The performance of epoxy materials depends not only on the structure and properties of the epoxy resin, the structure and properties of the curing agent and additives, but also on the ratio between them, but also on its molding and curing history. The same formula has very different structure and properties of cured products obtained under different curing process parameters and procedures. Therefore, the process does not have the same importance as the material design. The monitoring of the process and the prosecution of the quality of raw materials are also important links and indispensable means for obtaining high-quality epoxy materials. Material design and raw material prosecution provide the material basis for obtaining high-quality epoxy materials. However, whether or not a high-quality epoxy material can be obtained and the purpose of material design can be ensured by process design and process monitoring.
Epoxy resin curing process and influencing factors
The curing process of epoxy materials is a very complex process of physical changes and chemical changes, and there are many influencing factors. It can be summarized as follows:
(1) Wetting of solid materials (fibers, fillers, bonded surfaces, coated substrates, etc.) with epoxy glue (liquid epoxy resin, or epoxy resin solution, or epoxy resin) Dipping. Can also be made into prepregs or molding compounds. The main influencing factors are the compatibility of the glue liquid with the solid material (affinity, which can be improved by adjusting the glue liquid formulation design and solid surface treatment, etc.) and the viscosity of the glue liquid (depending on the glue liquid formulation and the ambient temperature).
(2) The material fills the cavity or leveling to form a dense object. The main influencing factor is the fluidity of the material, which is mainly the viscosity of the glue. It all depends on the glue formulation and the ambient temperature. Pressurization and vacuuming can be used to assist in filling and forming dense objects.
(3) Curing reaction. Under certain conditions, the epoxy oligomer starts to react with the curing agent and the modifier, from the gel to the gelation to the glass transition to the three-dimensional crosslinked structure cured product. The main influencing factor is the thermal history of the system. Including: preheating temperature, heating and cooling speed, curing temperature, curing time, post-curing temperature and time. In addition, the curing pressure also has a certain effect on the curing reaction and the compactness and shape stability of the product. The main influencing factors are glue formulation and ambient temperature and humidity.
(4) Structure formation of epoxy matrix (epoxy cured product). This is gradually formed as the epoxy curing reaction progresses. Including the formation of the chemical structure of the cured product and the aggregation structure of the cured product. The main influencing factors are the thermal history of the glue solution and system.
(5) Formation of the interface layer structure of the epoxy material. It is also gradually formed with the progress of epoxy curing reaction. Not only depends on the thermal history of the glue solution and system, but also closely related to the surface properties of materials such as fibers and fillers.
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