The modern office may contain several types of reproduction machines. They range from the ubiquitous dry-process photocopier to the rather special-purpose blueprint machine, the fax and mimeograph machines, as well as other types of duplicators. Within this article, the different devices will be grouped according to broad technology classes. Since dry-process photocopiers are so widespread, they will receive the greatest attention.
Photocopiers and Laser Printers
Most steps in conventional electrophotography (xerography) are directly analogous to those in photography. In the exposure step, the printed page or photograph to be copied is illuminated by a flash of bright light, and the reflected image is focused by a lens onto an electrically charged, light-sensitive photoreceptor, which loses its charge wherever the light hits its surface. The light will have hit in the same pattern as on the surface being copied. Next, developer, generally composed of large carrier beads with small, electrostatically charged particles adhering to them, is transported to the photoreceptor by a cascading or magnetic conveying process. The charged, latent image on the photoreceptor is developed when the finely divided powder (known as toner, dry imager or dry ink) is electrostatically attracted, separates out of the developer and remains on the image. Finally, the toner that has adhered to the imaged areas is electrostatically transferred (printed) to a sheet of plain paper and permanently fused to it (fixed) by the application of heat, or heat and pressure. Residual toner is removed from the photoreceptor by a cleaning process and deposited into a waste toner sump. The photoreceptor is then prepared for the next imaging cycle. Since the imaged paper removes only toner from the developer, the carrier that supplied it to the image is recirculated back into the developer housing and mixed with fresh toner that is metered into the system from a replaceable toner supply bottle or cartridge.
Many machines apply both pressure and heat to the toner-on-paper image during a fusing process. The heat is supplied by a fusing roll, which contacts the toned surface. Depending on the characteristics of the toner and fuser materials, some toner may stick to the fuser surface rather than to the paper, resulting in a deletion of part of the image on the copy. In order to prevent this, a fuser lubricant, commonly a silicone-based fluid, is applied to the surface of the fuser roll.
In laser printing, the image is first converted to an electronic format; that is, it is digitized into a series of very small dots (pixels) by a document scanner, or a digital image may be created directly in a computer. The digitized image is then written onto the photoreceptor in the laser printer by a laser beam. The remaining steps are essentially those of conventional xerography, wherein the image on the photoreceptor is transformed to paper or other surfaces.
Some photocopiers use a process known as liquid development. This differs from the conventional, dry process in that the developer is generally a liquid hydrocarbon carrier in which finely divided toner particles are dispersed. Development and transfer are generally analogous to the conventional processes, except that the developer is washed over the photoreceptor and the wet copy is dried by the evaporation of residual liquid upon the application of heat or both heat and pressure.
The consumables associated with photocopying are toners, developers, fuser lubricants and paper. Although not generally considered as consumables, photoreceptors, fuser and pressure rolls and various other parts routinely wear out and need replacement, especially in high-volume machines. These parts are generally not considered to be customer replaceable, and require special knowledge for their removal and the adjustment. Many new machines incorporate customer replaceable units (CRUs), which contain the photoreceptor and developer in a self-contained unit which the customer can replace. In these machines, the fuser rolls and so on either last the life of the machine or require separate repair. In a move toward reduced service costs and greater customer convenience, some companies are moving towards increased customer reparability, where repair can be made with no mechanical or electrical hazard risk to the customer and will, at most, require a telephone call to a support centre for assistance.
Toners produce the image on the finished copy. Dry toners are fine powders composed of plastics, colourants and small quantities of functional additives. A polymer (plastic) is usually the major component of a dry toner; styrene-acrylic, styrene-butadiene and polyester polymers are common examples. In black toners, different carbon blacks or pigments are used as the colourant, while in colour copying, various dyes or pigments are employed. During the toner manufacturing process, the carbon black or colourant and the polymer are melt mixed and most of the colourant becomes encapsulated by the polymer. Dry toners may also contain internal and/or external additives which help determine the toner’s static charging and/or flow characteristics.
Wet-process toners are similar to dry toners in that they consist of pigments and additives inside a polymer coating. The difference is that those components are purchased as a dispersion in an isoparaffinic hydrocarbon carrier.
Developers are usually mixtures of toner and carrier. Carriers literally carry toner to the surface of the photoreceptor and are frequently made of materials based on special grades of sand, glass, steel or ferrite types of substances. They may be coated with a small amount of polymer to achieve the desired behaviour in a specific application. Carrier/toner mixtures are known as two-component developers. Single-component developers do not use a separate carrier. Rather, they incorporate a compound like iron oxide into the toner and utilize a magnetic device for applying the developer to the photoreceptor.
Fuser lubricants are most often silicone-based fluids which are applied to fuser rolls to prevent toner offset from the developed image to the roll. While many are simple polydimethylsiloxanes (PDMSs), others contain a functional component to enhance their adhesion to the fuser roll. Some fuser lubricants are poured from a bottle into a sump, from which they are pumped and ultimately applied to the fuser roll. In other machines the lubricant may be applied via a saturated fabric web which wipes part of the roll’s surface, while in some smaller machines and printers, an oil-impregnated wick makes the application.
Most, if not all, modern photocopiers are made to perform well with various weights of ordinary, untreated bond paper. Special carbonless forms are made for some high-speed machines, and non-fusing transfer papers are produced for imaging in photocopiers and then applying the image to a T-shirt or other fabric with the application of heat and pressure in a press. Large engineering/architectural drawing copiers often produce their copies on a translucent velum.
Potential hazards and their prevention
Responsible manufacturers have worked hard to minimize the risk from any unique hazards in the photocopying process. However, material safety data sheets (MSDSs) should be obtained for any consumables or service chemicals used with a particular machine.
Perhaps the only unique material to which one may be significantly exposed in the photocopying process is toner. Modern, dry toners should not present a skin or eye hazard to any but perhaps the most sensitive individuals, and recently designed equipment utilizes toner cartridges and CRUs that minimize contact with bulk toner. Liquid toners, as well, should not be directly irritating to the skin. However, their isoparaffinic hydrocarbon carriers are solvents and can defat the skin, leading to dryness and cracking upon repeated exposure. These solvents may also be mildly irritating to the eyes.
Well-designed equipment will not present a bright light hazard, even if the platen is flashed with no original on it, and some illumination systems are interlocked with the platen cover to prevent any operator exposure to the light source. All laser printers are classified as Class I laser products, meaning that, under normal conditions of operation, the laser radiation (beam) is inaccessible, being contained within the printing process, and does not present a biological hazard. Additionally, the laser device should not require maintenance, and in the highly unusual event that access to the beam is required, the manufacturer must provide safe working procedures to be followed by a properly trained service technician.
Finally, properly manufactured hardware will not have sharp edges, pinch points or exposed shock hazards in areas where operators might place their hands.
Skin and eye hazards
In addition to dry toners not presenting a significant skin or eye hazard, one would expect the same with silicon oil-based fuser lubricants. Polydimethylsiloxanes (PDMSs) have been subjected to extensive toxicological evaluations and have generally been found to be benign. While some low-viscosity PDMSs may be eye irritants, those used as fuser lubricants usually are not, nor are they skin irritants. Regardless of actual irritation, any of these materials will be nuisances either on the skin or in the eyes. Affected skin may be washed with soap and water, and eyes should be flooded with water for several minutes.
Individuals frequently working with liquid toners, especially under potential splash conditions, may want to wear protective goggles, safety glasses with side shields, or a face shield if needed. Rubber or vinyl-coated gloves should prevent the dry skin problems mentioned above.
Papers are generally benign as well. However, there have been cases of significant skin irritation when proper care was not taken during processing. Poor manufacturing processes can also cause odour problems when the paper is heated in the fuser of a dry-process copier. Occasionally, the vellum in an engineering copier has not been properly processed and creates a hydrocarbon solvent odour problem.
In addition to the isoparaffinic base of liquid toners, numerous solvents are routinely used in machine upkeep. Included are platen and cover cleaners and film removers, which, typically, are alcohols or alcohol/water solutions containing small amounts of surfactants. Such solutions are eye irritants, but do not directly irritate the skin. However, like the liquid toner dispersants, their solvent action can defat skin and lead to eventual skin-cracking problems. Rubber or vinyl-coated gloves and goggles or safety glasses with side shields should be sufficient to preclude problems.
Ozone is usually the greatest concern of those in the general vicinity of photocopiers. The next most readily identified concerns would be toner, including paper dust, and volatile organic compounds (VOCs). Some situations also give rise to odour complaints.
Ozone is primarily generated by corona discharge from the devices (corotrons/scorotrons) which charge the photoreceptor in preparation for exposure and cleaning. At concentrations most apt to be encountered in photocopying, it can be identified by its pleasant, clover-like odour. Its low odour threshold (0.0076 to 0.036 ppm) gives it good “warning properties”, in that its presence can be detected before it reaches harmful concentrations. As it reaches concentrations which might produce headaches, eye irritation and breathing difficulty, its odour becomes strong and pungent. One should not expect ozone problems from well-maintained machines in properly ventilated areas. However, ozone may be detected when operators work in the machine’s exhaust stream, especially in the case of long copy runs. Odours that are identified as ozone by inexperienced operators are usually found to have arisen from other sources.
Toner has long been considered to be a nuisance particulate, or “particulate not otherwise classified” (PNOC). Studies performed by Xerox Corporation in the 1980s indicated that inhaled toner elicits the pulmonary responses one would expect from exposure to such insoluble particulate materials. They also demonstrated a lack of carcinogenic hazard at exposure concentrations well above those expected to be found in the office environment.
Paper dust consists of paper fibre fragments and sizers and fillers such as clay, titanium dioxide and calcium carbonate. All of these materials are considered to be PNOCs. No reasons for concern have been found for the paper dust exposures expected to occur in the office environment.
The emission of VOCs by photocopiers is a byproduct of their use in plastic toners and parts, rubbers and organic lubricants. Even so, exposures to individual organic chemicals in the environment of an operating photocopier are usually orders of magnitude below any occupational exposure limits.
Odour problems with modern photocopiers are most often an indication of inadequate ventilation. Treated papers, such as carbonless forms or image transfer papers, and occasionally vellums used in engineering copiers, may produce hydrocarbon solvent odours, but exposures will be well below any occupational exposure limits if ventilation is adequate for normal copying. Modern photocopiers are complex electro-mechanical devices which have some parts (fusers) operating at elevated temperatures. In addition to odours that are present during normal operation, odours also occur when a part fails under a heat load and the smoke and emissions from hot plastic and/or rubber are released. Obviously, one should not remain in the presence of such exposures. Common to nearly all odour problems are complaints of nausea and some sort of eye or mucous membrane irritation. These complaints are usually simply indications of exposure to an unknown, and probably unpleasant, odour, and are not necessarily signs of significant acute toxicity. In such cases, the exposed individual should seek fresh air, which nearly always leads to a rapid recovery. Even exposures to smoke and vapours from overheated parts are usually of such short duration that there is no need for concern. Even so, it is only prudent to seek medical advice if symptoms persist or exacerbate.
As discussed above, copiers produce heat, ozone and VOCs. While the siting and ventilation recommendations should be obtained from the manufacturer and should be followed, it is reasonable to expect that, for all but possibly the largest machines, location in a room having reasonable air circulation, more than two air changes per hour and adequate space around the machine for servicing will be sufficient to prevent ozone and odour issues. Naturally, this recommendation also assumes that all American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) recommendations for room occupants are also met. If more than one photocopier is added to a room, care should be taken to provide added ventilation and cooling capability. Large, high-volume machines may require special heat-control considerations.
Supplies do not require special considerations beyond those for the keeping of any flammable solvents and avoiding excessive heat. Paper should be kept in its box to the extent practical and the wrapper should not be opened until the paper is needed.
Facsimile (Fax) Machines
In facsimile reproduction, the document is scanned by a light source and the image is converted to an electronic form compatible with telephone communications. At the receiver, electro-optical systems decode and print the transmitted image via direct thermal, thermal transfer, xerographic or ink-jet processes.
Machines using the thermal processes have a linear print array like a printed circuit board, over which the copy paper is stepped during the printing process. There are about 200 contacts per inch across the width of the paper, which are rapidly heated when activated by an electric current. When hot, a contact either causes the contact spot on a treated copy paper to turn black (direct thermal) or the coating on a typewriter ribbon-like donor roll to deposit a black dot onto the copy paper (thermal transfer).
Fax machines which operate by the xerographic process use the telephone-transmitted signal to activate a laser beam and they then function the same as a laser printer. In a similar fashion, ink-jet machines function the same as ink-jet printers.
Paper, either treated or plain, donor rolls, toner and ink are the major materials used in faxing. Direct thermal papers are treated with leuco dyes, which turn from white to black when heated. Donor rolls contain a mixture of carbon black in a wax and polymer base, coated onto a film substrate. The mixture is sufficiently firm that it does not transfer to the skin when rubbed, but when heated it will transfer to the copy paper. Toners and inks are discussed in the photocopying and ink-jet printing sections.
Potential hazards and their prevention.
No unique hazards have been associated with fax machines. There have been odour complaints with some early direct thermal machines; however, as with many odours in the office environment, the problem is more indicative of a low odour threshold, and possibly inadequate ventilation, than a health problem. Thermal transfer machines usually are odour free, and no hazards have been identified with the donor rolls. Xerographic fax machines have the same potential problems as dry photocopiers; however, their low speed normally precludes any inhalation concerns.
Modern references to “blueprints” or “blueprint machines” generally mean diazo copies or copiers. These copiers are most often used with large architectural or engineering drawings made on a film, vellum or translucent paper base. Diazo-treated papers are acidic and contain a coupler which yields a colour change upon reaction with the diazo compound; however, the reaction is prevented by the acidity of the paper. The sheet to be copied is placed in contact with the treated paper and exposed to intense ultraviolet (UV) light from a fluorescent or mercury vapour source. The UV light breaks the diazo bond on the areas of the copy paper not protected from exposure by the image on the master, eliminating the possibility of subsequent reaction with the coupler. The master is then removed from contact with the treated paper, which is then exposed to an ammonia atmosphere. The alkalinity of the ammonia developer neutralizes the acidity of the paper, permitting the diazo/coupler colour-change reaction to produce a copy of the image on the parts of the paper which were protected from the UV by the image on the master.
Water and ammonia are the only diazo-process materials in addition to the treated paper.
Potential hazards and their prevention.
The obvious concern around diazo-process copiers is the exposure to ammonia, which can cause eye and mucous membrane irritation. Modern machines usually control emissions, and hence exposures are usually considerably less than 10 ppm. However, older equipment may require careful and frequent maintenance and possible local exhaust ventilation. Care should be taken when servicing a machine to avoid spills and prevent eye contact. Manufacturers’ recommendations regarding protective equipment should be followed. One should also be aware that improperly manufactured paper also has the potential for causing skin problems.
Digital Duplicators and Mimeographs
Digital duplicators and mimeographs share the same basic process in that a master stencil is “burned” or “cut” and placed onto an ink-containing drum, from which ink flows through the master onto the copy paper.
Stencils, inks and papers are the supplies used by these machines. The scanned image is digitally burned onto the mylar master of a digital duplicator, while it is electro-cut into a mimeograph’s paper stencil. A further difference is that digital duplicator inks are water based, though containing some petroleum solvent, while mimeograph inks are based on either a naphthenic distillate or a glycol ether/alcohol mixture.
Potential hazards and their prevention.
The primary hazards associated with digital duplicators and mimeographs are due to their inks, although there is a potential hot wax vapour exposure associated with burning the image onto the digital duplicator’s stencil and an ozone exposure during the electro-cutting of stencils. Both types of ink have the potential for eye and skin irritation, while mimeograph ink’s higher petroleum distillate content has a greater potential for causing dermatitis. The use of protective gloves while working with the inks, and adequate ventilation while making copies, should protect against skin and inhalation hazards.
Spirit duplicators use a reverse-image stencil which is coated with an alcohol-soluble dye. In processing, the copy paper is lightly coated with a methanol-based duplicating fluid, which removes a small amount of dye upon coming in contact with the stencil, resulting in image transfer to the copy paper. The copies may emit methanol for some time after duplication.
Paper, stencils and duplicating fluid are the main supplies for this equipment.
Potential hazards and their prevention.
Spirit duplicating fluids are usually methanol based, and hence are toxic if absorbed through the skin, inhaled or ingested; they are also flammable. Ventilation should be adequate to ensure operator exposures are below current occupational exposure limits and should include providing a ventilated area for drying. Some more recent duplicating fluids used are ethyl alcohol or propylene glycol based, which avoid the toxicity and flammability concerns of methanol. Manufacturers’ recommendations should be followed regarding the use of protective equipment when handling all duplicating fluids.