EP0543136B1 - Stabilisation d'images thermiques - Google Patents

Stabilisation d'images thermiques Download PDF

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Publication number
EP0543136B1
EP0543136B1 EP19920117365 EP92117365A EP0543136B1 EP 0543136 B1 EP0543136 B1 EP 0543136B1 EP 19920117365 EP19920117365 EP 19920117365 EP 92117365 A EP92117365 A EP 92117365A EP 0543136 B1 EP0543136 B1 EP 0543136B1
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Prior art keywords
color
imaging
forming
medium
compound
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EP19920117365
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German (de)
English (en)
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EP0543136A1 (fr
Inventor
Rong C. Liang
Rita S. Shon Baker
Stephen R. Sofen
Michael A. Young
William C. Schwarzel
Robert P. Short
Larry C. Takiff
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Polaroid Corp
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Polaroid Corp
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Priority claimed from US07/795,101 external-priority patent/US5206208A/en
Priority claimed from US07/795,102 external-priority patent/US5210064A/en
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    • 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
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers
    • B41M5/337—Additives; Binders
    • B41M5/3375—Non-macromolecular compounds
    • 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
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers
    • B41M5/323—Organic colour formers, e.g. leuco dyes

Definitions

  • This invention relates to stabilization of thermal images and/or sensitization of the thermal imaging media. More particularly, this invention relates to thermal imaging media, processes for forming images and imaged media in which a color-stabilizing additive is used to reduce fading of the images during projection of the image by passage of visible radiation through the image.
  • the sensitivity of the thermal imaging media of the invention is improved by the incorporation of the color-stabilizing additive therein.
  • Preferred imaging media described in these three applications are substantially as shown in Figure 1 of the accompanying drawings and comprise three separate color-forming layers containing yellow, cyan and magenta thermal color-forming compositions; each of these color-forming compositions comprises a color-forming compound which can produce the desired color and an infra-red absorber capable of absorbing infra-red radiation and thereby generating heat in the color-forming layer.
  • the three color-forming layers use infra-red absorbers absorbing at differing wavelengths so that each color-forming layer can be imaged independently; for example, specific imaging media disclosed in these three applications use infra-red absorbers having peak absorptions at approximately 792, 822 and 869 nm.
  • imaging media which have at least one color-forming layer comprising a color-forming composition adapted to undergo a change of color (from colorless to colored, from colored to colorless, or from one color to another) upon increase in the temperature of the color-forming layer above a color-forming temperature for a color-forming time.
  • the color change in such media need not be supplied by applying heat directly to the medium;
  • the color-forming composition may comprise a color-forming compound (also referred to herein as a "leuco dye”) which undergoes a change of color upon heating above a color-forming temperature, and an absorber capable of absorbing actinic (usually infra-red) radiation and thereby generating heat in the color-forming layer.
  • thermal imaging media When such a medium is exposed to appropriate actinic radiation, this radiation is absorbed by the absorber, thereby heating the color-forming compound and causing it to undergo its color change.
  • thermal imaging media have the advantage over conventional silver halide media of not requiring a post-exposure developing step. Such thermal imaging media also have the advantage that they are essentially insensitive to visible light, so that they can be handled under normal lighting conditions.
  • U.S. Patents Nos. 4,602,263 and 4,826,976 both describe thermal imaging systems for optical recording and particularly for forming color images. These thermal imaging systems rely upon the irreversible unimolecular fragmentation of one or more thermally unstable carbamate moieties of an organic compound to effect a visually discernible color shift.
  • U.S. Patents Nos. 4,602,263 and 4,826,976 both describe thermal imaging systems for optical recording and particularly for forming color images. These thermal imaging systems rely upon the irreversible unimolecular fragmentation of one or more thermally unstable carbamate moieties of an organic compound to effect a visually discernible color shift.
  • the color-developing component is a substantially colorless di- or triarylmethane imaging compound possessing within its di- or triarylmethane structure an aryl group substituted in the ortho position to the meso carbon atom with a moiety ring-closed on the meso carbon atom to form a 5- or 6-membered ring, said moiety possessing a nitrogen atom bonded directly to the meso carbon atom and the nitrogen atom being bound to a group with a masked acyl substituent that undergoes fragmentation upon heating to liberate the acyl group for effecting intramolecular acylation of the nitrogen atom to form a new group in the ortho position that cannot bond to the meso carbon atom, whereby the di- or triarylmethane compound is rendered colored.
  • thermal imaging systems using di- or triarylmethane compounds are described in U.S. Patents Nos. 4,720,450, while U.S. Patent No. 4,745,046 describes a thermal imaging system using as color-forming co-reactants a substantially colorless di- or triarylmethane compound possessing on the meso carbon atom within its di- or triarylmethane structure an aryl group substituted in the ortho position with a nucleophilic moiety which is ring-closed on the meso carbon atom, and an electrophilic reagent which, upon heating and contacting the di- or triarylmethane compound, undergoes a bimolecular nucleophilic substitution reaction with the nucleophilic moiety to form a colored, ring-opened di- or triarylmethane compound.
  • the aforementioned patents describe a preferred form of imaging medium for forming multicolor images; in this preferred imaging medium, three separate color-forming layers, capable of forming yellow, cyan and magenta dyes, respectively, are superposed on top of one another. Each of the three color-forming layers has an infra-red absorber associated therewith, these absorbers absorbing at differing wavelengths, for example 760, 820 and 880 nm. This medium is imagewise exposed to three lasers having wavelengths of 760, 820 and 880 nm. (In the present state of technology, solid state diode lasers emitting at about 760 to 1000 nm provide the highest output per unit cost.
  • This preferred type of imaging medium is capable of very high resolution images; for example, the medium can readily be used to produce a 2K line 35 mm slide (i.e., a slide having 2000 pixels in each line parallel to the long edges of the slide).
  • images produced from certain leuco dyes especially those described in the aforementioned U.S. Patents Nos. 4,720,449 and 4,960,901, tend to fade and/or undergo color shifts when those images are projected using powerful conventional slide projectors, for example xenon arc projectors, for extended periods of time.
  • fading and color shifts are undesirable and the need therefore exists for ways of preventing or at least reducing such fading and color shifts.
  • thermal color-forming reactions described in the aforementioned patents do not provide any amplification such as occurs in silver halide based imaging media, and consequently the media are relatively insensitive; typically, the thermal media require energy inputs of about 1 J/cm 2 per color-forming layer to achieve maximum transmission optical densities around 3.0, which are needed for acceptable slides. Accordingly, it would be advantageous to improve the sensitivity of these thermal imaging media so as to improve the speed of image formation and/or reduce the power requirements for the energy source used for imaging.
  • this invention provides a thermal imaging medium comprising at least one imaging layer, the imaging layer comprising a color-forming compound which undergoes a change of color upon heating above a color-forming temperature for a color-forming time, the color-forming compound being of the formula: and forming after its change in color a dye compound of the formula: in which formulae:
  • meso carbon atom is used herein in its conventional sense to refer to the carbon atom bonded to the groups Z and Z' in the compounds of Formula I and II.
  • hydroquinone is used herein generically to refer to any aromatic system in which a single phenyl ring bears two hydroxyl groups in positions para to one another.
  • the term as used herein includes not only derivatives of hydroquinone itself in which the phenyl ring is substituted, for example 2-phenyl-5-methylhydroquinone, but also compounds in which the phenyl ring bearing the hydroxyl groups is fused to one or more other aromatic rings, for example naphthohydroquinone.
  • quinone is used in a corresponding manner.
  • This invention also provides a process for forming an image, the process comprising:
  • this invention provides an imaged medium having imagewise colored and substantially uncolored areas, the substantially uncolored areas of the image comprising a color-forming compound which undergoes a change of color upon heating above a color-forming temperature for a color-forming time, the color-forming compound being of Formula I above and the colored areas of the image comprising a dye compound of Formula II above.
  • the imaged medum is characterized in that the colored and substantially uncolored areas further comprise a color-stabilizing and/or sensitizing additive comprising any one or more of a quinone, a hydroquinone and a source of zinc, nickel, copper(II), cobalt(II) or aluminum(III) cations
  • the thermal imaging medium of the present invention comprises a color-forming compound of Formula I (which, upon heating above a color-forming temperature for a color-forming time, forms a dye compound of Formula II) and a color-stabilizing additive. More than one color-stabilizing additive may be employed if desired.
  • hydroquinone rather than a quinone in the imaging medium and process of the present invention
  • hydroquinones seem to be somewhat more effective than the quinones.
  • Hydroquinones having an electron withdrawing substituent on the aromatic ring bearing the two hydroxyl groups are preferred, since they have been found to be more effective in preventing fading of images produced using the present process; the effectiveness of the hydroquinones in preventing image fading correlates well with the electron withdrawing ability of the substituent(s), but does not correlate with the redox potentials of the hydroquinones.
  • the or each electron withdrawing substituent may be, for example, a halogen atom or an alkyl group.
  • hydroquinones for use in the present medium and process are chlorohydroquinone, 2,5-dichlorohydroquinone, 2-methyl-5-phenylhydroquinone, phenylhydroquinone and 2,5-di-t-butylhydroquinone.
  • the imaging layer used in the imaging medium of the present invention normally contains a polymeric binder and, when the color-stabilizing additive is a quinone or hydroquinone, the quinone or hydroquinone used must of course be chosen so that it can be dispersed at the required concentration in the polymeric binder used, though in practice it is not usually difficult to disperse quinones and hydroquinones in the binders normally used in thermal imaging media. In general, it is recommended that quinones and hydroquinones containing strongly acid substituents be avoided, since these acid substituents may cause undesirable color formation of the color-forming compound during storage at ambient temperature.
  • zinc is preferred over the other metal cations for use in the imaging medium and process of the present invention.
  • zinc will typically increase the sensitivity of the medium at least about 30 percent.
  • certain relatively insensitive color-forming compounds which in the absence of zinc image so slowly that they are impractical for use in any commercially-useful imaging medium, are increased in sensitivity several hundred per cent by the addition of zinc.
  • Appropriate zinc salts are readily available and inexpensive.
  • zinc tends to be less likely than other cations to form unwanted colored complexes with other components of the imaging medium.
  • the source of metal cations used in the present imaging medium can be any metal compound which can be dispersed at the required concentration in the imaging layer and which does not adversely affect any of the components of that layer.
  • the imaging layer normally contains a polymeric binder and this polymeric binder typically restricts the sources of metal cations which can be used, since many inorganic metal salts cannot be dispersed at high concentrations in polymeric binders and/or adversely affect such binders.
  • strongly acidic salts for example, zinc salicylate, benzoate, ascorbate and phenolsulfonate, be avoided, since these acidic salts may cause undesirable color formation of the color-forming compound during storage at ambient temperature.
  • Zinc chloride and zinc nitrate are also sufficiently acidic to cause undesirable color formation in some leuco dyes, and hence are not recommended for use in the present invention.
  • Preferred metal sources are metal carboxylates; zinc acetate and isobutyrate are especially preferred because of their low cost and low molecular weight, which reduces the amount of the salt which has to be included in the imaging layer to provide a given amount of zinc cation.
  • the use of lower carboxylates containing less than about 8 carbon atoms is preferred, since higher carboxylates, which are waxy materials, tend not to give clear layers; for example, it has been found that zinc stearate is too waxy to give a clear coating.
  • Nickel, aluminum, copper(II) and cobalt(II) are all conveniently supplied as their acetates.
  • Another preferred source of zinc and/or nickel in the imaging media of the present invention is zinc and nickel rosinates, also known commercially as zinc and nickel resinates. These materials are rosin-based zinc and nickel salts with good solubility in the polymeric binders typically used in thermal imaging media. Rosin consists mainly of abietic acid, with minor proportions of hydrogenated abietic acids and other materials. Examples of rosinates which are available commercially and are useful in the present imaging media are the materials sold under the registered trademarks Zirex, Zinar, Zitro and Polytac100 by Arizona Chemical Company, 1001 East Business Highway 98, Panama City, Florida 32401, United States of America. The zinc derivatives described in U.S. Patent No. 5,008,237 may also be used.
  • the rate of projector fading and/or color shifting experienced with the imaged medium of the present invention varies considerably with the polymeric binder used in the imaging layer, and thus the optimum amount of color-stabilizing additive to be used in the imaging layer is best determined empirically.
  • the color-stabilizing additive is a quinone or hydroquinone
  • the color-stabilizing additive is a source of metal cations
  • the source provide at least about 0.1, and desirably at least about 0.25, mole of metal cation per mole of color-forming compound.
  • the color change undergone by the color-forming compound during imaging of the thermal imaging medium of the present invention may be from colorless to colored, or from one color to another), but in general it is preferred that the color change be from colorless to colored.
  • the term "colored” as used herein is not restricted to colors visible to the human eye; although the present invention may find its chief application in imaging media intended for the production of visible images, it may also be used in imaging media intended for the production of "images" which can only be read at non-visible (for example, infra-red) wavelengths.
  • Preferred color-forming compounds of Formula I are those in which Z and Z' each comprise a benzene ring, Z and Z' being linked via an oxygen atom bonded to the two benzene rings at positions ortho to the meso carbon atom, so that the Z-C-Z' grouping forms a xanthene nucleus.
  • Especially preferred compounds of this type are those in which the benzene rings of Z and Z' carry substituted amino groups at positions para to the meso carbon atom.
  • ring A comprise a benzene ring bearing, at its position para to the sulfonamide nitrogen atom, a carbamate moiety.
  • heat may be applied or induced imagewise in a variety of ways.
  • selective heating is produced in the color-forming layer itself by the conversion of electromagnetic radiation into heat
  • the light source is a laser emitting source such as a gas laser or semiconductor laser diode, preferably an infra-red laser.
  • the use of a laser beam is not only well suited for recording in a scanning mode but by utilizing a highly concentrated beam, radiant energy can be concentrated in a small area so that it is possible to record at high speed and high density. Also, it is a convenient way to record data as a heat pattern in response to transmitted signals, such as digitized information.
  • the imaging medium desirably comprises an absorber capable of absorbing infra-red radiation and thereby generating heat in the imaging layer.
  • the heat thus generated is transferred to the color-forming compound to initiate the color-forming reaction and effect the change in the absorption characteristics of the color-forming compound from colorless to colored.
  • the infrared absorber (which may also be referred to hereinafter as an "infra-red dye") should be in heat-conductive relationship with the color-forming compound, for example, in the same layer as the color-forming compound or in an adjacent layer.
  • the infra-red absorber preferably is an organic compound, such as a cyanine, merocyanine, squarylium, thiopyrylium or benzpyrylium dye, and preferably, is substantially non-absorbing in the visible region of the electromagnetic spectrum so that it will not contribute any substantial amount of color to the D min areas, i.e., the highlight areas of the image.
  • the light absorbed by the respective infra-red absorbers is converted into heat and the heat initiates the reaction to effect the formation of colored compounds in the color-forming layers. Since this type of imaging medium is imaged by infra-red radiation rather than by direct heating, a high resolution image is more easily achieved.
  • An especially preferred form of imaging medium of the present invention has at least two imaging layers, the at least two imaging layers comprising color-forming compounds arranged to produce dye compounds having differing colors, and comprising absorbers absorbing at differing wavelengths.
  • the infra-red absorbers are desirably selected such that they absorb radiation at different predetermined wavelengths above 700 nm sufficiently separated so that each color-forming layer may be exposed separately and independently of the others by using infra-red radiation at the particular wavelengths selectively absorbed by the respective infra-red absorbers.
  • three color-forming layers containing yellow, magenta and cyan color-forming compounds could have infra-red absorbers associated therewith that absorb radiation at 792 nm, 848 nm and 926 nm, respectively, and could be addressed by laser sources, for example, infra-red laser diodes, emitting laser beams at these respective wavelengths so that the three color-forming layers can be exposed independently of one another. While each layer may be exposed in a separate scan, it is usually preferred to expose all of the color-forming layers in a single scan using multiple laser sources of the appropriate wavelengths.
  • the color-forming compounds and associated infra-red absorbers may be arranged in an array of side-by-side dots or stripes in a single recording layer.
  • the color-forming compounds may comprise the subtractive primaries yellow, magenta and cyan or other combinations of colors, which combinations may additionally include black.
  • the leuco dyes generally are selected to give the subtractive colors cyan, magenta and yellow, as commonly employed in photographic processes to provide full natural color.
  • a full color imaging medium of this type having three imaging layers is described below with reference to Figure 1 of the accompanying drawings.
  • the imaging medium may be heated prior to or during exposure. This may be achieved using a heating platen or heated drum or by employing an additional laser source or other appropriate means for heating the medium while it is being exposed.
  • the imaging medium of the present invention can be prepared in a manner similar to the imaging media described in the aforementioned patents and applications.
  • the color-forming compound and any other components of the imaging layer are dispersed in an appropriate solvent, and the resultant liquid dispersion is coated onto a support, generally a polymer film, using conventional coating equipment, and the resultant liquid film dried to produce the imaging layer.
  • the layer may be applied as a dispersion or an emulsion.
  • the coating composition also may contain dispersing agents, plasticizers, defoaming agents, hindered amine light stabilizers and coating aids.
  • temperatures should be maintained below levels that will cause the color-forming reactions to occur rapidly so that the color-forming compounds will not be prematurely colored.
  • the additive is simply dispersed in the liquid dispersion with the other components of the imaging layer.
  • the present invention does not require extensive changes in the equipment or processes used to produce the thermal imaging medium.
  • the imaging medium of the present invention may contain additional layers and components as described in the aforementioned patents and applications.
  • the imaging medium typically includes a support on which the imaging layer(s) are deposited.
  • the support should be sufficiently thick as to permit easy handling of the imaging medium, and may be any material that substantially retains its dimensional stability during imaging. Desirably, the support has a thickness of at least about 50 ⁇ m.
  • the support must be sufficiently transparent that it does not raise excessively the D min of the final image.
  • the support must also be sufficiently transparent that it does not interfere with the imaging process, and is preferably non-birefringent, since if the medium is imaged through the support, a birefringent support may cause difficulties in focussing the laser (or other radiation source) at the proper level within the imaging medium.
  • Suitable supports include polyethylene, polypropylene, polycarbonate, cellulose acetate, and polystyrene.
  • the preferred material for the support is a polyester, desirably poly(ethylene terephthalate).
  • binders examples include poly(vinyl alcohol), poly(vinyl pyrrolidone), methyl cellulose, cellulose acetate butyrate, styrene-acrylonitrile copolymers, copolymers of styrene and butadiene, poly(methyl methacrylate), copolymers of methyl and ethyl acrylate, poly(vinyl acetate), poly(vinyl butyral), polyurethane, polycarbonate and poly(vinyl chloride).
  • the binder selected should not have any adverse effect on the leuco dye incorporated therein and may be selected to have a beneficial effect.
  • the binder should be substantially heat-stable at the temperatures encountered during image formation and it should be transparent so that it does not interfere with viewing of the color image. Where electromagnetic radiation is employed to induce imagewise heating, the binder also should transmit the light intended to initiate image formation.
  • the leuco dye in some imaging media of the type described in the aforementioned patents, there is a tendency for one or more of the colored materials produced during imaging to diffuse out of their color-forming layers, but such undesirable diffusion of colored material can be reduced or eliminated by dispersing the leuco dye in a first polymer having a glass transition temperature of at least about 50°C, preferably at least about 75°C, and most preferably at least about 95°C, and providing a diffusion-reducing layer in contact with the color-forming layer, this diffusion-reducing layer comprising a second polymer having a glass transition temperature of at least about 50°C and being essentially free from the color-forming composition.
  • the diffusion-reducing layer has a thickness of at least about 1 ⁇ m.
  • the first polymer is desirably an acrylic polymer, preferably poly(methyl methacrylate).
  • the imaging medium of the present invention advantageously comprises a bubble-suppressant layer superposed on the imaging layer and having a thickness of at least about 10 ⁇ m, such that, upon imagewise increase in the temperature of the imaging layer above the color-forming temperature for the color-forming time, in heated regions the imaging layer undergoes its change of color but remains essentially free from bubbles.
  • a subbing layer to improve adhesion to a support
  • interlayers for thermally insulating the imaging layers from each other
  • an ultra-violet screening layer having an ultraviolet absorber therein, or other auxiliary layers.
  • ultra-violet screening layers are desirably provided on both sides of the imaging layer(s); conveniently, one of the ultra-violet screening layers is provided by using as the support a polymer film containing an ultra-violet absorber, and such absorber-containing films are available commercially.
  • the imaging medium (generally designated 10) shown in Figure 1 is intended for use in the production of transparencies and comprises a substantially transparent support 12 formed of 4 mil (101 ⁇ m) poly(ethylene terephthalate) (PET) film incorporating an ultra-violet absorber.
  • PET poly(ethylene terephthalate)
  • Appropriate PET films are readily available commercially, for example as P4C1A (Registered Trade Mark) film from DuPont de Nemours., Wilmington, Delaware, United States of America.
  • the imaging medium 10 also comprises a diffusion-reducing subcoat 14 approximately 1 ⁇ m thick formed from a 10:1 w/w mixture of a water-dispersible styrene acrylic polymer (Joncryl (Registered Trade Mark) 538 sold by S.C. Johnson & Son, Inc., Racine Wisconsin 53403, United States of America) and a water-soluble acrylic polymer (Carboset (Registered Trade Mark) 526 sold by The B.F. Goodrich Co., Akron Ohio 44313, United States of America).
  • a diffusion-reducing subcoat 14 approximately 1 ⁇ m thick formed from a 10:1 w/w mixture of a water-dispersible styrene acrylic polymer (Joncryl (Registered Trade Mark) 538 sold by S.C. Johnson & Son, Inc., Racine Wisconsin 53403, United States of America) and a water-soluble acrylic polymer (Carboset (Registered Trade Mark) 526 sold by The B.F. Goodrich Co.
  • the diffusion-reducing subcoat 14 which has a glass transition temperature of approximately 55°C, serves the function of a conventional subcoat, namely increasing the adhesion of the imaging layer 16 (described in detail below) to the support 12.
  • the subcoat 14 also serves to reduce or eliminate migration of dye compound from the imaging layer 16 after imaging; if a conventional subcoat were employed in place of the diffusion-reducing subcoat 14, diffusion of the dye compound from the layer 16 into the subcoat after imaging might cause loss of sharpness of the image.
  • the subcoat 14 is coated onto the support 12 from an aqueous medium containing the water-dispersible and water-soluble polymers.
  • a yellow imaging layer 16 is in contact with the diffusion-reducing subcoat 14.
  • This imaging layer 16 is approximately 5 ⁇ m thick and comprises approximately 47.5 parts by weight of a leuco dye of the formula: in which R' is a tertiary butyl group (the compounds in which R' is an isobutyl or benzyl group may alternatively be used), 1.6 parts by weight of an infra-red dye of the formula: (prepared as described in copending and commonly owned International Application Publication No.
  • WO 92/09661 essentially, this dye is produced by condensing two moles of a 2-(1,1-dimethylethyl)-5,7-dimethoxy-4-methylbenzpyrylium salt with a croconate salt), 3.3 parts by weight of a hindered amine stabilizer (HALS-63 (Registered Trade Mark), sold by Fairmount Chemical Co., , Inc., 117 Blanchard Street, Newark NJ 07105, United States of America), and 47.5 parts by weight of a poly(methyl methacrylate) binder (Elvacite (Registered Trade Mark) 2021, sold by DuPont de Nemours, Wilmington, Delaware, United States of America; this material is stated by the manufacturer to be a methyl methacrylate/ethyl acrylate copolymer, but its glass transition temperature approximates that of poly(methyl methacrylate)).
  • This binder has a glass transition temperature of approximately 110°C.
  • the imaging layer 16 is applied by coating from a mixture
  • the diffusion-reducing layer 18 which, like the first diffusion-reducing layer 14, serves to prevent migration of dye compound from the yellow imaging layer 16 on storage after imaging.
  • the diffusion-reducing layer 18, which is approximately 2 ⁇ m thick, is formed of a water-dispersible styrene acrylic polymer (Joncryl 138 sold by S.C. Johnson & Son, Inc., Racine Wisconsin 53403, United States of America), and is coated from an aqueous dispersion. This layer has a glass transition temperature of approximately 60°C.
  • the next layer of the imaging medium 10 is a solvent-resistant interlayer 20 approximately 4.6 ⁇ m thick and composed of a major proportion of partially cross-linked polyurethane (NeoRez (Registered Trade Mark) XR-9637 polyurethane sold by ICI Resins US, Wilmington, Massachusetts, United States of America) and a minor proportion of poly(vinyl alcohol) (Airvol (Registered Trade Mark) 540, sold by Air Products and Chemicals, Inc., Allentown Pennsylvania 18195, United States of America).
  • This solvent-resistant interlayer 20 is coated from an aqueous dispersion.
  • the interlayer 20 not only helps to thermally insulate the imaging layers 14 and 22 (described below) from one another during imaging, but also prevents disruption and/or damage to the yellow imaging layer 16 and the diffusion-reducing layer 18 during coating of the magenta imaging layer 22. Since the yellow imaging layer 16 and the magenta imaging layer 22 are both coated from organic solution, if a solvent-resistant interlayer were not provided on the layer 16 before the layer 22 was coated, the organic solvent used to coat the layer 22 might disrupt, damage or extract leuco dye or infra-red absorber from the layer 16. Provision of the solvent-resistant interlayer 20, which is not dissolved by and does not swell in the organic solvent used to coat the layer 22, serves to prevent disruption of or damage to the layer 16 as the layer 22 is coated.
  • the solvent-resistant interlayer 20 serves to prevent the magenta leuco dye, infra-red dye and hindered amine light stabilizer from the layer 22 sinking into the diffusion-reducing layer 18 and the yellow imaging layer 16 as the layer 22 is being coated.
  • magenta imaging layer 22 which is approximately 3 ⁇ m thick and comprises approximately 47.25 parts by weight of a leuco dye of Formula III above (this leuco dye may be prepared by the methods described in the aforementioned US-A-4 720 449 and 4 960 901), approximately 5.02 parts by weight of chlorohydroquinone (thus giving a leuco dye: chlorohydroquinone molar ratio of about 1:0.75; alternatively, approximately 3.4 parts by weight of zinc acetate may be used, thus giving a leuco dye: zinc cation molar ratio of about 1:0.4), 1.62 parts by weight of an infra-red dye of the formula: (which may be prepared by reacting a compound of the formula: in which R'' is a halogen atom or an alkyl group, with diethylamine to introduce the -NEt 2 group on the squarylium ring, and then reacting the product with the 4-methylbenzpyryl
  • the infra-red dye of Formula IR2 above may be replaced by the dye of formula: (used in the form of its tetrafluoroborate salt) (this infra-red dye may be prepared by the process analogous to that used to prepare the infra-red dye of Formula IR2 above using the corresponding selenopyrylium squaric acid derivative and ammonia to introduce the amino group, followed by condensation of the product with a selenopyrylium salt; to prepare the selenopyrylium squaric acid derivative, the corresponding selenopyrylium salt is substituted for the benzpyrylium salt IV).
  • a second solvent-resistant interlayer 24 which is formed from the same material, and coated in the same manner as, the solvent-resistant interlayer 20.
  • a cyan imaging layer 26 which is approximately 3 ⁇ m thick and comprises approximately 49.5 parts by weight of a leuco dye of Formula IV above (this leuco dye may be prepared by the methods described in US-A-4 720 449 and 4 960 901), approximately 5.86 grams of chlorohydroquinone (thus giving a leuco dye: chlorohydroquinone molar ratio of about 1:0.75; alternatively approximately 3.97 grams of zinc acetate may be used to give a leuco dye: zinc cation molar ratio of about 1:0.4), 1.62 parts by weight of an infra-red dye of the formula: (which is preferably prepared by the process described in the copending and commonly owned EP-A-516 985; essentially this process comprises reacting a diester, diacid chloride or monoester monoacid chloride of squaric acid with a 2-(1,1-dimethylethyl)7-diethylamino-4-methyl
  • the infra-red dye of Formula IR4 above may be replaced by the dye of formula: (which may be prepared by a process analogous to that used to prepare the infra-red dye of Formula IR2 above, by reacting the intermediate of Formula V above with ammonia to introduce an amino group on the squarylium ring, then reacting the product with a 4-methylbenzpyrylium salt to produce the amino squarylium dye, and finally reacting this amino squarylium dye with pivaloyl chloride to produce the final pivaloylamino group on the squarylium ring).
  • the dye of formula: which may be prepared by a process analogous to that used to prepare the infra-red dye of Formula IR2 above, by reacting the intermediate of Formula V above with ammonia to introduce an amino group on the squarylium ring, then reacting the product with a 4-methylbenzpyrylium salt to produce the amino squarylium dye, and finally reacting this amino squarylium
  • the layers 14-26 of the imaging medium 10 are produced by coating on to the transparent support 12.
  • the remaining layers of the imaging medium 10, namely the transparent bubble-suppressant layer 32, the ultraviolet filter layer 30 and the adhesive layer 28 are not coated on to the layer 26 but rather are prepared as a separate unit and then laminated to the remaining layers of the medium.
  • the transparent bubble-suppressant layer 32 is a 1.75 mil (44 ⁇ m) PET film, a preferred film being that sold as ICI (Registered Trade Mark) 505 film by ICI Americas, Inc., Wilmington, Delaware, United States of America.
  • the bubble-suppressant layer 32 prevents the formation of bubbles in the imaging layers 16, 22 and 26 of the imaging medium 10 during imaging.
  • the ultraviolet filter layer 30 serves to protect the imaging layers 16, 22 and 26 from the effects of ambient ultraviolet radiation. It has been found that the leuco dyes are susceptible to undergoing color changes when exposed to ultraviolet radiation during storage before or after imaging; such color changes are obviously undesirable since they increase the D min of the image and may distort the colors therein.
  • the ultraviolet filter layer 30 is approximately 5 ⁇ m thick and comprises approximately 83 percent by weight of a poly(methyl methacrylate) (Elvacite 2043, sold by DuPont de Nemours, Wilmington, Massachusetts, United States of America), 16.6 percent by weight of an ultraviolet filter (Tinuvin (Registered Trade Mark) 328 sold by Ciba-Geigy, Ardsdale New York, United States of America) and 0.4 percent by weight of a wetting agent.
  • the ultraviolet filter layer 30 is prepared by coating on to the bubble-suppressant layer 32 from a solution in methyl ethyl ketone.
  • the adhesive layer which is approximately 2 ⁇ m thick, is formed of a water-dispersible styrene acrylic polymer (Joncryl 138 sold by S.C. Johnson & Son, Inc., Racine Wisconsin 53403, United States of America) and is coated on to the ultraviolet filter layer 30 from an aqueous dispersion.
  • a water-dispersible styrene acrylic polymer (Joncryl 138 sold by S.C. Johnson & Son, Inc., Racine Wisconsin 53403, United States of America)
  • the entire structure containing these three layers is laminated under heat (approximately 225°F, 107°C) and pressure to the structure containing the layers 12-26 to form the complete imaging medium 10.
  • the bubble-suppressant layer 32 may be formed by coating, rather than by lamination of a pre-formed film on to the layers 12-26. If the bubble-suppressant layer 32 is to be formed by coating, it is convenient to incorporate an ultra-violet absorber into the bubble-suppressant layer, thereby avoiding the need for a separate ultra-violet absorber layer. Thus, in this case, the layer 28 is coated on to the layer 26 using the solvent already described, and then the bubble-suppressant layer 32 containing the ultra-violet absorber may be coated on to the layer 28 from an aqueous medium.
  • the medium 10 is imaged by exposing it to the beams from three infra-red lasers having wavelengths of approximately 792, 848 and 926 nm.
  • the 926 nm beam images the yellow imaging layer 16
  • the 848 nm beam images the magenta imaging layer 22
  • the 792 nm beam images the cyan imaging layer 26.
  • a multicolor image is formed in the imaging medium 10, and this multicolor image requires no further development steps.
  • the medium 10 may be handled in normal room lighting prior to exposure, and the apparatus in which the imaging is performed need not be light-tight.
  • This Example illustrates the effect of chlorohydroquinone in increasing sensitivity of, and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • This simplified model comprised the support 12 incorporating an ultra-violet absorber, the cyan imaging layer 26 (with varying amounts of chlorohydroquinone, as described below, with the aforementioned Elvacite 2021 poly(methyl methacrylate) replacing the Estane 5715 used in the medium shown in Figure 1, and with the infra-red absorber being that of Formula VII above), an adhesive layer 28 and a bubble-suppressant layer 32, which was formed from the same polymeric film as the support 12 and thus incorporated an ultra-violet absorber.
  • the red optical densities of the various areas of the resultant images were measured using an X-Rite (Registered Trade Mark) 310 photographic densitometer (supplied by X-Rite, Inc., Grandville, Michigan) with the appropriate filter. The results are shown in Table 1 below and plotted in Figure 2 of the accompanying drawings, in which the red optical density achieved is plotted against writing speed.
  • burn-out This decrease in optical density with increasing exposure which is referred to as "burn-out".
  • burn-out is manifested as a positive slope of the optical density against writing speed curve at low writing speeds, since exposure is inversely proportional to writing speed.
  • the sensitivities of various media can only properly be compared at exposures and writing speeds where none of the media being compared are suffering from burn-out; in other words, when making sensitivity comparisons, the comparisons must be made in regions of optical density/writing speed curves where all the relevant curves have a significant negative slope.
  • quoted percentage increases in sensitivity are expressed as: [ ⁇ Average of (Optical Density of Sensitized Medium/Optical Density of Unsensitized Medium) ⁇ - 1] x 100% with the relevant range of writing speeds indicated in parentheses following the percentage.
  • This Example illustrates the effect of 2-methyl-5-phenylhydroquinone ("MPHQ”) in increasing sensitivity of, and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • MPHQ 2-methyl-5-phenylhydroquinone
  • Example 1 was repeated, except that the chlorohydroquinone used in that Example was replaced with equimolar amounts of 2-methyl-5-phenylhydroquinone.
  • the media were imaged and exposed in a projector in the same way as in Example 1.
  • the results are given in Table 2 below; the results of the imaging experiments are plotted in Figure 4, while the result of the projector experiments are plotted in Figure 5 below.
  • This Example illustrates the effect of varying amounts of 2-methyl-5-phenylhydroquinone in reducing projector fading of images formed from imaging media containing the cyan leuco dye of Formula IV above.
  • Example 2 was repeated, except that the media used were a control medium free from hydroquinone and media in which the imaging layer contained MPHQ at leuco cyan dye : MPHQ molar ratios of 1:0.14, 1:0.28, 1:0.37 and 1:0.49.
  • the media were imaged at writing speeds of 0.18, 0.22, 0.26, 0.32, 0.42 and 0.51 m/s, and exposed in a projector in the same way as in Examples 1 and 2.
  • the results are given in Table 3 below and plotted in Figure 6.
  • This Example illustrates the effect of varying amounts of 2,5-di-t-butylhydroquinone ("DtBHQ") in reducing projector fading of images formed from imaging media containing the cyan leuco dye of Formula IV above.
  • DtBHQ 2,5-di-t-butylhydroquinone
  • Example 3 was repeated, except that the media used were a control medium free from hydroquinone and media in which the imaging layer contained DtBHQ at leuco cyan dye: DtBHQ molar ratios of 1:0.24, 1:0.48, 1:0.71 and 1:0.84.
  • the media were imaged at writing speeds of 0.18, 0.22, 0.26, 0.32, 0.42 and 0.51 m/s, and exposed in a projector in the same way as in Examples 1 to 3.
  • the results are given in Table 4 below and plotted in Figure 7.
  • This Example illustrates the effect of 2,5-di-t-butylhydroquinone in reducing projector fading of images formed from imaging media containing the magenta leuco dye of Formula III above.
  • Example 4 was repeated, except that the cyan imaging layer was replaced with a magenta imaging layer similar to the magenta imaging layer 22 described above with reference to Figure 1 but containing the infra-red dye of Formula VI above. Only two media were used, namely a control medium free from hydroquinone and a medium in which the imaging layer contained DtBHQ at a leuco magenta dye : DtBHQ molar ratio of 1:0.76. The media were imaged at writing speeds of 0.18, 0.22, 0.26, 0.32, 0.42, 0.51 and 0.63 m/s, and exposed in a projector in the same way as in Examples 1 to 4, but for a period of 20 minutes.
  • Control DtBHQ/LM 0.76 Initial Green Density Change in O.D., % Initial Green Density Change in O.D., % 3.22 -3.7 3.18 5.0 3.19 -2.5 3.15 3.2 2.98 -7.0 3.04 2.0 1.96 -9.2 2.09 1.0 0.67 -12.0 0.67 -3.0 0.22 -18 0.24 -8.4
  • This Example illustrates the effect of catechol and resorcinol in increasing sensitivity of and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • Example 1 was repeated, except that the media used were the control medium, a medium containing catechol at a leuco dye : catechol molar ratio of 1:1.08, and a medium containing resorcinol at a leuco dye : resorcinol molar ratio of 1:1.05.
  • the infra-red optical densities of the three media at 792 nm were found to be 0.89, 1.09 and 1.05 respectively.
  • the media were imaged and exposed in a projector in the same way as in Example 1. The results are given in Table 6 below; the results of the imaging experiments are plotted in Figure 9, while the result of the projector experiments are plotted in Figure 10 below.
  • Example 1 was repeated, except that the media used were the control medium and three media in which the cyan imaging layer contained respectively PtBHQ, PHQ and DClHQ, each at a leuco dye : hydroquinone molar ratio of 1:0.5.
  • the media were imaged and exposed in a projector in the same way as in Example 1.
  • the results are given in Table 7 below; the results of the imaging experiments are plotted in Figure 11, while the results of the projector experiments are plotted in Figure 12 below.
  • This Example illustrates the effect of 2-methyl-5-phenylhydroquinone (“MPHQ”), phenylhydroquinone (“PHQ”), 2-phenyl-5-t-butyl-hydroquinone (“PtBHQ”), 2,5-di-t-butylhydroquinone (“DtBHQ”) and 2,5-dichlorohydroquinone (“DClHQ”) in reducing projector fading of images formed from imaging media containing the cyan leuco dye of Formula IV above.
  • MPHQ 2-methyl-5-phenylhydroquinone
  • PHQ phenylhydroquinone
  • PtBHQ 2-phenyl-5-t-butyl-hydroquinone
  • DtBHQ 2,5-di-t-butylhydroquinone
  • DClHQ 2,5-dichlorohydroquinone
  • Example 1 was repeated, except that the media used were a control medium free from hydroquinone and six media containing in which the cyan imaging layer contained respectively MPHQ, PHQ, PtBHQ, DtBHQ and DClHQ, each at a leuco cyan dye : hydroquinone molar ratio of 1:0.25.
  • the media were imaged at writing speeds of 0.18, 0.22, 0.26, 0.32, 0.42 and 0.51 m/s, and exposed in a projector in the same way as in Examples 1 to 3.
  • the results are given in Table 8 below and plotted in Figures 13 and 14 (the control results are shown in both Figures for ease of comparison).
  • the media used in these experiments were substantially similar to those used in Example 1 above.
  • the infra-red dye (VII - 0.36 g of a 1% w/v solution in 2-butanone), the cyan leuco dye (IV - 0.22 g) and 1.46 g of a 15% w/v solution of a poly(methyl methacrylate) in acetone were mixed together to form a clear solution, which was split into four equal portions of about 500 ⁇ l each.
  • MPHQ 2-methyl-5-phenylhydroquinone
  • DCBQ 2,6-dichloro--1,4-benzoquinone
  • AQ 9,10-anthraquinone
  • red and visible optical densities of unimaged portions of the four films were measured after imaging.
  • the films were stored at 70°C in an oven and these densities remeasured after 17, 41 and 65 hours storage.
  • Figures 16A and 16B respectively show the variation of red and visible optical densities respectively with storage time.
  • This Example illustrates the effect of zinc, aluminum and nickel cations in increasing sensitivity of, and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • the media used in this experiment were the same as in Example 1 above, and had a leuco dye : polymer weight ratio of 0.5 : 1.
  • Four media were prepared, a control in which the cyan color-forming layer contained no metal cations, a second medium in which the color-forming layer contained zinc acetate at a leuco dye : zinc molar ratio of 1:0.36, a third medium in which the color-forming layer contained aluminum acetate at a leuco dye : aluminum molar ratio of 1:0.23, and a fourth medium in which the color-forming layer contained nickel acetate at a leuco dye : nickel molar ratio of 1:0.32.
  • These four media were imaged and their optical densities recorded in the same way as in Example 1. The results are shown in Table 10 below and plotted in Figure 19 of the accompanying drawings.
  • This Example illustrates the effect of zinc isobutyrate in increasing sensitivity of, and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • the media used in this experiment were the same as in Example 1 above.
  • Four media were prepared, a control in which the cyan color-forming layer contained no zinc, and three others in which the color-forming layer contained zinc isobutyrate at leuco dye : zinc molar ratio of 1:0.2, 1:0.4 and 1:0.8.
  • These four media were imaged and their optical densities recorded in the same way as in Example 1, except that a 785 nm laser was used for imaging.
  • Table 11 below and plotted in Figure 21 of the accompanying drawings.
  • the addition of zinc to the cyan imaging layer rendered the medium more sensitive.
  • This Example illustrates the effect of copper(II) and cobalt(II) cations in reducing projector fading of images formed from imaging media containing the cyan leuco dye of Formula IV above.
  • the media used in this experiment were the same as in Example 1 above.
  • Three media were prepared, a control in which the cyan color-forming layer contained no metal cations, and two others in which the color-forming layer contained, respectively, copper(II) acetate and cobalt(II) acetate at a leuco dye : metal molar ratio of 1:0.2.
  • These three media were imaged and their optical densities recorded in the same way as in Example 1, except that a 785 nm laser was used for imaging.
  • This Example illustrates the effect of zinc rosinates in increasing sensitivity of, and reducing projector fading of images formed from, imaging media containing the cyan leuco dye of Formula IV above.
  • the media used in this experiment were the same as in Example 1 above.
  • Five media were prepared, a control in which the cyan color-forming layer contained no zinc, and four others in which the color-forming layer contained one of the zinc rosinates Zirex, Zinar, Zitro and Polytac100 (Zirex, Zinar, Zitro and Polytac100 are all Registered Trademarks) at a leuco dye : zinc molar ratio of 1:0.2.
  • These five media were imaged and their optical densities recorded in the same way as in Example 1, except that an 784 nm laser was used. The results are shown in Table 13 below and plotted in Figure 24 of the accompanying drawings.
  • the addition of zinc rosinates to the cyan imaging layer rendered the medium more sensitive.

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Claims (12)

  1. Support de formation thermique d'images, comportant au moins une couche de formation d'images, laquelle couche de formation d'images contient un composé chromogène qui subit un changement de couleur lorsqu'on le chauffe au-dessus d'une certaine température d'apparition de couleur pendant une certaine durée d'apparition de couleur, lequel composé chromogène a pour formule
    Figure 00680001
    et donne, lorsqu'il change de couleur, un composé colorant de formule
    Figure 00680002
    dans lesquelles formules :
    les cycles A et B sont des noyaux aromatiques ;
    Z et Z', qui peuvent être reliés autrement que par l'intermédiaire de l'atome de carbone méso, représentent des groupements qui suffisent à compléter, au sein du composé colorant, le système auxochromechromophore d'un colorant de type diarylméthane ou triarylméthane, Z et Z' étant tels que le composé colorant absorbe de la lumière dans le domaine visible ;
    L représente un groupe partant qui est éliminé lors d'un chauffage ;
    le trait interrompu situé entre le groupe SO2 et le cycle B indique que le cycle à fonction sulfonamide du composé chromogène peut comporter 5 ou 6 chaínons ;
    caractérisé en ce que la couche de formation d'images contient en outre un adjuvant stabilisateur de couleur et/ou sensibilisateur, qui comprend : (a) une quinone ; (b) une hydroquinone ; ou (c) une source de cations zinc, nickel, cuivre(II), cobalt(II) ou aluminium(III).
  2. Support de formation d'images conforme à la revendication 1, caractérisé en ce que l'adjuvant stabilisateur de couleur comprend une hydroquinone.
  3. Support de formation d'images conforme à la revendication 2, caractérisé en ce que, dans l'hydroquinone, un substituant électroattracteur est placé sur le noyau aromatique qui porte les deux groupes hydroxy.
  4. Support de formation d'images conforme à la revendication 3, caractérisé en ce que l'hydroquinone est de la chlorohydroquinone, de la 2,5-dichlorohydroquinone, de la 2-méthyl-5-phénylhydroquinone, de la phénylhydroquinone ou de la 2,5-di-t-butylhydroquinone.
  5. Support de formation d'images conforme à la revendication 2, caractérisé en ce que la couche de formation d'images confient en tout au moins environ 0,25 mole de quinone et d'hydroquinone par mole de composé chromogène.
  6. Support de formation d'images conforme à la revendication 1 caractérisé en ce que l'adjuvant stabilisateur de couleur comprend une source de cations zinc.
  7. Support de formation d'images conforme à l'une des revendications précédentes, caractérisé en ce que, dans le composé chromogène et dans le composé colorant, Z et Z' comportent chacun un cycle benzénique et sont aussi reliés par un atome d'oxygène lié à chacun des deux cycles benzéniques en position ortho par rapport à l'atome de carbone méso, de sorte que le groupement Z-C-Z' constitue un noyau xanthénique.
  8. Support de formation d'images conforme à l'une des revendications précédentes, caractérisé en ce qu'il y a un absorbeur capable d'absorber un rayonnement infrarouge et par là, de produire de la chaleur au sein de la couche de formation d'images et de provoquer le changement de couleur du composé chromogène.
  9. Support de formation d'images conforme à la revendication 8, caractérisé en ce qu'il y a au moins deux couches de formation d'images, lesquelles couches de formation d'images, au nombre d'au moins deux, contiennent des composés chromogènes capables de produire des composés colorants de couleurs différentes, et contiennent au moins deux absorbeurs qui absorbent des rayonnements de longueurs d'onde différentes.
  10. Procédé permettant de former une image, lequel procédé comporte :
    le fait de prendre un support de formation thermique d'images qui comporte au moins une couche de formation d'images contenant un composé chromogène ;
    le fait de chauffer, selon une image, la couche de formation d'images au-dessus d'une certaine température d'apparition de couleur et pendant une certaine durée d'apparition de couleur, ce qui provoque, dans les zones chauffées correspondant à l'image, la transformation d'au moins une partie du composé chromogène en composé colorant, et par là, la formation d'une image ;
    lequel procédé est caractérisé en ce que le support de formation d'images employé est un support de formation d'images conforme à l'une des revendications précédentes.
  11. Procédé conforme à la revendication 10, dans lequel on projette l'image obtenue en envoyant un rayonnement visible à travers l'image et dans lequel l'adjuvant stabilisateur de couleur qui se trouve au sein du support de formation d'images amoindrit la décoloration de l'image pendant la projection de celle-ci.
  12. Support sur lequel une image est formée et qui présente, selon cette image, des zones qui sont colorées et d'autres zones qui ne le sont pratiquement pas, où les zones pratiquement non colorées de l'image contiennent un composé chromogène qui subit un changement de couleur lorsqu'on le chauffe au-dessus d'une certaine température d'apparition de couleur pendant une certaine durée d'apparition de couleur, lequel composé chromogène a pour formule
    Figure 00710001
    et où les zones colorées de l'image contiennent un composé colorant de formule
    Figure 00710002
    dans lesquelles formules :
    les cycles A et B sont des noyaux aromatiques ;
    Z et Z', qui peuvent être reliés autrement que par l'intermédiaire de l'atome de carbone méso, représentent des groupements qui suffisent à compléter, au sein du composé colorant, le système auxochromechromophore d'un colorant de type diarylméthane ou triarylméthane, Z et Z' étant tels que le composé colorant absorbe de la lumière dans le domaine visible ;
    L représente un groupe partant qui est éliminé lors d'un chauffage ;
    le trait interrompu situé entre le groupe SO2 et le cycle B indique que le cycle à fonction sulfonamide du composé chromogène peut comporter 5 ou 6 chaínons ;
    caractérisé en ce que ces zones colorées et ces zones pratiquement non colorées contiennent en outre un adjuvant stabilisateur de couleur et/ou sensibilisateur, qui comprend : (a) une quinone ; (b) une hydroquinone ; ou (c) une source de cations zinc, nickel, cuire(II), cobalt(II) ou aluminium(III).
EP19920117365 1991-11-20 1992-10-10 Stabilisation d'images thermiques Expired - Lifetime EP0543136B1 (fr)

Applications Claiming Priority (4)

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US07/795,101 US5206208A (en) 1991-11-20 1991-11-20 Stabilization of thermal images
US795102 1991-11-20
US795101 1991-11-20
US07/795,102 US5210064A (en) 1991-11-20 1991-11-20 Stabilization of thermal images

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