Flexography

Known as flexographic printing or flexo, some typical applications for flexography are paper and plastic bags, milk cartons, disposable cups, and candy bar wrappers.

Flexography printing may also be used for envelopes, labels, and newspapers.

Flexography (also called surface printing), often abbreviated to flexo, is a method of printing most commonly used for packaging (labels, tape, bags, boxes, banners, etc.).A flexography print is made by creating a positive mirrored master of the required image as a 3D relief in a rubber or polymer material. A measured amount of ink is deposited upon the surface of the printing plate (or printing cylinder) using an engraved anilox roll whose texture holds a specific amount of ink. The print surface then rotates, contacting the print material which transfers the ink.

The flexible printing plate used in the final ink printing stage is light sensitive. A positive is placed over the plate, and is displayed to ultra-violet light. The plate is then 'washed' on a rotating drum in a tank of Toluene solvent, which removes the layer of material that received the ultra-violet light.

Originally flexography printing was basic in quality. Labels requiring high quality have generally been printed using the offset process until recently. In the last few years great advances have been made to the quality of flexography printing presses.

The greatest advances in flexography printing have been in the area of photopolymer printing plates, including improvements to the plate material and the method of plate creation, usually photographic exposure followed by chemical etching, though also by direct laser engraving. Digital direct to plate systems have dominated the industry recently with their better resolution and the ability to print four color process (or more) as well as offset. Some companies who make plates in house are going to trade shops to get these high quality plates. Laser-etched anilox rolls also play a part in the improvement of print quality. Full color picture printing is now possible, and some of the finer presses available today, in combination with a skilled operator, allow quality that rivals the lithographic process. One ongoing improvement has been the increasing ability to reproduce highlight tonal values, thereby providing a workaround for the very high dot gain associated with flexographic printing.

Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials. Flexographic inks, like those used in gravure and unlike those used in lithography, generally have a low viscosity. This enables faster drying and, as a result, faster production, which results in lower costs. Printing press speeds of up to 2000 FPM (600 meters per minute) are achievable now with modern technology high-end printers, like Flexotecnica .

ROTOGRAVURE :

Rotogravure (roto or gravure for short) is a type of intaglio printing process, in that it involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a copper cylinder because, like offset and flexography, it uses a rotary printing press. The vast majority of gravure presses print on reels of paper, rather than sheets of paper. (Sheet fed gravure is a small, specialty market.) Rotary gravure presses are the fastest and widest presses in operation, printing everything from narrow labels to 12-feet-wide rolls of vinyl flooring. Additional operations may be in-line with a gravure press, such as saddle stitching facilities for magazine/brochure work. Three methods of photoengraving have been used for engraving of gravure cylinders, where the cell open size or the depth of cells can be uniform or variable:

Gravure cylinders nowadays are typically engraved digitally by a diamond tipped or laser etching machine. On the gravure  cylinder, the engraved image is composed of small recessed cells (or 'dots') that act as tiny wells. Their depth and size control the amount of ink that gets transferred to the substrate (paper or other material, such as plastic or foil) via a process of pressure, osmosis, and electrostatic pull. (A patented process called "Electrostatic Assist" is sometimes used to enhance ink transfer.)A rotogravure printing press has one printing unit for each color, typically CMYK or cyan, magenta, yellow and key (printing terminology for black). The number of units varies depending on what colors are required to produce the final image. There are five basic components in each color unit: an engraved cylinder (whose circumference can change according to the layout of the job), an ink fountain, a doctor blade, an impression roller, and a dryer. While the press is in operation, the engraved cylinder is partially immersed in the ink fountain, filling the recessed cells. As the cylinder rotates, it draws ink out of the fountain with it. Acting as a squeegee, the doctor blade scrapes the cylinder before it makes contact with the paper, removing ink from the non-printing (non-recessed) areas. Next, the paper gets sandwiched between the impression roller and the gravure cylinder. This is where the ink gets transferred from the recessed cells to the paper. The purpose of the impression roller is to apply force, pressing the paper onto the gravure cylinder, ensuring even and maximum coverage of the ink. Then the paper goes through a dryer because it must be completely dry before going through the next color unit and absorbing another coat of ink. Because gravure is capable of transferring more ink to the paper than other printing processes, gravure is noted for its remarkable density range (light to shadow) and hence is a process of choice for fine art and photography reproduction, though not typically as clean an image as that of sheet fed litho or web offset litho. Gravure is widely used for long-run magazine printing in excess of 1 million copies. Gravure's major quality shortcoming is that all images, including type and "solids," are actually printed as dots. Other application area of gravure printing is in the flexible packaging sector. A wide range of substrates such as Polyethylene, Polypropylene, Polyester, BOPP etc. can be printed in the gravure press.