CA1263048A - Diffusion transfer imaging system - Google Patents

Abstract

ABSTRACT
DIFFUSION TRANSFER IMAGING SYSTEM
A process for forming an image which comprises image-wise exposing to radiation of selected wavelength a carrier element comprising, as image forming components, in one or more imaging layers coated on a support a bleachable dye in reactive association with iodonium ion thereby bleaching the dye in exposed areas to form a positive image, and thereafter transferring the positive dye image to a receptor which is either a receptor layer present on the carrier or a separate receptor element by providing a liquid medium between the positive dye image and receptor for a sufficient time to allow transfer of the dye image to the receptor.

Description

=l=

DIFF~SION TRANSFER~IMAGING SYSTEM

Field of the Invention This invention relates to a method of forming an image in which a sheet bearing a radiation-sensitive image-forming layer is image-wise exposed to record an image in said layer and thereafter the image-forming components are transferred to a receptor layer or sheet to form a permanent image. In 10 particular, the invention relates to a diffusion transfer imaging process employing a radiation-sensitive sheet comprising one or more bleachable dyes.
Background of the Invention Positive working non-silver systems in which an originally coloured species is decolourised (bleached) in an imagewise manner upon exposure to light have received a considerable amount of at~tention. A large variety of dyes and activators 20 have been disclosed for such systems, see, for example, J. Kosar, Light Sensitive Systems, page 387, Wiley, New York 1965.
The reaction relies on the fact that the dye absorption is sensitising the dyels own destruction or 25 decolourisation, for example a yellow dyes absorbs blue light; the excited dye thus formed reacts with an activator which releases the species to bleach the dye. similarly green light would destroy the magenta and red light the cyan dyes.
This dye bleach-out process is thus capable of produciny colour images in a simple way. However t in spite of its apparent simplicity, the bleach-out process poses a number of problems. In particular, ; the purity of the whites in the final image leaves ::
, =2~

much to be desiredl image stability may not be good and a fixing step may be required to stabilise the image.
Our copending European Patent Application No.
5 84301156.0 (Serial No. a 120 601) discloses a radiation-sensitive element capable of recording an image upon image-wise exposure to radiation of selected wavelength, the element cornprising, as the image-forming components, an effective amount of a 10 bleachable dye in reactive association with an iodonium ion.
The element is capable of recording a positive image simply upon exposure to radiation of selectecl wavelength; the radiation absorbed by the dye which is 15 in reactive association with an iodonium ion causes the dye to bleach. The dyes are believed to sensitise spectrally the reduction of the iodonium ion through the radiation absorbed by the dyes associated with the iodonium ion. Thereafter the element may be 20 stabilised to fix the image by destruction of the iodonium ion or by separation of the dye relative to the iodonium ion.
The dyes used may be of any colour and any chemical class which is capable of bleaching upon 25 exposure to radiation of selected wavelength in the presence of an iodonium ion.
By a suitable selection of dye an element may be prepared which is sensitive to radiation of a selected wavelength band within the general range 300 30to 110~ nm, the particular wavelength and the width of - the band depending upon the absorption characteristics of the dye. In generall where a dye has more than one absorption peak it is the wavelength corresponding to , :

-~LZ63~

the iongest wavelength peak at which one would choose to irradiate the element.
Elements intended for the production of images from radiation in the visible region (400 to 700 nm~
5 will contain dyes which will bleach from a coloured to a substantially colourless or very pale state. In practice, such bleachable dyes will undergo a change such that the transmission optical density at the ~ max will drop from 1.0 or more to less than 0.09, 10 preferably less than 0.05. The dyes will generally be coated on the support to provide an optical density of about 3.0 or more.
In the case of elements sensitive to ultraviolet radiation (300 to 400 nm) the dyes will 15 not normally be coloured to the eye and there may be no visible chanye upon exposure to ultraviolet radiation and bleaching. The image-wise exposed elements may be used as masks for further ultraviolet exposure after fixing.
Infrared sensitive elements contain dyes having an absorption peak in the wavelength range 700 to 1100 nm. These dyes may also have absorption peaks in the visible region before and/or after bleaching.
Thusl as well as providing a means for obtaining ~asks 25 for subsequent infrared exposure in a similar manner to the ultraviolet masks, infrared sensitive elements may record a visible image upon image-wise exposure to infrared radiation.
Exposure may be achieved with a wide variety 30 of sources including incandescent, gas discharge and laser sources. For laser scanning applications the laser beam may need to be focussed in order to achieve sufficient exposure.

, ~ .

The dyes used may be anionic, cationic or neutral. Anionic dyes give very good photo-sensitisation which is believed to be due l:o an intimate reactive association bet~een the negatively charged dye and the positively charged iodonium ion.
Also anionic dyes may readily be mordanted to cationic polymer binders and it is relatively simple to remove surplus iodonium ions in an aqueous bath in a fixing step if the mordanting polymer is cationic. However, 10 neutral dyes also give good results and are preferred over cationic dyes for overall photosensitivity.
Cationic dyes are least preferred since it is more difficult to achieve intimate reactive association between the positively charged dye and iodonium ion, 15 and selective removal of iodonium ion after imaging is more difficult.
The bleachable dyes Jnay be generically referred to as polymethine dyes which term characterises dyes having at least one electron donor 20 and one electron acceptor group linked by methine groups or aza analogues. The dyes have an oxidation potential between 0 and +1 volt, preferably between -~0.2 and +0.8 volt. The bleachable dyes may be selected from a wide range of known classes of dyes 25 including allopolar cyanine dye bases, complex cyanine, hemicyanine, merocyanine, azine, oxonol, streptocyanine and styryl.
~he dye and iodonium system has its greatest ~; sensitivity at the ~max f the longest wavelength 3D absorbance peak. Generally, it is necessary to irradiate the system with radiation of wavelength in the vicinity of this ~ma~ for bleaching to occur.
~ Thus, a combination of coloured dyes may be used, e.g.
:
,, .

yellow, magenta and cyan, in the same or different layers in an element and these can be selectively bleached by appropriate visible radiation to form a full colour imageO Monochromatic or polychromatic images may be produced using the photosensitive materials with relatively short exposure times in daylight or sunlight or even artificial sources of light ~e.g fluorescent lamps or laser beams). The exposure time, for adequate results, for example when 10 using an 0.5 kW tungsten lamp at a distance of 0.7 m, may be between 1 second to 10 minutes.
The iodonium salts used in the imaging system are compounds consisting of a cation wherein a positively charged iodine atom bears two covalently 15 bonded carbon atoms, and any anion. Preferably the acid from which the anion is derlvad has a pKa < 5.
The preferred compounds are diarylr arylJheteroaryl or diheteroaryl iodonium salts in which the carbon-to-iodine bonds are from aryl or heteroaryl groups.
20 Aliphatic iodonium salts are not normally thermally stable at temperatures above 0C. However, stabilised alkyl phenyl iodvnium salts such as those disclosed in Chem. Lett. 1982, 65-6 are stable at ambient temperatures and may be used.
The bleachable dye and iodonium salt are in reactive association on the support. Reactive association is defined as such physical proximity be~tween the compounds as to enable a chemical reaction to take place between them upon exposure to light. In 30 practice, the dye and iodonium salt are in the same layer or in adjacent layers on the support.
In general, the weight ratio of bleachable dye ~; ~ to iodonium salt in the element is in the range from 1 to 1:50, preferably in the range ~rom 1:2 to 1:10.

,,:

=6--The bleachable dye and iodonium salt may be applied to the support in a binder. Suitable binders are transparent or translucent~ are generally colourless and include natural polymers, synthetic resins/ polymers and copolymers, and other film forming media. The binders may range from thermoplastic to highly cross-linked, and may be coated from aqueous or organic solvents or emulsions.
Suitable supports include transparent film, 10 e.g. polyester, paper e.g. baryta-coated photographic paper, and metallised film. Opaque vesicular polyester films are also useful.
The fixiny of the radlation-sensitive elements may be effected by de~tructlon o~ the iodonium ion by 15 disrupting at least one of the carbon-to-iodine boncls since the resulting monoaryl iodine compound will not react with the dyeO The conversion of the iodonium salt to-its non-radiation sensitive form can be e$fected in a variety of fashions. Introduction of 20 ammonia and amines in reactive association with the iodonium ion, or a reaction caused on heating, or UV
irradiation of a nucleophilic anion such as I~, Br0, Cl~, BAr4~ ~etra-arylboronide), Ar ~ ~e.g.
phenoxide), or 4-NO2C6H4CO2~, with the iodonium ion, 25 will ef~ect the conversion.
An alternative method of achieving post-imaging stabilisation or fixing is to remove the iodonium ion from reactive association with the dye by washing with an appropriate solvent. For example, in 30 the case of elements using mordanted oxonol dyes and ~ water soluble iodonium salts formulated in gelatin, ;~ after imaging, the iodonium salt is simply removed by ~ an a~ueous wash, which leaves the immobilised dye in . ~

-7=

the binder. The dye stability to light is then equivalent to that of the dye alone. An element in which the dye and iodonium salt is formulated in polyvinylpyridine may be treated with aliphatic ketones to remove the iodonium salt and le~ve the dye in the binder.
The elements may be used as transparencies for use with overhead projectors, for making enlarged or duplicate copies of colour slides and for related lD graphics or printing applications, such as pre-press colour proofing materials.
Dye diffusion transfer systems are known and are becoming increasingly important in colour photography (see C.C. Van de Sande in Angew Chem.
15 1983, 22, 191-209). These systems allow ~rapid access~ colour images without a complicated processing sequence. The construction of these colour materials may be donor-receptor type te.g. Ektaflex commercially available from Kodak) integral peel-apart type (e.g.
20 Polaroid, E.H. Land, H.G. Rogers, V.K. Walworth in J.
Sturge Nebelette's Handbook of Photography and Reprography, 7th Ed. 1977, Chapter 12), or integral single sheet type (e.g. Photog. Sci. and Eng., 1976, 20~ 155). Silver halide diffusion transfer systems 2S are also known (e.g. E.H. Land. PhotogO Sci. and Eng., 1977~, 21, 225). Examples of ~iffusion transfer fixing in non-silver, dye-forming reactions employing solvent application to effect the transfer are disclosed in United States Patent Specification Nos. 3 460 313 and 30 3 598 583. The latter patent also describes a full-colour imaging element, applicable for preparation of colour proofs, fixed by transfer of dye precursors in register to a receptor. Other examples 'rr~le ~ K

( ,, ;
,, .
,,~, . ;, =8=

of non-silver diffusion transfer imaging systems are disclosed in British Patent Specification Nos.
1 057 703, 1 355 618 and 1 371 898.
It has now been found that certain dyes which are bleachable upon exposure to radiation in the presence of iodonium ion are susceptible to diffusion transfer and this property may be utilised to separate such dyes from the iodonium ion and produce a clean, stable image by transfer from a radiation-sensitive 10 layer to a receptor layer or separate receptor element.

Brief Summary of the Invention According to the present invention there is 1~ provided a process for forrning an image which comprises imaye-wise exposing to radiation of selected wavelength a carrier element comprising, as image forming components, in one or more imaging layers coated on a support a bleachable dye in reactive 20 association with iodonium ion thereby bleaching the dye in exposed areas to orm a positive image, and thereafter transferring the positive dye image to a receptor which is either a receptor layer present on the carrier or a separate receptor element by 25 providing a liquid medium between the positive dye image and receptor for a sufficient time to allow transfer oE the dye image to the receptor.
The process of the invention provides stable dye images, optio~ally full colour images, of high 30 quality with low background fog. The imaging system does not require the presence of silver halide.

.,.

=9 -Descri tion of the Preferred Embodiments P_ _ . _ __ In accordance with the invention the bleachable dye is soluble in a diffusion transfer S liquid and after imaye-wise exposure the positive dye image is transferred to a separate receptor or a receptor layer of the element by providing a transfer liquid between the dye image and receptor thereby causing diffusion transfer of the image to the 10 receptor~ This semi-dry process allows production of images withih a few minu.tes and the background fog levels are substantially reduced giving much cleaner images. Typically, fog levels are reduced from 0.15 to less than 0.05. This technique may be used to form 15 full colour images of high quality suitable for use in pre-press colour proofing.
The diEfusion transfer process utilises dyes which are soluble in a liquid, preferably an aqueous solvent. It is preferred that the bleached products zo Of the dye and iodonium ion are non-diffusing. This may normally be achieved by utilising iodonium compounds having a ballasting group. The dye-bleach system comprises a bleachable dye in reactive association with an iodonium ion is disclosed in our 25 copending European Patent Application No. 84301156.0 (Serial No. 0 120 601).
The process may be used to achieve a : multi-colour print either by sequentially transferring ~: dyes from separate carrier elements or by utilising a 30 carrier element having two or:more coloured dyes, e.g.
magenta, cyan and yellow, and transferring the dyes simultaneously.
~::

~ . , =10=

Suitable bleachable dyes may be generically referred to as polymethine dyes which term characterises dyes having at least one electron donor and one electron acceptor yroup linked by methine groups or aza analogues. The dyes have an oxidation potential between 0 and ~l volt, preferably between +0.2 and ~0.3 volt. The bleachable dyes may be selected from a wide range of known classes of dyes including allopolar cyanine dye bases, complex 10 cyanine, hemicyanine, merocyanine, azine, oxonol, streptocyanine and styryl.
The dyes useful in the invention are all bleachable dyes; dyes which bleach on exposure when in the presence of an iodonium ion. While any 15 polymethine dye may be transferred by difusion transfer providing it has a suitable solubility in the diffusion transfer solvent, e.g. more than 10 g/litre in 60% aqueous ethanol, it has been found that cationic and anionic dyes are preferable over neutral 20 dyes because of the possibility of mordanting the dye to a polyanionic or polycationic organic polymer on the surface of the receptor sheet.
In general, suitable dyes for use in the invention will have the structure:

R

in which:
n is 0, 1 or ~, and :

3~

=1~. =

Rl to R4 are selected to provide an electron donor moiety at one end of the conjugated chain and an electron acceptor moiety at the other r and may be selected from substituents including hydrogen, halogen, cyano, carboxy, alkoxy, hydroxy, nitro, alkyl, aryl groups or heterocyclic rings any of which may be substituted. The skeletal structure of the groups Rl to R4 generally contain up to 14 atoms selected from C, N, O and S. When the skeletal 10 structure of a Rl to R4 group is in the form of a linear chain there will usually be no more than 6 carbon atoms in the chain. When the skeletal structure is cyclic there will be no more than 7 atoms in any single ring. Cyclic structures may comprise 15 two or more fused rin~s containing up to 14 atoms. If the skeletal structure of a Rl to R4 group comprises two unfused cyclic groups there will be no more than 3 atoms in the linear chain between the groups.
Alternatively, Rl and R2 andjor R3 and R4 may 20 represent the necessary atoms to complete optionally substituted aryl groups or hetreocyclic rings, generally containing up to 14 atoms selected from C, N, O and S and having a structure as defined above.
The conjugated chain is preferably composed of 25 carbon atoms but may include one or more nitrogen atoms providing the conjugation is not disrupted. The free valences on the chain may be satisfied by hydrogen or any substituent of the type used in the cyanine dye art including fused riny systems.
The particular selection of substituents Rl to R4 effects the light absorbance properties of the dye which may be varied to provide absorption peaks ranging from the ultraviolet (300 to 400 nm), near ~ , , ' 63~

visible (400 to 500 nm), far visible (500 to 700 nm) and infrared (700 to 1100 nm).
~ yes of the above formula are well known particularly in the silver halide photographic art and are the subject of numerous patents. Exemplary dye structures are disclosed in ~he Theorgy of the Photographic Process, T.H. James, Ed. MacMillan, Editions 3 and 4, and Encyclopaedia o Chemical Technology, Kirk Othmer, 35d Edition, Vol. 18, 1983.
Within the above general structure of dyes are various classes of dye including:
1) Cyanine dyes of the general formula:

RS

in which:
p is an integer of 0 to 2~
R5 and R6 are independently hydrogen or substituents which may be present in conventional cyanine dyes~ e.g. alkyl (preferably of 1 to 4 ca~rbon atoms), etc., ~5 X~ represents an anion, and the groups A and B, which need not necessarily complete a cyclic structure with the methine chain, independently represent alkylr aryl or heterocyclic groups or the necessary atvms to complete heterocyclic 30 rings which may be the same or different. The skeletal structure of the groups A and ~ generally contain up to 14 atoms selected from C, N, O and S.
When the skeletal structure of A or B is in the form of a linear chain there will usually be no more than 6 . , -13=

carbon atoms in the chain. When the slceletal structure completed by A or B is cyclic there will be no more than 7 atoms in any single rins~ Cyclic structures may comprise two or more fu,sed rings 5 containing up to 14 atoms. If the skeletal structure complete by A or B comprises two unfused cyclic groups there will be no m~re than 3 atoms in the linear chain between the groups.
This class of dyes is very well known 10 particularly in the silver halide photographic art and are the subject of numerous patents. General references to these dyes include The Chemistry of Synthetic~es, K. Venkataraman ed., Academic Press, Vol. 4 (1971) and The Theor ~ lc 15 Processl T.H. James, ed., MacMillian, Editions 3 and 4.

2) Merocyanine dyes of the general formula:

,~0 in which:
q is an integer of 0 to 2, R5 and A are as defined above, and B is as defined above or may complete a carbocyclic ring.
These dyes are also well known in the silver halide photographic art and are described in The Theory of the Photo ~aphic_ rocess, referred to above.

3) Oxonols of the general formula:

.

`: ' =14=

~A~ ,B~

y~ o~

in which:
q is an integer of 0 to 2, A and B may be the same or different and are as defined above in relation to cyanine and 0 merocyanine dyes, and represents a cation.
Oxonol dyes are similarly well known in the silver halide photographic art and are disclosed in the above mentioned reference, ~ the 15 Pbotographic Process, J. Fabian and H. Hartman, Light Absorption of Organic Colourants, Springer ~erlag 1930 and United States Patent Specifisation No. 2 611 696.
Anionic bleachable dyes, of which oxonol dyes are a class, are particularly useful because of their 20 ability to associate closely with the iodonium cations. Anionic dyes in general will possess a delocalised negative charge.
Anionic dyes may be regarded as being prepared from a central portion containing delocalisable 25 electronic system and end units which allow stabilisation of the negative charge.
The central portion may generally be selected from molecules possessing two active aldehyde or aldehyde derived groups such as glutaconic aldehyde ~0and its anil salts, 3-methyl glutaconic dialdehyde and its anil saltsj and 3-anilinoacrolein and its anil salts. Thes~ central portions may react with end ur.it compounds contaihing active methylene groups Such as =15=

malononitrile, NC.CH2 COOR', where Rl is an allcyl group containing from 1 to 6 carbon atoms, e~g.
methyl, ethyl, propyl, butyl and hexyl groups, RISO2CH2CN and R'SO2CH2COR' in which R' is as defined above, 10 in which R~ is H or OH, ~ N~ N- Rl'i R"l - N ~ N - R"' O ~ and ~ S

in which each Rn' independently represent H or an alkyl group containing 1 to 6 carbon atoms.
The anionic dyes may have either the same end 20 units or two different units.
It is to be understood that these cyaniner merocyanine, anionic and oxonol dyes may bear substi~uents along the polymethine chain composed o C, N, O and S, and that these substituents Jnay 25 themselves join to form 5, 6 or 7 membered rings, or may bond with rings A and B to form further ringsl possibly with aromatic character. Rings A and B may also be substituted by C, N, H, O and S containing groups such as alkyl, substituted alkyl, alkoxy, amine (primary, secondary and tertiary), aryl (e.g. phenyl and substi~uted phenyl), halo, carboxyl, cyano, nitro, etc. Exemplary substituents are well known in the cyanine dye art.

-16=

Other known classes of dyes useful in the diffusion transfer process which possess an activated methylene chain include bisquinones, bisnaphthoquinones, hemicyanine, streptocyanine, anthraquinone, indamine, indoaniline and indophenol.
Preferred dyes for use in the invention are anionic, more preferably oxonol dyes because a) they give good sensitisation, believed to be due to an intimate reactive association between the negatively charged dye and the positively charged iodonium ion, b) they are highly water/alcohol soluble, thus being readily separable from the iodonium ion, c) readily mordanted to cationic polymer binders conventionally present in receptor layers (e.g. RD 173033-A39 G.A. Campbell) and d) readily prepared affording a range of dyes with absorption in the region 350 to 700 nm.
20 Oxonol dyes which diffuse readily out of gelatin layers are known, e.g. Japanese Patent Specification No. 49099620, ~uji. The dyes have an oxidation potential between 0 and +l volt, preferably between +0.2 and +0.8 V.
Examples of oxonol dyes include:
Yellow Dye 1 ~ C(:)2Et C~ ~
C OEt 460 nm (EtOH) .

=17_ Magenta Dye l S ~ ~ NHEt3 ~
560 nm ~EtOH) Cyan Dye 1 O

15 ~ ~ , Me NHEt3 O N ~ O
Me The cation of the oxonol dye need not be the 20 iodonium ion ~nd can be any cation including Li~, Na~
and K~ or quaternary ammonium cations, e.g. pyridinium or as represented by the formula:
.
RlU
Rll _ Rl3 ; in which Rl0 to Rl3 may be selected from a wide range of groups including hydrogen, alkyl, preferably of l 30to 4 carbon atoms, aryl, e.g. phenyl, aralkyl o~ up to 12 carbon atoms. Preferably at least one of R10 to Rl3 is hydrogen and the rest are alkyl or aralkyl si~ce such amines are readily available and allow easy ~ synthesis of the dyes.

: ::

~:~63~
=18=

The iodonium ions used in the invention are compounds consisting of a cation wherein a positively charged iodine atom bears two covalently bonded carbon atoms, and any anion. The preferred compounds are diaryl, aryl/heteroaryl or diheteroaryl iodonium salts in which the carbon-iodine bonds are from aryl or heteroaryl groups and one of the aryl or heteroaryl groups is substituted with an alkyloxy group.
Suitable iodonium salts may be represented by the lO formula:
Ar I~ A~
Ar2'~

15 in which:
Arl and Ar2 independently represent carbocyclic or heterocyclic aromatic-type groups generally having from 4 to 20 carbon atoms, or together with the iodine atom complete a heterocyclic 20 aromatic ring.
; These groups include substituted and unsubstituted aromatic hydrocarbon rings, e.g. phenyl or naphthyl, which may be substituted with alkyl groups, e.g.
methyl, alkoxy groups, e~g. methoxy, chlorine, 25 bromine, iodine, fluorine~ carboxy~ cyano or nitro groups or any combination thereof. Examples of hetero-aromatic groups include thienyl, furanyl and pyrazolyl which may be substituted with similar substituents as described above. Condensed 30 aromatic/hetero-aromatic groups, e.g. 3-indolinyl, may also be present, ; A~ represents an anion which may be incorporated lnto Arl or Ar2.

,, .. .

Preferably Arl and Ar2 do not have more than two substituents at the alpha-positions of the aryl groups. Most preferably Arl and Ar2 are both phenyl groups.
Preferred iodonium salts for use in the difusion transfer process incorporate a ballasting group to prevent transfer of the iodonium ion during the dye diffusion transfer step. Suitable ballasting groups may be presant on Arl and/or Ar2, preferably i.n 10 the para-position with respect to the I0 link, and are of the formula:

-oRl4 in which R14 represents a straight chain or branched alkyl or alkyl substituted with OH, oR15, (NR163)~ in which R15 and ~16 reprasent alkyl groups or a group having a quaternary group at the end of an alkyl chain, e.g. cH2-cH2-cH2~$he3x~. R14 should 20 preferably have at least 3 carbon atoms and generally not more than 20 carbon atoms.
The presence of the oR14 ensures transference of Ar2-OR14 to the bleached dye, thus resulting in immobilisation of the bleach product and low Dmin 25 values.
The alpha-positions of the Arl and Ar2 yroups may be linked together to include the iodine atom within a ring structure, e.g.

~; 3~ ~ ~ Z ~

in which Z is an oxygen or sulphur atom. An example of such an iodonium salt is:

= 2(~=

N02 I~ N2 PF6~

Other suitable iodonium salts include polymers containing the unit:
1 () / - CH- CH 2 -I

\A~ Ph /
in which Ph represents phenyl.
Examples of such polymers are disclosed in Yamada and Okowara, Makromol. Chemie, 1972, 152, 61-6.
Any anion may be used as the counter~ion A~
20 provided that the anion does not react with the iodonium cation under ambient temperatures. Suitable inorganic anions include halide anions, HS04~, and halogen-containing complex anions, e.g.
tetrafluoroborate, hexafluorophosphate, 2shexafluoroarsenate and hexa1uoroantimonate. Suitable organic anions include those of the formulae:
R17Cod~ or Rl7So3~

in which R17 is an alkyl or aryl group of up to 20 carbon atoms, e.g. a phenyl group, either of which may be substituted. ~xamples of such anions include CH3CO ~ and CF3CO ~.

.. , .

=21=

A~ may be present in Arl or Ar2, e.g.

in which A~ represents CO ~r etc.
Furthermore, A~ may be present in a molecule containing two or more anions, e.g. dicarboxylates 10 containing more than 4 carbon atoms.
The most significant contribution of the anion is its effect upon the solubility of the iodonium salt in different solvents or binders Most of the iodonium salts are known, they may 15 be readily prepared and solne are commercially available. The synthesis of sultable iodonium salts is disclosed in F.M. Beringer et al, Journal of the American Chemical Society, 80, 4279 (1958).
Suitable substrates for the donor (or carrier) 20 for use in both diffusion and sublimation transfer are plastics film, paper (cellulosic or synthetic fibre), metallised plastics film and plastic film to film or plastic film to paper laminates.
The substrate should be unaffected by the 25 processing conditions. For example, the substrate must possess adequate wet-strength and dimensional stability for use in diffusion transfer. A preferred substrate is a plastics film such as polycarbonate film, cellulose acetate film or most preferably `:

: : :

:,...................... :

=22=

polyester, e.g. poly(ethyleneterephthcllate~, which may be biaxially orientated.
The substrates may possess surface modifying or other coatings to enhance adhesion of imaginy layers~ to irnprove smoothness, etc. ~esin coated photographic grade paper is a suitable substrate. The plastics film may specifically possess a subbing layer which acts as a priming layer for gelatin and other hydrophilic coating.
Elements for use in the diffusion tran~fer process may comprise mixtures of dyes and iodonium salts dissolved in gelatin or oil-dispersed in gelatin, which, after image formation by visible light irradiation, are fixed by dye diffusion transfer to a 15 gelatin and mordant-coated receptor sheet, which may contain dye stabilisers. The iodonium salt and dye are coated with a polymeric binder layer on a substrate.
The quantity of the dye relative to the 20 iodonium salt is within the range of 1 to 50 weight percent. The quantity of iodonium salt plus dye in the coated layer falls within the range of 5 to 60%, assuming the remainder to be binder.
The polymeric binders are generally water-25 swellable of natural or synthetic origin, such asgelatin, gum arabic, poly~vinyl alcohol), poly(vinyl pyrrolidone). The polymers may contain cross-linking or other insolubilisation additives or may themselves be self-crosslinked to reduce solubility in the 30 diffusion transfer processing solution while still maintaining difusibility of the dye or dyes.
Preferred in the invention is gelatin which i9 crosslinked via its lysine groups with carbonyl ::

=~3=

compounds (e.g. glyoxal, glutaraldehyde). The binder must allow the diffusion transfer solvent to enter the imaged layer and thus allow diffusion of the unbleached dye or dyes to the receptor sheet. If more than one dye is to be transferred a general equivalence of diffusion ratios is desirable.
~ preferred dye, iodonium, polymer system for use in a diffusion transfer element is oxonol, diaryliodonium trifluoroacetate and gelatin, since the lO sensitive components are very soluble in gelatin.
The radiation-sensitive element may have single layer, multi-dye formulation or multi-layer, single dye per layer composites. Preferred elements should have less than lO micron dye layer thickness to 15 allow rapid dye diffusion. Thicker coatings result in long diffusion transfer times (e~g. 30 micron, 5 minutes for a transferred density of 2.5 reflected~.
The receptor material is generally a sheet material to which the dyes are transferred during the 20 diffusion process. Although the dyes may be transerred to untreated plastics film, paper (of cellulosic or synthetic fibre) or other receptive substrate material, it is normal for these to have surface modifying treatments.
The receptor substrate is generally selected from plastics film; paper (as above), metallised plastics film, and plastics film-to-film or film-to-paper laminates. These may be treated with surface modifying coatings to alter opacity, re1ectivity, smoothness, adhesion of subsequent coatings, tint and dye absorptivity. Preferably the substrate is a pIastics ilm such as biaxially ~6~
=2~=

oriented poly(ethylene terephthalate). Vesicular substrates, e.g. vesicular polyester, may be employed. The substrate preferably bears on an outer surface a polymeric coating which is swellable under the diffusion transfer conditions, e.g. gelatin cross-linked with metal ions such as Cr~+ or Ni~.
Additionally, it is highly desirable for a mordanting agent to be present in the receptor layer to prevent further diffusion of the dye thus serving 10 to maintain resolution. The mordanting agent is normally electrically charged polymer, bearing opposite charge to the dye being transferred. Thus, a polyanionic polymer would be used for positively charged cyanine dyes. Cationic mordants are most 15 preferred as they will render substantive oxonol dyes and will not mordant unreacted iodonium ion The use of anionic, e.g. oxonol dyes, is therefore highly advantageous for the above reasons and additionally because of the enhanced reactivity which these dyes 20 exhibit on exposure with iodon-ium ions. Charged metallic ions such as Cr3~ and Ni2~ may also be employed to effect mordanting, as may conventional mordanting agents. Examples of cationic mordanting polymers are:
~CH- CE~æ~q CH 2 ~

~9 in which:
q is an integer, and R9 and R10 are as defined above.

:,.

=25=

Integral constructions incorporating both the imageable layer and the receptor layer in a single construction for diffusion transfer offer certain advantages in processing ease, in tha~ there is no separate receptor construction. Integral constructions consist essentially of a transparent substrate bearing an imageable layer containing one or more bleachable dyes in reactive association with an iodonium ion and a receptor layer.
The substrate material is a transparent plastics film which is stable to diffusion transfer processing. A preEerred substrate is biaxially orientated poly(ethylene terephthalate) film. This may bear transparent priming or subbing layers.
The components of the imageable layer have been previously described. The bleachable dyes may be present in one or more layers.
The receptor layer normally contains a mordanting aid for the dye such as a poly~4-vinyl 20 pyridinium) polymer. Cationic polymers are preferred as they will not mordant any diffusing iodonium ion which may be subsequently washed out. Relative to the viewing surface of the final image, it may be necessary to include a backing layer containing a 25 white or coloured pigment in order to provide a suitable reflective background. This reflective layer preferabiy contains a white pigment, most preferably baryta or titanium dioxide. The reflective layer must allow diffusion of the bleachable dyes and thus 30 diffusion transfer processing solution permeable binders are required. Preferably, water swellable binders such as gelatin will be used for aqueous processing solutions. The reflective layer may ~i3~
-26=

exhibit mordanting properties or may contain a mordanting agent, although preferably the mordanting agent is in a separate layer.
Antihalation layers situated between the imageable layer and the reflective layer may also be incorporated. Again this antihalation layer must allow diffusion of the dyes. Carbon black dispersed in gelatin is a suitable composition for use with reflective coatings. An example of an integral construction for use in making a final image which is to be viewed by reflection is:
(a) a transparent substrate, e.g~ biaxially orientated polyester Eilm bearing a subbing layer, (b) a mordanting layer, e.g. poly~4-vinyl pyridinium) polymer, (c) a reflective layer, e.g. titanium dioxide in gelatin, (d) an antihalation layer, e.g. carbon black in gelatin, ~e) one or more imageable layers (donor layers), (f) optional transparent protective coating of a diffusion transfer liquid permeable binder, e g.
gelatin coated at 0.5 micron wet thickness.
In use the imageable donor layer is exposed in the normal manner. Thereafter the exposed composite is contacted with the diffusion transfer liquid for a sufficient time to allow penetration of the diffusion transfer liquid thruugh the outer layers to ~he receiving layers. Unreacted dye diffuses from the donor layer through the antihalation layer, through the reflective layer and is rendered substantive in the mordanting coating. The final image may be viewed through the transparent substrate and will naturally possess a white background.

-27=

An alternative preferred construction employs layers (b) to (e) in reverse order. After exposure through the transparent base, the difEusion transfer liquid is applied and this allows the dye(s3 to migrate back towards the mordanting layer.
Evaporation of the diffusion transfer liquid may aid this process. The ~inal image is viewed on a white background. A further construction is as above but omitting layers (c) and (d). Layers (b) and (e) may 10 be in that position or reversed.
After exposure and diffusion transfer processing a final image suitable for projection viewing i~ obtained.
With the integral construction the diffusion 15 transfer solvent may be applied by wiping, spraying, soaking, or by rollers~ etc., optionally within a processing bath. Transfer of the dyes is effected rapidly, typically 30 to 60 seconds.
While diffusion transfer is normally effected 20 at ambient temperature, elevated temperatures, e.g.
30C, may also be employed.
In order to control the rates of diffusion of the dyes, which may have importance when full colour images are being formed, diffusion controlling layers 25 may be included between the mordanting layer and the imaging layer and occasionally between individual dye layers.
An optional washing stage may be undertaken with the transferred image to remove residual iodonium 30 ions. Water washing for a short period, eOg. one minute, may be beneficial although in normal practice this will not be necessary.

:

-2~=

~ n order to achieve diffusion transfer the exposed donor sheet is rendered in close contact with the receptor layer, with the dye donor and dye receptor layers contacting. Transfer is achieved through the presence of the diffusion transfer liquid between the donor and receptor layers. It is essential that contact be maintained evenly and for a sufficient time to allow transfer to occur.
The diffusion transfer liquid may be applied 10 in a variety of manners, such as (a) passing the donor and receptor sheet in face-to-face disposition through an automatic processing bath containing diffusion transfer fluid, excess fluid being expelled when the sheets emerge through the exit rollers, (b) releasing the diffusion transfer liquid rom a pod and arranging this liquid to wet the donor and receptor layers, an~
~c) wiping or spraying or otherwise wetting either the donor or the receptor with diffusion transfer uid and then quickly bringing the other in face to face contact, thereafter removing excess while keeping the faces in intimate contact.
In all the above instances the donor and receptor are kept in face-to-face contact for sufficient time f;or transfer to occur; thereafter the sheets are separated to reveal the high quality transferred image.
The process solution is normally colourless and may contain water and invisible solvents which evaporate shortly after the layers are separated.

=29-The process solution preferably consists of aqueous alcohol (30 to 80~), with low molecular weight alcohols being preferred, leading to readily dried mateeialsO The process solution may be buffered ln the region p~ 5 to 8, and contain antioxidants such as ascorbic acid/sodium ascorbate to destroy any mobilised iodonium salt, or other additives.
In certain instances small quantities of iodonium salts may also migrate in which case it is 10 desirable to wash the receptor layer with solvent such as water, to remove the iodonium salts. Generally, it has been found that the dye is the major transferring species.
Alternatively to soluhilising the dye in the 15 binder it may be desirable to add an oil, water-immiscible, phase to the binder and allow the dye and iodonium salt to react primarily within a finely dispersed oil droplet. After exposure such a layer is processed with the dif~usion transfer solvent which 2a allows the unreacted dye to migrate towards the receptor layer.
The invention will now be illustrated by the following Examples.
In the following Examples the sensitivity of 25 the element was measured by the following technique.
A 2.5 cm square piece of each sample was exposed over an area of 2.5 mm2 with focussed light filtered, using a Kodak narrow band ilter (551.4 nm:power output =
2.36 x 10-3 W/cm2) and the change in the trans~issiQn 30 optical density with time was monitored using a Joyce Loebl Ltd. microdensitometer. A plot of transmission optical density versus time was made and the exposure time ~t) for the optical density to fall from DmaX -to .

=30=

(DmaX-l) was determined. The energy required (E) was calculated as the exposure time (t) x power output (= 2.36 x 10-3 W/cm2): this gives an indication of the sensitivity of the elements.
In all cases a significant recluction of backyround density was achieved after transfer which gave a much cleaner image. Typically the minimum density beEore transfer and after exposure was approximately 0.15, this reducing to approximately 10 0.05 or below after transfer.

:

~::

SL~ Dye Diffusion to Rece~

Cyan Dye 2 ll ~max 670 nm ~ ~ NHEt3 o A solution of the Cyan Dye 2 (0.03 g) in ethanol (8 ml) and water (2 ml) was added in yellow light to gelatin (3.6 9) in water (30 ml) containing ~5 Tergitol TMN-10 (Union Carbide, 10% aqueous, 1.5 ml) at 45C. Aqueous glyoxal (10%, 0.5 ml) and

4-methoxyphenyl phenyliodonium trifluoroacetate (2.0 g) dissolved in dimethylformamide ~2.5 ml) were then added in the dark.
2~ The mixture was loop-coated at approximately 20 micron dry thickness onto chilled, subbed polyester (4 mil) and dried at 25C i.n an air-circulated cupboard for one hour.
The density of the resulting film was 5.0 at 25 665 nm ~transmitted). The density and time response of the film on irradiation at 670 nm with a light ~ : output of 2.5 mW/cm2 was measured on a : microdensitometer, giviny a sensitivity o~ 4 x 105 mJ/m2 for speed point of Dmax-l~
~: ~ 30 A strip was contacted with an UGRA scale (the UGRA scale was an 1976 UGRA-Gretag-Plate Control Wedge PCW) in a vacuum frame, emulsion to emulsion, and an exposure given of 60 s at 0.7 m from a 4 kW metal ~: halide source (Philips HMP 17). The dyes rom the ;~ :
~ Jr~de 1~ rK
, ., , -32=

resulting image were transferred to a vesicular polyester receptor substra~e (75 micron). The substrate was coated with a gelatin receptor layer as follows.
A gelatin solution (3.6 g in 30 ml distilled water) at 40C, containing poly(4-vinylpyridinium) methosulphate ~0.04 g in 6 ml ethanol and 0.5 ml acetic acid3, chrome alum (0.05 g), and nickel chloride (0.05 g~ was loop-coated onto chilled subbed 10 polyester (4 mil) and dried at 25C in an air cixculated cupboard for one hour. The dried gelatin layer was ahout 30 micron thick, deposited at 0.4 g/dm2. Ideally a less than 10 micron thick dry gelatin layer is preferred to achieve the benefit of 15 better resolution.
The diffusion transfer was effected as follows:
1. The receptor was coated with the diffusion transfer process solution with X-Bar No. 6 (commercially available from R.K. Chemicals Ltd).
on a coating bed. The process solution was made up o water (40 ml), ethanol (20 ml), sodium acetate (1.0 y), glacial acetic acid (2.0 ml).
2. The imaged donor was placed on top of the receptor, emulsion to emulsionr and the composite pressed together by the K-Bar to ensure that air bubbles were removed.
fter 5 minutes contact the donor and receptor sheet were peeled apart, and the receptor given a 30 second water-wash to remove any small amoun~ of the iodonium salt which also transferred.
The properties of the donor and receptor , images are reported below.
; ~ The ra~nge of halftone dots retained on using a 120 lines per centimetre screen is also reported together with the resolution achieved.
le m~

. I :

~, j:

=33=

Donor Receptor Resolution 30U lines/mm 83 lines/mm Dot retention range 4 to 96% 4 to 96%
Dmax 5.0 (Transmitted) 2.6 tReflected) Dmin 0.25/400 nm 0.09/400 nm : (Transmitted) (Reflected) 10 Contrast -3.0 -4.0 _ There are no undercutting efects in the line patch target, showing that the difusion transferred dyes travel to the receptor wlthout si.gnificant 15 lateral spread which would result in unsharp images.

Exam~ 2 Three dye, full-colour co~in~
~:
~:~ 20 The following dyes were employed Yellow Dye 1 Magenta Dye l and Cyan Dye 2.
A solution of the yellow, magenta and cyan dyes (respectively 0.~3 g, 00025 g, 0.03 g) in ethanol : (6 ml) and water (3 ml) was added in yeIlow light to 25 an aqueous gelatin solution (3.6 g in 30 ml water~ at . 40C.

:; 30 ~

.. ..

3i~3 =34=

Aqueous Tergitol TMN-10 (Union Carbide, 10~, 2.0 ml) and glyoxal t30%, 0.5 ml) were added to the resulting solution and then 4-methoxyphenyl phenyl-iodonium trifluorsacetate (2.0 9) in dimethylformamide ~2.5 ml) was added in the dark. The radiation-sensitive mixture was coated onto clear subbed polyester ~4 mil) using a loop-coater at approximately 20 micron dry thickness.
After drying in an air cupboard for one hour 10 at 25C, the following tests were made using a microdensitometer and the appropriate narrow cut filters. The film was panchromatic in nature. The results in the following table were obtained by measuring the optical density at the wavelength o~
15 maximum absorbance oE the dye. The dyes were transferred without exposure, as in Example 1, the transfer time again being 5 minutes. The receptor of Example 1 was employed.

Dye Initial Transferred ~max Energy Peak Density Peak Density (nm) Sensitivity (Transmitted) (Reflected~ Dmax-l (x105 mJ/m2 Yellow 1 3.3 2.8 454 a 9 Magenta 1 3.5 2.1 562 b 27 Cyan 2 3.4 2.0 673 c 5 a Filter at 461.6 nm, output power 1.79 mW/cm2 ~ 30 b Filter at 551.4 nm, output power 2~89 mW/cm2 ;~ c Filter at; 670n7 nm, output power 2.52 mW/cm2 ,:

, ,. ;

= 3 Colour Proofing Application A sample of the above Example was exposed in the following manner, using half-tone colour separation positives. On top of the sample was placed the black colour separation positive ( thus the black information is retained from the start). On top of this assembly was placed the appropriate colour separation positive and Wratten filter. White light 10 exposure was given, e.g. from a metal halide lamp.

Exposure 1 : Filter 47B (blue) and Yellow Colour Separation Positive (CSP) Exposure 2 : Filter 61 (green) and Magenta CSP
15 Exposure 3 : Filter 29 (red) and Cyan CSP

Exposures were perormed in a vacuum frame with a 4 kW
metal halide source at a distance of 0.5 m.
The resulting half-tone, full-colour proof was 20 fixed by dye diffusion transfer to a vesicular polyester receptor, coated with gelatin and poly(4-vinylpyridinium) methosulphate as described in Example 1. A mirror image ccpy was obtained which retained the large range of 4 to 96~ halftone dots 25 (utilising a 120 lines per centimetre screen). There was no observable dot fill-in due to dye spread at the 96g dot level.

Colour proofing in this manner involves a 30 total of four steps, compared to the twelve necessary in most conventional pre-press prooing materials, e.g. Dupont Cromalin and 3M Matchprint. The invention also has ~on-lineR potential~ requiring only three e m~r~

. . , , -3~

exposures and one fixing step, This manner of exposure is known for dye forming reactions, as described in United States Patent Specification No.
3 598 583.
Examples 3 to 5 Effect of iodonium sa.lt on Dmin in rece~

10 Iodonium Salts Sensitivity Dmin (x105 mJ/m2) transferred _ _ _ _ _ A ~ ~ ~ OMe 11 0.20 CF3Co2~3 ' B ~ oEt 9 0.15 \~J
CF3CO2~

C ~ n-Bu S
2 5 CF3C02~) :

3~ :

,. . .

~3~9~

To a solution of Cyan Dye 2 (0.04 g~ in ethanol ~6 ml) and water ~2.5 ml) in gelatin ~3.6 g in 28 ml water) and Tergitol TMM-10 (10% alqueous, 1.5 ml) was added one of the above iodonium salts (0.5 g~ in dimethylformamide (1.5 ml) in the dark. Glyoxal (30%
aqueous solut~on 0.1 ml) was added and the ~ixture loop-coated onto subbed clear polyester (100 micron) and dried in air at 25C for one hour. A
30 micron dry layer resulted (0.4 g/dm2 deposition~.
The film was exposed as in Example 1 and dye transferred as in Example 1 to clear subbed polyester coated with gelatin and poly(4-vinyl pyridinium) methosulphate. The process solution used was made up as followq: water (40 ml), ethanol (20 ml), sodium 15 acetate 1,0 g)j acetic acid (2.0 ml), Tergitol TMN-10 (10% aqueous, 1.0 ml). After exposure and dye transfer as described in Example 1.
1. The Dmax in each case was measured as 3.8 in the donor and 1.5 in the receptor ~ 20 (transmittance~.
; 2. The sensitivity at 670.7 nm was determined from density/time plots on a microdensitometer as previously describedO

The sensitivity of the donor layer, the minimum (background) density on the receptor after transfer and the contrast value after transfer are recorded in the following table.

"
.. .

.

i' .

=3~

_ IodoniumSensitivity Dmin Gamma salt(x105 mJJm2) (400 nm) (Contrast) A 11 0.20 -3.5 B 9 0.15 -4 C 5 0.08 -4 The sensitivity of dye ~ransferred to the receptor was also investigated. The density/time plot at 670 nm showed bleaching only for the first S
seconds before levelling out to constant density. The 15 maximum optical density dropped only by about 0.2 over this period. In the case of a 30 second water-wash after the diffusion transfer to remove trace iodonium salt, there was no such small initial loss of density.
The larger the alkyl group on the iodonium 20 salt, the lower are the Dmin values at 400 nm. ~hus, there can be immobilisation of the bleach product by transference of the alkoxyphenyl group Erom the iodonium ion to the dye. The iodonium salt would normally be selected to provide a low minimum density, 25 e.g. less than 0.1 or preferably much lower.

_~l~tio A solution of 4-butoxyphenyI phenyliodonium trifluoroacetate (0.5 g) in DMF ~2.0 ml) was added in the dark to a solution of Cyan Dye 2 ~0.04 g) in ::
~ , ~~' .

i3~

- 3~

gelatin (3.6 g~, water (30 ml), ethanol (6 ml~, and Tergitol TMN-10 (10% aqueous, 1.5 ml) at 45C.
Glyoxal was added (30% aqueoust 0.5 ml) and the mixture loop-coated as in Example 1 onto clear, subbed polyester in the dark. After drying in the dark in an air-circulated cupboard at 25C for one hour. One strip of film was exposed to a 250W tungsten iodine source for 5 minutes. That strip w~re contacted with the receptor of Example 3. Dye transference was 10 permitted in 5 minutes using Process 501utions A and B
(Dmax). The maximum and minimum density on transfer was measured. Bleach product transference after 5 minutes using Process Solutions A and B was also measured by the minimum density figure. Iodonium ion transference, judged by any variation of the density/time plot at 670 nm, the maximum sensitivity peak of the dye was also measured.
The results are reported in the following Table 2~
Processinq Solution A
water 40 ml ethanol 20 ml acetic acid 1 0 g sodium acetate 2.0 g Teryitol TMN-10 (10~ aqueous) 005 ml Process ng Solution B
water 40 ml ethanol ~ n ml ascorbic acid 1.0 9 sodium isoa~scorbate 3.0 g Tergitol TMN-10 ~lU% aqueous) 0.5 ml -.,:

. ~ . i , . , =4o=

Table Results after transference of dye usin~ Solution A
(5 mins/20C) _ . _ _ _ Solution Dmax a Dmin a Image density change _ __ _ _ _ A 1.0 0.05 0.1/5 secs b B 1. OO . 05 No change a transmitted b 0.1 density drop in 5 seconds, stable subsequently.

~ hus, with Solution B, there is essentially no transference of the iodonium salt to the receptor.
The combination of a long-chain alkyl substituted iodonium salt and antioxidant anion (e.g. ascorbate) 20 is preferred.
The process solution has the following functions:
1. it mobilises the dye from the donor to the receptor (too rapid movement is not required, as this 25 will lead to loss of resolution).
2. it assists in immobilising the iodonium cation.
3. it contains stabilisers to give the dye light stability after transfer (e.g. antioxidants, oxygen energy quenchers~.
4. it may also contain oxygen-barrier polymers (e.g.
polyvinyl alcohol).
: ' ':

....

, '.

3~
=~1=

In the process Solution B, sodium isoascorbate performs two functions: a) immobilises the iodonium cation, and b~ reacts with oxygen in the receptor layer leading to oxonol dye stability in the receptor.

Example 7 An enlar~ed print_of a 35 mm slide The film of Example 2 was exposed to a 5x linearly expanded image from a 35 mm colour slide.
The light source was a 250 W tin halide lamp. After 20 minutes exposure, the resulting copy was stabilised b~ contacting with a vesicular polyester receptor, 15 coated as described in Example 2 with gelatin, poly(4-vinylpyridinium) methosulphate and chrome alum.
Process Solution B was used from Example 1. After 5 minutes, the receptor was separated and 30 second water-washed, to give an enlarged copy of the colour 20 slide.

Exam~

Integral Donor/Rece~or Construction The following layers A to D were sequentially deposited using No. 6 K-bar (R.K. Chemicals Co.) onto 4 mil subbed polyester, with air-drying at 20C for 1 hour between each coating. Layers A to C were 30 deposited in yellow 1Ight and layer D in the dark.

:~ :

., 3~

Poly~4-vinylpyridiniUm) methosulphate (0.2 9l and acetic acid (0.3 ml) was added at 45C to a gelatin solution (1 g in 10 ml water). ~rergitol TMN-10 (10~ aqueous, 0.3 ml) and chrome alum (0.05 g in 1 ml water) were then added, and the mixture coated and driedO
La~er_B:
Titanium dioxide (1 g) was added at 45C to a 10 gelatin solution (1 g ln 10 ml water). The mixture was ultrasonically mixed for 0.5 hour to disperse the TiO2 in the gelatin. Tergitol TMN-10 (10% aqueouQ, 0.3 ml) was added, followed by glyoxal (10%, 0.5 ml).
The white solution was coated over layer A and dried.
15 Layer C:
0.5 ml Rotring ink (india black~, Tergitol TMN-10 (10~, 0~3 ml) and glyoxal (10%, 0.5 ml) were added to a gelatin solution at 45C ~1 g in 10 ml water). The black mixture was coated over layer B and ~0 dried. (At this point, one side of the polyester base appears black (layer C) and the other white (layer B)~.
Layer D:
A mixture of oxonol dyes, Yellow Dye 1 (0.04 g), Ma~enta Dye 1 (0.04 g) and Cyan Dye 2 25 ~0.05 g) in ethanol (2 ml), water (1 ml) and DMF
(0.05 ml) was added at 45C to a 10% gelatin solution (10 ml). 4-Butoxyphenyl phenyliodonium trifluoroacetate (0.3 g in 1 ml DMF), Tergitol TMN-10 (10% aqueous, 0.6 ml~ and glyoxal (10%, 0.5 ml) was 30 added in ~he dark. The sensitive mixture was coated onto layer C and dried. (Note some yellow dye migrates to layer A and colours it yellow).

~3q;~

=. ~

The dried cornposite film was imaged in contact with a colour transparency using a 250 watt xenon light ~30 seconds at 10 cm). Application of the process solution described in Example 1 leads to transferenoe of the dye from layer D to layer A in 10 minutes. A colour print results.

Example 9 An oil dis ersion coatina to achieve im~roved __ P , _ ., lO sensitivity A 10~ gelatin solution at 45C was prepared to 10 ml, In the dark were mixed a solution of oxonol Cyan Dye 2 (0.~3 g) in 0.~ ml di-n-butylphthalate and 15 } ml butan-2-one and a solution o 4-butoxyphenyl phenyliodonium trifluoroacetate (0.2 g) in 1 ml butan-2-one, This sensitive mixture was added dropwise to the ~elatin solution with vigorous stirring. ~fter 90 seconds of vigorous agitation, 20 Tergitol TMN-10 (10% aqueous, 0.3 ml) and glyoxal (10%
aqueous, 0.3 ml) were added, The mixture was knife-coated at 3 mil wet thickness onto subbed polyester and dried in air at 20C for 1 hour. The film was analysed as follows:
25 1. The density at 670.7 nm was 4.5. The width at half-height of the dye absorption had increased to 70 nm from 45 nm in the non-dispersed coatingsO
2. ~ The sensitivity of the film was 2 x 105 mJ/m2 measured at the dye peak, using a microdensitometer, : ,:

: : . :

=44-3. Application of the process solution described in Example 1 leads to a transference of 30% of the dye ~as deduced by the transmitted density to the receptor after 5 minutes).

' '~
~: .
:: ::
.

.

Claims (12)

=45=
CLAIMS:

1. A process for forming an image which comprises image-wise exposing to radiation of selected wavelength a carrier element comprising, as image forming components, in one or more imaging layers coated on a support a bleachable dye in reactive association with iodonium ion thereby bleaching the dye in exposed areas to form a positive image, and thereafter transferring the positive dye image to a receptor which is either a receptor layer present on the carrier or a separate receptor element by providing a liquid medium between the positive dye image and receptor for a sufficient time to allow transfer of the dye image to the receptor.

2. A process as claimed in Claim 1, in which the iodonium compound has the general formula:
in which:
Ar1 and Ar2 independently represent carbocyclic or heterocyclic aromatic-type groups having 4 to 20 carbon atoms, or together with the iodine atom complete a heterocyclic aromatic ring, and A? represents an anion which may be incorporated into Ar1 or Ar2.

=46=

3. A process as claimed in Claim 2, in which at least one of Ar1 and Ar2 includes a substituent in which R14 represents a straight chain or branched chain alkyl group of at least 3 carbon atoms, optionally substituted with one or more groups selected from OH, OR15, (NR163)? in which R15 and R16 represent alkyl groups or a group having a quaternary group at the end of the alkyl chain.

4. A process as claimed in Claim 3, in which the carrier element comprises cyan, magenta and yellow bleachable dyes, the element being constructed and arranged to allow even transfer of each dye.

5. A process as claimed in Claim 3, in which the dye and iodonium salt are present in one or more layers in a polymeric binder, the weight ratio of dye to iodonium salt being in the range of from 1:1 to 1:50 and the binder is present in an amount from 50 to 98% by weight of the total weight of binder, dye and iodonium salt.

6. A process as claimed in Claim 3, in which the bleachable dye is soluble in an aqueous diffusion transfer liquid and the process comprises providing an aqueous medium between the positive dye image and receptor for a sufficient time to allow transfer of the dye image to the receptor.

, .

=47=

7. A process as claimed in Claim 3, in which the bleachable dye is selected from a polymethine dye of the formula:
in which:
n is 0, 1 or 2, and R1 to R4 are selected to provide an electron donor moiety at one end of the conjugated chain and an electron acceptor moiety at the other, and independently represent halogen, cyano, nitro, carboxy, alkoxy, hydroxy, alkyl, aryl groups or heterocyclic rings any of which may be substituted, said groups containing up to 14 atoms selected from C, N, O and S; or R1 and R2 and/or R3 and R4 may represent the necessary atoms to complete optionally substituted aryl groups or heterocyclic rings, containing up to 14 atoms selected from C, N, O and S, or an oxonol dye of the formula:
in which:

=48=

is an integer of 0 to 2, A and B independently represent alkyl, aryl or heterocyclic groups or the necessary atoms to complete heterocyclic rings which may be the same or different Y? represents a cation.

8. A process as claimed in Claim 6 or Claim 7, in which the receptor comprises a layer having a polymeric binder and optionally a mordant.

9. A process as claimed in Claim 6, in which the radiation-sensitive carrier element comprises a receptor layer separated from the imaging layer(s) by a layer containing carbon and/or titanium dioxide.

10. The combination of a radiation-sensitive carrier element comprising, as image-forming components, one or more imaging layers coated on a support, a bleachable dye in reactive association with iodonium ion and a separate receptor element comprising a substrate having coated thereon a receptor layer comprising a polymeric binder and optionally a mordant.

11. A radiation-sensitive element comprising, as image-forming components, one or more imaging layers coated on a support, a bleachable dye in reactive association with iodonium ion and a receptor layer comprising a polymeric binder and optionally a mordant.

12. An element as claimed in Claim 11, in which the receptor layer is separated from the imaging layer(s) by a layer containing carbon and/or titanium dioxide.