WO2004021255A1

WO2004021255A1 - Method of marking a plastic substrate with a light-emitting source

Info

Publication number: WO2004021255A1
Application number: PCT/IB2003/003520
Authority: WO
Inventors: Jean-Marie Verilhac; Cédric PERBEN; Hayat El Yamani; Eva Chignard
Original assignee: Axalto Sa; Schlumberger Malco
Priority date: 2002-08-27
Filing date: 2003-08-26
Publication date: 2004-03-11
Also published as: AU2003253146A1

Abstract

The invention concerns a method of marking a plastic substrate using a light-emitting source. An organic layer is deposited on the plastic substrate. The organic layer is arranged to change of colour in an irreversible manner under the action of the light-emitting source.

Description

Method of marking a plastic substrate with a light-emitting source.

FIELD OF THE INVENTION

The invention concerns a method of marking a plastic substrate using a light-emitting source. The plastic substrate is, for example, a smart card. The light-emitting source is, for example, a laser advantageously a C02 laser.

BACKGROUND OF THE INVENTION

Smart cards are generally personalised and identified using a bar code or an identification number. Various personalisation techniques exist, for example, ink jet marking, thermoprinting and laser marking.

As far as laser marking is concerned, various wavelengths are used, for example, C02 lasers at 10640 nm, YAG lasers (1064 nm, 532 nm or 355 nm), as well as excimer lasers. C02 lasers are amongst the cheapest available on the market and are frequently used in the treatment of materials and especially plastics.

The effect of the C02 laser beam on a plastic substrate varies considerably depending on the type of plastic used. Under the action of a C02 laser beam, the large majority of thermoplastic (styrene polymers, acrylics, polyethers, polyesters, polyolefins, etc.) and thermosetting materials are engraved. In other words the thermoplastic and thermosetting materials melt on their surface. This effect is used in the industrial welding of plastic parts.

Another restricted group of plastics (vinyl chloride or derivatives), reacts differently to the effect of a C02 laser giving more or less pronounced engraving as well as an intrinsic, coloured marking of the plastic. Due to the latter effect, this type of laser can be used to mark the material, as it can also be done by ink jet or thermoprinting. It is thus possible to obtain a contrasted marking, in particular a coloured marking on a white background.

To overcome the impossibility of marking plastics, which are not in the above-mentioned restricted group of plastics, one solution consists in depositing a layer comprising an already coloured ink on a white plastic support, which can be engraved by laser. The C02 laser beam decomposes the ink layer, thereby creating white marking on a background of coloured ink, through deterioration of the ink layer.

SUMMARY OF THE INVENTION

It is an object of the invention to allow both a reducing of the costs and an enhanced security.

According to one aspect of the invention a method of marking a plastic substrate using a light-emitting source is characterised in that an organic layer is deposited on the plastic substrate, the organic layer being arranged to change of colour in an irreversible manner under the action of the light- emitting source.

The plastic substrate is, for example, a smart card made of Acrylonitrile

Butadiene Styrene (hereinafter referred to as ABS). The light-emitting source is, for example, a laser, in particular a C02 laser. The organic layer is, for example, a polymer base or irreversible thermochromic ink.

In the absence of the organic layer, the ABS melts under the action of the

C02 laser but it does not change of colour. It is thus not possible to get a contrasted marking.

According to an advantage of the invention, under the action of the C02 laser, the plastic material melts and, at the same time, the colour of the organic layer is changing. A coloured marking embedded in the surface of the plastic subtract is obtained. The thus obtained coloured marking is therefore more durable, more stable and less falsifiable. According to another advantage of the invention, it is possible to obtain such a coloured marking on any type of plastic substrate (ABS, PET, PC, Polyolefins, etc.). It is in particular possible to obtain a coloured marking on light background with plastic substrates made of ABS by using, for example, a C02 laser.

Henceforward it is in particular possible to produce card bodies made of ABS with a card-by-card process. The card-by-card process consists in performing the various card manufacturing steps working with one card at a time, from printing to embedding. It differs from sheet manufacturing methods where the various manufacturing steps are carried out on sheets formed from several dozen cards. In addition to offering a certain degree of flexibility since the print setting times are much shorter and much less expensive (only a few cards are used to set the correct colours, whereas in the sheet method, setting is more difficult, and there is a greater number of rejects), the card-by-card process can also be used to eliminate certain manufacturing steps such as the rolling step. In particular, the card-by- card process is financially very attractive for small production runs. Various plastic card bodies can be used with this method, but moulded ABS cards remain the most profitable for this application, especially since the cavities can be moulded, which eliminates the subsequent cavity machining step. Note that contrary to cards made of ABS, cards made of PVC can not be moulded.

Note also that since ABS contains no halogen derivatives, making it very environmentally "clean", it meets the requirements of industrialists, which are striving to eliminate halogen-based products.

Another advantage of contrasted marking on light background is that it is easy to read or photocopy the marked inscription. Consequently, the invention allows both a reducing of the costs and an enhanced security.

BRIEF DESCRIPTION OF THE DRAWINGS

- Figure 1 illustrates the surface of a card before using a laser beam;

- Figure 2 illustrates the surface of a card after using a laser beam;

- Figure 3 illustrates the surface of a card before using a laser beam;

- Figure 4 illustrates the surface of a card after using a laser beam;

DETAILED DESCRIPTION

To better understand the invention, the invention will now be illustrated more in details in the context of marking plastic substrates, in particular smart cards, by using medium infrared (3-30μm) and far infrared (30- lOOOμm) laser.

According to a first embodiment, the organic layer is a polymer base, which can be marked by C02 laser. As illustrated in figure 1 and 2, the polymer base is deposited on the surface of the card body of a smart card. The polymer base can be, for example, a urea or melamine base. More generally, it can be any other type of base or polymer mixture which has a highly conjugated chemical structure, containing a certain number of close double bonds, making it easily carbonised. Bases containing halogenated groups could also be suitable for colour change under the effect of laser. These bases contain fragile bonds which, when broken, recombine to produce double bonds, which is favourable for carbonisation reactions. The polymer base can be deposited, for example, as a coating of type varnish, primer, ink, adhesive, etc. Thicknesses of less than one micron could be deposited, or thicknesses of a few microns, a few dozen microns or a few hundred microns depending on the deposition method. The coating can be deposited on the surface of the card body or inside a multilayer card structure. The laser beam is absorbed by the material and the coating. Under the thermal and chemical effect, carbonisation of the coating occurs, leaving a coloured mark, at the areas scanned by the laser. While marking the coating, the laser also partly melts the material on contact, so that the marking is printed on the surface in the plastic, thereby increasing its lifetime. The energies required to mark the coating are low, compared with those generally used. Note that if the laser power were too high, this would damage the coating layer and engrave the material without leaving any contrasted marking.

Since the marking can be carried out directly on the coating, it is possible to mark any support, which can be printed with this coating. Starting from the particular chemical framework of the coating, the formulation can be adapted so that it can be deposited by various printing methods (offset, flexography, lithography, serigraphy, spraying, etc.).

It is also be possible to include a base reactive to infrared (Hereinafter referred to as IR) laser, directly in the plastic matrix, as additives, pigments, alloy or even functional grafting on the plastic used. In this case, the plastic material can be marked directly.

According to another embodiment, the organic layer is an irreversible thermochromic ink. Under the thermal effect produced by the laser beam, the ink is activated and leaves a stable, durable coloured mark. In this case, the thermal effect produces a physical and chemical reaction, which is controllable, for example, in intensity.

The irreversible thermochromic ink used changes colour above a certain temperature. Visible marking can therefore be obtained, with black or coloured contrast, on a white or other background. In addition, by varying the type of ink used, several marking colours can be obtained. Offset, serigraphy, flexography, heliography, lithography inks, etc., already available on the market, can be used advantageously. The irreversible, thermochromic ink is deposited for example by dry or wet offset, serigraphy, flexography, heliography, lithography, or other printing or deposition techniques.

So as to improve the security aspect, an additional varnish layer can be deposited to protect the layer of ink. The laser beam engraves the surface of the material, leaving an indelible and non-falsifiable mark, an advantage with respect to other marking techniques such as for example thermoprinted marking which can be erased by simple mechanical or chemical attack. Note however that if a thermoprinting machine is used without ribbon, the heat generated by the thermoprinting pin can be used to activate the layer of irreversible thermochromic ink.

Photochromic inks which can be activated in the IR, as well as a label or other similar supports (scratch panel, signature panel, etc.) containing the substance reacting to IR laser, can also be used.

According to another aspect of the invention, a standard primer or varnish, which can be dried using UV radiation, and which comprises as additives, pigments arranged to change of colour under the action of laser beam, can also advantageously be deposited on an ABS card body using an offset printing process. The primer of varnish can be, for example, an acrylic base comprising pigments arranged to change of colour under the action of a laser beam. In addition to its standard gloss and scratch- resistance properties, this primer or varnish can thus be marked with C02 laser in order to personalise the card. In a card-by-card process a standard UV primer or varnish has just to be replaced by a UV primer or varnish comprising pigments arranged to change of colour under the action of laser beam. Therefore the manufacturing process remains very viable financially. Advantageously silicon can be added to the primer or varnish in order to have waterless effect. According to another aspect of the invention, as illustrated in figure 3 and 4, the coating can be deposited on several successive layers separated from each other by a layer of plastic or a different type of deposit. Each layer of coating (lb or 3b) could for example react differently to the C02 laser, producing different colours. By modifying the laser power, the layer to be reached can be selected according to the depth, the laser burning through the upper layers. This technique could form the seeds of a promising idea in the field of colour laser marking, a field still in its infancy. With this principle, it would also be possible to consider the creation of holographic figures.

Marking is produced by inputting sufficient energy to make the reactive base react. Advantageously, a laser of suitable wavelength could be used, » or any other technique likely to provide this energy input.

The invention is not restricted to the field of smart cards, but applies more generally to all plastic substrates.

The description hereinbefore illustrates a method of marking a plastic substrate using a light-emitting source, the method being characterised in that an organic layer is deposited on the plastic substrate, the organic layer being arranged to change of colour in an irreversible manner under the action of the light-emitting source.

The light-emitting source is, for example, a laser beam the wavelength of which is advantageously comprised in the medium infrared (3-30μm) or in the far infrared (30-1000μm) laser. The laser can be advantageously a C02 laser.

The plastic substrate can be any type of plastic, for example, PET, PC or Polyolefins. Advantageously the plastic substrate is made of ABS, in particular moulded ABS.

The organic layer can be, for example, a polymer base of highly conjugated chemical structure, comprising close double bonds so as to facilitate a reaction of carbonisation under the action of a laser beam. The organic layer can also be a urea or melamine base. Bases containing halogenated groups can also be used. The organic layer can also be an irreversible thermochromic ink or a photochromic ink. The organic layer can also be primer or varnish comprising pigments arranged to change of colour under the action of a laser beam. It can be in particular a primer or varnish made of acrylic and comprising such pigments.

More generally, any organic layer, which is arranged to change of colour under the action of a laser, can be used. The organic layer may also be a mixture of the various above-mentioned products.

The organic layer can be deposited by printing but also by coating or rolling.

Note that the term "base" used in this document must be understood in the sense of "product" and not in the sense of "base" as opposed to "acid".

Claims

1. Method of marking a plastic substrate using a light-emitting source, the method being characterised in that an organic layer is deposited on the plastic substrate, the organic layer being arranged to change of colour in a irreversible manner under the action of the light-emitting source.

2. The method according to claim 1, characterised in that the organic layer comprises a polymer base of highly conjugated chemical structure, comprising close double bonds.

3. The method according to claim 1, characterised in that the organic layer comprises an irreversible thermochromic ink.

4. The method according to claim 1, characterized in that the organic layer is made of a photochromic ink.

5. The method according to claim 1, characterised in that the organic layer comprises halogenated groups.

6. The method according to claim 1, characterised in that the organic layer is a primer or varnish made of acrylic and comprising pigments or alloys arranged to change of colour under the action of the light-emitting source.

7. The method according to claim 1, characterised in that the plastic substrate is made from Acrylonitrile Butadiene Styrene.

8. The method according to claim 2, characterised in that the polymer base comprises urea.

9. The method according to claim 2, characterised in that the polymer base comprises melamine.

10. The method according to claim 1, characterised in that the organic layer is deposited by coating.

11. The method according to claim 1, characterised in that the organic layer is deposited by printing.

12. The method according to claim 1, characterised in that the light- emitting source is a laser having wavelength in the medium infrared.

13. The method according to claim 1, characterised in that the light emitting source is a laser having wavelength in the far infrared.

14. The method according to claim 1, characterised in that the plastic substrate is a smart card.

15. A plastic substrate wherein the plastic substrate is provided with an organic layer, the organic layer being arranged to change of colour in a irreversible manner under the action of a light- emitting source.

16. The plastic substrate according to claim 15, wherein the plastic substrate is a smart card.

17. The plastic substrate according to claim 16, wherein the smart card is made of moulded ABS.