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
  • G03G9/087—Binders for toner particles
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08706—Polymers of alkenyl-aromatic compounds
  • G03G9/08708—Copolymers of styrene
• • 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
  • G03G9/1087—Specified elemental magnetic metal or alloy, e.g. alnico comprising iron, nickel, cobalt, and aluminum, or permalloy comprising iron and nickel
• • 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
  • G03G9/087—Binders for toner particles
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08706—Polymers of alkenyl-aromatic compounds
  • G03G9/08708—Copolymers of styrene
  • G03G9/08711—Copolymers of styrene with esters of acrylic or methacrylic acid
• • 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
  • G03G9/087—Binders for toner particles
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08737—Polymers derived from conjugated dienes
• • 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
  • G03G2215/00—Apparatus for electrophotographic processes
  • G03G2215/06—Developing structures, details
  • G03G2215/0602—Developer
  • G03G2215/0604—Developer solid type
  • G03G2215/0607—Developer solid type two-component
  • G03G2215/0609—Developer solid type two-component magnetic brush

Definitions

• This invention relates generally to a two-component type magnetic developer for developing electrostatically charged images in electrostatographic processes for generating documents suitable for magnetic image character recognition, and particularly to a two-component type magnetic developer for developing electrostatically charged images in electrostatographic processes for generating documents suitable for magnetic image character recognition which provides clear, sharp developed images having both excellent line and solid area development.
• Magnetic ink character recognition involves the encoding of certain magnetic image character recognition information (MICR) in accordance with the American National Standards Institute (ANSI) standards for MICR reading at the bottom line of personal and commercial checks.
• MICR characters appears as the printed numbers and symbols in the somewhat unique "futuristic" font at the bottom line of each check.
• the checks are printed with a magnetic ink containing magnetizable particles.
• the document When the information contained on the document is to be read, the document is passed through a sorter/reader which first magnetizes the magnetizable particles and subsequently detects a magnetic field of the symbols resulting from the magnetic retentivity of the ink.
• a sorter/reader which first magnetizes the magnetizable particles and subsequently detects a magnetic field of the symbols resulting from the magnetic retentivity of the ink.
• the characters and symbols involved identify the bank, the bank branch or the issuing source, and/or the account affected by the transaction.
• an electrostatic image of the desired hard copy is formed by selectively discharging a uniformly charged photoconductive surface, the photoreceptor, by a modulated scanned laser illuminator or light emitting diodes.
• a visible image is formed by delivering charged toner, made of a pigmented resin, to the photoreceptor surface in the development step.
• the charged toner adheres to the charged areas of the photoreceptor since the toner composition is selected such that the toner acquires a charge opposite in sign to the photoreceptor surface charge.
• the toner charging occurs through a triboelectric interaction between the toner and the carrier bead, a much larger magnetic particle, in which the particles rub together and acquire opposite electrostatic charges.
• the carrier serves the functions of charging the toner and transporting it to the photoreceptor under the control of magnetic fields in the developer housing.
• the developed image is subsequently transferred to paper by electric fields in the transfer station.
• the image on the paper is finally and permanently fixed in place by suitable fixing means such as a hot roll fuser while the photoreceptor is cleaned of any untransferred toner and uniformly discharged for reuse.
• the method for applying the developer mix which is described above is well-known and is referred to as the "magnetic brush" process or technique.
• Such a process can utilize apparatus of the type described, for example, in U.S. Patent No. 3,003,462 and often comprises a nonmagnetic rotatably mounted cylinder having fixed magnetic means mounted inside.
• the cylinder is arranged to rotate so that part of the surface is immersed in or otherwise contacted with a supply of developer mix.
• the granular mass comprising the developer mix is magnetically attracted to the surface of the cylinder.
• the particles of the developer mix arrange themselves in bristle-like formations resembling a brush.
• the bristle formations of developer mix tend to conform to the lines of magnetic flux, standing erect in the vicinity of the poles and lying substantially flat when the mix is outside the environment of the magnetic poles.
• the continuously rotating cylinder picks up developer mix from a supply source and then returns part or all of the material to the supply. This mode of operation assures that fresh mix is always available to the photoconductive surface at its point of contact with the brush.
• the roller performs the successive steps of developer mix pickup, brush formation, brush contact with the photoconductive element, brush collapse and finally mix release.
• this "magnetic brush” engages or contacts the electrostatic image bearing photoconductive surface, the toner particles are drawn from the brush, i.e.
• the toner particles are drawn away from the carrier particles, by the oppositely charged electrostatic image.
• more than one such magnetic roller device can be utilized in the process to apply the developer mix to the photoconductive element as in the case where large solid image areas such as logos and the like which require large amounts of toner are desired to be developed.
• the conductivity of the ferromagnetic carrier particles which form the "bristles" of the magnetic brush provides the effect of a development electrode having a very close spacing to the surface of the photoconductive or electrophotographic element being developed. By virtue of this development electrode effect it is to some extent possible to develop part of the toner in pictures and solid blacks as well as line copy. This ability to obtain solid area development with magnetic brush developing makes this mode of development advantageous where it is desired to print materials other than simple line copy.
• MICR encoded documents In the production of MICR encoded documents, this mode of development is particularly useful and suitable since magnetic toner particles must be used in the developer in order to provide MICR readable characters and symbols. That is, the developed characters must produce magnetic signals within defined limits when passed through a MICR reader so that the information can be read.
• An objective of this invention is to provide a magnetic developer which can be used in conventional electrostatographic processes for generating documents suitable for magnetic image character recognition which is capable of producing magnetic image character recognition images and characters of excellent MICR readable quality and overcomes the optical image density defect problems previously described.
• This invention provides a two-component type magnetic developer that can be used in known electrostatographic processes for generating documents suitable for use in magnetic image character recognition that can simultaneously provide both MICR images and characters of excellent MICR readable quality and developed images having excellent image density and sharpness.
• the two-component magnetic developer of the invention comprises a mixture of magnetic carrier particles composed of passivated acicular magnetic stainless steel particles containing at least 9 weight percent chromium, the surfaces of which comprise a thin protective layer that is rich in chromium, and a magnetic toner comprising particles of a binder resin medium and a magnetic material which is dispersed in the binder resin medium.
• a magnetic developer which can be used in known electrostatographic processes to generate documents which are suitable for magnetic ink character recognition which not only is capable of achieving high MICR image performance, i.e., high MICR readability, but a magnetic developer that also is capable of achieving high optical print quality, i.e., capable of providing developed images and characters of excellent image density and sharpness.
• the two-component magnetic developer composition of the invention is characterized in that it is formed of a mixture of particles of a magnetic toner comprising a binder resin medium and a magnetic material or component, such as magnetite, which is dispersed in the binder resin medium and particles of a magnetic carrier comprising a mass of passivated acicular magnetic stainless steel particles containing at least 9 weight percent chromium, the surfaces of which comprise a thin protective layer that is high in chromium.
• the magnetic toner particles are mixed with the specific magnetic carrier, that is, a magnetic carrier consisting of a mass of passivated acicular magnetic stainless steel particles containing at least 9 weight percent chromium and whose surfaces comprise a thin protective layer that is rich in chromium, and the resulting two-component developer is employed to develop electrostatically charged images in an electrostato- graphic process used to generate documents suitable for magnetic image character recognition
• the solid area image density and hence the image quality is prominently improved over the solid area image density and image quality attainable by the use of a two-component magnetic developer consisting of a mixture of the same magnetic toner particles and a magnetic carrier consisting of an ordinary magnetic carrier such as the ferrite carrier particles which are disclosed in Gruber et al such as iron powder or iron oxide as being a suitable carrier material for use with a magnetic toner such as magnetite in a two-component magnetic developer composition for developing electrostatographically charged images in an electrostatographic process used to generate documents suitable for magnetic image character recognition.
• the specific magnetic carrier that
• Reflection density measurements of the formed images show that when the specific magnetic carrier particles described herein are mixed with magnetic toner particles comprising a toner resin binder and magnetite dispersed within the binder, the image density is dramatically increased over the image density obtained when such carrier particles are not incorporated in the developer composition with the same magnetic toner but instead are replaced with an equivalent amount of uncoated sponge iron powder carrier particles.
• the passivated stainless steel particles described herein being more electrically conductive (i.e., having a higher surface conductivity) due to passivation treatment than the iron or steel carrier particles of Gruber et al, produce a stronger development electrode effect than the carrier particles of Gruber et al and thereby provide better solid area development than the solid area development provided by the Gruber et al carrier particles.
• the carrier chains which are composed of the passivated stainless steel particles described herein more electrically conductive than the chains of carrier particles of Gruber et al due to passivation treatment they are more electrically stable so that their conductivity remains stable for an extended period of time under development conditions.
• the acicular or ansiotropic shape of the passivated stainless steel carrier particles used in the developer mixes described herein also contributes to the enhancement of the development electrode effect.
• a long and narrow piece of magnetic material magnetizes along its length or long axis and has a stronger magnetic field than a spherical or bead-shaped piece of the same material. This is due to the smaller demagnetizing field in the long and narrow material resulting from the greater distance between the poles of the longer material.
• the strong magnetic contact between the individual carrier particles also is believed to prevent toner particles, which are insulative relative to the carrier particles due to the low conductive nature of the binder resin material which forms a part of the toner composition from working their way in between individual carrier particles at their points of contact as they would be expected to do in the case of the less tightly held spherically-shaped particles and increase the electrical resistance of the carrier chain.
• the carrier component of the two-component magnetic developer of the invention comprises a mass of passivated particles of acicular magnetic stainless steel.
• the passivated steel surface comprises a thin, tightly adherent, chromium-rich layer.
• the particles of magnetic stainless steel are passivated, most suitably, by treatment with nitric acid.
• the passivation of stainless steel apparently rids its surface of free iron, enriching it in chromium which oxidizes to form a layer that is chemically stable and inert under electrostatographic development conditions.
• the resultant passivated stainless steel carrier particles are characterized as having improved conductivity and stability.
• stainless steel designates a family of alloy steel of sufficiently high chromium content, e.g., at least 9 weight percent, to resist the corrosion or oxidation to which ordinary carbon steels are susceptible in a moist atmosphere. Not all stainless steels, however, can be used as carrier materials in the developer compositions described herein. The steel must be magnetic. Two types that meet this requirement are martensitic stainless steels, which contain from 10 to 18 weight percent chromium, and ferritic stainless steels, which contain from 15 to 30 weight percent chromium. Austenitic stainless steels contain a large amount of nickel (6 to 22 weight percent) and normally are nonmagnetic in the annealed condition.
• Passivation of stainless steel consists of any treatment that forms a thin protective film or layer on the surface of the steel.
• This layer which is transparent and microscopically thin, is rich in chromium relative to the untreated steel.
• the layer is more electrically conductive than the oxides of iron, and, being chemically stable, its conductivity remains stable for an extended period of time under development conditions.
• X-ray photoemission spectroscopy of the passivated surfaces indicates that the minimum thickness of the layer is 30 ⁇ and that the ratios of Cr/Fe, O/Fe and C/Fe are increased at the surface as compared with the untreated steel. It also indicates the chromium in the surface layers is in the form Cr(OH)3.
• a particularly useful method of passivating the stainless steel is by treatment with nitric acid.
• Other passivating treatments are known, however, and any passivating treatment that forms on the steel a surface that remains free of copper in the standard copper plating test can be used.
• the sample of steel typically a plate 2.5 cm x 5 cm x 0.16 cm is immersed in an acidified copper chloride solution containing 10 g of cupric chloride, 500 ml water and 5 ml hydrochloric acid at room temperature (20°C).
• Plating of copper onto the steel shows that the steel has a reactive surface and has not been passivated. If the steel remains free of copper it is, by definition, passivated and is useful as a carrier in the developers described herein.
• reaction conditions for passivating with nitric acid or other passivating agents can vary depending on the composition and, to some extent, the particle size of the stainless steel. Whether or not certain conditions or passivating agents are suitable can readily be determined by the copper plating test. In any event, for economy and good results nitric acid is particularly useful as the passivating agent.
• Especially suitable conditions for nitric passivation of stainless steels of American Iron and Steel Institute (AISI) grades 410 and 434 include: aqueous nitric acid concentration from 18 to 22 volume percent, preferably 20 volume percent; temperature of 50 to 90°C, preferably 60 to 80°C, and reaction time is 5 to 30 minutes, preferably 15 to 25 minutes. Other conditions can be used if the copper plating test shows that they do not in fact passivate the stainless steel.
• AISI American Iron and Steel Institute
• the acid treatment can be performed in different ways, including spraying and percolation.
• a particularly useful method is to form a slurry of the steel powder and the aqueous acid solution.
• the duration of this treatment will be influenced by the concentration of the acid, the temperature, the degree of agitation, and the particle size of the steel.
• the stainless steel powder is rinsed, preferably in water, and then any volatile water-visible solvent such as acetone or a lower alcohol such as methanol, ethanol or isopropanol.
• the rinsed carrier particles are dried, e.g., by agitating them in a current of warm air or nitrogen.
• Test No. 1 demonstrates the chemical stability of passivated stainless steel as compared with other steel or iron samples which have been treated in other ways.
• Nitric Acid Wash-One stainless steel plate was washed with a 20 volume percent nitric acid solution for 20 minutes. It was then rinsed in water for 5 minutes, next in methanol for 5 minutes and then air dried.
• Test No. 2 which is next described, compares the electrical properties of untreated and of passivated stainless steel powders.
• the stainless steel and iron powders were products of Hoeganaes Corp. of Riverton, N.J.
• the steel by analysis, was AISI type 410 L and contained iron as the major constituent and, by weight, 0.005% Al, 13.5% Cr, 0.025% Cu, ⁇ 0.0015% Mg, 0.07% Mn, 0.006% Mo, 0.04% Ni, 1.0% Si, 0.025% Ag and ⁇ 0.005% V.
• the treated and untreated stainless steel powders were tested for static resistance and breakdown voltage.
• Static resistance was measured across a magnetic brush as follows: The brush was formed by attracting 15 grams of carrier particles to one end of a cylindrical bar magnet of 2.5 cm diameter. The magnet was then suspended with the brush-carrying end 0.5 cm from a grounded brass plate. The resistance of the particles in the magnetic brush was then measured between the magnet and the plate by means of a voltohmmeter. The breakdown voltage was measured under dynamic operating conditions in the manner described in the patent to Kasper et al U.S. Pat. No. 4,076,857 of Feb. 28, 1978.
• the electrical resistance of the 410L stainless steel powder can be varied from 104 to 5 ohms by varying the hydrofluoric acid treatment time.
• Further control of the silicon content of the stainless steel surfaces can be achieved by high temperature annealing of the steel under high vacuum followed by treatment with hydrofluoric acid. For instance by heating the steel particles at 850°C in a high vacuum, the surface silicon content can be significantly increased. Then by etching with hydrofluoric acid the silicon content and the electrical resistance of the particles can be reduced to the desired level. The particles are passivated to stabilize their conductivity after the hydrofluoric acid treatment. By vacuum annealing and acid treatments as described it is possible to provide a range of selected electrical resistances for the stainless steel particles.”
• the developer is formed by mixing the passivated, acicular particles of stainless steel described previously with a magnetic toner. Mixing can be accomplished, for example, by the known dry-­blending method where the magnetic toner is supplied to a developer tank in an amount corresponding to the amount of the consumed magnetic toner and is mixed with the magnetic toner left in the tank whereby the developer is formed in situ.
• the developer normally will contain from 90 to 99 weight percent carrier and 10 to 1 weight percent toner.
• Magnetic toner compositions useful in the invention comprise particles composed of a binder resin medium having a particle size of from 3 to 30 microns, typically 0.5 to 25 microns, and a magnetic component or magnetically attractable material such as magnetite, having a particle size of 1 micron, or smaller, typically between 0.02 microns and 1.0 micron, and more preferably having an average particle size of 0.1 to 0.6 microns which is dispersed in the binder resin medium.
• the magnetic materials used in the toner compositions described herein are magnetic in that they are attracted to a magnet, however, they are not necessarily magnets themselves.
• Magnetite is a particularly useful magnetic material for use in the toner compositions of the invention.
• the shape of the particles is not particularly critical. Namely, fine cubic particles, amorphous particles, rounded particles and needle-like particles or combinations thereof may be used.
• Particularly useful magnetites are acicular magnetites commercially available from Pfizer Corporation as MO 4431 and MO 4232, cubical magnetites, MO 7029 commercially available from Pfizer Corporation, and Mapico Black, commercially available from Cities Service Company.
• Other useful magnetites which are commercially available include polyhedral magnetites, available from Hercules Incorporation as EX 1601 and XMT 100.
• the magnetic toner composition selected can contain mixtures of differently shaped magnetites.
• mixtures comprised of acicular and cubic magnetites that is, a mixture of hard magnetite and soft magnetite blends can be used.
• a mixture of hard magnetite and soft magnetite blends can be used.
• from 20 percent to 30 percent by weight of the hard magnetic substance can be selected and from 10 percent by weight to 30 percent by weight of a soft magnetic substance, such as Mapico Black, can be selected.
• binder resin medium there may be used polyamides, polyurethanes, epoxy, vinyl resins and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol.
• Any suitable vinyl resin may be employed in the toners described herein including homopolymers or copolymers of two or more vinyl monomers.
• vinyl monomeric units include styrene; vinyl naphthalene; ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; vinyl ester such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and like; esters of alpha-methylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl atrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate methyl-alphachloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and the like; acrylonitrile, methylacrylonitrile, acrylamide, vinyl
• toner resins containing a relatively high percentage of styrene are particularly useful since greater image definition and density is obtained with their use.
• the styrene resin employed may be a homopolymer of styrene or styrene homologs or copolymers of styrene with other monomeric groups containing a single methylene group attached to a carbon atom by a double bond. Any of the above typical monomeric units may be copolymerized with styrene by addition polymerization.
• Styrene resins may also be formed by the polymerization of mixtures of two or more unsaturated monomeric materials with a styrene monomer.
• the addition polymerization technique employed embraces known polymerization techniques such as free radical, anionic and cationic polymerization processes. Any of these vinyl resins may be blended with one or more other resins if desired, particularly other vinyl resins which insure good resistance against physical degradation.
• non-vinyl type thermoplastic resins may also be employed including resin modified phenolformalde­hyde resins, oil modified epoxy resins, polyurethane resins, cellulosic resins, polyether resins and mixtures thereof.
• Also useful as toner resins include those materials that are polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol as described in U.S. Patent Number 3,590,000.
• Especially useful resins are polystyrene resinous materials such as styrene butadiene resins, sstyrene butylmethacrylate copolymer resins, styrene acrylate copolymers, such as styrene butylacrylate copolymer resins, and the like.
• toner resin particles containing from 55 percent by weight of styrene to 80 percent by weight of styrene, and from 20 percent by weight of n-butylmethacrylate to 45 percent by weight of n-butylmethacrylate, or styrene butadiene resins containing from 85 percent by weight to 95 percent by weight of styrene, and from 5 percent by weight to 15 percent by weight of butadiene.
• auxilliary addenda or components for developers can also be incorporated into the magnetic toner compositions of the invention other known auxilliary addenda or components for developers.
• a pigment such as carbon black and/or a dye such as Acid Violet may be added singly or in combination in amounts of from 0.5 to 5 percent by weight based on the total composition so as to improve the hue of the developer.
• a filler such as calcium carbonate or powdery silica may be added in an amount of up to 20 percent by weight based on the total composition to obtain a bulking effect.
• an offset-preventing agent such as a silicon oil, a low-molecular weight olefin resin or wax may be used in an amount of 2 to 15 percent by weight based on the total composition.
• a pressure fixability-improving agent such as paraffin wax, an animal or vegetable wax or a fatty acid amide may be used in an amount of from 5 to 30 percent by weight based on the total composition.
• a flowability-improving agent such as a fine powder of polytetrafluoroethylene or finely divided silica (fumed silica) may be added in an amount of from 0.1 to 1.5 percent by weight based on the total composition.
• the magnetic component or material e.g., magnetite be present in an amount of from 20 percent by weight to 80 percent by weight, based on the sum of the amount of the binder medium and the magnetic material.
• any known method of toner particle formation may be utilized which results in toner of the desired properties. Typical of such methods are hot melt formation and mastication followed by attrition to the desired toner particle size.
• a polar organic solvent for example, an aromatic solvent such as benzene, xylene, or ethylbenzene, ketone such as acetone, methylethyl ketone or methylisobutyl ketone or an ether such as tetrahydrofuran or dioxane.
• a polar organic solvent for example, an aromatic solvent such as benzene, xylene, or ethylbenzene, ketone such as acetone, methylethyl ketone or methylisobutyl ketone or an ether such as tetrahydrofuran or dioxane.
• auxiliary addenda can be incorporated according to known recipes prior to mastication.
• magnetite is a particularly useful magnetic material for use in the toner compositions described herein, it is deemed that other magnetic materials can be used to form the stoner composition component of the invention as long as the particles which comprise the materials permit the achievement of the desired magnetic and electrical properties in the toner which is to be subsequently prepared and they are capable of providing images and characters that are MICR readable.
• magnetic materials include magnetic pigments selected from alloys of iron, cobalt, nickel, or manganese and the like, such as hematite, ferrite and other ferromagnetic alloys.
• the magnetic signal level is of substantial importance in magnetic image character recognition information systems since the amount of toner composition will vary in proportion to the signal level.
• the amount of toner composition will vary in proportion to the signal level.
• the stainless steel carrier particles are larger than the toner particles, e.g., with an average particle size from 20 to 1000 microns and typically 40 to 500 microns.
• a convenient way of obtaining particles of the desired particle size range is by screening a mass of particles with the standard screens. Particles that pass through a 35 mesh screen and are retained on a 325 mesh screen (U.S. Sieve Series) are especially suitable.
• electrostatographic imaging methods or processes referred to herein are meant those methods or processes, including xerographic processes, where images or characters are generated on suitable ssubstrates such as checks, for example, which images are developed with the magnetic developer compositions disclosed herein and wherein the images are permanently affixed thereto by suitable fixing means such as heat.
• the invention is further illustrated by the following examples and comparative tests.
• a toner composition was prepared as follows. A mixture containing 62 percent by weight of a poly(styrene-co-n-butylacrylate-co-divinyl benzene) containing 77 percent by weight of styrene, 25 percent by weight n-butylacrylate and 6 percent by weight divinyl benzene, 28 percent by weight of acicular magnetic particles available from Pfizer Corporation as Magnetite MO 4232 and 10 percent by weight Regal 300 Carbon Black available from Cabot Corporation was melt-kneaded and dispersed by a hot two-roll mill. The mixture was then cooled and roughly pulverized to a coarse grind state (150 mm) by a rough pulverizer. The mixture was finally pulverized in a fluid energy mill to obtain a toner having an average particle size of 9-11 microns by volume percent.
• a developer composition was then prepared by blending together in a twin-cone blender for 5 hours, 3 percent by weight of the above-mentioned toner composition and 97 percent by weight of carrier particles consisting of sponge iron powder which were obtained commercially from Hoeganaes Corporation as Hoeganaes EH having an average particles size of 125 microns.
• the iron powder was oxidized by fluidized bed oxidation as in U.S. Patent No. 3,767,477 and had a static resistance of 8 x 107 ohm.
• the toner and carrier were then roll milled for one hour to form the developer.
• a second developer composition was prepared by blending together 3 percent by weight of the toner composition as prepared in Example 1 and 97 percent by weight of carrier particles consisting of the same Hoeganaes EH sponge iron particles as described in Example 1 except that the iron powder was not oxidized by fluidized bed oxidation and had a static resistance of 4 x 104 ohm.
• a third developer composition was prepared by blending together 3 percent by weight of the toner composition as prepared in Example 1 and 97 percent by weight of carrier particles consisting of stainless steel (AISI 410L) containing iron as the major constituent and, by weight, 0.005% Al, 13.5% Cr, 0.025% Cu, ⁇ 0.0015% Mg, 0.07%Mn, 0.006% Mo, 0.04% Ni, 1.0% Si, 0.25% Ag, and ⁇ 0.005% V obtained commercially from Hoeganaes Corporation.
• the carrier particles have a static resistance of 1 x 107.
• a fourth developer composition was prepared by blending together 3 percent by weight of the toner composition as prepared in Example 1 and 97 percent by weight of the stainless steel carrier particles described in Example 3 except that the stainless steel powder was etched for 10 minutes with hydrofluoric acid (2.5 volume percent solution), then rinsed with water and allowed to dry. The dried particles were then passivated with nitric acid (20 volume percent solution), for 20 minutes and rinsed in water for minutes, next in methanol for 5 minutes and air dried. The resulting carrier particles had a static sresistance of 5.0 x 100 ohm.
• the developer compositions as prepared in Examples 1-4 were incorporated into a copying machine (Ektaprint® 1392 Printer supplied by Eastman Kodak Company) and the copying operation was carried out.
• the average image densities of copies of one-half inch (1.27 cm) solid black squares, made with the developers of Examples 1-4, were measured using a commercially available reflection densitometer obtained from X-RITE Corporation.
• the image sharpness of the copies was also determined based on the sharpness of a line image area of the obtained copy.
• the results of the copying test are shown in Table I below. TABLE I Developer Image Density Sharpness Example 1 0.7 Excellent Example 2 0.8 Excellent Example 3 0.8 Excellent Example 4 1.3 Excellent
• the two-component magnetic developer compositions of the invention have application for developing electrostatically charged images in any known electrostatographic processes used for generating documents suitable for magnetic image character recognition.
• the two-component magnetic developers of the invention can simultaneously provide both MICR images and characters of excellent MICR readable quality and developed images having excellent image density and sharpness.

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