LU83192A1 - METHOD AND DEVICE FOR FORMING A COATING ON A HOT GLASS SUBSTRATE BY CONTACT OF THE SUBSTRATE WITH AN INCLINED REAGENT CURRENT WHOSE TEMPERATURE IS INFLUENCED BY A PREHEATED GAS CURRENT - Google Patents

Description

The present invention relates to a method of forming a coating of metal or metal compound on a face of a hot glass substrate during its movement in a given direction by bringing said face into contact, at a coating station. through which the substrate passes, 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 includes a device for implementing such a method.

Methods of the type mentioned above are used to form coatings which modify the apparent color of the glass and / or which have other properties required with respect to the incident radiation, for example a reflection property of the infrared.

When forming a coating on a moving glass substrate by spraying, there are problems of controlling the thickness of the coating to meet given standards. The thickness of the coating forming in any area of the substrate surface is likely to be influenced by various factors. These include the sprayed rate, the direction of the spray compared to the direction of movement of the substrate and the temperature conditions of this area when coated.

It is known to discharge the droplets in the form of a current which is inclined downwards towards the substrate and in the general direction of movement of the substrate. It has been found that this direction of the spray is most beneficial for promoting stable conditions in the area where the droplets meet the substrate. But obviously, the fact of directing in this way the sprayed jet cannot by itself ensure a deposit of given thickness in a given area born of the substrate, even if the flow of material through the sprayer is strictly controlled.

i i The temperature conditions under which any zone of the substrate is coated depend inter alia on the temperature of this zone of the substrate at the time of spraying. A relatively high substrate temperature implies a relatively thick coating. It has previously been proposed to control the temperature t * t 2 of the substrate so that each zone is at an appropriate temperature when it is exposed to spraying, but far from it these attempts have led to satisfactory results. Adjustments to the temperature of the substrate, and in particular its temperature profile cross-sectional to its course at the coating station, could not be made with sufficient speed and precision for the needs of industrial production. For similar reasons it has been found that it is not appropriate to exercise control of the coating thickness only by controlling the temperature of the reactive materials supplying the sprayer.

One of the objects of the invention is to provide a coating method of the type indicated in which the temperature conditions at the coating station are influenced so as to facilitate control of the thickness of the coating.

The present invention relates to a method of forming a coating of metal or metal compound on a face of a hot glass substrate during its movement in a 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 substance (s) from which the coating of metal or metal compound is formed on said face, characterized in that the stream (s) i of droplets is (are) inclined downwards towards the substrate in front or rear direction and in that at least one stream of gas i 25 preheated is introduced into the medium above the substrate in such a way that gas flows in the same direction (front or rear) I above the substrate and comes into contact with this (s) stream (s) of taste - | telettes, the temperature of this gas stream (s) being such that this stream (s) influence (s) the temperature of the droplets on their path to the substrate.

j; One or more gas stream (s) operating according to the invention can constitute a very appropriate and effective control parameter to influence the thickness of the coating. The thermal exchange | that between the gas stream (s) and the droplets of pulverized material is more efficient than the heat exchange between this material and the hot substrate. Because the sprayed material is in a finely divided state when it comes into contact with the gas stream (s) that (these) can (can) influence the temperature of the sprayed material so as to affect the thickness of the coating forming on the substrate notwithstanding the very short contact time between the sprayed material and the gas stream (s).

The efficiency of the gas stream (s) for the set purpose depends on the downward tilt of the droplet stream (s) and the flow of the gas stream (s) above the substrate in the same general direction as that in which the current (s) of; 10 droplets is (are) tilted downwards, that is to say in the same general direction as that of the horizontal component or of the main horizontal component of the movement of the droplets. Under these conditions, the gas stream (s) can act in the desired manner while maintaining the condition of stability of the spray. This condition of stability is itself important to avoid unpredictable variations in the thickness of the coating.

"The invention is based on the discovery of the significant influence on the thickness of the coating, which can result from the heating or cooling of droplets containing generative material of the coating. A change in the temperature of the droplets changes the amount of thermal energy that is exchanged between the substrate and the droplets upon contact with the substrate, to form a given amount of coating material from the compound (s) ) coating precursor (s) contained in the 25-droplet. This phenomenon can in some cases be attributed to the influence of the gas stream (s) on the evaporation and / or decomposition of matter contained in the droplets, depending on their composition. For example when spraying a solution of a reagent intended to form the coating, heating or cooling the droplets may promote or delay the evaporation of solvent from the droplets and / or the decomposition of the reagent. However, the invention is not limited to methods in which such an explanation of the in-fluence of the gas stream (s) on the thickness of the coating applies. Tests show that in certain coating methods the amount of material intended to form the coating on the hot vL glass substrate, from a given amount of sprayed material is influenced by a change in the temperature of the materials. sprayed droplets to an extent which cannot be justified by the loss from the droplets either of an amount of coating precursor reagent or of an amount of carrier liquid, for example a solvent, of this reagent.

In preferred embodiments of the invention, the gas constituting the stream (s) is preheated to a temperature such that it heats the droplets. In general, the principle of the invention can be applied more satisfactorily by this means 10 and is of greater practical value on the industrial plane for the production of coated glass.

Advantageously, the droplets comprise a solution of a metallic compound and the gas stream (s) accelerates (s) or delays (s) the evaporation of solvent from the droplets.

The gas stream (s) can (can) act over the entire width of the surface of the substrate to be coated or selectively over one or more zones (s) of this width. In addition, the current (s) can be used as a control measure to quickly change the thickness or thickness profile of the coating. More specifically, one or more streams of gas may intervene to influence the temperature of the sprayed material similarly at any point across the path of the substrate so that the thickness of the coating is affected by similarly in any area transverse to the coated surface. Alternatively, the gas stream (s) 25 can (can) intervene to influence the temperature of the sprayed material selectively or differently in one or more region (s) transverse to the path. Advantageously, this selective or differential action is such that it compensates for at least partial-! . Also any tendency for variations in the thickness of the coating due to other factors, for example a variation in temperature. ! erosion of the substrate from one region to another, in certain preferred embodiments of the invention, the method is used for coating a continuous ribbon of glass.

Flat moving from a flat glass forming installation, for example during its movement along a tunnel or a gallery (for example an annealing gallery) inside which (of 7? 5 which) is located the coating station and the gas stream (s) differentially affect the temperature of the droplets moving to different regions through the path of the tape so as to promote the formation of a coating which has a substantially uniform thickness over the entire width coated with the tape. Such methods are useful, for example, in forming a coating of substantially uniform thickness on a continuous ribbon of glass which has just been formed in a flat glass drawing machine or in a float tank, during its movement, the along a tunnel or gallery.

During displacement along a gallery as mentioned above, the lateral edges of the substrate, which are closer to the lateral limits of the gallery, tend to cool faster than the middle part of the width of the substrate. For this reason, the temperature of these marginal regions tends to be somewhat lower than that of the middle part, upon arrival at the coating station. In the absence of any measures compensating for these phenomena, these temperature gradients transverse to the substrate would usually tend to cause a reduction in the thickness of the coating 20 towards the lateral edges of the substrate. Some compensation can occur, in practice, by using a sprayer which moves back and forth transversely to the path of the substrate as will be described later, for example due to the deceleration of the sprayer near the ends of its course, but this compensation 25 is not in itself sufficient to obtain the standards of uniformity of coating thickness which are often required today. By modi-i differentially trusting the temperature of the droplets moving to different regions located across the path of the substrate, by applying the present invention, more satisfactory compensation can be obtained. The way in which the temperature | * the gas stream (s) varies across the path of the substrate in order to obtain the desired compensation depends on the composition of the droplets of the sprayed material. For example, when spraying droplets containing a coating generating compound which can be evaporated or decomposed by heating the droplets to decrease the content of this compound in the residual droplets at their

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6 arriving on the substrate, the droplets moving towards a central region of the path of the substrate through the gallery should be more heated, or less cooled, than the droplets moving towards the lateral edges of the path in order to compensate for the 5 temperature gradients through the substrate mentioned above. As another example, when spraying a compound generating the coating dissolved in a solvent which can be evaporated from the droplets to a degree which depends on the temperature of the environment through which the droplets pass, the droplets moving towards the regions 10 marginal of the path of the substrate, should be more heated, or less cooled, than the droplets moving towards the central region of the path in order to compensate for the temperature gradients through the substrate mentioned above. It will easily be seen that in certain methods, depending on the composition of the droplets, the effect on the thickness of the coating of a change in the temperature of the droplets cannot be susceptible of such a simplified analysis, for example because the gas stream (s) can (can) promote or delay the evaporation or decomposition of both a coating-forming compound and the carrier liquid. However, tests in which droplets of a given composition are used can easily establish the appropriate temperature profile to be created by the gas stream (s) through the gallery, at the pos -

Ite coating, to form a coating having a determined thickness profile.

When developing a coating device for implementing the invention, it is necessary to ensure that the droplets keep a sufficient weight to prevent them from being entrained outside the current (s) ) of droplets through the neck (s). rant (s) of gas controlling the temperature, so that the stream (s) of droplets is (are) maintained in condition of stability. This weight is obviously affected by any evaporation of substance (s) from the droplets during their movement. But in methods j in which the solvent contained in the drops is evaporated | By the gas stream (s), it has been found in some cases that it is beneficial to evaporate droplets of solvent as much as possible while respecting the conditions of current stability. It appeared that the quality of the coating was particularly good when the evaporation of solvent was completed at the time of or immediately after the contact of the droplets with the hot substrate.

If it is required during a coating process 5 according to the invention to vary the thickness of the coating in any given region through the substrate, from droplets whose temperature is influenced by one or more streams ( s) of gas, this requirement can be very easily satisfied by adjusting the temperature to which the gas is brought before its release into the atmosphere on the surface of the substrate. It is much easier to vary the temperature of the gas stream (s) than to vary the temperature of the glass substrate or the coating material feeding the sprayer.

The droplets can be discharged by one or more streams, the combined area or areas of contact with the substrate covering the entire width of the surface of the substrate to be coated. In this case, the source (s) of the current (s) can (can) be stationary. Preferably, however, the zone (s) of meeting of the stream (s) of droplets with the substrate covers (s) only part of the width of the substrate to be coated and this (s) stream (s) ) is (are) repeatedly moved back and forth transversely to the path of the substrate, through the coating station, so that the current (s) act (s) on all of the width of the surface of the substrate to be coated. Under these circumstances, the stream (s) of gas acting on the droplets according to the invention can (can) exert transverse to the path of the substrate, a differential thermal action on the droplets which takes account of any tendency that would have the amount of coating material deposited per unit area to be greater near the side edges of the substrate, due to the deceleration of the sprayer as it approaches the ends of its stroke.

The stream (s) of droplets should remain stable during the coating process. This is easier to achieve if the or each stream is exposed continuously (as opposed to intermittent exposure) to the action of one or more streams of temperature controlling gas. In preferred embodiments of the invention, the stream (s) of preheated gas is (are) unloaded continuously, and the or each stream of droplets is intercepted continuously over its entire width by one or more gas stream (s).

Preferably, one or more gas stream (s) 5 is (are) discharged from a stationary orifice or from a series of stationary orifices extending or distributed (s) transverse to the path of the substrate. This makes it much easier to achieve effective temperature control. If the stream (s) of the droplet is (are) discharged at the coating station along a path transverse to the substrate, and if one or more gas stream (s) is (are) discharged ( s) so that a quantity of gas flows through this path, out of alignment with the stream (s) of droplets, this gas can exert a useful cleaning effect by eliminating vapors from the transverse path of ( of) current (s) and avoid! 15 both their imprisonment in this (these) current (s). In these circumstances- | these, the method also uses the invention which is the subject of the patent application filed the same day by the Applicant entitled

"Method and device for forming a coating on a hot glass substrate by displacing a stream of reagent transversely to the substrate and propelling gas through the path of this stream.

Advantageously, gas streams are continuously discharged from a series of ports as described above and quantities of gas supplied to different ports or groups of ports are preheated to temperatures which are set independently to control the coating thickness profile across the substrate.

The invention includes methods in which the current (s) are subjected to preheating which is automatically controlled in response to signals from a coating thickness sensing device on the surface. moving substrate at a detection station located in front of the coating station. The thickness of the coating can for example be determined using the property of the coating to reflect a laser beam. Other methods for determining the thickness of the coating are, for example, those which measure the back scattering of the β rays or which measure the reflection or IL · - 9 the transmission of light rays by means of a spectrophotometer and methods using an X-ray fluorescence detector or based on interferometry techniques or using a scanning microscope.

The gas forming the temperature-controlling gas stream (s) is preferably air. However, other gases can be used, for example an inert gas such as nitrogen. Preferably, the or each stream of gas is directed towards the or a stream of droplets so as to meet this stream of droplets in an area spaced from the substrate, above the latter. The energy of the droplets decreases from their source towards the substrate and by directing the gas stream (s) towards the droplets before they reach their minimum energy, it is easier to avoid that droplets are entrained out of their desired path in the current. It should be noted that the closer the zone of action of the gas stream (s) is to the source of the droplet stream, the shorter the time during which the droplets are directly exposed to the stream (s) (s).

The implementation of the present invention may include the simultaneous use of the invention described and claimed in the patent application filed the same day by the Applicant 20 entitled "Method and device for forming a coating on a hot glass substrate by bringing the substrate into contact with an inclined reactant current to which a jet of gas is directed As described in the text filed in support of this request, making flow a gas jet 25 backward of a downward inclined stream of coating material droplets, (the rear being where the droplets have the shortest path), it is easier to form optical coatings without appearance of coating defects causing light scattering at the interface between the glass substrate and the coating or on the coating surface. This is believed to be due to the interception or dilution of products parasitic reaction which can be dragged down behind the stream of droplets and come into contact with the glass or the coating it carries. The action of a stream of temperature-controlling gas on a stream of droplets, which occurs using the present invention, can therefore have the side effect of improving the quality of the coating.

However, as has been established in our patent application of the same day, in order to obtain the best improvements in the quality of the coating cited therein, it is preferable that a back gas jet be directed towards the rear of the area where the stream of droplets meets the substrate so that the rear gas jet is deflected against the current. Such a preferred embodiment of the invention described in our patent application filed on the same day can be carried out simultaneously with the application of the present invention using one or more gas streams to influence the temperature of the droplets moving towards the substrate and projecting a gas jet (which should not be preheated) in a downward inclination towards the substrate behind the stream of droplets so that the jet is deflected by the substrate against the rear of this 15 current.

It is very advantageous to combine the heating of the droplet current controlled according to the invention with the control of the temperature of the substrate just before the coating operation.

Using the present invention, the stream (s) of droplets is (are) preferably tilted downward and forward. With this arrangement, it is easier to form coatings of uniform structure, particularly if the coatings are thick. Such a spraying direction is claimed in British patent 1,516,032.

Preferably the stream (s) of droplets is (are) inclined (s) so that the angle between the axis (s) of the stream (s) of droplets and the face of substrate to be coated is of the order of 20 * to 60th and preferably of the order of 25th to 35 *. This characteristic facilitates the formation of coatings of good optical quality.

130 For best results, all parts of the droplet stream (s) should meet the substrate at a substantial angle to the vertical. Therefore, in the preferred embodiments of the invention at least one stream of droplets is used which is a parallel stream or is a stream which from its source diverges from an angle which is not greater than 30e, by example an angle of about 20th.

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Tests show that uniform coatings can be more easily formed if certain conditions are observed with regard to the perpendicular distance between the substrate to be coated and the source of the stream (s) of droplets. Preferably this distance, normally measured at the face of the substrate, is 15 to 35 cm. This range of distances 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 strip of glass in continuous longitudinal movement.

The invention includes methods in which the substrate is a continuous ribbon of flat glass moving from a flat glass forming facility. In certain very advantageous embodiments, the ribbon is a float glass ribbon produced from a float tank. In some methods according to the invention, the stream of droplet (s) meets the upper face of the ribbon of flat glass at a place, downstream of the flat glass forming installation, where the temperature of the glass is between 650 * and 100 * C.

The process according to the invention can be used to form different oxide coatings using a liquid composition, for example a solution of a metal salt. 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 face of 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 antimony, arsenic or fluorine ions . Metal salt. It can be used in conjunction with a reducing agent, for example phenylhydrazine, formaldehyde, alcohols and non-carbonated reducing agents such as hydroxylamine, 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 metallic oxide coatings which can be similarly formed include cadnium, magnesium and tungsten oxides. 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. By way of other examples, the invention can be used to form coatings by pyrolysis of organometallic compounds, for example carbonyls, and metallic acetylacetonates supplied in the form of droplets to the face of the substrate to be coated. Certain metallic acetates and alcoholates can also be used, for example tin dibutyl diacetate and titanium isopropylate. It 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 oxides of different metals.

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

The formation of parasitic deposits can be avoided or reduced by using an exhaust duct to extract gases from the environment from the stream (s) of droplets. Therefore, in some embodiments of the invention, suction forces are exerted in at least one exhaust duct to extract gases from the environment from the stream (s) of droplets in the same - »me direction (front or rear) as that in which the gas stream (s) are introduced into the medium above the substrate. These for-I 30 these suction are obviously controlled so as not to interrupt or make unstable (s) stream (s) of droplets. Such methods combine the implementation of the present invention and the invention which is the subject of British Patent 1,523. 991 of the Applicant and they can also include the invention described and claimed in the patent application filed by the Applicant on the same day and entitled "Method and device for forming a coating 13 on a substrate of hot glass at a coating station located in a tunnel and comprising a gas exhaust duct which forms or is associated with a screen. "The invention includes a device for forming a coating of metal or metal compound on one face of a glass substrate during its movement through a coating station, by a method according to the invention, as described above. The device according to the invention comprises a support for the substrate, means for moving a substrate in a given direction (hereinafter referred to as "before") while it is carried by a support and means for spraying for discharging at least one stream of droplets on the substrate carried by the support, characterized in that the spraying means are arranged for discharging the stream (s) of droplets at a downward and forward tilt or downward and backward 15, and in that means for discharging gas are provided for introducing a stream (s) of preheated gas into the medium surmounting the substrate so that this (these) stream (s) flow) in the same direction (front or rear) above the substrate and come into contact with the stream (s) of droplets so as to influence the temperature of the droplets of this (s) current (s) on their path to the substrate.

Preferably, the means for discharging gas comprise a series of gas discharge orifices distributed transversely along the path of the substrate and means are provided for preheating the quantities of gas supplying the various orifices or groups of orifices at different temperatures. .

The invention includes a device as described above and comprising means for determining the thickness of the coating on the moving substrate and for emitting signals which automatically control the preheating of the gas supplied to the gas discharge port (s). These detection means determine, for example, the thickness of a coating by determining its property of reflecting a laser beam.

In certain devices according to the invention, there are means for controlling the temperature of the substrate just before it is placed.

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Preferably the spraying means are arranged to discharge the stream (s) of droplets downwards and forwards.

In a preferred device according to the invention, the spraying means 5 are associated with a drive mechanism which repeatedly moves the spraying means back and forth along a path transverse to the path of the substrate.

Preference is given to a device in which the spraying means are arranged for discharging a stream of droplets in a direction such that the angle between its axis and the horizontal is of the order of 20 * to 60th. Preferably, the spraying means are arranged to discharge a current of J droplets which is a parallel current or a current which diverges from its source by an angle which is not greater than 30e, as has been I 15 described above.

i J ^. The invention comprises a device as described above installed in association with an installation for forming flat glass, for example a float tank, for coating a continuous ribbon of glass from this installation. Advantageously, the spraying means 20 are arranged so that, in operation, at least one stream of droplets meets the upper face of the glass ribbon in an area where the temperature of the glass is between 650 ° and 100 ° C. Certain devices according to the invention include gas evacuation means for extracting gases from the environment 125 from the stream (s) of droplets in the same direction (front or rear) as that in which the means for discharging of gas introduce the gas stream (s) into the medium surmounting the substrate.

Reference is now made to the appended schematic drawing comprising FIG. 1 which is a section in elevation of part of a | 30 flat glass manufacturing installation comprising a device for

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clothing for the implementation of the invention.

| The drawing shows part of an annealing gallery if 1 having a refractory vault and sole 2 and 3, along which a newly formed glass ribbon 4, supported by rollers 5, is conveyed 135 the direction indicated by arrow 6, from a ribbon forming section (not shown) of the flat glass manufacturing plant. The tape can for example be formed by a stretching machine of the Libbey-Owens type, or it can be formed by the float process.

The glass ribbon passes below a refractory screen 5 to a coating station inside the gallery.

Above the coating station are fixed rails 15 which extend transversely to the top of the gallery and form a circuit for a carriage 16. The carriage has rollers 17 which move along the wings of the rails. The carriage carries a vertical tu-10 be 18 inside which there are conduits such as 19 supplying compressed air and a liquid coating material, for example a solution of a coating generating compound, to a sprayer 20 which is carried by the tube 18.

The drive mechanism (not shown) moves the carriage 16 back and forth along the rails 15 so that the sprayer 20 moves back and forth transversely to the path of the glass ribbon 4. The sprayer discharges the coating solution in the form of a stable spray cone 21. The coating-generating material is transformed in contact with the hot glass ribbon into the metal oxide or other desired coating substance with which the ribbon is gradually coated over its entire width during its movement through the gallery.

A line 22 crosses the roof of the gallery, behind the rails 15 and brings preheated gas inside the gallery, to heat the spray stream 21 according to the invention. Line 22 comprises a single conduit of flat and elongated section which extends substantially over the entire width of the gallery, or it can comprise a plurality of conduits arranged one beside the other through the gallery. The lower portion 23 of the pipeline is arranged substantially horizontally and at a level such that the stream (s) of preheated gas leaving the discharge port (s) 24 of the pipeline and represented by the dashed lines 25, intersect (s) the spray jet 21 at a median region of the trajectories of the droplets during the movement of the jet back and forth across the path of the substrate.

The gas stream (s) can be preheated to a temperature.

ΐ '' ή i j 16 ture higher or lower than the ambient temperature of the coating station so that the current (s) reheat (s) or cool) the droplets during their movement towards the glass ribbon. It is preferable that the line 22 has a plurality of conduits side-by-side as described above and that there are heating means, for example electrical resistors, for heating independently to different temperatures the volumes of. . gases distributed by the various conduits. It is then possible to modify the temperatures of the droplets of the spray cone 21 to I ‘.10 a degree which varies during each given crossing of the glass ribbon.

I * In this way it is possible to compensate for any remaining inequalities in glass temperature over the width of the ribbon and the accelerations and decelerations of the sprayer during each crossing of the glass ribbon by the spray cone, in order to form a coating of thickness substantially uniform over this width.

* j | The gas discharged through the line 22 outside the spray jet 21 flows forward transversely to the transverse path of this jet and cooperates in keeping this path free of vapors which may otherwise be trapped in the spray jet 20 and have a detrimental effect on the quality of the coating, as described in the patent application filed the same day by the Applicant and entitled "Method and device for forming a coating on a hot glass substrate by displacement of a current of reagent transverse to the substrate and gas propulsion through the path of this current, already mentioned above.

The gas discharge rate preheated by the orifice (s) 24 is such that the spray cone 21 is not interrupted by the gas jets. The droplet trajectories are not significantly affected.

30 At places spaced forwards vis-à-vis the transverse course of the sprayer above the ribbon are discharge ducts 26 which extend through the gallery and

Are connected to means (not shown) for maintaining suction forces in these conduits. The object of this evacuation system 35 is to extract, towards the front, from the reciprocating path of the sprayer, gases surrounding the sprayed jet and to bring them into the pi - 17 inlet orifices 27 of the discharge conduits, as suggested by the broken lines 28, and in this way reduce the risk of parasitic surface deposits on the coating formed. The suction forces are adjusted so that the trajectories of the droplets 5 from the sprayer are substantially unaffected and the method is therefore in accordance with the invention described and claimed in British patent 1,523,991 cited above. before.

In addition to their influence on the temperature of the spray droplets, the streams of preheated gas coming from the pipe. 10 tion 22 intercept or dilute certain reaction products which can contaminate the environment at the rear of the spray jet and can be fed down and come into contact with the glass immediately before it is coated with the spray jet 21. This action, which is described and claimed in the aforementioned patent application filed on the same day by the Applicant and entitled "Method and device for forming a coating on a hot glass substrate by contacting the substrate with an inclined reactant stream vers. ... on which a gas jet is directed, can however be better achieved by propelling gas streams against the glass ribbon immediately behind the areas of contact with the sprayed jet so that these streams reach the rear region of the spray cone. The illustrated device can be modified by providing the line 22 with branch nozzles 29, as shown in internal lines. errored, so that a certain amount of the preheated gas supplied by the line 22 forms back streams of gas acting in this way.

The following are examples of methods according to the invention carried out using devices as described above.

Example 1 A coating device as described with reference to FIG. 1 is used to coat a 3-meter-wide glass ribbon during its movement along an annealing gallery, from a Libbey-Owens type glass drawing machine. The speed of the glass ribbon along the gallery is 1 meter / minute. The average temperature of the glass ribbon at the vJ coating station is about 600 ° C. The temperature of the marginal zones of the glass is considerably lower than that of the central part of the width of the ribbon.

The sprayer 20 is a pistol of a conventional type and operates at a pressure of the order of 4 kg / cm2. The sprayer is moved back and forth across the ribbon path at a height of 30 cm above the glass ribbon, so as to make it new (round trip per minute along a course extending just beyond each lateral end of the ribbon. The sprayer is directed so that the axis of the spray is 30 ° on the plane of the glass ribbon. The angle of the spray cone is 20th .

The sprayer is supplied with an aqueous solution of tin chloride at 25 ° C, this solution being formed by dissolving hydrated tin chloride (SnCl ^ H ^ O) in water at the rate of 1375 g. of tin chloride per liter and by addition per liter of 55 gr.

15 of NH.HF ,.

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The distribution rate of the coating solution | is adjusted to form on the glass ribbon a tin oxide coating doped with fluorine ions and having a thickness as close as

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possible from 7,500 A.

The suction forces in the exhaust duct are adjusted to maintain a continuous flow of gases extracted from the atmosphere surrounding the path of the spray cone, as arrows 28 suggest, without interrupting the spray cone.

Line 22 has ten conduits arranged side by side covering equal portions of tape width. The axes of the terminal discharge portions 23 of the conduits are 15 cm above the upper face of the glass ribbon and the discharge orifices 24 are at a horizontal distance of 25 cm from the path followed by the rear of the spray cone. moving. Preheated air 30 is supplied to the pipeline at a temperature such that an air stream is discharged from each orifice 24 at a temperature of the order of 600 ° C. Hot air is supplied to the pipeline at a flow rate d of around 1,800 m3 / h. to maintain at each of the ten conduits a jet 25 having a speed of 2 m / sec.

The preheating temperatures of the volumes of gas Y & supplied to the ten conduits can be independently adjusted in steps of 19 ° C. and the temperatures of the different volumes are independently adjusted to values such that the coating formed on the tape has a substantially uniform thickness over the whole. of the width of the tape, despite the temperature gradients across the tape by the time it reaches the coating station. The thickness of the coating at different locations through the tape is continuously detected at a location inside the gallery downstream of the evacuation conduits 26, by means of a laser beam and a response detector. v in the reflection of the laser beam; the signals emitted by the detector 10 are used automatically to control the temperatures of the gas jets. In the resulting product, the thickness of the coating at all o o the positions through the tape is 7.500 A + 200 A.

In a comparative test, in which the method was applied without using jets of preheated gas but under otherwise unchanged conditions, it was found that the coating formed on the substrate is thinner on the marginal portions of the tape than at its central portion. Variation in coating thickness

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compared to the desired value of 7.500 A cannot be reduced below +500 A.

By preheating the gas supplied to line 22 to lower temperatures, for example at temperatures of the order of 120 ° C., the rate of evaporation of the solvent can be reduced, which leads to thinner coatings.

In a variant of the method according to Example 1, a pipe 22 provided with bypass nozzles 29 was used, by which a quantity of preheated gas is discharged in the form of downward-inclined jets which meet the glass ribbon just at the back of the spray cone path and flows down the spray cone during its movement through the substrate. A comparison of glass coated under these conditions with glass coated in the absence of the influence of these rear jets of gas inclined downwards shows that these jets are beneficial in preventing or reducing the appearance of light scattering defects. at the glass-coating interface.

A coating method according to the invention can be! executed using the device shown in Figure 1, as well as i 20 I above, with the only modification that the glass ribbon moves! in the direction opposite to arrow 6. Under these circumstances, the stream of droplets is directed downward and backward in the direction provided in this description.

5 Example 2 The device shown in Figure 1 is used to coat a ribbon of float glass, 2.5 meters wide, with cobalt oxide during the movement of the ribbon along an annealing gallery at a speed of 4.5 m / min. The sprayer is supplied with a solution at 25 ° C. obtained by dissolving cobalt acetylacetonate

CoiCj-H ^ O ^ ZH ^ O in dimethyl formamide at a rate of 140 gr. acetylacetonate per liter of solvent. The sprayer is directed on the plane of the glass ribbon at an angle of 30 ° and is placed 25 cm above the ribbon and at a place in the gallery such that the droplets of sprayed solution meet the glass ribbon at a place where the glass has an average temperature of around 580eC. The sprayer is moved back and forth at the rate of 10 complete I cycles per minute. The discharge rate of the coating solution is adjusted to form on the glass a coating of oxide of

O

20 cobalt (COjO ^) having a thickness as close as possible to 920 A.

. Line 22 has ten conduits side by side I having their discharge orifices 24 located below the path of the sprayer and 10 cm above the glass ribbon. Hot air preheated to 350 ° C. is supplied by this pipe 22 at a flow rate of 1,500 m3 / h. to form side-by-side air currents 25 having a speed of 2 m / sec. The air flow temperatures can be individually adjusted in 20eC steps and the regulation is carried out according to signals from a coating thickness detector such as that of example 1, in order to maintain the thickness! 30 seur of the coating as uniform as possible over the width of the ru ban. We found that we can form a coating that has a thickness

Q O

from 920 A + 50 A over the entire width of the glass ribbon. In a comparative test in which the spray jet is not heated by gas streams, but which otherwise uses the same conditions, it has been found that it is impossible to obtain a coating having such uniformity. .

21

By heating the air supplied to line 22 to lower temperatures, for example at temperatures of the order of 150 ° C., adjustable in steps of 10 ° C., the rate of evaporation of dime-thylformamide from the droplets and the rate of decomposition 5-acetyl acetonate can be reduced, which leads to thinner coatings.

The preceding coating methods can be used 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 chosen from the group of iron. , cobalt, chromium and nickel, or by using several sprayers and by feeding the different sprayers simultaneously with different solutions.

Λ

Claims (15)

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, at a coating station 5 through which the substrate passes, 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, characterized in that the taste stream (s) are inclined downward towards the substrate in the forward or backward direction and in that at least one stream of preheated gas is introduced into the medium surmounting the substrate in such a way that gas flows in the same direction (front or rear) above the substrate and comes into contact with this stream (s) of droplets, the temperature of this stream (s) (s) of gas being such that this (s) current (s) 15 influence (s) the temperature of go utlets on their path to the substrate, Z. Method according to claim 1, characterized in that the gas constituting the stream (s) is preheated to a temperature such that it heats the droplets. 3. Method according to one of claims 1 or 2, ca characterized in that the gas stream (s) influence (s) the temperature of the droplets selectively or differently in one or more regions through the path of the substrate so as to at least partially compensate for any tendency for variations in coating thickness caused by other factors. 4. Method according to claim 3, characterized in that the substrate is a continuous ribbon of flat glass moving from a flat glass forming installation and in that the gas stream (s) affect differentially the temperature of the droplets moving to different regions across the path of the tape so as to promote the formation of a coating which has a substantially uniform thickness over the entire coated width / width of the tape. 5. Method according to one of claims 1 to 4, char- A- 23 characterized in that the droplets comprise a solution of a metallic compound and that the gas stream (s) accelerate or delay evaporation solvent for the droplets. 6. Method according to one of claims 1 to 5, characterized in that the stream (s) of preheated gas is (are) discharged ^) continuously and that the or each stream of droplets is intercepted continuously over its entire width by one or more gas stream (s). 7. Method according to one of claims 1 to 6, characterized in that one or more stream (s) of preheated gas is (are) discharged continuously from a stationary orifice or a series stationary orifices extending or distributed (s) transversely to the path of the substrate. 8. Method according to claim 7, characterized in that streams of preheated gas are discharged continuously from such a series of orifices and in that quantities of gas supplied to different orifices or groups of ports are preheated to temperatures which are independently controlled to control the coating thickness profile across the substrate. 9. Method according to one of claims 1 to 8, characterized in that the preheating of the gas forming the gas stream (s) is controlled automatically in response to signals emitted by a device for detecting the thickness of the coating on the moving substrate 25 at a detection station located in front of the coating station. 10. Method according to one of claims 1 to 9, characterized in that the or each stream of gas is directed towards the or a stream of droplets so as to meet this stream of taste- * · 30 telettes in an area spaced from the substrate, on top of it. 11. Method according to one of claims 1 to 10, 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 substrate. 12. Method according to one of claims 1 to 11, charac- terized in that des'forces of suction are exerted in at I * 24 minus a discharge conduit for extracting gases from the environment of (des ) stream (s) of droplets in the same direction (front or rear) as that in which the stream (s) of gas are introduced into the medium surmounting the substrate. 13. Device for forming a coating of metal or metal decomposed on one face of a glass substrate during its movement through a coating station, comprising a support for the substrate, means for moving a substrate in a given direction (hereinafter referred to as "before") while it is carried by a support and spraying means for discharging at least one stream of droplets onto the substrate carried by the support, characterized in that the spraying means are arranged for discharging the stream (s) of droplets at a downward and forward or downward and backward tilt, and in that means for discharging gas are designed to introduce a layer (s) of preheated gas into the medium surmounting the substrate so that this (these) current (s) flows (s) in the same direction (front or rear) above the substrate and come into contact with the stream (s) of droplets so as to influence the temperature of the droplets of this current (s) on their path to the substrate. 14. Device according to claim 13, characterized in that the means for discharging gas comprise a series of gas discharge orifices distributed transversely over the course of the substrate and in that means are provided for preheating to different temperatures the quantities of gas supplying the various orifices or groups of orifices. 15. Device according to one of claims 13 or 14, characterized in that it comprises means for determining the thickness of the coating on the moving substrate and for emitting signals which automatically control the preheating of the gas. 16. Device according to one of claims 13 to 15, 1 characterized in that it comprises means for evacuating gas to extract gases from the environment from (the) stream (s) of droplets 35 in the same direction (front or rear) than that in which the // means of discharging gas introduce the gas stream (s) into "25 * the medium surmounting the substrate. 1 4 <,