WO2015128489A1

WO2015128489A1 - Method and device for forming objects having variable optical properties and object thus obtained

Info

Publication number: WO2015128489A1
Application number: PCT/EP2015/054193
Authority: WO
Inventors: Jean-Pierre Massicot; Alain Foucou; Zbigniew Sagan
Original assignee: Advanced Track & Trace
Priority date: 2014-02-28
Filing date: 2015-02-27
Publication date: 2015-09-03
Also published as: FR3018126B1; EP3111375A1; FR3018126A1

Abstract

The object (10) has: a first surface (14) at least one zone of which bears a first grating (13) configured to polarise light; and a second surface (16), separate from the first surface and not contained in the same plane as the first surface, at least one zone of which bears a second grating (15) configured to polarise light, at least one of said zones bearing a nanostructure having a periodic structure having a period between about one hundred and one thousand nanometres, which structure is produced by a laser beam, said nanostructure forming one of said gratings or decreasing the polarisation of one of said gratings. In embodiments: said nanostructure forms one of said gratings for polarising light; or said nanostructure decreases the polarisation of one of said gratings.

Description

METHOD AND DEVICE FOR FORMING OBJECTS WITH VARIABLE OPTICAL CHARACTERISTICS AND OBJECT THUS OBTAINED

The present invention relates to a method and a device for forming objects with variable optical characteristics and an object thus obtained.

It applies, in particular, to the securing of surfaces, such as the surfaces of a document, for example an identity document or a means of payment.

Surface treatments, such as the formation of holograms, are known to differentiate an authentic document from a copy. Unfortunately, counterfeiters are now able to reproduce such surface treatments.

Document WO 02/1 1063 and its equivalent in English US 2003/023081 6 are known, which describe millimetric or micrometric structures constituting complex and expensive diffraction structures so that two different messages appear in the same zone, depending on the angle observing this area. Besides, the high realization cost which limits their possibilities of application, these structures can be reproduced by counterfeiters. In addition, they are limited to thick objects because of the number of layers to put in place.

The present invention aims to remedy all or part of these disadvantages. For this purpose, according to a first aspect, the present invention relates to an object having:

a first surface of which at least one zone carries a first network configured to polarize light,

a second surface, separated from the first surface and not lying in a plane common to the first surface, of which at least one zone carries a second network configured to polarize light,

at least one of said zones carrying a nanostructuration having a periodic structure having a period between a hundred and a thousand nanometers, carried out by a laser beam, said nanostructuring realizing a said network or reducing the polarization of a said network. The demonstration of the existence of periodic structures having a period of a few hundred nanometers has been scientifically performed (see, for example, the document by Messrs. GUILLERMIN, F. GARRELIE, N. SANNER, E. AUDOUARD, H. SODER "Mono- and multi-pulse formation of surface structures under static femtosecond irradiation" Accepted at Appl., Sc.253, 8075-879 - 2007).

Thanks to these provisions, nanostructuring is a modification of a polarizing network or a polarizing network, with a dispersion of optical characteristics related to the interaction between the laser beam and the material of a surface of the object. According to whether the object is illuminated so that an observation is made by transparency through two zones of the two surfaces or by reflection of light rays on such a zone, a message or effects of dispersion of optical characteristics. It is therefore possible to authenticate the object by these observations or by analysis of the dispersion of optical characteristics.

In embodiments, said nanostructuring realizes a said network for polarizing light.

In embodiments, said nanostructuring achieves polarization reduction of said network.

In embodiments, said nanostructuring represents a message.

In embodiments, said message is readable by the naked eye.

In embodiments, said nanostructuring forms random or unpredictable defects locally.

For example, the structure of nanostructures formed by ultrafast laser irradiation is not only characterized by a periodicity of the order of a few hundred nanometers. Finer features, or irregularities, such as the number of bifurcations between lines of pseudoperiodic nanostructures, the average length of the lines between two bifurcations, the shapes of the bifurcation figures, are also analyzed and quantified by image analysis algorithms. adapted. From a figure of nanostructures, can then be obtained a unique digital signature of a particular interaction between the laser and the material (in the manner of a fingerprint for a human being). This characteristic is stored for use in identification, authentication and traceability procedures. In embodiments, said two surfaces are two parallel outer faces of an at least partially transparent object.

In embodiments, at least one of said surfaces has a metallized layer.

According to a second aspect, the present invention provides an object forming device of the present invention, which comprises a source of polarized laser radiation.

It can be observed that the structure of nanostructures formed by ultrafast laser irradiation is characterized by a periodicity of the order of a few hundred nanometers.

In embodiments, the device of the present invention comprises two sources of laser radiation face to face surrounding the object being processed and forming two images in correspondence on two parallel surfaces of said object.

In embodiments, at least one said laser radiation source is a picosecond laser.

In embodiments, at least one said laser radiation source forms a document number on a surface of said object.

According to a third aspect, the present invention relates to a method of marking an object, which comprises:

a first step of forming a network configured to polarize light, on a surface of an object,

a second step of forming a network configured to polarize the light, on a second surface of the object, separated from the first surface and not included in a common plane with the first surface and

at least one nanostructuration step of a said surface by a laser beam.

The advantages, aims and particular characteristics of this device and this process being similar to those of the object object of the present invention, they are not recalled here.

Other advantages, aims and features of the present invention will emerge from the description which follows, made for explanatory and non-limiting purposes with reference to the accompanying drawings, in which: FIG. 1 represents, schematically and in section, a particular embodiment of an object which is the subject of the present invention,

FIG. 2 represents, schematically and in section, a particular embodiment of a device which is the subject of the present invention and

FIG. 3 represents, in the form of a logic diagram, steps of a particular embodiment of the method that is the subject of the present invention.

As of now, we note that the figures are not to scale.

FIG. 1 shows an object 10 comprising a transparent layer 11 and a metallized layer 12. For example, the transparent layer 11 is made of polyethylene.

A first surface 14 carries, including at least one zone, a first network 13 configured to polarize the light. A second surface 16, here the contact surface of the metallized layer 12 on the transparent layer 1 1, separated from the first surface 14, carries, in at least one zone, a second network 15 configured to polarize the light for at least one wavelength for which the grating 13 is polarizing.

At least one of the zones 13 and 15 carries a nanostructuration carried out by a laser beam, said nanostructuration realizing a said network or reducing the polarization of a said network.

It is recalled that the nanostructures have a periodic structure, having a period of a few hundred nanometers.

The demonstration of the existence of periodic structures having a period of a few hundred nanometers created by laser radiation has been scientifically performed (see, for example, the document by Messrs. GUILLERMIN, F. GARRELIE, N. SANNER, E. AUDOUARD, H. SODER "Mono-and multi-pulse formation of surface structures under static femtosecond irradiation" Accepted at Surf Appl., Sc.253, 8075-879 - 2007).

The structure of nanostructures formed by ultrafast laser irradiation is not only characterized by a periodicity of the order of a few hundred nanometers. Finer features, or irregularities, such as the number of bifurcations between lines of pseudo-periodic nanostructures, the average length of the lines between two bifurcations, the shapes of the bifurcation figures, are also analyzed and quantified by analysis algorithms. image adapted. From a nanostructure figure can then be obtained a signature unique digital system of a particular interaction between the laser and the material (in the manner of a fingerprint for a human being). This characteristic is stored for use in identification, authentication and traceability procedures.

More generally, the two surfaces carrying polarizing networks are not included in a common plane, so that a light ray can cross the two polarizing networks. In embodiments such as that illustrated in FIGS. 1 and 2, the two surfaces are two parallel outer faces of an at least partially transparent object.

Thus, by nanostructuring, a polarizing network or a modification of a polarizing network is produced with a dispersion of optical characteristics related to the interaction between the laser beam and the material of a surface of the object. Depending on whether the object is illuminated so that an observation is made by transparency through two zones of the two surfaces or by reflection of light rays on such a zone, a message or effects of dispersion of optical characteristics are observed. It is therefore possible to authenticate the object by these observations or by analysis of the dispersion of optical characteristics.

In embodiments, said nanostructuring achieves a polarization reduction of a said polarizing grating.

In embodiments, said nanostructuring represents a message, for example a readable message to the naked eye.

In embodiments, said nanostructuring forms random or unpredictable defects locally. These defects take, for example, the form of irregularities of ripples formed by the impact of a picosecond laser on a surface, as explained above.

As illustrated in FIG. 2, in one embodiment, an object forming device 20 of the present invention comprises a first source of polarized laser radiation 23, a second source of polarized laser radiation, sources 23 and 24 lying face to face on both sides of the object 20 and forming two images 21 and 22, in correspondence, on two parallel surfaces of the object 20. In embodiments, at least one said laser radiation source is a picosecond laser.

In embodiments, at least one said laser radiation source forms a document number on a surface of the object 20.

A substrate carries a network (in English "grating") polarizing. This network can be formed by known techniques or by illumination with a laser causing a nanostructuration. Preferably a laser emitting pulses of the order of one picosecond is implemented.

For example, a transparent layer, for example made of polyethylene carries a metallized layer whose inner surface (contact with the transparent layer) or the outer layer has the polarizing network.

The outer surface of the transparent layer is also provided with a polarizing network, preferably oriented at 90 ° of the network formed on the metal layer.

Preferably, for at least one of the surfaces carrying a network, zones do not carry the polarizing network, to constitute a message, positive or negative.

Thus, when we illuminate the transparent layer on the same side as its observation (with the naked eye or with a camera), the reflection presents a diffraction of the light and the appearance of a color, even of a message in color, especially when the angle of incidence deviates from the normal to the surface. On the contrary, when the device is illuminated on the other side as the observation, the crossing of the polarization angles causes the appearance of a message in the areas where one of the networks is not formed.

In embodiments, a surface pre-structuring is performed and then a message is added by local destruction of a polarizing network.

In embodiments, a surface pre-structuring is performed and then noise, that is to say random or locally unpredictable defects, is added by local destruction of one of the polarizing arrays. Preferably, this noise is achieved by laser nanostructuration by putting a picosecond laser.

In embodiments, with two lasers controlled in correspondence, two messages with different polarizations, preferably perpendicularly oriented, are produced. For example, points of five μηι are thus made. FIG. 3 shows, in a particular embodiment, a method of marking an object, which comprises:

a step 35 of forming two polarizing networks,

a step 40 of selecting an operating mode, between an operating mode to form a message, steps 45 to 55, before forming marks for the authentication of the object, and a mode of operation in which only the authentication marks are made, step 60 to 75,

during step 45, a message to be formed on non-coplanar surfaces of the object is determined, for example a serial number, a code, etc.

during step 50, the formation of at least part of the message is carried out by nanostructuring a first surface,

during step 55, the formation of at least part of the message is carried out by nanostructuring a second surface,

during step 60, a nanostructuration step of at least one surface, in or outside a polarizing array, is carried out by a laser beam, to form random irregularities and / or unpredictable locally, for example ripple irregularities,

during step 65, a capture of at least one image of a surface is carried out by reflection illumination, that is to say positioned on the same side of the object as the image sensor; ,

in the course of step 70, at least one image is captured by backlighting, the light source being, with respect to the image sensor, on the opposite side of the object and

during step 75, the captured images or single fingerprints obtained by processing these images and representing random irregularities and / or unpredictable locally, for example their locations on the object or respectively between them and, possibly, respectively, are memorized , their types.

For example, the two message portions made in steps 50 and 55 complement each other to form an intelligible message or a coherent code.

Claims

1. Object (10, 20) presenting:

a first surface (14) of which at least one zone carries a first network (13) configured to polarize light,

a second surface (1 6), separated from the first surface and not included in a common plane with the first surface, of which at least one zone carries a second network (15) configured to polarize light,

characterized in that at least one of said zones carries a nanostructuration having a periodic structures having a period between a hundred to a thousand nanometers, carried out by a laser beam, said nanostructuration realizing a said network or reducing the polarization of a said network.

An object (10, 20) according to claim 1, wherein said nanostructuring provides said grating for polarizing light.

An object (10, 20) according to claim 1, wherein said nanostructuring achieves polarization reduction of said network.

4. Object (10, 20) according to one of claims 1 to 3, wherein said nanostructuration represents a message.

An object (10, 20) according to claim 4, wherein said message is readable by the naked eye.

6. Object (10, 20) according to one of claims 1 to 5, wherein said nanostructuration forms random defects or unpredictable locally.

7. Object (10, 20) according to one of claims 1 to 6, wherein said two surfaces (14, 1 6) are two parallel outer faces of an at least partially transparent object.

8. Object (10, 20) according to one of claims 1 to 7, wherein at least one said surface (14, 1 6) comprises a metallized layer.

9. An object forming device (10, 20) according to one of claims 1 to 8, which comprises at least one source (23, 24) of polarized laser radiation.

10. Device according to claim 9, which comprises two sources (23, 24) of laser radiation face to face surrounding the object (10, 20) being processed and forming two images in correspondence on two parallel surfaces of said object.

1 1. Device according to one of claims 9 or 10, wherein at least one said source (23, 24) of laser radiation is a picosecond laser.

12. Device according to one of claims 9 to 1 1, wherein at least one said source (23, 24) of laser radiation forms a document number on a surface of said object (10, 20).

13. A method of marking an object (10, 20), characterized in that it comprises:

a first step (35) for forming a first network configured to polarize light, on a surface of an object,

a second step (35) for forming a second network configured to polarize light, on a second surface of the object, separated from the first surface and not included in a plane common to the first surface and

at least one nanostructuring step (50, 55, 60) having a periodic structure having a period between one hundred and one thousand nanometers of a said surface by a laser beam, said nanostructuring realizing a said network or reducing the polarization of a said network.