US2527261A - Production of photographic silver halide emulsions from gelatinanion soap complexes - Google Patents

Description

Patented Oct. 24, 1956 PRODUCTION or PHOTOGRAPHIC SILVER HALIDE EMULSIONS "FROM GELATIN- ANIoN soar ooMPrExEs v John Alfred Henry Hart, Kenneth George Alfred Pankhurst, and Robert Charles Morris Smith, Ilford England, assignors to .Ilford Limited, Ilford, England, a company of Great Britain No Drawingr Application October 19, 1945, Se-

rrial No. 623,445. In Great Britain October 30,

This invention relates tothe production of silver halide photographic emulsions.

Whenan anion soap is added to an emulsion of silver halide in gelatin, at alow pI-I- value or in the presence ofan electrolyte (whenthepH value need not necessarily be low); a-,.complex is v formed between the gelatin and anion soap and this separates out. carrying the silver" halide with it. 1*. f. It has now been discovered that the gelatin/ anionsoapcompl'exesithus formed, and also analogous. complexes formedwith a sulphonic acid containing a highly hydrophobic radicle: in=the anion, are readily dispersible in organic solvents, e. g. methyl alcohol. i According to this inven tion', therefore;photographic emulsions i-n -which the solvent mediurnis predominantly organic are formed by dispersing in an organic solvent medium a complex formed byprecipitating gelatin from its aqueous dispersion containing fsilver halide in sus'pension, by means of an a'nion'soap, or by means of a sulphonic acid "containing a highly hydrophobic radicle in the anion,"the said aqueous dispersion being at a pH value below the isoelectric point of the gelatin, orat a higher pH value and containing an electrolyte. The precipitated complexmay contain a small proportion of water and this be included in the organic solvent dispersion.

According to a further, feature of the invention, there is included in a photographicemul sion so formed a proportion ofanother colloid which is soluble. in the'solvent medium already present in the emulsion, or which issoluble in a solvent medium which is miscible with the" solvent medium already presentin the emulsion, tov forma stable combination" r The gelatin/ anion soap complex and analogous complexes formed from sulphonic;v acids as -defined above, containing silver halide, maybepre" pared by the addition of the anion soap solution to the gelatin silver halide emulsion and allowing the; gelatin, .complex-to sediment,- out, The complexes maybe redispersedin theorganic solvent medium without washing, but :it is preferred: towash the complex to remove unwanted 1ons. responding, free acid: may be employed. 'EIJhe technique of maintaining the originalaqueous.

dispersion of the colloid at a low. .pH .value ap- Instead of the anionysoap itself,; the cor-.

17 Claims. (o 95-4) pears to be equivalent in efiect to the use of the free acid, but the use of the free acid presents the advantage thaltithe resulting complex is not contaminated with the cation of the anion soap. Complexes free from. water-soluble salts are found to be more readily dispersible in some organic solvent media. v

,';-The invention will be described with particular reference to the useof anion soaps, but it is tobe understood that sulphonic acids which, though not true anion soaps, contain a highly hydro phobic anion, can be used'analogously.

It has been discoveredthat for each particular anion soap there is an optimum ratio of the soap to-the gelatin which results'inagelatin com.- plex'of; the highest solubility in organic solvents,

and a methodis .availablefor determining such optimum ratio in each particular case.

-. If an anion soap is added in gradually in creasing quantity to a gelatin solution at: low

" pH, or at higher pH in the presence of electrolyte,

a gelatin/anion soap complex forms and separates out. By measuring the amounts of the anion of the anion soap remaining in the supernatant liquid afterthe mixture has been allowed to stand-f0r some hours, thus reaching equilibrium, and plotting these quantities as ordinates against the quantities of anionsoap added as abscissae, using; a logarithmic scale, a curve is obtained showing a straight line rising portion followed by a fall where the complex begins. to

separate. The curve falls to a minimum value and thenrises -.again.- It has been discovered that, generally; speaking this minimum value (referred to asthe -infiexion point) represents the particular complex'having the greatest hydrophobic character andthe greatest solubility in organic solvents. The precise position of the infiexion point, however, depends on Various: fac tors, including the pI-I and the quantity of electrolyte present, if any. H

A curve of this type can be obtained in respect of any particular anion soap which it is desired to use, and it may be said that, as'a general proposition, where plain gelatin'is concerned; the

preferred conditions for obtaining the highest degree. of solubility inorganic solvents are that the anion "of theanion soapusedshould be as:

strongly hydrophobic as possible; the pH of the I. solution should be below the isoelectric point of emulsion, it is not always possible to achieve 1 these conditions owing to other factors involved in the technique of producingsatisfactory emulsions. For example, it is generally'not desirable;

to prepare photographic emulsions at a pH value lower than 3. Moreover, itf-gi's seldom practical to allow the emulsion to stand-with the anion soap over the long period whichflmay be necessary to obtain equilibriumf Accordingly, the preferred procedure is to ascertain theftrue infiexion point using a plain gelatin solution andan anion soap under conditions which approximate as closely as possible to the conditions which will be necessitated for a particular gelatin photographic emulsion, and then to use a quantity of anion soap with such emulsion which corresponds to that'portion of the curve which follows the inflexion point, i. e. to use a concentration of anion soap which is that at the inflexion point or slightly greater.

Moreover for emulsion-making it is generally desirable that the precipitated gelatin/anion soap complex should be soluble in water-miscible solvents since the precipitated complex invariably contains water, and it is difficult to remove this water without adversely afiecting the quality of the emulsion. To this end it is generally desirable to treat the-emulsion at a pH below the isoelectric point of the gelatin and in the presence of as little electrolyte as possible, since these conditions appear to favour the production of complexes soluble in water-miscible solvents. To ensure a low pH value it is preferred to use an emulsion which is at a pH value below the isoelectric point of the gelatin and then to add, either the free acid of the anion soap or the anion soap itself together with sufficient mineral acid to neutralise the cation of the anion soap. J r

Anion soaps are surface-active compounds in which the reduction in surface tension resultant on their addition to wateris due to the anion. The classification of soaps is discussed in the book Kolloidchemische Grundlagen der Textilveredlung by Dr. E. Valko 1937, at pages 519-522, to which reference is made for the meaning of the expression anion soaps."

Specific classes of compounds fallingwithin this generic expression are as follows:

(a) Soluble salts of long-chain-alkyl carboxylic acids, e. g. soluble salts 'of fatty acids containing 8 or more carbon atoms, as for example, oleic, ricinoleic, linoleic, stearic and palmitic acids. a 1

These, however, are in general much less satisfactory for use than: r

(b) Soluble salts of long-chain-alkyl sulphonic acids. 7

(c) Soluble salts of sulphated higher fatty alcohols, e. g. solublesalts of fatty alcohol sulphates of which the alkyl group contains at least 8-carbon atoms, as for-example the soluble salts of lauryl hydrogen sulphate and ole'yl hydrogen sulphate. H I i (d) Soluble salts of sulphatedsecondary alcohols containing at least 8 carbon atoms in the chain. I

(e) Soluble salts of alkylated aromatic sulphonic acids, e. g. soluble salts of alkyl benzene sulphonic acids, of alkyl naphthalene sulphonic acids and of alkylated hydroxy diphenyl sulphonic acids.

1(f) Soluble salts of long 'ch'ainealkyl esters of sulphated succinic acid; a: 1 I

Thus, it Will be seen that anion soaps containing sulphonic or sulphuric acid groups are preferred to those containing carboxylic acid groups.

The soluble salts may be formed from alkali metals," e. g. sodium and potassium, from ammonia or from amines, e. g. triethanolamine and cyclohe'xylamine. The anion soaps may contain amino residues in the anion of the soap as, for example, in the sodium salt of oleoyl amino ethane sulphonic acid which contains a carbonamido (NH.CO-) group.

The expression long-chain-alkyl is intended to mean at least 8, and preferably at least 12,

,. carbon atoms in the alkyl group.

Very many anion soaps are commercially products may conveniently be employed in the process of this invention. Thus suitable commercial products are the compounds sold under the trade names:

Nekal B-X Agral N Aresklene 375 Perminal N Dispersol Santomerse D Gardinol Sulphonated Lorol T. A. Igepon T Sulphonated Lorol N. 1-1.. Lissapol A Sulphonated Lorol C. Y. Lissapol C Sulphonated Ocenol Lissatan A- Teepol X Lohrinol Tergitol 4' Nekal A Tergitol 7 I Agral N is the sodium salt of an alkyl naphthalenesulphonic acid.

Aresklene 375 is the sodium. salt or an alkyloxydiphenyl disulphonic acid.

Dispersol is the sodium salt of dinaphthyl methane disulphonic acid.

Gardinol is an alkali metal sodium long-chainalkyl sulphate of 10 to 18 carbon atoms.

Igepon T is the sodium salt-of oleoylmethy1-.

amino-ethane sulphonic acid.

Lissapol A is sodium hexadecyl sulphate. Lissapol C is sodium hexadecyl sulphate.

Lissatan A is a condensation product of sodium Sulphonated Ocenol is a Sulphonated mixture of aliphatic unsaturated alcohols of 16 to 18 carbon atoms predominating in the latter.

H Teepol X is a mixture of sodium alkyl sulphates of 10 to 18 carbon atoms.

Tergitol 4 and Tergitol 7 are sodium secondaryalkyl sulphates. Such commercial detergents and still more the is triethanolarnine cyclohexylamine pure. (anion. soaps contained .-in.. them,- are much. preferred to the ordinary ,alkali-metal soaps of, fatty; acids referred to-; -under (a), above.-,. As already indicated, there may be used, insteadof;

theianion soap itself, the free acidderived from such soap.-

As indicated above, instead of true anion soapsh certain sulphonic acids of which the anion-is,

highlyhydrophobic may be employed. These...

may be simple acids,:for example'2-naphthol-1' sulphonic acid, l-naphtholl-sulphonic acidor anthraquinone-Z-sulphonic acid, or maybe more complex, for example dyestuffs such; as Kiton 3 Fast Yellow 3G (Colour Index No.645) ,which;

contains a sulpho-aryl-pyrazolone radicle} and Naphthalene Orange GS (ImperiaLChemieal- Industries Ltd.)

solvents-for dispersing the complexes are ,-thos e:- i

containing hydroxy groups, erg. methyl and etlh 1,

alcohols,- ethylene glycol mono methyl; eth ethyl lactate and diacetone alcoholt Organ solvents not containing hydroxy groups; are gen erally. only" useful together with some water, orf somehydroxy solvent, e. g; acetone, methyl ethyl kefipne, dioxane, methylene chloride,.,chloro form and' mesityl ,oxide aregpreferablyused in admixture'with water or methylalcohol. smallquanev titles of esters, e. g. methyl acetate, butyl.aeetate,-,

ethers,.e. gediethyl ether, andhydrocarbons, erg.

benzene and toluene, mayialso, be gincluded inthe,

solvent medium. The choiceof solvent Will' depend onthe particular nature-of;therfcomplex 1 Complexes formed at lowpH and containing a relatively low proportion ofthev anion. soap.,(or; corresponding acid) aregenerally more easily; soluble in polar solvents or; in solvents containing. some water, whilst those formed at higher,

pH values and containing, more anion soap. (on

corresponding acid) are generally soluble in-non-, polar solvents, e. g. toluene; The complexesmay beswollen in the organic solvent me dirnn zu'id dispersion is usually facilitated by. gentle;.

warming.

As already indicated',=, an important feature of this. invention is the formation of photographic.

emulsions which comprise a gelatin/anion soap complex, containing silver halide, dispersed in an organic solvent medium, together with a pro: portion of another colloid soluble in such organic solvent medium or in anorganic solvent medium miscible therewith. Suchother colloids may be, for example, cellulose esters, e. g. cellulos nitrate, cellulose acetate, far-hydrolysedcellulose esters (e. g. cellulose acetate having any acetyl content. of 20 to 30 polyvinyl acetates, poly-,

vinyl acetals, methyl methacrylate polymers and thepartial hydrolysis products thereof, .alkyd resins, and mixed interpolymers such as the interpolymers of maleic acid or anhydride: with styrene or methyl methacrylate. The following examples illustrate the inventlon, but are not to be regarded as limiting it in any way: 7 V

" Example I 500 cos. of a normal aqueous gelatino silver iodobromide emulsion containing 10% gelatin weremelted and diluted to 4 /2 litres with water. 'I'o this was added 100 grams of the commercial anion soap Agral N (essentially an alkyl naphthalene sodium sulphonate) dissolved in 1 litre of: water, and this was followed by 40 cos. of 2N.-

plex (containing suspended silver halide)" 'sep r t d. a .a. mas lr embl nat m It o washed with water, dissolved in 400' cc. warni methyl.v alcohol and-reprecipitated by adding, 100

cc. of. water; Adhering liquid was then removed, from the complex by allowing it ,to' drain, and the complex was then. re-dissolved in 400, c'ci warm methyl alcohol to form a satisfactory photographic emulsion. Its sensitometric characteristics ,were. substantially the sam as ,those of the original aqueousgelatin emulsion which it was, obtained.

, Example II To a photographic emulsion in methyl alcohol;

obtained in Example I was added, in turn:

Ethylene glycol mono-methylether 400 Low viscosity cellulose nitrate r1992, solution in methwl alcohol) 300 Acetone Z 400 The final emulsion so obtained was stable and suitable for coating by the usual techniques. It

ing layer since it adhered strongly tothe lacquer "was especiallysuitable, however, for coating by coating both in the dry condition and during all The emulsion developedstages of processing. normally, and it wasfolll d that th coating was not melted by hot water. I

,'In each of thefollowing Examples III to VI the range of'quant'ities of anion soap employedlieii. on theportion of the curve, referred to above,

which follows the infiexion point asdetermin d under comparable'conditions in the a bsenc' o "the's'ilver halide and allowing thecomplex separate until equilibrium conditions are reached? Example III Aiwatler-washed gelatin silver halide photo- I graphic emulsion of highcontrast characteristics w s d st and s ab l s It s h nd l teq. to a-gelatin concentration of 0.67%, it then con taining 0.51%suspended silver halide. The pH of the emulsion was then adjusted to 3.0 by the addition. of acid.

Portions of the emulsion were then adjusted to a temperature of 509. C. and quantities ofi.

various anion soapsat pI-I 2.2 were added. The

optimum quantities were found to be as follows:

irr 1 a e Der Anion Soap litre of emulsion I V Grams Dodeeyl sodium su1phate 2 to 4' Gardinol 3 0; 4 to 15 Agral N 5 to 10 PerminalN q 3.5 tolo Aresklene 375 3.5 to 8 1 TeepolX 10 to 30 Sant' mersel') 2.5 to 5; Aresket 240 7.1 to 31.6,. f Igepon 'I 7 to 15 In each case a precipitate of thesilver; ha li'tde;

suspended in a gelatin/anion soap complex,w

formed. Ten minutes after the addition r the anion soap the supernatant liquid was removed by decantation. The complex was then washed' With'water, dispersed in methyl alcohol (109cc.

forothe complex from 1 litre of t e emulsion),

re precipitated with water and re-dlspersed in methyl alcohol. The resulting dispersion was coated on glass or other convenient support and rlried. v

The resulting emulsion coatings were of satisfactory photographic quality and could be pros-*- essed in a developer of the normal constitution, fixed and washed in the usual way.

Example IV was of low gelatin concentration, it is not neces sary to work at such low gelatin concentrations; This example illustrates the preferred conditions for a simple anion soap, Aresket 240, with various dilutions of the emulsion, the general conditions being as in Example III.

Emulsion Concentration of Aresket 240 Gelatin Con- Silver Conper litre of centration centration emulsion Per Cent Per Cent Grams l. 34 l. 02 ll. 3 2.68 2. 04 17.7 4.02 3. 06 25. 2 5. 36 4. 08 29.0 6. 70 5.10 37. 8

The complexes thus obtained are readily'dispersible in methyl. alcohol to form emulsions for coating as in Example II.

EacampZe'V This example illustrates the effect of added electrolyte. 7 An emulsion was prepared as in Example III, except that thefpI-I was adjusted to.7.3 and ammonium nitrate was added to the extent necessary to form,a 0.5 Normal'solution.

The optimum quantities of anion soap were, found to. be: 1

. Quantityadded Am'on Soap per litre of emulsion Grams Teepol X 30 to 50 SantomerseD to v The resulting complexes, containing a substantial amount of adsorbed or absorbed water, were readily dispersible in-methyl alcohol to form emulsions suitable for coating as in Example III.

Example VI JIhisexample illustrates the use of a gelatin photographic emulsion of which the gelatin has a high isoelectric point. i

500 cc. of an emulsion made with an acidprocessed gelatin was diluted to a gelatin concentration of 0.67% when it contained 0.5% of suspended silver halide. Its pH was-adjusted to 6.0 and 4 cc. of a 63% solution of Aresket 240 was :added, the pH being maintained at 6.0 by further hydrochloric acid addition.

Thefre quired complex precipitated and was washed and.-

dispersed in methyl alcohol as in Example; III It will be noted that this complex was formed at the relatively high pH 6.0, but in the absence of added electrolyte.

cipitation under these conditions.

This is only practicable for the reasonthat th gelatin used had an ISO-1. electric point about pH 7.5. An emulsion made with normal lime-processed gelatin gave no pre- Although in the above examples the precipitated complexes have been re-dispersedin methyl alcoholtoform emulsions for coating, other water-miscible solvents may be used, for example ethyl alcohol and ethylene glycol monomethyl ether.

The silver halide emulsions of this inventory 1 may contain any of the usual additions to silver halide emulsions, e. g. optical sensitising dyes,

sulphur sensitisers as for instance allyl isothiocyanate, gold salts as described in British Patent) No. 570,393 and corresponding United States Patent -N0. 2,399,083, stabilisers, anti-fogging agents, toning agents and other agents for modifying the speed, contrast, graininess, foglevel and image colour of the products.

The invention provides photographic emulsions having a gelatin basis dispersed in organic solvent and the emulsions are therefore of value in a" number of special applications. As already indicated they are of particular value for spray coating. Normal gelatin silver halide emulsions present considerable difliculties in spray coating since it is usually necessary to maintain the emulsion warm in the spray-gun to prevent it setting therein. Moreover, the ordinary emulvisionswill not adhere firmly if sprayed on to lacquered metal sheet. Emulsions may be prepared according to this invention, however, which have little tendency to set in the spray-gun. Moreover, the organic solvent usually has a slight solvent action on lacquered surfaces and thus facilitates adhesion between such surfaces and the emulsion sprayed thereon.

The spray-coating of lacquered metal sheets with photographic emulsion is of particular value in the production of photo-templates. -In the commercial application of this process, however,- the users generally prefer that the emulsion should be supplied in dry granular condition sothat it may be re-dispersed when required to form an emulsion suitable for spraying. present emulsions are especially suitabl in this connection. Emulsions prepared in organic solvent media according to this invention can easily be dried by the well-known expedients of film drying, spray drying, and air drying of the emulsion in the form of a shredded set jelly, since the organic solvent readily evaporates. A furthermethod is to precipitate the emulsion by adding it to water and, after breaking up the precipitate, to air-dry the product. The following specific Example VII illustrates this techni'que. In this example the emulsion contains a matting agent, though this is not essential.

Example VII 200 grams of a gelatin silver halide emulsion: were melted at F. and to this was added 4- grams of Celite 204 (a commercial form of purified diatomaceous earth) dispersed in 600 cc; water containing 0.4 gm. gelatin. To the prod uct was added 35 cc. of Teepol X and the mixture' stirred. 25 cc. of normal hydrochloric acid was then added, the mixture allowed to stand for 15 minutes and the supernatant liquid decanted. The precipitate was washed with 500 cc. water for 2 minutes and the washing liquid decanted. The precipitate was then dissolved in 100 cc. of methyl alcohol at F. and then repricipitated by adding 75 cc. of distilled water.

The precipitate was then re-dissolved in 200 cc. methyl alcohol at 125 F., and 15 grams of cellu lose nitrate and 200 cc. of acetone were added.

200 cc. of the resulting emulsion was poured into 1 litre of cold distilled water and stirred. f

The resulting precipitate was shredded, soaked for 10 minutes in 500 cc. water, and then spread The out to dry. The lumps dried without adhering to one another to any serious extent.

Another useful method of forming dried emul-v sions from the emulsions in organic solvent prepared according to thisqinvention consists in shredding-the set jelly emulsion into water and then air-drying the shreds. This method is illustrated in" the following Example VIII.

' E ample VIII I An emulsion was prepared as in Example VII It was set to a jelly and shredded by pressing through a perforated plate into water. About 200 cc. of the emulsion was shredded in this way for 30 minutes and then melting at 125 F.

A dried emulsion suitable for re-constituting in water or aqueous alcohol can be made by a similar method, "the cellulose nitrate being omitted. Re-constitution can be effected bysoaking in water containing sufiicient sodium bicarbonate to neutralise the acid and melting at 120 F. An emulsion suitable for spraying can be made; by using 50 grams of the dried emulsion-shreds, 2 grams of sodium bicarbonate, 500 cc. of water and 500 cc. of ethyl alcohol (64 O.'P.).- "1

The emulsions 'of this invention, either as originally prepared or as re -constituted after drying, can be used in any process wher spraycoating is required. The production of phototemplates has alreadybeen mentioned, and another useful application is in the preparation of dials, nameplates and the like on metal or other surfaces. A further application is in the preparation of silk-screen printing surfaces. In this application the emulsion is sprayed on to stretched silk, dried, exposed, developed in a tanning developer and washed in hot water to produce a wash-out relief image. It is a peculiar characteristic of the emulsions of this invention that, though quite insoluble in water when coated, they tend to become soluble when allowed to stand in contact with alkali, as in normal development, though the emulsions are still not soluble in water except at high temperatures. Fixing in an acid fixing bath however; restores the ins'olubility of the complex even in hot water. Thus a suitable technique for using the emulsions in the production of silk screen relief images is to develop the exposed image in alkaline pyrocatechol, plunge the silk into hot water and then to-fix the wash-out relief image. An alternative technique is to prepare the wash-out relief image on a support from which it may be stripped and to transfer the image to a silk support.

The emulsions .of this. invention are also of value in colour photography. Thus they may contain dyes or. dye-intermediates, e. g. colourformers which react with the oxidation products of aromatic primary amino developing agents-to form quinone-imine .or azoemethine dyes, the colour-former being uniformly dispersed in the emulsion. The colour-former, especially where particulate or of very highumolecular weight,

.1 may be included in the original emulsion and precipitated with the complex, or it may be added tothe final emulsion. Many of th highmolecular weight colour-formers, which are preferred from the standpoint of being non-difiusing in the emulsion, are difficult to disperse in ordinary aqueous gelatin silver halid 'e'mulsions, but much more easily dispersed in the organic solvent emulsions ofthis invention.

The emulsions of this invention are permeable to ordinary alkaline developers, but the degree of permeability depends on the precise constitution of the emulsion. By a suitable selection. of an additional colloid, e. g. cellulose nitrate ora hydrophobic acid colloid, emulsions'of varying degree of developer-permeability may be made; and accordingly it is possible to build up a multilayer photographic material for'colour photography in which the several layers have different degrees of permeability to ordinary developers and,- by adjusting the constitution of the developers, e. g. by adding organic solvents, to develop each of the layersseparately. In such a process, by using aromatic primary amino developing agents containing different colourformers, images indifferent colours may be formed in the various layers, and by a suitable selection of colour-formers a final true-colour image may be obtained.

Another use to which the emulsions of this invention may be put isin the production of printing paper to be used for printing from Wet negatives. As already stated the emulsions of this invention have a good resistance to water, though they are readily developed by ordinary alkaline developing'solutions. Paper coated with emulsion according to this invention may be used for printing from wet negatives, though it is usually desirable to employ an emulsion containing a proportion of other colloids, e. g; cellulose nitrate and a methyl methacrylate-methacrylic acid co-polymer. Such emulsions not only have a good resistance to water but also a good resistance to hypo, which may be carried by the wet negative. Advantageously, in the production of weteprinting paper using the emulsions of this invention the emulsion should be supercoated with a layer of a plain gelatin/anion soap complex in organic solvent, as described in our copending United States application Serial No. 623,446, filed October 19, 1945, now Patent No'. 2,527,262, corresponding to British applications NOS. 21,092/44 and 24,779/44.

What we claim is: I I I r ,I

1. 'Aphotographic emulsion comprising a dis persionin a predominantly organic solvent me,- dium of a complex of gelatin with an anion soap which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersedtherethrough.

e 2. A photographic emulsion comprising a dis persion in a predominantly organic solvent medium of a complex of gelatin with an anion soap containing a sulphur acid group which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver 'halide grains which are dispersed therethrough;

3. A photographic emulsion comprising a dispersion in 'a predominantly organic solvent medium of a; complex of gelatin with a water-soluble salt of a sulphate'd higher fatty alcohol which is solublein a solution composed of methyl alcohol, said complex-being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough.

4. A photograhpic emulsion comprising a dispersion in a predominantly organic solvent me-' dium of a complex of gelatin with an anion soap which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough, said emulsion further containing a proportion of another colloid which is soluble in the said solvent medium.

5. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium of a complex of gelatin with a water-soluble salt of a long-chain-alkyl sulphonic acid which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough, said emulsion further containing a proportion of another colloid which is soluble in the said solvent medium.

6. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium of a complex of gelatin with a water-soluble salt of a sulphated higher fatty alcohol which is soluble in a, solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough, said emulsion further containing a proportion of cellulose nitrate.

7. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium of a complex of gelatin with a water-soluble salt of a long-chain-alkyl sulphonic acid which is solubly in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide rains which are dispersed therethrough, said emulsion further containing a pro-portion of cellulose nitrate and a proportion of a hydrophobic acid colloid.

8. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium containing methyl alcohol of a complex of gelatin with an anion soap which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough.

9. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium containing methyl alcohol of a complex of gelatin with a Water-soluble salt of a sulphated higher fatty alcohol which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough.

10. A photographic emulsion comprising a dispersion in a predominantly organic solvent medium containing methyl alcohol and acetone of a complex of gelatin with an anion soap which is soluble in a solution composed of methyl alcohol, said complex being the essential binding agent for light-sensitive silver halide grains which are dispersed therethrough, said emulsion further containing a proportion of another colloid which is soluble in the said solvent medium.

11. A method for the production of photographic emulsion in a predominantly organic sol- =2 vent medium which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, adding to such emulsion an anion soap in a concentration near the inflexion point at a pH below the isoelectric point of the gelatin and in the'presence of a minimum concentration of electrolyte whereby a complex of gelatin and the anion soap is precipitated which is soluble in a solution composed of methyl alcohol and contains the dispersed silver halide and redispersing the said complex with the dispersed silver halide in a predominantly organic solvent medium. l

12. A method for the production of photographic emulsion in a predominantly organic solvent containing hydroxyl groups which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, adding to such emulsion an anion soap in a concentration near the inflexion point at a pH below the isoelectric point of the gelatin and in the presence of a minimum concentration of electrolyte whereby a complex of gelatin and the anion soap is precipitated which is soluble in a solution composed of methyl alcohol and contains the dispersed silver halide and redispersing the said complex with the dispersed silver halide in a predominantly organic solvent containing hydroxyl groups.

13. A method for the production of photographic emulsion in a predominantly organic solvent medium which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, adding to such emulsion an anion soap containing a sulphur acid grouping in a concentration near the infiexion point at a pH below the isoelectric point of the gelatin and in'the presence of a minimum concentration of electrolyte whereby a complex of gelatin and the anion soap is precipitated which is soluble in a solution composed of methyl alcohol-and contains the dis persed silver halide and redispersing the said complex with the dispersed silver halide in a, predominantly organic solvent medium.

14. A method for the production of photographic emulsion in a predominantly organic solvent medium which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, adding to such solution ata pH below the isoelectric point of the gelatin an anion soap containing a sulphonic acid grouping, in a concentration near the inflexion point and in the presence of a minimum concentration of electrolyte whereby a complex of gelatin and the anion soap is precipitated which is soluble in a solution composed of methyl alcohol and contains the dispersed silver halide and redispersing said complex with the dispersed silver halide ina predominantly organic solvent medium.

15. A method for the production of photographic emulsion in a predominantly organic solvent medium which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, a water-soluble .salt of a long chain alk'yl sulphonic acid, in a. concentration near the inflexion point at a pH below the isoelectric point of the gelatin and in the presence of a minimum of electrolyte whereby a complex of gelatin and said salt is precipitated which is soluble in a solution composed of methyl alcohol and contains the dispersed silver halide and redispersing said complex with the dispersed silver halide in a predominantly organic solvent medium.

16. A method for the production of photographic emulsion in a predominantly organic solvent medium which comprises forming an'emulsion of silver halide in an aqueous solution of gelatin, a water-soluble salt of a sulphated higher fatty alcohol, in a concentration near the infiexion point at a pH below the isoelectric point of the gelatin and in the presence of a minimum of electrolyte whereby a complex of gelatinan'd 13 said salt is precipitated which is soluble in a'solution composed of methyl alcohol and contains the dispersed silver halide and redispersing said complex with the dispersed silver halide in a predominantly organic solvent medium.

17. A method for the production of photographic emulsion in a predominantly organic solvent medium which comprises forming an emulsion of silver halide in an aqueous solution of gelatin, a water-soluble salt of a long chain alkyl sulphonic acid, in a concentration near the inflexion point at a pH below the isoelectric point of the gelatin and in the presence of a minimum of electrolyte whereby a complex of gelatin and said salt is precipitated which is soluble in a solution composed of methyl alcohol and contains the dispersed silver halide and redispersing said complex with the dispersed silver halide in a predominantly organic solvent medium, washing said complex with the dispersed silver halide, drying it down to granular form and redispersing it in a predominantly organic solvent medium.

JOHN ALFRED HENRY HART. KENNETH GEORGE ALFRED PANKHURST. ROBERT CHARLES MORRIS SMITH.

14 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,290,794 Sheppard Jan. 7, 1919 1,844,716 Lambert Feb. 9, 1932 2,142,311 Heidenhain Jan. 3, 1939 2,258,755 Glaser Oct. 14, 1941 2,282,001 Russell et a1. May 5, 1942 2,304,940 'Mannes et a1. Dec. 15, 1942 2,324,831 Frohlich et al 1. July 20, 1943 2,489,341 Waller et al Nov. 29, 1949 FOREIGN PATENTS Number Country Date 537,256 Great Britain June 16, 1941 556,360 Great Britain Oct. 1, 1943 OTHER REFERENCES Journal of the American Chemical Society, De-

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Claims (1)

1. A PHOTOGRAPHIC EMULSION COMPRISING A DISPERSION IN A PREDOMINANTLY ORGANIC SOLVENT MEDIUM OF A COMPLEX OF GELATIN WITH AN ANION SOAP WHICH IS SOLUBLE IN A SOLUTION COMPOSED OF METHYL ALCOHOL, SAID COMPLEX BEING THE ESSENTIAL BINDING AGENT FOR LIGHT-SENSITIVE SILVER HALIDE GRAINS WHICH ARE DISPERSED THERETHROUGH.