EP0400220A1

EP0400220A1 - Laminated article for identification purposes

Info

Publication number: EP0400220A1
Application number: EP89201383A
Authority: EP
Inventors: Leon Louis Vermeulen; Robert Sophia Pauwels
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1989-05-31
Filing date: 1989-05-31
Publication date: 1990-12-05
Anticipated expiration: 2009-05-31
Also published as: DE68917916D1; EP0400220B1; JPH0342295A; DE68917916T2

Abstract

A laminated article containing visible information which article comprises two plastic resin sheets or layers at least one of which is transparent and having laminated inbetween at least one hydrophilic colloid layer containing photographically produced information and carrying or containing thermochromic liquid crystals of the cholesteric type in the form of a pattern or an indicium that can be made visible or obtains a change in colour by heating above 25 °C, said liquid crystals being arranged against a contrasting background having an optical density of at least 0.2 in its spectral absorption range.

Description

The present invention relates to a process for the production of a laminated identification card (I.D. card).
I.D. cards essentially comprise a card or document usually containing information relating to the bearer. Generally, a portion of the information is in the form of a photograph of the bearer. I.D. cards are used e.g. to establish a person's authorization to conduct certain activities (driver's licence) or the authorization to have access to certain areas (employee I.D. cards) or to engage in credit transactions (I.D. credit cards).
In view of the widespread use of I.D. cards, especially in commercial transactions, such as cashing checks, credit purchases, etc., it is important that the information contained in the I.D card cannot be altered and that the I.D. card gives maximum protection against counterfeiting, e.g. by photographic techniques and/or replacement of its data.
Normally the information in the I.D. card is protected by lamination between plastic sheets serving as support and covering sheet.
Many attempts have been made to obtain the perfect seal that is thus strong that it resists separation, e. g. by razor blade and/or wet treatment. The use of a pouch structure wherein only the border parts of the plastic sheets are sealed is not sufficiently tamper-proof since after cutting around the edge of the original card the pouch can be opened and some information such as the photograph can be removed and replaced by other information before resealing the pouch
Ideally, to avoid said shortcoming a "security seal" is established between the information-bearing element of the card or document and the plastic. As described in US-P 4,151,666 the security seal makes that if one should succeed in the removal of the plastic cover sheet also a substantial portion of the information containing part of the document should be removed too so that a damaged part remains adhering to the support. In this way a protection against mere substitution of information is obtained discouraging alteration of sealed documents.
In order to improve the identification security coded information invisible to the naked eye and being machine readable is often included into the laminate serving as an identification card. So, e.g. badges have been made that include magnetically encoded data to be read by a magnetic signal detector as in a magnetic tape recorder or include infrared markings to be read with an infrared card reader as described e.g. in US-P 4,583,766.
An other identification article described in published UK Patent Application 2 109 304 A and serving as identity document comprises markings or photograph, covered by a mask which is normally opaque but which upon applying a suitable electric field over a masking liquid crystal layer becomes at least translucent so that the covered material becomes visible.
Magnetic, infrared or electro-optical markings that are not visible require special badge reading devices that are rather complicated and may be out of service for a while. Therefore, to enhance security there is a need for a hidden verification feature that can be made visible by man made inspection and turns back to the original hidden state after inspection with the advantage that such reversible state cannot be reproduced photographically which makes it impossible to duplicate the document by photographic copying.
It is an object of the present invention to provide an identification document containing a verification feature that cooperates with a security seal laminate and which in non-activated state is invisible but can be easily made visible by heating below 120 °C, e.g. by a temperature raise in the range of 30 to 50 °C.
Other objects and advantages of the present invention will appear from the further description.
According to the present invention a laminated article containing visible information is provided comprising two plastic resin sheets or layers at least one of which is transparent and having laminated inbetween at least one hydrophilic colloid layer containing photographically produced information and carrying or containing thermochromic liquid crystals of the cholesteric type in the form of a pattern or an indicium that can be made visible or obtains a change in colour by heating above 25 °C, said liquid crystals being arranged against a contrasting background having an optical density of at least 0.2 in its spectral absorption range.
According to a preferred embodiment said background is black or dark blue coloured.
By liquid cristals of the cholesteric type is meant a chiral nematic liquid crystal material that has a natural twisted structure, the pitch of the twisted structure being of the order of the wavelengths of visible light. The pitch and period of the helical structure (the angle between each turn and the distance between the turns) gives rise to interference colours when light falls on said liquid crystal material [ref. Scientific American, Vol. 222, April 1970, p. 102.]. Changes in temperature or pressure alter the pitch and period so that new colours are produced. Cholesteric liquid crystals can therefore serve as the active elements in devices that map the distribution of temperatures and are used e.g. in the thermochromic industry for the manufacture of digital thermometers and temperature indicators of one type or another.
Thermochromic liquid crystals react to changes in temperature by changing colour. They do this by selectively reflecting a part of the visible light incident upon them, giving rise to reflection of almost all monochromatic colours. The reflected light varies with temperature characteristically from colourless to red at low temperatures, then through the colours of the visible spectrum to blue/violet and finally becomes colourless again at relatively high temperature. For best visualisation of the colour effects, the thermochromic liquid crystal materials are viewed against a black background to absorb the unreflected light. For maximum apparent density in the eye a colour change producing green is preferred.
Examples of thermochromic liquid crystals showing a temperature dependent change in colour are e.g. cholesteryl benzoate, cholesteryl chloride and anisylidene-p-aminophenylacetate. Below 32 °C the last-mentioned substance is a solid with gray appearance. Above that temperature it becomes a liquid crystal having colour, becoming colourless in the liquid state at 105 °C. By raising temperature the colour may change from red over yellow, green and blue to purple.
By using in the laminated article according to the present invention mixtures of liquid crystal material it is possible to obtain e.g. colour effects over the temperature range of 28 °C to 35 °C which is particularly interesting for hand checking an ID card by normal hand temperature.
The liquid crystal material applied in the form of a pattern or indicium may more particularly represent a fingerprint, signature, bar code, letter(s) and/or figure(s), line drawings etc. The pattern or indicium is either or not built up by screen dots, which means that it is present either or not as a halftone pattern.
In the laminated article of the present invention the thermochromic liquid crystals are applied preferably onto or in a hydrophilic colloid layer, e.g. a gelatin binder layer containing photographic information to be protected by lamination.
According to a preferred embodiment the hydrophilic colloid layer containing photographic information is an imagewise exposed and processed (developed and fixed) silver halide emulsion layer or is an image-receiving layer containing a photographic image obtained by the silver complex diffusion transfer reversal process or a dye diffusion transfer process based on silver halide photography.
In the production of a laminate according to the present invention any type of silver halide emulsion layer may be used. Information about silver halide emulsion preparation and composition can be found e.g. in Research Disclosure, December 1978, item 17643.
The composition of silver complex diffusion transfer reversal (DTR-) materials and processing are known e.g. from the book: "Photographic Silver Halide Diffusion Processes" by André Rott and Edith Weyde- Focal Press - London - New York (1972).
A survey of dye diffusion transfer materials is given in Research Disclosure, November 1976, item 15162 and by Christian C. Van de Sande in Angew. Chem. - Ed. Engl. 22 (1983) n° 3, 191-209.
In a silver halide emulsion layer or an image-receiving layer for silver complex or dye diffusion transfer processing gelatin is used preferably as hydrophilic colloid binder. Gelatin can, however, be replaced in part or integrallly by synthetic, semi-synthetic, or natural polymers. Synthetic substitutes for gelatin are e.g. polyvinyl alcohol, poly-N-vinyl pyrrolidone, polyvinyl imidazole, polyvinyl pyrazole, polyacrylamide, polyacrylic acid, and derivatives thereof, in particular copolymers thereof. Natural substitutes for gelatin are e.g. other proteins such as zein, albumin and casein, cellulose, saccharides, starch, and alginates. In general, the semi-synthetic substitutes for gelatin are modified natural products e.g. gelatin derivatives obtained by conversion of gelatin with alkylating or acylating agents or by grafting of polymerizable monomers on gelatin, and cellulose derivatives such as hydroxyalkyl cellulose, carboxymethyl cellulose, phthaloyl cellulose, and cellulose sulphates.
In DTR-image-receiving materials preferably gelatin is used as sole binding agent for its physical development nuclei or in combination with alginic acid derivatives, polyvinyl alcohol, starch and starch derivatives, particularly carboxymethylcellulose or gallactomannans (ref. the above mentioned book of André Rott and Edith Weyde, p. 49). Other organic binding agents of the synthetic type are e.g. poly-N-vinylpyrrolidinone, copolymers of polyvinyl ester and maleic anhydride. As inorganic binding agent colloidal silica has been mentioned, e.g. in US-P 2,698,237.
In dye diffusion transfer layers suited for use in the production of a laminate according to the present invention a hydrophilic colloid binder, preferably gelatin, is used in conjunction with a mordant for the transferred dyes. If acid dyes are to be mordanted, the dye image-receiving layer contains basic polymeric mordants such as polymers of amino-guanidine derivatives of vinyl methyl ketone as described e.g. in US-P 2,882,156, and basic polymeric mordants and derivatives, e.g. poly-4-vinylpyridine, the metho-p-toluene sulphonate of poly-2-vinylpyridine and similar compounds described in US-P 2,484,430, and the compounds described in the published DE-A 2,009,498 and 2,200,063. Other mordants are long-chain quaternary ammonium or phosphonium compounds or ternary sulphonium compounds, e.g. those described in US-P 3,271,147 and 3,271,148,, and cetyltrimethyl-ammonium bromide. Certain metal salts and their hydroxides that form sparingly soluble compounds with the acid dyes may be used too. The dye mordants are dispersed or molecularly divided in one of the usual hydrophilic binders in the image-receiving layer, e.g. in gelatin, polyvinylpyrrolidone or partly or completely hydrolysed cellulose esters.
In US-P 4,186,014 and unpublished EP-A No. 89 200 708.9 filed March 20, 1989 cationic polymeric mordants are described that are particularly suited for fixing anionic dyes, e.g. sulphinic acid salt dyes that are image-wise released by a redox-reaction described e.g. in published EP-A 0,004,399 and US-P 4,232,107.
The production of colour photographs by the dye diffusion transfer process is a very convenient method especially for the production of identification cards containing a colour photograph of the person to be identified.
The image-receiving layer can form part of a separate image-receiving material or form an integral combination with the light-sensitive layer(s) of the photographic material.
When the image-receiving layer is applied to a common hydrophobic resin support and remains associated with the silver halide emulsion layer(s) after processing of the photosensitive material, an alkali-permeable light-shielding layer, e.g. containing white pigment particles, is applied between the image-receiving layer and the silver halide emulsion layer(s) to mask the negative image with respect to the positive image as described e.g. in the already mentioned book of André Rott and Edith Weyde, page 141.
The pattern or indicium of thermochromic liquid crystal material can be applied by a spraying or printing technique to the layer containing the photographic information or other layer to be arranged inside the laminated article. Suitable printing techniques are offset printing, letter press printing or screen printing using an aqueous base ink containing the liquid crystals in dispersed state in a watersoluble polymeric binder, e.g. gelatin or polyacrylamide.
According to a preferred embodiment the liquid crystal material is encapsulated in gelatin or gelatin derivative crosslinked with a hardener e.g. an aldehyde. The encapsulation of the thermochromic liquid crystal material in gelatin derivatives the solubility of which is pH dependent may proceed as described e.g. in US-P 3,328,257. Operating with an aqueous ink containing gelatin-type microcapsules a good adherence to a hydrophilic colloid layer of the laminate is obtained.
In order to obtain a good contrast the thermochromic liquid crystal material is arranged against an underlying black area, e.g. obtained by printing a black ink area or spot on the hydrophilic colloid layer prior to producing therein the photographic information. According to another embodiment the contrasting black area is obtained by silver metal deposition or combination of dyes formed in the production of the photographic image. In a particular embodiment the black area is an area wherein black silver metal of sufficient optical density of a portrait obtained by silver halide photography is present.
In the production of an ID card laminate according to the present invention any type of paper support coated with a hydrophobic thermoplastic resin layer or any hydrophobic thermoplastic resin support may be used for coating thereon the imaging layer.
A preferred resin support for use in lamination by heat-sealing is made of a vinyl chloride polymer.
The term "vinyl chloride polymer" used herein includes the homopolymer, as well as any copolymer containing at least 50 % by weight of vinyl chloride units and including no hydrophilic recurring units.
Vinyl chloride copolymers serving as the support may contain one or more of the following comonomers : vinylidene chloride, vinyl acetate, acrylonitrile, styrene, butadiene, chloroprene, dichlorobutadiene, vinyl fluoride, vinylidene fluoride and trifluorochloroethylene.
The polyvinyl chloride serving as the support may be chlorinated to contain 60-65 % by weight of chlorine.
Many properties of polyvinyl chloride and its copolymers are improved by plasticization and their stability can be improved by stabilizers well known to those skilled in the art (see, e.g., F.W.Billmeyer, Textbook of Polymer Chemistry, Interscience Publishers, Inc., New York (1957) p. 311-315)).
The polyvinyl chloride support may contain pigments or dyes as colouring matter e.g. in an amount up to 5 % by weight. An opaque white appearance may be obtained by incorporation of white pigments, e.g. titanium dioxide particles.
As described in published EP-A 0 065 329 and corresponding US-P 4,429,032 a proper anchorage of a DTR-image receiving layer to a corona-discharge treated polyvinyl chloride support has been obtained by the use in the image-receiving layer of colloidal silica in a weight ratio of from 5/1 to 2/1 with respect to a hydrophilic binder such as gelatin. Other hydrophobic resin support and hydrophilic image layer combinations providing security sealing in ID laminates are described in published European Patent Applications (EP-A) 0 222 045, 0 250 658, 0 276 506 and non-published EP-A 88201426.9 filed July 7, 1988. The security sealing makes that if one should succeed in the removal of the plastic cover sheet also a substantial portion of the information and of the liquid crystals should be removed too with the partially torn off hydrophilic colloid layer, so that a damaged part remains adhering to the support.
According to a preferred embodiment the hydrophilic colloid layer containing the photographic image and containing or carrying the thermochromic liquid crystal material is applied on an opaque polyvinyl chloride support having a thickness of only 0.150 to 0.75 mm. A sheet of that thickness can still be manipulated easily in a mechanical printing process, e.g. screen, offset or intaglio printing. Before or after being coated with the necessary hydrophilic colloid layer(s) for imaging purposes other security or verification marks in the form of e.g. an electronic integrated circuit pattern, a watermark, finger prints, printed patterns known from bank notes, coded information, e.g. binary code information, signature or other printed personal data or marks that may be applied with fluorescent pigments, nacreous pigments giving special light-reflection effects, and/or visibly legible or ultraviolet-legible printing inks as described e.g. in GB-P 1,518,946 and US-P 4,105,333 can be applied.
Other possibilities to increase security against counterfeiting are the inclusion in the laminate of a fugitive ink pattern that becomes leached out or blurred by contact with moisture if one should succeed in opening the laminate by a wet treatment.
Further security feature patterns can be made by mildly radioactive isotopes and holograms as described, e.g. in DE-OS 2 639 952, GB-P 1,502,460 and 1,572,442 and US-P 3,668,795. The holographic patterns may be obtained in silver halide emulsion layers, normally Lippmann emulsions, especially designed for that purpose and can either or not be combined with a photograph.
According to an embodiment the silver halide emulsion layer for producing the hologram is applied to one side of the transparent cover sheet used in the manufacture of a laminate according to the present invention and laminated together with the image containing layer either or not separated therefrom by a transparent resin intersheet made of polyethylene or a resin sheet such as a polyvinyl chloride sheet coated with polyethylene.
When the resin sheet used as support of the laminate has to possess a thickness as required for an identification card to be inserted in a slot of an electronic identification apparatus, several sheets of matted polyvinyl chloride are stacked and laminated so as to reach a final thickness of e.g. 0.075 to 1 mm. The laminar article contains in that case preferably in the polyvinyl chloride support sheet, opacifying titanium dioxide and a suitable plasticizing agent. The support may be provided with an embossed structure.
The lamination of the basic polyvinyl chloride sheet carrying the information to other polyvinyl chloride sheets in order to reach the required support thickness proceeds with poor adherence when chemicals used in or stemming from the photographic image processing, e.g. developing agent, are still present and soiling the sheets. Therefore, in order to obtain a better mutual adherence of polyvinyl chloride sheets a cleaning step is preceding the lamination for removing these chemicals.
The cleaning proceeds preferably with the aid of a dissolved detergent that diminishes the surface tension in aqueous medium. Any commercial detergent can be used for that purpose. A survey of detergents can be found in the book "McCutcheon's Detergents & Emulsifiers 1978 North American Edition - McCutcheon Division, MC Publishing Co. 175 Rock Road, Glen Rock, NJ 07452 USA. Preference is given to anionic and non-ionic surface-active agents containing a polyethyleneoxide chain in their structure. Examples of such agents are described in US-P 3,663,229.
A preferred surfactant for the described purpose has the following structural formula and is called hereinafter surfactant A :
In a preferred embodiment the cleaning liquid contains also the self-cross-linking reaction product that improves in the lamination the adhesion of the information-carrying hydrophilic colloid layer(s) to the hydrophobic resin support and hydrophobic resin cover sheet.
The hydrophobic resin cover sheet of the laminate consists preferably of a resin having a lower glass transition temperature (Tg) and melting temperature (Tm) than the resin present in the support sheet. According to a preferred embodiment the cover sheet is a polyethylene terephthalate resin sheet coated with a resinous melt-adhesive layer, e.g. a polyalkylene layer, preferably polyethylene layer, having a glass transition temperature at least 40°C lower than the glass transition temperature of the resin of the support sheet of the laminar article. In this connection reference is made to the Tg values of polyethylene, polypropylene, polyvinyl chloride and polyethylene terephthalate being -20°C, +5°C, +80°C and +67°C respectively (see J.Chem. Educ., Vol. 61, No. 8. August 1984, p. 668).
The production of the laminar ID card proceeds by heat-sealing using heat and pressure. For example the polyvinyl chloride support coated with the hydrophilic imaging layer whereon the thermochromic liquid crystal has been printed is covered with a hydrophobic resin cover sheet as described above and pressed between flat plates under a pressure of e.g. 10 to 15 kg/m² at a temperature in the range of 120 to 150 °C or by using a hot roller laminator known to those skilled in the art. Cooling proceeds preferably under pressure to avoid distortion. The laminate may contain the hydrophilic colloid imaging layer over the whole area of the support or in a part thereof, e.g. leaving free the edge area to allow direct fusion contact of the border area as described in US-P 4,425,421.
The following examples illustrate the present invention without, however, limiting it thereto.
All parts, ratios and percentages are by weight unless otherwise stated. Structural formulae of ingredients used in the preparation of the identification card laminate according to the present invention are given after the description of the examples.

EXAMPLE 1

An opaque polyvinyl chloride sheet having a thickness of 200 µm was treated with an electrical discharge produced by a corona-discharge apparatus operated under the following conditions :
film-travelling speed : 20 m/min,
electrode spacing to film surface : 2 mm,
corona current : 0.55 A,
AC-voltage difference (peak value) : 10 kV,
frequency : 30 kHz.

The corona-treated surface was coated with the following composition to form an image-receiving layer for silver complex diffusion transfer reversal (DTR-) processing:

water	600 ml
3 % aqueous dispersion of colloidal Ag₂S.NiS nuclei	14 ml
30 % aqueous dispersion of colloidal silica (average particle size 0.025 um, pH : 8)	250 ml
5 % solution in methanol of siloxane compound X	50 ml
4 % aqueous solution of formaldehyde	10 ml
13.4 % aqueous dispersion of casein	200 ml
40 % aqueous dispersion of subbing ingredient S	100 ml
water up to	1234 ml

Said composition was applied at a wet coverage of 26 m²/l and dried.
A black-and-white photographic silver halide emulsion material was exposed to produce thereon a negative latent image (portrait and graphic information). By the common silver complex DTR-process using the above prepared image-receiving material in a tray-type processing apparatus a black-and-white silver image serving for identification purposes was produced thereon.
After leaving the processing tray the image-receiving material was led through a further tray containing an aqueous solution having the following composition :

water 750 ml

surfactant A 50 g

wet strength improving reaction product R 200 g
The treatment of the imaged image-receiving material with said liquid composition was carried out at 20 °C and lasted about 4 seconds.
Within the space of a black silver image area thermochromic micro-capsules dispersed in an aqueous solution of gelatin were applied by screen printing. The microcapsules were prepared as described in US-P 3,328,257 using anisylidene-p-aminophenylacetate in the hardened gelatin micro-envelopes.
Onto the dried image-receiving layer containing a liquid crystal pattern a transparent polyvinyl chloride sheet of 60 µm previously coated at one side with a transparent polyethylene sheet of 30 µm was laid and laminated with the polyethylene side in contact with the image-receiving layer. Flat steel plates were used for pressing the layers together under a pressure of 10 kg/cm2 at a temperature of 135°C.
Several sheets of matted polyvinyl chloride were stacked and laminated to the polyvinyl chloride support sheet so as to reach a final thickness of e.g. 0.075 to 1 mm. The polyvinyl chloride sheets used in that lamination contained opacifying titanium dioxide.
The obtained laminate contained at room temperature (20 °C) a visually hidden pattern of liquid crystal material that by raising the temperature above 35 °C changed its colour from red over yellow, green and blue to purple.

EXAMPLE 2

An opaque polyvinyl chloride sheet containing dispersed titanium dioxide and having a thickness of 200 um was treated with an electrical discharge produced by a corona discharge apparatus operated under the following conditions :
sheet travelling speed : 20 m/min,
electrode spacing to sheet surface : 2 mm,
corona current : 0.55 A,
AC voltage difference (peak value) : 10 kV,
frequency : 30 kHz.
The corona-treated polyvinyl chloride sheet was coated with the following composition, the quantities being expressed per m2, to produce a subbing layer :

gelatin 0.4 g

40 % aqueous dispersion of subbing ingredient S 5 ml

5 % solution in methanol of siloxane compound X 2.5 ml
The dried subbing layer was coated with a dye image receiving layer from the following composition, the quantities likewise being expressed per m2 :

gelatin 0.9 g

mordant M 2.25 g

The dye image receiving sheet was processed in combination with a photographic dye diffusion transfer material as described in the Example of US-P 4,496,645. Said photographic material was imagewise exposed and subsequently contacted for 1 minute with the dye image receiving material having the composition described above in a diffusion transfer apparatus COPYPROOF CP 38 (trade name of Agfa-Gevaert N.V. Belgium) ) having in its tray an alkaline basic processing liquid of the following composition :

water	800 ml
sodium hydroxide	25 g
sodium orthophosphate	25 g
cyclohexane dimethanol	25 g
2,2′-methylpropylpropane diol	25 g
N-ethylbenzene-pyridinium chloride	0.5 g
distilled water up to	1000 ml

After having left the processing tray the sheets were led through another tray containing the following aqueous composition :

water 750 ml

surfactant A 50 g

wet strength improving reaction product R 200 g

potassium iodide 7.5 g
Within the space of a black colour image area thermochromic micro-capsules dispersed in an aqueous solution of gelatin were applied by screen printing. The microcapsules were prepared as described in US-P 3,328,257 using anisylidene-p-aminophenylacetate in the hardened gelatin micro-envelopes.
After drying the thus treated sheets were laminated with a transparent cover sheet being a polyethylene terephthalate sheet having a thickness of 30 µm and being coated at one side with a thermoadhesive layer of polyethylene having a thickness of 30 µm. The lamination was carried out between flat steel plates pressing the polyethylene and image-bearing layers together for 5 minutes using a pressure of 10 kg/cm2 at a temperature of 135 °C. Said pressure was maintained during cooling to reach room temperature (20 °C) again.
The obtained laminate had a sealing thus strong that even after having been immersed in water for two days the sheet elements could not be peeled apart.

Formulae :

Surfactant A

Wet strength improving reaction product R

Is "reaction product 2" obtained as a 10 % by weight solution according to GB-P 1 269 381. In the preparation of said reaction product R a mixture of the polyamide defined as reaction product 1 in said GB-P and methyl-bis(3-amino-propyl)-amine were reacted with epichlorohydrin.

Siloxane compound X

Subbing ingredient S

"Subbing ingredient S" is the reaction product of :
(1) the polyester of adipic acid and hexanediol with average molecular weight 840, (23 %),
(2) 4,4′-diisocyanato-dicyclohexylmethane (14 %),
(3) dimethylolpropionic acid (2 %),
(4) trimethylamine (1.5 %),
the given percentages are by weight.
Subbing ingredient S is used as a dispersion in water containing 7.5 % by weight of N-methylpyrrolidinone.

Mordant M

Mordant M has the following structure (the percentage values are mole %) :
Said mordant is prepared analogously to Example 12 of US-P 4,186,014.

Claims

1. A laminated article containing visible information which article comprises two plastic resin sheets or layers at least one of which is transparent and having laminated inbetween at least one hydrophilic colloid layer containing photographically produced information and carrying or containing thermochromic liquid crystals of the cholesteric type in the form of a pattern or an indicium that can be made visible or obtains a change in colour by heating above 25 °C, said liquid crystals being arranged against a contrasting background having an optical density of at least 0.2 in its spectral absorption range.

2. A laminated article according to claim 1, wherein the thermochromic liquid crystals showing a temperature dependent change in colour are cholesteryl benzoate, cholesteryl chloride or anisylidene-p-aminophenylacetate.

3. A laminated article according to claim 1 or 2, wherein a mixture of liquid crystal material is used in order to obtain colour effects over the temperature range of 28 °C to 35 °C.

4. A laminated article according to any of the preceding claims, wherein the liquid crystal material is applied in the form of a fingerprint, signature, bar code, letter(s) and/or figure() or line drawings either or not built up by screen dots.

5. A laminated article according to any of the preceding claims, wherein the thermochromic liquid crystals are applied onto or into said hydrophilic colloid layer.

6. A laminated article according to claim 5, wherein said hydrophilic colloid layer contains photographic information obtained by an imagewise exposed and processed, i.e. developed and fixed, silver halide emulsion layer or is an image-receiving layer containing a photographic image obtained by the silver complex diffusion transfer reversal process or a dye diffusion transfer process based on silver halide photography.

7. A laminated article according to any of the preceding claims, wherein the pattern or indicium of thermochromic liquid crystal material is applied by a spraying or printing technique using an aqueous base ink containing the liquid crystals in dispersed state in an aqueous solution of watersoluble polymeric binder.

8. A laminated article according to any of the preceding claims, wherein the liquid crystal material is encapsulated in gelatin or gelatin derivative crosslinked with a hardener.

9. A laminated article according to any of the preceding claims, wherein the thermochromic liquid crystal material is arranged against an underlying black area obtained by printing a black ink area or spot on said hydrophilic colloid layer prior to producing therein the photographic information or obtained by silver metal deposition or combination of dyes formed in the production of a photographic image.

10. A laminated article according to any of the preceding claims, wherein the layer containing photographically produced information is present on a paper support coated with a hydrophobic thermoplastic resin layer or is present on a hydrophobic thermoplastic resin support.

11. A laminated article according to claim 10, wherein said resin support is made of a vinyl chloride polymer.