Method for producing a windshield having improved impact protection, and windshield of this kind

Abstract

The present invention relates to a method for producing a windshield (10), the method at least comprising the following method steps: a) providing an outer pane (1) and an inner pane (2), b) heating the outer pane (1) and the inner pane (2) to at least their softening temperature, c) jointly bending the outer pane (1) and the inner pane (2) or individually bending the outer pane (1) and the inner pane (2), d) cooling the outer pane (1) and the inner pane (2), e) laminating the outer pane (1) and the inner pane (2) with the interposition of a thermoplastic intermediate layer (3) to form a laminated pane (10). In step d), the outer pane (1) and / or the inner pane (2) are / is cooled in the first surface region (X1) at a first cooling rate (A1), and the outer pane (1) and / or the inner pane (2) are / is cooled in the second surface region (X2) at a second cooling rate (A2), and the absolute value of the first cooling rate (A1) is greater than the absolute value of the second cooling rate (A2), the cooling rates (A1, A2) in the associated surface region (X1, X2) prevailing at at least one pane surface of the inner pane (2) and / or of the outer pane (1).

Description

[0001] Method for producing a windshield with improved impact protection and windshield of the same

[0002] The invention relates to a method for producing a windshield with improved impact protection and to such a windshield.

[0003] Glazing for motor vehicles typically has a bend. Numerous methods for bending glass panes are known. The glass panes are heated to their bending temperature so that they become plastically deformable, and then bent into the desired shape by gravity bending, press bending and / or suction bending. In the case of composite panes, it is advantageous to bend the individual panes simultaneously. Glass panes bent in pairs are coordinated with each other in terms of their bending and are therefore particularly suitable for laminating together to form a composite pane. Methods for bending glass panes in pairs are known, for example, from EP1358131A2 or EP2463248A1. In so-called gravity bending (also known as sag bending), the glass pane, which is initially flat, is placed on the support surface of a bending mold.The pane is then heated to at least its softening temperature so that it adheres to the support surface under the influence of gravity. The shape of the glass pane can be influenced by the design of the support surface. The final bend can be achieved through gravity bending. One such process is known, for example, from GB 813069 A. However, for more complex pane shapes, multi-stage bending processes are often used. Typically, a pre-bend is created in a first bending step using gravity bending, while the final shape is created in a second bending step - often by press bending between two complementary bending dies. Such multi-stage bending processes are known, for example, from EP 1 836 136 B1, US 2004107729 A1, EP 0531152 A2 and EP 1371616 A1.Gravity bending processes also enable the congruent bending of a pair of panes, for example, a pair of panes to be laminated to form a composite pane. Panes bent in pairs exhibit smaller deviations in curvature than panes bent individually.

[0004] Particularly in the automotive industry, there is a trend towards the use of thinner and therefore lighter glass in laminated glass panes as part of the efforts to reduce weight and thus achieve fuel and energy savings. Nevertheless, this glazing must meet defined mechanical requirements laid down in relevant industry standards. This increases the safety requirements not only with regard to vehicle occupants, but also with regard to other road users such as pedestrians. In the event of a head-on collision between a pedestrian and a car, the pedestrian is highly likely to hit the hood of the car, with their head striking the windshield. This can result in serious or even fatal injuries to the pedestrian, particularly if their head penetrates the windshield and hits other objects such as the dashboard.Penetration of the windshield can be prevented by adjusting the materials and layer thicknesses of the laminated pane, which increases the manufacturing costs and weight of the laminated pane as well as the effort required for production.

[0005] JP 2008133141 A discloses a laminated pane comprising an outer glass pane and an inner glass pane which are joined together via an intermediate layer, wherein the intermediate layer has a first region and a second region and the intermediate layer has a higher tensile stiffness in the first region than in the second region.

[0006] DE 2640206 A1 describes a laminated windshield comprising two glass panes joined by a plastic interlayer, each of the glass panes having a thickness of 1.5 mm to 2.5 mm and a plane compression stress of 200 kg / cm 2 up to 500 kg / cm 2 has.

[0007] Accordingly, there is a need for a process for producing composite panes with improved impact protection that enables simple and cost-effective production without the use of additional raw materials.

[0008] The present invention is based on the object of providing a manufacturing method for windshields with improved impact protection, which enables simple production and does not increase the weight of the windshield.

[0009] The object of the invention is achieved by a method for producing a windshield comprising at least the following method steps:

[0010] (a) providing an outer pane and an inner pane, (b) heating the outer pane and the inner pane to at least their softening temperature,

[0011] (c) joint bending of the outer pane and the inner pane or individual bending of the outer pane and the inner pane,

[0012] (d) cooling of the outer pane and the inner pane,

[0013] (e) Laminating the outer pane and the inner pane with a thermoplastic intermediate layer to form a composite pane.

[0014] The windshield comprises an outer pane and an inner pane, which are joined together in step e) of the process via a thermoplastic intermediate layer. The windshield has a roof edge, an engine edge, and two opposing side edges that connect the roof edge and the engine edge. A first surface area of ​​the windshield is located in the immediate vicinity of the engine edge, while a second surface area of ​​the windshield is arranged directly adjacent to the first surface area between the first surface area and the roof edge.The inner pane and the outer pane also have a roof edge, a motor edge, two side edges, a first surface area and a second surface area, wherein these are arranged congruently after lamination of the inner pane and the outer pane, and the edges of the inner pane and the outer pane together form the roof edge, the motor edge and the side edges. In step d) of the method according to the invention, the outer pane and / or the inner pane in the first surface area are cooled at a first cooling rate and the outer pane and / or the inner pane in the second surface area are cooled at a second cooling rate, wherein the amount of the first cooling rate is greater than the amount of the second cooling rate. Thus, the inner pane and / or the outer pane in the first surface area adjacent to the motor edge are cooled more quickly than the inner pane and / or the outer pane in the second surface area.The cooling rate describes the cooling rate present on one of the pane surfaces, the inner and / or outer pane. The faster a pane of glass is cooled, the higher the surface compressive stresses that develop in the glass. The inventors utilized this principle to develop a process that allows the fracture properties of a windshield to be adjusted differently in the first and second surface areas of the pane.

[0015] The inventors have found that the windshield in the first surface area has improved fracture characteristics when an object strikes the windshield. The first surface area is the area adjacent to the engine edge, where a pedestrian's head is more likely to hit in the event of an accident. In the first surface area, where the outer pane and / or the inner pane of the windshield has higher surface compressive stress than in the second surface area, fracture occurs later when an object impacts. If glass breaks later after a head impact in the first surface area, impact of the head on elements located behind the windshield in the vehicle interior is avoided. In the second surface area of ​​the windshield, lower surface compressive stresses are introduced in the method according to the invention than in the first surface area.This results in premature breakage of the pane when an object strikes the second surface area. After one or both panes of glass break, a significant amount of energy is absorbed through the stretching of the thermoplastic interlayer and the at least partial delamination in the area of ​​the broken glass panes. The thermoplastic interlayer is stretchable and therefore gives way, so that the head is slowed down less abruptly and experiences a lower deceleration rate. To quantify head impact, the Head Injury Criterion (HIC), for example, is used, which assesses the severity of an impact based on the deceleration rate of the head. High deceleration rates are generally associated with high HIC values, which are consistent with severe injuries to the pedestrian's head. A low HIC value corresponds to a low risk of severe head injuries.A windshield manufactured according to the method according to the invention also offers greater safety for a pedestrian in the event of a traffic accident involving the pedestrian, since in a frontal collision the severity of the impact of the human head is mitigated by early fracture in the second surface area and later fracture in the first surface area of ​​the windshield.

[0016] The cooling rate of a surface area represents the average cooling rate in this surface area. The cooling rate within a surface area can be adjusted, for example, by gas flows applied to the disk, whereby, for example, the volume flow of the gas is selected to be larger in areas with a higher cooling rate than in areas with a lower cooling rate. Alternatively or additionally, a gas volume flow with a different temperature can be applied depending on the desired cooling rate. With reference to an exemplary embodiment of a method with gas cooling, the adjacent surface areas can be separated from one another, for example, by apertures arranged between the gas outlet openings, so that a sudden change in the cooling rates occurs along the area boundary between a first surface area and a second surface area.In a further exemplary embodiment of the method, no baffles or other separations are provided between gas outlets with different temperatures and / or volume flows. In this case, there is a first surface area with a first cooling rate, a second surface area with a second cooling rate, and a third surface area with a third cooling rate. The second surface area represents a transition between the first surface area and the third surface area, wherein in the first surface area the cooling rate is determined by a first volume flow impinging there, in the third surface area the cooling rate is determined by a second volume flow impinging in this area, and in the second surface area the first and second volume flows impinge in an overlapping manner and their sum determines the cooling rate of the second surface area.In this case, too, the surface areas are specifically defined based on the surfaces impacted by the gas volume flows, causing the corresponding cooling rate. The exposure of the pane to a gas is mentioned here merely as an example; the surface areas can also be designed using other cooling devices. If the cooling rate is determined based on various points regularly distributed along the pane, the surface areas according to the invention are derived therefrom, in the sense that neighboring points with the same or similar cooling rate lie within the same surface area. Preferably, the deviation of the cooling rate within a surface area is a maximum of 30%, preferably a maximum of 20%, in particular a maximum of 10%, based on the average cooling rate in this surface area.

[0017] The windshield is designed to separate the interior of a vehicle from the outside. A windshield is a window pane that is inserted into a window opening in the vehicle body or is intended to be inserted therein. The windshield is set into the opening provided for this purpose between the hood, the roof of the vehicle and the A-pillars of the vehicle body. The edge of the windshield closest to the vehicle's engine compartment when installed is called the engine edge, while the edge opposite the engine edge is called the roof edge and is oriented adjacent to the vehicle roof. The two edges of the windshield that run adjacent to the A-pillars are called the side edges of the windshield and connect the engine edge and the roof edge.The first pane represents the outer pane of the windshield, which faces the outside environment of the vehicle, while the second pane of the windshield forms the inner pane, which is oriented towards the vehicle interior. It is understood that the first pane, the second pane, and the thermoplastic intermediate layer have essentially the same external dimensions. The surface of the respective pane which, in the installed position, faces the outside environment of the vehicle is referred to as the outside surface. The surface of the respective pane which, in the installed position, faces the interior of the vehicle is referred to as the interior surface. The interior-side surface of the outer pane is connected to the outside surface of the inner pane via the thermoplastic intermediate layer.Typically, the outside surface of the outer pane is referred to as “Side I”, the inside surface of the outer pane as “Side II”, the outside surface of the inner pane as “Side III” and the inside surface of the inner pane as “Side IV”.

[0018] The windshield comprises at least a first surface region and a second surface region, wherein the first surface region is directly adjacent to the engine edge and the second surface region is directly adjacent to the first surface region on the side of the first surface region facing away from the engine edge. The first surface region and the second surface region are adjacent to one another and do not overlap. In a preferred embodiment of the method, the windshield comprises only a first surface region and a second surface region, the areas of which together make up the total surface area of ​​the windshield. In a further preferred embodiment, the windshield has at least a third surface region which is directly adjacent to the second surface region on the side of the second surface region facing away from the first surface region.Optionally, the windshield can comprise further surface areas, wherein the areas of the first surface area, the second surface area, the third surface area and optionally further surface areas add up to the total area of ​​the windshield. The first surface area is arranged directly adjacent to the engine edge, i.e. there is no further surface area between the engine edge and the first surface area. The second surface area is at a greater distance from the engine edge than the first surface area and is directly adjacent to the first surface area. A third surface area, if present, is at a greater distance from the engine edge than the second surface area and is directly adjacent to the second surface area. Analogously, further surface areas can be arranged beyond the third surface area.The sequence of surface areas with increasing distance from the engine edge is first surface area, second surface area, optionally third surface area and also optionally further surface areas. In a preferred embodiment of the method according to the invention, the ratio between the first cooling rate (A1) and the second cooling rate (A2) is A1 / A2 greater than or equal to 2, preferably A1 / A2 between 2 and 3, particularly preferably A1 / A2 between 2 and 2.5. In these areas, an advantageous increase in the surface compressive stresses is achieved in the first surface area compared to the second surface area, so that the windshield fractures later in the event of an impact with a body. At the same time, the ratio of the cooling rates is selected such that fracture of the windshield during the cooling process is avoided.Preferably, the cooling rate ratios mentioned are present on one or both of the pane surfaces exposed to the environment, i.e. on the interior surface of the inner pane and / or on the exterior surface of the outer pane.

[0019] Preferably, the outer pane and / or the inner pane are cooled in the first surface region at a first cooling rate A1 of between 6 K / s and 20 K / s, particularly preferably between 10 K / s and 15 K / s. In the second surface region, the cooling rate is preferably between 0.5 K / s and 2 K / s. Such a cooling rate A1 in the first surface region leads to advantageous surface compressive stresses, at which sufficient stone chip resistance and advantageous fracture properties in the event of an impact can be achieved. The cooling rate A2 in the second surface region is adapted to the cooling rate A1 of the first surface region in such a way that stresses at the transition between the two regions are further minimized.

[0020] The windshield of the method according to the invention preferably has precisely a first surface region and a second surface region which maintain the described ratio of the cooling rates. Thus, in the method according to the invention only two different cooling rates need to be implemented during the cooling process, thereby simplifying the method. In a further preferred embodiment, the windshield of the method according to the invention has a first, a second and a third surface region, wherein the preferred ratios of the first and second cooling rates are present between the first and second surface regions. In the third surface region, cooling takes place at a lower cooling rate than in the first surface region; the third surface region is therefore cooled more slowly than the first surface region.The second surface area serves as a transition area between the first and the third surface area, whereby a gradual transition can be created between areas with a high cooling rate and those with a low cooling rate.

[0021] At the start of the cooling process in step d), the outer pane and / or the inner pane preferably have a temperature of at least 500 °C, particularly preferably at least 520 °C. If the panes are cooled from such high initial temperatures, advantageously high compressive stresses can be achieved; in particular, improved fracture properties in the first surface area are achieved while maintaining the preferred cooling rates.

[0022] The cooling of the outer pane and / or the inner pane in step d) preferably takes place by convection or radiation. Suitable cooling devices are known to those skilled in the art. For convective cooling, for example, fans can be used, with one fan applying gas at a higher volume flow to the first surface area and another fan applying a lower gas volume flow to the second surface area.In a further embodiment, a first fan is arranged in the region of a first surface area of ​​the inner pane and / or outer pane and a second fan is arranged in the region of a third surface area of ​​the inner pane and / or outer pane, wherein the gas volume flow generated by the first fan is higher than the gas volume flow generated by the second fan and a second surface area lies between the first surface area and the third surface area, in which the gas volume flows of the first fan and the second fan partially overlap. Connected areas with an equally high impinging gas volume flow form a surface area with the same or similar cooling rate, while the value of the impinging gas volume flow changes at the area boundary between adjacent surface areas. The cooling rate therefore changes stepwise and abruptly from surface area to surface area.If the transition from a surface area with a low cooling rate to an area with a higher cooling rate is to be as homogeneous as possible, further surface areas can be provided between these two surface areas whose cooling rates lie between the cooling rates of the first-mentioned surface areas. The more intermediate surface areas are selected and the smaller these are, the more continuous the transition between high and low cooling rates. A gradual transition is maintained and only the small size of the surface areas leads to a more homogeneous transition. Instead of a first blower and a second blower, a single blower can also be used, followed by a distribution box for dividing the volume flow generated by the blower into a first gas volume flow for the first surface area and a second gas volume flow for the second surface area.The distribution box can contain flaps, baffles, nozzles, valves, and / or other elements for regulating and controlling a gas flow rate, allowing the ratio of the first gas flow rate to the second gas flow rate to be adjusted. In a preferred embodiment, the gas used for cooling is air. However, other gases, such as carbon dioxide or nitrogen, can also be used in principle. The temperature of the gas is lower than the temperature of the panes to be cooled and preferably corresponds to the ambient temperature, for example, 20°C to 40°C.

[0023] The bending of the outer pane and / or the inner pane in step c) takes place using standard industrial bending methods, which also include gravity bending and press bending. According to the invention, the cooling step in step d) is carried out immediately after the bending process, at a time when the temperature of the panes is high and must be reduced before the panes are joined in step e). In a prior art method not according to the invention, passive or active cooling of the panes is also provided between bending and lamination of the panes, down to a temperature at which lamination can take place. According to the invention, this step is replaced by an active cooling step, in which the panes are cooled at different cooling rates depending on the surface area. There is no additional time expenditure, so that the cycle time in the production cycle remains constant.

[0024] In a particularly preferred embodiment of the invention, the outer pane and the inner pane are bent using a gravity bending process. In particular, the inner pane and the outer pane are bent congruently, preferably congruently together.

[0025] In a conventional gravity bending process, gravity acts on the softened glass sheet, which then conforms to the bending mold. This process can be further assisted by applying excess pressure to the glass sheet. The excess pressure effectively presses the softened glass sheet into the bending mold, thereby assisting the effect of gravity. Devices for gravity bending at least one glass sheet comprise at least one lower gravity bending mold and one upper forming tool. The glass sheet to be bent is placed on the gravity bending mold and positioned between the gravity bending mold and the upper forming tool. The gravity bending mold has a support surface suitable for arranging at least one glass sheet thereon. The support surface determines the shape of the bent glass sheet.If the glass pane is heated to at least its softening temperature, it will adhere to the support surface under the influence of gravity, thereby achieving the desired shape. A gravity bending mold is a so-called lower mold onto which the pane can be placed so that the support surface touches the lower surface of the glass pane facing the ground. Typically, the edge area of ​​the glass pane protrudes all the way around the support surface. The support surface is preferably concave. A concave shape is understood to be a shape in which the corners and edges of the glass pane are bent away from the bending mold when in intended contact with the support surface.

[0026] The support surface can, for example, be formed over the entire surface and be brought into contact with the glass pane. In a preferred embodiment, however, the gravity bending mold has a frame-like support surface. Only the frame-like support surface is in direct contact with the glass pane, while the majority of the pane has no direct contact with the tool. This allows panes of particularly high optical quality to be produced. Such a tool can also be referred to as a ring (bending ring) or frame (frame shape). The support surface does not have to form a complete frame, but can also be interrupted.

[0027] In one possible embodiment, the gravity bending mold can be moved vertically relative to a second lower mold in order to transfer the glass pane between the gravity bending mold and the second lower mold. The gravity bending mold and the second lower mold are in particular part of a multi-part bending tool. Preferably, the second lower mold is also frame-like and concave. The gravity bending mold can be arranged within the second lower mold. This means that the support surface of the second lower mold has a larger circumference than the support surface of the gravity bending mold and is a greater distance from the center of the multi-part bending tool - the second lower mold therefore surrounds the gravity bending mold. Alternatively, the second lower mold can also be arranged within the gravity bending mold.The gravity mold can be moved vertically relative to the second lower mold to transfer the glass sheet between the gravity bending mold and the second lower mold. During the gravity bending process, the gravity bending mold is positioned above the second lower mold, and the sheet rests on the support surface of the gravity bending mold. The gravity bending mold is then moved vertically downwards relative to the second lower mold. The relative movement of the two molds is important, with the actual physical movement being able to be caused by the gravity bending mold (downward), the second lower mold (upward), or both. As soon as the support surface of the gravity bending mold is positioned below the support surface of the second lower mold, the glass sheet rests on the support surface of the second lower mold, and the support surface of the gravity bending mold is free.The glass pane is then transferred from the gravity bending mold to the second, lower mold. In an advantageous embodiment, the second, lower mold is also a gravity bending mold, but with a more pronounced curvature than the first gravity bending mold.

[0028] It makes sense for the support surface of the second lower mold to have a different geometry, particularly curvature, than the support surface of the gravity bending mold. The second lower mold is intended for a further bending step, in which a more complex, typically more strongly curved pane shape is achieved. Since the glass pane has the curvature determined by the gravity bending mold at the moment of transfer, it only rests on the second lower mold at a few points after transfer, typically in the area of ​​the pane corners. Only during the subsequent bending step does the glass pane assume the curvature determined by the support surface of the second lower mold and then rests over the entire support surface.

[0029] During the bending process, the upper forming tool is positioned opposite the support surface of the gravity bending mold so that a glass pane can be placed between the gravity bending mold and the forming tool. It is designed to generate overpressure on the surface of the glass pane placed on the support surface that faces away from the support surface. The forming tool is not designed as a mold with full-surface contact surface, but as a hollow mold. The forming tool has a cover, for example made of a metal sheet. The cover is shaped to form a cavity. The cavity is not a closed cavity, but rather has a large opening that faces the gravity bending mold. The tool can also be described as bell-shaped or hood-shaped.

[0030] A common gravity bending device also includes means for moving the gravity bending mold and the forming tool relative to each other. This brings the gravity bending mold and the forming tool closer together after the glass sheet has been placed on the gravity bending mold, so that the forming tool is brought into contact with the glass sheet. The approach can be achieved by moving the gravity bending mold, the forming tool, or both. In a preferred embodiment, the forming tool is moved and lowered onto the glass sheet while the gravity bending mold does not perform any vertical movement.

[0031] A gravity bending device also includes means for heating the glass sheet to its softening temperature. Typically, the gravity bending die and the upper forming tool are located within a heated bending furnace or chamber. The glass sheet can pass through a separate chamber, such as a tunnel furnace, for heating.

[0032] The gravity bending process described as an example can be the only bending step or part of a multi-stage bending process preceded or followed by additional bending steps. For example, after gravity bending and before cooling in step d), further bending steps can be performed, for example, by gravity bending, press bending, or suction bending. For this purpose, the pane can be transferred from the gravity bending mold to additional bending molds. In an advantageous embodiment, a complex pre-bending of the glass pane is achieved through two gravity bending steps, while the final pane shape is achieved in a subsequent press bending step. This allows particularly complex pane geometries to be realized.

[0033] The outer pane and / or the inner pane, preferably both panes, are formed in step c) of the method according to the invention, preferably by means of gravity bending. The inner pane and the outer pane can be bent simultaneously as two superimposed glass panes. This is particularly desirable because these panes are later to be laminated to form a laminated glass so that their shape is optimally coordinated. For this purpose, the glass panes are arranged flat on top of one another and bent together simultaneously and congruently. A release agent, for example a release powder or a fabric, is arranged between the glass panes so that the glass panes can be separated from one another again after bending. In a preferred embodiment of the method according to the invention, the outer pane and the inner pane are bent congruently together in pairs and then cooled together in pairs.Convective or radiative cooling preferably occurs from the interior-side surface of the inner pane. When the inner pane and outer pane are gravity-bent in pairs, the outer surface of the outer pane is generally the surface facing the gravity-bend die, while the interior-side surface of the inner pane represents the surface of the pair of panes facing the environment. The interior-side surface of the inner pane is therefore freely accessible, even when the pair of panes is resting on a gravity-bend die. A cooling device, such as a radiative or convective cooling device, is preferably positioned adjacent to the easily accessible interior-side surface of the inner pane. This creates surface compressive stresses, particularly on the interior-side surface of the inner pane, which are beneficial for the fracture behavior of the windshield being produced.

[0034] In a preferred embodiment of the method according to the invention, the outer pane and / or the outer pane are bent by press bending. Particularly preferably, the inner pane and the outer pane are bent simultaneously in pairs or one after the other by press bending in step c). A press bending process can be used as the sole bending process in step c) or can follow a gravity bending process. In the so-called press bending process, the pane or panes to be bent are arranged between two complementary tools which together exert a pressing action on the pane or panes in order to create the bend. In press bending, a lower press bending mold with a frame-like contact surface is often used, on which only the side edge of the glass pane rests along a circumferential contact line. The contact surface is typically flat and inclined inwards.This purely linear contact between the glass pane and the contact surface is advantageous in order to avoid tool marks and the associated reduction in optical quality. If the glass pane is pressed and deformed by the upper press-bending mold (often a so-called solid mold with a full-surface effective surface) into the lower press-bending mold, the contact line in question migrates from the outside to the inside as a result of the increasing bending of the pane on the contact surface. The linear contact with the contact surface is maintained throughout the entire process and the main surface of the pane does not come into contact with the lower press-bending mold. Press-bending processes of this type are described, for example, in DE10314267B3, WQ2007125973A1, EP0677488A2 or W09707066A1. An upper bending tool is understood to be a tool that contacts the upper main surface of the glass pane facing away from the ground. Its contact surface is directed downwards.A lower bending form is understood to be a form that contacts the lower main surface of the glass pane facing the ground. Its contact surface is directed upwards. The lower bending form has a full-surface contact surface. In the sense of the invention, a full-surface contact surface is understood to be a contact surface that comes into contact with the entire surface or a large part of the surface of the glass pane to be bent. The lower bending form can also be referred to as a solid form or massive bending form. These terms are familiar to those skilled in the art and serve in particular to distinguish it from a so-called frame form, which only has a frame-like contact surface that only comes into contact with a circumferential edge area of ​​the glass pane, while the majority of the glass pane, in particular its central area, has no direct contact with the frame form.

[0035] The glass sheet can be transferred to the storage mold after press bending using the upper bending tool that was used for press bending. For this purpose, the glass sheet remains in contact with the contact surface of the upper bending tool after press bending, the lower press bending tool is removed and the storage mold is moved under the bending tool so that the glass sheet can be placed on it. However, it is also possible for the glass sheet to remain on the lower bending tool after press bending and be removed from the upper bending tool. The upper bending tool is then available for the next bending step, which has advantages in terms of cycle time. The glass sheet is then taken from the lower bending tool by another tool, for example another upper press bending tool or a similarly designed holding tool, and placed on the storage mold.

[0036] In an advantageous embodiment, the process is applied simultaneously to at least two, preferably exactly two, glass panes lying on top of one another. The glass panes are held in pairs (i.e. as a pair of panes) simultaneously by the tool and bent during the bending process. The curvature of the two glass panes is then particularly congruent and coordinated, making the panes particularly suitable for laminating together to form a composite pane of high optical quality. If two or more glass panes are bent simultaneously, a release agent is preferably arranged between the panes so that the panes do not permanently adhere to one another. When bending in pairs, all process steps are carried out with the pair of panes - the glass panes, which are initially flat, are arranged on top of one another and subjected to pre-bending and press-bending together.

[0037] Depending on which of the panes is to be subjected to increased surface compressive stresses, the inner pane and the outer pane are preferably bent in pairs or preferably individually by means of gravity bending and / or press bending. During the bending process, the outer pane is generally the pane facing the lower bending mold, while the inner pane rests on the outer pane and faces away from the lower bending mold. If increased surface compressive stresses are to be provided, particularly in the first surface area of ​​the inner pane, the inner pane and the outer pane are preferably bent together and, after removal of the upper bending mold, subjected to the cooling step d), wherein a cooling device is arranged adjacent to the interior-side surface of the inner pane.In this case, the heat from the outer pane is dissipated via the inner pane, whereby the outer pane cools more slowly than the inner pane and thus has lower surface compressive stresses than the inner pane. If the outer pane is to have similar surface compressive stresses to the inner pane, the outer pane and the inner pane are preferably bent individually and individually subjected to the cooling step according to the invention, with the cooling device preferably being arranged on the interior-side surface of the outer pane and the inner pane.

[0038] The outer and inner panes are preferably made of soda-lime glass, as is common for window panes. The transition point of soda-lime glass is approximately 560°C, although its exact value depends on the precise composition. In principle, however, the glass pane can also be made of other types of glass, such as borosilicate glass, aluminosilicate glass, or quartz glass. The thickness of the panes is typically 0.5 mm to 5 mm, in particular 1.2 mm to 3 mm.

[0039] Typical bending temperatures for glass panes made of soda-lime glass range from 570°C to 700°C. Significantly exceeding the transition point can be preferable: on the one hand, the glass can be formed more easily and quickly due to its lower viscosity; on the other hand, higher temperatures are required to introduce the edge stress into the glass pane required for vehicle windows. The bending temperature for gravity bending is preferably from 600°C to 650°C, and for press bending it is at most 600°C, preferably 500°C to 600°C. The lower temperature during press bending results in better optical quality of the glass pane. The invention further comprises a windshield obtainable by the method according to the invention. The features described for the method according to the invention also apply to the windshield, and vice versa.

[0040] The windshield according to the invention comprises at least one outer pane made of glass with an outside surface, also referred to as side I, and an inside surface, also referred to as side II, and an inner pane made of glass with an outside surface, also referred to as side III, and an inside surface, also referred to as side IV. The inside surface II of the outer pane and the outside surface III of the inner pane are connected by a thermoplastic intermediate layer. The windshield has a roof edge, an engine edge and two side edges running between them. When installed in a vehicle body, the roof edge is adjacent to the vehicle roof, while the engine edge borders the hood of the vehicle. Two opposite side edges run between the engine edge and the roof edge, each of which is adjacent to a so-called A-pillar of the body.The windshield has at least a first surface area directly adjacent to the engine edge and a second surface area between the first surface area and the roof edge. The outer pane and / or the inner pane has a surface compressive stress of 11 MPa to 50 MPa, preferably 15 MPa to 30 MPa, in the first surface area, while the outer pane and / or the inner pane has a surface compressive stress of 2 MPa to 10 MPa in the second surface area.

[0041] Methods for determining surface compressive stresses are known to those skilled in the art. Various optical measuring instruments are commercially available for this purpose, such as differential surface refractometers (DSRs), epibiascopes, and scattered-light polariscopes. In DSR instruments, light passes through a prism onto the surface of the glass pane and is totally reflected. After exiting the prism, the light rays are passed through an interference filter, and the surface compressive stress can be determined from the difference to the initial radiation. Epibiascopes emit focused light onto the glass surface, creating boundary-layer waves whose elliptical oscillation state is modified by a fringe compensator. The resulting interference fringes exhibit an angle of inclination, which is a measure of the surface tension.Light scattering methods for measuring surface compressive stress utilize the so-called Tryndall effect, according to which light entering a transparent medium is scattered to a certain extent. The varying intensities of the scattered light along the light path within the medium are recorded and evaluated to determine the corresponding compressive stresses.

[0042] Preferably, all surface compressive stresses mentioned in connection with the invention are determined by epibiascopy, for example, using the LaserGasp epibiascope from Strainoptics. The other methods mentioned are also applicable.

[0043] On a windshield according to the invention, the surface areas can thus be determined by measuring the surface compressive stresses. If the surface compressive stress is determined at various points regularly distributed along the windshield, the surface areas according to the invention are determined in the sense that neighboring points with the same or similar surface compressive stresses lie within the same surface area. The deviation of the surface compressive stresses within a surface area is preferably a maximum of 30%, preferably a maximum of 20%, in particular a maximum of 10%, based on the average surface compressive stress present in this surface area.

[0044] The windshield according to the invention has improved fracture characteristics in the first surface area when an object strikes the windshield. The first surface area is the area adjacent to the engine edge, where a pedestrian's head is more likely to hit in the event of an accident. The targeted introduction of increased surface compressive stresses in the first surface area of ​​the outer pane and / or inner pane of the windshield leads to a delayed fracture in the first surface area and an early fracture in the second surface area when a body impacts. In the second surface area, after the fracture of one or both of the glass panes, a considerable amount of energy is absorbed due to the stretching of the thermoplastic intermediate layer and the at least partial delamination in the area of ​​the broken glass panes.The thermoplastic interlayer is stretchable and therefore yields, so that the head is slowed down less abruptly and experiences a lower deceleration rate. In the first surface area, which usually contains elements such as the dashboard behind the windshield, the glass breaks later, preventing the head from hitting objects behind it. To quantify head impact, the Head Injury Criterion (HIC), for example, is used. This assesses the severity of an impact based on the deceleration rate of the head. High deceleration rates are generally associated with high HIC values, which are consistent with severe injuries to the pedestrian's head. A low HIC value is synonymous with a low risk of serious head injuries. In the first surface area, higher surface compressive stresses are introduced into the glass, deliberately causing a later breakage.As a result, the windshield according to the invention also offers greater safety for a pedestrian in the event of a traffic accident involving the pedestrian, since the severity of the impact on the human head is mitigated in the event of a frontal collision.

[0045] In a preferred embodiment, the windshield in the first surface region has a surface compressive stress of 11 MPa to 50 MPa, preferably 15 MPa to 30 MPa, on the interior-facing surface of the outer pane and / or on the interior-facing surface of the inner pane. These surface compressive stresses are preferably applied to the interior-facing surface of the outer pane and / or the interior-facing surface of the inner pane, since a breakage of the windshield is not caused directly by the impact of an object on the outside of the windshield, but rather by the tensile stress generated in the glass, particularly on the interior-facing surfaces of the outer pane and the inner pane. This is particularly the case with semi-hard objects, such as a human head. The windshield breaks first at the points where the tensile stress is greatest.If an impact occurs on the outside surface of the outer pane, the greatest tensile stresses arise on the inside surface of the outer pane and on the inside surface of the inner pane. If the aforementioned surface compressive stresses are introduced into one of these surfaces, the desired subsequent fracture occurs there. Particularly preferably, the aforementioned surface compressive stresses are applied in the first surface region at least on the inside surface of the inner pane. On the one hand, the highest tensile stresses occur on this surface, and on the other hand, it is a pane surface that is easily accessible in the cooling step step d) following the bending step c). In a further possible embodiment, the aforementioned preferred surface compressive stresses are present on the outside surface of the outer pane and / or on the outside surface of the inner pane.This embodiment also allows an improvement in the fracture characteristics compared to windshields not according to the invention. However, the first embodiment, in which the aforementioned surface compressive stresses are present on the interior-side surfaces, has proven more advantageous for the reasons stated. The first surface area preferably occupies between 10% and 70%, preferably 15% to 50%, particularly preferably 20% to 40% of the total surface area of ​​the windshield. The stated preferred surface proportions of the first surface area are sufficient to achieve good safety in the head impact test.

[0046] Preferably, the first surface area extends at least in sections, starting from the motor edge of the windshield, towards the roof edge of the windshield by an amount that corresponds to 10% to 70% of the height of the windshield. The height of the windshield is determined by measuring the shortest distance to the roof edge at the relevant position of the motor edge. Subsequently, the amount by which the first surface area extends towards the roof edge is determined at the same position of the motor edge as the shortest distance between the motor edge and the upper edge of the first surface area offset towards the roof edge, thereby yielding the height of the first surface area at this position along the motor edge.This height of the first surface area is set in relation to the height of the windshield, in each case measured at the same position along the windshield, thereby determining the relative amount by which the first surface area extends from the edge of the engine towards the edge of the roof. The height to which the first surface area extends is determined as a function of the vehicle geometry, with the area in which a pedestrian's head would most likely hit in the event of an accident preferably lying in the first surface area. The first surface area is attached adjacent to the edge of the engine and extends from there, at least in sections, up to the aforementioned height of the windshield."Sectionally" means that the first surface area extends into the windshield in at least one section along the motor edge of the windshield up to the specified height in the direction of the roof edge, but can also have a lower height in other sections. The upper edge of the first surface area, i.e., the edge section of the first surface area that is the greatest distance from the motor edge of the windshield, preferably runs in a straight line or in a curved manner between the side edges of the windshield.

[0047] In a particularly preferred embodiment, the size of the first surface area is selected such that, when the windshield is installed in a motor vehicle, the size of the first surface area corresponds to at least 90% of the area of ​​the projection of the dashboard of the motor vehicle onto the windshield. Particularly preferably, the size of the first surface area corresponds at least to the area of ​​the projection of the dashboard onto the windshield. A windshield is always manufactured for a specific vehicle model, so that the vehicle model, its body structure, the installation situation in the vehicle and also the design of the dashboard are already known from the windshield itself. A common accident scenario involving pedestrians is that the pedestrian's head hits the windshield in the area of ​​the dashboard, which increases the likelihood of serious injuries.In this respect, it is advantageous to design the area of ​​the windshield which, when installed, is covered by a projection of the dashboard onto the windshield as the first surface area, whereby the windshield breaks later in this surface area and the head is prevented from coming into contact with the dashboard.

[0048] The thermoplastic intermediate layer preferably comprises polyvinyl butyral (PVB), polyurethane (PU), ionomers, and / or ethylene vinyl acetate (EVA), particularly preferably PVB. These materials have proven particularly suitable for securely bonding the panes to one another.

[0049] The thickness of the thermoplastic intermediate layer is preferably between 300 pm and 1000 pm, particularly preferably between 500 pm and 900 pm, in particular between 650 pm and 850 pm.

[0050] The outer and inner panes are made of glass, preferably 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.

[0051] The outer pane and the inner pane preferably each have a thickness of 0.8 mm to 2.5 mm, particularly preferably 1.2 mm to 2.2 mm. The thickness of the outer pane is typically from 1.0 mm to 2.5 mm. The thickness of the inner pane is preferably between 0.8 mm and 2.1 mm. The thickness of the outer pane is preferably greater than the thickness of the inner pane. For example, the outer pane can be 2.1 mm and the inner pane 1.1 mm thick, or the outer pane 1.8 mm and the inner pane 1.4 mm thick, or the outer pane 1.6 mm and the inner pane 1.1 mm thick, or the outer pane 1.6 mm and the inner pane 0.7 mm thick, or the outer pane 1.4 mm and the inner pane 1.1 mm thick. The inner pane, the outer pane and the thermoplastic intermediate layer can be clear and colorless, but can also be tinted or colored.The tint of the outer pane, inner pane, and thermoplastic interlayer is selected depending on the intended application of the laminated pane. For windshields, high transmission in the visible range of the light spectrum is desired, and dark tints of the components are avoided. The total transmission through the windshield, when used as a motor vehicle windshield, is greater than 70%, based on illuminant type A. The term "total transmission" refers to the procedure for testing the light transmission of motor vehicle windows specified in ECE-R 43, Annex 3, Section 9.1.

[0052] The windshield according to the invention is preferably curved in one or more directions of space, as is common for windshields of motor vehicles, with typical radii of curvature ranging from approximately 10 cm to approximately 40 m. However, the windshield can also be flat, for example, if it is intended for use on buses or tractors.

[0053] The inner pane, the outer pane and / or the thermoplastic intermediate layer may have further suitable coatings known per se, for example anti-reflective coatings, non-stick coatings, anti-scratch coatings, photocatalytic coatings or sun protection coatings or low-E coatings.

[0054] Automotive glazing, in particular windshields, rear windows, and roof windows, usually has a circumferential peripheral masking print made of opaque enamel, which serves in particular to protect the adhesive used to install the window from UV radiation and to visually conceal it. Preferably, at least the outer pane has such an opaque peripheral masking print; particularly preferably, both the outer pane and the inner pane are printed, so that visibility is prevented from both sides. The opaque masking print is applied, for example, in the form of a screen print, so that this screen print circumscribes the field of vision of the window or forms its outer edge. Any electrical conductors arranged in the edge region of the window, as well as any coating-free edge region provided in the case of coated panes, are preferably covered by this masking print and are thus visually concealed.The opaque screen printing can be applied to any level of the windshield.

[0055] The invention further relates to a motor vehicle comprising a windshield according to the invention, wherein the size of the first surface area is selected such that, in the installed state of the windshield in the motor vehicle, the size of the first surface area corresponds to at least 90% of the area of ​​the projection of the dashboard of the motor vehicle onto the windshield.

[0056] The invention is explained in more detail below with reference to a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

[0057] They show:

[0058] Fig. 1 is a plan view of an embodiment of a windshield according to the invention,

[0059] Fig. 2 shows a section of a cross section through the embodiment of a windshield according to the invention shown in Fig. 1 and

[0060] Fig. 3 is a flowchart of an embodiment of the method according to the invention.

[0061] Figure 1 shows a plan view of an embodiment of a windshield 10 according to the invention, while Figure 2 shows a section of a cross section through the embodiment shown in Figure 1 along the section line C'-C according to Figure 1.

[0062] The windshield 10 shown in Figures 1 and 2 comprises an outer pane 1 and an inner pane 2, which are connected to one another via a thermoplastic intermediate layer 3. The outer pane 1 has an outer surface I and an interior surface II. The inner pane 2 has an outer surface III and an interior surface IV. In the installed state of the windshield 10, the outer surfaces I, III point towards the surroundings, while the interior surfaces II, IV are oriented towards the vehicle interior in the installed state. The interior surface II of the outer pane 1 is connected to the outer surface III of the inner pane 2 via the thermoplastic intermediate layer 3.The windshield 10 has a roof edge D, an engine edge M opposite the roof edge, and two opposite side edges S that connect the engine edge M and the roof edge D. The windshield 10 has a first surface area X1 and a second surface area X2, wherein the first surface area X1 is arranged adjacent to the engine edge M.

[0063] In the first surface area X1, the windshield 10 has a surface compressive stress of 15 MPa to 30 MPa on the interior-side surface IV of the inner pane 2, while in the second surface area X2, the surface compressive stress of 2 MPa to 10 MPa is present on the interior-side surface IV of the inner pane 2. The outer pane 1 is, for example, a glass pane made of soda-lime glass with a thickness of 2.1 mm. The inner pane 2 is, for example, made of soda-lime glass and has a thickness of 1.6 mm.

[0064] The first surface area X1 has an upper edge 5 which is offset from the engine edge M in the direction of the roof edge D. The upper edge 5 of the first surface area X1 runs between the side edges K, whereby between the upper edge 5 of the first surface area X1 and the engine edge M there are higher surface compressive stresses on the interior-side surface IV of the inner pane 2 than on the interior-side surface IV of the inner pane 2 between the upper edge 5 and the roof edge D. This has proven to be particularly advantageous in order to achieve a later breakage of the windshield 10 in the first surface area X1 in the head impact test.

[0065] If the windshield 10 according to Figures 1 and 2 is installed in a conventional motor vehicle with a dashboard, the size of the first surface area is preferably selected such that the projection of the dashboard onto the windshield 10 lies within the first surface area X1. In the area of ​​the dashboard, a later fracture is to be induced by increasing the surface compressive stress. The later fracture of the glass leads to greater bending of the pane, with the kinetic energy of the head being stored as elastic energy. This elastic energy is used to create new surfaces when the windshield fractures. Therefore, a later fracture leads to a lower penetration depth of the head, since a greater amount of energy is dissipated from the impacting head.This later fracture is particularly advantageous in the dashboard area, as the head impact with the rigid dashboard located behind the windshield results in a very high amplitude and a long-lasting deceleration peak (approximately 15 ms to 17 ms), resulting in very high HIC values. Therefore, the initially higher deceleration peak caused by the elastic bending of the windshield is less problematic, as it reduces the amplitude of the secondary impact peak with the dashboard, thereby lowering the HIC value.

[0066] Figure 3 shows a preferred embodiment of the method according to the invention comprising the steps:

[0067] I Providing an outer pane 1 and an inner pane 2,

[0068] II Heating the outer pane 1 and the inner pane 2 to at least their softening temperature,

[0069] Illa joint bending of the outer pane 1 and the inner pane 2 in a gravity bending process and optionally further joint bending of the outer pane 1 and the inner pane 2 in a press bending process, or lllb joint bending of the outer pane 1 and the inner pane 2 in a press bending process,

[0070] IV Cooling the outer pane 1 and the inner pane 2, wherein the inner pane 2 is cooled in the first surface area X1 at a first cooling rate A1 and the inner pane 2 is cooled in the second surface area X2 at a second cooling rate A2 and the amount of the first cooling rate A1 is greater than the amount of the second cooling rate A2,

[0071] V Laminating the outer pane 1 and the inner pane 2 with a thermoplastic intermediate layer 3 to form a composite pane 10. List of reference symbols:

[0072] 10 Windshield

[0073] 1 outer pane

[0074] 2 inner pane

[0075] 3 thermoplastic intermediate layer

[0076] 5 Top edge of the first surface area X1

[0077] X1 first surface area

[0078] X2 second surface area

[0079] D roof edge

[0080] M engine edge

[0081] S side edges

[0082] CC' cutting line

[0083] I outside surface of the outer pane 1

[0084] 11 Interior surface of the outer pane 1

[0085] III outer surface of the inner pane 2

[0086] IV Interior surface of the inner pane 2

Claims

Patent claims 1. A method for producing a windshield (10) with at least one outer pane (1) made of glass, an inner pane (2) made of glass, a thermoplastic intermediate layer (3), a roof edge (D), a motor edge (M), two side edges (S) running therebetween, a first surface area (X1) immediately adjacent to the motor edge (M) and a second surface area (X2) immediately adjacent to the first surface area (X1) between the first surface area (X1) and the roof edge (D), at least comprising the following method steps: (a) providing an outer pane (1) and an inner pane (2), (b) heating the outer pane (1) and the inner pane (2) to at least their softening temperature, (c) joint bending of the outer pane (1) and the inner pane (2) or individual bending of the outer pane (1) and the inner pane (2), (d) cooling the outer pane (1) and the inner pane (2), (e) laminating the outer pane (1) and the inner pane (2) with the interposition of a thermoplastic intermediate layer (3) to form a composite pane (10), wherein in step d) the outer pane (1) and / or the inner pane (2) are cooled in the first surface area (X1) at a first cooling rate (A1) and the outer pane (1) and / or the inner pane (2) are cooled in the second surface area (X2) at a second cooling rate (A2) and the amount of the first cooling rate (A1) is greater than the amount of the second cooling rate (A2), wherein the cooling rates (A1, A2) are present in the associated surface area (X1, X2) on at least one pane surface of the inner pane (2) and / or the outer pane (1).

2. The method according to claim 1, wherein the ratio between the first cooling rate (A1) and the second cooling rate (A2) at A1 / A2 is greater than or equal to 2, preferably at A1 / A2 between 2 and 3, particularly preferably at A1 / A2 between 2 and 2.

5.

3. Method according to claim 1 or 2, wherein the outer pane (1) and / or the inner pane (2) are cooled in the first surface region (X1) at a first cooling rate (A1) between 6 K / s and 20 K / s, preferably between 10 K / s and 15 K / s.

4. Method according to one of claims 1 to 3, wherein the outer pane (1) and / or the inner pane (2) have a temperature of at least 500 °C, preferably at least 520 °C, at the start of the cooling process in step d).

5. The method according to any one of claims 1 to 4, wherein the cooling in step d) is carried out by convection or radiation.

6. Method according to one of claims 1 to 5, wherein the outer pane (1) and the inner pane (2) are bent in step c) in a gravity bending process, preferably bent congruently in a gravity bending process, particularly preferably bent congruently together in a gravity bending process.

7. Method according to one of claims 1 to 6, wherein the outer pane (1) and the inner pane (2) are bent in step c) simultaneously in pairs or one after the other individually by means of press bending.

8. Windshield (10) obtainable by a method according to one of claims 1 to 7, at least comprising an outer pane (1) made of glass with an outer surface (I) and an interior surface (II), an inner pane (2) made of glass with an outer surface (III) and an interior surface (IV), a thermoplastic intermediate layer (3) which connects the interior surface (II) of the outer pane (1) to the outer surface (III) of the inner pane (2), a roof edge (D), an engine edge (M), two side edges (S) running therebetween, a first surface area (X1) immediately adjacent to the engine edge (M) and a second surface area (X2) immediately adjacent to the first surface area (X1) between the first surface area (X1) and the roof edge (D), wherein the outer pane (1) and / or the inner pane (2) in the first surface area (X1) have a surface compressive stress of 11 MPa to 50 MPa,preferably from 15 MPa to 30 MPa and the outer pane (1) and / or the inner pane (2) in the second surface area (X2) has a surface compressive stress of 2 MPa to 10 MPa., 9. Windshield (10) according to claim 8, wherein in the first surface region (X1) a surface compressive stress of 11 MPa to 50 MPa, preferably of 15 MPa to 30 MPa, is present on the interior-side surface (II) of the outer pane (1) and / or on the interior-side surface (IV) of the inner pane (2).

10. Windshield (10) according to claim 8 or 9, wherein the first surface area (X1) occupies a proportion of 10% to 70%, preferably a proportion of 15% to 50%, particularly preferably 20% to 40% of the total surface area of ​​the composite pane (10).

11. Windshield (10) according to one of claims 8 to 10, wherein the first surface area (X1) extends at least in sections from the engine edge (M) by an amount in the direction of the roof edge (D) which corresponds to 10% to 70% of the height of the windshield (10).

12. Windshield (10) according to claim 11, wherein the size of the first surface area (X) is selected such that, in the installed state of the windshield (10) in a motor vehicle, the size of the first surface area (X) corresponds to at least 90% of the area of ​​the projection of the dashboard of the motor vehicle onto the windshield (10).

13. Windshield (10) according to one of claims 8 to 12, wherein the thermoplastic intermediate layer (3) comprises polyvinyl butyral (PVB), polyurethane (PU), ionomers and / or ethylene vinyl acetate (EVA).

14. Windshield (10) according to one of claims 8 to 13, wherein the outer pane (1) and the inner pane (2) each have a thickness of 0.8 mm to 2.5 mm, preferably of 1.2 mm to 2.2 mm.

15. Motor vehicle comprising a windshield (10) according to one of claims 8 to 14, wherein the size of the first surface area (X) is selected such that, in the installed state of the windshield (10) in the motor vehicle, the size of the first surface area (X) corresponds to at least 90% of the area of ​​the projection of the dashboard of the motor vehicle onto the windshield (10).

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