Ink Transit (Gravure)
July 2001
|
Gravure industry insiders tackle key issues for optimum ink transfer and reveal equipment developments aiding the cause.
by Jessica Millward, Associate Editor
Blade basics
Though gravure printing's consistency and dependability as a printing process are well-publicized, press operators should keep a close eye on doctor blade configuration. Max Daetwyler Product Sales Manager Marty Cansler affirms, "What is often crucial for consistent print quality is the ability of the doctor blade to provide clean and even ink application during the entire print run."
As he elaborates, maintaining the blade contact area is integral to controlling such print defects as hazing and color variation. Contact area is easily affected by changes in blade contact angle and in blade pressure, so the easiest solution is to keep contact area to a minimum. To do so, Cansler suggests using a thinner tipped blade, which produces a clean wipe, and wears less on both blade and cylinder. Because of their mechanical loading devices, older presses may not be suited for this type of blade, in which case Cansler recommends a long, tapered bevel blade.
Not too dry
Dry ink within the print cylinder presents another foe to effective ink transfer. Frank Passarelli, product business manager at Bobst Schiavi, shares his company's method for keeping ink fresh: "Encapsulate the printing group area to allow for an atmospheric condition that increases the solvent concentration within the encapsulated area." This technique avoids dry ink by keeping the cylinder humid after the printing nip. Passarelli maintains in doing so, press operators will avoid solvent evaporation from the residual ink inside the engraved cells.
Not too wet
Electrostatic Speed Assist (ESA) systems, designed to enhance ink transfer, aren't exactly a new development, but it is in recent years that they have become almost ubiquitous on gravure presses. However, Steve Siler, director of engineering at Hurletron, notes while ESA is often necessary for good ink transfer, the process may not be sufficient with some substrates.
Siler explains ESA works by raising the ink surface in the cell above the surface profile of the cylinder, which facilitates contact between ink and substrate. The difficulty lies in water-based inks.
"Water-based inks leave a slightly 'damp' substrate," says Siler, "It is commonly understood that damp webs do not readily hold electrostatic charges." While power supply currents can be increased for effective ESA usage in some cases, in others, the formulation is simply too conductive to support the necessary electric field.
by Jessica Millward, Associate Editor
Blade basics
Though gravure printing's consistency and dependability as a printing process are well-publicized, press operators should keep a close eye on doctor blade configuration. Max Daetwyler Product Sales Manager Marty Cansler affirms, "What is often crucial for consistent print quality is the ability of the doctor blade to provide clean and even ink application during the entire print run."
As he elaborates, maintaining the blade contact area is integral to controlling such print defects as hazing and color variation. Contact area is easily affected by changes in blade contact angle and in blade pressure, so the easiest solution is to keep contact area to a minimum. To do so, Cansler suggests using a thinner tipped blade, which produces a clean wipe, and wears less on both blade and cylinder. Because of their mechanical loading devices, older presses may not be suited for this type of blade, in which case Cansler recommends a long, tapered bevel blade.
Not too dry
Dry ink within the print cylinder presents another foe to effective ink transfer. Frank Passarelli, product business manager at Bobst Schiavi, shares his company's method for keeping ink fresh: "Encapsulate the printing group area to allow for an atmospheric condition that increases the solvent concentration within the encapsulated area." This technique avoids dry ink by keeping the cylinder humid after the printing nip. Passarelli maintains in doing so, press operators will avoid solvent evaporation from the residual ink inside the engraved cells.
Not too wet
Electrostatic Speed Assist (ESA) systems, designed to enhance ink transfer, aren't exactly a new development, but it is in recent years that they have become almost ubiquitous on gravure presses. However, Steve Siler, director of engineering at Hurletron, notes while ESA is often necessary for good ink transfer, the process may not be sufficient with some substrates.
Siler explains ESA works by raising the ink surface in the cell above the surface profile of the cylinder, which facilitates contact between ink and substrate. The difficulty lies in water-based inks.
"Water-based inks leave a slightly 'damp' substrate," says Siler, "It is commonly understood that damp webs do not readily hold electrostatic charges." While power supply currents can be increased for effective ESA usage in some cases, in others, the formulation is simply too conductive to support the necessary electric field.
Companies Mentioned:
 |
|
|
|||
|
|
|
Chemistry for the Graphic Arts
What the Printer Should Know About Paper