Method for manufacturing a card and card comprising at least one thermochromic pattern

0001The invention relates to a method of manufacturing a card formed of a plurality of layers of at least one polymeric material - in particular polycarbonate - hot-rolled and under pressure, and such a card.

0002<patcit id="pcit0001" dnum="EP0400220A"><text>EP 0400220</text></patcit> describes a laminated article for identification purposes (such as an identity card) comprising two sheets or layers of PVC at least one of which is transparent, between which is laminated a layer containing thermochromic liquid crystals arranged on a dark contrast background. These liquid crystals are applied in the form of an aqueous-based ink containing a water-soluble polymeric binder, for example gelatin or a polyacrylamide. As stated in this document, the hot and press-lamination of the PVC sheets carrying the information leads to adhesion problems. This document provides for a cleaning step preceding the lamination and aimed at removing the chemical compounds that are supposed to affect the adhesion of the different layers to one another. Nevertheless, this article does not

0003Various other attempts have been made to incorporate thermochromic patterns in boards formed of a plurality of thermoplastic hot-rolled and pressure-laminated layers. However, the thermochromic ink compositions known and envisaged especially in these applications are aqueous solvent compositions.<patcit id="pcit0002" dnum="EP2322587A"><text>EP2322587</text></patcit> describes an example of a thermochromic ink composition comprising microcapsules incorporating a thermochromic composition and UV absorbers dispersed in an aqueous solvent with a polymeric binder, for example acrylic.

0004In addition, many cards forming data carriers and used for identification or security purposes (bank cards, identity cards, driving licenses, individual access cards to sites or public transport, leaf Passport ...) are formed by hot lamination and under pressure of a plurality of layers of thermoplastic material -particularly polycarbonate, material also having many advantages in these applications (rigidity, durability, ease and reliability of markings ( variable inscriptions, reasons of safety ...), possibility of carrying out markings by laser ...) -. However, the inventors have found that the compositions of thermochromic ink with aqueous solvent proposed up to⁴ Pa) of polycarbonate layers. Indeed, these lamination conditions destroy the thermochromic effect provided by the thermochromic ink compositions printed on the polycarbonate layers. In addition, there are irreparable problems of adhesion of the polycarbonate layers with each other and with the printed thermochromic compositions. Also, known thermochromic ink compositions have a limited life of one or two years, which is insufficient in identification or security applications for which a service life of at least 10 years is required. (see in particular ISO 24789-1,2 (2012) - "Method of evaluation of identification (ID) card service life").

0005It should be noted in this respect that thermochromic inks compositions curing under irradiation with ultraviolet are also not compatible with hot lamination processes, the thermochromic activity being destroyed under the action of heat and / or in time, and provide a much less reactive thermochromic effect, insufficient in the aforementioned applications in which the thermochromic components are thermally insulated from the outside by at least one layer, in particular a polycarbonate layer.

0006Polycarbonate, synthetic papers and fiduciary papers are also sensitive to most organic solvents and are therefore not compatible with organic solvent based printing.

0007Consequently, the proposals that have been made to incorporate thermochromic patterns in hot-rolled and pressure-laminated boards - especially polycarbonate -, synthetic papers and fiduciary papers are only theoretical lessons that are not available in the past. practical on an industrial or commercial scale, in particular to manufacture data carriers usable for identification or security purposes.

0008The invention therefore aims to overcome these disadvantages.

0009The invention relates to a manufacturing method according to claim 1.

0010The thermochromic ink composition simultaneously:<ul><li>is compatible with hot lamination at a temperature above 150 ° C, typically of the order of 180 ° C,</li><li>can strongly adhere to a layer of thermoplastic material, in particular polycarbonate, and / or synthetic paper and / or on a fiduciary paper,</li><li>does not interfere with the adhesion of the layers of thermoplastic material - in particular polycarbonate - after their lamination under heat and under pressure,</li><li>has a thermochromic effect sufficiently reactive to be activatable through the thickness of at least one protective layer, in particular a layer of thermoplastic material -particularly polycarbonate-, or a security film or a layer of synthetic paper or fiduciary paper ,</li><li>has a persistent thermochromic effect lasting more than 10 years,</li><li>has a thermochromic effect resistant to light and temperature and humidity variations and shocks.</li></ul>

0011The thermochromic ink composition comprises in a liquid medium, said solvent, said solvent being aprotic:<ul><li>a dispersion of thermochromic microcapsules incorporating at least one leuco dye, and</li><li>a thermoplastic binder selected from the group consisting of polyacrylic polyesters, polyurethanes, and copolymers thereof.</li></ul>

0012Said solvent therefore belongs to the group of aprotic solvents and is in particular free of water and is not an aqueous solvent. It should be noted that the term "solvent" is used throughout the text to designate, like the terminology used in the field of ink compositions and printing, the liquid medium forming the base of the composition thermochromic ink, although this liquid medium is not strictly a solvent in the chemical sense of the term, the thermochromic microcapsules being dispersed in this liquid medium and not solubilized in the latter.

0013The inventors have found that the use of an aprotic solvent in the thermochromic ink composition makes it possible to obtain thermochromic prints which are then compatible with hot and press lamination, which have a thermochromic effect that is durable over many years. and sufficiently reactive to power is used through at least one thickness of thermoplastic material -particularly polycarbonate-, which exhibit excellent adhesion to thermoplastic materials, more particularly to rigid thermoplastic materials at room temperature -especially on polycarbonate- and not do not interfere with the adhesion of layers of such plastic materials - especially polycarbonate - when interposed between such layers. The The invention also makes it possible to obtain thermochromic prints which are then compatible with synthetic papers and fiduciary papers. No clear explanation can be given to this surprising phenomenon found by the inventors. It is possible, however, that the aprotic character of the solvent, although the latter is normally no longer present when the printing is cured (the solvent having been evaporated), plays a role in the subsequent resistance of the thermochromic microcapsules to hot lamination. and under pressure and / or in the operation of leuco dyes. More exactly, it is possible that the protic character of the aqueous solvents used until now in the compositions of

0014Said aprotic solvent must also be chosen to be compatible with the microcapsules and with the binder, and to be compatible with the printing technique used. Advantageously and according to the invention, the aprotic solvent is chosen from the group of solvents of screen printable compositions. Advantageously and according to the invention, said aprotic solvent has at least one of the following characteristics:<ul><li>it is chosen from the group of aprotic solvents having a dipolar moment of between 0 and 1.9 cm,</li><li>it is chosen from the group of aprotic solvents having a dielectric constant (permittivity with respect to the vacuum) of between 1.5 and 11,</li><li>it is chosen from the group of aprotic polar solvents,</li><li>it comprises at least one compound selected from the group consisting of n-alkyl propanoates and glycol propylenes (solvents particularly compatible with thermochromic microcapsules in melamine formaldehyde).</li></ul>

0015More particularly, in one advantageous embodiment a thermochromic ink composition comprises as a solvent a compound selected from the group consisting of n-propyl propanoate, n-butyl propanoate, n-pentyl propanoate, ethoxy-3-propanoate, 1-methoxy-2-propyl acetate, 1-propoxy-2-propanol, 1-propoxy-2-propyl acetate, 1-butoxy-2-propanol, (2-methoxy-1-methylethoxy) 2-propanol, 1- (2-methoxy-1-methylethoxy) -2-propyl acetate, 1- (2-propoxy-1-methylethoxy) 2-propanol, and [2- (2-methoxy methylethoxy) methylethoxy] propanol. Other examples are possible.

0016Furthermore, the thermoplastic binder is chosen in particular depending on the material used as a printing medium for the thermochromic ink composition. It is an advantage of the invention to allow the aforementioned problems to be solved with a large number of printing media that can be used to receive thermochromic printing. Thus the thermochromic ink composition can be optimized for printing on a support selected from the group of thermoplastic materials, synthetic papers, and fiduciary papers. It should be noted in this regard that the thermochromic ink composition can be optimized for printing on a solvent-sensitive medium such as polycarbonate supports and fiduciary papers.

0017The thermoplastic binder of the thermochromic ink composition can also be optimized for printing on a support intended to be hot rolled and under pressure (for example a laminate of thermoplastic layers forming a security and / or identification card such that 'a credit card).

0018The thermoplastic binder of the thermochromic ink composition can also be optimized to have a long life, especially of several years, for example of at least ten years.

0019In particular, by way of example, the thermoplastic binder of the thermochromic ink composition can be optimized for printing on a support made of a thermoplastic material selected from the group consisting of polycarbonate, PVC, and polyesters (polyterephthalate). ethylene PET, PETG). Other examples are possible.

0020Advantageously, the thermochromic ink composition more particularly intended for printing on a polycarbonate support comprises, as binder, a thermoplastic resin chosen from the group formed of alkyl poly (meth) acrylates and their copolymers.

0021In particular, by way of example, the thermoplastic binder of the thermochromic ink composition can be optimized for printing on a synthetic paper support chosen from the paper marketed under the trademark Teslin® by PPG, Monroeville, USA. paper sold under the trademark Neobond® by Neenah Lahnstein, Lahnstein, Germany, and paper marketed under the Polyart® brand by Arjobex, Boulogne, France. Other examples are possible.

0022In particular, by way of example, the thermoplastic binder of the thermochromic ink composition can be optimized for printing on a fiduciary paper support, such as a passport paper, a bank note paper, a paper ID card, driver's license paper, visa paper, birth certificate paper, customs seal paper, etc. Other examples are possible.

0023In the security and / or identification applications of the invention, the thermoplastic binder of the thermochromic ink composition may also be advantageously chosen to reveal attempts to falsify with solvents (chemical etching), and in particular a binder incorporating a solvent-soluble agent of an adhesive (when the thermochromic ink composition is used to print a thermochromic pattern on an adhesive card) as described for example by <patcit id="pcit0003" dnum="EP1109675A"><text>EP 1109675</text></patcit>.

0024Furthermore, another advantage of the thermochromic ink composition is to allow the addition of different additives in the solvent without disturbing the curing of the composition after printing.

0025In particular, the thermochromic ink composition advantageously comprises at least one anti-UV additive chosen from the group consisting of ultraviolet absorbing agents and light stabilizing agents (in particular of the HALS type ("hindered amine light stabilizers Such an ultraviolet absorber and / or light stabilizer of the thermochromic ink composition is incorporated in said aprotic solvent, and is in particular distinct from any ultraviolet absorbers and / or light stabilizers incorporated in the microcapsules. The thermochromic ink composition advantageously comprises between 1% and 10%, especially between 2% and 5%, by weight of an anti-UV additive.

0026As an anti-UV additive of the thermochromic ink composition, any ultraviolet absorber and / or light stabilizer compatible with the other components of the composition may be used. By way of example, mention may be made of the group of 2- (hydroxyphenyl) benzotriazoles (see especially "<nplcit id="ncit0001" npl-type="s"><text>Ultraviolet stabilizers of the 2- (hydroxyphenyl) benzotriazole class: influence of substituents on structure and spectra "J. Phys Chem., 1992, 96 (25), pp. 10225-10234</text></nplcit>); the group of 2-hydroxyphenyl-s-triazines (see in particular<patcit id="pcit0004" dnum="US5096489A"><text>US5096489</text></patcit>); and the group of 2,2,6,6-tetramethylpiperidines (TMP) (see in particular<nplcit id="ncit0002" npl-type="b"><text>"Oxidation inhibition in organic materials" Jan Pospisil, Peter P. Klemchuk CRC Press, 1989</text></nplcit>). Advantageously and according to the invention, it is possible to choose an ultraviolet absorber in the group of 2- (2-hydroxyphenyl) -benzotriazole (BTZ) and 2-hydroxyphenyl-s-triazine (HDT).

0027In an advantageous embodiment and according to the invention, the thermochromic ink composition comprises in said solvent between 15% and 35% by weight of thermochromic microcapsules, between 30% and 45% by weight of thermoplastic binder, between 1% and 10% by weight of at least one anti-UV additive.

0028The thermochromic pattern can be any: text (s), drawing (s), line (s), ... It can also be a solid (continuous printing on at least a portion of a surface of a layer of the map).

0029Advantageously and according to the invention at least one thermochromic pattern is printed with the thermochromic ink composition so as to be interposed between a surface layer of the card and a layer immediately underlying said surface layer. To do this, at least one thermochromic pattern is printed with the thermochromic ink composition on a surface layer of the card, that is to say on a layer of thermoplastic material -particularly polycarbonate- one side of which constitutes a free face of the board after hot and press lamination. Such a thermochromic pattern is advantageously printed on a face of said surface layer opposite to the face of the layer constituting the external free face of the card. Alternatively or in combination,

0030The invention also relates to a method of manufacturing a card and a card characterized in combination by all or some of the characteristics mentioned above or below.

0031Other objects, features and advantages of the invention will appear on reading the examples which follow.

EXAMPLE 1: Production of a thermochromic ink composition

0032A thermochromic ink composition is made by dispersing 20% ​​by weight of thermochromic microcapsules in a liquid mixture of an aprotic polar solvent and a thermoplastic resin.

0033The thermochromic ink composition comprises:<ul><li>20% by weight of thermochromic pigments (microcapsules),</li><li>40% by weight of methyl methacrylate copolymer as transparent binder,</li><li>26% by weight of 1- (2-methoxy-1-methylethoxy) 2-propanol,</li><li>10% ethyl ethoxy-3-propanoate,</li><li>4% by weight of 2-hydroxyphenyl-s-triazine (ultraviolet absorber).</li></ul>

0034The thermochromic microcapsules are microcapsules marketed under the trade name CHAMELEON® by Polychrom Co LTD, Ansan City, Korea.

0035The ultraviolet absorber is marketed under the reference TINUVIN® 400 by BASF, Ludwigshafen, Germany.

0036This ink has a viscosity of 7.0 Pa.s +/- 1 Pa.s

0037The ink can be printed with screen printing screens of 120 threads / cm allowing fine prints type frame of 80 dpi.

EXAMPLE 2 Manufacture of a Polycarbonate Card Incorporating Thermochromic Impressions

0038An ink composition obtained in accordance with Example 1 is printed in the form of a solid surface on one of the faces of two sheets of transparent polycarbonate whose thickness is of the order of 50 μm.

0039The ink is dried by hot air.

0040The printed polycarbonate sheets are associated with five other polycarbonate sheets interposed between the printed polycarbonate sheets so as to form a stack, the printed faces being placed in contact with the underlying sheets of the stack, i.e. say not constituting the outer faces of the latter. The five sheets of polycarbonate forming, with the two printed sheets, said stack are successively the following: a sheet of 100 microns of transparent polycarbonate; a sheet of 200 microns of white polycarbonate; a sheet of 200 microns of white polycarbonate; a sheet of 200 microns of white polycarbonate; a sheet of 100 microns of transparent polycarbonate.

0041The set of sheets forming this stack is laminated in a lamination press under the following conditions:<ul><li>1 min of rise at 180 ° C</li><li>12 min at 180 ° C under 30N / cm²</li><li>5 min at 180 ° C under 150 N / cm²</li><li>cooling at 26 ° C for 17.5 min at 180N / cm².</li></ul>

0042A map is obtained whose total thickness is equal to the sum of the thicknesses of the used polycarbonate sheets decreased by about 10%.

0043The thermochromic prints made with the thermochromic ink composition according to the invention are thus incorporated into the thickness of the card.

EXAMPLE 3: adhesion and durability tests

0044Durability tests are performed on polycarbonate cards as manufactured according to Example 2.

0045The adhesion between the various constituent layers of the card is evaluated according to different test protocol:<ul><li>peel measurement according to ISO 10373 - 90 ° to 300mm / min,</li><li>peel measurement after climatic aging according to ISO 24789-1 and 2,</li><li>bending test according to ISO 24789-1 and 2, 50,000 bends in length, 50,000 bends in width,</li><li>bending test after climatic aging according to ISO 24789-1 and 2,</li><li>bending test after exposure to artificial light according to ISO 24789-1 and 2</li></ul>

0046The peel measurement shows that the adhesion strength between the layers is greater than 3.5 N / cm.

0047In the flexural tests, no delamination occurs at the polycarbonate layers surrounding the thermochromic prints.

EXAMPLE 4: Lightfastness

0048The light fastness of the polycarbonate cards as manufactured according to Example 2 is evaluated by measuring the color difference (DE * Lab) of the thermochromic prints before and after exposure to artificial light. The measurement of the color is carried out when the thermochromic prints are in their first non-activated state, that is to say in the colored version of the thermochromic microcapsules.

0049The color difference is measured using a spectro-colorimeter (Spectropen® (Dr. Lange, Düsseldorf, Germany)) according to ISO 7724-3.

0050Thermochromic prints are exposed according to three test protocols:<ul><li>UVA exposure: 20h; UVA 340 nm; 60 ° C; 0.72 W / m²/ nm (ISO 4892),</li><li>exposure to artificial light according to ICAO 3.2 -2006-paragraph 5-14,</li><li>Xenon arc light exposure according to ISO 24789-1 and 2.</li></ul>

0051The DE color difference is less than 10 in the case of UVA exposure and less than 5 in the case of exposure to xenon arc artificial light.

0052With reversible thermochromic microcapsules colored unactivated and transparent in the activated state.

0053It is found that the thermochromic activity of the exposed samples with regard to the fading temperature range and the temperature recoloration range is identical to that of the unexposed samples.

EXAMPLE 5: Climatic behavior

0054The climatic behavior of the polycarbonate cards as manufactured according to Example 2 is evaluated according to the following test protocols:<ul><li>exposure to thermal cycling and stressful storage conditions according to ICAO 3.2-2006 paragraph 5.2 ("thermal cycling method") and paragraph 5.3 ("storage temperature stress method"),</li><li>exposure to high temperatures and humidity, thermal shock and thermal cycling according to ISO 24789-1 and 2, paragraph 5-7 ("temperature and humidity aging"), paragraph 5-8 ("temperature shock"), paragraph 5- 9 ("temperature and humidity cycling").</li></ul>

0055For the different test protocols, there is no loss of thermochromic activity, in terms of discoloration, change in the discoloration range and the recolouration range.