LU83189A1 - METHOD AND DEVICE FOR FORMING A COATING ON A HOT GLASS SUBSTRATE BY MOVING A REAGENT CURRENT CROSS-SUBSTRATE AND GAS PROPULSION THROUGH THIS CURRENT - Google Patents

Description

The present invention relates to a method of forming a coating of metal or metal compound on one face of a hot glass substrate during its movement in a given direction by bringing said face into contact, at a coating station. 5 ment through which passes the substrate, with at least one stream of droplets comprising one or more substance (s) from which or from which the coating of metal or metal compound is formed on said face. The invention also relates to a device intended for the implementation of such a method.

Such a method can be used to coat sheets of glass and to coat a continuous ribbon of flat glass just formed. The process can be used to form coatings, for example metallic oxide coatings, which modify the apparent color of the glass and / or which exhibit certain other desired properties with respect to the incident radiation, for example the property of reflecting the infrared.

Problems are encountered in the formation of coatings which have uniform properties. This is partly due to the difficulty of ensuring uniformity of structure and coating thickness from one area to another.

Various proposals have been made to improve the formation of uniform coatings, including discharging coating material as a downwardly inclined stream toward the substrate in the direction of its movement, and creating forces of suction in an evacuation duct arranged so as to extract gases surrounding the stream of droplets away from said stream, in the duct (cf. British patents 1,516,032 and 1,523,991).

Even if the conditions proposed in these prior patents are respected, defects sometimes appear inside and on the surface of the coating. These defects, although often not very marked, nevertheless disqualify the product from the high quality levels currently demanded. If the defects are on the surface of the coating, the quality of the product can in some cases, but not in all, be improved by a subsequent surface treatment, but obviously such additional treatments increase the cost of

»I

2 product.

The present invention provides a process in which the atmosphere at the coating station is acted upon in a manner which has been found to be useful in reducing the occurrence of structural defects in the coating and in enabling easier and safer production. high quality coatings.

The present invention provides a method of forming a coating of metal or metal compound on one side of a hot glass substrate during its movement in a given direction (hereinafter referred to as "before") by contacting the said face, at a coating station through which the substrate passes, with at least one stream of droplets comprising one or more substances (s) from which the coating of metal or metal compound is formed on said face, characterized in. The stream of droplets is or are repeatedly moved along a path transverse to the substrate and in that gas is propelled unidirectionally forward or backward through said transverse path, out of alignment with the stream (s) of droplets.

To simplify the rest of this description, we will generally state a single droplet current. But we can obviously use two or more, for example two located side by side.

Tests show that the process according to the invention is less likely to form coatings giving rise to internal light scattering. It is believed that these defects may result from the interception and entrainment by the current of droplets of vapor phase reaction products accumulating in the environment of the substrate and that the improvement resulting from the process will occur. The invention is at least partially due to the gas cleaning effect of the reaction products out of the flow of the droplet stream.

In preferred methods according to the invention, the stream of droplets is moved back and forth along the path transverse to the substrate and the discharge of the current takes place in naked conflict during these back and forth movements.

3

Under these circumstances, the process is easier to perform.

Preferably, the propelled gas is extracted from a source external to the normal atmosphere surmounting the substrate. The choice of gas to form the jet will be made taking into account the composition of the droplets and the composition of the coating to be formed on the substrate so that this gas does not itself give rise to undesirable chemical reactions. An inert gas or a gas which promotes or participates in a chemical reaction necessary for the formation of the coating can be used. Alternatively, the propelled gas may be gas which is propelled from locations upstream or downstream of the coating station, forward or backward along the substrate, by one or more fans or the like blowing devices.

In certain methods according to the invention, the propulsion of gas takes place from one or more orifice (s) which is (are) stationary and is carried out intermittently, adjusted in time with the movements of the stream of droplets along its transverse path so that the propelled gas does not meet the stream of droplets.

Gas propulsion can be carried out intermittently (out of phase with the successive crossings of the substrate by the stream of droplets) simultaneously from regions which are distributed across the path of the substrate so that gas flows over all regions except the opposite edges of the coated surface of the substrate. Preferably, however, the transverse path of the droplet current extends beyond the corresponding limits of the surface of the substrate to be coated and gas is propelled intermittently simultaneously through all the regions of the path between these limits. In this way, the entire face of the glass substrate can be coated.

In certain very advantageous methods according to the invention the gas propulsion is carried out continuously from one or more orifice (s) which is (are) displaced (s) through the path 35 of the substrate, in tandem with the source of the droplet current. Such methods have the advantage that during each moment of the coating process • 4 propelled gas can sweep reaction products of the atmosphere prevailing in the immediate vicinity of the stream of droplets.

Preferably, with each movement of the stream of 5 droplets through the substrate of the gas is propelled from a discharge orifice which follows the source of the stream of droplets in its movement so that the passage of the or of a current of droplets through a given region along the path is followed by a flow of gas through this region. This has been found to be the most effective method.

Preferably, the stream of droplets is inclined downward towards the substrate. In general, the use of an inclined current facilitates the formation of coatings of homogeneous structure, particularly if they are relatively thick coatings. Preferably the angle between the axis of the stream of droplets and the coated face of the substrate is of the order of 20e to 60 * and preferably of the order of 25e to 35e. For best results all parts of the droplet stream should meet the substrate at a substantial vertical tilt. Therefore, in the preferred embodiments of the invention the droplet current is a parallel current or a current which diverges from its source by an angle which is not greater than 30e.

The stream of droplets is preferably inclined downward and forward towards the substrate because this condition is most favorable for the homogeneity of the structure of the coating. In an alternative embodiment of the invention, the stream of droplets is tilted downward and backward toward the substrate. This condition can also give good results under certain circumstances, for example to form certain coatings when there is no strong natural draft current in the forward direction at the coating station.

Gas propulsion preferably occurs in the forward direction, i.e. in the direction of movement of the substrate. Natural draft currents normally flow to the coating station 35 in the forward direction and ambient conditions B favorable to the formation of high quality coatings can be more easily achieved by propelling the current (s). ) of cleaning gas in the same direction.

In preferred embodiments of the invention, the stream of droplets is tilted downward and forward toward the substrate and the gas is also propelled forward.

Tests show that uniform coatings can be more easily formed if certain conditions are observed with regard to the distance between the face of the substrate to be coated and the source of the droplet current. Preferably this distance, normally measured at the face of the substrate, is 15 to 35 cm. This range of distance has been found to be the most suitable, particularly when observing the preferred inclination and divergence of the droplet current cited above.

The invention is very suitable for coating a continuous ribbon of flat glass moving from a flat glass forming installation. The invention includes methods in which the substrate is a continuous ribbon of float glass from a float tank.

In certain applications of the invention, the stream of droplets meets the upper face of a ribbon of flat glass 20 which has just been formed at a place where the temperature of the glass is between 650 ° and 100 "C.

The method according to the invention can be used to form different oxide coatings using a liquid composition containing a metal salt. The cleaning of the atmosphere on the surface of the surface of the substrate to be coated makes it possible to obtain good quality coatings from solutions which release reactive vapors. Very advantageous methods according to the invention include methods where the droplets are droplets of a metal chloride solution from which a coating of metal oxide is formed on the substrate. In some of these methods, the solution is a solution of tin chloride, for example an aqueous medium or not containing stannic chloride and a doping agent, for example a substance providing ions of antimony, arsenic or fluorine. The metal salt can be used in conjunction with a reducing agent, for example phenylhydrazine, formaldehyde, alcohols and non carbonaceous reducing agents such as hydroxyamine and hydrogen. Other tin salts can be used in place of or in conjunction with stannic chloride, for example stannous oxalate or stannous bromide. Examples of other metal oxide coatings which can be similarly formed include the oxides of cadmium, magnesium and tungsten. To form such coatings, the coating composition can be prepared in the same way by forming an aqueous or organic solution of a metal compound and a reducing agent.

; Nitrate solutions can be used, for example, iron and indium nitrates, to form corresponding metal oxide coatings. As other examples, the invention can be used to form pyrolysis coatings of metallic organo compounds, for example carbonyls and metal acetylacetonates provided in the form of droplets on the face of the substrate to be coated. Certain metal acetates and alcoholates can also be used, for example tin dibutyl diacetate and titanium isopropylate. Π is within the scope of the invention to apply a composition containing salts of different metals so as to form a coating containing a mixture of different metals or of different metallic compounds.

A coating formed by a method according to the invention may in certain circumstances have a surface which has local structural defects, for example a surface which is not smooth due to parasitic deposits. Such defects can be removed by surface treatment after the coating has been formed. For example, the surface of the coating can be subjected to an abrasion treatment.

The formation of surface parasitic deposits can be avoided or reduced by creating suction forces downstream of the coating area. For this reason, in certain embodiments of the invention, suction forces are exerted in at least one exhaust duct to continuously extract gases from the environment from the path of the stream of droplets in the same direction (front or rear) as that in which gas is propelled along the substrate through this path.

/ The suction forces are obviously controlled & 7 so as not to interrupt or appreciably disturb the stream of droplets. Such methods combine the implementation of the present invention and the invention which is the subject of British patent 1,523. 991.

The invention comprises a device for forming a coating of metal or metal compound on a hot glass substrate by a method according to the invention as described above. A device according to the invention comprises means for moving the hot substrate in a given direction (hereinafter referred to as "before") through a coating station and in this station, spraying means for discharging at the minus a stream of droplets on the moving substrate and is characterized in that it comprises a mechanism for driving the spraying means to cause the stream (s) of droplets to move repeatedly along a transverse path to the forward direction and in that it comprises means for propelling gas unidirectionally forwards or backwards so that this gas flows through this path out of alignment with the current (s) ( s) droplets.

A device according to the invention can include any additional characteristic (s) which may be necessary in order to use each or more of the different additional process characteristics described above.

Preferably, the spraying means are placed in a tunnel through which the hot substrate is moved by the said moving means. Preferably, the means for propelling gas remove the propelled gas from a source outside the tunnel.

In certain embodiments of the device, a fixed orifice or series of orifices extends transversely to the path of the substrate and the means for propelling gas intermittently propel gas through this or these (s) ) out of phase with the movements of the spraying means through the substrate.

"

In other devices according to the invention, one or more orifice (s) is (are) movable (s) transversely along the tape, in tandem with the source (s) of current (s) of J droplets and the means of propelling gas propel gas of J? 8 continuously through this (these) orifice (s). Preferably, the drive mechanism moves the spraying means back and forth transversely to the path of the substrate concomitantly with gas discharge orifices located on either side of them and in that the means for propelling the gas discharge gas alternately through these orifices so as to follow the passage of a stream of droplets through a given region along its transverse path by a flow of gas through this region .

10 On. gives preference to a device in which the spraying means are arranged for discharging the stream (s) of droplets on the substrate at a downward inclination and preferably under a downward and forward inclination.

Preferably, the spraying means discharge at least one stream of droplets so that the angle between the axis (s) of the stream (s) of droplets and the plane of the substrate during its movement is between 25® and 35®. Preferably the spraying means are constructed to discharge at least one stream of droplets which is a parallel stream or a stream which diverges from its source by an angle which is not greater than 30, as is quoted above. Preferably the means for propelling gas are arranged to propel it in the forward direction.

The invention comprises a device as described above installed in association with a flat glass forming installation, for example a float tank, for coating a glass ribbon from this installation. Advantageously, the spraying means are arranged so that at least one stream of droplets meets the upper face of the ribbon in an area where the temperature of the glass is between 650 "C and 100" C.

30 Some devices according to the invention include gas evacuation means comprising at least one evacuation duct placed so as to extract gases from the transverse path, in j the same direction (front or rear) along the substrate as that in which the gas propulsion means propel gas through this path.

j. Certain embodiments of the invention, chosen by way of example, are illustrated in the appended schematic drawings in which FIG. 1 is a cross-section in elevation of a part of a glass-making installation. dish comprising a coating device according to the invention; FIG. 2 is an identical view of an installation provided with a modified coating device; Figure 3 shows in plan a detail of the coating device shown in Figure 2; and FIG. 4 is a cross-section in elevation of part of another installation comprising a coating device according to the invention.

In FIG. 1, the coating device is placed in a tunnel or annealing gallery 1 having a vault 2 and a sole 3. A glass ribbon 4 is moved through the gallery from the forming section installation tape. The annealing gallery can for example be associated with a glass-window drawing machine of the Libbey-Owens type, or it can be associated with a float tank in which the glass ribbon is formed by the float process.

The glass ribbon 4 is supported by rollers 5 and moves through the gallery forwards, in the direction 20 indicated by the arrow 6. Above the path of the glass ribbon, there are movable refractory screens 7 and 8 which define between them a compartment in which a coating of metallic compound is formed on the upper face of the glass ribbon during its movement along the gallery.

At a coating station in this compartment, a sprayer 9 is mounted above the horizontal path of the glass ribbon. The sprayer is connected to a mechanism (not shown) which moves it back and forth along a horizontal path normal to the direction of movement of the ribbon. The vertical distance between the sprayer and the top of the glass ribbon is 15 to 35 cm. The sprayer is oriented so that the droplets are discharged into a stable conical jet which is tilted down and forward on the glass ribbon. The axis of the current has an average angle of inclination on the ribbon of between 25 and 35 °, the angle of the cone being 35. from 20th.

At a distance of the order of 10 to 30 cm downstream from the downstream limit 10 of the zone where the stream of droplets meets the glass ribbon, there is a discharge duct 11 which is connected to means ( not shown) to maintain suction forces in the duct. The duct extends transversely to the path of the ribbon and is provided with a nozzle 12 defining a gas inlet passage in the form of a slot. The inlet opening for the nozzle is 1 to 20 cm above the glass ribbon.

Suction forces are created continuously in the conduit 11 when the device is in operation and 10 cause gases to flow from the environment of the droplet stream forward, away from the droplet stream and from the vicinity of the meeting area and have them enter the conduit. The suction forces are adjusted so as not to disturb the stability of the droplet current. The application of these suction forces reduces the risk of parasitic surface deposits on the coating formed, as mentioned above.

In the particular embodiment of the device illustrated, a second discharge conduit 13 is arranged at a certain distance downstream from the conduit 11. The second conduit extracts gases which flow downstream beyond the conduit 11.

Vertically below the sprayer and at a distance of 1 to 2 cm from the glass ribbon is a gas discharge tube 14 which extends transversely to the path of the substrate. This tube has a series of small close discharge openings 25 distributed along its length, and placed so that gas supplying this pressurized tube is discharged through these openings forward and parallel to the glass ribbon. The discharge of gas, for example compressed hot air, through the tube 14 is done intermittently. Gas discharge occurs each time the sprayer reaches the end of a stroke transverse to the substrate. Therefore the; * gas streams act along the tunnel, out of alignment with the stream of droplets coming from the sprayer. The gas discharged j? i through the tube 14 flows forwards through the transverse path of the sprayer and falls under the influence of the suction forces in the evacuation ducts 11 and 13. The structure of the coating formed [/ sur the glass ribbon is therefore improved, the coating being! · 11 without internal veil.

In the modified coating device shown in Figures Z and 3, in which the same numbers as in Figure 1 are used to represent the same parts of the device, there is a fixed transverse guide 15 along which a carriage is mounted 16. The carriage is provided with rollers 17 which move along the wings of the guide. The carriage supports a vertical tube 18 inside which there are several conduits for compressed air and spray solution. The air and the solution are supplied by flexible conduits, one of which, designated by 19, is shown in FIG. 2. Separate streams of hot air and of solution supply the sprayer 20 via a bypass 21 of the tube 18. Other streams of hot air flow lower inside the tube 18 and lead to unloading tubes 22 and 23 provided with unloading nozzles 24 at their ends. The flexible supply conduits which supply compressed air to the passages inside the tube 18 which are connected to the tubes 22 and 23, are provided with control valves (not shown) which during the transverse movement of the carriage back and forth - operate in such a way that hot compressed air is unloaded from a source (not shown) alternately by the tubes 22 and 23.

As the carriage moves in the direction of arrow 25 in Figure 3, hot air is discharged through the tube 22, the discharge through the tube 23 being blocked. As the carriage moves in the opposite direction, - through the ribbon, hot air is discharged only through tube 23. Each region along the path of the stream of droplets through the glass ribbon is thus thus swept by a stream of gas moving in the downstream direction immediately after the stream of droplets has passed through this region. The gas currents created in the atmosphere surmounting the ribbon by the discharge tubes 22 and 23 do not disturb the trajectories of the droplets coming from the sprayer despite these currents sweeping the transverse path of the stream of droplets.

The coating devices shown in Figures 1, 2 and 3 can also be used without modification to coat a glass substrate as it travels through the coating station in the direction opposite to arrow 6. Good results can also be obtained in this way under certain circumstances, for example in an installation in which there are no strong natural draft currents flowing through the coating station in the direction of movement of the material. substrate. However, the quality of the coating which can be obtained by the process illustrated is generally better, particularly when thick coatings are formed.

The device shown in FIG. 4 corresponds to that of FIG. 1, except for the arrangement of the spraying means. In the device shown in Figure 4, the stream of droplets is discharged by a sprayer 26 which is oriented vertically to discharge the stream of droplets vertically onto the glass ribbon.

Following are examples of methods according to the invention carried out by means of devices as described above.

Example 1

A device as described with reference to FIG. 1 is used to coat a glass ribbon 3 meters wide during its production by a drawing process of the Libbey-Owens type, the speed of the ribbon being. around 1 meter / minute. The coating device is installed in a position such that the temperature of the glass at its zone of contact with the stream of droplets is of the order of 600 ° C.

The sprayer is a conventional type gun and operates at a pressure of the order of 4 kg / cm2. The sprayer is moved back and forth across the path of the ribbon, at a height of 30 cm above the glass ribbon, so as to make nine round trips per minute. The sprayer is oriented so that the axis of the spray is 30 ° on the plane of the glass ribbon.

The sprayer is supplied with an aqueous solution of tin chloride obtained by dissolving hydrated tin chloride (SnCl ^. 2H ^ O) in water and adding a small amount of NH HF.

i / 4 2 / The distribution rate of the coating solution

2nd

13 is adjusted to form an oxide coating on the glass ribbon

O

of tin doped with fluorine ions having a thickness of 7,500 A.

Hot compressed air is discharged by the tube 14 intermittently forward along the glass ribbon, in de-phasing with the back and forth movements of the sprayer, to accelerate by this means, the evacuation of vapors from the droplet stream path. The hot air is discharged for less than a second each time the sprayer reaches the end of its travel near a side edge of the glass ribbon.

10 The suction forces in the evacuation conduits 11 and 13 are adjusted to maintain a vacuum of the order of 100 mm of water in the suction nozzle of each of the conduits 11 and 13, including the nozzles are 20 cm above the glass ribbon.

It has been found that the tin oxide coating formed in this way is almost free from internal defects. In other words, the coating is substantially free from causes of internal light deflection resulting in diffuse light transmission. It is assumed that this is due to the fact that the residual vapors or the decomposition products are not trapped in the spray 20 sprayed in its successive passages over the ribbon.

Instead of equipping the tube 14 with a series of gas discharge ports spaced apart over its length, it may have a single discharge port in the form of a slot.

In a modification of the above process, the pulper 25 is moved at the rate of 6 cycles per minute and the flow of spray

O

rization is adjusted to form a coating of 10,000 A thick.

One can use methods as described above for example to coat a ribbon of float glass moving from the float tank.

In another application, the device shown in FIG. 1 is used to coat sheets of glass which are transported along a tunnel 1 in the direction opposite to arrow 6, all other conditions being identical to those of 'example 1 indicated above. It has been found that the propulsion of gas through the tube 14 is in this case also beneficial in reducing the appearance of internal defects in the coating.

14

Example 2

A device as described with reference to Figures 2 and 3 is used to coat a glass ribbon having at its meeting point with the droplets a temperature of the order of 580eC.

The sprayer is fed with a solution of the reaction product of anhydrous SnCl 4 with methanol. The concentration of the solution is adjusted by means of dimethylformamide after addition of HCl to stabilize the solution and of NH 4 HF 4 as doping agent.

The suction forces are adjusted to maintain a vacuum of the order of 100 mm of water in the suction nozzles of the discharge conduits 11 and 13. The distribution of the coating solution is adjusted so as to form on the glass ribbon

O

a coating of SnO 4 doped with fluorine ions having 7,200 A thickness.

A jet of hot compressed air is continuously discharged either through the tube 22 or through the tube 23 during each passage of the sprayer through the path of the ribbon during its reciprocating movement. During each passage of the sprayer the hot air is discharged by that of these tubes which is driven behind the sprayer. The path of the stream of droplets transverse to the annealing gallery is thereby cleaned before the next movement of the spray jet through the glass ribbon, thus avoiding trapping of vapors in the spray jet. Suction forces are maintained continuously in the conduits 11 and 13 as in Example 1.

As in Example 1, it was found that the coating of SnO 3 formed on the glass ribbon is practically free of internal haze.

In a modification of the preceding process, in which substantially identical results are obtained, the coating solution used is replaced by a solution obtained by reacting SnCl 4 with acetic anhydride in stoichiometric proportions, slowly stirring the liquid. very syrupy brown-

Inoir obtained, to allow the evacuation of HCl, by diluting the mixture with dimethylformamide and by adding a few cubic centimeters-35 of a commercial solution at 40% by volume of HF as L doping agent.

15

Example 3

A strip of float glass having a width of approximately 2.5 meters is coated during its movement from the float tank, at a speed of 4.5 meters per minute, by means of a device 5 as shown in the figure 1.

The sprayer is a conventional type gun and works at a pressure of the order of 3 kg / cm2. The sprayer is mounted 25 cm above the glass ribbon and is oriented on the plane of the ribbon at an inclination of 30 °. The sprayer is moved at 10 at 10 cycles per minute. The sprayer is supplied with a solution obtained by dissolving cobalt acetylacetonate Co (C ^ H ^ O ^) 2H ^ O in dimethylformamide. The sprayer is placed so that this solution meets the glass ribbon at a point along its path where the glass has a temperature of around 15 580eC.

The suction nozzle 12 of the discharge conduit 11 is placed 20 cm above the glass ribbon. The suction forces are adjusted so that a depression of the order of 50 mm of water is maintained in the suction nozzle. The exhaust duct 13 20 is not used.

The discharge rate of the coating solution is adjusted so as to form on the glass ribbon a coating of cobalt oxide (Co, 0.) Having a thickness of the order of O J 4 920 A.

Hot compressed air is discharged intermittently through the tube 14. The hot air is discharged for less than a second at the end of each crossing of the glass ribbon by the sprayer. The quantity of hot air emitted is adjusted so that it carries the residual vapors forward, during the trans-30 versai flow of the stream of droplets, towards the exhaust duct 11 in which “forces d are continuously maintained.

The coating formed on the glass ribbon has a brownish tint when viewed in transmission and shows no trace of internal haze. In other words, the coating is free from internal defects causing scattering of incident light.

- y = * · The above coating process can be implemented to form colored layers composed of a mixture of oxides by feeding the sprayer with a solution containing a mixture of compounds of different metals, for example compounds of metals selected from the group iron, cobalt, chromium and nickel, 5 or by using several sprayers and by feeding different sprayers simultaneously with different solutions. i

Claims (14)

17 1. A method of forming a coating of metal or metal compound on one face of a hot glass substrate during its movement in a given direction (hereinafter called "before") by bringing said face into contact, a coating station through which the substrate passes, with at least one stream of droplets comprising one or more substance (s) from which the coating of metal or metal compound is formed on said face, characterized in that the stream (s) of droplets is or are moved repeatedly along a path transverse to the substrate and in that gas is propelled unidirectionally forwards or rear across the transverse channel, out of alignment with the stream (s) of droplets. 2. Method according to claim 1, characterized in that the propelled gas is extracted from a source external to the normal atmosphere surmounting the substrate. 3. Method according to one of claims 1 or 2, characterized in that the gas propulsion occurs from one or more orifice (s) which is (are) stationary (s) and is carried out intermittently , adjusted in time with the movements of the droplet stream (s) along the transverse path so that the propellant gas does not meet the droplet stream (s). 4. Method according to one of claims 1 or 2, characterized in that the gas propulsion is carried out continuously from one or more orifice (s) which is (are) moved (s) through of the path of the substrate, in tandem with the source of the stream (s) of droplets. 5. Method according to claim 4, characterized in that at each displacement of the stream (s) of droplets through v of the substrate, gas is propelled from an unloading orifice which follows the source of the ( des) stream (s) of droplets in its displacement-30 so that the passage of or a stream of droplets through a given region along the path is followed by a flow of gas au- across this region. . 6. Method according to one of claims 1 to 5, ca- // 4L characterized in that at least one stream of droplets is inclined towards * V 18 downwards towards the substrate. 7. Method according to one of claims 1 to 6, characterized in that the stream (s) of droplets is (are) inclined downward and forward towards the substrate. 8. Method according to one of claims 1 to 7, characterized in that the gas propulsion occurs in the forward direction. 9. Method according to one of claims 1 to 8, * characterized in that the droplets are droplets of a solution of a metal salt, for example a metal chloride, from which a coating of metal oxide is formed on the face of the substrate. 10. Method according to one of claims 1 to 9, characterized in that suction forces are exerted in at least one exhaust duct to continuously extract gases from the environment from the path of the (the) stream (s) of droplets, in the same direction (front or rear) as that in which gas is propelled along the substrate through this path. 11. Device for forming a coating of metal or metal compound on a hot glass substrate, comprising means for moving the hot substrate in a given direction (hereinafter referred to as "before") through a coating and in this station, spray means for discharging at least one stream of droplets on the moving substrate, charac-25 terized in that it comprises a mechanism, driving spray means to move repeatedly the stream (s) of droplets along a path transverse to the front direction and in that it comprises means for propelling gas unidirectionally forward or backward so that gas flows 30 through this course out of alignment with the stream (s) of “droplets. 12. Device according to claim 11, characterized in that the spraying means are placed in a tunnel through which the hot substrate is displaced by said displacement means and in that the propelled gas comes from an external source. v / superior to the tunnel. 4 * 19 13. Device according to one of claims 11 or 12, characterized in that the drive mechanism moves the spraying means back and forth transversely to the path of the substrate concomitantly with gas discharge orifices 5 located on either side of these and in that the means for propelling the gas discharge gas alternately through these orifices so as to follow the passage of a stream of droplets through a given region along its transverse course by a flow of gas through this region. 14. Device according to one of claims 11 to 13, characterized in that it comprises gas evacuation means comprising at least one evacuation duct placed so as to extract gases from the transverse path, in the same direction (front or rear) along the substrate than that in which the means for propelling gas, propel gas through this path. b