GAERF REVIEW COPY 8 Printing Processes NOT FORIntroduction SALE to Graphic Communication | 131 Printing Processes Chapter Preview The Printing Press Attributes of Print Traditional Print Processes Combination Printing Digital Printing Benefits Digital Print Engines Wide Format Devices and Digital Printing Presses Print Economics and the Future of Print SCAN 132 | Interactive Media: www.igcvideo/Chapter8 Web Links: www.igcbook/Chapter8 Overview Physical printing involves colored inks, toners, or other colorants repeatedly applied to sheets of paper, plastic, metal, or other materials. Conventional print processes range from traditional letterpress (raised surface) and gravure (engraved surface) to offset lithogra- phy, flexography, and screen-printing. Digital printing includes both inkjet and electrophotographic (EP) processes. This chapter covers the mechanical principles of putting ink or toner onto a substrate. Armed with this basic technical knowledge, you will be able to make better decisions when planning, designing, and managing your print projects. SCAN Introduction to Graphic Communication | 133 GAERF REVIEW COPY A Heidelberg sheetfed offset press and a manroland web offset press, both with multiple, in-line printing stations or units. two-color presses can suffice for simpler The Printing Press applications, while five- and six-color The press is the basic unit of the entire presses are common in commercial printing process. It is a precision instru- printing environments. Hi-fidelity or HiFi ment—far evolved from Gutenberg’s printing requires at least six units—typi- modified wine press. Although a press is cally adding orange and green ink to the typically the largest and heaviest piece normal CMYK process inks. Presses are of equipment used in printing, it is highly also manufactured with more than six controllable—to thousandths of a de- units for specialty printing purposes, gree—on matters such as cylinder pres- especially where custom or “spot” color sure, color balance, and image position- inks or varnishes are required. ing. Often operating at high speeds, with Multiple units allow the press to print computerized automation, and working more than one color on a substrate in a in concert with many other systems, a single pass through the press. (It is pos- press is a formidable piece of equipment. sible to print a four-color job on a one- Presses are configured as eithersheetfed unit press, but that requires a separate (individual sheets of cut paper) or web set-up—and wash-up—for each pass.) (continuous rolls of paper to be cut after Another important configuration isthe printing). They are configured with combination press—those that incorpo- printing stations or units—each one rate more than one printing process. For printing a different color or providing example, some presses use both flexog- other applications such as special coat- raphic and gravure printing processes to ings or varnishes, to enhance the look of create product packaging. Another the finished piece. common combination press uses a A typical configuration is a four-color combination of offset lithography and press, with each of the units printing one inkjet printing to create color publications of the four process colors (CMYK), as or direct mail pieces with unique, custom- discussed in Chapter 6. One-color and ized information (such as a mailing address) printed on each piece. 134 | Printing Processes NOT FOR SALE GAERF REVIEW COPY Combination presses are also used in security printing, where docu- ments must be produced that are difficult to copy or counterfeit. Scratch-off gaming or lottery tickets are produced on combination presses using many processes, including lithography, gravure, flexography, and inkjet printing. These presses sometimes have as many as sixteen units, because of the number of colors printed as well as the various layers of coatings needed to enhance security. Every printing process is character- ized by its image carrier or plate Common printing attributes include registration, characteristics. They are also dot gain, ink density, and trapping. characterized by the formulation of their inks (or toners in the case of electrostatic or electrophotographic or Important Print EP printing) and of the substrate types Attributes they are capable of handling. For exam- Regardless of what technique is used, ple, not every kind of paper can be used there are four important attributes of a with certain digital presses; special printed color image. Each of these can coatings are required for the inks or have a significant impact on the quality of toners to adhere properly. the work. Each process can be identified under Registration is the relative positioning of magnification, usually 12x or greater, by the image on the substrate and the someone skilled in the art of printing. relative positioning of each ink layer over Offset lithography has a different look another. If the positioning of ink colors than letterpress; gravure has a different over each other is not accurate, the look than flexography; inkjet printing has printed image will appear blurred. a different look than EP. Although the Dot Gain is the extent of growth that quality of print produced by these takes place in the size of a halftone dot or methods is constantly improving—mak- screen tint dot from the printing plate to ing it harder to tell with the naked eye— the printed sheet. All printing process- important differences remain. es—with the exception of electrostatic or electrophotographic printing—are subject to dot gain. It occurs because the ink is squeezed onto the substrate under pressure. Because the ink is a liquid and has a thickness to it, there is a tendency NOT FORIntroduction SALE to Graphic Communication | 135 GAERF REVIEW COPY for the ink to spread under the pressure. Trapping is the extent to which one film In inkjet printing, the ink is squirted onto of ink sticks to another when printing one the substrate and the force of the ink ink film over another. In four-color print- spot on the substrate causes the dot or ing, the yellow, magenta, cyan, and black spot to grow. Dot gain does not occur in halftone dots must partially overprint electrostatic printing because dry toner each other to satisfactorily produce the particles are used that do not grow. Dot resulting red, green, and blue colors gain influences the look of a printed needed in full-color printing. Ideally, 100 image. It is expected on the printing percent of an ink film will stick to the press and can be controlled in platemak- other. This often occurs when a wet ink ing or in building digital files for printing. film is applied to a dry one. However, in For example, if a dot gain of 30 percent is reality, because the inks are wet on a expected in the magenta ink being multicolor press, less than 100 percent of printed using the lithographic process, one ink film adheres to the other. If only there are ways of reducing the size of the 85 percent sticks or transfers, this is halftone or screen tint dot on the printing called 85 percent trapping. The degree plate that will print the magenta ink. to which trapping occurs influences the look of the final print. The percentage of Density is the intensity or visual strength of the ink that influences the color quality trapping too is measured with a densi- of the final printed image. In full-color tometer or a spectrophotometer. printing, standards have been estab- The term trapping was also once used to lished for ink density when all other describe the creation of overlapping printing press variables are properly areas between two adjoining colors. The controlled. In other words, the density goal of these overlaps—created by standard or target for yellow, magenta, specialized software like Luminous cyan, and black are different in full-color TrapWise and Scitex Full Auto Frame— printing. A densitometer is used to was to avoid noticeable gaps caused by measure the density of ink on a printed press or plate registration errors. The sheet. (A spectrophotometer, is used to problem itself has diminished with measure the actual color wavelengths as improvements in press technology. So, well as other attributes of color.) that alternate use of the word “trapping” is outside the scope of this book. Other components of a press that impact the appearance of the final printed piece include plate-to-blanket squeeze pressures (on offset presses), ink film thickness, the balance of fountain solution A densitometer measures the degree of darkness or light absorbance of a material—in this case a layer of ink or toner covering a substrate. (water) and ink, the pH 136 | Printing Processes NOT FOR SALE GAERF REVIEW COPY and conductivity of the fountain solution, variables scientifically—and with less roller settings and roller hardness, the manual labor—has been the goal of tension of the substrate going through a modern press manufacturers for many web press, and more. Controlling these decades. Traditional printing processes are being significantly displaced by digital. Shown here is the percentage of North American print sales (customer price per page impression), by printing process, 2012–2020. Traditional Printing Processes Although nearly all printing today has a relief printing, where the plate image is digital component, there are five technol- uniformly higher than the nonprinting ogies known as conventional or tradition- areas. By far the oldest of the convention- al printing processes: letterpress, offset al processes, it has declined significantly lithography, gravure, flexography, and in the past 50-60 years, as more efficient, screen-printing. With the exception of economical, and higher quality printing letterpress, all are represented by major processes emerged. press manufacturers, and occupy a Less than three percent of all printing in substantial portion of the multibillion the United States involves the letterpress dollar printing industry.