Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/12—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic in rotating drums
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/003—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic followed by coating of the granules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/18—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic using a vibrating apparatus
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/06—Metallic powder characterised by the shape of the particles
  • B22F1/065—Spherical particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
• • 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
  • G03G9/108—Ferrite carrier, e.g. magnetite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • Y—GENERAL 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49712—Ball making

Definitions

• toner a finely-divided electroscopic material referred to in the art as toner.
• the toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image.
• This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently affixed to the support surface as by heat.
• latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, one may form the latent image by'directly charging the layer in image configuration.
• the powder image may be fixed to the photoconductive layer if elimination of the powder image transfer step is desired.
• Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.
• the toner particles are electrostatically deposited and secured to the charged portion of the latent image and are not deposited on the uncharged or background portions of the image. Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier particles and unused toner particles are then recycled.
• This technique is extremely useful for the development of line copy images.
• the cascade development process is the most widely used commercial electrostatographic development technique. A general purpose ofiice copying machine incorporating this technique is described in U.S. Pat. No. 3,099,943.
• Another technique for developing electrostatic images is the magnetic brush process as disclosed, for example, in U.S. Pat. No. 2,874,063.
• a developer material containing toner and magnetic carrier particles is carried by a magnet.
• CARRIER MATERIAL CRITERIA The criteria for selection of suitable carrier materials are extremely rigid in that these materials must exhibit a unique balance of electrostatic properties.
• the carri- -er must be capable of inducing a triboelectric charge on the toner particles opposite in polarity to that of the image being developed in order to effect deposition of the toner particles on the latent image.
• the carrier must also exhibit sufficient electrostatic attraction for the toner particles to enable the carrier to be an effective scavenger for toner particles deposited on the discharged background of the photoconductive insulating layer.
• a property common to all carrier developers is a threshold force which the image developing forces must exceed in order to effect deposition.
• the retention force of the carrier is probably a combination of coulomb attraction between the toner and carrier, along with short-range contact forces. These retention forces account for the high contrast characteristic of all carrier developers as is desirable for line copy reproduction. It contributes to relatively clean, dustfree background or non-image areas, yet permits dense image development.
• Residual charge is almost invariably present in the nominally discharged or background areas of the latent image. Relatively low as this charge density is, it may .nevertheless be non-uniform, and such irregularities will be a source of small fields capable of trapping toner particles.
• This electrostatic noise in the background areas of the latent image is one of the primary sources of unwanted background toner.
• the carrier becomes more capable of accepting loosely held toner, especially that not held by fields associated with the latent image. Removal of toner from the carrier leaves upon it an opposite, unbalanced charge that is not immediately neutralized.
• developer is inninsically its own scavenging agent.
• a suitable carrier material that it can be capable of imparting charge to the toner particles through triboelectrification and yet exhibit sufficient electrostatic charge relative to the discharged portions of the photoconductor to attract stray toner particles thereby maintaining a clean background without interfering with the attraction of the toner particles by the latent image.
• the triboelectric relationship of the toner and carrier must be such that an acceptable development of the latent electrostatic image is produced, i.e., a dense image with low background.
• An excessively high triboelectric relationship produces low density image with clean background because of the inability of the electrostatic image to attract sufficient toner particles from the carrier.
• a low triboelectric relationship produces a socalled dusty developer which will develop very low contrast electrostatic patterns but will also produce high background densities. In order to obtain a practical developer, these extremes must be avoided.
• the average triboelectric relationship for the developer decreases with time because of cumulative physical damage to the carrier. Therefore, the ideal carrier is a material exhibiting a proper triboelectric relationship with the toner, uniformity of size within close tolerances and resistance to physical damage and impaction which can impair this critical relationship.
• Deterioration occurs when portions of or the entire coating separate from the carrier core.
• the separation may be in the form of chips, flakes or entire layers and is primarily caused by fragile, poorly adhering coating materials which fail upon impact and abrasive contact with machine parts and other carrier particles.
• Carriers having coatings which tend to chip and otherwise separate from the carrier core must be frequently replaced thereby increasing expense and consuming time.
• Print deletion and poor print quality occur when carriers having damaged coatings are not replaced. Fines and grit formed from carrier disintegration tend to drift and form unwanted deposits on critical machine parts and this coating has a charge which adds to the background on the electrostatographic imaging surface.
• carrier coatings having high compressive and tensile strength either do not adhere well to the carrier core or do not possess the desired triboelectric characteristics.
• the triboelectric and flow characteristics of many carriers are adversely affected when relative humidity is high.
• the triboelectric values of some carrier coatings fluctuate with changes in relative humidity and are not desirable for employment in electrostatographic copying systems, particularly in automatic machines which require carriers having stable and predictable triboelectric values.
• Another factor affecting the stability of carrier triboelectric properties is the susceptibility of carrier coatings to toner impaction.
• spheroids of substantially uniform size and within close dimensional tolerances has heretofore proved difficult and expensive.
• steel shot has heretofore been employed as a carrier; however, the process generally employed to make such shot involves dropping molten steel into an atomized spray of cold liquid, generally water, wherein it is cooled and the internal surface tension of the molten droplet acts to spheroidize the droplet.
• This process results in particles of considerably different particle size.
• the size distribution of particles obtained by such process ranges, for example, from about 200 microns to about 2,000 microns.
• Conventional separation procedures are insufficient to obtain particles of sufficiently close tolerances.
• Special procedures can be employed, if necessary; however, these procedures are tedious and expensive. Close tolerances are required for carrier particles in order to insure uniform development of the images. It would therefore be desirable to provide a method for forming essentially spheroidal carrier particles within close tolerances.
• the present invention provides a method of forming spheroidal particles of substantially uniform size comprising cutting rods of a malleable metal or plastic into lengths substantially equivalent to the diameter of said rods, continuously causing impingement of the cut rods with a rigid surface whereby essentially spheroidal particles are obtained within close tolerances.
• rods Any malleable material which can be drawn into or formed as wire rods, threads, etc., referred to herein collectively as rods, can be employed.
• metals such as steel, copper, nickel, aluminum, brass and the like, as well as plastics such as polystyrene, polycarbonates, polysulfones, poly(methylmethacrylate), poly(phenylene oxide) and the like can be suitably employed.
• the desired malleable material can be drawn into or formed as a rod of suitable diameter for use as a carrier particle.
• carrier particles range in diameter from about 50 to about 1,000 microns. Carrier particles within such range possess sufficient density and inertia to avoid adherence to the electrostatic image during the cascade development process.
• the rods can then be out either individually or in sheaths or strands to a length essentially equal to the diameter of said rods.
• the cut particles of malleable material which are generally in the form of right cylinders having a length to diameter ratio (L/D) of about 1 are then subjected to a spheroidizing process wherein they are deformed and cold worked until the particles assume a generally spheroidal shape.
• L/D length to diameter ratio
• This can be conveniently accomplished through continuous impingement of the cut particles with a rigid surface or particle.
• Various types of apparatus can be suitably employed for this purpose, for example, ball mills, tumbling mills, vibrating mills, blast mills, centrifugal mills and the like.
• the spheroidization process of the present invention is rapid and efficient producing a high yield of spheroidal carrier particles within very close tolerances, generally of about i 0.010 inches. Surprisingly, it has been found possible to obtain extremely close tolerances of about i 0.002 inches through use of the present process.
• the spherical carrier particles of the present invention may be employed uncoated or coated with suitable film forming materials by conventional techniques to alter the triboelectric properties thereof.
• Carrier coating materials are well known and disclosed for example in U.S. Pat. Nos. 2,618,551 and 3,467,634.
• EXAMPLE I A spool of stainless steel wire, 250 microns in diameter, is fed into a wire pellet cutting machine set to cut pellets of a length equal to the diameter of the wire. The pellets are formed at the rate of about 25 kilograms per hour.
• the pellets are fed to a vibrating mill comprising a spring-mounted cylinder with dual eccentric mechanisms running horizontally on each side of the mill.
• Discrete targets in the form of ceramic balls of relatively large diameter with respect to the pellets, occupy a major portion, i.e., about 80 percent of the mill volume.
• the pellets are charged to the mill and caused to undergo vibration and rotation at high speed subject to the action of the milling media caroming off each other as well as the walls of the chamber, giving rise to repeated impingement of the pellets with the ceramic balls causing deformation and cold working of the pellets.
• the effluent from the mill is essentially spherical steel particles of uniform diameter (250 microns) with a tolerance of i 0.002 inches (50 microns).
• the carrier particles so produced are suprisingly uniformly spherical.
• the spherical particles are then admixed with a toner comprising a styrene-n-butyl methacrylate copolymer, polyvinyl butyral and carbon black prepared by the method described in U.S. Pat. No. 3,079,342, in a ratio of 1 part toner to 200 parts carrier particles obtaining a substantially uniform coating thereof on all surfaces.
• the resulting developer mixture is fed to an automatic electrostatographic copying apparatus and employed therein for a period of 25,000 cycles. All reproductions obtained during this period are uniform with essentially no background deposits or dark spots.
• EXAMPLE II Low carbon steel wire having a diameter of 250 microns is cut into pellets having a length equal to the diameter of the wire as described in Example I.
• the cut pellets are then subjected to a spheroidizing process wherein the cut pellets are caused to impinge against discrete, hardened steel targets through use of a centrifugal throwing wheel.
• the pellets are continuously recirculated via a bucket conveyor and hurled at high velocities by a high speed revolving vaned wheel against the discrete steel targets which are being continuously, freely rotated in a rotating drum.
• the resulting sphericle particles are discharged from the drum through a screening separator and collected.
• the sphericle particles exhibit a diameter of 250 microns with a tolerance of 10.002 inches (50 microns). 4
• the carrier particles obtained inthe above manner are coated with a terpolymer reaction product described in Example IV of U.S. Pat. No. 3,467,634.
• the coated carrier beads are then mixed with a toner composition comprising a styrene-n-butyl methacrylate copolymer, polyvinyl butyral and carbon black prepared by the method described in U.S. Pat. No. 3,079,342, in a ratio of 1 part toner to parts carrier and the resulting developer is placed in an automatic electrostatographic apparatus for 200,000 cycles. All reproductions obtained during this period are uniform with essentially no background deposits or dark spots.
• EXAMPLE III Employing the procedure described in Example II, pellets cut from aluminum wire 600 microns in diameter are subjected to the spheroidizing process.
• a hardened steel plate was employed as the target and was situated with respect to the high speed revolving vaned wheel so that the full velocity of the particles is concentrated on the plate.
• Spherical particles are obtained exhibiting a diameter of 600 microns with a tolerance of $0.010 inches (250 microns).
• EXAMPLE IV Employing the procedure described in Example II, pellets cut from brass wire 600 microns in diameter are subjected to the spheroidizing process.
• ellipsoidal pieces of hardened steel having a major axis of about 2-3 inches are employed as the target and undergo continuous rotation in the rotating drum.
• Ellipsoidal or spherical targets of this type are preferred because the pellets undergoing spheroidization tend not to break in their presence and tend to undergo spheroidization at a faster rate.
• Spherical particles are obtained exhibiting a diameter of 600 microns with a tolerance of 10.002 inches (50 microns).
• Method for forming electrostatographic carrier particles of substantially uniform size comprising:
• the cold working zone is a milling zone, the major portion of which contains targets in the form of rigid balls, wherein said cut rods undergo vibration and rotation at high speed in said zone subject to the repeated impingement of said balls therewith to form essentially spherical carrier particles which are thereafter discharged from said zone.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Nanotechnology (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=21807744

Family Applications (1)

Country Status (7)

Cited By (4)

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• 1970
  • 1970-03-23 US US22086A patent/US3685113A/en not_active Expired - Lifetime
  • 1970-10-08 CA CA095,136A patent/CA941211A/en not_active Expired
• 1971
  • 1971-03-19 FR FR7110751A patent/FR2087879A5/fr not_active Expired
  • 1971-03-22 NL NL7103785A patent/NL7103785A/xx unknown
  • 1971-03-22 BE BE764635A patent/BE764635A/fr unknown
  • 1971-03-23 DE DE19712114016 patent/DE2114016A1/de active Pending
  • 1971-04-19 GB GB2497571*A patent/GB1347568A/en not_active Expired

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