Background of the Invention Dry MICR toners have been available for many years and are used, for example, in the electrophotographic printing of legends such as bank account numbers on checks and other documents that are machine readable by magnetic scanning techniques. An advantage of the use of dry MICR toners instead of magnetic flexographic inks is that the former allow use of computer generated imaging techniques to provide for short runs of documents such as personal checks, while the flexographic process requires the preparation of printing plates or their equivalents, thus rendering short print runs uneconomical. Moreover, flexographic inks, which generally contain magnetic particles dispersed in a drying oil vehicle, require a drying time that slows the printing rate. Flexographic magnetic inks such as those disclosed in U. S. Patent No. 3,998,160 may also require an external magnetic field during printing to magnetically orient the magnetic pigment particles.

Liquid electrophotographic printing methods for conventional black and white and color printing are known and in commercial use. Commercial examples include plain paper, liquid toner copiers supplied by Ricoh and Savin. Liquid developer electrophotographic methods are disclosed in U. S. Patent Nos.

4,378,422 and 4,786,576, which are incorporated herein by reference.

Dry MICR toners generally comprise magnetic particles dispersed in a fusible polymer composition together with other additives. This composition may then be encapsulated within a polymer shell to prevent agglomeration and enable the toner particles to remain"dry"and free flowing. The particles also contain or are coated with a charge control agent of the positive or negative type.

In the dry electrophotographic process, a charged latent image is created on a photoreceptor or imaging belt and exposed to dry toner that has an electrostatic charge to be attracted to the electrically charged latent image areas of the photoreceptor. Paper or other printable substrate having a greater or opposite charge contacts the photoreceptor surface, transferring the dry toner to the substrate. The substrate is then exposed to heat and/or pressure, causing the encapsulant walls of the toner particles to break or fuse, at which time the polymer within the particles fuses to the substrate.

Despite their widespread use, dry MICR toners have several notable deficiencies. For example, as is the case with dry toners generally, dusting and waste are problems during the printing process. The dusting and waste are not only uneconomical in the sense of requiring greater amounts of toner but they also require frequent cleaning of the machine. Due to the dry, dust- like nature of dry toner particles, toner accumulates in the printing apparatus over time during the printing operation. Some of this dusting is due to the dust-like nature of the toner and is unavoidable. Some is due to the less than 100% efficient transfer between the photoreceptor and the substrate. A large portion, however, is created during the formation of the toner image itself, prior to transfer, when the toner particles on non-image areas are removed.

Transfer of toner to non-image portions of the substrate is common, not only

in areas adjacent to the image, but at substrate borders and other areas as well. Additional waste is generated during manufacturing steps, including during micronizing and classifying the toner particles.

Further problems associated with dry MICR toners are associated with the nature of the printed image. First, U. S. Patent No. 4,859,590 incorporated herein by reference, discloses that the pile height of dry MICR toner images is relatively high, with pile heights of 7-9 um being typical within a range spanning 5 pm to 20 um. High pile heights cause numerous problems, the most significant of which are the necessity of maintaining the magnetic character recognition read head at a greater distance from the substrate, thus increasing the potential for read errors, and the loss of MICR image due to rubbing or peeling of the image from the substrate. Moreover, the thick print layers tend to peel away much more readily than thin layers.

The relatively large particle size (7-15 um) of dry toner particles prevents the printed images from having high resolution. The inability to create magnetic characters with precise edge definition further limits resolution and raises the read error rate in the dry toner process. The dry toner process inherently creates some scatter, particularly in the neighborhood of the image. The scatter produces a stray magnetic signal which decreases resolution and increases the read error rate. Dry toner MICR images also often exhibit poor solid area fill, the larger areas of the image having a"washed-out"appearance. The poor area fill is aesthetically displeasing, and may also affect the magnetic reading ability.

Finally, with respect to machine life, dry MICR toner particles tend to be somewhat abrasive. This abrasiveness may be due in part to the use of surface additives such as silica and/or magnetite, as taught by U. S. Patents

No. 5,510,221 and 5,482,805, both being incorporated herein by reference.

Additional patents that discuss dry MICR toners and their various characteristics include U. S. Patent Nos. 5,153,091; 5,486,443; 4,517,268; 5,147,744; and 4,859,550, each of which is incorporated herein by reference.

It would be desirable to provide a method for the preparation of MICR images that is non-dusting, that has high transfer efficiency, and that is capable of producing images that are more resistant to rub-off and peeling, while at the same time providing higher resolution images with less scatter. It would be further desirable to provide a method and an MICR developer requiring less frequent machine cleaning extending the life of the photoreceptor or imaging belt.

Summary of the Invention The present invention provides a liquid MICR developer containing ferromagnetic pigment-containing fusible resin particles dispersed in a carrier liquid of high resistivity that does not dissolve or swell the fusible polymer.

The subject invention further pertains to a MICR printing process employing the inventive liquid MICR developer.

The liquid MICR developer of the present invention provides significant advantages over the dry MICR toners that have been used thus far. The inventive liquid toners overcome the dusting problems of dry toners.

The inventive liquid toners also provide 100% or substantially 100% transfer efficiency during the transfer process. Both of these improvements lead to more efficient printing with less waste and downtime. Use of the inventive liquid MICR developer also produces a safer and cleaner workplace and reduces or eliminates much of the particulate emissions.

The present liquid MICR developers may be formulated with finer average particle sizes as compared to dry developers. The finer average particle sizes produce better print quality. The inventive liquid MICR developers also have improved solid area fill, better print definition, and better adhesion to the printed substrate. In addition, the liquid carrier extends the life of the photoconductor by providing lubrication at the development nip to reduce abrasion from the toner particles.

The invention also provides a process for preparing a magnetic ink character recognition developer in which particles containing a resin and a high coercivity magnetic powder are dispersed in a nonpolar liquid carrier. A charge control agent may be incorporated into the particles or added to the dispersion of particles in the carrier.

The invention further provides a process for printing a magnetically readable image that includes contacting the MICR developer of the invention to an imaging area bearing a charged image area. The particles of the MICR developer are electrostatically attracted to the image area to produce an image developed with the MICR toner. The developed image is then heated to fuse the MICR particles, producing an image with good definition and solid area fill that has excellent adhesion to the substrate.

Detailed Description of the Invention The liquid MICR developers of the present invention comprise a dispersion of magnetic pigment-containing, fusible polymer particles dispersed in an aliphatic hydrocarbon carrier liquid. The liquid MICR developers include external charge control agent (s) soluble in the aliphatic carrier liquid and may further include at least one wax to improve re- dispersion properties. The resin particles preferably contain one or more

color pigments, including carbon black pigments, to provide a colored image.

Carbon black is a preferred pigment.

In general, the MICR developer of the present invention is prepared by forming a uniform blend of the magnetic pigment, polymer resin, optional additional pigments, and other resin particle ingredients; forming resin particles from the blend; dispersing the resin particles in a liquid carrier; and reducing the average particle size by milling in the carrier liquid, preferably in the presence of a wax dispersion aid. A charge control agent may be added at any convenient time, whether before, during, or after the milling operation.

The invention has an option of adding the charge control agent entirely after the milling operation, thus allowing a single master batch to be used to formulate different liquid MICR developers having different charge control agents and/or different charge control agent concentrations. The liquid MICR developer can be supplied as a concentrate, thus decreasing the frequency of developer addition to the electrophotographic printing apparatus. These benefits cannot be obtained with dry MICR toners.

The magnetic powder or particles of the present invention must have a high coercivity value, greater than about 200 Oe, preferably between about 250 Oe and about 450 Oe, and more preferably between about 300 Oe and about 425 Oe. Suitable magnetic materials include, without limitation, acicular and cubical magnetic iron oxides, powdered ferromagnetic metals, aluminum/nickel/cobalt alloys, chromium oxides, and the like. Mixtures of magnetic particles may also be used. Magnetite particles are preferred. The squareness value (SR/CiS iS typically between about 0.2 and about 0.5. The magnetic pigment size should be such that small, uniformly pigmented polymer resin particles having a mean size less than 10 m, and preferably in

the range of about 3-4 gm, can be obtained. Preferably, the mean magnetic pigment particle size is less than about 4 pm, preferably in the range of about 0.1 m to about 2 m. Such magnetic particles are available, for example, from Pfizer, Magnox Corporation, ISK Magnetics, Toda Kogyo Corporation, and others. Cobalt-based powder particles are available from Nova Corporation.

The quantity of magnetic pigment required to be present in the developer's fusible particles is dependent upon the coercivity and remanance of the particular particles. Preferably, from about 20 weight percent to about 70 weight percent and more preferably from about 30 weight percent to about 60 weight percent of magnetic particles are used, these weight percentages being calculated relative to the total weight of the polymer particles. Smaller and larger amounts may be suitable as well.

The magnetic pigment or powder is included in an amount sufficient to produce a MICR reading of at least about 50, preferably from about 80 to about 130, and more preferably from about 110 to about 120. A MICR reading value represents an average reading of different print characters and is obtained according to the standard established by ANSI. The concentration of magnetic material required depends to some degree on the pile height of the printed character. Lower pile heights require a higher concentration of the magnetic particles in the developer particles in order to achieve the desired MICR reading.

The polymer resin used in making the magnetic pigment-containing toner particles should have certain properties. The polymer resin chosen should be compatible with the magnetic pigment; that is, it should be able to wet the pigment well so that the pigment is uniformly dispersed in the resin.

The polymer resin should also not dissolve in or be swollen by the aliphatic carrier liquid to any appreciable extent. Polymer resins having a solubility of less than about 1% by weight in a carrier liquid are considered to be insoluble for purposes of the present invention. Solubility of less than 0.1% by weight of the resin in the liquid carrier is preferred. Swelling of the resin by the liquid carrier may be assessed by conventional methods, for example by measuring any increase in bulk volume of particles put into the carrier. If the volume of the polymer particles increases less than about 5 volume percent, the polymer is considered not to be swollen by the liquid carrier. Preferably, the volume increase will be no more than about 1 %. A further test of swelling is the ability of polymer particles to be re-dispersed when immersed in a compatible liquid carrier without any appreciable change in particle size distribution that would indicate that the particles are agglomerated and/or coagulated.

The particles including the polymer resin should also be able to be milled to reduce particle size in a relatively dust-free operation. After fusing to form the image, the toner should remain adhered to the printed substrate without dusting and without appreciable rub off. Compatibility of a particular resin and magnetic particle combination can be observed by formation of a uniform blend that can be milled into the desired particle size for the toner composition without leaving significant amounts of magnetic particles not associated with the resin. In addition, the polymer resin should be fusible under the development or"fixing"conditions, but should not easily agglomerate in the toner. Suitable fusible resins include, without limitation, polyesters, polyolefins, polyamides, polyurethanes, homopolymers and copolymers of polymerizable monomers selected from acrylates,

methacrylates, styrene, acrylonitrile, and vinyl chloride, and other polymers that are useful in toners. Substantially non-polar, non-reactive resins such as polyethylene and polypropylene may be functionalized with polar or reactive functional groups such as carboxylic acid, hydroxyl, epoxide, or halogen groups to increase adhesion to the substrate. The polymer resin preferably has a softening point of from about 60°C and about 180°C, more preferably from about 70° and about 150°C.

The polymer should provide good adhesion of the MICR printed image to the substrate, which is generally paper, and should also exhibit good resistance to rub-off. Adhesion may be assessed by the Taber abrasion test established by TAPPI, by a semi-quantitative rub test, or a tape adhesion test.

Excessive removal of the image may be visually observed on the tape; a more precise method, however, is to measure the image density before and after tape pull. Rub-off may be assessed using a Southland dry rub tester.

In testing using the Sutherland dry rub tester, the fixed image is rubbed a number of times with strokes under a fixed weight. The image density is measured prior to and after the rub test to determine abrasion resistance.

The liquid MICR developer of the subject invention contains from about 1 % to about 5% solids by weight, preferably from about 1 % to about 3% solids by weight, based on the total weight of the MICR developer. In one aspect, the subject invention provides a developer concentrate that may be diluted or re-dispersed into addition carrier liquid in the electrophotographic apparatus. For this embodiment, the liquid MICR developer concentrates may contain from about 10 weight percent to about 30 weight percent solids, which can be diluted with sufficient carrier liquid to prepare liquid MICR developer having a solids content suitable for electrophotographic printing.

A color pigment (that is, a pigment other than the magnetic pigment) is preferably admixed with the polymer particles to provide a desired color of the image. The preferred magnetite magnetic pigment is black or dark brown, and preferably the color pigment, if included, aids in obtaining a jet black pigmentation. It may be possible to obtain inks of other colors when different magnetic pigments, such as the chromium oxides, are used. The color pigments included may be weakly magnetizable, but are generally not magnetizable to the extent necessary to meet the minimum coercivity requirement of 200 Oe. Preferred color pigments are intensely colored inorganic or organic pigments. In a preferred embodiment, carbon black pigments are included. Suitable carbon black pigments are available from many sources, including Cabot Corporation and Degussa. Color pigments may be advantageously used in amount of from about 0.1 weight percent to about 10 weight percent, preferably from about 1.0 weight percent to about 10 weight percent based on the weight of the magnetic pigment-containing polymer particles.

The carrier liquid should be nonpolar. Preferred nonpolar carrier liquids are liquid hydrocarbons, especially aliphatic hydrocarbon liquids. The aliphatic hydrocarbon carrier liquid preferably has a volume specific resistivity of at least about 107 Q cm, a Kauri-Butanol value of less than about 30, a dielectric constant of about 4 or less, and preferably a flash point of at least about 100°F. Also preferred are liquid carriers having a volume resistivity greater than about 1 Q-cm, more preferably greater than about 109 Q-cm.

Suitable carrier liquids are, in general, linear and/or branched aiiphatic hydrocarbons produced as relatively narrow distillation cuts, and thus are of relatively high purity. Examples of suitable hydrocarbon carriers include,

without limitation, mixtures of C9-11 or C9, 2 linear and/or branched aliphatic hydrocarbons. Specific examples of such carriers include, without limitation, the various petroleum distillates available from Exxon Chemicals under the tradenames Isopar and NorparS) and combinations of such hydrocarbon liquids. Among these, preferred carrier liquids include Isopar-G, Isopar-H, Isopar-K, Isopar-L, Isopar-M, sopar-V, and combinations of these. Suitable linear hydrocarbon carrier liquids are Norpar-12, Norpar-13, Norpar-15, and combinations of these. Mixtures of branched aliphatic and linear aliphatic solvents may be used.

In addition to the aliphatic carrier liquids, minor portions of other organic liquids may be added to the liquid phase so long as the compatibility with the polymer particles, the volume resistivity, dielectric constant, and other desirable properties of the carrier are retained. Examples of such solvents include, without limitation, the various aromatic distillates and oxygenated solvents such as 3-pentanone, cyclohexanone, various higher alkyl ethers, glycol ethers, and the like. Other organic liquids are generally present in the carrier liquid in minor amounts, i. e., less than about 20% by weight based on total liquid carrier weight, preferably less than about 5% by weight based on total liquid carrier weight. Most preferably, the carrier liquid is completely aliphatic hydrocarbon.

The liquid carrier phase preferably includes a wax component. Waxes are generally defined as materials that are solid at ambient temperature and can soften when heated and harden when cooled. The wax may plasticize the printed image. Useful waxes include, without limitation, naturally occurring waxes such as animal waxes, vegetable waxes, mineral waxes, and petroleum waxes, as well as synthetic waxes. Preferred among these are

hydrocarbon waxes, such as paraffin waxes; polyalkylene homopolymers and copolymers, especially polyethylene, polypropylene, and copolymers of alkenes having from 2 to about 10 carbon atoms, particularly copolymers of ethylene with alkenes having from 3 to about 10 carbon atoms, especially copolymers with propylene or butylene; microcrystalline waxes; carnuba waxes; montan waxes; Fischer-Tropsch waxes; fatty alcools; derivatives of fatty acids, especially those having from about 12 to about 18 carbon atoms, including stearic acid, palmitic acid, lauric acid, myristic acid, oleic acid, linoleic acid, and tall oil fatty acid, such derivatives including fatty amides and esters of fatty acids; hydrogenated oils, such as hydrogenated castor oil; polyethers, including polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and block copolymers of these; polytetrahydrofuran waxes; ethylene/vinyl acetate copolymer waxes; and mixtures of these.

Especially preferred are polyethylene waxes having molecular weights of preferably at least about 2000 and preferably below about 12,000; carnuba waxes; esters of fatty acids; montan waxes, polyamide waxes such as Ross Wax-100, Ross Wax-145, and Ross Wax-160, bayberry wax, Japan wax, paraffin wax, ethylene/vinyl acetate copolymer waxes; and mixtures of these.

The wax aids in the re-dispersibility of the MICR toner polymer particles and improves the fusing of the particles in the printing process. The wax may be included in amounts of from about 0.1 to about 3 weight percent, preferably from about 0.5 to 2 weight percent based on the total weight of the MICR developer.

An external charge control agent, or charge director, is also included.

A charge director may be included in the particle itself, but in one preferred embodiment a charge director is included in the carrier liquid. A charge

director included in the carrier liquid should be soluble in the carrier liquid.

Examples of suitable negative charge directors include, without limitation, lecithin, basic calcium petronate, basic barium petronate, sodium dialkylsulfosuccinate, polybutylene succinimide, and polymer oligomers containing amine groups. Examples of positive charge directors include, without limitation, metal soaps such as aluminum stearate, cobalt octoate, zirconium naphthenates, chromium alkylsalicylates, and the like. In addition to serving its primary function as a charge control agent, a charge director included in the carrier liquid may act as an anti-settling agent and/or improve re-dispersibility of a composition exhibiting some settling. Charge adjuvants may be used in conjunction with the charge control agents to enhance the charge and may be included in either the continuous phase or in the solid particles. Suitable examples of charge control agents and charge adjuvants may be found in the previously cited U. S. Patents No. 5,486,443; 5,153,091; 5,147,774; 4,859,550; and 4,517,268, which are incorporated herein by reference.

The liquid MICR developers may also contain a variety of other ingredients including addition dispersing aids, viscosity modifiers, surfactants, flow control agents, leveling agents, and the like.

The liquid MICR developers are preferably prepared by forming crude particles of a mixture of magnetic particles, polymer resin, and, optionally, pigment. The crude particles are then dispersed in a liquid carrier and further reduced by milling or other means to obtain the final desired particle size.

The primary particles may be prepared without solvent at a temperature higher than the softening point of the polymer resin by melt mixing or compounding the ingredients, or may be made with the aid of a solvent which

is later removed from the homogenous mixture by low pressure distillation, stripping with air or inert gas, or other such techniques. The ingredients are mixed until homogenous in devices such as twin screw extruders, Banbury mixers, two roll mixers, and so on. The homogenous melt is allowed to solidify and then is broken down or crushed into particles by a suitable device such as a Fitz mill, Waring blender, hammer mill, or equivalent device. Jet milling may be used to further reduce particle size if desired. The primary particle size is typically from about 50 microns to about 150 microns, and preferably it is 100 microns or less, such as in the range of from about 50 microns to about 100 microns.

Following the initial particle preparation, the primary particles are mixed with the carrier liquid. The mixture is typically about 30% by weight solid material, preferably from about 15% to about 50% by weight solid material, and more preferably from about 20% to about 40% by weight solid material. The dispersion of the primary particles is then subjected to further size reduction in ball mills, sand mills, horizontal mills, vertical mills, Niche mills, basket mills, or other equipment useful for this purpose until the mean particle size is from about 0.1 pm to about 10 um, preferably from about 1 pm to about 7 pm, even more preferably from about 1 micron to about 5 microns, and most preferably from about 1 pm to about 3 um. Particle size may be assessed by standard techniques such as by using a particle size analyzer, for example a Coulter, Malvern Horiba, Brinkman, or Microtrac particle size analyzer. The additives used in the carrier liquid, such as the charge control agents, charge adjuvants, wax, viscosity modifiers, dispersing aids, and so on, can be added before or after the process of size reduction of the particles.

In the printing process, the liquid MICR developer contacts the photoreceptor or imaging belt, developing the latent image portions with the MICR toner. The MICR toner should not adhere to non-image areas. The photoreceptor or imaging belt, now bearing the developed MICR image, comes into contact with a substrate having an opposite charge or a higher electrostatic charge of the same charge type. The developed MICR image transfers to the substrate due to the higher potential. The image-bearing substrate is then heated to a temperature at which the polymer particles fuse to the substrate, leaving a permanent image. Vaporized carrier liquid is preferably collected by condensation and recycled or burned for its fuel value.

The liquid MICR developers of the invention offer several notable advantages over dry MICR toners. Due to the smaller particle size, higher definition images and images having lower pile heights may be printed. The higher definition and lower pile height reduce the read error rate because the edges of the print, at which the change in magnetic flux density is the highest, are more abrupt. The decreased pile height allows the read head to more closely approach the substrate surface. Less flutter and other movement of the substrate is thus possible. The decreased pile height also significantly reduces the tendency for the peeling away of the image due to the increased flexibility of the printed image. The liquid MICR developers also produce less scatter around the print, again increasing the read reliability. Moreover, the carrier liquid serves as a lubricant between the substrate and the photoreceptor or imaging belt, significantly reducing the wear of these machine components.

The invention is illustrated by the following examples. The examples are merely illustrative and do not in any way limit the scope of the invention

as described and claimed. All parts are parts by weight unless otherwise noted.

Example 1. Preparation of Dry Dispersion 120.0 grams of a resin blend (20.0 g Reichold 382ES and 100.0 g Lawter P-3370) and 70.0 g of iron oxide (Magnox B-353) are melt mixed using a two-roll mill with a 1.3 to 1 friction ratio. During the melt mixing process, 10.0 g of carbon black (Cabot BPL) is added to the resin. The resultant uniform dispersion is then pulverized using a Fitz-Patrick mill (Model-M) and the pulverized material is collected through a 0.125 inch screen.

Example 2. Preparation of Dry Dispersion 100.0 g of a resin blend (20.0 g Reichold 382ES and 80.0 g Lawter P- 3370) and 90.0 g of iron oxide (Magnox B-353) are melt mixed using a two- roll mil with a 1.3 to 1 friction ratio. During the melt mixing process 10.0 g of carbon black (Cabot BPL) is added to the resin. The resultant uniform dispersion is then pulverized using a Fitz-Patrick mill (Model-M) and the material collected through a 0.125 inch screen.

Example 3. Preparation of Dry Dispersion 80.0 g of resin blend (20.0 g Reichold 382ES and 60.0 g Lawter P- 3370) and 110.0 g of iron oxide (Magnox B-353) are melt mixed using a two roll mill with a 1.3 to 1 friction ratio. Then 10.0 g of carbon black (Cabot BPL) is added to the resin during the melt mixing process. The resultant uniform dispersion is then pulverized using a Fitz-Patrick mill (Model-M) and the material collected through a 0.125 inch screen.

Example 4. Preparation of Liquid Toner Two methods are used to prepare liquid developers from the dry dispersions of Examples 1 through 3. Smaller batches are prepared using a Ball Mill and larger batches are prepared using a 1SDM Attritor.

1) 101.5 g of dry dispersion, 3.5 g of wax (Ross Wax 160) and 245.0 g carrier liquid (Isopar-LO) are charged into a ball mill and milled for 48 hours at 30% solids using zirconium oxide media. After 48 hours, 350 g of carrier liquid is added and the liquid developer diluted to 15% solids. The 15% solids developer was collected and bottled. The particle size of the batches is measured using a Horiba LA-910 particle size analyzer.

2) 551.0 g of dry dispersion, 19.0 g of wax (Ross-Wax-160) and 1330.0 g of carrier liquid (Isopar-LO) is charged into a 1 SDM Attritor (Union Process). The batches are processed for 4 hours at 1500 rpm using 2 mm stainless steel shot. The temperature of the batch is kept below 35°C. After four hours, the batch is diluted to 15% solids and bottled. The particle size of the liquid developer batches are measured using a Horiba LA-910 particle size analyzer.

Example 5. Preparation of Charge Control Agent Three charge control agents are used to charge the liquid developer batches to give appropriate conductivity and charge-to-mass ratio. CCA-1 is a zirconium salt of 2-ethylhexanoic acid in mineral spirits (available from OM Group, Inc.). CCA-2 is a dodecylbenzene sulfonic acid and proprietary components in a mixture of organic solvents (available from Dupont

Performance Products). CCA-3 is an aluminum metallo-organic complex from OMG Group, Inc.

Example 6. Preparation of Working Mix From the above liquid developer examples, a 2% working mix is prepared for the print test. 304.0 g of 15% concentrate was diluted with 1947.5 g of lsopar-LO. To this working mix the appropriate amount and type of charge control agent is added to bring up the conductivity to the level where the printer achieves optimum print quality. It is found that a conductivity of 20 to 30 pS/cm is desirable for the printer. The Q/m of the toners were also measured. It is desirable for the Q/m to be from about 80 to about 200 microcoulombs per gram A breadboard converted from a ND2/3 printer is used for print test evaluations.

Printing Evaluations of Liquid MICR developers As described in Example 6, liquid developer working mixes are prepared from the dry dispersion examples. A liquid developer machine is used for the print evaluation. The printer is an ND2/3 printer converted into a liquid developer machine to perform the evaluation. Check images were printed on preprinted forms for the print evaluation. For each toner MICR reading, background, image density, and adhesion to the paper is determined.

The liquid MICR developers made from Example 1 and Example 2 produce acceptable MICR readings. The best results are produced by developer made from Example 2 in combination with CCA-2, which produces a MICR reading of 127 with an image density of 1.3 to 1.4 without any background.

Shelf Life Study Example 2 is selected for shelf life study. The toner is subjected to forced aging for 72 hours at 125°F and 60% humidity. The physical properties are measured before and after the test. The important physical properties measured are conductivity (Scientifica 627 conductivity meter), re- dispersibility (the ability of a toner to re-disperse), plating (to determine the ability of a toner to plate on one electrode for a given time), OPT opposite polarity toner, to determine the amount of toner with opposite charge), and Q/m. There are no substantial changes in physical properties before and after the shelf life test, including no substantial change in the measured Q/m.

The invention has been described in detail with reference to preferred embodiments thereof. It should be understood, however, that variations and modifications can be made within the spirit and scope of the invention and of the following claims.