US3366482A - Process for the preparation of silver halide emulsions by the flocculation method - Google Patents

Description

United States Patent Ofitice 3,366,482 Patented Jan. 30, 1968 3,366,482 PROCESS FOR THE PREPARATION OF SILVER HALIDE EMULSIONS BY THE FLOCCULA- TION METHOD Heinrich Schaller and Walter Anderan, Fribourg, Switzerland, assignors to Ciba Limited, Basel, Switzerland, a Swiss company No Drawing. Continuation-impart of application Ser. No. 307,376, Sept. 9, 1963. This application Mar. 7, 1967, Ser. No. 621,117 Claims priority, application Switzerland, Sept. 13, 1962, 10,850/ 62 9 Claims. (CI. 96-94) ABSTRACT OF THE DISCLOSURE In the process for the preparation of photographic silver halide emulsions the extraneous soluble salts resulting from the reaction of silver nitrate with water-soluble halides in an aqueous gelatine solution, are removed by flocculation of the silver halide emulsion. The flocculation is carried out at a pH of 3 to 7 and the emulsion starts to flocculate immediately on the addition of the flocculating agent. The flocculating agents are colorless compounds that contain at least one six-membered heterocyclic ring made up of 3 to 4 carbon atoms, at the most one halogen atom being bound to a carbon atom of said heterocyclic ring, at least one aromatic radical, and at least one acidic group imparting solubility in Water to the compound. Thesix-membered heterocyclic ring Which may be substituted by at the most one halogen atom, e.g. bromine, but more especially chlorine, may also contain other substituents, under the conditions of this flocculating process, no gelatine derivatives are formed together with the flocculating agents.

Photographic silver halide emulsions of all kinds, especially color emulsions, may be prepared by this process.

Cross-reference This application is a continuation in part of applicants copending application Serial No. 307,376, filed Septemher 9, 1963, now abandoned the disclosure of which is relied on and incorporated by reference in this application.

Background The present invention relates to a process for the preparation of photographic silver halide emulsions in which the extraneous soluble salts are removed by flocculation of the silver halide.

In the preparation of photographic silver halide emulsions, a water-soluble silver salt, generally silver nitrate, is usually reacted with Water-soluble halides in an aqueous gelatine solution. The gelatine/silver halide emulsion thus formed contains water-soluble salts which are by-prodnets of the double decomposition reaction, and these salts have to be removed. The conventional method of removing the salts consists in solidifying the emulsion by cooling, comminuting it, and then washing out the salts with cold water.

Another method, known as the flocculation method,

consists in precipitating the silver halide and the gelatine or other colloid, separating the supernatant salt solution from the precipitate, and then dispersing the precipitate in a gelatine solution or in some other suitable layer colloid.

The flocculation method oflers a number of advantages; in particular, it makes possible the preparation of concentrated silver halide emulsions. Various methods of flocculating silver halide emulsions have been proposed, for example, flocculation with an inorganic salt, such as, for example, sodium sulfate. However, a large amount of the inorganic salt is required, and the precipitate has to be removed by washing out. Organic solvents can also be used for bringing about flocculation, but this method is expensive and the precipitates obtained are highly voluminous and still contain a large amount of liquid. It has also been proposed to use the salts of heavy metals as flocculating agents. However, such salts have the disadvantage that they harden the gelatine and the precipitates are very ditficult to re-disperse. It has also been suggested that anionic substances such as soaps be used, but in this process residual soap adheres tenaciously to the coagulate and tends to cause cloudiness in the emulsion.

Other methods are based on the use of gelatine derivatives. In the preparation of gelatine derivatives, at pH values of 8 to 11 or more involving reaction times of a few minutes up to 30 minutes however, the reactive amino groups of the gelatine undergo change, thus causing a change in the photographic and colloidochemical properties of the gelatine. Moreover, gelatine derivatives can only be flocculated at a low pH value, for example, at a pH value of about 3.5. In the case of highly sensitive ammonia emulsions, such as are used in the preparation of X-ray films, this unavoidable depression of the pH value to about 3.5 brings about a loss in sensitivity of the emulsion.

Detailed description The present invention is based on the observation that certain heterocyclic compounds are very suitable as flocculating agents. Accordingly, the present invention provides a process for the preparation of photographic silver halide emulsions by the flocculation method, which com-prises flocculating the emulsion at a pH of 3 to 7, and using as a flocculating agent a colorless compound containing (a) At least one six-membered heterocyclic ring made up of 3 to 4 carbon atoms, at the most one halogen atom being bound to a carbon atom of said heterocyclic ring;

(b) At least one aromatic radical, and

-(c) At least one acidic group imparting water-solubility to the compound, the emulsion starting to flocculate immediately on the addition of the flocculating agent.

The acidic group imparting solubility in Water present in a flocculating agent according to the invention may be, for example, a carboxylic acid group or a sulfato group, but is preferably a sulfonic acid group. The said flocculating agent must also contain at least one six-membered heterocyclic ring that contains as ring members either 3 carbon atoms and 3 nitrogen atoms or 4 carbon atoms and 2 nitrogen atoms. This six-membered heterocyclic ring may be substituted by at the most one halogen atom and/ or other substituents. Examples of suitable heterocyclic rings are the pyridazine and pyrimidine rings. Compounds that contain at least one 1:3:5-triazine radical are particularly suitable.

The compound to be used as a flocculating agent in the process of the present invention must contain at least one aromatic radical, advantageously an aromatic radical of the benzene or naphthalene series. The aromatic radical advantageously contains at least one substituent, for example, the group imparting solubility in Water, and is advantageously bound to the heterocyclic ring either directly or through a bridge, for example, a sulfur or oxygen atom, or preferably a nitrogen atom.

A 1:3:5-triazine compound may be substituted in, for example, each of the 2 and 4 positions by an aromatic radical of the kind defined. The 6 position may have as a substituent a halogen atom, for example, bromine, but more especially chlorine. Examples of suitable triazine compounds fall within the formula RiNH =N Ian-r m in which R and R' each represents a benzene or naphthalene radical containing at least one sulfonic acid group and Y represents a halogen atom. The benzene or naphthalene radical may contain another substituent, for example, -a further sulfonic acid group, a carboxylic acid group, an alkyl group such as a methyl or ethyl group, an alkoxy group such as a methoxy or ethoxy group, a halogen atom such as chlorine, fluorine or bromine, or a .group of more complex structure, for example, a trifluoromethyl group or a sulfonic acid amide group.

In general, the efificacy of the flocculating agent is enhanced by increasing the size of the molecule. Efiicacy is further increased by the incorporation of naphthalene radicals, such radicals advantageously being 1- or 2- amino-naphthalene-mono-, dior tri-sulfonic acids, which thus produce, for example, compounds of the formula R:NH

R's-NH in which R and R g each represents a naphthalene radical containing at least one sulfonic acid group.

A process which comprises condensing a condensation product of equimolecular proportions of cyanuric chloride and an aromatic amino-sulfonic acid, especially an aminonaphthalene disulfonic acid, with an aliphatic or aromatic diamine in a molar ratio of 1:1 results in the formation of a fiocculating agent that contains a free amino group. It has been observed that such amino compounds are highly effective at pH values around and 6.

Theseamino compounds may also be further condensed with a suitable reactive halogen compound, for example, with a condensation product of equimolecular proportions of cyanuric chloride and an aromatic sulfonic acid already mentioned. In such manner there are obtained, for example, flocculating agents that correspond to the formula in which R and R each represents a naphthalene radical containing at least one sulfonic acid group, and Z represents a bridge member. Symmetrical compounds of the kind defined may also be prepared by condensing cyanuric chloride with aminonaphthalene sulfonic acids and diamines in a molar ratio of 2:2: 1, respectively.

It is also possible to join together at the amino groups tWo identical molecules or two difierent molecules of the above-mentioned compounds containing a free amino group and formed from one molecule each of an aromatic amino sulfonic acid, cyanuric chloride and a diamine, the link being made through suitable bridge members. There may also be used triazine compounds that no longer contain a halogen atom bonded to the triazine ring. These are obtained, for example, when the last halogen atom in compounds of the kind defined above is exchanged for H0, H N or H CO groups or substituted amino groups.

The following compounds may be used as starting materials for the preparation of fiocculating agents having a composition given above:

l-aminobenzene-2-, -3- or -4-sulfonic acid, amino-methylbenzene sulfonic acids, amino-chlorobenzene sulfonic acids, amino-methoxybenzene sulfonic acids, 1-aminonaphthalene-4-, -5-, -6- or -7-sulfonic acid, 2-aminonaphthalene-4-, -5-, -6- or -7-sulfonic acid, 1-aminonaphthalene-2:5-, -2:6-, -3 28-, -4:6-, -4:7-,

-4:8-, -5 :7- or -6:8-disulfonic acid, 2-aminonaphthalene-1:7-, -3 16-, -3 27-, -4:7- or -5 Z7-disulfonic acid, but more especially, 2-arninonaphthalene-4 I 8-disulfonic acid, l-aminonaphthalene-2i4:6-, -3 2527-, -3 :6:8- or -4:6:8-

trisulfonic acid, aliphatic diamines of the formula in which n represents an integer of a value not greater than 5, 1 :4-diaminobenzene, 1 23-diaminobenzene-4-sulfonic acid, 1 I 3-diaminobenzene-4- or -5-ca rboxylic acid, 4:4-diaminodiphenyl, 4 4-diaminodiphenyl-2 Z'2'-diSlllfOniC acid, 4:4-diaminodiphenyl-3 :3'-dicarboxylic acid, 3 13'-dicarboxymethoxy-4:4'-diaminodiphenyl and. l Z5-diaminobenzene-3 :7-disulfonie acid.

Some of the flocculating agents in accordance with the invention may be prepared by conventional methods. The following are a number of triazine compounds in accordance with the invention. (The triazine radical of the formula HOaIS (I31 NHL HNCH:-CH2-NHQ 1103's ('31 (J1 SOaH NHAHNCHa-CHr-NH NH I SOsH HOaS (23) B0 8 1130-? (I)CH1 SOaH NH NH Z HN I HOsS 80311 SO H Bo s HO S i SOsH I C I We a r m a Cl N C- l I -C I l Cl s 1103s soln N N OCH1 13 00-- 11033 H0 8 H H H038 80 K I o\ l Cl N bk I N N Cl H0 8 SOaH o L o I I I SOsH H0 3 C1 C] HO S I S0 11 I C I H- N\ /N N\ /I 1' H f a scan HOJS The compounds given above may be used as flocculating agents in the usual manner. Depending on their constitution, small amounts of these agents. bring about good and immediate flocculation at a moderately raised temperature and at pH values in the range of from 3 to 7. It has been observed that, in the short time between the flocculation and any washing out operation, the flocculating agents of the invention do not chemically react with gelatine forming gelatine derivatives and do not cause hardening of the gelatine when used in the small amounts required, even when flocculation is carried out with halogen triazine compounds which are reactive.

In general, flocculation is advantageously brought about by adding an aqueous solution of the flocculating agent to the emulsion, and then adjusting the pH value of the emulsion to the requisite value. However, it is also possible to adjust the pH value first and then :add the flocculating agent. The silver halide precipitates along with the gelatine or other colloid in the form of fine granules and settles out very quickly. The precipitate contains only a very small amount of water so that it is generally not necessary to wash it out further. Should it appear necessary, however, the precipitate may be washed out once or several times with cold water; if necessary, the pH can be adjusted to a suitable value. The pH value for flocculation, is in the range of from 3 to 7, preferably 3 to 5, and the requisite amount of flocculating agent, for example, to 200% (calculated on the dry weight of the gelatine or other colloid) in the form of a dilute aqueous solution, depend not only on the flocculating agent itself, but also on the gelatine or other colloid concentration of the emulsion, the salt content, and other factors. The temperature at which flocculation is carried out has no great influence; it is advantageously within the range of to C., and it should always be such that no substantial amounts of gelatine or of another colloid react with the flocculating agent, in so far as the latter contains reactive groups.

Photographic silver halide emulsions of all kinds may be prepared by the process of the invention, especially color materials that contain either dyestufi components for color development or image dyestuffs for the silver dyestufi bleaching process.

The following examples illustrate the invention, the parts and percentages being by weight.

EXAMPLE 1 A solution of grams of silver nitrate in 600 milliliters of water is added in a period of 15 minutes at 50 C. to solution of 8 grams of gelatine, 44 grams of potassium bromide and 1 gram of potassium iodide in 600 milliliters of water. The mixture is allowed to mature for 10 minutes at 50 C. and is then cooled to 40 C. 30 milliliters of a aqueous solution of the compound of Formula 20 is then added, and the pH of the emulsion is adjusted to 4.5 to 5.0 by the addition of citric acid. The nature of the acid used has no influence on the flocculation process; acetic acid, hydrochloric acid, sulfuric acid or any other acid with a sulflcient degree of acidity can also be used. The silver halide precipitates at once along with the gelatine in the form of finely divided granules and settles out very quickly. The supernatant salt solution is decanted oif. A solution of 120 grams of gelatine in 1400 milliliters of water and having a temperature of 40 C. is added to the granules, and the pH value is adjusted to 7.0 by the addition of aqueous sodium hydroxide solution. The silver halide is redispersed by stirring for to 20 minutes at 40 C., and the emulsion is allowed to mature to optimum sensitivity in a known manner at 50 to 55 C.

Solutions of the compounds listed in the following Table I may also be used to bring about flocculation of silver halide/ gelatine emulsions by the above method instead of a solution of the compound of Formula 20. The amounts required, concentrations and pH values are also listed. All compounds yield emulsions having the same photographic properties.

TABLE I Amount, ml. of

Concentration, the solution percent of the solution pH value at which flocculation is efiected Formula N o The compound of the Formula 20 can be prepared as follows:

18.5 parts of trichlorotriazine (cyanuric chloride) are dissolved in 40 parts of acetone and precipitated in a finely divided state with 100 parts of water and 100 parts of ice. 30.3 parts of 2-amino-naphthalene-4:8-disulfonic acid in the form of the neutral sodium salt and dissolved in 150 parts of water are then added. The mixture is stirred for a period of from 30 to 60 minutes at 0 to 4 C. and dilute sodium carbonate solution is added until the pH value remains constant at 5 to 6.5. No diazotizable amino compound must be detectable at the end of this period. To this primary condensation product are added 35 parts of 4:4-diamino-diphenyl-2:2-disulfonic acid that had been dissolved in 400 parts of water at 40 C. in the form of the sodium salt. The mixture is maintained for 1 hour at 40 C. and at a pH value of 6 to 7, the pH value being adjusted with sodium carbonate or sodium borate solution. The secondary condensation product can be obtained by salting out (that is, by the addition of 25 parts of sodium chloride per 100 parts by volume of the reaction mixture). The product is the compound shown by the Formula 20.

This product may then be further condensed at 40 C. with the primary condensation product described above to process the compound of the Formula 28.

The compounds of the Formulae 23 to 26 may be prepared by the above method when, instead of trichlorotn'azine, equivalent proportions of 2-methoXy-4:6-dichloro-l :3 :S-triazine, 3-methoxy-4z5 -trichloropyridazine, 224:6 trichloropyrimidine or 4:5:6 trichloropyrimidine are used.

The other triazine compounds mentioned in these examples can likewise be prepared by methods in themselves known.

EXAMPLE 2 A solution of 50 grams of silver nitrate in 450 milliliters of water is added during a period of 20 minutes at a temperature of 65 C. to a solution of 5 grams of gelatine, 42 grams of potassium bromide and 2.2 grams of potassium iodide in 450 milliliters of Water. The mixture is allowed to mature for 15 minutes at 65 C. and is then cooled to 45 C. 20 milliliters of a 5% aqueous solution of the compound of the Formula 18 are added and the pH value is adjusted to 4.5 with citric acid. The silver halide along with the gelatine flocculates at once in the form of fine granules and settles out rapidly. After decanting the clear supernatant solution, the silver halide is redispersed in a solution of grams of gelatine in milliliters of water having a pH value of 7.2, and the emulsion is then allowed to mature to its optimum sensitivity in the conventional manner.

Solutions of the compounds listed in the following Table H may also be used in place of a solution of the compound of the Formula 18 in a process as described above.

TABLE II Formula Amount, ml. of Concentration, pH value at which No. the solution percent of the flocculation is solution efiected What is claimed is:

1. A process for the manufacture of a photographic silver halide emulsion by the flocculating method, which comprises flocculating the emulsion at a pH of 3 to 7, starting the emulsion to flocculate immediately after the first addition of flocculating agent, using as the flocculating agent a colorless compound containing (a) at least one six-membered heterocyclic ring made up of 3 to 4 carbon atoms, at the most one halogen atom being bound to a carbon atom of said heterocyclic ring,

(b) at least one aromatic radical, and

(c) at least one acidic group imparting water-solubility to the compound, the emulsion starting to flocculate immediately on the addition of the flocculating agent and the adjustment of the pH to a value of 3 to 7.

2. A process according to claim 1 for the manufacture of a photographic silver halide emulsion by the flocculating method, which comprises flocculating the emulsion at a pH of 3 to 7, starting the emulsion to flocculate immediately after the first addition of flocculating agent, using 11 12 as the fiocculating agent a colorless compound containing 6. A process according to claim 1 for the manufacture (a) at least one triazine radical, at the most one haloof a photographic silver halide emulsion by the flocculatgen atom being bound to a carbon atom of said triing method, which comprises flocculating the emulsion at azine radical. a pH of 3 to 7 using as the flocculating agent a colorless (b) at least one aromatic radical, and compound of the formula (c) at least one acidic group imparting water-solubil- Rz-NH HNR3 ity to the compound and the adjustment of the pH to a value of 3 to 7. 3. A process according to claim 1 for the manufacture /OHN"Z NH C\ of a photographic silver halide emulsion by the flocculat- 10 C=N N=O ing method, which comprises flocculating the emulsion at of 3 to startmg Pmulsion flocFulate wherein R and R each represents a naphthalene radical mediately after the first addition of flocculatmg agent, containing at least one lfo i a id group and Z repreas the flocculating agent colorless compound sents a bridge member, the emulsion starting to fiocculate tammg immediately on the addition of the flocculating agent and (a) at least one triazine radical, at the most one halothe adjustment of the PH to a value of 3 to p amnkbeing bound to a carbon atom of said 7. A process according to claim 1 for the manufacture azme radlcal of a photographic silver halide emulsion by the flocculat- (b) at least one aromailc f and ing method, which comprises flocculating the emulsion at (c) at least one sulfonlc acid group and the ad usta PH of 3 to 5 using as the fiocculafing agent the ment of the pH to a value of 3 to 7. pound of the formula 4. A process according to claim 1 for the manufacture C1 of a photographic silver halide emulsion by the flocculating method, which comprises flocculating the emulsion at Hogs pH of 3 to 7 using as the flocculating agent a colorless N N compound of the formula H, O

' I I Rr-JTIH HOaS SOa C-N N7 \FY F the emulsion starting to flocculate immediately on the addition of the flocculating agent and the adjustment of 1 the pH to a value of 3 to 5.

8. A process according to claim 1 for the manufacture wherein R and R' each contains at least one sulfonic of a photographic silver halide emulsion by the flocculatacid group and represents a member selected from the ing method, which comprises fiocculating the emulsion at group consisting of a benzene radical and a naphthalene a pH of 3 to 5 using as the fiocculating agent the comradical and Y represents a halogen atom the emulsion pound of the formula Cl (5 H033 r it NHC GNHOCH=CHC NH1 N I l S OaH starting to flocculate immediately on the addition of the the emulsion starting to flocculate immediately on the flocculating agent and the adjustment of the pH to a value addition of the flocculating agent and the adjustment of of 3 to 7. the pH to a value of 3 to 5.

5. A process according to claim 1 for the manufacture 9. A process according to claim 1 for the manufacture of a photographic silver halide emulsion by the flocculatof a photographic silver halide emulsion by the flocculating method which comprises flocculating the emulsion at ing method, which comprises flocculating the emulsion at a pH of 3 to 7 using as the flocculating agent a colorless a pH of 3 to 5 using as the flocculating agent the comcompound of the formula pound of the formula ('31 C11 0 0 ss S a t t NHO C-HN- N N SOQH EO3S S OaH T the emulsion starting to flocculate immediately on the ON addition of the flocculating agent and the adjustment of the pH to a value of 3 to 5.

References Cited R'2 H 7O wherein R and R' each represents a naphthalene radical UNITED STATES PATENTS containing at least one sulfonic acid group, the emulsion 3,138,461 6/1964 Ryan 96-94 starting to flocculate immediately on the addition of the 3,288,775 11/1966 Anderau et al 961l1 u i g ag t and the adjustment of the pH to a value of 3 to 7. J. TRAVIS BROWN, Acting Primary Examiner.