Printing refers to the process in which text and images are reproduced, generally onto paper using ink. This process is often done using a printing press, but there are many variations of printing presses that produce varying results.
This article is going to examine various methods of printing, and explain the entire printing process in simple to understand terms.
Methods of Printing
There have been numerous printing methods used and improved over the centuries. See Figure 1—Printing Methods for a list of some common printing methods today.
What many of these methods have in common involves printing on commercial equipment. Commercial equipment is generally needed for professional, high-quality print jobs that cannot be done at home.
Let’s look at the basic process of commercial printing. This guide will not tell you every detail about the printing process, but is covers the basics of how it works.
Process of Commercial Printing
Commercial printing is generally what we call offset lithography or offset printing. The process in simple terms can be explained this way. Text and images are placed on plates which are dampened first by water and then by ink. The ink adheres to the image area, and the water adheres to the image-free area.
Then the image is transferred to a rubber blanket, and from the rubber blanket to paper. The process is called "offset," since the image does not transfer directly to the paper from the plates.
Stages of Offset Lithography
The stages of commercial printing, or offset lithography printing, can be broken into four categories. They usually involve scanning artwork onto a computer and the use of specific software to set up the project, output onto high-resolution imagesetters, creating printing plates, and attaching the plates to a litho press for printing.
Stage 1 - Original Artwork
During the first stage of printing, original artwork is created by writers, editors, graphic designers and artists. This artwork may include the text and images for brochures, business cards, catalogs, flyers, magazines, newspapers, and more. The artwork is usually sent electronically and then scanned and entered into a computer for layout.
Stage 2 - Setup
In the second stage of printing, the artwork is first converted to film and what we call plates. Film negatives are usually created from digital files, and then the images from the negatives are transferred to the printing plates, similar to the photographic process. The plates are exposed to light, which creates a chemical reaction to transfer the image from the negative to the plate. Plates are created for each ink color (four-color process).
Stage 3 - Printing
The actual printing stage involves several steps, from paper setup to printout.
- In offset lithography, the paper is fed through the press from ton-size rolls of paper which is cut to size after high-speed printing. In offset lithography, the paper may also be fed into presses.
- The underlying principle of offset lithography involves the inking process. The ink is distributed to the plates through a series of rollers. On the press, the plates are dampened by water rollers and then by ink rollers. The rollers distribute the ink onto the plates. The ink sits on the surface of the paper.
- The offset process follows, in which the image area of the plate picks up the ink from the rollers. Water keeps ink off of the image-free areas of the plate. Each plate transfers its image to a rubber blanket that in turn transfers the image to the paper. Since the plate does not touch the paper, the term "offset" lithography is created. A heating and cooling process keeps the paper from smudging.
- The color process involves both color control and plate registration, which are performed with the help of computers. Plate registration is the perfect alignment of the printing plates as they apply the color. Color control involves the method in which the ink blends together. Ink amounts are adjusted via a control panel on the computer.
Stage 4 - Bindery
In the bindery stage, the printed product goes through the final steps toward completion. These steps involve trimming, folding and binding. Rolls of printed paper are cut and assembled so the pages are in order. Here pages are bound together by staples or glue if necessary.
Often, a machine called a stitcher folds the printed paper together and trims it to the requested size. The product is then ready for shipment.
The Bottom Line
There are various differences between the methods of printing. Most professional printing is done using a process called offset lithography. Some smaller jobs may be done digitally, as small machines become better and cheaper. In terms of offset lithography by commercial printers, here are some points:
- Printing of good, clean lines is often the result of aluminum plates used in the printing process.
- Generally, the more you pay, the better quality you will receive.
- It is the basic principle of offset printing, the difference between ink and water, that makes it work!
- Get your professional printing done through a commercial printer. Go for the best card stock, quality ink, clean and clear lines—essentially perfection! It is a reflection of you and your business!