When shopping for printing equipment or supplies, you are instantly bombarded with a hundred choices in a hundred price ranges, with confusing specifications and technical jargon your only guide. How do you know if you’re getting a deal, or getting ripped off? To make sure you get the best quality for the best price, you need to understand the basics of printing. This article will give you a quick crash course in the printing process. This will hopefully give you to better understand how printing works, and perhaps shed some light on the confusing labyrinth of technical specifications and specialized terminology.
First of all, there are many different types of printing. Inkjet and laser printing are perhaps the most well known because they are the technologies used in home computer printers, but many other types of printing exist. Screen printing, for example, is used for fabrics. Relief printing is used for catalogues, pad printing is used to print on three-dimensional objects, rotogravure is used for magazines, and flexography is common for packaging, labels, and newspapers.
This article, however, will focus on offset lithography printing, which is currently the most common industrial printing process. About 40% of all print jobs are produced with offset printing. Offset printing provides faster, higher-quality printing in larger volumes than other commercial printing processes. Currently, offset printing also provides the most efficient cost-to-performance ratio.
Offset printing is an indirect printing method, meaning the image (text or graphics) is transferred from one surface to another. In a nutshell, the image to be printed is wrapped around a printing plate, which is mounted on a cylinder. Another cylinder coated in ink rolls against the printing plate cylinder, coating the image in ink. As the printing plate cylinder continues to roll, the image is transferred from the printing plate to a rubber blanket around another cylinder. The print media (usually paper) is then rolled between this blanket cylinder and simple blank cylinder (called the impression cylinder). As the paper passes between the two cylinders (called rollers), the pressure transfers the image from the rubber blanket cylinder onto the page.
Keeping the ink only in the image areas (and avoid smudging, other imprints, etc) is essential to print quality. Keeping the ink only on the image areas and away from the non-image areas is achieved by using the principle that oil and water do not mix. Printing ink is oil-based. Therefore, before the paper is passed between the blanket and imprint cylinders and has the image transferred to it, the paper is run through a dampening system to apply a thin layer of wetting agent (called a fountain solution). When the ink is applied to the damp paper, the water in the fountain solution repels the oil-based ink, keeping the ink from bleeding into the blank non-image areas. At the same time, the ink on the image area repels the fountain solution. This is how a tidy, crisp, high-quality print image is achieved.
How large the circumference of these cylinders is determines how large of an image can be transferred. For example, a printing press with 8½ inch rollers could print on 8½ x 11 inch paper, but not on 11 x 14 inch paper. Printing presses are usually named for their roller circumference size, such as a 17 Inch Press or a 22 Inch Press.
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