Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ his invention relates to a photo~raphic silver
halide emulsion in which the sensitivity is increased by
sub-tllreshold prelimina~ exposure to ionising ra~iation at
any sta6e during precipitation of the silver halide but
before com~letion ol` this precipitation, so that tlle silver
halide grains of the emulsion contain an outer zone of
silver halide which is not expose~ to this sub-tllresllold
radiation.
Photographic silver halide emulsions are adjusted
to the desired sensitivity to light by physical or chemical
measures. In practice, it is generally desired to combine
the highest possible sensitivity with the least possible
~og. The incre~se in sensitivity is m~inly achieved
by so-called physical ripening and ohemical ripening or
after-ripening.
Other measures for increasing the sensitivity are also
~nown, but they have achieved very limited, if any
importance in practice. These measures include the
sensitization o~ plloto~rapllic silver halide layers by a
sub-tl~reshold diffuse preliminary exposure. l~len a layer
has been subjected to such a preliminary exposure, it is
more scnsitive to a second, imagewise exposure than an
i~cntical layer wllicll l~a~ IIVt bcen subjecte~ t~ tllis
preliminary treatment.
~5 By "su~-tllresllo1d'l is mcant an exposure W}~iC]I 011 itS
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own, doe~ not render the photographlc layer dcvelopable to
any signlficant extentO Thi~ di.ffu~e preliminary exposure may
be carried out, for ex~mple, wi.th light a~ described by
POC. BURTON and WoF~ BERG, Phot;.J. 86 B, 2 (1946) or wlth
ionizing radiation,.e~gO X-ray~ or ~-ray~ as desoribed by
D~Ro CALLABY, J.PhotogrOSci~ 13, 1 (1965~
The so-called sub.latent image nuclei produced by such
preliminary exposure to light or other radiation di~fer con-
siderably in their action and consequently al~o in their
size and nature, ~rom the ripening nuclei produced by
chemical ripening, e CgD with gold and/or sulphurO
According to U.SO Patent NoO 3,852,072~ the e~ect of the
sub-threshold preliminary exposure to high energy radiation,
is utilize~ by incorporatin6 a radioactive preparation in
the finished layer. This is said to increase the sensiti~-ity
of the layer, but it can hardly be of any practical
importance since it is extremely difficult, when incorporating
radioactive preparations in a photographic layer, to
prevent excessive fo6gin6 which would be liable to cause
spontaneous development and thereby render the photograpllic
layer unusable. Anotller reason why the e~fect of increasil10
the sensitivity by sub-threshold di~fuse preliminar~
exposure with hi6ll energy radiation llas not acquire~ any
importance in practice isi that the effect achieved is
considerably less than the increase in sensitivity
achieved by conventional measures, particularly chemical
ripening. It was not possible to employ a combination
o~ the kno~ measures because silver halide emulsions
whi~lllave been subjected to sub-threshold preliminary
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expo~ure as described above undergo such severa fogging when
Rubsequently ripened by chemical means that they become un-
usuableO I~ i~ an ob~ect of this invention to provide photo-
graphic ~ilver halide emulsions which have increased sensi-
tivityO Photographic silver halide emul~lon~ with increasedsensitivity have now been fou~ld, which are obtained by
exposing the silver halide emulsions to an ionisin6 radiation
at any stage of tlleir preparatiOn , this exposure to
radiation being carried out for va~in6 lengtl~s o~ time
an~ at various sta~cs of tlle preparation process accor(lill6
to the effect desired by always in such a manner tllat it
is termillated before the silver halide graills reacll tlleir
final size, so tllat the grain contains an outer p~ase of
silver halide wllicll has not been exposed to sub-tllreshold
radiation.
Tlle exposure to radiation may be continued throu~hout
the prccipitation prucess or it`may be carried out inter-
mittelltly, for example by interrupting preci~itation alld
then irradiatin~ the elnlllsion obtained at tl~e moment ~he
precipitation was interrupted, and then continuing t}le
precipitation process without irradiation. The-only necessary
condition is tl~at the e~posure to radiation must be stopped
before the silver halide crystals have reached their final
size. The axposure to radiation may be carried out within
a wide temperature range.
me ionising rays employed may be high energy electron
ray~, X-rays or, preferably, ~-rays, e~g. of a radioactive
element.
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The silver halide emulsion according to the in~ention
contains silver halide grains up to 99 % by volume of which
may contain, in their interior, sub-image nuclel obtained by
the irradiation with ionising :ray~ according to the inventionO
This means that exposure to the high energy rays must be
stopped at the latest when the emulsion grains ha~e reachc~
9S '0 by volume, and preferably when tlley have reached ~0 to
95 q' by volume of their final si~e.
The duration and intensity of irradiation shollld ~e
calculated so tllat wllen a sample which has been ta~en
immcdiately artel- irradiation w~s stopped ~llt ~ol e rul~tllcr
precipitation ol` the cululsion, is cast on a la~cr s~ trat~
dricd and dcvelol)cd Wit31011t lurther exposul~e to ligllt in a
developer of the following composition (5 minutes at 20C):
p-~lethyiaminophenol l 6
llydroquillone 3 6
Sodium sul~)hite 13 g
Sodium carbonate ~6 6
Potassium bromide l g
Water to make up to lO00 mlO
the quantit~ o~ cilver developed in the sample correspond~
to at the most 20~, preferably from l to 1050, of thc
quantity of silver halide in the layer.
This means that the silver halide grains have not become
spontaneously developable to full intensity by the
sub-threshold preliminary exposure.
The emulsion according to the invention may consist
of a single halideJ e.g. of chloride or bromide, or of a
~ halide mixture and the h~lides may also contain silvcr iodi~e,
¦ A-G 1581 5 _
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~7
in particular up to lO mol ~.
In the case of mixed silver halides, the mixed halide
may be uniformly distributed within tlle ~rain or tlle
individual halides may be present in different concentrations
within the grain. Emulsions of the last mentioned type
may be prepared, ~or exanple, by the processes described
in German Patent No. 1,169,290; Britis}l Patent No. 1,027,146
or German O~fenlegungsschriften No. 2,~08,2~9 and
2,332,80
Both homodisper~e silver halide emulsion~ and hetero-
disper~e emul~lons m~y be prepared by the process according
to the inventionO
By "l~omodisperse emulsions'l are meant those ~ ich h2Ye
a narrow grain size distribution. Preferably, about 95~0
~5 by wei~llt of tlle silver llalide ~r~ins Or SUC~I emulsions
llave a diameter wllicll deviates ~y not more than 40 ,b, pre~erably
not more tlla-l 30 ~, Irom tlle avera~e grain dialllcter.
Tlle silver halide grains may have any of the ~nown f~ls9
e.g. they may be cubica1, octalledric or mixed tetra-
decalledric.
~ y "lleterodisperse emulsions" are meant in particularemulsions whic~h llave a relatively wide distribution of
~rain sizes. Prelerably at least 10 ~b by wei~llt, more
preferab1y at least 20 ,' by wei~llt oI the silver halide
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grains in such emulsions have a diameter which deviates
by at least 40 C~6 from the avera~e grain diameter. Tlle
silver halide grains of l~eterodisperse emulsions are mainly
irregular in sllape.
The absolute value of the avera~e grain size of the
emulsions accordin~ to the invention or of the emulsions
prepared by tl~e process accordin~ to the invention m~y
vary within wide limits. Both fine-grained silver llalide
emulsiolls llaving an avera~e grain diameter belo~Y 0.5 ~m,
preferably below 0.3 ~um, and coarse-~raine~ emulsions with
avera~re grain diameters of between 0.5 and 4 ~lm may be
prepared, according to tlle intended purpose for WhiCIl t}le
photo~raphic material is to be used.
The hnown princlpla3 of preparing 3ilver halide emul~ion~,
as regard~ the condition3 o~ precipitation and ripening can be
applied~.
T}lus, in the case of heterodisperse emulsions, a suitable
aqueous halide solution having a certain gelatine content
would generally be proYided and an aqueous silver salt
solution, 6enlerally an aqueolls silver nitrate solution,
would be ad~ed with stirring. The process may be modified
in v~riolls ways as rcgal-~s tlle temyerature, pll or ~ g v.~ es,
depending on the intended use and nature of the emulsion.
Alternat:ively, tlle so-called double inflow proc~ss
may be employe~, particularly for the preparation Or
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7~1~
homodisperse emulsions. Suitable processes of tl~is type
have been described in British Patent No. 1,027,146 and
,
in the publication by E. KLEIN and E. MOI~AR .
"Beric~lte der Bunsen~esellsol~a~t f~r physil;aliscllc
Chemie, 67 (1963), pages 349 - 355.
Tlle usual hy~rophilic film ~ormers may be used as
protcctiYe colloi~s ~r ~in~ers for tlle silvcr llulidc cln~llsion
layer, for cxumple ~rotcins, in particular ~elatillc, ul~inic
acid or its derivatives ~ucll as its esters, amides OI`
salts, cellulose ~erivatives such as carboxymetllyl cellulose
and cellulose sul~hates, starches or derivatives tllereof or
lly~ropllilic syntlletic binders such as polyvinyl alcollol,
partially saponifie~ polyvinylacetate or polyvinylpyrrolidone.
~lixed with the llydrophilic bin~ers, tlle layers may contain
other-synt}letic binders in the rOrm of solutions or
dispersions, such us homopolymers or copolymers of acIylic
or metl~acrylic acid or derivatives thereof, such as ~lle
esters, amides or nitriles, or vinyl polymers such as vinyl
esters or vinyl ethers.
The usual substrate layers may be used for tlle emulsions
accordin~ to the invention, e.g. substrates o~ cellulose
esters such as cellulose acetate or cellulose acetobutyrate,
or polyesters, in particular polyetl~ylene tereplltllalate or
polyoarbonate~" especially t}~ose based on bis-phenylolpropalle.
~5 Pupcr sl~bstratcs mny also ~c llscd, an~ tllesc muy cl~utuin
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water impermeable polyole~in layers, e.g. layers of polyetllylene
or polypropylene. Glass~or metRl substrates may also ~c
used.
Since the emulsions according to the invention can be used
as negatiYe emulsions with high and maximum sen~itivity in one
preferred embodiment, ths silver halide emulsions which are pro-
cea~ed in the u~ual manner after pr~cipitation can be chemicallyripened to its optimum sensitivity on the surface. This
may be carrie(l out by any o~ the three main processes
~nown Ior chemical sensitization, namely ripening witll
noble metals and/or wit}l sulpllur compounds, optionally also
with selenium or telluriwn compounds, or reduction ripenin~.
Tlle eDIulsions may, of coursc, nlso ~e treated in ~l~ol~
manner by the addition of active 6clatine containin~ ccrtain
ripening compounds of the sulpllur groups. ~Sethods of
this type are known in tlle literature, and they have been
disclosed Ior examplc, in U.S. Patents No. l,574,'~ t;
l,6239~99 and 2,4lO,689.
The compounds used lor ripening with noble metals are
mainly gold compoun~s ~ut also compounds of metals of
~roup VIII of tlle Periodic System, e.g. ruthenium, rhodium,
palladillm, iridium or platinum. 5uitable salts Or these
metals include potassium chloroaurite; potassium
aurothiocyaLa~;e; po~as~iumlohloroaurate; gold
~5 trichloride; aluminium cllloropalladate; potassium chloro-
platinate and sodium chloropalladite.
A-G 1581 ~ 9 ~
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Tlle sulphur compounds used are mainly thiosulphates,
thioc~anates and or~anic sulphllr compounds
The kno-~ methods may be ùsed for reduction ripenil~-r,
e.~. ripening with tin (II) salts, polyamille, e.~.
dieth~lenetriamine, or bis(~-aminoethyl)-sulphid .
Tlle negative silver llalide emulsions of tlle type descri~ed
above have a preferential snrIace sensitivity. Such e~ulsion~
are generally characterised by optimal chemical ripening Or tlle
surface.
The process accordin6 to the invention and the emulsions
according to tlle invention are, however, also suitable for
the preparation of emulsiol~s of the internal nuclear t~-pe, i.e.
those whicll, cither preferentially or in addition, lla~e a
hi~h internal sensitivity. Accordin6 to the invention, such
emulsions are prepared by continuoùsly or intermittelltly
irradiating during the process Or preparation and chemically
ripening eitber at the same time or during subsequent
precipitation without irradiation, or producin~ a halide
pllase boundary to increase the internal sensitivity. Lastly,
the layered grain structures produced in this way are
precipitated to their final size. Such grains with a laycred
grain structure or l~nli~le phase b~ aries l)ave bccll (lexcri~cd
in the above ~entioned German Patent No. 1,169,290 and in
Gcrmall O~fenlc~ ssclllir-ten No. 2,~08,2;9 and 2,3~'~,802.
As will be clear from what has been said above, the
~-G 1581 - 10 -
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emulsions according to the invention or emulsions produced
b~ the process according to the invention may be used ill a
wide variety of ways They are preferably used as high
sensitivity negative emulsions but ~ay also be used for
the preparation of unfogged direct positive sil~er halide
emulsions, i.e. e~ulsions wllich have a relatively higll
internal grain sensitivity without a surface fog. Such
e~ulsions may be chemically sensitized on the surface to a
certain extent, and they are developed under fo~gin6
conditions.
The silver halide emulsions prepared by the process
according to the invcntion may contain the usual emulsions
additives, dcpending on the type of emulsion and thc pur~ose
for wllicll it is to be used.
Tlle emulsions may contain the usual stabilisers, e.g~
homopolar compounds or salts of mercury containing aromatic
or heterocyclic rin~s, such as mercaptotriazoles, sil~plc
mercury salts~ sulphonim mercury double salts and other
mercury co~lpounds. Azaindenes are also suitable stabilisers,
particularly tetra-an~ penta-azaindenes and esy~ially those
whicll are sul)stituted Wit}l hydroxyl or amino groups. Compounds
Or this type h~vo becn ~escribed in the article by B~rr, Z.
Wiss. Phot., /17(1962), pnges 2 to 58. Other suitable
stabilisers include, inter alia, heterocyclic mercapto
colllpoulllls, e.g. ~uhcrlyllllercaptotetra~ole, quaterllury llCllZO-
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766
thiazole deri~at~ves and b~nzotrla~ole"
Further ~uitable stabillzers have been described in
G~rman Offonlagungs-~chrlft 2 416 814.
The emulsions may also be spectrally ~ensitized. The
usual monomethine or polymethine dyes such as acid or basic
c-anines, hemicyanines, streptocyanines, merocyanines,
oxonoles, hemioxonoles and styryl dyest as well ~s trinuclear
or hi6ller nuclear methile dyes such as rllodacyanines or
neocyanines are suitable for this purpose. Sensitiæers of
this type have been describe~, for example, in tlle ~ork by
F.M. Hamer, "The Cyanine Dyes and Related Compounds" (1964),
Interscience Publishers, Jolln Wiley and Sons.
The present invention may be applied both to tlle
production of black and white image3 and to the production
of colour photo~raphic ima~es. The process for WlliCIl the
photographic material is used may vary, ~or example,
according to the gradation o~ the silver halide emulsion
layer, steep grad~tions bein~ suitable for phototechnical
purposes while medlum or flat gradatlcns are suitable Ior the
20 production oP blRck-aald-white continuous-tone im~ge~ or X-ray
photo6raplls, Coloured photo6ra~hic images may be pIoduced,
for example, according to the known principle o~ chromogellic
development in tlle presence o~ colour couplers whicll l'C~Ct
with the oxidation product o~ colour-producing p-pl~enylene-
dlamine de~elopers to form dyes.
These colour couplers may be added to the silver llalideemulsion layer9 or the ¢olour coupler may be added according
~: 15f~ ``;12 -
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3L~Z~7~i~
to ~he principle of the so-called incorporation develo~ment
process.
Incorporation of the colour couplers in the emulsion
layer may be carried out ~y the usual metllods, for e~atnple,
~ater soluble colour couplers which contain one or more
sulpllo or carboxyl ~roups in tbe form of the free acid or
of a salt ntay be a~ded to the casting solution for tlle
etnulsion from an aqueous solution, optionally in the presence
of an alkali. Colour couplers which are insoluble or insufI-
iciently soluble in water are added in the ~orm of a
solution in a suitable hi~h boiling, oil-forminO or low
boilin~ organic solvent or solvent mixture, WlliCIl lltay OI'
may not be miscible witll water. Tllls solution mn~ ~e
~ispersed in tho aqueous solution of a protecti~e colloid,
optionally in the presence of a surface active a~ent.
The entulsiol1s accordin~ to the invention may be
used in known manner $or instant colour develop~tent processes
or colour transfer processes. In tl~ese processes, tlle
dyes for t~le partial colour images diffuse illtO an ima~e
receiving layer wllere they became firmly fixed, or tlle colour
couplers diffuse into tl1e im~ge receivin~ layer wllere tlley
are convcrted to tl~c ima~o ~yo a~tcr tlle usual colou
ro~ucin~ ~evolo~)mettlt. Colour trans~er processes an~
couplers use~ in such processes have also been ~escribed in
U.S. Patents Nos. 2,983,606; 3,087,817; 3~185,567; 3,227,550;
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)766
3,227,551; 3,227,552; 3,227,551~; 3,253,915; 3,415,644;
3,415,645 and 3,415,646.
The emulsions according to the invention may also be
used for colour transfer processes in which tlle particular
layer also contains a diffusion resistant compound
col~ituting a dye or dye precursor from wllioll a diffusible
dye, preferably one containing acid groups, is released ~y the
oxidation products of t21e photo~raphic developers produced in
ima6ewise distribution when development is carried out in tlle
presence of the alkaline processing material.
Vsrious chemical compounds are available for this purpose.
The diffusion resistant colour producing substances according
to U.S. Patent No, 3,628,95", for example, are par~icularly
suitable. These compounds split off diffusible dyes when
tlley react with the oxidation products Or black and white
developers or colour developers. Another useful series of
compounds has been described in German Patent No. 1,095,115.
en these compounds react with oxidized colour developer,
they 6ive rise to diffusible dyes ~enerally belon~in~ to the
azomethine dye series. Another suitable colour producing
system has been described in U.S. Patent Nos. 3,443,939 and
3,l~l~3,9ll0. In this systcm, diffusible dyes are split off by
reaction witll oxidized developer substances w!licil is
accompanied by ring closure.
The invention will now be further described Witil
reference to the followin~ Examplcs.
¦-A-C 1581 ~ 4
76~i
~:XAMPLE 1
A h~modisperse silver bromide emulsion having a cubical
crystal structure and a particle ~ize o~ 003/um was prepared
by the double inflow of pota~sium bromide and silver nitrate
solutions under controllad condition~ at a pAg value of 6.8
and a pH of appr. 50
~ This emulsion used as starting emulsion was
divided into portions. Comparison emulsion (A) was
prepared from one portion of the starting emulsion by
continuing the~process of precipitation by pA~-controlled
double inflow of a 3N silver nitrate solution, adjusted
by nitric acid to pll = 3.0, an~ a ~N yotassium bromide
solution, the qll~ntity of silver bromide produced in tl~is
second stage of precipitation amounting to 25 ~ of the
qu3ntity of silver bromide present in the starting emulsion.
To prepare the emulsion (B) according to the invention,
an aliquot portion of the startin6 emulsion was e.~posed to a
cobalt 60 sollrce of ~-radiation for 30 minutes at
approxiolately 10C. Tllc ~ctivity of tlle emittcr w~s
about l,l x 109 S l and the distance between the source
of radiation an~ tlle emulsion about 0.4 m. After irradatio
had been tenninated, precipitation was continued in the
same way as in comparison emulsion (A). Both emulsions
were cast on film supports in the usual manner, exposed
behind a grey wedge and developed for five minutes in a
developer havin6 the coolllosition previously indicated
A-a 1581 - 15 -
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The threshold sensitiYl$ies recorded at a ~ensity of
S = 0.1 were as follows:
~nulsion (A) 13 stages (0.1)
ulsion (B) 16 sta~es.
Emulsioni(B) according to the invention thererore
has a higher sensitivity by 0.3 log It units.
E~PLE ~
An emulsion was precipitated by the addition of a
solution of 200 g of silver nitrate in 2 litres of ~ater
to a solution of 10 g of gelatine, 130 g of ammonium bromide
and 16 g of potassium iodide in 2 litres of ~ater.
The precipitated emulsion was freed ~rom ~oluble
salts by the usual method of flocculating and, after
redispersion in a solution of 200 g of gel~tine in 2 litres
o~ water, it was used as starting emulsion.
3~0 ml of lN silver nitrate, adjusted to pH = 3.0
with nitric acid, and 120 ml of 3N potassium bromide were
addcd to 900 ~ Or the starting emulsioD by a process of
double inflow for tllirty minutes at 60~C. Tlle resulting
emulsion was uscd as comparison emulsion (C). To
prepare tlle emulsion (D) according to the invention, a
furtller ~0 y, Or tlle startin~ emulsion were expo~ed to a
A-G 1581 - 16 ~
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cobalt 60 source of y-radiation at approximately IO~C.
Tlle activity of the emitter was 8.6 x lOlO S l and
the distance between the source of radiation and tl~e
emulsion was about 0.4 ID. After irradiation was tel~inated,
precipitation was continued as for comparison emulsivn (C).
Both emlllsions were then ripened at 50~C for 120 minutes,
after the addition of 9 ~l of 2.5 x lO 4 mol of Na_AIl(S203)2
~olution per 150 g of emulsion. The ripened emulsions
were then cast on film supports, exposed behind a grey
wedge and developed for five minute~ in the developer specified
above.
The thresllold sensitivities recorded at a density of
S = O.l were as ~ollow~:
Emulsion (C) 21 stages ~O.l~
~oulsion (D~ 25 stages
Tlle emulsion (D) according to the invention therefore
had a higher sensitivity by 0.4 log It units.
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