Method of preforming a curved thermoplastic laminate and preformed thermoplastic laminate

Abstract

The invention relates to a method for preforming a curved thermoplastic laminate to be incorporated into a combination window, the method comprising the following process steps: providing a thermoplastic laminate, clamping the thermoplastic laminate from opposite flat sides between a first flexible clamping layer and a second flexible clamping layer, applying a clamping force to the thermoplastic laminate, heating the clamped thermoplastic laminate, forming the clamped and heated thermoplastic laminate, and cooling the thermoplastic laminate. The invention also relates to a preformed thermoplastic laminate preformed by such a method and a system for preforming such a thermoplastic laminate.

Description

[0001] This invention relates to a method for preforming a bent thermoplastic laminate to be incorporated into a modular vehicle window. The invention also relates to bent thermoplastic laminates.

[0002] In the automotive industry, the demand for adding more functions to glass is constantly growing. As a result, active interlayers such as polymer-dispersed liquid crystal (PDLC), suspended particle devices (SPD), electrochromic technology, and electrophoresis, as well as passive interlayers, are increasingly being integrated into automotive glass.

[0003] Most active interlayers currently on the market are assembled from two or more layers of coated thermoplastic films. In most cases, these films are based on PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), with an ITO (indium tin oxide) coating on each side and / or a dispersed liquid crystal formulation, suspended particle device, or electrochromic substrate between the two conductive coatings. What all these layers have in common is that if current flows between the two conductive layers, the active state of the film changes from a static, translucent, diffuse state to a translucent, transparent state, or vice versa. This change in state thus alters the light transmittance and / or color of the interlayer. This technology is also known as "smart film technology," or, if integrated between two or more glass plates, "smart film sandwich technology." While PET and other plastic films, such as TAC (cellulose triacetate), are widely used, for example, in curved automotive glass and / or for optical applications due to their infrared reflectivity and / or heating properties, automotive windshields are typically curved in at least one direction. The demand for this technology is high due to the increasing need to incorporate thermoplastic films into car windows. Bending the thermoplastic film between two panes of glass often results in the thin film folding or wrinkling. To overcome this undesirable effect, it is known to place the thermoplastic film only on one pane of glass and pre-form the laminate of the thermoplastic film and glass sheet into the desired shape. A second pane of glass can then be applied, which reduces the amount of wrinkling in the thermoplastic film. However, using the same techniques, especially when double curvature is required, or when the curve amplitude is large, the amount of wrinkling is significant. Thermoforming before lamination is also a known method. However, existing production methods are not suitable for thermoforming smart films (or thermoplastic laminates). This is due to several factors. For example, dispersed polymers become brittle at thermoforming temperatures, smart films are often used for busbars and connectors, and smart films are often sensitive to weather conditions, so all edges should be covered within the laminate stack to provide edge encapsulation.

[0004] Generally, if a thin film material is bent from a planar shape into a hyperboloid, certain areas will experience localized compression and / or decompression (stretching), while other areas of the film remain unaffected. This depends on how the surface is curved, and the shape of the outer boundary has a significant impact on the presence or absence of localized compression and / or decompression in the film. Localized compression and / or decompression of the thin film material causes wrinkling, typically along its edges. The degree of wrinkling increases with the size of the film material, or when the curvature, especially the hyperbola, is stronger or greater. Generally, most spherically curved multilayer glass panels have a central region (near the center of gravity) where the film is stretched (decompressed) within the glass panel, and four compression regions near the center of the four longitudinal edges (edges).

[0005] The region of decompression or compression can be mathematically determined by drawing a set of geodesic splines (gs”) on the spherically curved surface(s), all of which begin from the same center point (cp) on the surface. In this case, a geodesic means that it describes the shortest possible path (elastic chord) from the starting center point (cp) to the perimeter of the surface boundary at a given angle, with adjacent geodesic splines (gs-next) starting from the same point (cp) on the surface in a repeating new direction. This operation is repeated to cover the 360° surface. All geodesic splines (gs”) are divided into a given number of equal segments, which are interconnected by geodesic cross splines (gcs”) to create geodesic triangles (gs', gcs', gcs”). The local surface area of ​​each triangular portion of the surface is then calculated. The length of each individual spline (a”) is calculated and redrawn from the same starting point (cp) in the same direction as the flat line (fl”), with the same length as the corresponding geodesic spline (gs”), while respecting the starting point and angle of the corresponding adjacent lines. These new flat line groups are then divided into the same number of equal segments as the corresponding geodesic spline (gs), and if these equal segments are now interconnected, the flat cross line (fcl’) will create a flat triangle. The percentage of decompression or compression in that particular region is then determined by calculating the surface area of ​​the local flat triangle and dividing the result by the result of its corresponding local curved triangle surface. If the result for a particular region is greater than 1, the region is compressed, and if the result is less than 1, the region is decompressed (stretched). If the result equals 1, then no stress was applied locally. The mathematical result will differ depending on the starting point (sp) on the surface. Furthermore, the relative plane of the flattened line group also affects the result; therefore, it is best to have it at a 90° angle to the vertical axis of the surface's centroid. The smaller the repetition angle and the greater the number of line segments, the more accurate the decompression / compression judgment will be.

[0006] In addition, the plasticity module needs to be calculated to understand the compensation level and flexibility of a particular thermoplastic smart film, thereby gaining insight into the specific amount of compression and / or decompression that the particular film can accept.

[0007] One of the current drawbacks of using active interlayer films is their limited applicability to hyperboloid curvatures, as the active interlayer film, according to existing technologies, is prone to wrinkling and / or cracking during lamination. The level at which laminated active interlayer films (smart films or thermoplastic laminates) begin to show problems is approximately 0.2% edge compression (1.002) and / or approximately 0.3% decompression (0.997) (uncompensated by the thermoplastic module). If the smart film interlayer is used for curved glass shapes exceeding these levels, preforming of the interlayer smart film is required to avoid unwanted wrinkles. Stretching the film can only partially absorb decompression, and the material may also be pulled from the edges towards the center, resulting in wrinkles. In practice, acceptable stress (decompression) levels can only be slightly higher than acceptable compression levels.

[0008] The result of using known methods is that the shrinkage of the inner and outer PET layers is never completely simultaneous and / or completely uniform, and the two layers may locally separate and / or wrinkle. These problems are even more pronounced when a vacuum is applied from the mold, in which case the film is sucked onto the mold on one side while there is no suction on the other (opposite) side. Therefore, pre-cut, pre-bonded, and pre-formed smart films are not a solution to avoid wrinkles and cracks.

[0009] When referring to a thermoplastic laminate in this application, this can be understood as at least one thermoplastic film, and preferably at least one adhesive layer. Preferably, the thermoplastic laminate comprises at least two thermoplastic films. Optionally, between the at least two thermoplastic films, the thermoplastic laminate includes a dispersed liquid crystal formulation, and / or a suspended particle device, and / or an electrochromic substrate and / or an electrophoresis device. Furthermore, the thermoplastic laminate may include at least two adhesive layers, wherein the adhesive layers preferably form the outer layer of the thermoplastic laminate.

[0010] Therefore, the object of the present invention is to provide a method for preforming hyperbolic laminates, wherein the laminates are not prone to wrinkling and cracking during hyperbolic molding.

[0011] Therefore, the present invention provides a method for preforming a curved thermoplastic laminate to be incorporated into a modular vehicle window, the method comprising the following processing steps: a) providing a thermoplastic laminate comprising at least one thermoplastic film and preferably comprising at least one adjacent adhesive layer; b) clamping the thermoplastic laminate between first and second flexible clamping layers from opposite flat sides; c) applying a clamping force to the thermoplastic laminate, the clamping force having at least a component perpendicular to the thermoplastic laminate located between the first and second clamping layers; d) heating the clamped thermoplastic laminate to a predetermined temperature; e) forming the clamped and heated thermoplastic laminate in contact with at least one mold component, wherein the contact surface of the mold component is a hyperboloid contact surface; and f) cooling the thermoplastic laminate, wherein the clamping force applied during processing step c) is at least partially maintained during processing step d).

[0012] This invention allows for the preforming of thermoplastic laminates without wrinkling due to the first and second clamping layers, even when the laminates are preformed with a relatively strong hyperbolic curvature. This is impossible according to the prior art, as most laminates are first heated and then formed only under the pressure of a mold. However, if the mold has a hyperbolic mold surface, this can lead to excessive compression and decompression of the laminate, resulting in wrinkles in areas where the compression or tension increases beyond a threshold. In this invention, this is prevented by applying clamping forces to the laminate. Preferably, during processing step c), clamping forces are applied to the thermoplastic laminate from opposite sides via the first and second flexible clamping layers. It is particularly advantageous when forces are applied to the laminate from either side (i.e., from the upper and lower surfaces of the laminate), which produces a uniformly compressed laminate, thereby significantly reducing the likelihood of wrinkles forming during mold forming. It has been found that applying a vacuum from the mold alone is insufficient, as the laminate is only sucked onto the mold on one side, while the other side remains unrestrained and prone to wrinkling. This is especially true when using multi-layer laminates, as a vacuum can retain only a single layer, while other layers can wrinkle significantly relative to the vacuum-retained layer. The laminate can be positioned in a generally flat orientation between the first and second clamping layers. This increases usability, especially when using multi-layer laminates, as positioning the laminate in this flat orientation is easy. Multiple laminates can be pre-placed between multiple first and second clamping layers, each clamping layer stored separately, which further allows for increased efficiency. After positioning the laminate onto one (first) clamping layer, another (second) clamping layer can be positioned on top of the laminate, covering it, thus forming a sandwich structure of clamping layers, laminates, and clamping layers, which is easy to handle and store. Note that the laminates distributed between the clamping layers can still be in a generally flat orientation, which further facilitates its handling and storage. However, the invention is not limited to this example; it is also conceivable to position the laminate between the clamping layers in a slightly curved direction. After the laminate is placed between the clamping layers, a clamping force is applied to the laminate. This clamping force can be applied from one side, for example, by pressing against the first clamping layer, thereby pushing the entire laminate towards the second clamping layer. However, preferably, the clamping force is applied to the thermoplastic laminate from opposite sides via the first and second flexible clamping layers. By applying a clamping force across the entire laminate, the position on the laminate is preserved even if limited shear forces occur during the molding step. The clamped thermoplastic laminate is heated before forming the laminate, which facilitates its formation. Preferably, during the heating step, the temperature of the thermoplastic laminate is heated above the glass transition temperature of the thermoplastic laminate, and optionally also to the rubbery state of the thermoplastic film. During the heating step, the clamping layers force the thermoplastic laminate to remain flat.Preferably, step e) is performed after the thermoplastic laminate reaches a predetermined temperature. The predetermined temperature is preferably equal to or higher than the glass transition temperature of the thermoplastic laminate, particularly its thermoplastic layers. Therefore, a generally wrinkle-free hyperboloid thermoplastic laminate can be pre-formed. Furthermore, the thermoplastic film can initially be in a stress-free state, i.e., at least one layer of thermoplastic film is placed without tension (e.g., tensile tension) within the interlayer. This specific sequence according to the invention (i.e., heating the laminate first, then forming the laminate) is advantageous. By heating the laminate before forming it, the molecules or polymer chains of the thermoplastic film are in a state that allows for greater movement or motion between the molecules or polymer chains without introducing excessive internal tension into the thermoplastic film, thereby reducing wrinkles. This is particularly advantageous when the thermoplastic film is heated in a flat state. Therefore, it is preferable that the thermoplastic laminate (especially the thermoplastic film) is heated without being subjected to bending and / or tensile forces. This results in more uniform heating of the thermoplastic laminate. Furthermore, heating the thermoplastic laminate (especially the thermoplastic film) increases the mobility of the molecules or polymer chains and makes it less susceptible to affecting the tension at the periphery of the thermoplastic laminate (especially the thermoplastic film). This tension, in particular, can lead to compressive tension and thus wrinkling of the thermoplastic film. Therefore, it is easier to achieve increased mobility of the thermoplastic film without introducing wrinkles. Preferably, at least one, preferably at least two, flexible clamping layers extend beyond the dimensions of the thermoplastic film located between the flexible clamping layers. That is, the thermoplastic laminate is clamped primarily only by the inner surfaces of the flexible clamping layers (i.e., the opposing surfaces of the clamping layers). Preferably, at least two flexible clamping layers substantially surround the entire thermoplastic laminate. That is, the surface area of ​​the thermoplastic laminate is smaller than the flexible surface area of ​​the flexible clamping layers. This allows for uniform pressure to be applied to the thermoplastic laminate up to its periphery. Therefore, it is not necessary to clamp the thermoplastic laminate around its periphery. This allows for the formation of a ready-to-use manufactured part without the need to remove excess material, particularly the material segment around the clamped periphery. The dimensions of the thermoplastic film, the functional film (e.g., a liquid crystal layer or an alternative thereof), and / or the adhesive layer can differ from each other. Therefore, the size of the thermoplastic film can be smaller than the size of the adhesive layer, which is advantageous when forming edge seals for thermoplastic laminates.

[0013] Currently, existing thermoforming methods do not allow for the simultaneous preforming of a combination of high-modulus and low-modulus layers. The high-modulus layer can be, for example, a PET or TAC layer, and the low-modulus layer can be, for example, a PVB or TPU layer. However, the present invention is not limited to these embodiments. This problem occurs particularly when the high-modulus layer is not stretched to the periphery of the low-modulus layer.

[0014] For example, in a thermoplastic laminate having a high-modulus thermoplastic film that is not stretched to the periphery of a low-modulus adhesive layer, and the thermoplastic laminate is to be clamped for preforming, the clamp is located around the periphery of the low-modulus adhesive layer. When preforming according to known methods, the low-modulus adhesive layer is stretched, particularly the portion extending beyond the high-modulus thermoplastic film toward its clamping location. This is undesirable because it introduces a difference in stretch between the low-modulus and high-modulus layers, potentially introducing wrinkles and / or inconsistencies into the thermoplastic laminate.

[0015] In other words, for example, the PET layer is not stretched to the periphery of the PVB layer. Known preforming methods produce wrinkles, which is an undesirable effect. This is particularly important in the case of automotive windows, where the thermoplastic film, especially its functional film, needs to be encapsulated by an adhesive layer to protect the thermoplastic laminate from external influences, such as weather. This requires the adhesive layer to extend beyond the periphery of the thermoplastic film, preferably extending beyond most or all of the periphery. However, the present invention allows the thermoplastic film and adhesive layer to be clamped on a critical surface, preferably the entire surface, thereby reducing varying elongation rates. Furthermore, the clamps can be located outside the periphery of the largest layer of the thermoplastic film and adhesive layer, such that the entire thermoplastic laminate is located between the clamping layers, and the vacuum provides substantially uniform pressure on the thermoplastic laminate. For this purpose, it is advantageous that the clamping layers are flexible clamping layers. This allows the clamping layers to be positioned on both sides of the thermoplastic laminate and can prevent wrinkle formation. That is, the flexible clamping layers can be adjusted according to the shape of the thermoplastic laminate before vacuum is formed. Therefore, wrinkles can be suppressed during laminate preforming. Therefore, thermoplastic laminates, especially the adhesive layer and the thermoplastic film, can be stretched at substantially the same rate, thus preventing these layers from being stretched unevenly and thus forming wrinkles and / or inconsistencies. Another advantage is the vacuum inside the flexible clamp, so the flexible clamping layer, which preferably airtightly surrounds and thus “wraps” the thermoplastic laminate, can degas the stack of thermoplastic and adhesive layers. This allows the frozen adhesive layer, after being heated and subsequently cooled, to form an integral whole with its encapsulated functional layer or film. The adhesive layer protects the sensitive functional layer or film from damage because it does not come into direct contact with the mold or clamp during the molding process. Moreover, this protection is maintained after preforming, during transport, and during the final lamination process on both sides of the glass.

[0016] During molding step e), the clamped and heated laminate is formed by at least one mold component. Specifically, the mold component is a hyperboloid mold component. The hyperboloid mold component can be a hyperboloid with a convex or concave surface. The clamping force applied during step c) is maintained at least partially during heating step d). Preferably, the clamping force applied during step c) is maintained at least partially during molding in step e), and preferably, the clamping force is maintained substantially completely during both the molding and heating steps. This prevents the laminate from wrinkling during the molding or heating steps. Typically, due to this molding step, i.e., without the clamping layer, shear forces or other forces are introduced into the laminate, causing it to wrinkle after a certain amount of deformation. It is conceivable that the clamped laminate (i.e., step e) is formed before heating in step d). That is, the thermoplastic laminate clamped during steps b) and c) is formed into the desired shape before the thermoplastic laminate, as in step d, is heated. After the laminate is shaped into the desired hyperboloid shape, it is cooled. Cooling of the laminate is preferably performed while it is still in the forming position. For this purpose, it can be cooled while the laminate is still between the first and second clamping layers. More preferably, the laminate is cooled while it is positioned between the clamping layers and on at least one mold component in its preferred hyperboloid shape. This cooling step substantially stabilizes or “freezes” the shape of the laminate.

[0017] This invention offers significant advantages over existing technologies. For example, vacuum forming (also known as pull forming) has several disadvantages. First, vacuum forming requires clamping the periphery of the sheet material to pull it onto a tool. This tool can be a female or male die. Pulling can be initiated, for example, by vacuum. After forming the product from the material sheet, the edges need to be trimmed to obtain the final molded product. Since the thermoplastic sheet in this invention is clamped between flexible layers, clamping the sheet is not required during the forming step. Therefore, there is no need to trim excess material from the periphery. This is crucial because thermoplastic films, especially when using liquid crystals, can introduce defects into the product. This is primarily because cutting the thermoplastic laminate with liquid crystals or other switchable films or active interlayers exposes the switchable film or active interlayer to the environment, where it may then oxidize. Therefore, this invention allows for the elimination of the entire production step of trimming the thermoplastic laminate.

[0018] When this application refers to preforming thermoplastic laminates to be incorporated into modular automotive windows, it specifically refers to thermoplastic laminates only. That is, it is not necessary to simultaneously form one or more sheets of glass. This process differs significantly from the purpose of this invention, in which essentially only the thermoplastic laminate is preformed, for example, with a predetermined curvature. This provides the advantage that the preformed thermoplastic laminate can be manufactured separately from the automotive glass. Furthermore, when stronger or greater curvature is required, the material property differences between the glass sheet and the thermoplastic laminate are too large, which inevitably leads to wrinkling of the thermoplastic laminate. Therefore, preforming of the thermoplastic laminate can provide a solution for achieving relatively strong or large curvature in such cases, especially in the case of double curvature, where the thermoplastic laminate does not wrinkle.

[0019] Preferably, the first and second clamping layers are substantially airtight. That is, during step b), the thermoplastic laminate is clamped between the first and second substantially airtight clamping layers. This prevents any gas from permeating through the clamping layers, which increases the clamping capacity of the layers and also allows for better clamping force to be applied to the laminate, further reducing the chance of wrinkling. For this purpose, the clamping layers or flexible film can be made of silicone, rubber, EPDM, airtight fabric, etc.

[0020] In another embodiment, the clamping force applied during processing step c) is applied to substantially the entire surface of at least one flat side, preferably two opposing flat sides, of the thermoplastic laminate. By applying the clamping force to the entire surface of at least one flat side, preferably two opposing flat sides, of the thermoplastic laminate, optimal distribution of the clamping force can be achieved. This ensures that all locations of the laminate are subjected to the same pressure. In other words, the clamping force is substantially the same at every location of the laminate, at least in its horizontal direction.

[0021] In another embodiment, flexible first and second clamping layers (flexible films) are attached to separate frames, which move between a clamped position and an unused position, in which the frames are pressed together and in the unused position, the frame components are separated. Preferably, the first and second flexible clamping layers are disposed on opposite sides of the frames so that these layers are optimally clamped. However, it is also conceivable that the flexible clamping layers are attached to opposite sides of the frames when sealing elements are provided on opposite sides of the frames, ensuring that the two frames are substantially completely airtight when pressed together in the clamped position. The dimensions of each frame are larger than the dimensions of the thermoplastic laminate, such that the laminate can be positioned inside the frames (boundaries). For this purpose, it is also preferred that the two frames are continuous separate frames. The frames can be made of, for example, metal, such as steel, aluminum, etc. Preferably, at least one of the frames, preferably each of the frames, has an inner perimeter greater than the perimeter of the thermoplastic laminate. In this way, the thermoplastic laminate is substantially entirely located between the flexible portions of the flexible clamping layers. This allows for the production of pre-formed laminates that do not require further processing, such as trimming excess material around the perimeter.

[0022] Preferably, during processing step c), the clamping force is increased by creating a vacuum between the first and second flexible clamping layers, thereby generating vacuum pressure on the relatively flat sides of the thermoplastic laminate. A vacuum can be applied to maintain the parallelism of the layers of the thermoplastic laminate during molding and heating steps. Preferably, gas is extracted from the enclosed space formed by the first and second flexible clamping layers clamping together via a vacuum supply device attached to the space. The vacuum supply device, such as a hose, can be integrally formed with the first and / or second clamping layers, or can be attached via a valve, preferably a one-way valve. During heating or molding, the vacuum supply device extracting air from the space enclosed by the first and second flexible clamping layers remains connected during heating and molding (and possibly also during cooling) so that the vacuum pressure is kept as low as possible. It is also conceivable to use a one-way valve so that a vacuum can be applied during preparation, i.e., when the laminate is positioned between the first and second flexible clamping layers. Subsequently, once the vacuum is properly applied, the vacuum hose can be disconnected. Assuming the space between the clamping layers does not lose its vacuum pressure, this allows for the storage of the laminate under vacuum pressure prior to subsequent steps, whereby the laminate is clamped between the first and second flexible clamping layers. Preferably, the curvature of the thermoplastic laminate comprises a maximum lens shape of 0.2 diopter, preferably 0.145 diopter, and more preferably 0.07 diopter. Optionally, the thermoplastic laminate substantially does not contain lens structures greater than 0.2 diopter, preferably 0.145 diopter, and more preferably 0.07 diopter. Preferably, the curvature in both directions is at least 0.01 diopter. Since this invention relates to thermoplastic laminates for automotive windows, lens formation is an undesirable effect as it can cause the driver to misjudge the distance to vehicles in front or behind.

[0023] In a preferred embodiment, during processing step f), the thermoplastic laminate is cooled by forcing cooling gas through at least one mold component. Thus, the thermoplastic laminate is in the desired form, and by cooling the laminate in that position, the laminate is stabilized (“frozen”) in that position, resulting in the laminate maintaining the desired shape. This can be achieved by using a mold comprising multiple small holes extending from the bottom side of the mold to the surface facing the laminate during molding. By blowing cooling gas through these small holes, the cold gas is forced against one of the flexible clamping layers, and thus cools the laminate clamped therein. Because the outer surface of the clamping layer adjacent to the mold has micro-surfaces—that is, no material can be infinitely smooth—the air blown through the mold can pass through the surfaces of the clamping layers and the mold facing the surface of the layer. It is also conceivable to use two half-molds, in which case this embodiment can be applied to both half-molds, allowing the laminate to be cooled from both surfaces.

[0024] Therefore, the laminate can be thermoformed from two frames, each covered by a flexible (airtight) membrane that is stretched and preferably airtightly mounted to the frame. Thus, the two frames together can form a flexible vacuum clamp, with the smart film, as the thermoplastic laminate, positioned in the middle. A vacuum can then be applied, preferably while the thermoplastic laminate remains flat and unheated. Subsequently, the frames, together with the clamping layer (flexible membrane), are held under vacuum, and the thermoplastic laminate is heated above its glass transition temperature, preferably between 90 and 170 degrees Celsius. The heated thermoplastic laminate can then be pressed against / pressed onto at least one mold, but preferably between two mold components. After the thermoforming of the thermoplastic laminate, the thermoplastic laminate (smart film) can be cooled to maintain its desired form / shape. Cooling can be achieved, for example, by applying cold air or another gas through the contact surfaces of the mold components. The pressure applied by the clamping layer should preferably be at a level that maintains sufficient pressure on the thermoplastic laminate throughout the heating phase and at least at the beginning of the cooling phase. Vacuum and the pressure applied by the clamping layer can prevent wrinkling of the film during heating and molding, and prevent tearing of the layers of the thermoplastic laminate during heating and molding. Preferably, the clamping layer has an anti-stick coating and / or a release layer, which can integrate one or two adhesive layers to the outside of the thermoplastic laminate, and thus assemble the thermoplastic laminate including one or two external adhesive layers in a single step. Preferably, at least one contact side of the flexible clamping layer is provided with an anti-stick layer or coating, wherein such anti-stick layer may also have a degassing surface structure. Such a degassing surface structure may also be present, or alternatively, in the outer layer of the thermoplastic laminate, and will help to evacuate the space between the clamping layers. It is also worth noting in this regard that the degassing surface of one or two outer layers of the thermoplastic laminate can also facilitate the subsequent lamination process (window cover) of the thermoplastic laminate (smart film) in the multilayer glass panel. The thickness of the flexible clamping layer can be related to the thickness of the thermoplastic laminate to be molded and the required pressure level applied by the clamping layer.

[0025] Preferably, the thermoplastic laminate comprises at least two thermoplastic films. Using the method according to the invention, a laminate comprising two or more thermoplastic films can be preformed without introducing wrinkles in any of the film layers. In addition to the thermoplastic films, the laminate may also comprise one or more layers of adhesive material, such as PVB, EVA, or TPU. Preferably, at least one side, more preferably both sides, of the thermoplastic films facing each other are coated with a conductive material, preferably indium tin oxide (ITO). Furthermore, it is conceivable that the thermoplastic laminate may include a dispersed liquid crystal formulation, and / or a suspended particle device, and / or an electrochromic substrate between the at least two thermoplastic films. This allows the preformed laminate to have a predetermined function. However, the invention is not limited to these embodiments. It is conceivable that any functional film or smart film can be included in the thermoplastic laminate, and therefore, according to the preforming method of the invention, a hyperboloid laminate substantially free of wrinkles in any of the included layers can be obtained.

[0026] Preferably, during processing step d), the thermoplastic laminate is heated to a temperature between 80°C and 160°C, preferably between 115°C and 135°C. These temperature ranges have proven to provide the thermoplastic laminate with a sufficient level of deformability without damaging the layers.

[0027] In another embodiment of the invention, at least two mating mold components are used, both having hyperboloidal contact surfaces used during step e). That is, step e) specifically involves forming a clamped and heated thermoplastic laminate between two opposing mold components, wherein the contact surfaces of the mold components are hyperboloidal contact surfaces. This allows for precise molding of the thermoplastic laminate. In addition to the pressure exerted by the clamping layers, mold forces are also applied by more or less pressing the two half-molds together. Using two cooperating half-molds for this purpose is advantageous because it results in a uniform pressure distribution. The half-molds are compatible with each other. For example, one half-mold may have a convex hyperboloid, while the other half may have a concave hyperboloid complementary to the first half. The shape of the mold is preferably chosen to be slightly more curved relative to the desired final curvature in the automotive glass. This is done to counteract the memory of the laminate material. That is, once the laminate is placed between glass plates and reheated, the material relaxes slightly, which may affect the pre-formed laminate, preventing it from bending sufficiently. By taking this slight deformation into account during the preforming stage, the curvature of the laminate is perfectly correct once it is reheated to be incorporated between the glass sheets of the automotive glass.

[0028] The present invention also relates to a preformed thermoplastic laminate comprising at least one thermoplastic film and at least one adhesive layer, the adhesive layer being directly or indirectly attached to one side of the thermoplastic film, and wherein the adhesive layer extends beyond at least a portion of the periphery of the thermoplastic film, wherein the thermoplastic film comprises curvature, particularly hypercurvature, and wherein the thermoplastic laminate has virtually no internal stress. The stress-free nature of the hyperboloid thermoplastic laminate can be understood as at least the mutual stress between the thermoplastic film and the adhesive layer being negligible. However, this can also be understood as the adhesive layer and the thermoplastic film having substantially the same elongation and / or compression ratio, particularly compared to the uncurved initial flat state of the thermoplastic laminate. This can be achieved particularly by the method according to the invention. Preferably, the thermoplastic laminate comprises at least two thermoplastic films. In particular, at least one, preferably both, facing sides of the thermoplastic films are coated with a conductive material, preferably indium tin oxide (ITO). It is conceivable that, between at least two thermoplastic films, the thermoplastic laminate includes a dispersed liquid crystal formulation, and / or a suspended particle device, and / or an electrochromic substrate. Preferably, the thermoplastic laminate includes two adhesive layers applied to the upper and lower surfaces of the thermoplastic films. In this respect, preferably, there is no mutual (residual) stress between the two adhesive layers and the thermoplastic films. The preformed thermoplastic laminate is preferably preformed by the method according to the invention. The same benefits demonstrated by the method according to the invention also apply here.

[0029] The present invention also relates to a preformed thermoplastic laminate, particularly a preformed thermoplastic laminate preformed by the method according to the invention. The preformed thermoplastic laminate according to the invention has the same advantages as those described in the method according to the invention. Therefore, the advantages related to this method are incorporated herein with reference to the advantages related to the preformed thermoplastic laminate according to the invention described above.

[0030] The present invention also relates to a system for preformed thermoplastic laminates, wherein the system is configured to perform the method according to the invention. The preformed thermoplastic laminates according to the invention have the same advantages as those described in the method according to the invention. Therefore, these advantages are also combined in the system for preformed thermoplastic laminates.

[0031] The invention will be further illustrated with reference to the non-limiting embodiments shown in the accompanying drawings. Herein lies:

[0032] - Figure 1 A schematic side view of the system used to perform this method; and

[0033] - Figure 2 A schematic perspective view and partially exploded view of the system.

[0034] Figure 1 A schematic side view of the first half-mold 1 and the second half-mold 1' is shown, wherein the surface 2 of the first half-mold 1 facing the thermoplastic laminate 5 is a hyperboloid, specifically a convex hyperboloid. The thermoplastic laminate 5 is depicted positioned between the first flexible clamping layer 3 and the second flexible clamping layer 3'. Both the first flexible clamping layer 3 and the second flexible clamping layer 3' are stretched and attached to the corresponding first frame member 4 and second frame member 4'. In the illustrated configuration, the clamping layers 3, 3' do not apply a clamping force to the laminate 5. However, a vacuum hose 6 attached to the first clamping layer 3 can be activated to extract the air surrounded by the first and second clamping layers 3, 3' and the frame members 4, 4'. If a negative pressure is achieved between the clamping layers 3, 3', these clamping layers 3, 3' will apply a clamping force to the thermoplastic laminate 5. Since the clamping force in this non-limiting embodiment is caused by a vacuum, the clamping force generated in the space surrounded by the clamping layers 3, 3' and the frame components 4, 4' is automatically applied from the opposite side of the thermoplastic laminate.

[0035] Figure 2 A schematic exploded perspective view depicting the process steps in the preforming of a bent thermoplastic laminate, wherein... Figure 1 Corresponding elements are indicated by the same reference numerals. In this figure, the laminate 5 is positioned on the clamping layer 3'. Subsequently, once the laminate 5 is correctly positioned on the clamping layer 3', the top frame component 4 and the bottom frame component 4' move toward each other, as indicated by arrows 6, 6'. Once the two frame components 4, 4' are placed together, (with...) Figure 1 (As shown), a clamping force can be applied to the laminate 5 to maintain the mutual orientation of the individual layers of the laminate 5. After the clamping force is applied, the laminate 5 is heated, and then pressed together by moving the two half molds 1, 1' toward each other (see arrows 7, 7'). After the half molds are pressed together and thus forced to conform to the shape of the mold surfaces 2, 2', the laminate 5 is cooled, for example, by forcing cooling gas through the molds 1, 1' to stabilize the laminate 5 in that position.

Claims

1. A method for preforming a curved thermoplastic laminate to be incorporated into a modular vehicle window, the method comprising the following processing steps: a) Providing a thermoplastic laminate, said thermoplastic laminate comprising at least one thermoplastic film, b) Clamp the thermoplastic laminate between the first flexible clamping layer and the second flexible clamping layer from opposite flat sides of the thermoplastic laminate. c) Applying a clamping force to the thermoplastic laminate, the clamping force having at least a component perpendicular to the thermoplastic laminate located between the first flexible clamping layer and the second flexible clamping layer. d) Heat the clamped thermoplastic laminate to a predetermined temperature. e) Forming a clamped and heated thermoplastic laminate in contact with at least one mold component, wherein the contact surface of the mold component is a hyperbolic contact surface, and f) Cooling the thermoplastic laminate, in, The clamping force applied during step c) is maintained at least partially during step d).

2. The method according to claim 1, wherein, The first flexible clamping layer and the second flexible clamping layer are generally airtight.

3. The method according to claim 1, wherein, During step c), the clamping force is applied to the thermoplastic laminate from opposite sides through the first flexible clamping layer and the second flexible clamping layer.

4. The method according to claim 2, wherein, During step c), the clamping force is applied to the thermoplastic laminate from opposite sides through the first flexible clamping layer and the second flexible clamping layer.

5. The method according to any one of claims 1-4, wherein, During step c), the clamping force is applied to substantially the entire surface of at least one flat side of the thermoplastic laminate.

6. The method according to any one of claims 1-4, wherein, During step c), the clamping force is applied to substantially the entire surface of the two opposing flat sides of the thermoplastic laminate.

7. The method according to any one of claims 1-4, wherein, The first flexible clamping layer and the second flexible clamping layer are attached to separate frame components, and the frame components move between a clamped position and an unused position, in which the frame components are pressed together and in the unused position the frame components are placed separately.

8. The method according to any one of claims 1-4, wherein, During step c), the clamping force is increased by creating a vacuum between the first flexible clamping layer and the second flexible clamping layer, thereby creating a vacuum pressure between the opposing flat sides of the thermoplastic laminate.

9. The method according to claim 8, wherein, Gas is extracted from the space enclosed by the first flexible clamping layer and the second flexible clamping layer, which are connected to the vacuum hose, via a vacuum hose.

10. The method according to any one of claims 1-4, wherein, During processing step f), the thermoplastic laminate is cooled by forcing cooling gas through at least one of the mold components.

11. The method according to any one of claims 1-4, wherein, The thermoplastic laminate comprises at least two thermoplastic films.

12. The method according to claim 11, wherein, A conductive material, namely indium tin oxide, is coated on at least one side of the thermoplastic film facing each other.

13. The method according to claim 11, wherein, A conductive material is coated on both opposite sides of the thermoplastic film, wherein the conductive material is indium tin oxide.

14. The method according to claim 11, wherein, Between the at least two thermoplastic films, the thermoplastic laminate includes a dispersed liquid crystal formulation, and / or a suspended particle device, and / or an electrochromic substrate.

15. The method according to claim 12 or 13, wherein, Between the at least two thermoplastic films, the thermoplastic laminate includes a dispersed liquid crystal formulation, and / or a suspended particle device, and / or an electrochromic substrate.

16. The method according to any one of claims 1-4, wherein, During step d), the thermoplastic laminate is heated to a temperature between 80°C and 160°C.

17. The method according to any one of claims 1-4, wherein, During step d), the thermoplastic laminate is heated to a temperature between 115°C and 135°C.

18. The method according to any one of claims 1-4, wherein, During step e), at least two cooperating mold components are used, both of which have hyperbolic contact surfaces.

19. The method according to any one of claims 1-4, wherein, An anti-stick layer is provided on the contact side of at least one of the first flexible clamping layer or the second flexible clamping layer, wherein the anti-stick layer has a degassing surface structure.

20. The method according to any one of claims 1-4, wherein, Step e) Forming the thermoplastic laminate between two opposing mold components, wherein the contact surfaces of the mold components are hyperbolic contact surfaces.

21. The method according to claim 1, wherein, The thermoplastic laminate includes at least one adjacent adhesive layer.

22. A preformed thermoplastic laminate, wherein, The thermoplastic laminate is preformed by the method according to any one of claims 1-21.

23. A system for preforming thermoplastic laminates, wherein, The system is configured to perform the method according to any one of claims 1-21.

Images