Composite layer for a composite pane

Abstract

The invention relates to a method for smoothing at least one surface (1.1, 2.1) of a thermoplastic layer (1, 2) by means of a smoothing film (8) at a temperature of 80°C to 140°C and at an overpressure of 1 bar to 15 bar. The invention also relates to a method for producing a composite layer (100) by laminating two thermoplastic layers (1, 2), wherein at least one of the layers (1, 2) has, prior to lamination and at least on its inner side, a smoothed surface (1.1, 2.1) having a roughness Rz of not more than 7 µm, and wherein the transmittance for visible light of the first thermoplastic layer (1) differs from the transmittance for visible light of the second thermoplastic layer (2). The invention also relates to a composite layer (100), that can be obtained by this method, for use in a composite pane (101), and to a composite pane (101) comprising such a composite layer (100).

Description

[0001] Composite layer for a composite disc

[0002] The invention relates to a composite layer for a composite disc, a composite disc with such a composite layer, a method for producing a composite layer using a thermoplastic layer and a method for producing such a thermoplastic layer.

[0003] There is a growing demand for glazing, particularly automotive glazing, that combines heat-absorbing properties with safety features. One product type that meets this demand consists of a laminated glass pane with an interlayer containing a tinted or colored thermoplastic safety film such as polyvinyl butyral (hereinafter referred to as PVB for simplicity). The tint of the interlayer reduces the transmission of heat radiation and simultaneously acts as a sunshade, making it particularly attractive for use in automotive roof glazing, but also windshields.

[0004] It can be advantageous to combine thermoplastic layers with different light transmittances—that is, to form composite layers—in order to achieve a specific color in the intermediate layer that would be difficult or impossible to achieve with just one layer. Tinted thermoplastic layers are also generally more expensive, making it worthwhile to combine heavily tinted layers with clear layers to achieve the desired thickness and color of the composite layer.

[0005] However, when laminating thermoplastic layers with different transmittances for visible light, undesirable visual defects regularly occur, which are called "cloudiness". This is a speckled color appearance that reduces the optical quality of the laminated glass.

[0006] To avoid these defects, a transparent interlayer is conventionally inserted between layers with different light transmission levels before lamination. This interlayer results in a more homogeneous appearance in the laminated glass, free of speckles. However, the use of an additional film incurs extra costs, and the interlayer significantly contributes to the overall thickness of the composite layer, which must be taken into account during manufacturing. Furthermore, other visual defects can occur during lamination due to the PET film, caused by its differing shrinkage properties compared to the layers of the interlayer intended for bonding. These optical defects often lead to net-like ("hammered") defects, also known as "orange skin."

[0007] Examples of previously known composite discs can be found in WO 2019 / 242915 A1, WO 2021 / 254976 A1, WO 2021 / 005162 A1 and WO 2021 / 204551 A1.

[0008] The object of the invention is therefore to provide a composite layer for a laminated glass panel, which comprises layers with different light transmittances and significantly reduces speckled effects, in particular being largely free of speckled effects (also known as "cloudiness"), without simultaneously introducing an effect such as "orange skin" into the composite layer. Furthermore, it is an object of the invention to provide a laminated glass panel with such a composite layer. Finally, a cost-effective and simple method for producing such a composite layer, as well as a method for producing the starting material for the composite layer, is to be provided.

[0009] The invention is solved by claims 1, 7, 8 and 12. Preferred embodiments are set forth in the dependent claims.

[0010] The invention relates to a composite layer for a composite disc. The composite layer comprises a first thermoplastic layer and a second thermoplastic layer, which are bonded together in direct contact with each other in a layer stack. In other words, there are no further layers or films between the first and second layers. The first layer has an inner surface facing the second layer and an outer surface facing away from the second layer. The second layer has an inner surface facing the first layer and an outer surface facing away from the first layer.The transmittance for visible light, i.e., light in a wavelength range of 380 nm to 780 nm, of the first layer at a given measurement point differs from the transmittance for visible light of the second layer at that same measurement point or in the immediate vicinity of that measurement point. Both the first and second layers can exhibit a higher transmittance for visible light. In other words, the first layer can have a higher transmittance for visible light than the second layer, and conversely, the second layer can have a higher transmittance for visible light than the first layer. These values ​​refer to a specific measurement point or a relatively small area immediately surrounding that point.

[0011] The transmittance for visible light is determined according to ISO 9050:2003 (see section 3.3 of the standard). Visible light refers to light in the wavelength spectrum from 380 nm to 780 nm. To determine the transmittance for visible light, the relative spectral distribution of illuminant D65 (see, for example, ISO 11664-2:2007) and / or the relative spectral distribution of illuminant A (see, for example, ISO 11664-2:2007) can be used. In other words, the described light transmittance ranges apply to determinations using illuminant A and / or illuminant D65. It is understood that the transmittance values ​​refer to the transmission of light rays from the inner surface to the outer surface or vice versa.

[0012] The inner surface of the first layer is in direct contact with the inner surface of the second layer. The layers are fused together via their inner surfaces, as is usual for composite layers. According to the invention, at least the inner surface of the first thermoplastic layer has a roughness value Rz of at most 7 pm before bonding. Preferably, the inner surface of the second thermoplastic layer also has a roughness value Rz of at most 7 pm. Preferably, the inner surface of the first layer and / or the inner surface of the second layer have a roughness value Rz of at least 1 pm. The term "roughness value Rz" for surfaces is generally familiar to those skilled in the art. It can be determined, for example, using the methods specified in DIN EN ISO 21920-2:2022-12 and DIN EN ISO 21920-3:2022-12.According to these standardized measuring methods, the roughness is determined as the arithmetic mean of roughness measured over five consecutive individual measuring sections, wherein the individual measuring sections have, for example, a length of 2.5 mm each and preferably also include leading and trailing areas traversed with a test specimen (e.g., a diamond tip). Within the scope of the invention, the expression that the roughness value Rz of a surface is neither higher and / or lower than a certain value means that the roughness value does not lie outside the maximum or minimum value in any area of ​​the surface. It is understood that the mean value of the roughness value Rz over the entire surface therefore also does not lie outside the range formed by the extreme values. The composite layer is intended to form a thermoplastic intermediate layer in a composite disc.Alternatively, it can also simply be intended to be a component of such an intermediate layer. The intermediate layer can therefore comprise, in addition to the composite layer according to the invention, further layers, films and / or elements.

[0013] The inventors have discovered that one cause of the visual defects, which appear as speckled effects ("cloudiness") in the finished composite panel, is related to the surface roughness prior to the lamination of two layers with different light transmittances. With increasing roughness, the thickness ratio of the two layers relative to each other is not constant across the entire surface of the composite layer, but varies. The thickness differences are so small that no high-contrast pattern forms, but only optical defects appearing as speckles. According to the invention, these speckled effects can be significantly avoided if at least one of the inner surfaces of the thermoplastic layers has a surface that is as smooth as possible, with a roughness value Rz of no more than 7 pm, prior to lamination to form the composite layer.This eliminates the need for conventional solutions to the problem, such as the use of transparent films between the layers that remain in the composite layer. This, in turn, saves material costs and prevents the composite layer from having an excessive thickness. The only other known method to avoid such speckled effects is to insert a film between the thermoplastic layers of the composite layer. However, this results in the hammered effect (also known as "orange skin"), which can also be avoided by the solution according to the invention. The finished composite layer can thus be clearly distinguished from composite layers whose thermoplastic layers did not have a surface roughness value of at most 7 pm before lamination. These are significant advantages of the invention.

[0014] It is understood that, according to the invention, the first and second layers are arranged overlapping in a planar fashion. "Overlapping in a planar fashion" within the meaning of the invention means that the main surface of the first layer is arranged substantially parallel to the main surface of the second layer. The main surface of the element describes that surface of the element with the largest extent. The inner surface and the outer surface of a layer are the (mutually congruent) main surfaces of the layer. In addition to an inner surface and an outer surface, each layer also comprises a circumferential edge surface that connects the inner surface to the outer surface. The "thickness" or "layer thickness" of an element refers to the extent that is substantially orthogonal to the main surface of the element (width of the circumferential edge surface).

[0015] The first and second layers are preferably arranged substantially congruently with each other. This means that the main surfaces of the first and second layers have the same area, whereby "same" can also refer to minor differences that may occur within typical tolerances known to those skilled in the art. However, it is also possible that the first and second layers are not arranged congruently, but only overlap in sections. Furthermore, within the scope of the invention, it is possible for the first layer to have a larger or smaller area than the second layer.

[0016] In a preferred embodiment of the invention, the inner surface of the first layer has a roughness value Rz of at most 5 pm before bonding with the second layer. This further suppresses visual defects. The optical quality of the composite layer is significantly improved. Alternatively, the inner surface of the second layer can also have a roughness value Rz of at most 7 pm before bonding with the first layer. Particularly preferably, the first layer has a roughness value Rz of at most 5 pm on its inner surface, and the second layer has a roughness value Rz of at most 7 pm, particularly 5 pm, on its inner surface. It is especially advantageous if both the inner surface of the first layer and the inner surface of the second layer are smoothed with a roughness value Rz of at most 7 pm.This unexpectedly and significantly improves the optical quality of the composite layer. Both the inner surface of the first layer and the inner surface of the second layer preferably exhibit a roughness value Rz of at least 1 pm.

[0017] In a further preferred embodiment, the composite layer also comprises a third thermoplastic layer. The third layer comprises an inner surface facing the first layer and an outer surface facing away from the first layer. The third layer is in direct contact with the outer surface of the first layer via its inner surface. The visible light transmittance of the first layer differs from the visible light transmittance of the third layer. Preferably, the outer surface of the first layer and / or the inner surface of the third layer has a roughness value Rz of at most 7 pm, particularly preferably at most 5 pm. Alternatively, the third layer can also be bonded to the second layer in the same manner.The composite layer can also comprise further thermoplastic layers, each thermoplastic layer preferably having a visible light transmittance that differs from that of the immediately adjacent layer(s) of the composite layer. Furthermore, preferably at least one of the surfaces located between two layers with different visible light transmittances has a roughness value Rz of at most 7 pm, and particularly preferably at most 5 pm. This variant allows for multilayer composites with any number of layers, enabling precise adjustment of the overall transmittance of the composite layer without the occurrence of optical defects caused by speckling.

[0018] In a particularly preferred embodiment A of the invention, the first thermoplastic layer has a visible light transmittance of at least 75%, preferably at least 80%, and more preferably at least 85%. Preferably, the first layer has a visible light transmittance of at most 99%, more preferably at most 95%, and more preferably at most 90%. Alternatively, the second thermoplastic layer has a visible light transmittance of at least 75%, preferably at least 80%, and more preferably at least 85%. More preferably, the second layer has a visible light transmittance of at most 99%, more preferably at most 95%, and more preferably at most 90%.

[0019] In a further particularly preferred embodiment B of the invention, the first thermoplastic layer has a visible light transmittance of at most 50% and at least 20%, preferably at most 40% and at least 10%, and particularly preferably at most 30% and at least 0.5%. Alternatively, the second thermoplastic layer has a visible light transmittance of at most 50% and at least 20%, preferably at most 40% and at least 10%, and particularly preferably at most 30% and at least 0.5%. In particular, the first layer is formed according to embodiment A and the second layer is formed according to embodiment B; or alternatively, the second layer is formed according to embodiment A and the first layer is formed according to embodiment B. The visible light transmittance of the composite layer is, for example, between 20% and 80%.Preferably, the transmittance for visible light of the first layer differs by at least 10%, preferably by at least 20%, particularly preferably by at least 30%, and especially by at least 50%, from the transmittance for visible light of the second thermoplastic layer. From a difference of 10%, and particularly from 20%, in transmittance, the speckled effects in composite panes of this type are particularly noticeable, so that the advantages of the invention are especially apparent.

[0020] In a further preferred embodiment of the composite layer, the layer thickness of the layer with the higher transmittance for visible light is from 10 pm to 2000 pm, preferably from 20 pm to 1000 pm, and particularly preferably from 100 pm to 800 pm. The layer with the lower transmittance for visible light preferably has a thickness of 100 pm to 2000 pm, particularly preferably from 200 pm to 1000 pm, and especially from 300 pm to 800 pm. As already explained, the "layer thickness" of an element refers to its extent that is essentially orthogonal to the main surface of the element (width of the circumferential edge surface). In the special case of a layer with an orthogonal extent that deviates from the main surface, the layer thickness is to be understood as the minimum of the orthogonal extent, i.e., it denotes its minimum orthogonal extension.At these layer thicknesses, the lamination of the layers is simplified, and the resulting composite layer exhibits fewer optical defects. The layer thickness of the composite layer is preferably from 200 pm to 3000 pm, more preferably from 350 pm to 2500 pm, for example, 0.38 mm or 0.84 mm. These are layer thicknesses that are preferred for automotive glazing.

[0021] The thermoplastic layers of the composite, i.e., at least the first and second layers, are preferably made of the same material, but can also be made of different thermoplastic materials. Using the same material is preferred because this results in fewer optical defects due to different refractive indices between the layers. The first and / or second layer contain at least polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), polyurethane, or mixtures or copolymers or derivatives thereof, preferably PVB, particularly preferably PVB and at least one plasticizer. Preferably, the first and / or second layer is based on PVB, EVA, polyurethane, or mixtures or copolymers or derivatives thereof, preferably PVB, particularly preferably PVB and at least one plasticizer.The best optical quality is surprisingly achieved when both the first and second layers contain PVB, preferably being PVB-based. If something is "based" on a polymeric material, it consists predominantly, i.e., at least 50%, preferably at least 60%, and particularly at least 70%, of that material. It may therefore still contain other materials such as stabilizers or plasticizers.

[0022] The first layer and / or the second layer can contain one or more dyes; thus, it is / are colored by at least one dye. Preferably, at least the layer with the lower transmittance contains at least one dye. The dye can be, for example, an ink or a color pigment. A particular advantage of organic inks over inorganic pigments is their easier spreadability. However, organic inks are not as stable as inorganic pigments and age more quickly. Inorganic pigments, however, tend to agglomerate more readily than organic inks. Suitable inks or color pigments for the respective application are known to those skilled in the art, so they will not be discussed in further detail below. The dye concentration in the dye-coated thermoplastic layer is preferably constant across its entire width, height, and thickness.

[0023] Furthermore, the invention extends to a composite pane comprising an outer pane and an inner pane, as well as a thermoplastic intermediate layer arranged between the inner and outer panes. The composite pane also includes the composite layer according to the invention. The composite layer is arranged over a flat area between the inner and outer panes of the composite pane. The composite layer is either a component of the thermoplastic intermediate layer or constitutes the thermoplastic intermediate layer on its own.

[0024] The laminated glass is preferably a vehicle window, in particular a vehicle roof window or a windshield. However, it can also be a

[0025] It can be a vehicle side window. The laminated glass can also be a

[0026] The product can be used as building glazing or as a component of building glazing, for example, as part of insulating glass. It can also be used as a decorative piece or as a component of a piece of furniture within the scope of the invention. In the case of a vehicle window, the term "inner pane" refers to the pane intended to face the interior of the vehicle when installed. The term "outer pane" refers to the pane intended to face the vehicle's external environment when installed. The composite pane according to the invention has an upper edge, a lower edge, and two side edges connecting the upper and lower edges. The upper edge refers to the edge of the composite pane intended to point upwards when installed. The lower edge refers to the edge intended to point downwards when installed.If the laminated glass is the windshield of a motor vehicle, the upper edge is often referred to as the roof edge and the lower edge as the engine edge.

[0027] The outer and inner panes each have an outer and an inner surface, and a circumferential edge running between them. The top edge, bottom edge, and side edges together form the circumferential edge. For the purposes of this invention, the outer surface is defined as the surface intended to face the external environment when installed. The inner surface is defined as the surface intended to face the interior when installed. The inner surface of the pane that represents the outer pane and the outer surface of the pane that represents the inner pane face each other and are connected by the thermoplastic intermediate layer.

[0028] The outer and inner panes are preferably made of glass, particularly soda-lime glass, as is common for window panes. However, the panes can also be made of other types of glass, such as quartz glass, borosilicate glass, or aluminosilicate glass, or of rigid, clear plastics, such as polycarbonate or polymethyl methacrylate.

[0029] The outer pane and / or the inner pane may have anti-reflective coatings, non-stick coatings, anti-scratch coatings, photocatalytic coatings, electrically heated coatings, sun protection coatings and / or low-E coatings.

[0030] The thickness of the inner and outer panes can vary widely and thus be adapted to the specific requirements. Preferably, the inner and outer panes have thicknesses of 1 mm to 5 mm, and particularly preferably of 1 mm to 3 mm. For example, the outer pane is 2.1 mm thick and the inner pane is 1.6 mm thick. However, the outer and inner panes, especially the inner pane, can also be made of thin glass with a thickness of, for example, 0.55 mm.

[0031] The thermoplastic intermediate layer has a thickness of, for example, 0.3 mm to 1.5 mm, preferably 0.4 mm to 1.2 mm, and particularly preferably 0.5 mm to 1.0 mm (including the composite layer). The intermediate layer preferably comprises one or more thermoplastic films, wherein the composite layer according to the invention is treated as a thermoplastic film in this sense. The intermediate layer is particularly preferably based on polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), or polyurethane (PU). This means that all thermoplastic films are preferably based on polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), or polyurethane (PU). Furthermore, the films or the entire intermediate layer can contain other components, such as plasticizers, stabilizers, or UV or IR blockers.

[0032] The composite pane according to the invention can additionally comprise a protective print, in particular made of a dark, preferably black, enamel. The protective print is, in particular, a peripheral, i.e., frame-like, protective print. The peripheral protective print primarily serves as UV protection for the adhesive used to mount the composite pane. The protective print can be opaque and cover the entire surface. The protective print can also be at least partially semi-transparent, for example, as a dot matrix, stripe matrix, or checkered matrix. Alternatively, the protective print can also have a gradient, for example, from an opaque covering to a semi-transparent covering. The protective print is typically applied to the interior surface of the outer pane and / or to the interior surface of the inner pane.

[0033] The laminated glass according to the invention is preferably curved in one or more directions in space, as is common for automotive windshields, with typical radii of curvature ranging from about 10 cm to about 40 m. However, the laminated glass can also be flat, for example, if it is intended as a windshield for buses, trains, or tractors.

[0034] In a preferred embodiment of the invention, the composite pane comprises a functional element, for example, a PDLC (polymer-dispersed liquid crystal) functional element, a suspended particle device (SPD) element, or an electrochromic functional element, which are arranged between the inner and outer panes. The aforementioned types of functional elements are generally known to those skilled in the art, so their function or composition will not be discussed further here. Preferably, the functional element is arranged between the outer pane and the composite layer. Particularly preferred are the following functional elements arranged between the outer and inner panes, starting from the inner pane:

[0035] - the composite layer according to the invention,

[0036] - a functional element and

[0037] - a thermoplastic film, for example colored or uncolored.

[0038] In another preferred embodiment, a coating or print is applied to the surface of the composite layer facing the inner or outer pane. The coating or print can be decorative elements, such as lettering or images, or it can be a functional coating or print, such as a low-E coating or a solar control coating.

[0039] In a further preferred embodiment, the composite panel comprises an acoustic damping layer, which in this order includes a first thermoplastic film, a functional layer, and a second thermoplastic film. The functional layer is arranged between the first and second thermoplastic films and exhibits higher plasticity and elasticity than the first and second films. This higher plasticity and elasticity can be achieved, for example, by using plasticizers in the functional layer. Particularly preferred is either the first thermoplastic layer or the second thermoplastic layer of the composite panel according to the invention.The thermoplastic layer of the composite layer, which also forms a thermoplastic film of the acoustic damping layer, preferably has a roughness value Rz of at least 10 pm, particularly preferably at least 20 pm, and especially at least 25 pm, on its outer surface. The outer surface of this layer faces the functional layer and is in direct contact with it (after the composite pane has been manufactured). This avoids so-called "mottle" effects caused by different refractive indices of the functional layer and the thermoplastic film. This embodiment is particularly preferred because this arrangement effectively avoids "cloudiness" and "Wo# / e" effects. Acoustic damping layers are used in composite panes to achieve sound insulation (for example, to reduce road noise in the vehicle interior) through the composite pane.Plasticizers are chemical compounds that make plastics softer, more flexible, more pliable, and / or more elastic. They shift the thermoelastic range of plastics to lower temperatures, so that the plastics exhibit the desired more elastic properties within the operating temperature range. Preferred plasticizers are carboxylic acid esters, especially low-volatility carboxylic acid esters, fats, oils, soft resins, and camphor. Other preferred plasticizers are aliphatic diesters of triethylene glycol or tetraethylene glycol. Particularly preferred plasticizers are 3G7, 3G8, or 4G7, where the first digit denotes the number of ethylene glycol units and the last digit the number of carbon atoms in the carboxylic acid moiety of the compound. Thus, 3G8 stands for triethylene glycol bis-(2-ethylhexanoate), i.e., a compound with the formula C4H9CH(CH2CH3)CO(OCH2CH2)3O2CCH(CH2CH3)C4H9.

[0040] Furthermore, the invention extends to a method for producing a thermoplastic layer which has a roughness value Rz of at most 7 pm, preferably at most 5 pm, on at least one surface (hereinafter also referred to as a smoothing method). The smoothing method comprises the following process steps:

[0041] (A) A layer stack is provided which includes a smoothing film that is arranged over a surface on a first surface of a thermoplastic layer. The adhesion of the smoothing film to the thermoplastic layer is less than or equal to 0.7 N / cm, preferably less than or equal to 0.4 N / cm.

[0042] (B) The stack of layers is then pressed at a temperature of 50 °C to 150 °C, preferably at a temperature of 80 °C to 140 °C, and at an overpressure of 1 bar to 15 bar, preferably 3 bar to 13 bar. It is understood that the pressure acts primarily orthogonally to the main surfaces of the smoothing film and the thermoplastic layer. Advantageously, no pressure is exerted on the circumferential side surface of the smoothing film and thermoplastic layer. This temperature range is particularly suitable for melting the thermoplastic layer without causing irreversible damage. Smoothing is achieved by the parallel pressure with the smoothing film. The pressure is just low enough to prevent damage, yet high enough to ensure homogeneous smoothing.

[0043] (C) Finally, the smoothing film is removed from the first surface of the thermoplastic layer, for example by peeling it off. Removal can be done manually or automatically, for example by machine. The roughness value Rz of the first surface can be adjusted, for example, by modifying the temperature, the material used for the layer, the pressure, and the type and properties of the smoothing film. For the purposes of this invention, "overpressure" means pressure measured relative to atmospheric pressure. An overpressure of 1 bar therefore corresponds to atmospheric pressure plus 1 bar additional pressure.

[0044] A thermoplastic layer produced by the smoothing process according to the invention is also described here. A layer smoothed in this way exhibits a very homogeneous roughness.

[0045] The pressing of the smoothing film onto the thermoplastic layer in process step (B) is preferably carried out for at least 10 min. Particularly preferably, the smoothing film is pressed onto the thermoplastic layer for at least 20 min and at most 180 min, particularly preferably for at least 30 min and at most 120 min, and especially for at least 40 min and at most 60 min.

[0046] The smoothing foil preferably has a roughness Rz of at most 10 pm, more preferably at most 7 pm, and most preferably at most 5 pm. At such Rz values, the quality of the smoothing can be improved.

[0047] The adhesion of the smoothing film to the thermoplastic layer can be determined according to ISO 8510-2:2006 using a 180° peel test. The peel test is a fundamental form of mechanical testing used to measure the strength of adhesion. In peel tests, a tensile force is applied to a flexible substrate that is bonded to another flexible substrate (e.g., adhesive tape, thin film, or rubber) or a rigid substrate (e.g., metal, hard plastic, or composite). In the exemplary 180° peel test for measuring the adhesion according to the invention, the thermoplastic layer is first stretched over a fixed handle, and the smoothing film is placed flat on the thermoplastic layer and clamped in place with a movable clamp. The smoothing film and the thermoplastic layer are then peeled away from each other at a constant angle of 180°.The average force required to separate the smoothing film and the thermoplastic layer along the length of the specimen is recorded and expressed in N / cm. Methods and instruments for determining adhesion using the peel test are generally known to those skilled in the art. Such instruments can be obtained commercially from companies like Instron, Ametek, or Mecmesin. Preferably, the thermoplastic layer and the smoothing film are cleaned, inspected for damage, and, if necessary, dried before the procedure is carried out.

[0048] A major advantage of this process is that it works at low temperatures and low pressures. Due to the low adhesion of the smoothing film to the thermoplastic layer, it can be removed without leaving any residue and reused after cleaning and mold treatment, if necessary. The process is also simple and requires minimal effort.

[0049] In a preferred embodiment of the smoothing process, the layer stack is pressed in a continuous process. Preferably, the layer stack is pressed in a calender process. Calender processes are generally known to those skilled in the art. A calender is a system consisting of at least one, preferably polished and heated, roller, for example made of chilled cast iron or steel. The calender can also contain several, preferably polished and heated, rollers arranged one above the other, for example made of chilled cast iron or steel, through the gaps of which the layer stack is passed. By passing the layer stack through the calender, the inner surface of the thermoplastic layer is smoothed, so that it subsequently has a roughness value Rz of at most 7 µm.For the smoothing process according to the invention, it is sufficient to press the smoothing film onto the thermoplastic layer using only one roller. The smoothing effect is improved by using multiple rollers. If more than one roller is used, any calender type I, L, F, and Z can be employed, with F and Z calenders being preferred. To reach the appropriate temperature, the calender rollers (also called calender rolls) can be heated. It is also possible to bring the layer stack to the required temperature of step (B) by means of thermal radiation from a radiant heater and / or by means of thermal convection, for example, in an oven. The calendering process represents a cost-effective, safe, and efficient method for smoothing the surfaces of thermoplastic layers.

[0050] In an alternative embodiment of the smoothing process according to the invention, the layer stack is pressed in a batch process. The batch process is a discontinuous manufacturing method. Therefore, only one layer stack can be processed at a time. The pressing of multiple layer stacks takes place sequentially and not continuously. A batch process could include arranging the layer stack between two substrates, preferably plates. The substrates are arranged flat on the layer stack. During process step (B), the layer stack is pressed through the substrates, which are moved in a straight line towards each other. It is possible that only one of the substrates is moved, while the other substrate serves, for example, as a stationary support plate for the layer stack, meaning that the upper substrate merely presses down on the lower substrate through the layer stack.Pressure on the layer stack can be generated by manual compression, the use of screws, evacuation (creating a vacuum), or the application of hydraulic pressure. To reach the appropriate temperature, the substrates can be heated. It is also possible to bring the layer stack to the required temperature for step (B) using thermal radiation from a radiant heater and / or thermal convection, for example, in an oven. The advantage of this batch process is its flexibility. The equipment for carrying it out can be provided and set up quickly. It can also be dismantled just as quickly, which makes the process particularly attractive as an interim solution, for example, before a continuous process becomes available.

[0051] The substrates can contain or consist of, for example, thermosetting polymers, preferably fluorinated polymers, glass, metal, or metal alloys. The substrates are preferably in plate form.

[0052] In a particularly preferred embodiment of the smoothing process according to the invention, the smoothing film is arranged in step (A) of the process between the thermoplastic layer and another thermoplastic layer, such that the first surface of the layer and a first surface of the other layer are arranged over the smoothing film. The adhesion of the smoothing film to the other layer is less than or equal to 0.7 N / cm, preferably less than or equal to 0.4 N / cm. In step (C) of the process, the smoothing film is also removed from the first surface of the other layer, for example by peeling off the smoothing film or the other layer, manually or automatically. As a result of the process, the other thermoplastic layer has a roughness value Rz of at most 7 pm, preferably at most 5 pm, on its first surface.In this way, the number of smoothed layers can be doubled in the same amount of time, making the process very attractive. This embodiment can be combined with all the aforementioned embodiments, in particular by using continuous processes, such as calendering processes, as well as discontinuous batch processes as described above in the pressing step. The roughness value Rz of the first surface of the subsequent layer can be adjusted, for example, by modifying the temperature, the material used for the layer, the pressure, and the type and properties of the smoothing film.

[0053] The smoothing film is preferably a polymer film, but can also be a metal film. Particularly preferably, the smoothing film contains or consists of polyethylene terephthalate or a fluorinated polymer, most preferably polytetrafluoroethylene. The smoothing film can also be based on polyethylene terephthalate or a fluorinated polymer, most preferably polytetrafluoroethylene. These materials exhibit low adhesion to most thermoplastics, making them particularly suitable as components of the smoothing film. The smoothing film preferably has a thickness of at least 50 µm, more preferably at least 200 µm, and particularly at least 0.5 mm. At these thicknesses, the application of the film is simplified because the smoothing film has a lower tendency to tear or wrinkle, which improves the smoothing quality.Regardless of the above, the smoothing film preferably has a layer thickness of at most 2 mm, preferably at most 1 mm. Greater thicknesses cause unnecessary material consumption and lead to greater stiffness of the film, which also increases the risk of cracking.

[0054] The invention also extends to a method for producing a composite layer according to the invention. The method comprises:

[0055] (D) A first thermoplastic layer and a second thermoplastic layer are arranged to form a layer stack, wherein an inner surface of the first layer is arranged planarly on an inner surface of the second layer, and wherein at least the inner surface of the first layer has a roughness value Rz of at most 7 pm, preferably at most 5 pm. The transmittance for visible light of the first thermoplastic layer differs from the transmittance for visible light of the second thermoplastic layer.

[0056] (E) The stack of layers is then laminated to form a composite layer.

[0057] The composite layer is preferably laminated as part of a thermoplastic intermediate layer or as the thermoplastic intermediate layer together with a first and a second pane (outer pane and inner pane) to form a composite pane. A composite pane produced in this way exhibits virtually no optical defects in the form of slight hatching. The lamination of the layer stack to form the composite layer thus takes place before the production of the composite pane. Within the scope of the invention, the specifications regarding thickness, material, and transmittance for visible light as described above for the composite layer according to the invention also apply to the first thermoplastic layer and second thermoplastic layer described here.

[0058] The layer stack is preferably subjected to a lamination step (E) for at least 10 min. Particularly preferably, the layer stack is laminated for at least 20 min and at most 180 min, particularly preferably for at least 30 min and at most 120 min, and especially for at least 40 min and at most 60 min.

[0059] In a particularly preferred embodiment of the method for producing a composite layer, the inner surface of the second thermoplastic layer also has a roughness value Rz of at most 7 pm, preferably at most 5 pm. This largely eliminates the optical effects known as "cloudiness".

[0060] In a particularly preferred embodiment of the method for producing a composite layer, the layer stack is laminated in step (E) at a temperature of 50 °C to 110 °C and an overpressure of at least 1 bar and at most 20 bar, preferably at least 3 bar and at most 15 bar. Under these conditions, a uniform and irreversible bonding of the layers to one another takes place.

[0061] In a further particularly preferred embodiment of the invention, the layer stack is laminated in process step (E) by means of a continuous process, preferably a calender process. Here, the layer stack can be heated and pressed by means of at least one, preferably polished and heated, calender roll, thereby lamination. Alternatively, the calender can also comprise several, preferably heated and polished, rolls arranged one above the other, for example made of chilled cast iron or steel, through the gaps of which the layer stack is passed. In principle, any calender type I, L, F, and Z can be used, with F and L calenders being preferred. To achieve the appropriate temperature, the calender rolls (also called calender rollers) can be heated.It is also possible to bring the layer stack to the required temperature of step (E) by means of thermal radiation from a radiant heater and / or by means of thermal convection, for example in an oven. The calendering process represents a cost-effective, safe and efficient method for the prelamination of thermoplastic layers.

[0062] In an alternative embodiment of the inventive manufacturing process for the composite layer, the layer stack is laminated in a batch process in step (E). Such a batch process could include arranging the layer stack between two substrates, preferably plates. The substrates are arranged flat on the layer stack. During process step (E), the layer stack is pressed by the substrates, which move in a straight line towards each other. It is possible that only one of the substrates is moved, while the other substrate serves, for example, as a support plate for the layer stack, meaning that the upper substrate simply presses down on the lower substrate through the layer stack. The pressure on the layer stack can be generated by manual compression, the use of screws, evacuation (application of a vacuum), or the application of hydraulic pressure.To reach the appropriate temperature, the substrates can be heated. It is also possible to bring the layer stack to the required temperature of step (E) using thermal radiation from a radiant heater and / or thermal convection, for example in an oven. The advantage of this batch process is its flexibility. The equipment for carrying it out can be provided and set up within a short time. However, it can also be dismantled just as quickly, which makes the process particularly interesting as an interim solution, for example, before a continuous process becomes available.

[0063] In a particularly preferred embodiment of the inventive manufacturing process for the composite layer, at least the inner surface of the first layer is produced using the inventive smoothing process. The first surface of the first layer in the smoothing process thus becomes, after smoothing, the inner surface of the first layer in the manufacturing process for the composite layer. In particular, the second layer is also produced using the inventive smoothing process and therefore also has a roughness value of at most 7 pm on its inner surface.

[0064] The manufacturing process for the composite layer according to the invention preferably comprises the smoothing process according to the invention, wherein the smoothing process is carried out for at least the first layer, and preferably also the second layer, before process step (D), and the first surface of the first layer in the smoothing process represents the inner surface of the first layer. If the smoothing process is also applied to the second layer, the first surface of the second layer in the smoothing process represents the inner surface of the second layer in the manufacturing process for the composite layer.

[0065] The various embodiments of the invention can be implemented individually or in any combination. In particular, the aforementioned features can be used not only in the specified combinations, but also in other combinations or on their own, unless they are explicitly described as possible only as alternatives to one another without departing from the scope of the present invention.

[0066] The invention is explained in more detail below with reference to exemplary embodiments, with reference to the accompanying figures. These show, in a simplified representation not to scale:

[0067] Figure 1 shows a cross-sectional view of an embodiment of a composite layer according to the invention.

[0068] Figure 2 shows an enlarged section of the composite layer in an interface region of the composite layer from Figure 1.

[0069] Figure 3 shows an enlarged section of a conventional composite layer in an interface region of the composite layer.

[0070] Figure 4 shows an enlarged image depicting optical defects (specks) of a conventional laminated glass pane.

[0071] Figure 5 shows a cross-sectional view of an embodiment of a composite disk according to the invention.

[0072] Figure 6 shows an embodiment of the inventive method for producing a surface of a thermoplastic layer with a surface roughness of at most 7 pm.

[0073] Figure 7 shows enlarged sections of the process from Figure 6 in the area of ​​the surface of the thermoplastic layer to be smoothed.

[0074] Figure 8 shows an embodiment of the inventive method for producing a composite layer according to the invention, and Figure 9 shows an alternative embodiment of the inventive method for producing surfaces of thermoplastic layers with a surface roughness of at most 7 pm.

[0075] Figures 1 and 2 show different aspects of an embodiment of a composite layer 100 according to the invention in a cross-sectional view. Figure 2 shows an enlarged section Z1 of an interface region of the composite layer 100 from Figure 1. The section Z1 is indicated by a dashed line in Figure 1. The composite layer 100 comprises a first thermoplastic layer 1 with an outer surface 1.1 and an inner surface 1.2, as well as a circumferential edge connecting the inner surface 1.2 with the outer surface 1.1. The composite layer 100 also comprises a second thermoplastic layer 2 with an outer surface 2.2 and an inner surface 2.1, as well as a circumferential edge connecting the inner surface 2.1 with the outer surface 2.2. The first thermoplastic layer 1 and the second thermoplastic layer 2 are, for example, PVB layers.The first layer 1, for example, has a thickness of 760 pm and a visible light transmittance of 30%. The second layer 2, for example, has a thickness of 380 pm and a visible light transmittance of 80%.

[0076] The first layer 1 and the second layer 2 are bonded together over their entire surface area, with the inner surfaces 1.2, 2.1 forming the interface between layers 1 and 2 in the composite layer 100. In other words, the first layer 1 is bonded to the inner surface 2.1 of the second layer 2 via its inner surface 1.2. The first layer 1 and the second layer 2 are firmly bonded together by means of a lamination process. Before lamination to form the composite layer 100, the first layer 1 has a roughness value Rz of at most 7 pm, for example, an average roughness value Rz of approximately 5 pm, on its inner surface 1.2. Figure 2 shows that this results in a significantly lower roughness R in the interface area of ​​the composite layer 100 than, for example, the roughness R of the interface area of ​​a generic composite layer 100 (shown in Figure 3), in which the inner surfaces 1.2, 2.One of the thermoplastic layers 1, 2 are not smoothed before lamination. The inner surfaces 1.2, 2.1 of the generic composite layer 100 therefore have a roughness value Rz of greater than 10 pm, for example, an average of 20 pm. Apart from this, the generic composite layer 100 of Figure 3 has an identical structure to the composite layer 100 of Figures 1 and 2. This is due to the lower roughness R in the interface region of the composite layer according to the invention.

[0077] The transmittance of visible light (TL1, TL2) is very similar regardless of the location of light transmission and exhibits significantly fewer speckled effects (S). In contrast, the generic composite layer 100 transmits light rays to varying degrees depending on the area they traverse within the composite layer 100. Thus, the transmittance (TL1) for light rays traveling a longer path through the first layer 1 is lower than the transmittance (TL2) for light rays traveling a shorter path. The length of the transmission path for the light rays depends primarily on the roughness (R) in the interface region. A high roughness (R) in the interface region, as shown in Figure 3, results in optically perceptible speckled effects (S) (also known as "cloudiness") in the composite disk 101 subsequently coated with the composite layer 100.Figure 4 shows an enlarged section of a composite disc 101 of this type, which exhibits such speckled effects S. The image contrast has been altered to better highlight the effects S. However, these effects are clearly visible even without such image manipulation, especially when viewing the composite disc 101 itself.

[0078] Figure 5 shows an embodiment of a composite pane 101 according to the invention. The composite pane 101 comprises an outer pane 3 and an inner pane 4. Both panes 3 and 4 are made, for example, of soda-lime glass and each has a thickness of 2.1 mm. Between the outer pane 3 and the inner pane 4, extending from the inner pane 4, a composite layer 100 according to the invention, as described for Figure 1, a functional layer 6, and a further thermoplastic layer 7 are arranged. The composite layer 100, the functional layer 6, and the further thermoplastic layer 6 together form a thermoplastic intermediate layer 5. The functional layer 6 is, for example, a PET film with a functional coating, such as a low-E coating (emissivity-reducing coating). The further thermoplastic layer 7 is, for example, a PVB layer with a thickness of 380 pm.The functional layer 6 is only optional in the composite disc.

[0079] 101 is ordered and can also be omitted.

[0080] Further elements can also be arranged within the thermoplastic intermediate layer 5. For example, electro-optical functional elements (not shown) such as PDLC functional elements (polymer-dispersed liquid crystals). The composite disk 101 can also include an optical waveguide provided with output coupling areas (not shown). Visible light can be coupled into the optical waveguide, propagating through it under total internal reflection and being coupled out of the composite disk 101 at the output coupling areas, where it can then be perceived as illumination. Such an optical waveguide can, for example, be the functional layer 6, which is a transparent film or glass sheet. The optical waveguide can also be formed by the inner disk 4.

[0081] Figures 6 and 7 show different aspects of a possible embodiment of a method according to the invention for producing a thermoplastic layer 1 with a roughness value Rz of at most 7 pm on at least one of its surfaces 1.1, 1.2. In a first step (A), a thermoplastic layer 1 and a smoothing film 8 are provided. The thermoplastic layer 1 is, for example, based on PVB and has, for example, a layer thickness of 760 pm and a visible light transmittance of 30%. However, the thermoplastic layer 1 can also be based on other thermoplastic materials. It can also have other layer thicknesses and, in particular, any other possible visible light transmittance from 0% to 100%. The smoothing film 8 is, for example, based on PET with a layer thickness of 75 pm.

[0082] The smoothing film 8 and the thermoplastic layer 1 are arranged in a layer stack (not shown in Figures 6(A) and 7(A)), with the smoothing film 8 being arranged over one of two main surfaces 1.2 of the thermoplastic layer 1. The surface 1.2 on which the smoothing film 8 is arranged is intended to form the inner surface 1.2 in a composite layer 100; for this reason, for the sake of simplicity, we refer to an inner surface 1.2 and an outer surface 1.1 of the thermoplastic layer 1. The inner surface 1.2 of the thermoplastic layer 1 has a roughness value Rz of greater than 10 pm, for example, an average of 20 pm. The roughness R of the layer 1 is shown in an enlarged section Z2 in Figure 7. The section Z2 is indicated by a dashed line in Figure 6.

[0083] In a second step (B), the layer stack from step (A) is arranged between two plate-shaped substrates 9. The substrates 9 are, for example, metal plates. The substrates 9 are located in a heating chamber, for example, an oven. After the layer stack has been arranged between the substrates 9, the oven is heated to, for example, 120 °C, and the substrates 9 are pressed against each other at, for example, 10 bar overpressure. The layer stack, i.e., the thermoplastic layer 1 and the smoothing film 8, is pressed through the substrates 9 for, for example, 60 minutes. Dashed arrows indicate the direction of the pressure, which is essentially orthogonal to the main surfaces of the substrates 9. An enlarged section Z3 in Figure 7 shows how this thermal pressure treatment reduces the roughness R of the thermoplastic layer 1 on the inner surface 1.2.The section Z3 is indicated by a dashed line in Figure 6.

[0084] In a third step (C), the layer stack is removed from the heating chamber and from the substrates 9, and the smoothing film 8 is removed from the inner surface 2.1 of the thermoplastic layer 1. The smoothing film 8 is, for example, peeled off the thermoplastic layer 1 manually. Due to the low adhesion of PET to PVB, the smoothing film 8 can be removed without leaving any residue (see enlarged section Z4 in Figure 7). The smoothed inner surface 1.2 of the thermoplastic layer 1 remains even after the removal of the smoothing film 8 and then exhibits, for example, a roughness value Rz of 5 pm.

[0085] Figure 8 shows an embodiment for producing a composite layer 100 according to the invention. In a first step (D), a stack of layers is formed consisting of a first thermoplastic layer 1 and a second thermoplastic layer 2. The first layer 1 is produced, for example, by the method described for Figures 6 and 7. The second thermoplastic layer 2 is, for example, based on PVB and has a layer thickness of 380 pm and a visible light transmittance of 80%. Both the first layer 1 and the second layer 2 have an inner surface 1.2, 2.1 and an outer surface 1.1, 2.2. The inner surface 1.2 of the first layer 1 has a roughness value Rz of, for example, an average of 5 pm. The inner surface 2.1 of the second layer 2 has, for example, an average roughness value Rz of 20 pm.However, it is also possible that both the inner surface 1.2 of the first layer 1 and the inner surface 2.1 of the second layer 2 have a roughness value Rz of at most 7 pm, preferably at most 5 pm.

[0086] The first layer 1 is arranged with its inner surface 1.2 flat against the inner surface 2.1 of the second layer 2, thus forming a layer stack. In a second step (E), the layer stack thus formed is laminated to form the composite layer 100. For this purpose, the layer stack is placed in a heating chamber, for example an oven, between two plate-shaped substrates 9. After the layer stack has been placed between the substrates 9, the heating chamber is heated to, for example, 120 °C and the substrates 9 are pressed against each other at, for example, 10 bar overpressure. The layer stack is pressed in this way for, for example, 10 minutes and thereby bonded together.

[0087] The variant shown in Figure 9 essentially corresponds to the variant shown in Figures 6 and 7, so only the differences will be discussed here, and otherwise reference is made to the description of Figures 6 and 7. Figure 9 shows an alternative method for producing thermoplastic layers 1, 2 with a roughness value Rz of at most 7 pm on at least one of their surfaces 1.1, 1.2, 2.1, 2.2. In step (A), the smoothing film 8 is arranged over a flat area between a first thermoplastic layer 1 and a second thermoplastic layer 2, forming a kind of sandwich with the smoothing film 8 in the middle. The inner surfaces 1.2, 2.1 of layers 1, 2 are arranged facing the smoothing film 8 and both have a roughness value Rz of greater than 10 pm, for example, an average of 20 pm. The second thermoplastic layer 2 is designed, for example, like the first thermoplastic layer 1.In the second step (B), the layer stack formed from the first and second layers 1, 2 and the smoothing film 8 is pressed in a Z-calender process. An overpressure of 10 bar is applied to the layer stack between two calender rollers 10. The calender rollers 10 are heated to a temperature of, for example, 100 °C.

[0088] In step (C), the smoothing film 8 is removed from the layer stack, resulting in both the first layer 1 and the second layer 2 having a roughness value Rz of at most 7 pm, for example 5 pm, on their inner surface 1.2, 2.1. The process has several advantages. Firstly, several thermoplastic layers can be smoothed simultaneously. Secondly, the calendering process can be carried out continuously, thus optimizing the yield.

[0089] Reference symbol list

[0090] 1 first thermoplastic layer

[0091] 1.1 Outer surface of the first layer 1

[0092] 1.2 Inner surface of the first layer 1

[0093] 2 second thermoplastic layer

[0094] 2.1 Inner surface of the second layer 2

[0095] 2.2 Outer surface of the second layer 2

[0096] 3 Outer pane

[0097] 4 inner disc

[0098] 5 thermoplastic intermediate layer

[0099] 6 functional layers

[0100] 7 additional thermoplastic layers

[0101] 8 smoothing foil

[0102] 9 Substrat

[0103] 10 Calender roller

[0104] 100 composite layer

[0105] 101 Composite disc

[0106] R roughness

[0107] S Speckle effects (“cloudiness”)

[0108] Z1 Enlarged section of the composite layer from Figure 1

[0109] Z2 Enlarged section of the first layer from Figure 6 (A)

[0110] Z3 Enlarged section of the first layer from Figure 6 (B)

[0111] Z4 Enlarged section of the first layer from Figure 6 (C)

[0112] TL1 Light transmittance thicker first layer 1

[0113] TL2 Light transmittance of thicker second layer 2

Claims

Patent claims 1. Composite layer (100) for a composite disk (101), comprising - a first thermoplastic layer (1) with an inner surface (1 .2) as well as - a second thermoplastic layer (2) which is in direct contact with the inner surface (1.2) of the first thermoplastic layer (1) via an inner surface (2.1), wherein the transmittance for visible light of the first thermoplastic layer (1) differs from the transmittance for visible light of the second thermoplastic layer (2), wherein at least the inner surface (1.2) of the first layer (1) has a roughness value Rz of at most 7 pm before being connected with the second layer (2).

2. Composite layer (100) according to claim 1, wherein the inner surface (1.2) of the first layer (1) has a roughness value Rz of at most 5 pm before bonding with the second layer (2).

3. Composite layer (100) according to claim 1 or 2, wherein the inner surface (2.1) of the second layer (2) has a roughness value Rz of at most 7 pm, preferably of at most 5 pm, before bonding with the first layer (1).

4. Composite layer (100) according to one of claims 1 to 3, wherein the transmittance for visible light of the first layer (1) or the second layer (2) is at least 75%, preferably at least 80%, in particular at least 85%, and the transmittance for visible light of the respective other layer (1, 2) is at most 50% and at least 0.5%.

5. Composite layer (100) according to one of claims 1 to 4, wherein the layer (1 , 2) with the higher transmittance for visible light has a layer thickness of 10 pm to 2000 pm, preferably from 20 pm to 1000 pm.

6. Composite layer (100) according to any one of claims 1 to 5, wherein the layer (1 , 2) with the lower transmittance for visible light has a layer thickness of 300 pm to 2000 pm, preferably of 400 pm to 1000 pm.

7. Composite disc (101), comprising - an outer pane (3) and an inner pane (4), wherein the composite layer (100) according to one of claims 1 to 6 is arranged planarly between the outer pane (3) and the inner pane (4) as a thermoplastic intermediate layer (5) or as a component of the thermoplastic intermediate layer (5).

8. Method for producing a thermoplastic layer (1 , 2) with at least one surface (1.2, 2.1) having a roughness value Rz of at most 7 pm, comprising (A) Arrangement of a layer stack, wherein a smoothing film (8) is arranged planarly on a first surface (1.2) of a thermoplastic layer (1) and wherein the adhesion of the smoothing film (8) to the layer (1) is less than or equal to 0.7 N / cm, and (B) Pressing the layer stack at a temperature of 50 °C to 150 °C, preferably at a temperature of 80 °C to 140 °C, and an overpressure of 1 bar to 15 bar, preferably 3 bar to 13 bar, and (C) Removal of the smoothing film (8) from the first surface (1.2) of layer (1).

9. Method according to claim 8, wherein the pressing (B) of the layer stack is carried out by means of a continuous process, preferably a calender process.

10. Method according to claim 8 or 9, wherein in step (A) the smoothing film (8) is arranged between the layer (1) and a further thermoplastic layer (2), such that the first surface (1.2) of the layer (1) and a first surface (2.1) of the further layer (2) are arranged planarly on the smoothing film (8), wherein the adhesion of the smoothing film (8) to the further layer (2) is less than or equal to 0.7 N / cm, and wherein in step (C) the smoothing film (8) is also removed from the first surface (2.1) of the further layer (2), for example by peeling.

11. Method according to any one of claims 8 to 10, wherein the smoothing film (8) contains or consists of at least polyethylene terephthalate or a fluorinated polymer, preferably polytetrafluoroethylene.

12. Method for producing a composite layer (100), comprising, (D) Arrangement of a first thermoplastic layer (1) and a second thermoplastic layer (2) to form a layer stack, wherein an inner surface (1.2) of the first layer (1) is planarly on an inner surface (2.1) of the second layer (2) is arranged and wherein at least the inner surface (1.2) of the first layer (1) has a roughness value Rz of at most 7 pm and wherein the transmittance for visible light of the first thermoplastic layer (1) differs from the transmittance for visible light of the second thermoplastic layer (2), (E) Laminating the stack of layers to form a composite layer (100).

13. Method according to claim 12, wherein the layer stack is laminated in step (E) at a temperature of 50 °C to 110 °C and an overpressure of at least 1 bar and at most 20 bar, preferably at least 3 bar and at most 15 bar.

14. A method according to claim 12 or 13, wherein the lamination (E) of the layer stack is carried out by means of a continuous process, preferably a calendering process.

15. A method according to any one of claims 12 to 14, wherein at least the inner surface (1.2) of the first layer (1) was produced by a method according to any one of claims 8 to 11.

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