Publication Date: 2004-Sep-19
The IP.com Prior Art Database
Various combinations of resin-curative-reinforcement for composite laminating are presented. These assemblies can be used singly or in combination to produce preimpregnated or partially preimpregnated laminating materials. They address improved tack, drape and shelf-life over conventional prepreg composite mateials.
Abstract: Various combinations of resin-curative-reinforcement for composite laminating are presented. These assemblies can be used singly or in combination to produce preimpregnated or partially preimpregnated laminating materials. They address improved tack, drape and shelf-life over conventional prepreg composite materials.
The use of prepregs is a well-known art in the field of making structural, semi-structural and decorative composite laminates. Prepregs are fibrous composite materials provided in the form of sheets, strips or continuous rolls. The resin matrix can be a thermoplastic or a thermosetting composition, however, thermosetting resin matrices are the most common. Examples of the thermosetting resin matrix include but are not limited to epoxy, phenolic, polyester, vinylester and polyimide. The reinforcement can be glass, carbon aramid, natural fibers, nylon or other polymer fibers and ceramics. The reinforcement yarns can be circular, non-circular or hollow and can be either staple or continuous or any combination of the above. Examples of the reinforcement forms include woven, non-woven, knit, mat, scrim or unidirectional webs used singly or in combination. The thermosetting resin matrix usually contains an admixed catalyst or hardener (curing agent) and in some cases an accelerator is added to effect polymerization or cure of the material when heated to the reactive temperature at which curing begins. Reinforcement fibers normally comprise about 55% to 70% of the total weight of the fiber-resin assembly. However, conventional prepreg has some disadvantages. Firstly, the admixture of the catalyst or hardener with the resin matrix yields a shelf-life limitation for the usability of the material. At room temperature or below, the curing agent reacts with the resin which results in a gradual increase in the resin viscosity which inhibits the necessary flow of the matrix into the reinforcement. It also results in the loss of tack and drape and eventually makes the prepreg unusable as a laminating material. This shelf-life problem is particularly significant when highly reactive curing agents are admixed with the resin matrix. In such circumstances, there may be only a few days of usability even when the material is stored in a refrigerated environment. Therefore, there are advantages from providing a prepreg assembly wherein the resin and the curing agent are separated until such time as heat and pressure are applied to initiate polymerization.
Composite prepreg assemblies can have the resin and the curing agent separated on opposite surfaces of the reinforcement or they can be separated on the same surface of the reinforcement. Additionally, they can be partially impregnated into the reinforcement or simply make contact with the reinforcement. When the matrix resin and curing agent are on the opposite sides of the reinforcement, they can be in a continu...