Process

The carton gravure printing & converting process is a mean of producing paper or carton board packaging in one continuous process. It utilizes a direct transfer method of printing onto a web of substrate, followed by converting (which may involve die-cutting, creasing and embossing), and subsequent sheeting or rewinding.

Gravure printing and converting presses use printing cylinders which have been laser engraved with cells capable of retaining ink, the size and pattern of which reflect the required image. These cells are forced to transfer their ink directly onto the substrate by a combination of pressure and capillary action, so producing the printed image.

Sophisticated handling processes then transport the printed web through converting equipment (such as die-cutting, creasing and embossing units), and/or to a sheeter or web rewinder.

The presses, which are also sometimes referred to as rotogravure printing and converting presses, are used in the cigarette packaging, liquid carton, and general folding carton industries, notably.

The layout of a gravure printing and converting press follows an in-line arrangement where the required number of printing and converting units is installed along a horizontal plane.

Each print unit comprises:

• Printing cylinder: a seamless tubular sleeve or full cylinder, of either steel, aluminum, plastic, or composite material, engraved with the color dedicated pattern of the image to be printed.
• Doctor blade:  the device that removes ink from the non-engraved portions of the printing cylinder and excess ink from the engraved sections.
• Impression roller: a rubber covered sleeve mounted on a steel mandrel. Its primary purpose is to press the substrate against the printing cylinder.  
• Inking system: consisting of an ink pan, ink reservoir, and ink pump with its dedicated hose set.
• Dryer: Air chamber or device that is to dry or polymerize inks by means of hot air or UV rays; before the next downstream color is applied on the web. Dryer capacities are determined based on the required printing speed, ink type, and ink lay down volume.

During the gravure printing process, the printing cylinder rotates, while being partially immersed in ink. The engraved cells fill up with ink and as the cylinder rotates clear of the ink pan, any ink excess is removed by the doctor blade. Rotating further, the ink-filled cells are pressed against the substrate by the impression roller, each then releasing their ink. The empty cells are plunged back into the ink for the next revolution.

The pressure of the roller, combined with the capillary draw of the substrate, create the direct ink transfer from the cell to the substrate.

As the printing roller rotates back into the ink pan, the printed area of the substrate proceeds through a dryer and onto the next printing unit, for another color, varnish of coating.

Precise color-to-color registration is achieved with automatic longitudinal and lateral integrated register control systems.

After each color has been printed and any coatings applied, the web travels on for converting, which may include different processes depending on the end users' markets. These may include die-cutting, punching, creasing/scoring, embossing/de-bossing, and piling, sheeting or rewinding. These are the dedicated converting units:

• Rotary die-cutter: Rotary die-cutter : suited for high production volumes, such as tobacco and liquid packaging industries.
• Flat-bed cutter-creaser:  delivering high levels of flexibility for medium to long runs, the flat-bed converting process is mainly used for tobacco and general folding carton industries.
• Sheeter: converting the printed web into individual sheets, this unit allows further off-line processing such as hot-foil stamping, silk screen printing, offset overprinting or further die-cutting.
• Rewinder: delivering the web to a reel allows further reel-to-reel processing like adding value to cigarette soft packs and labels.

The carton gravure printing & converting process add the maximum amount of value to paper or carton board packaging in a single pass.

The ability to print strong colors by using inks such as those with high pigment or metallic contents, and to convert them at high speeds, makes the process suitable for applications which require high image quality allied to additional value adding processes such as die-cutting and embossing.

The durable nature of the printing cylinders used makes it an ideal process for very long or regularly repeating runs, delivering cost advantages over other processes.

The modular design of the BOBST LEMANIC® range of carton gravure printing & converting presses means that users not only get the equipment for their current needs, but also gain the ability to meet future market requirements. Exclusive Registron® register and quality control systems, along with integrated defect ejection, carton stacking, and palletizing, have made BOBST presses a worldwide reference amongst end users.