DIAZONIUM IMAGING SYSTEM

Abstract: Novel light sensitive, heat developable imaging system incorporating a diazonium salt and a leuco dye in a binder.

Description: DIAZONIUM IMAGING SYSTEM Description Technical Field A novel light sensitive, heat developable imaging system incorporating a diazonium salt and a leuco dye in a binder is disclosed. The system is useful, for example, as a microfilm duplicating sheet or a heat sensitive recording material. Background Art U.S. Patent 3,390,997 discloses a light-sensitive admixture of an alkylthio, benzylthio, 2-phenylhydrazino or alkoxycarbonyl derivative of a triphenylmethane compound (a "leuco dye") and a selected non-volatile nitrogen-containing compound which functions as a photooxidant useful as an imaging system. The patent does not disclose the use of diazonium salts or materials which contain a pentavalent nitrogen atom. The light sensitive compounds of the present invention differ significantly from those of the patent which contain only trivalent nitrogen atoms. Furthermore, the present invention requires elevated temperatures, 82°C to 193°C, for image development, whereas the patent disclosure is of a room temperature developing system. An imaging system comprising a leuco dye, a diazonium salt, and nitrate ion in a binder is described in assignee's copending U.S. Patent Application, Serial Number 101,143 filed 07 December 1979. This four-part imaging system does not suggest the efficacy of the three-part imaging system of the present invention, and the chemical mechanisms in these diverse systems is believed to be different. Disclosure of the Invention The present invention relates to a light sensi¬ tive, heat developable imaging system comprising a &._ OMPI polymeric binder resin, a leuco dye, and a diazonium salt. In the practice of the present invention the chemical natur of the polymer including its acid content has not been foun to be a functional requirement. However, it is preferred t have an acid present (e.g., organic or inorganic acid) in the coating composition. Preferably, the acid is present in at least equi olar proportions to the diazonium salt. Furthermore, no oxidizing anion, including nitrat ion, is a necessary component of the present invention as i is in assignee's copending application mentioned above. If any nitrate ion is present, it is in amounts of less than 0.1 mole nitrate/1.0 mole dye. Other oxidizing anions and compounds may be present in greater or lesser amounts, but are not essential in the practice of the present invention. In the present invention, the leuco dye (a clear to faintly colored material), the diazonium salt and the •polymeric binder resin are incorporated in a solvent system and cast on any substrate such as paper, polymeric film suc as polyester, glass, metal, ceramics and the like. Upon irradiation by light, the diazonium salt is destroyed. The subsequent application of heat to the coating results in oxidation of the leuco dye by the diazonium salt to a colored form in the non-light struck portion of the coating. A positive-acting image is thus produced since color is generated where no light has contacted the coating. Although the precise mechanism of the image formation is not understood, as mentioned above the reaction appears to be an oxidation of the leuco dye during heat development by the diazonium salt which has not been decomposed by incident radiation. Detailed Description The present invention relates to a light sensitive, heat developable layer comprising a polymeric binder, a le. o dye, and a photosensitive diazonium salt. These ingredients are preferably in a homogeneous or molecular mixture with each other. The Binder Any natural or synthetic polymeric binder may be used in the practice of the present invention. Organic polymeric resins, preferably thermoplastic resins (although thermoset resins may be used), are generally preferred. The most preferred resins are polyvinyl acetate and polyvinyl chloride copolymers. Such resins as polyvinyl acetals, polyesters, polyvinyl resins, polyvinylpyrrolidone, 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. Where the proportions and activities of the leuco dye and diazonium salt require a particular developing time and temperature, the resin should be able to withstand those conditions. Generally it is preferred that the polymer not decompose or lose its structural integrity at 147°C for 60 seconds and most preferred that it not decompose or lose its structural integrity at 193°C for 5 minutes. Also, polymers must be compatible with the other components and solvents, in addition to having a reasonably low softening point for processability. Such polymers desirably are permeable to trapped gases. In addition to these requirements, the selected binder must be transparent or translucent and be either clear or lightly colored. This will ensure an obvious contrast with colored areas (non-light struck) after heat development. The binder may serve a number of additionally important purposes in the constructions of the present invention. The imageable materials may be 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 significantly improved. The binder should be present as at least 25% by weight of ingredients in the layer, more preferably as at least 50% by weight and most preferably as at least 70% by weight of dry ingredients (i.e., excluding solvents in the layer) . Dyes Leuco dyes are well known in the art. Ihese are colorless or lightly colored dyes which when subjected to an oxidation reaction form a colored dye. Ihese leuco dyes are described in the literature (e.g., Mees and James, "The Theory of the Photographic Process", 3rd Edition, published 1966, by Macrnillan Co. (N.Y.) , see pages 283-4, 390-1; and J. Koshar, "Light-Sensitive Systems", published 1965, by Wiley and Sons, Inc. (N.Y.) , see pages 367, 370-380, 406) . Amongst the best known leuco dyes are leuco crystal violet (LCV) and leuco malachite green (LMG) . Only those leuco dyes which can be converted to colored dyes by oxidation are useful in the practice of the present invention. 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 colored 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 present invention are discussed in detail below and include but are not limited to the following: Leuco Crystal Violet Leuco Ethyl Violet Leuco Malechite Green Leuco Victoria Blue-BGO Copiche H Leuco Atacryl Yellow-R Leuco Atacryl Orange-LGM Leuco Atlantic Fuchsine Leuco Atacryl Brilliant Red-4G Crude The leuco dyes of the present invention become colored due to oxidation, that is, they have absorbance after coloration in the visible portion of the electro¬ magnetic spectrum (approximately 400 to 700 nm) . The leuco dye should be present as at least about 0.3 by weight of the binder layer, preferably at least 1% by O Λ, WI weight, and most preferably at least 2% to 10% or more by weight of the dry weight of the imageable layer. In forming the leuco dye " layer or coating of the dye layer onto a substrate, temperatures should, of course, not be used during manufacture which would colorize the layer or decompose the diazonium salts. Some slight colorization is tolerable, with the initial leuco dye concentrations chosen so as to allow for anticipated colorization. It is preferred, however, that little or no leuco dye be colorized during forming or coating so that more standardized layers can be formed. Depending on the anticipated development temperature, the coating or forming temperature can be varied. Therefore, if the anticipated development temperature were, for example, 167°C, the drying temperature could be 138°C, and it would not be desirable for the layer to gain 20% of its optical density at the drying temperature in less than 4-5 minutes. Such a gain would be tolerable by correspond¬ ingly increasing the amount of leuco dye. There should be sufficient colorizable dye present in the colorizable layer of the present invention to provide an increase in optical density upon development of at least 0.2, more preferably 0.6, and most preferably 1.0 or greater. These increases can be measured at the development temperatures for the imaging materials, e.g., 132°C for 60 seconds. Thus the preferred limitation of at least 0.2 gain in optical density or absorbance of colorless light at 132°C for 60 seconds is based on the assumption of a development temperature of 132°C. For an anticipated higher or lower development temperature, the 0.2 gain in optical density or absorbance should occur at that development temperature within a reasonable period of time. A reasonable development temperature range is between 82°C and 193°C and a reasonable dwell time is between 5 seconds and 5 minutes, preferably at between 105°C and 167°C and for 10 to 180 seconds, with the longer times most likely associated with the lower development temperatures. Therefore, all of the absorbance characteristics are applicable to the generally useful development range of 82°C to 193°C. Diazonium Salts Light sensitive diazonium salts are well known in the art. Ηiese salts comprise a light sensitive aromatic nucleus with an external diazonium group and an anion associated therewith (e.g., J. Kosar, " ight-Sensitive System", published 1965, by John Wiley and Sons, Inc. (N.Y.) , see pages 202-214; and P. Glafkides, "Photographic Chemistry", Vol. II, published 1960, by Fountain Press (London) , see pages 709-725) . They may be generally represented by the formula: ArN + _= N X " wherein Ar is an aromatic nucleus, and X~ is an anion. Any anion may be used in the diazonium salt. Anions as diverse as zinc chloride, tri-isopropyl naphthalene sulfonate, fluoroborate (i.e., BF ~ ), and bisf perfluoro- alkylsulfonyl)methides may be used. Ihe change in anions may affect the speed of the imaging layer, but not its function. Any light sensitive aromatic diazonium nucleus, as known in the art, may also be used in the practice of the present invention. Ωiese diazonium nuclei, particularly those belonging to the classes pyrrolidine, morpholine, aniline, and diphenyl amine and its polymers are well known in the art and include, for example, P-anilinobenzene;. N- (4-diazo-2,4-dimethoxy phenyl) pyrrolidine; l-diazo-2, 4-diethoxy-4-τrorpholino benzene; 1-diazo-4-benzoyl amino-2,5-diethoxy benzene; 4-diazo-2, 5-dibutoxy phenyl morpholino; 4-diazo-1-dimethyl aniline; l-diazo-N,N- imethyl aniline; l-diazo-4-N-methyl-N-hydroxyethyl aniline; etc. O Additives Other materials which may be useful in the formulations of the present invention include reducers and complexors, plasticizers and polyketones, stablizers, surfactants, antistatic agents, coating aids, oxidizing materials (other than nitrate ion which may be present only in amounts less than 0.1 mole nitrate to 1.0 mole dye) , inhibitors, lubricants', flexibilizers, fillers and the like. All of this will be more thoroughly understood by consideration of the following examples: Examples 1-11 These examples examine the effect of using different binders in the formulation. Two separate solutions, A and B, were prepared. .Solution A comprised .020 g phthalic acid, .010 g catechol, .10 g Phenidone A (l-phenyl-3-pyrazolidone) , .200 g aromatic ketone resin, .200 g polymeric plasticizer (ter,2,4-trimethylpentane, 1,3-diol adipate 2-ethylhexanol terminated [900-1100 molecular weight] ) and 1.060 g methyl ethyl ketone (MEK) for a total weight of 1.5 g. Solution B comprised .051 g leuco crystal violet (4, 4 ' ,4 "- ethylidynetris- (N-N- dimethylaniline)) , .046 g leuco malachite green (ρ,p' -benzylidenebis- (N,N-dimethylaniline) ) , and 1.429 g tetrahydrofuran (THF) , for a total weight of 1.5 g. 1.5 g of each of solutions A and B were mixed with 0.1 g l-diazo-2,5-diethoxy-4-morpholino benzene borofluoride (DDMBB) and in each case with the stated amount( s) of binder(s), (see Table 1), to form a solution which was then coated on polyethylene terephthalate film to a thickness as noted in the table. The coated film was dried at 71°C, exposed to a mercury vapor lamp for 10 mete -candle-seconds, and then developed for 60 seconds at 132°C. The optical densities in the light struck (LS ) areas, also referred to as Dnin, and the non-light struck (NLS) areas, also referred to as Dmax, are recorded in Table 1. Phthalic acid is useful in these formulations to stablize the coating solution by preventing the diazonium salt from reacting before development. OM " WΪP Table 1 Thickness LS NLS Example B inder( s) Weight( g) micrometers (Dmin) (Dmax) 35% VC-VA-VAL-9135.7 a 32.5& tetrahydrofuran 1.7) 32.5% methyl ethyl ketone ) incompatible 35% PR-OS. 3 ) 32.5% tetrahydrofuran 1.7) 10 32.5% methyl ethyl ketone ) 35% V-VA-VAL-9136.7 32.5% tetrahydrofuran 2.4 66 .34 .90 32.5% methyl ethyl ketone 35% PR-OST 15 32.5% tetrahydrofuran 2.4 66 .20 .58 32.5% methyl ethyl ketone 15% CA-BR^ 10% methyl isobutyl ketone (MIBK) 8.0 112 .20 .80 20i ethanol Table 1 (continued) Thickness LS NLS Example Binder(s) Weight(g) micrometers (Dmin) (Dmax) 15% CA-BR" 10% methyl isobutyl ketone 8.0 112 .22 .73 20% ethanol 55% acetone 35% \E-VA-87A3-1 15% methyl isobutyl ketone 3.4 66 .27 1.08 10 50% methyl ethyl ketone 15% BR-AS 10% methyl isobutyl ketone 8.0 112 .20 .75 20% methanol 59i acetone 15 20% CAR* 20% methanol 6.0 91 .23 .70 10% methyl isobutyl ketone 50% acetone Table 1 (continued) Thickness LS NLS Example B inder( s) Weight( g) micrometers (Dmin) (Dmax) 10% methyl isobutyl ketone 8. 0 112 .25 .71 30% ethanol 45% methyl ethyl ketone 10 15% PVBR 10% methyl isobutyl ketone 8.0 112 .22 .55 10 20. ethanol 55% methyl ethyl ketone 11 25% VC- y Α-VAL-91 3 7 a 37. 5% methyl isobutyl ketone 4.8 81 .38 1.05 37.5. methyl ethyl ketone 15 a vinyl chloride vinyl acetate vinyl alcohol (91% 3%/5.7%) terpolymer b polyester resin - organic soluble cellulose acetate butyrate resin (Eastman 272-20) The change in optical density (ΔDensity) , i.e., Dmax-Dmin, is of great significance and values in excess of 1.0 are of commercial practicability. Examples 6 and 11 show the greatest changes in optical density (Dmax - Dmin) between light struck and non-light struck areas. It appears, therefore, that vinyl acetate and vinyl chloride copolymers, VC-VA-87/13-1 and VC-VA-VAL-91/3/5.7, are the preferred resins in the practice of this invention. Examples 12-19 These examples further investigate vinyl chloride and vinyl acetate binders. The reference solu¬ tion (1.5 g each of solutions A and B, and 0.1 g DDMBB) was prepared and mixed with the stated amount of binder (Table 2), then coated and treated as in examples 1-11. Results appear below. TflBLE 2 Thickness LS NLS E xample B inder Weight(g) micrometers (Dmin) (Dmax) ΔDensity 12 35% -JC--J -86 ^ 15% methyl isobutyl ketone 3.4 66 .25 .95 .70 50% methyl ethyl ketone 13 35% \-C-VA-87A3-l e 15% methyl isobutyl ketone 3.4 66 .26 1.00 .74 50. methyl ethyl ketone 10 14 35% V -VA-87Λ3-^ 15% methyl isobutyl ketone 3.4 66 .30 1.18 .88 50% methyl ethyl ketone 15 35% VC-VA-MA-36 _.3 _. J" 15% methyl isobutyl ketone 3.4 66 .27 .95 .68 15 50% methyl ethyl ketone 16 35% VC-VA-MA-84/L5/,8 ,m' 15% methyl isobutyl ketone 3.4 66 .30 .97 .67 50% methyl ethyl ketone TfiBLE 2 (continued) Thickness LS NLS Example B inder Weight(g) micrometers (Dmin) (Dmax) ΔDensity 17 35% VC-VA-VAL-91 3 β . 7 a 15% methyl isobutyl ketone 3.4 66 .35 1. 20 .85 5C& methyl ethyl ketone 18 35% \C-VA-90 10 n 7. 5% methyl isobutyl ketone 3.4 66 .31 1. 13 .82 23 methyl ethyl ketone 10 32. 5% tetrahydrofuran 19 15% CΑ-BFT 10% methyl isobutyl ketone 4.0 incompatible 20% ethanol 55% acetone 15 j vinyl chloride vinyl aceate (86% L4%) coplymer k vinyl chloride vinyl acetate (87%A3%) oopolymer- lower molecular weight than "e" 1 vinyl chloride vinyl acetate maleic acid (86% L3%l% . terpolmer m vinyl chloride vinyl acetate maleic acid (84% A5%/.8%) terpolymer n vinyl chloride vinyl acetate (90% L0%) copolymer. The binders of examples 12, 13 and 14 decrease progressively in molecular weight which correlates with a progressive decrease in softening points of these resins. It is of note that the ΔDensity increases as the soften- ing temperature of the resin decreases, reflecting better reacting conditions in softer resins. The binders of examples 15 and 16 are resins with acid content, a factor which did not enhance the ΔDensity. The resins of example 14 (lower molecular weight) and example 17 (hydrolyzed) provided the best ΔDensity of those tested in this group. Examples 20-33 The following acids and a control were screened with the resin of example 14 (VC-VA 87/13-2) using in each case O.lg DDMBB and 4.0g of a master batch solution com¬ prising 2.0g LCV, 18.Og toluene and a solution containing 60.Og of 40% VC-VA-87/13-2, 18% MIBK, 18% ethanol and 24% MEK: Example 20 no acid 21 phthalic ac id 22 4-methylphthalic acid 23 citric acid 24 3-nitrophthalic acid 25 5-sulfosalicylic acid 26 oxalic acid 27 glutaric acid 28 benzoic acid 29 2-naphthoic acid 30 acetic acid 31 nitric acid 32 hydrochloric acid 33 toluene sulfonic acid Although the most common effect appeared to be a reduction in both optical densities, Dmin and Dmax, the opposite was also true in some cases. Only nitric acid appeared to increase the maximum density and reduce the minimum density by stabilizing the diazo and also aiding in the oxidation of the leuco dye. This is an example of the effect of nitrate ion in the formulation and is the subject of assignee's copending application mentioned above. In sum, the non-nitrate acid content of the formulation has not been found to be a significant factor in the practice of this invention. Examples 34-52 In a search for materials which would lower the Dmin and increase the Dmax, tests were performed on the addition of small amounts (.05 g) of various reducers and complexors (antioxidants or chelating agents) in a solution of .01 g DDMBB and .85 g 1:1 methanol and acetone added to portions of a master batch comprising 2.2 g leuco crystal violet, 19.8 g toluene and 66.0 g of a solution containing 40% VC-VA-87/13-2, 10% methyl isobutyl ketone, and 50% methyl ethyl ketone. The materials tested were: Example 34 phenyl mercapto tetrazole 35 hydantoin 36 phthalazine 37 tetrachlorophthalic anhydride 38 Phenidone A 39 catechol 40 phthalazinone 41 phthalimide 42 benzotriazole 43 2-mercaptobenzothiazole 44 2-ethyl imidazole 45 thiourea 46 2-thiohydantoin 47 2,4,4-trimethylρentyl-^is_-(2-hydroxy-3 ,5-dimethylp methane 48 2,2'-methylenebis(4-methyl-6-tert butylphenol) O 49 2, 6-bis(2 '-hydroxy-3 '-tert buty1-5 '-methyl-benzyl)-4- methylphenol 50 1, 1, 3-trimethyl-5-carboxyl-3- (p-carboxylphenyl) indan 51 2,6-dichloro-4-benzenesulfonamido phenol 52 ascorbic acid Tetrachlorophthalic anhydride, 2 f 4 ,4-trimethylpentyl-bis- (2-hydroxy-3,5-dimethylphenyl)methane fTBHDM) , 2 ,6-bis (2'- hydroxy-3 '-tert butyl-5 '-methyl benzyl)-4-methylphenol, and 2,2'-methylenebis_(4-methyl-6-tert butylphenol) showed some degree of usefulness in ' increasing the ΔDensity compared to experiments without these materials. Phenidone A (l-phenyl-3-pyrazolidone) and ascorbic acid greatly depressed both the Qnin and Driax values and when studied at lower levels of concentration ( .01 g) were found to be useful in depressing the Dnin. Examples 53-68 •Small amounts of various polyketones, plasti- cizers, metal salts, and benzoyl peroxide were screened for their possible effect in lowering the softening point of the resin using 4 g of a master batch solution comprising 2.0 g leuco crystal violet, 18.0 g toluene, and 60.0 g of a solution containing 40% VC-VA-87 13-2, 18% methyl isobutyl ketone, 18% ethanol, and 24% methyl ethyl ketone. 0.1 g EDMBB dissolved in less than 1.0 g of 1:1 methyl alcohol and acetone was added. The materials tested were: Example 53 Mg ( C10 ) 2 , 0. 05g 54 gBr 2 • 6H 2 0, 0. 05 g 55 Mg S0 • 7H 2 0 , 0. 05 g 56 Mg (NO3 } 2 • 6H 2 0 , 0. 05 g 57 Mg Cl 2 • 6H 2 0 , 0. 05 g 58 benzoyl peroxide , 0. 05 g 59 aromatic polyketone res in ( Mohawk Industries ( MR-85 ) , 0. 20 g OMPI 60 polyketone resin , sof tening point 9 3-104 °C (Union Carbide Bakelite 251) , 0. 2g 61 polyketone res in , softening point 74-85 °C (Union Carbide Bakelite 252) , 0.2g 62 polymeric plasticizer ( ter , 2, 4- trimethylpentane , 1, 3-diol adipate 2- ethylhexanol terminated { 900-1100 molecular weight] ) , 0. 2g 63 Eastman PA-3 (Eastman proprietary product) , 0. 2 g 64 triethylene glycol di- 2-ethylhexoate , 0. 2g 65 dimethyl cellosolve phthalate , 0. 2 ' g 66 ascorbic acid , 0. Ol g 67 Phenidone A, O. Olg 68 control ( no additive) The results of these tests showed no dramatic improvement in ΔDensity. It was found that plasticizers and polyketones effectively lower the softening point of the polymeric binder, thereby increasing the rate of develop¬ ment. They have been found to be most effective in the higher softening resins (i.e. resins of higher molecular weight) as might be expected. Examples 69-97 These examples tested the effect of variations in the diazonium salts. Using 4 g of the same master batch just described a study was made of the effect of the following 29 diazonium salts on the Δ-Density, .1 g diazonium salt being dissolved in .9 g of a solution of 50% methanol and 50% acetone. Example 69 l-diazo-3-methyl-4-pyrrolidino benzene zinc chloride 70 N-(4-diazo-2, 5-dimethoxy phenyl) pyrrolidine borofluoride 71 N-(4-diazo-2, 5-diethoχy phenyl) pyrrolidine borofluoride 72 3-methyl-4-pyrrolidino benzene diazonium fluoroborate OMF 73 3-methoxy-4-pyrrolidino benzene diazonium fluoroborate 74 l-diazo-3-methyl-4-pyrrolidino benzene chloride zinc chloride 75 l-diazo-3-methyl-4-pyrrolidino benzene chloride fluoroborate 76 l-diazo-4-morpholino benzene 1/2 zinc chloride 77 l-diazo-2,5-dibutoxy-4-morpholino benzene sulfate 78 l-diazo-2,5-diethoxy-4-morpholino benzene 1/2 zinc chloride 79 l-diazo-2,5-dimethoxy-4-morpholino benzene zinc chloride 80 4-diazo-2,5-dimethoxy phenyl morpholino zinc chloride 81 l-diazo-2,5-diethoxy-4-morρholino benzene borofluoride 82 4-diazo-2,5-dibutoxy phenyl morpholino borofluoride 83 2,5-di-n-butoxy-4-morpholino benzene diazonium chloride 1/2 zinc chloride 84 l-diazo-4-N-methyl-N-hydroxyethyl aniline 1/2 zinc chloride 85 l-diazo-4-N,N-dimethyl aniline borofluoride 86 l-diazo-2-ethoxy-4-N,N-diethyl aniline zinc chloride 87 l-diazo-4-N,N-dimethyl aniline 1/2 zinc chloride 88 4-diazo-l-dimethyl aniline zinc chloride 89 4-diazo-l-diethyl aniline zinc chloride 90 diρhenylamine-4-diazonium borofluoride 91 (condensation product) diphenylamine-4-diazonium chloride 1/2 zinc chloride + formaldehyde 92 (condensation product) p-diazo diphenylamine chloride zinc chloride + formaldehyde 93 (condensation product) diphenylamine-4-diazonium tri-isopropyl naphthalene sulfonate + formaldehyde 94 (condensation product) 4-diazo diphenylamine su±fate + formaldehyde 95 p-nitrobenzene diazonium borofluoride 96 l-diazo-4-benzoyl amino-2,5-diethoxy benzene 1/2 zinc chloride 97 2,5-diethoxy-4-(p-tolyethio)benzene diazonium chloride 1/2 zinc chloride All of the diazonium salts proved useful in producing an image except p-nitrobenzene diazonium borofluoride which was very unstable and reacted prematurely in solution. Tests including diphenylamine-4-diazonium borofluoride (DDBF), l-diazo-2,5-diethoxy-4-morpholino benzene borofluoride and 2,5-diethoxy-4-(p-tolyethio)benzene diazonium chloride 1/2 zinc chloride gave the highest Dmax values but the ADensity values were not improved due to correspondingly higher Dmin values. Examples 98-127 A study was made of the most effective compounds from previous examples. A diazo solution containing 2.5 g DDBF (diphenylamine-4-diazonium borofluoride) and 22.5 g of 50% methanol/50% acetone was prepared. Also Master Batch #1 (1.6 g leuco crystal violet, 14.4 g toluene and 48.0 g of a solution containing 40% VC-VA-87/13-2 dissolved in 10% MIBK/50% MEK) and Master Batch #2 (0.8 g leuco crystal violet, 15.2 g toluene, and 48.0 g of solution containing 40% VC-VA-87/13-2 dissolved in 10% MIBK/50% MEK) were prepared. The materials listed below were also tested using 1.0 g diazo solution in 4.0 g Master Batch #1, and they were tested using 0.5 g diazo solution in 4.0 g Master Batch #2. Example 98,99 phthalic acid 100,101 nitric acid 102,103 ascorbic acid 104,105 TCCI 106,107 tetrachloro phthalic anhydride 108,109 Phenidone A 110,111 catechol 112,113 2,2'-methylenebis (4-methyl-6-tert butylphenol) 114,115 2,6-bis(2'-hydroxy-3'-tert butyl-5'-methylbenzyl)- 4-methylphenol 116,117 TBHDM 118,119 Mg(C10 4 ) 2 120,121 Mg(N0 3 ) 2 * 6H 2 0 122,123 MgBr 2 • 6H 2 0 124,125 Benzoyl Peroxide 126,127 Aromatic polyketone resin (Mohawk Industries MR-85) 1,1,2-trimethyl-5-carboxyl-3-(p-carboxyphenyl)indan (TCCI) and TBHDM were found to be effective in reducing the Dmin and thereby increasing the ΔDensity values to some extent. Examples 128-129 Anylsis of formulations containing variable amounts of Phenidone A, phthalic acid, 1:1 DDMBB and DDBF, leuco crystal violet, TCCI, ascorbic acid, and a solution of 40% VC-VA-87/13-2 dissolved in 10% MIBK/50% MEK, in addition to solvents, was made. The best results were obtained from formulations of examples 128 and 129, shown below in Table 3. Table 3 Examples No. 128 and 129 in g 128 129 phthalic acid 0.10 0.20 DDMBB/DDBF 0.075 0.075 acetone 0.875 0.775 LCV 0.075 0.075 TCCI 0.100 0.100 THF 0.825 0.825 40% VC-VA-87/13* -2 (10% MIBK/50% MEK) 4.0 4.0 Initial Density 0.18 0.04 LS (Dmin) 0.30 0.17 NLS (Dmax) 1.30 1.06 ΔDensity 1.0 0.89 Examples 130-139 These examples examine variations of the "best formulations" from the previous tests. Results are tabulated in Table 4. Initial density (D-.) refers to the optical density of the coating before exposure to light and heat and as noted previously Dmin refers to the optical density of the light struck areas after exposure to light and heat and Dmax refers to the optical density of the non-light struck area after exposure to light and heat. TABLE 4 03MPCCT_NTS(g) 40% VC-VA 87/13-2 100% MIBK phthalic 1:1 methanol Example LCV TCCI Phen A THF 50% acetone acid DDMBB DDMBS acetone acetone 130 .125 .150 1.725 4.0 .100 .125 1.775 131 .100 .100 1.800 4.0 .100 ■ .900 132 .100 .010 1.890 4.0 .100 .900 10 133 1 4 .100 . 1.890 4.0 .100 .900 134 .125 .150 .010 1.715 4.0 .100 .125 1.775 135 2 .125 .150 1.675 4.0 .100 .125 _—_ 1.775 136 2 .125 .150 .005 1.670 4.0 .150 .125 1.79R 137 2 ' 3 .125 .150 .005 1.670 4.0 .150 1.725 15 138 2 .125 .150 .005 1.670 4.0* .150 .125 0.725 2 139^ .125 .150 .005 1.670 4.0* .150 .125 .725 Formulation included .010g Ascorbic acid Formulation included .050g Catechol Formulation included .125g DDBF 20 Formulation included l.OOOg Methanol Resin solutin was added to diazo solution rather than LCV solution ** l-diazo-2,5-dibutoxy-4-morpholino benzene sulfate Examples 130, 131, 135 and 139 gave borderline commercial results, the Density values being respective¬ ly 1.16, 1.00, 1.02 and .94. The resolution in these cases is excellent, being in the order of 400 line pairs per mm. Additional experiments were run to test the effects upon the image produced by varying leuco dyes in the formulations. Leuco crystal violet and leuco male- chite green were the most effective dyes in the practice of this invention. All the dyes tested and listed below were found to have utility in the present invention but the formulations must be optimized to make a useful product. 1) Leuco Crystal Violet N(CH 3 ) 2 4,4' ,4"-methylidynetris-(N,N-dimethylaniline) 2) Leuco Malachite Green N(CH 3 ) 2 p-p'benzylidenebis-(N,N-dimethylaniline) 3 ) Copichem II leuco form 4) Leuco Atacryl Orange-LGM: Color Index Basic Orange 21, Comp. # 48035 (a Fischer's base type compound) H 5) Leuco Atacryl Brilliant Red -4G: Color Index Basic Red 14 CH. 6) Leuco Ethyl Violet: Color Index Basic Violet 4, comp. #42600 H 5 C 2 ;2 H 5 \ / N O FI V/IPO 7) Leuco Victoria Blue - BGO: Color Index Basic Blue 728a, comp. #44040 8) Leuco Atacryl Yellow - R: Color Index Basic Yellow 11, Comp. # 48055 ) Leuco Atlantic Fuchsine Crude OMPI

Claims: CLAIMS : 1. A light sensitive, heat developable layer comprising a polymeric binder, a leuco dye, and a photosensitive diazonium salt. 2. The layer according to claim 1 further comprising nitrate ion present in a mole ratio to the leuco dye of less than 0.1 nitrate ion/1.0 dye. 3. The layer of claim 2 wherein said leuco dye is present as at least 0.3% by weight of dry ingredients of the layer. 4. The layer of claim 2 wherein said leuco dye comprises at least 1% by weight of dry ingredients of said layer. 5. The layer of claim 2 wherein said leuco dye comprises 2% to 10% by weight of dry ingredients of said layer. 6. The layer of claim 2 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 0.2. 7. The layer of claim 2 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 0.6. 8. The layer of claim 2 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 1.0. O 9. The layer of claim 2 wherein said leuco dye is selected from the class consisting of leuco crystal violet and leuco malechite green. 10. The layer according to claim 2 wherein said layer comprises the diazonium salt l-diazo-2,5-diethoxy- 4-morpholino benzene borofluoride. 11. The layer according to claim 2 wherein the development temperature is between 82°C and 193°C. 12. The layer according to claim 2 wherein the development temperature is between 105°C and 167°C. 13. The layer according to claim 2 further comprising an acid. 14. The layer according to claim 2 wherein said layer comprises a binder selected from the classes consisting of polyvinyl chloride and polyvinyl acetate resins. 15. The layer according to claim 14 wherein said binder is present as at least 25% by weight of dry ingredients in the layer. 16. The layer according to claim 14 wherein said binder is present as at least 50% by weight of dry ingredients in the layer. 17. The layer according to claim 14 wherein said binder is present as at least 70% by weight of dry ingredients in the layer. A DED CLAIMS (received by the International Bureau on 24 April 1981 (24.04.81)) 1. A light sensitive, positive-acting, heat developable layer on a substrate, the dry ingredients of said layer comprising at least 25% by weight of a polymeric binder, at least 0.3% by weight of a leuco dye capable of being oxidized to a colored form, a sufficient amount of a photosensitive diazonium salt to oxidize said leuco dye, upon heating, to a colored form in non-light struck portions of said layer, and less than 0.1 mole nitrate ion per 1.0 mole leuco dye. 2. The layer of claim 1 wherein said leuco dye is present as at least 0.3% by weight of dry ingredients of the layer. 3. The layer of claim 1 wherein said leuco dye comprises at least 1% by weight of dry ingredients of said layer. 4. The layer of claim 1 wherein said leuco dye comprises 2% to 10% by weight of dry ingredients of said layer. 5. The layer of claim 1 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 0.2. 6. The layer of claim 1 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 0.6. 7. The layer of claim 1 wherein said leuco dye is present in a concentration sufficient to provide an increase in optical density upon development of at least 1.0. C? 8. The layer of claim 1 wherein sadi leuco dye is selected from the class consisting of leuco crystal violet and leuco malechite green. 9. The layer according to claim 1 wherein said layer comprises the diazonium salt l-diazo-2,5-diethoxy-4-morρholino benzene borofluoride. 10. The layer according to claim 1 wherein the development temperature is between 180°F (82°C) and 380°F (193°C) . 11. The layer according to claim 1 wherein the development temperature is between 220°F (105°C) and 350°F (167°C) . 12. The layer according to claim 1 wherein said layer comprises a binder selected from the classes consisting of polyvinyl chloride and polyvinyl acetate resins. 13. The layer according to claim 1 wherein said binder is present as at least 50% by weight of dry ingredients in the layer. 14. The layer according to claim 1 wherein said binder is present as at least 70% by weight of dry ingredients in the layer.

Inventors: GATZKE K
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: G03C1
IPC codes: G03C1