Glazing

Abstract

The invention relates to a heatable glazing comprising an electrically conductive coating and a data transmission window. The data transmission window comprises a plurality of grids made by ablations in the electrically conductive coating and at least one break line between adjacent grids. At least one of a width a of the grids and a distance b between adjacent grids is selected to maximise transmission of a predetermined frequency of electromagnetic radiation and to reduce the formation of hot spots. Preferred embodiments conform to a standard size of an ERTICO window and a frequency range from 5 GHz to 6 GHz.

Claims

1. A heatable glazing comprising: an electrically conductive coating a data transmission window in the electrically conductive coating wherein the data transmission window comprises: a plurality of ablations in the electrically conductive coating, arranged to provide a plurality of grids, the grids comprising segments in rows and columns; at least a break line, each break line an ablation arranged between adjacent grids; and at least one of a width a of the grids and a distance b between adjacent grids is selected to maximise transmission of a predetermined frequency of electromagnetic radiation for horizontally polarized waves wherein the one or more break lines are aligned vertically.

2. A heatable glazing according to claim 1, wherein the width a of the grids is in the range from 4 to 10 mm.

3. A heatable glazing according to claim 2, wherein the width a of the grids is in the range from 4 to 6 mm.

4. A heatable glazing according to claim 3, wherein the width a of the grids is in the range from 5 to 6 mm.

5. A heatable glazing according to claim 1, wherein the distance b between adjacent grids is in the range from 1 to 4 mm.

6. A heatable glazing according to claim 5, wherein the distance b between adjacent grids is in the range from 2 to 4 mm.

7. A heatable glazing according to claim 6, wherein the distance b between adjacent grids is in the range from 3 to 4 mm.

8. A heatable glazing according to claim 1, wherein a height c of the grids is greater than the width a of the grids.

9. A heatable glazing according to claim 8, wherein a height c of the grids is in the range from 50 to 100 mm.

10. A heatable glazing according to claim 9, wherein the height c of the grids is in the range from 65 to 75 mm.

11. A heatable glazing according to claim 1, wherein a width d of the data transmission window is greater than three times the sum of the width a of the grids and the distance b between adjacent grids, i.e. d>3(a+b).

12. A heatable glazing according to claim 1, wherein a width d of the data transmission window is in the range from 50 to 200 mm.

13. A heatable glazing according to claim 12, wherein the width d of the data transmission window is in the range from 130 to 140 mm.

14. A heatable glazing according to claim 1, wherein a width e of each segment of the grids is in the range from 0.5 to 5 mm.

15. A heatable glazing according to claim 1, wherein the heatable glazing further comprises a top busbar and a bottom busbar arranged substantially at right angles to the break lines.

16. A heatable glazing according to claim 1, wherein the predetermined frequency of electromagnetic radiation is in the range from 3 to 10 GHz.

17. A heatable glazing according to claim 16, wherein the predetermined frequency of electromagnetic radiation is in the range from 5 to 6 GHz.

18. A heatable glazing according to claim 1, wherein the transmission of electromagnetic radiation at the predetermined frequency through the data transmission window relative to free space is greater than or equal to 3 dB.

19. A heatable glazing according to claim 1, wherein a percentage conductive width b/(a+b) of the data transmission window is greater than or equal to 25%.

20. A heatable glazing according to claim 1, wherein the width a of the grids and the distance b between adjacent grids are selected to be integer multiples A and B of a width e of each segment of the grids.

21. A heatable glazing according to claim 14, wherein a height c of the grids is selected to be an integer multiple C of the width e of each segment of the grids.

22. A heatable glazing according to claim 1, wherein the heatable glazing comprises first and second plies of interlayer material, between first and second plies of glazing material and wherein the electrically conductive coating is on a carrier film, between the first and second plies of interlayer material.

23. A heatable glazing according to claim 1, wherein the heatable glazing comprises a ply of interlayer material, between first and second plies of glazing material and wherein the electrically conductive coating is on a surface of the first ply or the second ply of glazing material, and is in contact with the ply of interlayer material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) The invention will now be described by means of non-limiting examples with reference to the attached figures:

(3) FIG. 1 shows a glazing according to the invention in plan view.

(4) FIG. 2 shows a data transmission window according to the invention with four grids, each separated by a break line.

(5) FIG. 3 shows the data transmission window of FIG. 2 with parameters a to e.

(6) FIG. 4 shows a data transmission window according to the invention with four grids, each separated by a break line so b=2, each grid having a=6 and c=14.

(7) FIG. 5 shows a data transmission window according to the invention with four grids, each separated by two break lines, such that a=6 and b=3.

(8) FIG. 6 shows a cross-section of a glazing according to the invention comprising an electrically conductive coating on a carrier film.

(9) FIG. 7 shows a temperature distribution of a glazing according to the invention having a=6 and b=4 and a maximum temperature 83 C.

(10) FIG. 8 shows a temperature distribution of a glazing according to the invention having a=6 and b=2 and a maximum temperature 89 C.

(11) FIG. 9 shows a temperature distribution of a glazing according to the invention having a=6 and b=2 and the data transmission window having rounded corners and a maximum temperature 93 C.

(12) FIG. 10 shows a temperature distribution of a glazing according to the prior art, comprising a full grid data transmission window, having maximum temperature 114 C.

(13) FIG. 11 shows a temperature distribution of a glazing according to the prior art, comprising a pattern of dots, having maximum temperature 81 C. and only 50% coated area remaining.

(14) FIG. 12 shows a chart of transmission versus frequency in the range from 0.1 to 6 GHz for four glazings according to the invention, and a reference glazing without coating.

(15) FIG. 13 shows a chart of transmission versus frequency in the range from 5 to 6 GHz for four glazings according to the invention, and a reference glazing without coating.

(16) FIG. 14 shows a chart of transmission at 5.7 GHz versus width of grids for four glazings according to the invention, showing a maximum at a=6 mm.

(17) FIG. 15 shows a chart of transmission at 5.8 GHz versus percentage of conductive width for seven glazings according to the invention.

(18) FIG. 16 shows a chart of the same data as FIG. 15, grouped by distance b between adjacent grids, showing a transmission threshold of 0.5 dB and a percentage conductive width threshold of 35%.

(19) FIG. 17 shows dimensionless variables A, B, C and D based on unit width e.

DETAILED DESCRIPTION OF THE INVENTION

(20) FIG. 1 shows a glazing 1 according to the invention suitable for a vehicle windshield. In all the drawings and description, vertically refers to vertical orientation of the glazing 1, for example as installed in a vehicle. The glazing 1 comprises an electrically conductive coating 2, suitable for solar control. Such coatings are known in the art. The electrically conductive coating 2 comprises a data transmission window 3, suitable for allowing transmission of electromagnetic radiation at a predetermined frequency.

(21) The electrically conductive coating 2 prevents transmission at radio frequencies. Attenuation of transmission is in the range from 25 to 35 dB.

(22) The data transmission window 3 may be a standard size, such as defined in a standard of a European Intelligent Transport Systems Organisation (ERTICO), of height 70 mm and width 120 mm.

(23) Ablations in the electrically conductive coating 2 within the data transmission window 3 may be made by laser treatment known in the art. Ablations are made to form grids, comprising segments in rows and columns. A width of each segment is also known as the grid pitch and is approximately 1 mm. Ablations are formed having width approximately 50 to 100 micrometres.

(24) Grids provide radio frequency transmission but hinder DC heating currents, so a conventional data transmission window in a heatable glazing is a non-heated area and hot spots are formed at the edges of the data transmission window. So there is a long felt need to find the best compromise between heating uniformity, radio frequency transmission and solar performance.

(25) The present invention allows DC currents to flow vertically in part of the data transmission window 3, by providing a plurality of grids, i.e. providing a current path in the gap between adjacent grids.

(26) Furthermore the present invention maintains the grid pattern in the vertical direction, by means of one or more break lines between adjacent grids, maintaining radio frequency performance for horizontally polarised waves. Horizontal electrical currents in gaps between adjacent grids are blocked by the break lines, aligned vertically.

(27) FIG. 2 shows a data transmission window 3 in more detail, comprising four grids 31. Between each grid 31 is a break line 32.

(28) FIG. 3 shows a data transmission window 3 with defined by five parameters a to e. A width of the grids 31 is a. A distance between adjacent grids 31 is b. A height of the grids is c. A width of the data transmission window 3 is d. A width of each segment of the grids 31 is e.

(29) FIG. 4 shows a data transmission window 3 comprising four grids 31, each comprising six segments horizontally. Between each grid 31 is a break line 32. In this embodiment, the width of a segment is 1 mm and a distance between grids 31 and an adjacent break line 32 is 1 mm. So the width a of grids 31 and the distance b between adjacent grids 31 are easily measured in millimetres by counting the number of gaps between ablations. In this case a is 6 mm and b is 2 mm, which may be conveniently written a6, b2. In this figure one ablation on the right edge has been omitted to indicate that the pattern repeats to fill a required width d. A preferred embodiment for an ERTICO window consists of 15 grids of dimensions a6, b2.

(30) FIG. 5 shows a preferred embodiment, in which the data transmission window 3 comprises a plurality of grids 31, each comprising six segments horizontally, and two break lines 32 are arranged between adjacent grids, i.e. a6, b3, if e=1 mm. To fill an ERTICO window, the number of grids 31 is more than 15 if e is less than 1 mm. An alternative requirement for a width d 135 mm requires 17 grids if e is 1 mm. Although 12 vertical segments are shown for convenience, 70 vertical segments are needed to fill an ERTICO window if e is 1 mm.

(31) FIG. 6 shows a cross-section of a preferred embodiment, in which the glazing 1 comprises first and second plies of interlayer material 21, 22 between first and second plies of glazing material 11, 12. An electrically conductive coating 2 is on a carrier film 23, between the first and second plies of interlayer material 21, 22. A data transmission window 3 is provided in the electrically conductive coating 2.

(32) In an alternative embodiment (not shown), the glazing 1 comprises a ply of interlayer material 21 between first and second plies of glazing material 11, 12. An electrically conductive coating 3 is on a surface of the first ply or the second ply of glazing material 11, 12 and is in contact with the ply of interlayer material 21. This has the advantage of a simpler manufacturing process.

EXAMPLES

(33) Examples of the present invention were analyzed by computer simulation. A known Transmission Line Matrix (TLM) method of differential numerical modelling of electromagnetic field problems was used to simulate radio frequency transmission. A data transmission window 3 in each example has width 135 mm and height 70 mm and the glazing is two sheets of float glass, thickness 2.1 mm, bonded together by a ply of interlayer, thickness 0.7 mm. Width e of a segment is 1 mm.

(34) Temperature distribution was also modelled, based on 42 V, to identify maximum temperature in each example. A hot spot could be dangerous if touched by a person and could damage the coating, interlayer material or glazing. A maximum temperature in a range from 80 to 90 C. is a preferred.

(35) FIG. 7 shows a temperature distribution of a glazing according to the invention having a=6 and b=4 and a maximum temperature 83 C. The distance b between adjacent grids 31, i.e. the DC path, is wide to minimise hot spots.

(36) FIG. 8 shows a temperature distribution of a glazing according to the invention having a=6 and b=2 and a maximum temperature 89 C. The DC path is narrower than in FIG. 7, so that a repeating distance a+b of grids 31 is 8 mm. Therefore the data transmission window 3 contains more grids than in FIG. 7.

(37) FIG. 9 shows a temperature distribution of a glazing according to the invention having a=6 and b=2 and the data transmission window 3 has rounded corners and a maximum temperature 93 C.

(38) FIG. 10 shows a temperature distribution of a glazing according to the prior art, comprising a full grid data transmission window, having maximum temperature 114 C. In this comparative example, a single grid fills a conventional ERTICO window 3. The hot spot temperature is unacceptable.

(39) FIG. 11 shows a temperature distribution of a glazing according to the prior art EP1559167 (AGC/Roquiny), comprising a pattern of dots, having maximum temperature 81 C. and only 50% coated area remaining. Although hot spots are avoided, solar performance is sacrificed in the data transmission window 3.

(40) FIG. 12 shows a chart of transmission versus frequency in the range from 0.1 to 6 GHz for four glazings according to the invention, and a reference glazing without coating. A repeating distance a+b of grids 31 is 8 mm in all four glazings. As width a of the grids increases, a larger window for vertically polarized radio frequency waves is provided, so transmission increases.

(41) FIG. 13 shows a chart of transmission versus frequency in the range from 5 to 6 GHz for four glazings according to the invention, and a reference glazing without coating. FIG. 13 is a high resolution section of FIG. 12. Frequency dependence is observed, such that a transmission is maximised at a predetermined frequency of electromagnetic radiation. A maximum occurs at 5.7 GHz for a width a of the grids 31 in the range 4 to 6 mm, i.e. a distance b between grids 31 in the range from 3 to 5 mm. A different effect occurs for a greater than or equal to 7 mm, i.e. b less than or equal to 2 mm. Transmission performance is similar to a comparative example of a glazing without coating for a6, b3. In this example, combinations of a and b are selected such that a+b=9.

(42) FIG. 14 shows a chart of transmission at 5.7 GHz versus width of grids for the four glazings of FIG. 13 according to the invention, showing a maximum at a=6 mm. FIG. 14 shows optimization analysis for a width a of the grids 31 in cooperation with a distance b between adjacent grids 31. FIG. 13 and FIG. 14 together show that for a given frequency and a repeating distance a+b there is an optimum, i.e. a maximum.

(43) Surprisingly the inventors have found that for linear polarised vertical waves a field distribution is obtained which results in optimal transmission for a given frequency. After ablations according to the invention, typically 90% of the electrically conductive coating 2 in the data transmission window 3 remains, so solar performance is not sacrificed. Maximum temperature is in the range from 80 to 90 C. so hot spots are avoided.

(44) Experimental results for linear polarisation are for the critical case, which is vertical. Horizontal polarisation is not affected by choosing different values for a or b, because horizontal currents are not significantly affected by vertical current paths in the gap between adjacent grids. Some communication systems, for example for toll collection, have circular polarisation. The present invention is applicable for circular polarisation, even though the effects presented above are less pronounced.

(45) In a further embodiment according to the invention, both radio frequency transmission and heating uniformity are optimised. Heating uniformity is expected to improve as a distance b between adjacent grids increases. On the other hand, radio frequency transmission is optimised by selecting a width a of the grids and a distance b between adjacent grids in a particular combination. Prior art does not disclose a glazing in which a width a of the grids and a distance b between adjacent grids are selected together to optimise both radio frequency transmission and heating uniformity.

(46) According to the invention, an indicator of heating uniformity is a percentage conductive width, calculated as b/(a+b). The percentage conductive width quantifies the average conductance for DC heating of a proposed plurality of grids compared to the coating without laser ablations.

(47) FIG. 15 is a chart of transmission at 5.8 GHz versus percentage of conductive width for seven glazings according to the invention, from experimental results using circular polarisation. An advantage of using percentage conductive width as an independent variable is embodiments of the invention which are best for heating uniformity are shown to the right.

(48) FIG. 16 shows a chart of the same experimental results as FIG. 15, grouped by distance b between adjacent grids. Generally as b increases, heating uniformity improves. Thresholds for radio frequency transmission and percentage conductive width are applied. For example, a transmission threshold of 0.5 dB and a percentage conductive width threshold of 35% are applied. Both thresholds are exceeded by a5, b3. This embodiment represents an optimum of 0.3 dB radio frequency transmission (nearly equal to free space) and allows 3/(5+3)=37.5% of conductive width for heating.

(49) FIG. 17 shows a glazing according to the invention wherein variables a, b, c and d are integer multiples of width e of each segment. Thus dimensionless variables A, B, C and D are defined, counting in units of e. An advantage of this embodiment is that grids have an integer number of segments, which makes selection of dimensions easier.