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We have investigated the partial discharge (PD) due to electrical treeing degradation in low-density polyethylene (LDPE), ethylene - vinyl acetate copolymer (EVA) and ethylene - acrylic acid copolymer (EAA) by a computer-aided partial discharge measurement system which allowed us to obtain phase-resolved PD pulse data. The experimental results revealed that the PD magnitude was strongly affected by the instantaneous applied voltage and that the occurrence of a PD was determined by the time derivative of the applied voltage (). The PD pulse-sequence analysis revealed the following: (i) a PD occurs in a discharge path which consists of a tree trunk and branches extending from the trunk; (ii) in each discharge path at most one PD occurs per half cycle. Based on these facts, a model of PDs due to electrical treeing was proposed. The influences of applied voltage and frequency were investigated by applying a triangular voltage. The number and average magnitude of PDs increased linearly with applied voltage whereas the PD charge per cycle increased quadratically. These results are in good agreement with the model.

The encapsulation effect of thermal chemical-vapour-deposition polymer films (TCVDPF) has been studied for organic light-emitting diodes (OLED). We used poly-p-xylylene (PPX) and/or poly-2-chloro-p-xylylene (PCPX) films as TCVDPF. For the encapsulation, TCVDPF was deposited on the OLED during a dry process at room temperature. The lifetime of an encapsulated OLED with 0.6 µm thick TCVDPF was about four times longer than that of a non-encapsulated OLED in air. The lifetime of the OLED increased with increasing thickness of the TCVDPF. We conclude that the effect of TCVDPF encapsulation on the long-term stability of the OLED is due to the prevention of oxygen and moisture in air and several other factors.

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The authors prepared an organic electroluminescent diode (organic LED) with hole transport material and aluminium quinoiline and another organic LED with an additional electron blocking layer using the DCM partial doping method. The authors studied the change in the EL spectra accompanied by the applied current in the specimens by means of the peak separation method. The electron-hole recombination did not always occur at the emission layer near the interface between the hole transport layer and the Alq3 emission layer from the initial EL stage after electrons had been transported from cathode to the interface. It was proved that the emitting region is shifted from the cathode side to the anode side in the emission layer with increasing applied current, especially by electron injection from the cathode. In addition, from the measurement of the specimen with an electron blocking layer, the authors found that the dominant EL process is not due to the carrier trap model in an organic DCM-doped Alq3 LED.

The space charge distribution in low-density polyethylene (LDPE) was measured with the pulsed electroacoustic (PEA) method. We used three types of LDPE: LDPE-L and LDPE-H were prepared by the high pressure process, and m-LDPE was polymerized with a metallocene catalyst. Space charge in LDPE strongly depended upon the electrode material. Semiconductive electrodes enhanced carrier injection into LDPE and, as a result, space charge. The density, polymerization process, applied field, temperature and so on also affected the space charge behavior. This space charge behavior was compared with the results of dc current measurements.