Electrophotographic Performance of Phthalocyanine Pigment Composites Containing Titanyl Phthalocyanine

Spectral sensitivity is an important consideration in photoconductor formulation, depending on the particular type of electrophotographic device in which it is used. High sensitivity in both the near-IR and visible spectral regions would be desirable for a photoconductor to be used with a wide variety of exposure sources. One possible way to achieve this goal is to use a mixture of charge generation pigments with absorptions in the desired spectral regions. The phthalocyanine pigments are well known for their use as charge generation materials in organic photoconductor (OPC) formulations. The absorption spectra (and the spectral sensitivity) of these pigments vary according to the metal coordinating the phthalocyanine, and with coordination of different axial ligands (O2-, Cl-, OH-, etc.). In this paper, phthalocyanine pigment composites with different sensitometric properties are prepared by coprecipitation of titanyl phthalocyanine with another phthalocyanine pigment from an organic solvent/trifluoroacetic acid solution. The phthalocyanine pigments used in the composites were chosen on the basis of their structures relative to titanyl phthalocyanine (i.e., presence or absence of an axial ligand). The initial electrophotographic performance of the composites is measured, and compared with the pure components prepared in similar fashion. The sensitivity of the photoconductor can be varied in a systematic fashion by varying the composition of the composite, and the composites show enhanced sensitivity when compared to mixtures of the component pigments.