Description

Aqueous adhesive layer

Technical field of the Invention

[001] The invention relates to aqueous adhesive layers, in particular aqueous adhesive layers for PVC and PET substrates.

Background art for the invention

[002] Adhesive layers, also referred to as primers, are applied on various substrates to improve the adhesion of coatings, foils, sheets, etc. towards that substrate.

[003] Security cards, such as ID cards, drivers licenses, credit cards, etc. typically consist of an overlay laminated on a core support. The core support may carry visible information, such as alphanumeric information, logos and a picture of the card holder, and optionally also digital information stored in a magnetic strip or in an electronic chip (so-called smart card). Also information, which become visible upon exposure to radiation, UV or IR, may be provided. After lamination of the overlay on the core support, information may also be provided on the overlay.

[004] A principal objective of security cards is that they cannot be easily modified or reproduced in such a way that the modification or reproduction is difficult to distinguish from the original. Such modification usually involves de-laminating the overlay from the core support, altering the visible information on the card and re laminating, i.e. closing again, the card.

[005] The most widely used material in security cards is PVC (polyvinyl chloride), because of its low cost and its ease of printing and laminating. The biggest disadvantage of a PVC card body is the low durability, resulting in an effective lifetime of only 1 -3 years, much lower than the lifetime of the often expensive electronic chips. PC (polycarbonate) can be used for longer-life and more secure ID cards, but has a high production cost and a low resistance to torsion, scratching and chemicals. Other materials occasionally used for security card, like Teslin™and ABS are only suitable for very low-end or single-use cards.

[006] PET-G (Polyethylene Terephthalate Glycol) is a kind of amorphous polyester which has not been toughened like crystalline polyester but rather processed to become more compatible with standard PVC card manufacturing. Durability of PET-G cards is comparable to that of PVC cards.

[007] There is growing interest for crystalline polyethylene terephthalate (PET-C) especially for the overlay in security cards. PET-C is a material that is very durable and resistant to mechanical influences (flexion, torsion, scratches), chemical substances, moisture and temperature ranges. Untreated PET-C cannot be sealed or laminated to itself or to other materials, but requires additional adhesive coatings and layers to accomplish this.

[008] To avoid counterfeiting it is thus very important that the overlay has a very good adhesion to the core.

[009] As mentioned above, the overlay is typically laminated onto a core material, which is partly or even completely covered with ink. The adhesion of the overlay to such a core covered with ink may be different compared to the adhesion to a core having no ink on its surface.

[010] W02009/063058 (AGFA GEVAERT) discloses an overlay comprising a biaxially oriented polyester substrate and adhesion layer. The adhesion layer includes a polyester, a polyester-urethane or a copolymer of a chlorinated ethylene.

Although these overlays adhere well to a PVC, PC and PET-G core, they lose their adhesive properties when the core surface is printed completely or to a large extent with ink. Therefore a need exists to provide overlays based on crystalline polyethylene terephthalate (PET-C) that adhere well to both printed and unprinted PVC, PC and PET-G cores without requiring an extra ink receiving layer on the core body.

[01 1] EP-A 2567812 (AGFA GEVAERT) disclose an overlay comprising an adhesive layer of which the binder is a mixture of a first and a second polymer, wherein the first polymer is a copolymer comprising vinylacetate and vinylchloride and the second polymer is a copolymer of styrene, butadiene and methylmethacrylate or a copolymer of vinyl butyral, vinyl acetate and vinyl alcohol.

[012] Most prior art adhesive layers are solvent based layers, i.e. they are coated from solvent based compositions

[013] Aqueous adhesive layers, i.e. adhesive layers which are coated from an aqueous composition, are preferred for Health and Safety considerations. Also, drying efficiency of aqueous adhesive layers is typically higher compared to solvent borne adhesive layers. This results in more cost effective manufacturing of such aqueous adhesive layers.

[014] It is however often difficult with aqueous adhesive layers to combine good

adhesion properties with a sufficient water resistance. Summary of the invention

[015] It is an object of the present invention to provide an aqueous adhesive layer that has good adhesion properties and water resistance.

[016] The object of the invention is realized by the adhesive layer as defined in claim 1.

[017] It is another object of the invention to provide a security document that is difficult to counterfeit.

[018] That object is realized by the security document as defined in claim 12.

[019] Further objects of the invention will become apparent from the description

hereinafter.

Brief description of the drawings

[020] Figure 1 shows a schematic representation of an embodiment of a security

document according to the invention.

[021] Figure 2 shows a schematic representation of another embodiment of a security document according to the invention.

Detailed description of the invention

Definitions

[022] The terms“support” and“foil”, as used in disclosing the present invention, mean a self-supporting polymer-based sheet, which may be associated with one or more subbing layers. Supports and foils are usually manufactured through (co-)extrusion of polymer(s).

[023] The term“layer", as used in disclosing the present invention, is considered not to be self-supporting and is manufactured by coating it on a support or a foil.

[024] The term“lamella”, as used in disclosing the present invention, includes one or more foils and one or more layers.

[025] “PET” is an abbreviation for polyethylene terephthalate.

[026] “PET-G” is an abbreviation for polyethylene terephthalate glycol, the glycol

indicating glycol modifiers which are incorporated to minimize brittleness and premature aging that occur if unmodified amorphous polyethylene terephthalate (APET) would be used in the production of cards.

[027] “PET-C” is an abbreviation for crystalline PET, i.e. an oriented polyethylene

terephthalate. Such a polyethylene terephthalate support has excellent properties of dimensional stability. [028] The definitions of security features correspond with the normal definition as adhered to in the“Glossary of Security Documents - Security features and other related technical terms” as published by the Consilium of the Council of the European Union on August 25, 2008 (Version: v.10329.02.b.en) on its website: http://www.consilium.europa.eu/prado/EN/glossaryPopup.html.

Adhesive layer

[029] The aqueous adhesive layer comprises a first and a second binder, characterized in that the first binder includes a polyurethane-acrylate hybrid polymer wherein the polyurethane part has a glass transition temperature (Tg) from -75°C to 20°C and the acrylate part has a Tg from 65°C to 200°C, and the second binder is an aliphatic polyurethane.

[030] An aqueous adhesive layer is an adhesive layer provided from an aqueous

composition.

[031 ] An aqueous composition includes water as main solvent. The aqueous

composition preferably contains at least 70 wt% of water, more preferably at least 80 wt%, most preferably at least 90 wt% of water relative to the total weight of all solvents of the composition.

[032] The adhesive layer may further comprise other ingredients as long as it does not deteriorate its adhesion properties. Such ingredients include, for example surfactants to enhance the quality of the coating or colorants to provide an aesthetical or functional purpose. The adhesive layer may also comprise colloidal particles preferably being inorganic or organic colloidal particles. Preferred inorganic colloidal particles are colloidal silica particles. Suitable organic particles are crossl inked polystyrene particles.

[033] The adhesive layer may also comprise UV blocking agents, thickeners, antistatic agents, biocides, light stabilizers, other binders, solvents, etc.

[034] The aqueous composition may comprise other solvents. A particularly preferred solvent is 2,5,7,10 Tetraoxaundecane (TOU). It has been observed that the addition of TOU may improve the adhesion. The ratio of the amounts of water and TOU is preferably 85wt%/15wt%, more preferably 90wt%/10wt%, most preferably 95wt%/5wt% all relative to the total weight of the solvents.

[035] The adhesive layer is preferably provided on a support by coating. Any

conventional coating technique, such as dip coating, knife coating, extrusion coating, spin coating, slide hopper coating and curtain coating may be used for this purpose. [036] However, adhesive layer may also be provided on a support using a spraying or a jetting device, such as an inkjet print head. Using an inkjet print head allows the composition to be provided according to a pattern or image. The composition may also be provided using a screen printing device.

[037] The coated adhesive layer is then preferably dried to remove water and other solvents from the layer. In the drying process, heat is supplied to evaporate the water from the coated layer. Also, when the drying temperature is above the film forming temperature of the latex particles, these will coalesce to form a continuous film.

[038] The drying temperature may be optimized to obtain maximal adhesion properties.

Preferred drying temperatures are between 40°C and 160°C.

[039] In the manufacturing process of a support, the adhesive layer can be applied inline or offline. In an online process, there is the opportunity to carry out, after coating the adhesive layer onto the support, a stretching of the support including the adhesive layer. For example, when the support is a biaxially stretched PET film (BOPET film), the adhesive layer may be applied after a first stretching, preferably the longitudinal stretching, but before the second stretching, preferably the transversally stretching.

[040] The adhesive layer may also be applied inline after biaxially stretching the

support.

[041] The dry coating weight of the adhesive layer is preferably between 1 g/m ² and 30 g/m ² . For offline coatings the dry coating weight is preferably between 5 and 30 g/m ² , for inline coatings the dry coating weight is preferably between 1 and 10 g/m ² .

Polyurethane - acrylic hybrid polymers

[042] In the aqueous composition from which the adhesive layer is prepared, the

binders are present as latexes. A latex referred to herein is a polymer particle dispersion in an aqueous medium.

[043] Blends of polyurethane polymers and acrylic polymers do not always offer the best solution, as the polyurethane polymer and the acrylic polymer are not always compatible, especially at higher temperatures such as the lamination

temperatures used to prepare security cards.

[044] Instead of blending the polyurethane polymer with an acrylic polymer, it is

possible however to make hybrid polymers where the urethane and the acrylic are contained in the same particle. [045] These hybrids can be made for example by swelling a polyurethane with acrylic monomers and then, using the emulsion polymerization process, produce the acrylic polymer inside the polyurethane particle. In the hybrid particles, the urethane and acrylic polymer are intimately mixed.

[046] In a more preferred embodiment, monomers that have a functional group that is reactive towards groups present on the polyurethane polymer are used to covalently graft the acrylic polymer onto the polyurethane.

[047] Also functional monomers for crosslinking after film formation, such as carbonyl- functional monomers, can be incorporated into the hybrid polymer resulting in self-crosslinking, urethane-acrylic dispersions.

[048] It has now been found that the adhesion properties of adhesive layer containing polyurethane-acrylate hybrid polymers maybe optimized by selecting the proper polyurethane and acrylate parts for the hybrid polymer.

[049] Very good results were obtained with polyurethane-acrylate hybrid polymers of which the polyurethane part has a glass transition temperature (Tg) from -75°C to 20°C, preferably from -60 °C to 5°C, more preferably from -50°C to -5°C; and of which the acrylate part has a Tg from 65° to 200°C, preferably from 75°C to 175°C, more preferably from 85°C to 150°C.

[050] Examples of such polyurethane-acrylate hybrid polymers are Neorez R620 and Neopac R9020, both supplied by DSM Coating Resins, Waalwijk, The

Netherlands.

Aliphatic polyurethane

[051] A polyurethane is a polymer composed of organic units joined by carbamate (urethane) links.

[052] Polyurethanes are typically produced by reacting an isocyanate containing two or more isocyanate groups per molecule with a polyol containing on average two or more hydroxyl groups per molecule in the presence of a catalyst or by activation with ultraviolet light.

[053] The properties of a polyurethane are greatly influenced by the types of

isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with lots of crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. The crosslinking present in polyurethanes means that the polymer consists of a three- dimensional network and molecular weight is very high. In some respects a piece of polyurethane can be regarded as one giant molecule. One consequence of this is that typical polyurethanes do not soften or melt when they are heated; they are thermosetting polymers. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow

polyurethanes to have the very wide range of properties that make them such widely used polymers.

[054] Polyurethanes obtained with aliphatic polyisocyanates are referred to as aliphatic polyurethanes while a polyurethanes obtained with aromatic polyisocyanates are rerferred to as aromatic polyurethanes.

[055] A disadvantage of aromatic polyurethanes is typically yellowing when exposed to visible light. Such yellowing is unacceptable when used in security cards.

[056] The most important aliphatic and cycloaliphatic isocyanates are 1 ,6-hexa- methylene diisocyanate (HDI); 1 -isocyanato-3-isocyanatomethyl-3, 5, 5-trimethyl- cyclohexane (isophorone diisocyanate, IPDI); 4,4'-diisocyanato dicyclo- hexylmethane (H12MDI or hydrogenated MDI); and 3-bis(isocyanatomethyl) cyclohexane (H6XDI).

[057] Polyols can be polyether polyols, which are made by the reaction of

epoxides with an active hydrogen containing compounds. Polyester polyols are made by the polycondensation of multifunctional carboxylic acids and

poly hydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products. Specialty polyols include polyamide polyols, polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols.

[058] As mentioned earlier, it is the length of the polyol chain and the functionality that contribute much to the properties of the final polymer. Polyols used to make rigid polyurethanes have molecular weights in the hundreds, while those used to make flexible polyurethanes have molecular weights up to ten thousand or more.

[059] Preferred aliphatic polyurethanes are based on polyester polyols, polyether

polyols and polycarbonate polyols. Polyester polyols can be based on adipic acid and hexane diol. Preferred polyether polyols are based on polytetrahydrofuran or polytetramethylglycol and preferred polycarbonate polyols are based on hexane diol and dimethyl carbonate. [060] Particularly preferred aliphatic polyurethanes are based on a polyester polyol, the polyester polyol based on adipic, terephthalic, isophthalic and/or orthophthalic esters.

Laser additives

[061] Laser marking, i.e. writing information with a laser, is often used to provide

security information on a security card. Preferably the information is laser marked inside the security card making it more difficult to counterfeit.

[062] When the support of the overlay is transparent for the laser radiation, laser

marking may be carried out in the adhesive layer.

[063] The adhesion layer may contain a laser additive, which renders the security document more sensitive to laser radiation. A preferred laser radiation used to laser mark is infrared radiation, more preferably near infrared laser radiation.

[064] It is however important that the laser additive does not impart unwanted

background colouration to the security document. This may realized by using only small amounts of the laser additive and/or selecting laser additives that has minimal absorption in the visible region of the spectrum.

[065] Suitable laser additives include antimony metal, antimony oxide, carbon black, mica (sheet silicate) coated with metal oxides and tin-antimony mixed oxides. In WO 2006/042714, the dark coloration of plastics is obtained by the use of additives based on various phosphorus-containing mixed oxides of iron, copper, tin and/or antimony.

[066] Suitable commercially available laser additives include mica coated with

antimony-doped tin oxide sold under the trade name of Lazerflair™ 820 and 825 by MERCK; copper hydroxide phosphate sold under the trade name of

Fabulase™ 322 by BUDENHEIM; aluminium heptamolybdate sold under the trade name of AOM™ by HC STARCK; and antimony-doped tin oxide pigments such as Engelhard Mark-it™ sold by BASF.

[067] In a preferred embodiment the laser additive is carbon black. This avoids the use of heavy metals in manufacturing these security documents. Heavy metals are less desirable from an ecology point of view and may also cause problems for persons having a contact allergy based on heavy metals.

[068] Suitable carbon blacks include Special Black 25, Special Black 55, Special Black 250 and FarbrussT ^M FW2V all available from EVONIK; Monarch™ 1000 and Monarch™ 1300 available from SEPULCHRE; and Conductex™ 975 Ultra Powder available from COLUMBIAN CHEMICALS CO. [069] The use of carbon black pigments as laser additives may lead to an undesired background colouring of the security document precursor. For example, a too high concentration of carbon black in the adhesive layer of the security document having a white core may result in grey security documents. For that reason it is preferred to use carbon black particles having a numeric average particle size smaller than 300 nm, preferably between 5 nm and 250 nm, more preferably between 10 nm and 100 nm and most preferably between 30 nm and 60 nm. The average particle size of carbon black particles can be determined with a

Brookhaven Instruments Particle Sizer BI90plus based upon the principle of dynamic light scattering.

[070] Infrared absorbing dyes having substantial no absorption in the visible region may also be used as laser additives. Such dyes, as disclosed in for example WO2014/057018 (Agfa Gevaert), are particular suitable for use with a NIR laser, for example with a 1064 nm laser.

Overlay

[071] In a preferred embodiment, the overlay (10) comprises an adhesive layer (200) as described above provided on a support (100).

[072] The overlay according to this embodiment is then preferably laminated on a core (300) thereby forming the security card.

[073] The overlay may be laminated on one or both sides of the core, as shown in Figures 1 and 2.

[074] The overlay may however include additional layers or sheets, for example a subbing layer, an outer layer or a laser markable layer as described below.

Support

[075] The overlay preferably comprises a support (Figure 1 , 100), more preferably a transparent polymeric support,

[076] Suitable transparent polymeric supports include cellulose acetate propionate or cellulose acetate butyrate, polyesters, polyamides, polycarbonates, polyimides, polyolefins, polyvinylchlorides, polyvinylacetals, polyethers and poly- sulphonamides.

[077] Examples of suitable polyester substrates are based on polyesters like

polyethylene terephthalate (PET), polyethylene naphthalate (PEN),

(co)polyesters based on cyclohexyldimethanol (CHDM) (PETG), (co) polyesters based on 2,5-furandicarboxylic acid (FDCA) (REF), copolyesters based on isosorbide and polylactic acid (PLA).

[078] The support is preferably an oriented polyester support. Orienting a polyester support is achieved by stretching the support in a longitudinal direction, a transversal direction or both directions. The highest crystallinity of the polyester support is obtained by biaxia!ly stretching.

[079] The polyester is preferably biaxially stretched with a stretching factor of at least 2.0, more preferably at least 3.0 and most preferably a stretching factor of about 3.5. The temperature used during stretching is preferably at least 100°C, more preferably at least 140°C and most preferably about 160°C.

[080] The oriented polyester support is preferably a polyethylene terephthalate or a polyethylene napthalate support.

[081] In the most preferred embodiment, the oriented polyester support is a biaxially stretched polyethylene terephthalate support. Such a polyethylene terephthalate support has excellent properties of dimensional stability and is very durable and resistant to scratches and chemical substances.

[082] The biaxially stretched polyethylene terephthalate substrate should be sufficiently thick to be self-supporting, but thin enough to be flexed, folded or creased without cracking. Preferably, the biaxially stretched polyethylene terephthalate substrate has a thickness of between about 7 pm and about 100 pm, more preferably between about 10 pm and about 90 pm, most preferably between about 25 pm and about 80 pm.

[083] The manufacturing of polyester foils and supports is well-known in the art of preparing suitable supports for silver halide photographic films. For example,

GB 81 1066 (ICI) teaches a process to produce biaxially oriented polyethylene terephthalate (BOPET) foils and supports.

[084] The support preferably comprises subbing layers to improve the adhesion

between the support and layers provided thereon.

Subbing Layers

[085] The support (100) preferably comprises subbing layers to improve the adhesion between the support and layers provided thereon.

[086] Useful subbing layers for this purpose are well known in the photographic art and include, for example, polymers of vinylidene chloride such as vinylidene chloride/acrylonitrile/acrylic acid terpolymers or vinylidene chloride/methyl acrylate/itaconic acid terpolymers. [087] Suitable vinylidene chloride copolymers include: the copolymer of vinylidene chloride, N-tert.-butylacrylamide, n-butyl acrylate, and N-vinyl pyrrolidone

(e.g.70:23:3:4), the copolymer of vinylidene chloride, N-tert.-butylacrylamide, n- butyl acrylate, and itaconic acid (e.g. 70:21 :5:2), the copolymer of vinylidene chloride, N-tert.-butylacrylamide, and itaconic acid (e.g. 88:10:2), the copolymer of vinylidene chloride, n-butylmaleimide, and itaconic acid (e.g. 90:8:2), the copolymer of vinyl chloride, vinylidene chloride, and methacrylic acid (e.g.

65:30:5), the copolymer of vinylidene chloride, vinyl chloride, and itaconic acid (e.g. 70:26:4), the copolymer of vinyl chloride, n-butyl acrylate, and itaconic acid (e.g. 66:30:4), the copolymer of vinylidene chloride acrylate, and itaconic acid (e.g. 80:18:2), the copolymer of vinylidene chloride, methyl acrylate, and itaconic acid (e.g.90:8:2), the copolymer of vinyl chloride, vinylidene chloride, N- tert.-butylacrylamide, and itaconic acid (e.g. 50:30:18:2). All the ratios given between brackets in the above-mentioned copolymers are ratios by weight.

[088] In a preferred embodiment, the support is provided with a subbing layer including a copolymer selected from the group consisting of a hydroxyl-functional, partially- hydrolyzed vinyl chloride/vinyl acetate copolymer and a polyester-urethane.

[089] In a particular preferred embodiment, the support is provided with a subbing layer including a binder based on a polyester-urethane copolymer.

[090] In a more preferred embodiment, the polyester-urethane copolymer is an ionomer type polyester urethane, preferably using polyester segments based on terephthalic acid and ethylene glycol and hexamethylene diisocyanate.

[091] Suitable polyester-urethane copolymers are Hydran APX101 H, Hydran AP40N and Hydran AP20, all from DIC Europe GmbH or mixtures of different polyester- urethanes or mixtures of polyester-urethanes with other polymers.

[092] The application of subbing layers is well-known in the art of manufacturing

polyester supports for silver halide photographic films. For example, the preparation of such subbing layers is disclosed in US3649336 (AGFA) and GB 1441591 (AGFA).

[093] In a preferred embodiment, the subbing layer has a dry thickness of no more than 2 pm or preferably no more than 200 mg/m2.

[094] A preferred method of providing the subbing layers on the support is disclosed in EP-A 2374602 an EP-A 2567812 both from Agfa Gevaert.

[095] A preferred method comprises the steps of a) stretching a polyester substrate in either a longitudinal or a transversal direction; b) coating and drying a subbing layer on the stretched polyester substrate ; c) stretching the coated polyester substrate in the longitudinal or transversal direction not selected in step a) in order to obtain a coated biaxially stretched polyester substrate having a subbing layer.

Outer layer

[096] The overlay may also comprise an outer layer provided at a side of the support opposite to the side of the support upon which the adhesive layer is provided.

[097] Such an outer layer is preferably an ink receiving layer or a receiver layer for Dye Diffusion Thermal Transfer (D2T2) printing.

[098] The presence of such a layer enables the addition of information or other security information to the security document by for example inkjet printing or D2T2 printing.

Laser markable layer

[099] To provide laser marking properties to the overlay, an additional laser markable layer may be provided. Such a laser markable layer is preferably provided on the adhesive layer.

[0100] Any laser markable composition may be used to form the laser markable layer.

[0101] According to one embodiment, the laser markable layer is capable of forming a black colour upon exposure to infrared radiation by carbonization of ingredients, typically the binder, of the laser markable layer.

[0102] Such a laser markable layer, disclosed in for example EP-A 2335967, preferably comprises polymers selected from polycarbonate (PC), polybutylene

terephthalate (PBT), polyvinyl chloride (PVC), polystyrene (PS) and copolymers thereof, such as e.g. aromatic polyester-carbonate and acrylonitrile butadiene styrene (ABS). An optothermal converting agent, which absorbs infrared radiation and converts that radiation into heat, may be added to the laser markable layer to increase the marking density upon exposure to such infrared radiation.

[0103] Other laser markable compositions that may be used are those disclosed in for example W02002/074548, comprising a binder and an oxyanion of a multivalent metal, such as ammonium octamolybdate (AOM), which may be laser marked using a CO2 laser; W02006/018640 and WO2012/1 14121 , both comprising a diacetylene compound and which may be laser marked using a UV laser;

WO2007/141522 comprising a marking component, for example AOM, and a metal salt, for example reduced indium oxide, that absorbs laser irradiation at 780 to 2500 nm and may be laser marked using a NIR laser. [0104] Preferred! laser markable compositions include a leuco dye. Such laser markable compositions are disclosed in for example EP-A 2648920. A leuco dye is a substantially colourless compound, which may react with for example a colour developing agent to form a coloured dye. The reaction may be triggered by exposure to laser irradiation. Depending on the type of leuco dyes, or mixture of leuco dyes, any colour may be obtained.

[0105] The colour laser markable layers may comprise an optothermal converting agent such as an infrared absorbing dye (IR dye) or an infrared absorbing pigment (IR pigment), both absorbing the IR radiation and converting it into heat.

[0106] Preferred laser markable compositions comprises a leucodye, an optothermal converting agent and a colour developing agent or colour developing agent precursor. The composition may further comprise an acid scavenger and a UV absorber.

[0107] Aqueous laser markable compositions, compared to solvent based compositions, are preferred for health and safety reasons.

[0108] Aqueous laser markable compositions are disclosed in for example for example W02006/052842, W02008/030428 and WO2014/124052.

[0109] Particular preferred aqueous laser markable compositions are disclosed in the applications PCT/EP2016/061069 (filed 18-05-2016) and PCT/EP2016/060533 (filed on 1 1 -05-2016).

Core

[01 10] The security document preferably comprises a core.

[01 1 1] The core can be transparent, translucent or opaque.

[01 12] The core is preferably opaque. The advantage of an opaque core, preferably of a white colour, is that any information of the security document is more easily readable and that a colour image is more appealing by having a white

background.

[01 13] Suitable polymers for the core of the security document include cellulose acetate propionate or cellulose acetate butyrate, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, polycarbonates, polyimides, polyolefins, polyvinyl chlorides, polyvinylacetals, polyethers and polysulphonamides.

[01 14] Preferred polymeric cores are based on polycarbonate (PC), polyvinylchloride (PVC), and polyethylene terephthalate (PET). [01 15] Other preferred cores are based on so-called synthetic papers such as Synaps™ or Teslin® synthetic papers, respectively from Agfa Gevaert and Teslin.

[01 16] The core may also be based on paper, such as polyethylene or propylene coated paper.

[01 17] The core may be a single component extrudate, but can also be co-extrudate.

[01 18] Examples of suitable co-extrudates are PET/PETG and PET/PC.

[01 19] Instead of a coloured or whitened support, an opacifying layer can be coated onto a transparent support. Such opacifying layer preferably contains a white pigment with a refractive index greater than 1.60, preferably greater than 2.00, and most preferably greater than 2.60. The white pigments may be employed singly or in combination. Suitable white pigments include C.l. Pigment White 1 , 3, 4, 5, 6, 7, 10, 1 1 , 12, 14, 17, 18, 19, 21 , 24, 25, 27, 28 and 32. Preferably titanium dioxide is used as pigment with a refractive index greater than 1.60. Titanium oxide occurs in the crystalline forms of anatase type, rutile type and brookite type. In the present invention the rutile type is preferred because it has a very high refractive index, exhibiting a high covering power.

[0120] Methods to obtain opaque polyethylene terephthalate and biaxially oriented films thereof of have been disclosed in, e.g. US 2008238086 (AGFA).

Security Document

[0121] Preferred security documents are security cards, which are widely used for

various applications such as identification purposes (ID cards) and financial transfers (credit cards).

[0122] The security document may include an electronic chip and optionally an antenna.

[0123] In a preferred embodiment the security document is a so-called radio frequency identification card or RFID-card.

[0124] The security document may contain various security features, such as anti-copy patterns, guilloches, endless text, miniprint, microprint, nanoprint, rainbow colouring, 1 D-barcode, 2D-barcode, coloured fibres, fluorescent fibres and planchettes, fluorescent pigments, kinegrams™, overprint, relief embossing, perforations, metallic pigments, magnetic material, Metamora colours, microchips, RFID chips, images made with OVI (Optically Variable Ink) such as iridescent and photochromic ink, images made with thermochromic ink, phosphorescent pigments and dyes, OVD’s, watermarks including duotone and multitone watermarks, ghost images and security threads

[0125] A combination with one of the above security features increases the difficulty for falsifying a security document.

EXAMPLES

Materials

[0126] All materials used in the following examples were readily available from standard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS (Belgium) unless otherwise specified. The water used was deionized water.

[0127] Joncryl® U4190 is a‘NMP’ free aliphatic polyurethane dispersion available from BASF.

[0128] NeoRez® R620 is a polyurethane-acrylate hybrid polymer available from DSM Coating Resins.

The polyurethane part in NeoRez 620 is a polyether urethane based on polytetrahydrofuran and 12H-MDI (hexamethylene diisocyanate). The acrylate part is based on a methyl methacrylate homo- or copolymer. The Tg’s of the polyurethane part and the acrylate part are respectively appr. -7°C and 110°C.

[0129] NeoPac™ R9020 is a polyurethane-acrylate hybrid polymer available from DSM Coating Resins..

The polyurethane part of NeoPac R9020 is a polyester urethane prepared from a hexane diol - adipic acid based polyester and H12MDI = hydrogenated MDI (4,4'-diisocyanato dicyclo-hexylmethane). The acrylate part is based on a methyl methacrylate/butyl methacrylate copolymer. The Tg’s of the polyurethane part and the acrylate part are respectively appr. -49°C and 154°C.

[0130] A!berdingk is a polyurethane-acrylate hybrid polymer available as Alberdingk® APU 10140 from Alberdingk Boley.

Alberdingk APU 10140 is a polyurethane-acrylate hybrid polymer. The polyurethane part is a polyester urethane prepared from a hexane diol - adipic acid based polyester and 12H-MDI (4,4'-diisocyanato dicyclo-hexylmethane). The acrylic part is based on a methyl methacrylate/butyl methacrylate/styrene copolymer. The Tg’s of the polyurethane part and the acrylate part are respectively -30°C and 59°C. [0131] Daotan is an aliphatic polycarbonate polyurethane available as Daotan®

TW6450/30WA from Allnex. Daotan® TW6450/30WA contains polycarobante segments based on 1 ,6-hexane diol and dimethyl carbonate.

[0132] NeoPac™ PU480 is a polyurethane-alkyd hybrid polymer available from DSM Coating Resins.

[0133] Set Aqua 6510 is a styrene acrylic polymer available from Nuplex.

[0134] Joncryl® 678 is a styrene/alphamethyl styrene/acrylic acid copolymer available from BASF.

[0135] Viacryl is styrene/acrylic copolymer available as Viacryl® SC 6828w/45WA from Cytec.

[0136] NeocryKED XK-12 is an acrylic copolymer available from DSM Coating Resins.

[0137] Tivida® FL2500 is a fluorosurfactant available from Merck.

Preparation of subbed polyester PET-1

[0138] A coating composition SUB-1 was prepared by mixing the components according to Table 1 using a dissolver.

Table 1

[0139] After stretching a 1 100 pm thick polyethylene terephthalate substrate

longitudinally, the coating composition SUB-1 was coated onto the longitudinally stretched PET and dried.

[0140] The coated longitudinally stretched PET was then transversally stretched to produce a 63 pm thick transparent and glossy subbed biaxially stretched polyethylene terephthalate substrate PET-1.

[0141] The dry thickness of the subbing layer coated from SUB-1 was 211 mg/m ² . Methods

Adhesion

[0142] An overlay (OL) was prepared by hand coating an adhesive layer at 45°C onto the subbed polyester PET-1 at a wet coating thickness of 30 pm. The coating was subsequently dried at 130°C during 15 minutes.

[0143] The overlay was then laminated onto a PVC or PETG core (thickness 350 pm) using an Oasys laminator or a Lauffer laminator. The lamination times, pressures and temperatures were optimized for the different cores and overlays. Both plain or preprinted cores (using UV waterless offset printer and Supra UV WL Process Inks) were used.

[0144] After lamination, the security cards were then cut in a standard format for ID cards.

[0145] Dry adhesion was tested through a simple knife resistance test: a pen knife was used to slice the overlay and to attempt to peel away the overlay from the core material. If this was successfully removed with no, or very little resistance a quantitative analysis of 0 would be given to the dry adhesion of that product. Should the overlay not be able to be detached or damaged, a grade of 1 would be awarded to the dry adhesion. A scale ranging from 0 to 1 was applied for those cards with some resistance or minor detachment.

[0146] This test was repeated after 24 hours water submersion. This would often result in easier delaminable cards. Finally, a further adhesion test carried out was hot plate delamination where the card was placed on a heated surface for a few seconds before the overlay was attempted to be removed following the same technique and quantification as outlined for the dry adhesion tests.

Glass Transition Temperature

[0147] Glass Transition Temperatures (Tg) were measured by Differential Scanning Calorimetry (DSC). The polymer dispersions were pre-dried under vacuum at 50°C. A conventional heat (-80 to 180 °C) /cool (180 to -80°C)/heat (-80 to 180°C) DSC under Nitrogen Flow was used. The heating and cooling rate was 20°C/min. The Tg was determined in the second heating run.

Example 1

[0148] The adhesive layers were coated from an aqueous coating solution as described above. The dry weight of the ingredients are shown in Table 2 Table 2

[0149] The adhesion of the adhesive layers towads PETG and PCV was evaluated as described above. The results are shown in Table 3. The coating quality of some adhesive layers was too bad (due to non-compatibility of the binders) to evaluate the adhesion. These are indicated in Table 3 as Not Applicable (NA).

Table 3

[0150] The inventive adhesive layers INV-01 and INV-02 comprise respectively NeoRez R620 and NeoPac R9020 as polyurethane-acrylate hybrid polymer. These polyurethane-acrylate hybrid polymers have a Tg of the polyurethane part of lower than 20°C and a Tg of the acrylate part higher than 40°G.

[0151] The comparative adhesive layer COMP-01 also comprise a polyurethane-acrylate hybrid polymer. However, the Tg’s of the polyurethane and the acrylate parts are not within the claimed range. The Tg of the acrylic part is lower than 65°C.

[0152] The comparative adhesive layer COMP-02 also comprise a hybrid polymer,

however a polyurethane-alkyd hybrid polymer. The polyurethane part is a polyester urethane prepared from a phthalic acid anhydride based polyester polyol and isophorondiisocyanate (IPDI). The alkyd part is based on palmitic acid, stearic acid and oleic acid based esters. The Tg’s of the polyurethane part and the alkyd part are respectively -31 °C and 1 1 °C.

[0153] The comparative adhesive layer COMP-08 only comprises the aliphatic

polyurethane.

[0154] The comparative adhesive layers COMP-09 and 10 comprise only the

polyurethane-acrylate hybrid polymers according to the invention.