Method of reducing ink electrets in gravure web printing
OwnerGene H. Wolfeinventor
Life of this patent
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Abstract
A method of gravure printing utilizing electrostatic assist in the transfer of ink from a printing cylinder to a paper web. The potential of electrets formed in dry ink on the web is minimized by operating the last impression roll and cylinder with a DC potential of the polarity opposite that of the preceding impression rolls.
Claims36
In a gravure web press having multiple image cylinders and associated impression rolls forming nips through which a web passes, the press utilizing electrostatic assist with each impression roll operated at a DC potential with respect to the associated gravure cylinder to enhance the transfer of ink from the cylinder to the web, the method of reducing the potential of the electrets in the dry ink on the printed web, which comprises:
- creating an electric field in the web by at least one impression roll on the order of 5.times.10.sup.4 volts/cm, such that electric charges are trapped in electrets in the dry ink on the printed web and
- after electrets form in dry ink on the web, subjecting the web to an electric field opposite in polarity and at least equal in magnitude to the electric field created in the web by the impression rollers and image cylinders.
In a multicolor gravure press for printing both surfaces of a web, the press having a plurality of image cylinders, each with an associated impression roll forming a printing nip, the web passing serially through the nips of the cylinders and impression rolls, the cylinders and rolls being in a first section through which the web first passes for printing one surface of the web and a second section through which the web second passes for printing the second surface of the web, at least two impression rolls of the second section having a DC electric charge for electrostatic assist in transferring ink from the cylinder to the web, the method of reducing the potential of the electrets which comprises creating an electric field in the web by the first of said charged rolls on the order of 5.times.10.sup.4 volts/cm such that an electric charge is trapped in the dry ink on the printed web, and subjecting the web to a potential at least equal in magnitude and opposite in polarity to the electric field created in the web by the impression rollers and image cylinders.
Dependencies are inferred from the claim text.