What applications of printing can’t be replaced by a computer screen?
People often point to packaging as an area that still requires ink on paper. Another growth area where ink can’t be beat is signs and banners, and a host of other applications of large-format inkjet printing.
Frank Romano, professor emeritus at Rochester Institute of Technology, points out that printing is the most democratic form of communication — it doesn’t require a computer nor Internet connection. You’ll really understand what “democratic” means if you know about all the creative applications of inkjet printing technology.
Technology for inkjet printing includes the printer, ink and substrate (media), along with related technologies like computers, software applications, colour management instruments and software, and raster image processors (RIPs).
Printers. Inkjet printers originated with the pen plotters used for outputting computer-aided design and drafting (CADD) drawings. More recently, two main manufacturers — Seiko and Hewlett Packard — developed print heads that spit microscopic droplets of ink onto the substrate. Droplet sizes are measured in picoliters, billionths of a litre. The smaller the droplet size, the finer the resolution and higher the quality, but the slower the print speed. These new print head technologies provide a great leap in print speed and quality.
Piezoelectric. Seiko developed the piezoelectric print head, which uses a burst of electric current to eject an ink droplet from the print head. This type of print head is found in Epson, Canon and Océ printers, among others. Its main advantage is that the print head remains cool and, therefore, lasts for a long time. Its disadvantage is that the print heads are fairly expensive and are not user-replaceable, so replacing a damaged one can be costly. Print heads are fairly reliable, but can be damaged if they collide with the media or are not used for a long time.
Thermal. HP developed a different technology known as the thermal print head, which uses a burst of heat to eject a droplet from the print head. Thermal print heads are cheaper to make, but the heat causes them to wear out faster, so they must be replaced more frequently than piezoelectric print heads. Most of these printers, however, have user-replaceable print heads.
Ink. Ink includes three main components:
- Dye or pigment for colour
- Vehicle for dispersing the pigment and carrying it to the substrate
- Additives for viscosity control, rub resistance, adhesion, fade-resistance, and other properties.
Pigment. Inkjet printers are available with dye or pigment-based ink. Dye is a colourant that dissolves in water. A pigment consists of larger particles that don’t dissolve completely, but are suspended in the vehicle. Generally, dyes have brighter colours, but less fade resistance than pigments.
Vehicle. Consumer-market inkjet printers use water as the vehicle, so they are safe and convenient to use in the home and office. Some printers, like those from Epson, are made for pigment-only inks. Others, such as HP’s 5000 series (Figure 1), can be changed from dye to pigment—dye for more brilliant colours, and pigment for greater longevity.
In the late 1990s, manufacturers introduced industrial printers with solvent-based inks that were much more durable and fade-resistant than aqueous inks. Solvent is in the same chemical family as gasoline, so the ink emitted fumes, and the printers had to be ventilated.
In the early 2000s, some of the same manufacturers introduced so-called eco-solvent ink, based on glycols, which is in the same chemical family as antifreeze. Eco-solvent inks had the durability of solvent inks, but did not give off volatile compounds so were safe to use in an office environment without special ventilation.
In the mid-2000s, manufacturers introduced UV-curable inks that are colourful, durable, and fast-drying — but more expensive. Their vehicle is liquid plastic that hardens upon exposure to ultraviolet radiation. The print heads must have a UV source strong enough to cure the ink at production speeds, so this ink technology is confined to large industrial machines.
Printers. Inkjet printers range in size from home or office desktop models to flatbed UV-curable machines, some of which are larger than a 4-colour offset press and just as expensive.
Printers are generally described as belonging to one of two types:
- Roll-fed printers were developed from the first pen plotters. They’re designed to print media ranging in size from 18 to 64 inches long. The printer may drop prints into a bin or spool them onto a take-up roll. Roll-fed printers usually use aqueous, solvent or eco-solvent ink.
- Flatbed printers are designed for thicker substrates, like corrugated board or plastic. They usually use UV-curable ink.
Inkjet prints for outdoor or commercial use are commonly laminated with plastic for greater durability and longevity. Laminates are heat- or pressure-sensitive plastic, or liquid air-curable plastic, and may be applied to one or both sides of a print. Lamination increases fade- and water-resistance for long-term or outdoor applications. Some laminates impart a colour cast to prints, important in photographic reproductions. Laminates without colour casts are available, but are more expensive.
Infrastructure for Inkjet Printing
The printer or service provider that wants to get into inkjet printing will need to have a completely digital infrastructure in place. This includes a digital camera image capture, Mac or Windows PCs for processing images and creating documents, a raster image processor (RIP) for controlling the printer and a colour management system for matching original, monitor, proofs and prints.
While digital cameras, computers, and desktop publishing applications are commonplace, many readers may not be familiar with the specialized RIPs used for large-format printing or with the colour management software used to match colour.
RIPs. The RIP is the software that controls the printer. Its primary function is to convert vector- and bitmapped-graphic files into a customized raster, or pattern of horizontal and vertical inkjet droplets. Large-format RIPs are different from those used in commercial printing, such as Agfa Apogee, Kodak Printergy, and many others. The most popular large-format RIPs are Onyx Graphics’ PosterShop, SA International’s FlexiSIGN and PhotoPRINT, Wasatch Softworks’ SoftRIP and Electronics for Imaging’s Fiery, among many others. Some printers, such as HP’s, have available hardware RIPs built into the printer. Other printer manufacturers, such as Roland, offer their own RIPs.
Large-format RIPs have specialized job-handling features unique to inkjet printing, including the ability to preview, crop, rotate, size and position jobs. Another popular feature is nesting, or arrangement of multiple jobs to save media. Some RIPs keep track of print time and ink and media usage for billing purposes. Virtually all of today’s large-format RIPs use ICC profiles for accurate colour preview, proofing and printing.
Colour management. Due to the wide variety of printers, inks, media and RIPs, the large-format industry quickly recognized the value of using colour profiles based in the International Color Consortium (ICC) profile standard. Many media manufacturers offer profiles for the most popular printers, ink, and RIPs on their websites. However, the most versatile companies will want their own colour management system.
A colour management system consists of a handheld spectrophotometer and profiling program. Emissive instruments read monitor colour, while reflective instruments read printed colour. Many can do both.
Available colour management software can calibrate and profile digital cameras, monitors, printers and proofers. Devices that can be profiled are detailed in Table 1.
Applications of Inkjet
Signs and banners. Look anywhere. Signs and banners hang from street lights, ceilings and sides of buildings (Figure 4). They’re used for advertising, promotions, corporate identity, interior decoration and trade shows — almost anywhere you want to catch people’s attention or inform them. Such signs can be printed on paper or, more commonly, PVC, depending upon the durability and length of time they’re needed.
Backlits. These are usually inkjet-printed on clear plastic (polyester) material illuminated by a fluorescent light or LED box. They’re commonly used for advertising or promotional displays (e.g., restaurant, movie posters).
Floor graphics. What better way to get people’s attention than to put a sign right in front of them, under their feet? This is the idea behind floor graphics (Figure 6). For durability they’re usually printed with eco-solvent, solvent or UV-curable ink on slip-resistant PVC, or PVC covered with skid-resistant laminate for durability.
Artistic prints. Commonly seen at craft fairs and shopping malls, artists who sell signed, numbered prints of watercolour or oil paintings used to get their originals reproduced by lithography; however, the prepress costs made this impractical for fewer than 100 copies. Today, artists take advantage of inkjet’s wide colour gamut and ability to print small runs with high quality. Media favoured by artists includes watercolour paper and canvas. Prints can be made by pigmented aqueous, eco-solvent and UV-curable ink.
Photography. Inkjet printing has become the “digital darkroom,” all but replacing conventional darkrooms and photographic enlargers for making prints. The cost of aqueous inkjet printers and supplies has declined to the point where almost any professional photographer can buy a printer. And, with manufacturers claiming archival quality exceeding 200 years, their prints should be around for generations.
Custom wall coverings. Decorative wallpaper, known as “wall coverings,” for industrial use in hotels, restaurants and office buildings where paper isn’t strong enough, can now be printed by inkjet, either on paper or PVC. The process can be used for making custom patterns and murals that no one else has, or for prototyping mass-produced coverings to be printed by gravure.
Custom fabrics. Fabrics printed by inkjet can be used for custom-made curtains, room dividers, furniture (Figure 7), and clothing (Figure 8). Fabric with the greatest printability and colour gamut includes at least some polyester. As with wall coverings, inkjet can be used to print unique products or for prototyping products for the mass market.
Speciality media. A variety of even more specialized media is available for unique applications. Vehicle wraps (Figure 9) are very popular, where a car or bus is turned into a moving billboard. Vehicle wraps require special media that adheres securely, but can be removed without damaging the paint. The design continues from the body of the vehicle onto the windows with perforated media that allows occupants to see what’s outside. Reflective media is available for signs and for automobile and truck graphics. Corrugated paper and plastic laminate can be used to make point-of-purchase displays, including unique product stands and holders for retail display.
How to Buy Large-Format Printing
Large-format inkjet printing offers many opportunities for creative expression and attracting attention. To make intelligent buying decisions, the print buyer should know:
1. What is the application? Is it a poster, banner, floor graphic, point-of-purchase display, backlit graphic, vehicle wrap, or truck sign? This will determine the type of printer and media necessary.
2. How long should it last? This will determine the quality and durability of media, ink and (if necessary) laminate that must be used. Longevity can be quoted in days, weeks, months, or years. For example, banners for trade shows or events may need to last only a few days, while a truck graphic would need to last several years.
3. What is the size? This will determine the size of printer and media needed, as well as the cost of the media. Some specialized media can be very expensive, such as see-through (Figure 10), perforated and reflective, as well as artistic media, like acid-free watercolour paper and canvas.
4. What files are necessary? Files for type and flat colour could be resolution-independent vector graphics created in Adobe Illustrator or CorelDRAW, while photos would need to be captured on a digital camera and processed in a program like Photoshop or Corel Photo Paint. Probably every demo centre manager has had to explain to a prospective customer that the 250-KB, 4×6-inch image does not have a high enough resolution to make a 2×3-foot poster. On the other hand, some printers that do artistic reproductions send out the image capture to a studio with an expensive, large-format digital camera that can take a 20 or 40-megapixel file.
Onyx Graphics. www.onyxgfx.com
SA International. www.saintl.biz
Wasatch Computer Technology. www.wasatch.com
Electronics for Imaging. www.efi.com
Image Resolution for Inkjet Printing
For people with a background in traditional graphic arts, one thing that may be hard to get used to is that the image resolution requirements for large-format inkjet printed work are different from those for traditional printing. The recommended resolution for lithographic printing at normal viewing distance is twice the screen ruling, or 300-350 ppi for commercial-quality work. However, this applies to images seen at normal viewing distance, i.e., 14 inches.
In large format, a lot of images are obviously reproduced at larger sizes for viewing at longer distances. A commonly used formula says that the viewing distance for a document is normally equal to the diagonal. That is, if you produce a 3 x 4-foot poster, people could be expected to view this at a distance equal to the diagonal, which is a little more than 4 feet. (A geek could calculate the exact distance using the distance formula.) Recommended resolutions range from 200 ppi at normal viewing distance to 50 ppi for a large billboard that’s far away. The recommendations start at 200 ppi and not 300-350 because resolution requirements are lower for inkjet, since it uses stochastic screening.
A good example of this is a movie poster, which is intended to be viewed from several feet away. Up close, the poster may look pixelized, but when standing back you cannot see the pixels.