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Title: Humidity-insensitive ferrite developer materials
Claims: What is claimed is: 1. Humidity-insensitive electrostatographic ferrite carrier materials having an average particle diameter from between about 30 to about 1,000 microns, said carrier materials having been prepared by blending an essentially stoichiometric mixture of ferrite forming metal oxides, calcining the blended oxides in air at a temperature of up to about 2150.degree. F. for up to about 30 minutes to provide said blended oxides with a saturation magnetic moment of between about 6 to about 30 electromagnetic units per gram, milling the calcined oxides in a slurry to reduce the particle size of said calcined oxides to between about 0.8 microns and about 1.6 microns, adding to said slurry from about 0.02 to about 0.08 mole fraction of manganese oxide and about 0.001 to about 0.100 mole fraction of copper oxide based on all divalent metal oxides, adding a sodium-free deflocculant to said slurry in an amount of from about 0.5 to about 2.0 percent by weight based on the weight of said metal oxides, adding water to said slurry to provide a slurry having about 80.0 percent by weight of solids, pumping said slurry to hold/feed tanks with continuous mixing while adding a binder material to said slurry in an amount of from about 0.2 to about 1.5 percent by weight based on the weight of said metal oxides, spray-drying said slurry to form substantially spherical beads, screening said beads to obtain particles having a controlled size, firing said particles in air at a temperature of up to about 2500.degree. F. for about 4 to about 8 hours to provide them with a saturation magnetic moment of about 48 electromagnetic units per gram, deagglomerating said particles, and screening said particles to obtain ferrite particles characterized as having surface sodium in an amount of less than about 20 parts per million, surface zinc in an amount of less than about 5,000 parts per million, and a BET surface area of between about 170 cm.sup.2 /gram and about 500 cm.sup.2 /gram. 2. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said blend of oxides have been pelletized in the presence of water prior to calcining said blended oxides. 3. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 2 wherein said pelletized blend of oxides have been dried prior to calcination of said pelletized oxides. 4. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said sodium-free deflocculant is selected from the group consisting of the ammonium salt of polymethacrylic acid, pyrogallic acid, tannic acid and humic acid, and the ammonium salts of tripolyphosphate and hexametaphosphate. 5. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said sodium-free deflocculant comprises ammonium lignin sulfonate. 6. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said binder material is selected from the group consisting of polyvinyl alcohol, dextrin, lignosulfonates, and methyl cellulose. 7. Humidity-insensitive electrostatogrpahic ferrite carrier materials prepared in accordance with claim 1 wherein said binder material comprises gum arabic. 8. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said essentially stoichiometric mixture of metal oxides comprises the molar formulation (NiO.sub..33 ZnO.sub..67).sub..93 MnO.sub..05 CuO.sub..024 (Fe.sub.2 O.sub.3).sub..96. 9. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said essentially stoichiometric mixture of metal oxides comprises the molar formulation (NiO.sub.0.3 ZnO.sub.0.7).sub.0.93 MnO.sub.0.05 CuO.sub.0.02 (Fe.sub.2 O.sub.3).sub.0.99. 10. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said essentially stoichiometric mixture of metal oxides comprises the molar formulation NiO.sub.0.18 ZnO.sub.0.45 MgO.sub.0.3 MnO.sub.0.05 CuO.sub.0.06 .sup.. Fe.sub.2 O.sub.3. 11. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein said essentially stoichiometric mixture of metal oxides comprises the molar formulation MgO.sub.0.5 ZnO.sub.0.3 MnO.sub.0.05 CuO.sub.0.1 .sup.. Fe.sub.2 O.sub.3.sbsb.1.0 . 12. Humidity-insensitive electrostatographic ferrite carrier materials prepared in accordance with claim 1 wherein a coating of a polymer material has been applied to said ferrite particles. 13. An electrostatographic developer mixture comprising finely-divided toner particles electrostatically clinging to the surface of carrier particles, said carrier particles comprising humidity-insensitive ferrite beads having an average particle diameter of from between about 30 to about 1,000 microns, said carrier particles having been prepared by blending an essentially stoichiometric mixture of ferrite forming metal oxides, calcining the blended oxides in air at a temperature of up to about 2150.degree. F. for up to about 30 minutes to provide said blended oxides with a saturation magnetic moment of between about 6 to about 30 electromagnetic units per gram, milling the calcined oxides in a slurry to reduce the particle size of said calcined oxides to between about 0.8 microns and about 1.6 microns, adding to said slurry from about 0.02 to about 0.08 mole fraction of manganese oxide and about 0.001 to about 0.100 mole fraction of copper oxide based on all divalent metal oxides, adding a sodium-free deflocculant to said slurry in an amount of from about 0.5 to about 2.0 percent by weight based on the weight of said metal oxides, adding water to said slurry to provide a slurry having about 80.0 percent by weight of solids, pumping said slurry to hold/feed tanks with continuous mixing while adding a binder material to said slurry in an amount of from about 0.2 to about 1.5 percent by weight based on the weight of said metal oxides, spray-drying said slurry to form substantially spherical beads, screening said beads to obtain particles having a controlled size, firing said particles in air at a temperature of up to about 2500.degree. F. for about 4 to about 8 hours to provide them with a saturation magnetic moment of about 48 electromagnetic units per gram, deagglomerating said particles, and screening said particles to obtain ferrite particles characterized as having surface sodium in an amount of less than about 20 parts per million, surface zinc in an amount of less than about 5,000 parts per million, and a BET surface area of between about 170 cm.sup.2 /gram and about 500 cm.sup.2 /gram. 14. An electrostatographic imaging process comprising the steps of forming an electrostatic latent image on a surface and developing said electrostatic latent image by contacting said electrostatic latent image with a developer mixture comprising finely-divided toner particles electrostatically clinging to the surfaces of carrier particles, said carrier particles comprising humidity-insensitive ferrite beads having an average particle diameter from between about 30 to about 1,000 microns, said carrier particles having been prepared by blending an essentially stoichiometric mixture of ferrite forming metal oxides, calcining the blended oxides in air at a temperature of up to about 2150.degree. F. for up to about 30 minutes to provide said blended oxides with a saturation magnetic moment of between about 6 to about 30 electromagnetic units per gram, milling the calcined oxides in a slurry to reduce the particle size of said calcined oxides to between about 0.8 microns and about 1.6 microns, adding to said slurry from about 0.02 to about 0.08 mole fraction of manganese oxide and about 0.001 to about 0.100 mole fraction of copper oxide based on all divalent metal oxides, adding a sodium-free deflocculant to said slurry in an amount of from about 0.5 to about 2.0 percent by weight based on the weight of said metal oxides, adding water to said slurry to provide a slurry having about 80.0 percent by weight of solids, pumping said slurry to hold/feed tanks with continuous mixing while adding a binder material to said slurry in an amount of from about 0.2 to about 1.5 percent by weight based on the weight of said metal oxides, spray-drying said slurry to form substantially spherical beads, screening said beads to obtain particles having a controlled size, firing said particles in air at a temperature of up to about 2500.degree. F. for about 4 to about 8 hours to provide them with a saturation magnetic moment of about 48 electromagnetic units per gram, deagglomerating said particles, and screening said particles to obtain ferrite particles characterized as having surface sodium in an amount of less than about 20 parts per million, surface zinc in an amount of less than about 5,000 parts per million, and a BET surface area of between about 170 cm.sup.2 /gram and about 500 cm.sup.2 /gram, whereby at least a portion of said finely-divided toner particles are attracted to and held on said surface in conformance to said electrostatic latent image. Other info: Inventors: Berg, Allan C. (Rochester, NY, US) Fitzpatrick, John W. (Fairport, NY, US) Jones, Lewis O. (Webster, NY, US) Application Number: 626906 Filing Date: 1975-10-29 Publication_date: 1976-12-07 Assignee: Xerox Corporation (Stamford, CT) Primary Class(es): 430/120 252/62.53, 252/62.54, 252/62.6, 252/62.61, 427/469, 427/474, 428/407, 428/900, 430/111.33, 430/111.41, 430/137.1 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Hoffman, James R. Assistant Examiner: Attorney: |
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