| Anisotropic conductive film (ACF) is a kind of anisotropic polymer film, which consists of conductive particles, adhesive and additives. With the fast development of electronic information industry, ACF has been widely applied in various fields related to LCD and integrated circuit (IC), since it was used to connect LCD panel of electronic calculator for the first time in 1970s. ACF is of good conductivity and connectivity for the addition of conductive particles and adhesive respectively. Epoxy resin is a kind of thermosetting resin, which is an important base resin for ACF adhesive. Epoxy-based ACF has many outstanding performances, such as great adhesive stress, chemical resistance and low shrinkage. However, the curing reaction of traditional epoxy adhesive only happens at a high temperature, and the process costs a long time. In addition, the one-part adhesive shows poor storage stability. Therefore, for simple process and environmental concerns, the latent curing agent especially with moderate curing temperature becomes the optimal curing agent. In addition, the application of epoxy resin has been hindered by their fragile performance, poor impact resistance and weather fastness after curing. Thus, epoxy resin should be modified to meet different needs.In this paper, the appropriate curing agent with a moderate curing temperature for E-51 epoxy resin system was selected from various kinds of thermotropic curing agents. The curing process was traced by the differential scanning calorimetry (DSC) and infrared spectroscopy (FT-IR). The effects of curing were analyzed by FT-IR, the curing temperatures were measured by non-isothermal DSC, the curing times and the appropriate proportion for the system were measured by isothermal DSC. The experimental results showed that,2-methyl imidazole (2-MI) was the optimal latent curing agent for E-51 epoxy resin which could cure at moderate temperature and the curing process took a short time. As a result, the optimal adhesive ratio of 2-MI to E-51 was 7:100 by weight, and the curing temperature of this system was between 88.5℃and 93.7℃.Isothermal DSC method was employed to study the curing kinetics. The fitted results showed that, the cure kinetic mode of the 2-MI /E-51 curing system was Kamal model, which was a composite model combining the n-order model and the autocatalytic model. In addition, the autocatalytic kinetic was dominated in the curing process. The matrix epoxy resin was modified by adding a kind of hyperbranched polyester to extend the pot life of the adhesive. The system could keep steady at low temperature, because the hyperbranched polyester mainly separated the molecules of curing agent and epoxy resin. When the viscosity of the system decreased with the temperature rose, the curing reaction could take place gradually. The experimental results showed that, the adhesive system, which still could cured at moderate temperature rapidly, could be stored steady for more than 1 year below 5℃. In addition, Hardness tests showed that the uniformity of the curing product was also improved. |
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