Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles

Definitions

• This invention relates to improved mixtures for developing electrostatic and electrophotographic images, and more particularly to a tripartite developer mixture adapted to enhance the reproduction of half tone, continuous tone and other dark-area copy by cascade development.
• the photoconductive layer of a xerographic plate is first charged electrostatically, the charged surface then being exposed under light to the subject to be copied, thereby forming a latent electrostatic image.
• the latent image is developed by subjecting the image layer to a cascading operation of developer powder to produce a powder image, which is thereafter transferred and aflixed to paper or other transfer medium.
• developer materials consist of two major components; namely, electroscopic powder in combination with a carrier.
• Developers of this type are constituted by a dry mixture of loose, movable particles of finely divided electrostatically-attractable and pigmented powder, generally called toner powder, and separate granular carrier material.
• the granular material is composed of loose particles, each of which includes a core, such as a glass bead, which is encased in a triboelectric resinous coating.
• an intermediate bonding layer for example, a liquid resin which contains a hydrochloric acid catalyst, is first applied to the core particles.
• the casing and powder particles have a triboelectric relationship of opposing polarity, the powder particles thereby being electrostatically charged through triboelectric action by mixing with the granular carrier material to adhere movably to the surface of the carrier granules.
• the powder particles are attractable by an electrostatically-charged insulating layer; whereas the casing of the carrier which is correspondingly charged to opposite polarity, is adapted to attract the charged powder and to remove them from uncharged areas of the electrostatic latent image surface when cascaded thereacross.
• Suitable two-component developer mixtures are more fully disclosed in the Patents 2,618,551 and 2,618,552, issued on November 18, 1952, and in Patent 2,638,416, issued May 12, 1953.
• a tripartite developer constituted by a conventional two-component developer in conjunction with an additive which imparts superior performance characteristics to the resultant mixture.
• existing xerographic developers are rendered more effective when modified by the incorporation of certain electrically conductive additives. Iron, cobaltic oxide, stannous oxide, zinc and ferromauganese in powdered form are among the most effective additives discovered.
• a preferred form of toner for use in conjunction with an additive in accordance with the invention is that known commercially as the A-l toner.
• a toner of this type consists of particles of pigmenting material encased in or surrounded by an insulation material which acquires by contact with the granular carrier material an electrostatic charge having a polarity opposite to that acquired by the granular material and opposite to that of the photoconductive insulating layer of the plate.
• This toner is in the particle size range of from 0.1 to 20 microns and the granular carrier material is in the size range of from 30 to 200 mesh.
• the coloring material may be carbon or other suitable pigments and the insulating material may be a rosinmodified phenol-formaldehyde resin, such as known commercially as Amberol F-71, manufactured by Rohm & Haas Company, The Resinous Products Division, Washington Square, Philadelphia 5, Pennsylvania, or asphaltum, or other suitable material.
• a rosinmodified phenol-formaldehyde resin such as known commercially as Amberol F-71, manufactured by Rohm & Haas Company, The Resinous Products Division, Washington Square, Philadelphia 5, Pennsylvania, or asphaltum, or other suitable material.
• the pigmented electroscopic powder is prepared by first micronizing the resin material, such as Amberol P -71, after which it is mixed with approximately 5% by weight of carbon black or other pigmenting material and the mixture ball-milled for about four hours in a ceramic jar with stone pellets. The mixture is then heated to a temperature of about 300 F. or to flowing viscosity and mixed for five minutes in order to encase the pigmenting particles with the Amberol F71. The mass is then permitted to cool, after which it is broken into small chunks and again micronized.
• the resin material such as Amberol P -71
• the pigmented electroscopic powder is then in condition for mixing with a granular carrier such as polymerized methyl methacrylate, having a melting point of approximately 257 F., known commercially as Lucite and manufactured by E. I. du Pont de Nemours & Company, Wilmington, Delaware, of other material either conducting or insulating, provided the particles of granular material when brought in close contact with the electroscopic powder particles acquire a charge having an opposite polarity to that of the electroscopic,
• a granular carrier such as polymerized methyl methacrylate, having a melting point of approximately 257 F., known commercially as Lucite and manufactured by E. I. du Pont de Nemours & Company, Wilmington, Delaware, of other material either conducting or insulating, provided the particles of granular material when brought in close contact with the electroscopic powder particles acquire a charge having an opposite polarity to that of the electroscopic,
• the granular carrier material is selected so that the particles acquire a charge having the same polarity as that of the photoconductive insulating layer of the plate on which the electrostatic image is produced, and an electrical attractionfor the electroscopic powder particles considerably less than that of the charged areas of the plate and somewhat greater than the discharged areas of the plate.
• the optimum relationship of the three components constituting the developer mixture is as follows: 75 grams of carrier material, 0.6 gram of toner, and 1.3 grams of powdered additive.
• the volumetric equivalent of this relationship is five parts of toner to one part of additive powder.
• the additive particles are all in powder form and are preferably of a size that will pass through a 270 mesh screen.
• the selected additive is mixed thoroughly with the standard developer to form the tripartite developer in accordance with the invention.
• a lesser ratio of additive to toner may also be used with beneficial results; however, when this ratio is reduced to one part additive to ten parts of toner, the results are appreciably poorer with respect to dark area coverage than with the above-defined optimum relationship.
• the use of more additive than established by optimum relationship will also alford good dark area coverage, but when the ratio is raised to a point at which there is one part additive to three parts toner, dark streaks are produced on the background areas of the image. too much additive causes excessive deposition of toner in background areas, while too little additive lessens the desired effect.
• the resistivity (ohms-centimeterx of five of the above-listed additives in powdered form is as follows: Iron (2.20), stannous oxide (0.14), zinc (12.7), ferromang'anese (142), copper (12.7).
• magnesium selenite which has a resistivity of l2,lO0.O 10 is ineffective as an additive.
• polyethylene in powder form has a resistivity of 28,40O.O 10
• the nature of the above-listed additives with respect to the toner material is such as to resist or inhibit coating of the additive particles by toner particles.
• the theory which accounts for the effectiveness of the selected additives in improving the development of dark areas is based on the assumption that the additive, which is electrically conductive and has a strongly negative triboelectric relationship with respect to the carrier, functions by discharging small randomly distributed portions oflarge dark areas, or by preventing carrier particles from rials (not listed supra) having relatively good conductivity fail to operate efiectively as an additive for the purpose intended.
• barium chloride a White crystalline powder of good conductivity
• A-l toner whenmixed with A-l toner and thereafter examined under a microscope will exhibit a coated appearance, the white particles of chloride being coated with fine particles of toner.
• Silver chloride will exhibit the same coated appearance when similarly prepared.
• the additives in accordance with the invention are materials in powder form (a) possessing relatively good electrical conductivity, (b) having a tribm electric relationship to the carrier component of the developer which is strongly negative, and (c) exhibiting substantial freedom from a coating action by the.
• a tripartite developer for electrostatic latent images comprising a mixture of three components, said mixture comprising a first component constituted by loose, movable particles of electrostatically-attractable toner powder, a second component constituted by granular carrier material composed of loose particles, each particle of said second component including a core and a coating bonded thereto and each particle of said second component having a triboelectr-ic relationship of opposite polarity to the toner powder, and a third component constituted by a powder composed of particles having a resistivity in powder form of no greater than.
• said third component being added to a proper xerographic developer mixture of said first and said second component in the ratio range of from 1 part of said third component to 3 to parts of said first component.
• a tripartite developer for electrostatic latent images comprising a mixture of three components said mixture comprising a first component constituted by loose, movable particles of electrostatically-attractable toner powder, a second component constituted by granular carrier material composed of loose particles, each particle of said second component including a core and a coating bonded thereto and each particle of said second component having a triboelectric relationship of opposite polarity to the powder of said first component, and a third component constituted by a powder composed of particles having a resistivity in powder form of no greater than lead acetate, a strongly negative triboelectric relationship to said carrier particles and exhibiting freedom from coating action relative to said toner particles, said first component compriisng particles in the size range of from 0.1 to 20 microns, said second component comprising particles in the size range of from 30 to 200 mesh and said third component being of an intermediate size range between said first and said second components, and said third component being added to a proper xerographic developer mixture of said first and said second component in the ratio
• a developer for electrostatic latent images comprising a three component mixture, the first component comprising xerographic toner powder, the second component comprising xerographic carrier particles and the third component comprising an additive selected from the group consisting of iron, cobaltic oxide, stannous oxide, zinc, fer-romanganese, copper, basic cupric carbonate, zinc carbonate, manganese carbonate, cupric oxide, lead acetate, zirconium, and nickel carbonate, said first component comprising particles in the size range of from 0.1 to 20 microns, said second component comprising particles in the size range of from 30 to 200 mesh and said third component being of an intermediate size range between said first and said second components, and said third being added to a proper xerographic developer mixture of said first and said second component in the ratio range of from 1 part of said third component to 3 to 10 parts of said first component whereby the dark area coverage of the developer is enhanced.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)

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Cited By (21)

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Citations (6)

• 0
  • CA CA565006A patent/CA565006A/fr not_active Expired
• 1954
  • 1954-12-23 US US477380A patent/US2919247A/en not_active Expired - Lifetime

Patent Citations (6)

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