1. Reinforcement materials
Main requirements for prepreg reinforcement materials:
①Good wettability to resin;
②Good film-forming property to meet the requirements for molding of complex-shaped products;
③Meet the main performance requirements of products.
Reinforcement fibers include glass fiber, carbon fiber and aramid fiber. Commonly used reinforcement forms include unidirectional fiber, gingham, twill and multi-axial cloth.
2. Matrix materials
Main functions of matrix resin:
①Orient and position the fibers and bond them together;
②Transmit stress during the stress process of the product.
Generally speaking, it is difficult to meet the process performance requirements with a single resin. Usually, a combination of several resins is used to achieve process operation, such as using a combination of several different epoxy resins to increase the viscosity of the resin system at room temperature or low temperature. Phenolic epoxy resin can improve the reactivity and heat resistance of the resin system, and bisphenol A epoxy resin can adjust the viscosity of the resin system. Studies have shown that the best resin system for prepreg is a combination of liquid bisphenol A epoxy resin, solid bisphenol A epoxy resin and phenolic epoxy resin. The selection of matrix materials should take into account the performance requirements of the composite material itself and the process operation requirements. For example, the basic requirements of medium-temperature hot-melt epoxy resin prepreg are that it is not sticky in summer and not brittle in winter. This requires adjusting the proportion of different components so that the softening point of the resin system meets 36-37°C in summer and 30-32°C in winter, while limiting the curing temperature of the epoxy resin. The optimal temperature is generally 120-130°C, and the curing time does not exceed 90 minutes. 3. Curing system The curing system includes curing agent, accelerator, catalyst and diluent. According to the use requirements of prepreg, prepreg needs to have a certain storage period at room temperature. Therefore, the curing system usually uses a latent curing agent, which means that it does not react with the resin at room temperature and pressure, but under special temperature and pressure, it will promote the cross-linking and curing reaction of the resin. This is conducive to the storage of prepreg at room temperature. This type of curing agent is usually a dispersed curing agent, that is, it is solid at room temperature and cannot be dissolved in epoxy resin, but when heated to near its melting point, it can be miscible with epoxy resin and start a rapid curing reaction. The main function of the accelerator is to promote the dissolution of the curing agent in the resin matrix and increase the curing reaction rate; the toughening agent is to reduce the brittleness of the thermosetting resin matrix and improve its impact resistance; the diluent is mainly to reduce the viscosity of the resin and improve the process performance; the catalyst is mainly to promote the reaction of the resin in the curing and molding stage, but at room temperature and pressure, it is also in a "latent" state, which is very beneficial to the actual production operation of prepreg