Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/0018—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock using ink-fixing material, e.g. mordant, precipitating agent, after printing, e.g. by ink-jet printing, coating or spraying
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0011—Pre-treatment or treatment during printing of the recording material, e.g. heating, irradiating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0011—Pre-treatment or treatment during printing of the recording material, e.g. heating, irradiating
  • B41M5/0017—Application of ink-fixing material, e.g. mordant, precipitating agent, on the substrate prior to printing, e.g. by ink-jet printing, coating or spraying
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/0081—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock using electromagnetic radiation or waves, e.g. ultraviolet radiation, electron beams
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/009—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock using thermal means, e.g. infrared radiation, heat

Definitions

• the present invention relates to an ink jet recording method.
• non-impact printing processes e.g. electrostatographic printing, and ink jet printing (ref. e.g. "Principles of Non-Impact Printing” by Jerome L. Johnson (1986) - Palatino Press - Irvine CA, 92715 U.S.A.).
• ink-jet technology tiny drops of ink fluid are projected directly onto an ink-receptor surface.
• the placement of each drop on the printing substrate is controlled electronically.
• Printing is accomplished by moving the printing head across an ink-receptor member (sheet or web) or vice versa.
• Ink jet printing systems may be classified into two groups according to whether the ink drops are deflected or not.
• a stream of ink droplets is modulated by deflection forces (e.g. electrostatic forces after charging the ink droplets) to deposit the ink image-wise on an ink-receptor element (see e.g US-P 4,901,088).
• deflection forces e.g. electrostatic forces after charging the ink droplets
• ink is sprayed under pressure through a tiny glass nozzle about 10 microns in diameter. Although the ink emerges in a continuous stream traveling at about 60 meters per second, it quickly breaks into droplets under the influence of surface tension. Piezoelectric vibration in the megahertz range applied to the wall of the glass channel conducting the ink induces the formation of about one million droplets per second each drop having a diameter of about 30 microns.
• droplets are produced pulsewise and travel to the receptor material normally without further modification of their path.
• impulse droplet formation is based on electro-mechanical (piezo-electric) displacement of ink through a nozzle (see e.g. US-P 4,879,568 and 4,887,100 and EP-A 0 339 926 and 0 340 960).
• the displacement forces are thermal as is the case in the bubble jet printer (see for both systems said already mentioned book “Principles of Non-Impact Printing", pages 259-262), and for the "bubble jet printer” in particular US-P 4,914,736.
• ink jet printing could be used for producing images with increased optical density, say of more than 2.5 without droplet-superposition, or the number of superposed droplets could be reduced and yet high optical densities could be obtained within shorter writing times.
• the applied ink contains leuco or vat dyes.
• leuco or vat dyes convert to their permanent form when oxidized.
• the record medium is first coated or impregnated with an oxidizing agent.
• the dyes Upon combining with the oxidant, the dyes convert to their permanent form, becoming insoluble and having high tinctorial strength and excellent archival properties, such as water fastness and light fastness.
• no optical densities higher than 2 can be obtained therewith, certainly not within a short writing time.
• a first mode halftoning by screening is obtained by translating the continuous tone image in an array of dots of different size.
• a second halftoning technique is based on dot-density modulation at constant dot size.
• a third halftoning technique is based on dot construction via individual pixels. In the latter case in the formation of one dot the pixels may be distributed stochastically (forming a so-called dispersed dot) or are joining each other (clustered) in the dot cell in a certain geometric pattern.
• halftone dots are divided into a pattern formed by tiny spots (pixels) arranged in different number and geometrically different configuration in the dot area also called cell, to simulate a more or less continuously varying density, since the group of tiny spots that partially fill the area of each cell correspond with a certain percent of gray.
• the needed number of distinct gray steps in a copy having continuous tone appearance depends on the eye's ability to distinguish closely spaced grays. It is found that the human eye at normal reading distance can detect a reflectance modulation of about 0.5 % at a spatial frequency near 1 cycle/mm. The inverse of this just perceptible modulation has been interpreted as the maximum number of gray steps that the eye can perceive.
• a rule of thumb in the printing industry is that an acceptable continuous tone picture should contain at least 64 gradations (gray steps). This translates into 6 bits of data for creating the halftone cells. For good printing quality, 100 or more steps are desired.
• An 8-bit data set can produce a gray scale with 256 gradations which is preferred for images serving in medical diagnosis.
• the dithering process requires complicated driver circuits.
• binary (digital) operated electrophotographic systems in order to get around the problem of producing a multiplicity of pixels of equal density in one picture cell (halftone dot) a "multilevel" laser exposure source is used to expose pixels at more than one level of exposure. Operating that way a substantially greater number of unique halftone cells is produced and consequently a larger scale of continuous tone reproduction is obtained as explained in the above mentioned US-P 4,868,587.
• Ink jet printing and certainly drop-on-demand ink jet printing, is also a binary operated printing system which shows the above explained limitations in gray shade reproduction Of binary printers. Enlarged gray scale reproduction together with high (>2) optical density would be a real step forward in boosting image quality obtained by ink jet printing.
• an ink jet printing method comprises the steps of :
• Said image-wise deposition of the different inks may be such that droplets of any concentration may be deposited singly, i.e. separately, or at least partly in superposition.
• said receiving material is initially free from said reagent A and onto said receiving material one or more inks containing reagent A and one or more inks containing reagent B are deposited image-wise from separate ink jets, at least one of said reagents being deposited from different jets at different concentrations.
• the present invention includes the above defined ink jet printing method, wherein dithering and/or error diffusion is (are) applied for improving gray tone reproduction.
• the ink jets are produced with a plurality of ink jet printing heads or group of nozzles that are connected to non-communicating ink sources (ink containers or capsules) from which each printing head or group of nozzles is fed with an ink containing a said reagent B in different concentration.
• the printing heads e.g. four printing heads, or different nozzles are arranged aside in line with regard to a rotating drum carrying the receiving material and are moved on a lead screw to scan the surface of the receiving material.
• said four printing heads or four groups of nozzles are fed with different chemically reactive inks that yield by chemical reaction with the same chemically reactive receiving material optical densities (above the inherent density of the ink receiving material) of 0.01, 0.02, 0.28 and 0.63 respectively.
• optical densities above the inherent density of the ink receiving material
• the optical image density formed by the deposited and chemically reactive ink is combined with the optical density of a coloring agent present already in the ink before its deposition on the chemically reactive receiving material.
• both the reactants A and/or B may have a color on their own. Operating that way optical densities above 3 in any color can be obtained easily by choice of the reactants A and B optionally in conjunction with colorant(s) present in the reactive ink containing reactant(s) B.
• the ink has a color which is complementary to the color formed in the color reaction with the substances A and B. In that way a neutral black image may be formed.
• the method of the present invention is especially suited for the production of stable substantially black images of high optical density when said substances A and B represent a chemically reactive system mainly comprising a substantially colorless metal salt and a substantially colorless reducing agent producing therewith a substantially black deposit of finely divided metal in a redox-reaction.
• the metal image shows excellent archival stability.
• the metal salt may be an inorganic or organic metal salt.
• the metal salt is a silver salt.
• Reactants A and B can be selected from a wide range of color reaction agents for metal ions described by Fritz Feigl in the book “Spot Tests” - Elsevier Publishing Company - New York (1958).
• metal salts providing e.g. iron(III) ions that on complexing with thiocyanate ions (CNS) yield a deep red product or on complexing with 1,2-dihydroxybenzene-3,5-disulfonate form blue, deep violet or red products.
• CNS thiocyanate ions
• copper and molybdenum salts produce yellow-green and yellow products respectively.
• Iron (II) gives a green color with 8-hydroxy-quinoline-7-iodo-5-sulfonic acid, and iron (III) salts form with gallic acid black iron gallate.
• thermosensitive combinations of color reactants that are suitable for use according to the present invention are described.
• inks containing different amounts of reagent B, optionally in the presence of different amounts of colorant(s), are each image-wise projected by means of a separate multi-nozzle ink jet printing head onto said receiving material.
• a said reagent A is applied to said ink receiving material in substantial congruency with ink jet-deposited reagent B from (an) ink jet nozzle(s) not being the same as the ink jet nozzle(s) wherefrom a said reagent B is applied.
• the recording method of the present invention is carried out with an ink-image receiving material containing a substantially light-insensitive silver salt and an ink containing a reducing agent therefor.
• Particularly suited substantially light-insensitive silver salts are organic silver salts and more particularly the silver salts of aliphatic carboxylic acids known as fatty acids, wherein the aliphatic carbon chain has preferably at least 12 C-atoms, e.g. silver laurate, silver palmitate, silver stearate, silver hydroxystearate, silver oleate and silver behenate, and likewise silver dodecyl sulphonate described in US-P 4,504,575 and silver di-(2-ethylhexyl)-sulfosuccinate described in published European patent application 227 141.
• Useful modified aliphatic carboxylic acids with a thioether group are described e.g.
• the ink for use according to the present invention contains the reactive substance(s) A or B preferably in dissolved form but said substances A or B may be present in finely dispersed state by which is meant that they are present in the ink in the form of particles of nanometer size, e.g. having a size of 5 to 50 nm in order to avoid nozzle-clogging.
• colored "water-based”, “solvent-based” “mixed water/solvent-based” and “hot melt” or “phase change inks” can be used with the proviso that they contain at least one reagent for another reagent in the ink receiving material to form therein a colored product.
• Solvent-based ink-jet inks containing a major amount of organic solvent(s), but optionally containing some amount of water, are described e.g. in JP 55160070, JP 63152678, JP 63152679, JP 63152680, JP 61036382 and 61036381. Further are mentioned the low viscosity solvent-based inks described in EP 386349 and the inks described in US-P 4,386,961, 4,400,215, 4,957,553 and 4,822,418. Solvent-based inks with electrostatic deflection properties are described e.g. in JP 61181879. Presently, solvent-based inks contain methyl ethyl ketone, ethanol and methanol as primary solvent (ref. the already mentioned "Handbook of Imaging Materials", edited by Arthur S. Diamond, p. 540).
• Solvent-based inks containing a major amount of organic solvent(s) and that are particularly suited for use in thermal ink-jet printers (a type of drop-on-demand ink jet printers) are described in detail in published European patent application 0 413 442.
• the solvents used have boiling points from about 50 °C to about 200 °C and are e.g. members of the following group : alkyl glycol ethers, wherein the alkyl group has up to 4 carbon atoms, aromatic hydrocarbons, alkyl pyrrolidinones, ketones and lactones.
• Said ink is particularly suited for printing on a wide variety of plastic films and yields water-fast and smear resistant images.
• Hot melt inks for ink jet printing are described e.g. in US-P 4,659,383, 4,820,346, 4,931,095 and EP 20286, and their properties are discussed in the already mentioned "Handbook of Imaging Materials", edited by Arthur S. Diamond, p. 530.
• Ink-jet printing many of the commercially available ink-jet printers operate with water-base ink (see p. 43 of said book) by which is meant that such inks contain more than 70 % by weight of water. Small amounts of humectants such as glycols are added to reduce the evaporation rate and for continuous ink-jet printing the ink contains some salt in order to obtain a required electrical conductivity and chargeability for electrostatic droplet deflection.
• the inks for continuous ink jet printing are in practice water-base inks.
• the reducing agent of that system may be used in salt form and play the role of electrical conductivity increasing ingredient.
• Suitable organic reducing agents for the reduction of substantially light-insensitive organic silver salts are organic compounds containing at least one active hydrogen atom linked to O, N or C, such as is the case in aromatic di- and tri-hydroxy compounds, e.g. hydroquinone and substituted hydroquinones, catechol, pyrogallol, gallic acid and gallates; aminophenols, METOL (tradename), p-phenylenediamines, alkoxynaphthols, acetoacetonitriles, pyrazolidin-3-one type reducing agents, e.g.
• PHENIDONE (tradename), pyrazolin-5-ones, indanedione-1, 3 derivatives, hydroxytetrone acids, hydroxytetronimides, polyhydroxy spiro-bis-indane compounds, reductones, and ascorbic acid.
• Representatives for thermally activated reduction of organic silver salts are described e.g. in US-P 3,074,809, 3,080,254, 3,094,417, 3,887,378 and 4,082,901.
• the ink used according to the present invention in conjunction with an image-receiving material containing a reducible organic silver salt may contain a mixture of reducing agents, e.g. of (a) primary relatively strong reducing agent, and less active auxiliary reducing agent.
• the ink receiving material contains such auxiliary reducing agent.
• Sterically hindered phenols as described e.g. in US-P 4,001,026 are examples of auxiliary reducing agents that can be used in admixture with said organic silver salts without premature reduction reaction and fog-formation at room temperature in the "ink" receiving material used according to the present invention.
• On heating these auxiliary reducing agents become reactive partners in the reduction of a light-insensitive organic silver salt such as silver behenate.
• the silver image density depends on the amount of image-wise deposited reducing agent and the coverage of the substantially non-lightsensitive organic silver salt(s) in the ink image receiving material.
• the optical density obtained by the inherent color of the ink is added to that density.
• the reducible silver salt(s) and reducing agents are used in conjunction with a so-called toning agent known from thermography or photo-thermography.
• the toning agent may be present in the ink and/or in the ink receiving material.
• Suitable toning agents are the phthalimides and phthalazinones within the scope of the general formulae described in US-P 4,082,901. Further reference is made to the toning agents described in US-P 3,074,809, 3,446,648 and 3,844,797. Particularly useful toning agents are likewise the heterocyclic toner compounds of the benzoxazine dione or naphthoxazine dione type within the scope of following general formula : in which : X represents O or N-alkyl; each of R1, R2, R3 and R4 (same or different) represents hydrogen, alkyl, e.g.
• C1-C20 alkyl preferably C1-C4 alkyl, cycloalkyl, e.g. cyclopentyl or cyclohexyl, alkoxy, preferably methoxy or ethoxy, alkylthio with preferably up to 2 carbon atoms, hydroxy, dialkylamino of which the alkyl groups have preferably up to 2 carbon atoms or halogen, preferably chlorine or bromine; or R1 and R2 or R2 and R3 represent the ring members required to complete a fused aromatic ring, preferably a benzene ring, or R3 and R4 represent the ring members required to complete a fused aromatic aromatic or cyclohexane ring.
• a very useful toner such as 3,4-dihydro-2,4-dioxo-1,3,2H-benzoxazine within the scope of said general formula is disclosed in US-P 3,951,660.
• the ink and/or the ink receiving layer may contain other additives such as free fatty acids, surface-active agents, and substances called penetrants improving the take up of the ink in the ink receiving material.
• antistatic agents e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F3C(CF2)6CONH(CH2CH2O)-H.
• the ink receiving material may contain other additives, e.g. ultraviolet light absorbing compounds, white light reflecting and/or ultraviolet radiation reflecting pigments, colloidal silica, and/or optical brightening agents.
• additives e.g. ultraviolet light absorbing compounds, white light reflecting and/or ultraviolet radiation reflecting pigments, colloidal silica, and/or optical brightening agents.
• the ink receiving material contains the reactive substance(s) A preferably in a common film-forming binder.
• the binder has to be such that a layer is formed into which the reagent(s) contained in the ink can penetrate, optionally by the use of heat.
• the binder is preferably a thermoplastic waterinsoluble resin wherein said silver salt can be dispersed homogeneously or form therewith a solid-state solution.
• a thermoplastic waterinsoluble resin wherein said silver salt can be dispersed homogeneously or form therewith a solid-state solution.
• all kinds of natural, modified natural or synthetic resins may be used, e.g.
• cellulose derivatives such as ethylcellulose, cellulose esters, carboxymethylcellulose, starch ethers, polymers derived from ⁇ , ⁇ -ethylenically unsaturated compounds such as polyvinyl chloride, after-chlorinated polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl acetate and partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals, e.g. polyvinyl butyral, copolymers of acrylonitrile and acrylamide, polyacrylic acid esters, polymethacrylic acid esters and polyethylene or mixtures thereof.
• a particularly suitable ecologically interesting (halogen-free) binder is polyvinyl butyral. Polyvinyl butyral containing some vinyl alcohol units is marketed under the trade name BUTVAR B79 of Monsanto USA.
• the weight ratio of binder to organic silver salt is preferably in the range of 0.2 to 6, and the thickness of the recording layer is preferably in the range of 8 to 16 ⁇ m.
• the imaging layer containing the metal salt e.g. organic silver salt
• the above mentioned polymers or mixtures thereof forming the binder may be used in conjunction with waxes or "heat solvents” also called “thermal solvents” or “thermosolvents” improving the reaction speed of the redox-reaction at elevated temperature.
• heat solvents also called “thermal solvents” or “thermosolvents” improving the reaction speed of the redox-reaction at elevated temperature.
• heat solvent in this invention is meant a non-hydrolyzable organic material which is in solid state at temperatures below 50 °C but becomes on heating above that temperature a plasticizer for the binder of the layer wherein they are incorporated and possibly act then also as a solvent for at least one of the redox-reactants, e.g. the reducing agent for the organic silver salt.
• a plasticizer for the binder of the layer wherein they are incorporated and possibly act then also as a solvent for at least one of the redox-reactants, e.g. the reducing agent for the organic silver salt are useful for that purpose.
• a polyethylene glycol having a mean molecular weight in the range of 1,500 to 20,000 described in US-P 3,347,675.
• Heat-solvents may be used likewise in the by ink-jet applied ink, especially when they are water-soluble and can act as moistening agent for an organic water-insoluble binder layer wherein an organic silver salt is present. They improve the penetration of the reducing agent in said layer bringing about a much faster reactive contact with the reducible organic silver salt.
• An ink-image receiving layer containing said organic silver salt is commonly coated from an organic solvent containing the binder in dissolved form but may be applied from aqueous medium from a latex containing a dispersed polymer having some hydrophilic functionality.
• Polymers with hydrophilic functionality for forming an aqueous polymer dispersion (latex) are described e.g. in US-P 5,006,451, but serve therein for forming a barrier layer preventing unwanted diffusion of vanadium pentoxide serving as antistatic agent.
• the ink receiving material used in the method according to the present invention comprises a heat-developable photosensitive layer comprising a substantially light-insensitive silver salt, an organic reducing agent and a light-sensitive heavy metal compound, preferably light-sensitive silver halide, which upon exposure to activating electromagnetic radiation forms metal nuclei that upon heating of said layer initiate a redox reaction between the light-insensitive silver salt and the reducing agent applied by ink jet.
• a heat-developable photosensitive layer comprising a substantially light-insensitive silver salt, an organic reducing agent and a light-sensitive heavy metal compound, preferably light-sensitive silver halide, which upon exposure to activating electromagnetic radiation forms metal nuclei that upon heating of said layer initiate a redox reaction between the light-insensitive silver salt and the reducing agent applied by ink jet.
• Photo-thermographic recording materials are commercially available under the tradename DRY SILVER of 3M Company.
• the photo-thermographic material Prior to receiving the ink-jet ink image the photo-thermographic material is uniformly exposed to produce therein the above defined metal nuclei that upon heating activate the redox reaction in which the substantially light-insensitive silver salt is involved for forming a silver metal image.
• the reductor is applied image-wise by ink-jet no image-stabilization of the image-background area (being free from reductor) is necessary which is a major advantage for obtaining archival storage of the obtained images.
• a water-insoluble binder layer containing a said substantially light-insensitive organic silver salt is over-coated with a hydrophilic colloid or polymer top layer.
• the applied overcoat layer is capable of rapidly absorbing a water-base ink-jet ink containing a reducing agent as defined above.
• the receiving material After receiving the water-base ink image the receiving material is heated, e.g. in the range of 60 to 120 °C to allow the reducing agent to diffuse into the waterinsoluble binder layer containing the substantially non-lightsensitive silver salt.
• the hydrophilic water-soluble binder of the ink receiving layer accepting a reducing agent may be any hydrophilic colloid used in the preparation of photographic silver halide emulsion layers, preferably is a protein-type binding agent such as gelatin, casein, collagen, albumin, or gelatin derivative, e.g. acetylated gelatin.
• a protein-type binding agent such as gelatin, casein, collagen, albumin, or gelatin derivative, e.g. acetylated gelatin.
• Further suitable water-soluble binding agents are : dextran, gum arabic, zein, agar-agar, arrowroot and pectin, polyvinyl alcohol and poly-N-vinylpyrrolidone.
• the coating of the ink-image receiving layer may proceed by any coating technique e.g. as described in Modern Coating and Drying Technology, edited by Edward D. Cohen and Edgar B. Gutoff, (1992) VCH Publishers Inc. 220 East 23rd Street, Suite 909 New York, NY 10010, U.S.A.
• the support for the ink-image receiving layer used according to the present invention is preferably a thin sheet or weblike carrier material that should be stable preferably at heating temperatures of between 40 and 160 °C.
• the support is made from paper, polyethylene coated paper or transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate, polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate.
• the support may be subbed if need be to improve the adherence thereof of the layer containing at least one of said reactive substances A.
• the ink receiving material is preferably subjected to a uniform heat-treatment in the temperature range of 40 to 160 °C.
• the time and temperature required for substantially enhancing the optical density in the inked areas depends largely on the type of reactants A and B, their concentration in the ink and coverage in the ink-receiving material.
• a heating time in the range of 3 to 60 seconds at a temperature of about 100 °C is sufficient to obtain a desired optical density increase.
• the heat may be supplied by means of a hot body, e.g. hot metal roller, contacting the support of the ink-receiving material or may be supplied in the form of hot air, e.g. in a ventilated drying oven, and/or may be supplied in the form of radiant heat that is absorbed in the deposited ink markings which for that purpose may contain an infra-red light absorbing dye or pigment. Radiant heating may proceed with flash lamp, e.g. xenon gas discharge lamp, incandescent infra-red light lamp or by means of laser beam.
• flash lamp e.g. xenon gas discharge lamp, incandescent infra-red light lamp or by means of laser beam.
• the imaging method according to the present invention can be used for both the production of transparencies and reflection type prints.
• the support will be transparent or opaque, e.g. the support has a white light reflecting aspect.
• a paper base is used which may contain white light reflecting pigments, optionally also applied in an interlayer between the recording layer and said base.
• said base may be colourless or coloured, e.g. has a blue colour.
• a subbed polyethylene terephthalate support having a thickness of 100 ⁇ m was doctor blade-coated from a coating composition containing methyl ethyl ketone as a solvent and the following ingredients so as to obtain thereon after drying the following recording layer containing : silver behenate 6.50 g/m2 polyvinyl butyral (BUTVAR B79-tradename) 6.50 g/m2 3,4-dihydro-2,4-dioxo-1,3,2H-benzoxazine 0.74 g/m2 BAYSILON ⁇ l (tradename) 25 mg/m2
• a hydrophilic water-permeable receptor layer capable of absorbing an aqueous ink was coated from the following coating solution at a temperature of 45 °C : gelatin 5 g AEROSOL OT (tradename) 1% solution in water 0.5 ml water 95 g
• Said solution was doctor-blade coated so as to obtain a layer containing gelatin at a coverage of 5 g/m2 and AEROSOL OT (tradename) at a coverage of 5 mg/m2.
• AEROSOL OT is a tradename of American Cyanamid for di-iso.octylsulfosuccinate being an anionic wetting agent.
• the black color of the ink is due to a mixture of sulfonated yellow, magenta and cyan dyes, tetramethylammonium cations are present in conjunction with the anionic sulfonic acid groups.
• the ink contains about 89 % of water and 1,5-pentanediol as organic solvent together with polyethylene oxide type wetting agent and carboxymethyl cellulose as thickener.
• the composition of the ink 2 was the same as for ink 1 with the difference that only 50 mg of catechol was used.
• composition of the ink 3 is the same as for ink 1 with the difference that only 25 mg of catechol was used.
• composition of the ink 4 was the same as for ink 1 with the difference that no catechol was used.
• a first part (part I) of the printed surface was post-heated during 10 seconds by pressing the printed area against an aluminum block internally electrically heated at a temperature of 115 °C.
• a second part (part II) of the printed surface was left at room temperature (20 °C).
• the reductor catechol diffuses from the gelatin-containing layer into the recording layer (imaging layer) containing silver behenate and produces therein black silver metal increasing the optical density of the black ink image already obtained in the gelatin layer with the black water-soluble colorant of the applied ink.
• the measured minimum densities (Dmin) and maximum densities (Dmax) obtained with the different inks 1, 2, 3 and 4 are listed in the following Table 1. Said optical densities were measured in both of said parts I and II through an ortho filter with a MacBeth TD 904 densitometer. TABLE 1 Using ink 1 Part Dmin Dmax I 0.12 3.2 II 0.12 1.0 Using ink 2 Part Dmin Dmax I 0.12 2.5 II 0.12 1.0 Using ink 3 Part Dmin Dmax I 0.12 1.8 II 0.12 1.0 Using ink 4 Part Dmin Dmax I 0.12 1.0 II 0.12 1.0
• a subbed polyethylene terephthalate support having a thickness of 100 ⁇ m was doctor blade-coated from a coating composition containing methyl ethyl ketone as a solvent and the following ingredients so as to obtain thereon after drying the following ink receiving layer containing : silver behenate 4.42 g/m2 polyvinyl butyral (BUTVAR B79-tradename) 4.42 g/m2 3,4-dihydro-2,4-dioxo-1,3,2H-benzoxazine 0.34 g/m2 BAYSILON ⁇ l (tradename) 17 mg/m2
• the above defined ink receiving material was attached to a rotatable drum.
• a drop-on-demand piezoelectrically modulated ink jet head of XAAR Limited, Cambridge, England was used to spray successiveively droplets having a diameter of 100 ⁇ m of said different inks 1, 2, 3 and 4 in partly overlapping rectangular patterns .
• the overlap of said patterns was such that droplets were either or not superposed in number and kind of ink as mentioned in the following Table 2.
• the optical density was measured in transmission through an ortho filter using a MacBeth densitometer TD 904.

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• Thermal Sciences (AREA)
• Ink Jet Recording Methods And Recording Media Thereof (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)

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• 1994
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