Glass laminate with inlay obscuration having superior strength and optical quality

Abstract

The use of camera-based safety systems is growing at a rapid rate in modern automobiles. At the same time, windshields, where many of the cameras are mounted, are becoming larger and more complex in shape. As the industry moves towards vehicles with full autonomous capability, the number of cameras required and the resolution of the cameras are both increasing. However, the optical quality of the windshield is less than optimal. One of the problems is caused by the typical black enamel frit that is printed on the glass, prior to heating and bending, to hide or obscure the camera hardware. The abrupt thermal gradients during bending, caused by the heat absorbing black frit, result in a high level of distortion in the camera field of view. The object of this invention is to provide laminated automotive glazing having an obscuration area produced by creating an obscuration after heating and bending the glass by removing a portion of the plastic interlayer glass in or near the camera field of view (camera obscuration) or/and in the edges of the windshield (black band) and replacing it with an inlay made of a substantially opaque plastic or other suitable material in or near the camera field of view (camera obscuration) or/and in the edges of the windshield (black band) rather than printing and firing an enamel frit on the glass. This results in a laminate having superior optical quality, higher strength and a lower probability of breakage as compared to a laminate with a black enamel frit obscuration.

Claims

1. A laminate comprising: an outer glass layer having two oppositely disposed major faces; an inner glass layer having two oppositely disposed major faces; a plastic bonding interlayer disposed between and connecting opposite major faces of outer and inner glass layers, wherein said plastic bonding interlayer comprises at least one opening; and at least one obscuration disposed between the outer glass layer and the inner glass layer, wherein each obscuration of said at least one obscuration is an opaque inlay made of an opaque material inserted into an opening of said at least one opening.

2. The laminate of claim 1 wherein said at least one obscuration is at least two obscurations, a camera obscuration and a black band obscuration.

3. The laminate according to claim 1, wherein the inlay is an opaque plastic.

4. The laminate according to claim 3, wherein the opaque plastic is an opaque black plastic.

5. The laminate according to claim 4, wherein the plastic bonding layer and the opaque inlay are composed of the same type of plastic.

6. The laminate according to claim 5, wherein the plastic is a PVB interlayer.

7. The laminate according claim 1, wherein an opaque inlay of said at least one obscuration comprises at least one cutout in which a transparent plastic is inserted.

8. The laminate according to claim 7, wherein the opaque inlay comprising at least one cutout is a camera obscuration.

9. The laminate according to claim 7, wherein the transparent plastic is a PVB.

10. The laminate according to claim 1, further comprising a ceramic frit black band.

11. The laminate according to claim 10, wherein said at least one obscuration is a camera obscuration, and wherein the camera obscuration is separated from and spaced from the ceramic frit black band.

12. The laminate according to claim 1, wherein the laminate is a windshield.

13. The laminae according to claim 1, wherein the plastic bonding interlayer is selected from the group consisting of polyvinyl butyl (PVB), ethylene vinyl acetate (EVA), and thermoplastic polyurethane (TPU).

14. The laminate of claim 1 further comprising one or more additional plastic bonding interlayers.

15. The laminate of claim 14 wherein at least one plastic bonding layer is a wedge interlayer.

16. The laminate of claim 14 further comprising a film disposed between two plastic bonding interlayers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows a camera obscuration with “burn” line buffer.

(2) FIG. 1B shows a camera obscuration without burn line buffer.

(3) FIG. 2 shows an isometric view of panoramic windshield with camera obscuration and black band.

(4) FIG. 3A shows a cross section of laminate with single plastic layer and inlay camera obscuration.

(5) FIG. 3B shows a cross section of laminate with two plastic layers with film layer with inlay camera obscuration in outboard plastic layer.

(6) FIG. 4 shows an isometric view of windshield with gap between the camera obscuration and the black band.

(7) FIG. 5A shows a front view of windshield with gap between the camera obscuration and the black band.

(8) FIG. 5B shows a camera obscuration detail showing black and clear portions.

(9) FIG. 6A shows a double image without correction.

(10) FIG. 6B shows a double image with wedge/shaped interlayer correction.

(11) FIG. 7A shows a laminate with ordinary plastic interlayer.

(12) FIG. 7B shows a laminate with one ordinary plastic interlayer and one wedge/shaped plastic interlayer.

(13) FIG. 7C shows a laminate with two wedge/shaped plastic interlayers.

(14) FIG. 8 shows an isometric view of windshield with camera obscuration that overlaps the black band

REFERENCE NUMERALS

(15) 3 Wedge Interlayer 4 Plastic Bonding Interlayer 8 Obscuration 15 Buffer 16 Field of view 17 Film 32 Black Band 34 Camera Obscuration 40 Double image Angle 41 Observation point 42 Incident ray 43 Primary image 44 Secondary image 45 Wedge angle 46 Incident angle 52 Angle of deviation 56 Angle of inclination 101 First Surface of Glass 102 Second Surface of Glass 103 Third Surface of Glass 104 Fourth Surface of Glass 201 Outer layer 202 Inner layer

DETAILED DESCRIPTION OF THE INVENTION

(16) The invention eliminates the drawbacks associated with the fired black frit obscurations of the prior art by using the alternate method of the invention to provide the obscuration for the camera field of view after the glass has been heated and bent to shape. Removing the black frit from the glass during the bending process allows for a more uniform heat distribution across the part during bending which reduces residual stresses and the associated surface mismatch, warping and distortion caused by the thermal gradients.

(17) Laminated safety glass is made by bonding two sheets of annealed glass together using a thin sheet of a transparent thermo plastic bonding interlayer. 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 interlayer also helps to prevent penetration by objects striking the laminate from the exterior and in the event of a crash occupant retention is improved.

(18) In the drawings and discussion, the following terminology is used to describe the configuration of a laminated glazing. Typical automotive laminated glazing cross sections are illustrated in FIGS. 3A and 3B. A 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 bonding interlayer 4. The glass surface that is on the exterior of the vehicle is referred to as the first surface of the glass 101. The opposite face of the outer layer is the second surface of the glass 102. The glass surface that is on the interior of the vehicle is referred to as fourth surface of the glass 104. The opposite face of the inner layer is the third surface of the glass 103. Second surface of the glass 102 and third surface of the glass 103 are bonded together by the plastic bonding interlayer 4. FIGS. 3A and 3B also contain an inlay camera obscuration 34, 8. Obscurations are commonly comprised of black enamel frit printed on either the second surface of the glass 102 or fourth surface of the glass 104 or on both. The invention proposes a dark inlay as an obscuration. The laminate may have a coating (not shown) on one or more of the surfaces. The laminate may also comprise a film laminated 17 between at least two plastic bonding interlayer 4.

(19) The plastic bonding interlayer has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear plastic when bonding one glass layer to another glass layer. For automotive use, the most commonly used plastic bonding layer is polyvinyl butyl (PVB). 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. Interlayers are available with enhanced capabilities beyond bonding the glass layers together. The invention may include interlayers designed to dampen sound. Such interlayers are comprised whole or in part of a layer of plastic that is softer and more flexible than that normally used. The interlayer may also be of a type which has solar attenuating properties.

(20) The types of glass 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.

(21) 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. In the chemical tempering process, ions in and near the outside surface of the glass are exchanged with ions that are larger.

(22) This place the outer layer of glass in compression. Compressive strengths of up to 1,000 Mpa are possible.

(23) The glass layers are formed using gravity bending, press bending, cold bending or any other conventional means known in the art. Gravity and press bending methods for forming glass are well known in the art and will not be discussed in the present disclosure.

(24) The glass layers may be comprised of heat absorbing glass compositions as well as infrared reflecting and other types of coatings.

(25) Tempered monolithic windows can only make use of heat absorbing compositions to control solar load. One of the big advantages of a laminated window over a tempered is that a laminate can make use of infrared reflecting coatings and infrared reflecting films in addition to heat absorbing compositions.

(26) Infrared reflecting coatings include but are not limited to the various metal/dielectric layered coatings applied though magnetron sputtered vacuum deposition (MSVD) as well as others known in the art that are applied via pyrolytic, spray, controlled vapor deposition (CVD), dip and other methods.

(27) Infrared reflecting films include both metallic coated substrates as well as organic based optical films which reflect in the infrared.

(28) A heat absorbing window can be very effective, but the glass gets hot and transfers energy to the passenger compartment through convective transfer and radiation whereas the infrared reflecting coatings and films reflect the heat back to the atmosphere allowing the glass so stay cooler.

(29) In addition to the metallic and non-metallic films that reflect in the infra-red, a wide variety of other films are available for use in laminates to add capability and enhance other properties. To control light transmission there are available: electro chromic, photochromic, thermocromic and field effect films which are designed to be incorporated into laminates. Of particular interest are suspended particle devices (SPD) and polymer dispensed liquid crystal (PDLC) films which can quickly change state under the control of an electrical field. These films will be collectively referred to as performance films.

(30) If a combination of frit and the method of the invention are used for the obscurations 8, the black band 32 and the Camera obscuration 34, any difference in the appearance between the two may be noticeable. In that case, separating the Camera obscuration 34 from the black band 32, as shown in FIGS. 4 and 5 will improve the aesthetic.

(31) In the obscuration areas where the invention is applied, all of the detrimental effects of the black enamel frit on the glass are eliminated resulting in superior optical quality, lower stress, and a lower probability of breakage.

(32) In addition to the benefits to the finished laminate, the elimination of the non-uniform heating and high thermal gradient present in the black frit areas increases yields through the bending process and also, due to the higher strength and lower surface mismatch, increases yields through the lamination process.

(33) Distortion in windshields is measured in terms of refractive power. Refractive power is the change in the angular deviation along over distance. At a high enough level, it can result in noticeable optical distortion. The refractive power is expressed in diopters.

(34) $\begin{array}{cc}{D}_{\mathrm{.Math.}}=\frac{d{\alpha }_{\mathrm{.Math.}}}{\mathrm{dx}}\frac{1}{\cos \mathrm{.Math.}}& \left(1\right)\end{array}$

(35) Where:

(36) ε: angle formed between the incident ray of light and a line perpendicular to the surface normal of the glazing

(37) α.sub.ε: angular deviation

(38) D.sub.ε: refractive power

(39) Most large windshield production lines utilize online automated inspection system which scan the glass and produce a contour map showing the optical distortion in diopters.

(40) Laminates produced by this invention have significantly lower distortion in the areas near the obscurations as compared to the same and similar laminates produced with screen print black frit.

(41) Double image, another problem of the prior art, is illustrated in FIGS. 6A and 6B.

(42) An incident ray 42 of light enters the surface of the glass at an incident angle 46 and passes through the glazing to the observation point 41. The light bends (refracts) as it passes through the glazing The angle by which the light bends is known as the angle of deviation 52. This refraction of the light causes a shifting of the primary image 43 of the object observed.

(43) Some of the light from the incident ray 42 entering the glass is reflected back from the inside surface (fourth surface of the glass 104) and exits the glazing. A portion of the reflected light is again reflected back from outside surface (the first surface of the glass 101) resulting in a double image. The double image angle η 40 is the angle between the primary image 43 and secondary image 44 and the observation point 41. If the primary and secondary images are coincident, then the separation angle is zero. Regulatory requirements limit the separation angle to 15 minutes of arc for vision zone A (as defined by United Nations Regulation 42, revision 3) and 25 minutes of arc for vision zone B. However, it is well known that the maximum amount of double imaging imperceptible for the human eye is 7 minutes of arc.

(44) The double image angle, η 40, is calculated as shown in equation 2. It increases with decreasing the angle of inclination 56, increasing curvature of the fourth surface of the glass 104 and with increasing size of the glazing. The double image angle, η 40, can be reduced by altering the angle between the plies of glass as shown in FIGS. 7B y 7C. Normally, the glass surfaces are substantially parallel to each other. By creating a wedge angle 45 between the surfaces, the primary and secondary images can be shifted towards convergence.

(45) $\begin{array}{cc}\eta =\frac{2t\sin \left(\mathrm{.Math.}\right)}{R\sqrt{n^2-{\sin \left(\mathrm{.Math.}\right)}^2}}& \left(2\right)\end{array}$

(46) where:

(47) η: double image angle

(48) t: thickness of the glazing

(49) n: refractive index

(50) R: radius of curvature

(51) The angle between the plies of glass is adjusted through the use of an interlayer that has a non-uniform thickness, typically tapering from a thickness greater than the standard 0.76 mm at or near the top of the glazing a lesser thickness at the bottom. Such interlayers are produced through extrusion of the plastic. Such interlayers are known as “wedge” interlayers. They can also be formed, to a lesser extent by shaping (stretching) of the interlayer. Shaping is typically done to create a curved sunshade. Table 1 shows the wedge angle and reduction in thickness for a standard 0.76 mm thick interlayer over 1 meter as a function of sunshade radius.

(52) Note that wedge interlayer can be shaped to increase the wedge angle. Any combination of wedge and shaped interlayer can be used to obtain the desired results.

(53) FIG. 7A shows a laminate with two standard interlayers (plastic bonding interlayer 4), FIG. 7B shows a laminate with one wedge interlayer 3 with a film between them and FIG. 7C shows a laminate with two wedge interlayers 3 a film between them. Wedge interlayer 3 can be used to further reduce double vision.

(54) TABLE-US-00001 TABLE 1 Sunshade Radius vs. Wedge Angle Sunshade Interlayer Wedge Radius Thickness Angle m mm mrad 2.0000 0.5067 0.253 2.5000 0.5429 0.1017 3.0000 0.5700 0.190 3.5000 0.5911 0.169 4.0000 0.6080 0.152 4.5000 0.61018 0.138 5.0000 0.6333 0.127 5.5000 0.6431 0.117 6.0000 0.6514 0.109 6.5000 0.6587 0.101 7.0000 0.6650 0.095 7.5000 0.6706 0.089 8.0000 0.6756 0.084 8.5000 0.6800 0.080 9.0000 0.6840 0.076 9.5000 0.6876 0.072 10.0000 0.6909 0.069

(55) Experimental results have demonstrated the remarkable and unexpected magnitude of improvement of the invention. Fracture strength is more than doubled, MTF is drastically improved (see Graph 1), distortion is reduced by a factor of six and double image if reduced from 15″ to 3″. One should also note that all four of these parameters are critical to the operation of a safety camera.

(56) TABLE-US-00002 TABLE 2 Laminate with Laminate with Obscuration Black Frit Printed on Film Fracture Strength 60 Mpa 115 Mpa (ring-on-ring) Distortion (Camera 150 milli diopters 25 milli diopters window-5 mm from the black edge) Double image (Camera 15″ (arc minute) 3″ (arc minute) window-5 mm from the black edge)

(57) As camera system for cars improve and cars now have advanced driving assisted systems the vehicles windshield becomes an important component of the complex lens system that makes up the vehicle vision system. For our interest here, our windshield serves as a lens in front of the camera, comprising one component of a complex lens system. The best way to evaluate this system is by measuring the MTF.

(58) Modulation Transfer Function or “MTF” is the most widely used scientific method of describing lens performance. The modulation transfer function is, a measure of the transfer of modulation (or contrast) from the subject to the image. In other words, it measures how faithfully a lens reproduces (or transfers) detail from the object to the image produced by a lens. When we graph MTF we chart against contrast dropping from 100 to 0 and Spatial frequency (Nyquist frequency). Spatial frequency is the ability to resolve over distance and as contrast drops this ability gets weaker. Plotting this in X&Y gives us the total systems contrast and its ability to faithfully reproduce into the distance. This is especially important in semi-autonomous or autonomous driving vehicles as the focus will be the horizon and all images in the focal plane will need to be detectable both in shape and in size.

(59) Obscurations produced by the method of the invention have resulted in a remarkable improvement in system MTF as compared to the same production model with a normal frit obscuration.

Embodiment 1

(60) The windshield of FIG. 8 comprising a ceramic frit black band 32 and a camera obscuration 34 produced by means of on opaque black plastic PVB inlay, cut to size and inserted into a cutout in the plastic PVB interlayer. The inlay further comprising cutout within allowing for insertion of transparent PVB in the field of view for each of the two cameras. The inlay is assembled after bending and cooling of the glass during the lamination process at the point where the interlayer is normally inserted in to the assembly. No adhesion promoters are needed.

Embodiment 2

(61) The windshield of FIG. 8 comprising two wedge/shaped plastic interlayers sandwiching between them an infra-red heat reflecting PET film. A ceramic frit black band 32 is produced through ordinary means and an opaque black plastic PVB inlay, is cut to size and inserted into a cutout in the PVB interlayer. The inlay further comprises a cutout within allowing for insertion of transparent PVB in the field of view for each of the two cameras. The inlay is assembled after bending and cooling of the glass during the lamination process at the point where the interlayer is normally inserted in to the assembly. No adhesion promoters are needed.

(62) 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.