GB2201376A

GB2201376A - Security documents

Info

Publication number: GB2201376A
Application number: GB08800548A
Authority: GB
Inventors: Douglas Hugh Dayment; Robert John Pugh
Original assignee: Liquid Crystal Devices Ltd
Current assignee: Liquid Crystal Devices Ltd
Priority date: 1987-01-13
Filing date: 1988-01-12
Publication date: 1988-09-01
Anticipated expiration: 2008-01-12
Also published as: GB2201376B; GB8800548D0; GB8700689D0

Abstract

A security document, e.g. in the form of a credit card, cheque guarantee card, identity card or the like, carries a microencapsulated liquid crystal composition in a signature region of the document. The liquid crystal composition provides an image when subjected to sufficient pressure and undergoes a visible colour change when the security document is subjected to predetermined conditions, e.g. elevated temperatures, which do not damage the security document. The liquid crystal composition may comprise a thermochromic liquid crystal composition which clears at e.g. 50 DEG C, to reveal an underlying message e.g. "VALID", or a dark, light-absorbing backing.

Description

Security documents This invention relates to a security document of the kind provided with a signature space. The invention is primarily, but not exclusively, concerned with security documents of the kind referred to in the form of security cards such as credit cards, cheque guarantee cards and company identity cards. However the invention is also intended to cover other types of security document of the kind referred to, such as tickets, passports or other legal documents.

It is already known irom GB-A-1,598,702 and GB A-2,040,807 to embed a panel of sensitised material in plastics material of a security card, the sensitised material providing an image when subjected to sufficient pressure. In each of these known security cards, the sensitised material comprises two chemicals, one of which is encapsulated, the encapsulations being broken when pressure is applied to provide interaction between the chemicals causing a colour change.

Another known security card is disclosed in GB A-2,075,917 in which a printed core layer is covered on each of its two sides with an overlay of transparent film. In this known security card a piece of paper containing a microencapsulated liquid and acting as a signature space is sandwiched between the core layer and at least one of the overlays. When pressure is applied to the signature space, e.g. by means of a ball-point pen, the microcapsules, which contain a dye liquid, are ruptured and produce a visible mark.

A further known security document is disclosed in GB-A-1,387,389. This prior specification does not describe the use of a special type of signature panel, but discloses the use of capsules, at least 5 microns diameter and containing liquid crystal material, carried on the security document. The liquid crystal material is capable of undergoing a visible colour change when the security document is subjected to predetermined conditions, e.g.

elevated temperatures or electromagnetic fields, which do not damage the security document and is intended to assist in the detection of counterfeiting of security documents.

The -present invention seeks to provide a security document which is reasonably tamper-proof and which is difficult to counterfeit.

According to the present invention there is provided a security document carrying a microencapsulated liquid crystal composition in a signature region of the security document, the liquid crystal composition providing an image when subjected to sufficient pressure and being capable of undergoing a visible colour change when the security document is subjected to predetermined conditions which do not damage the security document.

Preferably the liquid crystal composition comprises a thermochromic liquid crystal composition. Preferably the thermochromic liquid crystal composition has a clearing point at an elevated temperature, e.g. 50"C, which does not damage the security document. In this case, a message, e.g. "VALID", or a dark, light absorbing backing, may be revealed beneath the liquid crystal composition as the clearing point is passed. Suitably the thermochromic liquid crystal composition has a low temperature dependence of colour - i.e. the composition displays a substantially constant colour, e.g. light green, when subjected to incident white light over a comparatively wide temperature range, e.g. from 0 C to 50 C, immediately below the clearing point of the composition.Alternatively it is possible for the thermochromic liquid crystal composition to display thermochromism over a predetermined temperature range. For example the composition may be selected to enter the liquid crystalline phase and to change colour, when viewed in incident white light, on heating to temperatures, e.g. from 30"C to 60"C, above normal room temperature.

The thermochromic liquid crystal composition may comprise a mixture of liquid crystal compounds. For example, the composition may comprise a mixture of chiral nematic liquid crystal compounds mixed in proportions to adjust the clearing point of the composition and a nematic liquid crystal compound mixed in a proportion to adjust the colour of the composition in its cholesteric phase. Typically the chiral nematic liquid crystal compounds comprise TM74 and TM75 (available from BDH Chemicals Ltd.) and the nematic liquid crystal compound comprises ME35 (also available from BDH Chemicals Ltd.).

Methods of achieving mixtures with a low temperature dependence of colour are described in an article by Dr. D.G. McDonnell entitled "Thermochromic Liquid Crystals" published by BDH Chemicals Ltd..

Preferably the security document comprises a first sheet, e.g. of opaque material and which typically may be of plastics material or card material, and at least one second sheet of flexible, transparent plastics material covering at least one side of said first sheet.

In this case layers of the microencapsulated, preferably thermochromic, liquid crystal composition and a backing layer of light-absorbing material, possibly arranged to display a written message, e.g. "VALID", or a number, are arranged between the, or one of the, second sheets and the first sheet. Most conveniently these layers are printed onto the second sheet before the latter is laminated to the first sheet.

Embodiments of the invention will now be described, by way of example, with reference to the drawing the sole figure of which is a schematic cross-sectional view, not drawn to scale, of a laminated security card.

The figure shows a credit card-sized printed, laminated security card generally designated by the reference numeral 1.- By way of example the security card 1 has a thickness of approximately 760 pm, a length of 87 mm and a width of 54.5 mm.

The security card 1 comprises a pair of transparent outer layers 2 and 3 of gloss or matt surfaced PVC which has been surface modified to eliminate static and to enable specially developed ink systems to key directly onto the modified surface during printing using a web offset lithographic process. Such surface modified PVC film is known in the printing art. The layers 2 and 3 may have the same or a different thickness, by way of example layer 2 having a thickness of 480 pm and layer 3 having a thickness of 240 pm.

Printed matter 4 and 5 is printed onto the inner surfaces of the two layers 2 and 3, respectively, by a conventional printing process, e.g. by a web offset lithographic process. In addition to the printed matter 4, microencapsulated liquid crystal material in the form of printing ink is printed onto the inner surface of the layer 2 to provide a rectangular signature panel 6. The liquid crystal material printing ink is not usually applied directly to the layer 2 but is printed onto a previously printed on "tie coat" 7 to improve adhesion of the printing inks to the layer 2.

The printing ink forming the signature panel 6 suitably comprises microencapsulated droplets of thermochromic liquid crystal material, the microcapsules preferably having a diameter less than 20 pm and typically having a diameter from 10-15 pm. The liquid crystal material is preferably chosen so as to have a low temperature dependence of colour and to have a clearing point at an elevated temperature, i.e. above normal room temperature. By way of example, the liquid crystal material may display the same colour, e.g. light green, over a comparatively wide temperature range, e.g. 0-50 C, immediately below the clearing point, e.g. 50"C.

At least one backing layer -is also printed over the signature panel 6. For example a single dark,e.g.

black, light absorbing layer 8 may be printed over the panel 6. This layer 8 may extend fully over the entire panel 6 or may be arranged to display a written message, e.g. "VALID". Alternatively the -"message" may be printed in two or more layers, e.g. a first backing layer. display ing the "message" in a light colour and a second backing layer covering the entire signature panel 6.

The layers 2 and 3, with the conventional printed material and the printed thermochromic liquid crystal material thereon, are adhesively bonded together with a high-tack adhesive, the adhesive forming a layer 9 which is opaque or translucent. Since the adhesive-layer 9 is opaque or translucent, 'the printed matter 4 and signature panel 6 are only visible through the transparent layer 2 when viewed from side A and the-printed matter 5 is only visible through the transparent layer 3 when viewed from side B. The layers 2 and 3 may typically be adhered by any high-tack adhesive which may be applied as a dry laminate or silk screen printed.

A user of the security card 1 initially completes the card by signing over the signature panel 6 through the layer 2 with a ball- point pen, a steel stylus or the like. The pressure applied through the layer 2 onto the signature panel 6 produces a clear indelible image as a result of the bursting of the capsules of the micro encapsulated thermochromic liquid crystal material.

The signature so produced cannot be erased by conventional erasing techniques.

A particular advantage of using a thermochromic liquid crystal composition for the signature panel 6 is that it provides additional security agairist counterfeiting. If the signature panel of the card 1 is heated to an elevated temperature, chosen to be above the clearing point of the liquid crystal composition but below the temperature which will damage the security card, the liquid crystal composition will clear to reveal the backing layer(s) behind the liquid crystal composition.

The backing layer(s) may merely indicate a change in colour, e.g. black instead of the typically light green colour of the panel 6 when the liquid crystal composition is at a temperature below its clearing point. Alternatively however a written message, e.g. "VALID", a personal identification number or the like may be revealed.

The invention can be applied to other types of security document such as passports or legal documents. For example in its simplest form, microencapsulated thermochromic liquid crystal material in the form of an ink may be applied to a signature region of a security document and a transparent, protective "varnish" applied over the liquid crystal material. The liquid crystal material could be applied over a "message", but this is not essential. All that is required is for the signature panel to show a colour change, when viewed in incident white light, when the liquid crystal material is heated to a temperature above its clearing point.

In other embodiments of the invention, the thermochromic liquid crystal material may be selected to display thermochromism, e.g. to change from red to green to blue, at elevated temperatures instead of having a precise clearing point. Alternatively other types of microencapsulated liquid crystal material may be employed. For example liquid crystal material which "clears" when subjected to e-lectromagnetic fields could be used instead of thermochromic liquid crystal material.

Claims

1. A security document carrying a microencapsulated liquid crystal composition in a signature region of the security document, the liquid crystal composition providing an image when subjected to sufficient pressure and being capable of undergoing a visible colour change when the security document is subjected to predetermined conditions which do not damage the security document.

2. A security document accprding to claim 1, in which the liquid crystal composition comprises a thermochromic liquid crystal composition.

3. A security document according to claim 2, in which the thermochromic liquid crystal composition has a clearing point at an elevated temperature, e.g. 50"C, which does not damage the security document.

4. A security document according to claim 3, in which a message or a dark, light absorbing backing, is located -beneath the liquid crystal composition and is revealed as the clearing point is passed.

5. A security document according to any one of claims 2 to 4, in which the thermochromic liquid crystal composition has a low temperature dependence of colour.

6. A security document according to any one of claims 2 to 4, in which the thermochromic liquid crystal composition displays thermochromism over a predetermined temperature range, e.g. from 30"C to 60 C.

7. A security document according to any one of claims 1 to 6, in which the thermochromic liquid crystal composition comprises a mixture of liquid crystal compounds

8. A security document according to claim 7, in which said composition comprises a mixture of chiral nematic liquid crystal compounds mixed in proportions to adjust the clearing point of the composition and a nematic liquid crystal compound mixed in a proportion to adjust the colour of the composition in its cholesteric phase.

9. A security document according to any one of the preceding claims comprising a first sheet and at least one second sheet of flexible, transparent plastics material covering at least one side of said first sheet, at least one layer of said microencapsulated liquid crystal composition and a backing layer of light-absorbing material being arranged between the, or one of the, second sheets and the first sheet.

10. A security document according to claim 9, in which the layer(s) of liquid crystal composition and the backing layer are printed onto the second sheet before the latter is laminated to the first sheet.

11. A security document according to claim 9 or 10, in which the first sheet is opaque.

12. A security document according to any one of claims 9 to 11, in which the first sheet is made of plastics material or card material.

13. A security document according to any one of the previous claims, in the form of a security card.

14. A security document constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawing.