HEATED LAMINATE WITH IMPROVED AESTHETIC

Abstract

Heated windshields, which utilize a transparent conductive coating, are increasing in popularity due to the rapid deice defog action and higher efficiency of such products. With the limited waste heat available in electric and hybrid electric vehicles, cabin heating and defrosting must be done with electric power. One of the problems in designing a heated windshield is hiding the busbars from view for the exterior of the vehicle. This is especially a problem when the coating is on the inner surface of the exterior glass layer which is the preferred embodiment for both solar control and defrosting. The normal black obscuration cannot be applied over the coating and it is very expensive to first paint and then coat the glass. The invention makes use of a thin conductive layer placed between the bus bars and the coating which serves to hide the bus bars from view providing a glazing with an improved aesthetic.

Claims

1. A laminated glass comprising: at least two glass layers, an outer glass layer and an inner glass layer; at least one plastic bonding layer; at least two bus bars; at least two thin sheets of a conductive material; and a transparent conductive layer; wherein said at least two thin sheets of a conductive material are positioned between the conductive layer and said at least two bus bars; and wherein said at least two glass layers, said at least two bus bars, said at least two thin sheets of a conductive material and the transparent conductive layer are bonded together to form a laminate by means of said at least one plastic bonding layer.

2. The laminate of claim 1 wherein the conductive material is a form of carbon.

3. The laminate of claim 1 wherein the conductive material is graphite.

4. The laminate of claim 1 wherein at least one of the at least two busbars is modified with discontinuities that break the flow of current from the bus bar to the conductive layer, such that power is not feed along the entire length of said bus bar.

5. The laminate of claim 1 wherein the conductive layer is a conductive coated film.

6. The laminate of claim 1 wherein the inner glass layer is chemically tempered.

7. The laminate of claim 1 wherein the inner glass layer is less than 1 mm thick.

8. The laminate of claim 1 wherein the inner glass layer is cold bent.

9. The laminate of claim 1 wherein the transparent conductive layer is a transparent conductive coating applied to one of the glass layers.

10. The laminate of claim 1 wherein the transparent conductive layer is a plastic film with a transparent conductive coating.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0030] These features and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, wherein:

[0031] FIG. 1A shows a cross section of a typical automotive laminate.

[0032] FIG. 1B shows a cross section of a typical automotive laminate having a performance film.

[0033] FIG. 2 shows a hated laminate having a conductive coating with graphite between busbar and coating.

[0034] FIG. 3 shows the top view of heated laminate with graphite between bus bar and number two surface conductive transparent coating.

[0035] FIG. 4 shows an exploded view of heated laminate with graphite between bus bar and number two surface conductive transparent coating.

[0036] FIG. 5 shows an exploded view of heated laminate with conductive material between bus bar and number two surface conductive transparent coating wherein busbars and conductive material are notched.

[0037] FIG. 6A shows a conductive coating with notched busbar and conductive material.

[0038] FIG. 6B shows a conductive coating with notches and busbar and conductive material.

REFERENCE NUMERALS OF DRAWINGS

[0039] 2 Glass

[0040] 4 Bonding/Adhesive Layer (interlayer)

[0041] 6 Obscuration/Black Frit

[0042] 20 Bus bar

[0043] 22 Conductive material (graphite)

[0044] 24 Conductive coating

[0045] 28 Coating deletion

[0046] 32 Power connector

[0047] 44 Performance film

[0048] 46 Tabs

[0049] 48 Discontinuities

[0050] 101 Surface one

[0051] 102 Surface two

[0052] 103 Surface three

[0053] 104 Surface four

[0054] 201 Outer layer

[0055] 202 Inner layer

DETAILED DESCRIPTION OF THE INVENTION

[0056] The following terminology is used to describe the laminated glazing of the invention.

[0057] A typical automotive laminate cross section is illustrated in FIGS. 1A and 1B. The laminate is comprised of two layers of glass, the exterior or outer 201 and interior or inner 202 that are permanently bonded together by a plastic layer 4 (interlayer). The glass surface that is on the exterior of the vehicle is referred to as surface one 101 or the number one surface. The opposite face of the outer glass layer 201 is surface two 102 or the number two surface. The glass surface that is on the interior of the vehicle is referred to as surface four 104 or the number four surface. The opposite face of the inner layer of glass 202 is surface three 103 or the number three surface. Surfaces two 102 and three 103 are bonded together by the plastic layer 4. An obscuration 6 may be also applied to the glass. Obscurations are commonly comprised of black enamel frit printed on either the number two 102 or number four surface 104 or on both. The laminate may also comprise a coating 24 on one or more of the surfaces. The laminate may also comprise a performance film 44 laminated between at least two plastic layers 4.

[0058] This black frit print obscuration 6 on many automotive glazings serves both a functional and an aesthetic role. The substantially opaque black print on the glass serves to protect the poly-urethane adhesive, used to bond the glass to the vehicle, from ultra-violet light and the degradation that it can cause. It also serves to hide the adhesive from view from the exterior of the vehicle. The black obscuration must be durable, lasting the life of the vehicle under all exposure and weather conditions. Part of the aesthetic requirement is that the black have a dark glossy appearance and a consistent appearance from part to part and over the time. A part produced today must match up with one that was produced and in service 20 years ago. The parts must also match up with the other parts in the vehicle which may not have been fabricated by the same manufacturer or with the same formulation of frit. Standard automotive black enamel inks (frits) have been developed that can meet these requirements.

[0059] Black enamel frit is comprised of pigments, carriers, binders and finely ground glass. Other materials are also sometimes added to enhance certain properties: the firing temperate, anti-stick, chemical resistance, etc. The black frit is applied to the glass using a silk screen or ink jet printing process prior to the heating and bending of the glass. As the flat glass is heated during the bending process, the powdered glass in the frit softens and melts, fusing to the surface of the glass. The black print becomes a permanent part of the glass. The frit is said to be fired when this takes place. This is a vitrification process which is very similar to the process used to apply enamel finishes on bathroom fixtures, pottery, china and appliances.

[0060] The types of glass 2 that may be used include but are not limited to: the common soda-lime variety typical of automotive glazing as well as aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and the various other inorganic solid amorphous compositions which undergo a glass transition and are classified as glass included those that are not transparent. The glass layers may be comprised of heat absorbing glass compositions as well as infrared reflecting and other types of coatings.

[0061] 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.

[0062] 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.

[0063] Aluminosilicate glass is make 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.

[0064] 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.

[0065] Laminated safety glass is made by bonding two sheets 201, 202 of annealed glass 2 together using a plastic bonding layer comprised of a thin sheet of transparent thermos plastic 4 (interlayer) as shown in FIG. 1.

[0066] A wide variety of films are available that can be incorporated into a laminate. The uses for these films include but are not limited to: solar control, variable light transmission, increased stiffness, increased structural integrity, improved penetration resistance, improved occupant retention, providing a barrier, tint, providing a sunshade, color correction, and as a substrate for functional and aesthetic graphics. The term film shall include these as well as other products that may be developed or which are currently available which enhance the performance, function, aesthetics or cost of a laminated glazing. Most films do not have adhesive properties. To incorporate into a laminate, sheets of plastic interlayer are needed on each side of the film to bond the film to the other layers of the laminate. Any film which incorporates a conductive layer has the potential to also be used to add a resistive heated circuit to the laminate in addition to its other function.

[0067] 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 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.

[0068] The glass layers may be annealed or strengthened. There are two processes that 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.

[0069] 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 3.2 mm 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 thinner glass using the typical blower type low pressure air quenching systems.

[0070] In the chemical tempering process, ions in and near the outside surface of the glass are exchanged with ions that are larger. This places the outer layer of glass in compression. 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.

[0071] 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.

[0072] 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 (<=1 mm) to shape.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The plastic bonding layer 4 (interlayer) has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear thermoset plastic.

[0077] For automotive use, the most commonly used bonding layer 4 (interlayer) is polyvinyl butyral (PVB). PVB has excellent adhesion to glass and is optically clear once laminated. It is produced by the reaction between polyvinyl alcohol and n-butyraldehyde. PVB is clear and has high adhesion to glass. However, PVB by itself, it is too brittle. Plasticizers must be added to make the material flexible and to give it the ability to dissipate energy over a wide range over the temperature range required for an automobile. Only a small number of plasticizers are used. They are typically linear dicarboxylic esters. Two in common use are di-n-hexyl adipate and tetra-ethylene glycol di-n-heptanoate. A typical automotive PVB interlayer is comprised of 30-40% plasticizer by weight.

[0078] In addition to polyvinyl butyl, ionoplast polymers, ethylene vinyl acetate (EVA), cast in place (CIP) liquid resin and thermoplastic polyurethane (TPU) can also be used. Automotive interlayers are made by an extrusion process with has a thickness tolerance and process variation. As a smooth surface tends to stick to the glass, making it difficult to position on the glass and to trap air, to facilitate the handling of the plastic sheet and the removal or air (deairing) from the laminate, the surface of the plastic is normally embossed contributing additional variation to the sheet. Standard thicknesses for automotive PVB interlayer at 0.38 mm and 0.76 mm (15 and 30 mil).

[0079] A laminate must have at least one interlayer. More than one is required if the laminate also comprises a film. Multiple interlayers are also sometimes used to alter the light transmittance of a laminate and to correct for optical aberrations.

[0080] The typical conductive coated heated windshield utilizes busbars that are in contact with the coating substantially across their entire length. One exception is where there is a coating deletion 28 or oblation to accommodate a rain sensor, camera or other device which will not operate in the presence of the coating. In this special case, the bus bar 20 will sometimes extend below the deletion area.

[0081] The bus bar is typically comprised of thin (5075 m) tinned copper cut to shape. The bus bar may utilize a conductive adhesive to adhere to the coating or may just be placed in direct contact with the coating with no adhesive. A common approach is to apply a non-conductive contact adhesive to the side of the bus bar that does not come into contact with the coating and then to apply the bus bars to the interlayer prior to lamination. This can be done in advance and offline, spreading up the final assembly of the laminate.

[0082] For very thin conductive materials we typical characterize the resistance in terms of the sheet resistance. The sheet resistance is the resistance that a rectangle, with perfect bus bar on two opposite sides, would have. Sheet resistance is specified in ohms per square. This is a dimensionally unitless quantity as it is not dependent upon the size of the rectangle. The bus bar to bus bar resistance remains the same regardless of the size of the rectangle.

[0083] The copper bus bars, due to the difference between the coefficient of thermal expansion of the copper and the glass, have a tendency to not lay flat on the glass. Over time, they also have a tendency to discolor as the metal reacts with the moisture in the interlayer. For these reasons, they do not present an acceptable aesthetic and must be hidden.

[0084] Rather than applying the bus bars directly to the coating, a thin aesthetically acceptable conductive material is first placed in contact with the coating. The bus bar is then placed in contact with the thin conductive material. The conductive material must be sufficiently larger than the bus bar so as to obscure if from view from the exterior of the vehicle. The thin conductive material may be substantially larger and even mimic the black band.

[0085] The heated laminated could have a conductive coating deposited directly onto a glass substrate or a plastic substrate in the case of a film. In the case of a film, an additional plastic interlayer layer is required for lamination.

[0086] In the other hand, the power consumption and distribution must often be compromised as many of the design parameters either set or can only be varied over a narrow range.

[0087] Being the thin aesthetic conductive material first placed in contact with the coating, and the bus bar then placed in contact with the thin aesthetic conductive material, the shape of both together and/or the conductive coating also could be altered such that the electrical connection between the bus bar through the conductive material and the coating is not continuous along the entire length of at least one of the bus bars. This in effect removes portions of the coating from the circuit, increasing the bus to bus overall resistance and lowering the total power. This also allows for tailoring of the power density.

[0088] The bus to bus resistance is a function of the conductive coating sheet resistance and the bus bar spacing. For a typical windshield, with bus bars running across the top and bottom, it is possible to get a power density in the 15-20 watt/dm2 range with a double silver coating and a 42-volt power supply. This may be too high. On an annealed glass part, we need to take care that the glass is not thermally shocked which can occur at this power level. The other constraint is available power. As the capacity of the power converter increases so does the weight and cost. The battery and alternator must also be able to handle the power required. Due to the large area of many windshields and the constraint on the design as discussed, it is possible to have a windshield that will draw more power than required or available. This is especially true if the design is also intended to maximize solar performance by using a highly conductive silver-based coating.

[0089] To correct this situation, the conductive material and the bus bar together to conductive coating interface could be modified such that power is not feed along the entire length of at least one of the bus bars. Discontinuities could be provided to break the flow of current from the bus bars to the coating. The actual number of and dimensions of the discontinuities could be determined through computer or physical modeling. In general, the less the area in contact, the higher the resistance. But, the relative locations of the discontinuities along each of the bus bars relative to each other are also important. The discontinuities may be arranged but are not limited to: overlapping, staggered or aligned or in any combination. The spacing may be uniform or non-uniform. The discontinuities may be symmetrical or nonsymmetrical.

[0090] The flow of current is influenced by the length and spacing of the discontinuities. If the spacing is too short, the effect on the resistance will be negligible. The length of each discontinuity and the spacing between should be at least 2.5% of the average distance between the opposite bus bars. If the spacing is to great, then we can have the opposite effect with areas of the windshield left without power. The length of each discontinuity and the spacing between should be no more than 20% of the average distance between the opposite bus bars. These percentages will vary with the relative location of the discontinuities on opposite bus bars to each other and is intended as a general rule of thumb to guide the initial design. It may be required to use a value that it less than or greater than the minimum and maximum.

[0091] A number of methods may be used to produce the discontinuities of the invention.

Description of Embodiments

[0092] 1. The laminate of embodiment one is illustrated in the exploded view of FIG. 4 and in the top view of FIG. 3. The outer glass layer 201 is comprised of 2.1 mm thick clear soda-lime glass. A conductive layer is formed by a silver based MSVD coating 24 applied to the flat outer glass layer 201 prior to cutting and bending. An abrasive wheel process is used to delete the conductive coating 24 starting at the edge of glass and extending to 6 mm inboard of the edge of glass. The outer 201 glass sheet is then cut to size. The inner glass layer 202 is comprised of a clear 2.1 mm thick soda-lime glass. A black frit obscuration 6 is printed on the number four surface. The two glass layers are heated and bent to shape. A sheet of 50 m thick graphite is cut to the size of the bus bars plus an additional 6 mm. The cut graphite 22 is then placed in contact with the conductive coating 24. No adhesive is used. A set of bus bars 20 comprised of 0.075 mm thick tinned copper are die cut to shape and applied to the graphite 22. Again, no adhesive is used. The coated outer glass layer 201, the uncoated inner glass layer 202, a sheet of 0.76 mm PVB plastic interlayer 4, the graphite 22 and the bus bars 20 are assembled. A standard autoclave process is used to laminate the layers. [0093] 2. The laminate of embodiment two is illustrated in the exploded view of FIG. 4 and in the top view of FIG. 3. The outer glass layer 201 is comprised of 2.1 mm thick clear soda-lime glass. A conductive layer 24 is formed by a silver based MSVD coating applied to the flat outer glass layer 201 prior to cutting and bending. An abrasive wheel process is used to delete the conductive coating 24 starting at the edge of glass and extending to 6 mm inboard of the edge of glass. The outer 201 glass sheet is then cut to size. The inner glass layer 202 is comprised of a clear 0.7 mm thick chemically tempered aluminosilicate glass. A black frit obscuration 6 is printed on the number four surface. The two glass layers are heated and bent to shape. A sheet of 50 m thick graphite 22 is cut to the size of the bus bars 20 plus an additional 6 mm. The cut graphite 22 is then placed in contact with the conductive coating 24. No adhesive is used. A set of bus bars 20 comprised of 0.075 mm thick tinned copper are die cut to shape and applied to the graphite 22. Again, no adhesive is used. The coated outer glass layer 21, the uncoated inner glass layer 202, a sheet of 0.76 mm PVB plastic interlayer 4, the graphite 22 and the bus bars 20 are assembled. A standard autoclave process is used to laminate the layers. [0094] 3. The laminate of embodiment three is illustrated in the exploded view of FIG. 4 and in the top view of FIG. 3. The outer glass layer 201 is comprised of 2.1 mm thick clear soda-lime glass. A conductive layer 24 is formed by a silver based MSVD coating applied to the flat outer glass layer 201 prior to cutting and bending. An abrasive wheel process is used to delete the conductive coating 24 starting at the edge of glass and extending to 6 mm inboard of the edge of glass. The outer glass layer 201 is then cut to size. The inner glass layer 202 is comprised of a flat clear 0.7 mm thick chemically tempered aluminosilicate glass. A black obscuration 6 is applied after lamination on the inner glass layer 202 using an organic ink. The outer glass layer 201 is heated and bent to shape. The inner glass layer 202 is heated and partially bent to shape. A sheet of 50 m thick graphite 22 is cut to the size of the bus bars 20 plus an additional 6 mm. The cut graphite 22 is then placed in contact with the conductive coating 24. No adhesive is used. A set of bus bars 20 comprised of 0.075 mm thick tinned copper are die cut to shape and applied to the graphite 22. Again, no adhesive is used. The coated outer glass layer 201, the uncoated inner glass layer 202, a sheet of 0.76 mm PVB plastic interlayer 4, the graphite 22 and the bus bars 20 are assembled. A standard autoclave process is used to laminate the layers and to cold bend the inner layer 202.

[0095] In some of the embodiments, the conductive material and the bus bars 20 are notched as shown in FIG. 5. The dark conductive material 22 and bus bar 20 may be formed in such a manner that the coating 24 is not in contact with them along its entire length. The notched areas do not make contact with the coating 24. The coating has been deleted from the edge of the glass to just past the inner edge of the notches (discontinuities) 48. The tabs 46 bridge the gap and the conductive material make contact with the coating 20 as shown in FIG. 6A.

[0096] Another embodiment as shown in FIG. 6B uses a simpler bus bar 20 and a conductive material that are not notched. The discontinuities 48 are formed through deletion of the coating 24, in effect, notching the coating 24 along the bus bars and leaving tabs 46 made of coating. The notches can be formed by a masking process, abrasive deletion or LASER oblation of the coating.

[0097] In another embodiment (not shown) the coating 24 and bus bars 20 are not notched. The coating 24 is deleted such that is does overlap or contact the bus bars. The conductive material is notched and is then used to bridge over the gap between the bus bar 20 and the coating 24 and also used to hide the busbar.

[0098] In preferred embodiments, thin dark sheets of graphite are used as conductive materials. Graphite has the added advantages of being a good conductor of electricity and an excellent conductor of heat, both of which are important. The graphite also serves to protect the coating from damage from the hard metal bus bars which can result in arcing, hot spots and failure.