AU2013357384B2 - Method for checking the authenticity of a security document - Google Patents

Abstract

The present invention concerns a method for checking the authenticity of a security document, in particularly a fiduciary document, which comprises an area with, within or at the surface of this area, a reversible mecanoluminescent compound of formula (i): In which R represents an alkyl chain comprising 1 to 12 carbon atoms, which comprises a step in which said area is subjected to ultraviolet radiation such that the whole of said area is visible to the naked eye in a first fluorescent colour (C1), characterised by the fact that it also comprises a step that consists of heating at least said area to a temperature of at least 50° C, without subjecting it to any friction or mechanical stress whatsoever, the revealing of the authenticity of said document being confirmed by the shift from said first colour (C1) to a second fluorescent colour (C2) different from the first.

Description

METHOD FOR CHECKING THE AUTHENTICITY OF A SECURITY DOCUMENT

The present invention relates to a method for checking the authenticity of a security document.

The present invention finds an application, notably in the field of the fiduciary industry and more particularly in the manufacturing of security documents.

By the expression of "security document", is meant a document, for example in paper, which includes in its inside and/or is coated with means allowing the manufacturing thereof to be secured, so as to make fraudulent reproduction impossible, at the very least particularly complicated, and to ensure authentication.

In the technical field of security documents, protection against counterfeiting is achieved and notably by a set of elements either integrated or applied to the support.

These security elements are classified according to several security levels. The securities are thus usually distributed according to three levels.

Security elements of the luminescent type are known to the person skilled in the art. Inks which are fluorescent, phosphorescent at one or multiple excitation wavelengths, are widely used in the field of security printing. Pieces of equipment for checking such inks are also widely known and used by the general public.

The use and massive dissemination of these inks notably in sectors other than fiduciary printing (pharmacy, decorative paints, toys, etc.) have facilitated their supply via non-secured routes (for example Internet) making them easier to be counterfeited.

Documents US 5,118,349 and WO 2003/053980 notably mention the use of rare earths. A certain number of purely organic compounds, having the property of luminescence mechanochromism have been described in the literature. These compounds are presented in a recent review (Chem. Soc. Rev. 2012, D0l:10.1039/C2CS35016E).

The compounds, so-called "multi-stimuli" compounds, reacting to two or several stimuli are rarer and none of them simultaneously react to two reversible and distinctive physico-chemical properties, i.e. mecanofluorochromism and thermofluorochromism which may be exerted either independently or additionally. Now, both of these properties may prove to be of interest in order to further make it more difficult to produce a fraudulent security document.

For example, a derivative of diphenyldibenzofulvene (Adv. Mater. 2011, 23, 3261-3265) is fluorescent green (500 nm), when it is pure and in the solid state. Subsequently to a mechanical perturbation, this fluorescence is extinguished. There is therefore a loss of the fluorescence property. The green fluorescence is spontaneously recovered at room temperature. The loss of fluorescence is also observed upon heating the compound in the pure condition to 90°C. In order to return to the initial green color, the compound requires heating up to its melting temperature (148°C) and then rapid cooling. These properties are incompatible with the use as a constituent of an ink or a fiduciary varnish.

Indeed, it is preferable not to heat the surface of the support (compound + support in the liquid phase) at a temperature equivalent to or greater than the melting point of the compound. At this temperature, the compound enters the liquid phase and it may react with the support, i.e. the material, for example the bank note on which it is affixed. By returning to the solid state (at room temperature), the compound may change its structural organization and thus lose its properties within the support.

Moreover from document WO-A-2011/068537, a family of compounds is known, which notably comprises the compound of the following formula

A composition which contains it has a reversible mechanochromic effect.

Starting with this product, the present applicant puts forward the fact that a composition, containing it, simultaneously fits two aforementioned reversible and distinct physico-chemical properties, i.e. mechanofluorochromism and thermofluorochromism which may be either exerted independently or additionally.

Thus, the present invention relates to a method for checking the authenticity of a security document, notably a fiduciary document, which includes at least one area with, within it or at the surface of this area, a reversible mechanoluminescent compound of formula:

wherein R represents an alkyl chain comprising 1 to 12 carbon atoms, a method which comprises a step in which said area is subject to ultraviolet radiation so that the totality of said area is visible to the naked eye under a first fluorescent color, characterized by the fact that it also comprises a step which consists in heating at least said area to a temperature of at least 50°C, without submitting it to the least friction or mechanical stress, disclosure of the authenticity of said document being confirmed by the transition from said first color to a second fluorescent color, different from the first.

According to other non-limiting and advantageous features of the invention, taken individually or as any combination: -the temperature to which is subject the compound is less than its melting temperature; - said temperature is comprised between 50 and 250°C; - said heating of said area to said temperature is performed for a period comprised between 1 and 10 seconds; - it comprises, before said heating step, a step during which a portion of said area is subject to a frictional force, so that this portion switches from said first fluorescent color to said second fluorescent color; -said aforementioned reversible compound is at the surface, and it is used when it is integrated within an ink or a varnish; -it is applied with a security document in which said compound is covered by a varnish, a varnish which moreover completely or partly covers the prints appearing on the security document; -it is applied with a security document in which said compound is covered by a continuous film in polymeric material, intended to completely or partly cover the prints appearing on the security document.

Other features and advantages of the invention will become apparent upon reading the detailed description which follows. It will be made with reference to the appended drawings wherein: - Figs. 1 to 3 are partial top views of a bank note illustrated in several different states corresponding to the method of the invention; - Fig. 4 is a diagram showing the different phenomena applied according to the invention. A security document which consists in a bank note 1 is schematically illustrated in a front view in Figs. 1 to 3. This may however be another type of security document as such as a visa or a passport. This is therefore a simple exemplary embodiment.

For reasons of facilitating the reading of the figures, only the monetary value of the note, in this case, the value "10" has been illustrated on this visible face 2 which for example is the front face. Of course, what is stated for the front face may be valid for the rear face 3.

All or part of the security means customarily used in the fiduciary field (hologram, security wire, watermark, etc.) may be integrated into this note, but are not illustrated thereon voluntarily.

As indicated above, the present invention relates to a method for checking the authenticity of a security document, notably a fiduciary document, which includes at least one area with, within it or at the surface of this area, a reversible mechanoluminescent compound of formula:

wherein R represents an alkyl chain comprising 1 to 12 carbon atoms.

The method for synthesizing such a family of compounds is known per se, and is notably described in the aforementioned document WO-A-2011/068537. A composition of the ink or varnish type may be made, by using a colorless or practically colorless "intaglio" matrix called "transparent blank" in terms of the trade, notably available from SICPA.

This matrix mainly consists of drying vegetable oils, of solvents, resins and additives (fillers, dryers). A compound fitting the formula I above is introduced into such a matrix at a level comprised between 1 and 10% by weight. Preferentially this level is 5%.

This ink or this varnish is then affixed on the constitutive fiduciary paper of the bank note 1 according to one of the methods known to the person skilled in the art.

In the example of Figs. 1 to 3, this is a uniform tint area forming an area 4 of oval form.

Of course, other shapes of areas may be contemplated and their number may be variable.

Depending on its structure (variation of the length of the chain R) and on the nature of the matrix (intaglio ink, offset ink, varnish), the compound I may have different fluorescence colors under UV irradiation (symbolized as R in the figures).

For example, for a level of 5% by weight, the compound I including 12 carbon atoms has a blue fluorescence color in an intaglio ink, while the compound I with 6 carbon atoms has green fluorescence in this same matrix. This color, referenced as Cl in Fig. 1 is homogeneous over the whole varnish or ink.

This situation, known from the state of the art, corresponds to state A of the summary Fig. 4.

For both of these compounds, as soon as a portion of the area 4 is subject to friction (for example by means of the edge of a coin, of a blunt object, etc.), the fluorescence switches from the blue color Cl to the yellow color C2 (Fig. 2).

With reference to Fig. 4, this corresponds to the switching from state A to state B. it is therefore possible to "write" on the surface and to reveal the "writing" produced by UV irradiation.

The change in the fluorescence color is only observed in the mechanically perturbed portion. The reversibility of this property ensures that the "writing" is erased by itself and at room temperature within a few minutes or within a few seconds by heating (30-50°C), as shown in Fig. 4.

According to the invention, it is possible to further improve the checking of the authenticity of the security document by applying a step for heating at least said area 4 to a temperature of at least 50°C.

Indeed, for these compounds, by providing heat, it is possible to induce a change in the fluorescence color over the whole surface subject to this thermal stimulus. This is a situation of Fig. 3 and this corresponds to the switching from state A to state C of Fig. 4.

Stopping the heating and then restarting the latter to a temperature of the order of 30 to 50°C gives the possibility of returning to state A.

It should be noted that state C, although fluorescent, no longer has the property of mechanofluorochromism. In other words, even if the area is subject to friction, it does not change color locally.

The area 4 having state B illustrated in Fig. 4 (obtained by friction) may be heated (to at least 50°C) in order to switch to state C. Return to the initial state A is accomplished by the aforementioned low temperature heating step (30°-50°C).

The heating time to said temperature of more than 50°C is generally comprised between 1 and 10 seconds.

Of course, it is important that the temperature obtained by the area 4 be less than the melting temperature of the compound I.

Thus, the melting temperature of the pure product wherein R=Ci2H25 is 158°C.

This temperature is variable depending on the length of the R group.

The present method gives the possibility of obtaining a significant change in the fluorescence color, either by friction, or by providing heat, as well as a loss of the mechanofluorochromism property by heating.

In the fiduciary field, on the security document, it is common to apply a varnish, which completely or partly covers the prints and/or other security elements appearing on the document.

In one alternative, a continuous film in polymeric material is applied, intended to completely or partly cover the prints appearing on the security document.

In both cases, this coating has a protective function.

As long as the thickness of this coating is not too large, the phenomena explained above are seen, in spite of the presence of said coating.

Practically, the man in the street or the merchant may observe the fluorescence of the area by means of a UV lamp and check by friction the change in color.

An apparatus combining a UV lamp and a heating means may be made available to banks in order to apply the present method.

Such an apparatus may also be integrated within an automatic machine for sorting bank notes.

Of course, simple tools such as a hairdryer or a heat gun may be used.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims (8)

1. A method for checking the authenticity of a security document (1), notably a fiduciary document, which includes at least one area (4) with, within it or at the surface of this area, a reversible mechanoluminescent compound of formula:

wherein R represents an alkyl chain comprising 1 to 12 carbon atoms, a method which comprises a step in which said area (4) is subject to ultraviolet radiation (R) so that the totality of said area is visible to the naked eye under a first fluorescent color (Cl), characterized by the fact that it also comprises a step which consists in heating at least said area (4) to a temperature of at least 50°C, without submitting it to the least friction or mechanical stress, disclosure of the authenticity of said document (1) being confirmed by switching from said first color (Cl) to a second fluorescent color (C2), different from the first.

2. The method according to claim 1, characterized by the fact that the temperature to which is subject the compound, is less than its melting temperature.

3. The method according to claim 1, characterized by the fact that said temperature is comprised between 50 and 250°C.

4. The method according to one of the preceding claims, characterized by the fact that said heating of said area (4) to said temperature is performed for a period comprised between 1 and 10 seconds.

5. The method according to one of the preceding claims, characterized by the fact that it comprises, before said heating step, a step during which a portion of said area (4) is subject to a frictional force, so that this portion switches from said first fluorescent color (Cl) to said second fluorescent color (C2).

6. The method according to one of the preceding claims, wherein said aforementioned reversible compound is at the surface, characterized by the fact that it is used when it is integrated within an ink or varnish.

7. The method according to one of the preceding claims, characterized in that it is applied with a security document wherein said compound is covered by a varnish, a varnish which moreover completely or partly covers the prints appearing on this security document (1).

8. The method according to one of the preceding claims, characterized in that it is applied with a security document wherein said compound is covered by a continuous film in polymeric material intended to completely or partly cover the prints appearing on the security document (1).