Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G7/00—Selection of materials for use in image-receiving members, i.e. for reversal by physical contact; Manufacture thereof
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/22—Processes involving a combination of more than one step according to groups G03G13/02 - G03G13/20
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/26—Electrographic processes using a charge pattern for the production of printing plates for non-xerographic printing processes

Definitions

• xerographic copying a latent image of the matter to be copied is formed as a residual electrostatic charge on a photosensitive surface.
• oppositely-charged particles of a thermoplastic powder are distributed over the surface they adhere to the charged area and are then transferred to paper, on to which they are fused by heat to form a permanent copy.
• Xerographic copying has the advantages that it is a dry process and that it gives a positive print of the original image. It has, of course, been recognised that these advantages would be equally desirable in the production of positive transparencies, which could then be used, for example, in optical projectors to assist lecturers; but in spite of this, it has not previously been possible to make transparencies by xerographic copying with the common form of xerographic apparatus, in which the photosensitive surface is a drum having an electrically conductive backing coated with vitreous selenium. Attempts to make such copies have encountered the difiiculty that heating to the temperature required to fuse the particles damages or destroys the transparent sheeting, while at lower temperatures the particles do not adhere permanently.
• charged particles are transferred from a photosensitive surface, in the manner described above, to a transparent film, which is then subjected to radiant heating sutficient to soften the particles and cause them to adhere to the film without damaging it, after which the film is heated under pressure to fuse the particles and fix them to the film.
• the use of a second heating stage, with pressure, to fuse the particles adhering to the film avoids damage to the film.
• the film must, of course, withstand heating to the temperature required to soften the particles used. I have found that the film may advantageously consist of triacetate film and that suitable thicknesses for the film are from .004 to .006". I prefer to use a thickness of 0.005".
• the temperature for softening the particles in the image-transfer stage is between 90 and 95 C. and if the fusion under pressure is carried out at a temperature of about 85 C. for a period of about 30 seconds.
• too low a temperature will result in an image with insufficient adherence to the film so that it cannot be handled without damage to the image. Too high a temperature will cause the film to begin to buckle.
• the fusing temperature can vary within a wide range provided that the period for which the temperature and pressure are maintained is suitably chosen.
• a fusing temperature of C. for a triacetate film requires not less than 25 seconds for satisfactory fusion and fixing of the image; and if the period is longer than about 45 seconds, the image may transfer partially to the pressure plate or drum.
• the period should be between 10 and 20 seconds.
• the temperature should be not less than 50 C. and not greater than 100 C. (preferably between 80 C. and C.) and the time not longer than 1 minute.
• the heating under pressure is conveniently performed" by pressing the power-carrying side of the film against a polished heated metal surface or platen, for example in a photographic dry mounting press. Alternatively, this heating under pressure may be carried out by passing the film between heated polished metal rollers. It is important to apply a sufficiently uniform pressure over the whole area of the film to prevent the film from buckling. We find that when the film is heated in this way the particles of powder fuse together as well as to the film base and that the image is thereby densified and sharpened almost to the extent that is achieved in a conventional photographic image.
• a useful feature of this method is that although the initial heating of the transparent sheet fixes the image sutficiently to permit the sheet to be transported through the xerographic copying machine and to be handled without damaging the image, nevertheless portions of the image can easily be removed by light abrasion (for example, with a rubber eraser), or by the use of a suitable solvent. This allows the user to retouch the image, i.e. remove unwanted matter before the final heating under pressure to firmly fix the image. This unwanted matter may, for example, be background speckling or may be unwanted portions of the images. Even when the image has been fixed, further additions may be made to it by hand using suitable opaque inks or paints.
• Copies made by xerography on a transparent sheet in this way may be used in various ways, for example as transparencies in an optical projector; as masters for high-speed dyeline printing; and as intermediate masters for the production of plates for photo-offset lithography.
• Melinex As an alternative to triacetate film, the transparent sheeting known as Melinex can be used.
• a method for producing positive xerographic transparencies comprising the steps of, forming a latent image of matter to be copied as a residual electrostatic charge on a photosensitive surface, developing the image by distributing oppositely-charged particles of thermoplastic powder over said surface whereupon said particles adhere to the charge areas, transferring said image-forming particles to a transparent film, heating said film and said particles suificiently to soften said particles so as to cause removable adherence thereof to said film without fusing the particles or damaging said film and thereafter further heating said image-bearing film under uniform pressure applied to substantially the whole of the film area to fuse said particles and fix them to said film whereby the image is densified and sharpened while the film is prevented from buckling.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fixing For Electrophotography (AREA)
• Combination Of More Than One Step In Electrophotography (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=9871105

Family Applications (1)

Country Status (6)

Cited By (7)

Families Citing this family (2)

• 1967
  • 1967-02-28 GB GB9392/67A patent/GB1215301A/en not_active Expired
• 1968
  • 1968-02-26 US US707943A patent/US3600210A/en not_active Expired - Lifetime
  • 1968-02-27 DE DE19681622358 patent/DE1622358A1/de active Pending
  • 1968-02-27 NL NL6802720A patent/NL6802720A/xx unknown
  • 1968-02-28 FR FR1556583D patent/FR1556583A/fr not_active Expired
  • 1968-02-28 SE SE2547/68A patent/SE325200B/xx unknown

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