Gravure printing & converting inline process

The carton gravure printing & converting process is a means 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 its 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 minute 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-cut, 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.

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 of:

• Printing cylinder: a seamless tubular sleeve or full cylinder, of either steel, aluminum, plastic, or composite material, which is engraved with the image to be printed
• Doctor blade:  the device that removes ink from the non-engraved portions of the printing cylinder and also removes excess ink from the engraved sections.
• Impression roller: a rubber covered sleeve that is 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 holding tank, and ink pump with delivery and return ink lines.
• Drier: a hot air or ultra-violet system which dries the ink once it is on the substrate and prior to it reaching the next printing unit. Drier 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 in the ink pan where the engraved cells fill with ink. As the cylinder rotates clear of the ink pan, any excess ink is removed by the doctor blade. Further around, the cylinder is brought into contact with the substrate, which is pressed against it by the rubber covered impression roller.

The pressure of the roller, along with the capillary draw of the substrate, results in the direct transfer of ink from the cells in the printing cylinder to the surface of 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, which is normally a different color or may be a varnish or coating.

Precise color to color registration is made possible via automatic side and length register control systems.

After each color has been printed and any coatings applied, the web travels on for conversion 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. A number of units deliver these processes:

• Rotary die-cutter: suited to high volumes, such as those in the tobacco or liquid packaging industries.
• Flat-bed die-cutter:  delivering high levels of flexibility for medium to long runs, the flat bed process is mainly used in general folding carton production.
• Sheeter: converting the printed web into individual sheets, this unit allows for further 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 such as adding value to soft pack cigarettes packaging 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 they need 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.