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The properties of epoxy materials depend not only on the structure and properties of the epoxy resin, the structure and properties of the curing agents and additives, but also the ratio between them, and also on the molding cure history. The same formulation has great differences in the structure and properties of the resulting cured product under different curing process parameters and procedures. Therefore, the process is not as important as the material design. The monitoring of the process and the quality control of the raw materials are also an important link and an indispensable means to obtain high-quality epoxy materials. Material design and raw material prosecution provide a material basis for obtaining high quality epoxy materials. However, the ability to obtain high-quality epoxy materials for material design is also ensured by process design and process monitoring.
Curing process and influencing factors of epoxy resin
The curing process of epoxy materials is a complex process of physical and chemical changes with many influencing factors. Can be summarized as follows:
(1) Epoxy glue (liquid epoxy glue, or epoxy resin solution, or epoxy melt) for wetting of solid materials (fibers, fillers, bonded surfaces, coated substrates, etc.) Impregnation. It can also be made into prepreg or molding compound. The main influencing factors are the compatibility of the glue with the solid material (affinity, which can be improved by adjusting the formulation design and solid surface treatment) and the viscosity of the glue (depending on the glue formulation and ambient temperature).
(2) The material is filled into the cavity or leveled to form a dense object. The main influencing factor is the fluidity of the material, 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) A curing reaction is carried out. Under certain conditions, the epoxy oligomer reacts with the curing agent and the modifier, from the glue to the gelation → vitrification → three-dimensional crosslinked structure cured product. The main influencing factor is the thermal history of the system. Including: preheating temperature, temperature rise and fall, 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 the glue formulation and ambient temperature and humidity.
(4) Structure formation of an epoxy group (epoxy cured product). This is gradually formed as the epoxy resin curing reaction progresses. It includes the formation of a chemical structure of the cured product and the formation of a solidified structure of the cured product. The main influencing factors are the thermal history of the glue formulation and system.
(5) Formation of an interface layer structure of an epoxy material. It is also gradually formed as the epoxy resin curing reaction progresses. It depends not only on the thermal history of the glue formulation and system, but also on the surface properties of materials such as fibers and fillers.
