Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-07-22
2003-10-28
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S611000, C430S620000, C430S631000
Reexamination Certificate
active
06638708
ABSTRACT:
FIELD OF INVENTION
This invention relates to dispersions of silver (carboxylate-n-alkyl thiolate) particles. The carboxylates are typically silver salts of long chain fatty acids and the thiolates are compounds that function as antifoggant compounds. These silver (carboxylate-n-alkyl thiolate) particles can be used to formulate imaging forming compositions that are useful in photothermographic or thermographic imaging elements.
DESCRIPTION RELATIVE TO PRIOR ART
Thermographic and photothermographic materials and imaging elements are well known in the photographic art. These materials are also known as heat developable photographic materials. Thermographic materials can form an image by the imagewise application of heat. Photothermographic materials include a light sensitive material, for example a silver halide. After imagewise exposure photothermographic materials are heated to moderately elevated temperatures to produce a developed image in the absence of separate processing solutions or baths.
An example of a known photothermographic silver halide material comprises (a) a hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer with (b) an organic solvent mixture, (c) a hydrophobic binder and (d) an oxidation-reduction image-forming composition. The oxidation-reduction imaging forming composition typically comprises (i) a silver carboxylate that is usually a silver salt of a long-chain fatty acid, such as silver behenate or silver stearate, in combination with (ii) an organic reducing agent, such as a phenolic reducing agent. It has been desirable to have hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer in such a photothermographic material because of the higher photosensitivity of the silver halide emulsion and the ease of control in preparation of the emulsion based on conventional aqueous silver halide gelatino emulsion technology.
A problem has been encountered in preparing these photothermographic silver halide materials. This problem involves the mixing of a hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer with an oxidation-reduction imaging forming composition. The imaging forming composition contains hydrophobic components including a hydrophobic binder, such as poly(vinyl butyral), and a silver salt of a long-chain fatty acid, such as a silver salt of behenic acid. Typically, when the hydrophilic photosensitive silver halide emulsion is mixed with the hydrophobic imaging forming materials and then coated on a suitable support to produce a photothermographic element, the resulting element produces a less than desired degree of photosensitivity, contrast and maximum density upon exposure and heat processing. This problem has been encountered in photothermographic silver halide materials, as described in, for example, U.S. Pat. No. 3,666,477 of Goffe, issued May 30, 1972. Goffe proposed addition of alkylene oxide polymers and a mercaptotetrazole derivative to the photothermographic material to help provide increased photosensitivity. In addition, a variety of organic solvents have been proposed in order to help prepare a photothermographic silver halide composition containing the described image-forming components. The organic solvents that have been proposed include isopropanol, acetone, toluene, methanol, 2-methoxyethanol, chlorinated solvents, acetone-toluene mixtures and certain non-aqueous polar organic solvents. The described individual solvents, such as isopropanol, have not provided the desired improved properties. There has been a continuing need to provide improved relative speed and contrast with the desired maximum image density while minimizing fog formation.
Recent developments have focused on providing imaging compositions, for example photothermographic compositions, that are aqueous based. Such compositions, compared to organic solvent-based compositions, have numerous coating advantages. For example, expensive organic solvent recovery systems are not necessary in the coating process.
It is known in the prior art (for example Katoh EP 0 803 764 A1) that mercapto (or thiol), disulfide and thion compounds may be added for the purposes of retarding or accelerating development, controlling development, improving spectral sensitization efficiency, and improving storage stability before and after development. Preferred compounds have structures represented by Ar—SM and Ar—S—S—Ar wherein M is a hydrogen atom or alkali metal atom, and Ar is an aromatic ring or fused aromatic ring having at least one nitrogen, sulfur, oxygen, selenium or tellurium atom.
Besides being expensive, the above mentioned compounds are in general hydrophobic solids. This means that they require special techniques such as media milling to prepare dispersions that are compatible with aqueous photothermographic elements. Simpler mercapto compounds that are less expensive, are water soluble but have the distinct disadvantage of having the characteristic ‘rotten egg’ smell of mercaptans. Non water soluble liquid mercaptans have the further disadvantage of tending to destabilize the colloids typically used to prepare aqueous photothermographic elements.
It is thus desirable to have a photothermographic compostions that incorporate mercaptans while avoiding the above mentioned expense and difficulty. It is particularly desirable to provide these compositions in an aqueous medium so that they can be conveniently coated.
SUMMARY OF THE INVENTION
In one aspect of the invention, there is provided a dispersion of silver-carboxylate particles having incorporated therein an n-alkyl thiolate compound. The invention can provide an aqueous nanoparticulate dispersions of silver (carboxylate-n-alkyl thiolate) particles that provide desired silver development kinetics and image density, while maintaining low fog. The invention also provides elements with superior keeping performance.
As noted, a characteristic of the present invention is that the silver-carboxylate particles have an n-alkyl thiolate compound incorporated into the structure of the particles. Being incorporated into the particle means that the n-alkyl thiolate is not free but rather is part of the particle in the same sense, for example, as would be a dopant. One of the characteristics of such a particle is that the x-ray diffraction pattern resembles the pattern obtained from the silver-carboxylate. In contrast, if silver carboxylate particles are simply mixed with silver-thiolate particles, a second novel crystallographic phase would be observed in the x-ray diffraction pattern of the mixture. These particles will be referred to as “silver (carboxylate-n-alkyl thiolate) particles”.
As will be seen from the comparative examples, it is important that the thiolates be n-alkyl thiolates. Similar compositions, except using tertiary-alkyl thiolates, do not produce the same desirable results. Similarly, it is important that the n-alkyl thiolate be incorporated in the particles. As the comparative examples show, simply mixing the n-alkyl thiolate with silver (carboxylate) particles does not produce the desired result.
In preferred embodiments of the invention, the silver (carboxylate-n-alkyl thiolate) particles incorporated into the aqueous or non aqueous composition exhibit nanoparticulate morphology. It is particularly preferred that at least a portion of the non-photosensitive source of reducible silver ions be provided in the form of a nanoparticulate dispersion of silver (carboxylate-n-alkyl thiolate) particles. By nanoparticulate, we mean that the silver (carboxylate-n-alkyl thiolate) particles in such dispersions preferably have a weight average particle size of less than 1000 nm when measured by any useful technique such as sedimentation field flow fractionation, photon correlation spectroscopy, or disk centrifugation. In one particular method of measuring particle size and its distribution is determined using a Horiba LA-920, He—Ne, laser particle size analyzer. This analyzer measures the particle size distribution by angular light scattering techniq
Dickinson David A.
Ghyzel Peter J.
Lelental Mark
Pitt Alan R.
Wear Trevor J.
Chea Thorl
Eastman Kodak Company
Hawley J. Jeffrey
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