WO2001088623A1 - Procede d'utilisation de supports magnetiques durs dans un processus electrographique - Google Patents

Procede d'utilisation de supports magnetiques durs dans un processus electrographique Download PDF

Info

Publication number
WO2001088623A1
WO2001088623A1 PCT/US2001/015510 US0115510W WO0188623A1 WO 2001088623 A1 WO2001088623 A1 WO 2001088623A1 US 0115510 W US0115510 W US 0115510W WO 0188623 A1 WO0188623 A1 WO 0188623A1
Authority
WO
WIPO (PCT)
Prior art keywords
carrier
ohm
image
toner
resistivity
Prior art date
Application number
PCT/US2001/015510
Other languages
English (en)
Inventor
Patrick Lambert
Eric C. Stelter
William K. Goebel
Peter S. Alexandrovich
Original Assignee
Heidelberg Digital L.L.C.
Nexpress Solutions L.L.C.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/572,989 external-priority patent/US6228549B1/en
Priority claimed from US09/572,988 external-priority patent/US6232026B1/en
Application filed by Heidelberg Digital L.L.C., Nexpress Solutions L.L.C. filed Critical Heidelberg Digital L.L.C.
Priority to CA002375345A priority Critical patent/CA2375345A1/fr
Priority to AU2001259764A priority patent/AU2001259764A1/en
Priority to JP2001584955A priority patent/JP2003533745A/ja
Publication of WO2001088623A1 publication Critical patent/WO2001088623A1/fr

Links

Classifications

    • 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
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G13/00—Electrographic processes using a charge pattern
    • G03G13/06—Developing
    • G03G13/08—Developing using a solid developer, e.g. powder developer
    • G03G13/09—Developing using a solid developer, e.g. powder developer using magnetic brush
    • 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
    • G03G9/1085—Ferrite carrier, e.g. magnetite with non-ferrous metal oxide, e.g. MgO-Fe2O3
    • 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
    • G03G9/1088—Binder-type carrier
    • 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
    • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
    • G03G9/1139—Inorganic components of coatings

Definitions

  • This invention relates to electrography and more particularly it relates to magnetic carrier particles and developers used for the dry development of electrostatic charge images.
  • an electrostatic charge image is formed on a dielectric surface, typically the surface of the photoconductive recording element. Development of this image is typically achieved by contacting it with a two-component developer comprising a mixture of pigmented resinous particles, known as toner, and magnetically attractable particles, known as carrier.
  • the carrier particles serve as sites against which the non-magnetic toner particles can impinge and thereby acquire a triboelectric charge opposite to that of the electrostatic image.
  • the toner particles are stripped from the carrier particles to which they had formerly adhered (via triboelectric forces) by the relatively strong electrostatic forces associated with the charge image. In this manner, the toner particles are deposited on the electrostatic image to render it visible.
  • a magnetic applicator also known as a magnetic brush
  • a magnetic brush which comprises a cylindrical sleeve of non-magnetic material having a magnetic core positioned therein.
  • the core usually comprises a plurality of parallel magnetic strips arranged around the core surface to present alternating north and south oriented magnetic fields. These fields project radially, through the sleeve, and serve to attract the developer composition to the sleeve outer surface to form what is commonly referred to in the art as a "brush” or "nap".
  • Either or both the cylindrical sleeve and the magnetic core are rotated with respect to each other to cause the developer to advance from a supply sump to a position in which it contacts the electrostatic image to be developed. After development, the toner depleted carrier particles are returned to the sump for toner replenishment.
  • carrier particles made of soft magnetic materials have been employed to carry and deliver the toner particles to the electrostatic image.
  • U.S. Pat. Nos. 4,546,060, 4,473,029 and 5,376,492 the teachings of which are incorporated herein by reference in their entirety, teach use of hard magnetic materials as carrier particles and also apparatus for development of electrostatic images utilizing such hard magnetic carrier particles.
  • the carrier particles comprise a hard magnetic material exhibiting a coercivity of at least 300 Oersteds when magnetically saturated and an induced magnetic moment of at least 20 EMU/gm when in an applied magnetic field of 1000 Oersteds.
  • the terms "hard” and “soft” when referring to magnetic materials have the generally accepted meaning as indicated on page 18 of Introduction To Magnetic Materials by B. D. Cullity published by Addison-Wesley Publishing Company, 1972.
  • These hard magnetic carrier materials represent a great advance over the use of soft magnetic carrier materials in that the speed of development is remarkably increased with good image development. Speeds as high as four times the maximum speed utilized in the use of soft magnetic carrier particles have been demonstrated.
  • the developer is moved in the same direction as the electrostatic image to be developed by high-speed rotation of the multi-pole magnetic core within the sleeve, with the developer being disposed on the outer surface of the sleeve. Rapid pole transitions on the sleeve are mechanically resisted by the carrier because of its high coercivity.
  • the rapid pole transitions for example as many as 467 per second at the sleeve surface when the magnetic core is rotated at a speed of 2000 revolutions per minute (rpm), create a highly energetic and vigorous movement of developer as it moves through the development zone.
  • This vigorous action constantly recirculates the toner to the sleeve surface and then back to the outside of the nap to provide toner for development.
  • This flipping action thus results in a continuous feed of fresh toner particles to the image.
  • this method provides high density, high quality images at relatively high development speeds.
  • U.S. Patent 4,764,445 discloses hard magnetic ferrite carrier particles for electrographic developing applications which contain from about 1 to about 5 percent by weight of lanthanum.
  • the speed of development in an electrographic process using conventional hard magnetic ferrite materials while higher than methods using other techniques, such as with soft magnetic carriers, is limited by the resistivity of such ferrite materials.
  • the patent discloses that addition of lanthanum to the hard magnetic ferrite crystal structure in the disclosed amounts results in a more conductive magnetic ferrite particle, yielding greater development efficiency and/or speed of development.
  • U.S. Patent 4,855,206 discloses adding neodymium, praseodymium, samarium, europium, or mixtures thereof, or a mixture of one or more of such elements and lanthanum, to a hard magnetic ferrite material to increase conductivity.
  • U.S. Patent 5,795,692 discloses a conductive carrier composition having a magnetic oxide core which is said to be coated with a layer of zinc metal that is the reaction product of zinc vapor and the magnetic oxide.
  • U.S. Patent 5,268,249 discloses magnetic carrier particles with a single-phase, W- type hexagonal crystal structure of the formula MFe ⁇ 6 Me 2 O 27 where M is strontium or barium and Me is a divalent transition metal selected from nickel, cobalt, copper, zinc, manganese, magnesium, or iron.
  • U.S. Patent 5,532,096 discloses a carrier which has been coated on the surface thereof with a layer obtained by curing a partially hydrolyzed sol obtained from at least one alkoxide selected from the group consisting of silicon alkoxides, titanium alkoxides, aluminum alkoxides, and zirconium alkoxides.
  • the disclosed carriers coated with such layer are said to be more durable in comparison to carriers coated with conventional resin coatings, such as those prepared using silicone, acrylic and styrene-acrylic resins.
  • image carrier pick-up or "l-CPU”.
  • l-CPU image carrier pick-up
  • the present invention concerns a method for development of an electrostatic image comprising contacting the image with a development system including at least one magnetic brush comprising: (a) a rotating magnetic core of a pre-selected magnetic field strength,
  • an electrographic developer composition comprising (i) charged toner particles, and (ii) oppositely charged hard magnetic carrier particles with a resistivity of from about 1x10 10 ohm-cm to about 1x10 5 ohm-cm and a (Q/m) carrier of greater than about 1 ⁇ C/g, the developer composition being disposed on the shell and in contact with the image, the method resulting in a carrier deposition density on the image of less than about 0.01 g/in 2 .
  • the invention concerns a method for development of an electrostatic image comprising contacting the image with at least one magnetic brush comprising (a) a rotating magnetic core of a pre-selected magnetic field strength, (b) an outer nonmagnetic shell disposed about the rotating core, and (c) an electrographic developer composition disposed on the shell and in contact with the image.
  • the developer composition comprises charged toner particles and oppositely charged carrier particles, the carrier particles comprising a hard magnetic material having a crystal structure substituted with at least one multi-valent metal of the formula M n+ , wherein n is an integer of at least 4.
  • the carrier particles comprise a hard magnetic ferrite material having a single-phase hexagonal crystal structure and represented by the formula:
  • P is selected from strontium, barium, or lead;
  • M is at least one metal selected from antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium, and mixtures thereof; and x is less than about 0.6.
  • the invention concerns a method for development of an electrostatic image comprising contacting the image with at least one magnetic brush comprising (a) a rotating magnetic core of a pre-selected magnetic field strength, (b) an outer nonmagnetic shell disposed about the rotating core, and (c) an electrographic developer composition disposed on the shell and in contact with the image, the developer composition comprising charged toner particles and oppositely charged carrier particles.
  • the carrier particles comprise (1) a core of a hard magnetic material having an outer surface and (2) a metal oxide composition disposed on the outer surface of the core represented by the formula On/ 2 wherein M is at least one multi-valent metal represented by M n+ , with n being an integer of at least 4.
  • the outer surface further defines a transition zone which extends from the outer surface and into the core of the hard magnetic material where the hard magnetic material has a crystal structure within the transition zone substituted with ions of the at least one multi- valent metal ion of formula M n+ as previously described.
  • the invention in another aspect, relates to a method for development of an electrostatic image comprising contacting the image with at least one magnetic brush comprising (a) a rotating magnetic core of a pre-selected magnetic field strength, (b) an outer nonmagnetic shell disposed about the rotating core, and (c) an electrographic developer composition disposed on the shell and in contact with the image, the developer composition comprising charged toner particles and oppositely charged carrier particles.
  • the carrier particles comprise a hard magnetic ferrite material having a single-phase hexagonal crystal structure represented by the formula:
  • P is selected from strontium, barium, or lead; and y is less than 0.1.
  • carrier particles for use in the development of electrostatic latent images which carriers comprise the hard magnetic ferrite material substituted with lanthanum as described in the preceding paragraph.
  • Fig. 1 is a graph of toner charge-to-mass (Q/m) versus toner concentration for a developer used in a method according to the present invention, the figure showing operating windows for three different toner particle sizes and illustrating an operating region for each which can yield desirable electrographic system performance.
  • Fig. 2 is a graph of both relative development efficiency (as defined hereinafter) and l-CPU data obtained in connection with Examples 5-7 and Comparative Example B discussed hereinafter.
  • Fig. 3 is a graph of both relative development efficiency (as defined hereinafter) and l-CPU data obtained in connection with Examples 8-10 and Comparative Example C discussed hereinafter.
  • Fig. 4 is a graph of resistivity (in ohm-cm) versus firing temperature for carriers prepared and evaluated in connection with Examples 11-13 and Comparative Example D discussed hereinafter.
  • Fig. 5 is a graph of l-CPU (grams deposited) versus (Q/m) ca rri e r data relating to Examples 43-46 and is discussed at the end of Example 46 hereinafter.
  • Fig. 6 is a graph of Mean Relative DE data versus toner particle size relating to Examples 43-52 and is discussed at the end of Example 52 hereinafter.
  • Fig. 7 is a graph of Mean (Q/m) t0 n e r data versus toner particle size relating to
  • Fig. 8 is a graph of Relative DE data versus Log e of (carrier resistivity/toner particle size) relating to Examples 43-52 and is discussed at the end of Example 52 hereinafter.
  • Fig. 9 is a graph of l-CPU (weight in grams) versus a function representing acquired carrier charge (in terms of ⁇ C/g) relating to Examples 43-52 and Comparative Example E, and is discussed at the end of Example 52 hereinafter.
  • the use of "hard” magnetic materials as carrier particles increases the speed of development dramatically when compared with carrier particles made of "soft” magnetic particles.
  • the preferred ferrite materials disclosed in these patents include barium, strontium and lead ferrites having the formula MO.6Fe 2 O 3 wherein M is barium, strontium or lead.
  • a preferred ferrite is strontium ferrite. These materials have a single-phase, hexagonal crystal structure. While the speed with which development can be carried out is much higher than prior techniques, they are limited by the resistivity of the above described ferrite materials which have the necessary magnetic properties for carrying out the development method.
  • development efficiency in percent is defined as the potential difference between the photoreceptor in developed image areas before and after development divided by the potential difference between the photoreceptor and the brush prior to development times 100. For example, in a charged area development configuration, if the photoreceptor film voltage is -250 volts and the magnetic brush is -50 volts, the potential difference is -200 volts prior to development.
  • the development efficiency is (-100 volts divided by -200 volts) times 100, which gives an efficiency of development of 50 percent. It can be readily seen that as the efficiency of the developer material increases the various parameters employed in the electrostatographic method can be altered in accordance therewith. For example, as the efficiency increases the voltage differential prior to development can be reduced in order to deposit the same amount of toner in image areas as was previously done at the lower efficiency. The same is true with regard to the exposure energy level employed to impart the latent electrostatic image on the photoreceptor film. The speed of the development step of the procedure can be increased as the efficiency increases since more toner can be deposited under the same conditions in a shorter period of time. Thus, higher development efficiency permits adjustment of the various parameters employed in the electrostatic process to result in savings in both energy and time.
  • the efficiency of development when employing hard magnetic carriers is limited by the resistivity of the materials themselves. For example, because these materials have a resistivity of approximately 1x10 11 ohm-cm, therefore, the efficiency typically obtained is approximately 50 percent.
  • the electrophotographic printing industry is presently interested in developing equipment with higher speed (pages per minute - ppm) and higher image quality. These two performance goals require materials, i.e., developer compositions, with characteristics that are in contraposition to each other. Higher image quality is associated with smaller toner particle size. Smaller toner size generally connotes reduced development efficiency (DE), and as such, limits machine speed. While adjustment of hardware operating conditions such as core speed, shell speed, gap setting and toning bias provide considerable latitude for high speed/high quality copying/printing, the material characteristics of the carrier component of the developer may also be manipulated.
  • DE development efficiency
  • l-CPU depends on carrier charge.
  • the carrier charge is opposite in polarity to the toner charge.
  • the carrier can be developed into background areas of the image, usually at a highest concentration in areas immediately adjacent to toned image areas where fringe electric fields are strongest.
  • the carrier acquires sufficient charge by conduction of such charge from the shell within the toning nip, the carrier can actually develop into image areas on the photoconductor.
  • a negative-charging toner is considered in the following discussion. Assuming charge neutrality for the toner and carrier particles, when the externally applied electric field (E) is zero, the carrier charge and the toner charge in the developer composition may be related to toner concentration (TC) according to the following Equation (1):
  • Equation (2) the initial carrier charge to mass ratio (in ⁇ C/g) can be stated by the following Equation (2):
  • Equation (3) Equation (3)
  • Q Ct /M c is the carrier charge to mass as a function of time;
  • Q Ci /M c is the initial carrier charge to mass as described above;
  • the rate constant k is 1/p ⁇ , in units of sec "1 ;
  • x signifies multiplication (not a variable);
  • t is the residence time in the toning nip in seconds; and the maximum final carrier charge is given by Q cf /M c .
  • Equation (3) quantitatively p is the resistivity of the developer composition and ⁇ is the dielectric constant of the developer composition.
  • the developer resistivity p can be measured as described in Examples 43-52 hereinafter.
  • the dielectric constant ⁇ is affected by the volume in the developer composition that is occupied by the toner. Increasing the toner particle size will displace carrier particles and correspondingly result in a proportionate decrease the dielectric constant of the developer composition. Due to this effect, ⁇ ⁇ 1/ D ⁇ 3 , where D ⁇ is the average particle size (diameter) of the toner particles.
  • the maximum carrier charge to mass ratio Q Cf /M c depends on the voltage difference between the electrostatic image on the photoconductive surface and the toning station shell sleeve. For a 400 volt potential difference with "bare carrier" (no toner), Q Cf /M c can be reasonably assumed to be about -2 ⁇ C/g. If toner is present, the potential difference between the shell sleeve and photoconductive surface at the trailing edge (exit) of the toning nip area is decreased by the charge of toner particles which develop into the image. The fractional development efficiency - DE - can be approximated as the fraction of the initial toning potential difference removed by development of the toner, and equals the development efficiency in percent divided by 100.
  • Example E hereinafter is used with the above-described model and confirms that l-CPU depends upon the charge that the carrier acquires in the toning nip area.
  • the present invention further relates to material and hardware parameters that provide operating spaces for higher development efficiency without increased l-CPU.
  • the drive to higher quality and higher speed systems necessitates a decrease in toner particle size from which a decrease in development efficiency follows.
  • the carrier conductivity should be further increased (in other words, the carrier's resistivity should be decreased) as the toner size decreases.
  • the enhancement in development rate should occur without noticeable l-CPU.
  • the toner size/concentration/charge space as illustrated by Fig. 1 is unwieldy and difficult to generalize over all anticipated operating ranges.
  • a table could be set up with data sets to indicate, for example, using each of the three toner sizes shown in Fig. 1 , the resistivity range required to maintain development efficiency along with the preferred range for limited l-CPU.
  • Data generally shows that the developers exhibiting the highest l-CPU have the lowest calculated (Q/m) carr i er as determined by charge neutrality. For example, as the toner concentration increases, the toner charge decreases by a small percentage, however, the net (Q/m) carr i er can double or triple in value. The higher the net (Q/m) carr i er the more difficult it is to induce the charge reversal of the carrier leading to l-CPU. As one goes to a smaller toner particle size, the increased toner Q/m can reduce l-CPU, but the lower toner concentration could also induce l-CPU.
  • (Q/m) ca rr i er be maintained at greater than about 1 ⁇ C/g, preferably greater than about 2 ⁇ C/g, more preferably greater than about 3 ⁇ C/g, and most preferably greater than about 4.0 ⁇ C/g.
  • the (Q/m) carr i er parameter can be controlled by adjusting the level of toner in the developer composition, as illustrated for example in Examples 43-52 hereinafter.
  • the present invention seeks to at least maintain development efficiency as toner size decreases, and therefore conductivity of the carrier should be increased proportionally, while (Q/m) carrier should be kept high, such as a value greater than about 1 ⁇ C/g as previously described.
  • the carrier resistivity When the carrier resistivity is selected to be within the foregoing range, it will generally result in a developer composition resistivity of desirably from about 1x10 12 ohm-cm to about 1x10 5 ohm-cm, preferably 1x10 10 ohm-cm to 1x10 7 ohm-cm.
  • the developer resistivity will generally be very similar to the carrier resistivity, since the developer composition is largely carrier.
  • Electrographic processes can operate at a process speed (which is defined as the speed at which the dielectric surface bearing the charge image thereon is passed through the development zone) of at least about 5 inches/sec, and typically high volume printers can operate at a speed of from about 110 pages per minute (PPM) to 180 PPM and up, which corresponds to a process speed of from about 15 to about 30 inches/sec, and a process speed of from about 15 to about 50 inches/sec would be preferred.
  • a process speed which is defined as the speed at which the dielectric surface bearing the charge image thereon is passed through the development zone
  • typically high volume printers can operate at a speed of from about 110 pages per minute (PPM) to 180 PPM and up, which corresponds to a process speed of from about 15 to about 30 inches/sec, and a process speed of from about 15 to about 50 inches/sec would be preferred.
  • Carriers with a resistivity toward the lower part of the foregoing ranges i.e., a resistivity of less than about 1x10 7 ohm- cm, i.e., from about 1x10 7 ohm-cm to about 1x10 5 ohm-cm, would be particularly advantageous for use in electrographic processes operating at relatively high process speeds. This is due to the fact that a higher process speed results in a proportional decrease in the residence time of carrier within the toning nip area, wherein residence time (in seconds) is defined as the toning nip width (in inches) divided by the process speed (in inch/sec).
  • the process speed can be increased to reduce the residence time of carrier in the toning nip area and obtain a decrease in l-CPU.
  • increasing process speed by a factor of ten such as from 5 inch/sec to 50 inch/sec, would allow one to utilize a carrier with a resistivity reduced by a factor of ten, i.e., for example, from 1x10 6 to 1x10 5 ohm-cm, and obtain similar l-CPU performance.
  • the geometry of the toning nip area can be altered, for example, so as to decrease the width of the toning nip area. This could be achieved, for example, by placing the photoconductive surface on a cylindrical drum, or if the surface is already on a drum, then by reducing the diameter of such drum. A reduction in the toning nip width by a factor of two, would similarly translate to a reduction in resistivity for the carrier by a factor of two as well.
  • l-CPU can be limited such that, in terms of deposition density for carrier (as described in Examples 43-52 hereinafter), such deposition density is desirably less than about 0.01 g/in 2 , preferably less than about 0.001 g/in 2 , and more preferably less than about 0.0001 g/in 2 .
  • the present invention contemplates use of certain hard magnetic materials as a carrier in an electrographic process, wherein the carrier has increased conductivity relative to conventionally used hard magnetic materials.
  • the carrier is a hard magnetic material substituted with multi-valent metals to increase the conductivity of the carrier.
  • a conductive metal oxide composition is placed on a core of a hard magnetic material.
  • the present invention in one embodiment, contemplates use of carriers substituted with an effective amount of at least one multi-valent metal ion into the crystalline lattice of a hard magnetic material, preferably a hard magnetic ferrite having a hexagonal crystal structure, the metal ion corresponding to the formula M n+ , where n is an integer of at least 4, i.e, 4, 5, or 6, so as to reduce the resistivity of the material while still maintaining desirable magnetic properties.
  • the resistivity of hard hexagonal ferrite carrier materials can be reduced from approximately 1x10 11 to approximately 1x10 5 ohm-cm, and preferably the resistivity and (Q/m) ca rr ie r are within the ranges specified hereinabove for inhibiting l-CPU, without affecting the high magnetic properties of the ferrite material.
  • the mechanism by which the resistivity of the ferrite materials are decreased is due to substitution of the above-described multi-valent metal ion into the iron lattices of the hexagonal ferrite crystal structure, rather than by replacement of Sr 2* Ba 2+ , or Pb 2+ in the sub-lattice or interstitially in the hexagonal ferrite lattice.
  • the M n+ multi-valent metal ion substituents force charge compensation in the ferric (Fe 3+ ) lattice; i.e., ferrous (Fe 2+ ) cations form.
  • the Fe 2+ /Fe 3+ charge couple thereby created provides a semi-conductive electronic pathway, resulting in ferrite compositions of higher conductivity.
  • a hard magnetic ferrite material doped with the M n+ multi- valent metal ion can be represented by the formula:
  • P is selected from strontium, barium, or lead;
  • M is selected from at least one of antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium, or mixtures thereof; and x is less than about 0.6.
  • P is selected from either strontium or barium, and more preferably strontium due to cost, magnetic properties, and environmental concerns.
  • M is preferably selected from silicon, zirconium, tin, or titanium due largely to cost and availability concerns.
  • the amount of the multi-valent metal ion employed is preferably sufficient to yield a value for x of less than about 0.3, and more preferably less than about 0.2 due to l-CPU concerns. If the multi-valent metal ion is employed in an amount greater than 0.6, the conductivity does not significantly increase relative to ferrites containing a lesser amount of the multi-valent metal ion.
  • a further advantage associated with the hard magnetic ferrites of the present invention is that by conducting a relatively light doping of the multi-valent metal ion into the ferrite material, one can see significant improvement in development efficiency, as is exemplified by the examples hereinbelow, as well as in copending U.S. Patent Application Serial No. 09/572,988, incorporated herein by reference in its entirety. Also, with respect to preparation of such hard magnetic materials, it is believed that substitution of such metal ions into the iron lattice offers processing advantages relative to a substitution into the Sr 2+ Ba 2+ , or Pb 2+ sub-lattice.
  • the amount substituted should be sufficient to increase the conductivity at least about one order of magnitude, i.e., a reduction in resistivity of at least about 1x10 1 ohm- cm.
  • the amount of metal substituted should be sufficient to give an x value of from about 0.01 to about 0.6, and preferably an amount sufficient to yield an x value of from about 0.02 to less than about 0.3, and more preferably an amount sufficient to yield an x value of from about 0.03 to less .than about 0.2 is employed.
  • the amount of the M n+ multi-valent metal ion substituted into the crystalline lattice be limited such that the resulting structure comprises substantially a single- phase hexagonal crystalline structure. While the amount of M n+ multi-valent metal ion employed can vary somewhat depending upon the M ⁇ + multi-valent metal ion and sintering conditions utilized in the preparation of the ferrite particles, the amount of the M n+ multi-valent metal ion can generally be added in an amount of up to about 10 percent by weight of the ferrite material and still maintain sufficiently high magnetic properties to tightly adhere the developer nap to the sleeve of the developer station.
  • additional phases in the PO/MO n 2 /Fe 2 O 3 phase diagram can form.
  • the presence of a minor amount, i.e., preferably less than 50 wt % based on total weight of carrier, of such additional phases does not adversely impact the beneficial properties of a substituted hexagonal crystal structure as previously described.
  • the preparation of hard magnetic materials generally, and hard, hexagonal crystal structure ferrites (Ba, Sr or Pb) in particular, are well documented in the literature. Any suitable method of making the hard magnetic particles may be employed, such as the methods disclosed in U.S. Pat. Nos.
  • Hard magnetic materials containing at least one multi-valent metal ion substituted into the crystalline lattice as described hereinabove can be prepared in a similar manner as described in the preceding paragraph by adding a source of the multi-valent metal ion to the formulation so that the metal ion is doped into the crystalline structure.
  • the hard magnetic material to be prepared is a hard magnetic strontium ferrite containing from about 1 to about 5 percent by weight of the multi-valent metal in its oxide or an oxide precursor form
  • from about 8 to 12 parts SrCO 3 about 1 to 5 parts of a source of the metal ion and 85 to 90 parts of Fe 2 O 3 are mixed with a dispersant polymer, gum arabic, and water as a solvent to form a slurry.
  • the solvent is removed by spray drying the slurry and the resultant green beads are fired at from about 1100°C to about 1300°C in an oxidizing environment to form the desired hard magnetic material described above.
  • the hard magnetic material is then deagglomerated to yield the component carrier bead particles with a particle size generally required of carrier particles, that is, less than about 100 ⁇ m and preferably from about 3 to 65 ⁇ m, and the resulting carrier particles are then permanently magnetized by subjecting them to an applied magnetic field of sufficient strength to induce a permanent magnetic hysteresis behavior.
  • Such carriers comprise a hard magnetic ferrite material having a single-phase hexagonal crystal structure and may be represented by the formula:
  • P is selected from strontium, barium, or lead; and y is less than 0.1.
  • Such carriers may be prepared using a source compound for the lanthanum metal ions generally in accordance with the foregoing metal substitution method and the method described in U.S. Patent 4,764,445, the relevant teachings of which are incorporated herein by reference.
  • the resistivity of the carrier is reduced to a value within a range of from about 1x10 10 ohm-cm to about 1x10 5 ohm-cm, more preferably from about 5x10 9 ohm-cm to about 1x10 6 ohm-cm, and even more preferably from about 5x10 9 ohm-cm to about 1x10 7 ohm-cm.
  • the foregoing resistivity ranges are preferred, since a resistivity value within such ranges can inhibit or at least reduce the amount of l-CPU without affecting the high magnetic properties of the hard magnetic material.
  • (Q/m) ca ⁇ ier for the carrier particles in the developer composition be greater than 1 ⁇ C/g as previously described.
  • the carrier particles of the present invention can, in such embodiments, provide high levels of development efficiency (and thereby a faster electrographic imaging process), without significant, or at least undesirable, levels of l-CPU, as is exemplified by the examples which follow hereinafter.
  • the present invention further contemplates, in another embodiment, use of a carrier comprised of a core of a hard magnetic material, preferably a hard magnetic ferrite, that has a conductive metal oxide composition deposited thereon and reacted with the hard magnetic material so as to reduce the overall resistivity of the carrier, while still maintaining the desirable magnetic properties of the hard magnetic material.
  • the composition is deposited onto the core in either a continuous or discontinuous form.
  • the outer surface of the hard magnetic core defines a transition zone which extends into the magnetic core, i.e., the transition zone is an area within the hard magnetic material near the outer surface of the core.
  • the transition zone may be visualized as a shell whose outer surface coincides with the outer surface of the particle.
  • the hard magnetic material's crystal structure preferably comprises a gradient of metal ions corresponding to the formula M n+ , where M and n are as previously defined for the metal oxide composition disposed on the core, which metal ions are substituted into the hard magnetic material's crystalline lattice.
  • grade it is meant that the metal ion concentration is greatest near the outer surface of the core, and such concentration within the crystal lattice decreases at levels deeper within the core. While not wishing to be bound by theory, it is believed, from size and charge considerations of the M n+ cations disclosed herein, that the resistivity of a hard magnetic ferrite could be decreased by substitution of the above-described multi-valent metal ions into the iron lattices of the hexagonal ferrite crystal structure, rather than by replacement of Sr 2* Ba 2+ , or Pb 2+ .
  • the M n+ multi-valent metal ion substituents as described hereinabove force a charge compensation in the ferric (Fe 3+ ) lattice; i.e., ferrous (Fe 2+ ) cations form.
  • the Fe 2+ /Fe 3+ charge couple thereby created provides a semi-conductive electronic pathway, resulting in ferrite compositions of higher conductivity.
  • the conductive metal oxide compositions of the present invention are generally tightly adherent to the core particle, and do not easily flake or spall off when used in an electrographic process.
  • the resistivity of hard magnetic carrier material can be reduced from approximately 1x10 11 ohm- cm by at least about one order of magnitude, i.e. to approximately 1x10 10 ohm-cm.
  • conductive in reference to the carrier and/or its metal oxide composition, it is meant that placing such composition on the core can result in a reduction of the carrier's resistivity of at least about one order of magnitude as mentioned above relative to a carrier of the hard magnetic material without said composition being disposed thereon.
  • the resistivity of the carrier is reduced to a value within a range of from about 1x10 10 ohm-cm to about 1x10 5 ohm-cm, more preferably from about 5x10 9 ohm-cm to about 1x10 6 ohm-cm, and even more preferably from about 5x10 9 ohm-cm to about 1x10 7 ohm-cm.
  • the foregoing resistivity ranges are preferred, since a resistivity value within such ranges can inhibit or at least reduce the amount of l-CPU without affecting the high magnetic properties of the hard magnetic material.
  • (Q/m) ca rr ie r for the carrier particles in the developer composition be greater than 1 ⁇ C/g as previously described.
  • the carrier particles of the present invention can, in such embodiments, provide high levels of development efficiency (and thereby a faster electrographic imaging process), without significant, or at least undesirable, levels of l-CPU, as is exemplified by the examples which follow hereinafter.
  • the conductive carriers of the present invention can exhibit no apparent deposition of carrier into the image, or only weak to light levels of deposition (a level of 2 or below based on the qualitative l-CPU determination described in the examples), and preferably, exhibit no visual evidence of deposition on the photoconductor (a level of 0 in the qualitative test) when the carriers of the invention are used in a electrographic process.
  • the carrier has a core of a hard magnetic ferrite material with a single-phase, hexagonal crystal structure.
  • the core preferably has an outer surface with a metal oxide composition disposed thereon represented by the formula MO n/2 , wherein M is at least one multi-valent metal represented by M n+ with n being an integer of at least 4.
  • n is 4, 5 or 6, and more preferably, n is 4 or 5. Most preferably, n is 4.
  • the metals for the conductive metal oxide composition are any metallic element that can form a multi-valent metal ion in the hard magnetic material's crystal structure such that n in the foregoing formula is 4 or more.
  • Such metals include, for example, antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium, and mixtures thereof.
  • the metal is selected from silicon, zirconium, tin, titanium, or mixtures thereof, which metals are more readily available and therefore have a relatively low raw material cost.
  • Examples of metal oxides which may be employed include GeO 2 , ZrO 2 , TiO 2) SnO 2 , and mixtures thereof.
  • the amount of metal oxide composition employed should be that which yields a conductive carrier, i.e., a drop in resistivity of at least about 1x10 1 ohm-cm relative to a carrier of the hard magnetic material without the metal oxide thereon as described above.
  • the metal oxide composition may be applied in an amount of from about 0.01 to about 3 weight percent based on total weight of the carrier.
  • the metal oxide composition is present in an amount of from about 0.02 to about 2 weight percent, and more preferably from about 0.025 to about 1 weight percent based on total carrier weight.
  • the conductive metal oxide composition on the core may further comprise at least one second metal oxide which does not substantially contribute toward enhancement of carrier conductivity, but may add charge tunability and/or coating (deposit) integrity, such as a glassy boron oxide (B 2 O 3 ) co-deposit, but preferably the second metal oxide is an alkali metal oxide, such as lithium oxide, potassium oxide, sodium oxide, or mixtures thereof, which can enhance conductivity, even when coated onto the carrier without a co-deposit of the multi-valent metal oxide.
  • second metal oxide is an alkali metal oxide, such as lithium oxide, potassium oxide, sodium oxide, or mixtures thereof, which can enhance conductivity, even when coated onto the carrier without a co-deposit of the multi-valent metal oxide.
  • a second metal oxide is employed in the conductive metal oxide composition, it is generally present in an amount of from 0.01 to about 1 weight percent, based on total carrier weight.
  • the conductive carriers of the present invention can be prepared by a solution coating and firing technique as described hereinafter.
  • a hard magnetic material in paniculate form is provided, which can be prepared by any method known to the art, such as those methods described in the foregoing art references.
  • the particulate material functions as the core for the carriers of the present invention.
  • the particulate core material is then admixed with a solution comprising a solvent and at least one metal oxide precursor compound.
  • the admixture is then heated, preferably with agitation as necessary, to remove solvent therefrom and provide a coating of the at least one metal oxide precursor compound on the surface of the core particles.
  • the so-coated particles are fired in an oxidizing atmosphere at a temperature sufficient to form the desired metal oxide composition on the outer surface of the core particles.
  • the amount of solution used should be sufficient to at least wet the surfaces of the particulate ferrite material. A significant excess of the solution is undesirable, since the solvent in the solution must be removed in subsequent processing steps.
  • the solution of at least one metal oxide precursor compound may be prepared by dissolving at least one metal oxide precursor compound into a suitable solvent.
  • the solvent should be easily vaporized since the preparation method disclosed herein involves removal of the solvent prior to formation of the conductive metal oxide composition.
  • Suitable solvents include water, and other common organic solvents such as methanol, ethanol, iso-propanol, toluene, hexane, and the like.
  • Preferred solvents are water, methanol, and iso-propanol.
  • solution it is also contemplated that a colloidal dispersion of the metal oxide precursor compound can be used.
  • the compounds employed for the metal oxide precursor solution are those which, upon firing in an oxidizing atmosphere at the temperatures described below, yield the desired metal oxides.
  • the compounds are those which may readily be dissolved into the above-described solvents and yield the metals as described hereinabove.
  • metal salts of organic acids, carbonates, halides, and nitrates are dissolvable and/or dispersible in common solvents and yield good results.
  • the amount of the at least one metal oxide precursor compound employed in the above-described coating solution is selected such that, upon firing, a metal oxide composition is obtained which is within the weight percent ranges previously given as to the proportion of the metal oxide composition in the final conductive carrier particles. Generally, an amount of from about 0.01 to about 5 weight percent of the metal oxide precursor compound in the solution is sufficient.
  • heat is applied to the admixture to remove excess solvent therefrom and obtain dry, or nearly dry, particles coated with the metal oxide precursor compounds.
  • This step may be accomplished by heating the admixture under moderate heat of about 100 to about 150°C for a time sufficient to remove the solvent without significant conversion of the metal oxide precursor compounds to their oxide forms.
  • the pressure used during the drying step can also be reduced in order to use lower temperatures for the drying step.
  • the so-coated core particles are fired, i.e., calcined, within an oxidizing atmosphere at a temperature sufficient to substantially convert the metal oxide precursor compounds to their oxide form.
  • this step can be accomplished in a high temperature furnace.
  • the temperature at which the precursor compounds thermally decompose and convert to their oxide form will depend on the precursor selected, but generally, a firing temperature of at least about 250°C is desired.
  • the firing temperature can be as high as about 1300°C.
  • the firing temperature is increased, there is typically a firing temperature at which a significant drop in the resulting carrier resistivity occurs.
  • the firing temperature is selected such that the resistivity for the final carrier is within the preferred ranges specified above due to l-CPU concerns.
  • the resulting conductive carrier may be deagglomerated to yield the carrier in its final form, that is, beads with a volume average particle diameter of less than 100 ⁇ m, preferably from about 3 to 65 ⁇ m, and more preferably, from about 5 to about 20 ⁇ m.
  • the resulting carrier particles are then magnetized by subjecting them to an applied magnetic field of sufficient strength to yield magnetic hysteresis behavior.
  • the so-coated hard magnetic ferrites as previously described can have significant improvement in development efficiency, as is exemplified by the examples hereinbelow, as well as in co-pending U.S. Patent Application Serial No. 09/572,989 previously incorporated herein by reference.
  • the present invention includes the use of two types of carrier particles.
  • the first of these carriers comprises a binder-free, particulate hard magnetic material, doped with at least one multi-valent metal ion and/or having a conductive metal oxide composition thereon as described above, and exhibiting the requisite coercivity and induced magnetic moment as previously described.
  • This type of carrier is preferred.
  • the second is heterogeneous and comprises a composite of a binder (also referred to as a matrix) and a magnetic material exhibiting the requisite coercivity and induced magnetic moment.
  • the hard magnetic material as previously described herein is dispersed as discrete smaller particles throughout the binder.
  • binders employed as known to those in the art can be highly resistive in nature, such as in the case of a polymeric binder, such as vinyl resins like polystyrene, polyester resins, nylon resins, and polyolefin resins as described in U.S. Patent 5,256,513.
  • any reduction in conductivity of the magnetic material may be offset by the resistivity of the binder selected.
  • the resistivity of these composite carriers must be comparable to the binder-less carrier in order for advantages concerning development efficiency as previously described to be realized. It may be desirable to add conductive carbon black to the binder to facilitate electrical conductance between the ferrite particles.
  • the individual bits of the magnetic ferrite material should preferably be of a relatively uniform size and sufficiently smaller in diameter than the composite carrier particle to be produced.
  • the average diameter of the magnetic material should be no more than about 20 percent of the average diameter of the carrier particle.
  • a much lower ratio of average diameter of magnetic component to carrier can be used. Excellent results are obtained with magnetic powders of the order of 5 ⁇ m down to 0.05 ⁇ m average diameter. Even finer powders can be used when the degree of subdivision does not produce unwanted modifications in the magnetic properties and the amount and character of the selected binder produce satisfactory strength, together with other desirable mechanical and electrical properties in the resulting carrier particle.
  • the concentration of the magnetic material in the composite can vary widely. Proportions of finely divided magnetic material, from about 20 percent by weight to about 90 percent by weight, of composite carrier can be used as long as the resistivity of the particles is that representative of the ferrite particles as described above.
  • the induced moment of composite carriers in a 1000 Oersteds applied field is dependent on the concentration of magnetic material in the particle. It will be appreciated, therefore, that the induced moment of the magnetic material should be sufficiently greater than about 20 EMU/gm to compensate for the effect upon such induced moment from dilution of the magnetic material in the binder. For example, one might find that, for a concentration of about 50 weight percent magnetic material in the composite particles, the 1000 Oersteds induced magnetic moment of the magnetic material should be at least about 40 EMU/gm to achieve the minimum level of 20 EMU/gm for the composite particles.
  • the binder material used with the finely divided magnetic material is selected to provide the required mechanical and electrical properties. It should (1) adhere well to the magnetic material, (2) facilitate formation of strong, smooth-surfaced particles and (3) preferably possess sufficient difference in triboelectric properties from the toner particles with which it will be used to insure the proper polarity and magnitude of electrostatic charge between the toner and carrier when the two are mixed.
  • the matrix can be organic, or inorganic, such as a matrix composed of glass, metal, silicone resin or the like.
  • an organic material is used such as a natural or synthetic polymeric resin or a mixture of such resins having appropriate mechanical properties.
  • Appropriate monomers include, for example, vinyl monomers such as alkyl acrylates and methacrylates, styrene and substituted styrenes, and basic monomers such as vinyl pyridines. Copolymers prepared with these and other vinyl monomers such as acidic monomers, e.g., acrylic or methacrylic acid, can be used. Such copolymers can advantageously contain small amounts of polyfunctional monomers such as divinylbenzene, glycol dimethacrylate, triallyl citrate and the like. Condensation polymers such as polyesters, polyamides or polycarbonates can also be employed.
  • Preparation of composite carrier particles according to this invention may involve the application of heat to soften thermoplastic material or to harden thermosetting material; evaporative drying to remove liquid vehicle; the use of pressure, or of heat and pressure, in molding, casting, extruding, or the like and in cutting or shearing to shape the carrier particles; grinding, e.g., in a ball mill to reduce carrier material to appropriate particle size; and sifting operations to classify the particles.
  • the powdered magnetic material is dispersed in a solution of the binder resin.
  • the solvent may then be evaporated and the resulting solid mass subdivided by grinding and screening to produce carrier particles of appropriate size.
  • emulsion or suspension polymerization is used to produce uniform carrier particles of excellent smoothness and useful life.
  • the coercivity of a magnetic material refers to the minimum external magnetic force necessary to reduce the induced magnetic moment from the remanance value to zero while it is held stationary in the external field, and after the material has been magnetically saturated, i.e., the material has been permanently magnetized.
  • a variety of apparatus and methods for the measurement of coercivity of the present carrier particles can be employed.
  • a Lakeshore Model 7300 Vibrating Sample Magnetometer available from Lakeshore Cryotronics of Westerville, Ohio, is used to measure the coercivity of powder particle samples.
  • the magnetic ferrite powder is mixed with a nonmagnetic polymer powder
  • the mixture is placed in a capillary tube, heated above the melting point of the polymer, and then allowed to cool to room temperature.
  • the filled capillary tube is then placed in the sample holder of the magnetometer and a magnetic hysteresis loop of external field (in Oersteds) versus induced magnetism (in EMU/gm) is plotted. During this measurement, the sample is exposed to an external field of 0 to ⁇ 8000 Oersteds.
  • the carrier particles may be coated to properly charge the toner particles of the developer. This can be done by forming a dry mixture of the hard magnetic material with a small amount of powdered resin, e.g., from about 0.05 to about 3.0 weight percent resin based on total weight of the magnetic material and resin, and then heating the mixture to fuse the resin. Such a low concentration of resin will form a thin or discontinuous layer of resin on the particles of the magnetic material. Since the presence of the metal oxide coating is intended to improve conductivity of carrier particles, the layer of resin on the carrier particles should be thin enough that the mass of particles remains suitably conductive. Preferably the resin layer is discontinuous for this reason; spots of bare carrier on each particle provide conductive contact.
  • preferred resins for the carrier coating include fluorocarbon polymers such as poly(tetrafluoroethylene), poly(vinylidene fluoride) and poly(vinylidene fluoride-co-tetrafluoroethylene)
  • preferred resins for the carrier include silicone resins, as well as mixtures of resins, such as a mixture of poly(vinylidene fluoride) and polymethylmethacrylate.
  • Various polymers suitable for such coatings are also described in U.S. Patent 5,512,403, the teachings of which are incorporated herein by reference in their entirety.
  • the developer is formed by mixing the carrier particles with toner particles in a suitable concentration.
  • high concentrations of toner can be employed.
  • the present developer preferably contains from about 70 to 99 weight percent carrier and about 30 to 1 weight percent toner based on the total weight of the developer; most preferably, such concentration is from about 75 to 99 weight percent carrier and from about 25 to 1 weight percent toner.
  • the toner component of the invention can be a powdered resin which is optionally colored. It normally is prepared by compounding a resin with a colorant, i.e., a dye or pigment, either in the form of a pigment flush (a special mixture of pigment press cake and resin well-known to the art) or pigment-resin masterbatch, as well as any other desired addenda known to art. If a developed image of low opacity is desired, no colorant need be added. Normally, however, a colorant is included and it can, in principle, be any of the materials mentioned in Colour Index, Vols. I and II, 2nd Edition. Carbon black is especially useful. The amount of colorant can vary over a wide range, e.g., from about 3 to about 20 weight percent of the toner component. Combinations of colorants may be used as well.
  • the mixture of resin and colorant is heated and milled to disperse the colorant and other addenda in the resin.
  • the mass is cooled, crushed into lumps and finely ground.
  • the resulting toner particles can range in diameter from about 0.5 to about 25 ⁇ m with a volume average particle diameter of from about 1 to about 16 ⁇ m, and preferably less than 11 ⁇ m, more preferably less than 8 ⁇ m, and even more preferably less than 6 ⁇ m.
  • the average particle size ratio of carrier to toner particles lies within the range from about 15:1 to about 1:1. However, carrier-to-toner average particle size ratios of as high as 50:1 are useful.
  • the toner resin can be selected from a wide variety of materials, including both natural and synthetic resins and modified natural resins, as disclosed, for example, in U.S. Patent No. 4,076,857.
  • Especially useful are the crosslinked polymers disclosed in U.S. Pat. Nos. 3,938,992 and 3,941,898.
  • the crosslinked or noncrosslinked copolymers of styrene or lower alkyl styrenes with acrylic monomers such as alkyl acrylates or methacrylates are particularly useful.
  • condensation polymers such as polyesters.
  • Numerous polymers suitable for use as toner resins are disclosed in U.S. Patent 4,833,060.
  • the teachings of U.S. Patents 3,938,992, 3,941,898, 4,076,857; and 4,833,060 are incorporated by reference herein in their entirety.
  • the shape of the toner can be irregular, as in the case of ground toners, or spherical.
  • Spherical particles are obtained by spray-drying a solution of the toner resin in a solvent.
  • spherical particles can be prepared by the polymer bead swelling technique disclosed in European Pat. No. 3905 published Sept. 5, 1979, to J. Ugelstad, as well as by suspension polymerization, such as the method disclosed in U.S. Patent 4,833,060, previously incorporated by reference.
  • the toner can also contain minor amounts of additional components as known to the art, such as charge control agents and antiblocking agents.
  • charge control agents are disclosed in U.S. Patents 3,893,935 and 4,206,064, and British Pat. No. 1,501 ,065, the teachings of which are incorporated herein by reference in their entirety.
  • Quaternary ammonium salt charge agents as disclosed in Research Disclosure, No. 21030, Volume 210, October, 1981 (published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, PO9 1EF, United Kingdom) are also useful.
  • an electrostatic image is brought into contact with a magnetic brush development station comprising a rotating- magnetic core, an outer non-magnetic shell, and dry developers as described hereinabove.
  • the electrostatic image so developed can be formed by a number of methods such as by imagewise photodecay of a photoreceptor, or imagewise application of a charge pattern on the surface of a dielectric recording element.
  • photoreceptors such as in high-speed electrophotographic copy devices
  • halftone screening to modify an electrostatic image can be employed, the combination of screening with development in accordance with the method for the present invention producing high-quality images exhibiting high Dmax and excellent tonal range.
  • Representative screening methods including those employing photoreceptors with integral half-tone screens are disclosed in U.S. Pat. No. 4,385,823.
  • Developers comprising magnetic carrier particles in accordance with the present invention when employed in an apparatus such as that described in U.S. Pat. No. 4,473,029 can exhibit a dramatic increase in development efficiency when compared with traditional magnetic ferrite materials as employed in U.S. Patent 4,473,029 when operated at the same voltage differential of the magnetic brush and photoconductive film.
  • the development efficiency can be improved at least from about 50 percent, and preferably up to 100 percent and even 200 percent, all other conditions of development remaining the same.
  • the operating conditions such as the voltage differential, the exposure energy employed in forming the latent electrostatic image, and the speed of development, may all be varied in order to achieve optimum conditions and results.
  • the invention is further illustrated by the following examples:
  • An precursor mixture for a strontium ferrite magnetic carrier is initially prepared by the following procedure.
  • a slurry of Fe 2 O 3 and SrCO 3 (at a molar ratio of 5.7:1) is prepared by adding 301.17 grams (g) of Fe 2 O 3 powder ( ⁇ ? phase - KFH-NA grade - available from Toda Koygo of Japan); 48.83 g SrCO 3 powder (Type D available from Chemical Products Corporation of Cartersville, Georgia); and 350 g of an aqueous binder solution to a 1250 milliliter (ml) glass bottle.
  • the binder solution is prepared by adding measured amounts of gum arabic (acacia powder available from Eastman Kodak Company of Rochester, New York) and ammonium polymethacrylate (DAXAD 32 available from W.R. Grace of Lexington, Massachusetts) sufficient to provide a solution containing 3.94 wt% gum arabic and 0.33 wt% ammonium polymethacrylate respectively.
  • the pH of the resulting slurry is thereafter adjusted with concentrated NH 4 OH to a value of about 8-9.
  • the above-described strontium ferrite precursor mixture is doped with Ge 4+ using germanium oxide powder (obtainable from Eagle Picher Industries of Quapaw, Oklahoma) as a source, without intentional substitution of the Ge 4+ ion at either the iron or strontium stoichiometries of the crystalline lattice.
  • germanium oxide powder obtainable from Eagle Picher Industries of Quapaw, Oklahoma
  • Table I a measured amount of the germanium oxide powder source material as shown in Table I is added as a dry powder to 100 parts of the strontium ferrite precursor mixture and the two are mixed.
  • Table I also gives the value for x in the formula PFe 12 . x M x O 19 .
  • Firing of the green bead is conducted by placing the green beads in alumina trays and charging them into a high temperature box furnace.
  • the temperature of the furnace is ramped at a rate of 7°C/min to a temperature 500°C, at which point the temperature is maintained at 500°C for 1 hour to burnout the binder portion of the green bead.
  • the furnace temperature is ramped at a rate of 5°C/min to the final firing temperature.
  • the furnace is held at the firing temperature of 1250°C for 10 hours, whereupon the furnace is allowed to cool without control (i.e., "free-fall") to room temperature.
  • the fired charges are deagglomerated with a mortar and pestle and screened through a 200 mesh screen to obtain strontium ferrite carrier particles doped with Ge 4+ multi-valent metal ions.
  • the resistivities measured for each resulting carrier are shown in Table I below.
  • Static resistivity is measured using a cylindrically-shaped electrical cell.
  • the cell employed has a cylindrical chamber therein which is concentric with the centerline of the cell.
  • the cell is in two parts, an upper section with an electrode piston located concentrically therein and aligned along the centerline of the cylinder, and a bottom section with an electrode base.
  • the upper section connects to the bottom section, thereby forming the cell's overall cylindrical shape.
  • the circular bottom surface of the piston within the upper section and the circular base of the bottom section define the ends of the cylindrical chamber within the cell.
  • the piston can be actuated and extended downwardly along the centerline of the cell by a small lever that extends radially outward from the cylinder.
  • the base of the bottom section of the cell has a small, centered electrode therein.
  • the piston in the upper section is itself an electrode and thereby forms the opposing electrode.
  • approximately 2.00 g of carrier to be tested is placed on the circular metal base in contact with the electrode.
  • the top portion of the cell is placed on the bottom electrode base and aligned.
  • the release lever is lowered and the piston electrode from the upper section is lowered onto the powder.
  • the depth of the powder is adjusted by physical rotation of the top portion of the cell to give a spacing of 0.04 inches.
  • the average resistivity (in ohm-cm) is determined by measurement of the electrical current flow through the cell using a Keithley Model 616 current meter (obtained from Keithley Corporation of Cleveland, Ohio) for three applied voltages in a range of 10-250 V. Resistivity is determined using Ohm's law.
  • the resulting doped carrier is used to prepare a two-component developer using a yellow polyester toner prepared substantially as described in U. S. Patent 4,833,060, the teachings of which are incorporated herein in their entirety.
  • the toner is made using 93 wt% of a polyester resin binder (Kao P obtained from Kao Company of Japan), 1.0 wt% of an aluminum complex of di-tert-butyl salicylic acid charge-control agent (Bontron E-88 obtained from Orient Chemical Co, Ltd. Of Japan), and 7.0 wt% of yellow pigment 180 (obtained from BASF of Germany), wherein the foregoing weight percentages are based on total weight of the toner.
  • the toner prepared has an average particle size of 7.1 ⁇ m as determined by a Coulter Counter device.
  • the developer is produced by mixing together each carrier with the above-described toner using a toner concentration (TC) of about 6 wt% (the actual value for TC is shown in Table I). For each example, the charge-to-mass ratio (Q/m) is measured and the value obtained is also shown in Table I.
  • Toner charge to mass (Q/m) is measured in microcoulombs per gram ( ⁇ C/g) within a "MECCA” device described hereinafter, after being subjected to the "exercise periods”, also as described hereinafter.
  • the first exercise period consists of vigorously shaking the developer to cause triboelectric charging by placing a 4-7 g portion of the developer into a 4 dram glass screw cap vial, capping the vial and shaking the vial on a "wrist-action" robot shaker operated at about 2 Hertz (Hz) and an overall amplitude of about 11 centimeters (cm) for 2 minutes.
  • the charge if obtained at this point, is commonly referred to as the "fresh" charge in the tables that follow hereinafter.
  • the developer is also subjected to an additional, exercise period of 2 minutes and/or
  • the toner Q/m ratio is measured in a MECCA device comprised of two spaced-apart, parallel, electrode plates which can apply both an electrical and magnetic field to the developer samples, thereby causing a separation of the two components of the mixture, i.e., carrier and toner particles, under the combined influence of a magnetic and electric field.
  • a 0.100 g sample of a developer mixture is placed on the bottom metal plate. The sample is then subjected for thirty (30) seconds to a 60 Hz magnetic field and potential of 2000 V across the plates, which causes developer agitation.
  • the toner particles are released from the carrier particles under the combined influence of the magnetic and electric fields and are attracted to and thereby deposit on the upper electrode plate, while the magnetic carrier particles are held on the lower plate.
  • An electrometer measures the accumulated charge of the toner on the upper plate.
  • the toner Q/m ratio in terms of microcoulombs per gram ( ⁇ C/g) is calculated by dividing the accumulated charge by the mass of the deposited toner taken from the upper plate.
  • the shell and photoconductor are set at a spacing of 0.020 inches, the core is rotated clockwise at 1000 rpm, and the shell is rotated at 15 rpm counter- clockwise.
  • the photoconductor is set to travel at a speed of 2 inches per second, while in the development section the photoconductor is set to travel at a speed of 5 inches per second.
  • the nap density is 0.24 g/in 2 .
  • the carrier particles and toner used are those as prepared in Examples 1-4 hereinabove, respectively.
  • the voltage on the photoconductor after charging and exposure to a step-wedge density target is measured by the first probe after development, the voltage on the photoconductor film in the developed areas is measured by the second probe.
  • the development efficiency is calculated for a high density area by comparison of the pre- and post-exposure voltages on the photoconductor. After development, the voltage on the photoconductive film in developed areas is measured, thereby allowing for calculation of a development efficiency for each example as shown in Table II.
  • Development efficiency is defined as a percentage of the potential difference between the photoreceptor in the developed image areas before and after toner development divided by the potential difference between the photoreceptor prior to development. For example, in a discharged area development configuration with a negative toner, if the photoconductor film voltage is -100 V and the magnetic brush is -500 V, the potential difference is 400 V prior to development. If during development, the film voltage is reduced by -200 V to -300 V in the image areas by the deposition of negative toner particles, the development efficiency would be 200 V/400 V, or 50%.
  • the relative development efficiency is calculated as a ratio of the measured development efficiency for a given example over the development efficiency of a developer prepared in substantially the same manner, except that the carrier employed has not been treated so as to have Ge 4+ ions substituted in the strontium ferrite carrier.
  • the reference to l-CPU is a qualitative determination of the extent to which carrier is being picked-up, i.e., deposited onto the photoconductor, and is determined by visually inspecting the high density region from the step-wedge image and comparing the density of deposited carrier particles.
  • a numerical scale is assigned to various levels of l-CPU deposition, with 0 - being none, 1 - very weak, 2 - weak, 3 - weak to moderate, 4 - moderate, 5 - moderate to high, 6 - high, and 7- very high. Table II
  • Comparative Example A the static resistivity, triboelectric properties, development efficiency, and l-CPU of a commercially-prepared SrFe 12 O-
  • the commercially available carrier is a SrFe 2 O 19 hard ferrite available from POWDERTECH of Valparaiso, Indiana. This carrier is used to make a developer with the same toner described in Examples 1-4.
  • the resistivity measured for the carrier is 2.0x10 10 ohm-cm, the toner Q/m is -71.1 ⁇ C/g, and the TC is 6.3 wt%.
  • 9 hard ferrite carrier is also tested for its performance in an electrographic process according to substantially the same procedures as set forth in Examples 1-4. All conditions, including the toner concentration and charge are substantially the same.
  • the relative development efficiency would be 1.00 based on the definition of development efficiency described in Examples 1-4 above.
  • the l-CPU level is 0, indicating that no visual deposition of carrier is apparent on the photoconductor.
  • Examples 5-10 the procedure of Examples 1-4 is substantially repeated, except as provided hereinafter.
  • the strontium ferrite precursor mixture prepared as described in Examples 1-4 is doped with La 3+ using La 2 (CO 3 ) 3 powder (obtained from POWDERTECH of Valpariso, Indiana) a source.
  • a measured amount of dry powder to yield an y value in the formula as shown in Table 111 is added to the precursor mixture prepared in Examples 1-4 and the two components are mixed.
  • the resulting mixture is placed in alumina trays and calcined in a high temperature box furnace at a temperature 1225°C and maintained at that temperature for 10 hours, whereupon the furnace is allowed to cool to provide a La 3+ doped strontium ferrite carrier.
  • the resulting carriers are further coated with 1.5 parts of a silicone resin per 100 parts of carrier.
  • the coating is obtained by curing a silicone resin on the carrier particles as follows.
  • the resin is initially formed by mixing 20 ml of methyltrimethoxysilane (98% obtained from Aldrich Company of Milwaukee, Wisconsin), 2.2 ml of dimethoxydimethylsilane (95% obtained from Aldrich of Milwaukee, Wisconsin), 1 ml of glacial acetic acid, and 8 ml of distilled water in a glass vessel. The mixture is stirred for one hour, and then allowed to stand overnight to complete hydrolysis.
  • the carrier particles are then placed in a metal tray and heated at a temperature of 230°C for 2 Vi hours in an oven to cure the silicone resin.
  • the so-coated carriers are then removed from the oven and allowed to cool to room temperature.
  • the resulting doped carrier is used to prepare a two-component developer using a conventionally prepared ground cyan polyester toner.
  • the toner is made with 93 parts of a polyester resin (Finetone 382 resin), 5 parts of copper phthalocyanine pigment, and 2 parts of 3,5 - ditertbutyl salicylic acid charge control agent (Bontron E-88 from Orient Chemical Co, Ltd), which toner mixture is ground and classified so as to have an average particle size of 8.0 ⁇ m as determined by a Coulter Counter.
  • the developer is produced by mixing together each carrier with the above-described toner using a toner concentration (TC) of about 10 wt% (the actual value for TC is shown in Table I).
  • TC toner concentration
  • Q/m charge-to-mass ratio
  • Comparative Examples B and C the procedures of Examples 5-10 are substantially repeated, except that the strontium ferrite material is doped with the lanthanum source material in an amount sufficient to yield an y value in the formula of 0.2.
  • the carrier is not coated with the silicone resin, while in Comparative Example C, the carrier is coated with the silicone resin substantially as described for Examples 8-10.
  • the static resistivity, triboelectric properties, development efficiency, and I- CPU of the La 3+ doped SrFe 12 O 19 hard ferrite carrier are measured according to substantially the same procedures as described in Examples 1-4 above. This carrier is used to make a developer with the same toner described in Examples 5-10.
  • the resistivity, triboelectric properties, development efficiencies and l-CPU are measured and are shown in Table III for comparison purposes.
  • Figs. 2 and 3 illustrate the relationship between resistivity and Rel DE and l-CPU.
  • the data from Examples 5-7 and Comparative Example B are plotted, with the large diamonds being data points for Rel DE and the small diamonds being data points for l-CPU.
  • Fig. 3 illustrates the data obtained for Examples 8-10 and Comparative Example C, where the large and small diamonds have the same meaning.
  • Figs. 2 and 3 show that by decreasing the carrier resistivity with La 3+ substitution into the ferrite material so that resistivity is from about 1.0x10 8 and up to less than the resistivity of the undoped ferrite material, one can operate with relatively high Rel DE values (in comparison to an undoped carrier) but also with acceptable levels for l-CPU.
  • a commercially-prepared SrFe 12 O ⁇ 9 hard ferrite carrier is coated with 1 part of GeO 2 per 100 parts of carrier (0.99 wt% based on total weight of the final carrier particles) and the temperature at which the carrier is fired is varied to show the effects of calcining temperature on the resulting carrier's resistivity and performance.
  • the coated carrier particles are prepared using SrFe 2 O 19 hard magnetic ferrite particles available from POWDERTECH of Valparaiso, Indiana.
  • a slurry of the ferrite particles is made by placing a 400 gram (g) amount of the SrFe ⁇ 2 O- ⁇ 9 ferrite particles into a glass dish, along with a combined solution of 66 milliliters (ml) of an ammonium germanate solution and 122 ml of methanol.
  • the ammonium germanate solution is made by adding, with agitation, a 120 g amount of GeO 2 powder (chemical grade - 99.999% purity) obtained from Eagle Picher Company of Quapaw, Oklahoma into 2,000 ml of distilled water in a appropriately sized glass flask, followed by dropwise addition of 33 ml of a concentrated NH 4 OH solution into the vessel to dissolve the GeO 2 powder.
  • the resulting ammonium germanate solution has a final pH of 8.5 with a germanium oxide content of 60 grams per liter
  • the slurry as described above is mixed under an infrared heat lamp to dryness, followed by overnight heating in an oven set at 100°C, so as to remove water. At this point, the chemical species present in the ammonium germanate solution have not yet thermally decomposed to an oxide form.
  • the so-coated carrier particles are then fired to thermally decompose the ammonium germanate surface coating by placing an aliquot of at least 20 g of the carrier particles into an alumina tray and charging them into a high temperature box furnace.
  • the temperature of the furnace is ramped at a rate of 7°C/min to a temperature of from 250°C (Example 11) to 600°C (Example 13) (the firing temperature for each example is listed in Table IV hereinafter), at which point the temperature is maintained for 2 hours. After firing for two hours, the furnace is allowed to cool without control (i.e., "free-fall") to room temperature.
  • the fired carrier charges are deagglomerated with a mortar and pestle and screened through a 200 mesh screen to obtain strontium ferrite carrier particles having GeO 2 deposited thereon.
  • the resistivities measured for each resulting carrier are shown in Table IV below.
  • Static resistivity of the carrier is measured by the procedure described in Examples 1-4.
  • the resistivities for each carrier are shown in Fig. 4, which is a graph of resistivity (in ohm-cm) versus firing temperature (in °C). As can be seen in Fig. 4, the resistivity of the carrier sharply drops at a firing temperature above 600°C.
  • the resulting coated carrier is used to prepare a two-component developer using the yellow polyester toner described in Examples 1-4.
  • the developer is produced by mixing together each carrier with the above-described toner using a toner concentration (TC) of about 6 wt% (the actual value for TC is shown in Table IV).
  • TC toner concentration
  • the toner charge-to-mass ratio (Q/m) t0ner and TC are measured as described in Examples 1-4 and the values obtained are also shown in Table IV.
  • Example D the procedures of Examples 11-13 are substantially repeated, except that the ferrite material coated with GeO 2 precursor compound is fired at a furnace temperature of 750°C. All other procedures are substantially the same as those in Examples 11-13.
  • the static resistivity, triboelectric properties, development efficiency, and I- CPU of the resulting coated ferrite carrier are measured according to substantially the same procedures as described in Examples 1-4 above. This carrier is used to make a developer with the same toner described in Examples 11-13.
  • the resistivity, triboelectric properties, development efficiencies and l-CPU are measured and are shown in Table IV for comparison purposes. The results are discussed above in connection with Examples 11-13 and are also shown in Fig. 4 for comparison purposes.
  • a commercially prepared SrFe 12 O ⁇ 9 hard ferrite carrier is coated with a mixed GeO 2 /B 2 O 3 coating and used in an electrographic process according to the present invention.
  • the carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 30 ml of an ammonium germanate - boric acid solution.
  • the ammonium germanate - boric acid solution is made by adding 10 ml of the ammonium germanate solution made as in Examples 11-13 with 10 ml of distilled water and 10 ml of a methanolic boric acid solution.
  • the methanolic boric acid solution is made by adding 0.22 g of H 3 BO 3 (reagent grade obtained from Acros Company of New Jersey) to the 10 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with a mixed GeO 2 /B 2 O 3 .
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 30 ml of an ammonium germanate - boric acid solution.
  • the ammonium germanate - boric acid solution is made by adding 10 ml of the ammonium germanate solution made as in Examples 11-13 with 10 ml of distilled water and 10 ml of a methanolic boric acid solution.
  • the methanolic boric acid solution is made by adding 0.44 g of H 3 BO 3 to the 10 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with a mixed GeO 2 /B 2 O 3 .oxide coating having the stoichiometry of 1.2 pph GeO 2 and 1.0 pph B 2 O 3 .
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe ⁇ 2 O 19 ferrite particles into a glass dish, along with 25 ml of an ammonium germanate - boric acid solution.
  • the ammonium germanate - boric acid solution is made by adding 5 ml of the ammonium germanate solution made as in Examples 11-13 with 10 ml of distilled water and 10 ml of a methanolic boric acid solution.
  • the methanolic boric acid solution is made by adding 0.44 g of H 3 BO 3 to the 10 ml of methanol.
  • Examples 11-13 The procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with a mixed GeO 2 /B 2 O 3 .oxide coating having the stoichiometry of 0.6 pph GeO 2 and 1.0 pph B 2 O 3 .
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 2 O 19 ferrite particles into a glass dish, along with 35 ml of an ammonium germanate - boric acid solution.
  • the ammonium germanate - boric acid solution is made by adding 5 ml of the ammonium germanate solution made as in Examples 11-13 with 10 ml of distilled water and 20 ml of a methanolic boric acid solution.
  • the methanolic boric acid solution is made by adding 0.88 g of H 3 BO 3 to the 20 ml of methanol.
  • Examples 11-13 The procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with a mixed GeO 2 /B 2 O 3 .oxide coating having the stoichiometry of 0.6 pph GeO 2 and 2.0 pph B 2 O 3 .
  • the resulting carrier is used to prepare a two-component developer using the yellow polyester toner using the procedure substantially as described in
  • Examples 1-4 For each example, the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt%) are measured as described in Examples 1-4, and the values obtained are also shown in Table V.
  • a commercially-prepared SrFe 12 O 19 hard ferrite carrier is coated with a mixed GeO 2 /Li 2 O coating and evaluated in an electrographic process according to the present invention.
  • the coated carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - lithium acetate solution.
  • the ammonium germanate - lithium acetate solution is made by adding 0.05 g of lithium acetate (98% grade obtained from Aldrich Company of St.
  • Examples 11-13 The procedure of Examples 11-13 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with a mixed GeO 2 /Li 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 (0.99 wt% based on total weight of the carrier) and 0.015 pph Li 2 O (0.015 wt%).
  • Example 19 a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe ⁇ 2 O ⁇ 9 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - lithium acetate solution.
  • the ammonium germanate - lithium acetate solution is made by adding 0.1 g of the lithium acetate used in Example 18 above into 11.7 ml of distilled water and the resulting solution is combined with 8.3 ml of the ammonium germanate solution made as in Examples 11-13.
  • the procedure of Example 18 is substantially repeated to yield a carrier coated with a mixed GeO 2 /Li 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 and 0.029 pph Li 2 O.
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe ⁇ 2 O ⁇ 9 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - lithium acetate solution.
  • the ammonium germanate - lithium acetate solution is made by adding 0.15 g of the lithium acetate used in Example 18 above into 11.7 ml of distilled water and the resulting solution is combined with 8.3 ml of the ammonium germanate solution made as in Examples 11-13.
  • the procedure of Example 18 is substantially repeated to yield a carrier coated with a mixed GeO 2 /Li 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 and 0.044 pph Li 2 O.
  • the resulting carriers are also used to prepare a two-component developer using the yellow polyester toner and procedure substantially as described in Examples 11-13.
  • the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt%) are measured as described in Examples 1-4, and the values obtained are also shown in Table VIII.
  • Table VIM charge-to-mass ratio
  • Example 21 a commercially-prepared SrFe 12 O 9 hard ferrite carrier is coated with a mixed GeO 2 /Na O coating according to the present invention by using two different sources for the Na 2 O component.
  • the coated carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - sodium acetate solution.
  • the ammonium germanate - sodium acetate solution is made by adding 0.05 g of sodium acetate (obtained from Aldrich Company of St.
  • Examples 1-4 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with a mixed GeO 2 /Na 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 (0.99 wt% based on total weight of the carrier) and 0.023 pph Na 2 O (0.023 wt%).
  • Example 22 a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - sodium acetate solution.
  • the ammonium germanate - sodium acetate solution is made by adding 0.10 g of the sodium acetate used in Example 21 above into 11.7 ml of distilled water and combining the resulting solution with 8.3 ml of the ammonium germanate solution made as in Examples 11-13.
  • the procedure of Example 21 is substantially repeated to yield a carrier coated with a mixed GeO 2 /Na 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 and 0.046 pph Na 2 O.
  • Example 23 a slurry of the ferrite particles is made by placing a 50 gram (g) amount of the SrFe ⁇ 2 O 19 ferrite particles into a glass dish, along with 20 ml of an ammonium germanate - sodium acetate solution.
  • the ammonium germanate - sodium acetate solution is made by adding 0.15 g of the sodium acetate used in Example 21 above into 11.7 ml of distilled water and combining the resulting solution with 8.3 ml of the ammonium germanate solution made as in Examples 11-13.
  • the procedure of Example 21 is substantially repeated to yield a carrier coated with a mixed GeO 2 /Na 2 O oxide coating having the stoichiometry of 1.0 pph GeO 2 and 0.068 pph Na 2 O.
  • the resulting carriers are also used to prepare a two-component developer using the yellow polyester toner and procedure substantially as described in Examples 1-4.
  • the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt%) are measured as described in Examples 1-4, and the values obtained are also shown in Table X.
  • Table X Table X
  • Examples 24-33 Preparation and Use of Strontium Ferrite Carriers with TiO 2 Coatings
  • a commercially-prepared SrFe 12 O 19 hard ferrite carrier is coated with a TiO 2 composition according to the present invention.
  • the carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe- ⁇ 2 O ⁇ 9 ferrite particles into a glass dish, along with 35 ml of a methanolic tetrabutylorthotitanate solution.
  • the methanolic tetrabutylorthotitanate solution is made by dissolving 1.065 g of tetrabutylorthotitanate (obtained from Eastman Kodak Company of Rochester, NY) into 35 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with 0.25 pph (0.25 wt % based on total weight of the carrier) of TiO 2 .
  • Example 25 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O ⁇ g ferrite particles into a glass dish, along with 35 ml of a methanolic tetrabutylorthotitanate solution.
  • the methanolic tetrabutylorthotitanate solution is made by dissolving 2.13 g of the tetrabutylorthotitanate into 35 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with 0.50 pph of TiO 2 .
  • Example 26 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 35 ml of a methanolic tetrabutylorthotitanate solution.
  • the methanolic tetrabutylorthotitanate solution is made by dissolving 4.26 g of the tetrabutylorthotitanate into 35 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with 1.0 pph of TiO 2 .
  • Example 27 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 2 O ⁇ 9 ferrite particles into a glass dish, along with 35 ml of a methanolic tetrabutylorthotitanate solution.
  • the methanolic tetrabutylorthotitanate solution is made by dissolving 6.39 g of the tetrabutylorthotitanate into 35 ml of methanol.
  • the procedure of Examples 1-7 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with 1.5 pph of TiO 2 .
  • Example 28 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O ⁇ 9 ferrite particles into a glass dish, along with 35 ml of a methanolic tetrabutylorthotitanate solution.
  • the methanolic tetrabutylorthotitanate solution is made by dissolving 8.52 g of the tetrabutylorthotitanate into 35 ml of methanol.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 600°C to yield a carrier coated with 2.0 pph of TiO 2 .
  • the resistivities measured for each resulting carrier are shown in Tables XI and XII below.
  • the resulting carriers are used to prepare a two-component developer with the yellow polyester toner and procedure substantially as described in Examples 11-13.
  • the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt %) are measured as in Examples 1-4, and the values obtained are also shown in Tables XI and XII.
  • Relative DE and l-CPU are also evaluated as in Examples 1-4.
  • a commercially-prepared SrFe 12 O 19 hard ferrite carrier is coated with a ZrO 2 coating according to the present invention.
  • the carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • Example 34 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 2 O 19 ferrite particles into a glass dish, along with 35 ml of an aqueous, colloidal zirconium acetate solution (NYACOL dispersion - 20% ZrO 2 content obtained from The PQ Corporation of Ashland, Massachusetts).
  • the zirconium acetate solution is made by combining 2.5 g of the zirconium acetate dispersion with an amount of distilled water sufficient to make up 35 ml of solution.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 0.5 pph of ZrO 2 .
  • Example 35 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 35 ml of an aqueous zirconium acetate solution prepared by combining 5.0 g of the zirconium acetate dispersion with distilled water.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 1.0 pph of ZrO 2 .
  • Example 36 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 2 O-
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 2.0 pph of ZrO 2 contend.
  • the resistivities measured for each resulting carrier are shown in Tables XIII and XIV below.
  • the resulting carriers are used to prepare a two-component developer with the yellow polyester toner and procedure substantially as described in Examples 11-13.
  • the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt %) are determined as in Examples 1-4, and the values obtained are also shown in Tables XIII and XIV.
  • Relative DE and l-CPU are also evaluated as in Examples 11-13.
  • a commercially-prepared SrFe 12 O ⁇ 9 hard ferrite carrier is coated with a SnO 2 coating according to an embodiment of the present invention.
  • the carriers are prepared using generally the procedures as described in Examples 11-13 above, except as provided hereinbelow.
  • a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 35 ml of an aqueous, colloidal tin oxide solution.
  • the aqueous tin oxide solution is made by combining 3.33 g of a colloidal tin oxide dispersion (Nyacol dispersion obtained from The PQ Corporation of Ashland, Massachusetts) with sufficient distilled water to make up a volume of 35 ml of solution.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 0.5 pph of SnO 2 .
  • Example 41 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 35 ml of an aqueous tin oxide solution.
  • the solution is prepared by adding 6.67 g of the colloidal tin oxide dispersion of Example 40 to sufficient distilled water to make up a volume of 35 ml.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 1.0 pph of SnO 2 .
  • Example 42 a slurry of the ferrite particles is made by placing a 100 g amount of the SrFe 12 O 19 ferrite particles into a glass dish, along with 35 ml of an aqueous tin oxide solution.
  • the solution is prepared by adding 13.34 g of the colloidal tin oxide dispersion of Example 40 to sufficient distilled water to make up a volume of 35 ml.
  • the procedure of Examples 11-13 is substantially repeated at a furnace temperature of 900°C to yield a carrier coated with 2.0 pph of SnO 2 .
  • the resistivities measured for each resulting carrier are shown in Table XV below.
  • the resulting carriers are used to prepare a two-component developer with the yellow polyester toner and procedure substantially as described in Examples 11-13.
  • the charge-to-mass ratio (Q/m) in microcoulombs per gram ( ⁇ C/g) and toner concentration (TC) in weight percent (wt%) are measured as in Examples 1-4, and the values obtained are also shown in Table XV.
  • Relative DE and l-CPU are also evaluated as in Examples 11-13.
  • Example 43 a series of two-component developer compositions with varying toner concentration are made from a commercially-available SrFe 12 O 19 hard ferrite carrier (obtained from POWDERTECH of Valparaiso, Indiana), which carrier is further coated with a SnO 2 coating by substantially following the procedure of Example 41 hereinabove, i.e., the carrier has a 1.0 pph SnO 2 coating and is fired at an oven temperature of 900°C.
  • the resistivity of the carrier is measured according to the procedure described in Examples 1-4, and is determined to be 8 x 10 7 ohm-cm.
  • the toner employed is prepared using 92 wt% of a conventionally-prepared poly(sytrene-co-butylacrylate) polymer resin obtained from Eastman Kodak Company of Rochester, NY, which resin is blended with 1 wt% of an organo-iron complex charge-control agent (T-77 obtainable from Hodagaya of Japan), and 7 wt% of carbon black (430 Black Pearls obtainable from Cabot Corporation).
  • T-77 obtainable from Hodagaya of Japan
  • carbon black 430 Black Pearls obtainable from Cabot Corporation.
  • the resulting raw toner mixture is ground and sieved to obtain a toner resin powder having an average particle size of 12.2 ⁇ m as determined using a Coulter Counter.
  • Example 43 Five different developer compositions are prepared, one for each of the five runs in Example 43, by mixing together the above-described carrier with varying amounts of the above-described toner so as to obtain developer compositions having a toner concentration (TC) of 6.4, 8.6, 10.7, 13.1 , and 15.1 wt% respectively, based on the total weight of the applicable developer composition.
  • TC toner concentration
  • the resistivity of the developer composition is measured immediately after making the developer composition by using substantially the same equipment and procedure used to determine carrier resistivity as described in Examples 1-4 hereinabove, except that 2.00 g of the so-made developer mixture is employed, rather than 2.00 g of carrier.
  • Table XVI The values obtained for developer resistivity are shown in Table XVI.
  • the toner charge-to-mass ratio - (Q/m) toner - is measured according to the procedure of Examples 1-4 hereinabove, and the values obtained are shown in Table XVI.
  • the carrier charge-to-mass ratio - (Q/m)car r ier - is then calculated from the measured (Q/m) to ner according to the following equation, with TC expressed as a weight percent:
  • the performance of each of the above-described developer compositions is then evaluated using the electrographic device and procedures substantially as described in Examples 1-4, except as provided hereinafter.
  • the entire photoconductive film (having rectangular dimensions of 5.5 inch by 8.25 inch, for an area of exposure of 45.375 in 2 ) is biased developed.
  • the grid voltage is set to give about +600 volts (V) potential on the photoconductive film, and a -400 V offset is set to yield a constant +400V potential from the shell to the photoconductive film.
  • the development efficiency is calculated based on the degree to which the +400 V potential is reduced during development of the photoconductive film with each developer composition relative to the original +400 V.
  • the device has a developer station employing a rotating magnetic core having 12 magnetic poles and a magnetic strength of 1000 Gauss.
  • the developer station also has a shell disposed about the rotating core, wherein the surfaces of the shell and photoconductive film are spaced apart from each other and are set to have a spacing of 0.020 inches.
  • the core is rotated clockwise at 1000 rpm, and the shell is rotated at 15 rpm counter-clockwise.
  • the photoconductive film is set to travel at a speed of 2 inches per second, while in the development section the photoconductive film is set to travel at a speed of 5 inches per second.
  • the nap density is 0.24 g/in 2 .
  • the toning nip width is 0.375 inches.
  • Relative development efficiency (Rel DE) is determined as in Examples 1-4 in reference to the development efficiency obtained using the developer in Run No. 3 of Example 47.
  • the l-CPU for each developer composition during each run is determined using a quantitative procedure as described hereinafter.
  • l-CPU is determined in each run by washing the toner (and any developed carrier) off of the photoconductive film after development using at least 15 ml of a solvent consisting of 50 wt% acetone and 50 wt% dichloromethane based on total weight of the mixed solvent.
  • the foregoing mixed solvent is sufficient to dissolve the toner resin, but not the carrier particles that may develop on the photoconductive film.
  • the remaining carrier particles are magnetically collected from the solvent, washed at least 3 times with the mixed solvent, and then dried.
  • the dried carrier particles collected from the photoconductive film are then weighed, and the amount of carrier obtained in each run is listed in Table XVI.
  • l-CPU in terms of carrier deposition density, i.e., grams of carrier developed per unit area of photoconductive film, based on 45.375 in 2 of area for exposure as previously described.
  • Example 43 Data For Carrier with 1.0 pph SnO? Coating (900°C)and Varying TC Level
  • Table XVI illustrates that by varying TC level in the developer composition, for example at a toner average particle size of about 12 ⁇ m, one can vary the toner concentration in the developer from about 6 to 15 wt%, based on total weight of the developer, and thereby adjust the (Q/m) carrier value for the developer composition and directly influence the l-CPU characteristic.
  • a desirable range for TC, for a developer composition comprised of a carrier with a given level of resistivity within the ranges as recited herein would be that sufficient to yield a deposition density of desirably less than about 0.01 g/in 2 , preferably less than about 0.001 g/in 2 , and more preferably less than about 0.0001 g/in 2 .
  • the data also suggest that l-CPU can be modulated by the (Q/m) carr i er value, particularly when the carrier resistivity is at or near a threshold value where l-CPU would otherwise reach an unacceptable level.
  • Example 44 the procedures described in Example 43 above are substantially repeated, except as provided hereinafter.
  • the commercially-available SrFe ⁇ 2 O 19 hard ferrite carrier is coated with a SnO 2 coating by substantially following the procedures of Examples
  • the resistivity of the resulting carrier is determined by substantially the same procedure, and is measured to be 1.5 x 10 8 ohm-cm, i.e., it is slightly more resistive relative to the carrier fired at 900°C used in Example 43, which is consistent with the general results obtained by Examples 11-13 hereinabove as shown in Fig. 4.
  • the toner is substantially similar to that employed in Example 43, except that it is ground and classified to yield a toner powder with an average particle size of 9.9 ⁇ m as determined by Coulter Counter.
  • the five developer compositions are made by substantially the same procedure, except that the amount of toner employed is sufficient to yield a TC of 5.1, 6.9, 9.1 , 11.0, and 12.9 wt% respectively, based on the total weight of the applicable developer composition.
  • the data obtained is shown in Table XVII below:
  • Example 44 Data For Carrier with 1.0 pph SnO? Coating (875°C), Toner (9.9 ⁇ m), and
  • Run Toner Size TC (Q/m) 1 (Q/m) 2 DE Rel DE* l-CPU l-CPU Dev. Resistivity No. ( ⁇ m) (wt%) ( ⁇ C/g) (txC/g) (grams) (g/in 2 ) (Ohm-cm)
  • Example 43 The results are consistent with Example 43.
  • Table XVII illustrates that by varying TC level in the developer composition, for example at a toner average particle size of about 10 ⁇ m, one can vary the toner concentration in the developer from about 5 to 13 wt%, based on total weight of the developer, and thereby TC adjust the (Q/m) carr ⁇ er value for the developer composition and directly influence the l-CPU characteristic.
  • the data suggest that l-CPU can be modulated by the (Q/m) ca r ⁇ er value.
  • Example 45 In Example 45, the procedures described in Example 43 above are substantially repeated except as provided hereinafter.
  • the carrier employed is the 1.0 pph SnO 2 coated carrier prepared as described in Example 43.
  • the toner employed is a yellow polyester toner prepared substantially as described in U. S. Patent 4,833,060, as described in Examples 1-4 hereinabove.
  • the toner is also surface-treated with 0.89 wt% (based on total weight of the toner) of silica (R972 from Degussa of Germany) to enhance toner flow properties.
  • the surface treatment is performed by powder blending the pulverized and classified toner particles with the R972 silica in a high-energy mixer Henschel FM75 mixer obtained from Thyssen Henschel Industrietechnik GmbH of Kassel, Germany.
  • the toner and the R972 silica are added to the mixer in amounts sufficient to yield the above-described weight percentage of silica, and thereafter the mixer is operated at a speed of 1745 revolutions per minute (rpm) for 2.5 minutes.
  • the resulting toner/silica mixture is collected and sieved with a 325 mesh screen to remove agglomerated silica particles.
  • the resulting sieved surface treated toner is then further employed to prepare developers as described hereinbelow.
  • the toner has an average particle size of 7.1 ⁇ m as determined by a Coulter Counter device.
  • the five developer compositions are made by substantially the same procedure described in Example 43, except that the amount of toner employed is sufficient to yield a TC of 3.7, 4.8, 5.9, 6.3, and 8.0 wt% respectively, based on the total weight of the applicable developer composition.
  • the data obtained is shown in Table XVIII below:
  • Example 45 Data For Carrier with 1.0 pph SnO? Coating (900°C), Toner (7.1 ⁇ m), and
  • Table XVIII illustrates that by varying TC level in the developer composition, for example at a toner average particle size of about 7 ⁇ m, one can vary the toner concentration in the developer from about 4 to 8 wt%, based on total weight of the developer, and thereby TC adjust the (Q/m) carr i er value for the developer composition and directly influence the l-CPU characteristic.
  • Example 46 the procedures described in Example 43 above are substantially repeated except as provided hereinafter.
  • the carrier employed is the 1.0 pph SnO 2 coated carrier prepared as described in Example 43.
  • the toner employed is made from 100 parts of a polyester resin binder, 1 part of a di-tertbutyl salicylic acid charge-control agent (Bontron E- 88 obtained from Orient Chemical Company of Japan) and 4 parts carbon black (Cabot 330 obtained from Cabot Corporation) and is prepared by conventional methods well-known in the art.
  • the toner is ground and classified so as to have an average particle size of 5.9 ⁇ m as determined by a Coulter Counter device.
  • the toner is also surface treated with 1.5 wt% (based on total weight of the toner) of silica (R972 from Degussa of Germany) to enhance flow properties by substantially the same procedure as described in Example 45.
  • the five developer compositions are made by substantially the same procedure described in Example 43, except that the amount of toner employed is sufficient to yield a TC of 3.8, 4.8, 5.6, 6.7, and 7.7 wt% respectively, based on the total weight of the applicable developer composition.
  • the data obtained is shown in Table XIX below:
  • Example 46 Data For Carrier with 1.0 pph SnO? Coating (900°C). Toner (5.9 um). and Varying TC Level
  • Table XIX show the same results illustrated by Examples 43-45.
  • the data in Table XIX illustrates that by varying TC level in the developer composition, for example at a toner average particle size of about 6 ⁇ m, one can vary the toner concentration in the developer from about 4 to 8 wt%, based on total weight of the developer, and thereby TC adjust the (Q/m) ca rrier value for the developer composition and directly influence the l-CPU characteristic.
  • each data set (in other words, the data for the 12.2 ⁇ m toner, 9.9 ⁇ m toner , 7.1 ⁇ m toner and 5.9 ⁇ m toner, respectively) supports the discussion hereinabove in relation to Fig. 1.
  • an operating window can be developed based on the developer resistivity and (Q/m) carr i er that defines the relationship between development efficiency and l-CPU.
  • adjusting the TC and maintaining the (Q/m) carr i er parameter preferably above 1 ⁇ C/g, more preferably greater than 3.0 ⁇ C/g, and most preferably greater than 4.0 ⁇ C/g, can yield reduced amounts of deposition density for carrier in the resulting image.
  • the relationship between l-CPU and (Q/m) carr i er is illustrated by Fig 5, which shows the data obtained for such parameters in Examples 43-46. Very low levels of l-CPU are generally obtained when the (Q/m) carr i er parameter is greater than 2 ⁇ C/g, and especially at higher levels for the (Q/m) carr ier parameter.
  • the carrier on the core has a positive charge level determined by the TC and (Q/m) to ner for the developer employed.
  • the carrier begins to charge negatively at a rate proportional to the toning bias and developer resistivity.
  • l-CPU should be minimal provided the carrier charge in the nip area is maintained at a positive level.
  • Example 47 the procedures described in Examples 43-46 above are substantially repeated, except as provided hereinafter.
  • the carrier employed is a 1.0 pph SnO 2 coated carrier prepared substantially as described in Example 43, except that it is fired at an oven temperature of 610°C.
  • the carrier has a resistivity of 2.1 x 10 10 ohm-cm.
  • the series of developers with varying TC levels is not provided, but developers are made using each of the four toners from Examples 43-46.
  • the toner employed in Run No. 1 is the black poly(styrene-co-butylacrylate) toner described in Example 43; the toner employed in Run No. 2 is the black poly(sytrene-co- butylacrylate) toner described in Example 44; the toner employed in Run No. 3 is the yellow polyester toner described in Example 45; and the toner employed in Run No. 4 is the black polyester toner described in Example 46.
  • the four developer compositions (carrier and the toners as previously described) are made by substantially the same procedure described in Example 43.
  • the TC employed in each developer composition is shown in Table XX, along with electrographic performance data: Table XX
  • Example 47 Data For Developers Made Using SnO 2 Coated Carrier (610°C), and Different
  • Example 48 the procedure described in Example 47 above is substantially repeated, except as provided hereinafter.
  • the carrier employed is a 1.0 pph SnO 2 coated carrier prepared substantially as described in Example 47, except that it is fired at an oven temperature of 825°C.
  • the carrier has a resistivity of 8.0 x 10 9 ohm-cm.
  • the TC employed in each developer composition is shown in Table XXI, along with electrographic performance data:
  • Example 48 Data For Developers Made Using SnO? Coated Carrier (825°C), and Different
  • Example 49 the procedure described in Example 47 above is substantially repeated, except as provided hereinafter.
  • the carrier employed is a 1.0 pph GeO 2 coated carrier prepared substantially as described in Examples 11-13, fired at an oven temperature of 750°C.
  • the carrier has a resistivity of 5.2 x 10 6 ohm-cm.
  • the TC employed in each developer composition is shown in Table XXII, along with electrographic performance data:
  • Example 49 Data For Developers Made Using GeO? Coated Carrier (750°C), and Different Particle Size Toners
  • Example 50 the procedures described in Example 47 are substantially repeated except as provided hereinafter.
  • the carrier employed is a strontium ferrite material doped with Lanthanum metal obtainable as carrier FXC4809 from POWDERTECH.
  • the carrier has a resistivity of 2.8 x 10 5 ohm-cm.
  • the series of developers with varying TC levels is not provided, but developers are made using each of the four toners from Examples 43-46.
  • the toner employed in Run No. 1 is the black poly(styrene-co-butylacrylate) toner described in Example 43; the toner employed in Run No. 2 is the black poly(sytrene-co- butylacrylate) toner described in Example 44; the toner employed in Run No. 3 is the yellow polyester toner described in Example 45; and the toner employed in Run No. 4 is the black polyester toner described in Example 46.
  • the four developer compositions (carrier and the toners as previously described) are made by substantially the same procedure described in Example 43.
  • the TC employed in each developer composition is shown in Table XXIII, along with electrographic performance data:
  • Example 50 Data For Developers Made Using Lanthanum Doped Carrier and Different
  • Run Toner Size TC (Q/m) 1 (Q/m) 2 DE Rel DE * l-CPU l-CPU Dev. Resistivity No. (um) (wt%) (uC/g) (uC/g) (grams) (g/in 2 ) (Ohm-cm)
  • Comparative Example E the procedure described in Example 47 above is substantially repeated, except as provided hereinafter.
  • the carrier employed is a conventional carrier substantially as described in Comparative Example A, except that it has a resistivity of 8 x 10 10 ohm-cm.
  • the TC employed in each developer composition is shown in Table XXIV, along with electrographic performance data:
  • Example 51 the procedure described in Example 44 above is substantially repeated except as provided hereinafter.
  • the commercially-available SrFe 12 O 19 hard ferrite carrier is coated with a SnO 2 coating by substantially following the procedures of Examples 41 and 43, i.e., the carrier is fired at an oven temperature of 900°C rather than 875°C.
  • the resistivity of the resulting carrier is 8 x 10 7 ohm-cm.
  • a series of developers is not provided, but the toner (9.9 ⁇ m) described in Example 44 is used with the above-described carrier to make a single developer composition with a TC of 8.9 wt% based on the total weight of the developer composition.
  • the data obtained is a Q/m toner of -42.1 ⁇ C/g; a Q/m earner of 4.1 ⁇ C/g; a DE of 0.645, a Rel DE of 2.62 (compared to the control carrier of Example 47, Run 3), Developer Resistivity of 4.7x10 7 Ohm-cm, and a l-CPU of 0.005 gram (and in terms of deposition density 1.10x10 " " g/in 2 ).
  • Example 52 the procedure described in Example 51 above is substantially repeated except as provided hereinafter.
  • the commercially-available SrFe ⁇ 2 O ⁇ 9 hard ferrite carrier is coated with a SnO 2 coating by substantially following the procedures of Examples 41 and 43, except that the carrier is fired at an oven temperature of 1025°C rather than 900°C.
  • the resistivity of the resulting carrier is 7.7 x 10 5 ohm-cm.
  • a series of developers is not provided, but the toner (9.9 ⁇ m) described in Example 44 is used with the above- described carrier to make a single developer composition with a TC of 9.0 wt% based on the total weight of the developer composition.
  • the data obtained is Q/m to n e r of -43.1 ⁇ C/g; Q/m carr ie r of 4.2 ⁇ C/g; DE of 0.832, Rel DE of 3.38 (compared to the control carrier of Example 47, Run 3), Developer Resistivity of 5.0x10 5 Ohm-cm, and a l-CPU of 0.0578 gram (and in terms of deposition density 1.27x10 "3 g/in 2 ).
  • Q ct /M c is calculated from Equation (3) described hereinabove in the Detailed Description section and the observed ICPU values are then plotted versus the calculated Q Ct /M c .
  • the resulting graph, Fig. 9, is generated using measured data for TC, Q ⁇ /M ⁇ in units of ⁇ C/g, p in units of ohm-cm, and DE.
  • the limiting value of Q cf /M c used is assumed to be approximately -2 ⁇ C/g, t is approximately 0.075 sec
  • Fig. 9 shows that l-CPU depends on the charge that the carrier acquires in the toning nip area, and that there is a threshold value for Q ct /M c below which l-CPU would acceptable.
  • Carriers and developer compositions comprised of barium and lead containing ferrites, commonly referred to as magnetoplumbite ferrites, with characteristics as described hereinabove are expected to achieve similar results when used as electrographic carrier materials.
  • Electronography and electrophotography as used herein are broad terms that include image forming processes involving the development of an electrostatic charge pattern formed on a surface with or without light exposure, and thus includes electrophotography and other similar processes.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Developing Agents For Electrophotography (AREA)
  • Magnetic Brush Developing In Electrophotography (AREA)
  • Dry Development In Electrophotography (AREA)
  • Discharging, Photosensitive Material Shape In Electrophotography (AREA)

Abstract

L'invention concerne des procédés destinés au développement d'une image électrostatique. Ces procédés font intervenir des compositions de révélateur avec des compositions de support magnétique dur pouvant présenter une efficacité de développement améliorée et des niveaux réduits de capture de support d'image. Lesdits procédés utilisent des particules de support magnétique dur modifiées de manière à présenter des niveaux spécifiques de résistivité, et notamment une résistivité comprise entre environ 1x105 ohm-cm et environ 1x1010 ohm-cm, ainsi qu'un rapport charge sur masse supérieur à environ 1,0 νC/g pour ces supports, lesquels permettent d'obtenir des vitesses de développement élevées sans pour autant impliquer des niveaux excessifs de capture de support d'image. Dans certains modes de réalisation, les matières magnétiques dures sont dopées, soit substituées en masse, avec des métaux multivalents en vue de réguler la résistivité. Dans d'autres modes de réalisation, lesdites matières magnétiques dures sont revêtues par au moins un oxyde de métal multivalent.
PCT/US2001/015510 2000-05-17 2001-05-14 Procede d'utilisation de supports magnetiques durs dans un processus electrographique WO2001088623A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CA002375345A CA2375345A1 (fr) 2000-05-17 2001-05-14 Procede d'utilisation de supports magnetiques durs dans un processus electrographique
AU2001259764A AU2001259764A1 (en) 2000-05-17 2001-05-14 Method for using hard magnetic carriers in an electrographic process
JP2001584955A JP2003533745A (ja) 2000-05-17 2001-05-14 エレクトログラフ処理において硬質磁気キャリアを用いるための方法

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US20494100P 2000-05-17 2000-05-17
US09/572,988 2000-05-17
US09/572,989 2000-05-17
US60/204,941 2000-05-17
US09/572,989 US6228549B1 (en) 2000-05-17 2000-05-17 Magnetic carrier particles
US09/572,988 US6232026B1 (en) 2000-05-17 2000-05-17 Magnetic carrier particles

Publications (1)

Publication Number Publication Date
WO2001088623A1 true WO2001088623A1 (fr) 2001-11-22

Family

ID=27394727

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2001/015510 WO2001088623A1 (fr) 2000-05-17 2001-05-14 Procede d'utilisation de supports magnetiques durs dans un processus electrographique

Country Status (5)

Country Link
EP (1) EP1156375A3 (fr)
JP (1) JP2003533745A (fr)
AU (1) AU2001259764A1 (fr)
CA (1) CA2375345A1 (fr)
WO (1) WO2001088623A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6121675B2 (ja) * 2012-09-27 2017-04-26 Ｄｏｗａエレクトロニクス株式会社 焼結粒子及びそれを用いた電子写真現像剤用キャリア、電子写真用現像剤並びに焼結粒子の製造方法
JP6569173B2 (ja) * 2015-01-28 2019-09-04 パウダーテック株式会社 外殻構造を有するフェライト粒子
JP6766134B2 (ja) * 2016-04-05 2020-10-07 パウダーテック株式会社 電子写真現像剤用フェライトキャリア芯材、電子写真現像剤用フェライトキャリア、電子写真現像剤及び電子写真現像剤用フェライトキャリア芯材の製造方法
CN109626984B (zh) * 2019-01-30 2020-11-27 浙江大学 一种低电场高介电可调锆掺杂钡铁氧体及其制备方法

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5989767A (en) * 1998-12-15 1999-11-23 Eastman Kodak Company Carrier particles for electrostatographic developers

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4368970A (en) * 1980-06-02 1983-01-18 Xerox Corporation Development process and apparatus
JPS58202456A (ja) * 1982-04-07 1983-11-25 Hitachi Metals Ltd 電子写真用フエライトキヤリア−
US4764445A (en) * 1987-06-15 1988-08-16 Eastman Kodak Company Electrographic magnetic carrier particles
US4855205A (en) * 1988-08-05 1989-08-08 Eastman Kodak Company Interdispersed two-phase ferrite composite and carrier therefrom
US4855206A (en) * 1988-08-05 1989-08-08 Eastman Kodak Company Rare earth containing magnetic carrier particles
US5061586A (en) * 1990-04-05 1991-10-29 Eastman Kodak Company Glass composite magnetic carrier particles
DE4140900A1 (de) * 1991-12-12 1993-06-17 Basf Ag Als carrier fuer die elektrophotographie geeignete teilchen
US5190841A (en) * 1991-12-19 1993-03-02 Eastman Kodak Company Two-phase ferroelectric-ferromagnetic composite and carrier therefrom
EP0580135B1 (fr) * 1992-07-22 1997-04-16 Canon Kabushiki Kaisha Véhiculeur pour électrophotographique, révélateur du type à deux composants et procédé de formation d'images
DE4403678A1 (de) * 1994-02-07 1995-08-10 Basf Ag Metalloxid- und metallbeschichtete Carrier für die Elektrophotographie
DE69511209T2 (de) * 1994-10-05 1999-11-25 Toda Kogyo Corp Magnetischer Träger für Elektrophotographie
US5998076A (en) * 1998-03-09 1999-12-07 Xerox Corporation Carrier
US5948585A (en) * 1998-07-16 1999-09-07 Eastman Kodak Company Optimized particulate surface treatment concentration for electrostatographic images produced in an electrostatographic engine that includes a compliant intermediate transfer member

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5989767A (en) * 1998-12-15 1999-11-23 Eastman Kodak Company Carrier particles for electrostatographic developers

Also Published As

Publication number Publication date
EP1156375A2 (fr) 2001-11-21
AU2001259764A1 (en) 2001-11-26
JP2003533745A (ja) 2003-11-11
EP1156375A3 (fr) 2002-08-21
CA2375345A1 (fr) 2001-11-22

Similar Documents

Publication Publication Date Title
US4764445A (en) Electrographic magnetic carrier particles
US5106714A (en) Interdispersed two-phase ferrite composite and electrographic magnetic carrier particles therefrom
AU555150B2 (en) Electrographic developer composition and method for using thesame
US5104761A (en) Interdispersed three-phase ferrite composite and electrographic magnetic carrier particles therefrom
EP1156376B1 (fr) Particules de support magnétiques
EP0547620B1 (fr) Composition ferroélectrique-ferromagnétique à deux phases et support obtenu à partir de ladite composition
US5061586A (en) Glass composite magnetic carrier particles
EP1156391B1 (fr) Procédé électrophotographique utilisant des compositions de développeurs contenant un matériau magnétique dur
US8039190B2 (en) Carrier core material for electrophotographic developer, carrier, and electrophotographic developer using the carrier
US5190842A (en) Two phase ferroelectric-ferromagnetic composite carrier
US5500320A (en) High speed developer compositions with ferrite carriers
US6232026B1 (en) Magnetic carrier particles
US6723481B2 (en) Method for using hard magnetic carriers in an electrographic process
EP1156375A2 (fr) Méthode électrophotograhique utilisant des particules de support contenant un matériau magnétique dur
WO2017175647A1 (fr) Matériau de noyau de support de ferrite pour révélateur électrophotographique, support de ferrite pour révélateur électrophotographique, révélateur électrophotographique, et procédé de production de matériau de noyau de support de ferrite pour révélateur électrophotographique

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AU AZ BA BB BG BR BY BZ CA CN CR CZ DM DZ EE GD GE GH GM HR HU ID IL IN IS JP KE KG KR KZ LC LK LR LS LT LV MA MD MG MK MN MW MX MZ NO NZ PL RO RU SD SG SI SK SL TJ TM TR TT TZ UA UG UZ VN YU ZA ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZW AM AZ BY KG KZ MD RU TJ TM BF BJ CF CG CI CM GA GN GW ML MR NE SN TD TG

ENP Entry into the national phase

Ref document number: 2375345

Country of ref document: CA

Ref country code: CA

Ref document number: 2375345

Kind code of ref document: A

Format of ref document f/p: F