Temperature-resistant laser-markable film, use and method of production

Abstract

Laser-markable film for use in the automotive industry, comprising - a contrast layer based on a cured acrylate lacquer composition, wherein the cured acrylate lacquer composition is based on a composition comprising ◯ 30 to 80 wt.% of a trifunctional oligomer A; ◯ 0 to 20 wt.% of a trifunctional monomer B; ◯ 1 to 30 wt.% of a difunctional monomer C; ◯ and 2 to 40 wt.% of a colouring pigment; - an engraving layer arranged above the contrast layer, characterized in that the film further - at least one adhesive layer arranged beneath the contrast layer, wherein the adhesive layer is a latent-reactive adhesive layer comprising a thermoplastic component having a melting temperature T(melt) of 35 °C ≤ T(melt) ≤ 90 °C and containing functional groups that can react with isocyanate, and an isocyanate-containing component that is dispersed in particulate form, in particular finely divided particulate form, in the thermoplastic component and is blocked, microencapsulated or deactivated in the region of the particle surface, wherein the particles have a melting temperature T(melt) of 40 °C ≤ T(melt) ≤ 120 °C, and wherein T(melt) ≥ T(melt), wherein the latent-reactive adhesive layer has a layer thickness of 20 µm to a maximum of 35 µm, and wherein the film meets the requirements of GB Standard GB / T 25978 for long-term temperature resistance (150°C, 1,600 hours).

Description

[0001] The present invention relates to a laser-writable film for use in the automotive industry, comprising a contrast layer based on a cured acrylate coating composition, wherein the cured acrylate coating composition is based on a composition comprising 30 to 80 wt. % of a trifunctional oligomer A; 0 to 20 wt. % of a trifunctional monomer B; 1 to 30 wt. % of a difunctional monomer C; and 2 to 40 wt. % of a coloring pigment; and an engraving layer arranged above the contrast layer, as well as laser-writable labels produced from the film. The present invention further relates to a process for producing a laser-writable film and the use of the films and labels produced.

[0002] The labeling of objects is becoming increasingly important. For example, in the automotive industry, conventional printed labels are being replaced by laser-markable labels. Laser-markable labels are used to place information and instructions such as tire pressure or fuel type on various components of motor vehicles. In addition to such instructions, laser-markable labels can also contain security information such as chassis and vehicle identification numbers. In the event of theft or an accident, such labels allow the vehicle and its production stages to be identified. The use of special security features such as holograms, permanent UV imprints (footprints) on the substrate to which the label was adhered, and the targeted selection of materials for laser-markable labels serve to make counterfeiting of the material more difficult and to detect tampering attempts.

[0003] Laser-markable labels are known from the prior art. These can be written on quickly, allow for high contrast of inscribed characters, and ensure high temperature resistance over short periods of time. DE 81 30 861 U1 discloses multilayer labels containing a thin and a thick lacquer layer that can withstand high temperatures over short periods of time. DE 100 48 665 A1 and DE 101 42 638 A1 describe laser-markable labels that can also withstand high temperatures over short periods of time.

[0004] However, when exposed to prolonged temperature influences, one or more layers of state-of-the-art labels shrink. It is suspected that this shrinkage is caused by a change in the surface area of one or more layers. The shrinkage of one or more layers within known labels manifests itself in the labels detaching near their edges. This detachment in itself represents a security problem in the case of sensitive data such as vehicle identification numbers, as the labels could potentially be removed completely undamaged and without leaving any residue. On the other hand, this shrinkage can lead to tension within the label if the expansion behavior of different layers within a label behaves differently as the temperature rises, or if chemical processes lead to shrinkage within a layer.This can be caused by aging processes, such as cross-linking reactions. Such stresses lead to cracking within the labels, which, on the one hand, does not sufficiently meet aesthetic requirements and, on the other, could falsely lead to suspicions of attempted tampering.

[0005] Given the increasing demands on the temperature resistance of laser-markable labels over extended periods, there was a need for improved films to serve as the starting material for corresponding laser-markable labels. All laser-markable labels and films known from the state of the art only partially met the increasing demands for tamper-evident protection and high temperature resistance. Particularly at high temperatures, the existing labels experienced a loss of dimensional stability in one or more layers, which manifested itself in shrinkage. This led to the associated edge lifting of the labels and the formation of cracks.

[0006] In this context, DE 10 2011 080 883 A1 discloses laser-markable films that can serve as starting material for the production of dimensionally stable laser-markable labels and whose chemical resistance is maintained or improved compared to prior art labels. Such films have a contrast layer based on a cured acrylate lacquer composition comprising 30 to 80 wt.% of a trifunctional oligomer A, 0 to 20 wt.% of a trifunctional monomer B, 1 to 30 wt.% of a difunctional monomer C, and 2 to 40 wt.% of a coloring pigment.

[0007] EP 2 179 857 A1 teaches layer structures for laser-engraved ID cards.

[0008] For the application of the film or the labels produced from it, the laser-markable film has a pressure-sensitive adhesive layer beneath the contrast layer. Suitable pressure-sensitive adhesives include all typical adhesives that exhibit high bond strength and tack, particularly acrylic adhesives, such as resin-modified acrylic adhesives, natural rubber adhesives, and synthetic rubber adhesives.

[0009] It has now been shown that the adhesives used for films and labels according to the state of the art are unfortunately not suitable for bonding them reliably and permanently. Especially on structured substrates, where a relatively thick layer of adhesive must be applied to achieve sufficiently good adhesion, it has been shown that, due to the thickness of the adhesive layer, it is possible to remove the film or label by cutting the adhesive layer without destroying it. This means that counterfeit protection cannot be guaranteed. Furthermore, the state-of-the-art films were unable to meet the long-term temperature resistance requirements of the automotive industry.

[0010] The present invention was therefore based on the object of providing a laser-markable film that can be easily and securely bonded to various substrates. However, the film is not forgery-proof and cannot be removed from the substrate without causing damage. The film must also meet the requirements of the automotive industry with regard to long-term temperature resistance (150°C, 1,600 hours) and be chemical-resistant, particularly to fluids regularly used in the automotive industry, such as gasoline or brake fluid.

[0011] This object is achieved in a film of the type mentioned at the outset in that it further comprises at least one, preferably precisely one, adhesive layer arranged beneath the contrast layer, wherein the adhesive layer is a latently reactive adhesive layer comprising a thermoplastic component having a melting temperature T(melt) of 35 °C ≤ T(melt) ≤ 90 °C and containing functional groups that can react with isocyanate, and an isocyanate-containing component that is present in particulate, in particular finely divided particulate, dispersed in the thermoplastic component and blocked, microencapsulated or substantially deactivated in the region of the particle surface, wherein the particles have a light-off temperature T(melt) of 40 °C ≤ T(melt) ≤ 120 °C, and wherein T(melt) ≥ T(melt). Finely divided particulate means having a particle size distribution with d 50< 50 µm, whereby the particle size distribution is preferably < 15 µm.

[0012] Such a film meets the requirements for high levels of anti-counterfeiting protection, as non-destructive removal from the substrate is not possible; long-term temperature resistance, meaning no peeling, shrinkage, cracking, or similar phenomena can be observed even at temperatures of 150 °C for 1,600 hours; and chemical resistance. This makes the film ideally suited for use as a counterfeit-proof, laser-markable film in various sectors, particularly in the automotive industry.

[0013] In this sense, chemical resistance means, for example, resistance to hydrocarbons such as motor vehicle fuels and solvents that could potentially come into contact with the labels.

[0014] For the purposes of this application, T(melt) is the melting temperature of the thermoplastic component and T(initiation) is the temperature at which the isocyanate groups of the particles dispersed in the thermoplastic component are enabled to react with the functional groups of the thermoplastic polyurethane (for example because they are distributed in the matrix with the thermoplastic polyurethane). In the case of blocked isocyanate groups, T(initiation) is the deblocking temperature; in the case of microencapsulation, T(initiation) is the release of isocyanate from the microcapsules (for example by melting the microcapsule shell); and in the case of isocyanates deactivated in the region of the surface of the isocyanate particles, T(initiation) is the melting of the isocyanate particles. For the purposes of this invention, all blocked, microencapsulated orIsocyanate-containing systems deactivated in the area of the particle surface that meet the T(light-off) specifications are conceivable. The thermoplastic polyurethanes and the isocyanate-containing component are preferably dispersible in an aqueous medium or dispersed in an aqueous medium.

[0015] Melting temperatures are determined using differential scanning calorimetry (DSC) according to DIN 53765-B-10 (1994). T(onset) is also determined using differential scanning calorimetry (DSC). The exothermic signal in the thermogram of the first heating curve at a heating rate of 10 K / min, which corresponds to the reaction of the isocyanate groups, is evaluated. The onset temperature of this signal is used as T(onset).

[0016] In a preferred embodiment of the present invention, the composition on which the acrylate coating composition is based comprises 50 to 60 wt.%, preferably 52 to 58 wt.% of the trifunctional oligomer A, 5 to 15 wt.%, preferably 8 to 12 wt.% of the trifunctional monomer B, and 5 to 15 wt.%, preferably 8 to 12 wt.% of the difunctional monomer C. The amount of the coloring pigment within the acrylate coating compositions of preferred embodiments depends on the type of material used. In the case of carbon black as the coloring pigment, for example, 2 to 7 wt.% is preferred, while in the case of TiO2, 15 to 40 wt.%, particularly preferably 22 to 28 wt.%, are preferably used. The trifunctional oligomer A, the trifunctional monomer B, and the difunctional monomer C are also referred to below as component A, component B, and component C, respectively.Surprisingly, it has been found that compositions containing components A, B and C as well as the coloring pigment in the stated amount result in particularly temperature-resistant cured acrylic coating compositions.

[0017] The engraving layer is a layer arranged above the contrast layer that can be inscribed using a single laser beam or multiple laser beams. During this inscription process, the engraving layer is ablated at the locations onto which a laser beam with appropriate energy is directed. With sufficient energy input, the engraving layer is completely removed locally, so that it is translucent at these locations. It is also conceivable for the engraving layer to be only partially ablated in some locations, resulting in an opaque appearance of the engraving layer at these locations. The engraving layer is preferably a lacquer layer that can be applied using a printing process. Preferred examples of corresponding printing lacquer layers include printing lacquers based on electron beam-curable or UV-curable acrylate lacquers.In an alternative embodiment of the invention, the engraving layer consists of a thin metal layer. The engraving layer preferably has a thickness of 1 to 30 µm, preferably 1 to 20 µm, particularly preferably 1 to 10 µm. If the thickness of the engraving layer is within this range, it is possible to provide a particularly temperature-resistant laser-inscribable film. Compared to the contrast layer, which preferably has a thickness of 20 to 300 µm, preferably 40 to 200 µm, particularly preferably 60 to 150 µm, the thickness of the engraving layer is preferably, for example, 10% of the thickness of the contrast layer or less.

[0018] The contrast layer of films according to the invention comprises a cured acrylate lacquer composition based on a composition comprising 30 to 80 wt. %, preferably 50 to 60 wt. %, particularly preferably 52 to 58 wt. % of a trifunctional oligomer A, 0 to 20 wt. %, preferably 5 to 15 wt. %, particularly preferably 8 to 12 wt. % of a trifunctional monomer B, 1 to 30 wt. %, preferably 5 to 15 wt. %, particularly preferably 8 to 12 wt. % of a difunctional monomer C, and 2 to 40 wt. % of a coloring pigment. The contrast layer of films according to the invention can be provided by curing a composition comprising components A, B, and C, as well as the coloring pigment. For this purpose, the composition is crosslinked by means of UV radiation, electron beam curing (hereinafter EBC), or thermally. Crosslinking is preferably carried out by EBC.

[0019] The contrast layer of films according to the invention comprises at least one coloring pigment. Coloring pigments within the meaning of the present invention include, without restriction, all coloring pigments that are used as dyes and / or brighteners in paints and varnishes. Examples of coloring pigments are titanium dioxide in the rutile modification (“TiO2”, for example rutile types from Kronos), carbon blacks (for example Printex types from Evonik) or other coloring pigments known to the person skilled in the art, as mentioned, for example, in the textbook on paints and coatings, volume 5 (Hans Kittel and Jürgen Spille, Hirzel Verlag (Stuttgart), 2003). The coloring pigment is preferably a pigment that is as weather-stable as possible. Titanium dioxide in the rutile modification is particularly preferred for the contrast layer. The color of the pigment is not essential to the invention.The contrast layer itself is not the main characteristic, but rather the color difference or contrast resulting from the engraving layer. The pigment used according to the invention serves to adjust the contrast that is created between the contrast layer and the engraving layer after the film has been inscribed, ie, after the engraving layer has been ablated by laser.

[0020] The trifunctional oligomer A is an oligomer with three unsaturated (meth)acrylate units per molecule, whose number-average molecular weight Mn (determined by GPC, calibration with a polystyrene standard) is preferably between 1000 and 5000 g / mol, preferably between 1400 and 3600 g / mol, preferably between 1800 and 2200 g / mol, and particularly preferably between 1900 and 2100 g / mol. A molecular weight Mn within this range has a positive influence on the long-term thermal stability of the cured acrylic coating composition, allowing particularly dimensionally stable contrast coatings to be obtained.

[0021] In a preferred embodiment, the trifunctional oligomer A is selected from the group of polyurethane tri(meth)acrylates and polyester tri(meth)acrylates, of which polyurethane tri(meth)acrylates are particularly preferred. The term (meth)acrylate encompasses acrylates, methacrylates, and mixtures thereof. The trifunctional oligomer A is preferably a polyurethane tri(meth)acrylate, particularly preferably a polyurethane triacrylate. Polyurethane tri(meth)acrylates are oligomers each having three unsaturated (meth)acrylate groups per molecule and several, i.e., at least two, urethane units. Examples of preferred polyurethane triacrylates are the aliphatic urethane triacrylates CN9260D75® and CN9278D80® from Sartomer, of which CN9260D75® is particularly preferred.

[0022] The trifunctional monomer B contains three unsaturated (meth)acrylate units per molecule and, in a preferred embodiment of the invention, has a molecular weight of 300 to 1000 g / mol, preferably 350 to 800 g / mol, preferably 350 to 600 g / mol, particularly preferably 400 to 450 g / mol. Component B is preferably selected from the group consisting of propoxylated and ethoxylated glycerol tri(meth)acrylates and propoxylated and ethoxylated trimethylolpropane tri(meth)acrylates of the general formula (I) or mixtures thereof: where R in formula I represents hydrogen or a methyl group; A represents hydrogen or an ethyl group; X, Y, and Z each independently represent a propylene or ethylene unit; and a, b and c are each independently an integer from 1 to 4, preferably 1 to 3, and a+b+c represents a number between 3 and 12, preferably from 3 to 9.In a particularly preferred embodiment of the invention, X, Y, and Z are propylene units. The trifunctional monomer is particularly preferably a propoxylated glycerol triacrylate. If the trifunctional monomer B is selected such that the molecular weight falls within the above-mentioned ranges and / or that the monomer B falls within the above-mentioned formula I, component B also exerts a positive influence on the temperature resistance of the contrast layer and thus of the laser-markable film.

[0023] The difunctional monomer C is a monomer having two unsaturated acrylate units per molecule. Component C preferably has a molecular weight of 100 to 1000 g / mol, preferably 180 to 350 g / mol, particularly preferably 220 to 280 g / mol, and is preferably selected from the group of ethylene glycol diacrylates of the general formula (II): and propylene glycol diacrylates of the general formula (III): or mixtures thereof, where n in the formulas II and III each independently represents an integer from 1 to 15, preferably from 1 to 9, particularly preferably from 2 to 6, and most preferably 3 or 4. In a particularly preferred embodiment of the present invention, the difunctional monomer C is triethylene glycol diacrylate.If the difunctional monomer C is selected such that the molecular weight falls within the above-mentioned ranges and / or that the monomer C falls under the above-mentioned formula II or III, component C also exerts a positive influence on the temperature resistance of the contrast layer and thus of the laser-markable film.

[0024] In a particularly preferred embodiment of the invention, the contrast layer is based on a composition comprising at least one polyurethane triacrylate, preferably CN9260D75® or CN9278D80® from Sartomer as component A, a propoxylated glycerol triacrylate of the formula I given above as component B, triethylene glycol diacrylate as component C and a pigment, for example titanium dioxide in the rutile modification.

[0025] The latent-reactive adhesive layer is preferably based on so-called 1K latent-reactive polyurethane, obtained from aqueous polyurethane dispersion, preferably Dispercoll U® from Bayer AG. The latently reactive adhesive films contain a thermoplastic component that has a melting temperature, T(melt), and contains functional groups that can react with isocyanate, as well as an isocyanate-containing component that is dispersed in the thermoplastic component in particulate form, particularly finely divided particulates, and is essentially deactivated in the area of the particle surface. Finely divided particulates mean having a particle size distribution with d 50 < 50 µm, whereby the particle size distribution is preferably < 15 µm.

[0026] The particles have a light-off temperature, T(light-off), for which T(melt) ≤ T(light-off). T(melt) is between 35 °C and 90 °C, preferably between 40 °C and 60 °C. T(light-off) is between 40 °C and 120 °C, preferably below 100 °C, most preferably below 90 °C. 50 °C is preferred as the lower limit, and 60 °C is particularly preferred. The latently reactive adhesive films are not pressure-sensitively tacky at room temperature, ensuring good (re-)positionability before thermal initiation and the start of the bond's bond strength buildup.

[0027] Particularly preferred is T(melt) < T(initiation), since this can reliably prevent unwanted triggering of the crosslinking reaction during the production of the web-shaped adhesive product.

[0028] The thermoplastic components used are preferably compounds functionalized with OH and / or NH2 groups. The thermoplastic component is very preferably at least a semicrystalline polyester polyurethane.

[0029] The latently reactive adhesive layer preferably contains an anionic, high-molecular polyurethane dispersion as a thermoplastic component, which has a melting temperature (in dried form) T(melt) of 35 °C ≤ T(melt) ≤ 90 °C, in particular 40 °C ≤ T(melt) ≤ 60 °C, and contains functional groups that can react with isocyanate, for example in the form of commercially available products from the above-mentioned Dispercoll U family; such as Dispercoll U53, Dispercoll U54, Dispercoll U56, Dispercoll U 8755, Dispercoll U XP 2815, Dispercoll VP KA 8758, Dispercoll U XP 2682, Dispercoll U 2824 XP, Dispercoll U XP 2701, Dispercoll U XP 2702, Dispercoll U XP 2710 and / or Dispercoll BL XP 2578 (a registered trademark of Bayer AG).

[0030] The latent-reactive adhesive layer preferably also contains toluene diisocyanate compounds (TDI compounds), such as Dispercoll BL XP 2514 (TDI dimer) and / or Aqualink U (dispersion of blocked TDI dimer) and / or isophorone diisocyanates (IPDI), such as Aqualink D (dispersion of blocked IPDI trimer), as an isocyanate-containing component. These components are dispersed in particulate form, particularly in finely divided form, within the thermoplastic component and are blocked, microencapsulated, or essentially deactivated in the area of the particle surface. The diisocyanates are used, for example, in the form of aqueous suspensions of the respective latent-reactive solid isocyanate. Aqualink is offered by Aquaspersions. The aforementioned diisocyanate products can be used as crosslinking components, particularly in combination with anionic, high-molecular polyurethane dispersions as thermoplastic components (such as the Dispercoll U products mentioned above).Other isocyanates, including monomeric and oligomeric compounds and polyisocyanates, can be used.

[0031] The latent-reactive adhesive layer may also contain other formulation components. These include thickeners, wetting agents, defoamers, fillers (e.g., thermally conductive), pigments, catalysts, anti-aging agents, light stabilizers, and other polymers for adjusting specific adhesive properties. Specific adhesive properties can be achieved, for example, by admixing aqueous dispersions of amorphous polymers (e.g., polyether urethanes or polyacrylates) and / or by admixing aqueous resin dispersions (especially based on rosin esters) or liquid resins.

[0032] Preferably, the latent-reactive adhesive layer is not pressure-sensitive at room temperature.

[0033] According to the invention, the at least one latent-reactive adhesive layer has a layer thickness of at least 10 µm to at most 500 µm, preferably of at least 15 µm to at most 250 µm, and very particularly preferably of 20 µm to at most 35 µm.

[0034] The present invention further relates to laser-writable labels produced from the film. This occurs in cutting or punching processes. Since the laser-writable film according to the invention has an adhesive layer, labels can be obtained by a single punching or cutting step that can be applied directly to various substrates without requiring a further coating step in finished form.

[0035] Laser-markable films according to the invention can be produced in various ways. However, in a preferred embodiment, the present invention relates to methods for producing laser-markable labels comprising the following steps: i) providing a support film; ii) applying the engraving layer to the support film; iii) applying an acrylate lacquer composition comprising components A, optionally B, C and the colouring pigment to the engraving layer; iv) curing the acrylic varnish composition to obtain the contrast layer; v) applying the latent-reactive adhesive layer to the contrast layer and covering the adhesive with a release paper or similar release liner; vi) and removing the support film.

[0036] In this process, conventional films based on various materials, such as polyethylene terephthalate (PET), can be used as the support film, which can also be referred to as the process liner. The application of both the engraving layer to the support film and the acrylic lacquer composition to the engraving layer can be achieved using conventional printing and coating processes. In a preferred embodiment of the invention, the acrylic lacquer composition is applied using a comma-coating technique.

[0037] Preferably, the adhesive layer is laminated in the form of a film to the film consisting of the engraving layer and the contrast layer. The adhesive layer film preferably has a basis weight of 10 g / m 2 up to 100 g / m 2 , preferably 15 g / m 2 up to 75 g / m 2 , particularly preferably 20 g / m 2 up to 60 g / m 2 , and in particular 25 g / m 2 up to 50 g / m 2 , on.

[0038] Finally, the present invention relates to the use of the films and labels produced in the automotive industry.

[0039] Surprisingly, it has been found that laser-markable films that can be produced by the described process and comprise a contrast layer based on the described acrylate coating composition according to the invention exhibit increased long-term temperature resistance compared to known films and labels of the prior art. Thus, the film according to the invention meets the requirements of GB Standard GB / T 25978 for long-term temperature resistance (150°C, 1,600 hours). This increased long-term temperature resistance is reflected in suppressed edge lifting of the films and labels applied to a substrate using an adhesive, as well as in a reduced tendency to crack upon prolonged exposure to high temperatures in the bonded state on the substrate.Surprisingly, films and labels according to the invention continue to offer excellent tamper protection despite their improved temperature resistance. Despite their temperature stability, they break in the area of the contrast layer in the event of a tamper attempt, for example, during a detachment attempt while bonded to a substrate. This breakage manifests itself externally in the form of a clearly visible crack. As a result, the labels according to the invention only indicate tamper attempts if such attempts have actually taken place.

[0040] The invention is explained in more detail below using an example. Unless otherwise stated, all quantities in the following examples are parts by weight based on the total composition. Production of the samples

[0041] To produce samples of laser-engravable films, in Examples 1 and 2 below, a 50 µm-thick polyester film was first printed as a support film on an SMB UV flexographic printing unit at a web speed of 15 m / min using Flexocure Gemini (black) from Flint to produce an engraving layer, resulting in a print height between 2 and 4 µm. The resulting coating was then UV-cured to produce the engraving layer using an E 70-2 (4)x1 BLK-2-SLC mercury lamp from IST Metz GmbH. The lamp output of the lamp was 80 W / cm.

[0042] To produce the contrast layer, 55 pieces CN 9260® Trifunctional urethane acrylate (oligomer) from Sartomer, M n 2000 g / mol 10 pieces SR9020® Trifunctional acrylate (reactive diluent) from Sartomer Propoxylated glyceryl triacrylate, M n 428 g / mol 10 pieces SR 272® Difunctional acrylate (reactive diluent), from Sartomer Triethylene glycol diacrylate, M n 258 g / mol 25 pieces Kronos 2160® Titanium dioxide The resulting mixture was combined in a Dispermat (Dissolver CN10 from VMA Getzmann) with a water-cooled dispersing container (capacity 1 l) and a 60 mm dissolver disk, and homogenized at a temperature of 40 °C for 20 minutes at 8000 rpm. The resulting composition was applied to the engraving layer using a doctor blade in a layer thickness of 100 µm and crosslinked by electron beam curing at 80 kGy and 240 kV to create the contrast layer.

[0043] The resulting composite of support foil / engraving layer / contrast layer was applied to Example 1: a 40 µm thick acrylic pressure-sensitive adhesive (see below) coated on one side with a release liner was applied before the polyester backing film was removed; Example 2: laminated a latent reactive adhesive film.

[0044] The resulting film was laser-labeled with a test lettering and a barcode using a Rofin Nd:YAG solid-state laser 50D and cut into 3 x 8 cm labels using this laser. Production of acrylic pressure-sensitive adhesive Example 1:

[0045] The pressure-sensitive adhesive used was a resin-modified acrylic adhesive consisting of 80 wt.% acrylate copolymer and 20 wt.% terpene-phenol resin. The copolymer was obtained by polymerizing 47.5 wt.% n-butyl acrylate, 47.5 wt.% 2-ethylhexyl acrylate, 2 wt.% glycidyl methacrylate, and 1 wt.% acrylic acid. Production of latent-reactive adhesive film Example 2:

[0046] A latent-reactive adhesive film was prepared from 100 parts of Dispercoll U53 (Bayer AG), 10 parts of Dispercoll BL XP 2514 (Bayer AG), and 1.5 parts of Borchigel 0625 (OMG Borchers). The formulation components were mixed as an aqueous dispersion in a drum with an anchor stirrer at 60 rpm for 15 minutes at room temperature. The solids content was adjusted to 46 wt.% by adding demineralized water.

[0047] Using a web coating system, a coating was produced on a temporary carrier in the form of a one-sided pretreated polyester film (PET in 50 µm thickness of the type Hostaphan GN4600A from Mitsubishi) using a doctor blade.

[0048] The material was then dehydrated in a drying tunnel at 40 °C for 15 minutes. The resulting bales were cut into rolls 50 mm wide and 100 m long. The samples had a latent-reactive adhesive film thickness of 40 µm. Test methods

[0049] To determine temperature resistance and tamper resistance, five labels each of the samples obtained according to Examples 1 to 4 were tested. The procedure was as follows. Temperature resistance:

[0050] The laser label is applied bubble-free to a 1 mm thick steel plate coated with a solvent-based acrylic clear coat from Kansai Paint (KINO 1210TW-2). After approximately 24 hours at room temperature, the sample is stored for 2300 hours at 150°C.

[0051] At the end of the storage period, the sample is examined for edge lift (the separation of the edges of the label from the substrate in mm - measured from the edge of the label) and the number of tears in the label. Furthermore, the shrinkage of the samples is measured (as a percentage of the original bonded area).

[0052] The results are given as the average of five samples and are graded on a scale of 1 to 6. A value of 1, that the edge lift is less than 0.1 mm and the shrinkage is less than 0.5%; furthermore, no cracks are visible; 2, that the edge lifting is less than 0.5 mm and the shrinkage is less than 2%; furthermore, no cracks are visible; however, edge lifting, shrinkage and / or cracking are so pronounced that a value of "1" was not achieved; 3, that the edge lifting is less than 2.0 mm and the shrinkage is less than 5%; furthermore, a maximum of 2 cracks are visible; however, edge lifting, shrinkage and / or cracking are so pronounced that a value of "2" was not achieved; 4, that the edge lifting is less than 5.0 mm and the shrinkage is less than 10%; furthermore, a maximum of 5 cracks are visible; however, edge lifting, shrinkage and / or cracking are so pronounced that a value of '3' was not achieved; 5, the label detaches completely from the substrate (“complete edge lift”) and the shrinkage is 10% or more; furthermore, up to 10 cracks are visible; 6, the label detaches completely from the substrate (“complete edge lift”) and the shrinkage is 10% or more; more than 10 cracks are visible. Tamper-proof:

[0053] In the tamper evidence test, the brittleness of the sample is examined after bubble-free bonding to a 1 mm thick steel plate coated with a clear coat from Kansai Paint (KINO 1210TW-2). For this purpose, an attempt is made to remove the sample from the substrate after a 24-hour waiting period following bubble-free bonding to the steel plate. The tamper resistance of the laser label material is classified into four levels (“1” to “4”). The tools used to remove the security label from the substrate without destruction are examined. “Destruction” in this context refers to the breaking of the label and the formation of cracks within the contrasting layer. A value of 4, that the label can be removed non-destructively by hand without additional tools; the tamper-evident nature is therefore insufficient; 3, that the label cannot be removed non-destructively by hand but can only be removed with a sharp metal blade; the tamper-evident nature is therefore also insufficient; 2, that the label cannot be removed non-destructively even with the aid of a sharp metal blade as the sole additional aid; however, non-destructive removal is possible using isopropanol as a solvent in combination with a sharp metal blade; the tamper-evident nature is considered sufficient; 1, that the label cannot be removed without damage even when using isopropanol as a solvent in combination with a sharp metal blade; in this case, the tamper resistance is rated as good. Results Test method Example 1 Example 2 Temperature resistance 2 1 Tamper-proof 3 1

[0054] The sample according to the invention (Example 2) demonstrates excellent tamper resistance with improved long-term temperature resistance. In comparison, the use of a conventional label with pressure-sensitive adhesive, with poorer temperature resistance, results in insufficient tamper resistance (Example 1).

Claims

[1] Laser-markable film for use in the automotive industry, comprising - a contrast layer based on a cured acrylate lacquer composition, wherein the cured acrylate lacquer composition is based on a composition comprising ◯ 30 to 80 wt.% of a trifunctional oligomer A; ◯ 0 to 20 wt.% of a trifunctional monomer B; ◯ 1 to 30 wt.% of a difunctional monomer C; ◯ and 2 to 40 wt.% of a colouring pigment; - an engraving layer arranged above the contrast layer, characterized by that the film continues - at least one adhesive layer arranged beneath the contrast layer, wherein the adhesive layer is a latent-reactive adhesive layer comprising a thermoplastic component having a melting temperature T(melt) of 35 °C ≤ T(melt) ≤ 90 °C and containing functional groups that can react with isocyanate, and an isocyanate-containing component that is dispersed in particulate form, in particular finely divided particulate form, in the thermoplastic component and is blocked, microencapsulated or deactivated in the region of the particle surface, wherein the particles have a melting temperature T(melt) of 40 °C ≤ T(melt) ≤ 120 °C, and wherein T(melt) ≥ T(melt), wherein the latent-reactive adhesive layer has a layer thickness of 20 µm to a maximum of 35 µm, and wherein the film meets the requirements of GB Standard GB / T 25978 for long-term temperature resistance (150°C, 1,600 hours). [2] Laser-markable film according to claim 1, characterized by that the trifunctional oligomer A is selected from the group of polyurethane tri(meth)acrylates and polyester tri(meth)acrylates. [3] Laser-writable film according to one of claims 1 or 2, characterized by that the trifunctional monomer B is selected from the group consisting of propoxylated and ethoxylated glycerol tri(meth)acrylates of the general formula I or mixtures thereof, wherein R in formula I represents hydrogen or methyl; A is hydrogen or an ethyl group; X, Y and Z each independently represent a propylene or ethylene unit; and a, b and c each independently represent an integer from 1 to 4, and a+b+c represents a number between 3 and 12. [4] Laser-markable film according to one of the preceding claims, characterized bythat the difunctional monomer C is selected from the group of ethylene glycol diacrylates of the general formula (II) and propylene glycol diacrylates of the general formula (III) or mixtures thereof, where n in the formulas (II) and (III) each independently represents an integer between 1 and 15. [5] Laser-markable film according to one of the preceding claims, characterized by that the composition on which the acrylic paint composition is based comprises 50 to 60 wt.% of the trifunctional oligomer A, 5 to 15 wt.% of the trifunctional monomer B and 5 to 15 wt.% of the difunctional monomer C. [6] Laser-writable film according to one of claims 1 to 5, characterized bythat the trifunctional oligomer A is an oligomer having three unsaturated (meth)acrylate units and a number-average molecular weight, Mn, of 1000 to 5000 g / mol; wherein the trifunctional monomer B is a monomer having three unsaturated (meth)acrylate units and a molecular weight of 300 to 1000 g / mol; and wherein the difunctional monomer C is a monomer having two unsaturated acrylate units per molecule and a molecular weight of 100 to 1000 g / mol. [7] Laser-writable film according to one of claims 1 to 6, characterized by that the light-off temperature of the particles T(light-off) is ≤ 100 °C, in particular ≤ 90 °C, preferably ≥ 50 °C, particularly preferably ≥ 60 °C. [8] Laser-writable film according to one of claims 1 to 7, characterized by that the melting temperature of the thermoplastic component T(melt) is: 40 °C ≤ T(melt) ≤ 60 °C. [9] Laser-writable film according to one of claims 1 to 8, characterized bythat the film is in the form of a label. [10] Use of the laser-inscribable film according to one of claims 1 to 8 or of the label according to claim 9 on components of motor vehicles. [11] A method for producing a laser-inscribable film according to at least one of the preceding claims 1 to 9, comprising the following steps: i) providing a support film; ii) applying an engraving layer to the support film; iii) applying an acrylic paint composition comprising ◯ 30 to 80 wt.% of a trifunctional oligomer A; ◯ 0 to 20 wt.% of a trifunctional monomer B; ◯ 1 to 30 wt.% of a difunctional monomer C; ◯ and 2 to 40 wt.% of a colouring pigment; iv) curing the acrylic varnish composition to obtain a contrasting layer; v) applying the latently reactive adhesive layer, which contains a thermoplastic component which has a melting temperature T(melt) of 35 °C ≤ T(melt) ≤ 90 °C and contains functional groups which can react with isocyanate, and an isocyanate-containing component which is present in particulate, in particular finely divided particulate, dispersed in the thermoplastic component and is blocked, microencapsulated or deactivated in the region of the particle surface, wherein the particles have a starting temperature T(melt) of 40 °C ≤ T(melt) ≤ 120 °C, and wherein T(melt) ≥ T(melt), to the contrast layer and covering the adhesive with a release paper or similar release liner; vi) and removing the support film.