BE695363A - - Google Patents

Description

  

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  NEW DIRECT POSITIVE EMULSIONS
WITH SILVER HALOGENIDES.
 EMI1.1
 



  The present invention relates to ôaiaà. -,>. i; ". photographic and preparation methods, and). more particularly direct phot positive emulsions and preparation methods, (;, these combinations.



  Photographic emulsions positivoa diz'e; .t ,. to the veiled silver halides of the prior art are not very sensitive. It is therefore very desirable to prepare new direct positive silver halide emulsions of increased sensitivity, and in particular direct positive emulsions having a high maximum density in the unexposed ranges.

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   Direct positive photographic emulsions containing grains of silver halides where at least 50/100 of the halides are represented by chloride ions are particularly useful. These direct positive emulsions can be developed and processed very quickly. Thus, the present invention relates to direct positive silver halide photographic emulsions in which the halides comprise an appreciable percentage of chloride ions.



   Noteworthy are the new direct positive photographic emulsions that are almost uniformly fogged, in substance or applied to a suitable carrier.
 EMI2.1
 according to the invention in that 11eB comprise at least 50/100 by mole of silver chloride and that the silver halide grains contain, adsorbed on their surface a) - a compound which is either an acceptor of silver. electrons for which the sum of the anodic polarographic potential and the cathodic polarographic potential is positive, i.e. a halogen acceptor whose potential
 EMI2.2
 anodic polarographic potential is less than 085 V and the cathodic polarographic potential is less than -1.0 V;

   and b) - an amount of bromide sufficient to effectively increase the sensitivity of the silver halides, this amount adding to the amount of the bromide ions present in the grains in the form of mixed silver halide.

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   According to a particular embodiment of the present invention, the direct positive photographic emulsions may also contain, adsorbed to their surface, a sufficient quantity of iodide to effectively increase the maximum developable density in the unexposed areas of the emulsion, this amount of iodide added to all iodide ions present in the grains in the form of mixed silver halide.



   The invention also extends to a method making it possible to increase the sensitivity of a direct positive emulsion, veiled in a uniform manner, comprising grains of silver halides, the halides of which consist of at least 50/100 in mole of chloride, which consists in contacting grains of silver halides, an electron acceptor or a halogen acceptor, and a sufficient quantity of water soluble burnt to effectively increase the sensitivity of the grains of silver halides.



   According to one embodiment of the process according to the invention, the silver halide grains are also placed in contact with a sufficient quantity of a water-soluble iodide to effectively increase the maximum developable density in the non-ranges. exposed of the emulsion.



   According to the invention, it has been found that the direct positive photographic emulsions with silver halides, the halides of which consist of at least 50/100 moles of chloride, exhibit a distinctly sensitive sensitivity.

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 when the surface of the silver halide grains is provided with a combination of a bromide and a compound which is an electron acceptor, or a halogen acceptor
It has further been found, according to the invention, that the maximum developable density of the emulsions according to the invention can be significantly increased by adding an iodide to the surface of said grains of silver halides.



   Any water soluble bromide can be used to increase the sensitivity of the emulsions according to the invention. As typical examples of bromides, there may be mentioned the bromides of ammonium, potassium, sodium, lithium, cadmium and strontium.



   In carrying out the process according to the invention, the water-soluble bromide is added to the emulsion, at a concentration sufficient to effectively increase the sensitivity of the emulsion. This concentration can vary considerably. In general, it can be said that adding from about 0.01 mole to about 0.2 mole of bromide per mole of silver halide gives a satisfactory increase in sensitivity. The most preferred concentrations for most emulsions are from about 0.04 moles to about 0.09 moles of bromide per mole of silver halide.

   Thus, the potassium bromide can be added at concentrations of between about 1 g and about 20 g and, advantageously, at concentrations of between about 4 g and about 9 g per mole of silver halide.

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  It can also be said that the surface of the silver halide grains of the emulsions according to the invention can advantageously bring about 0.01 mole to about 0.2 mole of bromide per mole of silver halide, and advantageously between about 0.04 moles and about 0.09 moles of bromide ions per mole of silver halide. This amount of bromide is in addition to the bromide ions contained in the emulsion in the form of mixed silver halides.



   A large number of soluble iodides can be used
 EMI5.1
 in water. As examples of:! '"": = -': - ". 3 'ab ...,' e ,, y there may be mentioned iodides of ammonium, potassium, sodium, lithium, cadmium or of strontium. The amount of iodide added to the emulsion should be sufficient to effectively increase the maximum developable density of the unexposed areas of the emulsion. This concentration can vary widely and, even, can be, for example, between about 0.002 moles and about 0.03 moles of water soluble iodide per mole of silver halides.



  Particularly good results are obtained when the water soluble iodide is added at a concentration of between about 0.003 mole and about 0.012 mole per mole of silver halide. For example, potassium iodide can be added to a concentration of between about 0.5 g and about 5 g per mole of silver halide and obtain an appreciable increase in the maximum density. It can also be said that the photographic silver halide emulsions according to the invention can contain, adsorbed on their surface

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 between about 0.002 moles and about 0.03 moles and preferably between about 0.003 moles and about 0.012 moles of iodide per mole of silver halide.



   According to the invention, the amount of bromide or of bromide and of iodide, present at the surface of the silver halide grains, is added to all the bromide or iodide ions present in the grains in the form of halides of mixed silver such as chlorobromide, chloroiodide or silver chlorobromoiodide.



   The electron acceptors or the halogen acceptors which give particularly advantageous results in the implementation of the present invention can be characterized by their polarographic half-wave potentials, that is to say by their potentials of. redox determined by polarography. The electron acceptors useful according to the invention have an anodic polarographic potential and a cathodic polarographic potential, the sum of which forms a positive sum. The halogen acceptors useful according to the invention have an anodic polarographic potential less than 0.85 V and a cathodic polarographic potential less than -1.0 V.

   Preferred halogen acceptors according to the invention have an anodic polarographic potential of less than 0.62 V and a cathodic polarographic potential which is less than -1.3 V. Measurements of cathodic potential can be made from a solution. 1 x 10-4 M electron acceptor in a solvent such as methanol containing lithium chloride (0.05 M) using an electrode

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 with drops of mercury, the polarographic half-wave potential corresponding to the most positive cathode wave being denoted by EC.

   Anodic potential measurements can be made from a solution of a 1 x 10-4 M aqueous solvent, for example a methanolic solution of the eleotron acceptor containing sodium acetate (0.05 M) and acetic acid (0.005 M), using a pyrolytic graphite pellet as an electrode, the half-wave, voltammetric potential corresponding to the most negative anodic response being designated by Ea. For each measurement, the reference electrode can be a silver-silver chloride electrode in a saturated aqueous solution of potassium chloride, at 20 C. Electrochemical measurements of this type are well known, and one can be found. description in the book "New Instrumental Methods in Electrochemistry", by P.

   Delahay, Intersoience Publishers Inc., New York, New York, 1954, in Polarography, by IM Kolthoff and JJ Lingane, 2nd edition, Intersoience Publishers, New York, New York, 1952 and in articles by Elving published in Analytical Chemistry, 36, 2426 (1964) and Adams published in Analytical Chemistry 30, 1576 (1958).



   Advantageously, the electron acceptors used according to the invention provide spectral sensitization such that the ratio of the relative sensitivity to "minus blue" to the relative sensitivity to blue of the emulsion is greater than 7, and advantageously greater than 10, when exposed to a tungsten light source through the Kodak Wratten no.16 and no.35 plus 38A filters, respectively. These electron acceptors

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 can be called spectral sensitizers - electron acceptors. However, electron acceptors which do not spectrum sensitize the emulsion can be used.



   A particularly useful class of electron acceptors which can be used in direct positive silver halide photographic emulsions and in processes for preparing such emulsions are cyanines such as imidazo-type dyes. [4,5-b] -quinoxaline. Dyes of this type are described in Belgian patent 660 253. In these dyes, the imidazo- [4,5-b] -quinoxaline nucleus is attached to the methine chain by the carbon atom in position 2,
Very good results are obtained with dyes of the indole type substituted in position 2 by an aromatic nucleus, in particular with cyanines containing an aromatic nucleus, in particular with cyanines containing an indole nucleus substituted by an aromatic radical in position 2. .

   Advantageously, these dyes also contain a desensitizing nucleus in addition to the indole nucleus. A desensitizing nucleus is a nucleus which gives a symmetrical carbocyanine such as its addition to a photographic silver chlorobromide emulsion containing 40/100 by mole of chloride and 60 / 100 by mole of bromide, at a concentration of between about 0.01 g and about 0.2 g of dye per atomogram of silver, produces, by capture of electrons, a loss of sensitivity to blue equal to at least 80 / 100, and advantageously greater than about 90/100.

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   A particularly useful class of spectral sensitizers-electron acceptors useful according to the invention corresponds to the following general formula: A - L - B where L represents a methine chain containing from 2 to 3 carbon atoms;

   A represents an indole ring substituted with an aromatic radical attached to the methine chain by the carbon in position 3 of the indole ring; and B represents an organic heterocyole, this nucleus being, when L represents a methine chain of 2 carbon atoms, a desensitizing nucleus, and the cyanine formed being an asymmetric dimethine cyanine, and when L represents a methine chain of 3 carbon atoms , B represents an indole ring substituted by an aromatic radical attached to the methine chain by the carbon atom in position 3 of the indole ring.

   A particularly useful desensitizer core, where L represents a methine chain containing 2 carbon atoms is a
 EMI9.1
 imidazo ring, 5 - quinoxalins attached by the carbon atom, in position 2 to the methine chain.



   Spectral sensitizers-electron acceptors of this type are dyes which can be prepared by any conventional method. One of these processes consists in bringing to reflux, in an appropriate solvent, a carboxaldehyde derivative of an indole substituted in position 2 by an aromatic radical, with a quaternary salt substituted by an aloyl radical of a compound containing the desired desensitizing nucleus. For example, a substituted indole-3-oarboxaldehyde can be brought to reflux in a solvent such as acetic anhydride.

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 in position 2 by an aromatic radioal on a salt
 EMI10.1
 2-aleoylamido, -> quinoxal.nium, or a 2-alkylene-pyrrolo-Z, 3-h7-pyridine to obtain the desired colorant.



   A preferred group of spectral electron acceptor sensitizers used according to the invention corresponds to the following general formula:
 EMI10.2
 where L represents a methine chain, for example
 EMI10.3
 -CH =, -C (CH3) = '-C (C6H5) =' etc .; A represents an aromatic ring such as the phenyl ring which may contain various groups such as an alkyl radical (eg methyl, ethyl, propyl, butyl, etc.), an alooxy radical (eg methoxy, ethoxy, propoxy, etc.). butoxy, eto.), a halogen radical such as bromine, chlorine or fluorine, an aryl radical such as phenyl, where A can be a heterocyclic aromatic radical, advantageously containing from 5 to 6 carbon atoms of which the heteroatom is advantageously nitrogen, sulfur or oxygen;

   R2, R3 each represent a hydrogen atom, a halogen atom such as chlorine, bromine or fluorine, an alkyl or alkoxy radical such as methyl, ethyl, propyl, butyl, methoxy, propoxy, hydroxyethyl, etc. ; where R2 and R3 taken together represent the atoms necessary to complete a condensed aromatic ring of 6 atoms

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 of carbon;

   R1 represents an alkyl radical, including a substituted alkyl radical, advantageously containing from 1 to 8 carbon atoms, including methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl , carboxyalkyl such as carboxyethyl or arboxybutyl, etc; R4 and R5 each represent an alkyl radical, including an
 EMI11.1
 substituted alkyl radical,.

   Advantageously, it has 1 to 18 carbon atoms, including methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, hexyl, dodecyl, octadecyl, benzyl, beta-phenylethyl, etc., a sulfoalkyl radical such as sulf obutyl, a sulfatoalkyl radical such as sulfatopropyl or sulfatobutyl, a carboxyalooyl radical such as carboxyethyl or carboxybutyl; an allyl or alkylenyl radical such as propenyl and butenyl; alkyl such as propargyl; cycloalkyl such as cyclobutyl and cyclohexyl; dialkyl, aminoalkyl such as dimethylaminomethyl and aryl such as phenyl, p-tolyl, o-tolyl, 3,4-dichlorophenyl, etc .;

   R6 has the same meaning as R2, or R6 considered together with R1 represents an aloylene radical such as trimethine or dimethine; R7 represents a halogen, nitrile or NO2 radical, n is an integer between zero and 3 and X represents an anion, advantageously an acid anion such as the anion
 EMI11.2
 chloride, bromide, iodide, p-tolubnosulfonate, thiocyanate, sulfonate, methyl sulfate, ethyl sulfate, perchlorate, and @@

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A related class of spectral sensitizers - electron acceptors particularly useful according to the invention are constituted by the pyrrolo- [2,3-b] pyrido dyes, for example those corresponding to the following formula
 EMI12.1
 where R12, R13,

   R13 each represents an alkyl radical such as methyl, ethyl, propyl or butyl or an aryl radical such as phenyl; and X have the meanings given above and Q represents a substituent selected from the group consisting of (1) - L = Q1, where Q1 represents the atoms necessary to complete a desensitizing ring forming a trimethine cyanine, such as a ring 6-nitrobenzothiazole, a 5-nitroindolenine ring, an imidazo- [4,5-b] -quinoxaline ring or a pyrrolo- '2,3-b $ -pyrido ring, for example a ring of formula
 EMI12.2
 where R15, R16, R17 each represent the same groups as those defining the radicals R12, R13 and R14, and (2)

   the atoms necessary to complete a desensitizing ring to form an oyanine dimethin such as a pyrazole ring or an indole ring substituted by a radical

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 aromatic in position 2 attached by the carbon atom in position 3 to the methine chain, for example a ring of formula!
 EMI13.1
 where R1, R2, R3 and R6 have the meanings mentioned above,
 EMI13.2
 Another class pa.rt1oult, .. PI1'l "'' '' - + :: .. -:. -; -:.: - spectral sensitizers-electron acceptors correspond to the following general formula
 EMI13.3
 where X, L, A, R1, R2, R3 and R6 have the meanings
 EMI13.4
 previously mentioned;

   A1 'R89 R9 $ R10 and Bzz have the same meanings, respectively, as A, R1, R2, R3 and R6; and Y represents a hydrogen atom, an aryl group such as phenyl, an alkyl radical such as methyl, ethyl, propyl, or butyl, or an alooxy radical such as methoxy, ethoxy, or propoxy, a substituted phenyl or aromatic heterocyclic radical such as a thiophene radical. Dyes of this type can be prepared by the process described in US Pat. No. 2,930,694.
 EMI13.5
 



  The symmetrical imidazo, 5 - quinoxaline trimethiniquca cyanines, each ring of which is attached by the carbon atom in position 2 to the methine chain are

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   electron acceptors useful according to the invention. Typical dyes are for example those which correspond to the general formula
 EMI14.1
 where X, L, R4 and R5 have the above meanings and R11 and R12 have the same values as R4 and R5, each of the radicals X1 represents a halogenated radioal such as bromine, chlorine or fluorine, and each n is a number integer between 0 and 3. Dyes of this type can be prepared by the process described in Belgian patent 660 253.



   Another group of electron acceptors useful according to the invention consists of pyrazolyl dyes such as those of the following general formula:
 EMI14.2
 where R7, n, R4, R5, L and X each have the meanings mentioned in the preceding formula (I), R18 and R19 each represent a substituent such as a hydrogen atom, an alkyl radical advantageously containing from 1 to 18 carbon atoms such as methyl, butyl, acetabulum, dodecyl, octadecyl, an aryl radical such as
 EMI14.3
 phenyl, p-tolyl, 3,4-dichlorophenyl, etc. and R2 has the same value as R4.

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   Dyes of this type can be prepared by conventional techniques. For example, a suitable method is to reflux in a suitable solvent such as acetic anhydride, a 2-alkyllimidazo salt.
 EMI15.1
 , 5 -> - quinoxa7.inium with a pyrazole-4-carboxaldehyde.



  One such dye is 1,3-diallyl-2- iodide
 EMI15.2
 - (3,5-dimthyl-1-phenyl-4-pyrazolyl) -viny-imidazo.



  , 5 - quinoxalinium, of formula 1
 EMI15.3
 This dye can be prepared by bringing to reflux
 EMI15.4
 1,3-diallyl-2-methy3imidao e5 - quinoxalinium p-tolueneaulfonate with 3,5-dimethyl.1-phnylpyrazole 4-oarboxyaldehyde in aoetic anhydride for an appropriate time, for example 10 min.



   Another class of electron acceptor sp @@ tr @@ x- sensitizers consists of nitro dyes such as cyanines and merocyanines containing at least one nucleus and advantageously two nuclei bearing desensitizing substituents such as NO2.



   Certain specific electron acceptors which give remarkable results according to the invention are the reaction products of a cyanine with a halogenating agent. Preferred electron acceptors of this type are those where the hydrogen atom of at least one methine group of cyanine is replaced by a halogen atom having an atomic weight of between about 35 and about 127, o ' that is, chlorine, bromine or iodine.

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 In these compounds, a carbon atom connecting the two nuclei of the dye molecule 'can carry two halogen atoms.

   As compounds. halogens, mention may be made of those represented by the formulas:
 EMI16.1
 where Z1 and Z2 each represent the non-metallic atoms necessary to complete a heterocycle of the type used in oyanins such as a benzothiazole-type ring, (eg benzothiazole, 4-chlorobenzothiazole, 5-ohlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, 5-methylbenzothiazole, 5-bromobenzothiazole, 4-phenylbenzothiazole, 5-phenyl-benzothiazole, 6-phenylbenzothiazole, 4-methoxybenzothiazole, 5-methoxybenzothiazole, 5-iodobenzothiazole, 5-iodobenzothiazole, 5-iodobenzothiazole ethoxybenzothiazole, 5-ethoxybenzothiazole, 5-hydroxylbenzothiazole, etc.);

   a nucleus of the naphthothia zole type (e.g. α-naphthothiazole, -naphthothiazole, 5-methoxy-ss-naphthothiazole, 5-ethyl-ss-naphthothiazole, 8-methoxy- [alpha] -naphthothiazole, 7 -methoxy-a-naphthothiazole, etc.); a benzoxazole-type ring (eg, benzoxazole, 5-ohlorobenzoxazole, 5-methylbenzoxazole, 5-phenylbenzoxazole, 5-methoxybenzoxazole, 5-ethoxybenzoxazole, 5-hydroxybenzoxazole, etc.); a nucleus of the type

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 EMI17.1
 naphthoxazole (eg α-naphthoxazole, 3-naphthoxaolei etc.); a benzoselenazole-like ring (eg, benzoseienazole, 5-chlorobenzoselenazole, 5-methyl-benzoselenazole, 5-hydroxybenzoselenazole, etc.);

   a nucleus of the naphthoselenazole type (for example c-naphtho-
 EMI17.2
 selenazole, p-naphthoselenazole, etc.); a quinoline-like nucleus including 2-quinolines (e.g. quinoline, 3-methylquinoline, 5-methylquinoline,
 EMI17.3
 7-methylquinoline, 8-methylquinoldine, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline, 6-hydroxyqv: inoline, 8-hydroxyquinoline, etc.); 4-quinolines (for example, quinoline, 6-methoxy-
 EMI17.4
 quinoline, 7-methoxyquinoline, 8-methoxyquinoldinet etc.); an isoquinoline-like nucleus (eg, 1-isoquinolines, 3-iooquinoline, etc.); each L radical represents a methine group as described above, X2 represents a chlorine, bromine or iodine atom;

   X1 and X each represent a hydrogen a hydrogen atom,
 EMI17.5
 of chlorine, bromine or iodine, at least one of rr'¯ax = X1 being chlorine, bromine or iodine; R1 and R2 each represent an alkyl radical, for example a lower alkyl radical such as methyl, ethyl, propyl, isopropyl, secondary butyl, butyl, tert-butyl, etc., a sulfoalkyl radical whose alkyl radical has 1 to 4 carbon atoms , such as sulfomethyl, sulfoethyl, sulfopropyl, sulfobutyl, etc. and a carboxyalkyl radical in which the alkyl radical has 1 to 4 carbon atoms, such as the carboxymethyl, carboxyethyl, arboxypropyl, carboxybutyl, etc .;

   

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 A represents an acid anion such as chloride ion, bromide,
 EMI18.1
 i odure, ################################ - ## p-tolueusulfonate, thiooyanate, methylsulfate, ethylsulfate, perchlorate, etc .; . y represents the number 1, 2 or 3 and d, m, n and p each represent the positive integer 1 or 2.



   The halogenated compounds described above can be prepared by halogenating a cyanine with chlorine, bromine or iodine. Any suitable halogenating agent can be used such as an aqueous alcoholic solution, (eg in methanol or ethanol) of an N-chlorosucoinimide, N-bromosuccinimide, N-iodosuccinimide or halogen. commercially available halogen-pyrrolidone complex, such as a bromopyrrolidone complex sold by General Aniline and Film Corp.



   With these halogenating agents, it is possible to replace a hydrogen atom of the methine chain by a halogen.



  In carbocyanines or dioarbocyanines, it is believed that the halogen substitution occurs at a terminal carbon of the methine chain. As mentioned earlier, a bonding carbon atom can carry two halogen atoms.



   The electron acceptors can be used in the direct positive silver halide photographic emulsions according to the invention at various concentrations. However, these compounds are advantageously used at concentrations of between about 100 mg and about 2 g of d-acceptor. electrons per mole of silver halide. Best results are obtained using 300 to 600 mg

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 EMI19.1
 of electron acceptor per mole of silver halide.



  As specific examples of suitable electron acceptors, there may be mentioned 1,1-dimethyl-2 bromide,
 EMI19.2
 2'-diphenyl-3,3'-indolocarboayanine; 2,2'-41- bromide. p-m $ thoxyphenyl1,1'-dimethyl-3,3'-indolocarboayanine; 1,1'-dimé% hyl-2,2 ', 8-triphenyl-3,3'indolocarboeyanine perchlorate; 1,3-diallyl-2- - (9-methyl-3-.carbazolylviny> -imidazo ', 5-quinoxalinium p-toluenesulfonate; 1,3-diethyl-11-methyl-21-ph6nyl iodide imidazo-, 5quinoxalino-3'-indolocarbocyanine; 1,1 ', 3,3'tetra6thylimidazo47,5-gquinoxalinocarbocycLninev p-toluenesulfonate 6-ahloro-1'-methyl-1,2', 3-triphenylimidazoì, 5- Ô quinoxalino-3'-indolocarbocyanine; 6, G '-d .chlbro-1,1', 3, 3 '-toyalino-3'-indolocarbocyanine p-tolueneaulfonate; iodide lpl'p3lt3'-t6tramethyl-2-phenyl-3indolopyrrolo ,, 3 -> - pyridocarbooyanine;

   perchlorate; 'l,' 1 ', 3v3,3', 3'-hexamthylpyrrolo - /, 3-> pyridooarbooyan3ne = 1,1 ', 3,3-tetramethyl-5-nitro-2'-phdnylindo-3' iodide indolocarbocyanine; p-tolueneau with 1 <1't3t3t "3 * <3 '*' hexamé% hyl-5,5'-dinitroindocarbocyaninej 3 -ethy3- 1methyl-2-phenyl-6'-nitro-3-indolothiacarbocyanina iodide ; 5'-chloro-1,3'-dimethyl-2-phenyl-6'-nitro-3-indolocarbocyanine ptoluenesulfonate; 5,5'-àichloro-3,3'-diethyl-6,6 iodide '-dinitrothiacarbocyanine; pinaoryptol yellow, 5-m-nitrobenzylidenerhodanine, 5-m-nitrobenzylidene-3-phenylrhodanine; lt3-diallyl-2-e- (3v5-dimdthyl-1phenyl-4-pyrazoiy.) .rvlimidazoa5-quinoxa3inium, 3thyl-5-m-nitrobenzylidenerhoè.re, 3-ethyl-5- (2,4dînitrobenzylidene) rhodanine, 5-on "robenzylidi no-3phnyirhodanina;

   1 'iodide, $ -% hyl-6-nII; -? thia-

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 EMI20.1
 .21-oyaniney ô-ohloro-4-nitro-bensotriazole 6-amino-methyl-2 '-methyl6 -quinoléihiwaviny quinahium dichloride, 4' - (jEL-n-'Mtyloxyphenyl) - '2,6- di (h-e% hylphenyl) thiapàrylium, etc.



   A preferred class of halogen acceptors which can be used in accordance with the invention comprises the spectral sensitizing merooyanins of the formula:
 EMI20.2
 where A represents the atoms necessary to complete a
 EMI20.3
 acidic heterocycle such as rhodanine, 2-thiohydsntotne, etc., B represents the atoms necessary to complete a heterooyol containing a basic nitrogen atom such as 1 heterocycle benzothiazole, naphthothiazole, benzoxazole, etc., each L radical represents a bond methine
 EMI20.4
 such that -CH =, -CCH3) = 'or -C (C6H5). and n is equal to 0.1 or 2.



   The halogen acceptor meroyanins useful according to the invention can also be represented by the formula:
 EMI20.5
 where m represents the whole number 1,2 -or 3, R represents an alkyl radical including a substituted alkyl radical, advantageously containing from 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, ootyl, a radical

 <Desc / Clms Page number 21>

   sultoalkyl such as sulfopropyl or sulfobutyl or sulfatoalooyl such as sulfatopropyl or sulfatobutyl or a carboxyalkyl radical such as carboxyethyl or carboxybutyl, or an aryl radical including a substituted aryl radical, for example phenyl, sulfophenyl, carboxyphenyl, tolyl, etc.,

   each L represents a substituted or unsubstituted methine radical, n is a positive number between 1 and 3, Z represents the non-metallic atoms necessary to complete a heterocycle of 5 to 6 carbon atoms, for example, a ring of the benzo- type
 EMI21.1
 thiazole, benzoxazole, benzoselenazole, c-naphthothiazolet 3-naphthothiazols, a-naphthoxazolep p-naphthoxazole, 'a-naphtoselenazole, p-naphthoselenazole, thiazoline,. simple thiazole, for example, 4-methylthiazole, 4-phenyl-
 EMI21.2
 thiazole, 4- (2-thienyl) ... thiazole, G., Ec. & - # 'e.for example, 4-methylselenazole, 4-phenylselenazole, etc., simple oxazole, for example, 4-methyloxazole, 4 -phenylquinole 5:

  born,
 EMI21.3
 thiazole, etc. 1 pyridine, 3,3-dialkoylindolenine, etc. and Q represents the non-metallic atoms necessary to complete a 5-atom heterocycle in the ring, for example a rhodanine ring, a 2-thio-2,4- (3,5) - ring
 EMI21.4
 oxazoledione, a 2-thiohydantoin ring, a 5-pyrazolone ring, etc.



   A class of halogen acceptors used more advantageously according to the invention can be represented by the formula
 EMI21.5
 

 <Desc / Clms Page number 22>

 where each R radical represents an alkyl radical, including a substituted alkyl radical, preferably containing from 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, acetabulum, a sulfoalkyl radical such as sulfopropyl or sulfobutyl , a sulfatoalkyl radical such as sulfatopropyl or sulfatobutyl, a carboxyalkyl radical such as carboxyethyl or carboxybutyl, or a radioal aryl, including a substituted aryl radical, for example phenyl, sulfophenyl, carboxyphenyl, tolyl, etc.,

   n is equal to 1 or 2, Z represents the non-metallic atoms necessary to complete a heterocyclic ring of 5 to 6 atoms in the heterocycle, and X represents an oxygen, sulfur, selenium atom or a group of formula -NE, where R represents an alkyl radical, including a substituted alkyl radical, advantageously containing
1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or
 EMI22.1
 sulfobutyl, a eu3.fatoalkyl radical such as sulfato-propyl or sulfatobutyl, or a carboxyalkyl radical such as carboxyethyl or carboxybutyl or an aryl radical,

   including a substituted aryl radical such as phenyl, sulfophenyl, arboxyphenyl, tolyl, etc. Appropriate procedures for preparing the dyes according to the invention are described in French patent 942 838.



   Specific examples of halogen acceptors which can be used according to the invention include 3-carbo-
 EMI22.2
 xymethyl-5-Lr3-ethyl-2-benzothiazolinylidene) ethyliden! 7 rhodanine; 3-ethyl.-5 3-ethyZ-2-benzothiazolinylidene) ethylidene7rhodanine; 3- (2-dimé% hylaminoethyl) -5-fl-

 <Desc / Clms Page number 23>

 
 EMI23.1
 (3-ethyl-2-benzothiazolinylidene) -2-butenyliden! 7rhodanine; 3-6thy1-5-, 13-ethyl-2-benzoxazoli.n yl3dene) ethylidenrhodanine; 3-carboxy% hyl-5-f3-e% hyl-2-benzoxazolinylidene) ethylid! 7rhodanine; 3-arboxymium% hyl-5-et3-methyl- '2-thiazolidinylidene) -1-methylethylideneyrhodanine; 3-carboxymethYl-5- (3-dthyl-4-methyl-4-thiazolin-2-ylidene) - rhodanine; 5-L'3-methyl-2-thiazolidinylidene) -1-methyl ethylidene% -3- (2-oulf oethyl) rhodanine; the sodium salt of 3-ethyl-5-3 - (- sulfobutyl} a (1H} -pyridyliden> rhodanino #;

   3-ethyl-5- (i-dthyl-4 (1H} -pyridylidene} rhodanine; 3-ethyl-5-L \ 3-ethyl-2-benzothiazolinl1idene) ethyliden! 7-2-thio-2,4- oxazolidenedione; 3-carboxymethyl-5-3-thyl-2
 EMI23.2
 
 EMI23.3
 benzoxazol.inylidene} ethyliâen> -2-thio-.2,4-oxazolidinedione; 3-ethyl-5-3-ethylnaphth, 1-oxazolin-2-ylidene} ethyl3.den-2-thio-2,4-oxazolidinedione; 1-oarboxymethyl-5-3-ethyl-2-benzothiazolinylidene} thyllden-3-phenyl-2 thiohydantoin; 1-carboxymethyl-5-L \ e-ethyl-2-benzoxazolinylidene} ethyliden-3-pheny2-2-thiohydantone ; 1-carboxy thyl-5- '1-thylnaphth o- ", 2-> thiaz oi in-2-ylidene) - ethyliden-3-phenyl-2-thiohydantoin; 3-heptyl-5- (1-methylnaphthoZT # 2-17thiazolin-2-ylidene) -1-phenyl-2-thiohydantoin; 5 - (3-ethyl-2-benzoxazolinylidene? 2-butenyliden / -1,3-diphnyl-2-thiohydantolne;

   4-f1-ethyl-! naphtho, 2-thiazolin-2 = ylidene) methylethyliden-3-methyl 1- (4-oulfophdnyl) -2-pyrazolin-5-one; 1-ethoxycarbonylmethyl-5-1-β-thylnaphth o 2-thiaz ol in-2-ylidene} a thyl iden.



  3- (4-nitrophenyl) -2-thiohydantolnel 5 - (3-ethyl-2benzothiazolinylidene) -2-butenylidenel-3-heptyl-2-thio-2,4-oxazolidinedione; 5-ZT1 * 3-diallylimidazoZZi5-b7-

 <Desc / Clms Page number 24>

 
 EMI24.1
 uinoxalin-2 (3H) -Ylidenejethylid> -3-ethylrhodanine; 3-ethyl-5- (3-methyl-2-thiazolinylidene) -ethylidene / - 2 - thio-2p4-oxaxolidinedione; 5-fl3- (2-oarboxyethyl) - 2-thiazolinylidene) -ethyliden-3-ethylrhodan: Lne; 5-3-methyl-2-thiazolidinylidene) -1-methylethyliden-3- (2-morpholinoethyl) rhodanine; 5-fl3- (2-oarboxyethyl-2-thiazolidinylidene) -1-methylethylidenfl-3-carboxymethylrhodanine; 5-3- (2-carboxyethyl) -2-thiazolidinylidene) - 1-methyletüyliden, g7-3 .- (2 methoxyethyl) rhodanine; J- (J-dimethylaminopropyl) -5-rJ-methyl-2-th1azolidinylidene) -. ethy1; den! 7rhodanine.



   The halogen acceptors useful according to the invention can be used in a wide variety of concentrations.



  However, halogen acceptors are generally used at concentrations of between about 200 mg and about 1 g, preferably between about 300 mg and about 600 mg per mole of silver halide.



   If desired, a combination of an electron acceptor and a halogen acceptor can be added to the emulsions according to the invention.



   In practicing the present invention, it has been found that very useful increases in sensitivity can be achieved when the water soluble bromide is added to the emulsion prior to the addition of the electron acceptor. or the halogen acceptor. However, the greatest increases in sensitivity are achieved when the halogen acceptor or electron acceptor is added to the emulsion prior to the addition of the water soluble bromide.

   This increase in sensitivity obtained by

 <Desc / Clms Page number 25>

 this last preferred succession of additions according to the invention does not require any waiting between the addition of the halogen or electron acceptor and the addition of bromide. Good increases in sensitivity are obtained by stirring the emulsion , adding a halogen or electron acceptor, then immediately adding the bromide without delay while stirring continuously. However, one can, if desired, wait a certain time between the two additions.



   The direct positive silver halide emulsions according to the invention can be uniformly hazy in any suitable manner, for example by light or by chemical hailing agents. It is preferred to use chemical veiling agents. Lastly, mention may be made of reducing agents such as stannous chloride, formaldehyde, thiourea dioxide, etc. In preferred embodiments of the invention, the invention is veiled by adding thereto a reducing agent such as thiourea dioxide and a compound of a metal more electropositive than silver such as a salt of thiourea. gold, for example potassium chloroaurate, as described in British patent 723,019.



   As typical reducing agents useful in the preparation of these emulsions, there may be mentioned stannous salts, for example stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra chloride.
 EMI25.1
 (hydroxymethyl) -phosphoniums etc. As typical examples

 <Desc / Clms Page number 26>

 of metal compounds more electropositive than silver, mention may be made of gold, rhodium, platinum, palladium, @ iridium, etc., advantageously in the form of soluble salts, for example potassium chloroaurate, the
 EMI26.1
 auric chloride '4) 2Pd014' etc.



   The useful concentrations of reducing agent and metal compound, for example a metal salt, can be varied considerably. In general, good results are obtained using about 0.05 mg to about 40 mg of a reducing agent per mole of silver halide and 0.5 mg to 15 mg of a metal compound per mole of silver halide. silver halide.



  Best results are obtained at the lowest concentrations of both the reducing agent and the metal compound.



   As previously mentioned, the term “cloudy emulsion” denotes emulsions in which the silver halide grains provide a density of at least 0.5 when they are developed, without exposure, for 5 min at 20 ° C. in Kodak Developer DK-50 having the following composition, when the emulsion is applied at a silver titre of between 5.4 mg / dm and 54 mg / dm.



   The composition of developer DK-50 is as follows:
 EMI26.2
 N-Methyl-p-aminophenol sulphate 2.5 g Anhydrous sodium sulphite ..................... 30.0 g Hydroquinone ....... ........................... 2.5 g Sodium ydtaborate ................ .......... 10.0 g Potassium bromide ........................... OP5 Water y 1W p. e ... a. e e. e W s s. 1. e y. e 1.0 l

 <Desc / Clms Page number 27>

 
The present invention can be carried out with direct positive emulsions in which the silver halide grains consist of a water-insoluble silver halide core, covered with an outer layer consisting of 'a hazy silver salt, insoluble in water which develops into silver without exposure.

   For example, the outer layer of the grains of these emulsions can be prepared by precipitating on the grains constituting the cores a water-insoluble, photosensitive silver salt in which it is possible to form a removable veil. by laundering. This outer layer has a sufficient thickness to prevent access to the core of the developer used in the treatment of emulsions according to the invention. The outer layer consisting of silver salt is veiled on the surface, so as to make it developable into metallic silver with the usual surface image developers.

   The silver salts constituting the outer layer are sufficiently hazy so as to provide a density at least equal to 0.5 when developing the emulsion which contains them, applied at a silver titre of 10.7 mg / dm2, and developed for 6 min at 20 ° C. in developer A below. This haze can be achieved by chemically sensitizing the silver salts and these outer layers, until haze appears, using the sensitizers described for sensitizing the silver ahlogenide grains constituting the cores of future emulsions. For this purpose, one can use a high intensity light, and other well known veiling agents.

   Although the nucleus does not require sensitization until haze formation, the

 <Desc / Clms Page number 28>

      outer layer is veiled. Haze formation by reducing sensitizer, sulphide sensitizer, using high pH and low pAg precipitation conditions, etc. can be used.

   We can also deposit the outer layer on the core before veiling: Developer A has the salivating composition:
 EMI28.1
 N-Methyl-p-aminophenol sulfate ............ 2.5 g
 EMI28.2
 
<tb>
<tb> Ascorbic acid <SEP> <SEP> ............................ <SEP> 10, o <SEP> g < SEP>
<tb> Metaborate <SEP> of <SEP> potassium <SEP> ..................... <SEP> 35.0 <SEP> g
<tb>
 
 EMI28.3
 Potassium bromide ............ <........... loo g Water q. $ Epe ww .w e ..... e.vs.w oeo 1 , 0 1
 EMI28.4
 
<tb>
<tb> pH <SEP> .........................................

   <SEP> 9.6
<tb>
 
Before the water-insoluble silver salt for forming the outer layer is added to the silver salt constituting the cores, the core emulsion is first chemically or physically sensitized by processes where 'centers are formed on these nuclei which promote the deposition of photolytic silver; these are centers which form latent image seeds. These centers can be obtained by various methods. Silver halide rings containing such centers made of a metal of Group VIII of the Periodic Table, for example palladium, iridium or platinum, etc. are particularly useful because these centers act as electron acceptors. Chemical sensitization processes of the type described by A. Hautot and H.



    Sauvenier in Science et Industries Photographiques vol. 28 - January 1957 - pages 1 to 23 and January 1957 pages 57 to 65 are particularly useful. We can

 <Desc / Clms Page number 29>

 divide chemical sensitization processes into three main classes, namely, sensitization by gold or a noble metal, sensitization by sulfur, for example a labile sulfur compound, and sensitization by reduction, for example treatment silver halides by a strong reducing agent which allows intro-. small particles of metallic silver in the crystal of silver ahlogenides.
 EMI29.1
 



  The present invention convlp "4 :: .. ::: ...:.> ,.":;:.; J.1'emen1i to direct positite emulsions with high sensitivity which comprise veiled silver halide grains. and an electron acceptor compound. The hazy silver halide grains of these emulsions have the following property when applied to a support, in the form of a photographic emulsion, so as to achieve a maximum density of at least about 1 per. treatment for about 6 min at 20 C in Kodak DK-50 developer, the maximum density obtained with this sample is at least about 30/100 greater than the maximum density of an identical emulsion which has been treated for 6 min at about 20 C in Kodak Developer DK-50 after having been bleached for about 10 minutes at about 20 C in the next bleaching bath hereinafter called bath B.

   
 EMI29.2
 
<tb>
<tb>



  <SEP> potassium cyanide <SEP> .............. <SEP> 50 <SEP> mg
<tb> Acetic acid <SEP> crystallizable <SEP> <SEP> 3.47 <SEP> ml
<tb> Sodium <SEP> acetate <SEP> <SEP> .................... <SEP> Il, 49 <SEP> g
<tb> Bromide <SEP> of <SEP> potassium <SEP> ................ <SEP> 119 <SEP> mg
<tb> Water <SEP> q.s.p .................. <SEP> 1 <SEP> 1
<tb>
 

 <Desc / Clms Page number 30>

 
The grains of these emulsions lose at least about 25/100 and generally at least about 40/100 of their haze density when bleached for
10 min at 20 C in the previous B bath.

   This haze density can be illustrated by applying the silver halide grains to a support in the form of a photographic emulsion so as to obtain a maximum density of at least 1 per treatment, for 6 minutes to approximately. 20 C, in Kodak developer DK-50, and comparing the density of this product with an identical product which is treated for 6 min at 20 C in Kçdak DK-50 developer after being bleached for about 10 min at 20 C in bleach bath B. As previously mentioned, the maximum density of the unbleached photographic material will be at least 30/100 greater, and generally 60/100 greater than the maximum density of an identical bleached sample.



   The silver halides used in the preparation of the photographic emulsions according to the invention include any photographic silver halides which contain at least 50/100 by mole of chloride, for example silver chloride, chlorobromide. silver, silver chlorobromoiodide, etc. Mixtures of emulsions can be used, for example mixtures of silver chloride and silver chlorobromide.

   Likewise, the core of the silver halide grains may consist of silver halides of different composition from the silver halides constituting the outer layer of the grain. In any case, the total amount of chloride present in the form of silver chloride or chlorohalides

 <Desc / Clms Page number 31>

 silver will constitute at least 50/100 by mole of all the silver halides of the emulsion.



   The silver halide grains having an average size less than about 1, preferably less than about 0.5, give particularly advantageous results. The silver halide grains can be regular and can have any suitable shape such as cubic or oct: a.hedral.



  For example, at least 95/100 by weight of the photographic silver halide grains may have a diameter which does not differ from the average grain diameter by less than about 40/100 and preferably less than about 30/100. The average grain diameter can be determined by usual methods, for example by a method described.
 EMI31.1
 by Trivel11 - ",. f ::" '; ytl, tulé t "Empirical Relations Between Sensitometry and Size-: rrequ ..... ¯: -. - # - '." . <. in Photography Emulsion Series "published in The Photography Journal - vol. 79-1949, pages 330-338.

   The hazy silver halide seeds of these direct positive photographic emulsions, according to the invention, provide a density of at least 0.5 when developed, without exposure, for 5 min, at 20 ° C., in the developer Kodak DK-50, when such an emulsion is applied at a titre of between about 5.4 mg / dm2 and 54 mg / dm2 of silver.



  These photographic silver halides can be applied at silver titers of between about 5.4 mg / dm2 and 54 mg / dm2 of silver.



   During the preparation of photogra-
 EMI31.2
 previous phiques, advantageously incorporates the aocp ':' I ..
 EMI31.3
 of electrons, the acceptor

 <Desc / Clms Page number 32>

 of halogen, bromide and iodide in the finished and washed photographic silver halide emulsion, and it should, of course, be evenly distributed throughout the emulsion. The methods of incorporating these adjuvants into emulsions are relatively simple and well known in the prior art. For example, they can be added to the emulsions in the form of solutions in suitable solvents, and in this case the solvent chosen should be completely free from any adverse effect on the photosensitive products prepared.

   Methanol, isopropanol, pyridine, water, etc. can be used. alone or as a mixture, as solvents for the electron and halogen acceptors useful according to the invention. The type of silver halide emulsions which can be sensitized with these dyes include any emulsion prepared with the hydrophilic colloids used as silver halide dispersants, for example, emulsions which include natural substances such as gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinylpyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, eto.

   The binder of the emulsion layer of the photographic material according to the invention may also contain dispersed polymerized vinyl compounds, such as those described in United States Patents 3,142,568, 3,193,386, 3,062,674, 3 220,844 and comprising the water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalooyl acrylates or methaorylates, etc.

 <Desc / Clms Page number 33>

 



   The new emulsions according to the invention can be applied on any suitable photographic support such as glass, for example a film of acetate.
 EMI33.1
 of cellulose, of cellulose aceftobutyrate, of polyester such as polyethylene glycol terephthalate, paper, barite paper, paper coated with a layer of polyold- fine, for example of polyethylene or polypropylene which can be electronically bombarded with so as to promote the adhesion of the emulsion.



     The following non-limiting examples illustrate the invention.



   These examples use the following halogen acceptors and electron acceptors:
 EMI33.2
 Dye 1 - i, -dlthyl-'i'-methyl-2'-phnylimidazo, 5-quinoxalino-3'-indolocarbocyanine iodide (electron acceptor) Dye II - Pinaoryptol yellow (d 'acceptor electrons)
 EMI33.3
 Dye III - 3-carboxymethyl-5 3-methyl-2 (3-thiazolinylidone) isopropylidene7rhodanine (halogen absorber) Dye IV - The sodium salt of 3-ethyl-5 - (4-sulfobutyl) -4 (1H) -pyridylidenrhodanine (halogen acceptor) Dye V - 2-L 'iodide - (3,5-dimethyl-1-phenyl-4pyrazolyl) viny-1, 3-diphny5.midazo, 5-quiranxalinium ( electron acceptor) Dye VI - La 3- ± (1,3-diethyl-2 (iH) -imidazo ± 4,5-gquinoxalinylidene) ethyliden-2H-pyridoL ', 2-pyrimidine-2,4- ( 3H) - dione (electron acceptor)

   Dye VII - 3-Ethyl-2-L \ 2-methyl-5-axo-3-phenyl-3-isoxazolin-4-yl) viny-o-nitrobenzothiazol.um methyl eufate (electron acceptor)
 EMI33.4
 Dye VIII - 1,1 ', 3,3,3', 3'-hexamethyl-5,5'-dinitroindooarbocyanine p-tolueneeulfonate (electron acceptor
 EMI33.5
 Dye IX - 5t5l-dichloro-3t3 iodide -diethyl-6161- dinitrothiacarbocyanine (electron acceptor) Dye X - La 3 - '(' 3-ethyl-6-nitro-2-benzothiazolinylidene) thyliden-2H- pyrido, 21% pyrimmin-2,4 (3H) -dione (electron acceptor).

 <Desc / Clms Page number 34>

 



   To these examples, the bromides and iodides are added after the halogen acceptor or the electron acceptor unless otherwise indicated.



     Example 1 shows the appreciable improvement in sensitivity obtained with the emulsions according to the invention, when one adds itou soluble bromides in water to a veiled direote positive emulsion of which the halides are constituted by 50/100 chloride, which halides contain a halogen acceptor or an electron tower. This example also shows the improvement in the maximum density obtained with the iodides used in combination with the bromides. Example 1 demonstrates that the use of bromide alone, that is to say without halogen or electron acceptor, does not allow any increase in sensitivity.



   EXAMPLE 1. -
A silver gelatin chloride emulsion having an average size of about 0.3 is prepared by simultaneously adding an aqueous solution of potassium chloride and an aqueous solution of silver nitrate to a strongly stirred aqueous gelatin solution at a temperature of. 70 C, in about 35 minutes. The emulsion is frozen, it is put into noodles and it is washed with cold water in the usual manner.



   This emulsion is veiled with a reducing compound and a gold derivative by first adding 0.2 mg of thiourea dioxide per gram atom of silver and heating for 1 hour at 65 C, then adding 4 mg of potassium chloroaurate per gram atom of silver and heating for
1 h at 65 C. The emulsion is divided into several fractions, and the ahlogene acceptors, the acceptors are added to these various fractions.

 <Desc / Clms Page number 35>

   electrons, potassium bromide and potassium iodide listed in Table 1 below.

   The emulsions thus obtained as well as the control emulsions are applied to cellulose acetate films with the titers of 1a, 7 mg / dm2 of silver and 37.6 mg / dm2 of gelatin, they are set and dried. These products are exposed in a variable intensity sensitometer, developed for 3 min at 65 C in the Kodak Developer D-19, fixed, washed and dried. The results obtained are given in Table I below. The sensitivities are measured at a density 0.3 less than the maximum density. ! all of the following examples.



   ,

 <Desc / Clms Page number 36>

 
 EMI36.1
 
<tb>, Halogen <SEP> acceptor <SEP> KI <SEP> KBr <SEP> Dmax <SEP> Bath
<tb> or <SEP> of electrons <SEP> Sensitivity <SEP> in <SEP> the <SEP> ranges <SEP> in <SEP> the <SEP> ranges
<tb> (g / at.g <SEP> d'Ag. <SEP>) <SEP> (g / at.g <SEP> d'Ag. <SEP>) <SEP> (g / at.g < SEP> of Ag.) <SEP> relative <SEP> unexposed <SEP> exposed
<tb>
 
 EMI36.2
 .. (0.15 lei 1.05
 EMI36.3
 
<tb> 1.0 <SEP> <0.15 <SEP> 1.33 <SEP> 1.36
<tb> 8.76 <SEP> <0.15 <SEP> 1.27 <SEP> 1.25
<tb>
 
 EMI36.4
 1.0 8.76 <0.15 1925 1.12 I 1.5 294 1.07 0.04 '1 125 i, o 0.54 1.41 0.07 1 195 81.76 15.9 1, 24 0.04 1.5 180 8.76 11.0 1.27 0.05 11 (1.0 0.15. 1, i9 Ce84 11 (1.0 190 1 ,:

   1927 0.04 nI1.0! 8, T6 '- 0.15 0.11 0.84 II 1.0 1.0 8.76 1.2 1.27 0.04 J191.000 190 8976 1591 1926 0.04 111 (0.5 1, 1 1.32 0.80 nI 0.5 1.0.! 0.15 1.24 1.07
 EMI36.5
 
<tb> III <SEP> 0.5 <SEP> 8.76 <SEP> 42.0 <SEP> 1.16 <SEP> 0.22
<tb> nI <SEP> 0.5 <SEP> 1.0 <SEP> 8.76 <SEP> 53.0 <SEP> 1.26 <SEP> 0.42
<tb>
 

 <Desc / Clms Page number 37>

 
Example 2 will illustrate the advantage of adding the halogen and electron acceptors in the order listed before the addition of the soluble bromide, or of the soluble bromide and iodide.

   This order of addition allows an increase in sensitivity greater than that obtained when the bromide (or the bromide and the iodide) are added * to the emuleion before the addition of the electron acceptors or d 'halogen.



    EXAMPLE 2. -
We prepare an emulsion like. Example 1, except that the seeds are left to grow to an average size of about 0.7.



  The emulsion is divided into several fractions. A halogen acceptor or an electron acceptor is added to various fractions of the emulsion before and after the addition of the salts, while stirring the emulsion, but without stopping between additions. The type and order of the additions * are mentioned in Table II below.

   These emulsions are applied as well as control emulsions are exposed and on. treats them as in Example 1 'except that the silver titre is 23.7 mg / dm2 and the gelatin titre is 45.6 mg / dm2 and that the development is 3 years 45' in the Kodak D Developer -85. The developers obtained are; mentioned in Table II below. In this table, the term "colorant" refers to the halogen or electron acceptor.

 <Desc / Clms Page number 38>

 
 EMI38.1
 



  - 'AB3JF1TJ here -
 EMI38.2
 Thalogem acceptor Order yr r Max sonibility main or dtelectrons in the ranges in the ranges (6 / at-g of Ag.) Of addition (, g / at.g of Ag.) (G / at.g dllàg. ) relative unexposed expos6on 1 (1.0) o, 2t 1934 0993 1 (1.0) dye first ## 8976 ## Oel6 0904 1 (1 0) dye first 190 --- 87 1934 Ot27 1 (1.0) dye first 1.0 8.76 363 1.17 0.07 If 1.0) -.1 first ## 8.76 2 0.54 0.13 1 (1.0) sol d 'first 190 ## 193 1942 0.21 1 190 salt first 1: 0 8976 60.0 0978 0922 nI o, 5 dye first ## ##, 0.76 1.32 0.67 III 0, 5 dye first ## 4.3B 240 0.74 0.08 IIi 0.5 dye first 1.0 ## 0.63 1932 1.0 III () 951 o dye first t, 0 4, 38 138 1946 1 0 111 (0.5) ..1 first 1.00 4938 331 1920 III 0.5 sol first 4938 331 1948 '8 11 105 sol first, 1.0 - 0.95 1951 9 y0.



  II1 Îo, 51 self first 1.0 4.38 60.0 1 A6 0 y0S I1t 05) dye first ## 7 58 1950 ot63 IV 0'S) dye first 4.38 795 0090 0906 IT (0 ; 5) dye first - 4.38 120 1 P66 OV15

 <Desc / Clms Page number 39>

 
Example 3 illustrates the implementation of the invention using a direct positive emulsion of the type containing grains * consisting of a central core of a water-insoluble silver salt which contains centers promoting deposition. of photolytic silver and an outer layer covering said core with a hazy, water-insoluble wear salt which develops it into silver without exposure.



    EXAMPLE 3.-
A gelatin-silver chloride emulsion is prepared by stirring simultaneously in about 20 minutes 1 1 of an aqueous solution of 4N silver nitrate and 1 1 of an aqueous solution of 4N sodium chloride, to a solution. strongly stirred aqueous solution of one liter of a 0.01 N sodium chloride solution at 70 C which contains 40 g of gelatin. Then 5 liters of water containing 280 g of gelatin are added and the emulsion is cooled. 1/8 of the gelatin-silver chloride emulsion obtained containing 5/1000 moles of silver chloride is melted at 40 C, 100 mg of potassium ohloroiridate dissolved in water are added, then heated emulsion at 70 C.

   This emulsion contains the silver chloride cores which contain physical discontinuities acting as electron acceptors; cores to which an outer layer of silver chloride is applied. The outer layer of silver chloride is formed by simultaneously adding to the core emulsion 500 ml of a 4N aqueous solution of silver nitrate and 500 ml of a 4N aqueous solution of sodium chloride, in About 20 minutes.

   The silver chloride constituting these external layers is veiled by reduction and by a compound of er, adding 0.2 mg of thiourea dioxide per

 <Desc / Clms Page number 40>

 gram atom of silver and heating 1 h at 65 C and adding 4 mg of potassium chloroaurate per gram atom of silver and heating for 1 h at 65 C, then added with stirring 160 g of diluted gelatin in 340 ml of water, then the emulsion is cooled. During the addition of the silver nitrate and sodium chloride to form both the nuclei and the erternals, these two solutions are added at substantially constant rates.

   Sufficient silver chloride forms in the outer layer to provide a ratio of 4 moles of silver chloride in the outer layer to 1 mole of silver chloride in the core. The silver chloride emulsion with cores coated with an outer layer is sheared, the gelatin content is increased to 160 g per mole of silver chloride and a sufficient quantity of water is added to have a manna of 4 kg per mole of silver chloride. The emulsion thus prepared is divided into several fractions and electron acceptors, halogen acceptors, potassium iodide and potassium bromide are added as mentioned in Table III below.

   These emulsions are applied to a film of cellulose acetate in the form of 19.3 mg / dm2 of silver and 43 mg / dm2 of gelatin. We then freeze the groin emulation! lying down and drying it. These products are exposed and they are treated as in Example 1 but the development is 30 s in the Developer.
Kodak D-72 diluted with an equal volume of water.

   The results obtained are mentioned) in Table III. '

 <Desc / Clms Page number 41>

 
 EMI41.1
 Halogen acceptor il Sensitivity Em8X Vain or & 96160trons in the ranges in the ranges (, K / at., G of Ag.) (G / at.g of Ag.) (G / at.g of Ag. ) relative unexposed, oxposed -. - ## 0 1.78 0.06 --- 4 38 bzz0 1 0.56 - 1.0 - 50.0 1.58 0.06 - 1.0 4.38 80.0 9, s0 0.06 ",,, .." ...... 't'> "". '"' I! /: I ....." ..., tl. "" "" ,,, ... ... "" ", ..........., ......... t,!" -, ......... ,,, .. "" ,,,,, "'' '' '' '¯ .... 1,>" "q] ,. o. \ ... w ...., .....



  T 1 O - - ± l at, 6 1.54 1.45 1 1, 0 4.38 55o, o 1.1: 0.03 I 1.19 1, o --- 36.0 1.39 0 , 11 IÎI, 01 t, o 4.38 39.0 1.39, 03 190 190 4938 75990 1.939 OtO3 Tft.O ## 1595 1.52 1.22 vfio 4.38 39890 1.46 0, (i ' Vil 1 9 010 1.0 - G 12.0 1, ° 0 !, 34 T (1; 0 --- 4938 50 190 1944 0202 V 1.0 1.0 - L 12.0 1.40 1.34 VIii, o} --- --- .L ... 12.0 1 32 1.30 wi, o 4.38 302.0 1.10 o, 03 1rI i'o z0 4 12.0 1, 40 1.36 VI 1.0 1.0 4 ,:

  38 4i9, 1.32 1936 vI 1.0 ± 1 2, o 1924 1.16 TM l go - # 4 a38 32.0 0.3 ° ove3 'VII 1.0 1, o..¯ ..., 2T.5 1.54 1 self VII (1, O) 1.0 4.38 1450.0 1.16 0.03

 <Desc / Clms Page number 42>

 
 EMI42.1
 - TABLEAC ¯III - (continued)
 EMI42.2
 Mnax làûin Aeceptsur d'halogâae KI Woe Sensitivity Dmax in the ranges - at gÎ'IÎÙ (glas.6 d'Ae.) (Glas.6 à'àg.) Rolativo Îln2ÀxÎfl lmÉllÀi (0 / at-6 d94.) (0 /at.6 Ag.) (gJa.tg &, 4.) relative unexposed exposed 4290 1930 0.15 TIII 1, o ## ..... 302 * 0 i, 30 o, 1 5 VIII 1.0 7 ::

   he? 27 5 1 26 0904 viii 1 gb 1.0 27 1.14 0 23 VIII 190. , 1.0. ,. 4938 .., '1.0 é, 28,, 0.06 ix i, 0 ¯ /.l2,o 1.40 1.31 ix 1 90 4 # 38 1 1 5, 0 40 0.68 ix 1 to 190 1795 1.40 0988 1toi 190 4o38 iloeo 1928 0.13 1, oÎ j, o 4, 38 1 jo, o 1, h8, 88 1.0 1.0 4.38 110.0 1.28 0.10 ± 1 2, o 1925 1925 X (1.0), 9 0.56 0.26 1.0 4t38 e 2 99 9, 26 9 g 18 1 110 190 l ..

   12.0 1 26 igie X 1.0 190 4938 (12.0, 26 1 J 18 X 1.0 1.0 4.38 451.0 0.78 0.02 III under, 9, 29 0.05 III 0.5 # 4938 229090 1.07 0.03 III o, 5 1, o - '60390 1907 0.05 III o, 5 ---., 38 2890, 0 1.38 0.04 III 0.5' o 4, y 2890.0, 38 0.04

 <Desc / Clms Page number 43>

 The following exempted 4 and 5 illustrate the lead of the invention with a silver chlorobromide emulsion uniformly haze *, the chloride content of the ohloro .. silver bromide enulsion being 90/100 in mole.



    EXAMPLE 4 -
An emulsion is prepared as in Example 1, that is to say that a sufficient quantity of potassium chloride is added during the precipitation so as to obtain a chlorine-silver brotide emulsion containing 90/100 in chloride mode. The emulsion is divided into several fractions and a halogen acceptor and an electron acceptor are added to various fractions * of the emulsion thus prepared, optionally adding potassium bromide as indicated in the following Table IV. the emulsions thus prepared on a film of cellulose acetate in the titers of 10.7 mg / dm2 of silver and of 40 mg / dm2 of gelatin.

   The products thus obtained are frozen, dried, exposed and treated as in Example 1 except that development is carried out in 1 min. The results * obtained are mentioned in Table IV below

 <Desc / Clms Page number 44>

 
TABLE IV
 EMI44.1
 
<tb>
<tb> Halogen <SEP> acceptor <SEP> KBr <SEP> g / <SEP> Sensitivity <SEP> Dmax <SEP> in <SEP> dmin <SEP> in
<tb> or <SEP> of electrons <SEP> mole <SEP> Ag <SEP> relative <SEP> the <SEP> ranges <SEP> the <SEP> ranges
<tb> (g / at.g.

   <SEP> of Ag) <SEP> not <SEP> exposed <SEP> exposed *
<tb> 1 (0.5) <SEP> --- <SEP> 7.3 <SEP> 1.48 <SEP> 0.06
<tb> 1 (0.5) <SEP> @ <SEP> 8.76 <SEP> 145.0 <SEP> 1.40 <SEP> 0.02
<tb> 111 (0.5) <SEP> ---- <SEP> 100.0 <SEP> 1.58 <SEP> 0.80
<tb> III (0.5 <SEP> 8.76 <SEP> 417.0 <SEP> 1.34 <SEP> 0.05
<tb>
   EXAMPLE -
 EMI44.2
 A silver gdla; tinc> -ohlorobromwe emulsion containing 90/100 chloride content is prepared using a procedure similar to that for the preparation of the emulsion of Example 3, adding a sufficient amount of sodium bromide. sodium combined with sodium ohloride so as to prepare a seed emulsion of silver halides consisting of cores covered with an outer layer, which contains 90/100 mole of chloride.

   The emulsion is divine in several fractions which are tested with an electron acceptor * and a halogen acceptor, optionally in the presence of potassium bromide as indicated in the following table V The emulsion * thus prepared is coated and we try them in the same way that in example 4 'We obtain the following results.



   TABLE V
 EMI44.3
 Halogen acceptor KBr g / Senaibilit4 Daax dane Da.iB A-m, or d'4leotro) M) noie AS relative to the unexposed ranges (6 / at.s. Of Ag) * ÉloÀéis'
 EMI44.4
 
<tb>
<tb> I (0.5) <SEP> 0.55 <SEP> 1.50 <SEP> 1.4
<tb> I (0.5) <SEP> 4.38 <SEP> 7.6 <SEP> 1.34 <SEP> 0.04
<tb> III <SEP> (0.5) <SEP> 100.0 <SEP> 1.42 <SEP> 0.07
<tb> III <SEP> (0.5) <SEP> 4.38 <SEP> 263.0 <SEP> '<SEP> 1.17 <SEP> 0,

  07
<tb> is *
<tb>
 

 <Desc / Clms Page number 45>

   @ '. Electron acceptors can be used according to the invention
 EMI45.1
 tron which are not boloranist like example 6 the rAcutr4rag EXAMPLE 6 -
 EMI45.2
 A 1mu181on is prepared as in Example 2 and divided into several fractions * to which the dibrominated 1918-diethyl-2p2t-cyanine chloride (i.e. that the carbon atom which connected the two nuclei carrying two bromine assets, this electron acceptor not removing a dye), possibly adding potassium bromide, We apply these
 EMI45.3
 impulse.

   we expose them and we treat them sumz example 2, the results. obtained are gathered in table V'1 nui-bezit TABLE VI
 EMI45.4
 Acceptors XI XBr Sn.lbl11t 'Dmax dana Suede dane d' 6leotroD8 e / mole gl'molo rola% ivo la * pasges 1 .. plago.



  (g / at.g.4'As) no tXPO.'88 e3q? o <t <e <
 EMI45.5
 
<tb>
<tb> --- Compound <SEP> I
<tb> (0.5) <SEP> ---- <SEP> ---- <SEP> 0.19 <SEP> 1.62 <SEP> 1.2
<tb> Compound <SEP> I
<tb> (0.5) <SEP> --- <SEP> 4.38 <SEP> ---- <SEP> 0.07 <SEP> 0.03
<tb> Compound <SEP> I
<tb> (0.5) <SEP> 1.0 <SEP> 4.38 <SEP> 18.0. <SEP> 1.08 <SEP> 0.04
<tb>
 
Results similar to those of the example are obtained with a photographic silver chloride emulsion clouded by high intensity light or by a strong reducing agent, for example etannous chloride. Good results are also obtained by combining a halogen acceptor with an electron acceptor absorbed both at the surface of the silver halide seeds.



   Of course, the invention is not limited to the embodiments described which have only been chosen by way of example.

 

Claims (1)

; ABSTRACT The present invention has in particular for objects @ 1 - a direct positive photographic emulsion, veiled * in a practically uniform manner, in substance or applied in one or more layers on a suitable photographic support, remarkable in particular by the following characteristics considered separately or in combinations: a) - it comprises seeds of silver halides, at least 50/100 in mole of this * halides being constituted by chloride, these seeds containing, adsorbed on their surface, a compound which is either an electron acceptor of which the as of the anodic polarographic potential and of the cathodic polarographic potential this positive, that is to say a halogen acceptor whose anodic polarographic potential is less than 0.85 V and the cathodic polarographic potential is less than -1.0 V and a sufficient amount of bromide to effectively increase the sensitivity of the silver halides, this amount adding, the amount of bromide ions present in the seeds as mixed silver halide; b) - the said silver halide grains also contain, absorbed at their surface, a sufficient quantity of an iodide to effectively increase the maximum developable density in the unexposed ranges of this emulsion, this quantity of iodide added from surplus iodide ions present in mixed silver halide seeds @ <Desc / Clms Page number 47> o) - the said bromide quality is between approximately 0.01 EMI47.1 mole and on .., 1 "" on 092 molo per gram atom of silver, and 1.Ii, '9'p., nt .... carefully between 0.04 and about OpOq mole per aom8-g0 d 'silver ; d) - said quantity of iodide is between approximately 0.002 mole EMI47.2 and about 0.03 drink, and autagousement between about 00efi5J -1> µ.r and about OpOI2 mol per gram atom of silver; 0), said direct positive p3aovographiqus emulsion is ,, # ',,: \ 1J ,,,; 1! {, I:.; /, J cement and silver halides include at rso.z. 80/100 in mole of chloride, EMI47.3 f) - the so-called silver halide seeds xtas'u Tailla paP, a combination of a reducing agent is of an aospceô l: h11: 1 mà =, 'more electropoeitating than 1'argent; g) - the so-called gs-aina of silver halogens aoat veiled of the practically uniform to.9Q! t by a combination of sodium dioxide and potassium chloroaurate; EMI47.4 h) - said eleotrona acceptor or a won dye; ibilî4atoi. / photographic which 1l1I) r.i! I1bili .. apootrally Si * ce 4n ;; 3, aoiesà; such that the ratio of lSena1bllU4 reln: f;! TI1i e, .u ni, ... "blou to the eeneibilii6 to blue is & up'riov h 7 1) - the said electron acceptor is a substituted indole dye @ by an aromatic radioal in position 2, an imidane dye ' EMI47.5 p5 - quinor, .a.ing a graealy3 dye, an ovieri> à2 zçrà "11: Â <>; [2,3-b] -pyrido, a dye substituted by a miter radical, or the reaction product of cyanine on a halogenating agent; EMI47.6 -) - said eleotronw aooeptor is, 3-diêihyl '- al *) 2sephetraimidaso.-5 - b.-quinoxol, ino3indoloearbo; sic: <Desc / Clms Page number 48> EMI48.1 said aooepteur 4'halon8 40rro * pon4 to the toraul..u1vante 8 EMI48.2 EMI48.3 where a starts equal to 0, 1 or 2 g â represents a molecular bond, 3 represents the atoms necessary to complete an h # * # ro9 cyole containing basic nitrogen; and A represents the lonstomen needed to complete im hdtdroqrole balance 3.) - said halogen receptor is 3-oasxor, ymbtii-5- (3 -m # * loy4 2 (3) -thi, azoliwlidôno) -isop * apylidôn fl-rhodanine, m) - the so-called grains of veiled silver halog4nuroe pownèdasi the property to provide a maximum 40n811; 6 to care 1 8; iYÙ'ÓD, when lying on a support in the form of a EMI48.4 6mû.sion of aax silver halide, and when processed, * for 6 minutes at approximately 2000 in the Kodak Developer DX-50, maximum density being at least 30/100% higher. the maximum density of an identical sample processed EMI48.5 for 6 n approximately 2000 datas 1e Kodak Developer 1> 1i-5iJ, after being bleached for approximately 10 minutes at approximately 20 C in a composition 1 bleach bath EMI48.6 <tb> <tb> <SEP> potassium <SEP> cyanide <SEP> 50 <SEP> mg <tb> Acetic acid <SEP> crystallizable <SEP> <SEP> 3.47 <SEP> ml <tb> Sodium <SEP> acetate <SEP> <SEP> 11.49 <SEP> g <tb> Bromide <SEP> of <SEP> potassium <SEP> 119 <SEP> mg <tb> Water <SEP> q.s.p. <SEP> 1 <SEP> 1 <SEP> 1 <tb> n) - at least 95/100 by mass of the so-called veiled silver halide seeds have a diameter which does not differ from the average diameter of the seeds by less than about 40/100 <Desc / Clms Page number 49> EMI49.1 gas proceeds allowing aooro1tre the .en8ibi11 'of an a'.ion EMI49.2 EMI49.3 po.itiT $ 41rQ1e veiled dalmanièro practically uniform oo * = n> enan% of seeds of silver halog4nvreA #. of which * in the Seine 50 moles pmp. ' .n1 mont oon.t1tu'o by Au ohloruao '<M'g9a'tj) go preceded being remarkable in particular by leu oaraotr1st1quea following seasiAa separately had in combination with) - on Piao * in contact with case graina 8Qi 1; (1) aecepiaM? c ..'.-. 4 tront Before an anodic polarogtaphic potential and an p. = ". '' '' '> 1" "cathodic polarograph Clonot the gum in positive *, Ir (' X '. -an acceptor of' halogen having a polarographic potential less than 0985 V and a pohrographic potential: iq, o OI '<"' H" - disc which is less than -1.0 Vt with a quantity; J \ .tf 'fiBG'-' u bromide soluble in water to increase ettioaoemont the monsibility of neck embossed with silver halide, b) - the so-called ilootrone acceptor or the said Oh1og aooeptor are added to the emulsion before the addition of the bromwo o) - the emultian obtained after the said treatment * is such that'Ma.Mt.'r 'we leb