David Richardson

Overview of the Printing Processes

The invention of printing dates back to China in the 11th century. In the latter part of the 15th century, Johannes Gutenburg first introduced moveable type and invented the printing press, thus creating the process of printing that is now common around the world. Since then, the printing process has expanded dramatically beyond simply printing of words on paper to printing of words and other forms of graphic arts on paper and other materials (substrates). In the 20th century, the packaging of all types of consumer products has taken printing to yet another level. Printing, packaging and publications, along with the closely associated field of coating and laminating, are found in everyday products and processes used in the home, at leisure and at work.

The art of placing words and pictures on paper or other substrates is moving in directions not anticipated even a few years ago. A very wide spectrum of technologies, ranging from the older and more traditional styles of printing to the newest technologies involving computers and related processes has evolved. This includes everything from the older technology of lead-based type in flat-bed presses to today’s modern web-fed, direct-to-plate presses (see figure 1). In some operations, these varying technologies are literally found side by side.

Figure 1. The finishing end of a printing process

There are four general types of printing and there are many safety, health and environmental hazards associated with these technologies.

1. Letterpress or relief printing. This process, used for many years in printing and publication, involves the creation of images, often letters or pictures, that are raised above a background or non-printing area. Ink is applied to the raised area, which is then placed into contact with the paper or other substrate which accepts the image.

There are several ways to create the relief image, such as assembly of individual letters by using moveable type, or by using the once common linotype machine or machine-created type. These processes are appropriate for simpler, shorter run printing tasks. For longer-running tasks, printing plates, often made of metal or plastic or rubber-type materials, are more appropriate. Using rubber or similar plates is often called flexography or flexographic printing.

Inks typical of this process can be either solvent or water based. Some newer inks, based on ultraviolet (UV) curing and other chemico-physical systems, are being developed and implemented in this printing system.

2. Intaglio or gravure printing. In intaglio or gravure printing processes, the image to be printed is recessed into the face of an engraved plate or cylinder. The plate or cylinder is bathed in ink. Excess ink is then removed from the non-engraved parts of the plate by use of a doctor blade. The plate or cylinder is then brought into contact with the paper or other substrate to which the ink transfers the image. This system of printing is very typical of long-run printed products, such as magazines and packaging materials.

Inks typically are solvent based, with toluene being the most common solvent in intaglio or gravure inks. Use of inks based on soybean oil and water is under way with some success. However, not all applications can utilize this newer technology.

3. Planographic or lithography printing. Dissimilar materials form the basis for planographic or lithographic printing. By using dissimilar materials, areas can be developed that are water receptive or water repelling (i.e., receptive to solvent ink). The solvent ink-receptive area will carry the image, while the water-receptive area will become the background or unprinted area. Thus, ink adheres only in specific areas for transfer to the paper or other substrate. In many instances, this step will involve transfer to an intermediate surface, known as the blanket, which will later be placed against the paper or other substrate. This transfer process is called offset printing, which is widely used for many printing, publication and packaging applications.

It should be noted that not all offset printing involves lithography. Depending upon the exact needs of the printing process, other printing methods may utilize elements of offset printing.

Inks used in planographic or lithographic printing are usually solvent based (i.e., not water based), but some inks that are not solvent based are rapidly being developed.

4. Porous or screen printing. Porous or screen printing uses a stencil placed over a fine mesh screen. The ink is applied to the open screen areas and pressed (squeegeed) over the stencil and open mesh area. The ink will transfer through the screen to the paper or other substrate under the screen. Screen printing is often used for simpler, low volume printing tasks, where this process may have a cost advantage. Typical use of this printing process is for textiles, posters, displays and wallpaper.

Inks for screen printing are either solvent or water based, depending largely on the substrate to be printed. Since the coating used in screen printing is often thicker, inks are typically more viscous than those used in other printing methods.

Preparation of Print-Ready Material

Preparing material for printing involves assembling the various materials, including text, photographs, artwork, illustrations and designs, that are the subject of reproduction into the printed material. All materials must be completely finalized because changes cannot be made after print plates are created. In order to correct errors, the process must be redone. Principles of graphic arts are applied at this point to insure proper aesthetics of the printed product.

The health and safety aspects of the graphic arts step of the printing process are generally regarded as less hazardous than the other aspects of printing. The generation of artwork may involve considerable physical strain, as well as health risks from the pigments, rubber cement, spray adhesives and other materials used. Much of this is being replaced by computerized graphics which is also discussed in the article “Commercial art” in the Entertainment and the arts chapter. The potential hazards of working with visual display units and computers are discussed elsewhere in this Encyclopaedia. Ergonomically sound workstations can alleviate the hazards.

Platemaking

The printing plates or cylinders that are typical of contemporary printing processes must be created for either process photography or computer-generated make-up. Often, the platemaking starts with a camera system that is used to create an image, which subsequently may be transferred by photochemical methods to the plate. Colours must be separated, and aspects of the print quality such as halftone imagery must be developed in this process. The photography used for platemaking is very sophisticated when compared to the typical home-use of a camera. Exceptionally fine sharpness, colour separation and register are needed to allow for the production of quality printed materials. With the introduction of the computer, much of the manual assembly and image development work has been eliminated.

The potential hazards seen in this part of the printing process are similar to those typical of the photographic industry and are discussed elsewhere in this chapter. Controlling potential chemical exposures is important during platemaking.

After the image is created, photomechanical processes are used to create the printing plate. The typical photomechanical processes for making plates can be grouped into the following:

Manual methods. Hand tools, engravers and knives can be used to create relief in the plate, or crayons can be used to create water-repelling areas on a lithography plate. (This is generally a method used in small production, or for special printing tasks.)

Mechanical methods. Lathes, ruling machines and similar types of mechanical equipment are used to create relief, or other equipment can be used to produce water-repelling areas on lithography plates.

Electrochemical methods. Electrochemical methods are used to deposit metals onto plates or cylinders.

Electronic methods. Electronic engravers are used to create relief on plates or cylinders.

Electrostatic methods. Xerographic or similar methods are used to create either relief or water-repelling image components on plates or cylinders.

Photomechanical methods. Photographic images can be transferred to the plates through light-sensitive coatings on the plate or cylinder.

Photomechanical platemaking is the most common process today. In many instances, two or more systems may be used to create the plate or cylinder.

The health and safety implications of making printing plates are extensive owing to the various methods used to create the plate. Mechanical methods, less used today than in the past, were the source of typical mechanical safety issues, including hazards arising from the use of hand tools and the larger mechanical equipment often seen in the machine shop. Risks related to hand safety and guarding are typical in platemaking using mechanical methods. Such platemaking often involves the use of oils and cleaners that may be flammable or toxic.

Older methods are often still in use in many facilities right alongside newer equipment and hazards can be spread. If the plate consists of movable type, a linotype machine, once very common in most printshops, would make type by casting lead into the shape of letters. The lead is melted and kept in a lead pot. With the lead pot present, many of the hazards associated with lead come directly into the printshop. Lead, which is discussed elsewhere in this Encyclopaedia, can enter the body through inhalation of lead compounds and by skin contamination with lead and lead-containing type which can then lead to lead ingestion. The result is possible chronic low-grade lead poisoning, with resultant nervous system dysfunction, kidney dysfunction and other toxicity.

Other methods of platemaking use chemical systems typical of plating or chemical etching to create an image on the plate or cylinder. This involves many different chemicals, including acids and heavy metals (zinc, chromium, copper and aluminium), along with organic chemical-based resin systems that make up some of the upper layers of the plate itself. Some systems now use petroleum-based solvents in the chemical processes of making plates. The potential health hazards from such chemicals must be considered in the safety effort undertaken for such a facility. Ventilation and personal protective equipment that are appropriate for chemicals used are very important. Additionally, the potential environmental effects of corrosives and heavy metals need to be taken into account as part of the safety effort for the chemistry of platemaking. Storage and mixing of these chemical systems also presents health risks which can be significant if a spill occurs.

Engraving systems, used in some instances to transfer the image to the plate or cylinder, also may present potential hazards. Standard systems of engraving will generate some metal contamination that can be a problem for those working with these systems. The newer systems utilize laser equipment to carve the image into the plate material. While this allows the elimination of some steps in the platemaking process, the presence of the laser may present a hazard to the eyes and skin. The laser may also be used to soften materials, such as plastics, rather than to heat them to vapourization, thus creating additional vapour- and fume-related problems for the workplace.

In most instances, the platemaking process is a relatively small portion of the total production operations of the printing facility, which automatically limits the risk present, since few people work in the platemaking area and smaller quantities of materials are typical of these types of operations. As technology progresses, fewer steps will be needed to translate the image to the plate, thus presenting fewer opportunities for hazards to have an impact on employees and the environment.

Ink Manufacture

Depending upon the technologies utilized, a variety of inks and coatings are used. Inks are typically made up of a carrier and pigment or dyes and resins that go to form the image.

The carrier allows the pigments and other components to remain in solution until the ink is dried. Typical printing ink carriers include alcohols, esters (acetates), ketones or water. Gravure inks often include large amounts of toluene. Newer inks may contain epoxidized soybean oil and other chemicals that are less hazardous because they are not volatile.

Another component of typical inks is the resin binder. The resin bender is used, after the solvent has dried, to hold the pigment to the substrate. Organic resins, some natural and others synthetic, such as acrylic resins, are routinely used in inks.

The pigment provides the colour. Pigment bases can come from a variety of chemicals including heavy metals and organic materials.

UV-cured inks are based on acrylates and do not contain carriers. They are not involved in the curing/drying process. These inks tend to be simply a resin and pigment system. The acrylates are potential skin and respiratory sensitizers.

There are many health and safety hazards associated with ink manufacture. Since ink make-up often includes flammable solvents, fire protection is important at any facility where ink manufacture is undertaken. Sprinkler systems and portable extinguishing equipment must be present and in full and complete operating condition. Since employees must know how to use the equipment, training is needed. Electrical systems should be instrinsically safe or involve purging or explosion proofing. Control of static is critical since many solvents can generate a static charge when run through a plastic hose or through the air. Humidity control, grounding and bonding are strongly recommended for static control.

Mixing equipment, from small mixers to large batch tanks, can impose many mechanical safety hazards. Mixer blades and systems must be guarded or otherwise protected during operation and while in make-ready and clean-up modes. Machine guards are needed and must be in place; when they are removed for maintenance-related activities, lockout/tagout programmes are essential.

Owing to the quantities of materials present, the handling of material may also present hazards. While it is recommended that all materials that are conveniently piped directly to the area of use be handled in such a manner, many ink components must be manually moved to the mixing area in bags, drums or other containers. This involves using not only mechanical equipment such as lift trucks and hoists, but also manual handling by the employee doing the mixing. Back strains and similar stresses are common in these operations. Training on correct lifting practices is an important aspect of preventive measures, as well as selecting mechanical lifting processes that require less direct human involvement.

With this much handling, spills and chemical handling incidents can occur. Systems should be in place to deal with such emergency situations. Also, care in storage to prevent spillage and possible mixing of incompatible materials is needed.

The specific chemicals and large amounts stored can lead to issues related to possible employee health exposures. Each component, whether carrier, resin or pigment, should be evaluated both individually and within the context of the ink system. The safety effort should include: industrial hygiene evaluation and sampling to determine whether exposures are judged acceptable; adequate ventilation for removal of toxic materials; and the use of appropriate personal protective equipment should be considered. Since spills and other opportunities for overexposure are present, emergency systems should be in place to render first aid. Safety showers, eye washes, first aid kits and medical surveillance are all recommended, otherwise injury to skin, eyes, respiratory system and other body systems may occur. Inputs can range from simple dermatitis resulting from skin exposure to solvents, to more permanent organ damage due to exposure to heavy-metal pigments, such as lead chromate, that are found in some ink formulations. The spectrum of possible toxicity is large because of the many materials that are used in various ink and coating manufacture. With newer technologies such as UV-curable inks, the hazard may change from standard solvent hazards to sensitization from repeated contact with skin. Care must be taken to fully understand the potential risks of the chemicals used in ink and coating manufacture. This is best done prior to formulation.

Since many inks contain materials that are potentially harmful if they find their way into the environment, controls on the ink-making process may be necessary. Additionally, residual materials including clean-up materials and wastes must be handled carefully, to minimize their impact on the environment.

With the strong worldwide emphasis on a better environment, more “earth friendly” inks are being introduced, which use water as the solvent and less toxic resins and pigments. This should help reduce the hazards related to ink manufacturing.

Printing

Printing involves taking the plate, placing an ink onto the plate, and transferring the ink to the substrate. In offset processes, the image is transferred from a plate wrapped around a cylinder to an intermediate rubber cylinder (blanket) before being transferred to the desired substrate. Substrates are not always limited to paper, although paper is one of the most common substrates. Many fancy labels are printed on vacuum-metallized polyester film, using conventional printing techniques. Laminated plastics may be fed into the printing press in sheets or as part of a continuous web that is later cut to specification to make packaging.

Since printing often involves colour, several printed layers may be placed onto the substrate and then dried prior to the addition of the next layer. All of this must be done very precisely in order to keep all the colours in register. This requires multiple printing stations and sophisticated controls to maintain proper speed and tension through the press.

The hazards associated with operating a printing press are similar to those involved in ink manufacturing. The fire hazard is critical. As with ink manufacturing, sprinkler systems and other means of fire protection are needed. Other systems may be mounted directly to the press. These serve as added controls in addition to the portable extinguishers which should be available. Electrical systems should meet the purged, explosion-proof or intrinsically safe requirements. Static electricity control is also important, especially with solvents like isopropyl alcohol and with web presses. Added to the handling of flammable liquids that can generate static while moving through plastic hoses or the air, most plastic films or webs will also generate very substantial static charges when they move over a metal roll. Humidity control, grounding and bonding are necessary for removing static, along with web-focused static elimination techniques.

Manual handling of printing equipment, substrate materials and related inks is another safety concern. Storage issues similar to those in ink manufacture are present. Minimizing manual handling of equipment, substrate materials and inks is recommended. Where this is not possible, routine and focused education is needed for those employed in the printing room.

Added to the safety issues in the printing room are the mechanical safety issues involving rapidly moving/rotating equipment along with a substrate moving along at speeds in excess of 1,500 feet per minute. Guarding systems and alarms are needed to help insure employee safety. Lockout and tagout systems are also needed during repair/maintenance functions.

With the amount of rotating equipment and the speeds that are common in many printing operations, noise is often a significant issue, especially when multiple presses are present, as in newspaper printing. If noise levels are not acceptable, a hearing conservation programme should be implemented that includes engineering controls.

Although inks are often dried into the air around the press, drying tunnels are recommended to reduce exposure to volatile solvents.

Also, in some higher-speed printing operations, ink misting may occur. Both solvent drying and possible ink misting present a risk of inhalation of possibly toxic chemicals. Further, routine management of the printing operation, filling of tanks and trays, cleaning of rolls and idlers, and related tasks may involve contact with inks and cleaning solvents.

As with ink manufacturing, a well constructed industrial hygiene sampling effort, along with adequate ventilation and personal protective equipment, is recommended. Since these presses, some of which are very large, need to be routinely cleaned, chemical solvents are often used, leading to further chemical contact. Handling procedures can reduce exposures but not entirely remove them, depending on the size of the printing operations. As noted previously, even new inks and coatings that represent better technology still may have hazards. For example, UV-curable inks are potential sensitizers when in contact with the skin, and there is potential exposure to hazardous levels of UV radiation.

Emissions from printing operations, along with clean-up solutions and waste inks, are potential issues of environmental concern. Air pollution abatement systems may be needed to capture and either destroy or reclaim solvents evaporated from inks after printing. Careful management of the wastes generated to minimize the impact on the environment is important. Waste handling systems are recommended where solvents or other components can be recycled. Newer technology using better solvents for clean-up are coming from current research efforts. This may reduce emissions and possible exposures. An active review of current clean-up technology is recommended to see if alternatives to solvent cleaning, such as using water-based solutions or vegetable oils, are available that will meet the requirements found in specific printing operations. However, water-based cleaning solutions that are contaminated with solvent-based inks may still require careful management both inside the printing operation and upon disposal.

Finishing

Once printed, the substrate typically needs some additional finishing prior to being prepared for final use. Some materials can be sent directly from the press to packaging equipment which will form the package and fill in the contents or will apply an adhesive and place the label onto the container. In other instances, a large amount of cutting or slitting to size is needed for final assembly of the book or other printed material.

The health and safety issues related to finishing are mostly mechanical safety issues. Since much of the finishing involves cutting to size, cuts and lacerations to the fingers, hands and wrist/arm are typical. Guarding is important and must be used as part of every task. Small knives and blades used by employees also need to be used carefully and stored and disposed of properly to prevent inadvertent cuts and lacerations. Larger systems also need the same level of attention in guarding and training to prevent accidents.

The material handling aspect of finishing is significant. This applies to the material to be finished as well as the final packaged printed product. Where mechanical equipment such as lift trucks, hoists and conveyors can be used, they are recommended. Where manual lifting and handling must occur, education on proper lifting should be undertaken.

Recent evaluation of this component of the printing process indicates that possible ergonomic stress is placed on the human body. Each task - cutting, sorting, packaging - should be reviewed to determine possible ergonomic implications. If ergonomic problems are found, changes in the workplace may be needed to reduce this possible stressor to acceptable levels. Often some form of automation can help, but there still remain in most printing operations many manual handling tasks that may create ergonomic stress. Job rotation can help reduce this problem.

Printing in the Future

There will always be a need to print words on a substrate. But the future of printing will involve more direct transfer of information from computer to press, as well as electronic printing, where words and images are impressed onto electromagnetic media and other substrates. While such electronic print can be viewed and read only through an electronic device, more and more printed text and literature will move from the printed substrate to the electronic substrate format. This will lessen many of the mechanical safety and health issues related to printing, but will increase the number of ergonomic health risks in the printing industry.

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