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Toner Under the Microscope


There are many different types of toner particles but they all share the fact that they are composed of a black pigment in a transparent thermoplastic matrix. The individual toner particles may be spherical, globular, or irrigular in shape in there unused condition. Once they have been bonded to paper they tend to be irregular in shape and often exhibit plastic deformation as a result of the forces that removed them from the paper to which they had been bonded. Sometimes a small fragment of paper will be attached to the toner particle that was worn from the surface of the printed paper.

Significance in the Environment:

The presence of these particles in the environment indicate the presence of a printer or copy machine. If unused toner particles are found in the environment it suggests that the machine is not functioning properly. There may be particle emission or ozone emission issues associated with the machine. These may result in a cosmetic problem (discoloring clothing), irritation of mucus membranes, or other problems, depending on the nature a quantity of materials being generated by the printer or copier. Ozone is a known toxin but the hazards of the other materials that are generated by printers and copiers are unknown. Particles generated by printers and copiers tend to be predominantly from the paper being used rather than the toner or inks used in them. Some wear plastic and wear metal particles are created from the moving parts of the machines but most of the particle come from the paper being feed through the friction drive of the machine. That is one of the many reasons why particle counts around copy machines and printers tend to vary from time to time with the same machine, the same level of activity, and even with "similar" paper. Particle counters cannot differentiate between toner, ink, particles of wear, or paper sizing particles. Literature such as that published by Linda Morawska should be interpreted cautiously, as she, herself, suggests.

Characteristic Features:

Toner particle may be often be recognized their transparent matrix and the distribution of black pigment particles. Some toners contain very small, well dispersed pigment and may appear completely black. They will exhibit very little if any reflectivity and no edge birefringence. Cenospheres exhibit much higher reflectivity and show a complex surface texture not seen in toner particles. Weld spheres exhibit edge birefringence between crossed polarizers, are smooth, and show surface reflectivity. The matrix for the toner particles is typically a polyethylene, a polystyrene, or a polyester. The polystyrene and some of the polyester matrices are soluble in acetone. In a tapelift processed using acetone the matrix will dissolve resulting in free pigment particles and thin films of matrix material together under the tape at the location of the original particle.

Associated Particles:

Toner particles are typical of office environments. They are typically found with mechanically abraded paper, paper sizing, toner coated paper fibers, and then with the other types of particles common in offices.

Morawska, Lidia, Congrong He, and len Taplin, "Particle Emission Characteristics of Office Printers", International Laboratory for Air Quality and Health (Queensland University of Technology); Queensland Department of Public Works, SF Gate, 2007-07-10, pp. 1–7.