Differences between flexo and offset

Flexo and offset are both popular, but they perform their tasks differently. It is important to understand what roles they perform and have a clear understanding of both types of printing process. The type of press to use depends on the final product and quality required, as well as volumes and substrates.

As the name suggests, flexo printing utilises flexible plates for a rotary printing process. The plates are made from a photopolymer compound and are flexible enough to be wrapped around a printing cylinder. The relief image on the plate is fixed via a laser image-setter and the polymer in the ‘non-print’ areas is washed away in a processing unit, where it is dissolved into a solvent or water solution. Ink is transferred from the ink well via a rotating ‘anilox’ roller onto the flexo plate. A separate printing station & flexo plate is required for each colour to be printed. The image is then printed directly onto the substrate. The printing plates are quite durable and if stored correctly, can be re-used several times, before they eventually need to be replaced.

For offset printing, again as the name suggests, ink is transferred (offset) via a series of rollers onto the printing plate. This can be either a flat-bed or rotary process – depending on the type of offset press. The plate is usually made of aluminium. The complete wet image (either single colour or multicolour) is then transferred onto a ‘blanket’ and in turn onto the substrate, before drying.

Offset printing usually consists of four ‘process’ colours; cyan, magenta, yellow and key (which is black). Each colour has a dedicated printing station. Any spot colours are made from a combination of the process colours. Ink can be water based or UV curable. 

Although process colours are also used in the flexo process, additional print stations tend to be used for spot colours.  Spot colours can be supplied pre-mixed, or can be mixed in-house, as required.

Flexo inks can also be water-based or UV curable. Solvent based inks can also be used. UV inks enable higher running speeds and can be left in the press at the end of the day, without the need to empty & clean each print station.  Water based inks need to be removed from the press, when it is not in use – to prevent ink from drying on the rollers & in the ink trays.