Commercial processes for papers and boards

The plate has image areas that attract printing ink and non-image areas that attract water. Ink and water do not mix, so the damp non-image areas resist the ink. This keeps the ink in the areas needed for the design.

During printing, the inked image transfers from the plate to the rubber-covered cylinder. The paper or board passes between this cylinder and an impression cylinder, which provides pressure so the image transfers onto the sheet. The press repeats this operation rapidly.

Building a full-colour print

Full-colour offset printing commonly uses CMYK: cyan, magenta, yellow and black. A separate plate is prepared for each colour, so a standard CMYK image uses four plates. Each colour is printed as a pattern of dots; together, these patterns form the finished picture or graphic.

The colour layers must line up accurately. This alignment is called registration. Registration marks provide reference points for checking the alignment: if the layers are displaced, details and edges will not match correctly.

Offset lithography is used for magazines, books, leaflets and printed packaging. Preparing the plates and setting up the press costs money, but the press then produces high-quality, consistent prints quickly. For a run of 50,000 colour leaflets, the initial set-up cost is spread across many copies, reducing its contribution to the cost of each leaflet. This makes the process particularly suitable for large print runs.

Die cutting: repeating a shape accurately

Die cutting uses a specially made tool called a die to press the required outline into paper or board. Shaped steel cutting rules are mounted in a base, such as plywood, to match the design. For packaging, this design is often a net: the flat shape that will later fold into a carton.

The sheet is positioned using guides or registration marks. A press then forces the die against it. Depending on the tooling fitted, the operation can create:

• Cuts, which pass through the material to separate the outline or openings.
• Creases, which prepare fold lines without cutting the sheet apart.
• Perforations, which make a line of small cuts while leaving connections between them.

After pressing, the unwanted material is removed. The remaining component can then be folded or assembled.

Combining speed with consistent quality

Die cutting is used for carton nets, greetings cards, labels, folders and display products. Making the die involves set-up and tooling costs, but the same die can produce identical shapes repeatedly. Compared with hand cutting 2,000 cartons, this reduces the time and labour needed for each component while maintaining a consistent shape.

For printed packaging, the sheet must be registered accurately before cutting. A correctly shaped net is not enough if the cut is displaced from the printed design. Printing registration aligns the colours with one another; die-cutting registration aligns the physical shape with the graphics.

• Transfer: printing plate → rubber blanket → paper or board.
• Image areas attract ink; non-image areas attract water and resist ink.
• Standard full-colour printing uses four CMYK plates: cyan, magenta, yellow and black.
• Registration keeps the colour layers aligned.
• Used for books, magazines, leaflets and packaging: high set-up cost, but fast, consistent, high-quality printing in large quantities.

Die cutting

• A shaped die is pressed against an aligned sheet of paper or board.
• Tooling can cut outlines, crease fold lines and create perforations.
• Remove waste, then fold or assemble the component.
• Used for carton nets, cards, labels and folders: tooling costs initially, then rapid, repeatable production with less labour per item.
• For printed products, cuts must register with the graphics.

Key distinction

Offset lithography prints the design; die cutting shapes the sheet. Both spread their initial set-up costs across repeated production.