CA1120766A - Photographic silver halide emulsions exposed to ionizing radiation prior to attaining final grain size - Google Patents

Abstract

PHOTOGRAPHIC SILVER HALIDE EMULSIONS
Abstract of the Disclosure Photographic silver halide emulsions with increased sensitivity are obtained by exposing the silver halide emulsions to an ionizing radiation during preparation, the exposure being terminated before the grains reach their final size.

Description

~ 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

~ 6.~

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 A-G 1581 - ~-. .

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.

.~ -o~

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 _ . I ?

:: ." 'i ' ; ~ '::.'.'' "' '~ , ~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 .1 ~Z~76~

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 ' ~ . .;, ,;', . , . ~ , I " ~., , '' ' 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 A-G 158t , - B - ~
!

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 ~

~LZ~7~i 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 -~Z~7~6 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-A-G 1$a1 : . ,.
.

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 -.

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;

)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 -.Z~766 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 ~

7~6 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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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photographic silver halide gelatine emulsion, in which the silver halide grains of the emulsion contain, in their interior, sub-latent image nuclei produced by ionising radiation during the preparation and, on their outside, a zone which is free from such nuclei, the nuclei being contained in such size and quantity that when as emulsion having grains which have been irradiated but on which no further silver halide has been precip-itated so that they do not contain the zone which is free from sub-latent image nuclei is developed with a developer of the following compositions:
p-Methylaminophenol 1 g Hydroquinone 3 g Sodium sulphite 13 g Sodium carbonate 26 g Potassium bromide 1 g Made up with water to 1000 ml, at a development temperature of 20°C and a development time of 5 minutes, a quantity of not more than 20 mole % of the silver halide emulsion which has been treated in this way is reduced to silver.

2, An emulsion as claimed in claim 1 in which the nuclei are contained in such a size and quantity that when an emulsion having grains which do not contain the zone which is free from sub-latent image nuclei in the developer specified in claim 1 under the conditions specified in claim 1, from 1 to 10 mole % of the quantity of silver halide is reduced to silver.

3. An emulsion as claimed in claim 1 or claim 2 in which the surfaces of the silver halide grains are chemically ripened.

4. A process for the preparation of a photographic silver halide emulsion by the precipitation of silver halide in aqueous solution in the presence of a protective colloid, in which the emulsion is exposed to an ionising radiation at a sub-threshold level during preparation, the irradia-tion being terminated before the grains reach their final size, and precipitation then being continued to the desired grain size.

5. A process as claimed in claim 4, in which irradiation is terminated when the emulsion grains reach at the most 98% by volume of their final size.

6. A process as claimed in claim 5, in which irradiation is terminated when the emulsion grains reach from 50 to 95% by volume of their final size.

7. A process as claimed in claim 4, in which irradiation is carried out with ?-rays or X-rays.

8. A process as claimed in claim 4, in which irradiation is carried out continously or intermittently during precipitation.

9, A process as claimed in claim 4, in which after precipitation, chemical ripening on the surface is carried out in the usual manner.