Method and an apparatus for fixing toner to a printing sheet or web with a laser beam

An apparatus for printing an image on a at least one of sheet and a web, comprising:

• means for charging a surface of said at least one of said sheet and web with a charge having a first polarity;
• means for separately and discretely charging a dry particulate toner with a charge having a second polarity and applying the charged toner said at least one of said sheet and web;
• means for generating a laser driving signal according to an input signal representing an image;
• means for outputting a laser beam according to the laser driving signal to melt the toner such that the toner is fixed upon the surface of said at least one of sheet and web by the laser beam;
• and
• means for charging said at least one of the sheet and web with a charge having said second polarity and for removing the toner which is not melted by said laser beam by electrostatic repulsion.

A method of printing an image on a paper, comprising the steps of:

• charging a sheet of paper with a persistent charge having a first polarity;
• separately and discretely charging a dry particulate toner with a charge having a second polarity;
• applying the charged toner uniformly over a predetermined area of said charged sheet of paper so that the toner is secured to said predetermined area by an electrostatic attraction produced by the difference between the first and second polarities;
• generating a laser driving signal according to an input signal representing an image;
• generating a laser beam so that the laser beam has an intensity which is variable in accordance with said laser driving signal;
• irradiating the toner on said sheet of paper with said laser and melting a selected portion of the toner on said the sheet of paper such that the selected portion of the toner is fixed upon the surface of said sheet of paper;
• and
• removing a remaining portion of the toner which is not melted by said melting step and which is not secured to said sheet of paper by changing the charge on said charged sheet of paper from said first polarity to said second polarity.

An apparatus for printing an image on a paper, comprising:

• toner application means for applying a dry particulate toner on a surface of a sheet of paper, said toner application means including means for inducing a first charge which persists over the entire surface of the paper and means for separately and discretely inducing a second and opposite charge in said toner, said toner being attracted to and secured to the surface of the paper by an electrostatic attraction produced by the first and second charges induced on the surface of the sheet paper and said toner, respectively;
• means for outputting a laser beam which is variable in accordance with a laser driving signal, said laser beam melting and discharging toner on said paper such that the toner which is melted is fixed to the surface of the paper by a laser beam spot incident upon the toner;
• means for generating said laser driving signal according to an input signal representing an image of varying intensity, said laser driving signal generating means producing said laser driving signal in a manner which drives said laser beam outputting means to produce an intermediate tone by area modulation of said laser beam in accordance with a pseudo grey scale;
• and
• means for removing toner which is not melted by said laser beam, said toner removing means including means for neutralizing the first charge on the paper and for inducing a charge on the surface of the sheet which is opposite to the first charge and which induces repulsion between the sheet of paper and toner which is not fixed to the sheet of paper.

An apparatus for printing an image on a sheet of paper, comprising:

• a rotatable cylindrical drum on which said sheet of paper is supported and transported continuously from a point of introduction to a point of exodus;
• paper electrification means, mounted at a first angular position juxtaposed an external surface of said drum, for inducing a persistent charge having a first polarity over an outer surface of said sheet of paper;
• toner application means, mounted at a second angular position juxtaposed the external surface of said drum, for imparting a charge having a second polarity on a dry particular toner and for dispersing the charged toner over a surface of said charge sheet;
• laser beam means for producing a laser beam and for irradiating the toner which is spread over the surface of said charged sheet in a manner to melt a selected portion of the toner and cause the selected portion to become discharged and fixed to said charged sheet;
• and
• excess toner removal means, mounted at a third angular position juxtaposed the external peripheral surface of said drum, for inducing a charge having said second polarity in said charged sheet after it has been irradiated with said laser beam, and for conditioning said charged sheet so that said charged sheet actively repels excess unmelted toner from said sheet.