US2726955A - Silver halide emulsions containing antiplumming and anti-bronzing agents - Google Patents

Description

United States Patent SILVER HALIDE EMULSIONS CONTAINING ANTI- PLUNIMIN G AND ANTI-BRONZING AGENTS Norman E. Parnell, East Brunswick Township, Middlesex County, N. J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 19, 1952, Serial No. 327,049

18 Claims. (Cl. 95-7) This invention relates to photographic silver halide emulsions and emulsion layers which have improved resistance to plumming and bronzing of developed images in photographic elements embodying such emulsions and to processes of making the same. More particularly, it relates to such emulsions and emulsion layers containing finely divided particles of an antiplumming agent suspended in wax particles.

This invention has for an objective the provision of improved photographic elements and particularly photographic papers. Another object is to improve the quality of the finished photographic image obtained when prints are dried upon hot ferrotype equipment. A further object is to provide photographic silver halide layers which are resistant to the phenomenon known as plumming, or bronzing, which occurs on hot ferrotyping photographic prints and is characterized by the formation of poor image color and a decrease in image density. An additional object is to improve the effectiveness of antiplumming agents in photographic silver halide emulsion layers. Still another object is the provision of plummingresistant photographic materials in which speed-loss and contrast-increase, encountered when employing an antiplumrning agent as an emulsion adjuvant, are minimized. Other objects will be apparent from the following description of the invention.

The above objects are attained and new and useful photographic emulsions and emulsion layers are obtained by bringing into intimate mixture with the lightsensitive silver halide grains or an aqueous dispersion thereof, in a water-permeable colloid, finely divided particles of a wax containing an anti-plumming agent. The particles of the latter agent are provided with a thin skin or coating, the thickness of which varies in accordance with the proportion of wax to agent. This coating effectively prevents the anti-plumming agent from acting upon the photosensitive silver halides during storage and treatment of the exposed photographic element in aqueous processing baths, but releases the agent when the photographic element is placed in contact with the hot ferrotype plate. 7 I

Various natural and synthetic waxes can be used for this purpose including mineral waxes, vegetable waxes, animal waxes, etc., including soft, hard and microcrystalline paraffin waxes; ozokerite, ceresin, carnauba wax, beeswax, montan wax, synthetic waxes, e. g., seekay wax obtained by chlorinating naphthalene, chlorinated biphenyl, higher aliphatic cyanides or nitriles, higher aliphatic acid amides, methylene distearamide, ethylene disteararnide and the corresponding bis amides from lauric, palmitic and oleic acid and mixtures of two or more of such amides, the synthetic wax sold under the trade name Ceramid by 'Glyco Products Co., Inc., New York, etc. The useful waxes, in general, should be solid at 25 C. and melt at the temperature used for the hot ferrotype plate, e. g., below l00 C. The parafiin waxes are preferred.

The'above waxes are-jwater-insoluble and-are not 2,726,955 Patented Dec. 13, 1955 ICC affected by the alkaline materials or acid materials present in the usual developing, fixing and stop baths used in processing exposed photographic papers to photographic images or pictures.

In general, the procedure for inertizating an antiplummiug agent consists of incorporating the anti-plumrning agent in the molten wax. If the anti-plumming compound is soluble in the wax or resin, a solution may be prepared; otherwise, it is necessary to form a solution using a common solvent, or a colloidal suspension with a suitable dispersing agent. In the case of 1-phenyl- S-mercaptotetrazole and related l-hydrocarbon-substituted S-mercaptotetrazoles and methylene stearamide, for example, it is possible to dissolve the anti-plurnming agent directly in the liquefied wax. By melting paraffin Wax and cooling carefully it is possible to disperse finely divided particles of l-phenyl-5-mercaptottetrazole, which is insoluble in paraflin wax, directly in the wax. However, dispersing agents, e. g., sodium p-tertiaryoctyiphenoxyethoxyethyl sulfonate, aid in securing stable suspensions. The Wax solution or dispersion may be dispersed in turn in Water, which may contain dispersing agents, a water-permeable colloid, e. g., gelatin, forming a suspension of Wax particles in which the anti-plumming agent particles are coated. The Water dispersion is then added to a silver halide photographic emulsion in the desired amount, coated on a suitable support, and air dried. These coatings, after receiving a standard exposure through a standard negative, are processed in the appropiate developer, acid stop and fixing solutions. The prints obtained when dried upon a hot ferrotype plate are essentally free from plumming and exhibit no loss in density, and no appreciable change in emulsion speed and contrast.

The preparation of the water dispersion of the resin solution or initial wax dispersion should be performed in a manner that will minimize leaching of the anti-plumming compound from the protective coating of wax. The use of water-insoluble solvents which have a high solvent action upon the anti-plumming agent, compared to the solubility in water, is advantageous, although satisfactory coating With the anti-plumming agent or inertization is possible with certain water-soluble solvents. Coating of the agent is usually aided by concentrating the wax and anti-plurnming agent in the same solvent phase. The choice of a solvent using the solute distribution laws of multiphase systems as a guiding principle tending from the submicroscopic to approximately 30 microns in diameter.

In dispersing the mixture of Wax and antiplumming agent directly in an aqueous colloid solution or aqueous colloid silver halide dispersion one may use small amounts of a dispersing agent. Suitable dispersing agents include sodium and potassium alkyl sulfates of 10 to 18 carbon atoms, sodium alkylsulfonates of 10 to 18 carbon atoms, polyoxyethylene ethers of ring-dehydration products of a hexitol (see U. S. Patent 2,400,532), sorbitan monosterate, etc. Good dispersion can be made without agents.

While it is preferable to disperse the wax-coated particles of the anti-plumrning agent in the colloid-silver halide dispersion the invention is not limited to this embodiment. ..Good.resnlts can..be obtained by. coating a layer of a water-permeable colloid containing the coated anti-plumming agent directly onto a colloid silver halide emulsion layer or by bathing such an emulsion layer with a dispersion of the wax-protected anti-plumming agent.

The invention will be further illustrated but is not intended to be limited by the following examples.

EXAMPLE I First, a suspension of finely-divided particles of l-phenyl--mercaptotetrazole, having a particle size of not more than 30 microns in their largest diameter, in paraffin Wax was formed by melting 200 grams of the Wax, adding 2 grams of sodium p-tertiary-octylphenoxyethoxyethyl sulfonate as a dispersant and then incorporating 20 grams of the l-pheuyl-S-mercaptotetrazole. By cooling slowly with good agitation, a dispersion of l-phenyl-S-mercaptotetrazole in the solid Wax was obtaine Next, a solution consisting of 5 grams of the polyoxyethylene ether of dodecyl alcohol in 150 ml. of distilled water was prepared and added to a high-speed liquid mixer of the type described in Osius U. S. Patent 2,109,501. A 4-gram portion of the suspension of wax-protected l-phenyl-S-mercaptotetrazole particles was then added and vigorously agitated for five minutes.

A chloro-bromide emulsion (AgCl=95.2 mole per cent, and AgBr=4.8 mole per cent) was prepared by a procedure which normally yields a standard contact printing speed emulsion. Immediately before coating this emulsion upon a baryta coated paper support, 50 ml. of the wax-protected l-phenyl-S-mercaptotetrazole dispersion was added to a quantity of emulsion having a silver content equivalent to that contained in 12.5 ml. of 3 N silver nitrate solution at 25 C. In all other respects the procedures for preparation and coating of contact printing paper type emulsion were followed. Control coatings were made at the same time with portions of the original emulsion, which included no 1-phenyl-5-mercaptotetrazole in one case, and the above wax-protected l-phenyl-S-metcaptotetrazole in a second case. The coatings were dried, and samples cut and exposed to a standard negative in the standard testing set-up for contact type emulsion to obtain matched prints. All prints were developed for one minute at 20 C. in developer made by diluting 1 part of the following stock solution:

Water ml 500 Metol g ams" 3.0 Sodium sulfite (anhydrous) do 45.0 Hydroquinone do 12.0 Sodium carbonate (anhydrous) do 67.5 Potasium bromide do.. 1.9

Water to make 1.0 liter. with 2 parts of water, rinsed in water, and .fixed in the following fixer solution:

Water ml 850 Sodium thiosulfate "grams-.. 240 Sodium sulfite (anhydrous) ....do 15.0 Acetic acid (28%) ml 48.0 Boric acid (crystals) grams 7.5 Potassium alum do 15.0

Add water to make 1.0 literfor five minutes. Processed prints from each coating were dried on a hot ferrotype plate, a cold ferrotype plate, and on a cheesecloth type screen to evaluate plumming. The results are tabulated as follows:

EXAMPLE n Initially, a dispersion of finely-divided particles of 1-phenyl-S-mercaptotetrazole protected with paraflin wax having a melting point of 60 C. was prepared by melting 20 grams of the wax, adding 0.5 gram of an oxidized fatty acid of 12 to 20 carbon atoms as a dispersing agent, and then slowly mixing in 2 grams of the anti-plumming compound. Upon cooling slowly with good agitation, a suspension of the 1-phenyl-5-mercaptotetrazole in the solid wax was formed. A 3-gram portion of this mixture was then added to a solution of 6 grams of polyoxyethylene sorbitan monolaurate (Tween 61 sold by Atlas Powder Co.) in ml. of distilled water contained in a high speed mixer of the type described in U. S. Patent 2,109,501 and blended for three minutes. The dispersion thus obtained was dilutedto 200 ml. and passed through a colloid mill three times, using a clearance settingof 0.002 inch and a speed of 12,000 R. P. M. The dispersion thus obtained was tested in the same manner as that described in Example 'I. A summary of the results is presented in Table II.

A solution containing 4 grams of l-phenyl-S-mercaptotetrazole dissolved in 36 grams of molten, synthetic wax having a melting point of 795 to 805 C. and comprising a mixture of the amides prepared by reacting stearic acid with stearyl amines was prepared initially. Next, to 100 ml. of distilled water in a high speed mixer as described in Example II, 6 grams of sorbitan tristearate polyoxyethylene ether (Span 65 sold by Atlas Powder Co.) were added and blended for 30 seconds. Then, 3 grams of the first molten solution were added and blended for three minutes. The resultant dispersion was diluted to 200 mLand passed through a colloid mill three successive times, the colloid ,mill being set for 0.002 inch clearance and 12,000 R. P. M. The dispersion obtained was evaluated in the manner given in Example I. The pertinent results are presented in Table Table III Grams l-phenyl-e gelative P] d Cow mercap oxposure umme on Emulsmn tetrazole, Time Hot Ferrd? g per emul- (see) e sion unit Control None Trace 20 Yes 2.0 Modifiedwith--. 1.360 None.. 33 Moderately 3.0

less than control. Modified with 0.720 ---do. Siight1y 2.0

wax+.

Similar results can .be obtained with ether N-alkyl stearamides including those made from interaction of lauric, palmitic, oleic, and stearic acids and mixtures of two or more thereof, with the corresponding monoamines, i. e., dodecyl, etc., and mixed amines.

' EXAMPLE IV A .solution wasepreparedsby dissolving 2 grams of l-phenyl-S-mercaptotetrazole in 20 grams of the molten synthetic wax described in Example III. Next, a mixture of 4 grams of polyoxyethylene sorbitan monolaurate (Tween 61 sold by Atlas Powder Co.) in 100 ml. of distilled water was prepared and blended for 30 seconds in a high-speed mixer (U. S. P. 2,101,501). A 4-gram portion of the solid wax-1-pheny1-5-mercaptotetrazole solution was crushed and added with the mixer in motion. Blending was continued for approximately three minutes. The resultant dispersion was tested as outlined in Ex- First, a solution composed of 0.75 gram of l-phenyl- S-mercaptotetrazole dissolved in 7.5 grams of molten stearyl stearamide was prepared and allowed to solidify. A Z-grarn portion of this solid solution was then added to 100 ml. of distilled water containing 5 grams of sorbitan monolaurate and 0.5 gram of cetyl-trimethylammonium bromide as a dispersant, and blended for three minutes in a high-speed mixer (U. S. P. 2,109,501). The resultant suspension was diluted to 150 ml. and passed through a colloid mill set for 0.002 inch clearance and 12,000 R. P. M. After milling, distilled water was used to rinse the emulsifying equipment and adjust the total volume to 250 ml. Results of the emulsion evaluation of the suspensoid obtained are tabulated in the following A second dispersion was made following the procedure given in Example I, except that (Tween 81) was substituted for sodium p-tertiary-octylphenoxyethoxyethyl sulfonate. This dispersion was tested along with the first, so that the controls are the same. The results are also given in Table V.

In the foregoing tables an emulsion unit is defined as that quantity of emulsion having a silver content equivalent to that of 500 ml. of 3 N AgNOa at 25 C.

The contrast grade in the foregoing tables was determined visually by comparing a print made in the standard manner with the scale of paper contrast grades used by E. I. du Pont de Nemours and Company in their control laboratory at Rochester, New York, to grade photographic paper products for trade purposes.

The above examples evidence that by coating antiplumming agent particles with a wax one can materially reduce the degree of plumming. Moreover, the quantity of the anti-plumming agent required to give effective antiplumming may be reduced by providing such a coating.

The invention is, of course, not limited to the use of the particular anti-plumming agent given in the foregoing examples as many other of such agents can be used with like results. Among the additional useful agents are the l-alkyl, l-aryl and l-cycloalkyl-5-mercaptotetrazoles, e. g., l-u-naphthyl-5-mercaptotetrazole, l-cyclohexyl-5-mercaptotetrazole, 1-methyl-S-mercaptotetrazole, l-ethyl-S-mercaptotetrazole; S:S'-methylene-bis-thiuronium iodide, S:S'- ethylene-bis-thiuronium bromide, S:S'-trimethylene-bisthiuronium bromide; 2:2'-methylenethio-bis-dihydroiminazole dihydroiodide, 2:2'-ethylenethio-bis-dihydroiminazole dihydrobromide, 2:2trimethylenethio-bis-dihydro iminazole dihydrobromide, 2:2'-ethylenethio-bis-(4-methyldihydroiminazole) dihydrobromide, 2:2'-trimethylenethio-bis-(4-methyliminazole) dihydrobromide, disodium- 2:2 ethylenethio bis (4-amino-6-hydroxypyrimidine), S:S'ethylene-bis-N-ethyl-thiuronium bromide, S:S-ethylene-bis-N:N-diethylthiuronium bromide, S:S'-trimethyl ene-bis-N:N"-triethylthiuronium bromide, S:S'-ethylenebis-N:N"-triethylthiuronium bromide, S:S-o-xylylenylbis-thiuronium bromide, S:S'-ethylenethio-bis-(l-methyldihydroiminazole)di p toluenesulfonate, S:S'-ethylene bis-N-phenyl-N-methylthiuronium bromide, 4:4-ethylene thio-bis-(4: 6-dithio-1 :3 5-thio diazine, 2:2'-ethylenethiobis-(S-thiol-l 3 4-thiodiazole), S-ethylthiuronium bromide, S-n-butylthiuronium bromide, S-cetyl thiuronium iodide, S-amidoethylthiuronium chloride, S-Z-thiazylamidomethylthiuronium chloride and S-Z-pyridylamidomethylthiuronium chloride, etc. Mixtures of two or more of the anti-plumming agents can be used. They may be used with the waxes described above or mixtures of two or more of such waxes.

The proportion of anti-plumming agent to wax may vary from 1 to 25 parts by weight of the former per part by weight of the latter. The optimum amounts will vary with the particular agent and wax. When the anti-plumming agent also has good anti-fogging properties it is best to keep the proportion of agent to wax in the higher portion of the above range.

Since waxes are insoluble in the pH ranges of the ordinary developing and fixing solutions the agents are essentially insolubilized or protected by the wax coating during aqueous processing of a photographic paper bearing an emulsion containing a wax-protected agent. The amount of free or exposed anti-plumming agent can be controlled to some extent by other factors among which are proper choice of solvents, concentrations, temperature, and the severity and time of application of the shearmg forces due to the dispersing equipment. It is also possible to use hydrophilic colloid, e. g., gelatin solutions as the dispersion media, so that photographic emulsion Wash technique may be used to remove non-protected particles, which are water-soluble. The anti-plumming agent is released by the heat of the hot ferrotype plate, which melts the protective Wax or resin coating.

The invention is not limited to gelatin silver halide emulsion and emulsion layers as many other water-permeable colloids can be used as the binding agent for the silver halide grains with like results. Among the additional useful materials are agar agar, alginic acid, sodium alginate, polyvinyl alcohol and its ethers and acetals including the color-former acetals of Jennings et al. U. S. P. 2,397,864, cellulose ethers, etc. partially hydrolyzed esters of cellulose, etc.

While the invention is particularly useful with photographic printing papers the support is not limited to paper but can be a cellulose derivative, e. g., cellulose acetate, cellulose nitrate, etc., a super polymer, e. g., nylon, poly: vinyl chloride, polyethylene terephthalate, etc. These supports may conatin an opacifying agent or bear a coating containing such an agent so that the surface is lightreflecting and the support does not transmit light.

An advantage of this invention is that it provides a simple and elfective method of improving the anti-plumming effect of anti-plumrning agents. Another advantage is that it reduces the quantity of anti-plumming agent necessary to produce an'adequate result. A further advantage is that it reduces the leaching of anti-plumming agents from water-permeable colloid silver halide emulsion layers. A still further advantage resides in the fact that the additional material involved, viz., the wax, is inexpensive. Yet another advantage is that the method of making the emulsions is simple and does not involve expensive apparatus.

As many .widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is otbe understood that the invention is not to be limited except as defined by the claims.

'What is claimed is:

1. A colloid silver halide emulsion having dispersed therethrough particles of a wax containing an agent taken fromthe group consisting of anti-plumming and antibronzing agents,.said agents being sulfurand nitrogencontaining organic compounds having the property of preventing the formation of bronze, to plum-colored silver images upon the hot-drying of developed silver photographic images.

2. A'water-permeable colloid silver halide emulsion layer having a wax in particulate form dispersed throughout such layer and having an anti-plumming agent, said agent being a sulfurand nitrogen-containing organic compound having the property of preventing the formation of bronzeto plum-colored silver images upon the hot drying of developed silver photographic images contained in the wax particles.

3. A water-permeable colloid silver halide emulsion having dispersed therethrough particles of wax containing an anti-plumming agent, said agent being a sulfurand nitrogen-containing organic compound having the property of 'preventingthe formation of bronze. to plumcolored silver images upon the hot drying of developed silver photographic images, said particles having an average diameter not greater than 30 microns and said wax being solid at temperatures of C. and melting at a temperature not greater than 100 C. i

4. A gelatino silver halide emulsion having dispersed therethrough particles of wax containing an anti-plumming agent, said agent being a sulfurand nitrogen-containing organic compound having the property of preventing the formation of bronzeto plum-colored silver images upon the hot drying of developed silver photographic images, said particles having an average diameter not' greater than microns and said Wax being solid at temperatures of 25 C. and melting at a temperature not greater than 100 'C.

5. A water-permeable colloid silver halide emulsionhaving dispersed therethrough particles of wax containing an agent taken from the group consisting of antiplumming and anti-.bronzing agents, said agents being sulfurand nitrogen-containing organic componnds'having the property of preventing the formation of bronzeto plum-colored silver images upon the hot-drying of developed silver photographic images, said particles having an average diameter not greater than 30 microns and said wax being solid at temperatures of 25 C. and melting at a temperature not greater than 100 C., theproportion of said agent to wax varying from 1 to 25 partsk, the proportion of anti-plumming agentto wax varying from i to 25 parts by weight of the former per 'part by weight of the latter.

7. A water pe'rmeable colloid silver halide emulsion having dispersed therethrough particles of a water-insoluble Wax containing a l-hydro'c'arbon-S-rnercaptotetrazole.

8. A water-permeable colloid silver halide emulsion having dispersed therethrough particles of a paraflin wax containing a 1-hydrocarbon-5-mercaptotetrazole.

'9. A gelatino silver halide emulsion having therethrough particles of paraffin wax containing l-phenyl-5 mercaptotetrazole.

10. A photographic element comprising a support hearing a colloid silver halide emulsion layer wherein silver halide grains have in proximity therewith particles of a wax containing an anti plumming agent, said agent being a sulfurand nitrogen-containing organic compound having the property of preventing the formation of bronzeto plum-colored silver images upon the hot drying of developed silver photographic images.

ll. An element as set forth in claim 10 wherein the wax particles are distributed throughout the emulsion.

12. An element as set forth in claim 10 wherein the wax particles are in a separate water-permeable colloid layer disposed on the outer surface of the emulsion layer. 13. A photographic element comprising a paper support bearing a waterrpermeable colloid silver halide emulsionlayer and having dispersed therethrough particles of a wax containing an anti-plumming agent, said agent being a sulfurand nitrogen-containing organic compound havingthe property of preventing the formation of bronzeto plum-colored silver images upon the hot drying of developed silver photographic images.

14. A photographic element comprising a paper support bearing -a water-permeable silver halide emulsion layer having dispersed therethrough particles of wax containing. an anti-plumming agent, said agent being a sulfurandnitrogen-containing organic compound having the property of preventing the formation of bronzeto plum-colored silver images upon the hot drying of developed silver photographic images, said particles having an average diameter not greaterthan 30 microns and said wax being solid at temperatures of 25 C. and melting at a temperature not greater than 100 C.

'15. A photographic printing paper comprising a baryta coated paper sheet bearing a gelatino silver halide emulsion having dispersed therethrough particles of wax containing an anti-plumming agent, said agent being a sulfurand nitrogen-containing organic compound having the coated paper sheet bearing a gelatino silver halide emulsion having dispersed therethrough particles of wax containing a 1-hydrocarbon-S-mercaptotetrazole, said particles. having an average diameter not greater than 30 microns andsaid wax being solid at temperatures of.

25 C. and melting at a temperature not greater than 17. A photographicprinting paper comprising a baryta coated paper sheet bearing a gelatino silver halide emul-.

1 sion having dispersed therethrough particles of wax containing a l-phenyl-S-mercaptotetrazole, said particles having an average diameter not greater than 30 microns and said wax being solid at temperatures of 2 5 C. and mel*- ing at a temperature notgreater than 100 C.

18. The process which comprises dispersing an antiplumming agent, said agentlbeing a sulfurand nitrogencontaining organic compound having the property of preventing the formation of bronzeto plum-colored silver images upon the hot drying: of developed silver photo- 9 graphic images in a wax and incorporating the wax-pro 2,221,873 tected particles of such agent in a light-sensitive colloid 2,256,390 silver halide emulsion.

References Cited in the file of this patent 561,875

UNITED STATES PATENTS 2,059,829 Ward Nov. 3, 1936 10 Knoefel Nov. 19, 1940 Hewitson Sept. 16, 1941 FOREIGN PATENTS Great Britain June 8, 1944