You can get from point A to point B in many different ways. You could walk, run or drive a car. You could ride a bike, take a train or fly in a plane. There is usually more than one way to do anything. This is just as true for printing as it is for traveling.
Though there may be many methods to achieve the same result, there are usually reasons for choosing one method over the other. When traveling, for instance, you wouldn’t typically walk from Chicago to Los Angeles, and it would be just as illogical to take a plane across town. There is similar reasoning when it comes to deciding which method of printing is best suited for each project.
When Johannes Gutenberg invented the moveable type printing press in the early 15th century he likely had no idea how it would change the world. His combination of adjustable letter molds, moveable type, ink, and a wooden corkscrew press comprised a device that allowed the mass production of written communications. The distribution of printed texts of religion, education and politics created a revolution like few other inventions ever have. As literacy boomed, printing allowed ideas to be spread throughout society at a rapid pace. Gutenberg’s most famous printed work was his 42-line Bible of which dozens of copies still exist today.
There may indeed be 1001 ways to print if one were to really explore the possibilities. If we define print as mechanically transferring pigment from one substrate to another, there is a huge number of variations one could consider a printing process – from squeezing sheets of vellum under a wooden press to printing tens of thousands of sheets per hour on a web press. There are certainly more ways to print than anyone would care to know, so I won’t attempt to go through them all. Here a few of the most common methods of printing, types of printers, and their intended uses.
A letterpress is a direct relief printing process and is what the early presses of the Renaissance period were. A letterpress involves individual blocks of wood or metal with a raised character on one end. These blocks are put into a frame, arranged to form the desired message or design, and ink is applied to the raised surface. The inked letters are then directly pressed onto a paper sheet or roll. Few letterpresses are still in operation today, though there are a few novelty shops that still use them to create authentic or artistic printed works.
Digital printing refers to any printing process where the image on the substrate is directly produced through a digital signal. Digital printing is best suited for relatively small runs and variable imaging. Digital printing devices generally use either inkjet printing technology or laser printing technology. Most home desktop printers fall into one of these two categories.
Inkjet printing is a form of digital printing that uses a print head mechanism that sprays very regulated droplets of ink directly onto a substrate. Inkjet printers usually produce full-color images. Inkjet printers are best suited for single or small print runs and variable imaging. Inkjet printing is utilized in the commercial printing industry for proofing due to its large color gamut and consistent reproduction capabilities. It is also used in wide format applications to produce large prints like billboards and full-color banners. Inkjet printers intended for high-quality imaging and proofing can print substrate sizes from 8.5 inches to 4 feet wide and use up to 11 different colors for process printing. Some grand format inkjet printers can be as large as 16 feet wide!
Laser printing is a form of digital printing that uses a laser-powered imaging system to transfer an image of toner to a metal drum. The toner is then transferred from the drum to a transfer belt, which transfers it to the paper. The toner on the paper is then heated by a high-temperature roller, which fuses the toner image, instantly curing it. Laser printers are best suited for small to medium print runs and variable printing. Most commercial digital presses utilize laser-printing technology and are used for products such as brochures, postcards and personalized printing.
Impact Dot Matrix Printing
The first desktop computer setups often included a dot matrix printer. You may remember that unforgettable zapping sound and the fun of creating long happy birthday banners. Impact dot matrix printers involve a computer-controlled print head that strikes the paper through an ink-covered ribbon and creates letters or patterns with a matrix of dots. Impact dot matrix technology is still used today in such devices like receipt printers.
Thermal printing is similar to laser printing but uses a coated film that is drawn between a fusing head and the substrate. When the fusing head selectively heats the film the coating is fused to the substrate. Thermal printers are typically small and used primarily for label and/or vinyl printing.
Dye-sublimation is a process used to print on polyester and polyester resin-coated products such as fabric or tiles. Dye-sub inks are used to first print an image on a special transfer paper and then, through heat and pressure, the image is transferred to the substrate. Sublimation refers to the process of the solid toner transforming directly into a gas, bypassing a liquid state, and penetrating the polyester fibers.
Screen printing is a direct to substrate process that involves a fine mesh screen that ink is pressed through onto the substrate. Certain areas of the screen are blocked out to prevent ink from passing through creating the desired design. Screen printing is often used in textile printing (t-shirts, fabric, etc.) and for larger print runs of small signs.
Offset lithography (referred to as offset or litho for short) is a rotary offset printing process that involves an imaged metal plate that transfers an inked image to a rubber blanket, which then transfers the image to the substrate. Lithography works on the basic principle that oil and water do not mix. The image plate has a thermal or light-sensitive coating that is exposed through a laser process in a CtP (computer-to-plate) device to create the image. The plate retains ink where it has been imaged and water repels ink where the plate has not been imaged. Offset refers to the fact that the image plate does not make direct contact with the substrate. Lithography setup cost is less than that of flexography or gravure and is best suited for efficient high-quality printing of medium to long production runs. Most high-volume commercial presses use offset lithography.
Flexography (referred to as flexo for short) is a rotary relief printing process that involves a flexible image plate that applies ink directly to the substrate. The basic principle is very similar to letterpress printing. The relief aspect of the image plate allows for printing on a variety of surfaces such as cardboard and other similar uneven substrates. Flexographic setup costs are relatively high and it is best suited for long production runs or products requiring relief printing. Unlike lithography, which uses oil-based inks, flexography (and rotogravure) can utilize water-based inks, which allows for printing on a wider array of substrates.
Rotogravure (referred to as gravure for short) is a rotary direct printing process that involves an etched metal plate containing cells that hold the ink to be transferred directly to the substrate. The depth of the cells determines the amount of ink carried, creating more or less ink density. Unlike flexography or offset lithography, the gravure plate is in direct contact with the ink fountain. Most gravure presses print on rolls of paper known as webs. Rotogravure setup cost is very high but the etched metal plates last for a long time without deterioration which makes gravure printing best suited for very long production runs with undiminishing quality.
UV printing involves using inks containing photoinitiators (light-sensitive molecules) that cause the ink to cure when exposed to ultra-violet light. Ink can be applied to a substrate and then cured instantly (changing from a liquid to a solid) with UV light so there is no absorption, dry time or issues during finishing processes. There are several print methods that utilize UV technology. UV screen printing is often used in commercial printing to apply gloss coatings or specialty effects. Flatbed inkjet printers, which can print directly to rigid substrates, utilize UV technology. UV light is also used to cure inks in various high-speed printing processes such as lithography and flexography. UV printing has become more and more popular in commercial printing due to its production efficiency benefits. UV inks are also 100% solvent-free so there is no emission of VOCs (volatile organic compounds) or hazardous air pollutants.
A sheetfed press refers to any press where a pre-cut sheet is fed through the press. The sheet can be paper, plastic, cardboard, or other material. Though sheetfed typically refers to offset lithography, it can also include flexography or rotogravure printing processes. Sheetfed presses run at speeds as high as 18,000 sheets per hour and are best suited for medium to large print runs. They are often used to produce high volumes of postcards, packaging materials and brochures.
Unlike a sheetfed press, a web press uses continuous rolls of paper instead of individual sheets. The large machines seen in movies running newspapers and taking up an entire room are web presses. Finishing processes such as cutting, collating and folding are often done inline. Web presses can utilize lithography, flexography or rotogravure methods to transfer ink. Web presses run at speeds of thousands of feet per minute and are best suited for very large print runs. They are often used to produce high volumes of newspapers, magazines and catalogs.
There are several variations of the processes and printers listed above, but hopefully this gives a little insight into the basic methods that can be used to produce a printed image. More information on the printing process and other related aspects can be found at philprint.com/resources/faq.