Donor roll for scavengeless development in a xerographic apparatus

Abstract

A donor roll for the conveyance of toner in a development system for an electrophotographic printer includes an outer surface of phenolic resin. The resin is doped to a suitable conductivity to facilitate a discharge time constant thereon of less than 300 microseconds. The donor roll is used in conjunction with an electrode structure as used in scavengeless development.

We claim: 
     
       1. An apparatus for developing an electrostatic latent image, comprising: a housing defining a chamber for storing a supply of developer material therein;   a donor roll, having an outer surface . .including phenolic resin.!., mounted at least partially in the chamber of said housing, said donor roll being adapted to advance developer material to the latent image, with the discharge time constant of the surface of the donor roll being less than 300 microseconds; and   an electrode member positioned in the space between the latent image and the donor roll, the electrode member being closely spaced from the donor roll and being electrically biased to detach toner particles from the donor roll so as to form a toner powder cloud in the space between the electrode member and the latent image with detached toner particles from the toner cloud developing the latent image.   
     
     
       2. An apparatus as in claim 1, wherein the . .phenolic resin.!. .Iadd.outer layer .Iaddend.of the donor roll is doped to a conductivity greater than 10 -8  (ohm-cm) -1 . 
     
     
       3. An apparatus as in claim 1, wherein the electrode member includes a plurality of small diameter wires. 
     
     
       4. An apparatus as in claim 1, further comprising: a transport roll mounted in the chamber of the housing and being positioned adjacent the donor roll, the transport roll being adapted to advance developer material to the donor roll; and   means for rotating the transport roll and the donor roll.   
     
     
       5. An apparatus as in claim 4, further comprising: means for applying an alternating electric field between the donor roll and the transport roll to assist in transferring at least a portion of the developer material from the transport roll to the donor roll.   
     
     
       6. An apparatus as in claim 5, wherein the applying means applies an electrical field that alternates at a selected frequency ranging between about 200 Hz and about 20 kHz with a voltage less than 400 V rms . 
     
     
       7. An apparatus for developing an electrostatic latent image, comprising: a housing defining a chamber for storing a supply of developer material therein;   a donor roll mounted at least partially in the chamber of said housing, said donor roll being adapted to advance developer material to the latent image; and   an electrode member positioned in the space between the latent image and the donor roll, the electrode member being closely spaced from the donor roll and being electrically biased to detach toner particles from the donor roll so as to form a toner powder cloud in the space between the donor roll and the latent image with detached toner particles from the toner cloud developing the latent image;   wherein the electrical discharge time constant of the surface of the donor roll is less than 300 microseconds.   
     
     
       8. An apparatus for developing an electrostatic latent image on a charge-retentive surface, comprising: a housing defining a chamber for storing a supply of developer material therein; and   a donor roll mounted at least partially in the chamber of said housing, said donor roll being adapted to advance developer material to the latent image, including a conductive inner portion and a substantially non-metallic outer layer, wherein the thickness of the outer layer divided by the dielectric constant thereof is less than the distance between the donor roll and the charge-retentive surface.   
     
     
       9. An apparatus as in claim 8, wherein the thickness of the outer layer divided by the dielectric constant thereof is less than the average diameter of particles in the developer material to be applied to the charge-retentive surface. 
     
     
       10. An apparatus as in claim 8, further comprising: an electrode member including at least one wire positioned in the space between the latent image and the donor roll, the electrode member being closely spaced from the donor roll and being electrically biased to detach toner particles from the donor roll so as to form a toner powder cloud in the space between the donor roll and the charge-retentive surface with detached toner particles from the toner cloud developing the latent image; and   wherein the thickness of the outer layer divided by the dielectric constant thereof is less than the diameter of the wire. .Iadd.   
     
     
       11.  An apparatus according to claim 1, wherein said outer surface of the donor roll includes phenolic resin. .Iaddend..Iadd. 
     
     
       12.  A donor roll for use in a machine in which a voltage differential is applied between a core of the donor roll and a charging region adjacent to an outer surface of the donor roll, the donor roll comprising: a cylindrical core; and   a layer secured to said cylindrical core, wherein said layer is formed of a semiconductive material selected to control an RC circuit time constant relating to electrical response of the semiconductive layer to the applied voltage differential. .Iaddend..Iadd.13. A donor roll according to claim 12, wherein the RC circuit time constant is less than 300 microseconds. .Iaddend..Iadd.14. A donor roll according to claim 12, wherein said layer comprises a phenolic material. .Iaddend..Iadd.15. A donor roll according to claim 12, wherein said layer has a thickness of 1 to 25 mils. .Iaddend..Iadd.16. A donor roll according to claim 12, wherein said layer has a thickness of 1 to 2 mm. .Iaddend..Iadd.17. A donor roll according to claim 12, wherein said core comprises a conductive material. .Iaddend..Iadd.18. A donor roll according to claim 17, wherein said core comprises aluminum. .Iaddend..Iadd.19. A donor roll according to claim 12, wherein a thickness of said layer divided by a dielectric constant thereof is less than a distance between the donor roll and the charging region.   
     
     
        .Iaddend..Iadd.20.  A donor roll according to claim 12, wherein said layer has a thickness less than 1.65 mm. .Iaddend..Iadd.21. A donor roll according to claim 20, wherein said layer has a thickness less than 0.33 
     
     
        mm. .Iaddend..Iadd.22.  An apparatus for developing an electrostatic latent image, comprising: a housing defining a chamber for storing a supply of developer material therein; and   a donor roll having a cylindrical core and a layer secured to said cylindrical core and mounted at least partially in the chamber of said housing, wherein said layer is formed of a semiconductive material selected to control an RC circuit time constant relating to electrical response of the semiconductive layer to the applied voltage differential.   
     
     
        .Iaddend..Iadd.23.  An apparatus according to claim 22, wherein the RC circuit time constant of said layer of said donor roll is less than 300 microseconds. .Iaddend..Iadd.24. An apparatus according to claim 22, wherein said layer comprises a phenolic material. .Iaddend..Iadd.25. An apparatus according to claim 22, wherein said layer has a thickness of 1 to 25 mils. .Iaddend..Iadd.26. An apparatus according to claim 22, wherein said layer has a thickness of 1 to 2 mm. .Iaddend..Iadd.27. An apparatus according to claim 22, wherein said core comprises a conductive material. .Iaddend..Iadd.28. An apparatus according to claim 27, wherein said core comprises aluminum. .Iaddend..Iadd.29. An apparatus according to claim 22, wherein a thickness of said layer divided by a dielectric constant thereof is less than a distance between the donor roll and the latent image. .Iaddend..Iadd.30. An apparatus according to claim 22, further comprising an electrode member positioned in the space between the latent image and the donor roll, the electrode member being closely spaced from the donor roll and being electrically biased to detach toner particles from the donor roll so as to form a toner powder cloud in the space between the electrode member and the latent image with detached toner particles from 
     
     
        the toner cloud developing the latent image. .Iaddend..Iadd.31.  An apparatus according to claim 22, wherein said layer has a thickness less than 1.65 mm. .Iaddend..Iadd.32. An apparatus according to claim 31, wherein said layer has a thickness of less than 0.33 mm. 
     
     
        .Iaddend..Iadd.     An electrophotographic printing machine of the type having a developer unit adapted to develop with toner an electrostatic latent image recorded on a photoconductive member, wherein the developer unit comprises: a housing defining a chamber for storing a supply of developer material therein; and   a donor roll having a cylindrical core and a layer secured to said cylindrical core and mounted at least partially in the chamber of said housing, wherein said layer is formed of a semiconductive material selected to control an RC circuit time constant relating to electrical response to the semiconductive layer to the applied voltage differential. .Iaddend..Iadd.34. A printing machine according to claim 33, wherein the RC circuit time constant of said layer of said donor roll is less than 300 microseconds. .Iaddend..Iadd.35. A printing machine according to claim 33, wherein said layer comprises a phenolic material. .Iaddend..Iadd.36. A printing machine according to claim 33, wherein said layer has a thickness of 1 to 25 mils. .Iaddend..Iadd.37. A printing machine according to claim 33, wherein said layer has a thickness of 1 to 2 mm. .Iaddend..Iadd.38. A printing machine according to claim 33, wherein said core comprises a conductive material. .Iaddend..Iadd.39. A printing machine according to claim 38, wherein said core comprises aluminum. .Iaddend..Iadd.40. A printing machine according to claim 33, wherein a thickness of said layer divided by a dielectric constant thereof is less than a distance between the donor roll and the latent image. .Iaddend..Iadd.41. A printing machine according to claim 33, further comprising an electrode member positioned in a space between the latent image and the donor roll, the electrode member being closely spaced from the donor roll and being electrically biased to detach toner particles from the donor roll so as to form a toner powder cloud in the space between the electrode member and the latent image with detached toner particles from the toner cloud developing the   
     
     
        latent image. .Iaddend..Iadd.42.  A printing machine according to claim 33, wherein said layer has a thickness less than 1.65 mm. 
     
     
        .Iaddend..Iadd.  .  A printing machine according to claim 42, wherein said 
     
     
        layer has a thickness less than 0.33 mm. .Iaddend..Iadd.44.  A donor roll of a scavengerless xerographic apparatus comprising: a cylindrical core; and   a layer secured to said cylindrical core and formed of a semiconductive material;   wherein a discharge time constant of said layer is selected to discharge a predetermined portion of a charge on said layer within a predetermined time period. .Iaddend.