Manual Handling

Epoxy vinyl ester prepregs

As known, vinyl ester resins are addition products of various epoxies and unsaturated mono-carboxylic acids, most commonly methacrylic acid. Industrial resins are commonly diluted with a low molecular weight monomer, such as styrene, vinyl toluene or methyl methacrylate, to reduce the room temperature viscosity of the mixture and yield a solution with a typical viscosity in the range of 200 to 2000 cps.

Due to the intrinsic nature of the epoxy vinyl ester resins, the resulted prepregs (i.e.: Simprex® and UV-preg®), require some handling cares that would make their use sustainable and valuable. Some cares are presented below:

a. Handling
  • Prepregs should be stored in their original packaging barrier film, or an equivalent film, and maintained air-tightness, at 68oF (20oC) and dry place.
  • After a partial use, the prepreg roll must be always wrapped and packed again into a barrier film.
  • The styrene content in the prepreg is ranging from 15 to 20%. The release film should not be removed from the prepreg only when ready for laying it up in the mold. Same thing, the top release should not be removed only when the next layer is ready for laying up in the mold. This precaution ensures good control of prepreg tackiness by preventing surface drying.
  • Usual precautions should be observed. The prepreg contains mainly uncured synthetic resins. The operator has to wear appropriate mask – respirator and work in a clean, dry (R.H. = 50% or less), and ventilated area. The use of clean disposable inert gloves provides protection for the operator and avoids contamination of material and components.

b. Processing
  • All Simprex® prepregs can be cured and processed similar to conventional epoxy prepregs, either in compression molding, vacuum bag, or autoclave.
  • During the lamination of Simprex® prepregs, similar to any other prepregs, it is convenient to debulk the materials every few layers by subjecting the stack to vacuum in a temporary bag or on a vacuum table. Other know-how techniques can be applied for proper debulking the prepreg layers before curing. Trapped air between layers will prevent proper curing.
  • Whatever the molding process is, the three keys for a successful curing are:

    o No trapped air between the layers, as well as between the mold and the first layer;

    o Apply a minimum pressure of 1 bar and maintain it along the whole curing time;

    o Apply increasing, or constant, heat in order to bring the inside temperature of the whole compressed prepreg layers, quite equal to the specified curing temperature, usually 120-125C, and maintain it for 20-25 min.
  • If maximum Tg and mechanical performance are required, post cure has to be considered at the specific recommended temperature, generally 140-160C, for 30-45 min.