Design for Print- Digital Printing

Digital Printing:

Most people give little thought to printed matter other than the content it provides.  Magazines, brochures, postcards, forms….they all share a common trait:  ink (or toner in the case of xerography) is embedded on a substrate, usually paper, and used to disseminate information. A great deal of effort usually goes into the production of printed pieces, starting with writing and graphic design produced to attract and appeal to readers, and finishing with the distribution of that content to its intended audience. But  many other steps must happen between them to culminate in a successful product.

Much of the information created and distributed today is readily suited for the Internet in the form of web pages, but no web page can create the vivid effects of a printed page, nor communicate a tactile response evident in a  superbly crafted sheet of paper.  Coatings, flourescent ink colors, foil and embossing treatments, and concrete, unchangeable layouts (one continual gripe of web designers is  that variables from web browsers to computer monitors can change the intended design and color of their designs in not so subtle ways) give the printed word ever more power.  So what does it take to make it all work?  Without delving into the processes needed for great writing, editing and graphic design, I’ll focus on what it takes from that point to actually get it all on paper.

Two primary processes are used today in most printed materials:  digital printing and offset printing.  Offset printing has been around for decades and control systems continue to evolved that aid in producing top-notch quality printed products.   Digital printing, utilizing toner instead of ink and an electrostatic process instead of printing plates, can often deliver similar value of quality.  So whats the difference?

Offset Printing Press

Offset printing presses utilize a natural law that water and oil don’t mix.  The printing plates used on offset presses, contrary to what most people might think, do not have any relief to them, meaning the areas of the plate that are intended to print to the paper are not raised (as is the case for letterpress printing, much like the type strike of traditional typewriters)…the aluminum plate is smooth, generally about 12/1000 inch thick, and is flexible for mounting around a cylinder on the press.  What makes the plate work is the use of water in addition to ink.    A printing plate is exposed, now most often on a drum imagesetter which is a kin to laser printers…a digital “image” being exposed by a laser to the plate rotating on a drum…rendering a plate that has image areas that attract ink.   The coating on the plate that is NOT image area, or what has not been exposed by the laser, is water receptive.  Once mounted on the printing press, a series of rollers apply a thin film of water to the plate, followed by additional rollers that apply ink to the plate.   This thin water film repels the oil-based ink leaving only the image areas of the plate with ink to transfer to the paper or other substrate.  A very delicate balance of water and ink must be maintained to achieve high quality printing.  So where does the term “offset” come into play?

Insite Printing's Komori LS629 Six Color Press

The thin metal plate carrying both a water film and ink film does not lend itself well to being pressed directly onto the paper…the results would be very poor reproduction quality.  Instead, the plate comes into contact with a rubber “blanket” that has a small amount of compressibility and is very receptive to ink.   The ink is fully transferred onto the rubber blanket which then is “offset” onto the paper.  The ability of the rubber to accept and release ink, along with its compressible nature allows offset printing to achieve very high quality results.   This entire process can run at over 40-50,000 cycles per hour on roll-fed presses, or 12-18,000 sheets per hour on sheetfed presses…what most observers would call “very fast” (something on the order of 5 sheets per second for sheetfed presses running 25×38 inch sheets, or the equivalent of 144,000 8 1/2 x 11 sheets per hour.)   Presses are equipped with computerized control systems, cooling systems, and heat dryers to allow for very fast production while maintaining superior and consistent quality.

What has been described in the previous paragraph is what is needed for one color, say a simple black ink on white paper brochure.   Full color printing needs four plates, Cyan, Magenta, Yellow, and Black (CMYK), and a full color printing press will have four separate printing towers, one for each color.  The combination of those colors can produce a full range of color, but still has its limits.  Some printing jobs will require additional color plates with specially mixed colors to achieve the right color palate.  For this reason, many offset presses have anywhere from four to ten printing towers in one press, each tower dedicated to one ink color and one plate.

Insite Printing uses the HP Indigo 3050 digital press

Digital copiers and digital presses use a similar process whereby they use CMYK toners but apply the images directly to the paper using a high-voltage electrostatic process.  One exception is the HP Indigo digital press (which Insite Printing uses) that uses liquid inks and an offset blanket.  Without getting into highly technical details, the main difference in digital presses is no need for a printing plate. The image is sent directly from a computer and printed.  Most people are familiar with this process in the form of desktop laser or inkjet printers.  This results in big up-front savings as there is no cost associated with making plates and the time it takes to hang plates on the press, align them, and adjust ink until the first good copy results.  This can take up to an hour on an offset press which usually bills at hundreds of dollars per hour. The cost of making the plates can also be significant.

On a digital press, generally the first copy off is saleable, and it takes only minutes to set up and run. The downside to digital is the cost per copy…the cost of consumables on a digital press (toner, electro imaging plates, and general maintenance) is much higher than traditional offset, and instead of running 144,000 8 1/2 x 11 sheets per hour, a fast digital press may produce only 4-5,000 8 1/2 x 11 images per hour.  A break-even point where traditional offset printing becomes more cost-effective than digital is usually around 2000  8 1/2 x 11 sheets.  Where a hundred sheets on a digital press might cost $100, on an offset press that can be nearly $400.   Likewise 5000 copies on an offset press might only be $600, while on a digital press could run as high as $1500.

Therefore digital printing is widely used for short-run applications, while offset is still king for longer runs. Digital printing does have other advantages in shorter turn around times (negating the need for prepress work such as plates), and the ability to do variable data printing which will be discussed in a future article, both of which can often justify higher costs. But getting the print onto the paper is only one part of a complete printing project.  Finishing is often required in the forms of cutting, folding, embossing, foil stamping, coating, packaging and/or mailing.  Watch for other articles on these aspects.