The wet method is also called the solution method, that is, the resin is dissolved in a low boiling point solvent to form a solution with a specific concentration, and then the fiber bundle or fabric is impregnated with the resin solution at a specified speed, and the resin is controlled by a doctor blade or a metering roller Content, and then dry in an oven to volatilize the low-boiling solvent, and finally wind up. The solution method is divided into drum winding method and continuous dipping method.
Roller winding method refers to winding the fiber bundle or fabric impregnated with the resin matrix on a metal cylinder. For each turn, the screw rod is fed one circle laterally, so that the fiber bundle is wound on the metal cylinder in parallel. After a full circle, cut along the drum bus bar to form a sheet of prepreg. This process has low efficiency and limited product specifications, and is currently only used for teaching or new product development. The continuous impregnation method is that several to tens of fiber bundles are dipped at the same time through the resin matrix dissolving tank, and then passed through the oven to volatilize the solvent and collected on the roll. Its length is not limited by the diameter of the metal cylinder like the roller method. [122. The wet method has the characteristics of simple equipment, convenient operation and great versatility. The main disadvantage is that it is difficult to accurately control the ratio of reinforcing fibers to the resin matrix, the uniform distribution of the resin matrix material is not easy to achieve, and the control of the volatile content is also difficult. In addition, since the volatilization of solvents used in the wet process will cause environmental pollution and cause certain harm to human health, the wet process has been gradually eliminated abroad. The dry method is also called the hot melt method. It first melts the resin at a high temperature, and then impregnates reinforcing fibers in different ways to make a prepreg. The dry method can be divided into one-step method and two-step method according to the processing state after the resin is melted: the one-step method is to directly immerse the fiber through a glue tank containing molten resin, and then dry and rewind; the two-step method is also called the film method, It first coats the melted resin on the dipping paper to make a film on a film making machine, and then it is laminated with fibers or fabrics and subjected to high temperature treatment. In order to ensure the stability of the resin content of the prepreg, the resin film and the fiber bundle are usually laminated in a "sandwich" structure, and finally the resin is melted and embedded into the fiber at high temperature to form the prepreg.
The advantages of the hot melt method: high control precision of prepreg resin content, low volatile content, low harm to the environment and human body; good surface appearance of the product, low porosity of the composite material, avoiding the stress concentration caused by the gap and the composite The harm of shortened material life; it is more convenient to control the quality of the film, and the gel time and viscosity of the resin can be monitored at any time. Disadvantages: The equipment is complicated and the process is cumbersome. It requires a low melting point of the thermosetting resin, and low viscosity in the molten state, which is prone to chemical reactions. For prepregs with a large thickness, the resin is easy to penetrate unevenly. In order to obtain a better fiber and resin interface, the reinforcing fiber is usually heated before being combined with the resin matrix to increase the activity of the fiber surface and improve the interface bonding of the fiber and resin.