US2846333A - Method of developing electrostatic images - Google Patents

Method of developing electrostatic images Download PDF

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Publication number
US2846333A
US2846333A US54417455A US2846333A US 2846333 A US2846333 A US 2846333A US 54417455 A US54417455 A US 54417455A US 2846333 A US2846333 A US 2846333A
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Prior art keywords
image
particles
powder
surface
electrostatic
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Joseph C Wilson
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Xerox Corp
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Xerox Corp
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    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03GELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00Apparatus for electrographic processes using a charge pattern
    • G03G15/06Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/09Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush
    • G03G15/0914Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush with a one-component toner
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S430/00Radiation imagery chemistry: process, composition, or product thereof
    • Y10S430/001Electric or magnetic imagery, e.g., xerography, electrography, magnetography, etc. Process, composition, or product
    • Y10S430/104One component toner

Description

Filed Nov. 1, 1955 N'N N INVENTOR. JOSEPH C. WILSON JTZ'OJ'UVEY METHOD OF DEVELOPING ELECTROSTATIC IMAGES Joseph C. Wilson, Rochester, N. Y., assignor to Haloid Xerox Inc., a corporation of New York Application November 1, 1955, Serial No. 544,174

2 Claims. (Cl. 11717.5)

My invention relates to xerography and more particularly to an improved method of developing an electrostatic image. The principal object of my invention is to form a better image in the finished print, particularly in the solid-area portions thereof.

In xerography it is usual to form an electrostatic latent image on a surface. One method of doing this is to charge a photoconductive insulating surface and then dissipate the charge selectively by exposure to a pattern of activating radiation. Other means of forming electrostatic latent images are set forth in U. S. 2,647,464 to James P. Ebert. Whether formed by these means or any other, the resulting electrostatic charge pattern is conventionally utilized by the deposition of an electroscopic material thereon through electrostatic attraction whereby there is formed a visible image of electroscopic particles corresponding to the electrostatic latent image. Alternately, the electrostatic charge pattern may be transferred to an insulating film and the electrostatic particles deposited thereon to form the visible image. In any case, this visible image in turn may be transferred to a second surface to form a xerographic print or may be fixed directly to the photoconductive surface.

The usual process of applying the developer to the latent electrostatic image is set forth in U. S. 2,618,552 and involves the use of a finely-divided colored material, called a toner, deposited on a slightly more coarselydivided material called a carrier. This two-component developer is cascaded across the electrostatic image areas. The toner and carrier, being rubbed against each other while cascading, impart an electrostatic charge to each other. This process is known as triboelectric charging. To produce a positive of the electrostatic image a toner and carrier are selected such that the toner will be charged to a polarity opposite to that of the electrostatic image, the carrier being charged to the same polarity as the electrostatic image. When a carrier particle bearing on its surface oppositely charged particles of toner crosses an area on the image surface having an electrostatic charge, the charge on the surface exerts a greater attraction for the toner than the carrier and retains the toner in the charged area and separates it from the carrier particles. The carrier particles being oppositely charged and having greater momentum are not retained by the charged areas of the plate. When a toned carrier particle passes over a non-image, i. e. non-charged, area of the plate, the electric attraction of the carrier particle for the toner particles is suflicient to retain the toner on the carrier preventing deposition in such areas as the carrier particles momentum carries both toner and carrier past. By this mechanism the image is developed, i. e. made visible.

I have found that I can obtain superior reproductions using a single magnetic material to serve the dual function of carrier and toner. Thus, superior solid area coverage is obtained; only one material need be handled, stored and processed; and finally the developer has the unique property that either positive or negative reproductions of United States Patent fitice 2,846,333 Fatented Aug. 5, 1958 2 an original may be made with equal ease by simply applying the proper electric potential to the magnet.

In carrying out my invention, the developer, in addition to being magnetic and having the proper distribution of particle size, should be of low electrical conductivity so as to avoid objectionable discharge of the latent image by the conductivity of the developer. I have found that certain ferromagnetic materials known as ferrites have the desired properties for use in the developer particles of my invention. These materials have a spec fic resistance higher than 1,000 ohms-cm. They also have high initial permeability. Examples of such ferrites are disclosed in U. S. patents to Jacob Louis Snoek, Nos. 2,452,529; 2,452,530; and 2,452,531; all dated October 26, 1948. They have the composition, MeFe O where Me is a bivalent material such as Mn, Co, Ni, Cu, Mg, Zn or Cd. They have the same crystal structure as Fe O These ferrites are prepared by a sintering process such as that used in the ceramic .industry. The component metal oxides are ground, sintered and reduced to proper size. Examples of suitable magnetic ferrites which have been found satisfactory are the materials known as H1 and C-159, Ferramic powder, manufactured by General Ceramic Corporation, Keasby, New Jersey; Plast Iron powder, AIBAIO manufactured by Plastic Metal Division of the National Radiator Company, Johnstown, Pennsylvania; and the material known as MP25 manufactured by Magnetic Powders, Inc., Johnstown, Pennsyl- Vania; I have obtained improved results with these and other ferrites. The initial permeability of the materials used by me, so far as known to me, ranged from to 1200, the maximum permeability from 183 to 4800. Their specific resistances ranged from 1x10 to 2x10 Good results have been obtained with developers ranging in size from to 325 mesh. This is not critical and even larger particle sizes may be used. It is important, however, that an appreciable portion of the particles have a particle size of no more than about 20 microns together with another appreciable portion of the particles being of such a weight that they are movable by gravity away from the finer particles adhering to the charged areas on the plate. In general, the ratio of fines to the rest of the particles is not at all critical and may vary over a wide range. Too small a portion of fines results in excessive development time; while too high a portion is apt to cause undesirable deposition in background areas. In general, the percentage of fines to the total powder should be from about 5 to about 35% by weight with an average of about 20% by weight. This developer may be applied to the surface containing the electrostatic image by a variety of means.

Referring to the drawings, Fig. l is an elevation of a hand device for applying the devolper to the image. Fig. 2 is an end view thereof. Fig. 3 is a top plan view of apparatus for applying the developer to the image, and Fig. 4 is a section taken on line 44 of Fig. 3.

I have obtained good results with the magnetic brush construction as shown in Fig. l and 2. This brush comprises a plurality of magnets 1 which are arranged side by side with corresponding poles adjacent each other. For example, in Fig. 1 all the north poles of magnet 1 are at the upper end of the brush and the south poles at the lower end. The magnets 1 are secured in any suitable way to the soft iron pole pieces 2 and 3 adjacent the respective poles. The pole piece 3 is preferably made .with its lower portion of pointed or V-shaped cross section as shown in Fig. 2.

In using the above described magnetic applicator, the magnetic developer particles are placed in a suitable trough, for example, a metallic trough of V-shaped cross section (not shown). The lower pointed end of the brush is then dipped into the developer. Because of the magnetic nature of the developer particles, the brush picks up the developer so that the developer particles adhere thereto in the form of the bristles of a brush (whence the name). The brush is then pressed upon the surface containing the latent electrostatic image so that the said surface is just touched by the developing material.. After this, the magnet is moved back and forth on the said surface until the image is developed to completion. The fines of the developer adhere to the charged image and the larger particles are removed with the applicator.

In Figs. 3 and 4 is shown one form of apparatus for magnetically applying the developer to the surface bearing the latent electrostatic image.

A shaft 4 mounted in bearings 5 and 6 has a plurality of spaced discs 7 secured thereto at an angle to the axis of the shaft. Magnets 8 and 9 (which may be made of Alnico) have their south poles connected by pole piece 10. The north poles of the magnets are connected magnetically to the shaft 4 through soft iron members 11, 12 and 11', 12' respectively. The edges of the discs should be in close proximity to the pole piece 10. Under the discs 7 is a trough 14 arranged to support the developing powder 17 so that the discs dip therein. The top and forward portions of the pole piece may be covered by a sheet 15 of brass so as to provide a suitable bearing surface against which the plate 16 carrying the electrostatic image may be readily moved in a vertical direction. A layer of dielectric material 18, such as polyethylene terephthalate, is placed between the brass sheet 16 and pole piecelt). Any suitable means (not shown) may be used to rotate the shaft 4 and to move the plate 16.

In operation, a magnetic circuit passes from the north poles of magnets 8 and 9 through the end pieces 11, 12, and 11, 12, into the rotary shaft and discs 7. A narrow gap of high magnetic flux density exists between the pole piece 10 and the edges of the discs 7. Accordingly, when a quantity of my improved developer is placed in the trough 14 and the shaft rotated, the upwardly, moving edges of the discs 7 adjacent the plate 16 attract and pick up the magnetic carrier particles and the powder adhering thereto, and move them into the high flux density magnetic gap and over the surface of the plate. Here, the powder is attracted to the oppositely charged latent electrostatic image and separated from the carrier particles which fall by gravity back into the trough 14 when they are carried beyond the region of high flux density in the magnetic gap. As the discs are inclined at an acute angle to the axis of rotation of the shaft, the edges of the disc brush the developer across the surface of the plate. At the same time, the plate is advanced vertically past the disc as shown by the arrow in Fig. 4 so that the developer will be applied over the entire surface of the charged plate.

As the powder is used up in operation additional powder must be added from time to time. Any means of fixing the resulting developed images known to those skilled in the art, such as those set forth in U. S. 2,297,691 to Chester F. Carlson, may be used.

A reversal reproduction of the original using the developer according to my invention may be easily obtained by applying the proper electric potential to the magnetic brush. Referring to Fig. 3, there is illustrated semidiagrammatically means for accomplishing this. These means include a battery 22 or similar D.-C. power source connected through a potentiometer 21 and electrical lead to shaft 4 which in turn is electrically connected to discs 7. Grounding sheet 15 places the electrostatic field across plate 16 when switch 23 is closed. I have obtained high quality reverse images by placing on the magnetic brush an electric potential of the same polar- A ity as in the electrostatic image and about twice the magnitude.

I have found that by the use of my invention improved solid area coverage is obtained in the image over that obtained if conventional methods were to be used. Even more unusual, either a positive or negative reproduction of the original may be obtained using the same developer merely by applying the proper electric potential to the magnetic brush. Finally, by using a single material as a developer, the advantages of handling and storing a single material are obtained.

While specific details of my invention have been described, many changes may be made in the details set forth without departing from the spiritand scope of my invention as defined in the appended claims.

I claim:

1. In a process wherein an electrostatic image is developed to yield an electrostatically adhering image of electrostatically attractable material, the improvement comprising contacting magnetic field producing means with an electroscopic developer powder consisting of a ferromagnetic ferrite of from about 100 to 325 mesh and having the composition MeFe O where Me is a bivalent metal whereby said powder is formed into brush-like streamers, the particles of said powder being electrostatically charged through triboelectric contact with each other, moving said field producing means relative to a surface bearing an electrostatic image so that said streamers contact said image, the electrostatic lines of force from said image attracting oppositely electrostatically charged particles from said streamers and depositing said particles on said surface to form on said surface a deposit of said powder faithfully corresponding to said image.

2. In a process wherein an electrostatic image is developed to yield an electrostatically adhering image of electrostatically attractable material, the improvement comprising contacting magnetic field producing means with an electroscopic developer powder consisting of a ferromagnetic ferrite of from about 100 to 325 mesh and having a specific resistance higher than 1,000 ohms-cm., an initial permeability not less than about and a maximum permeability not less than 183 whereby said powder is formed into brush-like streamers, the particles of said powder being electrostatically charged through triboelectric contact with each other, moving said field producing means relative to a surface bearing an electrostatic image so that said streamers contact said image, the electrostatic lines of force from said image attracting oppositely electrostatically charged particles from said streamers and depositing said particles on said surface to form on said surface a deposit of said powder faithfully corresponding to said image.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Young et al.: Electrofax, Reprint from R. C. A. Re

view, December 1954, vol. XV, No. 4, especially pages 471, 472, 480 and 481.

Berry et al.: F erromagnetography-High Speed, Gen eral Electric Review, July 1952, pages 20, 21, 22 and 61.

Claims (1)

1. IN A PROCESS WHEREIN AN ELECTROSTATIC IMAGE IS DEVELOPED TO YIELD AN ELECTROSTATICALLY ADHEREING IMAGE OF ELECTROSTATICALLY ATTRACTABLE MATERIAL, THE IMPROVEMENT COMPRISING CONTACTING MAGNETIC FIELD PRODUCING MEANS WITH AN ELECGROSCOPIC DEVELOPER POWDER CONSISTING OF A FERROMAGNETIC FERRITE OF FROM ABOUT 100 TO 325 MESH AND HAVING THE COMPOSITION MEFE2O4, WHERE ME IS A BIVALENT METAL WHEREBY SAID POWDER IS FORMED INTO BRUSH-LIKE STREAMERS, THE PARTICLES OF SAID POWDER BEING DELECTROSTATICALLY CHARGED THROUGH TRIBOELECTRIC CONTACT WITH EACH OTHER, MOVING SAID FIELD PRODUCING MEANS RELATIVE TO A SURFACE BEARING AN ELECTROSTATIC IMAGE SO THAT SAID STREAMERS CONTACT SAID IMAGE, THE ELECTROSTATIC LINES OF FORCE FROM SAID IMAGE ATTRACTING OPPOSITELY ELECTROSTATICALLY CHARGED PARTICLES FROM SAID STREAMERS AND DEPOSITING SAID PARTICLES ON SAID SURFACE TO FORM ON SAID SURFACE A DEPOSIT OF SAID POWDER FAITHFULLY CORRESPONDING TO SAID IMAGE.
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Cited By (50)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2970299A (en) * 1955-05-20 1961-01-31 Burroughs Corp Electrographic recording with magnetic material
US2976144A (en) * 1958-10-24 1961-03-21 Rca Corp Electrophotography
US2979026A (en) * 1958-06-19 1961-04-11 Rca Corp Film viewer and reproducer
US3032009A (en) * 1958-12-05 1962-05-01 Rca Corp Electrophotographic developing apparatus
US3037478A (en) * 1957-10-23 1962-06-05 American Photocopy Equip Co Apparatus for developing electrophotographic sheet
US3045644A (en) * 1957-06-06 1962-07-24 Xerox Corp Two-color electrostatic printing apparatus
US3093039A (en) * 1958-05-12 1963-06-11 Xerox Corp Apparatus for transferring powder images and method therefor
US3103445A (en) * 1963-09-10 Method of developing an electrostatic
US3144354A (en) * 1960-03-10 1964-08-11 Keuffel & Esser Co Electrographic printer
US3152924A (en) * 1961-05-24 1964-10-13 Robertson Photo Mechanix Inc Xerographic brush
US3155531A (en) * 1958-09-23 1964-11-03 Harris Intertype Corp Meagnetic liquid developer and method for electrostatic images
US3219014A (en) * 1962-12-04 1965-11-23 Xerox Corp Mechanical shield to protect magnetic core in xerographic developing apparatus
US3278439A (en) * 1963-09-10 1966-10-11 Addressograph Multigraph Developer mix
US3287150A (en) * 1965-02-10 1966-11-22 Xerox Corp Cascade development process with two-component developer
US3306193A (en) * 1964-09-14 1967-02-28 Continental Can Co Electrostatic screen printing with magnetic conveyer and moving base electrode
US3349703A (en) * 1967-04-24 1967-10-31 Interchem Corp Electrostatic printing with two groups of particles of same composition and different size
US3472695A (en) * 1964-02-06 1969-10-14 Agfa Ag Method for forming an image in a magnetizable ink layer
US3557751A (en) * 1967-05-20 1971-01-26 Minolta Camera Kk Device for dry development in electrophotography
US3627682A (en) * 1968-10-16 1971-12-14 Du Pont Encapsulated particulate binary magnetic toners for developing images
US3771184A (en) * 1971-12-30 1973-11-13 Xerox Corp Printing apparatus
JPS494532A (en) * 1972-03-15 1974-01-16
US3859913A (en) * 1970-08-28 1975-01-14 Heller William C Jun Apparatus and process for printing
US3898170A (en) * 1972-03-21 1975-08-05 Eastman Kodak Co Electrographic carrier vehicle and developer composition
US3909258A (en) * 1972-03-15 1975-09-30 Minnesota Mining & Mfg Electrographic development process
US3929657A (en) * 1973-09-05 1975-12-30 Xerox Corp Stoichiometric ferrite carriers
US4042518A (en) * 1973-09-05 1977-08-16 Xerox Corporation Stoichiometric ferrite carriers
JPS5298530A (en) * 1976-02-16 1977-08-18 Hitachi Metals Ltd Magnetic toner
JPS54139851U (en) * 1978-03-22 1979-09-28
US4171274A (en) * 1977-07-07 1979-10-16 Xerox Corporation Alteration of tesselated magnetic particles by fracture
US4172722A (en) * 1975-04-22 1979-10-30 Ricoh Co., Ltd. Electrostatic copying method for forming multiple copies
US4176078A (en) * 1977-06-02 1979-11-27 Xerox Corporation Field dependent toner having chrome complex coated magnetic particles
US4179388A (en) * 1977-04-18 1979-12-18 Xerox Corporation Electrostatographic developer with smooth surfaced carrier
US4185916A (en) * 1977-04-08 1980-01-29 Xerox Corporation Composite developer particles and apparatus for using same
US4210448A (en) * 1975-10-21 1980-07-01 Elfotec A.G. Process for electrophotographic image formation and transfer
US4242434A (en) * 1975-11-26 1980-12-30 Ricoh Company, Ltd. Toner composition for multiple copy electrostatic photography
US4251616A (en) * 1976-01-07 1981-02-17 Sublistatic Holding Sa Magnetic toners and development process
EP0026678A1 (en) * 1979-10-01 1981-04-08 Xerox Corporation Electrostatographic printing machine
US4265993A (en) * 1978-06-28 1981-05-05 Hitachi Metals, Ltd. Magnetic toner for electrostatic images and transfer copying
US4443102A (en) * 1982-04-28 1984-04-17 Xerox Corporation Compact development system
EP0106465A2 (en) * 1982-08-31 1984-04-25 Mita Industrial Co. Ltd. Method for developing electrostatic latent images
US4451837A (en) * 1980-09-18 1984-05-29 Xerox Corporation Conductive single component magnetic toner for use in electronic printing devices
US4453820A (en) * 1979-01-25 1984-06-12 Ricoh Company, Ltd. Electrostatographic apparatus
US4487825A (en) * 1981-01-22 1984-12-11 Xerox Corporation Conductive single component electrophotographic magnetic toner
WO1985002920A1 (en) * 1983-12-19 1985-07-04 Minnesota Mining And Manufacturing Company Magnetically attractable developer material transport apparatus
US4578337A (en) * 1983-04-15 1986-03-25 Minolta Camera Kabushiki Kaisha Dry process for developing electrostatic latent images with a developer comprising two kinds of magnetic carriers having different physical structure
US4865936A (en) * 1985-11-29 1989-09-12 Hitachi Metals, Ltd. Electrophotographic reversal development method using magnetic field and specified development gap
US4876575A (en) * 1988-05-31 1989-10-24 Xerox Corporation Printing apparatus including apparatus and method for charging and metering toner particles
US5422216A (en) * 1994-03-01 1995-06-06 Steward Developer composition and method of preparing the same
US5663027A (en) * 1989-12-28 1997-09-02 Minolta Camera Kabushiki Kaisha Two-component developer comprising specific magnetic toner and specific magnetic carrier
US5798198A (en) * 1993-04-09 1998-08-25 Powdertech Corporation Non-stoichiometric lithium ferrite carrier

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2452529A (en) * 1941-10-24 1948-10-26 Hartford Nat Bank & Trust Co Magnet core
US2452530A (en) * 1943-05-15 1948-10-26 Hartford Nat Bank & Trust Co Magnetic core
US2452531A (en) * 1943-05-31 1948-10-26 Hartford Nat Bank & Trust Co Process of manufacturing a magnetic material and magnetic core
US2618551A (en) * 1948-10-20 1952-11-18 Haloid Co Developer for electrostatic images
US2725304A (en) * 1951-08-31 1955-11-29 Haloid Co Process for developing an electrostatic latent image
US2786439A (en) * 1953-06-30 1957-03-26 Rca Corp Electrophotographic developing apparatus
US2786440A (en) * 1953-06-30 1957-03-26 Rca Corp Electrophotographic developing apparatus

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2452529A (en) * 1941-10-24 1948-10-26 Hartford Nat Bank & Trust Co Magnet core
US2452530A (en) * 1943-05-15 1948-10-26 Hartford Nat Bank & Trust Co Magnetic core
US2452531A (en) * 1943-05-31 1948-10-26 Hartford Nat Bank & Trust Co Process of manufacturing a magnetic material and magnetic core
US2618551A (en) * 1948-10-20 1952-11-18 Haloid Co Developer for electrostatic images
US2725304A (en) * 1951-08-31 1955-11-29 Haloid Co Process for developing an electrostatic latent image
US2786439A (en) * 1953-06-30 1957-03-26 Rca Corp Electrophotographic developing apparatus
US2786440A (en) * 1953-06-30 1957-03-26 Rca Corp Electrophotographic developing apparatus

Cited By (57)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3103445A (en) * 1963-09-10 Method of developing an electrostatic
US2970299A (en) * 1955-05-20 1961-01-31 Burroughs Corp Electrographic recording with magnetic material
US3045644A (en) * 1957-06-06 1962-07-24 Xerox Corp Two-color electrostatic printing apparatus
US3037478A (en) * 1957-10-23 1962-06-05 American Photocopy Equip Co Apparatus for developing electrophotographic sheet
US3093039A (en) * 1958-05-12 1963-06-11 Xerox Corp Apparatus for transferring powder images and method therefor
US2979026A (en) * 1958-06-19 1961-04-11 Rca Corp Film viewer and reproducer
US3155531A (en) * 1958-09-23 1964-11-03 Harris Intertype Corp Meagnetic liquid developer and method for electrostatic images
US2976144A (en) * 1958-10-24 1961-03-21 Rca Corp Electrophotography
US3032009A (en) * 1958-12-05 1962-05-01 Rca Corp Electrophotographic developing apparatus
US3144354A (en) * 1960-03-10 1964-08-11 Keuffel & Esser Co Electrographic printer
US3152924A (en) * 1961-05-24 1964-10-13 Robertson Photo Mechanix Inc Xerographic brush
US3219014A (en) * 1962-12-04 1965-11-23 Xerox Corp Mechanical shield to protect magnetic core in xerographic developing apparatus
US3278439A (en) * 1963-09-10 1966-10-11 Addressograph Multigraph Developer mix
US3472695A (en) * 1964-02-06 1969-10-14 Agfa Ag Method for forming an image in a magnetizable ink layer
US3306193A (en) * 1964-09-14 1967-02-28 Continental Can Co Electrostatic screen printing with magnetic conveyer and moving base electrode
US3287150A (en) * 1965-02-10 1966-11-22 Xerox Corp Cascade development process with two-component developer
US3349703A (en) * 1967-04-24 1967-10-31 Interchem Corp Electrostatic printing with two groups of particles of same composition and different size
US3557751A (en) * 1967-05-20 1971-01-26 Minolta Camera Kk Device for dry development in electrophotography
US3631838A (en) * 1967-05-20 1972-01-04 Minolta Camera Kk Device for dry development in electrophotography
US3627682A (en) * 1968-10-16 1971-12-14 Du Pont Encapsulated particulate binary magnetic toners for developing images
US3859913A (en) * 1970-08-28 1975-01-14 Heller William C Jun Apparatus and process for printing
US3771184A (en) * 1971-12-30 1973-11-13 Xerox Corp Printing apparatus
JPS494532A (en) * 1972-03-15 1974-01-16
US3909258A (en) * 1972-03-15 1975-09-30 Minnesota Mining & Mfg Electrographic development process
JPS562705B2 (en) * 1972-03-15 1981-01-21
US3898170A (en) * 1972-03-21 1975-08-05 Eastman Kodak Co Electrographic carrier vehicle and developer composition
US3929657A (en) * 1973-09-05 1975-12-30 Xerox Corp Stoichiometric ferrite carriers
US4042518A (en) * 1973-09-05 1977-08-16 Xerox Corporation Stoichiometric ferrite carriers
US4172722A (en) * 1975-04-22 1979-10-30 Ricoh Co., Ltd. Electrostatic copying method for forming multiple copies
US4210448A (en) * 1975-10-21 1980-07-01 Elfotec A.G. Process for electrophotographic image formation and transfer
US4242434A (en) * 1975-11-26 1980-12-30 Ricoh Company, Ltd. Toner composition for multiple copy electrostatic photography
US4251616A (en) * 1976-01-07 1981-02-17 Sublistatic Holding Sa Magnetic toners and development process
JPS5347178B2 (en) * 1976-02-16 1978-12-19
JPS5298530A (en) * 1976-02-16 1977-08-18 Hitachi Metals Ltd Magnetic toner
US4185916A (en) * 1977-04-08 1980-01-29 Xerox Corporation Composite developer particles and apparatus for using same
US4179388A (en) * 1977-04-18 1979-12-18 Xerox Corporation Electrostatographic developer with smooth surfaced carrier
US4176078A (en) * 1977-06-02 1979-11-27 Xerox Corporation Field dependent toner having chrome complex coated magnetic particles
US4171274A (en) * 1977-07-07 1979-10-16 Xerox Corporation Alteration of tesselated magnetic particles by fracture
JPS54139851U (en) * 1978-03-22 1979-09-28
JPS6020118Y2 (en) * 1978-03-22 1985-06-17
US4265993A (en) * 1978-06-28 1981-05-05 Hitachi Metals, Ltd. Magnetic toner for electrostatic images and transfer copying
US4453820A (en) * 1979-01-25 1984-06-12 Ricoh Company, Ltd. Electrostatographic apparatus
EP0026678A1 (en) * 1979-10-01 1981-04-08 Xerox Corporation Electrostatographic printing machine
US4451837A (en) * 1980-09-18 1984-05-29 Xerox Corporation Conductive single component magnetic toner for use in electronic printing devices
US4487825A (en) * 1981-01-22 1984-12-11 Xerox Corporation Conductive single component electrophotographic magnetic toner
US4443102A (en) * 1982-04-28 1984-04-17 Xerox Corporation Compact development system
EP0106465A3 (en) * 1982-08-31 1985-11-13 Mita Industrial Co. Ltd. Method for developing electrostatic latent images
EP0106465A2 (en) * 1982-08-31 1984-04-25 Mita Industrial Co. Ltd. Method for developing electrostatic latent images
US4578337A (en) * 1983-04-15 1986-03-25 Minolta Camera Kabushiki Kaisha Dry process for developing electrostatic latent images with a developer comprising two kinds of magnetic carriers having different physical structure
WO1985002920A1 (en) * 1983-12-19 1985-07-04 Minnesota Mining And Manufacturing Company Magnetically attractable developer material transport apparatus
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