What Is Offset Printing?

Offset printing is a technique where the image is transferred – or offset – from a plate to a rubber blanket, then onto the printing surface. Commercial offset printing is the standard printing system used globally – producing mass printing used by organisations and businesses of all kinds.

Offset lithography is simply another name for the method – and is used for anything from labelling packages to producing leaflets, magazines, and brochures in bulk. The process is efficient for small, medium, and large-scale production as results are consistently high quality.

What is offset printing? Read on…

What Is Offset Printing?

Offset lithography is a printing process where the image and the non-image area are on the same plate. This means the surface from which you print is completely flat and porous. The word lithograph means printed from stone and original plates were made from limestone.

The first rotary offset lithographic printing press was created in England in 1875 using a metal cylinder rather than a flat stone. Later the cardboard covering of the cylinder was changed to rubber – which is still the most commonly used material today.

Modern offset printing has many advantages as computer-to-plate technology has greatly increased quality.

Inks and Colours

Offset printing ink is oily in order to repel water – creating a surface where some parts contain a little water will repel the ink. So, image areas need to be lipophilic – accepting ink – and non-printing areas need to be hydrophilic – repellent to oil and receptive to water.

Offset printing uses four basic ink colours. These are:

• Cyan (C)
• Magenta (M)
• Yellow (Y)
• Black (K)

Each colour is applied separately – one plate per colour. When pressed into specific patterns small dots of CMYK form a wide range of colours.

Offset Printing Workings

See how offset printing works:

An offset printing machine will have three cylinders. The first one is known as the plate cylinder and is covered by a plastic or aluminium plate. And pre-treated to ensure the images attract ink and repel water. Each plate is customised according to the images and text that need to be printed onto the paper.

The second cylinder is referred to as the offset blanket cylinder. This cylinder is encased in a rubber blanket and rotates in the opposite way to the plate cylinder. When the cylinders roll against each other any water is squeezed out and ink is transferred onto the rubber blanket – creating a mirror image of the design.

The third cylinder is called the impression cylinder which is made from clean steel. Turning in the opposite direction to the blanket cylinder the ink is transferred from the rubber blanket to the paper.

Digital Printing vs Offset Printing

Digital printing doesn’t use plates – but transfers the image directly from the digital medium to the printing surface. As a direct print method, it’s ideal for individual pieces that need specific codes, or names and addresses. In fact, it’s a perfect solution for printing lower quantities as it’s both fast and effective.

As there aren’t any set up costs digital printing is economical for small print runs – and there are no minimum print numbers. However, it becomes very expensive when printing high volumes, and the quality is only good. Colours tend to look different than those shown on screen.

Offset Printing Advantages

The offset printing process has many advantages and these include:

• Consistent high-quality images
• Quick and easy production of printing plates
• A wide range of paper types can be used as well as special custom inks like metallic and Pantone colours
• Enhanced detail and accuracy in colour matching – colours are printed exactly
• Very cost-effective for large quantities of printing – it’s the cheapest way to produce quality prints in commercial printing quantities
• An option of custom finishes as the operator is able to adjust the amount of ink on the fountain roller – modifying the density of the colour in respective image areas
• A long printing plate life with properly developed plates achieving run lengths of more than a million impressions

And Finally…

Now you know the offset printing definition you can be confident in getting your project completed to the highest standard. High-quality inks and the correct weight of paper – with the best professional finishing options will make your commercial printing stand out. With the ongoing refinement of speed and plate durability, you’ll be opting for a print process designed to last.