Ophelia_Flexography

Flexography

Definition:

Frequently used for printing on plastic, foil, acetate film, brown paper, and other materials used in packaging, flexography-printing uses flexible printing plates made of rubber or plastic. The inked plates with a slightly raised image are rotated on a cylinder, which transfers the image to the substrate. Flexography uses fast-drying inks, is a high-speed print process, can print on many types of absorbent and non-absorbent materials, and can print continuous patterns.

The two major types of fluid inks used in flexography are water-base and alcohol-base. Alcohol-base inks are most often used to print on nonabsorbent substrates such as film and foil. Water-base inks most often are used on absorbent substrates such as paper and paperboard. Although, with changing technology, water-base inks are also used on nonabsorbent substrates.
In order to meet the often rigid specifications of today's flexible packaging requirements, the inkmaker should know: If the package will be exposed to sunlight, heat, cold, or moisture, How the package will be handled. If the ink must be resistant to such things as perspiration, soaps, alkalies, acids, alcohol, oil, fat, butter, or adhesives. What the surface to be printed will be. And finally, what type of press will be used--and at what speeds.
Flexographic presses are less complicated than those used for other printing processes. The typical flexographic press includes the four rollers shown here. A rubber fountain roll turning in an ink pan delivers ink to a steel or ceramic ink metering roll and then to the plate cylinder. The paper or other substrate to be printed then passes between the plate cylinder and a polished metal impression cylinder.
The purpose of the fountain roll is to pick up a heavy flow of thin ink from the ink pan or fountain and deliver it to the metering roll. The fountain roll and metering roll are set to rotate under pressure against each other. The fountain roll is driven slower than the metering roll causing it to squeeze away excess ink from the surface of the metering roll.
The typical ink metering roll is referred to as the anilox roll, seen here. The anilox roll surface is engraved with tiny uniform cells that carry and deposit a uniform ink film onto the plate. The cells are so small that they must be magnified to be seen. Anilox rolls with varying sizes and configurations of cells carry different amounts of ink depending on printing requirements.
The purpose of the anilox roll is to pass on a thin, even layer of ink to the plate. The pressure and speed difference between the anilox roll and fountain roll leave the ink primarily in the engraved cells of the anilox roll. The plate cylinder is a metal cylinder placed between the anilox roller and the impression cylinder. The anilox roll contacts the plate that is attached to the plate cylinder and deposits its ink onto the raised image areas. Plate cylinders come in various sizes. To change the number of times an image prints or repeats around a plate cylinder, the existing plate cylinder can be removed and another easily dropped into position.
The material to be printed, or substrate, passes between the plate cylinder and the polished metal impression cylinder. The impression cylinder backs up and supports the substrate as it contacts the printing plate. The gap, or nip, between these two cylinders must be just right to give the proper printing pressure.