Offset printing in its simplest form pretty much resembles the first printing press invented by Gutenberg. It consisted of moveable type, ink, and a flatbed table. Today, modern offset printing has achieved incredible speeds and quality. Rotary offset printing can achieve printing speeds of up to 100,000 copies per hour. Let’s break component of a modern day printing press and what it does.
Flying Paster: A flying paster is where the rolls of paper are loaded onto the offset printing press. Usually it holds two rolls. One is running and one is prepped to be spliced on. Splicing involves changing one roll to the next without solowing down the press. A piece of two-side tape is put on the roll and with precise timing, the paster sticks the expiring roll onto the new one.
Infeed: To prevent the paper from being baggy in the press, something must maintain a constant tension on the paper. There are complex terms to explain how this is done, but in its simplest sense, something is pulling on the paper at either end of the press to make it tight. This is done with a brake and dancer roller and an nip roller. The dancer roller moves in accord with the changing tension in the paper while brake keeps it tight. This is makes up the infeed that is so critical for maintaining web tension.
Printing Units: This is where offset printing takes place. Put very simply, ink flows from fountains onto a plate which transfers to the paper. This is accomplished by means of various rollers such as transfer, vibrator, and form roller. The transfer from the plate to the paper takes place by means of a blanket cylinder which effectively transfers ink and is spongy enough to handle various thicknesses of paper.
The Heatset Oven: Faster presses require an oven or dryer. The drying takes place in less than a second. Oils are boiled out of the ink and then cooled in a chill section. Offset printing is able to achieve high speeds only by speeding up this drying process.
The Folder: The offset printing industry demands many types of finished products. The fastest mode of printing today is done by the heatset web printing press which consists of all the components above. Most offset press folders can produce products in multiples of 8 pages. Typical components of a folder consists of nips, pin and tuck cylinder, chopper table and spider wheel. The finished product is then sent on a delivery line where further finishing or offline binding can take place.
While Gutenburg no doubt could not fathom how offset printing would develop, his innovative mind no doubt constantly thought of new ways of developing the process. The modern pressman continues to develop ways of speeding up the process and adding more components to make this possible. In this industry, speed and efficiently have not found a limit.