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
  • G03G9/09—Colouring agents for toner particles
  • G03G9/0906—Organic dyes
  • G03G9/091—Azo dyes
• • 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
  • G03G9/097—Plasticisers; Charge controlling agents
  • G03G9/09733—Organic compounds
  • G03G9/0975—Organic compounds anionic

Definitions

• the invention relates to electrographic materials, particularly toners and developers. This invention more particularly relates to negative charging, humidity stabilized toners and to developers including those toners.
• image charge patterns are formed on a support and are developed by treatment with an electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner.
• electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner.
• Toner particles are called toner particles or, collectively, toner.
• Two major types of developers, dry and liquid, are employed in the development of the charge patterns.
• the image charge pattern also referred to as an electrostatic latent image
• the electrostatic latent image is formed on an insulative surface of an electrostatographic element by any of a variety of methods.
• the electrostatic latent image may be formed electrophotographically, by imagewise photo-induced dissipation of the strength of portions of an electrostatic field of uniform strength previously formed on the surface of an electrophotographic element comprising a photoconductive layer and an electrically conductive substrate.
• the electrostatic latent image may be formed by direct electrical formation of an electrostatic field pattern on a surface of a dielectric material.
• One well-known type of electrostatographic developer comprises a dry mixture of toner particles and carrier particles. Developers of this type are employed in cascade and magnetic brush electrostatographic development processes.
• the toner particles and carrier particles differ triboelectrically, such that during mixing to form the developer, the toner particles acquire a charge of one polarity and the carrier particles acquire a charge of the opposite polarity. The opposite charges cause the toner particles to cling to the carrier particles.
• the electrostatic forces of the latent image sometimes in combination with an additional applied field, attract the toner particles.
• the toner particles are pulled away from the carrier particles and become electrostatically attached, in imagewise relation, to the latent image bearing surface.
• the resultant toner image can then be fixed, by application of heat or other known methods, depending upon the nature of the toner image and the surface, or can be transferred to another surface and then fixed.
• Toner particles often include charge control agents, which, desirably, provide high uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium.
• charge control agents which, desirably, provide high uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium.
• Positive charging toners, incorporating positive charge control agents have been widely used.
• Negative charging toners, incorporating negative charge control agents have been less common.
• US-A-3,565,805 teaches the additional of a liquid "tackifying agent" to a developer. Included amoung the listed agents are fatty acid amine surfactants.
• Great Britain Patent No. 1,117,224 teaches a process for producing toner particles using a surfactant.
• Numerous surfactants are listed. Among these are various sulfonation products including sulfonated derivatives of fatty acid esters, such as the diamyl or dioctyl esters of sodium sulfosuccinic acid.
• US-A-3,694,359 teaches toner that includes a wetting agent, such as sodium di-isooctyl-succin-1-sulfonate. Merrill and others states: "The wetting agent aids in promoting even, uniform contact between the toner and the paper support to which the toner image is ultimately fixed by heat. It is most advantageously used when fusing is accomplished through the use of infrared radiation, as it reproduces a uniform, high-density image otherwise difficult to obtain.” (column 6, lines 24-30)
• US-A-4,912,009 teaches that styrene-acrylic toners contaminated by surfactant used in producing the toner binder, tend to have unstable charging characteristics when subjected to changes in temperature and humidity.
• US-A-4,814,250 teaches toner that includes, as a charge control agent, a mixture of dioctylsodiumsulfosuccinate and sodium benzoate.
• US-A-4,624 teaches a charge-controlling and coloring agent having the general formula: where X1 and X2 are H, C1-C5 alkyl, C1-C5 alkoxy, nitro or halo; m, m', n, and n' are each from 1 to 3; R1 and R3 are H, C1-C5 alkyl, C1-C5 alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, or benzoylamino; Y+ is an ammonium ion, aliphatic ammonium ion, alicyclic ammonium ion or heterocyclic ammonium ion; and M is chromium, cobalt, or iron.
• a negative charge control agent having the structural formula: is marketed, by Hodagaya Chemical Co., for use in negative charging toners.
• the invention in its broader aspects, provides electrophotographic toners and developers having polymeric binder and a charge control agent that is a mixture of a first component having the general structure: and a second component having the general structure:
• X1 and X are each H, C1-C5 alkyl, C1-C5 alkoxy, nitro, or halo.
• R a and R b are each H, C1-C5 alkyl, C1-C5 alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, or benzoylamino.
• M is Cr, Co, or Fe.
• n, n', m, and m' are each 1, 2, or 3.
• Each R+ is a cation.
• R1 and R are each independently, alkyl having from 1 to 18 carbons.
• particle size used herein, or the term “size”, or “sized” as employed herein in reference to the term “particles”, means the median volume weighted diameter as measured by conventional diameter measuring devices, such as a Coulter Multisizer, sold by Coulter, Inc of Hialeah, Florida.
• Median volume weighted diameter is the diameter of an equivalent weight spherical particle which represents the median for a sample; that is, half of the mass of the sample is composed of smaller particles, and half of the mass of the sample is composed of larger particles than the median volume weighted diameter.
• charge control refers to a propensity to modify the triboelectric charging properties of the resulting toner.
• glass transition temperature means the temperature at which a polymer changes from a glassy state to a rubbery state. This temperature (Tg) can be measured by differential thermal analysis as disclosed in "Techniques and Methods of Polymer Evaluation", Vol. 1, Marcel Dekker, Inc., New York, 1966.
• the toner of the invention has a charge control agent comprising a mixture of two or three components.
• the first component is has the general structure: where X1 and X are each selected from H, C1-C5 alkyl, C1-C5 alkoxy, nitro and halo; m, m', n, and n' are each selected from integers from 1 to 3; R a and R b are each selected from H, C1-C5 alkyl, C1-C5 alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, and benzoylamino; R+ is a cation; and M is chromium, cobalt, or iron.
• the first component has the structural formula: where R+ is an inorganic cation, such as NH4+, Na+, H+, or a mixture thereof.
• the second component of the charge control agent of the invention is a material that is both a surfactant and a charge control agent. It is presently preferred that the second component be capable of acting as an anionic surfactant in water solution. It is also presently preferred that the second component be capable of use as a negative charge control agent, independent of any other charge control agent, in a negatively charging electrophotographic toner.
• the second component has the general structure: R+ is a cation. It is currently preferred that R be an inorganic cation. R1 and R are each, independently, alkyl having from 2 to 18 carbons.
• the second component is dioctyl sodium sulfosuccinate, which has the structural formula: Specific examples of the second component also include: and
• the charge control agent includes an optional third component: a flow control aid.
• the second component is a gummy solid that cannot be readily handled by conventional powder handling apparatus without the addition of the flow control aid.
• flow control aids include: silica, titania, and polymeric beads.
• a currently preferred flow control aid is an alkali metal benzoate salt, such as sodium benzoate. As Comparative Examples F demonstrate, the flow aid does not provide a charge control function in the developer.
• the charge control agent and each component thereof, is present in the toner of the invention in an amount effective to modify, and preferably, improve the properties of the toner. It is preferred that a charge control agent improve the charging characteristics of a toner, so the toner quickly charges to a negative value having a relatively large absolute magnitude and then maintains about the same level of charge. It is also preferred that a charge control agent improve the charge uniformity of a toner composition, that is, insure that substantially all of the individual toner particles exhibit a triboelectric charge of the same sign with respect to a given carrier.
• toner throw-off refers to the amount of toner powder thrown out of a developer mix as it is mechanically agitated, for example, within a development apparatus. Throw-off can cause unwanted background development and general contamination problems.
• the first and second components are each present in a sufficient concentration to effect the charging characteristics of the toner even if the other component were not present.
• the first component has a concentration, relative to the total weight of the toner of from 0.5 to 5.0 weight percent; or, more preferably, from 1.5 to 3.5 weight percent.
• the second component has a concentration of from 0.10 to 2.5 weight percent; or, more preferably, from 0.10 to 0.50 weight percent.
• the third component when present, has a concentration of from 0.02 to 0.4 weight percent.
• Both components of the charge control agent are dispersed within the toner.
• the first component is present in the toner in the form of fine particulate inclusions.
• the second charge control agent is not phase separated within the toner (at least in so far as phase separation visible in toner melted onto a glass slide under a microscope at 650 times magnification). This is an advantageous feature. It has been empirically determined that materials that cause a toner to separate into different phases can be correlated with increased clumping of the toner powder, and can also lead to irreproducible manufacture of toner.
• thermoplastic polymer binders employed as the toner matrix phase in the present invention can vary widely.
• amorphous toner polymers having a glass transition temperature in the range of 50°C to 120°C or blends of substantially amorphous polymers with substantially crystalline polymers having a melting temperature in the range of 65°C to 200°C are utilized in the present invention.
• such polymers have a molecular weight distribution including an insoluble, very high molecular weight fraction and one or more fractions having a number average molecular weight in the range of 1000 to 500,000 and a weight average molecular weight in the range of 2 X 103 to 2 X 106.
• the thermoplastic polymers used in the practice of this invention be substantially amorphous; however, as indicated above, mixtures of polymers can be employed, if desired, such as mixtures of substantially amorphous polymers with substantially crystalline polymers.
• Polymers useful as binders in the toner of the invention include styrenic/acrylic copolymers.
• preferred styrenic/acrylic copolymers have a glass transition temperature in the range of 50°C to 100°C.
• the resin is a copolymer of styrene and butyl acrylate, crosslinked with divinyl benzene; produced in a suspension or emulsion polymerization process.
• An initiator and, optionally, a chain transfer agent are used in the synthesis.
• the ratio of styrene to butyl acrylate is in the range of from 90:10 to 60:40 and the divinyl benzene is used at a level of 3 weight percent or less, preferably, at a level of 0.1 to 1.0 weight percent.
• the binder is a polymer disclosed in U.S. Patent Application No. 08/255,522, entitled “Particulate Polymer, Electrophotographic Toner, and Preparation Methods", filed June 8, 1994 by Sorriero and others.
• An optional but preferred component of the toner of the invention is colorant: a pigment or dye.
• Suitable dyes and pigments are disclosed, for example, in US-A-Re-31,072 and in US-A-4,160,644; US-A-4,416,965; US-A-4,414,152; and US-a-2,229,513.
• One particularly useful colorant for toners to be used in black and white electrostatographic copying machines and printers is carbon black. Colorants are generally employed in the range of from 1 to 30 weight percent on a total toner powder weight basis, and preferably in the range of 2 to 15 weight percent.
• the toner of the invention can also contain other additives of the type used in previous toners, including leveling agents, surfactants, stabilizers, and the like.
• the total quantity of such additives can vary. A present preference is to employ not more than 10 weight percent of such additives on a total toner powder composition weight basis.
• Dry styrenic/acrylic copolymer toners of this invention can optionally incorporate a small quantity of low surface energy material, as described in US-A-4,517,272 and US-A-4,758,491.
• the toner can contain a particulate additive on its surface such as the particulate additive disclosed in US-A-5,192,637.
• the charge control agent is incorporated into the toner.
• the two or three components of the charge control agent can each be added to the toner separately or may be combined in some manner before addition to the remaining ingredients of the toner. This should make it clear that the term "charge control agent” used herein is largely a matter of convenience. Charge control is observed when the two or three components are present in the toner. The nature of specific chemical and physical interactions among the components of the charge control agent and the other ingredients in the toner is not understood. The claimed invention is not, however, limited thereby.
• the components of the charge control agent of the invention can be mixed into the toner in any convenient manner, such as blending in the manner described in US-A-4,684,596 and US-A-4,394,430, with an appropriate polymeric binder material and any other desired addenda.
• the mixture is then ground to desired particle size to form a free-flowing powder of toner particles containing the charge agent.
• a preformed mechanical blend of particulate polymer particles, charge control agent, colorants and additives can, alternatively, be roll milled or extruded at a temperature sufficient to melt blend the polymer or mixture of polymers to achieve a uniformly blended composition.
• the resulting material after cooling, can be ground and classified, if desired, to achieve a desired toner powder size and size distribution.
• a melt blending temperature in the range of 90°C to 240°C is suitable using a roll mill or extruder.
• Melt blending times that is, the exposure period for melt blending at elevated temperature, are in the range of 1 to 60 minutes.
• the composition can be stored before being ground. Grinding can be carried out by any convenient procedure.
• the solid composition can be crushed and then ground using, for example, a fluid energy or jet mill, such as described in US-A-4,089,472. Classification can be accomplished using one or two steps.
• the polymer in place of melt blending or the like, can be dissolved in a solvent in which the charge control agent and other additives are also dissolved or are dispersed.
• the resulting solution can be spray dried to produce particulate toner powders.
• Limited coalescence polymer suspension procedures as disclosed in US-A-4,833,060 are particularly useful for producing small sized, uniform toner particles.
• the toner particles have an average diameter between 0.1 micrometers and 100 micrometers, and desirably have an average diameter in the range of from 4 micrometers and 30 micrometers for currently used electrostatographic processes.
• the size of the toner particles is believed to be relatively unimportant from the standpoint of the present invention; rather the exact size and size distribution is influenced by the end use application intended. So far as is now known, the toner particles can be used in all known electrostatographic copying processes.
• the developers of the invention include carrier and toner of the invention.
• Carriers can be conductive, non-conductive, magnetic, or non-magnetic. Carriers are particulate and can be glass beads; crystals of inorganic salts such as aluminum potassium chloride, ammonium chloride, or sodium nitrate; granules of zirconia, silicon, or silica; particles of hard resin such as poly(methyl methacrylate); and particles of elemental metal or alloy or oxide such as iron, steel, nickel, carborundum, cobalt, oxidized iron and mixtures of such materials. Examples of carriers are disclosed in US-A-3,850,663 and US-A-3,970,571.
• iron particles such as porous iron, particles having oxidized surfaces, steel particles, and other "hard” and “soft” ferromagnetic materials such as gamma ferric oxides or ferrites of barium, strontium, lead, magnesium, or aluminum.
• Such carriers are disclosed in US-A-4,042,518; US-A-4,478,925; and US-A-4,546,060.
• Carrier particles can be uncoated or can be coated with a thin layer of a film-forming resin to establish the correct triboelectric relationship and charge level with the toner employed.
• suitable resins are the polymers described in US-A-3,547,822; US-A-3,632,512; US-A-3,795,618 and US-A-3,898,170 and Belgian Patent No. 797,132.
• Other useful resins are fluorocarbons such as polytetrafluoroethylene, poly(vinylidene fluoride), mixtures of these, and copolymers of vinylidene fluoride and tetrafluoroethylene.
• Polymeric fluorocarbon coatings can aid the developer to meet the electrostatic force requirements mentioned above by shifting the carrier particles to a position in the triboelectric series different from that of the uncoated carrier core material to adjust the degree of triboelectric charging of both the carrier and toner particles.
• the polymeric fluorocarbon coatings can also reduce the frictional characteristics of the carrier particles in order to improve developer flow properties; reduce the surface hardness of the carrier particles to reduce carrier particle breakage and abrasion on the photoconductor and other components; reduce the tendency of toner particles or other materials to undesirably permanently adhere to carrier particles; and alter electrical resistance of the carrier particles.
• the carrier is strontium ferrite coated with fluorocarbon on a 0.5 percent weight/weight basis, and treated with an aqueous solution of 4 weight percent KOH and 4 weight percent of a 2 parts by weight to 1 parts by weight mixture of Na2S2O8 and Na2S2O5 as disclosed in U.S. Patent Application No. 08/127,382, filed Sept. 24, 1993, by William E. Yoerger.
• the fluorocarbon carrier is also referred to herein as "modified Kynar".
• the developer of the invention contains from 1 to 20 percent by weight of toner of the invention and from 80 to 99 percent by weight of carrier particles.
• carrier particles are larger than toner particles.
• Conventional carrier particles have a particle size of from 5 to 1200 micrometers and are generally from 20 to 200 micrometers.
• the toners of the invention are not limited to developers which have carrier and toner, and can be used, without carrier, as single component developer.
• the toner and developer of the invention can be used in a variety of ways to develop electrostatic charge patterns or latent images.
• Such developable charge patterns can be prepared by a number of methods and are then carried by a suitable element.
• the charge pattern can be carried, for example, on a light sensitive photoconductive element or a non-light-sensitive dielectric surface element, such as an insulator coated conductive sheet.
• One suitable development technique involves cascading developer across the electrostatic charge pattern.
• Another technique involves applying toner particles from a magnetic brush. This technique involves the use of magnetically attractable carrier cores. After imagewise deposition of the toner particles the image can be fixed, for example, by heating the toner to cause it to fuse to the substrate carrying the toner.
• the unfused image can be transferred to a receiver such as a blank sheet of copy paper and then fused to form a permanent image.
• An organic phase was prepared by combining divinyl benzene (1.40 grams), t-dodecanethiol (1.50 grams), azo-bis pentanenitrile (4 grams), styrene (160 grams), and butyl acrylate (40 grams).
• An aqueous phase was prepared by combining distilled water (400 grams), potassium dichromate ((0.10 grams), poly(n-methylaminoethanol)adipate (2 grams: as 20 grams of 10 weight/weight percent solution in distilled water), and LudoxTM brand colloidal silica marketed by E.I. du Pont de Nemours (2 grams: as 4 grams of a 50 weight/weight percent dispersion in distilled water).
• the organic and aqueous phases were emulsified using a high shear mixing device, a MicrofluidizerTM marketed by Microfluidics Corp. of (city,state).
• the resulting emulsion was placed in a three necked round bottom flask equipped with a mechanical stirrer, condenser, and nitrogen inlet.
• the flask was placed in a constant temperature bath at 77°C for 16 hours under continuous stirring.
• the flask was then vented, flushed with argon and heated to 85°C for another three hours.
• the resulting polymer was filtered, washed, and dried.
• a dry blend was prepared of 50.0 grams of the poly(styrene-co-butyl acrylate-co-divinylbenzene) binder and 3.5 grams of Regal 300TM carbon black, marketed by Cabot Corp., 1.25 grams of a material marketed as "T-77" by Hodagaya Chemical Co., of New York, New York, and 0.5 grams of Aerosol OT-B, marketed by American Cyanimid of Wayne, New Jersey.
• T-77 has the structural formula: Aerosol OT-B is a mixture of 85 parts by weight of a compound having the structural formula: and 15 parts by weight of sodium benzoate.
• the dry blend was added to a heated two-roll compounding mill. The roller surfaces were set to 150°C.
• the melt was exercised on the mill for 20 minutes, then was removed and cooled.
• the resulting slab was first coarse ground to 2mm size on a laboratory mill, then finely pulverized to approximately 12 micrometer size on a Trost TX jet mill.
• the toner thus prepared had a concentration of T-77 of 2.5 parts per hundred and a concentration of Aerosol OT-B of 1 part per hundred parts of styrene/n-butyl acrylate/divinyl-benzene binder resin. This toner was used in Examples 1a-1i.
• Untreated, coated carrier particles were prepared by mixing 0.5 grams of 0.3 micrometer poly(vinylidene fluoride) powder marketed by Pennwalt Corp. as Kynar 301F, and 100 grams of bare (uncoated) strontium ferrite core particles. The mixture was placed in a bottle and rolled on a roll mill for 1 hour to thoroughly disperse the polymer over the surface of the carrier. The mixture was then cured at 230°C for 2.5 hours to fuse the polymer to the surface of the particles. The volume average particle size of the carrier particles was from about 25 to 35 micrometers.
• Developer was prepared by mixing toner particles prepared as described above at a weight concentration of 10% toner with the carrier particles.
• Toner charge was measured in microcoulombs per gram of toner (mc/g) in a "MECCA" device at the indicated relative humidities.
• the developer Prior to measuring the toner charge, the developer was vigorously exercised to cause triboelectric charging by placing 4 gram samples of the developer into plastic vials, capping the vials, and placing each vial, for two minutes, on a "bottle-brush" device comprising a magnetic toning roller with a stationary shell and a magnetic core rotating at 2000 rpm. The magnetic core had 12 magnetic poles arranged around its periphery in alternating north-south fashion. After this exercise the developer samples were incubated in open topped vials, at the relative humidities indicated below, for a minimum of 16 hours.
• the toner charge level that is, the charge to mass ratio or Q/m
• Q/m the charge to mass ratio
• Toner Q/m was also taken after shaking the developer for 10 minutes on the wrist action shaker, and also after 2 minutes exercising on the bottle brush. Relative humidities were maintained for these procedures at the same levels as for the respective incubations.
• Toner charge level was measured for each sample by placing a 150 milligram sample of the charged developer in a MECCA apparatus and measuring the charge and mass of transferred toner in the MECCA apparatus. This involves placing the 150 milligram sample of the charged developer between electrode plates and subjecting it, simultaneously for 30 seconds, to a 60 Hz magnetic field and an electric field of about 2000 volts/cm between the plates. The toner is released from the carrier and is attracted to and collects on the plate having polarity opposite to the toner charge. The total toner charge is measured by an electrometer connected to the plate, and that value is divided by the weight of the toner on the plate to yield the charge per mass of toner (Q/m).
• Aerosol OT differs from Aerosol OT-B, only in that sodium benzoate is not present.
• the toner was evaluated only by the 2 min bottle-brush procedure at the indicated relative humidities. Results are presented in Table 2.
• Toners were prepared and evaluated substantially as described in Examples 1a-1i, except on a larger scale.
• 100 parts of poly(styrene-co-butylacrylate-co-divinylbenzene) was melt blended with 7 pph (7 parts per hundred parts of the binder polymer) of carbon black (Black Pearls 430, marketed by Cabot Corp., along with the amounts of T-77 and Aerosol OT-B indicated in Tables 3-4.
• the extrudate was ground into toner of approximately 12 micron volume weighted diameter on an Alpine Fluid Bed Grinder, Model 100AFG, marketed by Micron Powder Systems, Summit, New Jersey.
• the toners were evaluated for performance as a function of relative humidity on a modified Kynar coated carrier, as described in Examples 1a-1i. Results are reported in Table 3.
• Toners were prepared and evaluated substantially as described in Examples 4a-4x, with the exception that no OT-B was added. Results are reported in Table 4. TABLE 4 TONERS WITH T-77 ONLY Example T-77 (pph) OT-B (pph) RH (%) 2 min bottle-brush Q/m ( ⁇ C/g) A1 2.5 0 10 -10.4 A2 2.5 0 50 -15.3 A3 2.5 0 75 -18.7
• Developer was prepared for each of the toners indicated above, by mixing toner particles prepared as described above at a weight concentration of 12% toner with carrier particles comprising strontium ferrite cores thinly coated (approximately 2 percent by weight) with poly(methyl methacrylate).
• the volume average particle size of the carrier particles was from about 25 to 35 micrometers.
• Developer was prepared for each of the toners indicated above, by mixing toner particles prepared as described above at a weight concentration of 12% toner with carrier particles comprising strontium ferrite cores thinly coated (approximately 0.5 percent weight/weight) with dehydrofluorinated and oxidized fluorocarbon as disclosed in US-A-4,726,994.
• the volume average particle size of the carrier particles was from about 25 to 35 micrometers.
• Throw-off values were determined by taking the 4 gram developer sample that had been bottle-brush exercised for 10 minutes, admixing in 6% more toner to provide a final toner concentration of about 18%), followed by 2 minutes more exercise on the wrist action shaker. This developer was then placed on a roll containing a rotating magnetic core, similar to a magnetic brush roll used for electrostatic development. A Plexiglas housing contained the assembly, and had a vacuum filter funnel mounted directly over the roll. The weight of toner, in milligrams, collected on a piece of filter paper after one minute of running the magnetic core at 2000 revolutions per minute was reported as the throw-off value.

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