US-12617141-B2 - Method for pre-forming a curved thermoplastic laminate and pre-formed thermoplastic laminate

US12617141B2US 12617141 B2US12617141 B2US 12617141B2US-12617141-B2

Abstract

A method for pre-forming a curved thermoplastic laminate to be incorporated in composed automotive windows, the method including the processing steps of; providing a thermoplastic laminate, clamping said thermoplastic laminate from opposite flat sides between a first 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 pre-formed thermoplastic laminate that is pre-formed by such method as well a system for pre-forming such a thermoplastic laminate.

Inventors

Bartholomeus Leonardus Marinus Borcherd Driehuis

Assignees

AUTOGLAS D & K B.V.

Dates

Publication Date: 20260505
Application Date: 20220620
Priority Date: 20210621

Claims (17)

1 . A method for pre-forming a curved thermoplastic laminate to be incorporated in composed automotive windows, the method comprising the processing steps of; a) providing a thermoplastic laminate, said thermoplastic laminate comprising at least one thermoplastic film, b) clamping said thermoplastic laminate from opposite flat sides between a first and a second flexible clamping layer, c) applying a clamping force to the thermoplastic laminate, said clamping force having at least a component perpendicular to the thermoplastic laminate situated between the first and second clamping layer, d) heating the clamped thermoplastic laminate to a predefined temperature, e) forming the clamped and heated thermoplastic laminate in contact with at least one mould part, wherein the contact surface of the mould part is a double-curved contact surfaces, and f) cooling the thermoplastic laminate, wherein the clamping force applied during processing step c) is at least partially maintained during processing step d).
2 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein the flexible clamping layers are substantially gas impermeable.
3 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step c) the clamping force is applied to the thermoplastic laminate from opposite sides of the thermoplastic laminate by the first and second flexible clamping layer.
4 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step c) the clamping force is applied over substantially the entire surface of at least one flat side.
5 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein the flexible first and second clamping layer are attached to induvial frames and said frames are moved between a clamping position, wherein the frames are pressed together, and an inactive position, wherein the frame parts are placed apart.
6 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step c) the clamping force is increased by creating a vacuum between the flexible first and second clamping layers, causing an vacuum pressure on the opposite flat sides of the thermoplastic laminate.
7 . The method for pre-forming a curved thermoplastic laminate according to claim 6 , wherein gas is extracted from the space enclosed by the clamped together flexible first and second clamping layer via vacuum hose is attached to this space.
8 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step f) the thermoplastic laminate is cooled by forcing a cooling gas through at least one of the mould parts.
9 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein the thermoplastic laminate comprises at least two thermoplastic films.
10 . The method for pre-forming a curved thermoplastic laminate according to claim 9 , wherein at least one of the sides of the thermoplastic films facing towards each other are coated by a conductive material.
11 . The method for pre-forming a curved thermoplastic laminate according to claim 9 , wherein in between the at least two thermoplastic films the thermoplastic laminate comprises a dispersed liquid crystal formula, and/or a suspended-particle devices, and/or a electro chromic substrate.
12 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step d) the thermoplastic laminate is heated to a temperature situated between 80° C. and 160° C.
13 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein during processing step e) at least two collaborative mould parts are used, both mould parts having double-curved contact surfaces.
14 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein the contact side of at least one of the flexible first or second clamping layers is provided with an antistick layer.
15 . The method for pre-forming a curved thermoplastic laminate according to claim 1 , wherein step e) is in particular forming the clamped and heated thermoplastic laminate between two opposite mould parts, wherein the contact surfaces of the mould parts are double-curved contact surfaces.
16 . A pre-formed thermoplastic laminate, wherein the thermoplastic laminate is pre-formed by the method according to claim 1 .
17 . A system for pre-forming a thermoplastic laminate, wherein the system is configured for executing the method according claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the United States national phase of International Application No. PCT/NL2022/050349 filed Jun. 20, 2022, and claims priority to The Netherlands Patent Application No. 2028493 filed Jun. 21, 2021, the disclosures of which are hereby incorporated by reference in their entireties. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for pre-forming a curved thermoplastic laminate to be incorporated in a composed automotive window. The invention is further related to a curved thermoplastic laminate. Description of Related Art In the car industry there is a growing demand for adding more functionalities into the glass. Active interlayers like Polymer Dispersed Liquid Crystal (PDLC), Suspended Particle Devices (SPD), Electro Chrome technologies, electrophoresis, and also passive interlayers are therefor also more integrated into automotive glass. Most active interlayers now available on the market are assembled from 2 or more coated thermoplastic films. In most cases these films are PET (Polyethylene terephthalate) or PEN (polyethylene naphthalate) based films with on each of the facing sides an ITO (Indium Tin Oxide) coating and/or having in between two conductive coatings a dispersed liquid crystal formula, suspended-particle devices, or electro chromic substrates. All these layers have in common that if an electric current flows between two conductive layers the active state of the film changes from the static translucent diffuse state to a translucent clear state, or reverse. This change of state thus changes the light transmission and/or color of the intermediate layer. This technology is also known as “smart film technology” or if integrated between two or more glass sheets as “smart film interlayer technology”. Although PET and other plastic films like e.g. TAC (CeluloseTriacetate) are already widely used in curved automotive glass, e.g. for their infrared reflecting properties and/or heating properties, and/or they are used for their optical usage. Windshields of cars are often curved in at least one direction. Since the demand for incorporating thermoplastic films inside automotive windows is increasing, techniques for doing so are in high demand. Bending a thermoplastic film between two sheets of glass generally causes the thin thermoplastic film to fold or wrinkle. In order to overcome this undesirable effect, it is known to provide the thermoplastic film onto only one sheet of glass and preform said stack of the thermoplastic film and glass sheet into the desired shape. The second sheet of glass can subsequently be applied, which decreases the amount of wrinkling of the thermoplastic film. However, also using these techniques the amount of wrinkles is significant, in particular when a double curvature is needed, or when the magnitude of the curve is bigger. Also thermoforming before laminating is a known method. The already existing production methods are however not useable for thermoforming smart films (or thermoplastic laminates). This is caused by several circumstances. For instance the dispersed polymers are getting weak at thermoforming temperatures, smart films normally have busbars and connectors applied, and smart films are normally sensible for weather conditions so all edges should be covered inside the laminating stack all around to provide an edge encapsulation. In general, If a film material is bended from a flat shape in to a double curved surface, some regions will experience a local compression and/or decompression (stretch), while other regions of the film stays unaffected. This is dependent on how the surface is curved and also the shape of the outer boundary has a strong influence on local presence or absence of compression and/or decompression in the film. The local compression and/or decompression of the film material causes the film material to wrinkle, typically along the edges thereof. The degree of wrinkling increases as the film material is increased in size, or when the curvature, in particular the double curvature is stronger or larger. In general most spherically bended multilayered glass panel have a central area of where the film arranged inside the glass panel is stretched (decompressed)—near the middle of the gravity point—and four areas of compression near the middle of four longitudinal sides (edges). The areas where decompression or compression occurs can mathematically be determined by drawing a set of geodetic splines (gs″) over a spherically bend surface (s), were all geodetic splines (gs″) start from the same center point (cp) on the surface. Geodetic in this context means that it describes the shortest possible path (elastic string) from the starting center point (cp) to the boundary perimeter of the surface in a given angle to a neighboring geodetic spline (gs-next) starting for the same point (cp) on the surface in a repeatedly new directions. The repetition i