A Better Prepreg for Sandwich Panels
(February 2001) FiberCote Industries, Inc. has introduced a new product designed specifically for large sandwich panel production. Similar to first generation systems, E-717 is a self-adhesive, fire-retardant system that meets FAR 25.853 vertical burn requirements. But what makes E-717 different is that it is easier to handle, does not require refrigeration, and has superior peel strength and lower deflection at peak load. In addition, total cure cycle times as short as 30 minutes are possible. Versus first generation “rubber modified” systems, E-717 is dry and boardy at room temperature and does not require poly separator film, which actually makes large sheets easier and quicker to handle. In addition, single skin honeycomb sandwich panels fabricated with E-717 exhibit very low “telegraph” effect.
E-717 Benefits
E-717 prepregs are designed for flat or mildly contoured sandwich panels and laminates that require fire retardance and high stiffness and strength. E-717 prepregs offer several features and benefits, including significant part cost reduction and performance enhancement possibilities over “first generation” rubber modified epoxy prepregs.
| Feature | Dry and boardy / No poly required |
| Benefits | • Easier to handle than prepregs with tack and drape • Reduced labor costs associated with part lay-up and handling • Eliminate poly scrap and waste disposal cost |
| Feature | • Frozen storage not required. • Store at room temperature (72°F) for up to 3 months |
| Benefits | • Reduce/eliminate freezer storage capacity problems. • Reduce energy consumption associated with frozen storage • Possible to store prepreg in the lay-up area |
| Feature | Excellent adhesive properties and higher specific stiffness / lower panel deflection under load. 7781 Climbing Drum Peel = ~12 in-lb/in* 1 ply skin) and ~30+ in-lb/in* (2 ply skin). Long Beam Flex ~150+ in-lb/in* |
| Benefits | • Possible to increase panel load capabilities • Possible to increase panel stiffness without adding raw material cost or maintain panel stiffness and reduce raw material cost • Possible to reduce panel weight, i.e., reduce core weight and/or reduce prepreg weight |
| Feature | Short cycle times, i.e., 325°F* Isothermal, i.e., in hot/out hot = 30 minutes or less |
| Benefits | • Significantly reduce processing costs • Increase production throughput • Increase press capacity |
| Feature | Reduced “telegraph” effect on honeycomb sandwich panels |
| Benefits | • Smooth panel surface on single and 2-ply skins = less preparation for paint and finishing • Improved panel aesthetics and better panel appearance |
| Feature | Long rolls possible, i.e., 100-200 yards |
| Benefits | • Reduce labor cost associated with cutting table set-ups. • Reduce material scrap associated with cutting. |
| *Core = 0.50 inches thick, 1/8″ cell, 3 lb/ft3 Nomex, Cured for 30 minutes @325°F Isothermal, 40 psi | |
E-717 is a press-grade, self-adhesive and fire-retardant epoxy system that meets FAR 25.853 burn requirements. Designed specifically for sandwich panels and laminates that require high specific stiffness and strength, E-717 prepregs offer better translation of fiber properties at room temperature and at elevated temperature. Honeycomb sandwich panels fabricated with E-717 exhibit very low “telegraph” effect. Cure cycle times as short as 30 minutes are possible. If stored at ambient (72°F) or lower, E-717 prepregs do not require refrigeration for up to three months.
| Mechanical Property Test Method |
Test Condition °F |
E-717 / 7581* |
| Tensile Strength, ksi ASTM-D-638 |
RT Dry 160°F Dry |
73 61 |
| Tensile Modulus, msi ASTM-D-638 |
RT Dry 160°F Dry |
3.8 3.7 |
| Compression Strength, ksi ASTM-D-695 |
RT Dry 160°F Dry |
71 55 |
| Compression Modulus, msi ASTM-D-695 |
RT Dry 160°F Dry |
4.1 3.9 |
| Interlaminar Shear ASTM-D-2344 |
RT Dry 160°F Dry |
8.6 5.5 |
| Long Beam Flexure, psi ASTM-C-393 |
RT Dry | 146 |
| Climbing Drum Peel, in – lb/in) ASTM-D-1781 |
RT Dry | 12.5 |
Cure Cycles
Above properties were obtained via preheated (isothermal) press cure at 260°F at 50 psi for 90 minutes. Alternate press cure cycles recommended are 325°F (isothermal) at minimum 40 psi pressure for 30 minutes or 265°F (isothermal) at minimum 40 psi pressure for 60 minutes.
* 7581 construction is identical to 7781 construction except that 7581 uses an ECG 75 1/0 yarn (nominal 9 micron filament versus 7781 uses an ECDE 75 1/0 yarn (nominal 6 micron filament)
Note: All data given are typical and do not provide an adequate statistical basis for specification purposes. Representations made are believed to valid. However, seller makes not warranty of any kin concerning the use of this product.
FiberCote is a subsidiary of Park Electrochemical Corp. (NYSE – PKE).