US3767477A - Method for producing oxide coated iron powder of controlled resistance for electrostatic copying systems - Google Patents

Method for producing oxide coated iron powder of controlled resistance for electrostatic copying systems Download PDF

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Publication number
US3767477A
US3767477A US00212172A US3767477DA US3767477A US 3767477 A US3767477 A US 3767477A US 00212172 A US00212172 A US 00212172A US 3767477D A US3767477D A US 3767477DA US 3767477 A US3767477 A US 3767477A
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Prior art keywords
temperature
iron powder
air
inert gas
resistance
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US00212172A
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English (en)
Inventor
Cabe J Mc
J Perlowski
R Schur
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Eastman Kodak Co
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Eastman Kodak Co
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    • 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
    • G03G9/107—Developers with toner particles characterised by carrier particles having magnetic components
    • G03G9/1075—Structural characteristics of the carrier particles, e.g. shape or crystallographic structure

Definitions

  • BEG/NS EXTERNAL HEAT/N6 STEPZ I l l l i electrostatic copying systems has a uniform oxide film, and has a resistance which can be selectively controlled between 10 and 10 ohms, when produced by a five step program of:
  • Step 1 fluidizing iron powder in air while heating to a temperature between 500 and 750F, to initiate an exothermic reaction; and thereafter to a higher peak temperature between 750 and 1600F, desirably to about 950F, principally by the heat of exothermically oxidizing iron, which can be supplemented by external heating.
  • Step 2 introducing an inert gas such as N into the air and maintaining the temperature of the iron powder essentially constant at its peak temperature.
  • Step 3 discontinuing the flow of air but maintaining fluidization by introducing a stream of inert gas such as N Ar or He while reducing the temperature to between 125 and 700F.
  • Step 4 introducing air into the inert gas and cooling the fluidized iron powder to a temperature between 25 and 50F below that at the end of step 3.
  • the temperature at the beginning of this step determines the resistance of the product, the lower the temperature the lower the resistance, and vice versa.
  • Step 5 discontinuing the inert gas but maintaining fluidization in air while cooling the iron powder to a lower temperature suitable for removal.
  • the present invention relates to a novel method for producing oxide-coated iron (including alloy steel) powder of controlled resistance, suitable for use as a carrier of toner particles in an electrostatic copying system.
  • the Prior Art Iron powder has been used in the past as a carrier for toner particles to be used in electrostatic copying systems, such as the well known xerographic process. Sometimes such iron powder is coated with a polymeric material which improves the electrostatic copying action. In such systems it is important that the iron powder have a controlled resistance which may have different values for different specific operations.
  • the carrier resistance is a primary factor in determining image development characteristics, and results ranging from full fringing to full solid-area development, and points between, can be obtained depending on the mass resistance of the iron particles. The higher the powder resistance, the more fringy is the image, and vice versa. Control to secure the resistance for any desired image characteristic has been difficult, if not impossible, in the past.
  • the iron powder required as a carrier in electrostatic copying systems has been greatly improved so as to have an extremely uniform oxide film on each particle, which is also uniform from particle to particle.
  • the resistance of the oxide coated iron particles can be controlled to have selected specific values in the range between and 10 ohms, which is uniform throughout various batches of powder; and the oxide coated iron particles also have improved ability to be uniformly coated with a polymeric material when such a coating is desired.
  • This improved iron powder is secured by oxidizing iron powder while it is continuously fluidized with gas in a reaction chamber A five step program is employed, with continuous uninterrupted fluidization, as follows: I
  • Step l fluidizing the mass in a st ream of air while heating to a temperature between 5 0()-750F., desirably to about 650F, to initiate an exothermic reaction therein; and thereafter to a higher peak temperature between 750 and 1600F, desirably to about 950F, principally by the heat of exothermically oxidizing iron, which can be supplemented by external heating.
  • Step 2 introducing an inert gas into the stream of air and maintaining the temperature of the iron powder essentially constant at its peak temperature. The time at this peak temperature determines the weight percent of oxygen pick up, but not the resistance.
  • Step 3 discontinuing the flow of air into the reaction chamber, but maintaining fluidization therein by introducing a stream of inert gas such as N Ar or He therein and reducing the temperature of the iron powder to a lower temperature between l 25 and 70W:
  • a stream of inert gas such as N Ar or He
  • Step 4 introducing air into said stream of inert gas and cooling the fluidized iron powder to a temperature between z's' 'and 50F below that at the end of step 3, and thusly continuing incremental increases of air until the temperature of powder is below its reignition point.
  • the inert gas acts to prevent reignition while the temperature is above the ignition temperature, for example above about 50O F f belowthat temperature air cali supplant the inert gas without danger of exothermic reaction.
  • Step 5 discontinuing the inert gas but maintaining fluidization by again introducing a stream of air into the reaction chamber and reducing the temperature of the iron powder to a lower temperature suitable for removing the final oxidized iron powder product from said reaction chamber.
  • the most critical point for assuring that the desired resistance will be obtained is at the-end of step 3 and the beginning of step 4.
  • the resistance can be any selected v alue yvi thin ftlie range 10 toTO ohms depentfin g on the temperatureat that point.
  • the fluidized oxidation process described above can be carried out by the apparatus described her ein, or in We reactor desEifiaTed iii UI'S'. Pat NT)? 3 mm granted Nov. 14, 1967 to John S. Perlowski (one of the present inventors) and William E. Sillick, entitled Process For Manufacturing Magnetic Oxide, and as signed to Eastman Kodak Company like the present application.
  • EH sponge iron powder (-V'MSIT-FTKYITIESHUET Standard) are loaded into a fluidized bed reaction chamber 11 to provide a bed depth-to-width ratio greater than 1.
  • the powder then isfluidized with air supplied at about 68 scf/min. by aconduit l3 and passing up through a perforate plate 15.
  • the air may be at room temperature, or may be electrically or gas heated at?) to 30O4I) O F toexpedite theprocess.
  • the reactor is externally heated by the surrounding electrical resistance heaters 19, or by radiant heaters. Temperatures are measured by a thermocouple 20.- The time in the various steps is not critical; but the longer the time at peak temperature in step 2, the greater the amount of oxidation occurring.
  • Step 1 The temperature in the reaction chamber rises gradually to 630F, atpoint A on the graph of FIG. 1 at which point an exothermic reaction of iron; with the oxygen in the air commences, and the rate of heating rapidly increases spontaneously. At 700F heating of the air at 17 is stopped. Time to point B can;
  • Step 4- At point D unheated air flowing at 25 scf/min. is again introduced into mixture with the nitrogen flowing at 68 scf/min.
  • the temperature is reduced to about 30 below the temperature at point D over a Point D is extremely critical to the process because the temperature at which the oxidizing gas mixture is first applied determines the bulk resistance of the final oxidized iron particles. Temperatures in steps 1 and 2 are less critical, as long as oxidation occurs.
  • the purpose of the added N is to prevent reignition of the iron powder at the higher temperatures at point D.
  • Step 5 The cycle is then completed by discontinuing nitrogen addition and cooling the mass, while fluidigedinunheated airat 63 s cf/min, down to room temperature or any other desired temperature, such as 150F or lower, at which it is feasible to remove the oxidized iron powder product from the reaction chamber.
  • the final product When using a 560F temperature at point D and 530F at point E, the final product has a bulk resistamze of to lgflohms. At other temperatures for point D ranging from l25F to 700F, controlled bulk resistances in the range of 10 to 10'" ohms can be obtained; the lower the temperature at D the lower the bulkrcsistance.
  • Temperature F Resistance ohms 150 10 -40 500 10 S50 10'' 600 10" 700 l0"--l0 The process steps described above produce similar results as to powder resistance when applied to other types of iron powder, such as non porous atomized iron powder, for exarrrple the 70 mesh (US, Standard) spherical steel powder sold by Whittaker Corporation (Nuclear Metals Division), West Concord, Massachusetts.
  • a resistance cell 25 comprises a 10 inches long, narrow horizontal brass trough 27 having a lead connected to one side of an electrometer 29 set to read voltage on the 30 scale (General Radio Company, type [230A Electrometer).
  • a magnetic brush 33 comprises a shouldered han- 4 59a fllsatessyl sal ma 37 one inch in diameter encased within a cylindrical brass guard 39 so that the sides and end of the magnet are enclosed.
  • the guard has a lead which is connected to a second side of the electrometer.
  • the brush carrying the attracted powder sample on its end is removed and placed vertically in the resistance cell at one end thereof, with the brush's end surface spaced 5/32 inch from the brass trough but with the iron powder 41 in contact with the trough, and with the handle in contact with and riding on the tops of the Teflon tracks.
  • the brush then is moved uniformly along the Teflon tracks (into the drawing paper) toward the other end of the cell to give the adherent powder a cylindrical shape and size which will be uniform each time a measurement is made.
  • the five step oxidizing program described in detail above is particularly advantageous for producing oxidized core carrier particles, for electrostatic copying systems, having a selected specific resistance within the range of 10 to 10 ohms which has not been possible by other methods known to applicants at this time. Moreover, extremely good reproducibility has been obtained from batch to batch, when all batches are treated on the same program.
  • Fluidization is most effective in bringing a reactive atmosphere in innermost contact with the particulate materials. More conventional approaches such as tray or continuous belt roasting would yield a broader non uniform spectrum of results because top layers are exposed to more of the atmosphere.
  • the reaction is strongly exothermic, and from a safety viewpoint an inert gas can be quickly introduced into fluidized beds to stop the reaction.
  • Step 1 fluidizing said mass in a stream of air while heating to a temperature (A) between j QQf apd 150T i l t at an. th nn onfleei a and then to a higher peak temperature (B) between 750 and lQQOF at least principally by the heat of exothermically oxidizing iron;
  • Step 2 introducing an inert gas into said stream of air and maintaining the temperature of siad iron powder essentially at said peak temperature B;
  • Step 3 discontinuing the flow of air into said reaction chamber, but maintaining fluidization therein by introducing a stream of inert gas therein and reducing the temperature of said iron powder to a temperature D between 125 and 700l-T;
  • Step 4 introducing air and cooling the fluidized iron powder to a temperature below temperature D under conditions precluding reignition of said iron powder;
  • Step 5 continuing flu'idization of said iron powder while reducing the temperature of said iron powder to a lower temperature suitable for removing the oxidized iron powder product from said reaction chamber.
  • a method in accordance with claim 1 wherein the temperature at point D is about 700F for maximum powder resistance of between 10 and 10 ohms. 4. A method in accordance with claim 1. wherein the temperature at point D is about F for minimum pqwqe r staa a .10 9hms- 5. A method in accordance with claim 1 wherein, in step 4, said fluidized iron powder is cooled to a temperature between about 25 and about 50F below temperature D.
  • step 4 said air is introduced into said stream of inert gas.
  • step 4 said air supplants said inert gas, and the cooling of fluidized'iron powder in air proceeds through steps 4 and 5 to said lower temperature suitable for removing the final oxidized product from said reaction chamber.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Developing Agents For Electrophotography (AREA)
  • Compounds Of Iron (AREA)
  • Powder Metallurgy (AREA)
US00212172A 1971-12-27 1971-12-27 Method for producing oxide coated iron powder of controlled resistance for electrostatic copying systems Expired - Lifetime US3767477A (en)

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US21217271A 1971-12-27 1971-12-27

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US (1) US3767477A (OSRAM)
JP (1) JPS5611724B2 (OSRAM)
CA (1) CA975207A (OSRAM)
DE (1) DE2262745C3 (OSRAM)
FR (1) FR2167101A5 (OSRAM)
GB (1) GB1418880A (OSRAM)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3970571A (en) * 1974-12-20 1976-07-20 Eastman Kodak Company Method for producing improved electrographic developer
US4048349A (en) * 1973-12-07 1977-09-13 National Research Development Corporation Composite metal polymer films
US4115076A (en) * 1977-05-24 1978-09-19 Bethlehem Steel Corporation Abrasive material suitable for manually blast cleaning ferrous metals prior to painting
US4223085A (en) * 1976-04-05 1980-09-16 Xerox Corporation Semi-conductive nickel carrier particles
US4252881A (en) * 1978-12-11 1981-02-24 Xerox Corporation Developer mixture
US4310611A (en) * 1979-06-29 1982-01-12 Eastman Kodak Company Electrographic magnetic carrier particles
US4318735A (en) * 1979-06-18 1982-03-09 Toda Kogyo Corp. Process for preparing magnetic particles with metallic region therein, and magnetic particles prepared by the process
US4420330A (en) * 1981-04-25 1983-12-13 Basf Aktiengesellschaft Stabilization of pyrophoric ferromagnetic acicular metal particles consisting essentially of iron
US4425383A (en) 1982-07-06 1984-01-10 Xerox Corporation Process for oxidation of carrier particles
US4894305A (en) * 1984-05-17 1990-01-16 Xerox Corporation Carrier and developer compositions generated from fly ash particles
US20210237151A1 (en) * 2020-01-30 2021-08-05 Ap&C Advanced Powders & Coatings Inc. System and method for treating additive powder

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50127641A (OSRAM) * 1974-03-27 1975-10-07
JPS53110836A (en) * 1977-03-09 1978-09-27 Konishiroku Photo Ind Co Ltd Iron powder developing carrier for electrostatic image and its manufacture as well as developing and agent image formation method
JPS5913732B2 (ja) * 1977-07-05 1984-03-31 コニカ株式会社 鉄粉現像担体及びその製造方法並びに現像剤と画像形成方法
JPS5496033A (en) * 1977-12-21 1979-07-30 Hitachi Chemical Co Ltd Developing agent for reverse development
JPS5581352A (en) * 1978-12-07 1980-06-19 Hitachi Chem Co Ltd Dry type two-component developer for reversal development
US4229234A (en) * 1978-12-29 1980-10-21 Exxon Research & Engineering Co. Passivated, particulate high Curie temperature magnetic alloys
DE3419638C2 (de) * 1984-05-25 1987-02-26 MAN Technologie GmbH, 8000 München Verfahren zur oxidativen Erzeugung von Schutzschichten auf einer Legierung
DE3727383A1 (de) * 1987-08-17 1989-03-02 Basf Ag Carrier fuer reprographie und verfahren zur herstellung dieser carrier
GB2288411B (en) * 1994-03-24 1998-04-15 Silberline Ltd Metal pigments
US5849817A (en) * 1994-03-24 1998-12-15 Silberline Limited Metal pigments

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2197931A (en) * 1936-11-06 1940-04-23 Frank C Jacobs Magnetic testing material
US2365720A (en) * 1940-02-09 1944-12-26 Johnson Lab Inc High frequency core material and core

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5010805B1 (OSRAM) * 1967-12-29 1975-04-24

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2197931A (en) * 1936-11-06 1940-04-23 Frank C Jacobs Magnetic testing material
US2365720A (en) * 1940-02-09 1944-12-26 Johnson Lab Inc High frequency core material and core

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4048349A (en) * 1973-12-07 1977-09-13 National Research Development Corporation Composite metal polymer films
US3970571A (en) * 1974-12-20 1976-07-20 Eastman Kodak Company Method for producing improved electrographic developer
US4223085A (en) * 1976-04-05 1980-09-16 Xerox Corporation Semi-conductive nickel carrier particles
US4115076A (en) * 1977-05-24 1978-09-19 Bethlehem Steel Corporation Abrasive material suitable for manually blast cleaning ferrous metals prior to painting
US4252881A (en) * 1978-12-11 1981-02-24 Xerox Corporation Developer mixture
US4318735A (en) * 1979-06-18 1982-03-09 Toda Kogyo Corp. Process for preparing magnetic particles with metallic region therein, and magnetic particles prepared by the process
US4310611A (en) * 1979-06-29 1982-01-12 Eastman Kodak Company Electrographic magnetic carrier particles
US4420330A (en) * 1981-04-25 1983-12-13 Basf Aktiengesellschaft Stabilization of pyrophoric ferromagnetic acicular metal particles consisting essentially of iron
US4425383A (en) 1982-07-06 1984-01-10 Xerox Corporation Process for oxidation of carrier particles
US4894305A (en) * 1984-05-17 1990-01-16 Xerox Corporation Carrier and developer compositions generated from fly ash particles
US20210237151A1 (en) * 2020-01-30 2021-08-05 Ap&C Advanced Powders & Coatings Inc. System and method for treating additive powder

Also Published As

Publication number Publication date
JPS5611724B2 (OSRAM) 1981-03-17
FR2167101A5 (OSRAM) 1973-08-17
DE2262745C3 (de) 1981-05-14
JPS4873358A (OSRAM) 1973-10-03
CA975207A (en) 1975-09-30
DE2262745A1 (de) 1973-07-12
DE2262745B2 (de) 1980-10-02
GB1418880A (en) 1975-12-24

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