Abstract:
A novel liquid toner development system is disclosed. The liquid development system includes conductive core-shell particles comprising silver-copper or copper-silver. A novel apparatus and method relying on the novel liquid toner development system results in electro-conductive patterning capable of high conductivity with low background fogging, reduced processing time and reduced environmental impact.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 USC §119 to Japanese Patent Application No. 2013-122583 filed on Jun. 6, 2013, now Japanese Patent Registration No. 5,336,680 registered on Aug. 9, 2013, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention is directed to electro-conductive deposition methods. More particularly, the invention is directed to a liquid toner development system, and pattern forming method and apparatus capable of electro-conductive deposition. 
     2. Description of Related Art 
     Electro-conductive patterning is generally within the field of “printed electronics”, in which electrical conductors, or passive or active electrical components are formed on a substrate. Printed electronics is normally an additive process, wherein material is deposited on a substrate to form a predefined pattern. Multiple layers may be deposited of the same material or different, and may require secondary processes such as drying or curing to create the final form of electrical conductors or electrical components. 
     Many industrial printing technologies have been used for electro-conductive patterning. For example, screen printing, flexography, gravure, offset lithography and inkjet printing have been used for electro-conductive patterning with each having certain advantages and disadvantages. In the case of screen printing, it requires patterns formed from screens which are placed on a substrate, flooded with ink, then excess ink removed. This is a rudimentary process which is inexpensive, but is not suitable for high production volumes. Since the screen pattern is fixed, is not capable of producing variable patterns within a single set of screens. Gravure printing relies on engraved printing plates wherein the engraved features are filled with ink, then transferred to a substrate. This method is capable of high-quality and high-speed patterning, but is not capable of producing variable patterns within a single set of plates. Inkjet printing relies on a voltage impulse to propel droplets onto a substrate, resulting in a finally formed pattern. Inkjet printing is capable of high-quality printing, but is normally limited to a print swath of less than one inch. And further, print defects inherent in the technology normally requires an overlapping print mode (“shingling”) for full quality printing. Thus, a swathing print technology such as inkjet is inherently slow unless many expensive printheads are ganged together to improve printing speeds. Therefore, inkjet is normally preferred for low-volume printing. Inkjet printers also require low viscosity fluids for proper jetting, resulting in inks with high levels of solvent is which must be removed after patterning. This results in a further decrease in net throughput. Inkjet printing is a digital technology capable of changing patterns from one substrate to the next, which is a favorable property. 
     Another printing technology not normally considered for electro-conductive patterning is electrophotographic (EP) printing. EP printing is a digital technology which relies on a multi-stage electrostatic transfer of printed particles, such as “toner”, to a substrate. It is a page-wide technology capable of high speed and is capable of changing patterns from one substrate to the next. The electrostatic transfer process normally requires toner capable of holding an electrostatic charge, such as is common with polymers. The polymers normally interfere with the ability to form electrical conductors or components. 
     Previous attempts at conductive toner are discussed below: 
     Japanese Patent Laid-Open No. 2004-184598 teaches a liquid developer comprising toner particles in a binder resin with several metal particles evenly dispersed in a dispersion agent. The metal particles are of silver and copper, having an average metal particle diameter from 0.2 to 1.2 μm. The toner particle diameter is from 2.5 to 8 μm, and the developer contains 50 to 90 weight percent of toner particles. This is claimed to make the line edges sharper and reduce the circuit pattern line width. But, the method of &#39;598 requires a high sintering temperature (1,000° C., for example). This sintering temperature is incompatible with substrates used for printed circuit applications. 
     Japanese Patent Laid-Open No. 2004-048030 describes an electronic circuit manufacturing method and manufacturing apparatus using metal-containing charged toner particles with resin containing the metal particles. The metal is silver or copper, wherein the metal particle concentration rate is 10˜90 weight percent. It is pressure transferred to an intermediate transfer drum, then onto a substrate. The metal particles become the plating core and act like a catalyst for a plating response. It claims to reduce costs, increase productivity of multiproduct and small-quantity production and shorten the evaluation cycle for manufacturing. The method of &#39;030 also relies on a plating process (electrolytic or non-electrolytic) to improve the electrical conductivity, is giving rise to environmental issues normally associated with traditional plating processes. 
     Japanese Patent Laid-Open No. 2005-181621 teaches a developer which uses toner particles of copper/silver alloys to obtain a golden color output. The composition of the alloy is adjusted to affect the golden color. It claims that the resolution of wiring circuit without causing poor conductivity and the golden-color output can be improved. 
     The objective of the &#39;621 reference is not to achieve high electrical conductivity, but rather to obtain a specific golden color through the use of discrete alloy compositions. Additionally, a large amount of binder resin is used in order to improve the ability to control the charge, fixing, and dispersion, thereby reducing the opportunity for high conductivity. For Example, Example 1 in the document provides 70 parts of wax to 20 parts of metal particles and copolymers (such as lauryl methacrylate). Since &#39;621 relies on an intermediate transfer process, a high level of wax and resins is required to achieve intended results. 
     These examples describe circuit formation methods using electro-photography as being superior to conventional lithography, screen printing, and inkjet methods in terms of simplicity, low cost and mass-productivity. However, achieving high conductivity with EP technology has yet to be achieved. 
     Other issues not taught in these references, but required for an EP technology capable of reliably forming electro-conductive circuits, is to provide high adhesion to a substrate and with little to no background fogging. 
     It is therefore an object of the present invention to provide a liquid electrophotographic toner, apparatus, and method capable of patterning electrical conductors and components having high conductivity, high substrate adhesion, and with little to no background fogging. 
     SUMMARY 
     A novel liquid toner development system is disclosed for electro-conductive deposition applications. In particular, the liquid toner includes electro-conductive is particles containing a core-shell of Ag—Cu, or Cu—Ag. A novel deposition apparatus and deposition method is also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a - b  are cut-away illustrations, not to scale, of exemplary core-shell electro-conductive particles. 
         FIGS. 1   a ′,  1   b ′, and  1   b ″ show cut-away illustrations, not to scale, of imperfectly formed core-shell electro-conductive particles. 
         FIG. 1   c  shows a cut-away illustration, not to scale of an exemplary electro-conductive toner particle. 
         FIG. 1   c ′ shows a cut-away illustration, not to scale, of an electro-conductive toner particle which is made of an imperfectly formed core-shell electro-conductive particle. 
         FIG. 1   d  illustrates a liquid developer. 
         FIG. 2  schematically depicts, in cross-section, an exemplary conductive pattern forming apparatus. 
         FIGS. 3   a - b  provide experimental data inputs and results in tabular form. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the claims of the invention described herein. The present invention is capable of other embodiments and of being used in various applications. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of is at least one of the referenced item. 
     Reference is now made to  FIG. 1   a - b  which illustrates core shell electro-conductive particles. 
       FIG. 1   a  shows a core of silver  11  (having a chemical symbol Ag) plated by a shell of copper  12  (having a chemical symbol Cu). Copper-plated silver, designated Cu—Ag, is shown in reference number  13 . Cu—Ag  13  is not commercially available, but was plated by the inventors using an electroless process including a copper salt and EDTA in an aqueous solution. Cu—Ag  13  in the range of 0.1 μm diameter to 7.5 μm diameter were successfully plated and tested. 
       FIG. 1   b  shows a core-shell electro-conductive particle having a core of copper  12  and a shell of silver  11 . A silver plated copper particle, designated Ag—Cu, is shown in reference number  14 . Particles of this type are available from Fukuda Metal Foil &amp; Powder Co., Ltd. or Kiyokawa Plating Industry Co., Ltd., and may also be prepared by the method shown in Japanese Patent Laid-Open No. 2001-214080 Bulletin hereby incorporated by reference in its entirety. Ag—Cu  14  in the range of 0.1 μm diameter to 7.5 μm diameter were successfully tested. 
     In  FIGS. 1   a ′- b ′, irregularly shaped shells are shown, illustrating that the coating need not be perfectly coated to function properly. 
     Cu—Ag  13  or Ag—Cu  14  may be referred to collectively as “conductive particle(s)  13  or  14 . The Cu—Ag  13  or Ag—Cu  14  may contain small amounts of impurity elements in actual operation. 
       FIG. 1   c  shows an electro-conductive toner particle  16 , which includes conductive particle  13  or  14 , coated by a charge control agent  15  (described below) to form a conductive toner particle  16 . To affect or enhance the electrostatic charge of conductive particles  13  or  14 , additives known as charge directors or charge control agents ( 15 ) provide a coating. In this application, denaturalized polyvinylpyrrolidone (PVP) such as alkylation polyvinylpyrrolidone, acetic acid vinylpyrrolidone polymeric resin, acrylamide functionalized polyvinylpyrrolidone is suitable for the charge control is agent  15  in the liquid developer. In addition to denaturalized PVP, synthetic resin such as ethyl cellulose, methyl methacrylic acid resin, acrylic acid resin, alkyd resin, polyethylenimine oligomer, organic acid such as rhodine, phthalic acid, maleic acid, fumaric acid, lauric acid and stearic acid can be used as the charge control agent. A blend of denaturalized PVP resin, synthetic resin and organic acid may also be used. These charge control agents coat the conductive particles  13  or  14 , forming a shell over the conductive particles  13  or  14 , resulting in conductive toner particles  16 . These charge control agents  15  enable the conductive toner particles ( 16 ) to accept a charge in the developer and minimize clumping, thereby enabling the conductive toner particles  16  to flow uniformly. 
       FIG. 1   c ′ shows an electro-conductive toner particle  16 , wherein charge control agent  15  is shown coating an irregularly shaped conductive particle  13  or  14 . 
     It is preferable that the solid content composition of charge control agents  15  have a weight ratio between 1% to 15% of the combined total of conductive toner particle  16 . It is more preferred that this ratio is between 3% and 9%. 
       FIG. 1   d  shows a liquid developer  47  in an arbitrary container. The container is shown in dashed lines as not relevant to the description. The liquid developer  47  includes conductive toner particles  16  in a dispersion medium  17 . The dispersion medium  17  is an insulative liquid having electric resistivity of 1×10 9  Ωcm or higher. Example liquids capable of use as a dispersion medium  17  include aliphatic hydrocarbon, petroleum naphtha, other hydrocarbons and silicone oil. As to the aliphatic hydrocarbon, the following products are usable: Isopar L, G, H (ExxonMobil), IP Solvent 1620 (Idemitsu Petrochemical), Solutol (Phillips Petroleum), as petro-based naphtha Naphtha No. 1 through 6, other hydrocarbons such as Solvesso 100 and 150, Shell S.B.P., ShellSol (Shell Oil), Pegasol 1030, 2130, 3040, AS-100, ARO-40 (Mobil), Isododecane (BP Chemical), as silicone oil such as synthetic dimethylpolysiloxane, cyclic methyl poly siloxanes as well as KF96L (Shinetsu Silicone), KF994 (Shinetsu Silicone), and SH200 (Toray Dow Corning silicone). Further details related to the liquid developer  47  will be provided in the upcoming examples. 
     A conductive pattern forming apparatus, shown in  FIG. 2 , will now be described. A cylindrical drum forms an image holding body  10 , which is coated with a photo receptive surface (not shown). The image holding body  10  is commonly referred to as a photoconductor drum. A latent image (not shown) is formed on the image holding body  10  which is charged evenly by an electrostatic charger  21 . An image pattern is exposed by exposure device  31  which may be a light source such as a laser or an array of light emitting diodes (LEDs). 
       FIG. 2  discloses a so-called roller development method wherein the liquid developer  47  is lifted up by development roller  41  in developer device  40 . But not limiting to this method, other methods such as a method using a dish-shaped electrode (not shown) can be used if needed as long as the liquid developer  47  touches the image holding body  10 . 
     When the density of conductive toner particles  16  is high, and the viscosity of liquid developer  47  is high, it is possible for a separate roller (not shown) to apply the liquid developer  47  on development roller  41  and let it contact image holding body  10  (high viscosity contact development method). 
     Developer device  40  includes a developer housing  46 , containing the liquid developer  47  in addition to a development roller  41 , a squeeze roller  42 , a blade  43 , a scraper  44 , and a churning paddle  45 . The function of these components will now be described. Liquid developer  47  is provided from a supply device (not shown). The churning paddle  45  mixes the liquid developer  47 , causing conductive toner particles  16  to stay suspended, maintaining uniformity throughout dispersion medium  17 . When liquid developer  47  is left unattended, and if the specific gravity of electro-conductive particles is greater than the specific gravity of the disperse medium, sedimentation of conductive toner particles  16  may occur. In these cases churning paddle  45  is used to prevent sedimentation. 
     Development roller  41  picks up liquid developer  47 , causing a film (not shown) of fluid to contact image holding body  10  through a gap separating development roller  41  and image holding body  10 . Conductive toner particles  16  are transferred electrostatically to the imaged portion of the image holding body  10  (the is “developed image”). In the case of the roller development method, a gap is set up between development roller  41  and image holding body  10 . During operation the liquid developer fills this gap. When the density of conductive toner particles  16  is low, and the viscosity of liquid developer  47  is low, liquid developer  47  is lifted to make contact to the image holding body  10  by rotating the development roller  41  (roller development method by lifting). 
     The gap between development roller  41  and image holding body  10  is recommended to be set between 50 μm to 300 μm for said roller development method by lifting. For the roller development method by lifting, a squeezing measure is preferred, although it is not needed for the high viscosity contact development method. The squeezing measure can be selected from the roller method, corona method, air method and etc. The roller method is to spin squeeze roller  42  which is near image holding body  10  at high speed to let the excess developer liquid on image holding body  10  adhere, then scrape it off with scraper  44 . The corona method is to use the corona discharger (not shown) instead of squeeze roller  42  It is effective to squeeze off the excess liquid developer  47  electrically. The air method is to squeeze the excessive liquid with air pressure (not shown). 
     Most of the liquid developer  47 , excluding the transferred conductive toner particles  16 , are removed from development roll  41  by a blade  43 . The remaining layer of liquid developer  47  on image holding body  10  is metered off by the squeeze roller  42 .  FIG. 2  shows components to enable the roller squeeze method. Squeeze roller  42  maintains a gap to the image holding body  10  from 20 μm to 150 μm while spinning. The rotation speed of squeeze roller  42  is recommended about 2 to 4 times the rotation speed of image holding body  10 . 
     Squeeze roller  42  is cleaned of liquid developer  47  by the scraper  44 . The way to squeeze out the liquid can be chosen from the roller method, corona method and air method depending on the application. 
     The developed image rotates to a transfer unit  50 . The transfer unit  50  comprises regulating rollers  52  and a transfer charger  51 . Media  70 , which is dielectric, is transported from the media roll  71  to the transfer unit  50  by friction force of feeding rollers  91 . Transfer charger  51  charges the media  70  to a polarity opposite the charge is of the conductive toner particles  16 . 
     The conductive toner particles  16  are transferred to the media  70  assisted by mechanical force provided by regulating rollers  52 , which press the media  70  against the image holding body  10 . 
     The media  70 , now including conductive toner particles  16 , traverses past a dryer  81  wherein liquid such as dispersion medium  17  is evaporated. The media  70  then traverses past feeding rollers  91 , then cut to the appropriate size by media cutter  92  and ejected by media ejection unit  93 . 
     Any residual liquid developer, including residual conductive toner particles  16 , are cleaned from image holding body  10  by cleaning unit  60 . Cleaning unit  60  comprises cleaner housing  64 , a cleaning roller  61  and a cleaning blade  62 . The residual conductive toner particles  16  on image holding body  10  are uplifted by wetting liquid (not shown) through wetting liquid supply section (not shown) to cleaning roller  61 . This roller rotates such that mating surfaces are moving in opposite directions, uplifting any residue from the surface of image holding body  10 . The uplifted residue is scraped off by the cleaning blade  62 . The scraped toner particles are recovered into a waste liquid tank (not shown) connected to cleaner housing  64 . The wetting liquid (not shown) will preferably be the same as the dispersion medium  17 . 
     Following the cleaning step, any remaining static charge on image holding body  10  is removed by eraser  101 , thereby reinitialized the surface. 
     Returning again to the developer device  40 , a gap of about 50 μm to 300 μm between the development roller  41  and image holding body  10  is maintained. The liquid developer  47 , which is picked up by the development roller  41 , sufficiently transfers the electro-conductive toner particles  16  to the image holding body  10 . The gap is determined by the viscosity of the liquid developer  47 , which is in part determined by the conductive toner particle  16  density. A narrower gap of 50 μm is sufficient for lower viscosity liquids, while a gap of 300 um may be preferred for higher viscosity liquids. The churning paddle  45  rotates continuously during operation, maintaining a uniform dispersion of conductive toner particles  16  in the liquid developer  47 , thereby preventing sedimentation. 
     In an alternate developer device  40  configuration for high viscosity liquids, an intermediate roll (not shown) between liquid developer  47  and development roller  41  may be used. 
     For either configuration, the developer device  40  includes a squeeze roller  42  which rotates counter to the direction of the image holding body  10  and maintains a gap between these components. Squeeze roller  42  preferably rotates at a surface speed 2 to 4 times greater than the surface speed of the image holding body  10 . By so doing, the squeeze roller  42  regulates the thickness of the liquid developer  47 . This is most useful for lower viscosity liquid developers  47  as low viscosity fluids, being more like water, are more likely to form uncontrolled patterns on the image holding body  10 . A gap of 20 μm to 150 μm is preferred, depending on the viscosity of the liquid developer  47 . A scraper  44  is in contact with squeeze roller  42 , causing excessive fluid buildup to be scraped off and returned to the developer device  40 . 
     Non-contact alternatives to a squeeze roller  42  for regulating the thickness of liquid developer  47  includes a corona generating conductor (such as a wire, not shown), capable of generating a potential between the corona conductor and the coated image holding body  10 . A corona discharge creates an ion curtain extending across the width of the image holding body, impinging on the liquid coating, effectively leveling at least a portion of the coating. Another non-contact alternative is the use of an air curtain (not shown). 
     Turning now to the transfer unit  50  shown in  FIG. 2 , this module transfers the toner image on the image holding body  10  to the media  70 . Shown in  FIG. 2  is a direct transfer method, wherein the developed image is transferred directly from the image holding body  10  to the media  70 . Alternately, an intermediate transfer member (not shown) may receive the developed image, then transfer the image to media  70 . Intermediate transfer members are often used when multiple images are to be formed. The multiple images may be accumulated on the intermediate transfer member, thereby enabling a single transfer to the media  70 . 
     Direct transfer, such as with transfer unit  50 , may rely on mechanical or electrostatic means, but normally a combination of both. Regulating rollers  52  apply is pressure between the media  70  and image holding body  10 . The media  70  may travel at a speed slightly different than the surface speed of the image holding body  10 . The pressure, in combination with the difference in surface speed, causes a shear stress on the image, encouraging efficient transfer. The regulating rollers  52  may also be electrostatically charged to provide an electrical bias capable of attracting the toner to the media  70 . A corona conductor, such as transfer charger  51 , may also provide an electrical bias. A preferred embodiment includes a corona conductor for transfer charger  51 . It is also preferred that regulating rollers  52  do not directly contact image holding body  10  to minimize the disturbance of the transferred image. 
     Once the electro-conductive image has been transferred to the media  70 , the image is fixed to the media  70  via a sintering furnace (not shown). A sintering furnace may be attached to the printer, or may be a separate unit. 
     In general, sintering relies on one or more energy sources to evaporate or burn off any remaining dispersion medium  17  or charge control agent  15 , consolidate conductive particles  13  or  14  and fix them to the media  70 . 
     Sintering normally consolidates particles (such as conductive particles  13  or  14 ) at temperatures below the melting point of the conductive particles  13  or  14 , or the media  70 , whichever is lower. Energy sources, and time/temperature profiles at least depend on the particle material (such as silver  11  or copper  12 ), the diameter of the conductive particles  13  or  14 , the dispersion medium  17 , the media  70 , the level of conductivity required, and the operating environment of the electro-conductive circuit. Energy sources may be, for example, hot air, light, electromagnetic, resistance, or plasma. Additionally, it is preferred to sinter under a reduction environment by introducing hydrogen or non-oxygen gas since copper  12  is easily oxidized in air. A sintering apparatus will differ based on the many variables described heretofore. Therefore, an exemplary apparatus is not shown in the figures. 
     Metal particles achieve various levels of sintering as temperature increases. For example, silver particles may start to “neck”, connecting particles to particles, at a temperature of about 150° C., with more visible necking at 180° C. But as the is temperature increases to 250° C., silver atoms diffuse from grain boundaries at the intersections and continue to deposit on the interior surface of the pores, thereby filling up the remaining space, even though the melting temperature of silver  11  is much higher at about 960° C. Thus, a media  70  such as paper having a thermal limit of about 120° C. would limit the sintering process. But polyimide film, having a glass transition temperature of about 350° C., will enable a more robust sintering process. For green ceramic, sintering temperatures of the media  70  may approach the melting temperature of the particles, therefore one does not limit the other. 
     For the applications disclosed here, media  70  may be paper, resin film, ceramic green sheet, and so on as long as it is insulative material. 
     EXAMPLES 
     Operational Example 1 
     Cu—Ag  13  particles were prepared with following method: 4 g of copper (II) sulfate pentahydrate was dissolved in 400 g of purified water, then 4 g of ammonia water was added while stirring. Additionally, 8 g of ethylenediaminetetraacetate tetrasodium salt (EDTA 4Na) was added while stirring. Separately, 0.1 g of bipyridyl was dissolved in 8 g of ethyl alcohol, then it was added to the above copper sulfate solution to prepare the plating solution. 200 g of silver particle S211A (manufactured by Daiken chemical Co., Ltd., average particles diameter 1 μm) was added to the plating solution and dispersed for 2 minutes with 9500 rpm spin on the homogenizer. Then 4 g of formalin was added slowly while stirring at 100 rpm, heated at 40° C.˜50° C. and continued stirring for 30 minutes. After this process, it was rinsed 3 times with purified water, then dried for 2 hours at 80° C., resulting in Cu—Ag  13  particles. 
     A solution for forming a charge control agent  15  was prepared according to the following method: 7.5 g of Ganex V-220 (alkylated polyvinylpyrrolidone, made by ISP Japan) was added to 50 g of Isopar L (ExxonMobil) and heated to 50° C. to dissolve and let it cool down to room temperature. 
     Conductive toner particles  16  were formed by adding 100 g of the aforementioned Cu—Ag  13  particles to the aforementioned solution. In addition, 250 g of alumina balls of 5 mm diameter were included. This was sealed in a container and is rotated at a rate of 90 rpm for 2 hours on a ball mill rotation platform. When finished, the alumina balls were separated, resulting in Cu—Ag  13  particles coated with charge control agent  15  and the solution. 
     The liquid developer  47  was prepared by combining the aforementioned Cu—Ag  13  particles coated with charge control agent  15  and the solution with 160 g of Isopar L. This resulted in the liquid developer  47  having a charge control agent solid part ratio of 7.0% by weight. The term “charge control agent solid part ratio” is defined as the ratio of weight of the charge control agent solid part to the total weight of charge control agent sold part and weight of Cu—Ag particles. The particles were separated from the solution and analyzed using an inductively coupled plasma-atomic emission spectrometer (ICP-AES). The copper  12  content was 0.12 weight percent of the total (copper and silver). The diluted liquid developer was dried and observed under the scanning electron microscope (SEM) and it was verified that single conductive toner particles  16  were made of single electro-conductive particles. 
     The liquid developer  47  of Example 1 was used in the conductive pattern forming apparatus shown in  FIG. 2 . Polyimide having a thickness of 25 μm was used as dielectric media  70  in roll form. A positively charged single layer organic photoconductor was used for image holding body  10  with a rotation speed of 50 mm/s, having an initial surface potential charged of +600 V. An LED exposure device  31  was used to expose the image. A conductive development roller  41  was charged at the potential of +450 V, positioned to have a gap of 200 μm between the development roll  41  and image holding body  10  and rotated at the speed of 150 mm/s. 
     A squeeze roller  42  was charged at the potential of +450 V, positioned to have a gap of 50 μm between the squeeze roller  42  and image holding body  10 . The squeeze roller  42  was rotated at a speed of 150 mm/s. The conductive toner particles  16  on image holding body  10  were transferred to media  70  by applying −1 KV on the grid of scorotron which was used as a scorotron system transfer charger  51  in transfer unit  50 . For this step, regulating roller  52  was placed near the image holding body, however at the location where it did not touch the image holding body, in order for the media to contact the image holding body over the scorotron charging width. After the is media  70  on which the conductive toner particles  16  were transferred was cut by media cutter  92  to appropriate length, it was sintered in a sintering furnace apparatus at 250° C. temperature for one hour. 
     Testing of the resulting electro-conductive pattern was conducted after sintering, having a line width 0.3 mm, length 5 mm, and 5.0 μm thick. The electro-resistance was measured by 4-terminal sensing, having a volume resistivity of 4×10 −5  Ωcm. The image background fogging was ranked subjectively on a scale of 1 to 5, with 5 being the best (no visible background fogging). 
     Operational Example 2 
     Silver-plated copper particles can be obtained commercially as well as they can be manufactured through the method such as shown in the Japanese Patent Laid-Open No. 2001-214080 bulletin. 
     A solution for forming a charge control agent was prepared according to the following method: 1.0 g of oleic acid was dissolved in 100 g of ethyl alcohol placed in a container. 
     Conductive toner particles  16  were formed by providing 200 g of the aforementioned Ag—Cu  14  particles, in addition to 5 mm glass beads, to a container of the aforementioned solution. It was rotated for 4 hours on a ball mill rotation platform at 100 rpm speed. The glass beads were then separated out, and the remaining coated particles were dried at 80° C. for 1 hour in a dryer, resulting in conductive toner particles  16 . 
     The liquid developer  47  was prepared for Example 2 by providing 0.56 g of Luviskol VA64P (vinyl acetate-vinyl pyrrolidone copolymerized resin, made by BASF), dissolving it in a mixed solvent of 12.0 g of ethyl acetate and 12.0 g of xylene, then 3.73 g of rhodine and 1.87 g of maleic acid. Additionally, 1.34 g of Beckosol 1334-EL (alkyd resin, made by DIC) were dissolved. The mixture and 100 g of aforementioned surface treated silver plated copper (Ag—Cu  14 ) particles were sealed in a container with 250 g of 5 mm diameter glass beads, then rotated at a speed of 100 rpm for 4 hours on a ball mill rotation platform. When finished, hot air was blown-in to evaporate the ethyl is acetate and xylene. 50 g of Isopar L (made by ExxonMobil) was added and resealed and rotated at a speed of 100 rpm for 4 hours on the ball mill rotation platform. Then, the glass beads and surface treated silver plated copper (Ag—Cu  14 ) particles were separated. An additional 160 g of Isopar L was added to complete the liquid developer  47 . The charge control agent  15  solid part ratio to the liquid developer  47  was 7.0% by weight. 
     The liquid developer  47  of Example 2 was used in the conductive pattern forming apparatus shown in  FIG. 2 . The evaluation was done after the image with the electroconductive particles was formed and sintered the same way as Operation Example 1. In addition, rhodine, maleic acid and alkyd resin were charge control agents and the charge control solid part ratio for the liquid developer was 7.0 weight percent. Also, the toner particle which was the silver plated copper particle in the liquid developer was analyzed with the inductively coupled plasma-atomic emission spectrometry (ICP-AES) equipment and the silver content was 10 weight percent against the total of copper and silver. The diluted liquid developer was dried and observed under the scanning electron microscope (SEM) and it was verified that single conductive toner particles  16  were made of single electroconductive particles. The liquid developer&#39;s toner particles were positively charged and it was possible to develop the negatively charged latent image. The electroconductive pattern&#39;s thickness and electrical resistance of the image part, line width 0.3 mm and length 5 mm, were measured after sintering. The thickness of electroconductive pattern formed was 5.1 μm and the result of electrical resistance showed the conductive pattern&#39;s volume resistivity as 1.4×10 −4  Ωcm. The image background fogging rank was 5. 
     Test Data 
     Comparison Example 1, Operation Example 3˜7 
     Copper plating was varied from 0% to 0.24% weight. All other variables were the same as Operational Example 1. 
     Operation Example 8˜12 
     Silver particle diameter was varied from 0.1 μm to 7.5 μm. All other variables were the same as Operational Example 1. 
     Operation Example 13 
     Charge control agent  15  was changed to “G: WP-660” as follows. All other variables were the same as Operational Example 1. 
     7.5 g of Ganex WP-660 (alkylated polyvinylpyrrolidone, made by ISP Japan) was added to 50 g of Isopar L (made by ExxonMobil) and heated to 80° C. to dissolve and let it cooled down to the room temperature. This solution was slightly milky. 100 g of copper plated silver (Cu—Ag  13 ) particles prepared by the same method as Operation Example 1 were added to the solution and additionally 250 g of alumina balls of 5 mm diameter were added. They were placed and sealed in a container and rotated at a rate of 90 rpm for 2 hours on a ball mill rotation platform. When it was finished, the whole content was taken out and the alumina balls were separated. The liquid developer was prepared after 160 g of Isopar L was added. 
     Operation Example 14 
     Charge control agent  15  was changed to “L: VA64P” as follows. All other variables were the same as Operational Example 1. 
     3 g of rhodine and 3 g of maleic acid were dissolved in the mixed solution of 12.0 g of ethyl acetate and 12.0 g of xylene to prepare the organic acid solution. 1.5 g of Luviskol VA64P (vinyl acetate-vinyl pyrrolidone copolymerized resin, made by BASF) was dissolved in the mixed solvent. Additionally, 100 g of copper plated silver (Cu—Ag  13 ) particles which were prepared with the same method as Operation Example 1 was added with 250 g of alumina balls of 5 mm diameter in a container and sealed. The container was rotated at a speed of 90 rpm for 2 hours on the ball mill rotation platform then opened. Hot air from dryer was blown-in to evaporate the ethyl acetate and xylene. 50 g of Isopar L (made by ExxonMobil) was added and resealed and rotated again at a speed of 90 rpm for 2 hours on the ball mill rotation platform. Then, the container was opened and whole content was taken out to separate out the alumina balls. Additionally, 160 g of Isopar L was added to prepare the liquid developer. 
     Operation Example 15˜18 
     Charge control agent  15  included “G: V-220” as with Operational Example 1, but coating weight (C Cntl wt %) was varied from 1% to 15% weight. All other variables were the same as Operational Example 1. 
     Comparison Example 2, Operation Example 19˜23 
     Silver plating on copper was varied from 0% to 20% weight. All other variables were the same as Operational Example 2. 
     Operation Example 24˜28 
     Copper particle diameter was varied from 0.1 μm to 7.5 μm, and silver plating was held at 10% weight. All other variables were the same as Operational Example 2. 
     Operation Example 29 
     Charge control agent  15  was changed to “S-630” as follows. All other variables were the same as Operational Example 2. 
     0.73 g of S-630 (vinyl acetate-vinyl pyrrolidone copolymerized resin, made by ISP Japan) was dissolved in the mixed solution of 12.0 g of ethyl acetate and 12.0 g of xylene and in addition 3.64 g of rhodine and 1.82 g of maleic acid were dissolved in the mixed solution. Additionally, 1.31 g of Beckosol 1334-EL (alkyd resin, made by DIC) was dissolved. The mixture and 100 g of surface treated silver plated copper (Ag—Cu  14 ) particles prepared by the same method as Operation Example 2 were placed and sealed in a container with 250 g of glass beads of 5 mm diameter and rotated at a speed of 100 rpm for 4 hours on the ball mill rotation platform. When finished, hot air was blown-in to evaporate dry the ethyl acetate and xylene. 50 g of Isopar L (made by ExxonMobil) was added and resealed and rotated at a speed of 100 rpm for 4 hours on the ball mill rotation platform. Then, the glass beads were separated using the metal screen of 1 mm opening. Additionally, 160 g of Isopar L was added to prepare the liquid developer. 
     Operation Example 30 
     Charge control agent  15  was changed to “G: V-220” as follows. All other variables were the same as Operational Example 2. 
     3.75 g of Ganex V-220 (alkylated polyvinylpyrrolidone, made by ISP Japan) and 3.75 g of Beckosol 1334-EL (alkyd resin, made by DIC) were added to 50 g of Isopar L (made by ExxonMobil) and heated to 50° C. to dissolve. 100 g of surface treated Ag—Cu  14  particles which were prepared with same method as Operation Example 2 was added to the liquid and 250 g of glass beads of 5 mm diameter were added. It was sealed in a container and rotated at a rate of 100 rpm for 4 hours on a ball mill rotation platform. When it was finished, the glass beads were separated using the metal screen of 1 mm opening. 160 g of Isopar L was added, completing the preparation of the liquid developer  47 . 
     Operation Example 31 
     Charge control agent  15  was changed to “G: V-216” as follows. All other variables were the same as Operational Example 2. 
     7.5 g of Ganex V-216 (alkylated polyvinylpyrrolidone, made by ISP Japan) was placed in 50 g of Isopar L (made by ExxonMobil) and heated to 50° C. to dissolve. 100 g of surface treated Ag—Cu  14  particles which were prepared with the same method as Operation Example 2 was added to the liquid and 250 g of glass beads of 5 mm diameter were added. It was sealed in a container and rotated at a rate of 100 rpm for 4 hours on a ball mill rotation platform. When it was finished, the glass beads were separated using the metal screen of 1 mm opening. 160 g of Isopar L was added, completing the preparation of the liquid developer  47 . 
     Operation Example 32˜35 
     For these examples, the charge control agent  15  “L: VA64P” included varying weight ranging from 1% to 15% weight. All other variables were the same as Operational Example 2. 
     The developer was formulated with same the ratios of charge control agent, Luviskol VA64P (vinyl acetate-vinyl pyrrolidone copolymerized resin, made by BASF) and rhodine, maleic acid, Beckosol 1334-EL (alkyd resin, made by DIC) as in Operation Example 2, although the total amount was different. The charge control agent  15  solid part ratios contained in the liquid developer were 1, 3, 9 and 15 weight percent respectively. 
     See  FIG. 3   a  and  FIG. 3   b  for a table of input variables and results. 
     Discussion 
     It is clear from  FIG. 3   a  and  FIG. 3   b  that the dominant variable in achieving low volume resistivity and a favorable subjective ranking for background fogging is a conductive toner particle  16  containing a core-shell of Cu—Ag  13  or Ag—Cu  14 . Volume resistivity decreased relative to unplated copper  12  or silver  11  by at least one order of magnitude and, in most cases, three orders of magnitude. Further, background fogging for unplated copper  12  or silver  11  was poor in either case with a subjective ranking of 1, indicating a high level of background fogging. In this case, background fogging deposits conductive components in unwanted regions of the media  70 . For printed electronics applications, this is not only objectionable, but may alter the function of the printed electronic device—perhaps causing shorting of conductive traces or altering the values or even the functionality of components such as resistors, capacitors, or transistors. 
     A core-shell of Cu—Ag  13  was shown to be effective over the entire range tested—from 0.012% of total weight to 0.24%, and from silver  11  diameters ranging from 0.1 μm to 7.5 μm. 
     A core-shell of Ag—Cu  14  was shown to be effective over the entire range tested—1% of total weight to 20%, and from copper  12  diameters ranging from 0.1 μm to 7.5 μm. 
     Even with a range of charge control agent  15  chemistries and thicknesses, a core-shell having a core of either silver  11  or copper  12 , and wherein the shell is different from the core and is either copper  12  or silver  11 , surprising improvements resulted in the overall capabilities of a conductive pattern forming apparatus  1  wherein a liquid developer  47  is used. 
     It should also be noted that achieving a minimum thickness of an electro-conductive pattern is required if the conductive pattern forming apparatus  1  is to have industrial applicability.  FIG. 3   a  and  FIG. 3   b  show substantial increases in the thickness is of the electro-conductive pattern in nearly every case. In some cases, pattern thickness was increased by a factor of more than 20. This enables the technology to be used for many higher current carrying applications, thereby improving the industrial applicability. A single layer thickness, wherein the conductive pattern thickness is about the same as the diameter of conductive toner particles  16 , the probability of continuous conductivity is low. Therefore, good conductivity, the pattern thickness needs to be at least several times greater than the diameter of the particle as seen in the experimental results. 
     It is unclear to the inventors why Cu—Ag  13  particles or Ag—Cu  14  particles result in these substantial improvements over silver  11  or copper  12  particles alone. It is theorized that the chargeability improves as the polarized or ionized charging control agent can adhere easier if silver and copper exist within the particle. However, this phenomenon was found through the inventor&#39;s experimental work and the true mechanism is not necessarily clear. 
     It is contemplated, and will be clear to those skilled in the art that modifications and/or changes may be made to the embodiments of the disclosure. Accordingly, the foregoing description and the accompanying drawings are intended to be illustrative of the example embodiments only and not limiting thereto, in which the true spirit and scope of the present disclosure is determined by reference to the appended claims.