Have you ever wondered how your favourite paperbacks get made? Modern printing presses are fascinating pieces of machinery. They run amazingly fast – up to 2,000 pages per minute – yet manage great precision. This month, we’ll take a quick look at how they work and how a novel gets turned into something you can throw into your bag ready to read on the train.
What is Offset Lithography?
High-volume book printing relies on a process called offset lithography, but it’s not as complicated as the name makes it sound. The process starts by creating a set of “press plates” – thin and very flexible sheets of aluminium that carry images of the pages. Each one is much larger than a single paperback page (a plate is typically 50 by 70 cm), so each sheet will produce multiple pages. Typically, each press plate is responsible for 16 pages of a book.
The total number of pages in the book will be the number of pages per press plate multiplied by the number of plates used. This often means that a book will have a blank page or two at the back or front.
The metal sheet will have been chemically treated to resist ink. In preparation for printing, an image of the pages is laser-etched into the surface, removing the coating where the letters need to be. With that done, the press plate is ready to use. During printing, ink will stick to where the coating has been removed, but be repelled from the rest of the plate.
Over the years in which the printing process has been refined, it was found that printing directly from the hard surface of the press plate on to paper didn’t always produce the sharpest text. A big step in improvement came by introducing an intermediate stage, and this is where the term “offset” comes in. The ink remaining on the press plate is transferred to a rubber sheet (known as the “blanket”), and the paper is then pressed against the rubber instead or the metal. This picture demonstrates the principle:
To print, the press plate is first wetted with a mixture of water and chemicals, which clings to the metal where it hasn’t been etched. When the plate is then passed through the ink-applying rollers, the ink is repelled by the damp surface, but clings to where the plate was etched. Rollers A and B then press the flexible inked plate against the rubber blanket, and the ink is transferred to the rubber as shown in the picture.
An alternative to using water to dampen the plate is to use ink-repellent silicone instead, the process then being referred to as “waterless offset lithography”.
The next stage is to press the rubber blanket against the paper, which is done as they pass between rollers B and C. This transfers the ink to the face of the paper, producing a clean sharp image. The ink is then dried, either by heating or, more economically, by allowing it to dry by adsorption of the ink into the paper.
The picture above shows a simplified single-sided mechanism to explain the process, but in reality both sides of the paper are printed at once. If you look back at the diagram and imagine a second blanket being fed round roller C, you can see how the paper can be squeezed between the two blankets, allowing both sides to be printed simultaneously.
Web-Fed Offset Lithography Printing
Printing can be done using single large sheets of paper, with each one being picked up by jets of air and fed into the printing press one after the other. However, for mass paperbacks, large rolls of paper are used instead. Each roll is known in the printing trade as a “web”, and so this method is called “web-fed offset lithography.”
By continuously feeding the paper in this way, hundreds of meters can be printed every minute!
The book is printed in sections. Each press plate carries a unique barcode that is printed alongside each group of pages to differentiate the different sections. This allows the pages to be bound later in the correct order. The final cutting stage removes the barcodes.
Paperback Book Covers
Covers are produced separately on thicker paper. The type of paper used comes coated on only one side. This is the side to which ink will be applied; the inside is uncoated because it absorbs glue better, which helps the binding process. The direction of the paper’s grain is also taken into consideration: so that the cover bends round the spine without risk of creasing or cracking, the paper is printed so that the grain runs in a left-right direction rather than up-down.
The cover will be colour printed, which may use the same principle as described above, but with the paper fed through several consecutive stages, each one applying a different coloured ink, and only printing on one side.
It may then pass through more specialised processes such as lamination (which covers it in a thin plastic coating to make it more robust) or embossing.
Perfect Binding
For trade paperbacks, “perfect binding” is used to construct the complete book. The pages are compiled in the correct order, and hot glue is applied to the spine of the cover. The book is stuck together and then trimmed as a whole. This removes the barcodes and ensures all edges are perfectly aligned (hence the name).
Print on Demand
Offset-lithography is the most economic printing method for high volume production (over 10,000 copies per run), but the cost and time of creating the set of press plates makes it’s nonviable for lower quantities. This is where print-on-demand (POD) comes in, which uses a very different method. No press plate is required, so setup costs are much lower. It’s an approach that is perfect for small print runs and has therefore been adopted by small publishers, self publishers, and now also by the newly emerging “digital first” imprints of larger publishers.
Even one-offs can be produced, in which case, the computerised print system will collate several different books so that each large sheet of paper contains pages from more than just one book.
The principle is basically to use large double-sided laser printers to produce the pages and covers (or sometimes inkjet printers, which can give darker blacks). The pages are then cut and glued into their covers.
Ian Coates is the author of a thriller, Eavesdrop, first published by Bad Day Books, the suspense and thriller imprint of Assent Publishing. He worked in the high tech electronics industry for 30 years, where he specialised in the design of radio communication equipment. His intimate knowledge of that environment always triggered his imagination to think about the mysterious world of spies, and allowed him to bring a unique authenticity to his thriller. Ian is proud to support the British Science Association and donates a proportion of his book proceeds to that charity. He lives and writes in Worcestershire, England, and is a member of the Society of Authors and the International Thriller Writers Association.
His second thriller, Backlash, will be released later his year.
IanCoatesThrillers 