[0001] This invention relates to methods of preparing light-sensitive silver halide emulsions,
and to photographic materials incorporating layers of such emulsions.
[0002] Light-sensitive silver halide emulsions are conventionally prepared by reacting an
aqueous silver salt solution, e.g. silver nitrate, with an aqueous alkali metal halide
solution to cause precipitation of silver halide in the presence of a protective colloid.
After physical ripening to the desired average grain size and washing, a further amount
of protective colloid is added and the emulsion is subjected to chemical ripening.
[0003] The most commonly used protective colloid is gelatin. Although possessing many advantages,
the conventional gelatino-silver halide emulsion layers undergo considerable swelling
and subsequent shrinkage consequent upon absorption and release of processing liquids
during image processing. This lack of dimensional stability under processing conditions
can adversely affect image quality. Moreover, due to their rather slow absorption
and release of the processing liquids, such conventional gelatino-silver halide layers
cannot meet the rapid processing criteria which are often demanded. This is notwithstanding
the fact that rapid processing can to some extent be promoted by using light-sensitive
photographic materials which incorporate silver halide developing agents in or in
water-permeable relationship to the light-sensitive layer and using a two-step development
process comprising an activating and stabilising step instead of the conventional
development, fixing and washing steps. Stabilization processing is described in for
example US. Patent 4 030 924 and "Two bath rapid stabilization Process" published
in "British Journal of Photography" Vol. 114, No. 5583, July 21, 1967, pp. 620-621,
625.
[0004] With a view to forming light-sensitive layers which have good water-permeability
but which have greater dimensional stability than the conventional gelatino-silver
halide layers under processing conditions, many types of ingredients have been proposed
for use instead of or in addition to gelatin. These proposed ingredients include various
natural film-forming substances and synthetic resins, e.g. polyoxyethylene glycols,
polyvinylpyrrolidone, starch and starch derivatives. For the most part these prior
art binding agents have one or another disadvantageous effect on the mechanical or
photographic properties of the light-sensitive layer. In particular they tend to reduce
light-sensitivity.
[0005] Another substance proposed in the prior art as protective colloid binder in silver-halide
emulsions is colloidal silicic acid. This colloid has no or less adverse effects on
light-sensitivity and as disclosed in UK Patent 1276894 silver halide emulsions comprising
gelatin together with various proportions of silicic acid sol as binder have less
tendency to swell on treatment with aqeuous processing liquids than conventional gelatino-silver
halide emulsion layers of the same thickness. United States Patent 4 001 022 discloses
photographic elements which are described as suitable for rapid processing and which
comprise a support bearing an acidic developer layer and a basic gelatino-silver halide
emulsion layer, both of which layers contain a substantial amount of colloidal silica.
The binder in which the silver halide is dispersed comprises by weight about 6 to
40 percent of gelatin, the remainder being colloidal silica.
[0006] While the use of silicic acid sol as a protective colloid reduces swelling of light-sensitive
silver halide layers during liquid processing, the extent of that advantage has hitherto
been limited by the need for the concentration of the silicic acid sol to be restricted
in order to avoid making the emulsions physically unstable. The instability of silicic
acid sols when used as protective colloid binder for silver halide is recognised in
United States Patent 3 637 391. It is disclosed in that patent that if a silicic acid
sol of too high a concentration is used, agglomeration occurs when a reaction mixture
of alkali metal and silver salts is added to the sol. In order to oppose this agglomeration
the patent proposes treatment of the silicic acid sol with ethanol, the addition of
a homo or co-polymer of sufficiently water soluble monomer(s) or the polymerisation
of such monomer(s) in situ in the silicic acid sol. However the patent recommends
that the precipitated emulsion be redispersed in gelatin before being chemically ripened
and that the concentration of the silicic acid sol in the final emulsion should not
be more than 20% and preferably not more than 10% by weight.
[0007] The necessity to restrict the concentration of the silicic acid sol limits the advantage
which can be derived from the use of the sol in terms of for instance improved dimensional
stability of photographic layers formed from the emulsion.
[0008] An object of the present invention is to enable the proportion of silicic acid sol
used as a protective colloid in the preparation of silver halide emulsions to be substantially
increased without resulting in unacceptable physical instability of the emulsion.
[0009] According to the present invention there is provided a method of preparing a light-sensitive
silver halide emulsion by precipitating silver halide in the presence of colloidal
silicic acid serving as protective colloid, characterised in that the precipitation
takes place in the presence of an onium compound, except for ammonium bromide.
[0010] It has been found from a range of experiments using a variety of onium compounds
that they have an emulsion-stabilising effect when used as additive in the preparation
of light-sensitive silver halide emulsions by precipitating the silver halide in a
protective colloid consisting of or comprising colloidal silicic acid. The stabilising
effect can be demonstrated by a simple sedimentation test as hereinafter described.
The invention therefore makes it possible to form on a photographic support a light-sensitive
emulsion layer with a more favourable combination of the properties of water-permeability
and dimensional stability during wet development processing and subsequent drying.
Such a combination of properties is very desirable in the case of photographic materials
for rapid development processing.
[0011] In preferred embodiments of the invention, at least 75% by weight of the protective
colloid used in the silver halide precipitation step consists of silicic acid sol.
In the most preferred embodiments, such protective colloid consists entirely of such
sol. In the case that said colloid consists entirely of silicic acid sol, light-sensitive
layers which have the maximum dimensional stability benefit derivable from the use
of silicic acid sol as binder can be formed directly from the precipitated emulsion
after it has been ripened and washed.
[0012] However, it is to be understood that the invention is not restricted to methods wherein
silicic acid sol is used as the sole protective colloid in the precipitation of the
silver halide. The protective colloid used in that precipitation can comprise silicic
acid sol and a proportion of some other binder known as such in the photographic art.
In particular, the protective colloid can comprise silicic acid sol and gelatin.
[0013] If desired, additional silicic acid sol can be added to the emulsion after the precipitation
of the silver halide, e.g. during the subsequent redispersion of the emulsion.
[0014] It is also possible to add gelatin at the stage of redispersion of the emulsion.
[0015] The invention includes light-sensitive material comprising a support bearing at least
one light-sensitive silver halide emulsion layer which incorporates silicic acid sol
as a protective colloid binder, characterised in that said layer further comprises
an onium compound, except for ammonium bromide. The protective colloid binder of said
emulsion layer preferably comprises at least 75% by weight of silicic acid sol, and
most preferably it consists entirely of such sol.
[0016] As already indicated, a wide range of onium compounds have been tested and have been
found to be effective stabilisers for the purpose in view. The preferred onium compounds
according to the present invention can be represented by the following general formulae
:
A ⁺ X⁻
wherein
X⁻ represents an anion and
A⁺ represents an onium ion selected from any of the following general formulae :
wherein :
each of R₁ and R₃ (same or different) represents hydrogen, an alkylgroup, a substituted
alkyl group, a cycloalkyl group, an aryl group or a substituted aryl group,
R₂ represents any of the said groups represented by R₁ and R₃ or the atoms necessary
to close a heterocyclic nucleus with either R₁ or R₃,
the said onium ion being linked
1) to a polymer chain, or
2) via a bivalent organic linking group e.g., -0-, -S-, -S0₂-, ... to any other of
such onium structure, or
3) directly to any of the groups represented by R₁ except for hydrogen.
[0017] Suitable examples of onium compounds are disclosed in U.S. Patent 3,017,270.
[0018] In said specification suitable examples are mentioned of trialkyl sulfonium salts,
polysulfonium salts, tetraalkyl quaternary ammonium salts, quaternary ammonium salts
in which the quaternary nitrogen atom is a part of a ring system, cationic polyalkylene
oxide salts including e.g. quaternary ammonium and phosphonium and bis-quaternary
salts.
[0019] Onium salt polymers whereby the onium group may be e.g. an ammonium, phosphonium
or sulphonium group, are disclosed in U.S. Patent 4,525,446.
[0020] In order to provide stabilization of the precipitated silver halide when silicic
acid sol is used as protective colloid, the concentration of onium compound should
preferably be not less than 0.5x10⁻³ mol of onium compound and preferably be not higher
than 5x10⁻³ mol of onium compound per 90g of SiO₂.
[0021] The usual silicic acid sols are suitable for the process according to the invention,
regardless of whether the silicic acid has been prepared by a wet decomposition process
or a pyrogenic process.
[0022] Suitable silicic acid sols are commercially available such as the "Syton" silica
sols (a trademarked product of Monsanto Inorganic Chemicals Div.), the "Ludox" silica
sols (a trademarked product of duPont de Nemours & Co., Inc.), the "Nalco" and "Nalcoag"
silica sols (trademarked products of Nalco Chemical Co.), and the "Kieselsol, Types
100, 200, 300 and 600" (trademarked product of Bayer AG).
[0023] Preferably the colloidal silicic acid used has a specific surface area between 200
and 400 m2/g. When deciding upon the appropriate amount of colloidal silicic acid
to be used during the precipitation of the silver halide, the specific surface area
of the selected type of colloidal silicic acid should be taken into account.
[0024] Suitable results are also obtained when silicic acid sols containing up to 20 percent
by weight of aluminium oxide related to the solid content, are used.
[0025] The process of the invention is suitable for the preparation of silver halide emulsions,
the halide composition of which is not specifically limited and may be any composition
selected from i.a. chloride, bromide, iodide, chlorobromide, bromoiodide, and chlorobromoiodide.
The content of silver iodide is equal to or less than 20 mol%, preferably equal to
or less than 5 mol%, even more preferably equal to or less than 3 mol%.
[0026] The photographic silver halide emulsions used according to the present invention
can be prepared by mixing the halide and silver solutions in partially or fully controlled
conditions of temperature, concentrations, sequence of addition, and rates of addition.
The silver halide can be precipitated according to the single-jet method, the double-jet
method, or the conversion method.
[0027] Suitable preparation methods are described e.g. by P. Glafkides in "Chimie et Physique
Photographique", Paul Montel, Paris (1967), by G.F. Duffin in "Photographic Emulsion
Chemistry", The Focal Press, London (1966), and by in V.L. Zelikman et al in "Making
and Coating Photographic Emulsion", The Focal Press, London (1966).
[0028] The silver halide particles of the photographic emulsions used according to the present
invention may have a regular crystalline form such as a cubic or octahedral form or
they may have a transition form. They may also have an irregular crystalline form
such as a spherical form or a tabular form, or may otherwise have a composite crystal
form comprising a mixture of said regular and irregular crystalline forms.
[0029] The silver halide grains may have a multilayered grain structure. According to a
simple embodiment the grains may comprise a core and a shell, which may have different
halide compositions and/or may have undergone different modifications such as the
addition of dopes. The silver halide crystals can be doped e.g. with Rh³⁺, Ir⁴⁺, Cd²⁺,
Zn²⁺, Pb²⁺. Besides having a differently composed core and shell the silver halide
grains may also comprise different phases inbetween.
[0030] Further, during precipitation grain growth restrainers or accelerators may be added.
[0031] Two or more types of silver halide emulsions that have been prepared differently
can be mixed for forming a photographic emulsion for use in accordance with the present
invention.
[0032] The average size of the silver halide grains may range from 0,01 to 7 µm, preferably
from 0,01 µm up to 5 µm.
[0033] The size distribution of the silver halide particles of the photographic emulsions
to be used according to the present invention can be homodisperse or heterodisperse.
A homodisperse size distribution is obtained when 95% of the grains have a size that
does not deviate for more than 30% from the average grain size.
[0034] The emulsion can be desalted by ultra-centrifugal techniques, by dialysis, which
is a preferred method for the emulsions prepared in accordance with the present invention,
and ultrafiltration, by flocculation and re-dispersing, etc.
[0035] The light-sensitive silver halide emulsion can be a so-called primitive emulsion,
in other words an emulsion that has not been chemically sensitized. However, the light-sensitive
silver halide emulsion can be chemically sensitized as described i.a. in the above-mentioned
"Chimie et Physique Photographique" by P. Glafkides, in the above-mentioned "Photographic
Emulsion Chemistry" by G.F. Duffin, in the above-mentioned "Making and Coating Photographic
Emulsion" by V.L. Zelikman et al, and in "Die Grundlagen der Photographischen Prozesse
mit Silberhalogeniden" edited by H. Frieser and published by Akademische Verlagsgesellschaft
(1968). As described in said literature chemical sensitization can be carried out
by effecting the ripening in the presence of small amounts of compounds containing
sulphur e.g. thiosulphate, thiocyanate, thioureas, sulphites, mercapto compounds,
and rhodamines. The emulsions can be sensitized also by means of gold-sulphur ripeners
or by means of reductors e.g. tin compounds as described in GB-A 789,823, amines,
hydrazine derivatives, formamidine-sulphinic acids, and silane compounds. Chemical
sensitization can also be performed with small amounts of Ir, Rh, Ru, Pb, Cd, Hg,
Tl, Pd, Pt, or Au. One of these chemical sensitization methods or a combination thereof
can be used.
[0036] The light-sensitive silver halide emulsions can be spectrally sensitized with methine
dyes such as those described by F.M. Hamer in "The Cyanine Dyes and Related Compounds",
1964, John Wiley & Sons. Dyes that can be used for the purpose of spectral sensitization
include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine
dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. Particularly
valuable dyes are those belonging to the cyanine dyes, merocyanine dyes, complex merocyanine
dyes.
[0037] Other dyes, which per se do not have any spectral sensitization activity, or certain
other compounds, which do not substantially absorb visible radiation, can have a supersensitization
effect when they are incorporated together with said spectral sensitizing agents into
the emulsion. Suitable supersensitizers are i.a. heterocyclic mercapto compounds containing
at least one electronegative substituent as described e.g. in US-A 3,457,078, nitrogen-containing
heterocyclic ring-substituted aminostilbene compounds as described e.g. in US-A 2,933,390
and US-A 3,635,721, aromatic organic acid/formaldehyde condensation products as described
e.g. in US-A 3,743,510, cadmium salts, and azaindene compounds.
[0038] The silver halide emulsion for use in accordance with the present invention may comprise
compounds preventing the formation of fog or stabilizing the photographic characteristics
during the production or storage of photographic elements or during the photographic
treatment thereof. Many known compounds can be added as fog-inhibiting agent or stabilizer
to the silver halide emulsion. Suitable examples are i.a. the heterocyclic nitrogen-containing
compounds such as benzothiazolium salts, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles,
bromobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles,
mercaptothiadiazoles, aminotriazoles, benzotriazoles (preferably 5-methyl-benzotriazole),
nitrobenzotriazoles, mercaptotetrazoles, in particular 1-phenyl-5-mercapto-tetrazole,
mercaptopyrimidines, mercaptotriazines, benzothiazoline-2-thione, oxazoline-thione,
triazaindenes, tetrazaindenes and pentazaindenes, especially those described by Birr
in Z. Wiss. Phot. 47 (1952), pages 2-58, triazolopyrimidines such as those described
in GB-A 1,203,757, GB-A 1,209,146, JA-Appl. 75-39537, and GB-A 1,500,278, and 7-hydroxy-s-triazolo-[1,5-a]-pyrimidines
as described in US-A 4,727,017, and other compounds such as benzenethiosulphonic acid,
benzenethiosulphinic acid, benzenethiosulphonic acid amide. Other compounds that can
be used as fog-inhibiting compounds are metal salts such as e.g. mercury or cadmium
salts and the compounds described in Research Disclosure N° 17643 (1978), Chaptre
VI.
[0039] The fog-inhibiting agents or stabilizers can be added to the silver halide emulsion
prior to, during, or after the ripening thereof and mixtures of two or more of these
compounds can be used.
[0040] The photographic element of the present invention may further comprise various kinds
of surface-active agents in the photographic emulsion layer or in at least one other
hydrophilic colloid layer. Suitable surface-active agents include non-ionic agents
such as saponins, alkylene oxides e.g. polyethylene glycol, polyethylene glycol/polypropylene
glycol condensation products, polyethylene glycol alkyl ethers or polyethylene glycol
alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters,
polyalkylene glycol alkylamines or alkylamides, silicone-polyethylene oxide adducts,
glycidol derivatives, fatty acid esters of polyhydric alcohols and alkyl esters of
saccharides; anionic agents comprising an acid group such as a carboxy, sulpho, phospho,
sulphuric or phosphoric ester group; ampholytic agents such as aminoacids, aminoalkyl
sulphonic acids, aminoalkyl sulphates or phosphates, alkyl betaines, and amine-N-oxides;
and cationic agents such as alkylamine salts, aliphatic, aromatic, or heterocyclic
quaternary ammonium salts, aliphatic or heterocyclic ring-containing phosphonium or
sulphonium salts. Such surface-active agents can be used for various purposes e.g.
as coating aids, as compounds preventing electric charges, as compounds improving
slidability, as compounds facilitating dispersive emulsification, as compounds preventing
or reducing adhesion, and as compounds improving the photographic characteristics
e.g higher contrast, sensitization, and development acceleration.
[0041] Development acceleration can be accomplished with the aid of various compounds, preferably
polyalkylene derivatives having a molecular weight of at least 400 such as those described
in e.g. US-A 3,038,805 - 4,038,075 - 4,292,400.
[0042] The photographic element of the present invention may further comprise various other
additives such as e.g. compounds improving the dimensional stability of the photographic
element, UV-absorbers, spacing agents, hardeners, and plasticizers.
[0043] In case the emulsion has been prepared in accordance with the most preferred mode
of application of the invention, i.e. precipitation in the presence of silicic acid
sol only, and if the ratio by weight of silicic acid sol over silver halide exceeds
0.5 and preferably exceeds 1.0, the addition of supplemental hardening agents is not
required to the emulsion so as to form photographic materials.
[0044] So as to reach the weight ratios of 0.5 and preferably 1.0 of silicic acid sol over
silver halide, apart from silicic acid sol being added during redispersion of the
emulsion, supplemental silicic acid sol should be added shortly before coating the
silver halide emulsion concerned on a suitable substrate such as, preferably, a thermoplastic
resin e.g. polyethyleneterephtalate.
[0045] If, however, apart from the silicic acid sol (an) additional protective colloid is
(are) present during the precipitation, then suitable additives for improving the
dimensional stability of the photographic element may be added, i.a. dispersions of
a water-soluble or hardly soluble synthetic polymer e.g. polymers of alkyl (meth)acrylates,
alkoxy(meth)acrylates, glycidyl (meth)acrylates, (meth)acrylamides, vinyl esters,
acrylonitriles, olefins , and styrenes, or copolymers of the above with acrylic acids,
methacrylic acids, Alpha-Beta-unsaturated dicarboxylic acids, hydroxyalkyl (meth)acrylates,
sulphoalkyl (meth)acrylates, and styrene sulphonic acids.
[0046] Plasticizers suitable for incorporation in the emulsions according to the present
invention are e.g. glycol, glycerine, or the latexes of neutral film forming polymers
including polyvinylacetate, acrylates and methacrylates of lower alkanols, e.g. polyethylacrylate
and polybutylmethacrylate.
[0047] Suitable UV-absorbers are i.a. aryl-substituted benzotriazole compounds as described
in US-A 3,533,794, 4-thiazolidone compounds as described in US-A 3,314,794 and 3,352,681,
benzophenone compounds as described in JP-A 2784/71, cinnamic ester compounds as described
in US-A 3,705,805 and 3,707,375, butadiene compounds as described in US-A 4,045,229,
and benzoxazole compounds as described in US-A 3,700,455.
[0048] In general, the average particle size of spacing agents is comprised between 0.2
µm and 10 µm. Spacing agents can be soluble or insoluble in alkali. Alkali-insoluble
spacing agents usually remain permanently in the photographic element, whereas alkali-soluble
spacing agents usually are removed therefrom in an alkaline processing bath. Suitable
spacing agents can be made i.a. of polymethyl methacrylate, of copolymers of acrylic
acid and methyl methacrylate, and of hydroxypropylmethyl cellulose hexahydrophthalate.
Other suitable spacing agents have been desribed in US-A 4,614,708.
[0049] The photographic silver halide emulsions can be used in various types of photographic
elements such as i.a. in photographic elements for graphic arts and for so-called
amateur and professional photography, diffusion transfer reversal photographic elements,
low-speed and high-speed photographic elements.
[0050] The following examples illustrate the invention. All percentages are percentages
by weight unless otherwise stated.
Example I
[0051] A photographic emulsion was prepared and coated on a support according to the following
procedure :
300 ml of 30 % silica sol, 'Kieselsol 300F' (trademarked product of Bayer A.G.), 100
ml of 1 % solution of a stabilizing sulfonium compound corresponding to the following
formula :
and demineralised water up to a total volume of 2000 ml were mixed with constant stirring
in a 12 l stainless steel vessel. Then the temperature was stabilised at 20°C, the
pH adjusted to 3.0 by the addition of a sufficient amount of 6N sulfuric acid and
the pAg was adjusted to 9.0.
[0052] Precipitation in the above medium took place in two subsequent stages under balanced
double jet conditions (2.94 mol potassium bromide and 2.94 mol silver nitrate) and
was pAg-controlled by regulating the flow of the alkali metal salt. The latter was
realised according to the automated electronic control apparatus for silver halide
preparation disclosed by Claes and Peelaers in Photographische Korrespondenz 102,
Band Nr. 10/1967, pp. 162.
[0053] The following two stages took place during the precipitation :
- first a crystallisation stage during a period of five minutes under a constant flow
of 20 ml/min, followed by
- a ripening stage during a period of twenty five minutes under a steadily increasing
flow of 20 up to 52 ml/min.
[0054] The above two stages took place under a pH which was constantly held at 3.0, a pAg
constantly held at 9.0, with constant stirring and whereby the temperature of the
silver bromide dispersion was stabilised at 20°C.
[0055] Hereafter the emulsion contained approximately 110 g of silver nitrate per kg of
the dispersion.
[0056] Thereupon the dispersion was subject to dialysis in a Holoflow dialysing tube type
F60 (trademark producted of Fresenius AG,D6370 Oberursel, F.R. Germany, dialyse-volume
of 75 ml) forming part of a closed circuit wherein the dispersion was circulated.
In a first step the dispersion showing an electrical conductivity of 100 mS was concentrated
within 30 min to half of its volume whereupon dialysis continued for another 30 min
period. The desalted dispersion then showed an electrical conductivity of approximately
2 mS and contained 225 g of silver nitrate per kg solution.
[0057] The ratio of silica sol over silver nitrate was then 0.18, whereupon it was increased
up to 0.2 by the addition of a sufficient amount of 30 % silica sol.
[0058] The dispersion was subjected to chemical ripening during 30 min at a constant pH
level of 5.0 and pAg value of 9.0 at a stabilised temperature of 20°C by addition
of 2.2x10⁻⁶ mol of Au³⁺ per 50 g of silver nitrate and 1.26x10⁻⁴ mol of S₂0
per 50 g of silver nitrate.
[0059] Then the ratio of silica sol over silver nitrate was increased up to 0.5 by the addition
of supplemental silica sol and the dispersion was manually coated in a thermo-stabilised
coating table at 50°C, on a support consisting of polyethylene coated paper carrying
a gelatine containing substratum layer (comprising 0.4 g of gelatin per square meter)
is coated.
[0060] Exposure during 10 sec by a tungsten bulb through a grey step wedge (with constant
factor 0.2) after processing yields seventeen visually discernible density gradations
in the photographic strip.
[0061] The light intensity as measured with a MAVOLUX light meter, type 'Electronic' (trademarked
product of Gossen GmbH, D8520 Erlangen, F.R. Germany) on the strips amounts to 1350
Lux. Processing took place in a conventional metol hydrochinon developer (buffered
at a pH of 10.2 with sodium carbonate) during one minute, followed by fixation during
30 seconds in a 0.9 molar ammonium thiosulfate bath stabilised at a pH of 5, followed
by rinsing in water during 30 seconds.
Example II (comparative example I)
[0062] A photographic emulsion was prepared according to the procedure described in Example
I; however no stabilising compound was used. The stability of the precipitated silver
halide was extremely poor and heavy sedimentation occurred.
Examples III to XVII
[0063] Photographic emulsions were prepared according to the procedure described in Example
I, except that the following compounds were used as stabilising compound :
Example III : same stabilising compound as example I,
Examples IV and V : a monosulfonium compound according to the following structural
formula :
Examples VI and VII : a monosulfonium compound according to the following structural
formula :
Examples VIII and IX : a iodonium compound according to the following structural formula
:
Examples X and XI : a quaternary ammonium compound (pyridine-derivative) according
to the following structural formula :
Examples XII and XIII : a selenonium compound according to the following structural
formula :
Examples XIV and XV : a phosphonium compound according to the following structural
formula :
Examples XVI and XVII : a polyphosphonium compound according to the following structural
formula, n being 22 :
[0064] In the examples I and II the precipitation took place at a stabilised temperature
of 20°C. Since the stability of a silica sol decreases with increasing temperature,
the silver halide precipitation in all the other examples III to IXX has been carried
out at a temperature of 60°C so that the stabilizing effect of the onium compound
could better be evaluated.
[0065] In table I the concentrations at which the different onium-stabilising compounds
are used are set forth, as well as the results of the precipitation step in terms
of stability of the suspension and degree of sedimentation, if any.
[0066] The concentrations of stabilising compound set forth in Table I are all expressed
in 10⁻² mol of stabilising compound per 90 g of silica sol. The values set forth for
stability are the results of measurements resp. calculations in accordance with the
following procedure.
[0067] At the end of the precipitation step a 10 ml sample of emulsion is brought into a
10 ml graduated cylinder. The stability of the emulsion is then measured as a function
of time by checking the visuability of a sign (e.g. an arrow) which is affixed at
the rear of said graduated cylinder. When the sign is visual, the level till which
the visuability reaches is noted. The evolution of this level as a function of time
is taken as a measure for the stability.
[0068] The values measured in accordance with the preceding procedure are then plotted in
a graph as a function of time as illustrated in figure 1. In the abscis the time (expressed
in minutes) is set forth whereas in ordinate the level is noted. The ratio of the
surface under the graph for a period of 30 minutes over the surface of a constant
level of 10 held for a period of 30 minutes is regarded as a measure of stability.
[0069] The stability is then expressed as follows :
[0070] From the above it is apparent that the closer the stability value approaches 1, the
higher the stability of the emulsions.
[0071] If the value for stability equals 0, the stability is minimal, whereas if the value
equals 1, the stability is maximal.
[0072] The values for stability obtained in accordance with the above measurements and calculations
should be interpreted as follows :
- value equalling 1.00 :
- excellent stability, at least for a period of 30 minutes but in most cases for more
than two hours
- values between 1.00 and 0.97 :
- moderate stability
- values under 0.97 :
- insufficient stability (not suited for further processing).
[0073] The values set forth for sedimentation should be interpreted as follows :
- -
- : no formation of sediment
- +
- : some sedimentation
- ++
- : heavy sedimentation
- +++
- : very heavy sedimentation.
Example XVIII
[0075] A photographic tabular grain emulsion was prepared and coated on a support according
to the following procedure :
2000 ml of demineralised water, 83 ml of 30 % Kieselsol 300F (trademarked product
of Bayer AG), 18.5 ml of a 1 % solution of the stabilising compound as described in
Example I were mixed under constant stirring in a 12 l stainless steel vessel. After
heating up to 70°C (under continuous stirring), 1045 ml of demineralised water were
added, the pH of the solution was brought to 3.0 by the addition of 6N sulfuric acid,
and the pAg was brought to 9.49 by addition of a 2.94 molar solution of potassium
bromide.
[0076] Precipitation in the above medium took place in two subsequent stages :
1) under balanced double jet conditions during a period of 18 sec flows of silver
nitrate and potassium bromide were added at a rate of 25 ml/min; pAg control was effected
according to the same method as described for example I. Hereafter physical ripening
took place during 15 min at 70°C; then over a period of 5 minutes a silica sol solution
according to the following composition was added dropwise : 217 ml of 30 % silica
sol, 36 ml of a 1 % solution of the stabilising compound described in Example I, and
460 ml of demineralised water, the pH of the solution being adjusted to 3.0.
2) the pAg of the solution was adjusted to 9.05, then under balanced double jet conditions
and with the pAg control method as described hereinbefore, the flows of silver nitrate
and potassium bromide over a period of 64 min and 10 sec were steadily increased from
5 to 24.4 ml/min.
[0077] Hereafter the dispersion was cooled from 70 to 20°C under constant stirring and further
washed by dialysis as described in Example I. The aspect ratio was measured and found
to be between 2,5 and 6, but if so desired may be increased up to 12.
[0078] The results in terms of stability and possible sedimentation of the photographic
emulsion obtained according this procedure are also set forth in Table I.
Comparative examples II to IV
[0079] A photographic emulsion was prepared according to the procedure described in Example
I; however, instead of the sulfonium compound of said example the following compounds
were used (the use of these compounds is suggested for precipitation to take place
in the abscence of gelatin and in the presence of silica in the US Patent 3,637,391
cited hereinbefore) :
in comparative example II : ethanol (96 %)
in comparative example III : polyvinylalcohol
in comparative example IV : polyvinylalcohol
in comparative example V : polyacrylamide
[0080] In table II the results of said comparative examples in terms of stability and sedimentation
are set forth. The figures, resp. values for stability and sedimentation set forth
in Table II are the result of measurements resp. calculations according to the same
procedure as these set forth in Table I, and should be interpreted accordingly.
[0081] The polyvinylalcohols used in the comparative examples III and IV show an intrinsic
viscosity of 5, resp. 28, when measured at 20°C in a 4 % by weight aqueous solution
of said polyvinylalcohol.
[0082] From the above examples it is apparent that a fully stabilised silver halide dispersion
in silica sol without sedimentation can only be achieved when a stabilising compound
as described and claimed according to the present invention is used.
1. Ein Verfahren zur Bereitung einer lichtempfindlichen Silberhalogenidemulsion einschließlich
der Fällung von Silberhalogenid in Anwesenheit einer kolloidalen Kieselsäure, die
als Schutzkolloid dient, dadurch gekennzeichnet, daß die Fällung von Silberhalogenid
in Anwesenheit einer Oniumverbindung, Ammoniumbromid ausgenommen, stattfindet.
2. Das Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß die Oniumverbindung der
nachstehenden allgemeinen Formel entspricht:
A⁺ X⁻
in der bedeuten:
X⁻ ein Anion und
A⁺ ein Onium-Ion, das aus irgendwelcher der nachstehenden allgemeinen Formeln gewählt
wird:
in denen bedeuten:
R¹ und R³ (gleich oder verschieden) je ein Wasserstofatom, eine Alkylgruppe, eine
substituierte Alkylgruppe, eine Cycloalkylgruppe, eine Arylgruppe oder eine substituierte
Arylgruppe,
R² irgendwelche der von R¹ und R³ dargestellten Gruppen, oder die notwendigen Atome
zum Schließen eines heterocyclischen Ringes mit entweder R¹ oder R³,
wobei das Onium-Ion verbunden ist
1) mit einer Polymerkette, oder
2) über eine zweiwertige organische Verbindungsgruppe mit irgendwelcher anderen derartigen
Oniumstruktur, oder
3) direkt mit irgendwelcher der von R¹ dargestellten Gruppen, das Wasserstofatom ausgenommen.
3. Das Verfahren gemäß Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Oniumverbindung
in einem Gehalt anwesend ist, der zumindest mit 0,5 10⁻³ mol pro 90 g Kieselsäure-Sol
übereinstimmt.
4. Das Verfahren gemäß irgendwelchem der vorstehenden Ansprüche, dadurch gekennzeichnet,
daß die kolloidale Kieselsäure eine spezifische Oberfläche zwischen 200 und 400 m²/g
hat.
5. Das Verfahren gemäß irgendwelchem der vorstehenden Ansprüche, dadurch gekennzeichnet,
daß außer der kolloidalen Kieselsäure Gelatine als zusätzliches Schutzkolloid anwesend
ist.
6. Das Verfahren gemäß Anspruch 5, dadurch gekennzeichnet, daß zumindest 75 Gew.-% des
in der Silberhalogenid-Fällung verwendeten Schutzkolloids aus kolloidaler Kieselsäure
besteht.
7. Das Verfahren gemäß irgendwelchem der vorstehenden Ansprüche, das weiterhin das Wiederdispergieren
des niedergeschlagenen Silberhalogenids in Anwesenheit kolloidaler Kieselsäure umfaßt.
8. Ein lichtempfindliches Silberhalogenidmaterial, das einen Träger umfaßt, auf dem sich
zumindest eine lichtempfindliche Silberhalogenidschicht befindet, in die ein Kieselsäure-Sol
als schützendes Kolloidbindemittel und eine Oniumverbindung, Ammoniumbromid ausgenommen,
einverleibt sind.
9. Ein lichtempfindliches Material gemäß Anspruch 8, dadurch gekennzeichnet, daß die
Oniumverbindung der nachstehenden allgemeinen Formel entspricht:
A⁺ X⁻
in der bedeuten:
X⁻ ein Anion und
A⁺ ein Onium-Ion, das aus irgendwelcher der nachstehenden allgemeinen Formeln gewählt
wird:
in denen bedeuten:
R¹ und R³ (gleich oder verschieden) je ein Wasserstofatom, eine Alkylgruppe, eine
substituierte Alkylgruppe, eine Cycloalkylgruppe, eine Arylgruppe oder eine substituierte
Arylgruppe,
R² irgendwelche der von R¹ und R³ dargestellten Gruppen, oder die notwendigen Atome
zum Schließen eines heterocyclischen Ringes mit entweder R¹ oder R³,
wobei das Onium-Ion verbunden ist
1) mit einer Polymerkette, oder
2) über eine zweiwertige organische Verbindungsgruppe mit irgendwelcher anderen derartigen
Oniumstruktur, oder
3) direkt mit irgendwelcher der von R¹ dargestellten Gruppen, das Wasserstofatom ausgenommen.
10. Ein lichtempfindliches Material gemäß Anspruch 8 oder 9, dadurch gekennzeichnet, daß
die Oniumverbindung in einem Gehalt anwesend ist, der zumindest mit 0,5 10⁻³ mol pro
90 g kolloidale Kieselsäure übereinstimmt.
1. Un procédé pour la préparation d'une émulsion à l'halogénure d'argent sensible à la
lumière, y compris la phase de la précipitation d'halogénure d'argent en présence
d'acide silicique colloïdal servant de colloïde protecteur, caractérisé en ce que
la précipitation d'halogénure d'argent s'effectue en présence d'un composé onium,
excepté le bromure d'ammonium.
2. Le procédé selon la revendication 1, caractérisé en ce que le composé onium correspond
à la formule générale suivante:
A⁺ X⁻
dans laquelle:
X⁻ représente un anion, et
A⁺ représente un ion onium, choisi dans l'une quelconque des formules générales suivantes:
dans lesquelles:
R¹ et R³ (identiques ou différents) représentent chacun un atome d'hydrogène, un groupe
alkyle, un groupe alkyle substitué, un groupe cycloalkyle, un groupe aryle ou un groupe
aryle substitué,
R² l'un quelconque des groupes représentés par R¹ et R³, ou les atomes nécessaires
pour fermer un noyau hétérocyclique avec R¹ ou R³, l'ion onium étant lié
1) à une chaîne polymère, ou
2) via un groupe de liaison organique bivalent à n'importe quelle autre d'une telle
structure onium, ou
3) directement à l'un quelconque des groupes représentés par R¹, excepté l'atome d'hydrogène.
3. Le procédé selon la revendication 1 ou 2, caractérisé en ce que le composé onium est
présent dans un taux correspondant à au moins 0,5 10⁻³ mole par 90 g de sol d'acide
silicique.
4. Le procédé selon l'une quelconque des revendications précédentes, caractérisé en ce
que l'acide silicique colloïdal a une aire de surface spécifique entre 200 et 400
m²/g.
5. Le procédé selon l'une quelconque des revendications précédentes, caractérisé en ce
que, outre l'acide silicique colloïdal, de la gélatine est présente comme colloïde
protecteur additionnel.
6. Le procédé selon la revendication 5, caractérisé en ce qu'au moins 75 % en poids du
colloïde protecteur utilisé dans la phase de précipitation d'halogénure d'argent consiste
en acide silicique colloïdal.
7. Le procédé selon l'une quelconque des revendications précédentes comprenant en plus
la phase de la redispersion de l'halogénure d'argent précipité en présence d'acide
silicique colloïdal.
8. Un matériau à l'halogénure d'argent sensible à la lumière comprenant un support portant
au moins une couche à l'halogénure d'argent sensible à la lumière incorporant un sol
d'acide silicique comme liant colloïdal protecteur et un composé onium, à l'exception
de bromure d'ammonium.
9. Un matériau sensible à la lumière selon la revendication 8, caractérisé en ce que
le composé onium correspond à la formule générale suivante:
A⁺ X⁻
dans laquelle:
X⁻ représente un anion, et
A+ représente un ion onium, choisi dans l'une quelconque des formules générales suivantes:
dans lesquelles:
R¹ et R³ (identiques ou différents) représentent chacun un atome d'hydrogène, un groupe
alkyle, un groupe alkyle substitué, un groupe cycloalkyle, un groupe aryle ou un groupe
aryle substitué,
R² l'un quelconque des groupes représentés par R¹ et R³ ou les atomes nécessaires
pour fermer un noyau hétérocyclique avec R¹ ou R³, l'ion onium étant lié
1) à une chaîne polymère, ou
2) via un groupe de liaison organique bivalent à n'importe quelle autre d'une telle
structure onium, ou
3) directement à l'un quelconque des groupes représentés par R¹, excepté l'atome d'hydrogène.
10. Un matériau sensible à la lumière selon la revendication 8 ou 9, caractérisé en ce
que le composé onium est présent dans un taux correspondant à au moins 0,5 10⁻³ mole
par 90 g d'acide silicique colloïdal.