US 3615617 A
Description (OCR text may contain errors)
United States Patent Wolfgang Muller-Bardorff Cologne;
Wilhelm Saleck, Schildgen, Bergisch- Gladbach; Franz Moll, Cologne, Stammheim, all of Germany  App]. No. 780,885
 Inventors  STABILIZED PHOTOGRAPI-IIC MATERIAL WITH TETRAZOLE TI-IIOCARBONIC ACID ESTER 5 Claims, No Drawings  US. Cl 96/109,
 Int. Cl G03c 1/34  Field of Search 96/665, 109
 References Cited UNITED STATES PATENTS 3,071,465 l/l963 Dersch et al 96/109 X 3,244,521 4/1966 Dersch et al.... 96/109 X 3,311,474 3/1967 Willems etal. 96/109X Primary ExaminerNorman G. Torchin Assistant Examiner-John L. Goodrow Attorney-Connolly and I-Iutz ABSTRACT: This invention relates to a photographic silver halide emulsion the stability of which is improved by addition of substituted S-mercapto-tetrazole derivatives.
STABILIZED PHOTOGRAPHIC MATERIAL WITH TETRAZOLE TI-IIOCARBONIC ACID ESTER It is well known that photographic emulsions on storage become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development at unexposed areas. This phenomenon is commonly called fog or chemical fog. Fog depends both upon the nature of the emulsion and the conditions of development. For a given emulsion it increases with the degree of development. It is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is desirable to have emulsions as stable as possible under the condition of high temperature, which may occur in tropical climates. Fog usually appears over the whole area of the lightsensitive layer, but when severe is quite frequently nonuniform.
It is known that certain compounds particularly heterocyclic mercapto or imino compounds have an antifoggant and stabilizing effect when incorporated into photographic silver halide emulsions and so improve greatly the keeping qualities of the emulsions. Mostly the so-calledfog-inhibitors or stabilizers'form difficultly soluble or insoluble silver compounds with the silver ions of the photographic emulsion. It is also known that inorganic or organic mercury compounds can be used. Many of these stabilizers however, are of limited utility since they have a desensitizing effect or alter the gradation.
It is among the objects of the invention to provide stabilizers which cause no reduction in the sensitivity at concentrations at which they achieve sufficient stabilization. Another object is torprovide a photographic silver halide emulsion that is stable against the production of fog upon storage and stable with respect to the speed and contrast of the emulsion. Other objects and advantages will become apparent from a consideration of the following description and examples.
We now have found that photographic silver halide emulsions can be stabilized with respect to the formation of fog even under extreme storage conditions and with respect to speed and contrast of the emulsion very effectively by the addition of S-mercaptotetrazole derivatives of the following formula:
Rl is a hydrocarbon radical, in particular alkyl, preferably containing one to three carbon atoms, such as ethyl or propyl, or aryl, in particular a radical of the phenyl series, or aralkyl such as benzyl or phenyl ethyl;
Y represents (1 the grouping which is' linked to the carbonyl group through an oxygen or sulfur atom or (2) the group NR2R3 and R stands for alkyl having preferably up to five carbon atoms or for a radical of the phenyl series such as phenyl which may be substituted, for example, with halogen such as chlorine or bromine, alkyl having up to five carbon atoms such as methyl or ethyl, alkoxy or alkylthio, the alkyl groups ofwhich having up to five carbons atoms. R stands for hydrogen or for R Particular utility is exhibited by the following compounds:
The compounds can be made by reacting l-substituted mercaptotetrazoles known per se, for example in the form of their alkali metal salts, with an excess of phosgene to convert them into the chlorocarbonic acid thioesters. Further reaction with amines produce compounds such as 5-8, and with alkali metal salts of a mercaptotetrazole compound yield compounds such as l-4. It is also possible to react the S-mercaptotetrazoles with isocyanates, thereby obtaining compounds such as 5, 6, or 7. The alkali metal salts of the mercaptotetrazoles may also be reacted with chlorocarbonic acid esters, with produces symmetrical compounds of the type 1 directly.
The preparation of a few of these compounds is described in detail below.
COMPOUND 1 A solution of 11 g. of phosgene in 200 ml. of tetrachloromethane which has been freshly prepared at 5 C. is slowlyadded dropwise at 20 C. to a suspension of 40 g. (0.2 mol) of the sodium salt of 1-phenyl-5-mercaptotetrazole in 300 ml. of anhydrous tetrachloromethane, whereby the tetrazole is dissolved and the sodium chloride precipitates from this solution after some time. The reaction mixture is stirred for 4 to 5 hours at 50 C. and the solvent is then distilled off. The oily residue is taken up in ether, filtered and the filtrate is precipitated with petroleum ether. Compound 1 of m.p. l38-l39 C. is obtained after recrystallization from ether/petroleum ether.
COMPOUND 6 17.8 g. of l-phenyl-5-mercaptotetrazole are dissolved in 50 ml. of dry tetrahydrofuran and a solution of 15.35 g. (0.1 mol) of p-chlorophenyl isocyanate in 50 ml. of tetrahydrofuran is added dropwise. The solvent is concentrated by evaporation and the residue is precipitated with ether/petroleum ether.
The chlorocarbonic acid thioester of l-phenyl-S-mercaptotetrazole, which can be prepared as described below, is used as an intermediate for compounds 2, 3 and 8.
A vigorous stream of phosgene is passed into a suspension of 20 g. (0.1 mol) of the sodium salt of l-phenyl-5-mercap totetrazole in 250 ml. of dry tetrachloromethane, which causes a substantial amount of the salt to dissolve. The reaction mixture is then left to stir for 2 hours, while sodium chloride precipitates. This is removed by suction filtration. The mother liquor is slowly concentrated by evaporation, a syrupy residue being obtained which can be used directly. The chlorocarbonic acid thioester need not be isolated for the preparation of the compounds described below.
COMPOUND 2 The syrupy chlorocarbonic acid thioester is taken up in 200 ml. of anhydrous tetrachloromethane, and 15.2 g. of the sodium salt of l-ethyl-5-mercaptotetrazole are added. The reaction mixture is heated to 60 C. with stirring for 2 hours, the solution is concentrated by evaporation, taken up in ethanol and filtered, and the product is precipitated with petroleum ether. The resulting compound 2 is recrystallized from ether/petroleum ether.
COMPOUND 3 The same procedure is employed as that used for compound 2, but 21.4 g. of the sodium salt of l-benzyl-S-mercaptotetrazole is used.
COMPOUND 4 The syrupy thioester is taken up in 200 ml. of anhydrous tetrachloromethane, and 16.6 g. of the sodium salt of 1 propyl-S-mercaptotetrazole are added. The reaction mixture is heated to 60 C. with stirring for 2 hours and the resulting solution is filtered from the precipitated sodium chloride, concentrated by evaporation, taken up in ether and clarified with charcoal, and compound 4 is precipitated by adding petroleum ether.
COMPOUND 5 COMPOUND 7 The procedure is analogous to that used for compound 5 but 8.03 g. (0.11 mol) of n-butylamine are added instead of methylamine.
Compound 8 The procedure is analogous to that used for the preparation of compound 5 but 8.03 g. (0.11 mol.) of diethylamine are added.
The S-mercaptotetrazole derivatives which may be used according to the invention can be hydrolysed relatively easily, especially in alkaline media. Apart from being added to the silver halide emulsion layers, they may also be added to other layers since in any case they diffuse into the silver halide em ulsion layers before or during development. Other layer to which the substance is added may be water permeable intermediate or protective layers.
Since the mercapto group is protected, the sensitivity obtainable in the photographic emulsion is generally greater than when using stabilizers with free SH groups. The sensitivity is not deleteriously effected during storage.
A further advantage of the inventive emulsion is that images of particular fine grains are obtained. This effect is caused by the hydrolysis of the compounds in the alkaline developer to produce free mercapto groups, and which gradually slows down the development. At the same time, the maximum sensitivity is not reduced by the delayed release of the SH-group.
The tetrazole compounds can be added to the silver halide emulsion at any stage during the preparation of the emulsion.
It is preferred to incorporate these compounds before the after-ripening.
The photographic silver halide emulsions are prepared in accordance with common practice including the steps of:
l. Precipitation of the silver halide in the presence ofa protective colloid and physical ripening;
2. Removal as by washing from the resulting emulsion, the excess water-soluble salts that have formed as a result of the precipitation; and
3. Chemical ripening (after-ripening) the washed product to impart the desired sensitivity to the emulsion.
The stabilizers according to the invention can be used in any silver halide emulsion. Suitable silver halides for the emulsion are silver chloride, silver bromide or mixtures thereof, if desired containing up to 10 mols percent of silver iodide. The silver halides may be dispersed in the usual hydrophilic compounds such as carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, alginic acid and its salts, esters or amides or, preferably, gelatin.
The methods of incorporating the stabilizers in emulsions are relatively simple and well-known to those skilled in the art of emulsion making. It is convenient to add the stabilizers from solutions in appropriate solvents whereby the solven t kg. of emulsion. The specific concentration depends on the The emulsion which is ready for casting is divided into 4 type of the emulsion and on the effects desired. The optimum parts. concentration for any given emulsion will be apparent to those Part A is used as a control without further additive; skilled in the art upon making the tests and observations PartB contains an additional 1 mg. ofstabilizer No. l; customarily employed in the art of emulsion making. 5 Part C contains an additional 5 mg. of stabilizer No. l;
The emulsions can also be optically sensitized with cyanine Part D contains an additional mg. of stabilizer No. l. rhodacyanine or merocyanine dyes such as described by F. M. The samples are applied onto a cellulose acetate support, l-lamer The Cyanine Dyes and related Compounds lnterexposed in a sensitometer behind a grey step wedge, and science Publishers, (1964). developed at 20 C. in a developer of the following composi- The emulsions may also contain chemical sensitizers, e.g. 1 tion: reducing agents such as stannous salts, polyamines such as sodium sulfite anhydrous 7.0 g. diethyltriamine or sulfur compounds as described in U.S. Pat. borax 7.0 g. No. 1,574,944. For chemical sensitization, one may further hydroquinone 3.5 g. add to the given emulsions salts of noble metals such as p-monomethylaminophenol 3.5 g. ruthenium, rhodium, palladium, iridium, platinum or gold, as sodium citrate 7.0 g. described in the article by R. Koslowsky, Z. Wiss. phot. 46, P ium mi 3- 65-72 (1959). The emulsions may also contain polyalkylene m P to 1 With Walerv oxides, especially polyethylene oxide, and derivatives thereof, The res lt o the sens ometr c tests are given in table I as chemical sensitizers. below.
TABLE 1 Ai'telrI 3 days bstorgge in eat cup oar Development time 6 Development time 16 Development time 16' Sensitivity Sensitivity Sensitivity in DIN 'y Fog in DIN 1 Fog in DIN Fog Control 0. 44 0.11 Control 0.86 0.12 =1=0 0.80 0.15 +0.5 0.41 0.08 i0 0.88 0912 +0. 5 0. 84 0.13 3:0 0.42 0.07 :bO 0.79 0.11 +1 0.81 0.12 :i:0 0.39 0.06 0.5 0.78 0.09 .5 0.80 0.09
The emulsions according to the invention may additionally The fog-stabilizing effect can be clearly seen both after 6 contain the usual stabilizers, e.g. homopolar or salt-type comminutes and after 16 minutes development time, without the pounds of mercury with aromatic or heterocyclic rings, such sensitivity being reduced. The stabilizing effect is maintained as mercaptotriazoles, simple mercury salts, sulfonium mercury even on storage in the heating cupboard. double salts, and other mercury compounds. Other stabilizers which may be used include azaindenes, especially tetraalain- EXAMPLE 2 denes or pentaazamdenes, in particular those substituted with Another Series of tests was designed to demonstrate that a hydrofyl ammo q l comPounds W have been fog-stabilizing effect is obtained even without the use of an descnbed article photazaindolizine as a basic stabilizer although on comparison with (1952). Other suitable stabilizers include heterocyclic mertable 1 the Synergistic ff obtained using the combination Capto f p q f- P l F P quaternary with an azaindene stabilizer is clearly apparent. benzthlalole denvanves and benzufazoies' As is described in example 1, a similar emulsion is prepared The emulsions y be hardened the usual manner for for casting in the same manner but without the addition of the ample, with formaldehyde or halogen-substituted aldehydes azaindolizine. that contain a carboxyl p mucobromic acid, The emulsion was divided into 3 parts with the following addiketones, methanesulfonic acid esters and dialdehydes. ditions; The stabilizers which we have described may be used in p A n- 1 a l ith f nh dditi various kinds of photographic emulsions. In addition to being p B i 5 mg ofcompound N 1 useful in X-ray and other nonoptically sensitized emulsions Th im n-i l s are shown i m 2 TABLE 2 After 3 days storage in heat cupboard; Development time 6 Development time 16 Development time 16 Sensitivity Sensitivity Sensitivity in DIN 'r Fog in DIN 7 Fog in DIN y Fog Sample.
A Control 0.52 0. 10 Control 0. 76 0.15 8.6 0.34 0.60 B 2 0.51 0.06 -2 0.73 0. 09 -2.5 0.69 0.30
NOTE: 3=1 shutter opening or double sensitivity.
they may also be used in orthochromatic, panchromatic and EXAMPLE 3 infrared-sensitive emulsion. They may also be used for emulsions suitable for use in the silver salt diffusion process for 5 color-photographic emulsions and for photographic materials for the silver dye bleach process.
The stabilizers provided by the invention can also be applied to great advantage during after-ripening, as will be seen from the following examples.
A silver iodobromide emulsion containing 8 mols percent of EXAMPLE 1 silver iodide is prepared in the usual manner. For after-ripening, the pAg value is adjusted to 8.9 and the pH to 6.8 and the A highly sensitive silver iodobromide gelatin emulsion convi osity to about 20 op. The emulsion is then treated with taining 8 mols percent of Agl is prepared for casting by adding gold-I-thiocyanate and divided into four equal parts; (based 200 mg. of 4-hydroxy-6-methyl-i,3,3a,7-tetraazaindene, 600 on 300 g. of AgBr, 8 percent Agl).
mg. of saponin as wetting agent and 10 ml. of a 10 percent PartA control sample without further additives;
aqueous formaldehyde solution as hardener per kg. of emul- Part B additionally contains 8 mg. of compound 1;
sion. Part C additionally contains 10 mg. of compound 2;
Part D additionally contains 12 mg. of compound 3.
After-ripening is continued until maximum ripening has been obtained, and the samples are made ready for casting by the addition of 600 mg. of saponin as wetting agent, ml. of a 10 percent aqueous formaldehyde solution as hardener and 200 mg. of 4-hydroxy-6-methyl-l ,3,3a,7-tetraazaindene as basic stabilizer, all per kg.
The samples are then cast on a cellulose acetate support, exposed in a sensitometer behind a grey step wedge and developed at C. for 6 and I6 minutes in the developer described in example 1.
The results of the sensitometric tests are shown in table 3.
TABLE 3 EXAMPLE 5 Another series of tests was designed to demonstrate that the compounds according to the invention have a considerably better stabilizing effect than the known basic compound 1- phenyI-S-mercaptotetrazole. A highly sensitive silver iodobromide emulsion containing 5 mols percent of silver iodide was divided into five equal parts. (Amount used based on 300 g. of silver bromide).
Part A control sample without additives; Part B contains 4 mg. of compound 1; Part C contains 6 mg. of compound 1;
After 3 days storage in heat cupboard;
Development time 6 Sensitivity Sensitivity Sensitivity in DIN 'y Fog in DIN y Fog in DIN 'y Fog Sample A Control 0.56 0.09 Control 0.85 0. 15 +0. 5 0.82 0.37 B +0.5 0.51 0.08 +0.5 0.91 0.14 +0.3 0.81 0.28 C +0.5 0.50 0.07 +0.3 0. 90 0.12 +0.2 0 78 0.26 D +0.5 0. 49 0.07 1:0 2 0.88 0.13 +0.3 0 79 0.29
NOTE: 3=1 shutter opening or double sensitivity.
The table also gives results of a storagetest: The unexposed Part D contains 8 mg. of compound 1; samples were stored for 3 days at 60 C. This test shows that Part E contains 3 mg. of l'-phenyl-5-mercaptotetrazole.
not only is the formation offog suppressed in the fresh film but also after storage in a heating cupboard, which gives an indication of the stabilization effect on storage.
EXAMPLE 4 The same emulsion used in A and B in example 3 is optically sensitized by addition of 40 mg. of the panchromatic sensitizer of the formula:
and 20 mg. of the orthochromatic sensitizer of the formula:
TABLE 4 The emulsions ripened to maximum sensitivity at a pAg of 8.9, a pH of 6.9 and a viscosity of about 15 op. The solutions were prepared for casting by the addition of 600 mg. of saponin as wetting agent, 10 ml. of a 10 percent aqueous formaldehyde solution as hardener and 200 mg. of 4-hydroxy-6- methyl-l,3,3a,7-tetraazaindene as basic stabilizer per kg. of emulsion. The samples are applied onto a cellulose acetate support, exposed in a sensitometer behind a grey step wedge. Development is performed for 6 minutes at 20 C. in the developer given in example 1. The results of the sensitometric tests are shown in table 5 below.
TABLE 5 After 3 days storage in heating cupboard (60 C.)
Sensitivity Sensitivity in DIN 'y Fog in DIN 7 Fog Control 0.87 0. l2 0. 2 0. 74 0. 18 :i:0 0.83 0. 08 :bO. 1 0. 75 0. l0 :l:0 0. 84 0. 07 +0. 2 0. 74 0. 10 :i:0 0. 82 0. 07 +0. 3 0. 73 0. 09 :l:0 0. 0. 12 +0. 2 0. 75 0. 16
NOTE: 3=1 shutter opening or double sensitivity.
At a given sensitivity, the stabilizing effect of the l-phenyl- S-mercaptotetrazole derivative according to the invention is better than the known 1-phenyl-mercaptotetrazole when used as a ripening additive. This not only reduces fogging in test samples of the freshly prepared film but also on samples which have been heated in a heating cupboard. Also, it takes twice as long to achieve complete ripening when unsubstituted l-phenyl-mercaptotetrazoles are used.
1. A light-sensitive photographic composition having at least one silver halide emulsion layer, which contains a stabilizer ofthe following Formula:
NN it 1%- After 3 days storage in heat cupboard;
Development time 6 Development time 16' Sensitivity Sensitivity Sensitivity Development time 16' in DIN 1 Fog in DIN 'y Fog in DIN 'y Fog Control 0. 75 0. 18 Control 0. 0. 29 -O. 7 0. 84 0. 35 5:0 0. 81 0. 12 0. 5 1. 05 0. 22 -0. 5 0. 80 0. 25
in which R is alkyl having up to three carbon atoms; phenyl or benzyl; Yrepresents l the grouping which is linked to the carbonyl group through an oxygen or sulfur atom or (2) the group--NRR wherein R stands for alkyl or for a radical of the phenyl series, and R stands for 3. The composition of claim 3, wherein the stabilizer is a symmetrical bis-tetrazole dithiocarbonic acid ester.
4. The composition of claim 4, containing the stabilizer of the following formula:
5. The composition of claim 1, which contains in addition a stabilizer of the tetraazaindene series.
* t t i I