Laser markable security film

[0001] The present invention relates to security films containing a laser-marking layer and security documents containing these films.

Background Art [0002] Laser marking and laser engraving are well known techniques that are often used to prepare identification cards and security documents. However, in the literature, the term "laser engraving" is often incorrectly used to describe laser marking. Laser marking notices a change in color due to local heating of the material, causing carbonization. By changing the power of the ray you can get different shades of gray. During laser engraving, material is removed by ablation.

[0003] It is often mentioned in the literature that polycarbonate, PBT and ABS as polymers are laser labelable as such, i.e. in the absence of so-called "laser additives". However, laser additives are often added even with these polymers to further improve laser marking. The laser additive is a compound that absorbs light at the wavelength of the laser used, usually at 1064 nm (Nd: YAG), and converts it into heat.

[0004] Carbon black can be used as a laser additive; however, the carbon black is characterized by sufficient color intensity for its visibility before the laser beam is used, which may be disfiguring or interfering with the clarity of the mark after using the laser beam. These flaws became the driving force behind the search for more effective "colorless" additives. For example, US 6693657 (ENGELHARD CORP) discloses a YAG laser marking aid based on calcined powder of co-precipitated tin and antimony mixed oxides that produces a black mark contrasting with the surrounding area after exposure to YAG laser energy, but not showing previously significant color relative to the surrounding area or not causing a significant change in the properties of the material to which it was added. In general, alternative laser additives are based on heavy metals, which makes them less desirable from an ecological point of view.

Currently, the most commonly used polymer material in laser-marked identification cards and security documents is extruded polycarbonate film. However, polycarbonate films have several disadvantages. The most important are: their fragility, resulting in card cracking when bending, as well as the lack of resistance to organic solvents, which creates the possibility of falsification of a protected card.

[0005] Polyethylene terephthalate (PET) has high solvent resistance, high flexibility and is cheaper than polycarbonate, but has zero or very poor laser traceability.

[0006] EP 866750 A (SCHREINER ETIKETTEN) discloses laser-labelable label films based on white PET film with a black coating. Laser exposure ablates the black coating and reveals a white background. This structure makes it possible to make high-contrast inscriptions and drawings "white on black".

[0007] US 7541088 (MITSUBISHI POLYESTER FILM) discloses a biaxially oriented, heat stabilized, at least two-layer co-extruded film of polyethylene terephthalate (PET) or poly (2,6-naphthalate) ethylene (PEN), comprising a base layer and at least one outer layer. The base layer contains a white pigment and a laser absorber that has been coated with a carbonizable polymer. In col.3, lines 64-66 it is disclosed that only the combination of the laser marking additive and the white pigment and with the special structure of the coextruded layers creates the possibility of laser marking. The opaque structure of the coextruded layers prevents that the security prints, such as e.g. guilloches, below on the film, are visible through the structure of the laser-marking layer.

[0008] EP 1 852 270 (TECHNO POLYMER) discloses a laser marking laminate comprising: a layer A comprising a multi-color laser-inducible laser-marking thermoplastic polymer composition enabling obtaining markings having two or more color shades by exposing it with two or more energy laser lights differing from each other, whereby the composition meets the following requirements (1) and (2): (1) contains a chromatic coloring substance, a black substance that can be dispersed by itself or discolored when exposed to laser lights, and a thermoplastic polymer in the following mixing ratio, and (2) contains a chromatic coloring substance and a black substance in quantities of 0.001 up to 3 parts by weight and from 0.01 to 2 parts by weight, with respect to 100 parts by weight of thermoplastic polymer, and layer B formed on at least one surface of layer A, wherein layer B comprises a transparent thermoplastic resin and has a light transmittance of not less than 70% as a single layer.

[0009] EP 792 756 (NIPPON KAYAKU) discloses a laser marking article having a cured liquid composition layer comprising a high energy curable resin, a white dye and a developer, with a viscosity not exceeding 20 cP, measured with an E-type viscometer at 60 ° C .

[0010] Laser-marking protective films made by applying a laser-markable layer to a substrate have a number of advantages. During the production of such films, it is much easier than with the extrusion method to make changes in the laser-marking layer, e.g. in composition and thickness, as well as to add other layers, e.g. a specific adhesive layer. However, the amount of physical properties that are provided in the (co) extrusion process are not so obvious in overlay layers. There is a need for laser-marking protective films prepared by a coating method that would exhibit good physical properties regarding curling, adhesion and bending cracking.

Disclosure of the Invention

Summary of the Invention [0011] In order to overcome the above-described problems, in the preferred embodiments of the present invention a security film as defined in claim 1. [0012] The security film further enabled the surprisingly simple method of placing the security print and the data printed on the inside of the security document in such a way, that they are visible through a laser-marking layer, which makes it very difficult to forge.

[0013] Further advantages and embodiments of the present invention will become apparent from the following description.

Brief description of the drawings [0014] In figures 1 to 4, the following numbers mean:

• 1, 1 ', 6 = substrate, preferably PET-C;

• 2, 2 '= adhesive layer (SL);

• 3, 3 '= laser marking layer (LML);

• 4, 4 '= thermoadhesive layer (TAL);

• 5 = opaque core, eg white PETG;

• 7 = adhesive layer;

• 8 = transparent PETG;

• 10, 10 ', 10' '= security printing and printed information.

[0015] Figure 1 shows examples of possible structures of the protective film layers according to the present invention.

[0016] Figure 2 shows how the security films of the present invention can be used to produce security documents.

[0017] Figure 3 shows examples of one-sided laser-marking security documents.

[0018] Figure 4 shows examples of two-sided laser-marking security documents.

Definitions [0019] The terms "substrate" and "film" used in disclosing the present invention mean a self-reinforcing polymer sheet that can be attached to one or more adhesive layers, e.g., an adhesive layer. Substrates and films are usually produced by extrusion.

[0020] The term "layer" as used in disclosing the present invention means a non-reinforcing element that is produced by applying to a substrate or film.

[0021] "PET" is an abbreviation for polyethylene terephthalate.

[0022] "PETG" is an abbreviation for polyethylene terephthalate-glycol, with glycol being glycol modifiers added to reduce brittleness and reduce premature aging that occurs when unmodified amorphous polyethylene terephthalate (APET) is used in card production.

[0023] "PET-C" is an abbreviation for crystalline PET, i.e. biaxially stretched polyethylene terephthalate. This polyethylene terephthalate substrate has excellent dimensional stability.

[0024] The security definitions correspond to the normal definitions given in the "Glossary: ​​Secured documents, security and other related technical terms" published by the Council of the European Union's Consulium on 25 August 2008 (version v.10329.02.b.en) on its website:

<a href="http://www.consilium.europa.eu/prado/EN/glossaryPopup.html">http://www.consilium.europa.eu/prado/EN/glossaryPopup.html</a>.

[0025] The term "alkyl" means all possible variants for each number of carbon atoms in the alkyl group, i.e. for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl and 2-methylbutyl, etc.

[0026] The term "chlorinated ethylene" as used in disclosing the present invention means substituted ethylene with at least one chlorine atom, e.g. vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, trichloroethylene and tetrachloroethylene. Trichloroethylene and tetrachloroethylene are much more difficult to polymerize than vinyl chloride and vinylidene chloride.

Protective films [0027] The protective film according to the present invention comprises a biaxially oriented polyethylene terephthalate substrate and a laser marking layer, the laser marking layer comprising:

i) a laser additive, ii) a polymer selected from the group consisting of polystyrene, polycarbonate and styrene acrylonitrile, iii) initiator, and iv) at least 15 wt. radiation curable compound in relation to the total dry weight of the radiation detectable layer, wherein the radiation curable compound has a viscosity of less than 100 mPa.s at 25 ° C at a shear rate of 100 s^-1.

[0028] In a preferred embodiment, the backing film is a biaxially oriented polyethylene terephthalate backing provided with an adhesive layer.

[0029] In one embodiment of the protective film, the substrate is transparent. It allows reading through a laser-marking layer of security printing and data printed on the inside of the security document, which makes it very difficult to forge. This configuration is shown in the simplest form in Figure 1.a, where the laser-marking layer 3 has been applied to the adhesive layer 2 on the PETC SUP substrate. Layer configurations shown in Figures 1 to 4 are for reference only. For example, there may be a second adhesive layer between the adhesive layer 2 and the laser markable layer 3 in Figure 1.a; for example, the laser marking layer may be separated into two laser marking layers having the same or a different composition, e.g. a different content of laser additive.

[0030] In a preferred embodiment of the protective film, the polymer in the LML laser-marking layer is polystyrene. It has been noticed that polystyrene in overlay layers leads to higher optical densities for laser marking than e.g. polycarbonate or styrene-acrylonitrile.

[0031] In a preferred embodiment of the protective film, the radiation curable compound is (meth) acrylate, more preferably acrylate, and most preferably hexandiol diacrylate and / or alkoxylated hexandiol diacrylate.

[0032] In a preferred embodiment of the protective film, the laser additive is carbon black. Carbon black preferably has an average particle size less than 100 nm. The laser additive is preferably present in an amount less than 0.08 wt. based on the total weight of the laser-detectable polymer (s).

[0033] The security film may, as shown in Figure 1.c, further comprise a TAL thermoadhesive layer (4) on top of the LML laser-marking layer (3).

[0034] In one embodiment, the protective film further comprises a second SL2 adhesive layer (e.g. 2 'in Figure 1.b) on a SUP substrate on a different side of the SUP substrate than the side with the SL1 adhesive layer (2) and may have a TAL thermoadhesive layer (e.g. 4 in Figure 1.d) on top of the SL2 adhesive layer (2 ').

[0035] The TAL thermoadhesive layer preferably comprises a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol.

[0036] In a preferred embodiment, the SUP polyethylene terephthalate backing film has a thickness of 100 µm or less.

[0037] In another preferred embodiment, the protective film comprises a second laser marking layer located on a different side of the substrate than the side with the LML laser marking layer. This configuration is shown in Figures 1.f and 1.g, with two laser-marking layers 3 and 3 'applied on the 2 and 2' adhesive layers on both sides of the PETC 1 substrate, respectively. The thermoadhesive layer (4, 4 ') can be present on one or both layers laser-marking.

[0038] A method of making a protective film according to any one of claims 1 to 10 comprising the steps of:

a) preparing a transparent biaxially oriented polyethylene terephthalate substrate having an adhesive layer; and

b) applying a laser-marking layer to the adhesive layer using a composition comprising:

i) a laser additive, ii) a polymer selected from the group consisting of polystyrene, polycarbonate and styrene acrylonitrile, iii) initiator, and iv) at least 15 wt. radiation curable compound in relation to the total dry weight of the radiation detectable layer, wherein the radiation curable compound has a viscosity of less than 100 mPa.s at 25 ° C at a shear rate of 100 s^-1.

Security Documents [0039] The security document of the present invention has at least one security film of the present invention. Yes, a secured document can be used to identify a person named in a secured document.

[0040] Figure 2 shows how security documents having one or more laser-marking layers on one side of the opaque core 5 can be prepared using the security film of the present invention. Possible results of preparing unilaterally laser-marking documents secured by the lamination method shown in Figure 2 are shown in Figure 3. Figure 4 shows examples of double-sided laser-marked security documents that can be symmetrical (Figure 4.a) or asymmetrical (Figure 4.b) relative to the opaque core 5. The opaque core is preferably a white or slightly colored film, e.g. opaque PETG, on which dark laser markings are clearly visible.

[0041] In Figure 2.a, the protective film of Figure 3.c is laminated with the help of a thermoadhesive layer 4 on an opaque core 5 containing some security print 10, e.g. guilloches. It is also possible to position the laser-marking layer 3 as the outer layer by laminating the protective film of Figure 1. by means of the thermoadhesive layer 4 on the opaque core 5 containing some security print 10. Alternatively, the laser-marking layer 3 may also be protected by an overlay, preferably having PETC (6) as the outer film, as shown in Figures 2.c and 2.d. To laminate this overlay, preferably a thermoadhesive layer is present on either the laser-marking layer (4 in Figure 2.c) or on or on the overlap (9 in Figure 2.d). The overlay can contain successive layers or foils, e.g. adhesive layer 7 and transparent PETG film 8, and optionally may contain some security printing or printed information 10 ', printed e.g. by ink-jet printing or dye-sublimation method.

[0042] An advantage of the transparent substrate 1 in the security film is that the security print 10 on the opaque core 5 is visible through the laser-marking layer 3 as shown in Figures 3.a and 3.b. In Figure 3.c, two laser markable layers 3 and 3 'are present in the secured document. It was also noted that with laser marking higher optical densities are obtained in the laser-marking layer that is closest to the opaque layer or film, such as the opaque core 5. By controlling the thickness of the SUP (1) substrate in the protective film, a repeated image can be created in a traceable laser-layer 3 documents secured with Figure 3.c.

[0043] In a preferred embodiment, the security document comprises a white substrate or layer, preferably in close contact with the security film, more preferably with contact with the LML laser-marking layer. There may be an adhesive layer, preferably a TAL thermoadhesive layer, between the white substrate or the layer and the laser detectable LML layer.

[0044] Secured documents can also be laser markable on both sides of the core 5, as shown in Figure 4, by placing laser markable layers (3, 3 ', 3' ') on both sides of the opaque core 5. Security printing and printed information ( 10, 10 ', 10' ') can be in or on different layers and foils on both sides of the opaque core 5.

[0045] The security document can be a "smart card", which means an identification card containing an integrated circuit as a so-called electronic microprocessor. In a preferred embodiment, the document is secured by a so-called radio frequency identification card or RFID card.

[0046] The document is preferably secured with an identification card selected from the group consisting of an identity card, security card, driving license, social security card, membership card, time registration card, bank card, payment card and credit card. In a preferred embodiment, the document is secured with a personal identity card.

[0047] The security document preferably has the format specified in ISO 7810. ISO 7810 defines three formats for identity cards: ID-1 with dimensions of 85.60 mm x 53.98 mm and a thickness of 0.76 mm is specified in ISO 7813 as bank cards, credit cards, driving licenses and smart cards; ID-2 measuring 105 mm x 74 mm, as in German ID cards, usually 0.78 mm thick; and ID-3 with dimensions 125 mm x 88 mm, as in passports and visas. If the protected cards contain one or more contactless integrated circuits, greater thickness, e.g. 3 mm according to ISO 14443-1, is tolerated.

[0048] Various security measures are used to prevent forgeries of identification documents. One solution is to apply a line or guilloche to an identification image, such as a photograph. This way, if some material is later printed, the guilloche will appear white on an added black background. Other solutions include the addition of security elements, such as information printed with ink that reacts to ultraviolet radiation, a microliter hidden in an image or text, etc.

[0049] The security document according to the present invention may include other security features such as anti-xerox backgrounds, guilloche patterns, endless text, mini-print, micro-print, nano-print, iris printing, bar code, mosaic code, colored fibers, fluorescent fibers and broccoli, fluorescent pigments, OVD and DOVID (like holograms, 2D and 3D holograms, kinegrams ™, printing, relief, perforations, metallic pigments, magnetic material, metameric paints, microprocessors, RFID microprocessors, images made of OVI (optically variable paint) such as iridescent and photochromatic paint, images made of thermochromic paint, pigments and phosphorescent dyes, watermarks including two-tone and multi-tone watermarks, repeated images and security threads. [0050] The combination with one of the above security features increases the difficulty of forging a security document.

Substrates [0051] In a preferred embodiment of the security film according to the present invention, its substrate is a PET-C substrate. This biaxially stretched polyethylene terephthalate support has excellent dimensional stability, resistance to organic solvents, and flexibility.

[0052] The preparation of polyester substrates is well known in the art of preparing suitable substrates for silver halogen photographic films. For example, GB 811066 (ICI) describes a process for producing biaxially oriented films.

[0053] The backing of the protective film of the present invention should be thick enough to be self-reinforcing, but thin enough to be able to bend, fold and crease without cracking. The substrate has a thickness preferably from about 10 pm to 200 pm, more preferably from about 10 pm to about 100 pm, and most preferably from about 30 pm to about 65 pm.

[0054] In a preferred embodiment, PET-C is also used on the core of the security document, preferably in this case it is opaque.

Adhesive layers [0055] In the present invention, the substrate may be attached to an adhesive layer. The PET-C substrate is preferably provided with an adhesive layer comprising a polymer based on polyester, polyester urethane or a chlorinated ethylene copolymer, more preferably based on vinylidene chloride. Preferably at least 25 wt.%, More preferably at least 30 wt.%, And most preferably at least 45 wt.% Is contained in the polymer. vinylidene chloride monomer - based on the total weight of the polymer.

[0056] The use of adhesive layers is well known in the art of producing polyester supports for silver halogen photographic film. For example, US 3649336 (AGFA) and GB 1441591 (AGFA) teach such adhesive layers.

[0057] The step of biaxially stretching the polyethylene terephthalate substrate is preferably performed with an adhesive layer adhering to the polyethylene terephthalate substrate during at least part of the biaxial stretching process. A preferred stretching process includes the steps of: longitudinally stretching the polyethylene terephthalate substrate; applying a composition comprising a polyester, polyester urethane or vinylidene chloride copolymer to a longitudinally stretched polyethylene terephthalate substrate to form an adhesive layer adhering to the longitudinally stretched polyethylene terephthalate substrate; transverse stretching of the longitudinally stretched polyethylene terephthalate support. Preferred vinylidene chloride copolymers include: vinylidene chloride copolymer, N-tert-butylacrylamide, n-butyl acrylate and N-vinylpyrrolidone (e.g. 70: 23: 3: 4), vinylidene chloride copolymer, N-tert.-butylacrylamide , n-butyl acrylate and itaconic acid (e.g. 70: 21: 5: 2), a copolymer of vinylidene chloride, N-tert.-butylacrylamide and itaconic acid (e.g. 88: 10: 2), a copolymer of vinylidene chloride, n-butylmaleimide and itaconic acid (e.g. 90: 8: 2), a copolymer of vinyl chloride, vinylidene chloride and methacrylic acid (e.g. 65: 30: 5), a copolymer of vinylidene chloride, vinyl chloride and itaconic acid (e.g. 70: 26: 4), a copolymer of vinyl chloride, acrylate n-butyl and itaconic acid (e.g. 66: 30: 4), a copolymer of vinylidene chloride, n-butyl acrylate and itaconic acid (e.g. 80: 18: 2), a copolymer of vinylidene chloride, methyl acrylate and itaconic acid (e.g. 90: 8: 2), a copolymer of vinyl chloride, vinylidene chloride, N-tert-butylacrylamide and itaconic acid (e.g. 50: 30: 18: 2). All ratios given in parentheses for the above-mentioned copolymers are weight ratios.

[0059] In a preferred embodiment of the protective film according to the present invention, the adhesive layer has a dry thickness of not more than 2 pm or 200 mg / m. Laser Marking Layers [0060] The optional transparency of the security film according to the present invention and the low thickness of the laser markable layers are valuable advantages that provide many possibilities for the configuration of layers of a security document, e.g. applying a security print between the core and the laser markable layer. Commercially available laser marking films, such as the most commonly used polycarbonate films have a thickness of at least 50 µm, while with the protective film of the present invention the thickness of the laser marking layer may surprisingly be even less than 25 µm and still allow sufficient optical density to be obtained. The combination of a laser-marking layer with a PETC substrate has further benefits, such as solvent resistance and flexibility, which are the main shortcomings of polycarbonate films.

[0061] Polymers useful for laser marking, i.e. for carbonization, typically include polycarbonate (PC), polyethylene terephthalate (PBT), polyvinyl chloride (PVC), polystyrene (PS) and their copolymers, such as e.g. aromatic polyester-polycarbonate and acrylonitrile -butadiene-styrene (ABS). However, it has been found that only a few polymers are useful and that the presence of a laser additive is necessary to obtain sufficient optical density by laser marking in the relatively thin laser-markable protective film layers of the present invention.

[0062] The polymer useful for laser marking the security film of the present invention is selected from the group consisting of polystyrene, polycarbonate and styrene acrylonitrile. A mixture of two or more of these polymers can also be used.

[0063] In a preferred embodiment of the security film according to the present invention, the laser marking layer comprises polystyrene. It was noted that polystyrene provides the highest optical density when laser marking and that it also exhibits the highest laser sensitivity.

[0064] Laser-marking layers based on styrene-acrylonitrile polymers are sometimes considered less safe because toxic acrylonitrile may be released during laser marking.

[0065] The color change in polymeric materials is accelerated by the addition of a "laser additive" - ​​a substance that absorbs laser radiation and converts it into heat.

[0066] Useful laser additives include metallic antimony, carbon black, mica (flake silicate) coated with metal oxides and mixed oxides of tin and antimony. In WO 2006/042714 dark colors of polymeric materials were obtained by using additives based on various phosphorus-containing mixed oxides of iron, copper and / or antimony.

[0067] Useful commercially available laser additives include antimony doped tin oxide mica sold under the trade name Lazerflair^TM820 and 825 by MERCK; copper hydroxyphosphate sold under the trade name Fabulase^TM 322 by BUDENHEIM; aluminum heptamolybdate sold under the trade name AOM^tm by HC STARCK and antimony doped tin oxides pigments such as Engelhard Mark-it ™ sold by BASF.

[0068] In a preferred embodiment of the security film according to the present invention, the laser marking layer comprises soot particles. This avoids the use of heavy metals in the production of these security documents. Heavy metals are less desirable from an ecological point of view and can also create problems for people suffering from contact allergy to heavy metals.

[0069] Useful carbon blacks include Special Black 25, Special Black 55, Special Black 250 and FarbrussT^M FW2V - all available in EVONIK; Monarch ™ 1000 and Monarch ™ 1300 available in SEPULCHRE; and Conductex ™ 975 Ultra Powder available from COLUMBIAN CHEMICALS CO.

[0070] The use of carbon black pigments as laser additives can lead to undesirable background coloration of the security document precursor. For example, too high a concentration of soot in a laser-detectable layer of a document having a white background leads to gray protected documents. Too low soot causes a slower laser marking or the need to use more power to the laser, which leads to undesirable blistering. Both problems are solved in the present invention by using soot particles of small medium size and present in low concentration.

[0071] The number average particle size of the carbon black is preferably from 5 nm to 250 nm, more preferably from 10 nm to 100 nm, and most preferably from 30 nm to 60 nm. The numeric average soot particle size can be determined using a Brookhaven Instruments Particle Sizer BI90plus device based on the dynamic light scattering rule. The measurement settings of the BI90plus device are as follows: 5 series at 23 ° C, angle 90 °, wavelength 635 nm and graphics = correction function.

[0072] To avoid gray background coloring of the security document, the carbon black is preferably present in a concentration less than 0.08 wt.%, More preferably present in a concentration less than 0.08 wt.%, And most preferably present in the range from 0.01 to 0 , 03% by weight, based on the total weight of the laser-labelable polymer (s).

Adhesive layers [0073] In the production of security documents, the most commonly used lamination method is hot lamination; it is generally preferred over cold lamination. Hot laminators use heat activated glue that is heated as it passes through the laminator. The downside of hot laminators is that the thermosensitive layer may not be able to withstand the heat needed for lamination. Cold laminators use pressure sensitive adhesives that do not require heating. The laminator has rollers that compress laminated sheets. Cold laminators are faster and easier to use than hot laminators and do not discolor thermosensitive layers.

[0074] The lamination temperature when preparing security documents according to the present invention is preferably not higher than 180 ° C, more preferably not higher than 170 ° C, and most preferably not higher than 160 ° C.

[0075] In the protective films shown in Figures 1 to 4, a thermoadhesive layer was used each time, however, nothing prevents the use of an adhesive layer or self-adhesive film in any of the embodiments shown in Figures 1 to 4. In protective films and security documents of the present invention may also use a combination of self-adhesive and thermosensitive layers and films.

[0076] Suitable compositions for these pressure-sensitive and thermosensitive layers and films in security films and security documents of the present invention are well known to those skilled in the art.

[0077] A preferred hot melt film that is placed, for example, between the protective film and the opaque core just before lamination, is polyurethane film.

[0078] In contrast to biaxially oriented polyethylene terephthalate, the non-oriented PETG layer or film softens rapidly near the glass transition temperature and can therefore also be used for bonding purposes, as shown for example in US 2009032602 (TOYO BOSEKI).

[0079] Suitable thermoadhesive compositions are also disclosed in WO 2009/063058 (AGFA).

[0080] A preferred thermoadhesive layer is based on hydroxyl group containing partially hydrolyzed vinyl chloride / vinyl acetate resin, available under the trade name UCAR ™ VAGD Solution vinyl resin from Dow Chemical Company.

Polymeric overlays [0081] The security document of the present invention preferably has at least one polymeric overlay on top of the laser-marking layer. A security document may have several polymer overlays successively on it, for example containing some security features or information applied by imaging techniques such as inkjet printing, intaglio printing, screen printing, flexographic printing, driographic printing, electrophotographic printing, electrographic printing, stamping and offset printing. [0082] Suitable polymeric overlays that are laminated or applied include cellulose acetate propropionate, cellulose acetate butyrate, polyesters such as polyethylene terephthalate, polyethylene terephthalate, polyvinyl chloride, polyamides, polycarbonates, polyimides, polyolefins, polyvinylacetones.

[0083] In a preferred embodiment of the security document of the present invention, the polymeric overlay is polyvinyl chloride, polycarbonate or polyester. The polyester is preferably polyethylene terephthalate (PET) or polyethylene terephthalate-glycol, more preferably PET-C.

EXAMPLES

Materials [0084] All materials used in the following examples were readily available from standard supply sources such as ALDRICH CHEMICAL CO. (Belgium) and ACROS (Belgium), unless otherwise specified. The "water" used in the example was deionized water.

[0085] SPECIAL BLACK 25 is a carbon black with a primary particle size of about 56 nm and a BET specific surface area of ​​45 m / g, available in EVONIK.

MEK is an abbreviation for methyl ethyl ketone.

CN3102 is an oligomer blend containing aliphatic acrylic urethane and 2- (2-ethoxyethoxy) ethyl acrylate esters available as Sartomer ™ CN3102 from SARTOMER.

CN2505 is a tetrafunctional polyesteracrylate available as Craynor^TM CN2505 at SARTOMER.

SR295 is pentaerythritol tetraacrylate available as Sartomer ™ SR295 from SARTOMER. SR339 is 1,6-hexandiol 1,6-diacrylate available as Sartomer ™ SR238 from SARTOMER. SR339 is ethoxylated (3) bisphenol A diacrylate available as Sartomer ™ SR349 from SARTOMER.

SR610 is polyethylene glycol (600) diacrylate available as Sartomer ™ SR610 from SARTOMER.

CD561 is an alkoxylated haxandiol diacrylate sold under the trade name Sartomer^TM CD561 by SARTOMER.

PC01 is an abbreviation for Apec polycarbonate^TM 2050, available on BAYER.

PS02 is the abbreviation for Emperra ™ 171M, polystyrene available at INEOS.

SAN01 is an abbreviation for styrene-acrylonitrile copolymer available as DOW XZ 9518600 at DOW CHEMICAL. A 10% solution of this polymer in MEK has a viscosity of 7.1 mPa.s at 22 ° C.

PV01 is an abbreviation for polyvinyl butyral S LEC ™ BL 5 HP polymer available from SEKISUI.

PC01-sol is 20 wt. solution of PC01 in MEK.

PS01-sol is 20 wt. solution of PS01 in MEK.

PS02-sol is 30 wt. solution of PS01 in MEK.

SAN01-sol is 20 wt. solution of SAN01 in MEK.

PV01-sol is 20 wt. solution of PC01 in MEK.

I819 is phenyl (2,4,6-trimethylbenzoyl) phosphine oxide sold under the trade name Irgacure ™ 819 by CIBA SPECIALTY CHEMICALS.

TPO is an abbreviation for 10 wt. a solution in MEK 2,4,6-trimethylbenzoyldiphenylphosphine oxide available under the trade name Darocur ™ TPO in CIBA SPECIALTY CHEMICALS.

Bayhydrol ™ UH2558 is an aliphatic anionic polyurethane dispersion (containing approximately 37.2% dry matter), without cosolvents, based on polyesterurethane from isophorone diisocyanate, hexadiol and adipic acid, from BAYER.

Paresin is a dimethyltrimethylol melamine formaldehyde resin available under the trade name PAREZ ™ RESIN 613 from the American Cyanamid Company.

DR274 is a 10% aqueous copolymer solution of 60% poly (methylsilylquioxane) silylepoxide 60/40, available as TOSPEARL ™ 120 from GENERAL ELECTRIC.

DR270 is an aqueous solution containing 2.5 wt. DOWFAX ™ 2A1 and 2.5 wt. Surfynol^TM 420.

BS is an abbreviation for 10 wt. MEK Baysilon ™ Ol A silicone oil solution, available from BAYER and used as a surfactant.

Zylar ™ 631 is a copolymer of styrene, butadiene and methyl methacrylate from INEOS NOVA SERVICES BV.

UCAR^TM VAGD is a 90/4/6 wt. vinyl chloride / vinyl acetate / vinyl alcohol, available from UNION CARBIDE.

PEDOT / PSS is a 1.2% aqueous dispersion of poly (3,4-ethylene-oxythiophene) / polystyrenesulfonic acid (1: 246 by weight) obtained by the method described in US 5,354613 (AGFA).

VIN1 is 30% by weight aqueous solution of vinylidene chloride, methyl acrylate and acid copolymer (88: 10: 2 by weight).

Kelzan ™ S is xanthan gum from MERCK &amp; CO., Kelco Division, USA, which according to Technical Bulletin DB-19 is a polysaccharide containing mannose, glucose and glucuronide repeating units as mixed salts of potassium, sodium and calcium. Zonyl^TM FSO100 is a fluorine surfactant, more specifically a block copolymer of polyethylene glycol and polytetrafluoroethylene with the structure: F (CF2CF2) yCH2CH2O (CH2CH₂ABOUT)_xH, where x = 0 to about 15 and y = 1 to about 7 from DUPONT. Poligen ™ WE7 is 40% water latex of oxidized polyethylene from BASF.

PMMA is a 20% dispersion of spherical polymethyl methacrylate particles with a diameter of 0.1 pm. KIESELSOL ™ 100F is a 36% aqueous colloidal silica dispersion available at BAYER.

Liofol ™ UK 3640 is a polyurethane solvent adhesive (ethyl acetate) from Henkel. Liofol ™ UK 6800 is a hardener from Henkel for use with Liofol '^M UK 3640. MERSOLAT ™ H is a 76% aqueous sodium pentadecyl sulfonate paste from BAYER. Mersol is a 0.6% MERSOLAT solution^T H in water.

Mitsubishi White PET is a 75 pm white PET substrate W0175D027B available from MITSUBISHI.

The opaque PETG core is a 500g opaque PETG core.

DOWFAX^tm 2A1 is a surfactant (CASRN 12626-49-2) from DOW CHEMICAL.

Surfynol ™ 420 is a surfactant - bispolyethylene ether 2,4,7,9-tetramethyl-5-decin-4,7-diol from AIR PRODUCTS &amp; CHEMICALS.

Measurement methods

1. Optical density [0086] Optical density was measured by reflection using a Type 504 X-RITE spectrodensitometer using a visual filter.

2. Rolling [0087] The coated sample which was rolled was laid on a flat table and the distance between the table surface and the edge of the sample was measured. The greater this distance was measured in mm, the greater the curl of the coated sample. If the edge curls perpendicular to the table or beyond, "nm" (= not measured) is used.

3. Viscosity [0088] The viscosity of the coating composition was measured with a Brookfield DV-II + viscometer at 25 ° C at 6 rpm.

4. Blisters [0089] If an overlay has been placed on the laser detectable layer, then after the laser marking the overlay may detach from the laser detectable layer due to the formation of gases, e.g. CO2, and vapors of solvent residues in the laser detectable layer, causing blisters, mainly in the Dmax area. These blisters are visible to the naked eye.

5. Adhesion [0090] Adhesion was determined by separating the applied layer from the substrate (through an incision) in the corner of the coated sample, applying a piece of PVC Tesatape ™ 4104 tape and pulling the tape from the corner towards the opposite corner of the coated sample. If part of the applied layer peels off along with the tape, then the adhesion is considered insufficient ("Not OK"), in the alternative case the adhesion is considered sufficient ("OK"). EXAMPLE 1 [0091] This example shows the effect of the viscosity of a radiation curable compound on physical properties such as curling and blistering.

Preparation of the LADPC laser additive dispersion [0092] 5 g of the Special Black ™ 25 pigment and PC01 polycarbonate polymer were mixed in a dissolver (dissolution device) with 75 g of MEK organic solvent. The mixture was ground for seven days on a roller mill using 1 cm diameter soapstone balls at a rotation speed of 150 rpm. After milling, the dispersion was separated from the beads using a filter cloth and further diluted with PC01-sol polycarbonate solution to obtain a LADPC laser additive dispersion containing 2000 ppm carbon black pigment with respect to the polymer.

Preparation of the LADPV laser additive dispersion [0093] The LADPV laser tax dispersion was prepared in exactly the same way as LADPC, except that the PC01 polycarbonate polymer was replaced by PV01 polyvinyl butyral.

Preparation of protective films [0094] COMP-1 to COMP-6 comparative coating compositions and the inventive coating compositions INV-1 and INV-2 were prepared according to Table 1.

Table 1

<td rowspan="2">wt%</td><td colspan="9">Coating compositions</td>

<td>COMP -1</td><td>COM P-2</td><td>COM P-3</td><td>COM P-4</td><td>COM P-5</td><td>COM P-5</td><td>INV1</td><td>INV2</td><td>INV3</td>

<td>LADPC</td><td> 2,5</td><td> —</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td>

<td>LADPV</td><td> —</td><td> 2,5</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>PS01-sol</td><td> 97,5</td><td> —</td><td> 63,5</td><td> 63,5</td><td> 63,5</td><td> 63,5</td><td> 63,5</td><td> 63,5</td><td> 63,5</td>

<td>PV01-sol</td><td> —</td><td> 97,5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>CN3102</td><td> —</td><td> —</td><td> 6,6</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>CN2505</td><td> —</td><td> —</td><td> —</td><td> 6,6</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>SR295</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 6,6</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>SR349</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 6,6</td><td> —</td><td> —</td><td> 3,3</td>

<td>SR238</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 6,6</td><td> —</td><td> 3,3</td>

<td>SR610</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 6,6</td><td> —</td>

<td>I819</td><td> —</td><td> —</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td>

<td>MEK</td><td> —</td><td> —</td><td> 27,2</td><td> 27,2</td><td> 27,2</td><td> 27,2</td><td> 27,2</td><td> 27,2</td><td> 27,2</td>

[0095] The coating compositions COMP-1 to COMP-6 and INV-1 to INV-3 were applied to a wet film thickness of 100 pm on a Mitsubishi White PET substrate using an Elcometer Bird Film Applicator (from ELCOMETER INSTRUMENTS) and then dried for minutes at 50 ° C.

[0096] All coated samples were cured on a Fusion DRSE-120 conveyor, equipped with a Fusion VPS / 1600 lamp (type D), which moved the samples under a UV lamp on a belt at a speed of 20 m / min; UV radiation energy was 250 mJ / m².

Results and evaluation [0097] The folding and adhesion of each of the coated samples were evaluated. To evaluate the laser marking of the coated samples, first a transparent, non-laser-labelable 125 pm thick Polycarbonate film from Makrofol ™ DE 1-1 from BAYER was laminated to the laser-marking layer of each coated sample using an Oasys OLA6 / 7 laminator at 205 ° C. The presence of the overlay protects against laser engraving, i.e. ablation of the material caused by the laser, which leads to smaller Dmax in measurements. After lamination, a test image containing a wedge of different gray levels (six 9 x 9 mm squares) was applied to all coated samples using a Rofin RSM Powerline E (10 W) laser and 29 A and 22 kHz settings. The maximum optical density was measured in square 6 (RGB values ​​= 12 in this area in the bitmap image). The sensitivity of the laser marking was evaluated by measuring the optical density in square 4. The results are given in table 2.

Table 2

<td>Coated sample</td><td>Viscosity monomer (MPa.s)</td><td>collapsing (Mm)</td><td>Adhesion</td><td>dmin</td><td>tenderness</td><td>Dmax</td>

<td>COMP 1</td><td> —</td><td> 88</td><td>OKAY</td><td> 0,13</td><td> 0,84</td><td> 1,63</td>

<td>COMP-2</td><td> —</td><td> 7</td><td>OKAY</td><td> 0,13</td><td>nm</td><td> 0,42</td>

<td>COMP-3</td><td> 180</td><td> 62</td><td>Not OK</td><td> 0,13</td><td> 0,39</td><td> 1,03</td>

<td>COMP-4</td><td> 700</td><td> 43</td><td>Not OK</td><td> 0,16</td><td> 0,34</td><td> 0,56</td>

<td>COMP-5</td><td> 342</td><td> 34</td><td>OKAY</td><td> 0,13</td><td> 0,54</td><td> 1,09</td>

<td>COMP-6</td><td> 1600</td><td> 4</td><td>Not OK</td><td> 0,13</td><td> 0,64</td><td> 1,34</td>

<td>INV-1</td><td> 9</td><td> 0</td><td>OKAY</td><td> 0,12</td><td> 0,56</td><td> 1,10</td>

<td>INV-2</td><td> 90</td><td> 2</td><td>OKAY</td><td> 0,12</td><td> 0,31</td><td> 0,58</td>

<td>INV-3</td><td>9 and 1600</td><td> 5</td><td>OKAY</td><td> 0,18</td><td> 0,87</td><td> 1,23</td>

[0098] From table 2 it should be evident that minimal curling after drying the coating for 15 minutes at 50 ° C and good adhesion can only be obtained using at least one monomer having a viscosity of less than 100 mPa.s at 25 ° C and at shear rate 100 p^-1. However, it can also be seen from Table 2 that the type of monomer affects sensitometry. Better sensitivity and Dmax were obtained with hexandiol diacrylate compared to polyethylene glycol 6000 diacrylate. The coated and cured sample INV-3 shows that good physical properties and sensitometry can be obtained with a content of 16.5% hexandiol diacrylate (based on the dry weight of the laser detectable layer. The comparative COMP-3 coating clearly shows that not all polymers known to be laser-marked in the extruded form work equally well when applied as a layer.

EXAMPLE 2 [0100] This example illustrates the effect of a laser-labelable polymer type and radiation curable compound content on sensitometry and physical properties. Preparation of the laser additive dispersion [0101] The same laser additive dispersion was used as in EXAMPLE 1.

LADPS laser additive dispersion [0102] 5 g of Special Black ™ 25 pigment and PS01 polystyrene polymer were mixed in a dissolver (dissolution device) with 75 g of MEK organic solvent. The mixture was ground on a roller mill using 1 cm soapstone balls for seven days at a rotation speed of 150 rpm. After milling, the dispersion was separated from the beads using a filter cloth and further diluted with PS0114 sol polycarbonate solution to obtain a LADPS laser additive dispersion containing 2000 ppm carbon black pigment on the polymer.

Dispersion of LADSAN laser additive [0103] 5 g of Special Black pigment^TM 25 and 20 styrene-acrylonitrile polymer SAN01 was mixed in a dissolver (dissolution device) with 75 g of MEK organic solvent.

The mixture was ground on a roller mill using 1 cm soapstone balls for seven days at a rotation speed of 150 rpm. After milling, the dispersion was separated from the beads using a filter cloth and further diluted with a styrene-acrylonitrile SAN01-sol solution to obtain a LADSAN laser additive dispersion containing 2000 ppm carbon black pigment on the polymer.

Preparation of protective films [0104] Comparative coating compositions COMP-7 to COMP-12 and coating compositions according to the invention INV-4 to INV-9 were prepared according to table 3 and table 4.

Table 3

<td>wt%</td><td>COMP-7</td><td>COMP-8</td><td>COMP-9</td><td>INV-4</td><td>INV-5</td><td>COMP-10</td>

<td>LADSAN</td><td> 2,5</td><td> —</td><td> —</td><td> 2,5</td><td> 2,5</td><td> 2,5</td>

<td>LADPS</td><td> —</td><td> 2,5</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>LADPC</td><td> —</td><td> —</td><td> 2,5</td><td> —</td><td> —</td><td> —</td>

<td>SAN01-sol</td><td> 97,5</td><td> —</td><td> —</td><td> 68,5</td><td> 75,5</td><td> 84,5</td>

<td>PS01-sol</td><td> —</td><td> 97,5</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>PC01-sol</td><td> —</td><td> —</td><td> 97,5</td><td> —</td><td> —</td><td> —</td>

<td>SR238</td><td> —</td><td> —</td><td> —</td><td> 5,6</td><td> 4,2</td><td> 2,4</td>

<td>TPO</td><td> —</td><td> —</td><td> —</td><td> 0,2</td><td> 0,2</td><td> 0,2</td>

<td>MEK</td><td> —</td><td> —</td><td> —</td><td> 23,2</td><td> 17,6</td><td> 10,4</td>

[0105]

Table 4

<td>wt%</td><td>INV-6</td><td>INV-7</td><td>COMP-11</td><td>COMP-12</td><td>INV-8</td>

<td>LADSAN</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>LADPS</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> —</td><td> —</td>

<td>LADPC</td><td> —</td><td> —</td><td> —</td><td> 2,5</td><td> 2,5</td>

<td>SAN01-sol</td><td> —</td><td> —</td><td> —</td><td> —</td><td> —</td>

<td>PS01-sol</td><td> 68,5</td><td> 75,5</td><td> 84,5</td><td> —</td><td> —</td>

<td>PC01-sol</td><td> —</td><td> —</td><td> —</td><td> 84,5</td><td> 68,5</td>

<td>SR238</td><td> 5,6</td><td> 4,2</td><td> 2,4</td><td> 2,4</td><td> 5,6</td>

<td>TPO</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td><td> 0,2</td>

<td>MEK</td><td> 23,2</td><td> 17,6</td><td> 10,4</td><td> 10,4</td><td> 23,2</td>

[0106] Coating compositions COMP-7 to COMP-12 and INV-4 to INV-8 were applied to a wet coating thickness of 100 pm on a Mitsubishi White PET substrate using an applicator

Elcometer Bird Film Applicator (from ELCOMETER INSTRUMENTS), and then dried for 15 minutes at 80 ° C.

[0107] All coated samples were cured on a Fusion DRSE-120 conveyor equipped with a Fusion VPS / 1600 lamp (type D) which shifted the samples under a UV lamp onto ₂ belt at a speed of 20 m / min; UV radiation energy was 250 mJ / m.

Results and evaluation [0108] To evaluate the laser marking of coated samples, first transparent 125K thick Makrofol ™ DE 1-1 laser polycarbonate film was laminated with BAYER to the laser-marking layer of each coated sample using an Oasys OLA6 / 7 laminator at a temperature of 205 ° C. The presence of the overlay protects against laser engraving, i.e. ablation of the material caused by the laser, which leads to smaller Dmax in measurements. After lamination, all coated samples were laser marked with a test image containing a wedge of different gray levels (six 9 x 9 mm squares) using a Rofin RSM Powerline E laser and settings of 29 A and 22 kHz. The maximum optical density was measured in square 6 (RGB values ​​= 12 in this area in the bitmap image). The sensitivity of the laser marking was assessed by measuring the optical density in square 4. Coiling and blistering in each of the coated samples after laser marking were also assessed. The results are shown in Table 5 (nm means that the coiling parameter value was outside the measuring range.

Table 5

<td>A sample</td><td>wt% monomer</td><td>collapsing (Mm)</td><td>blisters</td><td>^Dmin</td><td>tenderness</td><td>^Dmax</td>

<td>COMP-7</td><td> 0</td><td> 55</td><td>Yes</td><td> 0,17</td><td> 0,67</td><td> 0,89</td>

<td>COMP-8</td><td> 0</td><td> 85</td><td>Yes</td><td> 0,16</td><td> 1,05</td><td> 1,49</td>

<td>COMP-9</td><td> 0</td><td>nm</td><td>Yes</td><td> 0,19</td><td> 0,98</td><td> 1,10</td>

<td>INV-4</td><td> 28</td><td> 0</td><td>No</td><td> 0,16</td><td> 1,12</td><td> 1,22</td>

<td>INV-5</td><td> 21</td><td> 0</td><td>No</td><td> 0,16</td><td> 1,23</td><td> 1,26</td>

<td>COMP-10</td><td> 12</td><td> 7</td><td>Yes</td><td> 0,16</td><td> 1,30</td><td> 1,30</td>

<td>INV-6</td><td> 28</td><td> 0</td><td>No</td><td> 0,15</td><td> 1,20</td><td> 1,25</td>

<td>INV-7</td><td> 21</td><td> 0</td><td>No</td><td> 0,16</td><td> 1,30</td><td> 1,32</td>

<td>COMP-11</td><td> 12</td><td> 6</td><td>Yes</td><td> 0,16</td><td> 1,18</td><td> 1,53</td>

<td>COMP-12</td><td> 12</td><td>nm</td><td>Yes</td><td> 0,16</td><td> 0,90</td><td> 1,24</td>

<td>INV-8</td><td> 28</td><td> 0</td><td>No</td><td> 0,15</td><td> 0,66</td><td> 1,24</td>

[0109] Based on the results in Table 5, it should be obvious that the use of 12 wt. low viscosity monomer is not sufficient to obtain a good curling value after drying the coating for 15 minutes at 80 ° C. Furthermore, after laser marking, no more bubbles are observed in Dmax in hardened, coated samples containing 21 and 28 wt. monomer with a viscosity of less than 100 mPa.s at 25 ° C at a shear rate of 100 s^-1. In this example, as well as in general, it has been noted that higher sensitivity for laser marking and Dmax can be obtained in laser-marking layers containing polystyrene as a laser-marking polymer.

EXAMPLE 3 [0110] Cracking may occur when bending the protected film. This example demonstrates that the type of low-viscous monomer affects the cracking phenomenon. Preparation of protective films [0111] The coating compositions INV-9 and INV-10 were prepared by mixing the ingredients according to table 6.

Table 6

<td>wt%</td><td>INV-9</td><td>INV-10</td>

<td>LADPS</td><td> 2,5</td><td> 2,5</td>

<td>PS02-sol</td><td> 68,5</td><td> 68,5</td>

<td>SR238</td><td> 5,6</td><td> —</td>

<td>CD561</td><td> —</td><td> 5,6</td>

<td>TPO</td><td> 0,2</td><td> 0,2</td>

<td>MEK</td><td> 23,2</td><td> 23,2</td>

[0112] The coating compositions INV-9 and INV-10 were applied to a wet coating thickness of 100 pm on a Mitsubishi White PET substrate using an Elcometer Bird Film applicator

Applicator (from ELCOMETER INSTRUMENTS), and then dried for 15 minutes at 80 ° C.

[0113] All coated samples were cured on a Fusion DRSE-120 conveyor equipped with a Fusion VPS / 1600 lamp (type D) which moved the samples under a UV lamp onto ₂ belt at a speed of 20 m / min; UV radiation energy was 250 mJ / m.

Results and evaluation [0114] Crack behavior was evaluated by bending the coated sample 45 ° and then visually checking the sample using a microscope. To assess the laser marking of the coated samples, first transparent, non-marking laser polycarbonate film with a thickness of 125 pm Makrofol ™ DE 1-1 from BAYER was laminated to a laser-marking layer of each coated sample using an Oasys OLA6 / 7 laminator at 205 ° C. The presence of the overlay protects against laser engraving, i.e. ablation of the material caused by the laser, which leads to smaller Dmax in measurements. After lamination, a test image containing a wedge with different gray levels (six 9 x 9 mm squares) was applied to all coated samples using a Rofin RSM Powerline E (10 W) laser and 29 A and 22 kHz settings. The maximum optical density was measured in square 6 (RGB values ​​= 12 in this area in the bitmap image). The sensitivity of the laser marking was evaluated by measuring the optical density in square 4. The results are given in table 7.

Table 7

<td>A sample</td><td>collapsing (Mm)</td><td>Cracks</td><td>^Dmin</td><td>tenderness</td><td>^Dmax</td>

<td>INV-9</td><td> 0</td><td>Yes</td><td> 0,15</td><td> 0,71</td><td> 1,3</td>

<td>INV-10</td><td> 0</td><td>No</td><td> 0,17</td><td> 0,59</td><td> 1,15</td>

[0115] Table 7 shows that the replacement of hexandiol diacrylate with alkoxylated hexandiol diacrylate results in improved fracture toughness of the respective protective films.

EXAMPLE 4 [0116] This example demonstrates how a duplicate image can be made by laser marking using a double-sided laser-marking security film.

Preparation of the PET-C1 substrate with PET-C [0117] The SUB-1 coating composition was prepared by mixing in a dissolver (dissolution device) the ingredients according to Table 8.

Table 8

<td>Ingredient</td><td>wt%</td>

<td>Water</td><td> 77,87</td>

<td>resorcinol</td><td> 0,99</td>

<td>Bayhydrol ™ UH2558</td><td> 18,55</td>

<td>Paresin</td><td> 0,57</td>

<td>DR274</td><td> 0,68</td>

<td>DR270</td><td> 1,34</td>

[0118] A polyethylene terephthalate sheet with a thickness of 1100 pm was first stretched longitudinally and then coated on both sides with a SUB-1 coating composition to a thickness of 10 pm (wet). After drying the longitudinally stretched and coated polyethylene terephthalate sheet, it was stretched transversely to obtain a 63 pm PET-C1 sheet coated with a transparent, shiny adhesive layer.

Preparation of the dispersion of the LADPS2 laser additive [0119] A concentrated soot dispersion was prepared by dissolving 300.0 g of PS02-sol in a vessel containing 127.5 g of MEK using a DISPERLUX dispersant^TM (DISPERLUX

SARL, Luxembourg). 22.5 g of Special Black 25 carbon black was added to the solution and mixed for 30 minutes. The vessel was then connected to a NETZSCH ZETAMILL mill filled with 50% balls of 0.4 mm diameter, made of yttrium stabilized zirconium ("abrasion resistant zirconia milling media" from TOSOH Co.). The mixture was circulated in the mill for 1 hour at a rotational speed of about 10.4 m / s (3000 rpm). 290 g of concentrated dispersion of laser additive were obtained.

[0120] Next, 8.0 g of concentrated laser additive dispersion was added to a 2000 ml plastic bottle containing 659.0 g MEK and 333.0 g PS2-sol. This mixture was ground on a roller mill (without the use of balls) for 1 hour at a rotational speed of 150 rpm to obtain a LADPS2 laser additive dispersion containing 2000 ppm Special Black 25.

Preparation of double-sided laser-marking protective film SF-1 [0121] Coating compositions CC-8 and CC-9 were prepared by mixing the ingredients in the order of Table 9.

Table 9

<td rowspan="2">wt%</td><td colspan="2">Coating compositions</td>

<td>CC-A</td><td>CC-B</td>

<td>BS</td><td> 0,10</td><td> 0,29</td>

<td>MEK</td><td> 86,16</td><td> 59,89</td>

<td>PS02</td><td> 7,42</td><td> 21,49</td>

<td>Zylar^TM 631</td><td> 1,11</td><td> 3,22</td>

<td>LADPS2</td><td> 1,00</td><td> 2,90</td>

<td>CD561</td><td> 3,01</td><td> 8,71</td>

<td>TPO</td><td> 1,20</td><td> 3,50</td>

[0122] The CC-A coating composition was then applied using an Elcometer Bird Film Applicator (ELCOMETER INSTRUMENTS) on both sides of a PET2 C-PET substrate having adhesive layers, with a coating thickness of 100 pm, and then dried for 15 minutes in 50 ° C.

[0123] The coated sample was partially cured on a Fusion DRSE120 conveyor, equipped with a Fusion VPS / 1600 lamp (type D), which moved the sample under a UV lamp on a belt at a speed of 20 m / min; UV radiation energy was 250 mJ / m². [0124] The coated sample was then coated on both sides with the CC-B coating composition using an Elcometer Bird Film Applicator (ELCOMETER INSTRUMENTS for a coating thickness of 100 µm, and then dried for 15 minutes at 50 ° C.

[0125] The coated sample was partially cured on a Fusion DRSE120 conveyor equipped with a Fusion VPS / 1600 lamp (type D) which moved the sample under the lamp

UV on the tape at a speed of 20 m / min; UV radiation energy was 250 mJ / m².

[0126] Both sides of the coated sample were coated with a thermoadhesive layer using the CC-C coating composition according to Table 10. The coating was done using an Elcometer Bird Film Applicator (ELCOMETER INSTRUMENTS for a coating thickness of 80 pm. The sample was then dried for 15 minutes at 50 ° C .

Table 10

<td>CC-10 components</td><td>wt%</td>

<td>MEK</td><td> 87,5</td>

<td>UCAR^tm vagd</td><td> 12,5</td>

[0127] The coated sample was cured on a Fusion DRSE-120 conveyor equipped with a Fusion VPS / 1600 lamp (type D) which moved the sample three times under a UV lamp on a belt at a speed of 20 m / min; UV radiation energy was 250 mJ / m². A double-sided laser-marking protective film SF-1 was obtained.

Preparation of the OV-1 overlay [0128] The SUB-2 and SUB-3 coating compositions were prepared by mixing in a dissolver (dissolution device) the components according to Table 11 or Table 12, respectively.

Table 11

<td>SUB-2 ingredients</td><td>ml</td>

<td>Water</td><td> 666,0</td>

<td>Vin1</td><td> 189,0</td>

<td>PEDOT / PSS</td><td> 82,3</td>

<td>KIESELSOL ™ 100F</td><td> 17,5</td>

<td>Mersol</td><td> 45,0</td>

[0129]

Table 12

<td>SUB-3 ingredients</td><td>g</td>

<td>Water</td><td> 939,9</td>

<td>26% NH4OH aqueous solution</td><td> 0,3</td>

<td>Kelzan ™ S.</td><td> 0,3</td>

<td>PEDOT / PSS</td><td> 30,0</td>

<td>KIESELSOL ™¹ 100F</td><td> 0,6</td>

<td>/ onyl ™ FSO100</td><td> 0,6</td>

<td>Poligen ™ WE7</td><td> 0,2</td>

<td>PMMA</td><td> 30,1</td>

[0130] A sheet of 1100 Lim polyethylene terephthalate was first stretched longitudinally and then coated with a SUB-2 coating composition on one side to a thickness of (wet) 9 gm. After drying, the longitudinally stretched and coated polyethylene terephthalate sheet was transversely stretched to give a 63 gm thick sheet, which was then coated on the same side as the SUB-2 adhesive layer, with SUB-3 coating composition to a wet thickness of 33 gm. The resulting layers were transparent and shiny.

[0131] An adhesive composition was prepared by mixing 50 g Liofol ™ UR 3640, polyurethane solvent adhesive (ethyl acetate) with 1 g of Liofol hardener^TM UR 6800. The adhesive composition was applied using a Braive coating apparatus with a 20 gm thickness (wet) wire on top of the adhesive layer prepared from the composition SUB-3 and dried for 2 minutes at 50 ° C. The overlay side with the applied adhesive layer was then laminated to a PETG 35 gm sheet (Rayopet from AMCOR) using a roller laminator to obtain the OV-1 overlay.

Preparation of the SD-1 security document and result [0132] The symmetrical double-sided laser-marking security film SF-1 was simultaneously laminated on one side to an opaque PETG 500 gm core, and on the other side against a PETG side, to an OV-1 overlay using a Laufferpress laminator LE with 10 minutes settings at 130 ° C, 125N, size A4, obtaining an SD-1 secured document.

[0133] The SD-1 secured document was laser marked with a test image containing a wedge of different gray levels (six 9 x 9 mm squares) using a Rofin RSM Powerline E (10 W) laser with 29 A and 22 kHz settings. The maximum optical density measured in square 6 (RGB values ​​= 12 in this area in the bitmap image) was 1.23.

[0134] After destruction of the laser-tagged document by delamination of the overlay and removal of layers between the 63 pm PETC and the 500 pm opaque PETG core, a duplicate image became visible in the outer laser-marking layer having an optical density of 0.07.