US2703282A - Increasing the exposure latitude of photographic emulsions by sensitizing - Google Patents

Increasing the exposure latitude of photographic emulsions by sensitizing Download PDF

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US2703282A
US2703282A US200865A US20086550A US2703282A US 2703282 A US2703282 A US 2703282A US 200865 A US200865 A US 200865A US 20086550 A US20086550 A US 20086550A US 2703282 A US2703282 A US 2703282A
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emulsion
sensitizing
latitude
emulsions
sodium
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Burt H Carroll
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Eastman Kodak Co
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C1/00—Photosensitive materials
    • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
    • G03C1/06—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein with non-macromolecular additives
    • G03C1/08—Sensitivity-increasing substances
    • G03C1/10—Organic substances
    • G03C1/102—Organic substances dyes other than methine dyes

Definitions

  • Claim. (Cl. 957) This invention relates to photography and particularly to a method of sensitizing silver halide emulsions to increase latitude.
  • Latitude as used in photographic terminology is the distance along the exposure axis of the characteristic curve in which an increase in exposure produces a substantially uniform increase in density, that is, it is the projected distance along the exposure axis of the straight line portion of the characteristic curve (Mees, Theory of Photographic Process .(1942) page 701). In the present case, latitude was measured as the distance along the exposure axis between the points where the gamma of the characteristic curve was 0.3 in the toe and 0.6 in the shoulder.
  • Total scale is defined as the distance along the exposure axis of the characteristic curve, between the extreme ends, that is, the toe-and shoulder of the characteristic curve. This includesreg'ions of underand over-exposure (Mees, supra, page 703).
  • Speed of the photographic material is expressed for present purposes as the reciprocal of the inertia of the material, that is,
  • Gamma is the tangent of the angle between the straight line portion of the characteristic curve and the exposure axis (Mees, supra, page 700).
  • my method of increasing latitude comprises 1 sensitizing a silver halide emulsion, for example, a silver bromide or silver chlorobromide emulsion, withean optical sensitizing dye, sensitizing another portion of the same emulsion with a different optical sensitizing dye for the same spectral region but which gives a different speed,
  • My method of sensitizing differs from super-sensitizing in that the optical sensitizers may, and normally will, each sensitize as though the other were not present.
  • the existence of super-sensitizing action of one or the other would not, however, prevent the use of my method; it will very rarely occur, however, since almost all of each of the dyes must remain on the grains to which they were originally added.
  • My method differs from emulsions designed to give variable contrast (U. S. Patent 2,384,598) in that the two sensitizers used must sensitize for the same spectral .region.
  • optical sensitizing dye used according to my invention should be relatively nondifrusing since the dyes must be retained on the silver halide grains to .whichthey are originally attached. Dyes of the following classes are suitable for use according to my invention.
  • Carbocyanines derived from fl-naphthothiazole substituted in the central position of the chain by alkyl or aryl groups (Brooker U. S. Patent 1,846,301). include Corresponding dyes from ,B-naphthothiazole nuclei substituted in the nucleus by halogen, alkyl or alkoxy may also be used.
  • the alkyl groups on the 3-positions may be replaced by hydroxyalkyl or carboxyalkyl, and the aryl group in the 9-position may be substituted by alkyl, halogen or alkoxy. These are red sensitizers.
  • Carbocyanines derived from substituted benzothiazole or benzselenazole substituted in the central position of the chain by alkyl or aryl groups for example, 3 ,3 ,9-triethyl-5 ,5 -dichloroselenacarbocyanine bromide (made by the method of White U. 8. 1,990,681 using 5-chloro-2-methyl-benzoselenazole instead of Z-methyl benzoselenazole). Theseare re'd sensitizers.
  • optical sensitizing dyes are used according to my invention at a concentration of from about 4 to 50 milligrams of sensitizing dye per liter of emulsion containing about 0.25 gram mole of silver halide per liter of emulsion, the preferred concentration varying with the dye and with the grain size of the emulsion in accordance with normal sensitizing practice. An excess of dye is to be avoided because .it .leaves unabsorbed dye which diffuses to grains carrying the other dye.
  • the sensitizing dyes of groups 1 to 4 above have the following structure:
  • R3 hydrogen, alkyl or aryl
  • R2 and R4 hydrogen and aryloxy
  • Ra being hydrogen when R2 and R4 are aryloxy
  • R2 and R4 being hydrogen when R3 is alkyl or aryl.
  • Example I A gelatino-silver chlorobromide emulsion containing gram mole of silver chlorobromide per liter was divided into two equal portions. To one portion there was added an alcoholic solution of the red sensitizer 3,3'-dimethyl-9-ethyl-4,5,4',5'-dibenzthiacarbocyanine chloride, 0.058 gram of sensitizer per mole of silver halide being used. The emulsion was digested for about five minutes at 50 C. with the dye. A portion of this emulsion was cooled to the coating temperature of approximately 38 C.
  • Example 2 The characteristics of the blend on exposure to red light were found to be 10/i Speed 113 Gamma 2.35 Latitude 55 or more Example 2 Two portions of the chlorobromide emulsion used in Example 1 were separately sensitized as described in Example 1 with different optical sensitizing dyes.
  • One-half of the emulsion was sensitized with the green sensitizer 3,3,9 triethyl 5,5 diphenyl oxacarbocyaniue bromide, 0.078 gram of sensitizer being used per mole of silver halide and the other half of the emulsion was sensitized with the green sensitizer l (2 benzothiazolyl) 3 methyl 4 [l methyl 2(1) B naphthothiazolylidene 1 ethylethylidene] 5 pyrazolone (see U. S. Patent 2,231,659, Example 15), 0.029 gram of sensitizer being used per mole of silver halide.
  • the portion sensitized with the first-mentioned dye when exposed through a Wratten Filter No. 1.2 transmitting light of about 500 to about 700 millimicron wave length was found to have a speed of 63, gamma of 3.46 and latitude of 12.5.
  • the portion sensitized with the second-mentioned dye when exposed and processed in the same way was found to have a speed of 19, gamma of 3.82 and latitude of about 16.
  • the blend when exposed and processed in the same way was found to have a speed of 54, gamma of 2.45 and latitude of or more.
  • Example 3 A portion of the emulsion sensitized to red light as described in Example was mixed with an equal amount of the emulsion sensitized to green light as described in Example 2, and the mixture was coated directly after mixing.
  • This method is useful in producing either black and white or color emulsions. It is especially useful in mixed grain processes of color photography where two or more batches of silver halide sensitive to spectral regions are incorporated in the same emulsion layer. In such cases it is desirable to have sufficient latitude in each of the difierent spectral regions so that the exposure light in the various spectral regions can be balanced to produce images having similar characteristic curves. The advantage in freedom from ditferences in development rate of the blended emulsions is obvious. My method also provides a blending procedure which is uniformly reproduceable from emulsion to emulsion.
  • I mean sensitizing for longer wave length than about 500 millimicrons in the case of a silver bromoiodide emulsion, about 450 millimicrons in the case of a pure silver bromide emulsion, or about 400 millimicrons in the case of a pure silver chloride emulsion; that is, the sensitizing should be for a longer wave length than the natural sensitivity or absorption of the emulsion.
  • the method of increasing the exposure latitude of a gelatino-silver halide emulsion which comprises dividing said emulsion into two approximately equal parts, sensitizing one part of said emulsion to red light with a 3,3- dimethyl 9 ethyl 4,5,4,5' dibenzthiacarbocyanine salt, sensitizing the other part of said emulsion to red light with a' 3,3-dimethyl-9-phenyl-4,5,4',5'-dibenzthiacanbo'cyanine salt, and mixing the parts so sensitized.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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  • General Physics & Mathematics (AREA)
  • Silver Salt Photography Or Processing Solution Therefor (AREA)
  • Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)

Description

United States Patent Burt H. Carroll, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application December 14, 1950, Serial No. 200,865
1 Claim. (Cl. 957) This invention relates to photography and particularly to a method of sensitizing silver halide emulsions to increase latitude.
Latitude as used in photographic terminology is the distance along the exposure axis of the characteristic curve in which an increase in exposure produces a substantially uniform increase in density, that is, it is the projected distance along the exposure axis of the straight line portion of the characteristic curve (Mees, Theory of Photographic Process .(1942) page 701). In the present case, latitudewas measured as the distance along the exposure axis between the points where the gamma of the characteristic curve was 0.3 in the toe and 0.6 in the shoulder.
Total scale is defined as the distance along the exposure axis of the characteristic curve, between the extreme ends, that is, the toe-and shoulder of the characteristic curve. This includesreg'ions of underand over-exposure (Mees, supra, page 703).
Speed of the photographic material .is expressed for present purposes as the reciprocal of the inertia of the material, that is,
where k is a constant and i is the inertia.
Gamma is the tangent of the angle between the straight line portion of the characteristic curve and the exposure axis (Mees, supra, page 700).
It is well known that silver halide emulsions of difierent speeds maybe blended to increase latitude (Neblette, Brehm and Priest, Elementary Photography (1942), pages 190 and 191). "Emulsions of different speeds may also be coated in separate layers'forthesamepurpose. This arrangement always has the probability that development rates ofthe emulsions will'not be thesame so that the characteristic curve will be distorted except under a singledevelopment condition.
It is therefore an object of the presentinvention to provide a method for increasingthe latitude ofa-photographic emulsion. A further object is to provide a method for increasing latitude without seriously changing the gamma orotherwise distorting the characteristic curve. Other objects will appear from the following description of my invention.
These. objects are accomplished by sensitizing diiferent portions of an emulsion with difierent optical sensitizers for the same spectral region and then mixing the portions so sensitized.
-In general, my method of increasing latitude comprises 1 sensitizing a silver halide emulsion, for example, a silver bromide or silver chlorobromide emulsion, withean optical sensitizing dye, sensitizing another portion of the same emulsion with a different optical sensitizing dye for the same spectral region but which gives a different speed,
2,703,282 Patented Mar. 1, 1955 about 25% of any one emulsion. It is also possible to coatthe emulsions as separate layers rather than mixing them and coating as a single layer.
My method of sensitizing differs from super-sensitizing in that the optical sensitizers may, and normally will, each sensitize as though the other were not present. The existence of super-sensitizing action of one or the other would not, however, prevent the use of my method; it will very rarely occur, however, since almost all of each of the dyes must remain on the grains to which they were originally added. My method differs from emulsions designed to give variable contrast (U. S. Patent 2,384,598) in that the two sensitizers used must sensitize for the same spectral .region.
It is obvious that the optical sensitizing dye used according to my invention should be relatively nondifrusing since the dyes must be retained on the silver halide grains to .whichthey are originally attached. Dyes of the following classes are suitable for use according to my invention.
(1) Carbocyanines derived from fl-naphthothiazole substituted in the central position of the chain by alkyl or aryl groups (Brooker U. S. Patent 1,846,301). include Corresponding dyes from ,B-naphthothiazole nuclei substituted in the nucleus by halogen, alkyl or alkoxy may also be used. The alkyl groups on the 3-positions may be replaced by hydroxyalkyl or carboxyalkyl, and the aryl group in the 9-position may be substituted by alkyl, halogen or alkoxy. These are red sensitizers.
(2) Carbocyanines derived from substituted benzothiazole or benzselenazole substituted in the central position of the chain by alkyl or aryl groups, for example, 3 ,3 ,9-triethyl-5 ,5 -dichloroselenacarbocyanine bromide (made by the method of White U. 8. 1,990,681 using 5-chloro-2-methyl-benzoselenazole instead of Z-methyl benzoselenazole). Theseare re'd sensitizers.
(3) 3,3 dimethyl -'8,10 aryloxythiacarboxyanines and oxacarbocyanines (Brooker and .White U. S. Patent 2,478,366). These include 3;3'-dimethyl-8,IO-m-toloxythiacarbocyanine bromide and -3,3'-dimethyl-8,l0-m-toloxyoxacarbocyanine bromide. These are red and green sensitizers, respectively.
(4) Carbocyanines derived from S-phenyl benzoxazole and S-(p-tolyl) benzoxazole substituted in the central position of the chain by alkyl or aryl groups, for example, 3,3',9'-triethyl-5 ,5 -diphenyl oxacarbocyanine bromide (See British Patent 496,116). These are green sensitizers.
(5) Complex merocyanines of U. S. Patent 2,454,629.
(6) Merocyanines derived from l-benzothiazolyl-S- pyrazolone, such as those disclosed in Brooker U. S. Patent 2,211,762.
The optical sensitizing dyes are used according to my invention at a concentration of from about 4 to 50 milligrams of sensitizing dye per liter of emulsion containing about 0.25 gram mole of silver halide per liter of emulsion, the preferred concentration varying with the dye and with the grain size of the emulsion in accordance with normal sensitizing practice. An excess of dye is to be avoided because .it .leaves unabsorbed dye which diffuses to grains carrying the other dye.
The sensitizing dyes of groups 1 to 4 above, have the following structure:
These where Z and Z=the atoms necessary to complete a B-naphthothiazole, 5-aryl benzoxazole or 5-aryl benzothiazole ring,
R and R1==alky1,
R3=hydrogen, alkyl or aryl,
R2 and R4=hydrogen and aryloxy, Ra being hydrogen when R2 and R4 are aryloxy, and R2 and R4 being hydrogen when R3 is alkyl or aryl.
The following table illustrates the increase in latitude which may be accomplished by blending suitable sensitized emulsions according to my invention.
My invention will now be described by reference to the following specific examples.
Example I A gelatino-silver chlorobromide emulsion containing gram mole of silver chlorobromide per liter was divided into two equal portions. To one portion there was added an alcoholic solution of the red sensitizer 3,3'-dimethyl-9-ethyl-4,5,4',5'-dibenzthiacarbocyanine chloride, 0.058 gram of sensitizer per mole of silver halide being used. The emulsion was digested for about five minutes at 50 C. with the dye. A portion of this emulsion was cooled to the coating temperature of approximately 38 C.
coated and tested. Characteristics to red light exposure were found to be 10/i Speed 130 Gamma 3.40 Latitude 19 To the second portion of emulsion there was added an alcoholic solution of the red sensitizer 3,3'-dimethyl-9- phenyl-4,5,4,5-dibenzthiacarbocyanine chloride, 0.058 gram of sensitizer being added per mole of silver halide. The emulsion was digested at 50 C. and a portion was cooled to 38 C., coated and tested. Characteristics to red light exposure were found to be 10/ i Speed Gamma 3.70 Latitude 10 The remaining portions of both emulsions were cooled to the coating temperature of 38 C. and blended and coated without delay. The characteristics of the blend on exposure to red light were found to be 10/i Speed 113 Gamma 2.35 Latitude 55 or more Example 2 Two portions of the chlorobromide emulsion used in Example 1 were separately sensitized as described in Example 1 with different optical sensitizing dyes. One-half of the emulsion was sensitized with the green sensitizer 3,3,9 triethyl 5,5 diphenyl oxacarbocyaniue bromide, 0.078 gram of sensitizer being used per mole of silver halide and the other half of the emulsion was sensitized with the green sensitizer l (2 benzothiazolyl) 3 methyl 4 [l methyl 2(1) B naphthothiazolylidene 1 ethylethylidene] 5 pyrazolone (see U. S. Patent 2,231,659, Example 15), 0.029 gram of sensitizer being used per mole of silver halide.
Upon coating and testing the emulsions separately, the portion sensitized with the first-mentioned dye when exposed through a Wratten Filter No. 1.2 transmitting light of about 500 to about 700 millimicron wave length was found to have a speed of 63, gamma of 3.46 and latitude of 12.5. The portion sensitized with the second-mentioned dye when exposed and processed in the same way was found to have a speed of 19, gamma of 3.82 and latitude of about 16. After blending the emulsions, the blend when exposed and processed in the same way was found to have a speed of 54, gamma of 2.45 and latitude of or more.
Example 3 A portion of the emulsion sensitized to red light as described in Example was mixed with an equal amount of the emulsion sensitized to green light as described in Example 2, and the mixture was coated directly after mixing.
After drying, the coating was exposed to a color chart and was processed as follows, all of the solutions being at 68 F.:
(l) Prehardened in the following solution for 3 minutes:
Sodium hexametaphosphate grams 0.5 Sodium bisulfite do 10 Formaldehyde (40% solution) cc 27 Sodium carbonate grams 10 Sodium sulfate do.. Potassium bromide do 2.5
Water to 1 liter.
(2) Washed for four minutes. (3) Developed in a black and white developer of the following composition for 8 minutes:
Grams Sodium hexametaphosphate Sodium sulfide 40 N-methyl-p-aminophenol sulfate 5.5 Hydroquinone 2.2 Sodium metaborate 25 Sodium thiocyanate 0.45 Potassium bromide 4.5 6-nitrobenzimidazole .02
Water to 1 liter.
(4) Washed for 10 minutes.
(5) Reexposed to red light through a Wratten No. 70 filter.
(6) Developed in a cyan developer of the following composition for 15 minutes:
Grams Sodium hexametaphosphate 0.5 Sodium sulfite 5 2-amino-5-diethylaminotoluene hydrochloridenu 2.8 Sodium carbonate 15 Potassium bromide 1.5 6-nitrobenzimidazole 0.15
2,4-dichloro-5-p-toluene sulfonamino-l-naphth'oL 0.4 Sodium hydroxide 2. Water to 1 liter.
Grams Sodium hexametaphosphate 0.5 Sodium sulfite 5 2-amino-5-diethyl toluene hydrochloride 2 Sodium carbonate 20 Potassium bromide 1 6-nitrobenzimidazole .01 Z-cyanoacetyl coumarone 2.5 Sodium hydroxide 2 Water to 1 liter.
l2) Washed for 10 minutes. (13) Treated for four minutes in the following ferrocyanide bath:
Grams Sodium hexametaphosphate 1 Potassium ferricyanide 80 Potassium bromide 40 Water to 1 liter.
(14) Fixed fortwo minutes in the following bath:
. Grams Sodium hexametaphosphate 10 Sodium sulfite 10 Sodium thiosulfate 320 Water to 1 liter.
( 15) Washed for 20 minutes. The image thus produced was satisfactory from the standpoint of color separation and image quality.
-It is apparent that my method has resulted in a substantial increase in the latitude of the blended emulsion.
This method is useful in producing either black and white or color emulsions. It is especially useful in mixed grain processes of color photography where two or more batches of silver halide sensitive to spectral regions are incorporated in the same emulsion layer. In such cases it is desirable to have sufficient latitude in each of the difierent spectral regions so that the exposure light in the various spectral regions can be balanced to produce images having similar characteristic curves. The advantage in freedom from ditferences in development rate of the blended emulsions is obvious. My method also provides a blending procedure which is uniformly reproduceable from emulsion to emulsion.
Where I refer in the claims'to sensitizing for a spectral region of longer wave length than that which is appreciably absorbed by said emulsion, I mean sensitizing for longer wave length than about 500 millimicrons in the case of a silver bromoiodide emulsion, about 450 millimicrons in the case of a pure silver bromide emulsion, or about 400 millimicrons in the case of a pure silver chloride emulsion; that is, the sensitizing should be for a longer wave length than the natural sensitivity or absorption of the emulsion.
It will be understood that my invention is to be taken asllirilited only by the scope of the appended claim.
c aim:
The method of increasing the exposure latitude of a gelatino-silver halide emulsion, which comprises dividing said emulsion into two approximately equal parts, sensitizing one part of said emulsion to red light with a 3,3- dimethyl 9 ethyl 4,5,4,5' dibenzthiacarbocyanine salt, sensitizing the other part of said emulsion to red light with a' 3,3-dimethyl-9-phenyl-4,5,4',5'-dibenzthiacanbo'cyanine salt, and mixing the parts so sensitized.
References Cited in the file of this patent OTHER REFERENCES Wall, Photographic Emulsions (1929), publ. by American Phot. Pub. Co., Boston; pp. -137.
Clerc, Photographic Theory and Practice, 2nd ed. (1931), publ. by Sir Isaac Pitman & Sons, Ltd., N. Y., p.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1113873B (en) * 1959-01-17 1961-09-14 Wolfen Filmfab Veb Process for sensitizing halide silver emulsions
US3003870A (en) * 1957-04-17 1961-10-10 Eastman Kodak Co Alteration of characteristic curve of zinc oxide electrophotographic materials
US3628960A (en) * 1967-04-21 1971-12-21 Agfa Gevaert Nv Light sensitive halide material with variable contrast

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1900869A (en) * 1931-08-25 1933-03-07 Eastman Kodak Co Color photographic material
US1926643A (en) * 1924-10-14 1933-09-12 Bialon Konrad Multicolor layer for color-photography and process of manufacturing the same
US1980941A (en) * 1927-11-12 1934-11-13 Leopold D Mannes Color photography
US2029946A (en) * 1932-12-10 1936-02-04 Chem Ind Basel Process of making photographic emulsions
US2295276A (en) * 1938-06-23 1942-09-08 Gen Aniline & Film Corp Photographic emulsion
US2384598A (en) * 1941-03-14 1945-09-11 Eastman Kodak Co Photographic material
US2388859A (en) * 1940-01-11 1945-11-13 Eastman Kodak Co Mixed grain emulsions
US2620272A (en) * 1947-05-12 1952-12-02 Bell & Howell Co Variable contrast photographic material and process of preparing it

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1926643A (en) * 1924-10-14 1933-09-12 Bialon Konrad Multicolor layer for color-photography and process of manufacturing the same
US1980941A (en) * 1927-11-12 1934-11-13 Leopold D Mannes Color photography
US1900869A (en) * 1931-08-25 1933-03-07 Eastman Kodak Co Color photographic material
US2029946A (en) * 1932-12-10 1936-02-04 Chem Ind Basel Process of making photographic emulsions
US2295276A (en) * 1938-06-23 1942-09-08 Gen Aniline & Film Corp Photographic emulsion
US2388859A (en) * 1940-01-11 1945-11-13 Eastman Kodak Co Mixed grain emulsions
US2384598A (en) * 1941-03-14 1945-09-11 Eastman Kodak Co Photographic material
US2620272A (en) * 1947-05-12 1952-12-02 Bell & Howell Co Variable contrast photographic material and process of preparing it

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3003870A (en) * 1957-04-17 1961-10-10 Eastman Kodak Co Alteration of characteristic curve of zinc oxide electrophotographic materials
DE1113873B (en) * 1959-01-17 1961-09-14 Wolfen Filmfab Veb Process for sensitizing halide silver emulsions
US3628960A (en) * 1967-04-21 1971-12-21 Agfa Gevaert Nv Light sensitive halide material with variable contrast

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