Characterization of Photocopier Toners By X-Ray Photoelectron Spectroscopy (XPS): How They Change With Age

A Past work in the examination of photocopier toners has used various infrared spectroscopic techniques and pyrolysis gas chromatography [1-7]. These approaches have been successful in differentiating between various photocopier toner “libraries”, but with some overlap among toner formulations from the same manufacturer. X-ray Photoelectron Spectroscopy is an instrumental technique that measures the surface composition of a solid sample in regards to both elemental and chemical species. Through the use of high energy x-rays, characteristic photoelectrons are generated from the uppermost 20-100 angstroms of the sample. Data are correlated with known binding energy values to identify the particular atomic species. Due to chemical shifts caused by the immediate molecular environment of the examined atoms, chemical species information is also obtained. For example, the energy of a carbon atom in graphite has a different value from carbon contained in polymeric materials. The carbon and oxygen species, as well as the ratio of carbon to oxygen, are useful for the characterization of the various toner samples. Since most xerographic toners are polymeric in nature, the carbon atoms specifically associated with alcohol, carbonyl or ether bonds yield useful information. Earlier work has shown that with age qualitative and quantitative changes occur [8-10]. This study involved the use of both heat and ultraviolet radiation to mimic the referenced changes on several different toner formulations. A variety of artificial aging conditions were evaluated and comparison with naturally aged samples categorized the parameters by which a toner samples “age” could be determined. The characteristic surface sensitivity of XPS allowed for the direct examination of samples taken from documents without separation of paper from the toner component. The ability to remove paper, and therefore its components, from the analysis results in a clean sample absent of any contamination. This contamination can be inorganic, such as titanium or calcium from fillers or whiteners, or organic, such as carbon species from cellulose fibers or starch used as a coating. This technique provides a methodology by which the “age” of toner containing documents can be determined. Future work will include a more comprehensive study.