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The choice of the correct anilox roller is of central importance for an optimal printing result

Update:14 Apr 2018
Summary:

The Anilox Roller is often referred to as the heart of […]

The Anilox Roller is often referred to as the heart of the flexographic press. It is designed to deliver a precise and consistent amount of ink to the printing plate. An roll is a hard cylinder, usually constructed of a steel or aluminum core which is coated by an industrial ceramic whose surface contains millions of very fine dimples, known as cells.The choice of the correct anilox roller is of central importance for an optimal printing result. Depending on the printing type, we recommend different engravings and cell volumes. The choice of the correct anilox roller is of central importance for an optimal printing result.A flexographic printer often face problems due to non availability of correct anilox roller. The purpose of this article is make an attempt to throw some light on this very important subject.

 

The flexo printing/coating process depends upon the precise controlled transfer of a liquid ink, varnish or coating.An anilox roll is simply a metering roll designed to consistently supply a uniform and measurable volume of ink onto the image carrier.Anilox roll is considered to be the heart of the flexographic press. Older methods of mechanically engraving cells in to the surface of a roll have been replaced, to a large extent, by the precise computer controlled laser engravings of ceramic coated steel rolls. In this process, millions of minute holes (cells) are drilled into the ceramic surface of the roll. Ink receptivity and releasing capabilities of the anilox roll is of higher importance and ink transfer capabilities of the plate are determined by the surface technology of plate, surface tension of plate & ink and plate to ink compatibility.The central part of the press is the anilox roller, the ink metering system unique to this process which allows the correct amount of ink to be carried to the printing plate. On the surface of the anilox roll are etched the cells which act as ink carriers. The number, shape and size of the cells required on the surface depends on the:

  • Ink used.
  • Amount to be transferred.
  • Material to be printed on.
  • Image to be printed.
  • Ink train configuration.

The latest anilox rolls are laser engraved, with cell counts currently up to 500 cells/cm, from a steel roller and coated in a fine ceramic. These laser engraved ceramic rolls, could last up to 10 years, depending on the wear they are exposed to from contact with the doctor blade. They provide an even, and consistent ink delivery in a controlled manner and provide narrow web flexo with a competitive edge in the leading packaging markets eg self adhesive labels for wines. Once the anilox is ‘charged’ with ink, the excess is wiped off with a flexible steel doctor blade.Besides the cell geometry, ink release capabilities of the cell is also affected by rheological properties of ink like; viscosity, surface tension, printing pressure between the plate cylinder and the impression cylinder, substrate properties, etc.Available engraving angles for anilox rolls are as follows; 90 degree angle, 45 degree angle, 30 degree angle and 60 degree angle.In 60 degree anilox angle, the hexagonal cell offers 15 per cent more cells on the same area.

 

Higher quantity of cells indicates a plus point concerning the ink transfer, as well as homogeneity.Diode pumped fiber optic lasers is used to engrave high line screens. Until recently, high line screen engraving could only be produced by using YAG (Yttrium Aluminum Garnet) lasers. It produces durable cell structure and excellent ink release characteristics.Since it has a low wavelength, it is able to engrave high line screens up to and above 2000 LPI.The cells are extremely smooth with a solid structure. Reports indicate an average of 10 to 15 % better ink release than YAG engraving of the same line screen and volume. Higher line screen rolls increase ink control and reduce dot gain. These high line screens have done much to increase flexo’s competitiveness with offset and gravure. It is very consistent and easy to maintain.

 

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