Screen Printing: How Mesh, Squeegee and Emulsion Set the Ink Layer

A screen print sits on the surface as a flat patch of colour, thicker than anything an offset press lays down. That depth is no accident. It comes from pushing ink through an open mesh with a rubber blade, and every part of the setup decides how much ink lands.

The mesh is the measuring cup

The screen is a woven fabric stretched over a frame and coated with a light-sensitive emulsion. Where the artwork sits, the emulsion is washed away and open holes remain. A coarse mesh with 86 to 110 threads per inch leaves wide openings and passes a heavy layer of ink. A fine mesh at 230 threads or more leaves small openings and lays down a thin, detailed film. Two screens with the same count can still differ, because thinner threads leave more open area and carry more ink.

Kiss Cutting: How Stickers Are Cut Without Cutting the Liner

A sheet of labels looks like one flat printed page. Peel a sticker off it and only that sticker comes away, with the rest of the sheet still sitting neatly in place. That behaviour comes from a cutting method called kiss cutting, where the blade goes through the sticker and the glue but stops at the liner underneath.

Cutting depth is the whole trick

Kiss cutting uses a steel rule die bent into the shape of the label. The die is mounted on a cylinder or a flat bed and pressed against the printed sheet until the rule cuts the face material and the adhesive layer. The blade must stop before it reaches the liner. Too shallow and the sticker is still attached and tears when it is peeled. Too deep and the liner is scored or cut through, which lets the sheet fall apart on the press and defeats the purpose of a release liner.

Gang Run Printing: How Several Jobs Share One Offset Sheet

Most small print jobs do not fill a printing press. A run of business cards, a batch of postcards, a folded leaflet: each one may take up a small corner of the sheet a large offset press can carry. Gang run printing fills the rest of that sheet with other jobs, so the press prints paid work instead of empty paper.

The sheet is planned before anything is printed

A gang run starts as a layout. The jobs are nested side by side and stacked down the sheet, arranged around their finished sizes, the quantity each buyer needs and the format the press will run. One plate may carry a dozen business cards, two postcards and a rack card in a single arrangement. The whole sheet is printed in one pass, then cut apart in finishing, and each loose piece goes to its own job.

Cold Foil: Metallic Effects Straight From the Press

Metallic print often brings to mind hot foil stamping: a heated die, a sheet of foil, pressure, and a bright shine pressed into the page. Cold foil reaches a similar visual result by a completely different route, one that runs inline on the printing press.

How cold foil transfers

The process starts with an adhesive printed onto the sheet, in exactly the shape of the metallic area. That adhesive is a printing unit's job, so it can carry fine detail and halftones like any other ink. A thin metallic foil film is then pressed against the wet adhesive as the sheet travels through the press. Where adhesive sits, the foil sticks. A UV lamp cures the adhesive inside the press, and the carrier film is stripped away with the foil left only where it was wanted.

EVA vs PUR: The Two Adhesives Behind Perfect-Bound Paperbacks

Open a softcover book and look down the spine gutter and you will usually find glue. Nearly every softcover book on a shelf is perfect bound: the folded pages are milled at the spine, roughened, and held together by a single adhesive. Which adhesive depends on two names: EVA and PUR.

EVA, the workhorse hot melt

EVA stands for ethylene-vinyl acetate. It is a hot-melt adhesive, applied molten at high temperature, and it sets in seconds as it cools. That speed is why EVA dominates high-volume paperback production: a binding line can turn a pile of trimmed book blocks into finished books without waiting on a chemical cure.

Inside an Offset Printing Unit: Plates, Blankets and the Impression Cylinder

The heart of an offset press is the printing unit, one for each ink color on the job. A four-color sheetfed press stacks four of these units in a row, and every one of them performs the same quiet sequence: plate, blanket, paper.

The plate cylinder

The image for one color is carried on a thin metal or polyester plate wrapped around the plate cylinder. The plate is flat and photographic: it has been exposed and processed so that image areas accept ink while non-image areas accept a film of dampening water and reject ink. Each revolution of the cylinder brings the plate under a train of ink rollers, and the ink sticks only where the plate tells it to.

Halftone Dots: How a Continuous-Tone Photo Becomes Ink on Paper

A printed photo is not really a photo at all. Look at it through a loupe and it dissolves into dots, thousands of tiny ink circles in different sizes. Turning the smooth tones of a photograph into dots a press can print is the job of halftoning, and it decides how sharp or how muddy an image looks on paper.

Why dots

A press cannot lay down a thin, half-strength layer of ink. Each printing unit either deposits a full film of ink or it does not. So continuous tone has to be faked with area: small dots of solid ink spaced closely read as a dense tone, small dots spaced widely read as a light one. The eye blends the dots at reading distance and sees a gray or a tinted tone.