A tetrafunctional type mesogenic epoxy（TGEPTA）was cured with two types of phenol novolac with different hydroxyl
equivalents and mesogenic group concentration. Thermal properties of TGEPTA thermosets were compared with those of bisphenol-A DGE（DGEBA）thermosets. Moreover, these data were summarized and discussed as a function of mesogenic concentration and crosslinking density. As a result, TGEPTA thermosets showed excellent thermal properties such as high thermal stability, Tg less, low thermal expansion and high thermal conductivity than DGEBA thermosets. These properties of TGEPTA thermosets are derived from the suppression of the network chain mobility based on the introduction of mesogenic groups and the high cross-linking density. In addition, thermal properties were improved at optimum compounding ratio of two types of phenol novolac in which concentration of mesogenic group and crosslinking density of network chain were balanced.
Interfacial interaction between binder and fillers in an epoxy-based electrically conductive adhesive containing silver flakes was investigated using TD（time-domain）-NMR spectroscopy. Two different types of diluents were used for the adhesive. Heterogeneity in the epoxy-based binder was clearly characterized by TD-NMR. In addition, interfacial interaction between filler surface and some domains formed in the binder was successfully analyzed by TD-NMR. When a reactive diluent（phenyl glycidyl ether, PGE）was used, a PGE-rich domain was clarified to preferentially interact with the fillers. The interfacial interaction caused by the addition of PGE was suggested to enhance interaction between fillers by a rheological analysis of the adhesive paste. Electrical conductivity development in the adhesives during curing was analyzed by a free-damped oscillation method concurrently with electrical resistance measurement. The analysis clarified formation of filler network was enhanced by the addition of PGE during curing. As a result of this work, TD-NMR can provide useful information for material design of electrically conductive adhesives.
Self-organization assembly（SOA）method is a way to form conductive paths using thermoset resin containing solder fillers applied between an electric component and a print circuit board（PCB）. A lot of phenomena such as movement, melting, coalescence and wetting of solder fillers, and reduction of surface oxide film, have to be controlled to realize the SOA method. The authors revealed the effect of viscosity of resin and reduction of oxide film on coalescence behavior of solder fillers. Since the viscosity of resin decreased at elevated temperature, solder fillers sank in the resin to the PCB before melting. Coalescence behavior depended on wettability of solder fillers in the resin. When the wettability was poor, the solder fillers were not coalesced sufficiently and many fillers left between electrodes. When the wettability was fine, the solder particles sunk on the PCB were fused together and subsequently separated and wetted on each electrode.
A phenolic-based electrically conductive adhesive containing copper fillers was prepared. The copper fillers were treated using tetraethylenepentamine（TEA）before mixing into the binder to suppress oxidation of the fillers. Although the adhesive exhibited lower electrical resistivity（50-100 μΩcm）after curing in air, variation in the resistivity during environmental tests was different depending on the curing temperature. When the adhesive was cured at 100℃, inter-filler conductive contacts and cross-linked polymer structure in the binder were not fully formed during curing. The electrical resistivity of the adhesive cured at 100℃ was varied during exposure to 85℃/85 %RH environment due to annealing effect and oxidation of the fillers. By contrast, the interfiller conductive contacts and cross-linked structure were sufficiently developed during curing at 150-200℃ to improve the electrical reliability. Therefore, curing condition is one of the important factors in determining the reliability of the adhesive.
Aluminum alloys are applying for civil engineering fields as a structure material. Non-heat-treatable aluminum alloy 5083-O, which has high strength and corrosion-resistance, excellent weldability and low temperature behavior and seawater resistance, is widely used for a civil engineering material. In this study, first, a technique to apply high-frequency induction heating to friction welding as an auxiliary heat source was developed. Then, friction welding experiments were conducted for 5083-O rods with this technique. The experiments were carried out under different temperatures by preheating with the induction heating, and the relation of the joint strength and the preheating temperatures was investigated. In order to understand the effect of the preheating on increased joint strengths, material structures of the joints were analyzed. Besides, the effects of induction heating to the welding parameters while friction welding were investigated. As a result, when using the induction heating while friction welding, the areas of plastic flow at the joint portions broadened to enhance the strength of the joints.