[0001] The present invention concerns a silver halide emulsion, and more particularly a
silver halide emulsion which resolves the problem of desensitisation which can be
caused by the spectral sensitising dye.
[0002] Silver halide photographic emulsions have a natural photosensitivity region which
is limited to ultraviolet, violet and blue. In order to obtain an acceptable colour
rendering, it is necessary to use compounds which have the property of being adsorbed
on the silver halide grains and making these grains sensitive to a wavelength region
extending, in the visible spectrum, beyond the intrinsic photosensitivity region of
the silver halides. The photosensitivity of the emulsion depends on the quantity of
spectral sensitisers adsorbed on the silver halide grains. It increases with the increase
in the quantity of spectral sensitising dyes up to a maximum sensitivity value. Beyond
this maximum, when the quantity of spectral sensitising dyes is increased a reduction
in sensitivity is observed. The quantity of dye which enables maximum sensitivity
to be obtained may vary according to the spectral sensitising dye and the size, shape
or composition of the halide grains.
[0003] The effect of the spectral sensitisers may therefore be reversed. In general, this
reversed effect, known as desensitisation, appears when the quantity of sensitisers
adsorbed on the surface of the halide grains exceeds a certain threshold. For certain
particular silver halide grains, this desensitisation appears as soon as the spectral
sensitiser covers 50% of the surface of the silver halide grains.
[0004] It is therefore important to be able to increase the quantity of spectral sensitisers
adsorbed on the silver halide grains without desensitisation resulting therefrom.
In photography, it is known that emulsions can be chemically sensitised in the presence
of one or more compounds of sulphur, gold and/or selenium in order to increase the
overall sensitivity of the photosensitive products obtained. Examples of chemical
sensitising compounds were described in Research Disclosure, No 308119, December 1989,
Section III.
[0005] In European patent 428,041, the emulsions are chemically sensitised in the presence
of conventional sulphur and gold compounds and a selenium compound having a labile
selenium atom.
[0006] In US patent 4,810,626, the silver halide emulsions were sensitised with a compound
of the tetrasubstituted selenourea or thiourea type.
[0007] In US patent 5,049,485, photographic products were sensitised by means of gold (I)
compounds (degrees of oxidation equal to 1) of formulae AUL
+X
- or AUL(L
1)
+X
- in which L is a mesoionic group, X is an anion and L
1 is a donor ligand of the Lewis base type. Such compounds have improved properties
compared with conventional gold compounds. In the examples, the chemical sensitisation
was implemented using the gold (I) compound in combination either with a conventional
sulphur compound (Na
2S
2O
3) or with a substituted thiourea. The sensitometric results show that the use of a
gold (I) compound in combination with a thiourea has no advantage compared with the
use of a gold (I) compound with Na
2S
2O
3 as disclosed in the patent cited above.
[0008] As the prior art set out above shows, it is known that the sensitivity of photographic
products can be improved by using sulphur compounds and gold compounds. However, none
of the documents cited above mentions the problems of desensitisation by a spectral
sensitising dye (hereinafter referred to as "dye desensitisation").
[0009] The object of the present invention is to obtain an emulsion having high sensitivity
whilst eliminating the problem of dye desensitisation.
[0010] In fact, we discovered that the problem of dye desensitisation which arose with core/sheel
emulsions disclosed in EP-A-0 618 484 could be resolved by associating these particular
emulsions with a chemical sensitisation by means of gold compounds with a degree of
oxidation equal to 1 (hereinafter referred to as gold (I)) which do not contain a
labile sulphur atom and by means of a thiourea.
[0011] The photographic emulsion according to the invention has improved sensitivity which
results from increasing the quantity of spectral sensitisers adsorbed on the silver
halide grains without causing dye desensitisation.
[0012] Although the combination of a thiourea and a gold (I) compound was described in US
patent 5,049,485, it was not known that this combination would make it possible to
avoid the dye desensitisation which occurs with certain types of silver halide emulsion.
[0013] The photographic emulsion of the present invention consists of silver halide grains
comprising a central zone (the core) consisting of at least two silver halides and
an outer zone (the shell) having a silver halide composition different from the composition
of the central zone, characterised in that
(1) the molar percentage of at least one of the silver halides which constitutes the
core with respect to the total number of moles of silver halides in the core decreases
between the centre of the grains and the core/shell interface,
(2) the chemical sensitisation of the grain was effected by means of at least one
thiourea and at least one gold (I) compound not containing any labile sulphur atom.
[0014] According to one embodiment, the proportion of at least one of the halides forming
the core decreases continuously between the centre of the grains and the core/shell
interface so that the difference between the molar percentage of each of the silver
halides between the centre of the grain and the core/shell interface is at least 10%,
the percentages being calculated from the total number of moles of silver halides
constituting the core.
[0015] The silver halide emulsion forming the core of the invention comprises at least two
silver halides chosen from amongst silver chloride, bromide and iodide.
[0016] The process for preparing such decreasing-profile emulsions consists of precipitating
successive regions having different silver halide compositions whilst simultaneously
introducing a solution of a silver salt and a solution of alkali metal halide(s),
hereinafter referred to as "halide solution" or "halide jet" containing one or more
alkaline halides. The process according to the invention is characterised in that,
during the precipitation of the core, a halide solution is used which comprises at
least two different halides, the concentrations of which are caused to vary inversely,
between initial values and predetermined final values. These variations are preferably
practically linear.
[0017] In order to avoid abrupt variations in the halide composition of the grain at the
core/shell interface, the final values of the concentration in the halide solution
used for the core are preferably equal to the concentrations of said halides in the
halide solution at the start of precipitation of the shell immediately adjacent to
the core.
[0018] The core of the silver halide grains of the emulsions of the invention preferably
consists of silver bromoiodide, silver chloroiodide or silver chlorobromoiodide with
a molar percentage of silver iodide which decreases between the centre of the grains
and the core/shell interface. In order to obtain such an emulsion having a bromoiodide
core, the silver bromoiodide core is precipitated whilst linearly decreasing the concentration
of iodide and linearly increasing the concentration of bromide in the halide jet consisting
of alkaline iodide and alkaline bromide. In this case, the iodide content in the grain
varies from a maximum value at the centre of the grain to a zero value at the core/shell
interface. The shell, which may consist of one or more silver halides other than iodide,
is then precipitated.
[0019] The overall quantity of silver iodide in the core is, within the framework of the
invention, between 10 and 30% molar with respect to the total number of moles of silver
halide contained in the core, and this proportion of iodide can vary between 36% at
the centre of the grain and 0% at the core/shell interface.
[0020] The shell of the grains constituting the emulsion may be formed by one or more layers
having identical or different silver halide compositions. According to one embodiment,
this shell does not contain any silver iodide.
[0021] The ratio of the number of moles of silver halide constituting the core to the number
of moles of silver halide constituting the shell is between 0.2 and 2. According to
one embodiment, the core of the grains is formed by silver bromoiodide, the shell
of the grains is formed by silver bromide and the core/shell molar ratio is 0.5.
[0022] The grains may have different morphologies, for example tabular, octahedral (faces
111), cubo-octahedral or cubic (faces 100). In one embodiment of the invention, the
grains are cubo-octahedral with a size of between 0.1 and 3.0 µm, and preferably 0.3
and 2.0 µm.
[0023] The thioureas which can be used in the present invention are tetrasubstituted thioureas
of formula:
in which each R
1, R
2, R
3 and R
4 group represents either separately a hydrogen atom, an alkyl, cycloalkyl or carbocyclic
or heterocyclic aryl radical, or an aralkyl radical, or R
2-R
3, R
3-R
4 or R
4-R
1 are combined to represent a heterocycle with 5 to 7 linkages, provided that at least
one of the R
1, R
2, R
3 or R
4 groups contains or is a nucleophilic group of the carboxylic, sulphinic, sulphonic,
hydroxamic, mercapto, sulphonamido or primary or secondary amino group.
[0024] The thioureas which can be used in the scope of this invention are described in detail
in US patent 4,810,626.
[0025] The radicals R
1, R
2, R
3 and R
4 which contain a nucleophilic group are, for example, chosen from amongst -COOH, -CH
2COOH, C
2H
4COOH, -CH
2SO
2H, -CH
2SO
3H, -C
2H
4SO
2H, -C
2H
4NHOH, -C
2H
4SH, -(CH
2)
2NHSO
2CH
3, -C
2H
4NHCH
3 and the corresponding salts.
[0027] The thioureas may be synthesised using the method described in US patent 4,810,626.
One method, for example, consists of reacting an aliphatic monoaminocarboxylic acid
with a dialkylthiocarbamoyl halide.
[0028] The quantities of thioureas may be between 10
-6 and 10
-1 mmole per mole of silver halide and preferably between 10
-4 and 10
-2 mmole per mole of silver halide.
[0029] The gold (I) compounds containing no labile sulphur atom are compounds which are
sufficiently stable to be used in the photographic emulsions without causing undesirable
secondary reactions. In particular the gold (I) compounds must not contain a labile
sulphur atom which would react with the silver present in the medium so as to form
silver sulphide, which would interfere with the chemical sensitisation of the emulsion.
In addition, the gold (I) compounds must be easily dispersable in the aqueous compositions
used in photography. The gold (I) compounds which may be used within the scope of
the invention were described in US patents 5 049 484 and 5 049 485.
[0030] According to one embodiment, these gold (I) compounds have the following structure:
in which R
1, R
2 and R
3 are each separately a hydrogen atom, or an alkyl, alkylene, alkyloxy, aryl or amino
group, substituted or otherwise, and X is an anion.
[0031] The quantity of gold (I) compounds which may be added to a silver halide emulsion
is between 10
-6 and 10
-1 mmol/mol of silver and preferably between 10
-4 and 10
-2 mmol/mol of silver.
[0032] Although the quantity of each of the chemically sensitising compounds differs widely
according to the conditions of use, the thioureas and gold (I) compounds are, according
to the invention, such that the molar ratio between the quantity of sulphur contained
in the thiourea and the quantity of gold (I) is between 1 and 4 and preferably 2 and
3.
[0033] The compounds described above may be used alone or in combination with conventional
sensitising agents known for the chemical sensitisation of photographic emulsions.
[0034] The thioureas and gold (I) compounds may be added to the silver halide emulsion together
or separately and at different stages of the sensitisation of the emulsion. The addition
of these chemical sensitisers to the emulsion may be effected in the presence of a
solvent for silver halides such as thioethers or thiocyanates.
[0035] The conditions for sensitising the silver halide grains, such as the pH, the pAg,
the temperature, etc, are not particularly limited when the compounds described here
are used. The pH is generally between 1 and 9, and preferably between 5 and 7, and
the pAg is generally between 5 and 12 and preferably between approximately 7 and 10.
The silver halide grains may be sensitised at a temperature between approximately
30 and 90°C, and it is preferred to use a temperature between approximately 35 and
70°C. The silver halide emulsion can be spectrally sensitised with spectral sensitising
dyes and in accordance with the chromating methods as described for example in Research
Disclosure, December 1989, No 308119, Section IV (hereinafter referred to as Research
Disclosure). These dyes may for example be cyanine, merocyanine, composite cyanine,
composite merocyanine and hemioxodol dyes. The dyes which are particularly useful
belong to the merocyanine class. These dyes contain, as a heterocyclic core, any core
generally used in cyanine dyes.
[0036] Within the scope of the invention, the spectral sensitising dyes are added to the
emulsion after the chemical sensitisation stage.
[0037] The emulsions of the present invention may be used in colour photographic products
of different types, such as negative, positive or reversal photographic products.
[0038] According to the invention, the colour photographic products comprise, in a conventional
manner, at least three elements which are respectively blue-, green- and red-sensitive
and which supply respectively the yellow, magenta and cyan components of the subtractive
synthesis of the colour image.
[0039] Colour photographic products generally comprise a support carrying at least one blue-sensitive
silver halide emulsion layer with which a yellow dye forming coupler is associated,
at least one green-sensitive silver halide emulsion layer with which a magenta dye
forming coupler is associated, and at least one red-sensitive silver halide emulsion
layer with which a cyan dye forming coupler is associated.
[0040] These products may contain other layers which are conventional in photographic products,
such as spacing layers, filter layers, anti-halo layers and immobilisation layers.
The support may be any suitable support used with photographic products. Conventional
supports comprise polymer films, paper (including polymer-coated paper), glass and
metal. Research Disclosure Section XVII supplies details concerning supports and auxiliary
layers for photographic products.
[0041] The silver halide emulsions of the invention and other layers on the photographic
products of this invention may contain, as a vehicle, hydrophilic colloids, used alone
or in combination with other polymer substances (for example latexes). Suitable hydrophilic
substances comprise natural substances such as proteins, protein derivatives, cellulose
derivatives, for example cellulose esters, gelatin, for example gelatin treated with
a base (cattle bone or tanned gelatin) or gelatin treated with an acid (pigskin gelatin),
gelatin derivatives, for example acetylated gelatin, phthylated gelatin, etc, polysaccharides
such as dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion,
agar-agar and albumin.
[0042] Surfactants may be incorporated in a layer of photographic emulsion or in another
hydrophilic colloidal layer as a coating additive to prevent the accumulation of static
charges, to improve the lubrication properties, to improve the dispersion of the emulsion,
to prevent adhesion and to improve the photographic characteristics such as rapid
access development, or increase in contrast or sensitisation.
[0043] The photographic emulsion of the present invention may contain dye image forming
couplers, that is to say compounds capable of reacting with an oxidation product of
an aromatic amine (generally a primary amine) to form a dye. Non-diffusible couplers
containing a ballast group are desirable. It is possible to use either couplers with
four equivalents or couplers with two equivalents. In addition, it is possible to
use couplers enabling the colours to be corrected, or couplers releasing a development
inhibiter in the course of development (referred to as a DIR coupler).
[0044] The photographic products of the invention may contain, inter alia, optical brighteners,
anti-fogging compounds, surfactants, plasticisers, lubricants, hardening agents, stabilising
agents, or absorption and/or diffusion agents as described in Sections V, VI, VIII,
XI, XII and XVI of the above-mentioned Research Disclosure.
The methods of adding these various compounds and the coating and drying methods are
described in Sections XIV and XV of the same Research Disclosure.
[0045] The products of the invention, after being exposed, undergo photographic processing
to develop the latent silver image and a colour image, in the presence of a coupler,
which, in certain cases, may be incorporated in the photographic product.
[0046] The photographic products are then washed and processed in a stabilising bath.
[0047] Development is effected by means of a reducing compound which makes it possible to
transform the exposed silver halide grains into metallic silver grains. This reducing
compound oxidises and its oxidised form reacts with the coupler to form a dye. These
compounds are chosen from amongst the aromatic primary amines such as paraphenylene
diamines, aminophenols, etc. These compounds may be used alone or in a mixture, or
with auxiliary developers. This bath may in addition contain a stabiliser such as
sulphites, a buffer such as carbonates, boric acid, borates or alkanolamines.
[0048] The following examples illustrate the invention and show that the emulsions according
to the invention have improved sensitivity without any problem of desensitisation
by the sensitiser.
EXAMPLES
A. PRECIPITATION OF EMULSIONS
EXAMPLE 1: Control Core/Shell emulsions Without silver halide Profile in the core (CSWP)
[0049] Using the double jet precipitation technique, an AgBrI cubo-octahedral emulsion of
the core/shell type is prepared as follows:
[0050] In a 20 litre reacting vessel under strong agitation containing an aqueous solution
of gelatin, NaBr and a growth modifier (M1) assisting the formation of cubo-octahedral
grains, nucleation is effected at 60°C and at a pH of 5.1 by introducing, over 70
seconds by the double jet method, a 0.5 M solution of AgNO
3 and a 0.5 M solution of NaBr. The flow of AgNO
3 is constant and the flow of NaBr is adjusted so that the pAg remains equal to 9.
(The pAg is the reciprocal of the logarithm of the silver ion concentration in the
vessel.)
[0051] After a waiting period, growth is effected in order to precipitate the AgBrI core
on the AgBr nuclei. To do this, in the solution maintained at 60°C, a solution of
AgNO
3, 2M is introduced over 48 minutes using the double jet method with a flow of the
type a + bt (a and b being constants and t the time in minutes) and the flow of halide
containing NaBr,NaI, 2M is adjusted to 18% mole NaI so that the pAg is constant and
equal to 9. 3.33 moles of AgBrI are precipitated.
[0052] The AgBr shell is then formed by introducing a solution of AgNO
3, 2M and a solution of NaBr, 2M at 60°C using the double jet method over 43 minutes.
The flow of AgNO
3 is constant and the flow of NaBr is adjusted so that the pAg remains constant and
equal to 9. 6.67 moles of AgBr are precipitated.
[0053] Finally the emulsion is washed at 40°C and at a pH of 3.8.
[0054] A control emulsion with cubo-octahedral grains is obtained, having a core of AgBrI
with a uniform iodide content of 18% molar and an AgBr shell. The total iodide content
of the grains is 3% molar. The size of this emulsion is determined by volumetric analysis
of the silver halide grains, which is carried out by electrolytic reduction. Such
a method is described by A Holland and A Feinerman in J. Applied Photo. Eng.
8, 165 (1982). This method makes it possible to obtain the volumetric distribution
of the grains. From this distribution, it is possible to calculate the equivalent
spherical diameter (ESD).
[0055] The emulsion obtained above has a grain size of approximately 1.2 µm.
EXAMPLE 2 :Core/Shell emulsions with Decreasing iodide Profile in the core (Invention CSDP)
[0056] The operating method of Example 1 is repeated except, during the core precipitation
step, the iodide concentration in the halide jet decreases linearly over time between
an initial concentration of 36% and a final concentration of 0%. Conversely, the bromide
concentration varies linearly between 64% at the start of the precipitation and 100%
at the end of the precipitation of the core.
[0057] The emulsion thus obtained consists of silver halide grains of the core/shell type
with an iodide content in the core which gradually reduces to a nil value at the interface.
The core/shell molar ratio is 0.5 with an iodide content in the core of 18%, the total
iodide content being 6%. The mean size of the grains is 1.16 µm.
B. SENSITISATION OF THE EMULSIONS
EXAMPLE 3
[0058] The emulsion of Example 2 is chemically sensitised by means of the gold (I) compound
of formula (A) (0.73 mg/mol Ag) and the thiourea of formula (B) (0.83 mg/mol Ag) in
the presence of sodium thiocyanate (150 mg/mol Ag) in accordance with the method described
below.
[0059] The chemical sensitisers are added to the emulsion maintained at 40°C, the pH being
adjusted to 6.4 and the pAg to 8.25.
[0060] After introduction of the chemical sensitisers, the emulsion is maintained at 70°C
for 25 min.
[0061] There is then added to this chemically sensitised emulsion maintained at 40°C, a
mixture of spectral sensitising dyes of formula:
[0062] The molar ratio of the sensitising dyes (I)/(II) is 3/1.
[0063] The quantity of spectral sensitising dyes is such that the coverage of the grains
is 55%, the coverage of the grain by the dye being defined as the surface area of
the grain covered by the dye compared with the total surface of the grain, expressed
as a percentage. This percentage is determined from the molecular dimension of the
dye when it is adsorbed on the grain (the impression of the dye) and from the surface
area of the grain.
[0064] The chemically and spectrally sensitised emulsion is coated on a cellulose triacetate
support with a silver content of 0.807 g/m
2, a gelatin content of 3.23 g/m
2 and coupler (C1) with a content of 1.05 g/m
2. This emulsion layer is covered with a gelatin top layer (2.15 g/m
2) containing a hardening agent.
[0065] The sample thus obtained is exposed by means of a Kodak sensitometer equipped with
a lamp with a colour temperature of 5500°K for 1/100 seconds. The sensitometer is
fitted with a Wratten 9 filter.
[0066] The sample is then developed using a standard Kodak Flexicolor C41® process which
comprises the following steps:
- development using a chromogenic developer,
- bleaching,
- first washing,
- fixing,
- second washing,
- stabilisation, and
- drying.
[0067] The sensitivity of the sample is assessed by the formula:
in which E represents the photographic exposure required to obtain a density D =
Dmin + 0.4.
[0068] The desensitisation by the dye (Δ) is assessed by means of the difference between
the intrinsic sensitivity of the emulsion and the sensitivity of the same emulsion
spectrally sensitised to the optimum extent.
[0069] "Intrinsic sensitivity" means the sensitivity of the emulsion before spectral sensitisation.
This intrinsic sensitivity is determined on a sample obtained from the emulsion chemically
sensitised according to the method described above, which is exposed at 365 nm and
processed using the Kodak Flexicolor C41
R process. The sensitivity as defined above is measured.
[0070] The granularity is the granularity normalised by the contrast, that is to say the
granularity measured for a maximum contrast.
[0071] The contrast (γ) is determined by the slope of the sensitometric curve measured between
Dmin + 0.4 and Dmin + 1.4.
EXAMPLE 4 (comp)
[0072] The CSDP emulsion of Example 2 is processed as described in Example 3 except that
the chemical sensitisation is effected by means of sodium thiosulphate pentahydrate
(0.70 mg/mol Ag) and potassium tetrachloroaurate (0.47 mg/mol Ag) in the presence
of sodium thiocyanate (150 mg/mol Ag) and acetamidophenyltetramercaptol (50 mg/mol)
which acts as an anti-fogging agent. After introduction of the chemical sensitisers,
the emulsion is maintained at 70°C for 25 min.
[0073] The emulsion is then coated, exposed and developed according to the method of Example
3.
EXAMPLE 5 (comp)
[0074] The CSDP emulsion of Example 2 is processed as described in Example 3 except that
the chemical sensitisation is effected by means of sodium thiosulphate pentahydrate
(1.3 mg/mol Ag) and potassium tetrachloroaurate (0.43 mg/mol Ag).
[0075] After introduction of the chemical sensitisers, the emulsion is maintained at 70°C
for 25 min.
[0076] The emulsion is then coated, exposed and developed according to the method of Example
3.
EXAMPLE 6 (comp)
[0077] The CSDP emulsion of Example 2 is processed as described in Example 3 except that
the chemical sensitisation is effected by means of sodium thiosulphate pentahydrate
(0.09 mg/mol Ag) and a gold (I) compound of formula Na
3[Au(S
2O
3)
3]2H
2O (0.65 mg/mol Ag) in the presence of sodium thiocyanate (150 mg/mol Ag) and acetamidophenyltetramercaptol
(50 mg/mol), which acts as an anti-fogging agent.
[0078] After introduction of the chemical sensitisers, the emulsion is maintained at 70°C
for 25 min.
[0079] The emulsion is then coated, exposed and developed according to the method of Example
3.
[0080] In this case, the addition of sulphur is effected by means of the thiosulphate and
the gold (I) compound, which contains labile sulphur atoms.
EXAMPLE 7 (comp)
[0081] The CSDP emulsion of Example 2 is processed as described in Example 3 except that
the chemical sensitisation is effected by means of sodium thiosulphate pentahydrate
(0.73 mg/mol Ag) and a gold (I) compound of formula Na
3[Au(S
2O
3)
3]2H
2O (0.60 mg/mol Ag). In this case, the addition of sulphur is effected by means of
the thiosulphate and the gold (I) compound, which contains labile sulphur atoms.
[0082] After introduction of the chemical sensitisers, the emulsion is maintained at 70°C
for 25 min.
[0083] The emulsion is then coated, exposed and developed according to the method of Example
3.
EXAMPLE 8 (Control)
[0084] The CSWP emulsion of Example 1 is processed as described in Example 3 except that
the chemical sensitisation is effected by means of sodium thiosulphate pentahydrate
(0.39 mg/mol Ag) and a gold (I) compound of formula Na
3[Au(S
2O
3)
3]2H
2O (2.88 mg/mol Ag) in the presence of sodium thiocyanate (200 mg/mol Ag).
[0085] The quantity of spectral sensitising dyes (S-1) used with such an emulsion is such
that the coverage of the grains is 80%. After introduction of the sensitising dyes,
the emulsion is maintained at 70°C for 20 min.
[0086] The emulsion is then coated, exposed and developed according to the method of Example
3.
EXAMPLE 9 (Control)
[0087] The CSWP emulsion of Example 1 is processed according to the method of Example 8
except that the chemical sensitisation is effected by means of the gold (I) compound
of formula (A) (2.03 mg/mol Ag) and the thiourea of formula (B) (2.22 mg/mol Ag) in
the presence of sodium thiocyanate (50 mg/mol Ag).
C. SENSITOMETRIC RESULTS
[0088] The sensitometric results of Examples 3 to 7 are set out in Table 1 below.
TABLE 1
|
Dmin |
Sens. |
Δ |
γ |
1000.Granu |
Ex.3 (Inv) |
0.10 |
118 |
2 |
0.84 |
24 |
Ex.4 (Comp) |
0.09 |
100 |
29 |
0.74 |
26 |
Ex.5 (Comp) |
0.11 |
107 |
15 |
0.87 |
26 |
Ex.6 (Comp) |
0.12 |
99 |
30 |
0.75 |
26 |
Ex.7 (Comp) |
0.10 |
109 |
15 |
0.83 |
25 |
[0089] The results show that the sensitivity and the dye desensitisation of the emulsions
of the present invention are improved compared with the same emulsion sensitised in
a conventional manner.
[0090] In addition, with the emulsions of the present invention, it is no longer necessary
to add an anti-fogging agent when the emulsion is sensitised in the presence of sodium
thiocyanate, which is a compound much used in photography.
[0091] Examples 6 and 7 show that the use of a conventional sulphur sensitiser and a gold
(I) compound containing labile sulphur atoms does not improve the dye desensitisation.
[0092] In addition, it should be noted that, when an emulsion is chemically sensitised by
means of a thiourea and a gold (I) compound containing labile sulphur atoms, silver
sulphide is formed in the emulsion, which amounts to sensitising the silver halide
emulsion in a conventional manner.
[0093] The sensitometric results of Examples 8 and 9 are set out in Table 2 below.
TABLE 2
|
Dmin |
Sens. |
Δ |
γ |
1000.Granu |
Ex.8 |
0.07 |
100 |
0 |
1.10 |
20 |
Ex.9. |
0.06 |
102 |
0 |
1.29 |
18 |
[0094] These results show that, when the silver halide emulsion is a core/shell emulsion
without a halide profile in the core, there is no problem of dye desensitisation.
In addition, it is clear from these results that the special chemical sensitisation
of the invention does not significantly increase the sensitivity of such an emulsion.
1. Photographic emulsion consisting of silver halide grains comprising a central zone
(the core) consisting of at least two silver halides and an outer zone (the shell)
having a silver halide composition different from the composition of the core, characterised
in that
(1) the molar percentage of at least one of the silver halides of the core with respect
to the total number of moles of silver halides in the core decreases between the centre
of the grains and the core/shell interface,
(2) the chemical sensitisation of the grain is effected by means of a thiourea and
a gold (I) compound not containing any labile sulphur atom.
2. Photographic emulsion according to Claim 1, in which the thiourea corresponds to the
formula
in which each R
1, R
2, R
3 and R
4 group represents either separately a hydrogen atom, an alkyl, cycloalkyl or carbocyclic
or heterocyclic aryl radical, or an aralkyl radical, or R
2-R
3, R
3-R
4 or R
4-R
1 are combined to represent a heterocycle with 5 to 7 linkages, provided that at least
one of the R
1, R
2, R
3 or R
4 groups contains or is a nucleophilic group of the carboxylic, sulphinic, sulphonic,
hydroxamic, mercapto, sulphonamido or primary or secondary amino group.
3. Emulsion according to Claim 2, in which the nucleophilic groups are chosen from amongst
-COOH, -CH2COOH, -C2H4COOH, -CH2SO2H, -CH2SO3H, -C2H4SO2H, -C2H4NHOH, -C2H4SH, -(CH2)2NHSO2CH3, -C2H4NHCH3 and the corresponding acid salts.
4. Emulsion according to Claim 1, in which the gold (I) compound corresponds to the formula
in which R
1, R
2 and R
3 are each separately a hydrogen atom, or an alkyl, alkylene, alkyloxy, aryl or amino
group, substituted or otherwise, and X is an anion.
5. Photographic emulsion according to Claim 1, in which the quantities of thiourea and
gold (I) compound are such that the molar ratio between the quantity of sulphur contained
in the thiourea and the quantity of gold (I) compound is between 1 and 4 and preferably
2 and 3.
6. Photographic emulsion according to Claim 4, in which the gold (I) compound is
7. Photographic emulsion according to Claim 2, in which the thiourea is
8. Photographic emulsion according to Claim 1, in which difference between the molar
percentage of each of the silver halides constituting the core between the centre
of the grains and the core/shell interface is at least 10%.
9. Photographic emulsion according to Claim 1, in which the core consists of silver bromoiodide,
silver chloroiodide or silver chlorobromoiodide.
10. Emulsion according to Claim 8, in which the core consists of silver bromoiodide and
the molar percentage of silver iodide in the core, with respect to the total number
of moles of silver halide in the core, decreases continuously between the centre of
the grains and the core/shell interface and the shell does not contain any silver
iodide.
11. Photographic emulsion according to Claim 8, in which the total molar percentage of
silver iodide in the core is between 10 and 30%, with respect to the total number
of moles of silver halide in the core.
12. Photographic emulsion according to Claim 8, in which the shell consists of several
layers having different halide compositions.
13. Photographic emulsion according to Claim 8, in which the ratio of the number of moles
of silver halide constituting the core to the number of moles of silver halide constituting
the shell is between 0.2 and 2.
14. Emulsion according to Claim 8, in which the core of the grains consists of silver
bromoiodide, the shell of silver bromide and the core/shell molar ratio is equal to
0.5.
15. Photographic emulsion according to Claim 14, in which the molar percentage of silver
iodide in the core varies between 36% at the centre and 0% at the interface, with
respect to the total number of moles of silver halide in the core.
16. Process for preparing the chemically sensitized photographic emulsion as defined in
any one of the preceding claims comprising precipitating successive zones having different
halide compositions by introducing simultaneously a solution of silver salt and a
solution of halide(s) of an alkali metal, the process characterised in that at least
during the precipitation of the central zone (the core), the halide solution contains
at least two different halides, the concentrations of which in the halide solution
vary practically linearly between predetermined initial values and final values which
are equal to the concentrations of these halides in the halide solution at the start
of the precipitation of the immediately adjacent zone of the shell.
1. Fotografische Emulsion, bestehend aus Silberhalogenid-Körnern mit einer zentralen
Zone (dem Kern), bestehend aus mindestens zwei Silberhalogeniden und einer äußeren
Zone (der Hülle) mit einer Silberhalogenid-Zusammensetzung, die von der Zusammensetzung
des Kernes verschieden ist,
dadurch
gekennzeichnet, daß
(1) der molare Prozentsatz von mindestens einem der Silberhalogenide des Kernes, bezüglich
der Gesamt-Anzahl von Molen an Silberhalogeniden in dem Kern, zwischen dem Zentrum
der Körner und der Kern/Hüllen-Grenzfläche abnimmt, und daß
(2) die chemische Sensibilisierung der Körner bewirkt wird mittels eines Thioharnstoffes
und einer Gold (I)-Verbindung, die kein labiles Schwefelatom enthält.
2. Fotografische Emulsion nach Anspruch 1, in der der Thioharnstoff der Formel entspricht:
worin jede Gruppe R
1, R
2, R
3 und R
4 entweder getrennt voneinander darstellt ein Wasserstoffatom, einen Alkyl-, Cycloalkyl-
oder carbocyclischen oder heterocyclischen Aryl-Rest, oder einen Aralkyl-Rest, oder
worin R
2-R
3, R
3-R
4 oder R
4-R
1 miteinander kombiniert sind, unter Bildung eines Heterozyklus mit 5 bis 7 Bindungen,
wobei gilt, daß mindestens eine der Gruppen R
1, R
2, R
3 oder R
4 eine nukleophile Gruppe, bestehend aus der carbocyclischen, sulfinischen, sulfonischen,
hydroxamischen, Mercapto-, Sulfonamido- oder primären oder sekundären Amino-Gruppe,
enthält oder aus einer solchen besteht.
3. Emulsion nach Anspruch 2, in der die nukleophilen Gruppen ausgewählt sind aus -COOH,
-CH2COOH, -C2H4COOH, -CH2SO2H, -CH2SO3H, -C2H4SO2H, -C2H4NHOH, -C2H4SH, -(CH2)2NHSO2CH3, -C2H4NHCH3 und den entsprechenden Säuresalzen.
4. Emulsion nach Anspruch 1, in der die Gold (I)-Verbindung der Formel entspricht:
worin R
1, R
2 und R
3 jeweils separat voneinander stehen für ein Wasserstoffatom, oder eine Alkyl-, Alkylen-,
Alkyloxy-, Aryl- oder Amino-Gruppe, die substituiert ist oder nicht, und worin X ein
Anion ist.
5. Fotografische Emulsion nach Anspruch 1, in der die Mengen an Thioharnstoff und Gold
(I)-Verbindung derart sind, daß das molare Verhältnis zwischen der Menge an Schwefel,
die in dem Thioharnstoff enthalten ist, und der Menge an Gold (I)-Verbindung zwischen
1 und 4, und vorzugsweise 2 und 3, liegt.
6. Fotografische Emulsion nach Anspruch 4, in der die Gold (I)-Verbindung der Formel
entspricht:
7. Fotografische Emulsion nach Anspruch 2, in der der Thioharnstoff besteht aus:
8. Fotografische Emulsion nach Anspruch 1, in der der Unterschied zwischen dem molaren
Prozentsatz von jedem der Silberhalogenide, die den Kern bilden, zwischen dem Zentrum
der Körner und der Kern/Hüllen-Grenzfläche bei mindestens 10 % liegt.
9. Fotografische Emulsion nach Anspruch 1, in der der Kern besteht aus Silberbromoiodid,
Silberchloroiodid oder Silberchlorobromoiodid.
10. Emulsion nach Anspruch 8, in der der Kern besteht aus Silberbromoiodid, und in der
der molare Prozentsatz an Silberiodid im Kern, bezüglich der Gesamt-Anzahl von Molen
an Silberhalogenid in dem Kern, kontinuierlich zwischen dem Zentrum der Körner und
der Kern/Hüllen-Grenzfläche abnimmt, und in der die Hülle kein Silberiodid enthält.
11. Fotografische Emulsion nach Anspruch 8, in der der gesamte molare Prozentsatz an Silberiodid
im Kern zwischen 10 und 30 %, bezüglich der Gesamt-Anzahl an Molen an Silberhalogenid
in dem Kern, liegt.
12. Fotografische Emulsion nach Anspruch 8, in der die Hülle aus mehreren Schichten unterschiedlicher
Halogenid-Zusammensetzungen besteht.
13. Fotografische Emulsion nach Anspruch 8, in der das Verhältnis der Anzahl von Molen
an Silberhalogenid, das den Kern bildet, zur Anzahl von Molen an Silberhalogenid,
das die Hülle bildet, zwischen 0,2 und 2 liegt.
14. Emulsion nach Anspruch 8, in der der Kern der Körner aus Silberbromoiodid besteht,
die Hülle aus Silberbromid, und in der das molare Kern/Hüllen-Verhältnis gleich 0,5
ist.
15. Fotografische Emulsion nach Anspruch 14, in der der molare Prozentsatz an Silberiodid
im Kern variiert zwischen 36 % im Zentrum und 0 % an der Grenzfläche, bezüglich der
Gesamt-Anzahl von Molen an Silberhalogenid im Kern.
16. Verfahren zur Herstellung der chemisch sensibilisierten, fotografischen Emulsion gemäß
einem der vorstehenden Ansprüche, bei dem man aufeinanderfolgend Zonen mit unterschiedlichen
Halogenid-Zusammensetzungen ausfällt, durch gleichzeitige Einführung einer Lösung
von Silbersalz und einer Lösung von Halogenid(en) eines Alkalimetalles, wobei das
Verfahren dadurch gekennzeichnet ist, daß mindestens während der Ausfällung der zentralen
Zone (des Kernes) die Halogenid-Lösung mindestens zwei unterschiedliche Halogenide
enthält, wobei die Konzentrationen in der Halogenid-Lösung praktisch linear variieren
zwischen vorbestimmten Ausgangs-Werten und End-Werten, die gleich sind den Konzentrationen
dieser Halogenide in der Halogenid-Lösung zu Beginn der Fällung der unmittelbar angrenzenden
Zone der Hülle.
1. Emulsion photographique constituée de grains d'halogénures d'argent comprenant une
zone centrale (core) constituée d'au moins deux halogénures d'argent et une zone externe
(shell) ayant une composition en halogénure d'argent différente de la composition
de la core, caractérisée en ce que
(1) le pourcentage molaire d'au moins un des halogénures d'argent de la core par rapport
au nombre de moles total d'halogénures d'argent de la core est décroissant entre le
centre des grains et l'interface core/shell,
(2) la sensibilisation chimique est effectuée au moyen d'une thiourée et d'un composé
d'or(I) ne contenant pas d'atome de soufre labile.
2. Emulsion photographique selon la revendication 1 dans laquelle la thiourée correspond
à la formule :
dans laquelle chaque groupe R
1, R
2, R
3 et R
4 représente soit séparément un atome d'hydrogène, un radical alkyle, cycloalkyle,
aryle carbocyclique ou hétérocyclique, un radical aralkyle, soit R
2-R
3, R
3-R
4 ou R
1-R
4 sont combinés pour représenter un hétérocycle de 5 à 7 chaînons, avec la condition
supplémentaire qu'au moins un des groupes R
1, R
2, R
3 ou R
4 contient ou est un groupe nucléophile de type carboxylique, sulfinique, sulfonique,
hydroxamique, mercapto, sulfonamido, amino primaire ou secondaire.
3. Emulsion selon la revendication 2 dans laquelle les groupes nucléophiles sont choisis
parmi -COOH, - CH2COOH, -C2H4COOH, -CH2SO2H, -CH2SO3H, -C2H4SO2H, - C2H4NHOH, -C2H4SH, -(CH2)2NHSO2CH3, -C2H4NHCH3 ainsi que les sels d'acide correspondants.
4. Emulsion selon la revendication 1 dans laquelle le composé d'or(I) correspond à la
formule
dans laquelle R
1, R
2 et R
3 sont chacun séparément un atome d'hydrogène, un groupe alkyle, alkylène, alkyloxy,
aryle, amino, substitué ou non, X est un anion.
5. Emulsion photographique selon la revendication 1, dans laquelle les quantités de thiourée
et de composé d'or(I) sont telles que le rapport molaire de la quantité de Soufre
contenu dans la thiourée sur la quantité d'or(I) est compris entre 1 et 4, de préférence
2 et 3
6. Emulsion photo graphique selon la revendication 4, dans laquelle le composé d'or est
7. Emulsion photographique selon la revendication 2, dans laquelle la thiourée est
8. Emulsion photographique selon la revendication 1 dans laquelle la différence du pourcentage
molaire de chacun des halogénures constituant la core entre le centre des grains et
l'interface core/shell est au moins égale à 10 %.
9. Emulsion photographique selon la revendication 1, dans laquelle la core est constituée
de bromoiodure d'argent, de chloroiodure d'argent ou de chlorobromoiodure d'argent.
10. Emulsion selon la revendication 8 dans laquelle la core est constituée de bromoiodure
d'argent et le pourcentage molaire d'iodure d'argent dans la core, par rapport au
nombre de moles total d'halogénures d'argent de la core décroît de façon continue
entre le centre des grains et l'interface core/shell et la shell ne contient pas d'iodure
d'argent.
11. Emulsion photographique selon la revendication 8, dans laquelle le pourcentage molaire
d'iodure d'argent global dans la core est compris entre 10 et 30 %, par rapport au
nombre de moles d'halogénures d'argent total de la core.
12. Emulsion photographique selon la revendication 8 dans laquelle la shell est constituée
de plusieurs couches ayant des compositions en halogénure différentes.
13. Emulsion photographique selon la revendication 8, dans laquelle le rapport du nombre
de moles d'halogénures d'argent constituant la core sur le nombre de moles d'halogénures
d'argent constituant la shell est compris entre 0,2 et 2.
14. Emulsion selon la revendication 8 dans laquelle la core des grains est constituée
de bromoiodure d'argent, la shell de bromure d'argent et le rapport molaire core/shell
est égal à 0,5.
15. Emulsion photographique selon la revendication 14 dans laquelle le pourcentage molaire
d'iodure d'argent dans la core varie entre 36 % au centre et 0 % à l'interface, par
rapport au nombre de moles total d'halogénures d'argent de la core.
16. Procédé de préparation de l'émulsion photographique sensibilisée chimiquement telle
que définie dans l'une quelconque des revendications précédentes, comprenant la précipitation
de zones successives ayant des compositions en halogénure différentes en introduisant
simultanément une solution de sel d'argent et une solution d'halogénure(s) d'un métal
alcalin, le procédé étant caractérisé en ce qu'au moins pendant la précipitation de
la zone centrale (core), la solution d'halogénure contient au moins deux halogénures
différents dont les concentrations dans la solution d'halogénure varient de façon
pratiquement linéaire entre des valeurs initiales prédéterminées et des valeurs finales
qui sont égales aux concentrations de ces halogénures dans la solution d'halogénure
au début de la précipitation de la zone de la shell immédiatement adjacente.