Functional plywood can produce constant heat by applying a voltage to the conductive bonding layer between wood sheets. Herein functional plywood was prepared by filling various microsized graphite particles (3.3-52.5μm in diameter) and nanosized carbon black (CB ; 29 nm) into a phenolic resin. To investigate the electrical conductivity, the resulting composite resin was coated onto a commercial glass slide. The effects of particle size, mass fraction of the conductive fillers (graphite and CB), and the weight ratio of graphite to the fillers (φ = graphite / (graphite + CB)) on the conductive properties of the composite resin, particularly the specific resistance and its variation coefficient, were estimated. A composite resin, which included at least 30 mass% of filler, yielded a relatively low variation coefficient for the specific resistance. Additionally, the composition of the resin had superior conductivity when the weight ratio was 55-66 mass% and the graphite particles were 22.9μm or less in diameter.
The above experiment indicated heating plywood was produced. Consequently, its surface temperature was measured. With respect to particle size, the standard deviation in the surface temperature of the plywood corresponded to that of the conductive properties on the glass slide. Hence, the method proposed herein using a glass slide is suitable for conductive characterization to determine the appropriate conditions to prepare heating plywood.