Interference pigments are in the form of light-reflecting crystal platelets of appropriate thickness to produce color by interference. These pigments exhibit a color play that verges on iridiscence and under a given angle of reflection will allow only the copying of a single color, whereas other colors appear under different angles of reflection, in other words these pigments show another color to the human eye depending on the observation angle. High nacreous luster is accompanied by high specular reflectance. In most light interference pigments the transmission color is generally the complement of the reflection color.

Observed in transmission, some particular light interference pigments having more pronounced covering aspect show a particular greyish color while observed in reflection mode they have a more pronounced color-shift effect due to their specific built up and composition.

Transmission color of light interference pigments is much weaker than reflection color, which color seen in the reflection mode is called hereinafter "normal" color, [ref. Number 2 in a series of Mearl Technical Bulletins "Nacreous (Pearlescent) Pigments and Interference Pigments by L.M. Greenstein Henry L. Mattin Laboratories Reprinted from Pigment Handbook, Vol. I, Properties and Economics, 2nd Edition, Edited by Peter A. Lewis, (1988) by permission of John Wiley & Sons, Inc. The Mearl Corporation, 41 East 42nd Street, New York, N.Y. 100017. p. 5 and 6].

In interference, the reflection and transmission colors vary with angle of incidence. The reflection maximum and minimum shift to lower wavelengths as the angle of incidence increases (ref. the above mentioned Mearl Technical Bulletin, p. 8. Variation in color with angle of incidence and observation is referred to as geometric metamerism or goniochromatism [ref. Johnston, R. M. Color Eng. , 5(3). 42-47, 54 (1967) and Hem endinger, H. and Johnston R.M. " A Goniospectrophotometer for Color Measurements" in Color 69 (M. Richter. ed) . Musterschmidt, Gδttingen, Germany (1970)].

3. Objects and Summary of the Invention

It is an object of the present invention to provide a security document having a transparent or translucent support and containing throught the presence of light interference pigments a verification feature that can not be copied by photographic techniques and

interference pigments A are present uniformly on one side of a transparent support TS and light interference pigments B different in color with respect to pigments A are present uniformly on the other side of said support, wherein the pigments A have underneath a pattern printed with "common" light reflecting pigments R having no light interference properties.

Fig. 3 represents a schematic sectional drawing of a security document according to the present invention wherein at one side of a transparent support TS a layer containing light interference pigments A has on top a printed pattern containing common light- reflecting pigments R. At the other side of said support a printed pattern containing said normal pigments R is overprinted with a pattern containing light interference pigments B.

Fig. 4 represents a schematic sectional drawing of a security document according to the present invention wherein patterns containing light interference pigments A at one side of a transparent support TS are printed over (1) a pattern containing "common" light reflecting pigments Rl of which the color is complementary to the color of said pigments A when seen with reflected light, (2) a pattern comprising "common" light reflecting pigments Rl mixed with colored fluorescent or phosphorescent pigments or dyes RF, and (3) patterns containing solely fluorescent or phosphorescent dyes that may be white by inspection with visible light but emit colored light when exposed to ultraviolet light. At the other side of said support TS light interference pigments B are printed over (1') an opaque pattern containing metallic pigments (aluminium or bronze flakes) M, (2') a pattern comprising metallic pigments M mixed with "common" light reflecting pigments R2 having a color complementary to the color of said light interference pigments B when seen with reflected light, and (3') a pattern comprising solely light reflecting pigments R2 having a color complementary to the color of said light interference pigments B when seen with reflected light.

5. Detailed Description of the Invention

A layer and/or pattern containing said light interference pigments (same or different) may be present at both sides of said transparent or translucent support.

The security document according to the present invention may contain in the same patterns and/or layer mixtures of different

already mentioned bulletin "Nacreous (Pearlescent) Pigments and Interference Pigments", p. 3-4.

Mica pigments serving as a substrate of the interference coatings are a group of hydrous aluminum silicate minerals with platy morphology and perfect basal (micaceous) cleavage. Examples of suitable micas are e.g. muscovite KA1 (AIS^OJQ) (OH)2 _• paragonite NaAl ₂ (AlSi ₃ O ₁₀ ) (0H) ₂ , phlogopite K(Mg.Fe) (AlSi ₃ 0 ₁₀ ) (OH) ₂ , biotite K(Fe.Mg) (AlSi ₃ 0 ₁₀ ) (0H) ₂ and lepidolite K(Li,Al) _{2 <5} . ₃ ^(Al _{j #0} _

0.5 ^Si 3.0-3.5°lθ)(° ^H )2 ^etc "

Details about the application of metal and/or metal oxide coatings on the mica platelets are further given in US-P 3,087,827,

4,434,010 and 5,059,245 and in published EP-A-45 851. EP-A-313 280.

DE-A-11 65 182. DE-A-32 37 264. DE-A-38 25 702 and DE-A-36 17 430 and DE-OS 41 41 069.

In a preferred embodiment according to the present invention interference pigments having a composition as described in published

German patent application DE-OS 41 41 069 are used.

Said interference pigments, called "Glanzpigmente" according to said

DE-OS are composed of silicate platelets coated with either :

A) a first layer of highly refractive metal oxide, and

B) a second black layer essentially consisting of metallic iron, molybdenum and/or wolfram, or coated with :

A) a first layer of highly refractive metal oxide, and

B) a second black layer essentially consisting of carbon or metal , and

C) a third layer of highly refractive metal oxide.

By the presence of a semi-transparent carbon layer said platelets have a high chemical resistance. The carbon layer is obtained by thermal decomposition of oxygen-containing hydrocarbon compounds which for each two carbon atoms contain at least one oxygen atom e.g. as in carbohydrates such as sorbitol.

The metal layer B) can be formed in a medium of inert gas from in-gas-phase-decomposable metal compounds, e.g. metal carbonyl compounds, and the metal oxide layers A) and C) are formed by decomposition in gas phase of volatile metal compounds in the presence of oxygen water vapour or mixtures thereof.

The first layer A) consists e.g. of the oxides of titanium, zirconium, tin and/or iron.

Mica platelets double-side coated with one or more metal oxide layers for use as interference pigments are commercially available e.g. under the tradenames IRIODINE (E. Merck, Darmstadt). FLONAC

pigment code 9331 has when observed in reflection mode a yellow color; seen in transmission the color of that pigment becomes complementary in color, i.e. blue. This is in accordance with the general property of light interference pigments of changing their color complementarily when changing their mode of viewing going from reflection to transmission mode.

Tests have been carried out in printing a security pattern on a transparent substrate in such a way that one part of a printing pattern was printed with blue light interference pigment (e.g. PALIOSECURE EC 1408 or FD 4187 of BASF - Germany) and another part was printed using a yellow interference pigment (e.g. IRIODINE 9231 of MERCK - Germany) . By changing the viewing conditions from transmission to reflection mode the differently printed parts changed their color complementarily, so that the colors became inverted, which is as already been said, an effect that cannot be reproduced photographically by color copying machines. Common xerographic copying machines make prints against a white background (the color of the side of the cover of the machine contacting the original is white light reflecting) . The light interference pigments that face the light source have high reflectance and show their normal color, whereas the "complementary" color is reproduced with tran-smitted light reflected by said cover.

Said property provides a strong security feature which makes e.g. that when a yellow light interference pigment background is surrounding an information pattern printed with a blue light interference pigment pattern a copying machine operating with transmitted light (that is reflected by its white cover) will provide a copy that has the printed information in yellow surrounded by a blue background which is the complementary in color from what can be seen directly in reflected light not passing through the document.

Further it has been found by us that when copying a transparent document printed with light interference pigments and overprinted with a fine guilloche design with common light reflecting pigment being no light interference pigment, the color of the guilloche pattern in the photocopy is different whether (1) the copy is made with the front side of the transparent document (original) directed towards the light source of the copying machine or (2) the copy is made with the light of said source directed through the rear of the transparent document towards the information pattern and image background at the front side receiving reflected light from the

SUBSTfTUTESHEET(RULE26)

non-covered zone only. In the covered zone the light interference pigments show in reflective mode their main color.

On inspection in transmission mode (holding the document to the light) or copying with transmitted light the patterns of common light-reflecting pigments from front and rear side of the document are added (combined) and may form an uninterrupted area in the field of light interference pigments showing their own complementary color or combination of said complementary colors in overlapping zones, which may result in a continuous grey area where the complementary colors each represent a complementary part of the visible spectrum, as is the case e.g. by having in congruency a zone containing yellow-reflecting light interference pigments and a zone containing blue-reflecting light interference pigments.

Light interference pigments may be mixed with fluorescent or phosphorescent pigments without blocking the light emitted thereby. Light interference pigments have always some transparency together with their high specular reflectance.

According to one embodiment the above mentioned photographically obtained image or pattern is produced by means of a black-and-white or colour developed photosensitive silver halide directly in a light-sensitive material itself or in a non-light-sensitive image receiving material having a transparent support.

According to another embodiment the above mentioned photographically obtained image or pattern is produced by means of a non-impact printing technique in which analog or digital input signals for controlling the printing of said image or pattern stem from light-information originating from a visible original, which light-information may be transformed into electrical signals that can be transduced and stored, e.g. on magnetic tape or optical disk. The visible original may be an object or living being or an already formed photograph of these.

A survey of non-impact printing techniques such as electro(photo)graphic printing, ink jet printing, photochemical printing and thermal transfer printing is given by Jerome L. Johnson in "Principles of Non Impact printing" Palatino Press - Irvine, California U.S.A. (1986) .

In accordance with an embodiment according to the present invention there is provided a document including a photographically obtained image or pattern and uniformly distributed interference pigments of a particular color are present in the document in combination with a printed pattern containing interference pigments

11

ifferent from the color of the uniformly distributed pigments. rdance with another embodiment according to the present ere is provided a document including a photographically ge or pattern and having at each side of its transparent nt support a layer wherein interference pigments are uniformly, and wherein said layers at opposite sides of have a different color by the presence of different pigments. rdance with a further embodiment according to the present ere is provided a document wherein uniformly distributed pigments are present in combination with pattern-wise red common light-reflecting pigments or dyes or white ting pigments, e.g. Tiθ2. The color of the interference er the copying angle is preferably the same as the color ted light-absorbing substances preventing thereby otocopying of the printed information that remains still the human eye under another observation angle, lg to still another embodiment in a document of the ntion a pattern of printed interference pigments is rneath and/or on top of a layer or support having a ntially the same as the color of said pattern containing rence pigments when seen in reflection or transmission

lg to an embodiment in the security document according to invention different interference pigments are present _h in a different layer at opposite sides of said it least one of said layers has underneath and/or on top itaining common light-reflecting pigments and/or dyes jht interference properties, and having preferably a itially the same as the color of at least one of the pigments when seen in reflection or transmission mode, lg to another embodiment in the security document the present invention at least one pattern containing -reflecting pigments and/or dyes is present which least partly covered with a pattern containing pigments. lg to a further embodiment in the document according to invention the support has been coated directly by ith a thin metal oxide layer or has been coated with _ide layer on top of a coating or pattern of said light

resin layer wherein they are impregnated by pressure and heat. On top of the pigments an adhesive, e.g. wax may be applied to improve adherence to the selected substrate. That substrate may have hydrophilic or hydrophobic surface properties.

Spray-coating may be applied for covering the whole surface of the substrate or only a part thereof producing "light interference rainbow-effects". By using varying mixtures of different interference pigments the intensity of one color can be made to decrease gradually while an increasing color intensity of another pigment comes up. The human eye will see the rainbow effect varying according to the perception angle and will recognize the basic color of each of the sprayed pigments, but a photocopier operating with a fixed copying angle will only reproduce, say a single yellowish- brown color and not the colors of the interference pigments that can be seen under different inspection angles.

The interference pigments can be used for pigmenting a commercial coating varnish which may then be used for pre-coating a security document substrate, e.g. opaque resin film or paper. The coating may proceed with common varnishing or impregnation machinery instead of using printing presses.

As already mentioned herein the uniformly applied interference pigments are advantageously combined with image-wise or pattern-wise applied interference pigments of another color.

The image-wise or pattern-wise application of interference pigments proceeds e.g. by printing with an ink containing said pigments. Suited printing processes are e.g. planographic offset printing, gravure printing, intaglio printing, screen printing, flexographic printing, relief printing, tampon printing, ink jet printing and toner-transfer printing from electro(photo)graphic recording materials.

For use in printing on hydrophilic layers or substrates the ink contains for example a 15 to 20 % by weight mixture of the interference pigments in a solution of cellulose nitrate in a polyethylene ether. Such ink has a good adherence on hydrophilic colloid layers such as gelatin-containing layers used in DTR- recording materials. Said ink is advantageously applied with a commercial screen press using a polyester screen with a 77 and 55 mesh. The interference colors gradually appear on drying the ink.

Thus applied ink patterns on a hydrophilic image-receiving layer for DTR-image production remain unchanged during DTR-processing.

The presence of the light interference pigments in one of the

ie opaque security document does not affect the to print thereon further graphic or alpha-numerical by any known printing technique. sy visual verification the light interference pigments are erably in a security document in a coverage of 0.3 g/πr d more preferably in a coverage between 0.7 g/m ² and 3

.nting of a light interference pigment-containing pattern on a substrate already covered e.g. by a hologram, iction pattern, metallic pattern that can be viewed printed pattern so that the properties of the pigments are added thereto, nted pattern containing interference pigments forms no a good adherence with laminated plastic resinous :erial. By proper selection of the binder of the ink it lted with the resin material laminated thereto, ng to a particular embodiment the light interference aining ink is applied on a temporary support, e.g. support, wherefrom the ink layer can be stripped off and to a permanent support, e.g. a glued and preprinted a security document. The ink layer, applied overall or :, after leaving the temporary support covers underlying data on the permanent support. For preventing opying these data have the same color as the pigment layer when seen under the copying angle. image contrast is available so that copying of the pre- is no longer possible. By applying a dried pigment-containing ink layer that is translucent the ata can be visually inspected therethrough by altering on angle, rdance with the preceding embodiment a security document the present invention, e.g. serving as I.D. card, is the form of a laminate in which the information- ayer(s) are sealed between protective resinous sheets. linates may be built up as described e.g. in US-P S-P 4,762,759, US-P 4,902.593, published EP-A 0 348 310 EP-A 0 462 330. By lamination tamper-proof documents which do not allow the opening of the laminate without image contained therein. The destruction of the seal isual fraude traces on the security document.

In accordance with a first mode in the security document according to the present invention a black-and-white photograph in the form of a silver image is formed by the silver salt diffusion transfer process, called herein DTR-process. According to said process dissolved silver halide salt is transferred imagewise in a special image receiving layer, called development nuclei containing layer, for reducing therein transferred silver salt, said development nuclei containing layer contains itself and/or in an overlaying and/or an underlaying layer uniformly distributed therein said interference pigments.

The light interference pigments may be present either in the image-receiving layer itself and/or in a waterpermeable top layer and/or in a subbing layer covering the support.

The presence of a dried water-impermeable ink pattern on the image-receiving layer blocks DTR-image formation. Thereby it is possible to arrange e.g. fine line patterns such as guilloches in the photograph creating that way an additional verification feature.

The principles of the DTR-process are described in U.S. patent No. 2,352,014 of Andre Rott, issued June 20, 1944. According to said process silver complexes are image-wise transferred by diffusion from a silver halide emulsion layer to an image-receiving layer, where they are converted, in the presence of development nuclei, into a silver image. For this purpose, an image-wise exposed silver halide emulsion layer is developed by means of a developing substance in the presence of a so-called silver halide solvent. In the exposed parts of the silver halide emulsion layer the silver halide is developed to metallic silver so that it cannot dissolve anymore and consequently cannot diffuse. In the non-exposed parts of the silver halide emulsion layer the silver halide is converted into soluble silver complexes by means of a silver halide complexing agent, acting as silver halide solvent, and said complexes are transferred by diffusion into an image-receiving layer being in waterpermeable contact with said emulsion layer to form by the catalytic action of said development nuclei, in so-called physical development, a silver-containing image in the image-receiving layer.

More details on the DTR-process can be found in "Photographic Silver Halide Diffusion Processes" by A. Rott and E. Weyde, Focal Press, London, New York (1972).

In accordance with a second mode in the opaque security document according to the present invention a color photograph in the form of one or more dye images is formed by the dye diffusion transfer

DTR-process) wherein the image-wise transfer of dye(s) _d by the development of (a) photo-exposed silver halide rer(s) , and wherein dye(s) is (are) transferred imagewise image receiving layer, called mordant layer, for fixing ιid mordant layer and/or an overlaying and/or an layer containing uniformly distributed therethrough said pigments. 'fusion transfer reversal processes are based on the iransfer of diffusible dye molecules from an image-wise rer halide emulsion material into a waterpermeable ring layer containing a mordant for the dye(s) . The liffusion of the dye(s) is controlled by the development >re image-wise exposed silver halide emulsion layers, production of a multicolor image are differently sensitized and contain respectively a yellow, magenta and .ecules. A survey of dye diffusion transfer imaging is been given by Christian C. Van de Sande in Angew. Engl. 22 _. (1983) n° 3, 191-209 and a particularly useful escribed in US-P 4.496,645. in dye diffusion transfer photography the type of en will depend upon the dye to be mordanted. If acid be mordanted, the image-receiving layer being a dye- ayer contains basic polymeric mordants such as polymers .nidine derivatives of vinyl methyl ketone such as US-P 2,882,156, and basic polymeric mordants and e.g. poly-4-vinylpyridine, the metho-p-toluene if poly-2-vinylpyridine and similar compounds described 4,430, and the compounds described in the published DE-A d 2,200,063. Other mordants are long-chain quaternary phosphonium compounds or ternary sulphonium compounds, escribed in US-P 3,271.147 and 3,271,148,, and .yl-ammonium bromide. Certain metal salts and their hat form sparingly soluble compounds with the acid dyes too. The dye mordants are dispersed or molecularly ne of the usual hydrophilic binders in the ing layer, e.g. in gelatin, polyvinylpyrrolidone or mpletely hydrolysed cellulose esters. 4,186,014 cationic polymeric mordants are described that arly suited for fixing anionic dyes, e.g. sulphinic acid at are image-wise released by a redox-reaction described ublished EP-A 0,004,399 and US-P 4,232,107,

The DTR process can be utilized for reproducing line originals e.g. printed documents, as well as for reproducing continuous tone originals, e.g. portraits.

By the fact that the DTR-image is based on diffusion transfer of imaging ingredients the image-receiving layer and optionally present covering layer(s) have to be waterpermeable.

The reproduction of black-and-white continuous tone images by the DTR-process requires the use of a recording material capable of yielding images with considerable lower gradation than is normally applied in document reproduction to ensure the correct tone rendering of continuous tones of the original. In document reproduction silver halide emulsion materials are used which normally mainly contain silver chloride. Silver chloride not only leads to a more rapid development but also to high contrast.

In U.S. patent. No. 3,985,561, to be read in conjunction herewith, a light-sensitive silver halide material is described wherein the silver halide is predominantly chloride and this material is capable of forming a continuous tone image on or in an image-receiving material by the diffusion transfer process.

According to said U.S. patent a continuous tone image is produced by the diffusion transfer process in or on an image- receiving layer through the use of a light-sensitive layer which contains a mixture of silver chloride and silver iodide and/or silver bromide dispersed in a hydrophilic colloid binder e.g. gelatin, wherein the silver chloride is present in an amount of at least 90 mole % based on the total mole of silver halide and wherein the weight ratio of hydrophilic colloid to silver halide, expressed as silver nitrate, is between 3:1 and about 10:1 by weight.

With these light-sensitive materials successful reproduction of continuous tone images can be obtained probably as a result of the presence of the indicated amounts of silver iodide and/or silver bromide and of the defined high ratio of hydrophillic colloid to silver halide.

According to U.S. patent No. 4,242,436 likewise to be read in conjunction herewith, the reproduction of continuous tone images can be improved by developing the photographic material with a mixture of developing agents comprising an o-dihydroxybenzene, e.g. catechol, a 3-pyrazolidinone e.g. a 1-aryl-3-pyrazolidinone and optionally a p-dihydroxybenzene, e.g. hydroquinone, the molar amount of the o-dihydroxybenzene in said mixture being larger than the

SUBSTITUTESHEET(RULΣ26)

ige-receiving layer may contain as physical development s, in operative contact with the developing nuclei, ompounds such as those described e.g. in DE-A-1 ,124,354; 471; US-P 4,072,526 and in EP 26520. ing to a preferred embodiment the processing liquid and/or ge-receiving material contains at least one image toning said case the image toning agent (s) may gradually diffusion from said image-receiving material into the .iquid and keep therein the concentration of said agents iy. In practice such can be realized by using the silver agents in a coverage in the range from 1 mg/m ² to 20 lydrophilic waterpermeable colloid layer. >y of suitable toning agents is given in the above .ok of Andre Rott and Edith Weyde, p. 61-65, preference to l-phenyl-lH-tetrazole-5-thiol , also called αercapto-tetrazole , tautomeric structures and derivatives as 1 - (2 ,3-dimethylphenyl) -5-mercapto-tetrazole, rhylcyclohexyl) -5-mercapto-tetrazole, .henyl) -5-mercapto-tetrazole, -4-methylphenyl) -5-mercapto-tetrazole,

.orophenyl) -5-mercapto-tetrazole. Further particularly lg agents are of the class of thiohydantoins and of the ϊnyl substituted mercapto-triazoles . Still further :s suitable for use in accordance with the preferred _f the present invention are the toning agents described

European patent applications 218752, 208346, 218753 .83.189. security documents according to the present invention the or translucent support is e.g. a clear resin film such support containing small amounts of pigments or Tying to some degree the support. For example, white .es as described e.g. in published European patent (EP-A) 0 324 192 are incorporated therein, resins suited for manufacturing transparent film e.g. polycarbonates, polyesters, preferably terephthalate , polystyrene and homo- and copolymers of .de. Further are mentioned cellulose esters e.g. riacetate. ve mentioned DTR image-receiving materials may be used in with any type of photosensitive material containing a le emulsion layer. For continuous tone reproduction the

silver halide comprises preferably a mixture of silver chloride, and silver iodide and/or silver bromide, at least 90 mole % based on the total mole of the silver halide being silver chloride, and the ratio by weight of hydrophillic colloid to silver halide expressed as silver nitrate is between 3:1 and 10:1.

The binder for the silver halide emulsion layer and other optional layers contained on the imaging element is preferably gelatin. But instead of or together with gelatin, use can be made of one or more othei natural and/or synthetic hydrophilic colloids, e.g. albumin, casein, zein, polyvinyl alcohol, alginic acids or salts thereof, cellulose derivatives such as carboxymethyl cellulose, modified gelatin, e.g. phthaloyl gelatin etc. The weight ratio in the silver halide emulsion layer of hydrophilic colloid binder to silver halide expressed as equivalent amount of silver nitrate to binder is e.g. in the range of 1:1 to 10:1, but preferably for continuous tone reproduction is between 3.5:1 and 6.7:1.

The silver halide emulsions may be coarse or fine grain and can be prepared by any of the well known procedures e.g. single jet emulsions, double jet emulsions such as Lipp ann emulsions, ammoniacal emulsions, thiocyanate- or thioether-ripened emulsions such as those described in US-P 2,222,264, 3.320,069, and 3.271,157. Surface image emulsions may be used or internal image emulsions may be used such as those described in US-P 2,592.250, 3,206,313, and 3,447,927. If desired, mixtures of surface and internal image emulsions may be used as described in US-P 2,996,382.

The silver halide particles of the photographic emulsions may have a regular crystalline form such as cubic or octahedral form or they may have a transition form. Regular-grain emulsions are described e.g. in J. Photogr. Sci. , Vol. 12, No. 5, Sept. /Oct. 1964. pp. 242-251. The silver halide grains may also have an almost spherical form or they may have a tabular form (so-called T-grains) , or may have composite crystal forms comprising a mixture of regular and irregular crystalline forms. The silver halide grains may have a multilayered structure having a core and shell of different halide composition. Besides having a differently composed core and shell the silver halide grains may comprise also different halide compositions and metal dopants inbetween.

The average size expressed as the average diameter of the silver halide grains may range from 0.2 to 1.2 urn, preferably between 0.2μm and O.δμm, and most preferably between 0.3μm and 0.6μm. The size

can be homodisperse or heterodispere. A homodisperse jution is obtained when 95 % of the grains have a size >t deviate more than 30 % from the average grain size, lsions can be chemically sensitized e.g. by adding :aining compounds during the chemical ripening stage e.g. .ocyanate, allyl thiourea, and sodium thiosulphate. Also .nts e.g. the tin compounds described in BE-A 493,464 and polyamines such as diethylene triamine or derivatives ane-sulphonic acid can be used as chemical sensitizers. Ie chemical sensitizers are noble metals and noble metal ch as gold, platinum, palladium, iridium, ruthenium and s method of chemical sensitization has been described :le of R.KOSLO SKY. Z. Wiss. Photogr. Photophys. 6. 65-72 (1951) . lsions can also be sensitized with polyalkylene oxide e.g. with polyethylene oxide having a molecular weight 0,000, or with condensation products of alkylene oxides c alcohols, glycols, cyclic dehydration products of kyl-substituted phenols, aliphatic carboxylic acids, lines, aliphatic diamines and amides. The condensation e a molecular weight of at least 700, preferably of more It is also possible to combine these sensitizers with s described in BE-P 537,278 and GB-P 727.982. rer halide emulsion may be sensitized panchromatically to duction of all colors of the visible part of the it may be orthochromatically sensitized, ctral photosensitivity of the silver halide can be proper spectral sensitization by means of the usual ymethine dyes such as acidic or basic cyanines , , oxonols, hemioxonols, styryl dyes or others, also tri- ar methine dyes e.g. rhodacyanines or neocyanines . Such sitizers have been described by e.g. F.M. HAMER in "The and Related Compounds" (1964) Interscience Publishers,

Sons , New York. rer halide emulsions may contain the usual stabilizers ar or salt-like compounds of mercury with aromatic or rings such as mercaptotriazoles , simple mercury salts, ercury double salts and other mercury compounds. Other jilizers are azaindenes, preferably tetra- or

_nes , especially those substituted with hydroxy or amino )ounds of this kind have been described by BIRR in Z.

SiBSTTTUTE SHEET (RULE 26)

iss. Photogr. Photophys. Photoche . 47, 2-27 (1952). Other suitable stabilizers are i.a. heterocyclic mercapto compounds e.g. phenylmercaptotetrazole. quaternary benzothiazole derivatives, and benzotriazole.

A survey of photographic silver halide emulsions and their preparation is given in Research Disclosure December 1989, item 308119.

Processing of the image-wise exposed photographic silver halide emulsion layer proceeds whilst in contact with an image receiving material according to the invention and is accomplished using an alkaline processing liquid having a pH preferably between 9 and 13. The pH of the alkaline processing liquid may be established using various alkaline substances. Suitable alkaline substances are inorganic alkali e.g. sodium hydroxide, potassium carbonate or alkanolamines or mixtures thereof. Preferably used alkanolamines are tertiary alkanolamines e.g. those described in EP-A-397925. EP- A-397926, EP-A-397927. EP-A-398435 and US-P 4,632,896. A combination of alkanolamines having both a pk _a above or below 9 or a combination of alkanolamines whereof at least one has a pk _a above 9 and another having a pk _a of 9 or less may also be used as disclosed in the Japanese patent applications laid open to the public numbers 73949/61, 73953/61, 169841/61, 212670/60, 73950/61, 73952/61, 102644/61. 226647/63. 229453/63, US-P-4.362.811. US-P 4,568.634 etc.. The concentration of these alkanolamines is preferably from 0.1 mol/1 to 0.9 mol/1.

Suitable developing agents for the exposed silver halide are e.g. hydroquinone-type and 1-phenyl-3-pyrazolidone-type developing agents as well as p-monomethylaminophenol and derivatives thereof. Preferably used is a combination of a hydroquinone-type and 1- phenyl-3-pyrazolidone-type developing agent wherein the latter is preferably incorporated in one of the layers comprised on the support of the photographic material. A preferred class of 1- phenyl-3-pyrazolidone-type developing agents is disclosed in the published EP-A 449340.

According to a preferred embodiment for continuous tone reproduction a mixture of developing agents comprising an o- dihydroxybenzene, e.g. catechol, a 3-pyrazolidinone e.g. a l-aryl-3- pyrazolidinone and optionally a p-dihydroxybenzene, e.g. hydroquinone the molar amount of the o-dihydroxybenzene in said mixture being larger than the molar amount of the 3-pyrazolidinone, and the p-dihydroxybenzene if any being present in a molar ratio of

about the dye diffusion transfer process and image receiving materials used therein are described in Research Disclosure November 1976. item 15162.

The present invention will now be illustrated by the following examples without however limiting it thereto. All ratios, percentages and parts are by weight unless otherwise specified.

EXAMPLE 1

- Preparation of photographic element for use in the DTR process

A gelatino silver halide emulsion was prepared by slowly running with stirring an aqueous solution of 1 mole of silver nitrate per liter into a gelatine solution containing per mole of silver nitrate 41 g of gelatin, 1.2 mole of sodium chloride, 0.08 mole of potassium bromide and 0.01 mole of potassium iodide.

The temperature during precipitation and the subsequent ripening process lasting three hours was kept at 40°C.

Before cooling, shredding and washing 214 g of gelatin were added per mole of silver halide. The washed noodles were molten and another 476 g of gelatin were added per mole of silver halide during the chemical ripening. After ripening 285 g of gelatin in the form of a 20 % aqueous solution were added to the emulsion per mole of silver halide as well as hydroquinone in an amount such that after coating 0.9 g of hydroquinone were present per nr and l-phenyl-4,4- dimethyl-3-pyrazolidinone in an amount such that 0.21 g thereof were present per m ² . The emulsion was coated at one side of a subbed water-resistant paper support consisting of a paper having a weight of 110 g/πr coated at both sides with a polyethylene stratum at a ratio of 20 g/m ² per side.

The emulsion was coated in such a way that an amount of silver equivalent to 1.5 g of silver nitrate was applied per m ² . The amount of gelatin corresponding therewith is 8.93 g/πr since the gelatin to silver nitrate weight ratio was 5.97.

- Preparation of image receiving material for use in the DTR process and containing light interference pigments

One side of a double-side subbed transparent polyethylene terephthalate support having a thickness of 0.1 mm was coated after

hydroxyethyl cellulose 1.0 g

Ethylenediaminetetraacetic acid tetrasodium salt 2.0 g

Na ₂ S0 ₃ 45.0 g

Na ₂ S ₂ 0 ₃ 14.0 g KBr 0.5 g l-Phenyl-5-mercapto-tetrazole 0.1 g

1- (3,4-Dichlorophenyl) -lH-tetrazole-5-thiol 0.02 g

N-methyl-ethanolamine 45.0 ml

N-methyl-diethanolamine 30.0 ml Water up to 1 1

When viewed in daylight under an angle of 90° in reflection mode the color of the non-printed area around the portrait (inspection at the front side) was blue due the presence of uniformly distributed therein PALIOSECURE type EC 1408 - BLUE (tradename) . In the transmission mode the color in that background area became slightly brownish yellow at the front side and blue at the rear side.

On copying the obtained document with a color copier (CANON CLC 500) the parts of the document around the portrait were reproduced grey (yellow plus blue) having the blue printed graphical information of non-iridiscent pigment with poor contrast thereon.

EXAMPLE 2

- Preparation of image-receiving element for use in dye diffusion transfer process

A transparent polyvinyl chloride sheet having a thickness of 0.100 mm was after corona treatment coated at one side with the following compositions for forming a subbing layer and mordanting layer respectively :

1. Subbing layer coating composition gelatin 4 g aqueous dispersion of blue PALIOSECURE type EC 1408 (tradename) containing 30 % of said blue pigment and 8 % of gelatin 200 g ingredient A 40 % solution dispersed in aqueous medium 250 ml

5 % solution of siloxane compound in ethanol 125 ml

12.5 % solution of saponine in ethanol/water 20/80 20 ml

Ingredient A is a polyester-polyurethane having the same

After leaving the processing tray the image-receiving sheet was led through a second tray containing an aqueous solution of the already mentioned wetting agent W corresponding with the following formula : iso-nonyl-phenoxy- (CH2-CH2-O)g-H and potassium iodide (ref. EP 0250657) .

After drying the processed sheet material it was laminated as described in US-P 4,902,593 to obtain a sealed I.D. card.

EXAMPLE 3

The interference pigments mentioned in Example 2 were applied uniformly in front and rear mordanting layers respectively instead of in the subbing layers of an image-receiving material suited for use in a dye diffusion transfer process.

- Preparation of the image-receiving element

A transparent polyvinyl chloride sheet having a thickness of 0.100 mm was after corona treatment coated at one side with the following compositions for forming a subbing layer and mordanting layer respectively :

1. Coating composition of the subbing layer

gelatin 20 g ingredient A 40 % solution dispersed in aqueous medium 250 ml

5 % solution of siloxane compound in ethanol 125 ml

12.5 % solution of saponine in ethanol/water 20/80 20 ml

The coating composition was applied coated at a dry coverage of 0.4 g/m ² of gelatin.

2. Coating composition of the front mordanting layer

gelatin 12 g aqueous dispersion of blue PALIOSECURE type EC 1408 (tradename) containing 30 % of said blue pigment and 8 % of gelatin 100 g mordant M (20 % solution) 250 ml saponine (12 %) and wetting agent W (5 %) in water 32 ml aqueous 4 % solution of formaldehyde 10 ml