Masaki Akatsuka

Influences of inorganic fillers on curing reactions of epoxy resins initiated with a boron trifluoride amine complex

Abstract Inorganic fillers are widely used for epoxy resins to improve mechanical and thermal properties. However, inorganic fillers may unexpectedly affect the curing reactions of such epoxy resins. In our present study, influences of inorganic fillers on the curing reactions of phenol novolac epoxy resin (EPN) initiated with boron trifluoride ethylamine complex (BF3MEA) are detailed. The gel times of epoxy resins containing alumina (Al2O3) fillers were longer than those of corresponding unfilled epoxy resins, indicating that Al2O3 fillers delayed the curing reactions of epoxy resins. Mechanisms were proposed and influences of aluminum hydroxide (Al(OH)3), silica (SiO2), and aluminum fluoride (AlF3) fillers were also described.

Thermal and mechanical properties of liquid crystalline epoxy resins as a function of mesogen concentration

Liquid crystalline thermosets are known to exhibit a number of improved characteristics in comparison with traditional plastics. We now describe quantitatively how the thermal and mechanical properties of a number of liquid crystalline epoxy resins vary with polymer mesogen concentration, using biphenyl- and biphenol-based diepoxides with varying spacer lengths and a range of aromatic diamine curing agents. Although macroscopically isotropic, the degree of order at the microdomain level can be related to the network physical properties, and thus increasing mesogen content leads to increased intermolecular interactions between the polymer chains and hence reduced micro-Brownian motion and reduced free volume. These properties are manifested as increased elastic moduli at high temperatures, reduced thermal coefficients of expansion, increased decomposition onset temperatures and reduced solvent absorption.

High thermal conductive epoxy resins with controlled high order structure

Present electrical devices have large calorific power, and improvement of heat dissipation has been a very important subject. In this paper, we developed the novel epoxy resins which increased the thermal conductivity that has been a barrier to heat dissipation. The medium of thermal conduction for insulating resins is phonons. Phonon conduction depends on the crystallinity, since it is a lattice vibration. The scattering of phonons happens on the interface of an amorphous structure. If there is a macroscopic amorphous structure although crystal structure exists on the microscopic level, we expected that high thermal conduction could be attained by reduced scattering of phonons through controlling the nano scale structure. Using an epoxy resin which has the mesogen structure would solve this problem because its easy to carry out an orientation with this structure. As a result, we confirmed that thermal conductivities become larger when the amounts of mesogens were increased. The epoxy resin (A) contains biphenyl mesogen, and the epoxy resin (B) contains even bigger mesogenic units. The epoxy resin (A) was about two times higher than the conventional epoxy resin, and the epoxy resin (B) was able to attain five times as much thermal conductivity as the conventional one.

Delamination mechanism of high-voltage coil insulators made from mica flakes and thermosetting epoxy resin

To clarify the delamination mechanism of high-voltage coil insulators made from mica flakes and epoxy resin due to static mechanical stress, the relationships between the shear strength of the insulator and the physical properties of the component materials were studied. The mechanism of their delamination was thought to be either a lack of epoxy resin between the mica flakes, interface failure between the mica flakes and the epoxy resin, or cleavage of the mica flakes. The first two mechanisms were discounted because the shear strength of the insulator was found to be independent of both the contact angle of the corresponding liquid epoxy resin on the mica flakes and the critical surface tension of the epoxy resin. Furthermore, the shear strength of the model insulator was improved by using an epoxy resin with a higher bending elastic modulus, implying that the delamination mechanism in this system is the cleavage of mica flakes. Therefore, the epoxy resin should have a high elastic modulus to ensure high delamination resistance, that is, the temperature to which the insulators are exposed should be lower than the glass transition temperature of the corresponding epoxy resin. Optical microscope studies also supported these results.