[0001] This invention relates to a new red and infrared dye-forming naphtholic couplers
and to silver halide photographic elements and processes employing such couplers.
[0002] Photographic elements comprising red and infrared dye-forming naphtholic couplers
are known. Such red and infrared dye-forming couplers are useful in, for example,
integral dye sound track images in motion picture films. An example of such a photographic
element is described in U.S. Patent 4,250,251 and U.S. Patent 4,178,183.
[0003] Although numerous red and infrared dye-forming couplers are known, a continuous
search has gone on for novel naphtholic couplers which produce dyes which absorb in
the red and infrared regions of the spectrum and which improve, or optimize for particular
applications, particular properties of the coupler. For example, a search has gone
on for novel naphtholic couplers which form red or infrared absorbing dyes which are
bathochromically shifted and have broad absorption peaks. Satisfactory couplers sought
preferably should provide reduction or elimination of silver needed for a sound track
image while maintaining dye image stability, reactivity and compatibility with other
components in the photographic element. The resulting dyes need to have the desired
dye hue and need to be particularly stable to fading, such as fading induced by heat
or ferrous ion solutions.
[0004] The present invention provides a novel class of red or infrared dye-forming naphtholic
couplers having a group Y in the 5-position on the naphtholic coupler that is capable
of promoting formation of red or infrared dye of increased stability. The group Y
in the 5-position of the naphtholic coupler has sufficient bulk to provide a bathochromic
shift in absorption of the resulting red or infrared dye formed upon oxidative coupling.
[0005] A photographic element according to the invention comprises a support bearing a photographic
silver halide emulsion and a dye-forming coupler, wherein the dye-forming coupler
is a naphtholic coupler capable of oxidative coupling to form a red or infrared absorbing
dye and comprising,
(a) hydrogen or a coupling-off group in the coupling position;
(b) a group, in the position ortho to the hydroxy group, which is represented by the
formula:
-

-R , wherein R is a substituent which enables the dye formed upon oxidative coupling
to absorb in the red or infrared region of the spectrum, preferably unsubstituted
or substituted alkoxy,
aryloxy, or

wherein R₁ is unsubstituted or substituted alkyl, heterocyclic, or unsubstituted
or substituted aryl group, provided that when R₁ is aryl substituted by fluorosulfonyl,
then further substituents are other than alkoxy or sulfone groups; and,
(c) a group Y in the 5-position on the naphtholic coupler which is capable of promoting
red or infrared dye formation and wherein the group Y has sufficient bulk to provide
a bathochromic shift in absorption of the resulting red or infrared dye. Combinations
of a fluorosulfonyl substituent on an R₁ aryl group with either alkoxy or sulfone
substituents leads to dye instability, especially in the fixing bath during processing.
[0006] The red or infrared dye-forming naphtholic coupler moiety as described can be any
red or infrared dye-forming naphtholic coupler moiety upon which the group Y is substituted
in the 5-position to provide a bathochromic shift in absorption in the red or infrared
dye formed from such a coupler moiety upon oxidative coupling. An example of such
a naphtholic coupler moiety is represented by the formula:

wherein
X is hydrogen or a coupling-off group;
R is a substituent which enables the dye formed upon oxidative coupling to absorb
in the red or infrared region of the spectrum, preferably unsubstituted or substituted
alkoxy, aryloxy, or

wherein R₁ is unsubstituted or substituted alkyl, heterocyclic group, such as a 5
or 6 member heterocyclic group or unsubstituted or substituted aryl, as defined;
Y is a group having sufficient bulk to provide bathochromic shift in absorption of
the red or infrared dye formed.
[0007] The group Y can be any group substituted in the 5-position of the naphtholic coupler
moiety and which has sufficient bulk to provide a bathochromically shifted absorption
in the red or infrared absorbing dye formed. Group Y is typically selected from the
group consisting of

alkylthio, alkyl, aryl, alkoxy, aryloxy, arylthio, carbonamido, carbamoyl, sulfonamido,
sulfamyl, ureido, sulfamido, heterocyclic, imido, ureido, and phosphonamido groups,
each of which groups is unsubstituted or substituted by means of at least one group
which increases steric bulk, and wherein R₂ and R₃ are individually hydrogen, unsubstituted
or substituted alkyl or aryl, or together are the atoms necessary to complete a five
or six member heterocyclic ring and wherein at least one of R₂ and R₃ is other than
hydrogen. An example of a preferred group Y is represented by the formula:

wherein R₃ is substituted or unsubstituted aryl, such as aryl containing 6 to 50
carbon atoms; substituted or unsubstituted alkyl, such as alkyl containing 4 to 24
carbon atoms; or
-SO₂R₄ or

-R₄ wherein R₄ is substituted or
unsubstituted aryl, such as aryl containing 6 to 50 carbon atoms; substituted or unsubstituted
alkyl, such as alkyl containing 1 to 30 carbon atoms; or heterocyclic.
[0008] Examples of such Y groups are as follows:

[0009] The naphtholic coupler moiety can contain substituents in other positions than the
2- and 5-positions. These substituents can be substituents known in the photographic
art to be useful on red or infrared dye-forming naphtholic couplers. The coupling
position of the naphtholic coupler, that is the 4-position, can be unsubstituted or
substituted by a coupling-off group which can modify the equivalency of the coupler,
its reactivity, its stability its dispersibility or which, upon release from the coupler,
interacts with other components of the photographic element of components of the processing
solutions.
[0011] The red or infrared dye-forming naphtholic couplers according to the invention can
be synthesized by methods known in the organic synthesis art. The process of synthesis
typically involves first attachment of the bulky substituent to an amino group in
the 5-position of a 2-carboxy-1-naphthol and then conversion of the 2-carboxy group
to its corresponding amide or ester. An illustrative method of preparation is as follows:
Synthesis Example A-

[0012] To a stirred solution of 20.3 gm (0.1 mol) 2-carboxy-5-amino-1-naphthol (1) in 700
ml tetrahydrofuran containing 36.4 gm (0.3 mol) dimethylaniline and 30 ml water
was added dropwise 31.1 gm (0.1 mol) 2,4-di-
tert-pentyl-phenoxyacetyl chloride (2). After 3 hours at room temperature the reaction
mixture was poured into ice-water containing 15 ml concentrated hydrochloric acid.
The resulting solid precipitate was collected, washed, and recrystallized from alcohol
and then from aqueous dimethylformamide to yield a gray solid, m.p.>200°C. Elemental
analysis, nmr, and infrared spectra were used to identify the desired intermediate
2-carboxy-1-naphthol compound (3).
[0013] Then, 30 ml of thionyl chloride was added dropwise to a stirred solution of 9.6 gm
(0.02 mol) (3) in 30 ml tetrahydrofuran. After 3 hours at room temperature, the volatile
components were removed at reduced pressure and room temperature. A solution of the
resultant acid chloride in 50 ml tetrahydrofuran was added dropwise to a stirred
solution of 3-amino-4-chlorobenzenesulfonyl fluoride in 30 ml tetrahydrofuran. After
3 hours at room temperature, the reaction mixture was poured into ice-water containing
15 ml of concentrated hydrochloric acid and the product was collected, washed, and
dried. Ethyl acetate recrystallization yielded the desired white solid product, m.p.
245-246°C, with the correct elemental analysis for the desired naphtholic coupler.
[0014] The couplers of this invention can be used in the ways and for the purposes that
couplers are used in the photographic art.
[0015] Typically, the couplers are incorporated in silver halide emulsions and the emulsions
coated on a support to form a photographic element. Alternatively, the couplers can
be incorporated in photographic elements adjacent to the silver halide emulsion where,
during development, the coupler will be in reactive association with development products
such as oxidized color developing agent. Thus, as used herein, the term "associated
therewith" signifies that the coupler is in the silver halide emulsion layer or in
an adjacent location where, during processing, it will come into reactive association
with silver halide development products.
[0016] The photographic elements can be single color elements or multicolor elements. Multicolor
elements contain dye image-forming units sensitive to each of the three primary regions
of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple
emulsion layers sensitive to a given region of the spectrum. The layers of the element,
including the layers of the image-forming units, can be arranged in various orders
as known in the art. In an alternative format, the emulsions sensitive to each of
the three primary regions of the spectrum can be disposed as a single segmented layer,
e.g., as by the use of microvessels as described in Whitmore U.S. Patent 4,362,806,
issued December 7, 1982.
[0017] A typical multicolor photographic element comprises a support bearing a cyan dye
image-forming unit comprised of at least one red-sensitive silver halide emulsion
layer having associated therewith at least one cyan dye-forming coupler, a magenta
dye image-forming unit comprising at least one green-sensitive silver halide emulsion
layer having associated therewith at least one magenta dye-forming coupler and a yellow
dye image-forming unit comprising at least one blue-sensitive silver halide emulsion
layer having associated therewith at least one yellow dye-forming coupler, at least
one of the layers of the element comprising a coupler of this invention. The element
can contain additional layers, such as filter layers, interlayers, overcoat layers,
subbing layers, and the like.
[0018] The silver halide emulsions employed in the elements of this invention can be either
negative-working or positive-working.
[0019] The red and infrared dye-forming naphtholic couplers are particularly useful in combination
with coupler solvents.
[0020] The red or infrared dye-forming naphtholic coupler is useful in a photographic element
in any location that enables the formation of red or infrared dye from the coupler
upon oxidative coupling during processing. The coupler can, for example, be in at
least one silver halide photographic emulsion layer, an overcoat layer, an interlayer,
or in various combinations of layers of a photographic element.
[0021] An illustrative element is a photographic element comprising a support bearing at
least one silver halid photographic emulsion layer comprising a coupler according
to the invention and a coupler solvent as described. The photographic element can
be used, for example, for forming a sound track or for forming a silver image and
a sound track. In a preferred photographic element a coupler as described enables
formation of an integral dye sound track. If a sound track comprising both dye and
silver is desired, the coupler can be of the bleach inhibitor release (BIR) type;
that is, it can release a bleach inhibitor. The bleach inhibitor moiety is conventionally
attached to the coupling position either directly or through a timing group.
[0022] Coupler solvents contemplated for use in combination with the above couplers include,
for example lower alkyl esters of phthalic acid, lower alkyl substituted triphenyl
phosphates and lower alkyl N-substituted aliphatic amides having at least 10 carbon
atoms.
[0023] The following are exemplary of preferred coupler solvents:
dimethyl phthalate
diethyl phthalate
di-
n-butyl phthalate
di-
i-amyl phthalate
di-
n-amyl phthalate
tri-
o-cresyl phosphate
tri-
m-cresyl phosphate
tri-
p-cresyl phosphate
o-cresyl diphenyl phosphate
N,N-diethyl lauramide
N,N-di-
n-butyl lauramide
N,N-diethyl capramide.
[0024] Coupler to coupler solvent weight ratios of from 5:1 to 1:2 are generally preferred.
For the lower alkyl esters of phthalic acids employed as coupler solvents it is preferred
that the coupler to solvent weight ratio be in the range of from 1:1 to 1:2. For the
triphenyl phosphate coupler solvents it is preferred that the weight ratio of coupler
to coupler solvent be in the range of from 4:1 to 1:1. For the N-substituted aliphatic
amides it is preferred that the weight ratio of coupler to coupler solvent be in the
range of from 4:1 to 2:1.
[0025] Coupler solvents of the type described above and techniques for dissolving couplers
therein are known to those skilled in the art. Techniques are also well known for
dispersing coupler-containing coupler solvents in hydrophilic colloid-containing
coating compositions useful in forming photographic elements. The coupler-containing
coupler solvent is typically dispersed in the hydrophilic colloid-containing coating
composition in the form of particles of relatively small size, typically from about
0.3 to about 3.0 microns in mean diameter, usually by colloid milling.
[0026] The term "integral sound track" indicates that a sound track and a photographic image
are formed in separate portions of the same element and that following exposure the
separate areas are concurrently and identically processed (i.e. requiring no process
steps other than those required for processing the photographic image portion) to
form sound track and photographic records, respectively.
[0027] In a form capable of recording multicolor images the photographic element contains
in addition to the support and the single layer unit described above at least two
additional layer units. The single layer unit described above can contain a red-sensitized
silver halide emulsion and be employed to form a cyan dye image as well as an infrared
absorbing dye image. The same dye can form both the cyan and the infrared absorbing
dye image, but is preferred in that instance that the single layer unit described
above be modified to include in addition a conventional cyan dye-forming coupler.
The cyan dye-forming coupler is preferably dispersed in separate coupler solvent particles
from those containing the infrared absorbing dye-forming coupler or coated without
employing a coupler solvent. A second layer unit is present containing a blue-sensitive
silver halide emulsion and a yellow dye-forming coupler, and a third layer unit is
present containing a green-sensitized silver halide emulsion and a magenta dye-forming
coupler. The construction of the second and third layer units and their relationship
to the first layer unit is conventional.
[0028] In another form, which is specifically preferred, the photographic element is provided
with four separate layer units. Three layer units are conventional cyan, magenta and
yellow dye-forming layer units of the type found in conventional silver halide photographic
elements intended to form multicolor dye images. The fourth layer unit can be identical
to the single layer unit described above. In a preferred form the silve halide emulsion
in the fourth layer unit is sensitized to a portion of the spectrum to which the remaining
layers are relatively insensitive. For example, the fourth layer unit emulsion can
be spectrally sensitized to the infrared portion of the spectrum or to portions of
the visible spectrum which lie at the fringes of the spectral regions the remaining
layer units are intended to record.
[0029] Still other variant forms of the photographic elements can be employed. For example,
the emulsion of the sound track layer unit can be employed with only its native spectral
sensitivity. In this instance the response of the sound track layer unit is confined
to exposure to ultraviolet and the adjacent blue portion of the spectrum, the blue
response varying to some extent with the silver halide chosen. In still another variant
form the speed rather than the spectral response of the sound track recording layer
unit can be different from that of another, image-forming layer unit. The sound track
recording layer can be either faster or slower than an image-forming layer unit of
similar spectral response. A combination of both differing spectral response and speed
can also be employed to allow selective exposure of the sound track and image-forming
layer units.
[0030] While any photographically useful amount of particles of the infrared absorbing dye-forming
coupler and coupler solvent can be present in the layer units described above, for
sound track applications employing typical photocells it is preferred that these
particles be present in a concentration sufficient to provide a maximum dye density
of at least 1.0 over the spectral region of from 750 to 850 nm, preferably at least
2. Such dye densities can be obtained readily with the preferred coupler-coupler
solvent combinations within the concentration ranges conventionally employed for
coupler solvent particles containing cyan, magenta and yellow dye-forming couplers.
Generally, coupler concentrations ranging from about 0.40 to 1.30 g/m² are contemplated,
preferably from about 0.65 to 1.05 g/m², optimally from about 0.75 to 0.95 g/m².
[0031] The photographic silver halide emulsion layers, adjacent hydrophilic colloid-containing
layers and other layers, including overcoat, subbing and interlayer coatings of conventional
character, can contain various colloids alone or in combination as vehicles. Suitable
hydrophilic vehicle materials include both naturally-occurring substances such as
proteins, for example gelatin, gelatin derivatives, cellulose derivatives, polysaccharides
such as dextran, gum arabic and the like; and synthetic polymeric substances such
as water soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers
and the like.
[0032] The photographic elements can be prepared and can contain addenda known to be useful
in the photographic art, particularly those addenda known to be useful in photographic
elements for forming red or infrared absorbing dyes, such as described in U.S. Patent
4,250,251 and
Research Disclosure, December, 1978, Item No 17643 published by Kenneth Mason Publications, Ltd., The
Old Harbourmaster's, 8 North Street, Emsworth, Hampshire PO107DD, England.
[0033] The silver halide emulsion and remaining layers of the photographic elements can
be coated on any conventional photographic support. For projection film application
including an integral sound track the support is transparent. For such applications
conventional photographic film supports can be employed such as cellulose nitrate
film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film, poly(ethylene
terephthalate) film, polycarbonate film and similar resinous film supports.
[0034] In one preferred mode of exposure the photographic element is panchromatically exposed
and an edge portion of the film is exposed to infrared radiation to form the sound
track. When this mode of exposure is undertaken, the silver halide grains in the sound
track recording layer unit are spectrally sensitized with infrared absorbing spectral
sensitizing dyes.
[0035] The photographic elements can be processed to form dye images which correspond to
or are reversals of the silver halide rendered selectively developable by imagewise
exposure by conventional techniques. Multicolor reversal dye images can be formed
in photographic elements having differentially spectrally sensitized silver halide
layers by black-and-white development followed by a single color development step,
as illustrated by the Kodak Ektachrome E4 and E6 and Agfa processes described in
British Journal of Photography Annual, 1977, pp. 194-197, and
British Journal of Photography, pp. 668-669. The photographic elements can be adapted for direct color reversal
processing (i.e., production of reversal color images without prior black-and-white
development) (Kodak, Ektachrome, Kodacolor and Flexicolor are trademarks of Eastman
Kodak Company, U.S.A.).
[0036] Multicolor dye images which correspond to the silver halide rendered selectively
developable by imagewise exposure, typically negative dye images, can be produced
by processing, as illustrated by the Kodak Kodacolor C-22, the Kodak Flexicolor C-41
and the Agfa color processes described in
British Journal of Photography Annual, 1977, pp. 201-205. The photographic elements can also be processed by the Kodak
Ektaprint-3 and -300 processes as described in Kodak Color Dataguide, 5th Ed., 1975,
pp. 18-19, and the Agfa color process as described in
British Journal of Photography Annual, 1977, pp. 205-206.
[0037] In a specific preferred application the photographic elements are employed to form
a motion picture film for projection containing an integral sound track useful in
a projector having an S-1 photocell. The photographic element is comprised of a transparent
film support on which are coated, in the order recited, a red-sensitized cyan dye-forming
coupler containing first layer unit, a green-sensitized magenta dye-forming coupler
containing a second layer unit, a blue-sensitive yellow dye-forming coupler containing
third layer unit and an infrared-sensitized fourth layer unit containing coupler solvent
particles according to this invention, as has been described above. The picture recording
portion of the element is flashed to infrared and is then exposed to the blue, green
and red portions of the spectrum through a master image film. The master image film
has a transparent support and has been processed so that it carries a positive multicolor
dye image. The edge of the photographic element on which the integral sound track
is to be formed is panchromatically exposed through a positive sound track master
by a light source to which at least the fourth layer unit is sensitive. In a preferred
form this is a white light source which exposes the red-sensitized, green-sensitized
and blue-sensitive layer units. The fourth layer unit by reason of its native sensitivity
to blue light is also exposed by the white light source. The white light source can
also emit infrared to expose the fourth layer unit. The photographic element after
exposure of both the picture and sound track areas is reversal processed. In reversal
processing of negative-working silver halide emulsions, positive dye images are formed
in unexposed areas. Since the picture area was uniformly flashed to infrared, no density
attributable to the fourth layer unit is present in the picture area. In the sound
track area the major portion of the infrared density is attributable to the fourth
layer unit, but the other layer units can also add to the total infrared density.
[0038] In processing to form dye images in the manner described above any conventional color
developing agent can be employed which will permit the formation of a dye. Depending
upon the specific color developing agent selected, the maximum dye densities, the
wavelength of the peak densities and the increased breadth of bathochromic absorption
will vary. The color developing agent 4-amino-3-methyl-N-ethyl-N-β-(methanesulfonamido)ethylaniline
sulfate hydrate has been observed to produce infrared absorbing dye images having
a maximum density in excess of 1.0, often in excess of 2.0, not only at 800 nm, but
over the entire spectral region of from about 725 to about 850 nm.
[0039] The following examples further illustrate the invention.
Examples 1-6
[0040] Photographic elements were prepared by coating a cellulose acetate butyrate film
support with a photosensitive layer containing a silver bromoiodide emulsion at 0.91
gm Ag/m², gelatin at 3.78 g/m², and one of the couplers identified below dispersed
in one-half its weight of dibutyl phthalate and coated at 1.62 x 10
-3 moles/m². The photosensitive layer was overcoated with a layer containing gelatin
at 1.08 g/m² and bis-vinylsulfonylmethyl ether at 1.75 weight percent based on total
gelatin.
[0041] Samples of each element were exposed through a graduated-density test object and
processed at 40°C employing the following color developer Solution A:
Color Developer Solution A
[0042] 4-Amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulfate 3.55 g
Potassium sulfite 2.0 g
Potassium carbonate (anhydrous) 30.0 g
Potassium bromide 1.25 g
Potassium iodide 6.0 mg
Water to: 1.0 L
pH adjusted to: 10.0
[0043] Development was followed by the conventional steps of bleaching, fixing, washing,
and drying. Spectral absorption curves for the resulting well-defined step images
were plotted for each element to determine the dye absorption maximum (λ-max) listed
in Table I. Processed strips of each element containing a dye image were subjected
either to a six week wet oven (60°C/70% RH) keeping test or to a five minute ferrous
ion solution test.
Ferrous Ion Solution (made under nitrogen purging)
[0044] Degassed distilled water 750 ml
Ethylenediaminetetraacetic acid 32.12 g
Ammonium hydroxide (conc. soln.) 15 ml
Ferrous sulfate 7 H₂O 27.8 g
Ammonium hydroxide and water to: 1.0 L
(Nitric acid to adjust pH downward) pH 5.0
[0045] The results are given in following Table I.
[0046] The results presented in Table I indicate that the bulky C-5 substituents provide
the couplers of this invention with the capacity to form dyes of much longer wavelength
absorption than those from the comparison couplers. In addition, it can be seen that
with any given ballast group in the 2-position, increasing the bulk of the 5-substituent
generally increases the dye stability to attack by ferrous ion. Dyes produced according
to the invention are also resistant to fading under conditions of high humidity at
elevated temperatures.

Example 6
[0048] This comparative example illustrates that desirable properties of photographic couplers
comprising a napholic moiety capable of forming a red or infrared absorbing dye depend
not only upon the effects of the 5-position substituent Y, but also upon substituents
at the 2-position.
[0049] A photographic coating of very fine grain silver bromide emulsion (807 mg Ag/m²)
and 3229 mg Ag/m² of gelatin on a film support was overcoated with 1080 mg/m² of gelatin
and 86 mg/m² of bis (vinylsulfonyl) ether hardener. Strips of this element were imagewise
exposed to light through a step tablet and then developed ten minutes at 24°C in developers
prepared by adding a 2.5 ml solution containing 1.25 mmole of each of the couplers
of Table IIA in dimethylformamide to 250 mL of the following developer solution (Developer
Solution A):
Developer Solution A: CD-2 color developer (as described in column 23 of U.S. Patent
4,340,664 3.2 g
Sodium Sulfite 0.65 g
Potassium Bromide 1.0 g
Potassium Phosphate 13.25 g
Water to 1 L, pH 12
Development was followed by a 5 minute water wash, and 30 seconds in a fixer solution
(Fixer Solution A) before final water washing and drying.
[0050] The fixer sensitivity (dye density loss) was observed and indicated in following
Table II and compared with the fixer sensitivity for the dye from coupler 5 of the
invention in Part B of Table II. Coupler 5 was incorporated in an emulsion layer as
in Example 1 and, after imagewise exposure, processed in a developer solution (Developer
Solution A) containing CD-2 color developer.
[0051] Fixer Solution A had the following composition:
Ammonium Thiosulfate 120 g
Potassium Metabisulfite 20 g
Potassium Iodide 2 g
Water to 1 L

[0052] Data in Table II indicates that the presence of a fluorosulfonyl substituent on
the anilino ring can lead to undesired dye sensitivity in the fixer. The presence
of additional alkoxy or sulfone substituents appears to enhance this sensitivity while
the presence of halogen substituents stabilizes the dye. Best stability to the fixer
while maintaining the desired long wavelength absorption was achieved by a dye formed
from a coupler of this invention which contains a bulky Y group.
Examples 7-18 Coupler Solvent Effects on Dye Hue and Stability
[0053] Photographic elements were prepared and processed as in Example 1 except that both
dibutyl phthalate (DBP) and diethyl lauramide (DEL) coupler solvents were employed
as noted in Table III and color developer Solutions B and C were used which contained
2.45 g per liter of 4-amino-3-methyl-N,N-diethylaniline hydrochloride or 5.0 gm per
liter of 4-amino-3-methyl-N-ethyl-N-β-(methanesulfonamido)ethylaniline sulfate, respectively,
in place of the Solution A developing agent.
[0054] The λ-max and density at λ800 nm were determined for the dyes formed in each element
and processed strips were subjected to a 77°C low humidity keeping test for one week.
The resulting percent change in density is noted for each in Table III.

[0055] The choice of coupler solvent and coupler solvent level can affect the dye hue obtained
with any given developer. A bathochromic shift is attained by lowering the coupler
solvent level from 1:2 to 1:0.5, which often results in increased 800 nm absorption
useful for optical sound track images.
[0056] Couplers dispersed in the lower level of diethyl lauramide gave dyes with Developer
C which were among the best for resistance to fading by dry heat.
[0057] Unlike the infrared dyes of the prior art which have double peaks in their absorption
spectra indicative of microcrystallization, the infrared dyes of this invention have
broad bathochromically shifted absorptions independent of the level of residual unused
coupler present with the dye.