Obscuration having superior strength and optical quality for an automotive laminate

Abstract

The object of this invention is to provide a laminated automotive glazing having an obscuration area produced by printing the obscuration on a film laminated between at least two layers of plastic interlayers rather than printing and firing an enamel frit onto 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. An automotive laminated windshield, wherein at least one portion of the windshield serves as a window for at least one camera, said windshield comprises: at least two glass layers; at least one film layer positioned between the glass layers; at least two plastic interlayers to attach the glass layers to said at least one film layer; and at least one equipment obscuration for said at least one camera window printed onto said at least one film layer, such that at least one machine vision parameter selected from the group consisting of fracture strength, distortion and Modulation Transfer Function is improved in said at least one portion of the windshield serving as a camera window in comparison with that of the corresponding portion with a black enamel frit obscuration.

2. The automotive laminated windshield of claim 1 wherein one film layer of said at least one film layer is a PET film layer.

3. The automotive laminated windshield of claim 1 wherein at least one plastic interlayer of said at least two plastic interlayers is a wedge interlayer.

4. The automotive laminated windshield of claim 1 further comprising a performance film plastic layer.

5. The automotive laminated windshield of claim 1 wherein said at least one obscuration for said at least one camera window is printed using a printing process selected from the group consisting of inkjet printing, screen printing and pad printing.

6. The automotive laminated windshield of claim 1 wherein said at least one obscuration for said one camera window is printed with an ink selected from the group consisting of solvent inks and UV inks.

7. The automotive laminated windshield of claim 1 further comprising an obscuration band printed as a black enamel frit obscuration.

8. The automotive laminated windshield of claim 7 wherein said at least one obscuration for said at least one camera window is separated from and spaced from the obscuration band.

9. The automotive laminated windshield of claim 1 wherein the film layer is comprised of at least one layer composition.

10. The automotive laminated windshield of claim 9 wherein said at least one layer composition is selected from the group consisting of metal based heat reflecting films, non-metal based heat reflecting films, tint films, heat absorbing films, Suspended Particle Device (SPD) films, Polymer Dispersed Liquid Chrystal (PDLC) films, conductive coated films, PET (polyethylene terephthalate) and combinations thereof.

11. The automotive laminate windshield of claim 1 wherein said at least one equipment obscuration comprises an opening to provide a forward field of view for each camera.

12. The automotive laminate windshield of claim 1 wherein the distortion parameter is improved between 1% and 83%, preferably between 1% and 50%.

13. A vehicle utilizing the laminate of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a typical automotive windshield with a black band obscuration 32, a wiper rest obscuration 31 and an equipment obscuration 34 extending downward from the black band obscuration, having openings 30 to provide a forward field of view for two cameras.

(2) FIG. 2 shows an automotive windshield with a black band 32, a wiper rest obscuration 31 and an obscuration 34 separated from the black band, having openings 30 to provide a forward field of view for two cameras.8

(3) FIG. 3 shows a panoramic automotive windshield with a black band 32, a wiper rest obscuration 31 and an obscuration 34 separated from the black band, having openings 30 to provide a forward field of view for two cameras.

(4) FIG. 4 shows the obscuration 8 of the prior art, a black enamel frit applied to the fourth surface 24.

(5) FIG. 5 shows the obscuration 8 printed on the film 17 facing the third surface 23,

(6) FIG. 6 shows the obscuration 8 printed on both side of the film 17.

(7) FIG. 7 consists of:

(8) FIG. 7A shows a laminate with interlayers of uniform thickness

(9) FIG. 7B shows a laminate with one interlayer sheet of uniform thickness and one with a wedge angle greater than zero.

(10) FIG. 7C shows a laminate with two interlayer sheets having a wedge angle greater than zero.

(11) FIG. 8 consists of:

(12) FIG. 8A shows the path of light through a laminate with interlayers of uniform thickness.

(13) FIG. 8B shows the path of light through a laminate with interlayers having a wedge angle greater than zero.

(14) FIG. 9 consists of:

(15) FIG. 9A shows a black frit obscuration 8 and the buffer zone 15 between the black frit and camera filed of view 16.

(16) FIG. 9B shows an obscuration 8 printed on film with no buffer zone 15 between the black frit and camera field of view 16.

(17) FIG. 10 shows a graph of the MTF measured in the upper camera area.

REFERENCE NUMERALS

(18) 3 Wedge Plastic Interlayer 4 Plastic Interlayer 5 Glass 6 Sunshade 8 Obscuration 10 Equipment Mounted To Glass 11 Adhesive 12 Device Housing 14 Cover 15 Buffer 16 Field of view 17 Film 21 First Surface of Glass 22 Second Surface of Glass 23 Third Surface of Glass 24 Fourth Surface of Glass 30 Openings in Equipment Obscuration 31 Wiper Rest Obscuration 32 Black Band Obscuration 34 Equipment Obscuration 40 Double image Angle 41 Observation point 42 Incident ray from image 43 Primary image 44 Secondary image 45 Wedge angle 46 Incident angle 48 Refracted ray 50 Surface normal 52 Angle of deviation 56 Inclination angle

DETAILED DESCRIPTION OF THE INVENTION

(19) The invention eliminates the drawbacks associated with the black frit obscurations of the prior art by printing at least some of the obscurations on a plastic film layer which is then laminated as an integral part of the glazing. This 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.

(20) Film, as used in this document shall refer to single ply/layer compositions as well as films comprised of multiple layers. A common plastic used in such films is PET (polyethylene terephthalate) but as can be appreciated can be of any other composition found to be suitable can be used. Some examples include but are not limited to: metal based heat reflecting films, non-metal based heat reflecting films, tint films, and heat absorbing films, Suspended Particle Device (SPD) films, Polymer Dispersed Liquid Chrystal (PDLL) films, conductive coated films, and ordinary PET.

(21) There are many PET based automotive film products in production providing a ready base of field proven performance films that can be used as the film of the invention. One of the most common and oldest has a heat reflecting coating for enhancing solar load control. Others include but are not limited to: films used to improve occupant retention, stiffen the laminate and provide for variable control of visible light transmission. To laminate these films 17, two layers of interlayer 4 are needed to achieve the required adhesion to the glass and to the film. An obscuration 16 can be printed on either or both sides of the film.

(22) The obscurations of the immediate invention are not limited to inkjet printing as is the prior art. The obscurations can be printed using inkjet, screen print, pad print or any other conventional printing means. The obscurations can be printed on either or both sides of the film.

(23) The unaltered original surface of the interlayer is able to bond to the glass and retains its adhesion to the glass. The addition of the film 17 increases the penetration resistance of the laminate. As a result, the printed area of the sheet does not need to have as high of a level of adhesion to the interlayer as the interlayer needs to have to the glass. This opens the possibility of uses a wider range of inks than possible than with inks that need to be printed directly onto an interlayer.

(24) During development, five printing technologies were evaluated and more than sixteen inks were tested. The criteria for the inks was based upon appearance (opacity and color), adhesion of ink to the PET, adhesion of ink to the interlayers and durability. The objective was to find a black color ink with high opacity, having good adhesion to PET and interlayers and durability.

(25) A variety of different inks were tested using screen-printing. Solvent inks and UV inks for screen-printing process were evaluated. Both, UV and solvent inks had good durability results. Both inks also presented good adhesion results on PET penetrating into the substrate and creating a permanent bond. The UV ink was selected for prototype production due to the fast cure time, no need to add a catalyst and low volatile content. The UV ink is also ready to use with no need to add any catalyst and is instantly hardened by intense UV light polymerization (curing). The high reactivity of the ink delivered good curing results. UV ink properties give flexibility to work on large and small format printing. Surprisingly, it was found that obscurations printed in this manner also could be printed directly onto the interlayer.

(26) Some modifications to the ink were required. The ink modifications included tuning the UV frequency response and removing silicon from the formulation. It was found that the silicon lead to delamination in the areas near the glass edge. Broad band UV was found to cause warping or modulus of the substrate due to over saturation of energy. Restricting the overall bandwidth to a specific wavelength enhanced the ability to cure the ink using less overall energy. The obscuration produced has a dark black color and a shiny gloss comparable to black frit. The printed sheets are then cut to size and assembled into the laminate. For large scale production, roll to roll printing could be used.

(27) Protection of the polyurethane adhesive from UV is achieved thorough the opacity of the ink in combination with the use of a UV blocking interlayer. Such UV blocking interlayers are well known in the art and have been in common use for many years.

(28) To aid in the alignment of the printed sheet 17 when assembling the laminate, registration marks can be printed on the sheet 17.

(29) Another benefit of the process is the ability to fine tune the optical properties and appearance of the laminate. A near limitless range of colors can be produced. Properties in the non-visible portion of the spectrum can also be enhanced. Some performance films are sensitive and degrade over time, with exposure to the near UV. Additives that absorb or reflect the specific wavelengths of interest can be added to the ink to achieve targeted optical properties.

(30) If a combination of frit and ink are used for the black band 32 and the equipment obscuration 34, any difference in the appearance between the two may be noticeable. In that case, separating the equipment obscuration 34 from the black band, as shown in FIG. 2, will improve the aesthetic. The transition line between the black band 32 and the wiper rest 31 will not generally be visible.

(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 noticable optical distortion. The refractive power is expressed in diopters.

(34) $\begin{array}{cc}{D}_{\mathrm{.Math.}}=\frac{d{}_{\mathrm{.Math.}}}{\mathrm{dx}}\frac{1}{\cos \mathrm{.Math.}}& \left(1\right)\end{array}$ Where:
: angle formed between the ray of light 42 and a line perpendicular to the surface of the glazing 50
.sub.: angular deviation
D.sub.: refractive power

(35) 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.

(36) 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.

(37) Double image, another problem of the prior art, is illustrated in FIGS. 8A and 8B.

(38) A ray of light 42 enters the surface of the glass at an incident angle 46 and passes through the glazing to the observer 41. The light bends (refracts) as it passes through the glazing. The angle by which the light bends is known as the angular deviation 52. This refraction of the light causes a shifting of the apparent position 43 of the object observed

(39) Some of the light from the ray 42 entering the glass is reflected back from the inside surface 24 and exits the glazing. A portion of the reflected light is again reflected back from outside surface 21 resulting in a double image. The separation angle 40 is the angle between the primary 43 and secondary image 44 and the observer 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.

(40) The double image angle, 40, is calculated as shown in equation 2. It increases with decreasing angle of inclination 56, increasing curvature of the glass surface 24 and with increasing size of the glazing. The double image angle, 40, can be reduced by altering the angle between the plies of glass as shown in FIG. 8B. Normally, the glass surfaces are substantially parallel to each other. By creating an angle 45 between the surfaces, the primary and secondary images can be shifted towards convergence.

(41) $\begin{array}{cc}=\frac{2t\sin \left(\mathrm{.Math.}\right)}{R\sqrt{n^2-{\sin \left(\mathrm{.Math.}\right)}^2}}& \left(2\right)\end{array}$ where:
: double image angle
t: thickness of the glazing
n: refractive index
R: radius of curvature

(42) 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 6. 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.

(43) 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.

(44) FIGS. 7A, 7B and 7C show: a laminate with two standard interlayers, a laminate with one wedge interlayer and a laminate with two wedge interlayers.

(45) Wedge interlayer can be used with a printed obscuration to further reduce double vision.

(46) TABLE-US-00001 TABLE 1 Sunshade Radius vs. Wedge Angle Sunshade Radius Interlayer Thickness Wedge Angle m mm mrad 2.0000 0.5067 0.253 2.5000 0.5429 0.217 3.0000 0.5700 0.190 3.5000 0.5911 0.169 4.0000 0.6080 0.152 4.5000 0.6218 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

(47) Enamel frit and printed ink can both be used on the same part and in any combination that is convenient. As an example, the obscurations could be printed on the sheet 17, while the other markings and images can be made with a conventional black screen print. The markings and images do not have the same detrimental effect as the obscuration prints, due to their small size and function.

(48) Experimental results have demonstrated the remarkable and unexpected magnitude of improvement of the invention and are shown in the following table (Table 2) and graphs. Fracture strength is more than doubled, MTF is drastically improved (see FIG. 10), 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.

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

(50) 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, see FIG. 10.

(51) 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 in this 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 locus will be the horizon and all images in the focal plane will need to be detectable both in shape and in size.

(52) Printing the obscuration has resulted in a remarkable improvement in system MTF as compared to the same production model with a normal frit obscuration.

ADVANTAGES

(53) 1. Best in class optics. 2. Frit induced surface defects are eliminated. 3. Residual stress caused by non-uniform heating of the frit is eliminated. 4. Residual stress caused surface mismatch due to the frit is eliminated. 5. Low distortion, comparable to ordinary clear glass. 6. LOW double image, comparable to ordinary clear glass. 7. Lower probability of breakage. 8. Higher yield during bending due to elimination of non-uniform heating. 9. Higher yields during lamination due to higher strength, lower residual stress and less surface mismatch.

Embodiment 1

(54) The windshield of FIG. 1 comprising a black enamel frit band 32, a black enamel frit wiper rest area 31 one wedge interlayer, and an equipment obscuration 8, 34 printed on one surface of the plastic sheet 17 (FIG. 5).

Embodiment 2

(55) The windshield of FIG. 1 comprising a black enamel frit band 32, a black enamel frit wiper rest area 31 and an equipment obscuration 8, 34 printed on both surfaces of the film 17 (FIG. 6).

Embodiment 3

(56) The windshield of FIG. 1 comprising a wiper rest 31, black band 32 and an equipment obscuration 8, 34 printed on one surface of the film 17 (FIG. 5).

Embodiment 4

(57) The windshield of FIG. 1 comprising a wiper rest 31, black band 32 and an equipment obscuration 8, 34 printed on both surfaces of the film 17 (FIG. 6).

Embodiment 5

(58) The windshield of FIG. 1 comprising a film 17, a wiper rest 31, black band 32 and an equipment obscuration 8, 34 printed on one surface of the film (FIG. 5).

Embodiment 6

(59) The obscuration combinations of the previous embodiments, 1-5, further comprising an equipment obscuration separate from the black band and spaced from said black band by at least 3 mm illustrated in FIG. 2.

Embodiment 7

(60) A panoramic windshield (FIG. 3) with the equipment obscuration printing on one surface of the film 17 and an enamel frit wiper rest/black band.

Embodiment 8

(61) A panoramic windshield (FIG. 3) comprising and equipment obscuration printed on both surfaces of the film 17 (FIG. 6).