Field of the Invention

The invention relates to the field of automotive laminated glazing.

Background of the Invention

The use of camera-based safety systems, requiring a wide field of view and a high level of optical clarity, is growing at a rapid rate. As the industry moves towards full autonomous capability, the number of cameras and the resolution of the cameras are both increasing. At the same time, windshields, where many of the cameras are mounted, are becoming larger and more complex in shape.

The main cameras require a high, forward looking field of view and hence it is typically mounted on the windshield and in the area cleared by the wipers. Camera based systems are used to provide a wide array of safety functions including adaptive cruise control, obstacle detection, lane departure warning and support for partial and full autonomous operation. Many of these applications require the use of multiple cameras. A clear undistorted field of view, with minimal double imaging, a high level of light transmission with unaltered natural color is especially critical for camera-based systems to perform as intended. It is essential for these systems to be able to quickly differentiate between objects, capture text, identify signage, and operate with minimal lighting. Further, as the resolution of the cameras increases, the need for a clear distortion free field of view increases.

At the same time, the glazed area of vehicles has been steadily increasing and, in the process, displacing other heavier materials. The popular large glass panoramic roofs and windshields are just one example of this trend. A panoramic windshield is a windshield on which the top edge has been substantially extended such that it comprises a portion of the vehicle roof.

The optical quality of windshields is based upon the requirements for human vision. However, the human eye can analyze and filter an image far better than a computer even though today’s cameras have far greater resolution. As one would expect, the requirements for human vision are not the same as for a camera system. In general, for computer vision, the optical requirements are more similar to that of a precision lens system and a human eye. This may change in the future but for now and the foreseeable future, the optical quality of windshield will need to be better than required for just human vision.

While the optical clarity of a windshield in the camera field of view may be adequate when the vehicle initially is put into service, that quality deteriorates over time as the glass surface is abraded and weathers. While a badly abraded and weathered windshield may continue to be suitable for manual human driving, it will not meet the needs of an autonomous vehicle. A small chip which would not require even a repair, may require replacement of the whole windshield if in the camera field of view. Just the normal wear from normal everyday impact with small particles, hail and the action of the wiper blades results in microscopic scratches and cracks in the glass that diffract the impinging light. The glass itself also reacts chemically with water from the moisture content of the air, rain and snow slowly weakening and degrading the windshield optically as well.

It would be desirable to improve the durability of a windshield with respect to these defects that reduce the optical life of the laminate.

Brief Summary of the Invention

The present invention comprises a laminate having, as the exterior layer, a non-standard glass composition and in addition to or in place of a hard coating. The outer glass layer imparts a higher resistant to both abrasion and weathering than that achieved with standard uncoated soda-lime glass as used in typical automotive laminates.

Brief Description of the Several Views of the Drawings

Figure 1 shows the cross section of a laminate construction. Reference Numerals of Drawings

4 Plastic bonding layer

6 Obscuration/Black Frit/Black organic paint

101 Surface one

102 Surface two

103 Surface three

104 Surface four

201 Outer layer

202 Inner layer

Detailed Description of the Invention

Most of the worlds’ flat glass is produced by the float glass process, first commercialized in the l950s. In the float glass process, the raw ingredients are melted in a large refractory vessel and then the molten glass is extruded from the vessel onto a bath of molten tin where the glass floats. The thickness of the glass is controlled by the speed at which the molten glass is drawn from the vessel. As the glass cools and hardens, the glass ribbon transfers to rollers.

Most of the glass used for containers and windows is soda-lime glass. Soda-lime glass is made from sodium carbonate (soda), lime (calcium carbonate), dolomite, silicon dioxide (silica), aluminum oxide (alumina), and small quantities of substances added to alter the color and other properties.

The formulation of soda-lime glass is a compromise between cost and performance. Glass can be made that is more durable, chemical, weather and scratch resistant but at a higher cost.

There are other types of glass which have higher cost but which also have higher chemical, weather and scratch resistant which are primarily found in specialty applications including laboratory glassware, kitchen glassware, stove tops, process equipment, precision optics and others.

Borosilicate glass is a type of glass that contains boric oxide. It has a low coefficient of thermal expansion and a high resistance to corrosive chemical. It is commonly used to make light bulbs, laboratory glassware, and cooking utensils.

Aluminosilicate glass is made with aluminum oxide. It is even more resistant to chemicals than borosilicate glass and it can withstand higher temperatures. Chemically tempered Aluminosilicate glass is widely used for displays on smart phones and other electronic devices.

One of the drawbacks of glass is that it is a brittle material that fails under relatively low loading when placed in tension.

Metals and many other types of materials have an ultimate yield strength at which point the material will fail. However, with glass we can only specify a probability of breakage for a given value of stress. Looking at glass at the molecular level, we would expect the strength to be very high. In fact, what we find in practice is that glass has a very high compressive strength, as expected, but very low tensile strength.

For a given set of glass test specimens, with identical loading, the point of failure at first glance might appear to be a random variable. In fact, the yield point follows a Weibull distribution and the probability of breakage can be calculated as a function of, stress, duration, surface area, surface defects and the modulus of glass.

To the naked eye, float glass appears to be near perfect. Any defects that may be present as so small as to not be visible. But, in fact, at the microscopic level, the surface appears rough and can be seen to be dotted with flaws. When the glass is placed in tension, these surface defects tend to open and expand, eventually leading to failure. Therefore, laminated automotive glass almost always fails in tension. Even when not in tension, the surface defects react with the moisture in the environment and slowly “grow” over time. This is known as slow crack growth.

Laminates, in general, are articles comprised of multiple sheets of thin, relative to their length and width, material, with each thin sheet having two oppositely disposed major faces and typically of relatively uniform thickness, which are permanently bonded to one and other across at least one major face of each sheet.

Laminated safety glass is made by bonding two sheets of annealed glass one outer glass layer 201 and one inner glass layer 202 are bent together using a plastic bonding layer comprised of a thin sheet of transparent thermo plastic bonding layer 4 as shown in Figure 1.

Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range. This process relieves any 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 plastic layer helping to maintain the structural integrity of the glass. A vehicle with a broken windshield can still be operated. The plastic bonding layer 4 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 glass layers of the present invention may be annealed or strengthened. Two processes can be used to increase the strength of glass. They are thermal strengthening, in which the hot glass is rapidly cooled (quenched) and chemical tempering which achieves the same effect through an ion exchange chemical treatment.

Heat strengthened, full temper soda-lime float glass, with a compressive strength in the range of at least 70 MPa, can be used in all vehicle positions other than the windshield. Heat strengthened (tempered) glass has a layer of high compression on the outside surfaces of the glass, balanced by tension on the inside of the glass which is produced by the rapid cooling of the hot softened glass. When tempered glass breaks, the tension and compression are no longer in balance and the glass breaks into small beads with dull edges. Tempered glass is much stronger than annealed laminated glass. The thickness limits of the typical automotive heat strengthening process are in the 3.2mm to 3.6 mm range. This is due to the rapid heat transfer that is required. It is not possible to achieve the high surface compression needed with a thinner outer layer and/or inner layer using the typical blower type low pressure air quenching systems.

In the chemical tempering process, ions in and near the outside surface of the glass are exchanged with ions that are larger. This process places the surface one 101 and surface two 102 of the outer layer 201 and surfaces three 103 and surface four 104 of inner layer 202 in compression (Fig.l). Compressive strengths of up to 1, 000 MPa are possible. The typical methods involved submerging the glass in a tank of molten salt where the ion exchange takes place. The glass surface must not have any paint or coatings that will interfere with the ion exchange process.

The glass layers are formed using gravity bending, press bending, cold bending or any other conventional means known in the art. In the gravity bending process, the glass flat is supported near the edge of glass and then heated. The hot glass sags to the desired shape under the force of gravity. With press bending, the flat glass is heated and then bent on a full of partial surface mold. Air pressure and vacuum are often used to assist the bending process. Gravity and press bending methods for forming glass are well known in the art and will not be discussed in detail in the present disclosure.

Cold bending is a relatively new technology. As the name suggest, the glass is bent, while cold to its final shape, without the use of heat. On parts with minimal curvature a flat sheet of glass can be bent cold to the contour of the part. This is possible because as the thickness of glass decreases, the sheets become increasingly more flexible and can be bent without inducing stress levels high enough to significantly increase the long term probability of breakage. Thin sheets of annealed soda-lime glass, in thicknesses of about 1 mm, can be bent to large radii cylindrical shapes (greater than 6 m). When the glass is chemically, or heat strengthened the glass can endure much higher levels of stress and can be bent along both major axis. The process is primarily used to bend chemically tempered thin glass sheets (<=l mm) to shape.

Cylindrical shapes can be formed with a radius in one direction of less than 4 meters. Shapes with compound bend, that is curvature in the direction of both principle axis can be formed with a radius of curvature in each direction of as small as approximately 8 meters. Of course, much depends upon the surface area of the parts and the types and thicknesses of the substrates.

The cold bent glass will remain in tension and tend to distort the shape of the bent layer that it is bonded to. Therefore, the bent layer must be compensated to offset the tension. For more complex shapes with a high level of curvature, the flat glass may need to be partially thermally bent prior to cold bending.

The glass to be cold bent is placed with a bent to shape layer and with a bonding layer placed between the glass to be cold bent and the bent glass layer. The assembly is placed in what is known as a vacuum bag. The vacuum bag is an airtight set of plastic sheets, enclosing the assembly and bonded together it the edges, which allows for the air to be evacuated from the assembly and which also applies pressure on the assembly forcing the layers into contact. The assembly, in the evacuated vacuum bag, is then heated to seal the assembly. The assembly is next placed into an autoclave which heats the assembly and applies high pressure. This completes the cold bending process as the flat glass at this point has conformed to the shape of the bent layer and is permanently affixed. The cold bending process is very similar to a standard vacuum bag/autoclave process, well known in the art, except for having an unbent glass layer added to the stack of glass.

A number of coatings have been developed to reduce the susceptibility to impact damage.

A wide range of coatings, used to enhance the performance and properties of glass, are available and in common use. These include but are not limited to anti-reflective, hydrophobic, hydrophilic, self-healing, self-cleaning, anti-bacterial, anti-scratch, anti graffiti, anti-fingerprint and anti-glare.

Methods of application include Magnetron Sputtered Vacuum Deposition (MSVD) as well as others known in the art that are applied via pyrolytic, spray, controlled vapor deposition (CVD), dip, sol-gel and other methods.

Most coatings fall into one of two groups: hard coats and soft coats. Hard coats are durable and can be exposed to weather and touch. Soft coats are easily damaged by touch and exposure. Soft coats are generally protected by applying to one of the enclosed surfaces of an insulated glass unit or, in a laminate, to one of the major faces adjacent to the plastic bonding layer.

A common hard coat, sometimes applied over top of and to protect a soft coat, is silica. Silica can be applied by MSVD, sol-gel and other means. A silica overcoat can render the surface of glass harder than the original uncoated glass. Even harder transparent materials, such as sapphire and a form of diamond, can also be applied to the glass substrate of the present invention.

Description of Embodiments

1. A windshield comprising a 2.1 mm outer layer 201 of borosilicate glass and an inner layer 202 of 2.1 mm soda- lime solar green glass. The glass layers are press bent to shape independently. A single 0.76 mm solar absorbing plastic bonding layer 4 is used. A black frit 6 is applied to surface four 104 of glass.

2. A windshield comprising a 2.1 mm outer layer 201 of borosilicate glass and an inner layer 202 of 2.1 mm soda-lime solar green glass. A hard coat of silica is applied to surface one 101 of glass by a sol-gel dip coat process. The glass layers are press bent to shape. A single 0.76 mm solar absorbing plastic bonding layer 4 is used. A black frit 6 is applied to surface four 104 of glass.

3. A windshield comprising a 2.1 mm outer layer 201 of solar green soda- lime glass and an inner layer 202 of 2.1 mm solar green soda-lime glass. A hard coat of diamond like carbon is applied to surface one 101 of glass by a MSVD process. The glass layers are gravity bent to shape. A single 0.76 mm plastic bonding layer 4 is used. A black frit 6 is applied to surface four 104 surface of glass.

4. A windshield comprising a 2.1 mm outer layer 201 of borosilicate glass and an inner layer 202 of 0.7 chemically tempered aluminosilicate glass. A hard coat of silica is applied to surface one 101 of glass by a sol-gel dip coat process. The glass layers are press bent to shape. A single 0.76 mm solar absorbing plastic bonding layer 4 is used. A black frit 6 is applied to surface four 104 of glass.

5. A windshield comprising a 2.1 mm outer layer 201 of borosilicate glass and an inner layer 202 of 0.7 chemically tempered aluminosilicate glass. The outer glass layer 201 is press bent to shape. The inner glass layer 202 is cold bent. A single 0.76 mm solar absorbing plastic bonding layer 4 is used. A black organic paint 6 is applied to surface four 104 of glass.

6. A windshield comprising a 2.1 mm outer layer 201 of solar green soda- lime glass and an inner layer 202 of 2.1 mm solar green soda-lime glass. A hard coat of sapphire is applied to surface one 101 of glass by the MSVD process. The glass layers are gravity bent to shape. A single 0.76 mm plastic bonding layer 4 is used. A black frit 6 is applied to surface four 104 of glass. It must be understood that this invention is not limited to the embodiments described and illustrated above. A person skilled in the art will understand that numerous variations and/or modifications can be carried out that do not depart from the spirit of the invention, which is only defined by the following claims.