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Offset litho printing and flexography, also known as flexo, are two of the most common commercial printing methods. They are both suitable for printing large amounts -- unlike digital printing, which is only suitable for short runs. However, there are other differences which mean that they are each better suited to certain types of printing job.
Lithographic printing was initially developed using a stone (lithographic limestone) or, later, a smooth metal plate. Offset litho printing is so called because it then offsets the image onto a rubber blanket which is used as the actual printing plate. Flexo uses a relief image -- so the letters stand out -- on a flexible rubber plate. These flexo plates can be reused easily.
Litho printing is entirely based on the principle that oil and water do not mix. It uses a mixture of oil-based inks and a water-based film to attract the inks to the printing areas, and keep the non-printing areas ink-free. Flexo uses water-based inks with a low viscosity, which makes them faster-drying than typical litho inks.
Litho printing is most effective on flat paper and cardboard. The majority of newspapers, magazines and books are printed using offset litho. Flexo printing is suitable for any type of material, including plastic, metallic films and cellophane. It is widely used for food packaging.
Flexo presses are very fast. They can print up to 600m per minute, usually on large rolls of material that are then cut down to the correct size. It is possible to change the plates very quickly, which makes short runs feasible and economic. Setting up a litho machine takes time, which is why they are best used for long runs. The oil-based inks have a long drying time, which makes this a more costly method of printing.
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