US3917485A - Method of making photographic silver halide emulsions and products thereof - Google Patents

Abstract

A method is disclosed of making an internally sensitive photographic silver halide emulsion. In this method further silver halide is laid down on the grains of a surface sensitive or surface fogged emulsion so that excesses of silver and halide ions are alternately produced. In one preferred form a desensitizer is added to the completed internally sensitive emulsion, which desensitizer has a cathodic polarographic halfwave potential less negative that -1.0 volt. In another preferred form a sensitizing dye can be added to the internally sensitive emulsion. The invention is also directed to the silver halide emulsions formed by these methods.

Description

United States Patent 1191 Morgan Nov. 4, 1975 [54] METHOD OF MAKING PHOTOGRAPHIC 3,206,313 9/1965 Porter et al 96/101 x SILVER HALIDE EMULSIONS AND 3,367,778 2/1968 Berriman 3,687,676 8/1972 Spence et a1. 96/101 x PRODUCTS THEREOF John Morgan, Ruislip, England Eastman Kodak Company, Rochester, NY.

Filed: Sept. 3, 1974 Appl. No.: 502,695

Related US. Application Data Inventor:

Assignee:

US. Cl 96/101; 96/94 R; 96/120; 96/125 Int. CL G03C 1/36; G03C l/O2; GO3C 1/08 Field of Search 96/101, 64, 94 R, 120, 96/125, 108

References Cited UNITED STATES PATENTS Primary Examiner -David Klein Assistant Examiner-Aalfonso T. Suro Pico Attorney, Agent, or Firm-C. 0. Thomas [57] ABSTRACT A method is disclosed of making an internally sensitive photographic silver halide emulsion. In this method further silver halide is laid down on the grains of a surface sensitive or surface fogged emulsion so that excesses of silver and halide ions are alternately produced. In one preferred form a desensitizer is added to the completed internally sensitive emulsion, which desensitizer has a cathodic polarographic halfwave potential less negative that -1.0 volt. In another preferred form a sensitizing dye can be added to the internally sensitive emulsion. The invention is also directed to the silver halide emulsions formed by these methods.

18 Claims, No Drawings METHOD OF MAKING PHOTOGRAPHIC SILVER HALIDE EMULSIONS AND PRODUCTS THEREOF CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my earlier filed, copending US. Pat. application Ser. No. 431,453, filed Jan. 7, 1974, now abandoned.

This invention relates to a method of making photographic silver halide emulsions and to silver halide emulsions made thereby.

Photographic silver halide emulsions which form la tent image predominantly in the interior of the silver halide grain are often called internal latent image emulsions. A number of ways of preparing them have been described, for example, in British Specification Nos. 581,792, 581,789, 635,841, 1,027,146 and 1,011,062.

A typical method for preparing such emulsions is described in British Specification No. 1,011,062 (US. Pat. No. 3,206,313). This involves blending a very fine grain silver halide emulsion, such as a Lippmann emulsion, with a surface sensitized emulsion having considerably larger average grain size. This blend is then held under conditions and for a period of time sufficient to cause the silver halide of the fine grain emulsion to dissolve and recrystallize on the grains of the surface sensitized emulsion. This results in silver halide grains having a core derived from the surface sensitized grains and a shell of silver halide derived from the fine grain emulsion. Since the silver halide shell covers the sensitivity sites previously present on the surface of the silver halide grains, these sensitivity sites are now buried in the silver halide grains.

This method of preparing internally sensitive photographic silver halide emulsions can be relatively complicated. It requires careful control of the conditions under which the blend of fine grain and coarse grain emulsions is ripened if a desirable product is to be obtained. Furthermore, not all emulsions are useful as the coarse grain core emulsions. This is particularly true of emulsions whose grains vary considerablyin size, such as can occur in polydispersed emulsions.

The present invention provides a relatively simple procedure for making internally sensitive photographic silver halide emulsions, which procedure is applicable to convert a variety of surface sensitive or surface fogged silver halide emulsions (including polydispersed emulsions of varied grain size) to internally sensitive photographic silver halide emulsions.

According to the present invention there is provided a method of making an internally sensitive photographic silver halide emulsion in which further silver halide is laid down on grains of a surface sensitive or surface fogged silver halide emulsion by producing alternate excesses of silver ions and halide ions in solution during precipitation of additional silver halide onto the silver halide grains.

The present invention also provides an internally sensitive photographic silver halide emulsion comprising initially surface sensitive or surface fogged grains and, on each of said grains, a surface layer of silver halide precipitated from a solution containing alternate excesses of silver and halide ions during precipitation.

The present invention can be applied to any conventional surface sensitive or surface fogged silver halide emulsion. The surface sensitive or surface fogged silver halide emulsion can be that which has been employed alone, in combination with other emulsions or as a core emulsion in forming an internally sensitive emulsion.

Such emulsions and their formation are well known to those skilled in the art and are disclosed, for example, in US. Pat. Nos. 2,222,264; 3,320,069; 3,271,175; 2,592,250; 3,206,313; 3,367,778; 3,447,927; 3,447,927; 2,184,013; 2,541,472; 3,501,307; 2,563,785; 2,456,953 and 2,861,885, the disclosures of which are here incorporated by reference.

Preferred surface sensitive emulsions are those that have been chemically sensitized--e.g. gold or noble metal sensitized, sulfur or selenium sensitized and/or reduction sensitized. The silver halide grains in one preferred form can also be treated with salts of noble metals, such as ruthenium, palladium, platinum, iridium, rhodium, and iron. When the emulsion is surface fogged this can be achieved using conventional nucleating agents or by fogging through uniform exposure.

My invention is particularly applicable to surface sensitive or surface fogged emulsions having a wide distribution of grain sizes, as can be formed either by blending or by the method of precipitation chosen-- -e.g., using a single jet precipitation technique. My invention is also fully compatible with the use of monodispersed emulsions or those having a relatively restricted range of grain sizes, as have been heretofore conventionally employed in forming internally sensitized emulsions. It is a specific advantage of my invention that it can be applied to emulsions generally regardless of grain size or grain size distribution. Thus, my invention is applicable to Lippman emulsions, relatively coarse grain radiographic emulsions, monodispersed emulsions and polydispersed emulsions generally.

To form silver halide layers on the surface sensitive or surface fogged silver halide grains in order to convert these grains to internally sensitive silver halide grains the surface sensitive emulsion is brought into contact with a conventional silver halide precipitation solution. Silver halide layers can then be formed on the surface sensitive or fogged grains using generally the same materials and techniques useful in forming silver halide grains (i.e., the procedures disclosed in the patents cited above), except as specifically modified to achieve the advantages of my invention.

Typically the precipitation solution includes a silver salt and an alkali metal halide which interact in a double decomposition reaction to form silver halide and an alkali metal salt by-product which remains in solution. To avoid clumping of the silver halide grains during additional silver halide precipitation, small amounts of a peptizer, such as gelatin or some other conventional hydrophilic colloid, is present during precipitation. Suitable peptizers are disclosed. for example in Product Licensing Index, Volume 92, December 1971.publication 9232, paragraph VIII. The peptizer can be that used to form the surface sensitive or surface fogged silver halide emulsion or, if desired, additional peptizer can be added during formation of the silver halide layers.

Any conventional technique for bringing together the silver and the halide containing salts in the presence of the surface sensitive or surface fogged silver halide emulsion can be employed, provided an excess of silver or halide ions can be produced and the excess reversed at will. According to one approach, to the surface sensitive or fogged emulsion is added both the silver and bromide salts, but with one being present in excess. Subsequently additional quantities of the silver and the halide salts are alternately added so that the excess of ions above the stoichiometric required amount is successively shifted between the silver halide ions present. In one form then, the formation of silver halide layers can be viewed as an alternate jet mode of precipitation. Instead of actually interrupting the flow of silver salt and halide salt periodically, it is also possible to sequentially restrict the flow of the separate jets and/or sequentially increase the flow of the separate jets. The silver and the halide salts can be added directly as salts, but are preferably added in aqueous solution.

As an example, sufficient silver nitrate solution is added to the precipitation solution to adjust the pAg of the emulsion to the silver side, e.g., to a pAg of 5.0 (from 4 to 6.5, most preferably generally), then sufficient potassium halide solution is added to adjust the pAg of the emulsion to the halide side, e. g., to a pAg of 8.0 (from 7.5 to 10, most preferable generally), and this pAg adjustment cycle may be repeated several times. After each successive cycle the surface speed and contrast is reduced, as judged by development in a normal commercial developer of low silver halide solvent content. Development in an internal developer, i.e., one containing an appreciable content of silver halide solvent, will however yield an image with speed and contrast similar to the original surface emulsion.

Good results can be obtained using pAg figures other than those given above. It is desirable that the silver excess should not be too great--typically a pAg no less than 4 is desirable, and the temperature and time that the emulsion is held at the low pAg should be as low as conveniently possible, otherwise there is a tendency for fog to develop. In general, temperatures of not more than 40C and times of to 30 seconds for each part of the cycle yield the best results.

If precipitation is conducted above 40C, the shift in the neutral pAg of the precipitation solution must be considered in chosing the pAg levels in cycling. For example, whereas a neutral pAg is about 7.0 at room temperature, at 80C the neutral pAg is about 5.5. Generally cycling of at least one pAg unit and, preferably, two pAg units on either side of pAg neutrality is contemplated. As expressed in this specification, pAg values and ranges are related to temperatures in the range of from room temperature to 40C.

Although the added silver halide may be of any constitution, the best results are obtained when the silver halide is silver bromoiodide. In adjusting the pAg it is preferred to employ bromoiodide solutions rich in iodide. Thus, for example, good results are obtained with 75 percent bromide, 25 percent iodide (mole percentages).

Generally between 7 and cycles are sufficient to suppress the normal surface sensitivity completely, al-

though a beneficial degree of internal sensitivity can be achieved with a few as 3 cycles or less. The number of cycles for any specific application will vary with the grain size of the emulsion, halide make-up of the added layers, and the crystal habit of the original grains, but can be readily ascertained by one skilled in the art.

The emulsions prepared by the present process need not be fully internal latent image emulsions, but can retain significant surface sensitivity if only a few pAg cycles have been used. Thus, emulsions having any desired balance of internal and surface sensitivities can be produced using my process.

It is not certain whether all the additional silver halide is laid down on the surface of the grains or whether some is precipitated separately in the gelatin phase and subsequently transferred to the grains by Ostwald ripening, or whether some remains permanently as a separate fine grain precipitate. Nevertheless it is thought that by this technique thin layers, of perhaps 10 to 100 ion pairs of additional silver halide each, are laid down. It is not necessary to the practice of the invention to accept this particular theory, but it is supported by the fact that the number of cycles necessary to suppress the surface sensitivity is less in the case of octahedral grains than those of cubic habit, since in the former case it might be expected that a whole layer of ions would more easily be absorbed for each pAg change.

It is not even necessary to complete the pAg cycles before exposure; conversion of an existing latent image from surface to internal can be achieved by the pAg cycling technique in the same way as conversion of the sensitivity. Thus if a liquid emulsion is fogged by exposure to light, and subjected to an appropriate number of cycles, a clean emulsion with internal fog results.

An advantage of this invention is the suppression of the desensitizing action of spectral sensitizing dyes. All sensitizing dyes tend to desensitize the natural sensitivity of a photographic emulsion in the blue region, and is practice this sets a limit to the amount of dye it is possible to add to an emulsion. Moreover there are specific interactions between emulsions of well defined crystal habit and certain classes of sensitizing dye (e.g. octahedral emulsions and carbocyanines) that results in excessive desensitization, as noted by Markocki (J. Photo. Sci. 1965, 13,

This desensitization can be substantially reduced or even completely overcome by using the present cycling technique to interpolate silver halide between the dye at the surface and the sensitivity below. Moreover, this reduction in desensitization is often not accompanied by any adverse action on the efficiency of sensitization, i.e. the relation between the speed in the dye band and the basic blue sensitivity of the emulsion is unchanged.

Thus, in a preferred embodiment, the initially sensitive silver halide emulsions of this invention are particularly suitable for use with sensitizing dyes or desensitizers which are added to the emulsion at a concentration which would desensitize the emulsion if it had not been subjected to the present cycling technique. Typical sensitizing dyes having a primary absorption peak less than 700 millimicrons are described in Belgian Pat. No. 770,293 while typical sensitizing dyes having a primary absorption peak greater than 700 millimicrons are described in U.S. Pat. No. 3,690,891. The desensitizers or electron acceptors useful in the emulsion of this invention are described in US. Pat. No. 3,687,676. The concentrations of the sensitizing dyes and desensitizers can be described as being above that which would produce a loss in blue sensitivity in a sulfur and gold surface sensitized silver bromoiodide emulsion (6 mole percent iodide) of similar grain size of at least 0.3 log B when developed in a surface developer such as Kodak D-19.

It is, of course, recognized that lower, conventional concentrations of sensitizers and desensitizers can be employed, as is taught in the art in connection with core-shell emulsions. Preferred desensitizers are those conventional desensitizers characterized by having a cathodic polarographic half-wave potential (Ec) less negative than I .0 volt.

Cathodic measurements are made with a l X 10 molar solution of the electron acceptor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic half-wave potential for the most positive cathodic wave being designated E Anodic measurements are made with l X molor aqueous solvent solution, for example, aqueous methanolic solutions of the electron acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste or pyrolytic graphite electrode, with the voltametric half peak potential for the most negative anodic response being designated E In each measurement, the reference electrode is an aqueous silversilver chloride (saturated potassium chloride) electrode at 20C. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, New York, 1954; Polarography, by Kolthoff and Lingane, 2nd Edition, lnterscience Publishers, New York, New York, 1952, Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams.

The present emulsions may be made by any of the techniques employed in the art and may contain emulsion addenda including coating aids, antifoggants and speed-increasing compounds. The emulsions may be coated on a variety of supports. A review of emulsion chemistry and applications of photographic emulsions appear in Product Licensing Index December 1971 pages 107-1 10, Industrial Opportunities Ltd., Havant, Hampshire.

The present emulsions may be used to obtain directpositive images preferably by exposing them imagewise unfogged and then developing in the presence of fogging or nucleating agents in known manner.

It is to be appreciated that the emulsions formed according to my invention can be further modified, as by the incorporation of addenda, coated, exposed and processed by procedures known to those skilled in the art. Such teachings can be summarized at least in part, for example, in Product Licensing Index, Volume 92, published December 1971, publication 9232, pages 107 through 110.

The following Examples illustrate the invention. The developers referred to as D19 and Dl9b have compositions corresponding to Kodak Developers D19 and D19b respectively given in the Kodak Limited Data Book. The work Kodak is a registered trade mark.

EXAMPLE 1 An emulsion was prepared by running a solution of 100 grams silver nitrate in 500 cc of distilled water at 55C. into a solution of grams gelatin, 75 grams potassium bromide and 4.5 grams potassium iodide in 750 cc of distilled water at 60C. for over 10 minutes. After heating for 30 minutes at 60C., 125 grams of active gelatin dissolved in 500 cc of water at 60C. was added, the suspension was set to gel, shredded and washed 40 minutes in running water. It was then re-melted and heated for a further period of 40 minutes at 55C., the final volume being adjusted to 1750 cc with water.

This method of preparation gives crystals which form latent image preferentially at the surface, as shown below:

A 200 cc sample of the suspension was exposed for one minute at a distance of 6 feet from a 100 w lamp in the liquid state at 35C. with efficient stirring, held at this temperature for 5 minutes, then coated on glass plates and allowed to dry. Two of these plates were then developed, one for 15 minutes in Dl9b developer 6 and the other for 5 minutes in D19b containing 20 g/liter of hypo, after first bleaching for 5 minutes in 3 percent potassium ferricyanide and rinsing in water for 5 minutes. The first plate had a density of 3.6, while the second had a density of 0.92, showing that the latent image was predominantly on the surface of the grains.

A second sample was exposed in exactly the same manner and subjected to 10 pAg cycles in the following manner. 1.0 N silver nitrate solution was added to give a silver ion excess (pAg 5.0), the suspension held for 15 seconds, then 0.95 N potassium bromide, 0.05 N potassium iodide solution (the same bromide-iodide ratio as the silver halide crystals) was added to restore the halide excess (pAg 8.5) followed by another 15 seconds holding. The quantities of the solutions added for each part of the cycle had been pre-detennined by electrometric titration of a separate sample. At the conclusion of the ten cycles, the suspension was coated on glass and dried as before. In this case, however, a plate developed for 5 minutes in Dl9b had a density of 0.31, while one developed in. the D19b containing hypo, without preliminary bleach, had a density of 2.40.

It would thus appear that the passage through successive baths of silver and halide ions had in fact laid down a shell of fresh silver halide on the crystals covering the latent image. Development then only occurs when solvent is present to remove this shell. Further runs showed that for most dyes the major degree of desensitization is suppressed after six or seven cycles and after ten cycles little further improvement can be observed.

EXAMPLE 2 A fully chemically sensitized fast negative bromoiodide emulsion of 8 mole percent iodide content with mainly triangular grains of average edge length 1.55 p. and thickness 0.3 ,u was subjected to 10 pAg cycles as in Example 1 but using a 0.75 N potassium bromide, 0.25 N potassium iodide solution to restore the pAg to the higher level. On coating plates, exposing and developing for 5 minutes in D19b at 20C, only a ghost image resulted. Addition of 20 g/liter of sodium thiosulphate to the developer gave an image of speed and contrast only slightly lower than that of the uncycled emulsion.

EXAMPLE 3 Addition of 0.44 grams of the sensitizing dye 3-3- dimethyl-9-ethyl-4,5,4', 5-di|benzothiacarbocyanine iodide (E =1. 12v and E, =+0.58v) per mole of silver halide to the pAg cycled emulsion of Example 2 yielded an emulsion that gave an internal image of normal dye sensitivity, judged by a wedge spectrogram, but again virtually no image when developed in a surface developer. A similar result was obtained even when the dye was added to the emulsion before the pAg cycles.

EXAMPLE 4 A pure bromide emulsion with monodispersed grains of octahedral habit and edge-length 0.51 p. was prepared, and sulphur sensitized to optimum speed by digestion for 30 minutes at 65C with 3.5 mg sodium thiosulphate per mole Ag. One portion was then subjected to 10 pAg cycles as in Example 2, and film coatings with 225 mg Ag per square foot were prepared of 1. the untreated emulsion 2. the same as l, with the addition of 400 mg of the sensitizating dye anhydro-bis-(5,6-dichloro-l- 7 ethyl-3 ,3 -sulfobutyl-2-benzimidazole) trimethinecyanine hydroxide (E =1.60v and E =-l-.53v) 3. the pAg cycled emulsion EXAMPLE 6 The same cycling conditions and solutions were used as in Example 5,'but a fully digested cubic-grained 4. the same as 3, with theaddition of the sensitizing g emulsion of the Same grain Size was p y d while the sensitizing dye was a merocyanine, 3-carbox- Strips of the film were exposed on an Eastman IB seny y -b I sitometer through blue (Wratten 47B) and minus blue t y h -y )-p P- -y (Wratten 12 58) filters, and developed in D19 devell0 thlothlazohd'4'one (Er= l-47V and Eu=O-53v)' The oper for 3 minutes at 20C A further set was exposed results Show that 9 Cycles 1 to PP in the Same way and developed in D19 developer to the surface sensitiv1ty of a cubic emuls1on, but agam which 10 g of sodium thiosulphate has been added per the desensmzmg acne of the dye reduced" liter. The results are shown below, the speeds quoted bemg the relat1ve log speeds for a density of 0.1 above 15 D19 Development D19 10 gm! g- Sodium Thiosulphate Number Sensi- Minus Minus of pAg tizing Blue Blue Blue Blue cycles Dye Speed Y Speed Speed Y Speed Developer Compositions D19 Dl9b 0 0 2.55 1.68 2.37 0.88 p-methylamlnophenol sulphate 2.0 g 2.2 g 20 0 400 mg 1,10 1.70 1.53 1.03 1.25 1.43 sodium sulphite (anhydrous) 90.0 g 72.0 g A hydroquinone 8.0 g 8.8 g 10 0 1.95 0.34 2.47 0.85 sodium carbonate 45.0 g 48.0 g 10 400 mg/ 2.02 0.50 2.32 2.17 0.77 2.57 potassium bromide 5.0 g 4.0 g mole Ag water to 1 liter 1 liter 20 0 0.20 2.24 0.66

Examples 5 and 6 show further that the reduction of desensitization by dyes may be obtained when insuffisflmple Blue P u Minus ue posure cient silver halide has been added to reduce the surface speed speed sensitivity substantially, so that normal commercial de- D19 Development velopers with no added solvent may still develop the la- Comm 337 tent image effectively. 2. Control dye 0.30 1.82 0.69 1.54 3. 1O pAg cycles 0 0 EXAMPLE 7 (ghost) L Q cycles 0 2 U 0 U 3 5 lntemal latent image emulsions may be used for preyc g 05 D19 +Sodium Thiosulphate Development panng dlrect p p Images y uslng treat 1 Came] 2,19 8] ment and processing as revealed e.g. 1n Bntish Pat. 3 Control y Specification No. 581,773 and US. Pat. Nos. 2' :8 S2: :3; gig 1 1 2,568,786 and 2,497,875. The emulsions prepared by dye 0 pAg cycling technlque of the present mventlon may be used in the same manner. Thus a pAg cycled emulsion coating prepared and coated as in Example 4 was exposed and processed with a viscous processing solution. EXAMPLE 5 The solution contained 20 g sodium hydroxide, 40 g so- The gradual covering of the sensivitity is shown in dium Sulphite, 1 g 0f Potassium bromide, g 'P this example. The same emulsion, cycling technique, y -r3y g y q g sensitizing dye and development conditions were used y -N 'p' lf y and 2 g y y y as in Example 4, but this time film coatings were made 1056 one hue of f Th l$ Viscous fleveloper was after different numbers of pAg cycles. In the following Spread on the emulslon coatmg at a thlckness of P results, the speeds quoted are relative log speeds for a Proxlmately after 45 secsdel/Flopmem at density of 0.3 above fog after 3 minutes D19 developb Yempferaturer w SFOPPed by f the l ment at 206C tron w1th d1lute acet1c acid, and the image fixed w1th sodium thiosulphate solution in the normal way. The image thus obtained was a direct positive image of ap- Number of without Dye with Dye Minus 55 proximately the same speed as the negative images ob- P cycles Blue Blue Blue tained by internal image development.

Speed Y Speed Y Speed 0 2.16 2.66 0.60 1.60 1.04 EXAMPLE 8 I, 3'32 {23 Portions of the bromide emulsion of Example 4 were g 7: sensitized with a variety of dyes, while other portions of 10 0 0 0 0 0 this emulsion were subjected to one pAg cycle using the solutions of Example 2. The sensitizers used were: A. (3,3-diethylbenzothiazole) heptamethinecyanine This illustrates that the emulsion was ent1re1y coni di E 72 Eu :0 2 verted to an internally sensitized emulsion lacking sur- B. (3,3'-dicthylbenzoselenazole)pentamethinecyaface sensitivity in 10 pAg cycles and that in 5 cycles the major portion of surface sensitivity had been internalized.

nine bromide, E 0.84 E, 0.46. C. (5,5-dichloro-3,3'-diethylbenzothiazole) trimethincyanine iodide E 0.86 E 0.84.

D. (1,3-diethyl-2-imidazo-[4,5-6]quinoxaline) 1- methyl-2-phenyl -3-indole) dimethinecyanine iodide, E 0.63 E, 1.0.

E. (l,3-diallyl-2-imidazo-[4,5,-6]quinoxaline) (3,5,-

dimethyl-1-phenyl-4-pyrazole) dim ethinecyanine iodide, E -0.52 E l.0 calc. 2.14

Strips of the film were exposed as in Example 4 and developed using a normal commercial surface developer for 5 minutes at 21C. The results are shown below.

Blue Speed Minus Blue Speed N0 pAg N0 pAg Cycle cycle Cycle cycle Control for dye A 2.04 2.03

25mg dye A/mol 1.17 1.58 0.35 1.16 Control for dye B 1.85 1.90

150mg Dye B/mol 0.58 1.67 0.40 1.55 Control for dye C 2.1 1 1.74

400mg dye C/mol 0.97 1.16 0.91 1.27 Control for dye D 2.05 2.27

25mg dye D/mol 1.37 2.16 0.98 2.26 Control for dye E 2.22 1.98 5mg dye E/mol 1.05 1.70

(Dye E does not extend the spectral sensitivity far enough to give minus blue speed figures).

EXAMPLE 9 A polydispersed, high speed sulfur and gold sensitized bromoidide emulsion was pAg cycled as follows:

A 1.0 N solution of silver nitrate was added to the chemically sensitized emulsion at 40C until a pAg of 4.0 was obtained. The emulsion was then held for seconds. A 1.0 N solution of halide salts (a mixture of potassium bromide and potassium iodide, 1 1.2 mole percent iodide) was then added to bring the pAg up to 8.0. The above procedure was repeated five times, and the emulsion was then adjusted to a pAg of 8.1.

To portions of the pAg cycled emulsion and the parent emulsion were added the infrared sensitizing dye 3,3-diethylselenadicarbocyanine ethylsulfate at 0, 100, 200, 400 and 800 mg dye per silver mole. The emulsions were then coated on a film support, exposed and developed for 6 minutes in Kodak Developer D-l9 to which a silver halide solvent had been added. The following results were observed:

At 100 mg of dye per silver mole and at all higher levels of dye the parent emulsion was severely desensitized in the blue region. At 200 mg of dye per mole of silver the parent emulsion produced no response in the infrared region of the spectrum. By contrast the pAg cycled emulsion showed improved infrared spectral sensitization with maximum infrared speed being achieved at 200 mg of dye per mole of silver.

The invention has been described with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

1 claim:

1. A method of making an internally sensitive photographic silver halide emulsion in which additional silver halide is precipitated onto silver halide grains of a surface sensitive or surface fogged silver halide emulsion characterized in that alternate excesses of silver ions and halide ions are caused to be present during precipitation.

2. A method according to claim 1 characterized in that the alternate excesses comprise a pAg adjustment cycle in which sufficient silver salt is caused to be present to adjust the pAg of the emulsion so that an excess of silver ions are present as compared to halide ions and sufficient alkali metal halide salt is then caused to be present to adjust the pAg so that an excess of halide ions are present as compared to silver ions.

3. A method according to claim 2 in which the silver salt is silver nitrate and the alkali metal salt is potassium halide.

4. A method according to claim 3 in which the potas sium halide is at least one of potassium bromide and potassium iodide.

5. A method according to claim 2 in which the alternate excesses take place at a temperature of not more than 40C and for times of from 15 to 30 seconds for each part of the pAg adjustment cycle.

6. A method according to claim 5 in which the pAg is at least 4 when an excess of silver ions are present and up to 10 when as excess of halide ions are present.

7. A method according to claim 5 in which the pAg is in the range of from 4 to 6.5 when an excess of silver ions are present and in the range of from 8 to 10 when an excess of halide ions are present.

8. A method according to claim 2 in which at least 3 pAg cycles are employed.

9. A method according to claim 5 in which at least 7 pAg cycles are employed.

10. A method according to claim 1 in which the surface sensitive or surface fogged silver halide emulsion is a silver bromoiodide emulsion.

11. A method according to claim 1 in which a spectral sensitizing dye or a desensitizer is caused to be present in the internally sensitive photographic silver halide emulsion.

12. A method according to claim 1 1 in which the sensitizing dye or desensitizer is added to the internally sensitive silverhalide photographic emulsion after the precipitation of additional silver halide onto the grains.

13. A method according to claim 1 l in which the sensitizing dye or desensitizer is added to the internally sensitive silver halide emulsion in a concentration that would at least partially desensitize the surface sensitive emulsion.

14. A method according to claim 13 in which the sensitizing dye or desensitizer is added to the internally sensitive silver halide emulsion in a concentration that would producea loss in blue speed sensitivity in a sulfur and gold surfacesensitized silver bromoiodide emulsion (6 mole percent iodide) of similar grain size of at least 0.3 log E when developed in surface developer Kodak D-19.

15. A method according to claim 11 in which a desensitizer is caused to be present having a cathodic polarographic half-wave potential less negative than 1 .0 volt.

16. A method according to claim 1 in which the surface sensitive emulsion has been chemically sensitized on its surface.

17. A method according to claim 16 in which the surface sensitive emulsion has been sulfur sensitized 18. A method according to claim 1 including the additional step of fogging the internally sensitive photographic silver halide emulsion to form an emulsion useful in forming direct positive images.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,9l7, t85 DATED November t, 1975 INVENTOR(S) John Morgan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, first column, after "[58] Field of Search" and before "[56] References Cited", insert --[30] Foreign Application Priority Date British Application 2687 filed January 18, 1973 British Application 15127 filed March 29, l973; column 2, line 5, "Aalfonso" should read --Alfonso.

Column 2, line 3, "3,271,175" should read --3,27l,l57--.

Column 3, line l t, "preferably" should read --preferable--; line 55, "a few" should read --as few.

Column t, line 12, "absorbed" should read -adsorbed.

Column 8, line 20, L00 mg mole Ag" (table, second column) should read tOO mg/mole Ag-.

Column 9, line 3, after 1.0.", insert --calc. l. t9--; line 21, (table, column t), 0.98" should read -O.93--.

Signed and Scaled this T wenty-seventh D 3) of June I978 [SEAL] Attest:

RU MASON DONALD W. BANNER Arresting O/ficer Commissioner of Patents and Trademarks

Claims (18)

1. A METHOD OF MAKING AN INTERNALLY SENSITIVE PHOTOGRAHIC SILVER HALIDE EMULSION IN WHICH ADDITIONAL SILVER HALIDE IS PERCIPITATED ONTO SILVER HALIDE GRAINS OF A SURFACE SENSITIVE OR SURFACE FOGGED SILVER HALIDE EMULSION CHARACTERIZED IN THAT ALTERNATE EXCESS OF SILVER IONS AND HALIDE IONS ARE CAUSED TO BE PRESENT DURING PRECIPITATION.

2. A METHOD ACCORDING TO CLAIM 1 CHARACTERIZED IN THAT THE ALTERNATE EXCESS COMPRISE A PLAG ADJUSTMENT CYCLE IN WHICH SUFFICIENT SILVER SALT IS CAUSED TO BE PRESENT TO ADJUST THE PAG OF THE EMULSION SO THAT AN EXCESS OF SILVER IONS ARE PRESENT AS COMPARED TO HALIDE IONS AND SUFFICIENT ALKALI METAL HALIDE SALT IS THEN CAUSED TO BE PRESENT TO ADJUST THE PAG SO THAT AN EXCESDD OF HALIDE IONS ARE PRESENT AS COMPARED TO SILVER IONS.

3. A method according to claim 2 in which the silver salt is silver nitrate and the alkali metal salt is potassium halide.

4. A method according to claim 3 in which the potassium halide is at least one of potassium bromide and potassium iodide.

5. A method according to claim 2 in which the alternate excesses take place at a temperature of not more than 40*C and for times of from 15 to 30 seconds for each part of the pAg adjustment cycle.

6. A method according to claim 5 in which the pAg is at least 4 when an excess of silver ions are present and up to 10 when as excess of halide ions are present.

7. A method according to claim 5 in which the pAg is in the range of from 4 to 6.5 when an excess of silver ions are present and in the range of from 8 to 10 when an excess of halide ions are present.

8. A method according to claim 2 in which at least 3 pAg cycles are employed.

9. A method according to claim 5 in which at least 7 pAg cycles are employed.

10. A method according to claim 1 in which the surface sensitive or surface fogged silver halide emulsion is a silver bromoiodide emulsion.

11. A method according to claim 1 in which a spectral sensitizing dye or a desensitizer is caused to be present in the internally sensitive photographic silver halide emulsion.

12. A method according to claim 11 in which the sensitizing dye or desensitizer is added to the internally sensitive silver halide photographic emulsion after the precipitation of additional silver halide onto the grains.

13. A method according to claim 11 in which the sensitizing dye or desensitizer is added to the internally sensitive silver halide emulsion in a concentration that would at least partially desensitize the surface sensitive emulsion.

14. A method accOrding to claim 13 in which the sensitizing dye or desensitizer is added to the internally sensitive silver halide emulsion in a concentration that would produce a loss in blue speed sensitivity in a sulfur and gold surface sensitized silver bromoiodide emulsion (6 mole percent iodide) of similar grain size of at least 0.3 log E when developed in surface developer Kodak D-19.

15. A method according to claim 11 in which a desensitizer is caused to be present having a cathodic polarographic half-wave potential less negative than -1.0 volt.

16. A method according to claim 1 in which the surface sensitive emulsion has been chemically sensitized on its surface.

17. A method according to claim 16 in which the surface sensitive emulsion has been sulfur sensitized

18. A method according to claim 1 including the additional step of fogging the internally sensitive photographic silver halide emulsion to form an emulsion useful in forming direct positive images.