FIELD OF THE INVENTION
[0001] The present invention relates to a photosensitive silver halide emulsion, a method
for making such emulsion and a photosensitive material containing said emulsion. More
specifically the present invention is related to a high sensitive silver halide photographic
material with an increased image contrast.
BACKGROUND OF THE INVENTION
[0002] For several photographic applications the need exists to have the disposal of a reproduction
material which exhibits increased image contrast upon exposure to radiation and subsequent
processing. This need originates from the knowledge that image contrast (also called
'gradation') is directly related with the appearance of sharpness. Photographic products
showing increased gradation are known therefore to exhibit a higher sharpness and
a better quality of reproduced image details.
One way to increase gradation of an emulsion is by doping the emulsion with a metal
ion or its complex. The metal ion or complex, also called dopant, is therefore supplied
to the silver halide emulsion during precipitation and is incorporated in the internal
crystal structure.
Depending on the concentration of dopants in said crystal structure the photographic
properties will differ. The ligands of the dopant are also included in the crystal
structure and will modify the photographic properties as well.
Generally an increase of gradation by addition of dopants is also accompanied by a
decrease of sensitivity further depending on the kind of metal ion, its valency, ligand
structure and amount of metal-complex added during precipitation.
This sensitivity decrease can advantageously be used to make less light-sensitive
materials which can be handled under safelight conditions. In several graphic art
applications these materials are e.g. used for roomlight operations, as in contact
printing of halftone film materials where negative or positive copies are made from
screened originals by dot per dot reproduction.
The dopants which will be discussed here are characterised by building a deep electron
trap in a silver halide crystal lattice. Such trap is called 'deep' if following two
conditions are fulfilled: the LUMO of the incorporated molecular entity should be
at least 0.5 eV below the conduction band of the silver halide crystal, and the trapping
life-time at room temperature should be higher than 0.2 seconds (see R.S.Eachus, M.T.Olm
in 'Cryst.Latt.Def.and Amorph.Mat.',1989(18)297-313). The LUMO is defined as the 'lowest
unoccupied molecular orbital' of the related complex which can trap an electron from
the conduction band (see D.F.Shriver, P.W.Atkins, C.H.Langford in "Inorganic Chemistry'-Oxford
Univ.Press (1990), Oxford-Melbourne-Tokyo).
[0003] All patents which will be discussed hereinafter are related with transition metal
complexes acting as deep electron traps. From a lot of patents related with this topic
US-A 4,933,272 from McDugle et al should be mentioned. This patent discloses doping
agents containing a nitrosyl or thionitrosyl coordination ligand together with a transition
metal from the groups 5 up to 10 (also including 10) of the periodic table of the
elements. The same author describes dopants containing transition metal complexes
with carbonyl-ligands in EP-A 0 415 481. In WO 92/16876 Beavers et al describe a combination
of a homogeneously distributed deep electron trap (a transition metal complex with
a nitrosyl ligand) and a more 'shallow electron trap' (an iridium salt) in the outer
shell of the grain. The iridium-center is known to trap photo-electrons temporarily
in some cases: at room temperature the electrons will be released in a characteristic
time in the order of 0.02 to ca 10 seconds depending on the structure and composition
of the silver halide host lattice (see R.S.Eachus and M.T.Olm in the literature cited
above). Added in small amounts the said iridium dopant is especially in favour of
an improvement of the high intensity reciprocity failure and latent image stability.
Increasing the contrast as much as possible needs a rather high amount of dopant homogeneously
distributed over the crystal volume which is also required in order to keep maximum
density and to prevent solarization. This has its consequences in using automatic
processors where the increasing load of metal complexes by continuous processing asks
for special attention in regeneration afterwards. The sensitometric problems as density-loss
and solarisation can be solved by a method given by Gingello and Schmidt in EP-A 0
697 619 proposing a non-uniform incorporation of the same dopants. Therefore the metal
complexes are built in mainly in the outer region of the crystals.
Most of the emulsions doped with the metal complexes mentioned hereinbefore have a
high contrast but are suffering from low sensitivity (as is desired in the case of
roomlight-handling). It is however unacceptable for other applications like the reproduction
of colour negatives. Colour photography requires perfect matching of the characteristic
curves of the blue, green and red sensitive emulsion layers. Control of contrast and
of sensitivity for the different emulsions is necessary in order to get a final copy
with an acceptable image quality.
[0004] Minimizing the sensitivity loss by use of a dopant in order to get a gradation increase
is the special object for which a solution has to be found. Several patents are related
with problems as loss in sensitivity by doping with metal complexes while a lot of
applications on the contrary need a high gradation and a high sensitivity as well.
Normally sensitivity or speed decreases when gradation increases and vice versa. Breaking
through this 'sensitivity-gradation'-relationship is therefore the first object of
these patents.
One solution which has been proposed frequently is a chemical ripening of such an
emulsion with a labile selenium or tellurium compound. Yoshida e.g. in US-A 5,348,850
suggests an increase in sensitivity while keeping a high contrast by chemical sensitization
with labile Se- or Te-compounds and using a well defined rhodacyanine spectral sensitizer.
In this case the Se- or Te-sensitization provides a deep trap at the crystal surface
(giving high sensitivity) which is in competition with a deep internal electron trap
(giving rise to a high gradation). This way of working normally results in a silver
halide light sensitive photographic material which is very susceptible to fog formation.
Another possibility to overcome the sensitivity problem can be realised with an adapted
processing starting with a high sensitivity where the difference in developability
of the latent image of the silver halide emulsion crystals is becoming very low because
of the very high activity of the developing agent. This however can easily lead to
the formation of fog.
In EP-A 0 552 650 a silver halide material is described which has an increased sensitivity
by doping with a polyvalent metal complex. The polyvalent metal compounds used in
this case are however not satisfying the conditions of having a DET-activity (DET=deep
electron trap) incorporated in the silver halide microcrystals. The result which is
realized in an iodide containing silver halide emulsion does not show an increase
in gradation. It is also interesting to see that doping with the kind of compounds
used in EP-A 0 552 650 in combination with a internal reduction sensitization does
not lead to the desired increase of the gradation even if the complexed polyvalent
metal ion is incorporated in the center of the grain as is teached therein.
[0005] However the problem of sensitivity-loss in doped emulsion crystals can be solved
by adding a second type of dopant. This can be a temporary electron trap as IrCl
63- or even a more shallow electron trap as Ru(CN)
64- or Fe(CN)
64- which can be locally concentrated within a certain area of the crystal volume. This
has e.g. been demonstrated by Asami in EP-A 0 423 765 wherein doping with ferri- or
ferro-complexes in the outer space area of the AgCl(Br)-crystal gives an increase
of gradation and a decrease of loss in sensitivity. In US-A 5,051,344 Kuno teaches
that doping with ferro- or iridium(+3)-ions in the crystal shell of the silver halide
emulsion gives a higher gradation and sensitivity. The same effect is described by
Oozeki and Ikari in JP-A 6-222487 with a Ru-, Fe- or Ir-complex in the surface area
of the crystal. The activity of deep electron traps is also demonstrated by three
patents issued to Bell: US-A 5,474,888, US-A 5,480,771 and US-A 5,500,335 propose
the use of an [Os(NO)Cl
5]
2--complex which is uniformly distributed throughout the crystal or on its surface which
gives a very small gradation increase by an equal or little lower sensitivity. For
tabular crystals Olm et al (US-A 5,503,970), Daubendiek et al (US-A 5,503,971) and
Kuromoto et al (US-A 5,462,849) suggest that doping in epitaxilly grown protrusions
gives an increase in gradation and sensitivity.
Doping in outer regions of the silver halide crystal volume however may lead to interactions
between additives added during chemical sensitization and before coating on one hand
and superficially present metal ions at the other hand. These interactions can easily
influence preservation properties of the chemically ripened emulsion, thereby asking
for new measures in order to prevent such disadvantageous influences.
[0006] As discussed hereinbefore film systems were related with preservation of sensitivity
while increasing gradation or they were focussed on getting improved sensitivity for
the same gradation. To summarize: all these patents were targeting the same goal which
will be called hereinafter "getting a better sensitivity-gradation-relationship".
OBJECTS OF THE INVENTION
[0007] It is therefore a first object of the present invention to provide an improved method
of doping a light-sensitive silver halide photographic emulsion in order to provide
a better sensitivity-gradation-relationship for said emulsion after processing of
an exposed light-sensitive photographic material coated with said emulsion.
[0008] It is a further object of the present invention to provide a method which needs a
smaller amount of dopant in favour of ecology, in order to get a better sensitivity
and an almost unchanged gradation.
[0009] It is a further object of the present invention to provide a method for making a
light-sensitive silver halide photographic material using a silver halide emulsion
with an increased sensitivity-gradation-relationship as mentioned hereinbefore.
[0010] It is moreover an object of the present invention to provide a method for increasing
the photographic activity of a dopant incorporated in a silver halide emulsion.
[0011] Further objects of the present invention will become apparent from the description
hereinafter.
SUMMARY OF THE INVENTION
[0012] The above mentioned objects are realised by a photosensitive image-forming element
comprising on a support at least one photosensitive layer containing silver halide
crystals internally doped in the center of the crystal volume with a transition metal
complex while satisfying equation (I):

where

wherein d
1 represents a spherical equivalent diameter (SED), expressed in µm, corresponding
with a central part of said crystal doped with the said transition metal complex,
d expressed in µm represents a SED representing the whole crystal while Q represents
the concentration of the transition metal complex, expressed in 10
-9 mole/mole of silver halide and wherein the said introduced transition metal complex
has the following general formula (1):

wherein:
- M represents a metal selected from the group consisting of an element from Group 5
up to Group 10 of the Periodic System of the Elements;
- X and Y, which are different from each other, each represent one of the elements selected
from the group consisting of Cl, Br and I;
- L represents any anorganic or organic ligand but preferably a ligand selected from
the group consisting of NO, NS, OH, H2O, CN, CO, CH3CN, CNS, NCS, NO2, F, SeCN, CNSe,
TeCN, CNTe, OCN, CNO, N3 and COO;
- n and m each equals an integer having a value from 0 to 6 while n+m equals 4, 5 or
6;
- q equals 0, 1 or 2 while

and
- r equals 1, 2, 3 or 4.
The spherical equivalent diameter (SED) of the crystal represents the diameter of
the sphere which has the same volume as the average volume of the silver halide crystals
of the said emulsion.
[0013] Preferred embodiments of the invention are disclosed in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
[0014] While the present invention will hereinafter be described in connection with preferred
embodiments thereof, it will be understood that it is not intended to limit the invention
to those embodiments. On the contrary, it is intended to cover all alternatives, modifications,
and equivalents as may be included within the spirit and scope of the invention as
defined by the appending claims.
[0015] The precipitation of a photosensitive silver halide emulsion is conducted in an aqueous
dispersing medium including, at least during grain growth, a peptizer wherein silver
ions and halide ions are brought together. Grain structure and properties can be selected
by control of several parameters like precipitation temperature, pH and relative proportion
of the silver and halide ions in the dispersing medium. In order to avoid fog formation
the precipitation is commonly conducted on the halide side of the equivalence point
which is defined as 'the point at which the silver and halide ion activity is equal'.
[0016] The silver halide emulsions of the current invention are prepared in the presence
of compounds which can be occluded in the crystal structure. Such a compound (also
called dopant) is replacing an appropiate amount of silver and halide ions in the
silver halide lattice. The dopant can be distinguished from the metal-complex introduced
in the emulsion as an additive by EPR- or ENDOR-techniques. The EPR-technique and
sample preparation is described in US-A 5,457,021 by Olm et al and by H.Vercammen,
T.Ceulemans, D.Schoenmakers, P.Moens and D.Vandenbroucke in Proc. ICS&T of 49
th Ann.Conf., p.54 (19-24 may, 1994 Minneanapolis). The description of the ENDOR-technique
is given in the same Proc.Ann.Conf., p.56 by P.Moens, H.Vercammen, D.Vandenbroucke,
F.Callens and D.Schoenmakers. These so-called dopants are modifying the crystal structure
and are further influencing the properties of the crystal. A lot of parameters like
sensitivity, gradation, pressure sensitivity, high or low intensity reciprocity failure,
stability, dye desensitization, and several other sensitometric aspects of a photosensitive
silver halide emulsion can be modified by selection of the dopant, including its concentration,
its valency and location in the crystal in case of incorporation of the single metal
ion. When coordination complexes or even oligomeric coordination complexes are used
the different ligands bound at the central metal ion can be occluded in the crystal
lattice too and can in this way influence the photographic properties of the silver
halide material as well (Res.Discl.,38957 (1996) pag 591, section I-D). The dopant
utilized in accordance with the present invention is a transition metal complex which
can be defined by the general formula (1) as described hereinbefore.
[0017] Dopants which can be utilised with respect to the objects of the present invention
should be incorporated in the silver halide crystals in such a way that they satisfy
equation (I) hereinbefore. It is important to know that the lowest value of 'FORM'
is equal to zero. This actually happens if a low amount of dopant is located in the
extreme center of the crystal or in the contrary almost reaches its surface.
[0018] Introducing one or more dopants in the silver halide emulsion normally tends to increase
the gradation of the image-forming element comprising the said emulsion after subsequent
illumination and processing. It is frequently accompanied by a decrease in photographic
sensitivity. This characteristic is used advantageously in photosensitive image-forming
elements for roomlight or daylight operations. As discussed already before, the location
of the dopant plays a dominant role in the fine tuning of the sensitometric characteristics
of the material comprising the emulsion containing one or more dopants. It is utilised
advantageously in several inventions where the dopant is non-uniformly distributed
in the silver halide crystal. Delocalisation of the dopant as described in patents
mentioned in' the Background of the Invention' are resulting in an improvement of
the photographic sensitometry (as sensitivity, stability, gradation and so on). In
all these proposals the dopants are introduced in the outer regions of the silver
halide crystals which easily leads to interactions between the molecules of the dopants
superficially present in the silver halide crystals at one side and chemical addenda
at the other side which are distributed in a dispersion surrounding the grains and
which are necessary for the chemical sensitization and in a later phase of the emulsion
production process for the coating of the ripened silver halide emulsion on the base.
[0019] Introducing the dopants according to the general formula (1) in the photosensitive
silver halide crystals of the present invention leads to an image-forming element
with improved quality with respect to gradation and sensitivity if the conditions
for the location and concentration of the dopant are satisfied as stated in the equations
(I) and (II) of the present invention. That means that the dopants should be incorporated
in the center of the crystals starting almost from the center up to 95% of the average
diameter of the emulsion crystals, but preferable up to not more than 75%, and more
preferably up to max 50% of the average crystal diameter of the emulsion crystals.
It is important to know that the doping procedure always can start just after ending
the nucleation step in order to avoid interference of dopants in the formation of
the nuclei. Preferably this corresponds with addition of the said dopants after having
precipitated about 3 % of silver halide, more preferably about 5 %.
[0020] Dopants which can be used for this invention according to formula (1) are essentially
those which act as a deep and permanent electron trap in a silver halide crystal and
which satisfies (as taught already before) two conditions: the LUMO of the incorporated
molecular entity should be at least 0.5 eV below the conduction band of the silver
halide crystal, and the trapping life-time at room temperature should be longer than
0.2 seconds (see R.S.Eachus, M.T.Olm in 'Cryst.Latt.Def.and Amorph.Mat.', 1989(18)297-313).
The LUMO is defined as the 'lowest unoccupied molecular orbital' of the related complex
which can trap an electron from the conduction band (see D.F.Shriver, P.W.Atkins,
C.H.Langford in "Inorganic Chemistry'- Oxford Univ.Press (1990), Oxford-Melbourne-Tokyo).
Examples of these traps can be find in EP-A 0 606 895, EP-A 0 415 481, US-A 4,835,093
and in US-A 5,348,850.
[0021] The doping procedure itself can normally be executed at any stage during the grain
growth phase of the emulsion preparation where the reactants are added to the reaction
vessel in the form of solutions of silver and halide salts or in the form of preformed
silverhalide nuclei or fine grains which easily dissolve in the precipitation medium.
It is important to know that the dopants can also be added in an indirect way by addition
of a dispersion containing very fine soluble silver halide grains or nuclei comprising
the dopant.
[0022] The individual reactants can be added through surface or subsurface delivery tubes
by hydrostatic pressure or by an automatic delivery system for maintaining the control
of pH and/or pAg in the reaction vessel and of the rate of the reactant solutions
introduced in it. The reactant solutions or dispersions can be added at a constant
rate or a constantly increasing or fluctuating rate, if desired in combination with
stepwise delivery procedures. More details about the possible ways in making a silver
halide emulsion which can be principally used in practizising this invention are summarized
in Res.Discl.,38957 (1996)591-639 section I-C.
[0023] Special attention has to be paid to the way the dopants are introduced during the
grain growth process. The stability of the metal ligand complex in the solution can
be very limited. Therefore the solution containing the dopants is preferentially introduced
via a third jet, in a zone in the reactor where the compounds are rapidly incorporated
in the growing microcrystals. The advantage of the use of a third jet is that a solvent
can be used for the given dopant which is most suitable for the stability of that
compound. Further the temperature of the dopant solution can be adjusted in order
to maximize the stability too. The most stable conditions for the dopant solution
are tested by UV-VIS absorption. The third jet itself can be adjusted automatically
or manually. The dopant can be added at a constant rate or at any rate profile as
for instance in JP-A 03 163 438 wherein the dopant is occluded in two different concentrations
in the silver halide grains of a direct positive emulsion having the highest concentration
closest to the grain centre. This patent describes a method to get a silver halide
emulsion with improved gradation without paying attention to the sensitivity level
which in the contrary is also the target of the present invention.
[0024] The photographic emulsions prepared in this way contain silver halide crystal comprising
chloride, bromide or iodide alone or combinations thereof. Other silver salts which
can be incorporated in a limited amount in the silver halide lattice are silver phosphate,
silver thiocyanate, silver citrate and some other silver salts. The chloride and bromide
halide can be combined in all ratios to form a silverchlorobromide salt. Iodide ions
however can be coprecipitated with chloride and/or bromide ions in forming a iodohalide
with an iodide amount which depends on the saturation limit of iodide in the lattice
with the given halide composition; this means up to a maximum amount of about 40 mole
percent in silver iodobromide and up to at most 13 mole procent in silver iodochloride
both based on silver.
[0025] The composition of the halide can change in the crystal in a continous or discontinous
way. Emulsions containing crystals composed of various sections with different halide
compositions are used for several photographic applications. Such a structure with
a difference in halide composition between the center and the rest of the crystal
(what is called 'core-shell'-emulsion) or with more than two crystal parts differing
in halide composition (called a 'band'-emulsion) may occur. The changes in halide
composition can be realised by direct precipitation or in an indirect way by conversion
where fine silver halide grains of a certain halide composition are dissolved in the
presence of the so-called host grains forming a 'shell' or 'band' on the given grain.
The crystals formed by the methods described above have a morphology which can be
tabular or non-tabular like cubic, octahedral, etc. In tabular crystals the aspect
ratio (ratio of equivalent circular diameter to thickness) can vary from low (<2)
over 'medium' (2 till 8) to high (>8) where specially in the case of the ultra thin
tabular crystals high aspect ratios can be realised. The major faces of the formed
tabular grains can have a {111} or a {100}-habitus the structure of which is (respectively)
stable or has to be stabilised (for instance by a 'habitus modifying agent'). In the
class of non-tabular grains there are a lot of possibilities which can be divided
in the more regular shaped crystals or the crystals with a mixed crystal habit.
[0026] The photographic emulsion of the present invention contains chloride, bromide and
iodide as well, preferable chloride and bromide, and most preferred chloride without
excluding the presence of the other halides. The present invention is suitable for
an application in high speed camera-films, in radiographic materials, in graphic art
films, in color paper and in others. Therefore a great variety of halide combinations
should be covered. However for the chloride containing silver halides as AgClBrI,
AgClI and AgClBr the prefered chloride concentration is at least 10 mol% and most
prefered not less than 50 mol% which conditions are also encountered in many other
silver halide photographic systems like those which are described e.g. in EP-A 0 264
288 and EP-A 0 552 650.
[0027] The present invention is applicable to crystals comprising any combination of halides
which can even occasionally exist together with other silver salts as mentioned above.
It is important to note that physical grain structures with two or more different
halide compositions in one crystal can be used in combination with partially doping
according the present invention. It is also interesting to know that the central part
of the crystal doped according to the present invention does not necessarily need
to cover the central part(s) of the same crystal which are distinguished from the
other parts of the crystal by a difference in halide composition. This means that
a internally doped crystal can match more than one crystal part with different halide
compositions.
[0028] The emulsions can include silver halide grains of any conventional shape or size.
Specifically the emulsions can include coarse, medium or fine silver halide grains.
The silver halide emulsions can be either monodisperse or polydisperse after precipitation.
[0029] Besides the dopants which are deep electron traps as described by formula (1) other
dopants can be added to the silver halide emulsion. These are essentially introduced
because of their specific influence on the photographic characteristics. Different
classes of dopants are known: dopants (such as IrCl
63-) resulting in a non-permanent trapping behaviour can be a shallow electron trap (such
as Ru(CN)
62-) (see Res.Discl.,36736 (1994)657.), or a recombination or hole trapping center. These
dopants are essentially all those not obeying the conditions for a deep electron trap.
Many examples of this category have already been described in the patent literature
but cover different silver halide systems like those mentioned hereinbefore in WO
92/16876, EP-A 0 264 288, EP-A 0 552 650 and EP-A 0 752 614.
[0030] After precipitation the emulsions can be coagulated and washed in order to remove
the excess soluble salts. These procedures are together with different alternative
methods like dia- or ultrafiltration and ion-exchange described in Res.Discl., 38957(1996),
section III. The silver halide emulsions of this invention which are prepared in one
of the ways described hereinbefore contain crystals which have a spherical equivalent
diameter (SED) of not more than 1.0 µm but preferable less than 0.5 µm. The spherical
equivalent diameter (SED) of the crystal represents the diameter of the sphere which
has the same volume as the average volume of the silver halide crystals of the said
emulsion.
[0031] The emulsions can be surface-sensitive emulsions which form latent images primarily
on the surface of the silver halide grains or they can be emulsions forming their
latent-image primarily in the interior of the silver halide grain. Further the emulsions
can be negative-working emulsions such as surface sensitive emulsions or unfogged
internal latent image-forming emulsions. However direct-positive emulsions of the
unfogged, latent image-forming type which are positive-working by development in the
presence of a nucleating agent, and even pre-fogged direct-positive emulsions can
be used in the present invention.
[0032] The silver halide emulsions can be surface-sensitized by chemical sensitization which
can be done in many different ways, in presence of a chalcogen as sulfur, selenium
or tellurium, in presence of a noble metal as for instance gold or in combination
with a chalcogen and noble metal. In a particular embodiment a sulphur sensitizer
can be added in form of a dispersion of solid particles as has been described in EP-A
0 752 614. This can also be done by reduction sensitization if desired combined with
the chalcogen/noble metal-sensitization. The presence of certain 'modifying' agents
as for instance spectral sensitizers which can optimize the chemical sensitization
process are often used. A complete description of all the different possibilities
with respect to this subject can be found in Res.Discl.,38957(1996), section IV.
[0033] In a next step the silver halide emulsions are spectrally sensitized with dyes from
different classes which include polymethine dyes comprising cyanines, merocyanines,
tri-, tetra-and polynuclear cyanines and merocyanines, oxanols, hemioxanols, styryls,
merostyryls and so on. Sometimes more than one spectral sensitizer may be used in
the case that a larger part of the spectrum has to be covered. Combinations of several
spectral sensitizers are sometimes used to get supersensitization, which means that
in a certain region of the spectrum the sensitization is greater than that from any
concentration of one of the dyes alone or that which would result from the additive
effect of the dyes. Generally supersensitization can be attained by using selected
combinations of spectral sensitizing dyes and other addenda such as stabilizers, development
accelerators or inhibitors, brighteners, coating aids, and so on. A good description
of all the possibilities in spectral sensitization which are important with respect
to this invention can be found in Res.Discl., 38957(1996) section V.
[0034] In the case that desensitizers should be used, as for instance in pre-fogged direct-positive
or in daylight handling materials, various chemical compounds are proposed for practical
use. Principally all these compounds which are used as desensitizers in silver halide
materials and which are for instance summarized in EP-A 0 477 436 can be used in combination
with the elements of this invention.
[0035] The photographic elements comprising the said silver halide emulsions can include
various compounds which should play a certain role in the material itself or afterwards
in the processing, finishing or warehousing the photographic material. These products
can be stabilizers and anti-foggants (see Res.Discl., 38957(1996) section VII), hardeners
(see Res.Discl.,38957(1996) section IIB), brighteners (see Res.Discl.,38957(1996)
section VI), light absorbers and scattering materials (see Res.Discl.,38957(1996)
section VIII), coating aids (see Res.Discl.,38957(1996) section IXA), antistatic agents
(see Res.Discl.,38957(1996) section IXC), matting agents (see Res.Discl.,38957(1996)
section IXD) and development modifiers (see Res.Discl.,38957(1996) section XVIII).
The silver halide material can also contain different types of couplers, which can
be incorpated as described in Res.Discl.,38957(1996) section X.
[0036] The photographic elements can be coated on a variety of supports as described in
Res.Discl.,38957(1996) section XV and the references cited therein. The photographic
elements can be exposed to actinic radiation, specially in the visible, near-ultraviolet
and near-infrared region of the spectrum, to form a latent image (see Res.Discl.,
38957(1996) section XVI).
[0037] This latent-image can be processed in order to form a visible image (see Res.Discl.,38957
(1996) section XIX). While the invention is specially focussed on Cl-containing photosensitive
silver halide materials, automatic processing is advantagely used in order to get
rapid and convenient processing. In order to prevent the disadvantages (as for instance
the formation of silver sludge) of automatic processing these materials a preferred
method of processing is described in EP-A 0 732 619. The developer mentioned in the
last reference contains a combination of hydrochinon, an auxiliary developing agent,
ascorbic acid or one of its isomers or derivatives, and a small amount of a thiocyanate
salt. In more general terms this has already been described for silver halide systems
as those mentioned e.g. in EP-A 0 552 650 and EP-A 0 752 614. But it is recommended
to apply the method and to use the various ascorbic acid analogues as described in
EP-A 0 732 619, which is incorporated herein by reference.
[0038] Processing to form a visible dye image for colour materials means contacting the
element with a colour developing agent in order to reduce developable silver halide
and to oxidize the colour developing agent which in turn normally reacts with the
coupler to form a dye (see Res.Discl.,38957(1996) section XX)
[0039] Having described in detail preferred embodiments of the current invention, it will
now be apparent to those skilled in the art that numerous modifications can be made
therein without departing from the scope of the invention as defined in the claims
mentioned hereinafter.
[0040] The invention can be better appreciated by reference to the following specific examples.
They are intended to be illustrative and not exhaustive about the requirements of
the invention as described herinbefore and as summarized in the claims nailing on
to the essentials of this invention. The present invention, however, is not limited
thereto.
Example 1:
Preparation of emulsion A1:
[0041]
Solution A1 : |
gelatin |
75 g |
demineralised water |
1500ml |
AgNO3 |
0.04g |
Solution A2 : |
AgNO3 |
750g |
demineralised water |
1500ml |
Solution A3 : |
NaCl |
257.7g |
demineralised water |
1500ml |
Solution Dot1 : |
NaCl |
225g |
acetic acid |
5ml |
demineralised water added to make |
1 l |
K2[RuCl5(NO)] |
1.372 10-3 g |
The pH of the solutions A1 and A3 was brought to a pH of 2.8 using a sulphuric acid
solution. The solutions A2 and A3 were kept at room temperature, while solution A1
was heated to 50 degree C. The pAg was set to 7.05 using a sodium chloride solution.
Solution A2 was added to solution A1 at a constant rate, while solution A3 was added
at a rate in order to keep the pAg constant at pH=7,05 during 3 minutes. Afterwards
the addition rate for solution A2 was slighlty raised while the addition rate of solution
A3 was varied in order to raise the pAg over 0.5 units in 4 minutes. Solution A2 was
further added at an accelerating rate of 0,202 ml/minute, while solution A3 was added
at a rate sufficient to keep the pAg constant at 7,5.
The emulsion was diafiltrated afterwards to a volume of 2.5 l and desalted by ultrafiltration
at constant pAg =7.8. After the washing procedure 150 g of gelatin was added to the
precipitate and water was added in order to obtain a total weight of 3.75 kg.
The thus prepared silver chloride emulsion has a homodisperse grain size distribution,
having an average grain size of 0.42 µm and a variance of about 15% in grain size.
[0042] Emulsions A2 to A5 were prepared in the same way, while the addition of 159 ml of
the solution Dot1, containing a Ru- complex, to solution A1 was carried out at a constant
rate using a third jet at different moments during the precipation. The position of
the dopant in the emulsion grains is expressed as the percentage of the crystal volume
reached at the moment where the addition of the third jet is started and the percentage
of the crystal volume at the moment where the addition of the dopant solution is stopped.
The location of the dopants, the grain diameter d, the diameter d
1 of the sphere containing the dopant situated as far as possible from the grain centre,
the value of the parameter FORM [see formula (II)] and the concentration of th dopant
are shown in table A.1. The silver chloride emulsions were subsequently ripened at
a pAg and pH equal to 7.9 and 4.6 respectively, with a gold tetrachloride solution
(5 10
-7 mole/mole Ag) and a dimethylcarbamoylsulfide compound (10
-6 mole/mole Ag) at 50 degrees C for 150 minutes. These emulsions were spectrally sensitized
with a blue sensitizer. The pH was adjusted to a value of 5.2 afterwards.
Table A.1
Location and concentration of the RuCl5NO-dopant in an AgCl crystal. |
|
Location |
Conc. (10-9 mole/mole Ag) |
d (µm) |
d1 (µm) |
FORM |
A1 |
- |
- |
0.420 |
- |
0 |
A2 |
5-100% |
128 |
0.422 |
0.422 |
0 |
A3 |
5-80% |
128 |
0.424 |
0.394 |
20 |
A4 |
5-20% |
128 |
0.429 |
0.251 |
21 |
A5 |
80-100% |
128 |
0.423 |
0.423 |
0 |
The emulsions were coated on a substrated PET base in an amount of 4 g of gelatin/m
2 and 2.5 g Ag/m
2. A layer containing gelatin (0.5 g per m
2), a vinylsulphonic hardener and surfactants were coated on top of the emulsion layer.
The photographic materials were image-wise exposed through a step-wedge original using
a 10
-3 sec Xe flash. The exposed photographic materials were developed in a G101 commercial
developer using a Rapiline 66-3 machine at 35 degree C for 25 sec, and fixed at 33
degree C for 25 sec in a G 333c commercial fixer to which a hardener (Aditan) was
added. All these commercial products are trademarket names from Agfa-Gevaert.
The fog level is low for all the materials, i.e. 0.03 to 0.04. The relative speed
is the logarithm of the ratio of the energy of the illumination needed in order to
obtain an optical density equal to the density

, i.e. at the density where about 50% of the coated silver halide is image-wise reduced,
relative to the energy to get the same density of the non-doped emulsion. A positive
number indicates that more energy is needed by exposing in order to obtain the same
optical density. A more positive number is indicative for a less sensitive emulsion.
The contrast is measured around this sensitivity point (between 25% and 75% of density).
The relative contrast is expressed as the ratio (in percentage) of the contrast of
the doped emulsion versus the non-doped emulsion. The sensitivity and contrast in
the shoulder portion of the sensitometric curve are derived in a similar way. This
sensitivity is the illumination energy in order to get a density

of the doped emulsion relative to the illumination energy to get the same density
of the non-doped emulsion, while the contrast in the shoulder of the sensitometric
curve is measured between 70 and 90% of the density

.
The sensitometric parameters are given in table A.2.
The advantages of the actual invention becomes most evident in the experiments where
values of the parameter FORM obeye equation (I), especially in the shoulder of the
sensitometric curve. The 'normal'- and the 'shoulder'-contrast are significantly influenced
by the location of the dopant in the microcrystals. The results clearly show that
the 'overall' doping (A2) gives a strong
Table A.2
Influence of the location of the RuCl5(NO)2- dopant on the (shoulder-)sensitivity and contrast. |
|
Location |
Relative Sens. |
Relative contrast (%) |
Relative Shoulder sens. |
Shoulder contrast (%) |
|
A1 |
- |
- |
100 |
- |
100 |
Comparative |
A2 |
5-100% |
.63 |
221 |
.53 |
218 |
Comparative |
A3 |
5-80% |
.66 |
222 |
.54 |
292 |
Invention |
A4 |
5-20% |
.69 |
253 |
.56 |
250 |
Invention |
A5 |
80-100% |
.51 |
153 |
.43 |
119 |
Comparative |
contrast increase and a decrease in sensitivity (factor 4!) if compared with the
non-doped emulsion (A1). It is further clearly demonstrated that 'moving' the dopant
to the shell of the crystals (A2 to A5) gives a decrease in contrast and a small increase
in sensitivity (as in A2), while introducing the dopant more to the center of the
crystals (going from A2 to A3 to A4, thus locating the dopant in a band from 5-100
%, over 5-80 % to 5-20 %) further increases the contrast while almost no decrease
in sensitivity is observed. Increasing the concentration of the dopant in A2 in order
to enhance the contrast to the value obtained for emulsion A4 would result in a much
lower sensitivity.
This permits to reach a higher practical maximum density as required for instance
in graphical applications using a laser recorder exposure.
Example 2 :
Preparation of AgCl-emulsion B1:
[0043]
Solution B1 : |
gelatin |
75 g |
demineralised water |
1500ml |
AgNO3 |
0.04g |
Solution B2 : |
AgNO3 |
750g |
demineralised water |
1500ml |
Solution B3 : |
NaCl |
257.7g |
demineralised water |
1500ml |
Solution Dot2 : |
NaCl |
225g |
acetic acid |
5ml |
demineralised water added to make |
1 l |
K2[RuCl5.(NO)] |
6.9 10-3 g |
[0044] The pH of the solutions B1 and B3 was brought to a pH value of 2.8 using a sulphuric
acid solution. The solutions B2 and B3 were kept at room temperature, while solution
B1 was heated to 50 degree C. The pAg was set to 7.05 using a sodium chloride solution.
Solution B2 was added to solution B1 at a constant rate at 5 ml/min., while solution
B3 was added at a rate in order to keep the pAg constant during 3 minutes. Afterwards
the addition rate for solution B2 was slighlty raised up to 6.2 ml/min. while the
addition rate of solution B3 was varied in order to raise the pAg over 0.5 units in
4 minutes. Solution B2 was further added at an accelerated rate of 0.202 ml/min.,
while solution B3 was added at a rate sufficient to keep pAg constant.
The emulsion was diafiltrated afterwards to a volume of 2.5 l and desalted by ultrafiltration
at constant pAg of 7. After the washing procedure 150 g of gelatin was added to the
precipitate and demineralised water was added in order to get a total weight of 3.75
kg.
The thus prepared silver chloride emulsion has a homodisperse grain size distribution,
having a mean grain size of 0.42 µm and a variance of about 15% in grain size.
[0045] Emulsions B2 to B3, also containing AgCl were prepared in the same way, except for
the addition of 15.9 ml of the solution Dot2, containing the same Ru-complex as in
example 1, which was added to solution B1 at a constant addition rate using a third
jet at different moments during the precipation. The position of the dopant in the
emulsion grains is expressed as the percentage of the crystal volume at the moment
where the addition of the third jet is started and the percentage of the crystal volume
at the moment where the addition of the dopant solution is stopped. The location of
the dopants and the grain size are shown in table B.1. The AgBr-emulsions B4 to B6
were prepared in a similar way :
Solution B4 : |
gelatin |
75 g |
demineralised water |
1500ml |
AgNO3 |
0.04g |
Solution B5 : |
AgNO3 |
750g |
demineralised water |
1500ml |
Solution B6 : |
KBr |
524.8g |
demineralised water |
1500ml |
The pH of the solutions B4 and B6 was brought to a pH of 2.8 using a sulphuric acid
solution. The solutions B5 and B6 were kept at room temperature, while solution B4
was heated to 50 degree C. The pAg was set to a value of 6.4 with a potasium bromide
solution. Solution B5 was added to solution B4 at a constant rate of 1.25 ml/min.
while solution B6 was added at a rate in order to keep the pAg constant at 6.4 during
3 minutes. Afterwards the pAg was raised to 8.14 using solution B6. Solution B5 was
further added at an acceleration rate 0.133 ml/min., while solution B6 was added at
a rate sufficient to keep the pAg constant at 8.14.
The emulsion was diafiltrated afterwards to a volume of 2.5 l and desalted by ultrafiltration
at constant pAg of 8.3. After the washing procedure 150 g gelatin was added to the
precipitate and demineralised water was added to get a total weight of 3.75 kg.
The thus prepared silver bromide emulsion has a homodisperse grain size distribution,
with a mean grain size of 0.34 µm and a variance of about 8% in grain size.
[0046] Emulsions B5 and B6 were prepared in the same way as emulsion B4, except that these
emulsions were doped with a Ru complex as indicated in table B.1. The addition of
17.9 ml of the dopant solution Dot2 to solution B4 during the precipition of the AgBr
was carried out by using a third jet.
[0047] The silver chloride emulsions were subsequently ripened at a pAg and pH equal to
7.9 and 4.6 respectively, with a gold salt (5 10
-7 mole/mole Ag) and a sulfur compound (10
-6 mole/mole Ag) at 50 degrees C for 150 min. The emulsions were further stabilized
with triazaindolizine. A part of these emulsions was spectrally sensitized with a
green light-absorbing sensitizer. The pH was afterwards adjusted to a value of 5.2.
The emulsions were coated on a substrated PET base in an amount of 4 g of gelatin
per m
2 and 2.5 g Ag/m
2. A layer containing gelatin (0.5 g gel/m
2), a vinyl sulphonyl hardener and surfactants was coated on top of the
Table B.1
RuCl5NO-dopant situated at different locations of an AgCl- and AgBr-crystal. |
Nr |
|
Location |
Conc. (10-9 mole/mole Ag) |
d (µm) |
d1 (µm) |
FORM |
B1 |
AgCl |
- |
- |
0.425 |
- |
- |
B2 |
AgCl |
5 - 20 % |
64 |
0.423 |
0.247 |
11 |
B3 |
AgCl |
80 - 100 % |
64 |
0.434 |
0.434 |
0 |
B4 |
AgBr |
- |
- |
0.348 |
- |
- |
B5 |
AgBr |
5 - 20 % |
72 |
0.328 |
0.192 |
12 |
B6 |
AgBr |
80 - 100 % |
72 |
0.343 |
0.343 |
0 |
emulsion layer. The photographic materials were image-wise exposed through an step-wedge
original using a 10
-3 sec Xe flash. The exposed photographic materials were developed in a G101 commercial
developer using a Rapiline 66-3 machine at 35 degree C for 25 sec, and fixed at 33
degree C for 25 sec in a G 333c commercial fixer to which a hardener (Aditan) was
added. All the commercial products are trademarket names of Agfa-Gevaert.
The relative speed is expressed as the logarithm of the ratio of the illumination-energy
needed in order to obtain an optical density equal to the density

, i.e. at the density where about 50% of the coated silver halide is image-wise reduced
relative to the energy to get the same density for the non-doped emulsion. Again,
a positive number indicates that more energy is needed in the illumination in order
to obtain the same optical density. A more positive number is therefor indicative
for a less sensitive emulsion. The fog level is for all the materials low, i.e. 0.03
to 0.04. The contrast is measured around this
Table B.2
Sensitometric results of doping an AgCl crystal with a RuCl5NO-dopant at different locations. |
|
Location |
Dye |
Relative sens. |
Relative contrast |
|
B1 |
- |
no |
- |
100 |
comp. |
B2 |
inner shell |
no |
.67 |
226 |
invent. |
B3 |
outer shell |
no |
.87 |
100 |
comp. |
B1 |
- |
yes |
- |
100 |
comp. |
B2 |
inner shell |
yes |
.75 |
194 |
invent. |
B3 |
outer shell |
yes |
.95 |
102 |
comp. |
sensitivity point (between 25% and 75% of density). The relative contrast is expressed
as the ratio (in percentage) of the contrast of the doped emulsion versus the none
doped emulsion. The sensitometric parameters are given in table B.2.
[0048] The silver bromide emulsions were ripened at a pAg and pH equal to 7.8 and 4.6 respectivily,
with gold salt (5 10
-6 mole/mole Ag) and sulfur salt (8.6 10
-6 mole/mole Ag) at 50 degrees C for 150 minutes. After the addition of a green light-absorbing
sensitizer the silver bromide were coated in a similar way as the AgCl emulsions B1
to B3. The exposure, processing and sensitometric evaluation of the photographic materials
were performed in the same way as described as hereinbefore. The sensitometric parameters
are given in table B.3 where next to the 'normal' contrast and sensitivity also the
values for the 'shoulder' are given. The shoulder sensivitiy and contrast are measured
in the same way as described hereinbefore in example 1.
Table B.3
The sensitometric results of an AgBr-emulsion doped with K2RuCl5(NO) situated at different locations in the crystal. |
|
|
Dye |
Relative sens. |
Rel. Contrast (%) |
Relative Shoulder sens. |
Relative Shoulder Contrast |
|
B4 |
- |
yes |
- |
100 |
- |
100 |
Comparative |
B5 |
inner shell |
yes |
.28 |
122 |
.22 |
121 |
Invention |
B6 |
outer shell |
yes |
.66 |
68 |
.47 |
116 |
comparative |
The influence of the location of the dopant on the gradation and sensitivity of the
doped emulsion is similar as observed in example 1. For AgCl there is a strong increase
of the contrast by 'moving' the dopant from the outer region of the crystal (B3) to
the core (B2) the sensitivity increases significantly as well. This happens in the
emulsion with and without the presence of a spectral sensitizer. For the doped AgBr
emulsion with spectral sensitization the same relationship is clearly established.
Example 3
Preparation of emulsion C1:
[0049]
Solution C1 : |
gelatin |
75 g |
demineralised water |
1500ml |
Solution C2 : |
AgNO3 |
750g |
demineralised water |
1500ml |
Solution C3 : |
NaCl |
257.7g |
demineralised water |
1500ml |
Solution C4 : |
NaCl |
228.87g |
demineralised water |
1375ml |
Sol. Dot4 |
125ml |
Solution Dot3 : |
NaCl |
250g |
acetic acid |
5ml |
demineralised water added to make |
1 liter |
Na3RhCl6.12H2O |
17.04g |
Solution Dot4 : |
NaCl |
250g |
acetic acid |
5ml |
demineralised water added to make |
1 liter |
Na3RhCl6.12H2O |
2.13g |
The pH of the solutions C1 and C3 was brought to a pH of 3.5 using a HNO
3 solution. The solutions C2 and C3 were kept at room temperature, while solution C1
was heated to 40 degree C. The pAg was set at a value of 7.95 using a sodium chloride
solution. Solution C2 was added to solution C1 at a constant rate, while solution
C3 was added at a rate in order to keep the pAg constant during 3 minutes. Afterwards
solution C2 was added at an accelerated rate, while solution C3 was added at a rate
sufficient to keep the pAg constant.
The resulting silver chloride was precipitated by adding a polystyrene sulphonic acid.
The precipitate was rinsed several times by using a low concentrated NaCl solution
(0.539 mg NaCl per liter demineralised water), and subsequently redispersed by adding
195 g of gelatin to the precipitate and chlorinated water in order to get a total
weight of 3.250 kg.
The so prepared silver chloride emulsion has a homodisperse grain size distribution
with a mean grain size of 0.20 µm and a variance in grain size of about 20%.
[0050] Emulsions C2 and C3 were prepared in the same way. For the precipitation of emulsion
C2 the addition of 15.6 ml of solution Dot3 was carried out by using a third jet between
the moments that
Table C.1
RhCl63--dopant situated at different locations in an AgCl-crystal. |
Nr |
|
mole Rh3+/mole Ag |
d (µm) |
d1 (µm) |
FORM |
C1 |
none |
0 |
0.206 |
- |
0 |
C2 |
6-21% |
100 10-6 |
0.211 |
0.125 |
16469 |
C3 |
0-100% |
100 10-6 |
0.200 |
0.200 |
0 |
respectivily 6 and 21% of the silver was added. Emulsion C3 was prepared identical
to emulsion C1 except that for the precipitation solution C4 was used instead of solution
C3.
Emulsion specifications are given in Table C.1 The emulsions were further prefogged.
Therefore the pH was adjusted at a value of 7.0 using NaOH and the pAg was set at
7.95 using a chloride solution. At 55 degrees C 9.676 10
-6 mole thioureumdioxyde was added per mole silver. After 15 minutes 1.241 10
-6 mole of a gold salt was added per mole of silver and after another minute 3.23 10
-6 mole of sodium toluenethiosulphonate was added per mole of silver. The fogging process
was continued for 3 hours at this temperature.
Than 5.2 mmole per mole of silver of a nitrobenzimidazole-5(6) desensitizer was added
to the emulsions followed by coating on a PET base in an amount of 3.5 g of silver
and 2.2 g of gelatin both per m
2. A top layer containing hardener and surfactants was coated on the emulsion layer.
[0051] The photographic materials were image-wise exposed through an step-wedge original
using a QL 100 LI equipement. Using a PRINTON LI the illumination time was adjusted
to 150 units. The exposed photographic materials were developed in a G101 commercial
developer using a Rapiline 66-3 machine at 35 degree C for 25 sec, and fixed at 33
degree C for 25 sec in a G 333c commercial fixer to which a hardener (Aditan) was
added. All these commercial products are trademarket names of Agfa-Gevaert.
The practical evaluation of the relative speed and contrast were performed as described
hereinbefore. The sensitometric parameters are given in table C.2
Table C.2
Sensitometric results of AgCl-emulsions in relation with different locations of a
Rh-salt in the crystal. |
|
Dopant |
Sensitivity |
Contrast (%) |
|
C1 |
none |
- |
100 |
Comparative |
C2 |
6-21% |
.02 |
107 |
Invention |
C3 |
0-100% |
.31 |
64 |
Comparative |
The sensitometric results with a prefogged direct-positive AgCl emulsion clearly
demonstrate, as was expected of the value of the parameter FORM (see equation II)
that introducing the dopant in the core instead of in the outer regions of the crystal
leads to a significant increase of the contrast without loosing sensitivity.
Example 4
Preparation of emulsion D1:
[0052]
Solution D1 : |
gelatin |
25 g |
demineralised water |
1000ml |
Solution D2 : |
AgNO3 |
250g |
demineralised water |
500ml |
Solution D3 : |
NaCl |
85.91g |
demineralised water |
500ml |
Solution Dot5 : |
NaCl |
58.44g |
acetic acid |
5ml |
demineralised water added to make |
1 liter |
Na3RhCl6.12H2O |
17.04g |
The pH of the solutions D1 and D3 was brought to a pH of 3.0 using a HNO
3 solution. The solutions D2 and D3 were kept at room temperature, while solution D1
was heated to 40 degrees C. The pAg was adjusted at 8.24 by using a sodium chloride
solution. Solution D2 was added to solution D1 at a constant rate, while solution
D3 was added at a rate in order to keep the pAg-value constant during 3 minutes. Afterwards
solution D2 was added at an accelerated rate, while solution D3 was added at a rate
sufficient to keep the pAg constant. The addition of 2.5 ml of dopant solution Dot5
was carried out by using a third jet between the moment that the first 10% of silver
was reacted and te end of the precipitation.
The resulting silver chloride was precipitated by adding a polystyrene sulphonic acid.
The precipitate was rinsed several times by using a low concentrated NaCl solution
(0.539 mg NaCl per liter demineralised water) and subsequently redispersed by adding
50 g of gelatin to the precipitate and chlorinated water in order to get a total weight
of 1.250 kg.
The so prepared silver chloride emulsion has a homodisperse grain size distribution
with a mean grain size of 0.14 µm and a variance in grain size of about 24%.
[0053] Emulsions D2 and D3 were prepared in the same way. For the precipitation of emulsion
D2 the addition of 2.5ml of solution Dot5 was carried out by using a third jet between
the moments that respectivily 10 and 20% of the silver was added. For emulsion D3
was it between the moments that 90 and 100% of the silver was added. Emulsion specifications
are given in table D.1
Table D.1
Location and concentration of a Rh-dopant situated in an AgCl-crystal. |
Nr |
|
10-6 mole Rh3+/mole Ag |
Dopant-solution |
d (µm) |
d1 (µm) |
FORM |
D1 |
10-100% |
48,237 |
Dot5 |
0.147 |
0.147 |
0 |
D2 |
10-20% |
48,237 |
Dot5 |
0.139 |
0.081 |
7706 |
D3 |
90-100% |
48,237 |
Dot5 |
0.147 |
0.147 |
0 |
Before chemical sensitizing the pH was adjusted at 5 by using NaOH while the pAg
was adjusted at 7.27. The chemical sensitization was carried out at 45 degrees C by
adding an amount of 2.14 10
-5 mole sulphur salt per mole silver halide and 1.48 10
-5 mole gold salt per mole silver halide while keeping the emulsion at this temperature
for three hours.
Than 5.2 mmole per mole of silver of a nitrobenzimidazole-5(6) desensitizer was added
to the emulsions followed by coating on a PET base in an amount of 3.5 g of silver
and 2.2 g of gelatin both per m
2. A toplayer containing hardener and surfactants was coated on the emulsion layer.
[0054] The photographic materials were image-wise exposed for 10 seconds through an step-wedge
original using a CDL 1030 equipement on level 1. The development was carried out as
described in example 3.
[0055] The relative speed is the logarithm of the ratio of the energy of the illumination
needed to obtain an optical density equal to the 0.3 above fog level, relative to
the illumination energy needed to get the same density for the emulsion with the dopants
homogeneously spread in the crystal between 10 and 100% of the crystal volume. The
contrast is measured in the foot of the sensitometric curve between reference densities
0.05 and 0.3 above fog level. The relative contrast is expressed as the ratio in percentage
of the contrast of the doped emulsion versus the emulsion with the dopants homogeneously
spread in the crystal between 10 and 100% of the crystal volume. The sensitometric
parameters are given in table D.2
As can be seen in this experiment and as expected from the value of the parameter
FORM (equation II), the activity of the electron trap increases rapidly by 'moving'
the dopant from the outer regions to the center of the crystal.
Table D.2
Sensitometric results of a Rh-doped AgCl-emulsion as a function of the location of
the dopant. |
|
Dopant-solution |
Location |
Rel. Sens. |
Rel. Contrast |
|
D1 |
Dot5 |
10-100% |
- |
100 |
Comparative |
D2 |
Dot5 |
10-20% |
.08 |
105 |
Invention |
D3 |
Dot5 |
90-100% |
.83 |
44 |
Comparative |
While the invention has been described in detail and with reference to specific embodiments
thereof, it will be apparant to one skilled in the art that various changes and modifications
can be made therein without departing from the spirit and the scope thereof.