Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified radiation sensitive composition with color...
Reexamination Certificate
1999-03-10
2002-07-16
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified radiation sensitive composition with color...
Reexamination Certificate
active
06420103
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of silver halide light sensitive photographic elements, and in particular to photographic elements having at least one yellow imaging layer comprising a yellow dye forming coupler and an alkyl citrate coupler solvent.
BACKGROUND OF THE INVENTION
Various techniques are known for dispersing hydrophobic photographically useful compounds such as photographic couplers into photographic element layer coating compositions comprising hydrophilic colloids.
Photographic dye forming couplers, as well as other hydrophobic photographically useful compounds, are typically incorporated into a hydrophilic colloid layer of a photographic element by first forming an aqueous dispersion of the couplers and then mixing such dispersion with the layer coating solution. An organic solvent is typically used to dissolve the coupler, and the resulting organic solution is then dispersed in an aqueous medium to form the aqueous dispersion.
The organic phase of these dispersions frequently includes high boiling or permanent organic solvents, either alone or with low boiling or water miscible solvents which are removed after dispersion formation. Permanent high boiling solvents have a boiling point sufficiently high, generally above 100° C. and preferably above 150° C. at atmospheric pressure, such that they are not evaporated under normal dispersion making and photographic layer coating procedures. Permanent high boiling coupler solvents are primarily used in the conventional “oil-protection” dispersion method whereby the organic solvent remains in the dispersion, and thereby is incorporated into the emulsion layer coating solution and ultimately into the photographic element.
The conventional “oil in water” dispersion method for incorporating hydrophobic couplers is described, e.g., in U.S. Pat. No. 2,322,027 by Jelly and Vittum. In such conventional process, the coupler is dissolved in a high boiling water immiscible solvent, mixed with aqueous gelatin, and dispersed using a colloid mill or homogenizer. The presence of the high boiling solvent provides a stable environment for the hydrophobic coupler, as well as generally increasing the reactivity of the coupler upon photographic processing.
A wide variety of organic solvents have been disclosed for use in dispersing photographic couplers and other photographically useful compounds. The choice of solvent or solvents to be used in a specific coupler dispersion formulation is governed by the desire to achieve a proper balance of dispersing properties with photographic performance properties. Dispersing properties include dissolution of the photographic couplers and additional photographic useful materials, dispersability in gelatin to form a fine particle dispersion, stability of the dispersion with respect to growth in particle size and crystallization of the photographic couplers and materials both in cold storage and in a melted state. Photographic properties which can be affected by the coupler solvent choice include the amount of dye formed under certain processing conditions, the hue of the dye, and the stability of the dye image to light, heat and humidity. The cost of the solvent, its effects on the environment, and its physical properties such as boiling point, viscosity, refractive index and the like are also important factors.
In formulating dispersions for yellow image dye-forming couplers, it is particularly important to balance photographic reactivity with dye stability to light, as yellow image dyes in photographic materials typically perform poorer relative to cyan and magenta image dyes with respect to dye image light stability, especially in view of recent advances obtained for magenta dye light stability. Phthalic acid esters such as dibutylphthalate have been found to be effective coupler solvents for yellow image dye-forming couplers, and have been commercially used. Such solvents, however, have been identified as possessing potentially undesirable biological properties. Hence, it is desired to identify alternative solvents to be used with yellow couplers which are more benign in terms of their potential health and environmental effects, but which still provide all the desirable photographic properties.
Citrate esters are a known class of organic solvents which have been suggested for use in photographic elements as in U.S. Pat. No. 5,286,616. Citrate ester solvents may be acetylated or non-acetylated. Non-acetylated citrate ester solvents have a free hydroxyl group, while the acetylated citrate ester solvents replace the hydrogen in the hydroxyl group with an acetyl group, —COOR, where R is an alkyl or aryl substituent.
The selection of an alternative solvent specifically for use with yellow dye forming couplers has required significant exploration and research in order to provide a coupler dispersion which provides desired functionality. It would be desirable to provide a silver halide photographic element which contains a yellow image forming layer comprising a yellow coupler and a coupler solvent which meets such objectives.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the invention, a silver halide light sensitive photographic element is disclosed comprising a support bearing at least one yellow image forming hydrophilic colloid layer comprising a yellow dye-forming coupler and a trialkyl citrate coupler solvent of the formula C
3
H
4
(OH)(CO
2
R)
3
, where each R independently represents an alkyl group and the total number of carbon atoms for the three R groups combined is greater than 6.
In accordance with a particular embodiment of the invention, a color paper photographic element is disclosed comprising a reflective support bearing cyan, magenta and yellow dye forming silver halide emulsion hydrophilic colloid layer units sensitized to the red, green and blue regions of the spectrum, wherein the yellow dye forming unit comprises at least one layer hydrophilic colloid layer comprising a yellow dye-forming coupler and a trialkyl citrate coupler solvent as described above.
We have found that the combination of such citrate ester solvents with yellow dye forming couplers in photographic elements surprisingly leads to both good reactivity and good image-dye light stability. The advantages of the invention are particularly useful for photographic color paper elements on reflective supports, although they will also be useful for motion picture print film and other projection or display films on transparent or diffuse supports.
DETAILED DESCRIPTION OF THE INVENTION
The photographic elements of the invention comprise at least one yellow image forming hydrophilic colloid layer comprising a yellow image dye forming coupler and a trialkyl citrate coupler solvent of the formula C
3
H
4
(OH)(CO
2
R)
3
, where each R independently represents an alkyl group and the total number of carbon atoms for the three R groups combined is greater than 6. Citrate ester solvents used in accordance with the invention preferably are of the following formula (I):
wherein each of R
1
, R
2
and R
3
independently represents an alkyl group and the sum of the number of carbon atoms in R
1
, R
2
and R
3
combined is at least 7, more preferably at least 9 and less than or equal to 30, and most preferably from 12 to 18. The alkyl groups may be substituted with photographically acceptable substituents which do not substantially detrimentally effect photographic performance. Specific examples of citrate ester solvents for use in accordance with the invention include the following solvents I-1 through I-6, wherein the R
1
, R
2
and R
3
groups are indicated in reference to formula (I) above.
Solvent
R
1
R
2
R
3
I-1
Butyl
Butyl
Butyl
I-2
Propyl
Propyl
Propyl
I-3
Hexyl
Hexyl
Hexyl
I-4
2-ethylhexyl
2-ethylhexyl
2-ethylhexyl
I-5
Methyl
Ethyl
Butyl
I-6
Ethyl
Ethyl
Propyl
Particularly preferred solvents include I-1 (tributyl citrate), I-2 (tripentyl citrate), and I-3 (trihexyl citrate).
Couplers that form yellow dyes upon reaction with oxidized color developing agent and which
Honan James S.
Miller David D.
Rosiek Thomas A.
Thomas Brian
Anderson Andrew J.
Eastman Kodak Company
Le Hoa Van
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