Ink jet printing process

Abstract: A process comprising (a) incorporating into an ink jet printing apparatus (1) a developing composition comprising a liquid vehicle and a color developer; (2) an oxidizing composition comprising a liquid vehicle and an oxidizing agent; (3) a coloring composition comprising a liquid vehicle and a dye coupler; and (4) a fixing composition comprising a liquid vehicle and a fixative; (b) causing droplets of the developing composition to be ejected in an imagewise pattern onto the substrate; (c) causing droplets of the oxidizing composition to be ejected in an imagewise pattern onto the substrate; (d) causing droplets of the coloring composition to be ejected in an imagewise pattern onto the substrate; and (e) causing droplets of the fixing composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising all four of the developing composition, the oxidizing composition, the coloring composition, and the fixing composition, said portions forming a printed image. Specific embodiments of the present invention are directed to the realization of continuous tone and gray scale in images by (1) control of the time at which color forming reactions are quenched by controlling the time period between deposition of the color forming liquids and deposition of the fixing liquid; (2) control of the extent of color forming reactions by limitation of the quantity of one of the color forming liquids; or (3) control of pixel size by drop placement control over the overlap areas of drops of color forming liquids.

Description: The present invention is directed to an ink jet printing process. More specifically, the present invention is directed to an ink jet printing process wherein color forming liquids ("inks") are jetted onto a substrate. One embodiment of the present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a developing composition comprising a liquid vehicle and a color developer; (2) an oxidizing composition comprising a liquid vehicle and an oxidizing agent; (3) a coloring composition comprising a liquid vehicle and a dye coupler; and (4) a fixing composition comprising a liquid vehicle and a fixative; (b) causing droplets of the developing composition to be ejected in an imagewise pattern onto the substrate; (c) causing droplets of the oxidizing composition to be ejected in an imagewise pattern onto the substrate; (d) causing droplets of the coloring composition to be ejected in an imagewise pattern onto the substrate; and (e) causing droplets of the fixing composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising all four of the developing composition, the oxidizing composition, the coloring composition, and the fixing composition, said portions forming a printed image. While known compositions and processes are suitable for their intended purposes, a need remains for improved ink jet printing processes. In addition, a need remains for ink jet printing processes which enable generation of photographic quality images on plain paper. Further, a need remains for ink jet printing processes which enable increased color gamut. Additionally, a need remains for ink jet printing processes which enable increased color intensity. There is also a need for ink jet printing processes which generate permanent and waterfast images. In addition, there is a need for ink jet printing processes which exhibit desirable throughput speed. Further, there is a need for ink jet printing processes which enable gray level printing without specific regard to drop ejector resolution, wherein near continuous tone or multigray level images can be realized with simple 300 dpi (dots per inch) drop ejectors. Additionally, there is a need for ink jet printing processes which enable the printing of continuous tone pictorial images without specific regard to drop ejector resolution. A need also remains for ink jet printing processes which enable production of variable spot sizes. In addition, a need remains for ink jet printing processes which enable production of high resolution images. JP-A-57-018264 discloses a printing method, wherein small drops of ink of plural types which are generally colorless in a normal state are exhausted separately, mixed in a recording material and colored. EP-A-0641670 relates to an ink jet printing method comprising the step of image-wise projecting by means of an ink set in a liquid in the form of droplets onto a receiving material containing at least one reagent A with at least one reagent B contained in the ink droplets so as to form a colored product by color reaction, and optionally uniformly heating said receiving material and/or uniformly exposing it to chemically active electromagnetic radiation to start or enhance said color reaction. Figure 1 is a perspective view illustrating a multicolor, multi-printhead, scanning type thermal ink jet printer useful for the present invention; Figure 2 is a view taken along line B-B of Figure 1, illustrating the nozzle arrays of the multicolor, multi-printhead thermal ink jet recording head assembly; Figure 3 is an isometric view of a multicolor, single printhead thermal ink jet printer having replaceable ink jet supply tanks useful for the present invention; Figure 4 is a partially exploded isometric view of a multicolor, single printhead thermal ink jet cartridge used in the printer of Figure 3 with integral printhead and ink connectors and replaceable ink tanks; Figure 5 is a schematic, partially shown side elevation view of an acoustic ink jet printer useful for the present invention; Figure 6 is a schematic representation of an acoustic ink jet printhead used in the apparatus of Figure 5 and showing ink droplets moving toward a recording medium on the transport belt; Figure 7 is an unscaled, cross-sectional view of a first embodiment acoustic droplet ejector which is shown ejecting a droplet of a marking fluid; Figure 8 is an unscaled cross-sectional view of a second embodiment acoustic droplet ejector which is shown ejecting a droplet of a marking fluid; Figure 9 is an top-down schematic depiction of an array of acoustic droplet ejectors in one ejector unit; Figure 10 is a top-down schematic view of the organization of a plurality of ejector units in a color printhead; Figure 11 is a cross-sectional view of one embodiment of the present invention, a material deposition head having multiple ejection units; Figure 12 is a perspective view of the structure of Figure 11; Figure 13 is a schematic front elevation view of a portion of an extended width or full width printhead which has been assembled from a plurality of partial width array thermal ink jet or acoustic ink jet printheads; and Figure 14 illustrates schematically a process of the present invention wherein gray scale images are generated by overlapping droplets. The present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a developing composition comprising a liquid vehicle and a color developer; (2) an oxidizing composition comprising a liquid vehicle and an oxidizing agent; (3) a coloring composition comprising a liquid vehicle and a dye coupler; and (4) a fixing composition comprising a liquid vehicle and a fixative; (b) causing droplets of the developing composition to be ejected in an imagewise pattern onto the substrate; (c) causing droplets of the oxidizing composition to be ejected in an imagewise pattern onto the substrate; (d) causing droplets of the coloring composition to be ejected in an imagewise pattern onto the substrate; and (e) causing droplets of the fixing composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising all four of the developing composition, the oxidizing composition, the coloring composition, and the fixing composition, said portions forming a printed image. In one embodiment, only one coloring composition is incorporated into the printing apparatus, and the resulting images are of a single color. In another embodiment, at least two different coloring compositions are incorporated into the printing apparatus, and the resulting images are of at least two different colors. In one specific embodiment, three different coloring compositions are incorporated into the printing apparatus, one containing a cyan dye coupler, one containing a magenta dye coupler, and one containing a yellow dye coupler, thereby enabling the production of full color images. Specific embodiments of the present invention are directed to the realization of continuous tone and gray scale in images by (1) control of the time at which color forming reactions are quenched by controlling the time period between deposition of the color forming liquids and deposition of the fixing liquid; (2) control of the extent of color forming reactions by limitation of the quantity of one of the color forming liquids (i.e., the coloring composition, the developing composition, or the oxidizing composition); or (3) control of pixel size by drop placement control over the overlap areas of drops of color forming liquids. The present invention can employ any suitable or desired ink jet printing apparatus, including continuous stream ink jet printers, piezoelectric ink jet printers, thermal ink jet printers, acoustic ink jet printers, hot melt ink jet printers of any of the above types, or the like. To make a composite, multi-color image, recording heads (delivering a developing composition, an oxidizing composition, a coloring composition containing a yellow dye coupler, a coloring composition containing a magenta dye coupler, a coloring composition containing a cyan dye coupler, and a fixing composition, respectively) are mounted in respective cartridge holders provided on the carriage 2. In another embodiment, four recording heads are provided, with one delivering a coloring composition, wherein the resulting images are monochrome. Each cartridge holder includes appropriate mechanical, electrical and fluid couplings so that selected ink drivers can be activated in response to a suitable driving signal from a controller to expel ink from the cartridges onto a recording substrate supported upon a platen. It will be appreciated that the number of liquids applied to the substrate, and accordingly the number of ink supplies or containers, can be varied as desired. For example, for monochrome printing, the printer will apply to the substrate four liquids, namely a developing composition, an oxidizing composition, a fixing composition, and the coloring composition of the desired color. In multicolor printing, black may be applied in addition to cyan, magenta, and yellow, and the printer will apply to the substrate seven liquids, namely a developing composition, an oxidizing composition, a fixing composition, and the cyan, magenta, yellow, and black coloring compositions. Additional examples of suitable printing apparatus for the present invention are disclosed in, for example, U.S. Patents 5,568,169, 5,565,113, 5,596,355, 5,371,531, 4,797,693, 5,198,054, Any order of deposition of dye coupler, developer, and oxidizing agent can be employed; typically, the selected order is dependent on the specific reagents employed and their formulations. Fixative is always deposited last. In one embodiment of the present invention, the timing of the deposition of the fixative determines the color intensity. When developer, coupler, and oxidizer come together, the reaction to form the dye starts. The intensity of the color depends on the amount of dye formed. Deposition of the fixative at different times along the reaction profile stops the dye forming reactions, and the amount of dye formed at that moment in time determines the color tone or intensity. Developer and coupler can usually be deposited without regard to time. Once oxidizer and developer come together, however, the timing of deposition of coupler and fixative becomes more important, because the oxidized developer is highly reactive and should be reacted with the coupler relatively soon after its formation. In one embodiment of the present invention, a multiplicity of intensity or "gray" levels within a particular color can be obtained by controlling the time between the point at which the developing composition, oxidizing composition, and coloring composition all come together and the point at which the fixing composition is deposited. The reaction between the dye coupler and the oxidized developer can be halted at a point short of maximum color intensity, thereby creating one or more "gray" levels of color. In another embodiment of the present invention, a multiplicity of intensity or "gray" levels within a particular color can be obtained by jetting fixed amounts of developing composition and coloring composition onto the substrate in combination with varying amounts of oxidizing composition, with the oxidizing agent in the oxidizing composition being present in reaction limiting quantities with respect to the color developer in the developing composition and the dye coupler in the coloring composition. More specifically, the printhead for jetting the oxidizing composition can have a multiplicity of channels, each of which jet a different volume of oxidizing compound, as required. Alternatively, the printhead for jetting the oxidizing composition can jet drops of very small volume, and multiple small drops of oxidizing composition can be deposited at a given pixel location, depending on the intensity or "darkness" or saturation of color desired at that pixel location. High resolution gray level printing can thus be obtained without loss of throughput speed, which might otherwise be associated with gray level ink jet printing processes. Alternatively, instead of varying the amount or volume of oxidizing composition, the amount or volume of developing composition and/or the amount or volume of coloring composition can be varied by the above methods to obtain gray level prints. In yet another embodiment of the present invention, high resolution and gray scale images can be generated by generating spots of varying sizes on the substrate. More specifically, the developing composition, coloring composition(s), and oxidizing composition are jetted in an imagewise pattern so that the overlap of droplets of these three compositions is controlled. Pixel size can thereby be modulated to realize variable spot sizes, and high resolution gray level printing can thus be obtained without loss of throughput speed which might otherwise be associated with gray level ink jet printing processes. As illustrated schematically in Figure 14, the developer composition droplets 201, the oxidizing composition droplets 203, and the coloring composition droplets 205 can be jetted onto the substrate 207 with varying amounts of overlap 209, thereby forming image areas of varying size. In a full color printing process, three coloring compositions are employed to form varying size image areas of, for example, cyan, magenta, and yellow. The developing composition generally comprises a liquid vehicle and a color developer or developing agent, and functions as a color forming component in the process of the present invention. For the purpose of simplicity, the developing composition will at times hereinafter be referred to as an ink. Any liquid can be employed as the major component of the liquid vehicle, provided that it dissolves or disperses the components of the composition and is of a viscosity appropriate for the selected drop ejector. For example, in thermal ink jet printing systems, a preferred liquid vehicle is water. In other drop ejectors, such as those employing continuous stream processes, piezoelectric ink jet printers, acoustic ink jet printers, and the like, other liquids can also be employed, such as hydrocarbons, glycols, ethers, sulfones such as sulfolane, pyrrolidinones such as 2-pyrrolidinone and N-methyl pyrrolidinone, other dipolar aprotic solvents, and the like, as well as mixtures thereof. The developing composition can also contain other components which might improve its performance as an ink jet ink, such as humectants, penetrants, cosolvents, jetting aids, or the like, set forth in more detail hereinbelow. The developing composition typically contains the color developer in an amount of from about 0.05 to about 15 percent by weight of the developing composition, preferably from about 0.1 to about 10 percent by weight of the developing composition, and more preferably from about 0.5 to about 5 percent by weight of the developing composition, although the amount can be outside of these ranges. Examples of color developers or developing agents include phenylenediamines, of the formulae wherein R is a hydrogen atom, an alkyl group, preferably with from 1 to about 4 carbon atoms, or a substituted alkyl group, wherein the benzene ring can be substituted, and wherein 2 or more substituents can be joined together to form additional rings, such as p-phenylenediamine, of the formula o-phenylenediamine, monomethyl-p-phenylenediamine, and the like. Particularly preferred as color developers are N,N-dialkyl-p-phenylenediamines, of the general formula wherein each of R 1 and R 2 , independently of the other, is an alkyl group, preferably with from 1 to about 4 carbon atoms, or a substituted alkyl group, wherein the benzene ring can be substituted, and wherein 2 or more substituents can be joined together to form additional rings. Specific examples of N,N-dialkyl-p-phenylenediamines include N,N-dimethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine hydrochloride, N,N-diethyl-p-phenylenediamine hemisulfate, N,N-diethyl-p-phenylenediamine sulfur dioxide complex, N,N-diethyl-toluene-2,5-diamine hydrochloride, 2-(p-amino-N-ethylanilino)ethanol sulfate, N-ethyl-N-(β-methanesulphonamidoethyl)-4-aminoaniline, N-(2-(4-amino-N-ethyl-m-toluidino)ethyl)-methanesulfonamide sesquisulfate hydrate, 2-((4-amino-m-tolyl)ethylamino)ethanol sulfate, 4-(N-ethyl-N-2-methane sulfonylaminoethyl)-2-methylphenylene diamine sesquisulfate, and the like. The latter is particularly preferred because, as a function of pH, it can exist in cationic and zwitterionic forms and both forms can react with an ionized dye coupler, albeit at different rates. Also suitable are hydroquinones, of the formula wherein the benzene ring can be substituted, and wherein 2 or more substituents can be joined together to form additional rings, such as hydroquinone, of the formula chlorohydroquinone, bromohydroquinone, toluhydroquinone, methoxyhydroquinone, and the like, catechol, of the formula and its derivatives, such as pyrogallol, 4-phenyl catechol, gallic acid, methyl gallate, gallacetophenone, methyl ester of gentisic acid, daphnetin, 5,8-methano-5,6,7,8-tetrahydro-1,4-dihydroxynaphthalene, and the like. Also suitable are p-aminophenols, of the general formula wherein R 1 and R 2 each, independently of the other, are hydrogen atoms, alkyl groups, preferably with from 1 to about 4 carbon atoms, or substituted alkyl groups, wherein the benzene ring can be substituted, and wherein 2 or more substituents can be joined together to form additional rings, such as p-aminophenol, o-aminophenol, 2-methyl-p-aminophenol, 2-hydroxymethyl-p-aminophenol, 1-amino-2-naphthol-6-sulfonic acid (Eikonogen), 1-amino-2-naphthol-3,6-disulfonic acid (Diogen), 4-aminophenol hydrochloride, N-methyl-p-aminophenol (Metol), 2,4-diaminophenol (Amidol), 2,4-diaminophenol dihydrochloride, 2,3,4-triaminophenol, Triamol, N-(4-hydroxyphenyl)glycine (Glycin), 4-(hydroxyethylamino)-3-methyl-1-hydroxybenzene, 4-(di(hydroxyethyl)amino)-1-hydroxybenzene, N-(2'-hydroxy-5'-aminobenzyl)-3-hydroxyaniline hydrochloride, 4-amino-2-benzylaminophenol, 2-amino-4-(p-hydroxybenzylamino)-phenol, m-methyl-p-hydroxy-N-phenylmorpholine, 1-(4-hydroxyphenyl)-pyrrolidine, p-hydroxydiphenylamine (Duratol), p-aminosalicylic acid (Neol), 2-methyl-4-aminophenol hydrochloride (Monomet), N-(hydroxyethyl)-o-aminophenol (Atomal), 3-(hydroxymethyl)-4-hydroxyaniline hemisulfate (Edinol), and the like; Diphenal, of the formula and the like. Mixtures of two or more developers can also be used. Commercially available examples of suitable developers include CD-2 [diethylamino-o-toluidine hydrochloride, CAS# 2051-79-8], CD-3 [4-(N-ethyl-N-2-methane sulfonylaminoethyl)-2-methylphenylene diamine sesquisulfate, CAS# 25646-71-3], and CD-4 [2-[(4-amino-m-tolyl)ethylamino]ethanol sulfate, CAS#25646-77-9], all available from Eastman Kodak Co., Rochester, NY, and the like. Further information regarding color developers is disclosed in, for example, SPSE Handbook of Photographic Science and Engineering, W. Thomas, Jr., ed., John Wiley & Sons (New York 1973); Neblette's Handbook of Photography and Reprography , 7th ed., J. Sturge, ed., Van Nostrand Reinhold Co. (New York 1977); Modern Photographic Processing , G. Haist, John Wiley & Sons (New York 1979); U.S. Patents 477,486, 1,799,568, 1,712,716, 1,758,892, 1,758,762, 2,610,122 2,385,763, 3,622,629, 3,762,922, 1,937,844, 3,265,499, 3,134,673, 3,091,530, 2,193,015, 2,688,549, 2,688,548, 2,691,589, 3,672,896, 2,289,367, 3,241,967, 3,330,839, 2,685,516, 2,852,374, 3,672,891, 1,939,231, 2,181,944, 3,459,549, 1,390,260, 1,663,959, 2,587,276, 2,857,275, 2,857,274, 3,293,034, 3,287,125, 3,287,124, 3,455,916, 2,843,481, 3,723,117, 2,596,978, 1,082,622, 2,220,929, 2,419,975, 2,685,514, 3,782,949, 853,643, 2,943,109, and 2,397,676; British Patents 1,191,535, 295,939, 1,210,417, 1,273,081, 1,003,783, 928,671, 989,383, 430,264, 767,700, 783,727, 542,502, 650,911, 679,677, 728,368, 757,271, 997,033, 761,301, 954,106, 679,678, 757,840, 459,665, 479,466, 1,122,085, 1,327,033, 1,191,535, 1,327,034, 1,327,035, 1,154,385, 943,928, 466,625, and 466,626; French Patents 1,480,920, 1,380,163, and 325,385; German Patents 945,606, 955,025, 158,741, 875,048, 870,418, 945,606, 1,151,175, 1,047,618, 1,079,455, 34,342, 36,746, and 97,596; Canadian Patent 931,009. In silver halide development processes, the developer generally is oxidized by interaction with the silver halide in the film. For the instant invention, the developer is reacted with an oxidant or oxidizing agent. The developer, upon oxidation, is converted to a form capable of reacting with a dye coupler to form a dye. For example, a developer of the N,N-dialkyl-p-phenylenediamine class, upon oxidation, is converted to the quinone diimine, as follows: wherein X is an anion derived from the oxidant. The oxidizing composition generally comprises a liquid vehicle and an oxidizing agent, and functions as a color forming component in the process of the present invention. For the purpose of simplicity, the developing composition will at times hereinafter be referred to as an ink. Any liquid can be employed as the major component of the liquid vehicle, provided that it dissolves or disperses the components of the composition and is of a viscosity appropriate for the selected drop ejector. For example, in thermal ink jet printing systems, a preferred liquid vehicle is water. In other drop ejectors, such as those employing continuous stream processes, piezoelectric ink jet printers, acoustic ink jet printers, and the like, other liquids can also be employed, such as hydrocarbons, glycols, ethers, sulfones such as sulfolane, pyrrolidinones such as 2-pyrrolidinone and N-methyl pyrrolidinone, other dipolar aprotic solvents, and the like, as well as mixtures thereof. The oxidizing composition can also contain other components which might improve its performance as an ink jet ink, such as humectants, penetrants, cosolvents, jetting aids, or the like, set forth in more detail hereinbelow. The oxidizing composition typically contains the oxidizing agent in an amount of from about 0.05 to about 15 percent by weight of the oxidizing composition, preferably from about 0.1 to about 10 percent by weight of the oxidizing composition, and more preferably from about 0.5 to about 5 percent by weight of the oxidizing composition, although the amount can be outside of these ranges. The reaction between the oxidizing agent and the color developer is stoichiometric, and to obtain full color intensity, a full stoichiometric amount or an excess amount of oxidizing agent is employed to oxidize all of the developer. In one embodiment of the present invention, color tone or intensity is controlled by the deposition of variable stoichiometrically insufficient amounts of oxidizing agent. Examples of suitable oxidizing agents include potassium peroxydisulfate, ammonium peroxydisulfate, hydrogen peroxide, alkylhydroperoxides, of the general formula wherein R 1 , R 2 , and R 3 each, independently of the others, are alkyl groups, preferably with 1 or 2 carbon atoms, although the number of carbon atoms can be outside of this range, or alkylaryl groups, preferably with from 7 to about 9 carbon atoms, although the number of carbon atoms can be outside of this range, such as t-butyl hydroperoxide, cumene hydroperoxide, and the like, dialkylperoxides, of the general formula wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each, independently of the others, are alkyl groups, preferably with 1 or 2 carbon atoms, although the number of carbon atoms can be outside of this range, or alkylaryl groups, preferably with from 7 to about 9 carbon atoms, although the number of carbon atoms can be outside of this range, such as di-t-butylperoxide, dicumylperoxide, and the like, wherein the class of dialkyl peroxides also includes substituted dialkyl peroxides, such as t-butylperoxybenzoate, t-butylperoxy isopropyl carbonate, and the like, diacylperoxides, of the general formula wherein R 1 and R 2 are each, independently of the others, alkyl groups, preferably with 1 or 2 carbon atoms, aryl groups, preferably with from 6 to about 9 carbon atoms, or alkylaryl groups, preferably with from 7 to about 9 carbon atoms, such as benzoyl peroxide, pivaloyl peroxide, and the like, peroxycarbonates, such as sodium percarbonate and the like, and the like, as well as mixtures thereof. Peroxides such as the above are available from, for example, Aldrich Chemical Co., Milwaukee, Wl, and Alfa Aesar, division of Johnson Matthey Catalog Co., Inc., Ward Hill, MA. As indicated, the developer in its oxidized form can react with a dye coupler to form a dye. The coloring composition generally comprises a liquid vehicle and a dye coupler, and functions as a color forming component in the process of the present invention. For the purpose of simplicity, the developing composition will at times hereinafter be referred to as an ink. Any liquid can be employed as the major component of the liquid vehicle, provided that it dissolves or disperses the components of the composition and is of a viscosity appropriate for the selected drop ejector. For example, in thermal ink jet printing systems, a preferred liquid vehicle is water. In other drop ejectors, such as those employing continuous stream processes, piezoelectric ink jet printers, acoustic ink jet printers, and the like, other liquids can also be employed, such as hydrocarbons, glycols, ethers, sulfones such as sulfolane, pyrrolidinones such as 2-pyrrolidinone and N-methyl pyrrolidinone, other dipolar aprotic solvents, and the like, as well as mixtures thereof. The coloring composition can also contain other components which might improve its performance as an ink jet ink, such as humectants, penetrants, cosolvents, jetting aids, or the like, set forth in more detail hereinbelow. The coloring composition typically contains the dye coupler in an amount of from about 0.05 to about 15 percent by weight of the coloring composition, preferably from about 0.1 to about 10 percent by weight of the coloring composition, and more preferably from about 0.5 to about 5 percent by weight of the coloring composition, although the amount can be outside of these ranges. The reaction between the dye coupler and the color developer is stoichiometric, and to obtain full color intensity, a full stoichiometric amount or an excess amount of oxidizing agent is employed to oxidize all of the developer. In one embodiment of the present invention, color tone or intensity is controlled by the deposition of variable stoichiometrically insufficient amounts of dye coupler. Examples of suitable cyan dye couplers include substituted phenols and α-naphthols, including those of the general formulae and the like, wherein X is a hydrogen atom, a chlorine atom, an alkoxy group (-OR), an aryloxy group (-OAr), or a thioaryl group (-SAr), n is an integer representing the number of repeat -CH 2 - units, and preferably is from about 1 to about 3, R and R' each, independently of the others, are organic segments which provide desired solubility characteristics, such as alkyl groups, preferably with from 1 to about 22 carbon atoms, or polar solubilizing groups, such as -COOH or -SO 3 H, and Ar is an aryl group, including substituted aryl groups, preferably with from 6 to about 14 carbon atoms, or an arylalkyl group, including substituted arylalkyl groups, preferably with from 7 to about 36 carbon atoms. Amphiphilic cyan couplers, such as 1-N-stearoyl-3-N-(1'-hydroxy-2'-naphthoyl)-phenylenediamine-4-sulphonic acid, believed to be of the formula or a salt thereof, such as a sodium salt, are particularly preferred for water based ink formulations such as those suitable for thermal ink jet printing. Examples of suitable yellow dye couplers include β-ketocarboxamides and pivaloylacetanilides, of the general formulae and wherein X is a hydrogen atom, a chlorine atom, a -OSO 2 R group, a -SO 2 R group, a -O-C(=O)R group, or a -SAr group, wherein R is an alkyl group, preferably with from 1 to about 22 carbon atoms, and Ar is an aryl group, preferably with from 6 to about 22 carbon atoms, Y, Z, and "ballast" are each, independently of the others, solubilizing groups, such as an alkyl group (-R), a carboxyl group, a sulfonyl group, or an alkylamide group (-NH-COR), wherein R is an alkyl group, preferably with from 1 to about 22 carbon atoms. Substituents Y and Z can be used to attach ballasting or solubilizing groups and to alter the reactivity of the coupler and the hue of the resulting dyes. Coupling to the oxidized developer generally occurs with displacement of substituent X. Specific examples of suitable yellow dye couplers include 4-(p-toluenesulfonylamino)-ω-benzoylacetanilide, α-benzoyl-o-methoxyacetanilide, dichloroacetanilide, and the like. Amphiphilic yellow couplers, such as para -stearoylaminobenzoyl-acetanilide-3',5'-dicarboxylic acid, believed to be of the formula or meta -stearoylamino-benzoyl-acetanilide- para '-carboxylic acid, believed to be of the formula or salts thereof, such as the sodium salts, are particularly preferred for water based ink formulations such as those suitable for thermal ink jet printing. Examples of suitable magenta dye couplers include those derived from the 1-aryl-2-pyrazolin-5-ones, of the general formulae and wherein X is ―S―R ―S―Ar or ―N=N―Ar, R, R', and R" each, independently of the others, are organic segments which provide desired solubility characteristics, such as alkyl groups, preferably with from 1 to about 22 carbon atoms, or polar solubilizing groups, such as -COOH or -SO 3 H, and Ar is an aryl group, including substituted aryl groups, preferably with from 6 to about 14 carbon atoms, or an arylalkyl group, including substituted arylalkyl groups, preferably with from 7 to about 36 carbon atoms, the pyrazolo-(3,2,-c)-5-triazoles and related isomers, of the general formula wherein X is a chlorine atom, a thioalkyl group (-SR), a thioaryl group (-SAr), or an aryloxy group (-OAr), n is an integer representing the number of repeat -CH 2 - units, and preferably is from 0 to about 3, R is an alkyl group, preferably with from 1 to about 22 carbon atoms, Ar is an aryl group, preferably with from 6 to about 22 carbon atoms, and "ballast" represents a solubilizing group, such as an alkyl group (-R), a carboxyl group, a sulfonyl group, or an alkylamide group (-NH-COR), wherein R is an alkyl group, preferably with from 1 to about 22 carbon atoms, and the like. Also suitable are cyanoacetyl derivatives of cyclic systems, such as cyanoacetylcoumarone, indazolones, of the general formula wherein A is a hydrogen atom or a substituent selected to optimize characteristics such as solubility, reactivity, hue, stability, or the like. For example, substituents such as sulfonate (-SO 3 ) or carboxylate (-COOH) can enhance water solubility and suitability for use in aqueous liquids. Specific examples of suitable magenta dye couplers include 2-cyanoacetyl coumarone, 1-(2,4,6-trichlorophenyl)-3-p-nitroanilino-2-pyrazoline-5-one, and the like. Amphiphilic magenta couplers, such as 3-heptadecyl-1-(4'-sulfophenyl)-2-pyrazoline-5-one, believed to be of the formula wherein X is a hydrogen atom or a chlorine atom, or 1-(5'-sulpho-3'-stearoylaminophenyl)-2-pyrazoline-5-one, believed to be of the formula or salts thereof, such as the sodium salts, are particularly preferred for water based ink formulations such as those suitable for use in thermal ink jet printing. Further information regarding dye couplers is disclosed in, for example, SPSE Handbook of Photographic Science and Engineering , W. Thomas, Jr., ed., John Wiley & Sons (New York 1973); Neblette's Handbook of Photography and Reprography , 7th ed., J. Sturge, ed., Van Nostrand Reinhold Co. (New York 1977); and "The Chemistry of Color Photography," W. C. Guida et al., Journal of Chemical Education , Vol. 52, No. 10, p. 622 (October 1975). At least one of the developing composition, coloring composition, and oxidizing composition is of a pH sufficiently alkaline to drive the coupling reaction between the oxidized developer and the dye coupler. Accordingly, at least one of these compositions typically also includes a base and/or a buffer. While it is generally simplest to include the base and/or buffer in the oxidizing composition, the developing composition and/or the coloring composition can also have its pH adjusted to an appropriate level to enable the coupling reaction. The composition(s) containing a base and/or a buffer, and having its pH adjusted to enable the coupling reaction, will hereinafter be referred to as the pH adjusted composition. The pH of the pH adjusted composition generally is over about 9, and preferably is from about 10 to about 13, although the value can be outside of this range. Examples of compositions which can be added to the pH adjusted composition to obtain the desired pH include hydroxides such as sodium hydroxide, tetramethylammonium hydroxide, and the like, potassium carbonate, sodium phosphate, or the like, as well as mixtures thereof. The fixing composition generally comprises a liquid vehicle and a fixative. For the purpose of simplicity, the fixing composition will at times hereinafter be referred to as an ink. Any liquid can be employed as the major component of the liquid vehicle, provided that it dissolves or disperses the components of the composition and is of a viscosity appropriate for the selected drop ejector. For example, in thermal ink jet printing systems, a preferred liquid vehicle is water. In other drop ejectors, such as those employing continuous stream processes, piezoelectric ink jet printers, acoustic ink jet printers, and the like, other liquids can also be employed, such as hydrocarbons, glycols, ethers, sulfones such as sulfolane, pyrrolidinones such as 2-pyrrolidinone and N-methyl pyrrolidinone, other dipolar aprotic solvents, and the like, as well as mixtures thereof. The fixing composition can also contain other components which might improve its performance as an ink jet ink, such as humectants, penetrants, cosolvents, jetting aids, or the like, set forth in more detail hereinbelow. Typically, the fixative is a mixture of a weakly acidic reagent and a reducing agent. The acid is present in the fixing composition in an amount sufficient to neutralize base from the developing composition, coloring composition, and/or oxidizing composition in the initially formed image. The reducing agent is present in the fixing composition in an amount sufficient to quench excess oxidizing components in the initially formed image. The fixing composition typically contains the fixative mixture in an amount of from about 0.1 to about 10 percent by weight of the fixing composition, preferably from about 1 to about 5 percent by weight of the fixing composition, although the amount can be outside of these ranges. Examples of suitable weakly acidic fixative components include ascorbic acid, phthalic acid, benzoic acid, acetic acid, maleic acid succinic acid, poly(acrylic acid), poly(methacrylic acid), copoly(styrene/maleic acid), copoly(methylvinylether/maleic acid), and the like, as well as mixtures thereof. Examples of suitable reducing fixative components include ascorbic acid, sodium sulfite, sodium bisulfite, glucose and other reducing sugars, and the like, as well as mixtures thereof. As stated hereinabove, the developing composition, the oxidizing composition, the coloring composition, and the fixing composition (hereinafter collectively referred to as inks or ink compositions of or for the present invention) all generally have compositions which render them suitable for use as ink jet inks in an ink jet printing apparatus. Ink jet inks generally contain an aqueous liquid vehicle. The liquid vehicle can consist solely of water, or it can comprise a mixture of water and a water soluble or water miscible organic component, such as ethylene glycol, propylene glycol, diethylene glycols, glycerine, dipropylene glycols, polyethylene glycols, polypropylene glycols, amides, ethers, urea, substituted ureas, ethers, carboxylic acids and their salts, esters, alcohols, organosulfides, organosulfoxides, sulfones (such as sulfolane), alcohol derivatives, carbitol, butyl carbitol, cellusolve, tripropylene glycol monomethyl ether, ether derivatives, amino alcohols, ketones, N-methylpyrrolidinone, 2-pyrrolidinone, cyclohexylpyrrolidone, hydroxyethers, amides, sulfoxides, lactones, polyelectrolytes, methyl sulfonylethanol, imidazole, betaine, and other water soluble or water miscible materials, as well as mixtures thereof. When mixtures of water and water soluble or miscible organic liquids are selected as the liquid vehicle, the water to organic ratio typically ranges from about 100:0 to about 30:70, and preferably from about 97:3 to about 40:60. The non-water component of the liquid vehicle generally serves as a humectant or cosolvent which has a boiling point higher than that of water (100°C). In the ink compositions of the present invention, the liquid vehicle is typically present in an amount of from about 80 to about 99.9 percent by weight of the ink, and preferably from about 90 to about 99 percent by weight of the ink, although the amount can be outside these ranges. Other optional additives to the inks of the present invention include pH controlling agents such as acids or, bases, phosphate salts, carboxylates salts, sulfite salts, amine salts, and the like, present in an amount of from 0 to about 1 percent by weight of the ink and preferably from about 0.01 to about 1 percent by weight of the ink, or the like. One or more surfactants or wetting agents can also be added to the ink. These additives may be of the cationic, anionic, or nonionic types. Suitable surfactants and wetting agents include sodium lauryl sulfate, Tamol® SN, Tamol® LG, those of the Triton® series available from Rohm and Haas Company, those of the Marasperse® series, those of the Igepal® series available from GAF Company, those of the Tergitol® series, and other commercially available surfactants. These surfactants and wetting agents are present in any desired or effective amounts, generally from 0 to about 15 percent by weight of the ink, and preferably from about 0.01 to about 8 percent by weight of the ink, although the amount can be outside of this range. The ink compositions used in the present invention are generally of a viscosity suitable for use in thermal ink jet printing processes. At room temperature (i.e., about 25°C), typically, the ink viscosity is no more than about 10 mPa.s, and preferably is from about 1 to about 5 mPa.s, more preferably from about 1 to about 4 mPa.s, although the viscosity can be outside this range, particularly for applications such as acoustic ink jet printing. Ink compositions used in the present invention can be of any suitable or desired pH. At least one of the developing composition, coloring composition, and oxidizing composition is sufficiently alkaline to foster the coupling reaction between the color developer and the dye coupler. Ink compositions suitable for ink jet printing can be prepared by any suitable process. Typically, the inks are prepared by simple mixing of the ingredients. One process entails mixing all of the ink ingredients together and filtering the mixture to obtain an ink. Inks can be prepared by mixing the ingredients, heating if desired, and filtering, followed by adding any desired additional additives to the mixture and mixing at room temperature with moderate shaking until a homogeneous mixture is obtained, typically from about 5 to about 10 minutes. Alternatively, the optional ink additives can be mixed with the other ink ingredients during the ink preparation process, which takes place according to any desired procedure, such as by mixing all the ingredients, heating if desired, and filtering. In one specific embodiment of the present invention, the ink jet printing apparatus employs a thermal ink jet process wherein the ink in the nozzles is selectively heated in an imagewise pattern, thereby causing droplets of the ink to be ejected in imagewise pattern. In another specific embodiment, the printing apparatus employs an acoustic ink jet process, wherein droplets of the ink are caused to be ejected in imagewise pattern by acoustic beams. Other methods, such as piezoelectric drop on demand ink jet printing, continuous stream ink jet printing, hot melt ink jet printing, or the like, can also be employed. Any suitable substrate or recording sheet can be employed, including plain papers such as Xerox® 4024 papers, Xerox® Image Series papers, Courtland 4024 DP paper, ruled notebook paper, bond paper, silica coated papers such as Sharp Company silica coated paper, JuJo paper, and the like, transparency materials, fabrics, textile products, plastics, polymeric films, inorganic substrates such as metals and wood, and the like. In a preferred embodiment, the process entails printing onto a porous or ink absorbent substrate, such as plain paper. In embodiments of the present invention wherein special substrates or receiver sheets are used, it can be advantageous to use a paper coated with absorbing layers for specific dye couplers. As disclosed in, for example, Japanese Patent Publication JP 9030107 A, when coloring agents are localized at a specific depth in the receiving sheet, improved color reproduction can be achieved because agents of different color tone do not mingle at the same depth in the absorbing layer. The specific embodiments of the present invention which enable production of gray-level images have been illustrated hereinabove in the specific context of photographic, including color photographic, materials and development processes. These embodiments of the present invention, namely (1) providing a multiplicity of intensity or "gray" levels within a particular color by controlling the time between the point at which the developing composition, oxidizing composition, and coloring composition all come together and the point at which the fixing composition is deposited; (2) providing a multiplicity of intensity or "gray" levels within a particular color by jetting fixed amounts of one of (a) the developing composition, (b) the coloring composition, or (c) the oxidizing composition onto the substrate in combination with varying amounts the other two compositions, with the limited composition being present in reaction limiting quantities with respect to the other two compositions; and (3) jetting the developing composition, coloring composition(s), and oxidizing composition in an imagewise pattern so that the overlap of droplets of these three compositions is controlled, thereby modulating pixel size to realize variable spot sizes, can also be realized by a multiplicity of other specific chemistries. In some of these embodiments, no fixative is needed; in other embodiments, only two color forming liquid compositions are used instead of three. One embodiment of the present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein at time T 1 , the color forming composition has formed an image on the substrate, at time T 2 , the reacting composition is deposited onto a first portion P 1 of the image, and at time T 3 , the reacting composition is deposited onto a second portion P 2 of the image, wherein time period T 1 to T 2 is less than time period T 1 to T 3 , thereby resulting in second portion P 2 having a different color intensity from first portion P 1 . Another embodiment of the present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein one of (i) the color forming composition and (ii) the reacting composition is applied to the substrate in fixed volumes per pixel, and the other of (i) and (ii) is applied to the substrate in varying volume per pixel, thereby varying the intensity of color of the printed image. Yet another embodiment of the present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein droplets of the color forming composition and droplets of the reacting composition are applied to the substrate in an imagewise pattern so that droplets of color forming composition and reacting composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the color forming composition and reacting composition overlap. For example, the present invention includes embodiments wherein more than one color forming agent is combined into a single "ink" or liquid composition for printing. For example, the color developer and the dye coupler can be included in a single "ink" or liquid composition, thereby eliminating the need for a separate developing composition and the need for a separate printhead and cartridge for printing said developing composition. In this embodiment, the use of quinone color developers may be preferred over diamine color developers in view of the higher reactivity (and potential unstability in this embodiment) of the diamines. In addition, dye developer molecules, commonly used in instant photography, can be used in place of distinct color developer and dye coupler molecules. In this embodiment, the color developer and the dye coupler are covalently bonded in a single molecule. Otherwise, the process is analogous to that described hereinabove with respect to materials commonly used in conventional photography. Further information on the dye developer molecules and processes for the use thereof is disclosed in, for example, "Color Photography, Instant," by Vivian K Walworth and Stanley H. Mervis in The Encyclopedia of Chemical Technology , 4th Edition, Vol. 6, pp.1003-1048, John Wiley & Sons, New York (1993); U.S. Patent 3,443,940; U.S. Patent 2,983,606; U.S. Patent 3,255,001; U.S. Patent 3,201,384; U.S. Patent 3,246,985; U.S. Patent 3,857,855; U.S. Patent 4,264,701; M. Idelson, I.R. Karday, B. H. Mark, D. O. Richter, and V. H. Hooper, Inorg. Chem. 6 , 450 (1967); E. M. Idelson, Dyes and Pigments 3 , 191 (1982); and H. G. Rogers, E. M. Idelson, R. F. W. Cieciuch, and S. M. Bloom, J. Photogr. Sci. 22 , 138 (1974). Further, leuco or vat dyes, which are typically colorless unless and until reacted with an oxidizing agent or pH altering agent, can be used in combination with oxidative reagents or pH-altering reagents to visualize them. In this embodiment, no fixative is needed. Otherwise, the process is analogous to that described hereinabove with respect to materials commonly used in conventional photography. Further information on leuco and vat dyes and processes for the use thereof is disclosed in, for example, IBM Technical Disclosure Bulletin , Vol. 23, No. 4, p. 1387 (September 1980); U.S. Patent 1,055,115; British Patent 15055/12; and German Patent 257,167. Additionally, metal vanadates and polyphenolic compounds, such as gallic acid, tannic acid, dihydroxybenzene carboxylic acids, or dihydroxynaphthalene carboxylic acids, can be used to create durable black images. Otherwise, the process is analogous to that described hereinabove with respect to materials commonly used in conventional photography. Further information on metal vanadates and polyphenolics and processes for the use thereof is disclosed in, for example, Japanese Patent Publication JP 77049366 B, British Patent Publication GB 1398334, and German Patent Publication DE 2505077. EXAMPLE I A developer composition was prepared by admixing 5 parts by weight CD-3 developer (4-(N-ethyl-N-2-methanesulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate monohydrate, obtained from Eastman Kodak Co., Rochester, NY), 70 parts by weight of deionized water, 11 parts by weight of tripropylene glycol monomethyl ether (DOWANOL® TPM, obtained from Dow Chemical Co.), 10 parts by weight of dipropylene glycol, 0.05 parts by weight of polyethylene oxide (poly(ethylene glycol)-bisphenol A diglycidyl ether adduct, molecular weight 18,500, obtained from Polysciences), and 3 parts by weight of potassium carbonate. An oxidizing composition was prepared by admixing 74 parts by weight of deionized water, 11 parts by weight of tripropylene glycol monomethyl ether (DOWANOL® TPM, obtained from Dow Chemical Co.), 10 parts by weight of dipropylene glycol, 0.05 parts by weight of polyethylene oxide (poly(ethylene glycol)-bisphenol A diglycidyl ether adduct, molecular weight 18,500, obtained from Polysciences), 3 parts by weight of potassium carbonate, and 3 parts by weight of potassium peroxodisulfate (K 2 S 2 O 8 ). A cyan coloring composition was prepared by admixing 74 parts by weight of deionized water, 11 parts by weight of tripropylene glycol monomethyl ether (DOWANOL® TPM, obtained from Dow Chemical Co.), 10 parts by weight of dipropylene glycol, 0.05 parts by weight of polyethylene oxide (poly(ethylene glycol)-bisphenol A diglycidyl ether adduct, molecular weight 18,500, obtained from Polysciences), and 5 parts by weight of a α-naphthol cyan dye coupler (N-(2-acetamidophenethyl)-1-hydroxy-2-naphthamide, obtained from Fisher Scientific (ACROS ORGANICS), Pittsburgh, PA). A magenta coloring composition was made by the same process except that the dye coupler used was 5 parts by weight of a pyrazolinone magenta dye coupler (1-(2,4,6-trichlorophenyl)-3-(p-nitroanilino)-2-pyrazoline-5-one, obtained from Fisher Scientific (ACROS ORGANICS), Pittsburgh, PA). A yellow coloring composition was made by the same process except that the dye coupler used was 5 parts by weight of a β-ketocarboxamide yellow dye coupler (2-benzoylacetanilide, obtained from Fisher Scientific (ACROS ORGANICS), Pittsburgh, PA). A fixing composition was prepared by admixing 70 parts by weight of deionized water, 11 parts by weight of tripropylene glycol monomethyl ether (DOWANOL® TPM, obtained from Dow Chemical Co.), 10 parts by weight of dipropylene glycol, 0.05 parts by weight of polyethylene oxide (poly(ethylene glycol)-bisphenol A diglycidyl ether adduct, molecular weight 18,500, obtained from Polysciences), 5 parts by weight of poly(methyl vinyl ether/maleic acid) (GANTREZ MS-955, obtained from GAF Corp., Wayne, NJ), and 4 parts by weight of sodium sulfite (Na 2 SO 3 ). A microliter syringe was then used to deposit controlled volumes of the developer composition onto XEROX® Color Xpressions® paper. Stoichiometric quantities of the oxidizing composition and the cyan coloring composition were then deposited directly onto the spots containing the developer composition to yield intensely colored cyan spots. The process was repeated with varying volumes of the oxidizing composition to yield cyan colored spots of varying intensity. The process was repeated so that the droplets of developing composition, oxidizing composition, and coloring composition did not overlap completely. Intensely colored cyan spots of fractional size (compared to those obtained with 100 percent droplet overlap) were obtained only in those areas wherein the droplets of developing composition, oxidizing composition, and coloring composition overlapped. The reactions were quenched by deposition of a stoichiometric excess of the fixing composition onto the developed spots.

Claims: A process which comprises (a) incorporating into an ink jet printing apparatus (1) a developing composition comprising a liquid vehicle and a color developer; (2) an oxidizing composition comprising a liquid vehicle and an oxidizing agent; (3) a coloring composition comprising a liquid vehicle and a dye coupler; and (4) a fixing composition comprising a liquid vehicle and a fixative; (b) causing droplets of the developing composition to be ejected in an imagewise pattern onto the substrate; (c) causing droplets of the oxidizing composition to be ejected in an imagewise pattern onto the substrate; (d) causing droplets of the coloring composition to be ejected in an imagewise pattern onto the substrate; and (e) causing droplets of the fixing composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising all four of the developing composition, the oxidizing composition, the coloring composition, and the fixing composition, said portions forming a printed image. The process according to claim 1 wherein first, second, and third coloring compositions are incorporated into the printing apparatus and caused to be ejected onto the substrate, wherein the first coloring composition comprises a liquid vehicle and a cyan dye coupler, the second coloring composition comprises a liquid vehicle and a magenta dye coupler, and the third coloring composition comprises a liquid vehicle and a yellow dye coupler. The process according to claim 1 or 2 wherein two of (i) the developing composition, (ii) the coloring composition, and (iii) the oxidizing composition are applied to the substrate in fixed volumes per pixel, and the remaining composition of (i), (ii), and (iii) is applied to the substrate in varying volume per pixel, thereby varying the intensity of color of the printed image. The process according to claim 3 wherein the remaining composition is applied to the substrate through a printhead having a plurality of ink channels, wherein droplets of the remaining composition of at least two different volumes are formed by jetting the remaining composition from the ink channels. The process according to any of claims 1 to 4 wherein droplets of the developing composition, droplets of the coloring composition, and droplets of the oxidizing composition are applied to the substrate in an imagewise pattern so that droplets of developing composition, coloring composition, and oxidizing composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the developing composition, coloring composition, and oxidizing composition overlap. The process according to any of claims 1 to 5 wherein at time T 1 , the developing composition, oxidizing composition, and coloring composition have overlapped on the substrate to react and form an image, at time T 2 , the fixing composition is deposited onto a first portion P 1 of the image, and at time T 3 , the fixing composition is deposited onto a second portion P 2 of the image, wherein time period T 1 to T 2 is less than time period T 1 to T 3 , thereby resulting in second portion P 2 having a different color intensity from first portion P 1 . A process which comprises (a) incorporating into an inkjet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein at time T 1 , the color forming composition has formed an image on the substrate, at time T 2 , the reacting composition is deposited onto a first portion P 1 of the image, and at time T 3 , the reacting composition is deposited onto a second portion P 2 of the image, wherein time period T 1 to T 2 is less than time period T 1 to T 3 , thereby resulting in second portion P 2 having a different color intensity from first portion P 1 . A process which comprises (a) incorporating into an inkjet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein one of (i) the color forming composition and (ii) the reacting composition is applied to the substrate in fixed volumes per pixel, and the other of (i) and (ii) is applied to the substrate in varying volume per pixel, thereby varying the intensity of color of the printed image. A process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein droplets of the color forming composition and droplets of the reacting composition are applied to the substrate in an imagewise pattern so that droplets of color forming composition and reacting composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the color forming composition and reacting composition overlap, wherein the color forming composition comprises a color developer molecule and the reacting composition comprises an oxidizing agent. The process according to claim 7 or 8, wherein the color forming composition comprises (a) a color developer molecule and the reacting composition comprises an oxidizing agent; (b) a leuco dye or vat dye and the reacting composition comprises an oxidizing agent or pH altering agent; (c) a metal vanadate and the reacting composition comprises a polyphenolic compound; (d) a mixture of two of (i) a developing composition, (ii) a coloring composition, and (iii) an oxidizing composition, and the reacting composition comprises the remaining composition of (i), (ii), and (iii). A process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein droplets of the color forming composition and droplets of the reacting composition are applied to the substrate in an imagewise pattern so that droplets of color forming composition and reacting composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the color forming composition and reacting composition overlap, wherein the color forming composition comprises a leuco dye or vat dye and the reacting composition comprises an oxidizing agent or pH altering agent. A process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein droplets of the color forming composition and droplets of the reacting composition are applied to the substrate in an imagewise pattern so that droplets of color forming composition and reacting composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the color forming composition and reacting composition overlap, wherein the color forming composition comprises a metal vanadate and the reacting composition comprises a polyphenolic compound. A process which comprises (a) incorporating into an ink jet printing apparatus (1) a color forming composition comprising a liquid vehicle and at least one color forming agent; and (2) a reacting composition comprising a liquid vehicle and at least one material capable of reacting with the color forming agent to cause a desired color to form; (b) causing droplets of the color forming composition to be ejected in an imagewise pattern onto the substrate; and (c) causing droplets of the reacting composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising both the color forming composition and the reacting composition, said portions forming a printed image, wherein droplets of the color forming composition and droplets of the reacting composition are applied to the substrate in an imagewise pattern so that droplets of color forming composition and reacting composition overlap in a controlled pattern, thereby forming spots of varying sizes on the substrate, said spots being formed in areas where droplets of the color forming composition and reacting composition overlap, wherein the color forming composition comprises a mixture of two of (i) a developing composition, (ii) a coloring composition, and (iii) an oxidizing composition, and the reacting composition comprises the remaining composition of (i), (ii), and (iii).

Inventors: LIMBURG WILLIAM W, LUCA DAVID J, MCGRANE KATHLEEN M, SMITH THOMAS W, LIMBURG, WILLIAM W., LUCA, DAVID J., MCGRANE, KATHLEEN M., SMITH, THOMAS W.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1999
Main classification: B41J2
IPC codes: B41J2, C09D11, B41M5