Flexographic printing is not a new process. The first flexographic printing machine was developed in 1890 in England. The flexographic, or aniline printing press as it was called then was manufactured en masse in England until the 1920s, when production moved to Germany.
Back then, the flexographic printer was used in the food packaging industry, at least until the inks were banned because they were unsuitable for printing food labels. This contributed to increasingly low printer sales in the 1940s. Today, flexographic printing is a popular type thanks to recent technological developments.
Some typical examples of flexographic printing include the printing you see on plastic and paper pages, disposable cups, milk cartons and candy wrappers. Newspapers, envelopes and labels can also be printed using this method.
Flexographic printing is a type of direct rotary printing. This type of printing involves using a raised image located on a flexible relief surface on a cylinder. The cylinder turns, rolling and basically stamping images and words onto various media.
The printing plate itself is created using either an etching, UV or moulding process. The plate is then mounted onto the cylinder. After mounting, the cylinder is inserted into the printing press where ink is applied to the plate using small cups that are filled with it. The plate used in flexographic printing is designed to produce a consistent print. It requires no restructuring, meaning that there is no risk of image variance or irregularity.
There are several choices for inks used in a flexographic printer. Those needing printing on paper and cardboard are best off with water-based inks. Drying time can be completely eliminated when ultraviolet curing or electron beam inks are chosen for printing on cellophane and plastic. Commercial printing, such as that on wallpaper and plastics works best with solvent-based ink.
For printing on materials like cardboard, the paper’s moisture content on will affect the ability of the ink to cleanly print. For non-paper materials like polyethene, treating of the surface by reorienting surface electrons can assist with ink adhesion. However, there is a risk of over-treating, which can cause issues with printing.
Printing on polyester is becoming more popular, thanks to its high degree of chemical stability and durability. However, polyester – like plastic – does experience a reduction in tensile strength at high temperatures, which can make printing difficult.
Polyvinyl chloride is a type of vinyl film used in over 200 million pounds of packaging yearly. Vinyl film like this is water and chemical resistant, and very rarely requires surface treatment to improve adhesion of the ink.
A flexographic printing press can be configured in three ways: the in-line press, the central impression press, and the stack press.
The in-line press offers multiple colours, with separate stations for each being mounted in line horizontally. The in-line press makes reverse printing easier, thanks to turning bars which can be used to turn the web over.
The central impression press delivers the impression cylinder to each stationary colour station. This allows for the easier maintaining of proper registration. However, this type of press is not a good choice where reverse printing is required.
The stack press features vertically-stacked colour stations, each having its own plate, cylinder, inking rollers and impression cylinder. The web can also be easily reversed, allowing for double-sided, one-pass printing.
Although other printing methods – such as those used to produce inkjet labels – may offer simplicity in terms of setup and time to final production, the value of flexographic printing simply cannot be denied.