Printing

Gravure, Flexography and Sheet-Fed Off-Set

Gravure

Gravure is a type of the intaglio printing process that involves engraving the image onto an image carrier. Gravure printing presses two large print reels of paper together rather than sheets of paper. This type of printing is the fastest and widest printing press in operation.
It is capable of transferring more ink to the paper than other printing processes, and is also noted for its remarkable density range.

A gravure printing press has one designated printing unit for each color, commonly CMYK. While the press is in operation, the engraved cylinder is partially immersed into 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,
by pressing the paper onto the gravure cylinder, ensuring maximum coverage of 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.

Flexography

Flexography is the most common type
of printing used for packaging.

A flex graphic 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 (water-based, rather than oil based) 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 exposed to ultra-violet light. The plate is then ‘washed’ on rotating drum in a tank of Toluene solvent, which removes the layer of material that received the ultra-violet light.

The benefits of flexographic printing are:

Better resolution and ability to print four color process
(or more).
Increased ability to reproduce highlight tonal values.
Uses a wider range of inks, and can print on
a variety of different materials.
Inks have low viscosity to enable faster drying,
which results in faster production and lower costs.

Sheet-Fed Off-Set Printing

Sheet-fed off-set printing is the most dominant and widely used method of printing. Large individual sheets of paper are fed into an offset printer to be printed.

The main benefit of off-set printing is its consistent image quality and respect of volume and paper costs.
The process initially starts with computer created thin metal photosensitive plates that carry the image to be printed. The plates are chemically treated so the oil-based ink will adhere to the image area, and water to the non-image area. The plate’s first contact is with rollers of
a clean solution of water and then is inked by other roller. The inked image is then transferred from the plate to
a rubber blanket, and then transferred from the rubber blanket to the paper’s surface.

The resilience of this process creates the possibility of printing on a wide variety of surfaces for large quantities. Spot colors and CMYK colors can be used with
this process.