Abstract:
An ink jet printing apparatus for producing an image on an ink receiver in response to an in put image, comprising: at least one ink reservoir for providing ink for printing the image; a print head means coupled to an ink receiver and at least one ink reservoir, for disposing ink spots on the ink receiver; and a processing tank coupled to the ink receiver, for providing a fluid for treating the ink spots disposed on the receiver thereby improving the stability, durability and quality of the image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to commonly assigned, concurrently filed: 
     (1) U.S. patent application Ser. No. 09/083,673, filed May 22, 1998, entitled &#34;APPARATUS WITH SPRAY BAR FOR IMPROVED DURABILITY&#34; of Wen et al., 
     (2) U.S. patent application Ser. No. 09/083,876, filed May 22, 1998, entitled &#34;INK JET PRINTING APPARATUS WITH PRINT HEAD FOR IMPROVED IMAGE QUALITY&#34; of Wen et al., 
     (3) U.S. patent application Ser. No. 09/083,605, filed May 22, 1998, entitled &#34;PIGMENTED INK JET PRINTS OVERCOATED WITH HARDENERS&#34; of Erdtmann et al., 
     (4) U.S. patent application Ser. No. 09/083,875, filed May 22, 1998, entitled &#34;INK JET IMAGES ON PVA OVERCOATED WITH HARDNER SOLUTION&#34; of Erdtmann et al., 
     (5) U.S. patent application Ser. No. 09/083,871, filed May 22, 1998, entitled &#34;WATERFST INK JET IMAGES TREATED WITH HARDNERS&#34; of Erdtmann et al. 
     The disclosures of these related applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a apparatus and to a method of improving the image stability of the prints provided by ink jet printing. 
     BACKGROUND OF THE INVENTION 
     In the field of ink jet printing, there have existed long felt needs for making images waterfast and also durable against physical abrasion. One method practiced in the art is to laminate a clear film on the printed image after the image has been printed on a receiver. However, such a lamination method is time consuming and often produces undesirable waste due to print handling and unusable prints caused by the air bubbles trapped between the lamination sheet and the ink receiver. The lamination method also increases media and equipment costs because of the additional sheet and apparatus involved. 
     U.S. Pat. No. 5,635,969 discloses an ink jet printer that includes a print head for depositing an ink precursor on the ink recording medium. The ink precursor conditions the ink recording medium before colored ink spots are placed on the conditioned areas. The preconditioning of the recording medium can be used for reducing paper cockle and color bleed, for decreasing dry time, and for improving dot shape. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an ink jet apparatus that produces prints with improved image stability and durability. It is a further object of the present invention to provide such an ink jet apparatus that is simple and easy to use. It is a further object of the present invention to provide such an ink jet apparatus that operates in a time- and energy-efficient manner. 
     These objects are achieved by an ink jet printing apparatus for producing an image on an ink receiver in response to an in put image, comprising: at least one ink reservoir for providing ink for printing the image; a print head means coupled to an ink receiver and at least one ink reservoir, for disposing ink spots on the ink receiver; a processing tank containing a fluid for treating the ink spots disposed on the receiver, thereby improving the stability, durability, and quality of the image. 
     Images produced by the apparatus and method of the invention are waterfast and have good wet adhesion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a side view of a printing apparatus in accordance with the present invention showing the printing of an ink jet image; 
     FIG. 2 is top view of the ink jet printing apparatus of FIG. 1; 
     FIG. 3a is a side view of the processing tank before the receiver is immersed in the fluid for treatment; and 
     FIG. 3b is a side view of the processing tank when the receiver is immersed in the fluid for treatment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described with relation to an apparatus that is capable of producing an ink jet print and providing a protection fluid on the print. 
     Referring to FIG. 1, a ink jet printing apparatus 10 is shown to comprise a computer 20, ink jet print heads 31-34, ink reservoirs 41-44, a receiver transport 70, a platen 90, and a processing tank 40 (shown in FIG. 3a and 3b). An ink receiver 80 is shown to be supported by a the platen 90. The computer 20 can include a microprocessor, a memory, a monitor, a user interface, and electronic control of the print heads 31-34. Stored within the memory of the computer are image processing programs for color and tone conversion, halftoning and so on, which are well known in the art. In the present invention, the ink jet printing apparatus 10 can be a drop-on-demand ink jet printer that selectively activates the ink jet print heads 31-34 to transfer ink drops 100 to produce ink spots 110 in an imagewise pattern on the receiver 80. The ink jet printing apparatus 10 can also be a continuous ink jet printer as is also well known in the art. The print heads 31-34 can comprise one or a plurality of ink nozzles. The print heads 31-34 can exist in different forms, for example, piezo-electric or thermal ink jet print heads. An example of a piezoelectric ink jet print head is shown in commonly assigned U.S. Pat. No. 5,598,196. 
     The print heads 31-34 are labeled K for black ink; C for cyan ink; M for magenta ink; and Y for yellow ink. The ink reservoirs 41-44 respectively contain black, cyan, magenta, and yellow inks that are supplied to the ink jet print heads 31-34 of the corresponding colors. Although not shown in FIG. 1, the ink jet printing apparatus 10 can also include print heads and reservoirs for other colored inks such as red, green, blue, etc. Several ink densities can also be used for each color. The colorants in the inks can be dyes or pigments. 
     The ink receiver 80 can be common paper having sufficient fibers to provide a capillary force to draw the ink from the mixing chambers into the paper. Synthetic papers can also be used. The receiver 80 can comprise a layer that is porous to the inks, an ink absorbing layer, as well as materials with a strong affinity and mordanting effect for the inks. Exemplary receivers are disclosed in U.S. Pat. No. 5,605,750. The ink receiver 80 is supported by the platen 90. The platen 90 can exist in many forms such as a flat platen surface as shown in FIG. 1, or an external or internal drum surface. 
     FIG. 2 illustrates a top view of the ink jet printing apparatus 10 in accordance with the present invention. The ink receiver 80 is transported by the receiver transport 70 on the platen 90 in a slow scan direction as indicated by an arrow. The receiver transport 70 includes a motor 150 that drives a shaft 160 and rollers 170. A plurality of rollers 170 are shown for evenly applying forces across the receiver 80. The rollers are typically provided with a layer of elastomer material such as polyurethane or silicon rubber for providing sufficient friction between the roller surface and the receiver 80. The print heads 31-34 are shown to move across the receiver 80 in a fast scan direction as indicated by the arrow. For clarity, the transport mechanism for the print heads are not shown in FIG. 2. A printed image 130 is shown, which is formed by the ink spots 110 as shown in FIG. 1. 
     FIGS. 3a shows a side views of the processing tank 40 when the receiver is immersed in the fluid for treatment. FIG. 3b shows a similar side view of the processing tank when the receiver is immersed in the fluid for treatment. The processing tank 40 includes a tank body 45 that contains a protection fluid 50. The protection fluid 50 is preferably colorless. 
     The processing tank 40 also includes mechanical components for receiving and supporting the receiver 80, and for transporting the protection fluid 50 in and out of the protection fluid 50. The receiver 80 covered with ink spots 110 is supported by a mesh support 200. The mesh support 200 is supported by rail supports 220 via connectors 210. The rail supports 220 are fixed to the bottom surface inside the tank body 45 by bases 230. The mesh support 200 can be transported along the rail supports 220 by motor 240 in the upward and downward direction so that the receiver 80 is moved into and out of the protection fluid 50. The motor 240 drives the mesh support 200 using a mechanism of belt 250 and pulley 260. The mesh support 200 is connected to belt 250 through belt connector 270. The motor 240 is supported by a motor support 280 such as a column, supported by base 290. 
     It will be further appreciated that the present invention is compatible with digital printing apparatus other than ink jet printers. These printers May include digital silver halide printer, electrophotographic printer, and thermal dye transfer printers. A processing containing protection fluids such as hardener fluid can be incorporated into these printers to enhance the durability and quality of the printed images. 
     A typical printing operation is now described. A digital image is input to the computer 20. Alternatively, the computer 20 can produce the digital image itself. The image is then processed by image processing algorithms as described above. The electric signals representing the processed image data is ten sent to the print heads 31-34 for driving the print heads for ink ejection. During printing, the print heads 31-34 under the control of the computer 20 scans along the fast scan direction. The ink receiver 80 also controlled by the computer 20 is transported by the receiver transport 70 along the slow scan direction. The computer 20 controls the print heads 31-34 according to the input digital image to eject ink drops 100 to form ink spots 110 on the receiver 80. To avoid excessive ink on the receiver 80, an image area can be printed in a multiple number of printing passes by the print heads 31-34. 
     After the image is produced on the receiver 80, the receiver 80 is moved to the top of the mesh support 200 in the processing tank 40. The computer 20 subsequently controls the motor 240 to move the mesh support 200 and the receiver 80 down into the fluid 50. The receiver 80 with the printed ink spots 110 are immersed in the fluid. As described below, the fluid can include a hardener solution. The hardener solution hardens the ink spot 110 on the ink receiver 80 and therefore improves waterfastness and physical durability of the printed image. The motor 240 under the control of computer 20 then moves the mesh support 200 upward out of the fluid 50. The duration of the time when the receiver 80 is immersed in the fluid 50 can be controlled by computer 20 for the optimum image characteristics. The excess fluid on the receiver 80 is then drained off through the meshes in the mesh support 200. After drying, the receiver 80 is ready for use by the user. 
     Inks suitable for the present invention are now described. Inks useful for ink jet recording processes generally comprise at least a mixture of a solvent and a colorant. The preferred solvent is de-ionized water, and the colorant is either a pigment or a dye. Pigments are often preferred over dyes because they generally offer improved waterfastness and lightfastness. 
     Pigmented inks are most commonly prepared in two steps: 
     1. a pigment milling step in which the as-received pigment is deaggregated into its primary particle size, and 
     2. a dilution step in which the pigment mill grind is converted into the ink formulation described below. 
     Processes for preparing pigmented ink jet inks involve blending the pigment, an additive known as a stabilizer or dispersant, a liquid carrier medium, grinding media, and other optional addenda such as surfactants and defoamers. This pigment slurry is then milled using any of a variety of hardware such as ball mills, media mills, high-speed dispersers, or roll mills. 
     In the practice of the present invention, any of the known pigments can be used. The exact choice of pigment will depend upon the specific color reproduction and image stability requirements of the printer and application. For a list of pigments useful in ink jet inks, see U.S. Pat. No. 5,085,698, column 7, line 10 through column 8, line 48. 
     The liquid carrier medium can also vary widely and again will depend on the nature of the ink jet printer for which the inks are intended. For printers which use aqueous inks, water, or a mixture of water with miscible organic co-solvents, is the preferred carrier medium. 
     The dispersant is another important ingredient in the mill grind. Although there are many dispersants known in the art, the choice of the most suitable dispersant will often be a function of the carrier medium and the type of pigment being used. Preferred dispersants for aqueous ink jet inks include sodium dodecyl sulfate, acrylic and styrene-acrylic copolymers, such as those disclosed in U.S. Pat. Nos. 5,085,698 and 5,172,133, and sulfonated styrenics, such as those disclosed in U.S. Pat. No. 4,597,794. Most preferred dispersants are salts of oleyl methyl tauride. 
     In the dilution step, other ingredients are also commonly added to the formulation for ink jet inks. Cosolvents (0-20 wt %) are added to help prevent the ink from drying out or crusting in the orifices of the printhead or to help the ink penetrate the receiving substrate, especially when the substrate is a porous paper. Preferred cosolvents for the inks of the present invention are glycerol, ethylene glycol, propylene glycol, 2-methyl-2,4,-pentanediol, diethylene glycol, and mixtures thereof, at overall concentrations ranging from 5 to 20 wt %. 
     A biocide (0.0001-1.0 wt %) can be added to prevent unwanted microbial growth which May occur in the ink over time. A preferred biocide for the inks of the present invention is Proxel GXL™ (1,2-benzisothiozolin-3-one, obtained from Zeneca Colours) at a final concentration of 0.005-0.5 wt %. 
     Other optional additives which May be present in ink jet inks include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, and defoamers. 
     In the present invention, the protection fluid as described above can include an aqueous solution. The aqueous solution can comprise one or more cosolvents, a surfactant, and a compound containing a hardening agent such as an aldehyde, a blocked aldehyde such as 2,3-dihydroxy-1,4-dioxane (DHD), an active olefin or a blocked active olefin and the like would be applied to the ink image on receiver 80 by the processing tank 40 as described above. Hardeners are defined as any additive which causes chemical cross-linking. Blocked hardeners are substances, usually derived from the active hardener, that release the active compound under appropriate conditions (The Theory of the Photographic Process, 4 th  Edition, T. H. James, 1977, Macmillan Publishing CO., page 81). 
     It is contemplated that other hardening agents May be useful in the instant invention. Some compounds known to be effective hardening agents are blocked aldehydes such as 2,3-dihydroxy-1,4-dioxane (DHD) and its derivatives, acetates of the dialdehydes and hemiacetals, various bisulfite adducts, and 2,5-dimethoxytetrahydrofuran. Aldehyde containing compounds that are effective hardening agents are also useful in the practice of this invention. Some compounds known to be effective hardening agents are 3-hydroxybutyraldehyde (U.S. Pat. No. 2,059,817), crotonaldehyde, the homologous series of dialdehydes ranging from glyoxal to adipaldehyde, diglycolaldehyde (U.S. Pat. No. 3,304,179) and various aromatic dialdehydes (U.S. Pat. Nos. 3,565,632 and 3,762,926). Active olefin containing compounds that are effective hardening agents are also useful in the practice of this invention. In the context of the present invention, active olefinic compounds are defined as compounds having two or more olefinic bonds, especially unsubstituted vinyl groups, activated by adjacent electron withdrawing groups (The Theory of the Photographic Process, 4 th  Edition, T. H. James, 1977, Macmillan Publishing Co., page 82).Some compounds known to be effective hardening agents are divinyl ketone, resorcinol bis(vinylsulfonate) (U.S. Pat. No. 3,689,274), 4,6-bis(vinylsulfonyl)-m-xylene (U.S. Pat. No. 2,994,611), bis(vinylsulfonylalkyl) ethers and amines (U.S. Pat. Nos. 3,642,486 and 3,490,911), 1,3,5-tris(vinylsulfonyl) hexahydro-s-triazine, diacrylamide (U.S. Pat. No. 3,635,718), 1,3-bis(acryloyl)urea (U.S. Pat. No. 3,640,720), N,N&#39;-bismaleimides (U.S. Pat. No. 2,992,109) bisisomaleimides (U.S. Pat. No. 3,232,763) and bis(2-acetoxyethyl) ketone (U.S. Pat. No. 3,360,372). Blocked active olefins of the type bis(2-acetoxyethyl) ketone and 3,8-dioxodecane-1,10-bis(pyridinium perchlorate), May also be used. (The Theory of the Photographic Process, 4 th  Edition, T. H. James, 1977, Macmillan Publishing CO.) Additional related hardening agents can be found in Research Disclosure, Vol. 365, September 1994, Item 36544, II, B. Hardeners. 
     Still other preferred additives are inorganic hardeners such as aluminum salts, especially the sulfate, potassium and ammonium alums, ammonium zirconium carbonate, chromium salts such as chromium sulfate and chromium alum, and salts of titanium dioxide, zirconium dioxide, and the like. All arc employed at concentrations ranging from 0.10 to 5.0 weight percent of active ingredients in the solution. 
     Combinations of organic and inorganic hardeners May also be used. Most preferred is the combination of chrome alum (chromium (III) potassium sulfate dodecahydrate) or aluminum sulfate and 2,3-dihydroxy-1,4-dioxane (DHD) at total hardener concentrations ranging from 0.10 to 5.0 wt. Most preferred is the combination of aluminum sulfate and 2,3-dihydroxy-1,4-dioxane (DHD) having a total hardener concentration ranging between 0.25 and 2.0 weight percent of active ingredients in the hardener solution. 
     Additional related hardeners can be found in, The Theory Of The Photographic Process, 4 th  Edition, T. H. James, 1977, Macmillan Publishing CO. pages 77-87, and in Research Disclosure, Vol. 365, September 1994, Item 36544, II, B. Hardeners. 
     It has been unexpectedly found that improved waterfastness, and excellent wet adhesion properties on gelatin coatings can be achieved when pigmented ink images printed on said coatings are submerged into a solution bath containing hardeners such as aldehydes, blocked aldehydes, active olefins and blocked active olefins. Most preferred are glyoxal, DHD, and formaldehyde, all at concentrations ranging from about 0.10 to 5.0 wt % 
     The present invention is better illustrated by the following examples: 
     COMPARATIVE EXAMPLE A (w/o hardener) 
     
         ______________________________________Mill Grind______________________________________Polymeric beads, mean diameter of 50 ∞m (milling                      325.0  gmedia)Bis(phthalocyanylalumino)tetra-Phenyldisiloxane (cyan                      35.0   gpigment) Manufactured by Eastman KodakOleoyl methyl taurine, (OMT) sodium salt                      17.5   gDeionized water            197.5  gProxel GXL ™](biocide from Zeneca)                      0.2    g______________________________________ 
    
     The above components were milled using a high energy media mill manufactured by Morehouse-Cowles Hochmeyer. The mill was run for 8 hours at room temperature. An aliquot of the above dispersion to yield 1.0 g pigment was mixed with 8.0 g diethylene glycol, and additional deionized water for a total of 50.0 g. This ink was filtered through 3-μm filter and introduced into an empty Hewlett-Packard 51626A print cartridge. Images were made with a Hewlett-Packard DeskJet™ 540 printer on medium weight resin coated paper containing an imaging layer. 
     The resin coated paper stock had been previously treated with a corona discharge treatment(CDT) and coated with an imaging layer consisting of about 800 mg/ft 2  of gelatin. Poor waterfastness and wet adhesion was observed in the D max  areas. In the low density patches (about 0.50), and with narrow lines (˜1/32 nd  of an inch) the pigmented ink image floated to the surface immediately when immersed in distilled water. 
     COMPARATIVE EXAMPLE B (w/o hardener) 
     An ink was prepared in a similar manner as described in Comparative Example A. except, the cyan pigment was replaced with 1.45 g of a quinacridone magenta pigment (red pigment 122) from Sun Chemical Co. The ink was printed as in Comparative Example A and poor waterfastness and wet adhesion were observed. 
     EXAMPLE 1 
     An ink was prepared in the same manner as that described in Comparative Example A. This ink was printed on resin coated paper stock which had been previously treated with a corona discharge treatment(CDT) and coated with an imaging layer consisting of about 800 mg/ft 2  of gelatin. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 2.03 g of 37 wt % solution of formaldehyde obtained from Aldrich Chemicals to obtain a final concentration of 1.50 wt %, and additional deionized water for a total of 50.0 g. The overcoat solution was introduced into an empty Hewlett-Packard 51626A print cartridge. This solution was overcoated at 100% coverage on the above pigmented ink image. Excellent waterfastness and wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties were also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 2 
     An ink was prepared in the same manner as that described in Comparative Ex. B. This ink was printed on resin coated paper stock which had been previously treated with a corona discharge treatment(CDT) and coated with an imaging layer consisting of about 800 mg/ft 2  of gelatin. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 2.03 g of 37 wt % solution of formaldehyde obtained from Aldrich Chemicals to obtain a final concentration of 1.50 wt %, and additional deionized water for a total of 50.0 g. The overcoat solution was introduced into an empty Hewlett-Packard 51626A print cartridge. This solution was overcoated at 100% coverage on the above pigmented ink image. Excellent waterfastness and wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 3 
     An ink was prepared in the same manner as that described in Comparative Ex. A. This ink was printed on resin coated paper stock which had been previously treated with a corona discharge treatment(CDT) and coated with an imaging layer consisting of about 800 mg/ft 2  of gelatin. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 1.25 g of 40 wt % solution of glyoxal obtained from Aldrich Chemicals to obtain a final concentration of 1.0 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image, in a manner similar to the above examples. Good waterfastness and very good wet adhesion were observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties were also observed in lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 4 
     An ink was prepared in the same manner as that described in Comparative Example B. This ink was printed on resin coated paper stock which had been previously treated with a corona discharge treatment(CDT) and coated with an imaging layer consisting of about 800 mg/ft 2  of gelatin. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 1.25 g of 40 wt % solution of glyoxal obtained from Aldrich Chemicals to obtain a final concentration of 1.0 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Excellent waterfastness and very good wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 5 
     An ink was prepared and printed in the same manner as that described in Comparative Example A. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 5.00 g of 10 wt % solution of 2,3-dihydroxy-1,4-dioxane (DHD) obtained from Aldrich to obtain a final hardener concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Very good waterfastness and good wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 6 
     An ink was prepared and printed in the same manner as that described in Comparative Example B. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 5.00 g of 10 wt % solution of 2,3-dihydroxy-1,4-dioxane (DHD) obtained from Aldrich to obtain a final hardener concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Very good waterfastness and excellent wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 7 
     An ink was prepared and printed as in Comparataive Example A. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 25.00 g of 2.0 wt % solution of bis-(vinylsulfonyl)-methane ether (BVSME) to obtain a final concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Very good waterfastness and wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 8 
     An ink was prepared and printed as in Comparative Example B. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 25.00 g of 2.0 wt % solution of BVSME to obtain a final concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Excellent waterfastness and wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 9 
     An ink was prepared and printed as in Comparative Example A. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 27.78 g of 1.80 wt % solution of bis-(vinylsulfonyl)-methane (BVSM) to obtain a final concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Excellent waterfastness and very good wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     EXAMPLE 10 
     An ink was prepared and printed as in Comparative Example A. 
     An overcoat solution was prepared consisting of 8.0 g of diethylene glycol, 5.00 g of a 10.0% solution of Air Products Surfynol® 465, 27.78 g of 1.80 wt % solution of BVSM to obtain a final concentration of 1.00 wt %, and additional deionized water for a total of 50.0 g. This solution was overcoated on the above pigmented ink image. Excellent waterfastness and wet adhesion was observed in the 100% fill areas (D max ). Excellent waterfastness and wet adhesion properties was also observed at lower density patches, and with thin narrow lines (˜1/32 nd  of an inch). 
     Ink Characterization 
     The images printed from the examples and comparative examples were evaluated by measuring the optical densities in three area patches with maximum ink coverage, using an X-Rite™ Photographic Densitometer. The average of the three readings is reported. Waterfastness was determined by immersing samples of printed images in distilled water for 1 hour and then allowing the samples to dry for at least 12 hours. The optical density was measured before immersion in water and after immersion in water and drying. Waterfastness is determined as the per cent of retained optical density after immersion in water and drying. After the samples had been immersed in water for half an hour the samples were physically rubbed to ascertain if the pigmented ink image would rub off with pressure (wet adhesion). This was done on a D max  patch (100% fill), at a mid-density point (0.50-1.0), and on narrow lines (˜1/32 nd  of an inch). They were subjectively rated based on the following scale: excellent=no discernible difference in image density or appearance; very good=very slight density loss; good=moderate density loss; fair=image rubs off easily; and poor=image floats off surface of paper while immersed in water. 
     
                                           TABLE 1__________________________________________________________________________Examples 1-12 are summarized in the following table.              Hardener %         Hardener              Amount                   Density                       Retained                            Wet Adhesion                                   Wet AdhesionExampleReceiver     Pigment         Type (wt %)                   Before                       Density                            (D.sub.max Patch)                                   (Lines + D.sub.min)__________________________________________________________________________Comp. Agelatin     cyan         None None 1.83                       71   Fair   PoorComp. Bgelatin     p.r. 122         None None 2.05                        3   Poor   Poor1    gelatin     cyan         FA    1.50                   1.79                       96   Excellent                                   Excellent2    gelatin     p.r. 122         FA    1.50                   2.10                       91   Excellent                                   Excellent3    gelatin     cyan         glyoxal              1.0  1.89                       82   Good   Excellent4    gelatin     p.r. 122         glyoxal              1.0  2.03                       101  Very Good                                   Excellent5    gelatin     cyan         DHD  1.0  1.85                       89   Good   Excellent6    gelatin     p.r. 122         DHD  1.0  2.10                       83   Excellent                                   Excellent7    gelatin     cyan         BVSME              1.0  1.82                       89   Very Good                                   Excellent8    gelatin     p.r. 122         BVSME              1.0  2.01                       97   Excellent                                   Excellent9    gelatin     cyan         BVSM 1.0  1.83                       97   Very Good                                   Excellent10   gelatin     p.r. 122         BVSM 1.0  1.95                       102  Excellent                                   Excellent__________________________________________________________________________ p.r. = pigment red BVSME = bis(vinylsulfonyl)-methane ether DHD = 2,3dihydroxy-1,4-dioxane BVSM = bis(vinylsulfonyl)-methane FA = formaldehyde 
    
     The results indicate that significant enhancement of waterfastness and wet adhesion properties of images printed on gelatin, can be achieved when the printed image is submerged into aa solution containing hardeners such as aldehydes, blocked aldehydes(DHD), active olefins and blocked active olefins, and the like. The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     
         ______________________________________PARTS LIST______________________________________  10     ink jet printing apparatus  20     computer  31-34  print heads  40     processing tank  41-44  ink reservoirs  50     fluid  70     receiver transport  80     ink receiver  90     platen  100    ink drop  110    ink spot  130    printed image  150, 240         motor  160    shaft  170    roller  200    a mesh support 200  210    connector  220    rail supports 220  230, 290         bases 230  250    belt  260    pulley  270    belt connector  280    motor support______________________________________