Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/52—Compositions containing diazo compounds as photosensitive substances
  • G03C1/61—Compositions containing diazo compounds as photosensitive substances with non-macromolecular additives
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/72—Photosensitive compositions not covered by the groups G03C1/005 - G03C1/705
  • G03C1/73—Photosensitive compositions not covered by the groups G03C1/005 - G03C1/705 containing organic compounds
  • G03C1/732—Leuco dyes
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C7/00—Multicolour photographic processes or agents therefor; Regeneration of such processing agents; Photosensitive materials for multicolour processes
  • G03C7/02—Direct bleach-out processes; Materials therefor; Preparing or processing such materials

Definitions

• the present invention relates to light sensitive imaging systems. More particularly the invention relates to light sensitive, thermally developable diazonium salt imaging systems.
• the present invention provides an imageable layer comprising a) a polymeric binder, b) a bleachable or leuco dye, c) a photosensitive diazonium salt and d) a nitrate salt in a molar ratio to the dye b) of at least 0.1 nitrate ion/1.0 dye, the cation of the said nitrate salt being non-reactive with the dye b), said nitrate salt liberating HN0 3 , NO, N0 2 or N 2 0 2 to bleach said bleachable dye or oxidise said leuco dye when the layer is heated to no more than 200°C for 60 seconds.
• a material which supplies hydrogen ion such as an acidic material, and in particular an acid
• an acidic material is a desirable ingredient. Both positive and negative activating systems may be produced. After exposing the system to light, the application of heat will develop the image by bleaching the dye or oxidising the leuco dye more rapidly in either the exposed or unexposed region. The presence of the acidic material accelerates the decolourisation or colourising phenomenon.
• the leuco dye When a leuco dye is used in place of a dye, the leuco dye is oxidised to form a coloured dye upon the application of heat.
• a positive acting system or negative acting system will result because of the differential rate of oxidation occurring in exposed and unexposed regions.
• the four required ingredients are 1) a bleachable dye or a leuco dye, 2) a nitrate salt, 3) a light sensitive diazonium salt, and 4) a polymeric resin.
• An acidic material constitutes the preferred fifth ingredient.
• Any natural or synthetic polymeric binder may be used in the practice of the present invention.
• the pH of the resin has been found to affect only the speed of the decolorizing or colorizing effect. If the speed is not important, any resin may be used.
• Organic polymeric resins preferably thermoplastic resins (although thermoset resins may be used), are generally preferred. Where speed is more important, either the more acidic resins should be used or an acid should be added to the system to reduce the pH and increase the rate of decolorizing or colorizing (i.e., leuco dye oxidizing).
• Such resins as polyvinyl acetals, polyesters, polyvinyl resins, polyvinylpyrolidone, polyesters, polycarbonates, polyamides, polyvinyl butyral, polyacrylates, cellulose esters, copolymers and blends of these classes of resins, and others have been used with particular success.
• Natural polymeric materials such as gelatin and gum arabic may also be used.
• the resin should be able to withstand these conditions.
• the polymer not decompose or lose its structural integrity at 200°F (93°C) 30 seconds and most preferred that it not decompose or lose its structural integrity at 260°F (127°C) for 30 seconds.
• the binder serves a number of additionally important purposes in the constructions of the present invention.
• the imageable materials are protected from ambient conditions such as moisture.
• the consistency of the coating and its image quality are improved.
• the durability of the final image is also signficantly improved.
• the binder should be present as at least 25% by weight of ingredients in the layer, more preferably as 50% by weight and most preferably as at least 70% by weight of dry ingredients (i.e., excluding solvents in the layer).
• Nitrate salts are themselves well known. It may be supplied as various compound forms, but are preferably provided as a metal salt, and most preferably provided as a hydrated metal salt. Other ions which are ordinarily good oxidizing ions such as nitrite, chlorate, iodate, perchlorate, periodate, and persulfate do not provide comparable results. Extremely active oxidizing agents, such as iodate, even used in relatively smaller proportions to prevent complete and immediate oxidation or decolorization of dyes, do not perform nearly as well as nitrate ion compositions. The performance of nitrate is so far superior to any other ion that it is apparently unique in the practice of the present invention.
• the better oxidizing ions other than nitrate can produce a maximum density (O max ) in the image of about 0.90 and a minimum density (D min ) of 0.25 in their best construction
• the better constructions with nitrate ions can have a °max in excess of 1.0 and a D min below 0.20 or even 0.10.
• nitrates of zinc, cadmium, potassium, calcium, zirconyl, nickel, aluminum, chromium, iron, copper, tin, magnesium, lead, silver and cobalt, ammonium nitrate, and ceric ammonium nitrate have been used.
• the nitrate salt component of the present invention must be present in a form within the imaging layer so that oxidizing quantities of HN0 3 , NO, N0 2 , or N 2 0 4 will be provided within the layer when it is heated to a temperature no greater than 200°C for 60 seconds and preferably no greater than 160°C for 60 or most preferably 30 seconds. This may be accomplished with many different types of salts, both organic and inorganic, and in variously different types of constructions.
• the most convenient way of providing such thermal oxidant providing nitrate salts is to provide a hydrated nitrate salt such as aluminium nitrate nonahydrate (AI(NO 3 ) 3' 9H 2 0).
• This salt when heated in a binder, will generate HNO 3 , NO, NO 2 and/or N 2 O 4 in various amounts.
• the binder should not be at such a high pH that the liberated nitric acid would be immediately neutralized as this would adversely affect the oxidizing capability of the system. It is not essential that a completely acidic or neutral pH environment be provided, but pH levels above 8.5 may in many cases completely prevent oxidation. It is therefore desired that the nitrate salt containing layer have a pH less than 7.5, preferably equal to or less than 7.0, and more preferably equal to or less than 6.5.
• non-hydrated salts in layers having a pH less than 7.5, and preferably in an acidic environment are also capable of providing HN0 3 , NO, N0 2 and/or N 2 0 4 in sufficient quantities to provide the oxidizing capability necessary for practice of the present invention.
• Ammonium nitrate for example, does not enable good oxidation in the present invention in a layer having a pH of 8.0 or higher, but when a moderate strength organic acid such as phthalic acid is added to lower the pH to below 7.0, a quite acceptable imaging system is provided.
• organic salts in non-alkaline environments are also quite useful in the practice of the present invention.
• nitrated quaternary ammonium salts such as guanidinium nitrate work quite well in acid environments, but will not provide any useful image at alkaline pH levels of 8.0 or higher.
• the alkaline environment causes any oxidizing agent (e.g., HN0 3 , NO, N0 2 and/or N 2 0 4 ) which is liberated from the nitrate salt to be preferentially reacted with hydroxy ions or other neutralizing moieties so as to prevent oxidation of the dyes.
• any oxidizing agent e.g., HN0 3 , NO, N0 2 and/or N 2 0 4
• the environment of the nitrate salt as a pH no greater than 7.0 and more preferably less than 6.5.
• Non-reactive salts are defined in the practice of the present invention as those salts the cations of which do not spontaneously oxidize the dyes that they are associated with at room temperature. This may be readily determined in a number of fashions.
• the dye and a non-nitrate (preferably halide) salt of the cation may be codissolved in a solution. If the salt oxidizes the dye spontaneously (within two minutes) at room temperature, it is a reactive salt.
• Such salts as silver nitrate, in which the cation is itself a strong oxidizing agent, is a reactive salt. Ceric nitrate is also reactive, while hydrated cerous nitrate is not.
• Preferred salts are the hydrated metal salts such as nickel nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, ferric nitrate nonahydrate, cupric nitrate trihydrate, zinc nitrate, hexahydrate, cadmium nitrate, tetrahydrate, bismuth nitrate pentahydrate, thorium nitrate tetrahydrate, cobalt nitrate hexahydrate, gadolinium or lanthanum nitrate nonahydrate, mixtures of these hydrated nitrates and the like.
• Non-hydrated or organic nitrates may be admixed therewith.
• Organic nitrates are also quite useful in the practice of the present invention. These nitrates are usually in the form of quaternary nitrogen containing compounds such as guanidinium nitrate, pyridinium nitrate, and the like. Nitrated dyes will also be useful, but again, they must be used in an environment which will not neutralize any liberated HN0 3 , NO, N0 2 , and/or N 2 0 4 .
• the nitrate salt is present in an amount to provide at least 0.10 moles of nitrate ion per mole of dye. It is more preferred to have at least 0.30 or 0.50 moles of ion per mole of dye. Even amounts of from 1.0 to 100 moles of nitrate ion per mole of dye have been found useful. With dyes having relatively higher oxidation potentials, more nitrate is desirable.
• the dyes which are useful in the decolorizable systems of the present invention are any bleachable dye. In some constructions it may be preferable to use those which have an oxidation potential of less than or equal to +1.0. These dyes may be selected from any class of dyes. These classes include but are not limited to methines, indamines, anthraquinones, triarylemethanes, benzylidenes, monoazos, oxazines, azines, thiazines, xanthenes, indigoids, oxonols, cyanines, merocyanines, phenols, naphthols, pyrazolones, and others, of which most are classified by the Colour Index System.
• oxidation potentials is well known to the ordinarily skilled artisan.
• the measurements in the present invention are taken by measuring the voltage and current transferred between a carbon and a platinum electrode through the appropriate solution.
• 0.1 M lithium chloride in anhydrous methanol with 1 to 10 millimoles/liter of the appropriate dye was the standard solution used in the measurements given herein with a saturated calomel electrode.
• Leuco dyes are well known in the art. These are colorless dyes which when subjected to an oxidation reaction form a coloured dye. These leuco dyes are well known in the art (e.g., The Theory of the Photographic Process, 1966 3rd Ed., Mees and James, pp. 283-4, 390-1, Macmillan Co., N.Y.; and Light-Sensitive Systems, Kosar, pp. 367, 370-380, 406 (1965) Wiley and Sons, Inc., N.Y.).
• leuco malachite blue leuco crystal violet
• leuco malachite green leuco malachite green
• Acid or base sensitive dyes such as phenolphthalein and other indicator dyes are not useful in the present invention unless they are also oxidizable to a coloured state. Indicator dyes would only form transient images or would be too sensitive to changes in the environment.
• the dyes which have been specifically shown to work in the decolorizable systems of the present invention include but are not limited to the following: wherein
• the decolorizable dyes to be used according to the present invention are preferably colored, that is, having absorbance in the visible portion of the electromagnetic spectrum (approximately 400 to 700 nm), but may also be colorless, having absorbance only or predominantly in the infrared (700 to 1100 nm) or ultraviolet (310 to 400 nm) portions of the electromagnetic spectrum.
• the images where colorless dyes are used must then be viewed through a filter, by a ultraviolet or infrared sensitive apparatus, or by some enhancement technique.
• decolorizable dye present in the layers of this invention so that an optical density of at least 0.1 in the visible portions of the spectrum is present or at least 15% of incident colorless light (including ultraviolet or infrared) is absorbed. It is preferred that an optical density of at least 0.5 or 0.8 be obtained and most preferably that there be sufficient dye so that an optical density of at least 1.0 be obtained in the layer.
• colorless dyes e.g., ultraviolet and infrared absorbing dyes
• the leuco dye should be present as at least about 0.3% by weight of the total weight of the light sensitive binder layer, preferably at least 1% by weight, and most preferably at least 2% to 10% or more (e.g., 15%) by weight of the dry weight of the imageable layer. This weight percent is also useful estimating the minimum amount for the decolorizable dyes.
• the proportions of nitrate ion and decolorizable dye should be such that on heating the layer at 260°F (127°C) for 30 seconds there is at least a 20% reduction in optical density in exposed areas of positive acting systems or unexposed areas in negative acting systems. With a mechanical viewing of the image, a lower reduction in optical density is useful.
• the relative proportion of nitrate ion to dye may vary. As a general rule, at least 0.1 moles of nitrate ion per mole of dye (whether colorizable (i.e., leuco dye) or decolorizable) is desirable in the practice of the present invention.
• At least 0.3 or 0.5 moles of nitrate per mole of dye is more preferred, and at least 0.7 or 0.9 moles of nitrate per mole of dye is most preferred. It is usually desired that the decolorizable layers of the present invention provide more than a 20% reduction in optical density upon exposure and development. At least 50% or 60% is preferred and at least 90% or 95% reduction in optical density is most preferred. These reductions can be measured at the development temperatures for the imaging materials, e.g., 130°C for 60 seconds or 155°C for 45 seconds.
• the acids optionally useful in the present invention are acids as generally known to the skilled chemist.
• Organic acids are preferred, but inorganic acids (generally in relatively smaller concentrations) are also useful.
• Organic acids having carboxylic groups are more preferred.
• the acid may be present in a ratio of from 0 to 10 times the amount of the nitrate ion. More preferably it is present in amounts from 0.2 to 2.0 times the amount of nitrate ion.
• temperatures should, of course, not be used during manufacture which would completely colorize or decolorize the layer or decompose the diazonium salts.
• Some colorization or decolorization is tolerable, with the initial dye or leuco dye concentrations chosen so as to allow for anticipated changes. It is preferred, however, that little or no leuco dye or dye be oxidized during forming or coating so that more standardized layers can be formed.
• the coating or forming temperature can be varied. Therefore, if the anticipated development temperature were, for example, 350°F (167°C), the drying temperature could be 280°F (138°C).
• a reasonable development temperature range is between 180°F (82°C) and 380°F (193°C) and a reasonable dwell time is between 5 seconds and 5 minutes, preferably at between 220°F (105°C) and 350°F (167°C) and for 10 to 180 seconds, with the longer times most likely associated with the lower development temperatures. Therefore, the absorbance characteristics should be considered in relationship to the generally useful development range of 82°C to 193°C.
• Light sensitive diazonium salts are well known in the art. These salts comprise a light sensitive aromatic nucleus with an external diazonium group and an anion associated therewith (e.g., "Light-Sensitive Systems,” Kosar, pp. 202-214, John Wiley and Sons, Inc. 1965, N.Y.; and Photographic Chemistry, Vol. II, P. Glafkides, pp. 709-725, Fountain Press, London). They may be generally represented by the formula: wherein Ar is an aromatic nucleus, and X- is an anion.
• Any anion may be used on the diazonium salt.
• Anions as diverse as zinc chloride, tri-isopropyl naphthalene sulfonate, fluoroborate (i.e., BFQ ), and bis(per-fluoroalkylsulfonyl)methides may be used.
• the change in anions may affect the speed of the imaging layer, but not its function.
• Any light sensitive aromatic diazonium salts, as known in the art, may also be used in the practice of the present invention. These diazonium salts are well known in the art and may be derived from, for example P-anilinobenzene;
• the imaging layers of the present invention may contain various materials in combination with the essential ingredients of the present invention.
• lubricants e.g., ascorbic acid, hindered phenols, phenidone, etc. in amounts that would not prevent oxidation of the dyes when heated
• surfactants e.g., ascorbic acid, hindered phenols, phenidone, etc. in amounts that would not prevent oxidation of the dyes when heated
• surfactants e.g., antistatic agents, mild oxidizing agents in addition to the nitrate, and brighteners may be used without adversely affecting practice of the invention.
• a reference coating solution was prepared by mixing 66.67 g of a 15% solution of cellulose acetate butyrate (in a solvent solution comprising 10 parts methylisobutylketone, 20 parts methanol, and 55 parts acetone) with 0.05 g phenidone A, 0.15 g phthalic acid, 0.49 g benzotriazole, 0.38 g of 1 - diazo-2,5-dimethoxy-4-morpholinobenzene zinc chloride, 0.335 g leuco crystal violet, 4.43 g methanol, 12.50 g acetone, and 5.00 g tetrahydrofuran.
• each nitrate shown in the table below was dissolved in methanol to a total weight of 1 g, and this was added to 9 g of the reference coating solution.
• Each final solution was coated at 1 fl m (4 mils) wet thickness onto polyethylene terephthalate film and dried for four minutes at 71 °C.
• Each coated film was imagewise exposed to ultra- violet light until the diazonium salt in the light struck areas was decomposed.
• One portion of each film was developed at 99°C and another sample was developed at 139°C for various times, visually determining when optimum development occurred.
• the optical density in the light struck (LS) areas and the non-light struck (NLS) areas was recorded. The results appear below, with all developing times (Dev. Time) reported in seconds.
• a nitrate solution comprising 0.23 g Al(NO 3 ) 3 ⁇ 9H 2 O in 19.77 g methanol was prepared.
• the selected diazonium salts were added to this solution to form 2 g portions which were then added to 8 g portions of the reference coating solution of Examples 19-45. These were then coated and dried as in the previous examples. Again, the diazonium salts were in approximately equimolar proportions to the dye.
• the coated film was exposed, developed, and evaluated as in the previous examples.
• a light sensitive system according to the present invention was constructed in the following manner.
• a solution was prepared by mixing the following ingredients:
• the first was of 0.10 g Crystal Violet, 5 ml of methanol, and 5 ml of N-methyl-pyrrolidone (plasticizer).
• the second solution was made from 4 g magnesium nitrate hexahydrate (Mg(NO 3 ) 2 ⁇ 6H 2 O) and 75 ml of methanol.
• the third solution comprised 20 g cellulose acetate, 10 ml methyl isobutyl ketone, and 70 ml acetone.
• 3 ml of the first solution was mixed with 3 ml of the second solution an 12.5 g of the third solution.
• To this was added 0.03 g of 3-methyl-4-pyrrolidino- benzene diazonium-tetrafluoroborate. This solution was coated onto clear polyethyleneterephthalate film at 1 ⁇ m (4 mils) wet thickness and dried for 4 minutes at 70°C.
• the dried film was imagewise exposed to ultraviolet light until the diazonium salt had been decomposed in the light struck areas. Upon heating to 130°C for 40 seconds, a readable image developed. The dye was bleached far more in the light struck areas than in the non-light struck areas, providing a positive image.
• Example 55 was duplicated except that an equal weight of the leuco dye 1(2-(1,3,3-trimethyl- indolyl))-2-(p-morpholinylphenyl)ethene was used in place of the leuco crystal violet. A substantially similar result was obtained, except that the image was, negative, red and somewhat less dense.
• Example 55 was duplicated except that an equal molar amount of leuco malachite green was used in place of the leuco crystal violet. A green positive image was produced after exposure and development as in Example 59.
• Example 55 was duplicated except an equal molar amount of the leuco dye was used in place of leuco crystal violet. A light blue positive image was produced after exposure and development as in Example 55.
• Example 55 was repeated except that the cellulose acetate butyrate solution was replaced with 15 g of a 30% by weight solution of cellulose acetate propionate in a 10:20:40 solution of the same solvent respectively. When imaged and the developed at 99°C, a strong negative image was produced.
• Example 55 was repeated except that equimolar proportions of the following dyes were used in place of the leuco crystal violet:
• Example 55 The sheets were coated and dried as in Example 55. Each of the coated polyester sheets were initially colored due to the presence of the dye. Exposure and development was the same as in that Example, but the images were now generally positive images, with the color density the lowest where light struck.
• the imaging layers of the present invention must allow reactive association amongst the active ingredients in order to enable imaging. That is, the individual ingredients may not be separated by impenetrable barriers within the layer, as in dispersed immiscible phases.
• the active ingredients are homogeneously mixed (e.g., a molecular mixture of ingredients) within the layer. They may be individually maintained in heat softenable binders which are dispersed or mixed within the layer and which soften upon heating to allow migration of ingredients, but this would require a longer development time.
• a reasonable basis for determining the acidity of the coating composition is to evaluate the stability of a specific diazonium salt in the composition.
• the specific salt of Example 19 if more than 25% by weight of the diazonium salt decomposes, the pH is probably too much above 7.0.
• amplification in the leuco dye containing construction is meant that more than one molecule of dye is formed for each absorbed photon of radiation.
• the degree of amplification that is the ratio of the number of dye molecules formed to photons absorbed, may be as high as 1 x 10 3.

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• Materials Engineering (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)
• Heat Sensitive Colour Forming Recording (AREA)
• Transforming Light Signals Into Electric Signals (AREA)

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• 1980
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