Environmental Engineering Reference
In-Depth Information
Wet-process photocopiers are widely
used in Canada and, to a lesser extent, the U.S. They emit large quantities
of C
a.
Wet-process photocopiers.
isoparaffinic hydrocarbons, and therefore have the potential to
cause significant indoor contamination by these volatile organic compounds
(VOCs). Because of high emission rates and their significant contribution to
total VOC levels, they are believed to be potential contributors to SBS-type
symptom prevalence rates in some buildings. Several complaint investiga-
tions have implicated wet-process photocopiers as a cause of a variety of
irritation-type symptoms.
-C
10
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Electrostatic, or
xerographic, copiers have been in use for over four decades. They are the
most common copy machines used in offices. Because of the high voltages
used, they can be a significant source of ozone (O
b.
Electrostatic copying machines and laser printers.
). Emissions vary widely
and newer products have been designed to reduce O
3
emissions. Electrostatic
copiers also emit toner particles. Toner powder consists of carbon black and
a resin that adheres carbon black to paper; particle size is 10 to 20
3
m. Because
of the electrostatic charge imparted on toner particles, they are deposited on
surfaces near operating machines.
Laser or electrophotographic printers also appear to be a source of con-
taminants to which office workers may be exposed. Laser printers use a high-
voltage generator that charges the surface of a continuously rotating photo-
conducting drum. The drum surface is exposed to a scanning laser beam
that discharges the photoconducting surface selectively (in accordance with
the pattern to be printed). The toner is charged with an electrostatic potential
and is attracted to the drum surface where a negative image is produced.
Paper is brought into contact with it and toner is transferred by a second
high-voltage generator. The image is made fast, or fused, by thermal or
chemical means. In the latter case, laser printers use a mixture of Freon and
acetone, which are emitted from the machine. Emissions of a variety of
compounds have been associated with laser printers employing heat fusion.
These emissions appear to be toner decomposition products. Unlike electro-
static copiers, laser printers do not produce significant quantities of O
ยต
or
carbon black. Toner particles are so highly charged that they are quickly
deposited on machine surfaces.
As indicated above, emissions from heat-fusing laser printers appear to
be primarily associated with toner resins and decomposition products. One
of the more common laser printer toners is described as consisting of 10%
carbon black, 5% charge control agents (derived from diphenyl hydrozones),
and 85% styrene-acrylate copolymer binder.
Vapor emissions from electrostatic copiers include residual monomers
from toner resins and decomposition products including (1) unstable ozo-
nides, diperoxides, and epoxides and (2) oxygenated hydrocarbons such as
lower aldehydes, ketones, and organic acids.
A variety of vapor-phase substances are emitted from toners used in
electrostatic and laser printers. These include solvent residues (benzene,
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