Static: Why Sheets Stick Together and Dust Finds the Print

Paper arrives wrapped in a moisture barrier, and the wrap is there for a reason. A sheet of coated paper sitting at 23C and 50% relative humidity holds a thin film of water on its surface, and that film drains electrical charge. Unwrap a pallet in a dry pressroom in February and the same sheet becomes an insulator.

Static builds where two surfaces separate. Every sheet that lifts off the pile at the feeder carries a charge, and the sheet below it takes the opposite one. Below about 40% relative humidity the charge has nowhere to go. The symptoms are easy to read. The feeder pulls two sheets and the second one prints a ghost. A single sheet clings to the feed board and arrives late, so the gripper takes it out of register. The delivery pile leans because each sheet lands charged and repels the one before it.

Tape Binding: The Strip That Holds a Softcover Together

A tape bound book looks like a perfect bound book from the shelf. The difference is at the spine: instead of a glued cover wrapped around a milled block, a strip of cloth or paper carries the adhesive and wraps a few millimetres onto both covers.

Where the tape goes

The block is jogged and clamped, the spine edge is notched or left square, and a tape coated with hot melt is applied along the edge. The tape is wider than the block is thick, so it folds over onto the front and back cover by 3 to 5 mm.

Why a Hardcover Case Warps After It Is Built

A case cover comes off the casing-in line flat and comes back from the warehouse bowed. The bow is not a fault of the printing. It is a moisture imbalance built into the boards, the wrap and the paste, and it shows up hours or days later when the two faces of the case lose water at different rates.

A case is a sandwich with two different skins

Greyboard is made from recovered fibre, pressed and dried. It has a machine direction, and it takes up and gives off moisture through both faces. When the board sits in a room at 40 per cent relative humidity, it dries from the outside in, the surface fibres shrink, and the sheet curls toward the dry face.

Slipcases: The Box a Hardcover Book Lives In

A slipcase is the simplest piece of packaging in bookbinding and the one most often got wrong. It is a five-sided box, open on one long edge, sized to the book it protects. No lid, no hinge, no magnet. The book slides in and out, and everything about the case has to allow that movement while still holding the block square.

How it is built

Three panels of greyboard: two sides and a spine. The boards are usually 1.5 to 2.0 mm, wrapped in cloth, paper or a printed sheet that turns over the edges and lines the inside. The wrap is one piece, glued to the outside, turned in at the top and bottom edges, then carried across the inside face so the raw board never shows.

Dampening: The Water Side of an Offset Press

Offset lithography works because oil and water do not mix. The plate carries an image in a thin photosensitive layer that accepts ink, and a grained aluminium surface that accepts water. Every revolution of the press puts both onto the plate, and the image holds only while the two stay separated. The dampening unit is the part that delivers the water, and it is usually the part a buyer never hears about until a job starts printing inconsistently.

What the unit contains

A dampening unit has a pan of fountain solution, a metering roller, a chrome or ceramic transfer roller and one or two form rollers that touch the plate. In the older contact system, a ductor roller swings between the pan and the roller train, feeding a pulse of solution on each cycle. In continuous dampening, a metering roller runs against a chrome roller at a controlled speed and the film is transferred without the swing. Continuous systems hold a steadier film, which matters on long runs and on presses running at high speed.

Anilox: The Roll That Decides How Much Ink Reaches the Plate

Flexo has no ink keys. The amount of ink that reaches the plate is set by one roll and by the pattern of cells cut into its surface.

An anilox roll is a steel cylinder coated with ceramic, then laser engraved with hundreds of thousands of small cells. The roll turns in an ink bath or against an enclosed chamber. A doctor blade scrapes the surface clean, so the only ink left is what sits inside the cells. The plate touches the roll and lifts that ink out.

Wash-Up: What It Takes to Clean a Press Between Colours

A press does not stop when the last sheet of a job leaves the delivery. The ink has to come off the rollers, the blankets and the plates before the next job can run, and that cleaning step is called wash-up.

Offset ink is a paste of pigment, resin and oil. Water will not move it. The wash is a solvent or a vegetable-oil based cleaner that dissolves the resin and carries the pigment away. On a modern press the wash-up unit does the work: a blade or a trough presses solvent against the ink rollers while they turn, the dirty liquid drains into a waste container, and the cycle repeats with clean solvent until the rollers stop giving up colour.