GB1598924A

GB1598924A - Vehicle windows

Info

Publication number: GB1598924A
Application number: GB32580/77A
Authority: GB
Original assignee: BFG Glassgroup GIE
Current assignee: BFG Glassgroup GIE
Priority date: 1977-08-03
Filing date: 1977-08-03
Publication date: 1981-09-23
Also published as: DE2833234C2; JPS5428321A; JPS6353140B2; NL188346B; NL7807868A; DE2833234A1; FR2399331A1; NL188346C; ES472899A1; BE869062A; IT7868630A0; IT1159892B; FR2399331B1

Description

(54) IMPROVEMENTS IN VEHICLE WINDOWS (71) We, BFG GLASSGROUP, a Groupement d'Interet Economique established under the laws of France (French Ordinance dated 23rd September 1967) of Rue Caumartin 43, Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to vehicle windows. The invention has particular reference to windows of road vehicles, but is also applicable to windows of other vehicles such as trains, aircraft and ships.

It is well known that vehicle windows, especially motor car windows are apt to become covered in condensation during cold nights and that layers of ice covering the windows will be formed if the ambient temperature is low enough. Obviously any such ice has to be removed before the vehicle can be driven safely. This is often done by switching on an electrical resistance heater incorporated in the window (if such is provided) or simply by heating the whole of the interior of the vehicle.

It is an object of the present invention to provide a vehicle with windows which are less apt to become covered in condensation or ice, and which, if such an ice covering is formed, can be de-iced more rapidly.

According to the present invention, there is provided a vehicle characterised in that it has at least one window whose outside bears a light-transmitting coating which increases the mfra-red reflectivity of the window and which coating has a resistivity (measured as herein specified) of less than 50Q/a.

Preferably the front and/or rear window(s) of the vehicle are so coated, and optimally, all windows of the vehicle are so coated.

By virtue of the presence of such a coating, a coated window cools more slowly during cold nights, so that condensation and icing are at least delayed and thereby reduced or even prevented, and furthermore the interior of the vehicle cools more slowly, so that if ice should form on a window it can be melted off more rapidly.

A further and perhaps surprising advantage is apparent during hot weather, namely that such a coating delays heating of the interior of the vehicle, so that it does not become uncomfortably hot when stationary.

Preferably, the or at least one said coating has a resistivity (measured as herein specified) of less than 20R/n, since this has a favourable effect on the light-transmissivity of the coated window.

In fact the values given for the resistivity of a thin transparent coating as envisaged by the present invention can depend on the method of measurement used. Accordingly, the following method is specified.

Four brass electrode rods A, B, C, D are taken and one end of each is sharpened to a cone whose internal angle is 900. These rods are held in an insulating block so that the points of the cones are in a straight line 6 mm apart. The points of these rods are placed in contact with the coating whose resistivity it is desired to measure and a D.C.

potential of 11.5 volts is applied between the end pair A,D of electrodes. The potential difference VBC between the central pair of electrodes B,C is measured using a high input impedance voltmeter, as is the voltage VR across a standard resistance R in series with the end pair of electrodes A,D.

Considering a coating of large area having resistivity Ro (ohms per square) on an insulating support, the potential V at a distance d from a pount fed with current I is given by I V=RE, ln d 27 Since the electrode C is twice as far from the electrode A as the electrode B, the potential difference Vec reduces to I ln2 Vec=Ro K From this, and substituting VR R V,,. R.n RD= Ve. ln2 Provided that the dimensions of the coating on the sheet are large (25 times or more) compared with the spacing between the end electrodes A,D this formula will give a result accurate to within 1%.

Preferably, said coating imparts to the window an emissivity of at most 0.35, and optimally at most 0.2. This increases the delay in cooling in cold weather and also increases the delay in heating in hot weather.

Advantageously, the transmissivity of the or at least one said coated window in respect of visible light is at least 70%. This degree of transmissivity enables occupants of the vehicle to see out clearly during normal conditions, and it is fact a legal requirement for road vehicle wind-screens in some countries.

Preferably, the or at least one said coating has a thickness of between 7000 and 10000 A. Coatings of such thicknesses give uniform light transmission, and non-uniform interference effects are largely eliminated.

Advantageously, the or at least one said coating is a metal oxide coating. Tin oxide (SnO2) and indium oxide (In2O3) coatings are especially preferred. Tin oxide coatings in particular are highly resistant to deterioration by atmospheric agents such as water vapour and are abrasion resistant.

This latter feature is particularly important in the case of road vehicle windscreens.

Indium oxide does not give quite such good results and is slightly more expensive to use, but nonetheless indium oxide coatings do give very satisfactory results.

Titanium nitride coatings have also been used with satisfactory results.

Preferably the or are at least one said coating includes a doping agent since this enables the best resistivity and emissivity values to be achieved. Such doping agent may for example be chlorine and/or fluorine. Antimony, arsenic, cadmium and tellurium have also been used as doping agents.

A said coating may be applied to a sheet of glass for use as a vehicle window in any convenient manner. For example a fluorine doped tin oxide coating can be obtained by the thermal decomposition of SnCI4 and NH4F. HF or a chlorine doped coating of indium oxide can be obtained by pyrolysis of a solution of InCI3.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a car windscreen constructed in accordance with the invention, and Figures 2 to 6 are graphs which indicate comparative temperature measurements as they vary during the course of time.

In Figure 1, a car windscreen generally indicated at I is held in a frame 2 leading between the car bonnet 3 and its roof 4. The windscreen I which is of tempered glass has on its exterior surface a coating 5 which is light-transmitting and increases the infrared reflectivity of the windscreen, and has a resistivity of less than 50 Q/Ci.

In Figures 2 to 6 the ordindate is marked with "C and the abscissa with the local time in hours at the test site. Local time was two hours in advance of solar time so that the sun was at the meridian at 14.00 hours.

The temperature measurements were made on two motor cars of the same age, model and colour, one car having ordinary uncoated windows, the other having all its windows coated in accordance with the invention.

The coating used was SnO2 doped with Fions. The windscreen and rear window of the car were coated to a thickness of 9000 A (resistivity 15 Q/n) and the side windows were coated to a thickness of 7000 A (resistivity 19 Q/D). The emissivity in each case was approximately 0.25. The coatings were applied to the exteriors of the windows.

Figure 2 indicates the difference in temperature between the external surface of the coated and uncoated windscreens at night under a clear sky, the coated windscreen being always warmer than the uncoated windscreen; Figure 3 indicates the difference in temperature between the external surface of the two windscreens during the day under a clear sky, the coated windscreen again being always warmer than the uncoated windscreen; Figure 4A indicates the difference in temperature between the interiors of the two cars at night under a clear sky, the car having the uncoated windows starting warmer but becoming cooler than the car having coated windows; Figure 4B indicates the difference in temperature between the interior surfaces of the two windscreens at night under an overcast sky, the coated windscreen being warmer than the other, Figure 5 indicates the difference in temperature between the interiors of the two cars during a clear summer day, the car with the coated windows being generally cooler than the other, and Figure 6 indicates the actual temperatures monitored in the interiors of the two cars during another clear day in summer.

From Figure 2 it will be noted that the difference in temperature of the two windscreen exteriors dropped quite rapidly at about sunset (20.53 hours on the day in question as indicated by the falling arrow) but that between 22.00 hours and sunrise the next day (just after 7.00 hours as indicated by the rising arrow) the coated windscreen remained between 1" and 2"C warmer than the uncoated windscreen. In fact the least difference, 1.2"C occurred at about 04.00 hours.

It is perhaps surprising that this apparently small temperature difference should have any marked effect, but it was found that the maximum windscreen area covered in condensation in the morning was reduced by as much as 80 or 90% by adopting the coating.

From Figure 3 is will be noted that the external temperature of the coated windscreen rose more rapidly in the morning than did the external temperature of the uncoated windscreen so that any condensation or ice which does form is more rapidly driven off.

Figure 4A shows that on a particular day at 21.00 hours (sunset) the interior of the car having coated windows was some 0.7"C cooler than the other, but that the other car cooled more rapidly than the one with the coated windows so that after 22.00 hours the interior of the car with the coated windows was warmer and remained so until sunrise (at 7.00 hours).

Figure 4B shows differences in temperature between the interior surfaces of the coated and uncoated windscreens on another night when the sky was overcast and that even under such conditions where the advantage afforded by the invention might be expected to be at its minimum, the coated windscreen remained warmer. In fact showers of rain fell shortly before 01.00 hours and between 02.00 and 03.00 hours, and this had a deleterious effect on the emissivity of the windscreen. The emissivity of water is about 0.9, and rain drops which were found to cover about 30% of the area of the windscreen raised its emissivity from 0.25 to 0.35.

Figure 5 indicates the difference in temperature between the interiors of the two cars on a clear summer day. It will be noted that up to 11.00 hours this temperature difference was small, but that as the sun rose higher, the temperature difference rose quite rapidly so that at 11.20 hours the car with the coated windows was nearly 60C cooler than the other, and that by 13.00 hours it was 10"C cooler. It will be seen that between 14.00 and 14.30 hours there is an inversion where the car with the coated windows was briefly up to 1 0C hotter than the car with uncoated windows, but nevertheless, for the greater part of the hottest part of the day, the interior of the car with coated windows was appreciably cooler than the other.

Figure 6 shows the actual temperatures measured in the interiors of the two cars during another clear day in summer. From this graph it will be seen that from 10.30 hours, the temperature in the car with the coated windows (as represented by the solid line) was markedly lower than the temperature within the other car (broken line) and that the difference between these temperatures was at its greatest during the period extending from 1+ hours before to IT hours after the passage of the sun through the meridian at 14.00 hours.

It will be appreciated that variations in wind conditions from those subsisting during the temperature measurements described above will necessarily affect the absolute values of the temperature monitored. Nevertheless, a favourable difference in the temperatures as described above will still be found.

It will also be appreciated that a favourable difference in the temperatures will be found if one or more of the tempered windows of the vehicle is replaced by a laminated window which has been coated in accordance with the invention.

WHAT WE CLAIM IS: 1. A vehicle characterised in that it has at least one window whose outside bears a light-transmitting coating which in creases the infra-red reflectivity of tlie window and which coating has a resistivity (measured as herein specified) of less than 50Q/n.

2. A vehicle according to claim 1, characterised in that the front and/or rear window(s) of the vehicle are so coated.

3. A vehicle according to claim 2 characterised in that all windows of the vehicle are so coated.

4. A vehicle according to any preceding claim, characterised in that the or at least one said coating has a resistivity (measured as herein specified) of less than 20/71.

5. A vehicle according to any preceding claim, characterised in that said coating imparts to the window an emissivity of at most 0.35.

6. A vehicle according to any preceding claim, characterised in that the transmissivity of the or at least one said coated window in respect of visible light is at least 70%.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. two cars during a clear summer day, the car with the coated windows being generally cooler than the other, and Figure 6 indicates the actual temperatures monitored in the interiors of the two cars during another clear day in summer. From Figure 2 it will be noted that the difference in temperature of the two windscreen exteriors dropped quite rapidly at about sunset (20.53 hours on the day in question as indicated by the falling arrow) but that between 22.00 hours and sunrise the next day (just after 7.00 hours as indicated by the rising arrow) the coated windscreen remained between 1" and 2"C warmer than the uncoated windscreen. In fact the least difference, 1.2"C occurred at about 04.00 hours. It is perhaps surprising that this apparently small temperature difference should have any marked effect, but it was found that the maximum windscreen area covered in condensation in the morning was reduced by as much as 80 or 90% by adopting the coating. From Figure 3 is will be noted that the external temperature of the coated windscreen rose more rapidly in the morning than did the external temperature of the uncoated windscreen so that any condensation or ice which does form is more rapidly driven off. Figure 4A shows that on a particular day at 21.00 hours (sunset) the interior of the car having coated windows was some 0.7"C cooler than the other, but that the other car cooled more rapidly than the one with the coated windows so that after 22.00 hours the interior of the car with the coated windows was warmer and remained so until sunrise (at 7.00 hours). Figure 4B shows differences in temperature between the interior surfaces of the coated and uncoated windscreens on another night when the sky was overcast and that even under such conditions where the advantage afforded by the invention might be expected to be at its minimum, the coated windscreen remained warmer. In fact showers of rain fell shortly before 01.00 hours and between 02.00 and 03.00 hours, and this had a deleterious effect on the emissivity of the windscreen. The emissivity of water is about 0.9, and rain drops which were found to cover about 30% of the area of the windscreen raised its emissivity from 0.25 to 0.35. Figure 5 indicates the difference in temperature between the interiors of the two cars on a clear summer day. It will be noted that up to 11.00 hours this temperature difference was small, but that as the sun rose higher, the temperature difference rose quite rapidly so that at 11.20 hours the car with the coated windows was nearly 60C cooler than the other, and that by 13.00 hours it was 10"C cooler. It will be seen that between 14.00 and 14.30 hours there is an inversion where the car with the coated windows was briefly up to 1 0C hotter than the car with uncoated windows, but nevertheless, for the greater part of the hottest part of the day, the interior of the car with coated windows was appreciably cooler than the other. Figure 6 shows the actual temperatures measured in the interiors of the two cars during another clear day in summer. From this graph it will be seen that from 10.30 hours, the temperature in the car with the coated windows (as represented by the solid line) was markedly lower than the temperature within the other car (broken line) and that the difference between these temperatures was at its greatest during the period extending from 1+ hours before to IT hours after the passage of the sun through the meridian at 14.00 hours. It will be appreciated that variations in wind conditions from those subsisting during the temperature measurements described above will necessarily affect the absolute values of the temperature monitored. Nevertheless, a favourable difference in the temperatures as described above will still be found. It will also be appreciated that a favourable difference in the temperatures will be found if one or more of the tempered windows of the vehicle is replaced by a laminated window which has been coated in accordance with the invention. WHAT WE CLAIM IS:

1. A vehicle characterised in that it has at least one window whose outside bears a light-transmitting coating which in creases the infra-red reflectivity of tlie window and which coating has a resistivity (measured as herein specified) of less than 50Q/n.

7. A vehicle according to any preceding

claim, characterised in that the or at least one said coating has a thickness of between 7000 and 10000 A.

8. A vehicle according to any preceding claim, characterised in that the or at least one said coating is a metal oxide coating.

9. A vehicle according to claim 8, characterised in that said coating comprises tin oxide (SnO2) or indium oxide (In2O3).

10. A vehicle according to claim 8 or 9, characterised in that the or at least one said coating includes a doping agent preferably selected from one or more of chlorine, fluorine, antimony, arsenic, cadmium and tellurium.

11. A vehicle according to claim I and.

substantially as herein described.