WO2024141982A1

WO2024141982A1 - Laminated glazing with offset edges and method of manufacture

Info

Publication number: WO2024141982A1
Application number: PCT/IB2023/063337
Authority: WO
Inventors: Fabian VEGA; Kubo TOMOYUKI; Jean Marie LE NY
Original assignee: Agp Worldwide Operations Gmbh
Priority date: 2022-12-28
Filing date: 2023-12-28
Publication date: 2024-07-04

Abstract

The present invention provides a laminated glazing with two opposite offset edges on the second glass layer, which can be produced using the doublet bending method to improve optical quality and cost. The laminate is made of a first glass layer with a length lf, width wf, and edges, at least one bonding layer, and a second glass layer with a length ls, width ws, and edges. Either the length ls or width ws of the second glass layer is smaller than the corresponding dimension of the first glass layer by at least 25 mm, creating the offset edges. The other dimension of the second glass layer has matching dimensions to the corresponding dimension of the first glass layer. The offset edges of the second glass layer are annealed to have a compressive stress of equal to or less than 7 MPa. The invention also includes a method for manufacturing the laminated glazing using a bending mold, heating and cooling the glass layers, and laminating them together with a bonding layer.

Description

LAMINATED GLAZING WITH OFFSET EDGES AND METHOD OF MANUFACTURE

FIELD OF THE INVENTION

The invention relates to the field of laminated automotive glazing with offset edges and the method for manufacturing a glazing with offset edges.

BACKGROUND OF THE INVENTION

Over the last several years, it has been seen the electronic content of automobiles grow at a higher rate than any other category of technology. Concurrently, the complexity of modern automotive glazing has been increasing as these same advances in electronic technology have made it practical to integrate various new safety, comfort, and convenience functions with the vehicle glazing.

Another factor driving this trend comes from the increase in the average glazed surface area of most vehicles. This increase has two primary benefits. First, weight is reduced as the glazing is used to displace heavier materials. The other benefit is that the larger glazed area increases the field of view of the vehicle occupants and lets in more natural light helping to offset the closed in and claustrophobic feeling that can sometimes result from the smaller passenger compartment interior volume. However, with a substantial percent of the vehicle internal and exterior surface area now comprised by the glazing, it has become even more important to combine functionality with the glazing as the nonglazed areas where the various components can be mounted has decreased.

Different applications on automotive laminated glazing could require the innermost glass pane to be shorter than the outermost glass pane in at least one or even all sides. The offset edges created by the difference in size could allow for the integration of several technologies and devices. In the following paragraphs there are a few examples of these applications.

Automotive laminated glazing may further comprise edge illumination means. Edge injection of light into a glazing can be used to provide low-level ambient cabin illumination. In this method, the glass functions as a wave guide for the light injected along the edges, where light is subjected to Total Internal Reflection (TIR). Light is injected by means of a light source such as a set of LEDs or other lighting means optically coupled to the edge of glass. The light is decoupled and refracted by a light dispersing means on the glass surface. This type of product is illustrated in Figure 2 where a laminated roof is shown with two light injection means 40 mounted to the laminate on opposite sides. Light dispersing materials are known that when applied to glass are substantially invisible when the lighting means is in the off state, allowing the glazing to still function as a window, while providing bright illumination in the on state.

Light may also be dispersed by means of various LASER, chemical and abrasive methods that introduce surface defects which will refract the internally reflected light. This application of TIR edge injection illumination has been demonstrated in several prior art documents, such as in W02020201973A, WO2023156939 and US63/371.340.

In another application, automotive laminated glazing may also comprise a defrosting injection means, wherein high intensity infrared light is injected into the edge of glass at an angle that allows the energy to undergo TIR when the surface of the glass is free of external elements water, fog, ice or debris, but allows the energy to decouple when water or ice is present. This provides rapid and efficient clearing of fog and ice such as demonstrated by WO2023073593A.

In yet another application, automotive laminated glazing may also comprise an edge injection glass defect detection and quality evaluation means, wherein the injected light is decoupled by the presence of surface defects, debris, ice, or water. The decoupled light is detected by sensors along the edge of glass or by a camera. In this manner, the condition of the glazing can be evaluated. The data can be used to operate the defrosters or wiper system and to indicate when the glazing needs repair or replacement such as disclosed by WO2022264115A.

In yet another application, automotive laminated glazing may also comprise edge injection holographic illumination means. The edge injection with LASER light is also being developed as a means of illuminating a holographic film embedded within the laminate.

Light can be injected into the edge of an ordinary unmodified laminate. However, the light injection means required by all TIR applications has a length, width and height which must be accommodated by the glazing and mounting structure. The light must be injected along the edge of glass with the light injection means at least partially located outboard of the edge of glass. With both layers of glass, the same size, the light injection means must be mounted outboard of the edge of glass. To do so, the opening that the glazing is mounted in must be made larger or the glazing must be made smaller. Either approach is not desirable as they require major changes to the glazing or the opening. It is also necessary to protect the light emitting means from the external elements, so it is not desirable to have any portion of the light emitting means exposed to the vehicle exterior.

For accommodating light injection as well as other technologies, it is customary to have a laminated glazing wherein the innermost glass layer is shorter than the outermost glass layer, providing a glazing with offset edges. When curving the two glass layers in a doublet bending process by gravity, the weight distribution on the crown/ring mold will not be uniform and will naturally create over-bending on the peripheral regions of the outer glass layer that extend over the inner glass. This could lead to curvature mismatch within the set of glass layers, such as generating regions of what is called as “gaps” between the internal surfaces of the outer and inner glass panes that will ultimately create problems when laminated. In these cases, it is conventional to have inner and outer glass layers bent individually and separately, following what is called singlet bending process. A few of the drawbacks of singlet bending are extended production times and increased costs. However, the main drawback is that due to natural process variations, the singlet bending process could lead to curvature mismatch within the set of glass panes (resulting, again in regions of gaps between the interior surfaces of the inner and the outer glass layers, typically above 0.3 mm). This again might result in lamination problems such as trapped air-bubbles, optical distortion, and ultimately increase the risk of glass breakage.

It is noted that either the inner or the outer glass layer might accommodate for the light injection or the insertion of other technologies, depending upon the application and that may comprise offset edges.

Thus, when it is described a first glass layer as having an offset relative to the second glass layer, it is understood that the first glass layer may be the inner or the outer glass layer and the second glass layer the remaining layer. In addition, the laminate must have at least two glass layers but may have more than two as is common with ballistic resistant glazing. In the case where there are more than two glass layers, the first glass layer is the one that extends over the remaining layers and any or all of the remaining layers may be considered as the second glass layer. It would be highly desirable to be able to produce laminates with an offset edge by the doublet gravity bending process, which results in a glazing with improved curvature surface matching and a method for manufacturing such a glazing.

BRIEF SUMMARY OF THE INVENTION

The present disclosure provides a solution for the above-mentioned issues by a curved laminated glazing having two opposite offset edges on the second glass layer, wherein said glazing is comprised of a first glass layer, having a length of l_f, a width of Wf, and edges, at least one bonding layer, and a second glass layer, having a length l_s, a width w_s, and edges, wherein either one of the length l_s or the width w_s is smaller than either one of the corresponding width Wf of the length l_f of the first glass layer by at least 25 mm, forming two opposite offset edges, and the other length l_s or width w_s has matching dimensions to the corresponding length l_f or width Wf of the first glass layer; and the offset edges of the second glass layers are annealed to a compressive stress of equal or less than 7 MPa.

A method for manufacturing of a curved laminated glazing with offset edges comprising the steps of

- providing a bending mold, having a length l_m and width w_m, wherein said l_m and w_m define the periphery of the mold;

- providing a first glass layer, having a length l_f and a width Wf, wherein said and Wf define the periphery of the first glass layer, and is larger than l_m and Wf is larger than w_m;

- providing a second glass layer, having a length l_s and a width w_s, wherein either l_s is smaller than l_m or w_s is smaller than w_m;

- placing the first glass layer onto the bending mold;

- placing the second glass layer onto the first glass layer; wherein the first glass layer is configured to receive the second glass layer such that: any pair of opposite sides of the second glass layer is supported by the first glass layer surface such that it is inboard within the region circumscribed by the periphery of the mold; and the other pair of opposite sides of the second glass layer is supported by the first glass layer surface extending outboard of the area circumscribed by the periphery of the mold;

- curving the first and the second glass layers simultaneously by heating to at least the glass transition temperature range of the first glass layer, allowing the hot glass layers to sag to the desired shape under the force of gravity on the mold;

- cooling said curved first and second glass layers, such as to achieve annealing;

- placing at least one bonding layer between the curved first and the second glass layers; and

- laminating the said bonding layers and said curved first and the second glass layers together.

Advantages

Glass layers are annealed.

Offset edges are annealed.

Higher throughput than singlet pressing method.

- Allows for the use of a thin second glass layer when compared to singlet bending. Can be fabricated using existing gravity bending method, facilities, and tooling.

BRIEF DESCRIPTION OF THE DRAWINGS AND THE REFERENCE NUMBERALS

Figure 1A illustrates the cross section of a typical laminated glazing.

Figure 1B illustrates the cross section of a typical laminate comprising performance film and an IR reflecting coating.

Figure 2 shows an schematic of a top view of laminated roof of the prior art with entire edge of the inner glass layer offset.

Figure 3A shows the cross-section AA of Figure 2.

Figure 3B shows the cross-section BB of Figure 2. Figure 4 shows an schematic of a top view of a laminated roof with left and right opposite edges offset.

Figure 5A is an isometric exploded view of the laminated roof with left and right opposite edges offset of Figure 4.

Figure 6A shows the cross-section CC of Figure 4.

Figure 6B shows the cross-section DD of Figure 4.

Figure 7A is an isometric view of a bending mold.

Figure 7B is a side view of a bending mold.

Figure 8A is an isometric view of a bending mold with flat glass layers stacked.

Figure 8B is an isometric view of a bending mold with a bent glass layers stacked.

Figure 9 shows the top view of a bending mold with bent glass.

Figure 10A is the cross-section EE of Figure 9.

Figure 10B is the cross-section FF of Figure 9.

Figure 11 shows a bounding box.

Reference Numerals of Drawings

2 Glass

4 Bonding layer

6 Obscuration/Black Paint

10 Lighting means

12 Performance film

18 Infrared reflecting coating

22 Gravity bending mold

24 Ring

26 Point support 28 Line support

30 Edge of glass

32 High stress

34 Low stress

36 Offset

38 Flat unbent glass

40 Light injection means

42 Bent glass

50 Bounding box

52 Laminated glazing

60 Depth of bend

62 Length

64 Width

101 Exterior side of the first glass layer (201), number one surface.

102 Interior side of the first glass layer (201), number two surface.

103 Exterior side of the second glass layer (202), number three surface.

104 Interior side of the second glass layer (202), number four surface.

201 First glass layer

202 Second glass layer

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure can be understood by reference to the detailed descriptions, drawings, examples, and claims, of this disclosure. However, it is to be understood that this disclosure is not limited to the specific compositions, articles, devices, and methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing aspects only and is not intended to be limiting.

The term “glass” may refer to a wide range of inorganic materials, including those that are not transparent. In this document, embodiments will be described to transparent glasses but should be understood that opaque material glasses can also be used. From a scientific standpoint, glass is defined as a state of matter comprising a non-crystalline amorphous solid that lacks the ordered molecular structure of true solids. Glasses have the mechanical rigidity of crystals with the random structure of liquids.

A glazing is an article comprised of at least one layer of a transparent material which serves to provide for the transmission of light and/or to provide for viewing of the side opposite the viewer and which is mounted in an opening in a building, vehicle, wall or roof or other framing member or enclosure.

The structure of the invention is described in terms of the layers comprising the glazing. The meaning of “layer,” as used in this context, shall include the common definition of the word: a sheet, quantity, or thickness, of material, typically of some homogeneous substance and one of several. It was noted that the layers are generally substantially flat at least at the macro level.

When multiple layers that vary widely in thickness are illustrated, it is not always possible to show the layer thicknesses to scale without losing clarity. Unless otherwise stated in the description, all figures are to be considered as for illustrative purposes and are not drawn to scale and thus shall not be construed as a limitation.

Left, right, front, and rear shall be defined relative to an occupant of the vehicle seated and facing in the normal forward direction of the vehicle. Inboard and outboard are relative to the center of the glazing with inboard being the direction from the edge of the glazing towards the center and outboard from the edge of glass in the direction away from the center of the glazing.

In this patent document, the various glazed positions of the vehicle are described using terms that are appropriate for the relative orientation of the glazing in the vehicle. For example, the edges or a windshield or backlite are referred to as the top and bottom edges, as well as the left and right edges. Similarly, the edges of side door glazing are referred to as the top and bottom edges, as well as the front or fore edge and the rear or aft edge. For a roof glazing, the edges are referred to as the front, rear, left and right edges. It should be noted that the glazing shapes are not typically rectangular, and the edges generally have some curvature, rather than being straight.

Laminates, in general, are articles comprised of multiple sheets of thin, relative to their length and width, material, with each thin sheet of relatively uniform thickness having two oppositely disposed major faces and two pairs of opposite edges. In a laminated glazing, the glass layers are permanently bonded to one and other across at least one major face of each sheet by means of a bonding layer, sometimes referred to as an interlayer.

Laminated glazing is increasingly being used to make the front doors of cars. The laminated construction increases the time that it takes to break into a vehicle, improving security and the laminated cross section acts to deaden noise. Special sound deadening bonding layers are available to further improve sound deadening. Laminates also allow for the use of solar control coatings.

The bonding layer has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear thermoset plastic. For automotive use, the most commonly used bonding layer is polyvinyl butyral (PVB). PVB is a highly engineered thermoplastic which has excellent adhesion to glass and is optically clear once laminated. Additionally, ethylene vinyl acetate (EVA) or thermoplastic polyurethane (TPU) may be used as bonding layers. The bonding layer also helps to prevent penetration by objects striking the laminate from the exterior and in the event of a crash occupant retention is improved.

The flat unbent glass layers of a laminate have a length and width defined by the dimensions of the minimum sized rectangle that can be fit to the layers. In the same manner, the dimensions of the bent glass are described by the dimensions of the minimum sized box that the glass will fit in. This is known as a bounding box 50 which is illustrated in Figure 11. In this example, the length “L” 62 is the dimension of the box in the x direction, the width “W’ 64 is the dimension in the y direction and the depth of bend (DOB) 60 is the z dimension.

An automotive laminate is comprised of at least two layers of glass, the exterior or outermost layer 201 and the interior or innermost layer 202. A typical automotive laminate having two glass layers, 2, has a cross section illustrated in Figure 1A. In this figure, the glass surface of the exterior glass layer 201 that faces the exterior of the vehicle is referred to as surface one, 101 , or the number one surface. The opposite surface of the exterior glass layer 201 is surface two, 102, or the number two surface. The surface of the interior glass layer 202, that faces the interior of the vehicle is referred to as surface four, 104, or the number four surface. The opposite surface of the interior glass layer 202 is surface three, 103, or the number three surface. Surfaces two, 102, and three, 103, are permanently bonded together by the bonding layer 4. An obscuration 6 may be also applied to the glass. Obscurations are commonly comprised of black enamel frit print on either the number two, 102, or number four surface, 104, or on both.

The laminate may have a coating 18 on one or more of the surfaces. The laminate may also comprise a film 12 laminated between at least two bonding layers 4. This is illustrated by Figure 1 B.

A variety of glass compositions may be used in the fabrication of the invention, and not limited to soda-lime glass borosilicate glass, aluminosilicate glass, and lithiumaluminosilicate.

A range of glass thicknesses may also be used in the fabrication of the invention. Typical windshields have glass layers, such as the interior and the exterior, that range from 1.4 mm to 5.0 mm. However, this is not to be taken as a limitation. The actual thickness is dependent upon a number of factors including the intended application, the total size of the glazing, the installation angle, and the intended service life to name just some. Laminates with a chemically tempered inner glass layer with a thickness of less than 1.0 mm are known and mostly common.

Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range which is the range of temperatures where the glass transitions from a “liquid” to a “solid”. This process relieves much of the stress left in the glass from the bending process. Annealed glass breaks into large shards with sharp edges. When laminated glass breaks, the shards of broken glass are held together, much like the pieces of a jigsaw puzzle, by the bonding layer, helping to maintain the structural integrity of the glass. A vehicle with a broken windshield can still be operated, annealed glass should be understood as having a compressive stress no more than 7 MPa.

It should be noted that automotive annealed glass is not completely free of stress. During the bending process, the glass is heated to a temperature within the glass transition range, the glass is rarely if ever isothermal. This is a deliberate design choice. To prevent optical defects, no more heat is applied than needed to bend the glass. However, the portions of the glazing with more curvature will require a higher temperature to make the glass soft enough to be formed. Large thermal gradients also result from the use of heat absorbing glass compositions as well as Low-e and infrared reflecting coatings on the glass. If held in the annealing range long enough all stress can be removed, however, there is a tradeoff between throughput and optimum anneal in the time that is allowed for the glass to cool.

In the present disclosure, it is described a first glass layer with two opposite edges moved inboard of the second glass layer edges resulting in offset edges. These offset edges are not offset in a geometric sense, but rather they are adjusted to compensate for the components that need to be mounted on the second glass layer. This adjustment may involve reducing, making smaller, moving inboard, or diminishing the edges of the first glass layer that need to be mounted to the second glass layer.

In the present disclosure, geometric offset curves or surfaces are defined as a locus of the points which are at a constant distance along the normal vector from the generator curves or surfaces. In slightly less technical terms, an offset curve is one that is created by taking a point set on the generating curve or surface, drawing a line though each point such that the line is normal to the curve or surface, and then creating the offset curve or surface though a set of points that are a constant distance along each of the lines wherein the line is also normal to the generated offset curve or surface.

It is also possible to have a geometric offset curve that is offset in a surface, rather than in a straight line. In this case, the distance between points on the offset curve is not measured along a straight line, but rather it is measured along the surface itself, ensuring that the true distance along the surface is constant.

An offset glass edge may in fact be a true geometric offset but need not be one. Often, working in computer aided design (CAD), we will design the offset glass edge by first creating a curve offset in the surface from the edge curve and then adjust as may be needed. When the edge curve is offset, the radius of curvature of the generated curve will increase or decrease by the offset distance. As an example, if the corners of a glass layer have a radius of 25 mm and the offset distance is equal to 25 mm inboard, the resulting offset curves will meet at a point with a radius of zero. Generally, such an offset curve will have a fillet applied at the intersection rather than leaving it at a point. If the offset distance is greater than 25 mm, the radius will be negative, and the curve will be inverted, requiring additional trimming to deviate from a true offset curve. This can be seen in Figure 2, where the corners of the glass have a small radius, but the inboard edge of the black obscuration is offset 100 mm inboard from the edge of the glass 30. Rather than having the corners of the black obscuration meet at a point, a large fillet has been applied. It is important to note that the geometric definition of an offset curve should not be considered a limitation with regard to the offset edge of the laminate.

For the purposes of this document, an offset edge is defined as any portion of the edge of the second glass layer that is inboard of the corresponding portion of the edge of the first glass layer. The offset distance may be constant or variable. Furthermore, the offset may be along the entire edge, or it does not need to be along an entire edge. In one embodiment the entirety of the two-offset inboard opposite edges of the second glass layer are offset. In another embodiment the two said inboard opposite edges of the second glass layer are offset along up to 90% of the length, or up to 80%, or up to 70%, or up to 50% of the length of each corresponding edge of the first glass layer, depending upon the dimensions of the components to be mounted to the glass. The opposite offset edges may be dimensionally symmetrical or asymmetrical. That is to say that the shape and offset distance need not be the same for both edges. Nor do they need to be mirror images. The length of each edge that is offset does not need to be the same.

The edge offset 36 distance is defined as the minimum distance between a point on the offset edge 30 of a first glass layer 201 to the edge 30 of a second glass layer 202 as measured on the surface (See Figure 6B). This is a discrete value at a point. However, the average, typical, mean, or maximum distance may be used to describe the offset distance as all will normally have similar values and should not be taken as a limitation.

An example of a laminate with offset edges that does not meet the geometric definition is shown in Figure 2. The edge 30 of the inner glass layer 202 has an offset distance 36 of 80 mm as measured inboard from the edge 30 of the outer glass layer 201 along the glass surface. However, the four corners have been rounded with 25 mm fillets. As a result, the distance along the corners is greater than 80 mm. We also cannot connect corresponding points with a line normal to both edges. Therefore, as the offset distance is not constant, this is not a true geometric offset curve as the offset distance is not constant. However, it is an offset edge.

Figure 2 is one of the embodiments of this invention. Two light injection means 40 are mounted to the surface two, 102, of the outer glass layer 201 along the length of the glazing. A 100 mm wide black obscuration is printed on surface two, 102. Cross sections A and B are shown in Figures 3A and 3B. In both, the offset distance 36 is 80 mm. In Figure 3B, the light injection means 40 is shown. This configuration, with the inner glass layer 202 substantially smaller than the outer glass layer 201 around the entire periphery, limits the methods that may be used to bend the glass layers to shape.

Glass can be bent without heating. Very thin chemically tempered glass, in which an ion exchange process is used to strengthen the glass is sometimes used in a non-thermal bending process known as cold bending. Cold bending is a relatively new technology. As the name suggests, the glass is bent, while cold to its final shape, without the use of heat. However, as the glass only undergoes elastic deformation, at any point on the bent area of the glass one side, i.e., major surface, of the glass will have a substantially higher level of stress than on the opposite side of the glass. If annealed glass is used, one side will be in compression and the other in tension.

Cold bending can be used to produce a laminate with an offset edge on one of the glass layers. However, one of the layers must be thermally bent and also stiff enough to resist deformation by the cold bent glass layer. Cold bending is limited to relatively simple large radii curvature parts. Also, the high level of stress results in a non-uniform index of refraction which limits the types of TIR applications that this type of laminate may be used for. Cold bending also tends to be substantially more expensive than thermally bent glazing requiring equipment not normally found in automotive glass factories.

Thermal bending of glass involves heating the glass into the glass transition temperature range where it is bent to shape then cooling the glass to freeze in the change in shape. In this case, glass undergoes a permanent plastic deformation. The glass can be slowly cooled to relieve stress process known as annealing, or rapidly cooled to heat strengthen it.

While there are various methods used to thermally bend the glass layers comprising a laminate, they all fall into two categories, singlet bending and doublet bending. Doublet bending is a method in which two or more glass layers are stacked together, heated, and simultaneously bent to shape using the same tooling.

One variety of doublet bending is the doublet gravity bending method. In this method, the set of cold flat at least two glass layers are first placed on a negative mold, such as a crown or ring. The mold supports the set of glass layers at or near the edge of glass. The glass layers are then heated into the glass transition temperature range where the hot glass layers are allowed to sag under the influence of gravity, to the final shape becoming curved. After bending, the curved glass layers are annealed by cooling slowly to allow residual stresses to be relieved.

A typical negative gravity bending mold 22, also called ring, is shown in Figures 7A and 7B. The glass is supported by a ring 24 fabricated from thin metal stock, typically 3 mm wide stainless steel. The ring 24 supports the first glass layer 201 , contacting the glass, along the rings’ narrow edge. The ring is formed normal to the surface of glass as illustrated in Figures 10A and 10B. To minimize the potential for marking of the hot glass by the ring, the ring is typically kept as far outboard and close to the edge 30 of the glass layers as possible.

Figure 11 shows a typical laminate within a bounding box 50. The laminate, with large surface radii and a relatively shallow depth of bend 60, the z dimension of the bounding box, a solid continuous ring may be used as shown in Figures 7A, 7B, 8A, 8B and 9. The flat glass 38 must sit level on the ring 24, otherwise the glass may slide off of the ring during bending. The position of the glazing must be rotated as needed to level the corners of the glazing. This is the position that the glazing would be in if it were set against a flat and level surface. When the flat glass 38 is loaded onto the ring 24, as shown in Figure 8A, it will initially contact the high points on the ring which initially provide point support 26 for the flat glass. As the glass is heated it sags and the initial point support 26 contact converts to line support 28 as the glass takes on the shape of the ring as illustrated in Figure 8B.

The main advantage to doublet gravity bending is that no contact is made with the surface of the glass, other than the small area near the edge of glass, during heating and forming. This reduces the probability of marking of the glass. The ring of the mold contacts the glass in an area where not as much heat is needed, further reducing the likelihood of marking of the glass. This area, near the edge of glass, is often covered by trim or an encapsulation and not visible once installed in the vehicle which also makes marking less critical. Another big advantage to the method is that, as the two of more flat glass layers are stacked onto the same mold and bent as a set, an excellent match between the layers can be achieved which is a requirement for good optical quality and durability.

Doublet bent glass tends to have very low levels of residual stress due to the slow controlled cooling that is a part of the process. Most annealed laminated windshield have a level of stress across a substantial portion of the area that is no more than 7 MPa, preferably less than 3.5 MPa. In practice, in the clear daylight opening, inboard of the black paint, the stress level is typically so low as to be barely detectable.

However, in doublet gravity bending the edge of glass tends to be in compression once cooled. This is because the edge will cool faster due to the fact that the glass radiates and is convectively cooled along the edge surface of the glass in addition to the two exposed major surfaces of the glass.

The metal negative mold ring, which has a high value of thermal conductivity, supporting and in contact with the glass also acts as a heat sink. Also, the edge is not heated to as high a temperature as the area inboard to avoid marking from the mold supporting the edge of glass. As a result, the edge, and an area extending inboard, typically around 6 to 12 mm inboard, to as far as the portion that is in direct contact with the supporting ring and sometimes slightly beyond, typically cools faster and freezes resulting in a compressive stress higher than 7MPa, most probably higher than 10 MPa. This is desirable as this makes the glazing more resistant to breakage during handling and installation as well to torsional loads applied as the vehicle body twists. Some bending methods have been modified to rapidly cool the edge of the glazing while allowing the remainder of the glazing to anneal.

Doublet bending also allows for the use of very thin glass layers for at least one of the glass layers. A very thin layer can be supported by the thicker second glass layer. Glass layers that are asymmetrical in thickness have become more and more common. A thicker layer is often used for the outer glass layer where it is subjected to and helps to protect against impact from debris, rain, and snow while a thinner lighter layer is used for the inner glass layer. The outer glass layer (first glass layer) is often twice as thick as the inner layers (second glass layer) and sometimes three times as thick. For very thin glass the outer thickness can be four times thicker or more than the inner glass layer. With the doublet method different glass compositions can be used for the layers provided that the glass transition ranges overlap sufficiently, i.e. , the first glass layer may be a different composition of glass than the second glass layer.

Gravity doublet bending was used almost exclusively for many years to bend most high- volume series production windshields due to the low cost and high throughput of the process as well as repeatability and accuracy of the curvature of the final product.

In response to the industry needs for better surface control, the industry has been moving toward a modified hybrid form of doublet gravity bending. Rather than depending upon just gravity to form the glass, a full or partial surface press is used in conjunction with the gravity bending method. The glass is at least partially bent using a traditional gravity bending method and then, in the final stage, the press is used to bend the glass. The hot glass may continue to sag after being pressed as it is not rapidly cooled. Often vacuum is used to aid compliance to the shape of the press. This bending method has the advantage in that it can be adapted to an existing gravity bending line and to existing gravity bending tooling. The layers of the laminate are doublet bent in sets simultaneously as with traditional gravity bending.

For even better surface control, singlet bending was developed. This process is similar to the process used to produce tempered parts. The inner and outer glass layers are bent separately. Each flat glass ply runs through a furnace to heat it and is then mated to a full surface press. The glass is then rapidly transferred from the press to a quench where the glass is rapidly cooled, and the shape is frozen. The shape of the glass may change slightly during the transition from the press to the quench. This is normally compensated for by the press. The quenching process heat strengthens the glass but does not achieve a full or high level of temper which is not allowed for windshields.

The main drawback to singlet bending is that the throughput is lower than a comparable gravity bending line as the glass layers must be separately bent versus the simultaneous bending of each set with gravity bending.

The main drawback of singlet bending is that although it allows for a better surface control within the same glass layer, there is a larger surface mismatch compared to doublet bending parts, between the separately bent glass layers that are later joined together to compose a laminated glazing. Typically, for the singlet bending method, the surface bend tolerance of each glass layer is +/- 1.5 mm. This means that there is the potential to have some sets of glass layers with a gap between the two facing surfaces of up to 3.0 mm. The vacuum and pressure of the lamination process force the two glass layers together but leave residual areas of compression and tension which is undesirable. This will result most certainly into trapped air bubbles, optical distortion and lamination problems. Doublet bent sets of glass, on the other hand will match to within 10s of microns. Typically, when two glass layers are bent simultaneously by the doublet method, the gap between the internal surfaces of the first and the second glass layers is below 0.3 mm.

Another disadvantage of the singlet bending method is that the glass layer is not annealed and has high levels of residual stress, in excess of the maximum of 7 MPa. The cost of singlet bending tooling can be substantially more depending upon volume and other factors.

Singlet bending is also not suited for use with very thin glass. However, glass layers as thin as 1.4 mm have become common place and even thinner glass is being introduced which cannot be formed by the singlet bending method. The thinner glass tends to break, warp, and wrap around the rollers when heated using a singlet method.

Singlet bending has typically been used to produce laminated door glazing as they are too small to economically produce by gravity bending. Optical quality is not as critical on door glazing as it is on automotive glazing. The use of singlet bending has also seen rapid growth as the market for large laminated automotive glazing has grown. These larger parts can be difficult to produce by any of the doublet bending methods due to process and product limitations.

As mentioned in the background of the invention, there might be applications wherein a glazing with offset edges on one of the glass layers is needed.

In the present disclosure, a glazing with offset edges is defined as comprising a first glass layer having a length of l_f, a width of Wf, and edges; a second glass layer, having a length l_s, a width w_s, and edges, having two opposite edges that are offset by having either one of the length l_s or the width w_s being smaller than either one of the corresponding width Wf of the length l_f of the first glass layer by at least 20 mm, preferably 25 mm, and more preferably 30 mm.

To the day, this type of glazing is being produced by the singlet bending method. When trying to bend a set of glass layers using the doublet bending method, the areas where the edge is offset, there is just a single layer of glass (first glass layer) to absorb the thermal energy and so the glass will run hotter than in the doublet areas where there are two thickness of glass. If the edge of the second glass is inboard within the area circumscribed by the ring periphery, the ring will not provide sufficient support for the second glass layer. The edge of the second glass acts as a fulcrum and tend to crease the softer and hotter first glass along the edge of the second glass. This may result in a substantial deviation from the desired shape (overbending may occur) and also will certainly cause undesirable distortion when viewed in reflection.

Normally in the industry, to avoid this, doublet gravity bending cannot be used to produce this type of laminate. Instead, it is produced by means of the singlet bending process.

Surprisingly, it was found that if one of the two dimensions (length or width) of the second glass layer is larger than the corresponding dimension of the mold, and the glazing is positioned onto the first glass layer such as a pair of two opposite sides of the first glass layer are positioned outboard of the area circumscribed by the ring periphery, it is possible to bend such glass layers by gravity doublet method and achieve a glazing with improved matching surfaces. Improved matching surfaces mean that the distance between the internal surfaces of the first glass layer and the second glass layers is a gap of less than 0.3 mm.

Advantageously, doublet gravity bending of sets of glass layers with a second glass layer offset distance along two opposite edges of at least 15 mm, 25 mm, 50 mm and greater than 75 mm has successfully been achieved. Not only is the bent surface within dimensional specifications, but there is also little or no reflected distortion along the edge. Further, the offset edge of the second glass layer is also annealed with compressive stress of no more than 10 MPa, preferably less than or equal to 7 MPa, rather than being in compression as would be the case had the glass been formed using conventional singlet press-bending or doublet bending with no offset edge. The low level of stress in the offset edge result is a more uniform index of refraction giving the edge superior optical properties.

In one advantageous embodiment, the pair of opposite sides of the second glass layer that does not have the offset should have similar dimensions to the corresponding length or width Wf of the first glass layer, within acceptable process dimensional tolerances. Typically in the industry, the acceptable dimensional tolerance is within +/- 3.00 mm, and preferably within +/- 5.00 mm. In the doublet bending method, as shown in Figures 8A, 8B, 10A and 10B, the glass is supported by the ring 24 of a gravity bending mold 22. The offset distance 36 of a second glass layer 202 with an offset edge 30 that spans the entire periphery must be less than the distance from the edge of the glass layer 201 to the inner edge of the ring. This inner edge of the ring, which contacts surface one, 101 , of the first glass layer 201 provides line support 28 for the glass. The support line 28 provides support to both glass layers when the two glass layers overlap at the support line 28.

Description of Embodiments and Examples

Example one is the large panoramic laminated roof shown in Figures 4, 5, 6A, 6B and 11. The length in the x direction is 1700 mm and in the y 1200 mm. The depth of bending is 90 mm. The second glass layer 202 is the inner glass layer and is comprised of ultraclear 1.6 mm thick soda-lime glass. The first glass layer 201 is the outer glass layer and is 100% thicker than the inner glass layer 202, at 3.2 mm and is comprised of dark solar green soda-lime glass. The outer glass layer has a black obscuration, black band, printed onto surface two, 102, which is 100 mm wide. The two glass layers are laminated together with a 0.76 mm thick layer of PVB bonding layer. The two opposite edges, running from the front to the back of the inner glass layer 202 are offset inboard by an offset distance 36 of 80 mm each. A set of two light injection means 40 are mounted to surface two, 102, of the outer glass layer 201.

The laminate with offset edges is manufactured by providing a set of glass layers, a bonding layer, a bending mold, a heating means. The glass layers are placed on the bending mold. The glass is heated by the heating means and allowed to sag under the force of gravity. Optionally a partial surface positive mold press or full surface positive mold press may be used. The bent glass is allowed to slowly cool and anneal. A bonding layer is placed between the bent sets of glass, the air is evacuated and then pressure, and heat are used to permanently bond the glass layers together.

In the first step of the method of manufacture of example one, the two glass layers are each cut on a computer numeric control, CNC, glass cutting machine. After the glass is cut, the edges of each are ground by a diamond wheel on a CNC grinding machine.

Each glass layer is washed. The outer glass layer is then screen printed with a black enamel frit. The outer glass layer with the printed obscuration frit is then heated to fire the frit into the glass surface. The two glass layers, the inner and the outer, are then brought together and aligned. The glass layers are bent by means of a doublet gravity bending process. The negative gravity bending mold 22 is shown in Figures 7 A, 7B, 8A, 8B, 9, 10A and 10B. The set of flat glass 30 layers is initially loaded onto the bending mold 22 as shown in Figure 8A where the glass contacts the mold and is supported at the four support points of the mold 26. The mold with glass layers is heated in a furnace to bring the glass layers into the glass transition range. The hot glass is allowed to sag under the force of gravity. When the desired shape has been achieved, the glass is slowly cooled so as to relieve any residual stress.

Figure 8B shows the bending mold with the glass conforming to the shape of the mold after bending. A top view of the glass resting on the mold is shown in Figure 9. Figure 10A shows the cross-section EE of Figure 9, where the edges 30 of the two glass layers overlap. In Figure 10B the cross-section FF of Figure 9 is shown. The edge of the inner glass layer 202 is offset by a maximum offset distance 36 of 80 mm inboard of the edge 30 of the outer glass layer 201. The edges 30 of the outer glass layer 201 and the inner glass layer 202 of the cross-section EE in the general area near the edge and the ring 24 will be in compression. This area in compression is illustrated by the region 32. However, as we can see in the cross-section FF of Figure 10B, the edge of the outer glass layer 201 will be in compression while the offset edge 30 of the inner layer 202 will be annealed, illustrated by region 34.

The two glass layers are annealed to a residual stress level that is less than 10 MPa, preferably less than or equal to 7 MPa in the areas inboard of the edge of glass. The offset edges are annealed with a residual stress level of less than 10 MPa, preferably less than or equal to 7 MPa.

The edges and the area between the edge of the first glass layer and just inboard of the bending mold ring supporting the glass will tend to be in compression with a level of stress of a minimum of 10 MPa.

Embodiments

Embodiment 1 is similar to the example with the exception of the offset edges. The edges are offset along 90% of the length of each edge. Embodiment 2 is similar to the example with the exception of the offset edges. The edges are offset along 80% of the length of each edge.

Embodiment s is similar to the example with the exception of the offset edges. The edges are offset along 70% of the length of each edge.

Embodiment 4 is similar to the example with the exception of the inner glass thickness. The inner glass thickness is 1.2 mm.

Embodiment 5 is similar to the example with the exception of the inner glass thickness. The inner glass thickness is 0.8 mm.

Embodiment 6 is similar to the example with the exception of the offset edges. The offset edges are dimensionally asymmetrical.

Embodiment 7 is similar to the example with the exception of outer glass layer composition. The outer glass comprises a borosilicate glass.

Embodiment 8 is similar to the example with the exception of the offset edges. The offset edge distance is 60 mm.

Embodiment 9 is similar to the example with the exception of the offset edges. The offset edge distance is 40 mm.

Embodiment 10 comprises any of the preceding embodiments further equipped with at least one of the following: an interior cabin illumination system, a holographic display system, a safety detection and glass quality detection system, moisture detection system and an infra-red heating system.

Claims

1. A laminated glazing with offset edges, comprising: at least one bonding layer; a first glass layer, having a length of l_f, a width of Wf, and edges; a second glass layer, having a length l_s, a width w_s, and edges; wherein either one of the length l_s or the width w_s is smaller than either one of the corresponding width Wf of the length l_f of the first glass layer by at least 25 mm, forming two opposite offset edges; and wherein the other length l_s or width w_s has matching dimensions to the corresponding length l_f or width Wf of the first glass layer; and the offset edges of the second glass layer have a compressive stress of equal or less than 7 MPa.

2. The laminated glazing with offset edges of any of the preceding claims, wherein the entirety of the two-offset inboard opposite edges of the second glass layer are offset.

3. The laminated glazing with offset edges of any of the preceding claims, wherein the two said inboard opposite edges of the second glass layer are offset along up to 90% of the length of each corresponding edge of the first glass layer.

4. The laminated glazing with offset edges of any of the preceding claims, wherein the two said inboard opposite edges of the second glass layer are offset along up to 70% of the length of each corresponding edge of the first glass layer.

5. The laminated glazing with offset edges of any of the preceding claims, wherein the edge offset of the second glass layer is at least 30 mm from the corresponding edge of the first glass layer.

6. The laminated glazing with offset edges of any of the preceding claims, wherein the edge offset of the second glass layer is at least 50 mm from the corresponding edge of the first glass layer.

7. The laminated glazing with offset edges of any of the preceding claims, wherein the edge offset of the second glass layer is at least 75 mm from the corresponding edge of the first glass layer.

8. The laminated glazing with offset edges of any of the preceding claims, wherein the first glass layer is at least twice, three times, or four times as thick as the second glass layer.

9. The laminated glazing with offset edges of any of the preceding claims, wherein the first glass layer is a different composition of glass than the second glass layer.

10. The laminated glazing with offset edges of any of the preceding claims, wherein the offset edges are dimensionally not symmetrical.

11. The laminated glazing with offset edges of any of the preceding claims, further comprising any of the following: an edge illumination means, defrosting injection means, edge injection glass defect detection and quality evaluation means, and edge injection holographic illumination means.

12. A method for manufacturing a laminated glazing with offset edges, comprising the steps of:

- placing the first glass layer onto the bending mold;

- placing the second glass layer onto the first glass layer; wherein the first glass layer is configured to receive the second glass layer such that: any pair of opposite sides of the second glass layer is supported by the first glass layer surface is inboard within the region circumscribed by the periphery of the mold; and the other pair of opposite sides of the second glass layer is supported by the first glass layer surface extending outboard of the area circumscribed by the periphery of the mold;

- cooling said curved first and second glass layers, such as to achieve annealing; - placing at least one bonding layer between the curved first and the second glass layers; and

13. The method of the preceding claim, further comprising the step of curving the hot glass with a partial surface positive mold press.

14. The method of claim 12, further comprising the step of curving the hot glass with a full surface positive mold press.