Imaging using a coagulable ink on an intermediate member

Apparatus and method of making an ink-jet-ink-derived material image on a receiver. An ink jet device is used to form a coagulable ink image on a member, the ink image including a coagulable marking ink and a non-marking ink. Each smallest resolved imaging area of the ink image includes a predetermined mixed volume of the coagulable marking ink and the non-marking ink, the predetermined mixed volume being coagulable. Coagulates are formed within the coagulable ink image, and excess liquid is removed from the coagulates to form an ink-jet-ink-derived material image. The ink-jet-ink-derived image is transferred from the operational surface of the intermediate member to another member, which another member may be a receiver member, a drum or a web.

FIELD OF THE INVENTION

The invention relates in general to digital image recording and printing in an apparatus including an ink jet device for forming an ink image on a member. In particular, a first ink and a second ink are used in the ink jet device wherein at least one of the first and second inks is a coagulable ink, an electric field is applied to the ink image on the intermediate member to form a concentrated image, excess liquid is removed from the concentrated image, and the residual image is subsequently transferred to a receiver.

BACKGROUND OF THE INVENTION

An imaging method and apparatus involving electrocoagulation of a primarily aqueous dispersion has been disclosed by the Castegnier et al. patents (e.g., U.S. Pat. Nos. 3,892,645, 4,555,320, 4,661,222, 4,895,629, 5,538,601, 5,609,802, 5,693,206, 5,727,462, 5,908,541 and 6,045,674) wherein an electric current is passed between a positive electrode (or an array of positive electrodes) and a negative electrode (in an array of negative electrodes) to produce an electrocoagulated deposit on the positive electrode. An imagewise electrocoagulated deposit may be transferred to a receiver such as paper to form a single color image, e.g., a black image, on the paper. Alternatively, imagewise electrocoagulated deposits of different colors may be sequentially deposited, e.g., on a positively biased belt, so as to form a full color image for subsequent transfer to a receiver. A squeegee blade apparatus for removing excess liquid is disclosed in the Castegnier et al. patents (U.S. Pat. Nos. 5,928,486 and 6,090,257). A difficulty inherent in the electrocoagulation technique is that image uniformity requires an extremely accurate distance between each pair of opposing positive and negative electrodes, typically about 50 micrometers. Moreover, the image resolution is limited by the diameter of individually addressable electrodes and also by the fact that these electrodes must be isolated from one another by a thickness of insulating material between them. There are other difficulties, e.g. that the electrical power density required for creating an electrocoagulated image is relatively high, that special materials are needed to suppress unwanted gas generation near the electrodes, and that electrodes must be protected against electrolytic erosion. The Castegnier et al. patent (U.S. Pat. No. 4,555,320) discloses a relatively low resolution of 200 dots per inch requiring 25 watts of power (50 volts, 500 ma) to produce 100,000 developed dots per second, which is equivalent to about 100 microcoulombs of charge delivered in about 0.4 second per developed dot, resulting in a significant power density of about 4.1 watts/in2if every imaging pixel is developed (maximum density flat field image). The Castegnier patent (U.S. Pat. No. 4,764,264) discloses a resolution of 200 dots per inch requiring 25 watts of power to produce 1,000,000 developed dots per second, each developed dot requiring passage of 25 microcoulombs of charge.

In related copending U.S. patent application Ser. No. 09/973,244, now U.S. Pat. No. 6,682,189 entitled Ink Jet Imaging Via Coagulation On An Intermediate Member by John W. May, et al., the contents of which are incorporated herein by reference, certain embodiments are disclosed for using an ink jet device to form an ink image on an intermediate member, which ink is an electrocoagulable ink. By jetting a predetermined variable number of droplets on each imaging pixel of an operational surface of the intermediate member, the resulting ink image on the intermediate member has a predetermined variable amount of coagulable ink per pixel. The ink image is moved into contact with an electrocoagulation member, which electrocoagulation member makes physical contact with the variable amounts of liquid of the ink jet image on the intermediate member. Passage of electric current between an electrode included in the electrocoagulation member and a sub-surface electrode included in the intermediate member results in passage of corresponding currents through the variable amounts of electrocoagulable ink, thereby causing an imagewise formation of coagulate deposits on the intermediate member. An excess liquid phase not included in the coagulate deposits is removed from the coagulate deposits while the coagulate deposits remain on the intermediate member, and the coagulate deposits are subsequently transferred to a receiver member. There are certain limitations, which may be associated with the above-described embodiments. These limitations include: (1) a difficulty associated with providing a small enough gap, between the operational surface of the intermediate member and the electrocoagulation member, so that every differing amount of electrocoagulable ink in the ink image can be contacted by the electrocoagulation member, i.e., so that electrocoagulation can occur efficiently at every imaging pixel where there is ink; (2) if, in fact, the gap is made thus sufficiently small, there is a difficulty with a possible blurring of the image as a result of a squashing of the larger amounts of the variable amounts of ink; (3) after the coagulate deposits are formed on the intermediate member, there is a difficulty in efficiently removing the corresponding variable amounts of excess liquid phase from the coagulate deposits; (4) owing to a varying thickness from pixel to pixel of the coagulate deposits, a high efficiency of transfer to a receiver of the thinnest of such deposits may be difficult to achieve.

In related copending U.S. patent application Ser. No. 09/973,239, now U.S. Pat. No. 6,769,423 entitled Ink Jet Process Including Removal Of Excess Liquid From An Intermediate Member by Arun Chowdry, et al., the contents of which are incorporated herein by reference, certain embodiments are disclosed for using an ink jet device to form a colloidal ink image on an intermediate member, which ink is nonaqueous colloidal dispersion of electrically charged pigmented particles in an insulating carrier liquid, similar to a liquid developer for use in electrostatography. By jetting a predetermined variable number of droplets on each imaging pixel of an operational surface of the intermediate member, the resulting colloidal ink image on the intermediate member has a predetermined variable amount of colloidal dispersion per pixel. In one of the disclosed embodiments, the colloidal ink image is moved into proximity with an electrode member, which electrode member makes physical contact with the variable amounts of liquid of the ink jet image on the intermediate member. An electric field applied between an electrode included in the electrocoagulation member and a sub-surface electrode included in the intermediate member urges the charged particles of the dispersion to form a concentrated image on the operational surface of the intermediate member. An excess carrier liquid not included in the concentrated image is removed from the concentrated image while the particles remain on the intermediate member, and the particles thus left behind on the operational surface are subsequently transferred to a receiver member. In other disclosed embodiments, the electrode member does not touch the ink image, and in yet other disclosed embodiments, a corona charging device is used to charge the variable amounts of liquid in the ink image, thereby producing internal electric fields within the variable amounts of liquid for urging the corresponding charged particles in each imaging pixel to migrate to the operational surface. There are certain limitations, which maybe associated with one or more of the above-described embodiments. These limitations include: (1′) a difficulty associated with providing a small enough gap, between the operational surface of the intermediate member and a contacting electrode member, so that every differing amount of ink in the ink image can be contacted by the contacting electrode member, i.e., so that particle migration can occur efficiently at every imaging pixel where there is ink; (2′) if, in fact, the gap is made thus sufficiently small, there is a difficulty with a possible blurring of the image as a result of a squashing of the larger amounts of the variable amounts of ink; (3′) after the concentrated image is formed on the intermediate member, there is a difficulty in efficiently removing the corresponding variable amounts of excess carrier liquid; (4′) owing to a varying thickness from pixel to pixel of the deposits of migrated particles, a high efficiency of transfer to a receiver of the thinnest of such deposits may be difficult to achieve.

SUMMARY OF THE INVENTION

The invention provides a digital imaging method and apparatus including: an ink jet device which includes a first source of ink for imagewise delivering predetermined variable amounts of a first ink and a second source of ink for imagewise delivering predetermined variable complementary amounts of a second ink, of which first and second inks at least one is a coagulable marking ink; an intermediate member having an operational surface upon which a coagulable primary ink jet image is formed from the first and second inks by ink droplets produced by the ink jet device; a mechanism to cause a formation of coagulates in the coagulable primary ink jet image; a liquid removal mechanism for removing excess liquid from the coagulates; a transfer mechanism for transferring liquid-depleted coagulates to a receiver member so as to form an ink-jet-ink-derived material image on the receiver member; and, a regeneration mechanism for regenerating the operational surface prior to forming a new primary image thereon. The first and second inks include nonaqueous colloidal dispersions, aqueous-based colloidal dispersions, and electrocoagulable inks.

In one aspect of the invention, the first ink is a dispersion of pigmented particles dispersed in a carrier liquid, and the second ink is made with a similar carrier liquid, which second ink contains substantially no particles. The predetermined amounts of the second ink become mixed with corresponding complementary amounts of the first ink on the operational surface of the intermediate member so as to form the coagulable primary image thereon. In alternative embodiments of this aspect of the invention, the second ink is made with unpigmented particles similarly dispersed in a similar carrier fluid, such that when the second ink becomes mixed with the first ink to form the primary image, imagewise complementary amounts of the unpigmented particles are included with the pigmented particles in the primary image. In a preferred embodiment of this aspect of the invention, the first ink is a nonaqueous colloidal dispersion of charged pigmented particles in an insulating carrier liquid, and the second ink is made with a similar nonaqueous insulating liquid, which second ink contains substantially no colloidal particles, such that imagewise variable complementary amounts of the second ink are included in the coagulable primary image. In a preferred alternative embodiment of this aspect of the invention, the second ink is made with unpigmented similarly charged particles similarly dispersed in a similar insulating carrier fluid, such that imagewise variable complementary amounts of the unpigmented particles are included in the primary image. In both of the above-described preferred embodiment and the above-described preferred alternative embodiment of this aspect of the invention, a preferred mechanism to cause a formation of coagulates is an electric field mechanism which causes charged colloidal particles in the primary image to migrate to the operational surface, on which operational surface are thereby formed coagulates of the colloidal particles; and, after excess liquid has been removed by the liquid removal mechanism, the liquid-depleted coagulates are transferred to the receiver member to form an ink-jet-ink-derived pigmented particulate image thereon. In other preferred alternative embodiments of this first aspect of the invention similarly utilizing a non-marking second ink which contains coagulable non-marking particles, the mechanism to cause a formation of coagulates includes: a mechanism for a heating or a cooling of the primary image on the intermediate member; a mechanism for adding a dissolved salt to the liquid of an aqueous-based primary image; a mechanism for altering the pH of the liquid of an aqueous-based primary image; a mechanism for causing a desorption or a decomposition of polymeric moieties adsorbed on sterically stabilized particles of a primary image; a mechanism for adding dissolved polymeric molecules to destabilize a sterically stabilized dispersion of a primary image; and, a mechanism for adding a hetero-colloid to form hetero-coagulates in a primary image.

In an other aspect of the invention, the first ink of a preferred embodiment is an electrocoagulable first ink containing a colorant, and the second ink is made with a similar fluid and which second ink contains substantially no electrocoagulable material. In a preferred alternative embodiment of this other aspect of the invention, the second ink is also a coagulable ink containing no added colorant, which coagulable second ink becomes mixed with the coagulable first ink to form the coagulable primary image. In the embodiments of this other aspect of the invention, an electrocoagulation member, included in an electrocoagulation mechanism, provides an electric field and a source of electrical current for imagewise forming, on the operational surface, electrocoagulates containing the colorant in an electrocoagulated image; and, after excess liquid has been removed by the liquid removal mechanism, an electrocoagulate liquid-depleted image is transferred to the receiver member to form a colored ink-jet-ink-derived electrocoagulate material image thereon.

In embodiments in which the coagulable primary image includes a nonaqueous colloidal dispersion of pigmented particles, the liquid removal mechanism is similar to any known mechanism for removing a carrier liquid from a liquid-developed toner image situated on an electrostatographic primary imaging member or intermediate transfer member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides an improved method and apparatus for ink jet imaging, the apparatus employing an ink jet device utilizing a coagulable ink. The ink jet device produces ink droplets according to a known manner for deposition on an intermediate member, which intermediate member has an operational surface upon which a primary ink jet image is formed by the ink jet device. The ink jet device includes a first source of ink for a first ink and a second source of ink for a second ink, of which first and second inks at least one is a marking coagulable ink jet ink. The first ink and the second ink are preferably both nonaqueous, or alternatively are preferably both aqueous-based. The liquid vehicle for an aqueous-based ink is usually water. However, an aqueous-based ink may contain a proportion, typically a minor proportion, of any suitable miscible nonaqueous solvent. In certain embodiments, the marking coagulable ink is a nonaqueous colloidal dispersion of pigmented particles in an insulating carrier liquid, and coagulates are made therefrom in the primary image by means of an applied electric field. In other embodiments, the marking coagulable ink is an electrocoagulable ink, from which colored coagulates are made in the primary image by a passage of an electrical current through the primary image. Preferably, coagulates are formed immediately adjacent or directly on the operational surface of the intermediate member. A liquid removing mechanism for removing excess liquid from the coagulates produces a liquid-depleted image on the intermediate member. Finally, a transfer mechanism is provided for transferring the liquid-depleted image from the intermediate member to a receiver member, and a regeneration mechanism is subsequently employed to regenerate the operational surface of the intermediate member prior to forming a new primary image thereon.

Referring now to the accompanying drawings,FIG. 1a,b,cschematically show formation of a primary ink jet image, which primary image includes a first liquid ink and a second liquid ink, of which first and second inks at least one is a marking coagulable ink jet ink. A marking ink is henceforth an ink that ultimately produces a color (including black) on a receiver member.FIG. 1ais a sketch of a portion of a digitally formed image made of the first ink deposited on the intermediate member by the first source of ink, which image has a gray scale such that individual imaging pixels are shown to contain variable quantities of the first ink deposited on the operational surface, indicated by the numeral1c, of the intermediate member,1d. As is well known, such a variation in the amount of liquid can be produced by an imagewise delivery of multiple ink droplets per pixel. For example, an as-deposited amount labeled3ais formed by a greater number of droplets than an amount labeled2aon an adjacent pixel, while the amount labeled2ais greater than the amount labeled4a. Between the two amounts labeled2athere is a shown a bare pixel containing no ink. To produce a gray scale, an imaging pixel of the primary image may have zero ink deposited, or a pixel may contain a plurality of droplets, e.g., as many as twenty or more droplets of a marking ink per pixel to achieve maximum image density, as is known in the art. As is also well known, ink jet ink droplets having a variable size may be created by an ink jet device, thereby providing an alternate way of creating a gray scale.

FIG. 1billustrates schematically the result of imagewise depositing predetermined amounts of the second ink, from the second ink jet source of ink, on an imagewise deposit of the first ink, where the first ink portions are shown as hatched and the second ink portions are shown as clear. InFIG. 2b, the single primed (′) entities correspond to those ofFIG. 1a, and as indicated in the drawing, amounts of the second ink shown as2band4bare respectively associated with amounts2a′ and4a′ of the first ink, with amount2bsmaller than amount4b. Amount1bof the second ink, located on the previously bare pixel inFIG. 1a, is greater than amount4b, and amount4bis greater than the amount2b. The first and second inks are preferably mutually miscible, and more preferably the first and second inks are made of similar liquids. Generally, the subject invention includes sequential or concurrent depositions of the marking and non-marking inks, i.e., in any pixel of the primary image, one or another of the following occurs: all of the marking ink arrives first; all of the non-marking ink arrives first; the arrivals of the two inks overlap partially in time; or, the time periods of arrival of both marking and non-marking inks overlap substantially completely. In preferred embodiments of inks, total volume is conserved when any amounts of each of the first and second inks are mixed together, i.e., the total volume is the sum of the individual volumes. Moreover, in preferred embodiments of inks both the first ink and the second ink are substantially insoluble in, and substantially nonabsorbable by, the intermediate member1c. However, the invention is not limited to such preferred first and second inks, and in particular, total volume may not be conserved when amounts of the first and second inks are mixed. For purpose of illustration, let it be assumed that the first ink (shown for example as hatched inFIG. 1b) is a marking coagulable ink from which colored coagulates may be formed, and let it also be assumed that the second ink (shown for example as unhatched inFIG. 1b) produces no color. Henceforth, an ink which produces no color, i.e., which is substantially colorless, or which includes no added colorant nor forms a colorant, is referred to as a non-marking ink. Let it be further assumed that volume is conserved when amounts of these first and second inks ofFIG. 1bare mixed. For each pixel in an imaging area on the operational surface, a total amount of liquid per pixel inFIG. 1bcontains a first number of droplets, P, of the first ink, and a second number of droplets, Q, of the second ink, and the total number of droplets in each pixel, N, is given by N =P +Q. Let it be assumed for purpose of illustration that N is the same for every pixel of a primary image. Then, as shown inFIG. 1b, it follows that if an amount3a′ of the marking first ink is the largest predetermined amount of the first ink delivered to any pixel, then in a resulting final image on a receiver, this largest predetermined amount corresponds to a maximum achievable density, Dmax. In association with the amount of marking ink3a′, there is shown no added amount of the non-marking second ink, i.e., Q =0, so that the amount3a′ is equal to N, i.e., P =N. Similarly, there is no marking ink associated with the amount of non-marking second ink labeled1b, so that P =0 and Q =N, and the amount1bcorresponds to a minimum achievable final image density, i.e., Dmin. It is preferred, as indicated in the example illustration ofFIG. 1b, that N represents a substantially constant total number of droplets delivered by both the first and second sources of ink to each of the imaging pixels, and this will be the case when volume is conserved upon mixing, as was assumed for the above discussion. However, in certain embodiments, it may be desirable for N not to be substantially constant for all pixels in a primary image, but alternatively that N has a functional dependence, e.g., a linear dependence, on the number of droplets of marking ink used per pixel. It is also preferred, as illustrated inFIG. 1b, that pixels corresponding to the maximum achievable density in an image contain only the marking coagualable ink and no component of the non-marking ink. However, in certain other embodiments, a constant number, R, of extra droplets of the non-marking ink may be delivered to each pixel. For example, assuming N in certain embodiments to be constant for all pixels, the total number of droplets per pixel, N +R, is therefore also constant, with N including, as described above, respective numbers of droplets P and Q of the marking and non-marking inks, and with Q +R being the total number of non-marking droplets per pixel.

Generally, it will be evident that complementary numbers of marking and non-marking particles are included in each pixel of a primary image, or equivalently, complementary numbers of droplets of marking ink and droplets of non-marking ink are used per pixel. For such embodiments, the term “complementary” means that as a number of droplets of a marking ink delivered per pixel, say W, is made larger, a complementary number of droplets, say X, of a non-marking ink delivered to the same pixel is made correspondingly smaller, and preferably, as described above, the corresponding sum (W +X) is substantially constant for every pixel of the primary image. Alternatively, in other embodiments, the term “complementary” may refer to respective volumes of the marking and non-marking inks deposited in a pixel of a primary image. In these other embodiments, a volume including a number of droplets, Y, of a marking ink becomes mixed in a given pixel with a complementary volume including a number of droplets, Z, of a non-marking ink, such that a resulting total volume per pixel resulting from the mixing of the (Y +Z) droplets is preferably substantially constant for all pixels of the primary image.

FIG. 1cshows the result of an intermixing of the first and second inks, in each imaging pixel, so as to form a primary image on the intermediate member. The single primed (′) entities correspond to those ofFIG. 1a, and the double primed entities (″) correspond to those ofFIG. 1b. The degrees of hatching represent relative amounts of the marking ink included in the pixels, with the heaviest hatching representing the maximum achievable density in a final image on a receiver. Although for simplicity of exposition only two levels of hatching are illustrated inFIG. 1c, it will be henceforth understood in the described embodiments that for high quality imaging there will be many density level differences between Dmin and Dmax, with pixels containing corresponding proportions of marking ink to create these density level differences. In a preferred embodiment, the volumes of liquid in each imaging pixel of the primary image is substantially the same. If, however, in certain embodiments total volume is not conserved when intermixing takes place, it will be evident that the total number of droplets delivered to a pixel will need to vary, depending on the quantity of marking ink delivered to a given pixel. Thus, in order to provide a same total volume of liquid on each pixel after intermixing, the sum of P +Q will not be a constant in such a case, and will vary from pixel to pixel, with the individual predetermined numbers of droplets P and Q properly adjusted imagewise so as to account for any volume change upon intermixing of the two fluids of the marking and non-marking inks. It is a prerequisite of the subject invention that any intermixed liquid on any pixel of the primary image that contains a proportion of a coagulable ink is also coagulable, which proportion includes a first ink and a second ink delivered respectively by the first source of ink and the second source of ink.

FIG. 1dillustrates a preferred embodiment of a primary image corresponding toFIG. 1c, wherein the marking ink is a colloidal dispersion of pigmented particles, and each of the single primed (′), double primed (′) and triple primed (′″) entities refers to a corresponding entity labeled with one less prime inFIG. 1c. The liquid in a given pixel contains a plurality, including zero, of the pigmented particles. Thus, in the liquid1b″, there are no pigmented particles. The liquids4c′,2c′, and3a′″, respectively contain pluralities5a,5b, and5c, of the pigmented particles, plurality5cbeing larger than5b, and5blarger than5a. Any non-marking ink included in the liquids1b″,4c′,2c′, and3a′″ contains substantially no particles, and is preferably colorless.

FIG. 1eillustrates a preferred embodiment of a primary image corresponding toFIG. 1c, i.e., after intermixing of the marking and non-marking inks has occurred, wherein the marking ink is a dispersion, preferably a colloidal dispersion, of pigmented particles in a first carrier liquid and the non-marking ink is a dispersion, preferably a colloidal dispersion, of unpigmented particles in a second carrier liquid. The marking and non-marking dispersions are preferably similar to one another. Thus, except for any added pigmentation or other added coloration, the marking and non-marking particles are preferably made from similar materials. Also, it is preferred that any colloidal stabilizations of the marking and non-marking dispersions are similar and preferably identical. Further, it is preferred that the first and second carrier liquids are similar and preferably identical. Each of the single primed (′), double primed (′), triple primed (′″), and quadruple primed (″″) entities refers to a corresponding entity labeled with one less prime inFIG. 1d. The liquid in a given pixel contains a plurality, including zero, of the pigmented particles. Thus, in the liquid1b′″, there are no pigmented particles. The liquids4c″,2c″, and3a″″, respectively contain pluralities5a′,5b′, and5c′, of the pigmented particles, plurality5c′ being larger than5b′, and5b′ larger than5a′. Corresponding complementary pluralities of unpigmented particles from the non-marking ink are included in the liquids3a″″,2c″,4c″, and1b′, which pluralities of unpigmented particles are respectively labeled5d,5e,5f, and5g, where plurality5g>plurality5f>plurality5e>plurality5d. Moreover, in a most preferred embodiment, the total number of particles of dispersion in each pixel, including the pigmented and the unpigmented particles, is substantially constant, as indicated schematically inFIG. 1e. Also, in a most preferred embodiment, each of the amounts of liquid,1b′″,4c′,2c′, and3a″″ has substantially the same volume. Generally, a co-coagulate is formed from the pigmented particles and the unpigmented particles included in any intermixed inks contained in a given imaging pixel of a primary image on the operational surface. Preferably, such a co-coagulate, formed adjacent the operational surface of the intermediate member1d″″, is a uniform mixture of the pigmented and unpigmented particles contained in the given pixel. However, in certain embodiments, it may be preferred that a stratified co-coagulate material or a nonuniformly mixed co-coagulate material be formed adjacent the operational surface of the intermediate member1d″″, and this may be made to happen by for example respectively providing different electrophoretic mobilities for the pigmented and unpigmented particles. Moreover, in certain other embodiments, it can be advantageous to deliver from the ink jet device to each pixel of the primary image an extra number of droplets of the non-marking unpigmented particulate ink, for subsequent improvements of fusing and image gloss properties as described more fully below.

In another embodiment (not illustrated) an electrocoagulable marking ink is utilized in a primary image (instead of the colloidal dispersion of marking particles shown inFIG. 1d) and the primary image contains imagewise-varying complementary quantities of a marking electrocoagulable ink and a non-marking ink, the non-marking ink containing for example no coagulable material, by analogy withFIG. 1d. In a similar fashion to the previous embodiments, the total volume of liquid is made substantially the same in each imaging pixel of the primary image, which total volume includes both any marking electrocoagulable ink and any preferably miscible intermixed non-marking ink. This is accomplished by delivering from the first and second sources of ink an appropriate number of droplets of each of the first and second inks, so as to produce a constant volume of liquid per imaging pixel, which volume per pixel contains any required proportion of the marking electrocoagulable ink.

In another embodiment (not illustrated) a marking electrocoagulable coagulable ink and a non-marking electrocoagulable ink are used to jointly form a primary image, the non-marking coagulable ink containing a coagulable material by analogy withFIG. 1d. Thus, the marking electrocoagulable ink provides a colored electrocoagulate component deposited on the operational surface of the intermediate member, and the non-marking electrocoagulable ink provides a complementary amount of co-deposited, substantially uncolored, electrocoagulate. Preferably, in each imaging pixel an amount of colored electrocoagulate and a complementary amount substantially uncolored electrocoagulate together form an intimately mixed co-electrocoagulate on the operational surface. In this other most preferred embodiment, in similar fashion to the embodiments ofFIG. 1, the total volume of liquid is made substantially the same in each imaging pixel of the primary image, which total volume per pixel includes both any marking electro-coagulable ink and any intermixed preferably miscible non-marking electro-coagulable ink. This is accomplished by delivering from the first and second sources of ink an appropriate number of droplets of each of the first and second electrocoagulable inks per pixel, so as to produce in a constant total volume per pixel of the primary image a required predetermined proportion of the marking electrocoagulable coagulable ink. Generally, according to the invention, a coelectrocoagulate is formed adjacent the operational surface in any given imaging pixel. Preferably, such a co-electrocoagulate is a uniform mixture of the marking and non-marking electrocoagulates contained in the given pixel. However, in certain embodiments, a stratified co-electrocoagulate material or a nonuniformly mixed co-electrocoagulate material may be usefully formed adjacent the operational surface of the intermediate member.

FIG. 2shows a preferred embodiment of a ink jet imaging apparatus for creating gray scale images according to the invention. The imaging apparatus, designated generally by the numeral20, includes: an ink jet device21for depositing ink droplets26and27to form a primary ink jet image on the operational surface of an intermediate member roller28mounted on shaft28arotating in a direction of an arrow labeled C, a Coagulate Formation Process Zone22for forming coagulates in the primary image, an Excess Liquid Removal Process Zone23for forming a liquid-depleted material image, a Transfer Process Zone24for transferring the liquid-depleted material image from roller28to a receiver member, and a Regeneration Process Zone25for preparing the intermediate member for a fresh primary image. A receiver sheet29a, moving in a direction of arrow A, is shown approaching Transfer Process Zone24. A receiver sheet29bis shown leaving the Transfer Process Zone in a direction of arrow B. Receiver29bcarries a liquid-depleted material image derived from a primary ink jet image previously formed by ink jet device21on intermediate member28, which liquid-depleted material image is transferred in Process Zone24from intermediate member28to a receiver, e.g., receiver29b. Intermediate member roller28may be rotated by a motor drive applied to shaft28a, or alternatively by a frictional drive produced by a frictional engagement with another rotating member (not shown).

In an alternate embodiment, intermediate member28may be in the form of an endless web onto which is deposited a primary ink jet image by ink jet device21, which web is driven or transported past or through the various Process Zones22,23,24and25. The liquid-depleted material image is transferred from the web to a receiver member in Transfer Process Zone14.

Coagulate Formation Process Zone22, Excess Liquid Removal Process Zone23, Transfer Process Zone24and Regeneration Process Zone25may include the use of rotatable elements. The rotatable elements of the subject invention are shown as both rollers and webs in the examples of this description but may also include drums, wheels, rings, cylinders, belts, loops, segmented platens, platen-like surfaces, and receiver members, which receiver members include receiver members moving through nips or adhered to drums or transport belts.

The ink jet device21may include any known apparatus for jetting droplets of a liquid ink in a controlled imagewise fashion on to the operational surface of intermediate member (IM)28, with digital electronic signals controlling in known manner a variable number of droplets delivered to each imaging pixel on the operational surface. A primary image made on the operational surface by the liquid ink droplets26,27may be a continuous tone image, or it may be a half-tone image including gray-level half-tones, frequency modulated half-tones, area-modulated half-tones and binary halftones as are well known in the art. The conventional and well-known terms “continuous tone” and “half-tone” refer here not only to any place-to-place variations of the quantity of either of the marking or non-marking inks within the image on the operational surface, but also to any corresponding color or density that may subsequently be produced or induced in imagewise fashion by these same variations of the quantity of either ink. An imaging pixel is defined in terms of the image resolution, such that if the resolution were, say, 400 dots per inch (dpi), then a square pixel for example would occupy an area on the operational surface having dimensions of 63.5 μm×63.5 μm. Thus, an imaging pixel is a smallest resolved imaging area in a primary image. The operational surface of IM28includes any portion of the surface of the intermediate member upon which a primary ink jet image may be formed by ink jet device21.

The ink jet device21includes a continuous ink jet printer and a drop-on-demand ink jet printer including a thermal type of ink jet printer, a bubble-jet type of ink jet printer, and a piezoelectric type of ink jet printer. A drop-on-demand ink jet printer is preferred. The ink jet device21includes a first source (not illustrated) of a first ink and a second source (not illustrated) of a second ink, at least one of which first ink and second ink is a coagulable ink. Furthermore, one of the first ink and the second ink is a preferably marking ink and the other is preferably a non-marking ink. On any pixel of the primary image, preselected numbers of droplets of the first and second inks are deposited, e.g., sequentially or concurrently, from the first and second sources. Thus, for a sequential deposition of the two inks on a given pixel of the primary image on the operational surface, all of a preselected number of droplets of a marking ink, e.g., droplets26may arrive before any of a complementary preselected number of droplets27of a non-marking ink, or vice versa. Altematively, the times of arrival of the first and second inks on a given pixel may partially overlap, or, the first and second inks may arrive on a given pixel during substantially the same period of time. Moreover, the ink jet device21may include both the first source of ink and the second source of ink located in a same unit of apparatus, or, the first and second sources may be located in two distinct units of apparatus, e.g., arranged tandemly.

Each of the first and second sources of ink in ink jet device21is typically included in a writehead (not shown) which includes a plurality of electronically controlled individually addressable jets, which plurality may be disposed in a full-width array, i.e., along the operational width of roller28in a direction parallel to the axis of shaft28a. Alternatively, as is well known, the writehead may include a relatively smaller array of jets and the writehead is translated back and forth in directions parallel to the axis of shaft28aas the operational surface of roller28rotates. The inks used by the ink jet device21are provided from respective reservoirs (not shown) and it is preferred that the composition of the ink droplets26,27be substantially the same as the composition of the respective ink in the respective reservoir. A writehead preferably produces a negligible segregation of components of the ink, i.e., certain components are not intentionally preferentially retained by the writehead and certain other components are not intentionally preferentially jetted in the droplets26,27. More specifically, it is preferred that no applied fields are used in the writehead, e.g., such as when using a colloidal particulate ink so as to respectively increase the number of particles per unit volume in the respective jetted droplets26or27to a value higher than the respective number of particles per unit volume within the respective reservoir.

Inks for use in ink jet device21include marking and non-marking nonaqueous inks. Preferred marking and non-marking inks are dispersions, preferably colloidal dispersions, of particles in an insulating carrier liquid. The particles of a nonaqueous marking ink include any suitable colorant. Preferably, the particles of a marking ink are pigmented particles, and more preferably, solid pigmented particles; and preferably the particles of a non-marking ink are unpigmented particles, and more preferably, solid unpigmented particles. However, particles which are not colored may be used in a marking ink, including solid or liquid particles containing precursor chemicals that may be subsequently transformed, by any suitable chemical or physical process, into a material image having any useful property, composition or color, e.g., transformed when an ink-jet-ink-derived image is located either on intermediate member28or on a receiver, e.g., receiver29b. A volume percentage of dispersed particulates in a nonaqueous colloidal ink useful in the invention may have any suitable value, typically between about 3% and 50%. Formulations similar to, or identical with, commercially available (nonaqueous) electrophotographic liquid developers may be used as inks for practicing the invention. Nonaqueous inks useful for the invention may be sterically stabilized dispersions, or may include both steric and electrostatic stabilization. Preferably, the dispersed particles carry an electrostatic charge, and polymeric counterions in the surrounding carrier fluid provide overall electrical neutrality. The particle sizes or particle size distributions of the particles used are similar to the particle sizes or particle size distributions of the particles used in commercial electrophotographic liquid developers. Particulate marking and non-marking nonaqueous ink dispersions useful for practice of the invention may be made by any known method, including grinding methods, precipitation methods, spray drying methods, limited coalescence methods, and so forth. Particulate marking and non-marking ink dispersions useful for practice of the invention may be formulated in any known way, such as by including dispersal agents, stabilizing agents, drying agents, glossing agents, and so forth. Pigmented particles used in marking ink dispersions of the invention may include one or more pigments, plus suitable binders for the pigments. Unpigmented particles used in non-marking ink dispersions are made primarily of binder material, which binder material is preferably similar to or identical with the binder used for marking particles, and which binder is preferably substantially colorless. Thus, in a final image transferred to a receiver in Transfer Process Zone24, which final image contains both pigmented marking particles and unpigmented non-marking particles, it is preferable that an optical density of such a final image is proportional to the volume fraction of pigmented marking particles in the final image. A binder for either pigmented or unpigmented particles is typically made of one or more synthetic polymeric materials, which polymeric materials are selected to have good fusing properties for fusing a particulate image to a receiver for creating an output print, as described more fully below. Pigments used for marking ink dispersions are preferably commercially available pigments and may be crystalline or amorphous. Typically, a pigment is comminuted to very small sizes, e.g., sub-nanometer sizes, and dispersed substantially uniformly in a binder by known methods. It is preferred that pigments and binders used to make ink dispersions for the invention are substantially insoluble in the carrier liquids used for the dispersions. An alternative, non-marking, nonaqueous ink, for use in ink jet ink device21, contains no unpigmented particles and consists primarily of a nonaqueous liquid, which liquid is preferably similar or identical to a carrier liquid used to formulate a pigmented particulate marking ink dispersion or an unpigmented particulate non-marking ink dispersion. Such a non-marking ink, when admixing with any marking ink dispersion to form a primary image on the operational surface of intermediate member28, acts simply as a completely miscible diluent, and produces substantially no contribution to an optical density of a final image on a receiver. Particularly useful are mixtures of alkanes marketed by Exxon under the tradename Isopar, and various Isopars are available. Preferred Isopars are those having a flash point of 140° F. and above, such as Isopar L and Isopar M. However, other, lower molecular weight Isopars, such as Isopar G, may be used. It is also preferred to employ a concentrated precursor dispersion for both a marking ink dispersion and for a non-marking ink dispersion as used in ink jet device21. A precursor dispersion may be manufactured as a concentrate having a high volume percentage of particulates, which concentrate is diluted with a respective carrier fluid to form a resulting respective ink prior to introducing the respective ink into the respective reservoir of the ink jet device21.

Alternative inks for use in ink jet device21include marking and non-marking electrocoagulable inks, which are preferably aqueous-based inks. Any suitable electrocoagulable ink may be used in the practice of the subject invention. For example, an electrocoagulable ink for use in the invention includes any electrolytic ally coagulable colloid, which colloid may include a colorant or a finely divided pigment for use in a marking ink. Colloidal electrocoagulable inks having water as the dispersion medium are described, for example, in the Castegnier et al. patent (U.S. Pat. No. 5,928,417). An embodiment of an aqueous-based non-marking ink, for use in the invention with an aqueous-based electrocoagulable marking ink, may include no electrocoagulable component, i.e., which non-marking ink acts simply as a diluent when used to form a primary image with the aqueous-based electrocoagulable marking ink. Nevertheless, any such diluted portion of a primary image is required to be electrocoagulable. Preferably, an optical density of any electrocoagulate produced by electrocoagulation of any portion of such a diluted primary image is proportional to the volume fraction of the marking component in such an electrocoagulate.

A preferred embodiment of a non-marking ink for use with an aqueous-based electrocoagulable marking ink is an aqueous-based electrocoagulable ink, which electrocoagulable ink includes an electrocoagulable colloid that does not include any added colorant or pigment, which electrocoagulable colloid is preferably colorless before and after electrocoagulation. Such an electrocoagulable non-marking ink is preferably an aqueous-based colloidal dispersion very similar in nature to the preferred aqueous-based dispersion of the marking electrocoagulable ink, i.e., which electrocoagulable non-marking dispersion preferably includes similar materials, such as for example similar polymeric materials, similar stabilizers, similar dispersants, and so forth, such as used for formulating the marking electrocoagulable ink. Any admixture of such a preferred non-marking electrocoagulable ink with an electrocoagulable marking ink results in an electrocoagulable ink which, upon electrocoagulation, forms co-electrocoagulates from the combined marking and non-marking electrocoagulable components. Preferably, an optical density of any co-electrocoagulate produced by electrocoagulation of the combined marking and non-marking components is proportional to the volume fraction of the marking component in such a co-electrocoagulate.

In the Excess Liquid Removal Process Zone13, excess liquid is removed from the coagulates formed in the Coagulate Formation Process Zone12. In general, a portion, preferably a major portion, of the liquid is removed from the coagulates so as to form a liquid-depleted image, which liquid-depleted image can in certain cases retain a significant amount of residual liquid. In certain circumstances substantially all of the liquid may be removed to form the liquid-depleted image. Excess Liquid Removal Process Zone23includes an excess liquid removal device, which is any of the following known devices: a squeegee (roller or blade), an external blotter device, an evaporation device, a vacuum device, a skiving device, and an air knife device. These excess liquid removal devices are described more fully in related copending U.S. patent application Ser. No. 09/973,239, now U.S. Pat. No. 6,719,423 entitled Ink Jet Process Including Removal Of Excess Liquid From An Intermediate Member by Arun Chowdry, et al., and related copending U.S. patent application Ser. No. 09/973,244 now U.S. Pat. No. 6,682,189, entitled Ink Jet Imaging Via Coagulation On An Intermediate Member by John W. May, et al. Any other suitable excess liquid removal device or process may be used.

Transfer Process Zone24for transferring an ink-jet-ink-derived material image from intermediate member (IM)28to a receiver member includes any known transfer device, e.g., an electrostatic transfer device, a thermal transfer device, and a pressure transfer device, such as described fully in related copending U.S. patent application Ser. No. 09/973,239, U.S. Pat. No. 6,719,423 entitled Ink Jet Process Including Removal Of Excess Liquid From An Intermediate Member by Arun Chowdry, et al., and related copending U.S. patent application Ser. No. 09/973,244, now U.S. Pat. No. 6,682,189 entitled Ink Jet Imaging Via Coagulation On An Intermediate Member by John W. May, et al. As is well known, both an electrostatic transfer device and a thermal transfer device can be used with an externally applied pressure. An electrostatic transfer device for use in Transfer Process Zone24typically includes a backup roller (not shown), which backup roller is electrically biased by a power supply (not shown). The backup roller co-rotates in a pressure nip relationship with IM28, and a receiver member such as sheet29ais translated through the nip formed between the backup roller and IM28. An ink-jet-ink-derived material image carrying an electrostatic net charge is transferable by an electrostatic transfer device from IM28to the receiver, i.e., an electric field is provided between IM28and the backup roller to urge transfer of the ink-jet-ink-derived material image. For use to augment electrostatic transfer when an ink-jet-ink-derived material image on IM28has a low electrostatic charge or is uncharged, a charging device (not shown) such as for example a corona charger or a roller charger or any other suitable charging device may be located between Excess Liquid Removal Process Zone23and Transfer Process Zone24, which charging device may be used to suitably charge the ink-jet-ink-derived liquid-depleted material image prior to subsequent electrostatic transfer of the material image in Transfer Process Zone24. Alternatively, a thermal transfer device may be used to transfer the ink-jet-ink-derived material image, which thermal transfer device can include a heated backup roller (not shown), which backup roller is heated by an external heat source such as a source of radiant heat or by a heated roller (not shown) contacting the backup roller (not shown). Alternatively, the backup roller for thermal transfer can be heated by an internal source of heat. The backup roller for thermal transfer co-rotates in a pressure nip relationship with IM28, and a receiver member such as sheet29ais translated through the nip formed between the heated backup roller and IM28. In certain embodiments, IM28may be similarly heated, either from an internal or external source of heat. As an alternative, a thermal Transfer Process Zone24may include a transfusing device, wherein an ink-jet-ink-derived material image is thermally transferred to and simultaneously fused to a receiver. As yet another alternative, a pressure transfer device may be used in Transfer Process Zone24to transfer an ink-jet-ink-derived material image, which pressure transfer device includes a backup pressure roller (not shown) which pressure roller co-rotates in a pressure nip relationship with IM28, and a receiver member such as sheet19ais translated through the nip formed between the pressure backup roller and IM28. In such a pressure transfer device, an adhesion of the ink-jet-ink-derived material image is preferably much greater on the surface of the receiver than on the operational surface of IM16, and preferably the adhesion to the operational surface of IM16is negligible.

As an alternative to the use of receiver sheets such as sheets19a,19bin the Transfer Process Zone24of any of the above-described embodiments, a receiver in the form of a continuous web (not illustrated) may be used in Transfer Process Zone24, which web passes through a pressure nip formed between roller28and a transfer backup roller (not illustrated). A receiver in the form of a continuous web may be made of paper or any other suitable material.

In other alternative embodiments, a transport web (not illustrated) to which receiver sheets are adhered may be used in Transfer Process Zone24to transport receiver sheets through a pressure nip formed between roller28and a transfer backup roller (not illustrated).

A receiver, for example receiver19b, which has passed through Transfer Process Zone24may be moved in the direction of arrow B to a fusing station (not shown in FIG.2).

Apparatus20may be included as a color module in a full color ink jet imaging machine. A receiver such as receiver19b, which has received an ink-jet-ink-derived material image of a particular color from IM28, may be transported through another module entirely similar to apparatus20, wherein an ink-jet-ink-derived material image of a different color may be transferred from a similar intermediate member in a similar Transfer Process Zone, which different color image is transferred atop and in registration with the ink-jet-ink-derived material image transferred to the receiver in apparatus20. In a set of such similar modules arranged in tandem, ink-jet-ink-derived material images forming a complete color set may be successively transferred in registry one atop the other, thereby creating a full color material image on a receiver. The resulting full color material image may then be transported to a fusing station wherein the material image is fused to the receiver. In one embodiment of such a full color ink jet imaging machine, the receiver member is adhered to a transport web for carrying the receiver through the respective color modules and thence to the fusing station. In another embodiment (not illustrated) of such a full color ink jet imaging machine, the receiver member is adhered to a rotatable member, such as for example a large drum, which receiver member is rotated past each of the respective modules wherein in each module a different color liquid-depleted ink-jet-ink-derived material image is transferred in register atop any previously transferred liquid-depleted ink-jet-ink-derived material image(s). An alternative embodiment (not illustrated) of a full color ink jet imaging machine includes a plurality of modules, each of which respectively includes an ink jet ink device similar to device21, a Coagulate Formation Process Zone similar to zone22, an Excess Liquid Removal Process Zone similar to zone23, and a Regeneration Process Zone similar to zone25, wherein a different color liquid-depleted ink-jet-ink-derived material image is transferred in a respective transfer process zone to a common rotatable member, such as for example a large drum. In this alternative embodiment of a full color ink jet imaging machine, each different color liquid-depleted ink-jet-ink-derived material image is respectively transferred to the common rotatable member in register atop any previously transferred liquid-depleted ink-jet-ink-derived material image(s) thereon so as to build up a fill color image on the common rotatable member, whereupon the full color image is subsequently transferred in a full color image transfer station from the common rotatable member to a receiver member.

The operational surface of intermediate member28, after leaving the Transfer Process Zone24, is rotated to a Regeneration Process Zone25where the operational surface is prepared for a new primary image to be subsequently formed by ink jet device21. In one embodiment, the Regeneration Process Zone is a cleaning process zone wherein residual material of the liquid-depleted material image is substantially removed using known devices or methods, including use of a cleaning blade (not shown) or a squeegee (not shown) to scrape the operational surface substantially clean. Alternatively, a cleaning roller (not shown) or web (not shown) is provided to which residual material of the liquid-depleted material image adheres, thereby producing a substantially clean operational surface in Regeneration Process Zone25. As another alternative, an external vacuum device (not shown) may be used in Regeneration Process Zone25to suck up and possibly recycle any residual liquid from the operational surface of member28. Any other known suitable cleaning mechanisms, including brushes, wipers, solvent applicators, and so forth (not shown), may be used to form a regenerated surface.

FIG. 3a,billustrates the effect of using a corona charging device as a preferred electric field mechanism for forming coagulates in a primary image of a nonaqueous dispersion of charged particles. In schematic side view inFIG. 3a, atwo-fluid primary image is shown corresponding toFIG. 1d, and this primary image includes several imaging pixels containing drops formed by an intermixing of droplets of a nonaqueous marking ink and droplets of a nonaqueous non-marking ink co-deposited on an operational surface9bof an intermediate member, e.g., a roller or a web, by ink jet device21, which ink jet device as described above includes a first source of a first ink and a second source of a second ink. All of the drops of the primary image ofFIG. 3a are preferably of substantially equal volume, containing complementary amounts of the first and second inks, as previously described above. The intermediate member (not separately identified) includes a layered structure9ahaving one or more layers and a grounded electrode9cshown located below the layered structure9a. The marking ink which is used to form the primary image is a dispersion of charged pigmented particles6edispersed in a carrier liquid6g, i.e., the drop labeled6crepresents Dmax. Drop6c(strong hatching) contains no non-marking ink, and therefore has the maximum number of particles per unit volume in an imaging pixel of the primary image. The non-marking ink contains no added particles and is miscible with the carrier fluid6g. Drop6a(no hatching) representing Dmin, is made entirely of the non-marking ink,6d, and therefore contains no added particles. Each drop labeled6b(medium hatching) includes a mixture of the marking and non-marking inks, so that the liquid6his a mixture of the liquids6dand6g. The charged particles6emay have positive or negative polarity (here shown as positive) and their charges are balanced by oppositely charged counterions or micelles6fin the liquid of each drop mixture. Layered structure9ais preferred to be electrically insulating and is adhered to electrode9c, which electrode may be the surface of a metallic drum, e.g., made of aluminum or other suitable metal, on which layer9ais formed or coated. As an alternative, electrode9ccan be a thin conductive layer, e.g., made of nickel or other suitable metal, which electrode is coated on or adhered to a support (not shown) made of any suitable material, e.g., a polymeric material. The support may be included in a web, or may surround a metallic drum so as to form an intermediate member roller, e.g., intermediate roller28. Alternatively, layered structure9amay be semiconductive.FIG. 3b, in which primed (′) entities correspond to unprimed entities inFIG. 3a, illustrates the result of corona charging of the primary image ofFIG. 3aby a corona charging device (not shown). The polarity of the corona ions deposited on the primary image is the same as that of particles6e(here positive) so that for example positive corona ions8aare shown at the outer surface of drop6c′ in non-injecting contact with the carrier liquid6g′. Other non-injecting corona ions8aare shown deposited by the corona charging device on the surfaces of drops6a′ and6b′. Induced counter charges8bon electrode9c′ provide electric fields in layered structure9a′ and within the drops of the primary image. As a result of the fields within the drops, particles6eare shown as having migrated towards the operational surface9b′ where they preferably form compact layers, e.g., layers7a,7bof coagulates held down by the electrostatic attraction from the corresponding countercharges8bas well as by dispersion or van der Waals type attractive forces. The counterions or micelles6fare shown migrated to the outer surfaces of drops6b′,6c′, thereby partially compensating or neutralizing the corona charges8a. The corona charging device includes any known corona charging device, e.g., an AC or a DC charger, and may further include one or both of a plurality of corona wires and a grid. As previously described above, after formation of coagulate layers such as7a,7bby the charging action of the corona charging device, any excess liquid is removed from the image on the intermediate member by any suitable means in the Excess Liquid Removal Process Zone23ofFIG. 2, and the liquid-depleted layers7a,7btransferred by any suitable means from the intermediate member to a receiver in the Transfer Process Zone24.

In the above preferred electric field mechanism using a corona charging device for causing coagulation, it is preferable to use a non-marking ink which is a dispersion of unpigmented particles, rather than a non-marking ink containing no particles as described in reference toFIG. 3a,b. Thus, every pixel of a two-fluid primary image contains a mixture of an amount of a dispersion of marking pigmented particles dispersed in a first carrier liquid, and a complementary amount of a preferred dispersion of non-marking unpigmented particles dispersed in a second carrier liquid, e.g., as described above with reference toFIG. 1e, such that both dispersions are co-deposited on the operational surface of the intermediate member as the first and second inks by the ink jet device21. Thus, by analogy and with further reference toFIG. 3a, each pixel of the primary image contains a complementary number of non-marking unpigmented particles, in addition to the marking pigmented particles (not separately illustrated). The non-marking unpigmented particles of the preferred non-marking ink are preferably similarly charged and have the same polarity as the marking pigmented particles, and the corresponding counterions associated with the non-marking unpigmented particles are preferably similar in nature to the counterions associated with the marking pigmented particles, and more preferably, identical in nature to the counterions associated with the marking pigmented particles. Preferably, the first and second carrier liquids are similar to one another, and more preferably, the first and second carrier liquids are identical. In a primary image using this preferred non-marking ink, a Dmax pixel, e.g., a pixel corresponding to drop6cinFIG. 3a, contains no amount of the dispersion of non-marking unpigmented particles. Similarly, a Dmin pixel, e.g., corresponding to drop6ainFIG. 3a, contains no amount of the dispersion of marking pigmented particles, and an intermediate density pixel, corresponding to drops6b, contains an admixture of the two dispersions. In each of the pixels included in the primary image, the volume of liquid per pixel is preferably substantially the same. By analogy and with reference toFIG. 3b, the charging action of the corona charging device produces a Dmax pigmented-particle coagulate, entirely corresponding to layer7band containing no added unpigmented particles. On the other hand, a preferably colorless unpigmented-particle coagulate layer will be formed by the corona charging device in a Dmin pixel (no such corresponding layer is formed in drop6a′). A mixed particle coagulate layer, containing both pigmented and unpigmented particles, will be formed in an intermediate density pixel (i.e., corresponding to drops6b′ in which only pigmented particles form the coagulate layer7a). It is preferred that any thickness of any coagulate layer, formed on the operational surface of the intermediate member and including marking particles, non-marking particles or both marking and non-marking particles, is substantially the same. As previously described above, after formation of such coagulate layers by the charging action of the corona charging device, any excess liquid is removed from the image on the intermediate member by any suitable means in the Excess Liquid Removal Process Zone23ofFIG. 2, and the liquid-depleted layers transferred by any suitable means from the intermediate member to a receiver in the Transfer Process Zone24. It will be especially noted that, for the preferred situation wherein any thickness of a coagulate layer containing any proportion of pigmented and unpigmented particles is substantially the same, the resulting efficiency of transfer to a receiver will generally be much more uniform than for the varyingly thick coagulate layers such as layers7a,7bformed as inFIG. 3b. Moreover, it will be evident that after transfer to the receiver of any ink-jet-ink-derived material image formed by utilizing this preferred non-marking ink dispersion, the resulting unfused image quality will be superior as compared to utilizing a non-marking ink containing no particles. The improved image quality results from the more uniform transfer of the resulting liquid-depleted image, including a more efficient transfer of the material in the lower density pixels. Following any subsequent fusing of the resulting ink-jet-ink-derived material image to the receiver, the resulting image quality will be superior as compared to that obtained by using a non-marking ink containing no particles, i.e., the gloss will be much more uniform. Also, a perceived image mottle, such as caused by a nonuniform thickness of the ink-jet-ink-derived material image produced by using a non-marking ink containing no particles, will be much reduced. It should be noted that the physical properties of the non-marking particles of the preferred non-marking ink can be advantageously tailored, e.g., for improved fusing and improved gloss of an ink-jet-ink-derived material image on a receiver. Moreover, in conjunction with use of a corona charging device in the Coagulate Formation Process Zone22, it can be advantageous to deliver from the ink jet device21to each pixel of a primary image an extra number of droplets of the non-marking unpigmented particulate ink, for further improvements of fusing and image gloss properties after subsequent transfer of the corresponding liquid-depleted image to the receiver.

FIGS. 4a,b,cillustrates schematically the effect of using an external non-contacting electrode device as another embodiment of an electric field mechanism for forming coagulates in a primary image of a nonaqueous dispersion of charged particles. In schematic side view inFIG. 4a, atwo-fluid primary image is shown corresponding toFIGS. 1dand3a. The primary image similarly includes imaging pixels containing drops lob formed by an intermixing of droplets of a nonaqueous marking pigmented ink dispersion and droplets of a nonaqueous non-marking ink, both inks similar to those described with reference toFIG. 3aand co-deposited on an operational surface11bof an intermediate member, e.g., a roller or a web, by ink jet device21. The intermediate member (not separately identified) similarly includes a similar layered structure11a, and a similar grounded electrode11c. All of the drops10a,b,cof the primary image ofFIG. 4aare preferably of substantially equal volume, containing complementary amounts of the two inks, as previously described above, with drop10gsimilar to10acontaining only non-marking ink (no hatching), drop10bcontaining a mixture of marking ink and non-marking ink (medium hatching), and drop10ccontaining only marking ink (strong hatching). Each drop such as10bincludes charged particles10ewhich particles may have positive or negative polarity (here shown as positive) and their charges are balanced by oppositely charged counterions or micelles10fin the mixed nonaqueous carrier liquid10d, which counterions or micelles originated in the marking ink. As indicated by arrow D, the primary image ofFIG. 4ais moved beneath a biased non-contacting electrode13connected to a variable voltage supply12, which electrode is in close proximity to drops10a′,b′,c′. InFIG. 4b, single primed (′) elements correspond to the unprimed elements ofFIG. 4a. The electrode13is biased to the same polarity as that of particles10e(here positive). Thus, a positive polarity on electrode13produces an electric field between electrode13and electrode11c′ so as to cause a polarization of drops10b′,c′ which polarization is produced by migration of the positive marking particles to the operational surface11b′ so as to form respective layers14a,bof coagulated particles, and by corresponding migration of the respective counterions (here negative) to give surface charges15a,b. The electrode13may be covered with a protective layer (not shown), which protective layer has a surface facing the primary image yet not in contact with any portion of the primary image. The layers14a,binclude pigmented particles all of which are in direct contact with one another or with surface11b′.FIG. 4cshows the situation after moving the image on the intermediate member away from the influence of electrode13, as indicated by arrow E. InFIG. 4c, a concentrated two-fluid primary image is shown in which the double primed (″) elements correspond to the single primed elements ofFIG. 4b. The surface charges14a,bofFIG. 4bhave been attracted downwards towards the opposite charges in the coagulate layers, so as to form layers in which the charged particles14a′,b′ are compensated or neutralized by the corresponding countercharges15a′,b′. By virtue of dispersion or van der Waals type attractive forces, particles14a′,b′ are adhered to operational surface11b″. To enhance the strength of the dispersion or van der Waals type attractive forces between ink particles and the intermediate member11a′, the intermediate member preferably has a high dielectric constant. For example, a polyurethane having a dielectric constant of about6is particularly useful for inclusion in the intermediate member, as compared with many common polymers having a dielectric constant close to 3. Fluoropolymers are also useful in this regard. Suitable particulate fillers may be provided in the intermediate member11a″ to increase the dielectric constant. Owing to the electroneutrality of all the drops10a″,b″,c″ any excess liquid located above the particles14a′,b′ is readily removed by any suitable means, e.g., in Excess Liquid Removal Process Zone23, as described earlier above.

In the above preferred electric field device including a non-contacting electrode device for causing coagulation, it is preferable to use a non-marking ink which is a dispersion of unpigmented particles, rather than a non-marking ink containing no particles as described in reference toFIGS. 4a,b,c. Thus, every pixel of a two-fluid primary image contains a mixture of an amount of a dispersion of marking pigmented particles dispersed in a first carrier liquid, and a complementary amount of a preferred dispersion of non-marking unpigmented particles dispersed in a second carrier liquid, e.g., as described above with reference toFIG. 1e, such that both dispersions are co-deposited on the operational surface of the intermediate member as the first and second inks by the ink jet device21. Thus, by analogy and with further reference toFIG. 4a, each pixel of the primary image contains a complementary number of non-marking unpigmented particles, in addition to the marking pigmented particles (not separately illustrated). The non-marking unpigmented particles of the preferred non-marking ink are preferably similarly charged and have the same polarity as the marking pigmented particles, and the corresponding counterions associated with the non-marking unpigmented particles are preferably similar in nature to the counterions associated with the marking pigmented particles, and more preferably, identical in nature to the counterions associated with the marking pigmented particles. Preferably, the first and second carrier liquids are similar to one another, and more preferably, the first and second carrier liquids are identical. In a primary image using this preferred non-marking ink, a Dmax pixel, e.g., a pixel corresponding to drop11cinFIG. 4a, contains no amount of the dispersion of non-marking unpigmented particles. Similarly, a Dmin pixel, e.g., corresponding to drop11ainFIG. 4a, contains no amount of the dispersion of marking pigmented particles, and an intermediate density pixel, corresponding to drops10b, contains an admixture of the two dispersions. In each of the pixels included in the primary image, the volume of liquid per pixel is preferably substantially the same. By analogy and with reference toFIG. 4b, the electric field action of the non-contacting electrode device produces a Dmax pigmented-particle coagulate, entirely corresponding to layer14band containing no added unpigmented particles. On the other hand, a preferably colorless unpigmented-particle coagulate layer will be formed by the non-contacting electrode device in a Dmin pixel (no such corresponding layer is formed in drop10a′). A mixed particle coagulate layer, containing both pigmented and unpigmented particles, will be formed in an intermediate density pixel (i.e., corresponding to drops10b′ in which only pigmented particles form the coagulate layer14a). In a two-fluid concentrated image on the operational surface of the intermediate member, it is preferred that any thickness of any coagulate layer, which coagulate layer includes marking particles, non-marking particles or both marking and non-marking particles, is substantially the same. As previously described above, after formation of such coagulate layers by the electric field action of the non-contacting electrode device, any excess liquid is removed from the image on the intermediate member by any suitable means, e.g., in the Excess Liquid Removal Process Zone23ofFIG. 2, and the liquid-depleted layers transferred by any suitable means from the intermediate member to a receiver in the Transfer Process Zone24. It will be especially noted that, for the preferred situation wherein any thickness of a coagulate layer containing any proportion of pigmented and unpigmented particles is substantially the same, the resulting efficiency of transfer to a receiver will generally be much more uniform than for the varyingly thick coagulate layers such as layers14a,14bformed as inFIG. 4b. Moreover, it will be evident that after transfer to the receiver of any ink-jet-ink-derived material image formed by utilizing this preferred non-marking ink dispersion, the resulting unfused image quality will be superior as compared to utilizing a non-marking ink containing no particles. The improved image quality results from the more uniform transfer of the resulting liquid-depleted image, including a more efficient transfer of the material in the lower density pixels. Following any subsequent fusing of the resulting ink-jet-ink-derived material image to the receiver, the resulting image quality will be superior as compared to that obtained by using a non-marking ink containing no particles, i.e., the gloss will be much more uniform. Also, a perceived image mottle, such as caused by a nonuniform thickness of the ink-jet-ink-derived material image produced by using the previous embodiment, will be much reduced. It should be noted that the physical properties of the non-marking particles of the preferred non-marking ink can be advantageously tailored, e.g., for improved fusing and improved gloss of an ink-jet-ink-derived material image on a receiver. Moreover, in conjunction with use of a non-contacting electrode device in the Coagulate Formation Process Zone22, it can be advantageous to deliver from the ink jet device21to each pixel of a primary image an extra number of droplets of the non-marking unpigmented particulate ink, for further improvements of fusing and image gloss properties after subsequent transfer of the corresponding liquid-depleted image to the receiver.

FIG. 5aschematically illustrates, in an elevational side view, as indicated by the numeral70, a use of yet another electric field mechanism for forming coagulates in a primary image of a nonaqueous dispersion of charged particles. A portion of a contacting electrode device30is shown in proximity to an intermediate member40and separated therefrom by a uniform gap79(contacting electrode device not fully illustrated). Within the gap79, and preferably just filling this gap, is a primary image (corresponding to the primary images shown inFIGS. 1c,d) which primary image was priorly formed on the intermediate member40which has been moved beneath the contacting electrode device30. The contacting electrode device is preferably a rotatable member, e.g., a roller or a web, which rotatable member is held by a positioning device to define the gap79, which positioning device preferably includes a controller for producing a constant force or pressure against the liquid within the gap. Alternatively, and preferably, a rotatable contacting electrode device having the form of a roller may be mechanically “floated” on the liquid in the gap, in manner as is done in a conventional off-set printing press. A preferred width of gap79lies in a range of approximately between 5 micrometers and 100 micrometers, although any suitable gap width may be used. Generally speaking, the higher the image resolution (dpi) the smaller the gap. As indicated for the primary image ofFIG. 1d, the primary image corresponding toFIG. 5ais made by an intermixing of droplets of a nonaqueous marking ink and droplets of a nonaqueous non-marking ink co-deposited so as to form the primary image by ink jet device21. The marking ink which is used to form the primary image is a dispersion of charged pigmented particles dispersed in a carrier liquid. The non-marking ink contains no marking particles and is miscible with the carrier fluid of the marking ink. All of the pixels of the primary image ofFIG. 5apreferably have substantially equal volumes, with each pixel containing complementary amounts of the marking and non-marking inks, as previously described above. Thus, the liquid of pixels labeled74contain only non-marking ink (corresponding to Dmin) and the pixels labeled71contain only marking ink (corresponding to Dmax). The pixels labeled72and73contain mixtures of the marking and non-marking inks, with pixels72containing more marking ink than pixel73. Thus, increasing amounts of hatching indicate increasing proportions of marking ink per pixel.

The contacting electrode device30includes a power supply75for biasing with an applied voltage an electrode32located within the contacting electrode device in order to provide, with grounded electrode42located within the intermediate member40, an electric field in the liquid contained within gap79. The electric field is in a direction to urge any charged particles in the primary image to migrate towards the outer surface of the intermediate member40. For clarity of exposition, the illustration ofFIG. 5ais a hypothetical snapshot before this electric field has acted for any significant time; i.e., before significant migration of the charged particles included in the liquid of the primary image. Electrode32is preferably covered by a thin layer or layers33, which layer is preferably insulating. Alternatively, layer33is semiconductive. The thickness of layer(s)33is not critical, but is preferred to be thinner than about 1 millimeter and more preferably thinner than about10micrometers. Preferably, layer33is wettable by the marking ink, the non-marking ink, or any mixture of the marking ink and the non-marking ink.

The intermediate member40includes a preferably compliant layer43formed on a support41and an optional thin outer layer44formed on layer43. Preferably intermediate member40is a roller and support41is a metallic drum, e.g., made of aluminum or any other suitable metal, which drum is preferably grounded (grounding of layer41not shown inFIG. 5a) or connected to a suitable voltage from a source of potential such as a power supply (not shown). An optional thin conductive electrode layer42is shown sandwiched between layers41and43which layer is connected to ground (as shown) or to a power supply (not shown). In an alternative embodiment, intermediate member40is an endless web. In this alternative embodiment, a flexible conductive electrode layer42is provided sandwiched between layer43and a flexible support41, which support may include polymeric materials including reinforced materials. In another alternative embodiment, support41is included in a linearly-movable platen, or adhered to a linearly-movable platen.

Layer43has a thickness preferably in a range of approximately between 0.5 mm and 10 mm, and more preferably, between 0.5 mm and 3 mm. In certain embodiments, layer43is electrically insulating. In preferred embodiments, layer43is semiconducting and has a resistivity preferably less than approximately 1010ohm-cm and more preferably less than 107ohm-cm. Layer43is preferably made from a group of materials including polyurethanes, fluoroelastomers, and rubbers including fluororubbers and silicone rubbers, although any other suitable material may be used. For controlling resistivity, layer43may include a particulate filler or may be doped with compounds such as for example antistats. In other embodiments in which outer layer44is not included, the outer surface of layer43is preferred to have a suitable surface energy controlled within a suitable range by a thin coating (not shown) of any suitable surface active material or a surfactant.

Optional layer44has a thickness preferably in a range of approximately between 1 micrometer and 20 micrometers. Layer44is preferred to be both flexible and hard, and is preferably made from a group of materials including sol-gels, ceramers, and polyurethanes. Other materials, including fluorosilicones and fluororubbers, may alternatively be used. Layer44preferably has a high dielectric constant and suitable particulate fillers may be provided in layer44to increase the dielectric constant. An outer surface of layer44is preferred to have a suitable surface energy which may be controlled within a suitable range by a thin extra coating (not shown) of any suitable surface active material or a surfactant.

FIG. 5b, in which single primed (′) quantities refer to the unprimed similar quantities inFIG. 5a, shows the effect of the action of the electric field produced by power supply75′. Marking particles in the pixels71′,72′ and73′ are shown migrated down to respectively form the respective concentrated coagulate layers76c,76band76aon the outer surface of layer44′.

Above the respective layers76c,76band76aare respective liquids77c,77b, and77a, which liquids are preferably completely exhausted of any marking particles. Any counterions respectively contained in the respective pixels are migrated to the outer surface of layer73′ (counterions not shown). The point in time shown inFIG. 5brepresents the time before the rotating intermediate member40moves the image away from the contacting electrode device30towards the Excess Liquid Removal Process Zone23, i.e., before breaking contact with the liquid in the gap79′. After leaving the Coagulate Formation Process Zone22, the electrostatic charges on the particles in the layers76c,76band76ainduce countercharges in the electrode42′, causing mutual attractions between the electrostatic charges on the particles and the respective counterions, thereby holding the layers76c,76band76aadhered to the outer surface of the intermediate member40. This electrostatic adhesion holds the layers76c,76band76afirmly in position during subsequent removal of excess liquid in the Excess Liquid removal process Zone23.

In the above yet another preferred electric field mechanism using a contacting electrode device, it is preferable to use a non-marking ink which is a dispersion of unpigmented particles, rather than a non-marking ink containing no particles as described in reference toFIGS. 5a,b. Thus, every pixel of a two-fluid primary image contains a mixture of an amount of a dispersion of marking pigmented particles dispersed in a first carrier liquid, and a complementary amount of a preferred dispersion of non-marking unpigmented particles dispersed in a second carrier liquid, e.g., as described above with reference toFIG. 1e, such that both dispersions are co-deposited on the operational surface of the intermediate member as the first and second inks by the ink jet device21. Thus, in this preferred usage of a contacting electrode mechanism, and by analogy and with further reference toFIG. 5a, each pixel of the primary image which is neither a Dmax pixel or a Dmin pixel contains a complementary number of non-marking unpigmented particles, in addition to the marking pigmented particles (not separately illustrated). The non-marking unpigmented particles of the preferred non-marking ink are preferably similarly charged and have the same polarity as the marking pigmented particles, and the corresponding counterions associated with the non-marking unpigmented particles are preferably similar in nature to the counterions associated with the marking pigmented particles, and more preferably, identical in nature to the counterions associated with the marking pigmented particles. Preferably, the first and second carrier liquids are similar to one another, and more preferably, the first and second carrier liquids are identical. In a primary image using this preferred non-marking ink, a Dmax pixel, e.g., corresponding to a pixel71inFIG. 5a, contains no amount of the dispersion of non-marking unpigmented particles. Similarly, a Dmin pixel, e.g., corresponding to a pixel74inFIG. 5a, contains no amount of the dispersion of marking pigmented particles, and an intermediate density pixel, corresponding to a pixel72or73, contains an admixture of the two dispersions. In each of the pixels included in the primary image, the volume of liquid per pixel is preferably substantially the same. By analogy and with reference toFIG. 5b, the electric field action of the contacting electrode device produces a Dmax pigmented-particle coagulate, entirely corresponding to layer76cand containing no added unpigmented particles. On the other hand, a preferably colorless unpigmented-particle coagulate layer will be formed by the contacting electrode device in a Dmin pixel, such as pixel74′. A mixed particle co-coagulate layer, containing both pigmented and unpigmented particles, will be formed in an intermediate density pixel, such as pixel72′ or73′. It is preferred that any thickness of any coagulate layer caused to be formed on the surface of intermediate member40′ by use of the electrode device30′, which coagulate layer includes marking particles, non-marking particles or both marking and non-marking particles, is substantially the same. As previously described above, after formation of such coagulate layers by the electric field action of the contacting electrode device, any excess liquid is removed from the image on the intermediate member by any suitable means, e.g., in Excess Liquid Removal Process Zone23ofFIG. 2, and the liquid-depleted layers transferred by any suitable means from the intermediate member to a receiver in the Transfer Process Zone24. Owing to the advantageous fact that the amounts of excess liquid per pixel are substantially the same for all pixels, it will be generally easier for these amounts of liquid to be efficiently removed, e.g., in an Excess Liquid Removal Process Zone23, than would be the case for the nonuniform amounts of excess liquid77a,b,cand78inFIG. 5b.

It will be especially noted that, for the preferred situation wherein any thickness of a coagulate layer containing any proportion of pigmented and unpigmented particles is substantially the same, the resulting efficiency of transfer to a receiver will generally be much more uniform than for the varyingly thick coagulate layers such as formed in pixels71′,72′,73′, and74′ ofFIG. 5b. Moreover, it will be evident that after transfer to the receiver of any ink-jet-ink-derived material image formed by utilizing this preferred non-marking ink dispersion, the resulting unfused image quality will be superior as compared to utilizing a non-marking ink containing no particles. The improved image quality results from the more uniform transfer of the resulting liquid-depleted image, including a more efficient transfer of the material in the lower density pixels. Following any subsequent fusing of the resulting ink-jet-ink-derived material image to the receiver, the resulting image quality will be superior as compared to that obtained by using a non-marking ink containing no particles, i.e., the gloss will be much more uniform. Also, a perceived image mottle, such as caused by a nonuniform thickness of the ink-jet-ink-derived material image produced by using the previous embodiment, will be much reduced. It should be noted that the physical properties of the non-marking particles of the preferred non-marking ink can be advantageously tailored, e.g., for improved fusing and improved gloss of an ink-jet-ink-derived material image on a receiver. Moreover, in conjunction with use of a non-contacting electrode device in the Coagulate Formation Process Zone22, it can be advantageous to deliver from the ink jet device21to each pixel of a primary image an extra number of droplets of the non-marking unpigmented particulate ink, for further improvements of fusing and image gloss properties after subsequent transfer of the corresponding liquid-depleted image to the receiver.

FIG. 6aschematically illustrates, in an elevational side view, indicated by the numeral80, of a portion of apparatus for forming electrocoagulates in a primary image, wherein an electrocoagulation member90is included in an electrocoagulation mechanism (entire mechanism not illustrated). Electrocoagulation member90is shown in proximity to an intermediate member50and separated therefrom by a uniform gap89. Within the gap89, and preferably just filling this gap, is a primary image (corresponding to the primary images shown inFIGS. 1c,d) which primary image was priorly formed on an intermediate member50which has been moved beneath the electrocoagulation member90. As indicated for the primary image ofFIG. 1d, the primary image corresponding toFIG. 6ais made by an intermixing of droplets of an aqueous-based electrocoagulable marking ink and droplets of an aqueous-based non-marking ink co-deposited so as to form the primary image by ink jet device21. The non-marking ink contains no electrocoagulable material, is preferably substantially colorless, and is miscible with the electrocoagulable marking ink. All of the pixels of the primary image ofFIG. 6apreferably have substantially equal volumes, with each pixel containing complementary amounts of the marking and non-marking inks, as previously described above. Thus, the liquid of pixels labeled84contain only non-marking ink (corresponding to Dmin) and the pixels labeled81contain only marking ink (corresponding to Dmax). The pixels labeled82and83contain mixtures of the marking and non-marking inks, with pixels82containing more marking ink than pixel83. Thus, increasing amounts of hatching indicate increasing proportions of electrocoagulable marking ink per pixel.

The electrocoagulation member90is preferably a rotatable member, e.g., a roller or a web, which rotatable member is held by a positioning device to define the gap89, which positioning device preferably includes a controller for producing a constant force or pressure against the liquid within the gap. Alternatively, and preferably, a rotatable electrocoagulation member having the form of a roller may be mechanically “floated” on the liquid in the gap, in manner as is done in a conventional off-set printing press. A preferred width of the gap89lies in a range of approximately between 5 micrometers and 100 micrometers, although any suitable gap width may be used. Generally speaking, the higher the image resolution (dpi) the smaller the gap. The electrocoagulation member90includes an electrode92connected to a source85of both voltage and current for causing electrocoagulation. The electrode92of the electrocoagulation member90may be a bare electrode. Alternatively, and preferably, electrode92is covered by an electrolytically inert protective layer93which is resistant to degradation as might otherwise be caused by passage of current during electrocoagulation. Protective layer93preferably has a resistivity of less than 104ohm-cm, and more preferably, less than 5×102ohm-cm. The electrode92is adhered to a support91.

The intermediate member50includes a sub-surface electrode52sandwiched between a support51and a compliant layer53(or layers53), which compliant layer is covered by a protective outer layer54. It is preferred that the sub-surface electrode52be positive with respect to the electrode92of the electrocoagulation member90, which sub-surface electrode is preferably grounded. Such a configuration is preferable when electrocoagulation member90has for example the form of an endless web, support91then preferably being a flexible material. Alternatively, the sub-surface electrode is positive and is connected to a source (not shown) of both voltage and current while the electrode of the electrocoagulation member may be grounded, and for this configuration electrocoagulation member90has for example a preferred form of a roller, the support91being a rigid drum preferably made of a metal such as aluminum, and wherein the electrode92may in certain embodiments be dispensed with and not included in electrocoagulation member90. Notwithstanding the above-described preferred biasing, with sub-surface electrode52positive with respect to the electrode92, a reverse polarity in which sub-surface electrode52is negative with respect to the electrode92may be suitable for certain electrocoagulable ink embodiments. The characteristics of the support51and the electrode52of intermediate member50are respectively otherwise similar to those of the respective layers41and42of intermediate member40inFIG. 5a.

Apart from certain different characteristics described below in this paragraph, the properties and dimensions of the layers53and54of intermediate member50are respectively otherwise similar to those of the respective layers43and44of intermediate member40inFIG. 5a. In particular, a difference is that each of any compliant layers53disposed on the sub-surface electrode preferably has a resistivity of less than104ohm-cm, and more preferably, less than 5×102ohm-cm. Another difference is that outer layer54is selected to be electrolytically inert, i.e., is resistant to degradation as might otherwise be caused by passage of current during electrocoagulation.

The situation after electrocoagulation is shown schematically inFIG. 6b, wherein the primed (′) entities have the same characteristics and dimensions as the corresponding unprimed entities ofFIG. 6a. As indicated inFIG. 6b, after electrocoagulation is complete, e.g., in pixels respectively labeled81′,82′, and83′, a corresponding respective thickness86a,b,cof marking electrocoagulate material on the surface of layer54′ is greatest for pixel81′, intermediate for pixel82′, and least for pixel83′, while pixel84′ contains no electrocoagulate. These respective thicknesses of electrocoagulate reflect the respective amounts of electrocoagulable material present in the corresponding pixels81,82,83and84of the primary image ofFIG. 6a, as indicated by the degrees of hatching. The situation shown inFIG. 6bobtains before the rotating intermediate member50′ moves the image away from the electrocoagulating member90′ for subsequent removal of the corresponding respective excess amounts87a,b,c,dof liquid, in order to form a liquid-depleted ink-jet-ink-derived electrocoagulate material image on the operational surface of the intermediate member.

For use with an electrocoagulation member it is preferred to use a non-marking ink which is electrocoagulable, rather than a non-marking ink containing no electrocoagulable material as described in reference toFIGS. 6a,b. Thus, every pixel of a two-fluid primary image contains a mixture of an amount of a marking electrocoagulable ink, and a complementary amount of a preferred non-marking electrocoagulable ink, as described above with reference toFIG. 1e, such that both electrocoagulable inks are co-deposited on the operational surface of the intermediate member as the first and second inks by the ink jet device21. Thus, by analogy and with further reference toFIG. 6a, each pixel of the primary image in this preferred embodiment contains a complementary volume of non-marking electrocoagulable ink, in addition to the non-marking electrocoagulable ink (not separately illustrated prior to electrocoagulation). Except that electrocoagulates made from the non-marking electrocoagulable ink contain no colorant material, the non-marking electrocoagulable ink is preferably otherwise similar to the marking electrocoagulable ink, and more preferably, identical in nature to the marking electrocoagulable ink (except for any added colorant material). In a primary image using this preferred non-marking ink, a Dmax pixel, e.g., corresponding to a pixel81inFIG. 6a, contains no amount of the non-marking electrocoagulable ink. Similarly, a Dmin pixel, e.g., corresponding to a pixel84inFIG. 6a, contains no amount of the non-marking electrocoagulable ink, and an intermediate density pixel, corresponding to a pixel82or83, contains an admixture of the two electrocoagulable inks. In each of the pixels included in the primary image, the volume of liquid per pixel is preferably substantially the same.

After electrocoagulation, the situation is shown inFIG. 6c, wherein double primed (″) entities correspond entirely to the unprimed entities inFIG. 6a. In pixels where both marking and non-marking electrocoagulable inks were present in the primary image, colored co-electrocoagulates are produced. As indicated inFIG. 6c, after electrocoagulation is complete, e.g., in pixels respectively labeled81″,82″,83″, and84″ a corresponding coloration or optical density, as indicated by the degrees of cross-hatching, of a corresponding respective electrocoagulate layer88a,b,c,d, is greatest for a pixel81″, less for a pixel82″, and least for a pixel83″, while the electrocoagulate in a pixel84″ is uncolored being made entirely from the non-marking electrocoagulable ink. The respective thicknesses of electrocoagulate in each pixel is preferably substantially the same, reflecting preferred respective complementary amounts of the marking and non-marking electrocoagulable inks present in the corresponding pixels of the primary image. Similarly, the volumes of exhausted liquid88e,f,g,habove each of the respective electrocoagulate layers is preferably substantially the same. The situation shown inFIG. 6bobtains before the rotating intermediate member50′ moves the image away from the electrocoagulating member90′ for subsequent removal of the corresponding respective excess amounts87e,f,g,hof liquid, in order to form a liquid-depleted ink-jet-ink-derived electrocoagulate material image on the operational surface of the intermediate member. Owing to the advantageous fact that the amounts87e,f,g,hof excess liquid per pixel are substantially the same for all pixels, it will be generally easier for these amounts of liquid to be efficiently removed, e.g., in an Excess Liquid Removal Process Zone23, than would be the case for the nonuniform amounts of excess liquid87a,b,c,dinFIG. 6b.

It will be especially noted that, for the preferred situation wherein any thickness of an electrocoagulate layer containing any proportion of pigmented and unpigmented particles is substantially the same, the resulting efficiency of transfer to a receiver will generally be much more uniform and complete than for the varyingly thick electrocoagulate layers such as in pixels81′,82′,83′, and84′ inFIG. 6b. Moreover, it will be evident that after transfer to the receiver of any ink-jet-ink-derived material image formed by utilizing the preferred non-marking electrocoagulable ink, the resulting unfused image quality will be superior as compared to utilizing a non-marking ink containing no electrocoagulable material. The improved image quality results from the more uniform transfer of the resulting liquid-depleted image, including a more efficient transfer of the material in the lower density pixels. Following any subsequent fusing of the resulting ink-jet-ink-derived material image to the receiver, the resulting image quality will be superior as compared to that obtained by using a non-marking ink containing no electrocoagulable material, i.e., the gloss will be much more uniform. Also, a perceived image mottle, such as caused by a nonuniform thickness of the ink-jet-ink-derived material image produced by using the previous embodiment, will be much reduced. It should be noted that the physical properties of the non-marking particles of the preferred non-marking ink can be advantageously tailored, e.g., for improved fusing and improved gloss of an ink-jet-ink-derived material image on a receiver. Moreover, in conjunction with use of a non-contacting electrode device in the Coagulate Formation Process Zone22, it can be advantageous to deliver from the ink jet device21to each pixel of a primary image an extra number of droplets of the non-marking unpigmented particulate ink, for further improvements of fusing and image gloss properties after subsequent transfer of the corresponding liquid-depleted image to the receiver.

Any suitable marking electrocoagulable ink or non-marking electrocoagulable ink may be used. Such an electrocoagulable ink may form electrocoagulates or co-electrocoagulates of any pre-selected color, including a substantially colorless electrocoagulate such as in a pixel containing no marking electrocoagulable ink, e.g., as shown inFIG. 6c. Electrocoagulates, produced by passage of electrical current through the liquid included in a primary image spontaneously form an electrocoagulated layer in direct contact with the operational surface, which electrocoagulated layer is located below a residual layer of excess liquid exhausted of electrocoagulable components, as illustrated inFIGS. 6b,c.

In yet other embodiments of the invention (not illustrated), alternative mechanisms other than electric field mechanisms are used to cause formation of coagulates in the Coagulate Process Formation Zone22. As for certain previous embodiments described above, in certain of these yet other embodiments one of the first and second inks used in the ink jet device21is a marking ink, which marking ink is preferably a dispersion of colored, preferably pigmented, particles in a carrier liquid, the other ink containing no particles and preferably being otherwise similar to the carrier liquid of the marking ink. However, in preferred embodiments of these yet other embodiments, both the first and second inks are dispersions of particles in a respective carrier liquid, one of the inks being a dispersion of marking particles which particles are preferably pigmented particles, and the other ink being a dispersion of non-marking, preferably colorless, unpigmented, particles. In these preferred yet other embodiments, an amount of coagulated material produced from each pixel of the primary image in the Coagulate Process Formation Zone22is preferably substantially uniform for all pixels of an image, which amount includes imagewise varying complementary amounts of both marking and non-marking particles, wherein some pixels contain only marking particles and some pixels contain only non-marking particles, as fully described above for previous embodiments. To cause formation of coagulates in a primary image by any of the alternative mechanisms described below, complementary volumes of the marking and non-marking inks are co-deposited by the ink jet device21so as to preferably produce substantially the same total volume of liquid in each pixel of the primary image, wherein some pixels contain only the marking ink and some pixels contain only the non-marking ink. These alternative mechanisms for forming coagulates in a primary image include mechanisms for forming coagulates as disclosed in the above-referenced related co-pending U.S. patent application Ser. No. 09/973,244 filed on even date herewith in the names of John W. May, et al. The term “coagulate”, as used hereafter in the following descriptions of these alternative mechanisms, includes flocs, aggregates, or agglomerates.

One alternative mechanism for inducing formation of coagulates in a primary image is a salt donation mechanism, wherein a dissolved salt including a multivalent cation or anion is introduced into the liquid of the primary image, which primary image priorly includes an electrostatically stabilized aqueous-based ink dispersion of particles. For introducing the multivalent salt as a solution, the salt donation mechanism may include a sponge, a squeegee blade, a spray device, or a secondary ink jet device for depositing on each pixel of the primary image at least a critical amount of the salt solution for causing coagulates to form. Salts of divalent cations may include inorganic salts of Mg+2, Ca+2, Mn+2, Ni+2, Co+2, Cu30 2, Zn+2, and so forth. It is especially preferred to use salts of trivalent cations, including inorganic salts of Al+3, Fe+3, Ce+3, and so forth, or quadrivalent ions such as Ce+4, Zr+4, and so forth. Salts of divalent anions may include SO4−2, CO3−2, and so forth. It is especially preferred to use salts of trivalent anions, including inorganic salts of Fe(CN)6−3, PO4−3, and so forth. A multivalent salt may be added to a primary image after formation of the primary image, or it may be applied to the operational surface of the intermediate member, i.e., prior to forming the primary image and after regenerating the operational surface in the Regeneration Process Zone25.

Another alternative mechanism for inducing formation of coagulates in a primary image is a pH-altering donation mechanism for introducing a pH-altering material to the solution of the primary image, which primary image includes an electrostatically stabilized aqueous-based ink dispersion of particles. When the particles included in the primary image are negatively charged, an acidic solution is introduced by the pH-altering donation mechanism for causing formation of coagulates, and conversely, a basic solution is introduced if the particles are positively charged. Preferably, at least a critical amount of pH-altering solution is added to each pixel of the primary image, which critical amount produces a condition known as the point of zero charge (pzc), thereby causing destabilization of the dispersion and formation of coagulates. The pH-altering donation mechanism includes a sponge, a squeegee blade, a spray device, or a secondary ink jet device for depositing on each pixel of the primary image at least a corresponding critical amount of the pH-altering solution. A pH-altering material may be added to a primary image after formation of the primary image, or it may be applied to the operational surface of the intermediate member, i.e., prior to forming the primary image and after regenerating the operational surface in the Regeneration Process Zone25.

Yet another alternative mechanism for inducing formation of coagulates in a primary image is a non-solvent donation mechanism for introducing into a primary image a critical quantity of a non-solvent liquid, which non-solvent is miscible with the liquid of the primary image. Prior to any addition of the non-solvent liquid, the primary image includes either a nonaqueous or an aqueous-based sterically stabilized ink dispersion of particles, which particles are stabilized by polymeric moieties bonded or adsorbed to the surfaces of the particles and which moieties include extended chain portions which are compatible with and are solubilized by the liquid in which the particles are dispersed. The non-solvent liquid may be a nonaqueous liquid or an aqueous-based liquid. The non-solvent liquid, which is miscible with the liquid of the primary image in which the particles are dispersed, is not compatible with the polymeric moieties. By using the non-solvent donation mechanism to add at least a critical amount of the non-solvent liquid, the extended chain portions of the polymeric moieties change their configurational shapes from extended shapes to tight conformations, allowing interparticle van der Waals or dispersion forces to act so as to rapidly cause formation of flocs or coagulates. The non-solvent donation mechanism includes a sponge, a squeegee blade, a spray device, or a secondary ink jet device for depositing on each pixel of the primary image at least a corresponding critical amount of the non-solvent liquid. A non-solvent liquid may be added to a primary image after formation of the primary image, or it may be applied to the operational surface of the intermediate member, i.e., prior to forming the primary image and after regenerating the operational surface in the Regeneration Process Zone25.

Still yet another alternative mechanism for inducing formation of coagulates in a primary image is a denuding agent mechanism for at least partially destroying, debonding, or desorbing sterically stabilizing polymeric moieties bound to the surfaces of a sterically stabilized dispersion of ink particles included in a primary image. The resulting comparatively unshielded or denuded particles are no longer protected by steric stabilization, and are subject to formation of coagulates as a result of their mutual attractions caused by van der Waals or dispersion forces between them. The denuding agent mechanism preferably includes a source of radiation, e.g., which radiation is selectively absorbed by the polymeric moieties, thereby causing a heating or a photochemical reaction for cleaving or destroying the polymeric chains of the sterically stabilizing moieties. Any other suitable denuding mechanism may be used.

A further alternative mechanism for inducing formation of coagulates is a temperature-altering mechanism for a heating or a cooling of the primary image, which primary image includes an aqueous-based or a nonaqueous particulate ink dispersion having steric stabilization. A choice of heating or cooling by the temperature-altering mechanism is determined by the relative magnitudes of the enthalpy and entropy contributions to the free energy of close approach of sterically stabilized particles in the primary image. When the dispersion is stabilized by enthalpic stabilization (more typical for aqueous-based dispersions) the temperature-altering mechanism heats the primary image to cause formation of flocs or coagulates. Conversely, when the dispersion is stabilized by entropic stabilization (more typical for nonaqueous dispersions) the temperature-altering mechanism cools the primary image to cause formation of flocs or coagulates. The temperature-altering mechanism includes: a source of radiant energy for heating, e.g., infrared radiation; a source of heat located within the intermediate member; an external contacting heated member; a source for cooling located within the intermediate member, such as a Peltier effect cooling device; a coolant circulated in conduits of a coolant circulating system; or an external contacting cooling member. Any suitable temperature-altering mechanism may be used.

A still further alternative mechanism for inducing formation of coagulates is a hetero-colloid donation mechanism for addition of a hetero-colloid liquid to a primary image. The primary image includes an ink dispersion of charged particles plus corresponding counterions distributed within the liquid of the dispersion. The hetero-colloid liquid is a colloidal dispersion of charged particles having a polarity opposite to a polarity of the charged particles of the primary image. After addition of hetero-colloid liquid to the primary image, electrostatic attractions between the oppositely charged particles of the ink particles and the hetero-colloid particles causes hetero-coagulates to be formed. Preferably, the primary image dispersion and the hetero-colloid liquid are mutually miscible. Particles of the hetero-colloid preferably provide any useful function, e.g., enhancing the transferability of the hetero-coagulates to a receiver, or improving in a fusing station the fusibility of an image previously transferred to a receiver. The hetero-colloid donation mechanism includes a sponge, a squeegee blade, a spray device, and a secondary ink jet device for depositing on each pixel of the primary image at least a corresponding critical amount of the hetero-colloid for inducing formation of coagulates. A hetero-colloid liquid may be added to a primary image after formation of the primary image, or it may be applied to the operational surface of the intermediate member, i.e., prior to forming the primary image and after regenerating the operational surface in the Regeneration Process Zone25.

Yet a still further alternative mechanism for inducing formation of coagulates is a polymer-solution-donation mechanism for introducing a polymeric material which is compatible with the liquid of a primary image so as to induce a depletion flocculation in the primary image. The polymeric material is preferably dispersed as a colloid in a fluid (or dissolved in a fluid) for addition to a primary image, which polymeric material is not adsorbed by the ink particles dispersed in the primary image liquid. The fluid is preferably miscible with the liquid of the primary image, which includes an electrostatically stabilized dispersion of particles. The polymer-solution-donation mechanism includes a sponge, a squeegee, a spray device, and a secondary ink jet device for depositing on each pixel of the primary image at least a corresponding critical amount of the polymeric material for inducing depletion flocculation. The polymer material may be added to a primary image after formation of the primary image, or it may be applied to the operational surface of the intermediate member, i.e., prior to forming the primary image and after regenerating the operational surface in the Regeneration Process Zone25. Following a formation of coagulates in a primary image by an alternative mechanism for inducing formation of coagulates as described above, excess liquid is removed in the Excess Liquid Removal Process Zone23by any suitable device, and the resulting liquid-depleted ink-jet-ink-derived material images transferred to a receiver by a suitable transfer mechanism in Transfer Process Zone24.

Notwithstanding disclosure hereinabove relating to rotatable intermediate members, an intermediate member may in certain other embodiments be a linearly-movable planar member, e.g., in the form of a plate or a platen, or, the intermediate member may be mounted on a plate or a platen. In an imaging apparatus including a planar intermediate member, the planar intermediate member is moved along a linear path past various devices or process zones having characteristics similar to those described above with reference toFIG. 2, which devices or process zones are disposed along a direction of motion of the plate or platen. Thus, in an apparatus which includes a linearly-movable planar intermediate member, the devices or process zones can be disposed sequentially in the following order: an ink jet device similar to that ofFIG. 2; a Coagulate Formation Process Zone; an Excess Liquid Removal Process Zone; a Transfer Process Zone; and, a Regeneration Process Zone, wherein the ink jet device is located near a starting position for ultimately forming an image on a receiver provided in the Transfer Process Zone, and the Regeneration Process Zone is located after the Transfer Process Zone near an ending position along the direction of motion. Alternatively, the Regeneration Process Zone may be located near a starting position and the Transfer Process Zone located near the ending position. After the platen reaches the ending position, the direction of the platen is reversed and the platen is moved back to the starting position.

The present invention has certain advantages over the inventions disclosed in related copending U.S. patent application Ser. No. 09/973,239, entitled Ink Jet Process Including Removal Of Excess Liquid From An Intermediate Member by Arun Chowdry, et al., and related copending U.S. patent application Ser. No. 09/973,244, now U.S. Pat. No. 6,682,189 entitled Ink Jet Imaging Via Coagulation On An Intermediate Member by John W. May, et al. An important feature of the present invention is that a substantially constant volume of liquid is preferably deposited in each pixel of a primary image by the ink jet device, which liquid includes at least one of the marking and non-marking inks. By comparison with art wherein only marking ink is used to form a primary image, in the present invention problems are much reduced relating to image spreading during formation of the primary image by the ink jet device. Similarly, by comparison with other art wherein only marking ink is used to form a primary image, problems are much reduced relating to image spreading during the removal of excess liquid (prior to transfer of an ink-jet-ink-derived material image to a receiver). When only one ink is used, different pixels of a primary image contain variable numbers of droplets, and there is a problem of sideways squashing of the liquid in those pixels containing larger volumes ink when a contacting device is used to remove the excess liquid, resulting in reduced image sharpness and resolution. In relation to these problems, the present invention is advantageously not as dependent on surface energies and spreading coefficients to maintain image integrity against image spreading. Moreover, because each pixel of the primary image contains preferably substantially the same volume of liquid, it is easier to provide a uniform spacing for a noncontacting electrode or to provide a more uniform current density in an electrocoagulable primary image. In preferred embodiments in which the non-marking ink is a dispersion of preferably colorless or unpigmented particles, it is easier to remove excess liquid using a contacting excess liquid removal device, inasmuch as an amount of excess liquid is preferably substantially the same in each pixel after coagulates have been formed. Similarly, in preferred electrocoagulation embodiments in which the non-marking ink is made of a preferably colorless or unpigmented electrocoagulable material, it is easier to remove excess liquid using a contacting excess liquid removal device, inasmuch as an amount of excess liquid is preferably substantially the same in each pixel after electrocoagulates have been formed. Moreover, when the non-marking ink is either a dispersion of colorless or unpigmented particles, or alternatively when the non-marking ink is made of a preferably colorless or unpigmented electrocoagulable material, transfer of the corresponding liquid-depleted ink-jet-ink-derived material to a receiver or to another member is advantageously more uniform and more complete. As a result of such more uniform transfer, a resulting image on a receiver will have superior gloss characteristics after fusing, thereby providing a customer with more attractive prints.