EP0513820A2

EP0513820A2 - Conditioning roller and method of operation for use with a photoconductive drum in an electrophotographic color printer

Info

Publication number: EP0513820A2
Application number: EP92108240A
Authority: EP
Inventors: Thomas Camis; James G. Bearss; James A. Hall
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1991-05-17
Filing date: 1992-05-15
Publication date: 1992-11-19
Also published as: EP0513820A3

Abstract

Liquid toner conditioning apparatus and method for use in an electrophotographic color printer and including a stabilizing roller (76) (Figure 3) positioned adjacent to the surface of a photoconductive drum (10) and operative for transforming discrete color toner particles on the surface of the drum (10) into a stabilized unitary polymeric film structure which may be directly transferred onto an adjacent print medium. Advantageously, the stabilizing roller (76) comprises a deformable roller member including a soft open cell conductive foam (78), such as a wettable polyurethane foam which is disposed on a biased slip ring (80). The bias slip ring (80) is in turn formed on the outer surface of a central motor driven metal roller core member (82), and a suitable DC bias connection (86, 88) is applied to the slip ring. The applied DC bias voltage (88) has the same polarity as the desired charge on the toner and of an opposite polarity to the counter ions within the isopar carrier fluid for transporting the toner on the surface of the photoconductive drum (10). Therefore, when the conductive deformable conditioning roller (76) is rotatably driven (48, 50) against the surface of the photoconductive drum (10), it provides three (3) critically important functions. First, it absorbs isopar fluid from the surface of the photoconductive drum (10) which reduces isopar carry out on the media (30). Secondly, it compresses the toner image electrostatically on the drum (10) to preserve its fidelity inasmuch as the polarity of the applied DC bias (88) repels the like charged toner ions into the surface of the photoconductive drum. Thirdly, the DC bias (88) applied to the slip ring (80) pulls counter ions in the isopar fluid from the surface of the drum (10) to thereby leave a desirable positive net charge on the toner as its proceeds to the print media (30).

Description

Technical Field

This invention relates generally to electrophotographic printing and more particularly to electrophotographic color printing using liquid toners for transferring developed color images directly from a photoconductor to an adjacent print medium.

Related Application

In the European Patent Application entitled "Electrostatically Assisted Transfer Roller and Method for Directly Transferring Liquid Toner to a Print Medium" and filed by the present applicant (Hewlett-Packard Company) on the same date as this application, there are disclosed and claimed still further new and useful improvements in the field of electrographic color printing. This invention and claimed process uses transparent color liquid electrostatic toners in a novel direct transfer technique for developing the composite color image on the surface of a photoconductive drum and then transferring the image directly to the print media. The disclosure of this other European patent application is incorporated herein by reference.
The present invention described herein represents still further new and useful improvements in the art and technology of electrophotographic color printing, and particularly in the field of electrophotographic color printing using transparent liquid electrostatic color toners and conditioning rollers for preparing a developed color image for transfer to a print medium with good print quality and fidelity.

Background Art

In the field of electrophotographic color printing, one conventional approach to developing a color image on an organic photoconductor and then transferring the developed color image to an adjacent print medium is to use a so-called intermediate transfer member (ITM) which is located between a surface of the organic photoconductive drum and the surface of the print medium. Using this approach, liquid toners of cyan, yellow, magenta, and black are first transferred electrostatically in series from a conventional source of liquid toners to the surface of the organic photoconductor and then developed thereon such as by writing the desired color image with a controlled laser beam or other suitable light source. Color liquid toners are generally well known in the art of electrophotographic printing and are described in some detail, for example, in U.S. Patent Nos. 4,925,766 and 4,946,753 issued to Elmasry et al and entitled "Liquid Electrophotographic Toners", both incorporated herein by reference.
When each of the colors of cyan, yellow, magenta, and black are individually developed on the organic photoconductive drum, the intermediate transfer member is then brought into intimate contact with the surface of the drum and is rotated against the drum surface to thereby transfer the written color images from the surface of the photoconductive drum to the intermediate transfer member. One example of a printing process using an intermediate transfer member in the transfer of the image from the photoconductive drum to the print media disclosed in U.S. Patent No. 4,286,039 issued to Landa et al and incorporated herein by reference.
The use of the above described intermediate transfer member has been required in the above conventional electrophotographic color printing apparatus because of the fact that intimate contact between the toner and the print surface receiving the toner was essential for high quality transfer of the image from the surface of the photoconductive drum. The requirement for the use of this intermediate transfer member not only added cost and complexity to the electrophotographic printing apparatus, but it also brought with it critical alignment, reliability, and associated maintenance problems. In addition, since the developed liquid toners formed on the surface of the photoconductive drum were in discrete particle form and not held together satisfactorily within a properly charged unitary cohesive structure, prior attempts to transfer the color toners directly from the photoconductive drum to the print medium failed to completely transfer all of the developed toners to the print medium, thereby resulting in an unacceptable print quality.

Disclosure of Invention

The general purpose and principal object of the present invention is to provide a new and improved electrophotographic color printing apparatus which is operative to transfer the developed color toners and color images directly from the surface of a photoconductive drum to an adjacent print medium without going through an intermediate transfer step such as that described above using an intermediate transfer member positioned between the drum and the print medium.
Another object of this invention is to provide a new and improved electrophotographic color printing apparatus of the type described which is operative to eliminate the cost and complexity brought about by the prior art requirement for using this intermediate transfer member.
Another object of this invention is to provide a new and improved electrophotographic color printing apparatus of the type described which allows one to reduce the amount of liquid carrier which is transferred onto the photoconductive drum during the color image development process.
Another object of this invention is to provide a new and improved color printing apparatus of the type described which is operative in an alternative embodiment for the image conditioning roller to simultaneously reduce the amount of isopar fluid on the photoconductive drum, compress the toner images electrostatically to hold the color images in place and preserve their fidelity, and produce a desired net charge on the toner as it proceeds from the conditioning roller toward the print media.
A unique and novel feature of this invention is the provision of a new and improved electrophotographic color printing apparatus of the type described which operates to form a compressed cohesive polymeric thin film structure of the developed color image. This thin film structure can then be transferred directly to the print medium with a high degree of resulting print quality heretofore unavailable with known direct transfer electrophotographic color liquid toner printing techniques.
Another feature of this invention is the provision of a new and improved electrophotographic color printing apparatus of the type described which operates to utilize a combination of mechanical, electrical and thermal energy to help prepare the developed color images for direct transfer to an adjacent media. This is accomplished by the use of a compliant toner conditioning roller which is electrically biased and heated and includes a soft smooth elastomeric outer surface which operates in intimate contact with an adjacent photoconductor surface.
Another feature of this invention is a provision of a new and improved electrophotographic color printing apparatus of the type described which employs a novel electrical and thermal conditioning roller scheme useful to stabilize the color image on the surface of the photoconductive drum, thereby preserving its fidelity and preventing it from adhering to the roller while the amount of liquid fluid surrounding the image, such as an isopar hydrocarbon, is reduced. In addition, the use of low level heating applied to the conditioning roller serves to initiate the transformation from discrete toner particles into a polymeric film structure on the surface of the photoconductive drum. Furthermore, electrical and mechanical forces applied to this soft conditioning roller operate to preserve the fidelity of the toner-on-toner images developed on the adjacent photoconductive drum.
Another feature of this invention is the provision of a liquid toner conditioning apparatus of the type described wherein either AC bias or DC bias or both can be adjusted to charge the toner to the proper sign and optimum charge level before being applied to the print medium.
Another feature of this invention in an alternative embodiment thereof as shown in Figure 3 herein is the provision of a new and improved conditioning roller which is multifunctional in purpose and includes a deformable roller consisting of a soft open cell conductive foam, such as a wettable polyurethane foam, disposed on a biased slip ring which, in turn, has been formed on an inner motor-driven metal roller core member. A suitable DC bias is applied to the slip ring with the opposite polarity as the charge on the counter ions within the isopar carrier fluid for the color toner on the photoconductive drum. Therefore, when the conductive deformable conditioning roller is rotatably driven against the surface of the photoconductive drum, it not only absorbs excess isopar carrier fluid from the surface of the drum, but it also compresses the toner image electrostatically on the drum to preserve its fidelity and it also pulls counter ions in the isopar fluid from the surface of the drum to thereby leave a net charge on the toner as is desired as the toner proceeds toward the print media.
Another feature of this invention is the provision of a new and improved method of operating a conditioning roller of the type used with a photoconductive drum within an electrophotographic color printer. This method includes the steps of; dispensing liquid color toner within an isopar carrier fluid on the surface of the photoconductive drum, absorbing isopar fluid from the surface of the photoconductive drum, while simultaneously electrostatically compressing a toner image on the surface of the drum to preserve the fidelity of an image being developed, while simultaneously removing counter ions from the isopar fluid to leave a net charge on the liquid toner as it proceeds to the print medium.
The above described method of operation is carried out by rolling a soft wettable conductive foam, such as a polyurethane foam, against the surface of the photoconductive drum upon which color images are being developed in the liquid toner.
The above purpose, objects, novel features, and related advantages of this invention are accomplished by the development of an electrophotographic color printing apparatus which includes, in combination, a photoconductive drum adjacent to which is positioned a source of liquid toner and electrostatic toner transferring means associated with the source of liquid toner for transferring the liquid color toners to the surface of the photoconductive drum. Image writing means are also positioned adjacent to the surface of the photoconductive drum for developing the color toners, and liquid toner conditioning means are positioned in intimate contact with the surface of the photoconductive drum for preparing and conditioning tile developed color liquid toner layers for direct transfer front the surface of the photoconductive drum to an adjacent print medium.
In a preferred embodiment of this invention, the liquid toner conditioning means includes means for compressing the toner image on the surface of the photoconductive drum using a combination of electrostatic and mechanical forces and thermal energy, thereby stabilizing the image on the surface of the drum and preserving its fidelity and preventing it from adhering to the toner conditioning apparatus.
Also in a preferred embodiment of the invention, the toner conditioning means used for treating the liquid toner includes a deformable stabilizing roller which is rotatably mounted adjacent to the surface of the photoconductive drum, and this roller has an inner core member and a soft and smooth outer core member. In this novel arrangement, the inner core member may advantageously be provided with a source of heat and is further connected to a source of either DC bias or AC bias or both. Thus, the stabilizing roller is operative to utilize a combination of mechanical, electrical and thermal energy to condition the developed color images for direct transfer from the photoconductive drum to the adjacent print media.
Also in a preferred embodiment of the invention, the developed color image which has been conditioned by the toner conditioning roller is transferred to the print media using a heated transfer roller which may, if desired, be also connected to a source of DC bias voltage to electrostatically assist in the direct transfer of the color image to the print media in accordance with the novel teachings in the above identified European Patent application.
The above brief summary of the invention, together with its attendant advantages and novel features, will become more readily apparent from the following description of the accompanying drawings.

Brief Description of the Drawings

Figure 1 is an abbreviated schematic cross sectional view of an electrophotographic color printer constructed in accordance with the present invention.
Figure 2 is an enlarged view of the toner conditioning apparatus portion of the printer combination shown in Figure 1 and according to one embodiment of the invention.
Figure 3 is an enlarged view of the toner conditioning apparatus portion of printer combination shown in Figure 1 and according to another, alternative embodiment of the invention.

Detailed Description

Referring now to Figure 1, there is shown an organic photoconductive drum 10 which is positioned adjacent to a source 12 of monochromatic (e.g. laser) light 14 used for developing color images on the surface of the drum 10. The apparatus in Figure 1 further includes a conventional corona charge mechanism 16 for the drum 10 and a conventional drum surface cleaning apparatus 18 mounted as shown adjacent to the surface of the photoconductive drum 10.
Cyan, yellow, magenta, and black color liquid toner sources 20, 22, 24, and 26 are located as shown adjacent to the lower surface of the photoconductive drum 10, and these color and black sources of transparent liquid toner are constructed and operated in a well known manner understood by those skilled in the electrophotographic color printing arts and are therefor not described in any significant detail herein. For a further discussion of the general construction and operation of these color and black sources 20, 22, 24, and 26 of liquid toner, reference may be made to the above identified Elmasry et al and Landa et al patents.
A heated and electrically biased transfer roller is designated generally as 28 and is rotatably mounted as shown above the upper surface of the photoconductive drum 10. The transfer roller 28 is operative to be driven against the upper surface of a print medium 30, such as paper, which passes between the outer surface of the transfer roller 28 and the outer surface of the organic photoconductive drum 10. Preferably, the transfer roller 28 is constructed and operated in accordance with the principles and teachings in the above identified European patent application,
and will include a conductive inner core member 32 within which a heater element 34 is located. The conductive inner cOre or metal sleeve member 32 is surrounded at its outer surface by a first cylindrically formed elastomer layer 36 which in turn is coated by a thin outer protective coating 38. The metal inner core member 32 is connected by way of a conductor 40 to a source 42 of electrical bias, the other side of which is grounded at node 45.
A cylindrical air gap separates the centrally located heater element 34 from the inner metal sleeve 38, and the heater element which is positioned at the axis of rotation of the transfer roller 28 will preferably be an elongated quartz heater tube. This heater tube will typically be heated during an image transfer operation to a controlled elevated temperature on the order of 80 - 90°C or greater to provide the thermal energy in combination with electrical and mechanical forces in the nip zone of the transfer roller 28 which makes direct contact with the media 30. Typically, the inner metal sleeve 32 will be DC biased to a voltage in excess of minus 900 volts DC, and a mechanical pressure will also be applied to the nip zone at a level on the order of five (5) psi or greater.
Referring now to both Figures 1 and 2, a liquid toner conditioning and stabilizing apparatus is indicated generally as 46 and is located as shown on the right hand side of the photoconductive drum 10. This toner conditioning apparatus 46 is operatively driven by a drive motor 48 and drive belt 50 and is in intimate contact with the outer surface of the photoconductive drum 10. The toner conditioning and stabilizing apparatus 46 also includes a centrally disposed heating element 52 which is surrounded first by a cylindrical air gap 54 and then by an inner metal roller core 56 of a suitable metal such as aluminum. The heating element 52 may also be an elongated quartz tube positioned at the rotational axis of the conditioning roller 46. The roller core member 56 is surrounded by a metal slip ring 58 which is in turn connected through a bias electrode 60 and an interconnect pin 62 within the adjacent housing 64 to source 66 of DC bias, the other side of which is grounded at node 68. The outer surface of the metal slip ring 58 is surrounded by a soft core elastomer material 70 having a very smooth outer surface 72 which material is described in greater detail below.
The outer core member 70 may for example be a conductive silicone or a conductive polyurethane material. The reason that the soft core material 70 appears discontinuous in the figures is that the elements 60, 62, and 64 of the biasing arrangement for the slip ring 58 are located in front of the soft core roller 70 in Figure 2.
In operation, the heated and biased transfer roller 28 and media 30 are initially moved away from the surface of the organic photoconductive drum 10 during the exposure and development process used for developing layers of cyan, yellow, magenta, and black transparent color toners, one on top of another, on the surface of the photoconductive drum 10. After each successive layer of cyan, yellow, magenta, and black color toner is initially applied to the surface of the photoconductive drum 10, it is then treated with the toner conditioning apparatus 46 on the right hand side of the drum 10 and then subsequently exposed by light 14 from the monochromatic light source 12 on the left hand side of the photoconductive drum 10.
Then, after the cyan, yellow, magenta, and black color toners have all been exposed and developed to a desired composite image one on top of another and conditioned and stabilized in series by the toner conditioning apparatus 46, the heated and biased transfer roller 28 and print medium 30 are then brought into intimate contact in the position shown in Figure 1 with the surface of the photoconductive drum 10. Here the composite developed color image is transferred to the lower surface of the print medium 30 as a unitary and cohesive polymeric film which holds tightly together all of the developed color toners. As will be seen below, in the absence of using the toner conditioning and stabilizing apparatus 46 as shown in Figures 1 and 2, these color toners would be transferred in discrete particle form from the surface of the photoconductive drum 10 to the underside of the print medium 30. And, as previously indicated, prior art direct transfer electrophotographic color printers have been characterized by a somewhat inefficient and ineffective transfer of all of the developed color images and the discrete particle color toners onto a print medium. However, in accordance with the present invention, a high quality color image is now provided on the under surface of the print media 30.
Each of the sources of color liquid transparent toners 20, 22, 24, and may include a combination of negatively charged toner particles which are immersed in a charged isopar toner carrier liquid. When the positively charged surface of the photoconductive drum 10 rotates past these liquid toner sources 20, 22, 24, and 26, the negatively charged toner particles are electrostatically pulled onto the surface of the photoconductive drum 10, while simultaneously the positively charged counter ions are stripped away from their negatively charged nuclei and onto an adjacent negatively charged substrate (not shown). However, some of the carrier liquid is pulled onto the surface of the photoconductive drum 10 along with the negatively charged toner particles which it surrounds and therefore needs to be conditioned and stabilized in order to develop the color-on-color layers of toner into a cohesive and unitary polymeric film. This is accomplished by operation of the toner conditioning and stabilizing apparatus 46 as shown on the right hand side of Figure 1 and in the enlarged cross section view in Figure 2.
From the above description of the toner conditioning apparatus 46, it is seen that this apparatus is operative to provide a combination of mechanical pressure, electrostatic forces, and a low level of thermal energy to the successive layers of liquid toner as they pass, in succession counter-clockwise against the smooth surface 72 of the outer conditioning soft core roller member 70. The outer roller member 70 is preferably a soft elastomeric material such as a polyurethane or conductive silicone material having a volume resistivity less than about 10⁸ ohm · centimeters and a Shore A Hardness less than 30. The soft elastomeric roller 70 outer cover layer must be designed to have a smooth surface finish which is useful to preserve the fidelity of images and must also be blade cleaned to remove excess carrier fluid therefrom, using, for example, wiper blade 74.
The inner core 56 of the toner conditioning apparatus 46 is a cylindrical metal sleeve such as aluminum and biased to a maximum allowable DC potential of the same polarity as that of the liquid toner particles. This feature is useful in order to provide a recharging of any electrically discharged toner particles which will naturally take place during the operation of the above color toner development process. Both DC and AC bias may be used on conductor 62 to provide the proper sign and level of toner charge for the efficient transfer of the developed polymeric film on the outer surface of the photoconductive drum 10 directly onto the undersurface of the print medium 30.
Thus, there has been described herein a novel electrophotographic color printing and toner conditioning apparatus 46 which is operative in an efficient manner to properly prepare developed transparent color liquid toners for direct transfer to a receiving sheet of paper. The electrically biased and heated conditioning roller 46 which is in intimate contact with the surface of the photoconductive drum 10 compresses the charged toner particles thereon which are received by the conditioning apparatus 46 in discrete particle form. This electrostatic and mechanical compression by the toner conditioning apparatus 46 of the multiple and serially deposited discrete particle films operates to preserve the fidelity of the images superimposed one upon another, and it also helps prevent degradation of these images. Such degradation may otherwise take the form of poor edge acuity around printed characters, streaks, and general toner scattering.
The electrostatic pressure, P _e, acting on the various toner layers can be shown from Maxwell's well known stress equation to be directly related to the net charge on the toner film times the average of the electrical field above and below the toner film. That is to say:

${Equation 1: P}_{e} {= [E}_{AT} + E_{BT} {)/2] · σ}_{net}$

where E _AT is the electrostatic field above the toner layer, E _BT is the electrostatic field below the toner layer and σ _net is equal to the net charge on the toner layer on the photoconductive drum 10. This relationship is applicable to the electrostatic pressure, P _e, at both the toner conditioning and stabilizing roller 46 and also to the electrostatically assisted transfer roller 28.
Thus, the biased and heated roller conditioning apparatus 46 will also serve to apply the proper toner charge level and polarity in the case where toners become charge deficient as indicated above. This toner conditioning apparatus 46 is also used to reduce and limit undesirable amounts of liquid carrier (e.g. isopar) that is normally carried out onto the print medium due to its presence on the photoconductor in both image and background regions. This isopar fluid is significantly removed by the conditioning apparatus 46 whose smooth outer surface 72 is continuously cleaned by the wiping action of the cleaning blade 74 as previously described to scrape away residual isopar from the surface 72 of the conditioning roller 46. Optimum cleaning is achieved by the use of a sharp cleaning blade 74 which brushes in intimate contact with the smooth surface 72 of the roller member 46 thereby enabling the isopar excess liquid to be collected in an adjacent container (not shown).
Referring now to Figure 3, there is shown an improved image conditioning roller in accordance with an alternative embodiment of the invention. This conditioning roller is designated generally as 76 and includes an outer soft open cell conductive foam member 78 which is preferably an open cell polyurethane foam. The soft open cell conductive wettable foam deformable roller member 78 is disposed on an inner cylindrical slip ring 80 which, in turn, has been formed on the outer surface of a central metal roller core member 82.
The slip ring member 80 is electrically biased by means of a metal brush 84 which is connected by way of conductor 86 to a source 88 of DC bias voltage. A brush holder member 90 is positioned as shown to hold the brush 84 against the slip ring 80 and it includes an opening therein through which the conductor 86 passes between the brush 84 and the source 88 of DC bias voltage.
An excess fluid carrier accumulation member 92 is positioned as shown to receive the excess isopar carrier fluid as the deformable foam roller member 78 rotates against the outer surface of the photoconductive drum member 10. As in the earlier described embodiment of Figure 2, the conditioning apparatus 76 is rotatably driven in a clockwise direction as shown by use of a drive motor 48 and belt 50 which is wound around the outer surface of the metal roller core member 82 on the reverse side of the roller conditioning apparatus 76 as viewed in Figure 3.
The electrical bias 88 applied to the slip ring 80 of the conditioning roller apparatus 76 will always be of the opposite polarity as the polarity of the counter ions within the isopar carrier fluid for the liquid toner on the surface of the photoconductive drum 10. In this manner, not only does the conductive soft open cell foam roller member 78 absorb the excess isopar liquid as it rotates against the surface of the photoconductive drum 10, but a voltage of appropriate polarity applied at bias node 88 to the slip ring 80 and to the conductive roller member 78 will cause charged counter ions to be pulled out of the isopar liquid and into the foam member 78.
With positively charged toner particles and negatively charged counter ions, a positive voltage is applied at node 88 and the conditioning roller apparatus 76 will leave a net positive charge on the toner. Moreover and equally important, however, is the fact that in this case the positive DC voltage applied as electrical bias to the slip ring 80 will thus repel the net positive charge on the toner and thereby cause the toner images on the photoconductive drum 10 to be electrostatically compressed on the surface thereof, thereby holding the toner images firmly in place on the drum surface to thereby preserve image fidelity.
Various modifications may be made in and to the above described preferred embodiment without departing from the spirit and scope of this invention. For example, the present invention is not limited by the particular materials or geometric configuration of the conditioning roller described herein, and this toner stabilizing roller 46, 76 may be used in combination with many different types of electrophotographic writing schemes, with alternatively charged toner systems, with color toner transferring techniques for applying toner to the photoconductive drum and with various different additional schemes for aiding in the direct transfer of the developed color toners from the surface of the photoconductive drum to an adjacent print media. Also, it should be understood that the present invention is not limited to use with the particular transfer roller apparatus 28 described herein. Accordingly, these and other design modifications are clearly within the scope of the following appended claims.

Claims

A method of electrophotographic color printing where color images are developed using liquid toner on the surface of a photoconductive drum (10) and then transferred to an adjacent print media (30) which passes between a surface of said drum (10) and the surface of an adjacent transfer roller (28), which method comprises the steps of:
a. absorbing isopar fluid from the surface of said photoconductive drum (10), while simultaneously,

b. electrostatically compressing a toner image on the surface of said drum (10) to preserve the fidelity of said image, while simultaneously

c. removing counter ions from said isopar fluid to leave a net charge on said liquid toner as it proceeds to said print media (30).
The method defined in Claim 1 wherein said steps of absorbing, compressing and removing are accomplished simultaneously by rolling a deformable soft wettable conductive foam (78), such as a polyurethane foam, against a surface of said photoconductive drum (10) upon which said liquid toner is used in the development of color images.
A liquid toner conditioner for an electrophotographic color printer of the type having a photoconductive drum (10) therein, said conditioner comprising a deformable roller (76) formed of a soft open cell wettable conductive foam (78).
The conditioner defined in Claim 3 wherein said conductive foam is disposed on a slip ring (80) which is operative to receive a DC bias voltage (88).
The conditioner defined in Claim 4 wherein said slip ring is disposed on a roller core member (82) which is rotatably driven to thereby rotate said conductive foam (78) against the surface of said photoconductive drum (10), whereby said liquid toner conditioner absorbs isopar fluid from the surface of said drum, compresses toner images on the surface of said drum to preserve their fidelity, and attracts counter ions from said isopar fluid from the surface of said drum to leave a desirable net charge on the toner as it proceeds toward a print medium (30).
Electrophotographic color printing apparatus comprising: a photoconductive drum (10), a source of liquid toner (20, 22, 24, 26) adjacent to said photoconductive drum (10), electrostatic transfer means associated with said source of liquid toner for transferring said liquid toner to the surface of said photoconductive drum (10), means (12, 14) adjacent to said photoconductive drum (10) for developing images in said toners thereon, and characterized by liquid toner conditioning means (46, 76) positioned in intimate contact with said photoconductive drum (10) for preparing and conditioning the developed color liquid toner layers on said drum (10) for direct transfer from the surface of said drum to an adjacent print medium (30).
The apparatus as claimed in Claim 6 wherein said liquid toner conditioning means includes a roller member rotatably mounted adjacent to said photoconductive drum (10) and having an inner core member (56, 82) and an outer cover (70, 72, 78) thereon operative to rotate in direct contact with the surface of said photoconductive drum (10), thereby stabilizing the image on the surface of said drum (10) and preserving its fidelity and preventing it from adhering to said roller member while the amount of fluid vehicle carrying said toners is reduced.
The apparatus as claimed in claims 6 or 7 further characterized in that said liquid toner conditioning means includes a deformable roller (76) comprising a wettable soft open cell conductive foam (78), such as a polyurethane foam, disposed on a slip ring (80), with said slip ring (80) being, in turn, formed on an inner motor driven metal roller core member (82), whereby a suitable DC bias (88) may be applied to said slip ring (80) with a polarity opposite to that of the charge on counter ions within a carrier fluid for said color toner on said photoconductive drum, whereby when said conditioning roller (76) is rotatably driven against the surface of said photoconductive drum (10) it absorbs isopar fluid from said surface and also compresses the toner image electrostatically on the surface of said photoconductive drum to preserve its fidelity.
The apparatus defined in claim 7 which further includes:
a. means for affixing a source of heat (52) adjacent to said inner core member (56) of said conditioning means, and

b. means (62) connecting said inner core member (56) of said condition means to a source (66) of either AC bias or DC bias or both.
The apparatus claimed in any one of Claims 6, 7 or 9 wherein said outer cover (70) of said conditioning means is a soft elastomeric material.
The apparatus as claimed in Claim 6 wherein said liquid toner conditioning means (46) includes means for stabilizing and compressing the toner image on the surface of said photoconductive drum (10) using both thermal (52), electrostatic (66) and mechanical (72) forces.
A method for directly transferring developed color images on the surface of a photoconductive drum (10) to an adjacent print media (30) characterized by converting developed color toner layers on the surface of a photoconductive drum (10) from discrete particle form to a thin stabilized polymeric film structure containing said developed images and further reducing the liquid content of said toner layers from the level used to initially apply the liquid toners (20, 22, 24, 26) to the surface of said photoconductive drum (10).
The method claimed in Claim 12 wherein said conversion is accomplished by using either electrostatic forces (66) or mechanical forces (72) or both and further and alternatively using thermal energy applied to said photoconductive drum (10) if desired, whereby a controlled low level heating (52) applied to the surface of said drum (10) serves to initiate the transformation of said toner layers from discrete toner particles into a unitary stabilized polymeric film structure.
Conditioning and stabilizing apparatus for integrating and converting toner from discrete particle form into a cohesive and unitary polymeric film, comprising:
a. photoconductive means (10) having an outer surface thereof for receiving successive films of cyan, yellow, magenta, and black liquid toners (20, 22, 24, 26), and

b. conditioning and stabilizing means (46, 76) positioned in intimate contact with said surface of said photoconductive member (10) and operative for applying a combination of mechanical pressure (72, 84) and electrostatic forces (66, 88) to said surface of said photoconductive member, whereby said liquid toners (20, 22, 24, 26) may be compressed into a unitary and cohesive polymeric film with the toner particles therein recharged for subsequent transfer to a selected print medium.
The apparatus claimed in Claim 14 wherein said conditioning and stabilizing means includes:
a. a roller apparatus having an inner core member (56) containing a heating element (52) and connected to a source of either AC bias or DC bias (66) or both, and

b. an outer roller member (70) surrounding said inner core member and operative to be driven against the surface of said photoconductive member (10) for applying a combination of thermal (52), mechanical (72), and electrical forces (66) thereto.
The apparatus claimed in Claim 14 wherein said conditioning and stabilizing means includes a deformable roller (76) comprising a wettable soft open cell conductive foam (78), such as a polyurethane foam, disposed on a slip ring (80), with said slip ring (80) being, in turn, formed on an inner motor driven metal roller core member (82), whereby a suitable DC bias (88) may be applied to said slip ring (80) with a polarity opposite to that of the charge on counter ions within a carrier fluid for said toner.
A method for converting toners in discrete particle form into a cohesive and unitary polymeric film which comprises the steps of:
a. developing a plurality of color and black liquid transparent toners (20, 22, 24, 26) on the surface of a photoconductive member (10), and

b. simultaneously applying mechanical (72, 84), and electrical (66, 88) energy in series to said multiple liquid color toners in discrete particle form to thereby convert said toners into said cohesive and unitary polymeric film.
The method defined in Claim 10 which further includes, in step b., simultaneously removing toner carrier fluid such as an isopar from the unitary polymeric film being developed to thereby reduce the amount of carrier fluid that is ultimately transferred to a print medium (30).
The method defined in Claims 17 or 18 which includes rotatably driving a toner conditioning roller (46) against the surface of said photoconductive member (10) to thereby convert said discrete toner particles to said cohesive and unitary polymeric film.
Electrophotographic color printing apparatus of the type including a photoconductive drum (10) for receiving a source of liquid toner adjacent to one surface thereof, means (20, 22, 24, 26) associated with the liquid toner for transferring the liquid toner to the surface of the photoconductive drum, development means (12, 14) adjacent to the photoconductive drum (10) for developing images in toners thereon, and transfer means (28) for transferring images from the surface of the photoconductive drum (10) to an adjacent print media (30), characterized in that: an improved conditioning roller apparatus (76) is rotatably mounted and rotatably driven in intimate contact with the surface of the photoconductive drum (10) and includes a deformable soft open cell conductive foam roller (78) disposed upon the surface of a biased slip ring (80), and a motor driven metal roller core member (82) positioned within the interior of the biased slip ring (80), and means (86) for applying a DC bias voltage (88) to said slip ring (80) with a polarity opposite to the polarity of the charge on the counter ions within an isopar carrier fluid for color toner on the photoconductive drum, so that when the conductive deformable conditioning roller (76) is rotatably driven against the surface of the photoconductive drum (10), it not only absorbs isopar fluid from the surface of the photoconductive drum (10), but it also compresses the toner image electrostatically on the surface of the drum to preserve its fidelity and thereby further operates to leave a net charge on the toner as is desirable as the toner proceeds toward the print media (30).