EP3150399B1

EP3150399B1 - A security element against counterfeiting security printing, especially banknotes

Info

Publication number: EP3150399B1
Application number: EP15460085.2A
Authority: EP
Inventors: Wojciech Rybka
Original assignee: Individual
Current assignee: Rybka Wojciech
Priority date: 2015-09-30
Filing date: 2015-09-30
Publication date: 2018-08-08
Anticipated expiration: 2035-09-30
Also published as: PL3150399T3; EP3150399A1

Description

The invention relates to a security element protecting against counterfeiting security printing, especially for banknotes and other security printing (e.g. pre-numbered forms), enabling the verification of the authenticity of a document.
Security printing is a type of printing, the execution of which by unauthorised persons is hampered by deliberate application of safeguards by which the safety of legitimate users is ensured. Used securities in varying degrees can protect against certain forms of counterfeiting. Securities, banknotes or important documents sometimes have a number of different security features difficult enough to falsify that they are called highly protected prints.
There are three levels of security:

a) the first degree - security based on organoleptic properties - for users without tools,
b) the second degree - securities verified using basic tools, e.g. magnifying glass, UV lamp,
c) the third degree - security verified by experts (specialists) in appropriately equipped la boratories.

Banknotes have securities to protect against counterfeiting and thus belong to the group of security printing. The most widely used securities are:

special, secret recipe paper conferring specific mechanical and optical properties;
replacing paper with polymer substrate difficult to print on;
use of microprinting;
recto-verso; it is a picture visible in the lumen, created with the finely fitting elements located on both sides of a banknote.
a description on the recto;
hot-stamping foil with metallic holographic pattern;
embossment resulting from intaglio printing;
complex graphics, yet distinct, with strong saturation and gloss paint;
watermark, especially visible against the light;
a security thread in the form of a metal strip recessed inwardly in paper with spacing forming an inscription;
printing with an optically variable ink - seen in front and at a sharp angle it changes colour;
ribbing;
drawings visible under UV light.

Part of banknote security is kept secret and is a strict secret data of central banks issuing banknotes.
Due to the continuous development of counterfeiting techniques constant search for new methods of document protection against illegal copying is needed. The aim of the present invention is therefore to provide a new kind of security.
This objective was achieved through the use of graphene quantum dots (Graphene Quantum Dot, GQD).
Quantum dots (QD) are semiconductor nanocrystals with sizes ranging from 2-10 nm. They are very specific type of substance with properties intermediate between semiconductors and quantum particles. A limited number of atoms and a diameter of a few nanometres gives the quantum dots unique properties of absorption and emission of radiation, which result from the presence of the effect of the quantum limit (quantum confinement effect). This means that the excitation energy emitted by the photons will depend on the composition of the crystal and its size. Just as semiconductors, quantum dots absorb photons of light with such energy that gives you the ability to transfer electrons from the non-activated to one of the higher available energy levels. Otherwise, there is an emission process, because the wavelength emitted by light depends on the size of the dots. Hence, having a semiconductive material we can get markers having different colours, which are characteristic of quantum dots.
Nanoparticles with a small diameter core (2 nm) have fluorescence at a wavelength corresponding to blue light and even ultraviolet radiation (UV). When the diameter of the quantum dot core increases, the wavelength of the radiation emitted by the visible light increases, up to infrared radiation (IR). By modifying the composition and choosing the size of the nanocrystals, fluorescence in the full spectrum from ultraviolet (UV) to the infrared (IR) is obtained.
The radiation may be absorbed by quantum dots in a broad spectrum (Fig. 1), and their molar absorption coefficient increases towards the UV. Thus the excitation can be made of many kinds of dots using one light source, since there is no requirement to apply excitation at a pre-set wavelength. In turn, the profile of the fluorescence emission of quantum dots is narrow and has a small half-width value (FWHM 125 nm). This allows for simultaneous use of multiple markers having different colours without fear of overlapping of the signals. The nanocrystals can be repeatedly excited, with no noticeable decrease in fluorescence because they have a high quantum yield of fluorescence and long radiation (10-100 ns).
Graphene quantum dots (GQD) can also be prepared from graphite carbon fibres. This was successfully done with acids and chemical exfoliation (Fig. 2). By varying the process parameters a whole family of graphene quantum dots the size of the order of 1-4 nm can be made. It should be noted that the optical properties of the dots (quantum confinement effect) depend directly on their size, i.e. the colour of photoluminescence. The resulting structures are two-dimensional, so in fact they produce graphene quantum discs.
Graphene quantum dots are stable because the level of luminescence (resistant to photobleaching).
WO2012068177A1 discloses a multilayered security device comprising a first layer in the form or a flexible and/or stretchable material and a second layer overlying the first layer, comprising a coating composition comprising a polymer binder and graphene sheets. Also disclosed is a method of making a multilayered security device, comprising applying a coating composition comprising graphene sheets to a patterned substrate.
WO2012068182A1 discloses a method of making a printed article having areas with different conductivities. The method comprising forming an image on a substrate by applying at least one medium to at least a portion of the substrate and overcoating some or all of the imaged substrate with at least one electrically and/or thermally conductive coating composition. The coasting composition may contain graphene sheets and a polymer binder. The substrate may have the form of a flexible and/or stretchable material.
Another document WO2014114690A1 discloses a security feature in the form of a composition allows markings to be produced that are not visually noticeable and easy to detect. The marking composition comprises a carbon derivative in the form of nanoparticles having size of approx. 100 nm or less and may have the form of graphene.
Yet another document WO2012130370A1 discloses a security element with an optically variable color layer. The optically variable color layer includes a plurality of microcapsules, each of which exhibits a capsule shell, a carrier liquid enclosed in the capsule shell, and at least one optically variable and magnetically alignable pigment having at least one magnetic layer and having at least one non-magnetic layer. The multilayer pigment are formed by nanoparticles having non-magnetic carbon casing which can especially consist of one or more graphene layers.
The invention relates to a security element against counterfeiting as defined in claim 1. Preferably, the security element comprises graphene quantum dots (GQDs) of different sizes.
Preferably at least one quantum dot (GQD), preferably all quantum dots (GQDs) are an integral part of the flexible layer of graphene nanocomposite material.
Preferably, graphene in the security element is in a pure or doped form.
Preferably, the diameter of the graphene nanoparticle is from 1 nm to 11 nm and contains from 1 to 20 layers of graphene.
Preferably, the adhesive layer is a polymer.
The invention also includes use of a security element according to the invention as defined in claim 8. The invention is further a system for checking the authenticity of security printing as defined in claim 9. The invention also applies to a method for checking the authenticity of security printing as defined in claim 10. The security element is made of nanocomposite, one of whose components is a binder, preferably a polymer, which ensures its integrity, hardness, flexibility and resistance to compression, and the other is the second layer of plotted quantum dots (GQDs). Flexible nanocomposite material is a material of heterogeneous structure composed of two or more components with different properties. The properties of the composites are not the sum or average of the properties of its components, and the material used in its construction exhibits anisotropy of physical properties.
The security element is made of a composite material resistant to:

moisture and condensation
splashing
water-damage
corrosion
dust
multiple deformation
changes in temperature in the range -40°C to + 70°C

The mere presence of the structure of the graphene in a protected document is an additional security factor, as commercial production of graphene in the form of a single structure is not yet available to potential counterfeiters.
The invention will now be further described in preferred embodiments with reference to the accompanying drawings, in which successive figures show:

Fig. 3 - pattern made of graphene quantum dots (GODs) on a flexible substrate - a polymer,
Fig. 5 - examples of setting of GQDs nanolayers in an elastic nanocomposite layer,
Fig. 6 - operating principle of inherent security element.

Security element 1 is one of the layers of security printing 3. The security element 1 in the above example is not an integral part of other securities and may, but does not need to be placed in the same layer as other securities such as a hologram.
The presented security is a separate solution, not interfering directly with any other group of the above mentioned securities.
The security element 1 based on the modification technology is not limited by current layout, shape and size. It does not require a constant power source. But dedicated devices by which detection is carried out 5 require it.
The structure of the nanocomposite material 2 of the security element 1 takes into account:

the use of a variable number of layers of polymer P in the material - the number of coats applied is dependent on the conditions in which the security element will operate.
The use of a variable number and size of the graphene quantum dots GQD, if the use such structure gives is necessary to increase the efficiency of the security element 1.

The operation of GQD security feature

Security element 1 designed with quantum dots GQDs will be unique for each security printing 3. After treatment with a source of radiation 4, it starts to emit light in an adequate band characteristics. The luminescent effect will then be identified by the assigned detection device 5, verified and compared with the standard base 6, followed by a confirmation or denial of compliance.

Examples of application of a security element

Other examples of the use of a security element (1) are authentication of pre-numbered documents, such as:

a passport-the security element is an integral part of the cover;
payment cards - the top layer of the card;
other documents in the form of a payment card, such as a driving license, ID card;
excise bands and prints;
personal identifiers;
license forms, certificates, etc.;
label for products with high value and at risk of counterfeiting;

Claims

A security element (1) against counterfeiting security printing (3), in particular banknotes, comprising at least one graphene quantum dot (GQD) that is a graphene nanoparticle with a diameter of from 0.5 nm to 60 nm, containing from 1 to 90 layers of graphene (G) disposed in a flexible layer of graphene nanocomposite material (2), wherein the elastic layer of graphene nanocomposite material (2) comprises at least one graphene layer (G) and two layers of adhesive (P), wherein the at least one layer of graphene (G) is located directly between the two layers of adhesive (P).
A security element according to claim 1, characterised in that it comprises the graphene quantum dots (GQDs) of different sizes.
A security element according to claim 1 or 2, characterised in that at least one quantum dot (GQD), preferably all quantum dots (GQDs) are an integral part of the flexible layer of graphene nanocomposite material (2).
A security element according to claim 1, 2 or 3, characterised in that the graphene is present in pure or doped form.
A security element according to any preceding claims 1-4, characterized in that the diameter of the graphene nanoparticle is from 1 nm to 11 nm.
A security element according to any preceding claims 1-5, characterized in that the graphene nanoparticle contains from 1 to 20 layers of graphene (G).
A security element according to any preceding claims 1-6, characterized in that the adhesive layer (P) is a polymer.
Use of a security element (1) according to any one of claims from 1 to 7 for securing banknotes, holograms, documents, passports, credit cards, excise bands, excise forms, personal identifiers, certificates or product labels.
A system for checking an authenticity of security printing (3), in particular banknotes, characterised in that it comprises:
- A security element (1) according to any one of claims 1 to 7,

- A device (4) adapted to emit radiation in the range suitable for excitation of at least one graphene quantum dot (GQD), preferably all of graphene quantum dots (GQDs) contained in a security element, and

- A detector (5) adapted to detect luminescence radiation of at least one graphene quantum dot (GQD), preferably all of graphene quantum dots (GQDs) contained in the security element.
A method of verifying an authenticity of security printing (3), in particular banknotes, characterised in that a system according to claim 9 is used.