As production printing operations strive for greater speed, quality, and flexibility, vendors of high-end digital production printers provide an ever-increasing array of new technologies and functionality. Digital color, variable data printing (VDP), direct mail, and TransPromo applications drive many of the requirements for these platforms. A full range of options are available, each with its own set of advantages and disadvantages.

Given the many technologies, characteristics, and options available in production printing systems, understanding the tradeoffs and determining those that are best suited for specific applications is challenging.

Here we discuss some of the major options for digital color production presses, with an emphasis on technologies and characteristics of the evolving inkjet market.

Laser or Inkjet?
When considering digital production presses, an obvious decision making factor is the type of print engine technology that best fits the job at hand. The two primary choices include laser electrophotographic and inkjet systems. Most major hardware vendors provide different models based on each of these technologies, and each addresses a different set of requirements.

Electrophotographic
Electrophotographic (EP) printers use an electrostatic charge to transfer toner from a photo-sensitive drum onto paper, which is then fused to fix the image. EP printers provide higher resolutions and image quality in monochrome and color than inkjets, and therefore are often the top choice when image quality is paramount, such as in graphic arts and full-process color applications. However, this increase in quality comes at the expense of print speed and cost per page.

EP printing is a mature technology, and most vendors offer both monochrome and color products. Supplies are readily available, and operating and servicing requirements are well understood and predictable. Monochrome speeds continue to improve but may be nearing a limit due to existing technologies. Speeds for full-color printing are improving rapidly and in some cases are approaching those of B&W, but there do not appear to be any major technological advancements reducing operating costs substantially.

Inkjet
Inkjet systems create an image by projecting small ink droplets directly onto the substrate. Inkjets have a number of advantages over EP printers, including faster print throughput, better modularity and scalability with simpler configurations, and variable costs based on coverage. However, inkjet systems do not achieve the resolutions that high-end EP systems are capable of. Inkjet systems typically produce lower-quality images. The printheads that form the foundation of inkjet systems are sophisticated and require complex ink chemist- ries and delivery systems.

In general, inkjet systems are based on newer technologies and are adopted earlier in the market cycle than EP systems. An inkjet printer incorporates a number of individual printheads, each of which manages a single ink color, and the technology of the printhead is a key determinant in the quality, cost, and speed of image creation. There are two major categories of inkjet printing technologies—continuous inkjet and drop on demand.

Continuous inkjet (CIJ) printing uses a method by which a stream of ink droplets is continuously ejected from the printhead. A variable electric charge is applied to each droplet based on where the dot is to be placed on the paper, and an electric field is applied to direct the droplet appropriately. Excess ink is deflected into a collection system where it is recycled for later use. CIJ systems are faster and the technology is more mature than drop on demand (DOD) systems, but CIJ systems also require more sophisticated materials and techniques for managing ink viscosity.

DOD is a newer printing technology, which creates individual ink droplets as required to create an image. Most high-speed DOD systems use piezoelectric technology that ejects the ink droplet by applying an electric charge to a piezo material within the printhead, which deforms to eject the ink droplet. DOD systems can provide higher resolutions and support a wider range of inks than CIJ systems, but cannot match their speed. Many vendors are now providing DOD systems, speed and reliability continue to improve, and module costs are dropping. These systems’ acquisition costs are typically lower, but ongoing operating costs are higher.

Color to Dye For
A common topic of debate when discussing inkjet printers is the relative advantage of dye- versus pigment-based inks. Each has distinct benefits and applicability for specific requirements.

Dye-based inks are created by dissolving dye in water, alcohol, or oil—with water being the most common solution. Dye-based inks have the advantage of being less expensive than pigment-based inks, and typically produce a wider range of brighter and vibrant colors. When projected onto paper, dye-based ink is absorbed, which can cause a degree of bleeding depending on the characteristics and finish of the paper. Dye-based inks are also less water-fast, which can make them more susceptible to smearing and smudging. One important restriction to consider when using dye-based ink is its limited color-fastness, which leads to fading over time when exposed to light or airborne pollutants.

Pigmented inks are created by suspending non-soluble microscopic pigment particles in a transport medium, typically water. Pigmented inks are more expensive than dye-based inks, but offer a number of advantages. Pigmented inks are not absorbed into the paper like dye-based inks, but rather lie on or near the surface. As a result, their image quality is less dependent on paper quality, is less prone to smearing, and provides for sharper text and higher quality graphics. In addition, less bleed-through is encountered in duplex printing operations.

One of the key benefits of pigment-based ink is its color-fastness, in which resistance to fading makes it an ideal choice when long-term image quality is a high priority, as with archiving applications for a long period of time.

Consider This
When choosing a color print platform consider the image quality and its ability to manage the client’s custom colors. Primary characteristics supporting image quality in inkjet systems is actual and perceived resolution, and the gradations and management of color that are produced for a given drop.

Some systems produce variable drop sizes, which can produce better perceived image quality for a given resolution. Others support a greater color depth—or variations—each droplet, resulting in greater control over the exact tones comprising an image.

Many high-end inkjet systems produce monochrome output, highlight—or spot—color, and full-process color output. One advantage of high-end inkjet systems is the flexibility to upgrade from monochrome to full-color as needed.

Highlight color is often used to call attention to data relevant to the recipient, or to provide the producer with specific branding or document composition opportunities. It represents a cost-effective compromise between B&W and full-color printing. Several vendors offer user-defined colors for company branding. Full-process color varies from business color, which provides adequate quality for charts and other business data, to full graphics arts quality printing used in photographic applications, brochures, catalogues, or magazines.

Decisions, Decisions
There are a wide range of options for color digital printing, including both electrophotographic and inkjet systems. Vendors, including Hewlett-Packard, InfoPrint Solutions Company, Kodak’s Graphic Communications Group, Océ, Punch Graphix, and Xerox offer such systems. In our next issue we’ll dig deeper into digital production presses and offer a comprehensive round-up, complete with vendor commentary, end-user profiles, and a new trends analyst.

Today’s technologies provide a wide range of options for firms looking at production digital color printers. Each machine offers its own strengths and weaknesses, and none is ideal for every application. By understanding how and why the various technologies available in the market today affect printer output and the user’s business objectives, organizations can make informed decisions and are assured of optimal solutions. Organizations should approach digital color production as an integrated part of an overall document strategy.