Northern CompositesIn-stock composite materialsPrepreg

Prepreg

The term “prepreg” refers to woven or unidirectional fibers pre-impregnated with a thermoset polymer matrix, such as epoxy, BMI, cyanate ester, phenolic, etc. The fibers used in prepreg include glass fibers, basalt fibers, carbon fibers and aramid fibers. Prepregs are available for nearly every application with a wide variety of resin systems. The proper curing agent is already included within the resin systems, therefore, the prepreg is ready to lay up into the mold. Pressure and heat are then used to cure the laminate.

The impregnation process allows the precise control of fiber to resin ratio, as well as, ply thickness. Excess resin is removed from the reinforcement and a partial cure results in a pliable state known as a B-stage. As heat activates the curing process, prepregs in the B-stage require refrigeration for storage and shipment.

There are some advantages as well as disadvantages to the use of prepregs.

Advantages:
Repeatable and uniform: As impregnation is performed under strict controlled environments, resin content and ply thickness will be uniform.

Less mess and waste: Unlike hand layup resin cups, drips, hand rollers and cleanup are not issues when dealing with prepreg materials. As prepregs can be handled at room temperatures, you are no longer racing against the clock to avoid the resin from setting before your work is complete.

Lower cure times: Unlike wet lamination which can require up to 5 days to cure, prepreg cures are measured in hours.

Maximum strength: Even applying vacuum bagging, wet layup seldom will allow resin contents < 50%. Prepregs have the desired resin content built in.

Better looking parts: With the elimination of air bubbles, prepregs allow smooth glossy surfaces more easily than with hand laminated parts.

Disadvantages:
Usable Shelf Life: As a prepreg is a catalyzed material, shipping and storage in refrigeration are required.

Cost: # for # prepreg materials are more costly than those used in wet lamination. The net cost of part manufacture need not be so.

Heat needed: A heat source and vacuum bagging are needed to properly cure prepreg materials. While most fabricators will employ the use of an autoclave, there are several out of autoclave (OOA) and Vacuum Bag Only (VBO) techniques that are used.

Applications
There are many applications that benefit from the use of prepreg materials These include aerospace, racing, sailing and boat building, sporting goods medical applications such as prosthetics, wind turbines, and more.

Processing
As prepregs cure at elevated temperatures, they can be processed using an autoclave or hot pressing. The best quality is achieved using an autoclave. Combining pressure and vacuum results in high fiber volume and low void content.

Out of Autoclave
Advances in out of autoclave (OOA) processing continue to improve performance and lower cost for composite structures. Vacuum bag only (VBO), can deliver less than one percent (1%) void content required for primary structures in the aerospace industry.

You can find some of the prepreg materials that we offer here, or contact us to speak with a technical sales rep to help determine the best material for your needs.

Prepregs now provided by Hexcel.