Electrostatic copier

Claim 2

The method of claim 1 wherein the photoconductive medium comprises photoconductive particles having an insulating coating including a colouring medium to produce the coloured photoconductive particles, characterised in that the coloured photoconductive particles are suspended in an insulating carrier liquid prior to application to the said sheet, and the said coating on the particles so produced is relatively insoluble in the said carrier liquid.

Claim 3

The method of claim 1 wherein the photoconductive medium comprises photoconductive particles having an insulating coating including a colouring medium to produce the coloured photoconductive particles, characterised in that the coloured photoconductive particles are suspended in an insulating carrier liquid prior to application to the said sheet and the said coating on the particles is relatively insoluble in the said carrier liquid, further characterised in that the selective removal of the photoconductive film from the non-image areas is effected by washing with a liquid which is a partial solvent for the said coating on the particles to render the coating tacky whereby the particles remaining on the image area bond to the sheet when the sheet surface is dried to remove the washing liquid.

Claim 4

The method of claim 1 characterised by applying to said sheet a coloured photoconductive medium to form a uniform photoconductive film over the surface of said sheet, said photoconductor being particulate and having a coating of coloured insulating medium on said particles, charging the said photoconductor electrically in the dark to hold said photoconductor to said sheet by electrostatic attraction while dark conditions are maintained, exposing the said photoconductor film to electro-magnetic waves to produce a latent image on said photoconductor film by discharging the photoconductor in non-image areas and thus terminating the electrical hold but maintaining the photoconductor in place by surface tension due to the presence of a wetting liquid, subjecting the imaged photoconductor film while still under dark conditions to a washing action to remove the said photoconductor film from the non-image areas to leave a visible image in the image areas, using as the washing liquid an insulator medium which softens the insulating medium on the photoconductive particles to fix the particles to the sheet when the washing liquid is removed, and drying the said sheet to remove the said liquid.

Claim 5

The method of claim 1 wherein the photoconductive medium comprises photoconductive zinc oxide particles having an insulating coating ground on to the zinc oxide while the coating medium is in solution and and including a colouring medium to produce the coloured insulated photoconductive particles, and characterised in that the coloured photoconductive particles are suspended in an insulating carrier liquid prior to application to the said sheet.

Claim 6

The method of claim 1 wherein the photoconductive medium comprises photoconductive zinc oxide particles coated with an insulating resin or wax or gum, by grinding in a solvent for the resin or wax or gum and including a colouring medium to produce the coloured photoconductive particles, the said coloured photoconductive particles so produced being suspended in a hydrocarbon carrier liquid prior to application to the said sheet, the said coating on the particles so produced being relatively insoluble in the said hydrocarbon carrier liquid.

Claim 7

The method of claim 1 wherein the photoconductive medium comprises photoconductive zinc oxide particles having an insulating of resin or wax or gum and including a colouring medium to produce the coloured photoconductive particles, characterised in that the coloured photoconductive particles are suspended in an insulating carrier liquid prior to application to the said sheet and the said coating on the particles is relatively insoluBle in the said carrier liquid, further characterised in that the selective removal of the photoconductive film from the non-image areas is effected by washing with a liquid which is a partial solvent for the said coating to render the coating tacky whereby the particles remaining on the image area bond to the sheet when the sheet surface is dried to remove the washing liquid.

Claim 8

The method of claim 1 characterised by applying to said sheet a coloured photoconductive medium to form a uniform photoconductive film over the surface of said sheet, said photoconductor being particulate photoconductive zinc oxide having a coating of insulating material on said particles formed by grinding the zinc oxide with a dissolved resin or wax or gum taken from the group comprising a vinyl resin, a copolymer polyvinyl resin, a paraffin wax, a chlorinated diphenyl, phenolphthalein, gum copal, or ester gum, and including a colouring medium taken from the group of Nigrosin Black, Disulphine Blue, Erythrosin B, Rose Bengal, Brilliant Green, Fuchsin, or Erioglaucine Blue, charging the said photoconductor particles so produced electrically in the dark while suspended in an insulating liquid to hold said photoconductor to said sheet by electrostatic attraction while dark conditions are maintained, exposing the said photoconductor film to electromagnetic waves to produce a latent image on said photoconductor film by discharging the photoconductor in non-image areas and thus terminating the electrical hold but maintaining the photoconductor in place by surface tension due to the presence of the insulating liquid, subjecting the imaged photoconductor film while still under dark conditions to a washing action to remove the said photoconductor film from the non-image areas to leave a visible image in the image areas, and fixing the said photoconductive image by using as the washing liquid an insulator medium which softens the coating on the photoconductive particles and then drying the said particles.