Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-05-29
2003-09-23
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
Reexamination Certificate
active
06623918
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to the preparation of radiation sensitive high bromide silver halide photographic emulsions. It particularly relates to the preparation of the exterior portions of silver halide emulsion grains after formation of a core.
DEFINITION OF TERMS
In referring to grains and emulsions containing two or more halides, the halides are named in order of ascending concentrations.
The term “high bromide” and “high chloride” in referring to silver halide grains and emulsions indicate greater than 50 mole percent bromide or chloride, respectively, based on total silver.
The term “equivalent circular diameter” or “ECD” indicates the diameter of a circle having an area equal to the projected area of a grain or particle.
The term “size” in referring to grains and particles, unless otherwise described, indicates ECD.
The term “regular grain” refers to a silver halide grain that is internally free of stacking faults, which include twin planes and screw dislocations.
The term “tabular grain” is one having two parallel crystal faces that are clearly larger than any other crystal face and in which the ratio of ECD to grain thickness, referred to as aspect ratio, is at least two.
A tabular grain emulsion is an emulsion in which tabular grains account for greater than 50 percent of total grain projected area.
The term “central portion” or “core” in referring to silver halide grains refers to an interior portion of the grain structure that is first precipitated relative to a later precipitated portion.
The term “shell” in referring to silver halide grains refers to an exterior portion of the silver halide grain which is precipitated on a central portion.
The term “dopant” is employed to indicate any material within the rock salt face centered cubic crystal lattice structure of a silver halide grain other than silver ion or halide ion.
The term “dopant band” is employed to indicate the portion of the grain formed during the time that dopant was introduced to the grain during precipitation process.
The term “normalized shell molar addition rate”, hereinafter assigned the symbol R
s
, is a measure of the intensity of rate of addition of silver salt solution to a reaction vessel during formation of a shell. R
s
is defined by the formula:
R
s
=
M
s
M
t
t
s
2
where M
s
is the number of moles of silver halides added to the reaction vessel during the formation of the shell, t
s
is the run time, in minutes, of the silver salt solution for the formation of the shell, and M
t
is total moles of silver halides in the reaction vessel at the end of the precipitation.
The term “log E” is the logarithm of exposure in lux-seconds.
Photographic speed is reported in relative log units and therefore referred to as relative log speed. 1.0 relative log speed unit is equal to 0.01 log E.
The term “contrast” or “&ggr;” is employed to indicate the slope of a line drawn from stated density points on the characteristic curve.
The term “rapid access processing” and “rapid access processor” are employed to indicate the capability of providing dry-to-dry processing in 90 seconds or less. The term “dry-to-dry” is used to indicate the processing cycle that occurs between the time a dry, imagewise exposed element enters a processor to the time it emerges, developed, fixed and dry.
Research Disclosure
is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England.
BACKGROUND OF THE INVENTION
Double-jet precipitation is a common practice in the making of silver halide emulsions. Silver salt solution and halide salt solution are introduced simultaneously, but separately, into a precipitation reactor under mixing. In order to achieve desired crystal characteristics, typically, the silver ion activity or the halide ion activity is controlled during the precipitation by adjusting the feed rates of the salt solutions using either a silver ion sensor or a halide ion sensor.
Formation of silver halide emulsions typically involves a crystal nuclei-forming step wherein addition of silver ion results primarily in the precipitation of new crystal nuclei, and a subsequent double-jet growth step wherein the rate at which silver and halide are introduced is controlled to primarily grow the crystals already previously formed while avoiding the formation of new seed grains, i.e., renucleation. Addition rate control to avoid renucleation, and thereby generally provide for a more monodisperse grain size final grain population, is generally well known in the art, as illustrated by Wilgus German OLS No. 2,107,118; Irie U.S. Pat. No. 3,650,757; Kurz U.S. Pat. No. 3,672,900, Saito U.S. Pat. No. 4,242,445; Teitschied et al European Patent Application 80102242; “Growth Mechanism of AgBr Crystals in Gelatin Solution”, Photographic Science and Engineering, Vol. 21, No. 1, January/February 1977, p. 14, et seq. The term “critical crystal growth rate” is used in the art to describe the growth rate obtained at the maximum rate of silver ion and halide ion addition which does not produce renucleation. While maintaining silver and halide addition rates below that which form new grain populations is advantageous during grain growth in terms of controlling the emulsion grain population characteristics, it also can restrict obtainable emulsion concentrations (i.e., batch yields) and lengthen emulsion manufacturing times.
U.S. Pat. Nos. 5,549,879; 6,043,019; 6,048,683 and 6,265,145 disclose double jet techniques for preparing silver halide grains wherein silver and halide salt solutions are added at a “pulsed flow” rate designed to generate a second grain population (i.e., at a rate above that which would provide for the critical crystal growth rate), with multiple short “pulses” being separated by hold periods designed to allow the new grain population to be ripened out. U.S. Pat. No. 5,549,879, e.g., discloses introducing an aqueous silver nitrate solution from a remote source by a conduit which terminates close to an adjacent inlet zone of a mixing device, which is disclosed in greater detail in
Research Disclosure
, Vol. 382, February 1996, Item 38213. Simultaneously with the introduction of the aqueous silver nitrate solution and in an opposing direction, aqueous halide solution is introduced from a remote source by a conduit which terminates close to an adjacent inlet zone of the mixing device. The mixing device is vertically disposed in a reaction vessel and attached to the end of a shaft, driven at high speed by any suitable means. The lower end of the rotating mixing device is spaced up from the bottom of the vessel, but beneath the surface of the aqueous silver halide emulsion contained within the vessel. Baffles, sufficient in number to inhibit horizontal rotation of the contents of the vessel are located around the mixing device. The described apparatus is operated in a “pulse flow” manner comprising the steps of: (a) providing an aqueous solution containing silver halide particles having a first grain size; (b) continuously mixing the aqueous solution containing silver halide particles; (c) simultaneously introducing a soluble silver salt solution and a soluble halide salt solution into a reaction vessel of high velocity turbulent flow confined within the aqueous solution for a time t, wherein high is at least 1000 rpm; (d) simultaneously halting the introduction of the soluble silver salt solution and the soluble halide salt solution into the reaction for a time T wherein T>t, thereby allowing the silver halide particles to grow; and (e) repeating steps (c) and (d) until the silver halide particles attain a second grain size greater than the first grain size. Advantages of the pulse flow technique described include permitting easier scalability of the precipitation method. There is no disclosure of use of such pulse flow technique to enable larger emulsion concentrations (i.e., batch yields) or shorten emulsion manufacturing times. To the contrary, the disclosed need for relatively long hold times between pulsed addition of silver and halide s
Hasberg Dirk J.
Jones, Jr. Ralph W.
Mehta Rajesh V.
Anderson Andrew J.
Eastman Kodak Company
Le Hoa Van
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