The Process Of Lithographic Printing
A litho printing press has either four or eight ink terminals. Each terminal has a specific ink colour in the CMYK spectrum: Cyan, Magenta, Yellow, and Black (Key). There will be eight terminals for presses that automatically print double-sided products. In these presses, the paper is fed through the first four terminals for one side, then flipped using rollers, and the other side is immediately printed by the following four terminals.
First, to get the image onto paper, some etching is involved. The digital image, submitted as a PDF, is converted so that the design can be etched onto four large aluminium plates. There is a plate for each of the CMYK colours, and each is loaded into their relevant colour terminal on the printing press.
Ink is distributed onto the metal plates and pressed onto a blanket roller. The image is then transferred from this blanket roller onto the paper, and then the paper is fed through to the next ink terminal for the next layer of colour.
At the end of printing, a drying technique is used. This can either be in the form of a spray, which prevents the sheets from sticking together when stacked, and sheets are left to dry for about an hour. Alternatively, a UV dryer can be added to the end of the printing press if UV inks have been used, which will instantly set the ink.
Why Is Lithographic Printing Still Used?
It may seem that, with the advances of technology in digital printing, lithographic printing is now outdated. However, litho is still a very economical way to print very large runs, and machines will run several thousand more sheets per hour than digital presses.
Lithographic is also economical in terms of waste: for print projects which are smaller than the B2 size aluminium plate used, several can be lined up on the same plate. This means that many projects can be run at once. For example, 72 different business cards can be printed at the same time, instead of lining up 72 different projects.
The economies of scale presented by this technique are great: there is less paper wastage, as every available inch is used and only a minimum is trimmed (and then recycled). Machines use less power, as they are running multiple projects simultaneously rather than in sequence over a longer period. Finally, large paper rolls are used which are then trimmed to size after printing; this reduces the amount of down-time between projects as there is no need to switch in or load up pallets of paper.
[LINK TO DIGITAL PRINTING BLOG] Digital printing presses can use paper rolls, which are also more economical to purchase than pallets of paper, but it is more common to have paper loaded into trays (much like an oversized office printer!).
Want To Know More?
You can ask us anything about how we print on our Heidelberg lithographic printing presses! If you’re really eager, you can also book a factory tour to see your project as it’s printed. Contact us today to find out more. [LINK TO CONTACT]