Laser Engravable Labels

Abstract

The present invention relates to coextruded acrylic foils made from impact-modified polyalkyl(meth)acrylates and to laser-engravable labels comprising these foils. The coextruded acrylic foils are designed for laser marking and comprise a contrast layer having at least one inorganic filler and an engraving layer disposed on the contrast layer and having at least one colorant.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to coextruded acrylic foils made from impact-modified polyalkyl(meth)acrylates and laser-engravable labels comprising these foils. The coextruded acrylic foils are designed for laser marking and include a contrast layer having at least one inorganic filler and an engraving layer disposed on the contrast layer and having at least one colorant. The contrast layer and the engraving layer contain one or more impact modifiers. In preferred embodiments, the laser-engravable labels are fairly brittle, so that unauthorized attempts to remove the label from the substrate will destroy the label. Typically, laser-engravable labels do not have intentional breaks such as slits or perforations.

[0002] In contrast to other commonly used materials, the laser-engravable labels of the present invention have a high softening temperature and excellent weathering stability, especially outstanding UV stability. In some embodiments, the labels can also be designed to exhibit excellent chemical resistance in the presence of various chemicals commonly used in the automotive field. Such labels can be used in applications at temperatures above 100°C without showing signs of shrinkage in any dimension. Such applications include, among others, electronic product identification labels, labels for electronic modules, such as chips operating at elevated temperatures, electric engines and light-emitting devices, under-hood labels for various automobiles, road tax badges, document seals, product anti-theft labels, etc.

[0003] Prior art Laser-engravable labels are becoming increasingly important in the electronics and automotive industries, for example, as type plates, process sequence control labels, and warranty and test labels, because they can be quickly engraved and applied to the target substrate in fully automated manufacturing processes. Often, these applications inherently require a greater or lesser degree of protection against counterfeiting. Typically, the bonding strength of the label to the substrate is high compared to the strength (flexural strength or tear strength) of the label itself. Ideally, therefore, such labels cannot be removed from the labeled item without destruction.

[0004] Laser-engravable labels are used to place technical information and instructions, such as recommended tire pressure or fuel type, on various components of a vehicle. In addition, laser-engravable labels can also include safety information, such as chassis and vehicle identification numbers, registration numbers, etc. The corresponding label allows conclusions to be drawn about the vehicle and its stage of production in the manufacturing industry in the event of theft, illegal dumping, or an accident.

[0005] Laser-engravable labels that allow for high contrast of written characters are known in the prior art.For example, German Utility Model No. 8130861, German Patent Application Publication No. 10048665, and German Patent Application Publication No. 10142638 describe multi-layer labels including a thin acrylate-based lacquer layer and a thick acrylate-based lacquer layer.During the production of these labels, at least two differently colored acrylate-based layers are coated on top of each other.Before each subsequent coating step, the previously coated layer is cured, thus serving as a solid substrate for the subsequent coating.The corresponding manufacturing process involves multiple subsequent coating and curing steps, which requires complex equipment for the entire procedure and limits efficiency.

[0006] JP 2017-111344 A describes a laser-engravable foil having a white layer and a backing layer that can be made of various thermoplastic materials. The method for producing both layers of the foil is not particularly limited and can include, for example, extrusion coating or solvent coating. However, JP 2017-111344 A does not teach the production of acrylic laser-engravable foil by coextrusion.

[0007] WO 2019 / 057645 describes a laser-engravable foil that can be produced by coextrusion using a chill roll process. The foil includes an acrylic contrast layer and an acrylic engraving layer disposed on the contrast layer, and is reported to have low shrinkage over a wide temperature range. According to the teachings of WO 2019 / 057645, to ensure a sufficient degree of brittleness, either the contrast layer or the engraving layer must necessarily be free of impact modifiers. WO 2019 / 057645 reports that the foil was successfully coextruded at an extrusion speed of 4 m / min using laboratory-scale equipment.

[0008] Anti-counterfeit labels in general, and laser-engravable labels in particular, are very fragile, making their production and handling on an industrial scale much more difficult than that of typical self-adhesive labels. For example, when acrylic laser-engravable foils are produced by coextrusion, handling and use of such foils becomes problematic because they can easily break or tear during production.

[0009] Furthermore, laser-engravable labels are typically manufactured from a label substrate that includes a surface layer (face substrate), an adhesive, such as a pressure-sensitive adhesive (PSA) layer, adhered to the surface layer, optionally a release coating layer, and a support layer removably attached to the adhesive or release coating layer. The label substrate is generally provided in roll form. Individual laser-engravable labels are typically manufactured by die-cutting (kiss-cutting) the surface layer and PSA layer, then removing the surrounding waste matrix, leaving the individual labels attached to the support layer. Because the surface layer material is very brittle, the waste matrix can easily break or tear, making its removal very problematic. Typical label manufacturing processes operate at speeds of at least 25 m / min or more. As speeds increase, process stability decreases and the risk of the waste matrix breaking or tearing during removal increases. However, slowing the process or increasing the web width of the waste matrix to allow for better removal of the waste matrix incurs significant cost penalties, efficiency losses, and is often ineffective.

[0010] In principle, problems associated with breakage or tearing of the waste matrix could be at least partially alleviated by increasing the distance between individual labels, i.e., the web width of the waste matrix. However, this would inevitably increase the amount of waste generated during label production and reduce process efficiency. Therefore, such an approach would not be feasible from an economical or environmental standpoint.

[0011] Our research has shown that the foil described in WO 2019 / 057645 is not suitable for large-scale production at high extrusion rates due to its high brittleness. In particular, the foil of WO 2019 / 057645 easily tears even during extrusion. Investigations have shown that initial cracks easily form in the more brittle layer that does not contain impact modifiers, which then propagate to the layer containing the impact modifiers, leading to complete fracture of the foil. This result is surprising because impact modifiers in acrylic materials typically inhibit the formation and propagation of such cracks.

[0012] technical challenges In light of the prior art, the problem addressed by the present invention was to provide a laser-engravable foil for use in laser-engravable labels that is sufficiently brittle for anti-counterfeiting applications. In particular, it would be desirable for such a foil to be capable of being produced by coextrusion at high extrusion rates and be usable in a cost-effective manufacturing process in which individual labels are produced by kiss-cutting the surface layer and PSA layer, followed by removal of the surrounding waste matrix, leaving the individual labels attached to the support layer. Furthermore, the desired foil should ideally exhibit substantially no signs of shrinkage at elevated temperatures.

[0013] Additionally, it was important that the laser-engravable label have sufficiently low initial tear strength, low tear propagation resistance, and a short tear path to make it susceptible to complete rupture in an attempt to tamper with the foil, yet still be capable of being manufactured and processed without tearing.

[0014] In a further aspect, the present invention addressed the problem of providing a self-adhesive, laser-engravable anti-counterfeit label that can be manufactured efficiently, is printable, and is suitable for long-term outdoor use.

[0015] Finally, the present invention addressed the problem of developing a safe and cost-effective process for producing the above-described laser-engravable foils and self-adhesive labels comprising said foils.

[0016] solution The present invention is based on the surprising discovery that the mechanical stability of coextruded acrylic foils can be significantly improved by ensuring that at least the contrast layer and engraving layer of the foil contain at least one impact modifier. Because there is no acrylic layer that does not contain impact modifiers, the formation of undesirable cracks that propagate throughout the foil no longer occurs. This allows for industrial-scale coextrusion of foils at high extrusion speeds. At the same time, the brittleness of the laser-engravable foils can be fine-tuned to prevent the unauthorized removal of affixed labels from the substrate. Additionally, the inventors surprisingly found that these foils exhibit excellent behavior during the die-cutting (kiss-cutting) process and subsequent stripping of the waste matrix. Thus, laser-engravable labels containing the foils of the present invention can be advantageously produced by kiss-cutting individual labels, followed by removal of the surrounding waste matrix, leaving the individual labels attached to the support layer. Undesirable breakage of the waste matrix does not occur, even at operating speeds of at least 25 m / min or higher.

[0017] Thus, one aspect of the present invention relates to a coextruded acrylic foil comprising Layer A and Layer B. Layer A comprises, based on the weight of Layer A: 30.0% to 98.5% by weight of one or more acrylic polymers A; 1.0 wt. % to 40.0 wt. % of one or more impact modifiers; 0.5% to 20.0% by weight of one or more colorants; 0.0% to 10.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, The cumulative content of the acrylic polymer A and the impact modifier in the layer A is 60.0 wt % to 99.5 wt % based on the weight of the layer A.

[0018] Layer B, based on the weight of Layer B: 10.0% to 92.5% by weight of one or more acrylic polymers B; 2.5 wt.% to 35.0 wt.% of one or more impact modifiers; 5.0% to 35.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, The cumulative content of the acrylic polymer B and the impact modifier in the layer B is 60.0% by weight to 95.0% by weight based on the weight of the layer B.

[0019] As will be readily understood by those skilled in the art, the term "foil" as used herein refers to a sheet having a thickness of less than 5 mm, more preferably less than 1 mm. The foil of the present invention can be advantageously used as a protective coating, but the term "foil" as used herein should generally be distinguished from the term "coating." A coating is typically the top layer of a multilayer substrate and cannot be handled separately from the substrate. In contrast to a coating, the foil of the present invention is not necessarily a layer of a multilayer article, i.e., it is not necessarily attached to any substrate, and therefore can be handled separately and used for a variety of different purposes.

[0020] A further aspect of the invention is a coating comprising at least the following layers: a) a layer made of acrylic foil, preferably having a thickness of 10 μm to 200 μm; b) an adhesive layer, preferably having a thickness of 20 μm to 30 μm; c) a release coating layer, preferably having a thickness of 0.6 μm to 0.8 μm, and d) a support layer, preferably having a thickness of 30 μm to 50 μm; The present invention relates to an engravable label comprising the above in the listed order and / or having a thickness of 80 μm to 300 μm.

[0021] Yet another aspect of the present invention is a laminate for producing the laser-engravable label described above, comprising at least the following layers: a) a liner layer preferably having an initial tear resistance of 50 N to 500 N measured according to ASTM D1004 (2013) using a foil having a thickness of 50.0 μm; and b) a layer made of acrylic foil The present invention relates to laminates, including:

[0022] Yet another aspect of the present invention is a method for making a plurality of individual self-adhesive laser-engravable labels, comprising at least the following steps: i) producing the acrylic foil defined above using an extruder; and ii) optionally bonding a liner layer downstream of the extruder to the acrylic foil of step i), resulting in a laminate; iii) bonding an adhesive layer, optionally a release coating layer and a support layer onto the laminate from step ii), resulting in a label substrate. iv) optionally removing the liner layer; v) kiss-cutting the label substrate obtained in step iii) and removing the resulting waste matrix, resulting in a plurality of individual self-adhesive, laser-engravable labels on the support layer. The present invention relates to a method comprising:

[0023] Finally, the present invention relates to the use of coextruded acrylic foils for producing laser-engravable labels. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram of an endless label substrate 1 after a kiss-cut process. In a subsequent process step, the waste matrix 3 is removed from the support layer, thereby leaving a plurality of individual laser-engravable labels 2 attached to the support layer. [Figure 2] FIG. 1 shows a side view of a laser-engravable label 2 comprising at least the following layers: a) coextruded acrylic foil 4, b) adhesive layer 7, c) optionally, release coating layer 8, and d) support layer 9. Coextruded acrylic foil 4 comprises layer A5 and layer B6. [Figure 3] FIG. 1 is a side view of an endless label substrate 12 before the kiss-cut process, comprising at least the following layers: a) optionally a liner layer 10, b) a co-extruded acrylic foil 4 comprising layers A5 and B6, c) an adhesive layer 7, d) optionally a release coating layer 8, and e) a support layer 9. The laminate 11 typically consists of two layers: a layer formed by the co-extruded acrylic foil 4, and a liner layer 10.

[0025] Detailed Description The coextruded acrylic foil of the present invention comprises at least Layer A and Layer B, wherein Layer A comprises, based on the weight of Layer A: 30.0% to 98.5% by weight, preferably 40.0% to 95.0% by weight, more preferably 50.0% to 93.0% by weight of acrylic polymer A; 1.0 wt.% to 40.0 wt.%, preferably 4.0 wt.% to 35.0 wt.%, more preferably 6.0 wt.% to 30.0 wt.% of one or more impact modifiers; 0.5% to 20.0% by weight, preferably 1.0% to 18.0% by weight, more preferably 1.0% to 15.0% by weight of one or more colorants; 0.0 wt % to 10.0 wt %, preferably 0.0 wt % to 7.0 wt %, more preferably 0.0 wt % to 5.0 wt % of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, The cumulative content of acrylic polymer A and impact modifier in layer A is 60.0 to 99.5% by weight, preferably 60.0 to 99.0% by weight, and more preferably 65.0 to 99.0% by weight, based on the weight of layer A.

[0026] Layer B, based on the weight of Layer B: 30.0% to 92.5% by weight, preferably 34.0% to 90.0% by weight, more preferably 40.0% to 85.0% by weight of acrylic polymer B; 2.5% to 35.0% by weight, preferably 4.0% to 33.0% by weight, more preferably 6.0% to 30.0% by weight of one or more impact modifiers; 5.0% to 35.0% by weight, preferably 6.0% to 33.0% by weight, more preferably 9.0% to 33.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, The cumulative content of acrylic polymer B and impact modifier in layer B is 60.0% by weight to 95.0% by weight, preferably 60.0% by weight to 94.0% by weight, and more preferably 60.0% by weight to 91.0% by weight, based on the weight of layer B.

[0027] In addition to the above advantages, the inventors have surprisingly found that the behavior of the coextruded acrylic foil during extrusion on an industrial scale and during the die-cutting (kiss-cutting) process, and subsequent stripping of the waste matrix, is highly dependent on the ratio of the amount of impact modifier to the amount of inorganic filler and colorant in layers A and B of the coextruded foil.

[0028] In particular, the content (wt. %) of one or more impact modifiers in layer A with respect to the mechanical properties of the coextruded acrylic foil imABut the following relationship: (n fA +n pA )≦n imA ≦7 * (n fA +n pA ) Preferably 1.2 * (n fA +n pA )≦n imA ≦6.5 * (n fA +n pA ) More preferably 1.3 * (n fA +n pA )≦n imA ≦6 * (n fA +n pA ) [n fA is the content (wt%) of one or more inorganic fillers, n pA is the content (in % by weight) of one or more colorants in layer A.

[0029] Similarly, with regard to the behavior of coextruded acrylic foils, the content (wt. %) of one or more impact modifiers in layer B during extrusion and die-cutting (kiss-cutting) processes on an industrial scale is imB The following relationships: 0.25 * n fB ≦n imB ≦2 * n fB Preferably 0.3 * n fB ≦n imB ≦1.8 * n fB More preferably 0.4 * n fB ≦n imB ≦1.5 * n fB [n fBis the content (in %) of one or more inorganic fillers in layer B] has been shown to be very beneficial.

[0030] In these embodiments, laser-engravable labels comprising the foils of the present invention can be produced utilizing a process in which individual labels are kiss-cut and then the surrounding waste matrix is ​​removed, leaving the individual labels attached to the substrate, without undesirable fracture of the waste matrix, even at operating speeds of at least 25 m / min or greater.

[0031] In this application, the content of one or more impact modifiers n im is the content of the net impact modifier. Therefore, if the corresponding impact modifier is a rubber particle, n im is the content of rubber particles. If the corresponding impact modifier is a core-shell or core-shell-shell particle, n im is the content of the whole particle.

[0032] Thus, one embodiment of the present invention is a co-extruded acrylic foil comprising at least Layer A and Layer B, wherein Layer A comprises, based on the weight of Layer A: 30.0% to 98.5% by weight of acrylic polymer A; 1.0 wt. % to 40.0 wt. % of one or more impact modifiers; 0.5% to 20.0% by weight of one or more colorants; 0.0% to 10.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer A and the impact modifier in the layer A is 60.0 wt % to 99.5 wt % based on the weight of the layer A; Content (wt%) of one or more impact modifiers in Layer A imA But the following relationship: (n fA +n pA )≦n imA ≦7 * (n fA +n pA ) [n fA is the content (wt%) of one or more inorganic fillers, and n pA is the content (wt %) of one or more colorants in Layer A, Layer B, based on the weight of Layer B, 30.0% to 92.5% by weight of acrylic polymer B; 2.5 wt.% to 35.0 wt.% of one or more impact modifiers; 5.0% to 35.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer B and the impact modifier in Layer B is 60.0% by weight to 95.0% by weight, based on the weight of Layer B; Content (wt%) of one or more impact modifiers in Layer B imB But the following relationship: 0.25 * n fB ≦n imB ≦2 * n fB [n fB is the content (wt %) of one or more inorganic fillers in Layer B.

[0033] Furthermore, the balance between, on the one hand, suitability for manufacturing processes utilizing a kiss-cut process followed by removal of the waste matrix, and, on the other hand, the ability to resist unauthorized attempts to remove the laser-engravable label from the intended substrate, is particularly advantageous for coextruded acrylic foils comprising at least Layer A and Layer B; Layer A, based on the weight of Layer A: 40.0% to 95.0% by weight of acrylic polymer A; 4.0 wt.% to 35.0 wt.% of one or more impact modifiers; 1.0% to 18.0% by weight of one or more colorants; 0.0% to 7.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer A and the impact modifier in the layer A is 60.0 wt % to 99.0 wt % based on the weight of the layer A; Content (wt%) of one or more impact modifiers in Layer A imA is the following relation: 1.2 * (n fA +n pA )≦n imA ≦6.5 * (n fA +n pA ) [n fA is the content (wt%) of one or more inorganic fillers, and n pA is the content (wt %) of one or more colorants in Layer A, Layer B, based on the weight of Layer B: 34.0% to 90.0% by weight of acrylic polymer B; 4.0 wt.% to 33.0 wt.% of one or more impact modifiers; 6.0% to 33.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer B and the impact modifier in Layer B is 60.0 wt % to 94.0 wt % based on the weight of Layer B; Content (wt%) of one or more impact modifiers in Layer BimB is the following relation: 0.3 * n fB ≦n imB ≦1.8 * n fB [n fB is the content (wt %) of one or more inorganic fillers in Layer B.

[0034] Furthermore, the overall properties of the co-extruded acrylic foil can be further improved when the co-extruded acrylic foil comprises at least one layer A and layer B, wherein layer A has a weight of: 50.0% to 93.0% by weight of acrylic polymer A; 6.0 wt.% to 30.0 wt.% of one or more impact modifiers; 1.0% to 15.0% by weight of one or more colorants; 0.0 wt % to 10.0 wt %, preferably 0.0 wt % to 7.0 wt %, more preferably 0.0 wt % to 5.0 wt % of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer A and the impact modifier in the layer A is 65.0 wt % to 99.0 wt % based on the weight of the layer A; Content (wt%) of one or more impact modifiers in Layer A imA is the following relation: 1.3 * (n fA +n pA )≦n imA ≦6 * (n fA +n pA ) [n fA is the content (wt%) of one or more inorganic fillers, and n pA is the content (wt %) of one or more colorants in Layer A, Layer B, based on the weight of Layer B: 40.0% to 85.0% by weight of acrylic polymer B; 6.0 wt.% to 30.0 wt.% of one or more impact modifiers; 9.0% to 33.0% by weight of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer B and the impact modifier in Layer B is 60.0 wt % to 91.0 wt % based on the weight of Layer B; Content (wt%) of one or more impact modifiers in Layer B imB is the following relation: 0.4 * n fB ≦n imB ≦1.5 * n fB [n fB is the content (wt %) of one or more inorganic fillers in Layer B.

[0035] Coextruded acrylic foils with particularly low shrinkage at elevated temperatures can be obtained when at least one of the acrylic polymers A and / or at least one of the acrylic polymers B has a glass transition temperature of at least 110°C, preferably at least 120°C. In this regard, it has surprisingly been found that even when only one of the two layers A or B has a glass transition temperature of at least 110°C, preferably at least 120°C, the entire acrylic foil has a low shrinkage at elevated temperatures. In other words, at elevated temperatures, the layer with the higher glass transition temperature provides sufficient mechanical support to the layer with the lower glass transition temperature, thereby avoiding undesired shrinkage of the foil.

[0036] The glass transition temperature Tg of the acrylic polymer can be determined in a known manner by differential scanning calorimetry (DSC). DSC measurements can be carried out, for example, on a DSC822e instrument from Mettler-Toledo AG in accordance with the standard DIN EN ISO 11357. For this purpose, two cycles are carried out within the interval from -80°C to 150°C. The heating / cooling rate is preferably 10°C / min. The glass transition temperature Tg can typically be calculated using the half-height technique in the transition region.

[0037] Alternatively, for example, when DSC measurements are not possible, the glass transition temperature Tg can be roughly calculated in advance using the Fox equation. Fox TG, Bull. Am. Physics Soc. 1 , 3, p. 123 (1956), 1 / Tg=x1 / Tg1+x2 / Tg2++x n / Tg n In the formula, x n is the mass fraction of monomer n (wt% / 100), and Tg n is the glass transition temperature (in Kelvin) of the homopolymer of monomer n. Those skilled in the art can find further useful hints in the Polymer Handbook, 2nd Edition, J. Wiley & Sons, New York (1975), which gives Tg values ​​for the most common homopolymers.

[0038] Poly(meth)acrylimide In one embodiment of the present invention, acrylic polymer A and / or acrylic polymer B independently comprise at least 50 wt. %, preferably at least 60 wt. %, and most preferably at least 70 wt. %, based on the weight of PMMI, of a compound of formula (I): [ka] [In the formula, R 1 and R 2 are independently selected from hydrogen and a methyl group; R1 and R 2 is preferably represented by a methyl group, R 3 is hydrogen or a C1-C4 alkyl group, preferably a methyl group].

[0039] Preferably, acrylic layer A and / or acrylic layer B comprises 30.0 wt % to 98.0 wt %, preferably 30.0 wt % to 92.5 wt %, more preferably 40.0 wt % to 80.0 wt %, and even more preferably 45.0 wt % to 75.0 wt % PMMI, based on the weight of the corresponding layer A or layer B.

[0040] Methods for producing PMMI are disclosed, for example, in EP-A-216505, EP-A-666161, or EP-A-776910, the entire disclosures of which are incorporated herein by reference. Starting materials used in the production of PMMI include polymers derived from alkyl esters of methacrylic acid, generally composed of more than 50.0 wt.%, preferably more than 80.0 wt.%, and particularly preferably 95.0-100.0 wt.% alkyl ester units of methacrylic acid having 1 to 4 carbon atoms in the alkyl group. Methyl methacrylate is preferred. Preferred polymers are composed of at least 80.0 wt.%, preferably more than 90.0 wt.%, and particularly preferably more than 95.0 wt.% methyl methacrylate. Comonomers that can be used include any monomer copolymerizable with methyl methacrylate, particularly alkyl esters of acrylic acid having 1 to 4 carbon atoms in the alkyl group, acrylonitrile or methacrylonitrile, acrylamide or methacrylamide, styrene, or maleic anhydride. Thermoplastically processable polymers of this type are preferred, having a reduced viscosity in the range of 20 ml / g to 92 ml / g, preferably 50 ml / g to 80 ml / g (measured according to ISO 8257 (2006), part 2). They are used in the form of powders or pellets, the median particle size of which is about 0.03 mm to 3 mm.

[0041] In the process steps, ammonia is first used as the imidizing agent, and in subsequent steps of the process, C 1~4 An alkylamine, typically methylamine, is used, and it is important that the molar ratio of ammonia to methylamine used is 1:0.5 to 1:3, preferably 1:0.8 to 1:2.7, and particularly preferably 1:0.9 to 1:1.1. Below this range, haze may increase in the resulting polymethacrylimide. If a molar excess of methylamine is present relative to the ammonia used, the proportion of carboxylic acid groups in the polymer will unnecessarily increase.

[0042] The reaction with the imidizing agent is preferably terminated before the polymer is completely imidized. To this end, the total amount of imidizing agent used can be, for example, 0.2 to 2.5 moles, preferably 0.5 to 1.5 moles, and particularly preferably 0.8 to 1.2 moles per mole of ester unit. However, the specified quantitative ratio of ammonia to methylamine should always be maintained. This then results in a polymer composed of approximately 20 to 80 mole percent cyclic methacrylimide units and only a small amount of methacrylic acid units (less than 5.0 wt%).

[0043] The imidization process can be carried out in a manner known per se, essentially as described, for example, in EP 441148. Imidization proceeds best at temperatures above the melting point of the starting polymer or at least 20°C above the Vicat B softening point according to ISO 306 (2014). It is more preferable to select a reaction temperature at least 20°C above the softening point of the resulting imidized polymer. The Vicat softening point of the imidized polymer is generally a target variable in the process, and the degree of imidization to be achieved is defined accordingly, so it is also easy to determine the minimum temperature required. A temperature range of 140°C to 300°C, particularly 150°C to 260°C, and particularly preferably 180°C to 220°C, is preferred. Excessively high reaction temperatures can sometimes lead to a decrease in viscosity, possibly caused by some chain termination of the polymer. To prevent unnecessary thermal stress of the polymer, the reaction temperature can be increased gradually or stepwise, starting, for example, from a temperature slightly above the melting point of the starting polymer, and only at the final stage can it exceed the softening point of the imidized final product by at least 20°C. It is preferable to operate at autogenous pressure within the reaction stage, which can be from 50 to 500 bar. Decompression can be performed between process stages, for example, for devolatilization. The temperature of the reaction mixture must then be reduced and then increased to the required value. If an imidizing agent is introduced under reaction conditions, an appropriate elevated pressure must, of course, be used for this purpose.

[0044] The partial or complete imidization of polymers of alkyl esters of methacrylic acid by reaction with an imidizing agent, such as a primary amine, is disclosed, for example, in U.S. Patent No. 2,146,209. The polymer is heated to a temperature of 140°C to 250°C with the imidizing agent in the presence or absence of a solvent, if appropriate under pressure.

[0045] Typically, PMMI for use in the present invention has a weight average molecular weight Mw of 80,000 g / mol to 200,000 g / mol, preferably 90,000 g / mol to 150,000 g / mol, as determined by GPC using PMMA as the standard. Such materials are commercially available from Röhm GmbH (Darmstadt, Germany) under the trademark PLEXIMID®. Suitable products include, but are not limited to, PLEXIMID® TT50, PLEXIMID® TT70, PLEXIMID® 8805, PLEXIMID® 8813, and PLEXIMID® 8817.

[0046] Polyalkyl(meth)acrylate In a further embodiment of the present invention, acrylic polymer A and / or acrylic polymer B are independently a polyalkyl(meth)acrylate.

[0047] Polyalkyl(meth)acrylates are usually obtained by free radical polymerization of a mixture containing an alkyl(meth)acrylate, typically methyl methacrylate (a), and at least one additional (meth)acrylate (b). These mixtures generally contain at least 50% by weight, preferably at least 60% by weight, particularly preferably at least 80% by weight, and even more preferably at least 90% by weight of methyl methacrylate (a), based on the weight of the monomers. The amount of methyl methacrylate (a) typically used is 50.0% to 99.9% by weight, preferably 80.0% to 99.0% by weight, particularly preferably 90.0% to 99.0% by weight, based on the weight of the monomers.

[0048] These mixtures for producing polyalkyl(meth)acrylates may also contain other (meth)acrylates (b) copolymerizable with methyl methacrylate (a). The term "(meth)acrylate" as used herein is meant to encompass methacrylates, acrylates, and mixtures thereof. The (meth)acrylates may be derived from saturated alcohols, such as methyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; or from unsaturated alcohols, such as allyl (meth)acrylate, vinyl (meth)acrylate; or from aryl (meth)acrylates, such as benzyl (meth)acrylate or phenyl (meth)acrylate, cycloalkyl (meth)acrylates, such as 3-vinylcyclohexyl (meth)acrylate, bornyl (meth)acrylate, etc. hydroxyalkyl (meth)acrylates such as 3-hydroxypropyl (meth)acrylate, 3,4-dihydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate; glycol di(meth)acrylates such as 1,4-butanediol (meth)acrylate; amides and nitriles of (meth)acrylic acid such as N-(3-dimethylaminopropyl)(meth)acrylamide, N-(diethylphosphono)-(meth)acrylamide, 1-methacryloylamido-2-methyl-2-propanol; and polyfunctional (meth)acrylates such as trimethyloylpropane tri(meth)acrylate.

[0049] The amount of (meth)acrylic comonomer (b) generally used is 0.1% by weight to 50.0% by weight, preferably 1.0% by weight to 20.0% by weight, particularly preferably 1.0% by weight to 10.0% by weight, based on the weight of the monomer, and the compounds herein can be used alone or in the form of a mixture.

[0050] The polymerization reaction is generally initiated by known free radical initiators.Preferred initiators include, inter alia, azo initiators, such as AIBN and 1,1-azobiscyclohexanecarbonitrile, and peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl 2-ethylperhexanoate, ketone peroxides, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxyisopropyl carbonate, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, Those skilled in the art will be familiar with tert-butyl 2-ethylperoxyhexanoate, tert-butyl 3,5,5-trimethylperoxyhexanoate, dicumyl peroxide, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis(4-tert-butylcyclohexyl)peroxydicarbonate, mixtures of two or more of the aforementioned compounds, and mixtures of the aforementioned compounds with compounds not mentioned but which are also capable of forming free radicals.

[0051] The composition to be polymerized may contain not only the above-mentioned methyl methacrylate (a) and (meth)acrylate (b), but also other unsaturated monomers copolymerizable with methyl methacrylate and the above-mentioned (meth)acrylates. Among these are, inter alia, 1-alkenes such as 1-hexene and 1-heptene; branched alkenes such as vinylcyclohexane, 3,3-dimethyl-1-propene, 3-methyl-1-diisobutylene, 4-methyl-1-pentene, and norbornene; acrylonitrile; vinyl esters such as vinyl acetate; styrene, substituted styrenes having alkyl substituents in the side chain, such as α-methylstyrene and α-ethylstyrene, substituted styrenes having alkyl substituents on the ring, such as vinyltoluene and p-methylstyrene, halogenated styrenes such as monochlorostyrene, dichlorostyrene, tribromostyrene, and tetrabromostyrene; vinyl ethers and isoprenyl ethers; maleic acid derivatives such as maleic anhydride, methylmaleic anhydride, maleimide, and methylmaleimide; and dienes such as divinylbenzene.

[0052] The amount of these comonomers (c) generally used is 0.0% by weight to 20.0% by weight, preferably 0.0% by weight to 15.0% by weight, particularly preferably 0.0% by weight to 10.0% by weight, based on the weight of the monomers; these compounds can be used herein alone or in the form of a mixture.

[0053] As the polymerizable component, (a) 50.0% by weight to 99.9% by weight of methyl methacrylate; (b) 0.1 wt% to 50.0 wt% of an acrylic acid ester of a C1-4 alcohol; (c) 0.0% by weight to 10.0% by weight of a monomer copolymerizable with monomers (a) and (b). More preferred is a polyalkyl(meth)acrylate obtained by polymerizing a composition having the formula:

[0054] In yet another embodiment, polyalkyl(meth)acrylates composed of 85.0 to 99.5% by weight methyl methacrylate and 0.5 to 15.0% by weight methyl acrylate are preferred, with amounts herein being based on 100% by weight of polymerizable components. Particularly advantageous copolymers are those obtained by copolymerizing 90.0 to 99.5% by weight methyl methacrylate with 0.5 to 10.0% by weight methyl acrylate, with amounts based on 100% by weight of polymerizable components. For example, the polyalkyl(meth)acrylate can contain 91.0% by weight methyl methacrylate and 9.0% by weight methyl acrylate, 96.0% by weight methyl methacrylate and 4.0% by weight methyl acrylate, or 99.0% by weight methyl methacrylate and 1.0% by weight methyl acrylate. The polyalkyl(meth)acrylates typically have a Vicat softening point VSP (ISO 306 (2013), method B50) of at least 90°C, preferably from 95°C to 112°C.

[0055] The weight-average molar mass Mw of the polyalkyl(meth)acrylates is generally in the range of 80,000 g / mol to 300,000 g / mol. Particularly advantageous mechanical properties are obtained from foils using polyalkyl(meth)acrylates having an average molar mass Mw (determined in each case by GPC against PMMA calibration standards and THF as eluent) in the range of 80,000 g / mol to 200,000 g / mol, preferably in the range of 100,000 g / mol to 180,000 g / mol, more preferably in the range of 120,000 g / mol to 180,000 g / mol.

[0056] Suitable polyalkyl(meth)acrylates for use in the foils of the present invention are commercially available from Röhm GmbH (Darmstadt, Germany) under the trademark PLEXIGLAS®. Such products include, but are not limited to, PLEXIGLAS® 7N, PLEXIGLAS® 7H, PLEXIGLAS® 8N, PLEXIGLAS® 8H, and PLEXIGLAS® Heatresist FT15.

[0057] The foil of the present invention typically comprises 0.0 wt % to 30.0 wt %, preferably 0.0 wt % to 25.0 wt %, more preferably 0.0 wt % to 20.0 wt %, of polyalkyl (meth)acrylate, based on the weight of the coextruded acrylic foil.

[0058] Impact modifier Impact modifiers for use in the present invention are well known and may have different chemical compositions and polymer structures. Impact modifiers may be crosslinked or thermoplastic. Additionally, impact modifiers may be in the form of particles, such as core-shell, core-shell-shell, or core-shell-shell-shell particles. Typically, particulate impact modifiers have an average particle size of 20 nm to 500 nm, preferably 50 nm to 450 nm, more preferably 100 nm to 400 nm, and most preferably 150 nm to 350 nm. In this context, "particulate" generally refers to crosslinked impact modifiers having a core-shell, core-shell-shell, or core-shell-shell-shell structure. The average particle size can be determined by methods known to those skilled in the art, such as photon correlation spectroscopy according to standard DIN ISO 13321 (2004).

[0059] In the simplest case, particulate impact modifiers are crosslinked particles obtained by emulsion polymerization and having an average particle size in the range of 10 to 150 nm, preferably 20 to 100 nm, and in particular 30 to 90 nm. They generally consist of at least 20.0% by weight, preferably 20.0 to 99.0% by weight, and particularly preferably 30.0 to 98.0% by weight, of butyl acrylate, and 0.1 to 2.0% by weight, preferably 0.5 to 1.0% by weight, of a crosslinking monomer, such as a polyfunctional (meth)acrylate, for example, allyl methacrylate, and, if appropriate, other monomers, such as 0.0 to 10.0% by weight, preferably 0.5 to 5.0% by weight, of a C1-C4-alkyl methacrylate, for example, ethyl acrylate or butyl methacrylate, preferably methyl acrylate, or other vinyl-polymerizable monomers, for example, styrene.

[0060] Preferred impact modifiers are polymer particles which may have a two- or three-layer core-shell structure and are obtained by emulsion polymerization (see, for example, EP-A-0 113 924, EP-A-0 522 351, EP-A-0 465 049 and EP-A-0 683 028). The foils of the present invention typically require suitable average particle sizes of these emulsion polymers in the range of 20 nm to 500 nm, preferably 50 nm to 450 nm, more preferably 100 nm to 400 nm, and most preferably 150 nm to 350 nm.

[0061] A three-layer or three-phase structure having one core and two shells can be produced as follows: The innermost (hard) shell can, for example, consist essentially of methyl methacrylate, a small proportion of a comonomer, such as ethyl acrylate, and some proportion of a crosslinker, such as allyl methacrylate. The middle (soft) shell can, for example, consist of a copolymer containing butyl acrylate and, if appropriate, styrene, while the outermost (hard) shell is essentially the same as the matrix polymer, thus providing compatibility and good bonding with the matrix.

[0062] The proportion of polybutyl acrylate in the core or shell of the impact modifier having a two-layer or three-layer core-shell structure is important for the function of the impact modifier, and is preferably in the range of 20.0 wt % to 99.0 wt %, particularly preferably in the range of 30.0 wt % to 98.0 wt %, and even more preferably in the range of 40.0 wt % to 97.0 wt %, based on the total weight of the impact modifier.

[0063] In addition to particulate impact modifiers containing butyl acrylate copolymers, siloxane-containing impact modifiers can also be used. However, the use of such modifiers is less advantageous because their presence in coextruded acrylic foils tends to be detrimental to the printability of the foil.

[0064] Methyl methacrylate-butadiene-styrene (MBS) core-shell impact modifiers are also well suited for use in the foils of the present invention due to their excellent compatibility with PMMI. Corresponding impact modifiers are commercially available under the trademark Clearstrength® from several manufacturers, such as Arkema France, and include products such as Clearstrength® XT100, Clearstrength® 140, Clearstrength® 223, Clearstrength® 303H, Clearstrength® 320, Clearstrength® 350, and Clearstrength® 859. Also suitable are MBS core-shell impact modifiers manufactured by Dow Chemical Company under the PARALOID™ trademark, such as the products PARALOID™ EXL-2620, PARALOID™ EXL™ 2650J, PARALOID™ EXL-2690, PARALOID™ EXL-2691, PARALOID™ EXL-2668, and PARALOID™ EXL-3361. The use of these impact modifiers makes it possible to produce PMMI foils with particularly low haze values ​​and excellent optical transparency.

[0065] In some embodiments, the use of core-shell-shell-shell impact modifiers is advantageous in terms of the mechanical properties of the foils of the invention. Corresponding impact modifiers are described in detail in patent application WO 2014 / 035608, the entire disclosure of which is incorporated herein by reference.

[0066] Thermoplastic impact modifiers have a different mechanism of action than particulate impact modifiers. They are generally mixed with a matrix material. If domains are formed, as in the case of block copolymers, the preferred size of these domains (which can be determined, for example, by electron microscopy) corresponds to the preferred size of the core-shell particles.

[0067] There are various classes of thermoplastic impact modifiers. One example is aliphatic TPU (thermoplastic polyurethane), such as the Desmopan® products available from Covestro AG. For example, TPU Desmopan® WDP85784A, WDP85092A, WDP89085A, and WDP89051D, all of which have refractive indices between 1.490 and 1.500, are particularly suitable as impact modifiers.

[0068] A further class of thermoplastic polymers suitable for use as impact modifiers in the foils of the invention are acrylic TPEs comprising methacrylate-acrylate block copolymers, in particular PMMA-poly-n-butylacrylate-PMMA triblock copolymers, which are marketed by Kuraray under the product name Kurarity®. The poly-n-butylacrylate blocks form nanodomains with a size of 10 nm to 20 nm in the polymer matrix.

[0069] In addition to the thermoplastic impact modifiers mentioned above, thermoplastic impact modifiers including PVDF can also be used. However, the use of such modifiers is less advantageous because their presence in coextruded acrylic foils tends to impair the printability of the foil.

[0070] The cumulative content of the poly(meth)acrylimide, polyalkyl(meth)acrylate, and impact modifier (hereinafter referred to as "impact-modified acrylic polymer A") in Layer A is typically adjusted to 60% to 99.5% by weight, more preferably 70.0% to 98.0% by weight, and more preferably 80.0% to 96.0% by weight, based on the weight of Layer A. The cumulative content of the poly(meth)acrylimide, polyalkyl(meth)acrylate, and impact modifier (hereinafter referred to as "impact-modified acrylic polymer B") in Layer B is typically adjusted to 60% to 95.0% by weight, more preferably 65.0% to 95.0% by weight, and more preferably 70.0% to 90.0% by weight, based on the weight of Layer B.

[0071] inorganic fillers The presence of inorganic fillers in the coextruded acrylic foil of the present invention serves multiple purposes. The presence of inorganic fillers can impart a desired color and transparency to the coextruded acrylic foil. For example, the presence of titanium dioxide in the coextruded acrylic foil renders the foil white and substantially opaque. In addition, it has surprisingly been found that the amount of inorganic filler has a strong influence on the behavior of the foil during handling, particularly during industrial-scale coextrusion and the behavior of the waste matrix after the kiss-cut process during the production of laser-engravable labels.

[0072] The inorganic fillers in Layers A and B are not particularly limited and may be independently selected from zirconium dioxide, titanium dioxide, preferably rutile titanium dioxide, silica, preferably fused silica, barium sulfate, aluminum trihydroxide, mica, zinc oxide, zinc sulfide, clay, muscovite, and calcium carbonate.

[0073] Ideally, the inorganic filler exhibits a 45 μm screen residue of 0.1% by weight or less, i.e., there is substantially no agglomerate with a particle size greater than 45 μm, which is highly advantageous for use according to the invention. This allows the inorganic filler to be particularly homogeneously distributed in the matrix of the poly(meth)acrylate foil without the presence of large filler agglomerates, and therefore the resulting foil exhibits a substantially uniform appearance and has suitable mechanical properties. In general, the presence of a large amount of large filler agglomerates in the foil is disadvantageous because such agglomerates tend to cause cracks in the foil, thereby reducing the initial tear strength at random locations on the foil.

[0074] In a preferred embodiment, the inorganic filler has a weight average particle size d in the range of 0.05 μm to 10.0 μm, more preferably 0.1 μm to 5.0 μm, particularly preferably 0.1 μm to 1.0 μm, and even more preferably 0.1 μm to 0.5 μm. 50 Weight average particle diameter d 50can be measured by any suitable method known to those skilled in the art, for example by photon correlation spectroscopy according to standard DIN ISO 13321 (2004) when using commercially available instruments, for example the N5 Submicron Particle Size Analyzer from Beckman Coulter Inc, or, for particles having a size above 1.0 μm, by static light scattering using an instrument such as the SZ-10 Nanoparticle Analyzer from Horiba Scientific Ltd.

[0075] To ensure a particularly homogeneous dispersion of the inorganic filler particles in the poly(meth)acrylate matrix material, it is further advantageous for the inorganic filler to have an oil absorption of 5 g / 100 g filler or more, preferably 10 g / 100 g filler or more, particularly preferably 15 g / 100 g filler or more. It is further advantageous for the inorganic filler to have an oil absorption of 100 g / 100 g filler or less, preferably 70 g / 100 g filler or less, particularly preferably 50 g / 100 g filler or less. The oil absorption can be determined according to the standard DIN EN ISO 787-5 (1995).

[0076] For example, if it is desired to color Layer B white, titanium dioxide may be advantageously used as a filler. Typically, the rutile or anatase forms of titanium dioxide may be used, with the rutile form being particularly preferred due to its low photocatalytic activity. Such materials can be produced by the chloride process and are commercially available from various suppliers, for example, KRONOS TITAN GmbH (Leverkusen, Germany).

[0077] Suitable titanium dioxide fillers may or may not be modified with water-insoluble oxides of aluminum, silicon, zinc, or other reagents; these reagent materials are specifically incorporated to improve the properties of the colorant in use. Ideally, the titanium dioxide filler should be free of extenders such as barium sulfate, clay, magnesium silicate, whiteners, etc. Titanium dioxide fillers classified as Types II, III, and IV according to ASTM D476 (2015) are particularly preferred.

[0078] Layer B typically contains 5.0% by weight to 35.0% by weight, preferably 7.5% by weight to 32.5% by weight, and more preferably 10.0% by weight to 30.0% by weight, based on the weight of Layer B.

[0079] coloring agent The colorant for use in Layer A of the foil is not particularly limited. In a preferred embodiment, the colorant is a pigment. In some embodiments, Layer A of the film can be colored black. Suitable pigments for this purpose can be selected from, for example, carbon black, iron oxide, especially iron(III) oxide, cobalt oxide, aniline black, and perylene black, with carbon black being particularly suitable. In other embodiments, a red color in Layer A can be prepared by using at least one red pigment. Suitable red pigments include (Color Index CI) Pigment Red (PR) 48:2, 48:3, 57:1, 101, 112, 122, 144, 166, 168, 178, 179, 202, 214, 254, 255, 264, 272, 276, 277, and Pigment Violet (PV) 19, but are not limited to these.

[0080] The concentration of pigment in Layer A is determined by the desired L * The concentration is generally in the range of 0.5 to 20.0 wt. %, preferably 1.0 to 10.0 wt. %, more preferably 1.5 to 7.0 wt. %, based on the weight of layer A.

[0081] The average primary particle size of the carbon black pigment is usually in the range of 5.0 to 100.0 nm, more preferably 7.0 to 60.0 nm. 50 can be determined by methods known to those skilled in the art, for example, by photon correlation spectroscopy according to standard DIN ISO 13320 (2004) when using commercially available equipment such as the LS 13 320 Laser Diffraction Particle Size Analyzer from Beckman Coulter Inc. Furthermore, the specific surface area of ​​the particles measured by the BET method, standard ISO 9277, is between 50 and 500 m 2 / g, e.g., 70 to 400 m 2 It has been shown that selecting carbon black particles with a % wt. / g yields advantageous foil properties. The carbon black can be treated or untreated. For example, carbon black can be treated with certain gases or organic substances, such as butyllithium. Such treatments can modify or functionalize the surface, further promoting compatibility with the polymer matrix of Layer A.

[0082] Carbon black suitable for use in the foils of the present invention differs from so-called conductive black in that it has low or no electrical conductivity. Compared to the carbon black used herein, conductive black has a specific morphology and superlattice structure to achieve high electrical conductivity. In contrast, the carbon black particles used herein are very easily dispersed in thermoplastic resins, resulting in virtually no agglomerated regions of carbon black, which may result in corresponding electrical conductivity. Suitable carbon blacks are commercially available under numerous trade names and in numerous forms, such as pellets or powders. For example, suitable carbon blacks are available under the trade name BLACK PEARLS®, in wet-processed pellet form under the names ELFTEX®, REGAL®, and CSX®, and in agglomerated form under the names MONARCH®, ELFTEX®, REGAL®, and MOGUL®, all available from Cabot Corporation. Printex® 60 and Printex® 90 (Orion Engineered Carbons GmbH) are also suitable for this purpose.

[0083] In a further preferred embodiment, the colorant in Layer A is a dye. Suitable dyes include, in particular, red dyes, i.e., those designated as Solvent Red, Acid Red, or Modern Red by their Color Index (CI). Examples include anthraquinone dyes such as Solvent Red 111, 143, 145, 146, 150, 151, 155, 168, 169, 172, 175, 181, 207, 222, 227, 230, 245, and 247; perinone dyes such as Solvent Red 135, 162, and 179; and monoazo dyes such as Solvent Red 195.

[0084] UV absorbers and stabilizers UV absorbers and UV stabilizers for use in the foils of the present invention are well known and are described in detail, for example, in Hans Zweifel's Plastics Additives Handbook, Hanser Verlag, 5th Edition, 2001, p. 141 ff. UV stabilizers are understood to include UV stabilizers and free radical scavengers.

[0085] UV absorbers may, for example, come from the groups of substituted benzophenones, salicylates, cinnamates, oxanilides, benzoxazinones, hydroxyphenylbenzotriazoles, triazines or benzylidene malonates. The best known representative UV stabilizers / free radical scavengers are provided by the group of sterically hindered amines (hindered amine light stabilizers, HALS).

[0086] Advantageously, the combination of UV absorber and UV stabilizer used in the coextruded acrylic foil comprises the following components: Component A: UV absorber of the benzotriazole type, Component B: UV absorber of triazine type, Component C: UV stabilizer (HALS compound) It is composed of:

[0087] The individual components can be used in the form of individual substances or mixtures.

[0088] Benzotriazole-type UV absorbers are known in the prior art and are typically 2-(2'-hydroxyphenyl)benzotriazoles. Corresponding compounds include, in particular, 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole, 2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)benzotriazole, 2-(5'-tert-butyl-2'-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-5'-(1,1,3,3-tetramethylbutyl)phenyl)benzotriazole, 2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)- 5-Chloro-benzotriazole, 2-(3'-tert-butyl-2'-hydroxy-5'-methylphenyl)-5-chloro-benzotriazole, 2-(3'-sec-butyl-5'-tert-butyl-2'-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-4'-octyloxyphenyl)benzotriazole, 2-(3',5'-di-tert-amyl-2'-hydroxyphenyl)benzotriazole, 2-(3',5'-bis-(α,α-Dimethylbenzyl)-2'-hydroxyphenyl)benzotriazole, 2-(3'-tert-butyl-2'-hydroxy-5'-(2-octyloxycarbonylethyl)phenyl)-5-chloro-benzotriazole, 2-(3'-tert-butyl-5'-[2-(2-ethylhexyloxy)-carbonylethyl]-2'-hydroxyphenyl)-5-chloro-benzotriazole, 2-(3'-tert-butyl-2'-hydroxy-5'-(2-methoxycarbonylethyl)phenyl)-5-chloro-benzotriazole, 2 -(3'-tert-butyl-2'-hydroxy-5'-(2-meta-oxycarbonylethyl)phenyl)benzotriazole, 2-(3'-tert-butyl-2'-hydroxy-5'-(2-octyloxycarbonyl-ethyl)phenyl)benzotriazole, 2-(3'-tert-butyl-5'-[2-(2-ethylhexyloxy)carbonylethyl]-2'-hydroxy-phenyl)benzotriazole, 2-(3'-dodecyl-2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(3'-tert-butyl- 2'-Hydroxy-5'-(2-isooctyloxy-carbonylethyl)phenylbenzotriazole, 2,2'-methylene-bis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazol-2-ylphenol]; transesterification product of 2-[3'-tert-butyl-5'-(2-methoxycarbonylethyl)-2'-hydroxyphenyl]-2H-benzotriazole with polyethylene glycol 300; [R-CH2CH2-COO-CH2CH2-, where R=3'-tert-butyl-4'-hydroxy-5 '-2H-benzotriazol-2-ylphenyl, 2-[2'-hydroxy-3'-(α,α-dimethylbenzyl)-5'-(1,1,3,3-tetramethylbutyl)-phenyl]-benzotriazole; 2-[2'-hydroxy-3'-(1,1,3,3-tetramethylbutyl)-5'-(α,α-dimethylbenzyl)-phenyl]benzotriazole. Further examples of benzotriazole-type UV absorbers that can be used include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-[2-hydroxy-3,5-di(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3-sec-butyl-5-tert-butylphenyl)benzotriazole and 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, phenol, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)].

[0089] These compounds are commercially available, for example as Tinuvin® 360 and Tinuvin® 234, from BASF SE (Ludwigshafen, Germany).

[0090] The amount of benzotriazole-type UV absorbers used is 0.1% to 5.0% by weight, preferably 0.2% to 3.0% by weight, and very particularly preferably 0.5% to 2.0% by weight, based on the weight of the coextruded acrylic foil. It is also possible to use mixtures of different benzotriazole-type UV absorbers.

[0091] The triazine type UV absorber is typically 2-(2-hydroxyphenyl)-1,3,5-triazine.Preferably used 2-(2-hydroxyphenyl)-1,3,5-triazines include, inter alia, 2,4,6-tris(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-octyloxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2-hydroxy-4-propyl-oxyphenyl)-6- (2,4-dimethylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-octyloxyphenyl)-4,6-bis(4-methylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-tridecyloxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[2-hydroxy-4-(2-hydroxy-3-butyloxyphenyl)] 2-[2-hydroxy-4-(2-hydroxy-3-octyloxypropyloxy)phenyl]-4,6-bis(2,4-dimethyl)-1,3,5-triazine, 2-[4-(dodecyloxy / tridecyloxy-2-hydroxypropoxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[2-hydroxy-4-(2-hydroxy-3-dodecyloxypropyloxy)phenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, )phenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-hexyloxy)phenyl-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2,4,6-tris[2-hydroxy-4-(3-butoxy-2-hydroxypropoxy)phenyl]-1,3,5-triazine, 2-(2-hydroxyphenyl)-4-(4-methoxyphenyl)-6-phenyl-1,3,5-triazine, 2-{2-hydroxy-4-[3-(2-ethylhexyl-1-oxy)-2-hydroxypropyloxy]phenyl}-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(4-[2-ethylhexyloxy]-2-hydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine. Triazine-type UV absorbers, such as 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol, can also be used.

[0092] These compounds are commercially available, for example, under the trademarks Tinuvin® 1600, Tinuvin® 1577 or Tinuvin® 1545 from BASF SE (Ludwigshafen, Germany).

[0093] The amount of triazine-type UV absorber is 0.1 to 5.0% by weight, preferably 0.2 to 3.0% by weight, very particularly preferably 0.5 to 2.0% by weight, based on the weight of the foil. It is also possible to use mixtures of different triazine-type UV absorbers.

[0094] The foils of the present invention may further contain one or more UV stabilizers which typically act as antioxidants, radical scavengers, etc. Particularly preferred UV stabilizers are sterically hindered phenols and HALS type additives.

[0095] Sterically hindered amines, or HALS (hindered amine light stabilizers), UV stabilizers are known per se. They can be used to inhibit aging in paints and plastics, especially polyolefin plastics (Kunststoffe, 74 (1984) 10, pp. 620-623; Farbe + Lack, Volume 96, 9 / 1990, pp. 689-693). The tetramethylpiperidine group present in HALS compounds is responsible for the stabilizing effect. This class of compounds can be unsubstituted on the piperidine nitrogen or substituted with alkyl or acyl groups on the piperidine nitrogen. Sterically hindered amines do not absorb in the UV region. They capture the formed free radicals, which UV absorbers cannot do. Examples of HALS compounds which have a stabilizing effect and which can also be used in the form of mixtures are: bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro(4,5)-decane-2,5-dione, bis(2,2,6,6-tetramethyl-4-piperidyl)succinate, poly(N-β-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidine succinate) or bis(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate.

[0096] These compounds are commercially available, for example, under the trademarks Tinuvin® 123, Tinuvin® 144 or Tinuvin® 292 from BASF SE (Ludwigshafen, Germany).

[0097] The amount of HALS compound used in the foil is typically 0.0 to 5.0% by weight, preferably 0.1 to 3.0% by weight, and very particularly preferably 0.2 to 2.0% by weight, based on the weight of the foil. It is also possible to use mixtures of different HALS compounds.

[0098] Sterically hindered phenols are also suitable for use in the foils of the present invention. Preferred sterically hindered phenols include, inter alia, 6-tert-butyl-3-methylphenyl derivatives, 2,6-di-tert-butyl-p-cresol, 2,6-tert-butyl-4-ethylphenol, 2,2'-methylenebis-(4-ethyl-6-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl-m-cresol), 4,4'-thiobis(6-tert-butyl-m-cresol), 4,4'-dihydroxydiphenylcyclohexane, alkylated bisphenols, styrenated phenols, 2,6-di-tert-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenyl), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), stearyl-β(3,5-di-4-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3-5-di-tert-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane. Commercially available sterically hindered phenols include Sumilizer™ BHT BP-76, WXR, GA-80, and BP-101 (Sumitomo Chemical, Osaka, Japan), Irganox® 1076, 565, 1035, 1425WL, 3114, 1330, and 1010 (BASF SE, Ludwigshafen, Germany), MARK AO-50, -80, -30, -20, -330, and -60 (ADEKA Polymer Additives, Mulhouse, France), and Tominox® SS, TT (Mitsubishi Chemical Corporation, Yoshitomi, Japan).

[0099] In general, the foils of the present invention typically contain 0.0% to 5.0% by weight of one or more UV absorbers and 0.0% to 5.0% by weight of one or more UV stabilizers, based on the weight of the coextruded acrylic foil.

[0100] Co-extruded acrylic foil To optimally serve its intended purpose, the coextruded acrylic foil of the present invention preferably has a tensile strength of 20.0 MPa to 70.0 MPa, measured according to DIN EN ISO 527-3 / 2 / 100 (2003) using a foil having a thickness of 50.0 μm. Foils having a tensile strength of less than 20.0 MPa will still be suitable for use in accordance with the present invention, but great care will need to be taken during their manufacture and handling, as the foil may tear easily.

[0101] On the other hand, although the co-extruded acrylic foils of the present invention having a tensile strength above 70.0 MPa are very suitable for the manufacturing process of laser-engravable labels, the use of such labels increases the risk that after removing such labels from the substrate to be initially labeled using a thin sharp blade (e.g., a razor blade), they may re-stick onto another substrate.

[0102] In view of having a good balance between handling and brittleness of the foil, the initial tear resistance is preferably in the range of 1.0 N to 15.0 N. The tensile strength of coextruded acrylic foils can be determined by common methods known to those skilled in the art, such as the method described in standard DIN EN ISO 527-3 / 2 / 100 (2003), and is typically measured in the extrusion direction.

[0103] Preferably, the coextruded acrylic foil has a tear propagation resistance of 0.01 N to 1.50 N, preferably 0.1 N to 1.00 N, measured according to ASTM D1938(2014) using a foil having a thickness of 50.0 μm. Tear propagation resistance is typically measured in the extrusion direction.

[0104] Furthermore, to ensure an optimal balance between the processability of the coextruded acrylic foil and the ability of the final laser-engravable label to withstand unauthorized attempts to remove it, the coextruded acrylic foil preferably has an elongation at break ranging between 0.5% and 30%, measured according to DIN EN ISO 527-3 / 2 / 100 (2003) using a foil having a thickness of 50.0 μm, with an elongation at break ranging between 2.0% and 20.0% being particularly advantageous with regard to handling.

[0105] If the elongation at break is less than 2.0%, the foil's flexibility is too low, making it difficult to handle and requiring careful attention to avoid damaging the foil during production. In such circumstances, the manufacturing process may need to be run at a slower speed. On the other hand, if the elongation at break is greater than 30.0%, the foil tends to be less brittle. Therefore, when attempting to remove a laser-engravable label with a thin, sharp blade, small mechanical deformations of the foil may not necessarily result in complete breakage. This increases the risk that an experienced person skilled in using a sufficiently thin, sharp tool will successfully remove the laser-engravable label from its original substrate (e.g., a replaceable part in a vehicle engine) and reattach it to another object (a non-genuine replaceable part). The elongation at break of coextruded acrylic foil can be measured by common methods known to those skilled in the art, such as those described in standard DIN EN ISO 527-3 / 2 / 100 (2003).

[0106] According to the invention, there are also various influencing factors, by varying which the skilled person can adjust the elongation at break of the foil of the invention in the desired direction.

[0107] The major influencing factors are the amounts of impact modifier and inorganic filler. More specifically, as the concentration of impact modifier increases, the elongation at break also increases, and therefore, according to the present invention, a small amount of impact modifier contributes to a low elongation at break.

[0108] In one preferred embodiment, the initial tear resistance of the coextruded acrylic foil is at least 10 times, preferably at least 50 times, and even more preferably 100 times, its tear propagation resistance. This is particularly advantageous, as it ensures that even a small foil break that occurs during an attempt to fraudulently remove the laser-engravable label from the substrate will rapidly propagate throughout the entire label, completely destroying it. This further reduces the risk of fraudulent label removal.

[0109] In one embodiment, the dimensional stability of the extruded foil of the present invention at 120°C (60 min) is 0.7% or less, preferably 0.5% or less in the machine direction (direction of extrusion) and 0.5% or less, preferably 0.3% or less in the cross direction (direction perpendicular to the machine direction).

[0110] The dimensional stability can be measured according to the standard DIN EN ISO 11501 (2004) using a foil having a thickness of 50.0 μm. The measurement can be carried out at 120° C. for 30 minutes.

[0111] Furthermore, the foils of the present invention have excellent chemical resistance in the presence of common chemicals such as disinfectants, detergents, etc. and a variety of fluids commonly used in road vehicles such as hydraulic oil, engine oil, etc. This makes the foils highly suitable for use as under-hood labels in automobiles.

[0112] The thickness of the coextruded acrylic foil of the present invention is preferably in the range of 10.0 μm to 200.0 μm. If the thickness is less than 10.0 μm, great care must be taken during the manufacturing and handling of the foil to avoid breakage. On the other hand, if the foil thickness exceeds 200.0 μm, its mechanical stability is significantly increased, similarly increasing the risk of the foil being damaged during unauthorized label removal attempts. Furthermore, a high foil thickness results in a high thickness of the laser-engravable label containing it, which may be disadvantageous for aesthetic or other reasons. From the viewpoint of having a good balance between handling and flatness, the thickness of the coextruded acrylic foil is preferably in the range of 30.0 μm to 90.0 μm, with a range of 40.0 μm to 75.0 μm being even more preferred.

[0113] Typically, layer A has a thickness d of 2 μm to 100 μm, preferably 5 μm to 90 μm, more preferably 10 μm to 80 μm. A The layer B has a thickness d of usually 5 μm to 100 μm, preferably 10 μm to 90 μm, and more preferably 20 μm to 80 μm. B It has.

[0114] The thickness of the foil of the present invention and its individual layers A and B can be determined by mechanical scanning according to the standard ISO 4593 (1993). Preferably, however, the thickness of the foil of the present invention is determined using micrographs obtained using a scanning electron microscope such as a JEOL JSM-IT300 (commercially available from JEOL GmbH, Freising, Germany). For this purpose, the foil sample can be frozen in liquid nitrogen and mechanically destroyed, and the fresh surface is analyzed. For example, the following parameters can be used to perform the measurement: Current source: A variable flow of electrons from a tungsten filament (cathode) Vacuum system: Rotary pump / oil diffusion pump XYZ rotation-tilt: Fully motor-driven Working distance (WD): 5-70mm (common: 10mm) Sample rotation: 360° Specimen tilt: -5 to 90° (depending on WD) Magnification: 10x~300,000x Maximum resolution: about 3nm Detector: Secondary electrons (SE) Backscattered electrons (BSE, 5 segments) Energy Dispersive X-ray Analysis (EDS)

[0115] Detailed configuration of the line preferably used for manufacturing the foil of the present invention The acrylic foil used in accordance with the present invention is preferably produced by a coextrusion process. In contrast to foils produced by a solution coating process, coextruded acrylic foils are substantially free of volatile organic compounds such as solvents, which is highly advantageous for toxicity and environmental reasons. The individual components of layers A and B of the coextruded acrylic foil can be blended before or even during the extrusion process.

[0116] For the extrusion of co-extruded acrylic foils, a line having at least the following components can be used: extruder, optionally a melt pump; optional melt filtration equipment, an optional static blending element, Flat foil die, a polishing stack or chill roll, and Winding machine.

[0117] In the process of the present invention, the hot melt is extruded from the die of the extruder onto the nip between two polishing rolls or onto a chill roll. The optimum melt temperature depends, for example, on the composition of the mixture and can therefore vary within a wide range. The preferred temperature of the molding composition up to the point of entry into the die is in the range of 170°C to 320°C, more preferably in the range of 200°C to 290°C, and most preferably in the range of 220°C to 280°C. The temperature of the polishing roll is preferably below 150°C, more preferably between 60°C and 140°C.

[0118] In one embodiment, the die temperature is higher than the temperature of the mixture before it enters the die. The die temperature is preferably set 10°C higher, more preferably 20°C higher, and most preferably 30°C higher than the temperature of the mixture before it enters the die. Thus, preferred die temperatures are in the range of 160°C to 330°C, more preferably 190°C to 300°C.

[0119] The polishing stack can consist of two or three polishing rolls. Polishing rolls are widely known in the art and are used to obtain high gloss. Nevertheless, rolls other than polishing rolls, such as matte rolls, can also be used in the process of the present invention. A sheet is formed at the nip between the first two polishing rolls, which is then cooled simultaneously to form a foil.

[0120] Alternatively, chill rolls are known to those skilled in the art. Here, the melt sheet can be deposited on a single chill roll, which is then transported further. The chill roll is preferably located above the polishing stack. Alternatively, extrusion can be particularly advantageously carried out using the equipment described in US Patent Application Publication Nos. 2016 / 0159995 and 2017 / 0306188, the entire disclosures of which are incorporated herein by reference. Particularly good surface quality of the foil can be ensured if the die and roll have chrome surfaces, in particular if these chrome surfaces have a roughness Ra (according to DIN 4768 (1990)) of less than 0.10 μm, preferably less than 0.08 μm.

[0121] To ensure that the coextruded acrylic foil is substantially free of impurities, a filter can optionally be placed before the melt enters the die. The mesh size of the filter is generally determined by the starting materials used and can therefore vary within a wide range. Mesh sizes generally range from 300 μm to 20 μm. A filter with two or more screens with different mesh sizes can be placed before the die. These filters are commercially available. To obtain high-quality foil, it is also advantageous to use particularly pure raw materials.

[0122] Optionally, a static mixing element may also be installed upstream of the flat foil die, which may be used to mix ingredients such as colorants, stabilizers or additives into the polymer melt, or up to 5% by weight of a second polymer may be mixed into the material, for example in melt form, from a second extruder.

[0123] The pressure at which the molten mixture is forced into the die can be controlled, for example, by the screw speed. The pressure is typically in the range of 40 bar to 300 bar, but this does not limit the method of the present invention. Therefore, the speed at which a foil can be obtained according to the present invention is generally higher than 5 m / min, more particularly higher than 10 m / min.

[0124] To ensure a particularly uniform transport of the melt, a melt pump may additionally be installed upstream of the flat foil die.

[0125] To further improve the handling of the coextruded acrylic foil of the present invention, it is advantageous if a liner layer 10 is bonded to the coextruded acrylic foil 4 downstream of the extruder of step i) at a temperature below the glass transition temperature of the acrylic polymer used, thereby obtaining a laminate 11.

[0126] The resulting laminate 11 typically comprises two layers (see Figure 3): a layer formed by coextrusion of acrylic foil 4; and 10 liner layers It consists of:

[0127] In one embodiment, the liner layer 10 is self-adhesive. Alternatively, the liner layer 10 may have an adhesive layer, which may be advantageously used to bond the liner layer 10 to a co-extruded acrylic foil 4 having a matte surface. In a further embodiment, the liner layer 10 may have a layer of polyethylene copolymer instead of an adhesive layer. Such a liner is advantageously used with a co-extruded acrylic foil 4 having a glossy surface.

[0128] To ensure good mechanical stability and particularly high tear strength of the laminate 11, the liner layer 10 advantageously has an initial tear resistance of preferably 50 N to 500 N measured in accordance with ASTM D1004 (2013). The material of the liner layer 10 is not particularly limited, as long as it has sufficient tear resistance and can be selected from one of the following: polyethylene, polypropylene, polyimide, polyethylene terephthalate and polyethylene naphthalate, preferably biaxially oriented polypropylene or biaxially oriented polyethylene terephthalate or mixtures thereof (biaxially oriented polypropylene or biaxially oriented polyethylene terephthalate being particularly preferred).

[0129] In subsequent process steps, laminate 11 undergoes bonding of adhesive layer 7, optionally release coating layer 8, and support layer 9 to provide label substrate 12 (FIG. 3). These process steps are well known to those skilled in the art and are described in detail, for example, in U.S. Patent Application Publication Nos. 2004 / 0091657 and 2011 / 0132522.

[0130] In a preferred embodiment, the method comprises at least the following steps: i) producing a coextruded acrylic foil 4 according to any one of claims 1 to 9 using an extruder; and ii) downstream of the extruder, bonding a liner layer 10 to the co-extruded acrylic foil 4 from step i). Includes:

[0131] The laminate 11 obtained in step ii) can then be passed between several rolls, at least one of which facing the side of the coextruded acrylic foil 4 is a cooled roll.

[0132] Alternatively, the method comprises at least the following steps: i) producing a co-extruded acrylic foil according to any one of claims 1 to 9 using an extruder; ii) passing the co-extruded acrylic foil obtained in step i) between a plurality of rolls, at least one of which is a chill roll; and iii) bonding a liner layer to the co-extruded acrylic foil from step ii). may include:

[0133] Typically, adhesive layer 7 consists essentially of a pressure-sensitive adhesive (PSA). The backing layer typically comprises paper or a plastic foil material and may be coated with a release coating layer 8. Various release coating compositions are known, such as those described in U.S. Pat. No. 6,406,787. Non-PSA adhesive compositions may be particularly used in embodiments where the foam backing layer is porous (e.g., paper) and the foam substrate is exposed on the non-viewing side of the label.

[0134] The PSAs suitable for the present invention are preferably selected from the group consisting of alkyl acrylate polymers and copolymers, copolymers of alkyl acrylate and acrylic acid, terpolymers of alkyl acrylate, acrylic acid, and vinyl lactate, alkyl vinyl ether polymers and copolymers, polyisoalkylenes, polyalkyldienes, alkyldiene-styrene copolymers, styrene-isoprene-styrene block copolymers, polydialkylsiloxanes, polyalkylphenylsiloxanes, natural rubber, synthetic rubber, chlorinated rubber, latex crepe, rosin, coumarone resins, alkyd polymers, and polyacrylate esters, and mixtures thereof. Examples include polyisobutylene, polybutadiene, or butadiene-styrene copolymers, and mixtures thereof (such polymers and copolymers preferably do not have reactive moieties, i.e., do not oxidize in the presence of air); silicone-based compounds, such as polydimethylsiloxanes, and polymethylphenylsiloxanes combined with other resins and / or oils.

[0135] Other suitable PSAs include tacky thermoplastics and tacky thermoplastic elastomers, where the tackifier comprises one or more compounds that increase the tackiness of the composition. An example of a tacky thermoplastic resin useful as a strong PSA is a vinyl acetate / ethylene copolymer known under the trade name VYNATHENE EY 902-30 (available from Quantum Chemicals, Cincinnati, Ohio), a combination of substantially equal proportions of tackifiers known under the trade names PICCOTEX LC (a water-based white thermoplastic resin produced by copolymerization of α-methylstyrene monomer with vinyltoluene, having a ring and ball softening point of about 87°C to 95°C, available from Hercules Incorporated, Wilmington, Delaware) and WINGTACK 10 (a liquid aliphatic C-5 petroleum hydrocarbon resin available from Goodyear Chemical), and an organic solvent such as toluene. An example of a tacky thermoplastic elastomer useful as a strong PSA is a styrene-poly(ethylene-butylene)-styrene block copolymer known under the tradename KRATON G1657 (available from Shell Chemicals) in combination with one or more low molecular weight hydrocarbon resins known under the tradename REGALREZ (manufactured by Hercules) and an organic solvent such as toluene. Both of these formulations can be applied using a knife coater and air-dried or air-dried followed by oven-drying. Of course, the present invention is not limited to the use of these particular combinations of thermoplastic resin, thermoplastic elastomer, and tackifier.

[0136] Some currently preferred PSAs exhibit long shelf life and resistance to thinning under atmospheric conditions and include acrylic copolymer adhesives such as those disclosed in U.S. Pat. No. 24,906. One example of such an acrylic copolymer is a 95.5:4.5 (measured in parts by weight) isooctyl acrylate / acrylic acid copolymer. Another preferred adhesive is a copolymer of a 90:10 weight ratio combination of these two monomers. Still other preferred adhesives are terpolymers of ethyl acrylate, butyl acrylate, and acrylic acid; copolymers of isooctyl acrylate and acrylamide; and terpolymers of isooctyl acrylate, vinyl acetate, and acrylic acid.

[0137] Acrylic PSAs are applied from a coatable composition containing an organic solvent, such as a heptane:isopropanol solvent mixture, which can then be evaporated to leave a pressure-sensitive adhesive coating. This layer is preferably about 0.038 centimeters (cm) to about 0.11 cm (5 to 15 mils) thick when the substrate is retroreflective sheeting.

[0138] PSAs useful in the present invention may also be characterized as having a 180° peel adhesion in the range of about 10 to about 1000 g / cm, more preferably at least about 50 g / cm. For strong PSAs, the 180° peel adhesion is typically in the range of about 200 g / cm to about 600 g / cm, measured using a standard test procedure. In this procedure, the force required to remove (i.e., peel) the PSA-coated substrate from the test substrate is referred to as the "peel adhesion" value. A standard glass plate is cleaned with a solvent (e.g., one wash with diacetone alcohol followed by three washes with n-heptane). Next, a PSA-backed adhesive-coated sample is applied, PSA-side down, along the center of the standard glass plate with very light tension. The sample is then rolled once with a 2.04 kg hand roller. The standard glass plate is then secured to the horizontal plate of a standard peel adhesion tester, such as one known under the trademark "IMASS." One end of the sample is then attached to a hook that is part of a peel adhesion tester. The sample is peeled from the standard glass plate at a 180° angle (i.e., one end of the sample is pulled toward the other end) by moving the platen horizontally at a rate of 228.6 cm / min, and the force required for various dwell times is recorded in g / cm of sample width.

[0139] The release coating layer 8, which is typically a siloxane coating, serves the purpose of reducing the adhesion between the adhesive layer 7 and the support layer 9. Typically, the release coating layer 8 makes it possible to achieve a dynamic coefficient of friction of less than 0.35, preferably less than 0.25, determined according to standard ASTM D1894(2014).

[0140] Finally, the label substrate 1 is kiss-cut to form a plurality of individual self-adhesive, laser-engravable labels 2 bonded to the support layer 9. Kiss-cutting can be done by mechanical die-cutting as described in U.S. Patent Application Publication No. 2011 / 0132522, or by using a laser. In a subsequent step, the waste matrix 3 surrounding the individual self-adhesive, laser-engravable labels 2 is peeled from the support layer 9 without risk of fracture.

[0141] To minimize waste formation, the distance between individual labels (i.e., the width of the stripes in the waste matrix) is maintained in the range of 1.0 mm to 10.0 mm, more preferably 2.0 mm to 8.0 mm, and even more preferably 3.0 mm to 5.0 mm. As noted above, undesired breakage of the waste matrix does not occur. Typically, the peel force during this operation is less than 30 g / in, preferably less than 20 g / in, and even more preferably 1 g / in to 10 g / in, as measured using a T-peel test with tesaband® 7475 tape manufactured by tesa SE (Norderstedt, Germany).

[0142] Laser Engravable Labels The laser-engravable label 2 of the present invention comprises at least the following layers in the listed order (see FIG. 2): a) a layer consisting of the coextruded acrylic foil 4 described above, b) adhesive layer 7, c) a release coating layer 8, and d) Support layer9.

[0143] Typically, the laser-engravable label of the present invention has a thickness of 50.0 μm to 300.0 μm, more preferably 100.0 μm to 200.0 μm.

[0144] In an exemplary embodiment, Layer 4 (co-extruded acrylic foil) may have a thickness of 10.0 μm to 200.0 μm, more preferably 30 μm to 150 μm, even more preferably 40.0 μm to 100.0 μm; The adhesive layer 7 may have a thickness of 10.0 μm to 40.0 μm, more preferably 20.0 μm to 30.0 μm; The release coating layer 8 may have a thickness of 0.01 μm to 1.5 μm, preferably 0.5 μm to 1.2 μm, more preferably 0.6 μm to 0.8 μm; and The support layer 9 may have a thickness of 20.0 μm to 70.0 μm, preferably 30.0 μm to 50.0 μm.

[0145] The size of laser-engravable labels can in principle be freely chosen and is limited only by the dimensions of the extrusion die and / or glazing stack used for their production. This means that the format is virtually freely selectable.

[0146] Trimming and kiss-cutting of the coextruded acrylic foil is preferably accomplished by die cutting, cutting, laser cutting or laser die cutting, with laser cutting or laser die cutting being particularly preferred.

[0147] Optionally, but not necessarily, the co-extruded acrylic foil produced in accordance with the present invention may additionally be provided with ridges, cuts, slits or perforations or notches to further facilitate destruction of the label during an attempt to tamper with the label, although such additional means are not required.

[0148] Laser-engravable labels are well suited for producing electronic product identification labels, automotive under-hood labels, chip cards, heat-resistant documents, and seals. One exemplary use case is barcode labels in various parts of automobile engines. The labels can withstand the engine's operating temperatures without noticeable shrinkage and are chemically resistant to fluids such as brake fluid, hydraulic fluid, and engine oil. The labels are destroyed when an unauthorized attempt is made to remove them from an engine part for transfer to a non-original, interchangeable part.

[0149] As a further example, the label of the present invention may bear a vehicle identification number and may be advantageously used under the hood of a vehicle: any attempt to fraudulently remove the label from the vehicle in order to apply it to another vehicle will result in the label being destroyed.

[0150] Experimental Department Examples 1 to 25 Foils comprising layers A and B were produced by adapter coextrusion using the chill roll method at an extrusion speed of 7.3 m / min using a 35 mm diameter single screw extruder and a 25 mm diameter single screw coextruder from Dr. Collin GmbH (Ebersberg, Germany) under the following conditions: Extruder screw temperature: 240℃~270℃ Die temperature: 240℃~285℃ Melt temperature at die: 240℃~285℃ Roll temperature: 50℃~120℃.

[0151] Alternatively, the manufacture of the foil can be achieved by a multi-manifold co-extrusion process or a combination of adapters and multi-manifold co-extrusion.

[0152] The pigment used in Layer A was Carbon Black FW1 (Pigment Black 7) available from Cary Company (Addison, USA).

[0153] As a filler, 4.0 g / cm 2 available from KRONOS TITAN GmbH (Germany) was used. 3 density (DIN EN ISO 787-10) and oil absorption of titanium dioxide of 17 g / 100 g (DIN EN ISO 787-5) * Titanium dioxide (rutile) having the following structure was used.

[0154] Acrylic polymer 1 in the examples below was PMMI PLEXIMID® TT50 available from Roehm GmbH (Darmstadt, Germany).

[0155] Acrylic polymer 2 mentioned in the examples below is a copolymer of 99 wt. % methyl methacrylate and 1 wt. % methyl acrylate, with a weight average molecular weight Mw of 110,000 g / mol (measured by GPC against PMMA standard) and was available from Röhm GmbH (Darmstadt, Germany).

[0156] Acrylic polymer 3 mentioned in the examples below is a copolymer of 96 wt. % methyl methacrylate and 4 wt. % methyl acrylate, with a weight average molecular weight Mw of 155,000 g / mol (measured by GPC against PMMA standard) and was available from Röhm GmbH (Darmstadt, Germany).

[0157] Acrylic polymer 4 given in the examples below was a copolymer of 75% by weight of MMA, 15% by weight of styrene and 10% by weight of maleic anhydride, the weight-average molar mass Mw of which was about 140,000 g / mol (determined by GPC against PMMA standard).

[0158] Impact Modifier 1 was ACRYPET™ IR 441 available from Mitsubishi Chemical Co (Japan).

[0159] Impact modifier 2 was Paraloid™ EXL-2688 available from Dow Chemical Co. (USA).

[0160] Impact Modifier 3 was a butyl acrylate based acrylic core-shell-shell impact modifier.

[0161] This foil can be used to produce self-adhesive, laser-engravable labels without undesirable breakage of the waste matrix.

[0162] The compositions and layer thicknesses of the foils of Examples 1 to 25 are summarized in Table 1 below: [Table 1-1] [Table 1-2]

[0163] Mechanical property evaluation The mechanical properties of the foils were measured on four identical samples using a Zwick Roell Z005 testing system available from Zwick GmbH & Co. KG (Ulm, Germany), with five tests performed for each sample. Prior to measurement, all specimens were conditioned at 23°C and 50% relative humidity for at least 16 hours.

[0164] The tensile strength and elongation at break were determined according to DIN EN ISO 527-3 (2019) at 100 mm / min.

[0165] The initial tear resistance was measured at 51 mm / min (initial grip spacing 25.4 mm) according to ASTM D 1004 / - / 51(2013). The standard tear resistance was calculated by dividing the initial tear resistance by the thickness of the specimen, thus eliminating small differences in thickness and making the samples more comparable.

[0166] Tear propagation force was measured according to ASTM D 1938(2019), where the conditioning was greater than 40 hours before testing.

[0167] The foils of Examples 5 and 6 did not contain an impact modifier in one of the layers and therefore exemplify the teaching of WO 2019 / 057645. These foils were not suitable for industrial scale production as they were very brittle and difficult to handle.

[0168] In contrast to the foils of Examples 5 and 6, the foils of the invention had an advantageous combination of mechanical properties for use in laser-engravable labels. [Table 2-1] [Table 2-2]

[0169] [Table 3]

[0170] Evaluating shrinkage at elevated temperatures The shrinkage of the samples was measured in the extrusion direction and transverse direction at 120°C, 130°C, 140°C, 150°C and 160°C (60 min) according to standard DIN 53377 (2015). Materials with high shrinkage at elevated temperatures are generally not suitable for labeling vehicle parts that can reach such temperatures.

[0171] The foils of Examples 1 and 2 contained PMMI as the acrylic polymer in layers A and B, and therefore, as expected, had fairly low shrinkage in the extrusion direction even at a temperature of 160°C. The foils of Examples 11 and 12 contained a blend of polymethyl methacrylate, which has relatively low heat resistance, in both layers. Therefore, these foils had high shrinkage at or above 130°C. The foils of Examples 5, 6, 7, and 23 contained a copolymer of MMA, styrene, and maleic anhydride. Because this material has relatively high heat resistance, the foils had low shrinkage at temperatures below 140°C. At higher temperatures, significant shrinkage occurred in the extrusion direction.

[0172] The foils of Examples 16-19 contained PMMI in one of the layers, and the other layer contained polymethyl methacrylate, which has low heat resistance. Surprisingly, whether PMMI was present in only one layer or both layers, it was sufficient to ensure that the foils had only moderate shrinkage at high temperatures.

Claims

1. A co-extruded acrylic foil comprising a layer A and a layer B, wherein the layer A comprises, based on the weight of the layer A: 30.0% to 98.5% by weight of one or more acrylic polymers A, 1.0 wt. % to 40.0 wt. % of one or more impact modifiers; 0.5% to 20.0% by weight of one or more colorants; 0.0 wt. % to 10.0 wt. % of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer A and the impact modifier in the layer A is 60.0 wt % to 99.5 wt % based on the weight of the layer A; The layer B contains, based on the weight of the layer B, 30.0% to 92.5% by weight of one or more acrylic polymers B, 2.5 wt.% to 35.0 wt.% of one or more impact modifiers; 5.0 wt.% to 35.0 wt.% of one or more inorganic fillers; 0.0% to 5.0% by weight of one or more UV absorbers, and 0.0% to 5.0% by weight of one or more UV stabilizers Including, the cumulative content of the acrylic polymer B and the impact modifier in the layer B is 60.0 wt % to 95.0 wt % based on the weight of the layer B; the inorganic fillers in said layers A and B are independently selected from zirconium dioxide, titanium dioxide, silica, barium sulfate, aluminum trihydroxide, mica, zinc oxide, zinc sulfide, clay, muscovite, and calcium carbonate; the colorant is a pigment selected from carbon black, iron oxide, cobalt oxide, aniline black, perylene black, Pigment Red 48:2, Pigment Red 48:3, Pigment Red 57:1, Pigment Red 101, Pigment Red 112, Pigment Red 122, Pigment Red 144, Pigment Red 166, Pigment Red 168, Pigment Red 178, Pigment Red 179, Pigment Red 202, Pigment Red 214, Pigment Red 254, Pigment Red 255, Pigment Red 264, Pigment Red 272, Pigment Red 276, Pigment Red 277, and Pigment Violet 19, or a dye selected from anthraquinone dyes, perinone dyes, and monoazo dyes; the foil has a thickness of 10 μm to 200 μm; The layer A has a thickness d A of 5 μm to 100 μm, and the layer B has a thickness d B of 5 μm to 100 μm; Co-extruded acrylic foil.

2. The content (wt%) of one or more impact modifiers in the layer A, n ｉｍＡ But the following relationship: (n ｆＡ +n ｐＡ )≦n ｉｍＡ ≦7 ＊ (n ｆＡ +n ｐＡ ) [n ｆＡ is the content (wt%) of the inorganic filler in Layer A, n ｐＡ is the content (wt %) of said colorant in said Layer A; and The content (wt%) of the impact modifier in Layer B ｉｍＢ But the following relationship: 0.25 ＊ n ｆＢ ≦n ｉｍＢ ≦2 ＊ n ｆＢ [n ｆＢ is the content (wt %) of said inorganic filler in said layer B.

3. 3. The coextruded acrylic foil according to claim 1, wherein at least one of the acrylic polymers A and / or at least one of the acrylic polymers B has a glass transition temperature of at least 110°C.

4. The acrylic polymer A and / or the acrylic polymer B independently comprise at least 50% by weight, based on the weight of the poly(meth)acrylimide, of formula (I): 【Chemistry 1】 [In the formula, R １ and R ２ are independently selected from hydrogen and a methyl group; R ３ is hydrogen or C １ ~C ４ 4. The coextruded acrylic foil according to claim 1, wherein the poly(meth)acrylamide comprises repeating units of the formula: - alkyl group.

5. the acrylic polymer A and / or the acrylic polymer B independently have an average molar mass Mw of 50,000 g / mol to 300,000 g / mol, determined by GPC against PMMA calibration standards and THF as eluent, and the polymerizable component is, based on the weight of the polymerizable composition, (a) 50.0% to 99.9% by weight of methyl methacrylate; (b) 0.1 wt. % to 50.0 wt. % of an acrylic acid ester of a C1 to C4 alcohol; (c) 0.0% to 10.0% by weight of at least one additional monomer copolymerizable with said monomers (a) and (b).

5. The coextruded acrylic foil according to claim 1, obtained by polymerization of a composition comprising:

6. the foil has an elongation at break of 0.5% to 15%, measured according to DIN EN ISO 527-3 (2019), and / or an initial tear resistance of 0.1 N to 30.0 N, measured according to ASTM D1004(2013); and / or Tear propagation resistance of 0.01N to 1.00N measured according to ASTM D1938(2019) 6. The coextruded acrylic foil according to claim 1, wherein

7. At least the following layers: a) a layer consisting of a coextruded acrylic foil as defined in any one of claims 1 to 6 having a thickness of 10 μm to 200 μm; b) an adhesive layer having a thickness of 20 μm to 30 μm; c) a release coating layer having a thickness of 0.6 μm to 0.8 μm; and d) a support layer having a thickness of 30 μm to 50 μm A laser-engravable label comprising the above in the listed order and / or having a thickness of 80 μm to 300 μm.

8. 8. A laminate for producing a laser-engravable label according to claim 7, comprising at least the following layers: a) a liner layer having an initial tear resistance of 50 N to 500 N, measured in accordance with ASTM D1004-13; b) a layer consisting of a coextruded acrylic foil according to any one of claims 1 to 6 Including laminate.

9. 9. The laminate of claim 8, wherein the liner layer consists essentially of a polymeric material selected from the group consisting of polyethylene, polypropylene, polyimide, polyethylene terephthalate, and polyethylene naphthalate.

10. At least the following steps: i) producing the coextruded acrylic foil of any one of claims 1 to 6 using an extruder; ii) passing the co-extruded acrylic foil obtained in step i) between a plurality of rolls, at least one of which is a chill roll; and iii) bonding a liner layer to the coextruded acrylic foil from step ii).

10. A method for producing a laminate according to claim 8 or 9, comprising:

11. At least the following steps: i) producing the coextruded acrylic foil of any one of claims 1 to 6 using an extruder; ii) optionally bonding a liner layer to the co-extruded acrylic foil from step i) downstream of the extruder, resulting in a laminate; iii) bonding an adhesive layer, optionally a release coating layer and a support layer onto the laminate from step ii) or the co-extruded acrylic foil from step i), to obtain a label substrate; and iv) kiss-cutting the label substrate obtained in step iii) and removing the resulting waste matrix, resulting in a plurality of individual self-adhesive, laser-engravable labels on the support layer. A method for producing the self-adhesive laser-engravable label of any one of claims 1 to 6, comprising:

12. 10. Use of the coextruded acrylic foil according to any one of claims 1 to 6 for producing laser-engravable labels.

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