material is pre-cut it is placed in the mold.

The time before a resin system starts to cure after it is catalyzed is known as “out-time’. With wet resin systems this is measured in hours (2-4). The out-time on most pre-pregs is typically 2-4 weeks. After that time the builder needs to cure the part under pressure (vacuum bag or autoclave) and heat (oven or autoclave). The nature of pre-preg allows us to work uninterrupted for days on end placing the laminates in the mold. This means that very large parts can be laminated without interruption into massive monolithic structures.

This shows a tailored corner of pre-preg on the Revenge 35 LT hull:

Kevlar Pre-Preg