Method of and apparatus for pyrolytically forming an oxide coating on a hot glass substrate

Method and device for pyrolytically forming an oxide coating on a hot glass substrate.

The present invention relates to a method and a device for pyrolytically forming a coating of silicon oxide on a hot glass substrate.

The present invention is the result of research relating to various problems associated with the pyrolytic formation of silicon oxide coatings on glass. Silicon oxide coatings can be used as single coatings on glass for different purposes, or as one of the layers of a multi-layer coating. For example, silicon oxide coatings can be used as sublayers which must be topped with other layers which can be of one or more different oxide (s) or other materials such as as metals, or as top layers deposited over one or more sublayers. The presence of a coating of silicon oxide on soda-lime glass has the particular advantage of inhibiting the migration of sodium ions from the glass, whether by leaching in the case of a sheet devoid of other coating, or whether by diffusion or by any other mechanism, in an upper coating layer, during the formation of this upper layer or over time. For example, it has been found that in the pyrolytic formation of a coating of tin oxide from stannic chloride on a soda-lime glass substrate, sodium chloride tends to be incorporated into the coating as a reaction product of glass with the coating forming material or its reaction products, and this causes haze in the coating. The presence of a sublayer or an upper layer of silicon oxide can also have a very advantageous effect by reducing undesirable interference effects due to variations in the thickness of the total coating.

The use of a silane, in particular of SiH 2, as a coating-forming material is well known per se for forming pyrolytic coatings on glass. The silane decomposes at temperatures above 400 ° C, and silicon coatings can be formed. However, it is difficult to oxidize such a silicon coating in situ to form a silicon oxide coating. For this reason, it is preferable to react the silane directly with oxygen. In order for this reaction to occur to deposit silicon oxide on the glass substrate rather than on any part of

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coating equipment, all known proposals for using a silane-containing coating forming material in forming a silicon oxide coating have insisted that the coating forming material can mix with oxygen only at the interior of a coating chamber which is open on the substrate to be coated, at a place where these materials can contact the substrate directly. We have found, however, that this is not favorable for producing high quality and uniform quality silicon oxide coatings, and in particular, problems arise in obtaining a coating of uniform thickness across the width of the substrate.

One of the objects of the present invention is to reduce these problems.

The present invention relates to a method for pyrolytically forming a coating of silicon oxide on a hot glass substrate while it passes through a coating chamber by bringing the substrate into contact, in the presence of oxygen. with a coating forming material containing silane, characterized in that the coating forming material containing vapor phase silane and gaseous oxygen are thoroughly mixed before entering the coating chamber and coming into contact with the substrate.

A method according to the present invention, due to the early mixing of the coating reagents, is very advantageous for obtaining a uniform coating across the width of the substrate. Surprisingly, early mixing does not lead to a premature reaction of the coating forming material as suggested by prior art teaching, and it is in fact favorable to the production of high quality silicon oxide coatings .

Preferably, the substrate reaches the coating chamber at a temperature of at least 400 ° C. Such temperatures are very suitable for the rapid formation of a coating of silicon oxide from a coating forming material containing silane. It will also be noted that in general, the higher the temperature of the glass during the formation of the coating, the faster the coating reaction, so that the efficiency of the coating operation, i.e. the proportion coating form material which is converted into useful coating oxide, is increased, and for a given speed of advancement of the tape, it is possible, if desired, to form a thicker coating. Also for this reason, preferably, the coating-forming material comes into contact with the glass for the first time when the latter has a temperature of at least 650 ° C. For many

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uses, glass can have a temperature between 700 ° C and 750 ° C when it comes into contact with the coating forming material for the first time.

The invention can be used to form a silicon oxide coating on pre-cut and reheated glass sheets, if desired. However, when it is desired to manufacture pyrolytically coated flat glass, it is preferable to proceed when the glass is freshly formed. Acting in this manner provides economic advantages because it is not necessary to reheat the glass for the pyrolysis reactions to occur, as well as advantages with regard to the quality of the coating, since it is assured that the surface of the virgin glass. Therefore, preferably, the mixture of oxygen and coating forming material is brought into contact with an upper face of a hot glass substrate made of freshly formed flat glass.

The coating chamber may for example be located in or near the upstream end of an annealing gallery through which the ribbon advances, and the ribbon may be formed in a drawing machine or in a float chamber.

However, it has been found that certain problems arise when converting a gallery previously used for annealing uncoated glass to form a gallery and a coating station for producing coated glass. Such problems arise due to the temperature conditions which may be different for forming a pyrolytic coating on the one hand and for strictly speaking annealing the glass on the other hand, and due to constraints of space available for having a filling station. coating. The problem is more complex if it is desired to form a multi-layer coating, when obviously two or more coating stations would be necessary. In addition, the coating reactions have a cooling effect on the glass; not only is the glass cooled everywhere, but also, the coated surface tends to be cooled more than the uncoated surface: therefore a different temperature regime must often be established inside an annealing gallery equipped with one or more coating stations when switching from the production of coated glass to that of non-coated glass. coated and vice versa, and sometimes even when there is a substantial change in the thickness of the coating applied to the glass.

In order to reduce these problems, preferably, the mixture of oxygen and coating forming material is contacted with an upper face of a hot float glass substrate while the glass is in a

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float chamber in which it is formed.

By operating according to this preferred embodiment of the invention and by forming the coating inside the float chamber, the need to find a space for the coating station is avoided in or near the upstream end of the annealing gallery. Furthermore, we have discovered that it is possible to ensure that the temperature of the glass ribbon leaving the float chamber is substantially unchanged, whether the ribbon is coated or not, and therefore there is no need to change the regime. temperature in an annealing gallery when the coating chamber is operated or when its operation is stopped.

It is quite surprising to propose forming an oxide coating inside a float chamber. The float chambers contain a bath of molten metal, consisting entirely or mainly of tin, which is fairly easily oxidizable at the temperatures necessary for spreading the glass and for polishing it with fire, and therefore it is universal practice to maintain a reducing atmosphere inside the float chamber, because any surface impurity of the metal bath entrained by the ribbon of glass ribbon would be a source of defects in the glass produced. Typically, such an atmosphere contains about 95% nitrogen and about 5% oxygen and is maintained under a slight overpressure to prevent oxygen from the ambient atmosphere from entering the float chamber. Much research has also been carried out on the removal of impurities which almost always form on the surface of the metal bath despite all the precautions taken to avoid the penetration of oxygen into the float chamber. It therefore goes against the teaching relating to the production of float glass to deliberately maintain oxidizing conditions in the floating chamber. However, we have discovered that it is possible to create oxidizing conditions inside a float chamber without causing the expected problems. We believe this is due at least in part to the fact that the coating forming material is contacted with said face in a coating chamber. The use of a coating chamber facilitates the confinement of the oxidizing conditions, the coating-forming material, and the products of the coating reaction, so that their effect on the metal bath in the float chamber can be rendered low or negligible.

The coating can be formed anywhere along the float chamber downstream from where the tape has reached its final width, and the effective position chosen will depend on the desired temperature to initiate the coating.

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on the glass. The glass is extracted from the float chamber to pass into the annealing gallery at a temperature which is usually between 570 ° C and 670 ° C. Ribbon temperatures above 570 ° C are per se suitable for pyrolytic coating reactions to occur, so that the coating chamber can in fact be arranged very close to the outlet of the float chamber. Preferably, however, the coating forming material contacts the glass at a location along the float chamber such that the glass has a temperature of at least 50 ° C higher, and preferably at least 100 ° C, at the temperature at which the glass would leave the float chamber if no coating was formed there. The adoption of this preferred feature of the invention offers the advantage that there is a long period of time for the tape to regain the heat lost during the coating reactions so that, when it leaves the float chamber , its temperature is not substantially affected by the coating operation.

Advantageously, the coating-forming material comes into contact with the glass in a said coating chamber, which is delimited by the path of the substrate and a box open downwards, and in that the coating chamber is maintained under suction substantially around of its entire periphery. This helps to avoid the escape of coating formative material and coating reaction products from the coating chamber to the surrounding space.

Preferably, said suction induces an incoming flow of ambient atmosphere surrounding substantially the entire periphery of the coating chamber. This creates a pneumatic seal between the oxidizing conditions inside the coating chamber and the ambient atmosphere.

In preferred embodiments of the invention, silane as a coating forming material is supplied to the coating chamber in the vapor phase in a substantially inert carrier gas stream and oxygen is introduced into the carrier gas stream containing silane before it enters the coating chamber. While it is essential when operating according to the invention that the oxygen and the coating forming material are thoroughly mixed before entering the float chamber, it is also advantageous to be able to control the period of time during which these reagents are mixed before entering the coating chamber. The routing of the silane to the coating chamber in a substantially inert carrier gas stream and the subsequent introduction of oxygen into this carrier gas stream allows the selection of the point where

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oxygen must be introduced in order to obtain this control.

Advantageously, nitrogen is used as the substantially inert carrier gas. Nitrogen is sufficiently inert for the purpose pursued, and it is inexpensive compared to noble gases.

The necessary oxygen can be introduced in the form of pure oxygen, but this unnecessarily increases costs and, preferably, air is supplied to the carrier gas stream to introduce oxygen therein.

The coating forming material and / or oxygen can suitably be introduced into the carrier gas stream by means of a venturi.

In preferred embodiments of the invention, turbulence is induced in the carrier gas stream to provide intimate mixing of the substantially inert carrier gas and the silane. A certain amount of turbulence can be induced if a venturi is used, as mentioned above, but it can be increased for example by the use of a supply line having a narrowing downstream of the point of introduction of the coating formative material. Such a narrowing can be asymmetrical. Intimate mixing of the coating formative material in the carrier gas is provided by inducing turbulence.

For similar reasons, advantageously, turbulence is induced in the carrier gas stream after oxygen has been introduced into it to ensure an intimate mixture of carrier gas containing silane and oxygen.

The rate at which coating reagents are to be supplied depends to some extent on the desired thickness of the coating to be formed and the speed at which the substrate passes through the coating chamber. Preferably, the silane as a coating-forming material is introduced into the coating chamber with a partial pressure of between 0.1% and 1.5%. A concentration within these limits is suitable for forming coatings of between approximately 30nm and 240nm on a substrate going at a speed up to 20 meters per minute.

Advantageously, to produce coated glass which moves at a speed of less than about 10 meters per minute, the silane as coating forming material is introduced into the coating chamber with a partial pressure of between 0.1% and 0, 4%.

Preferably, oxygen is introduced into the coating chamber with a partial pressure of between 0.6% and 20%. A concentration within these limits is also suitable for forming coatings of around 30nm at

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240nm on a substrate going at a speed up to 20 meters per minute.

To produce coated glass which moves at a speed of less than about 10 meters per minute, it is advantageous that oxygen is introduced into the coating chamber with a partial pressure of between 0.6% and 6.5%.

Preferably, measures are taken to limit the transfer of heat energy to the coating forming material during its movement towards the glass. This keeps the temperature of the coating reagents lower than that which ambient conditions would otherwise dictate, and further contributes to reducing any tendency for a premature reaction.

Advantageously, the coating-forming material comes into contact with the glass via at least one slit which extends, or which extends together, above at least most of the width of the coating which is to be formed on glass. This facilitates the formation of a coating having a uniform thickness over the width of the glass substrate.

The invention extends to a device for pyrolytically forming a silicon oxide coating on an upper face of a hot glass substrate, characterized in that it comprises support means for conveying the substrate along a path which passes through a coating chamber delimited by the path of the substrate and a box open downwards, means for supplying into the coating chamber vapor-forming coating material which is premixed with oxygen and means for sucking out of the coating chamber the atmosphere containing products of the coating reaction and unused coating formative material.

Such a device can be constructed very simply in order to obtain an early mixing of the gaseous oxygen and the coating formative material before they reach the coating chamber. We have discovered that this early mixing of the coating reagents in the vapor phase in turn offers significant advantages in obtaining a uniform coating across the width of the substrate. Surprisingly, early mixing does not lead to a premature reaction of the coating formant as might be expected, and it is in fact favorable to the production of high quality coatings.

Such a device can be used to coat individual heated glass sheets if desired. Alternatively, as in certain preferred embodiments of the invention, the coating chamber is arranged inside, or upstream, of a horizontal annealing gallery

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fed with freshly formed glass ribbon. This has the advantage of avoiding the need for a heating device.

However, it is generally preferred that said support means is a bath of molten metal in a float chamber, and that the coating chamber is arranged inside the float chamber.

Such a device has the advantage of simplifying the construction of an annealing gallery supplied with glass coming from the float chamber. The reason is that during the time it takes for the tape to pass from the coating station, further into the float chamber and the annealing gallery, the temperature profile of the coated tape can return to an equilibrium state which will have been disturbed by the heat extracted during the coating deposition process. Therefore, a device for regulating the temperature inside the annealing gallery must not take into account the differences between the production of glass when this coating station is operating or not, so that the temperature control at the interior of the gallery can be greatly simplified. The advantage of simplifying the construction of an annealing gallery which is supplied with glass is even more important when it is desired to produce glass having a multi-layer coating, because in the case of a production plant for pre-existing glass, there may simply be no space outside the float chamber for the desired number of coating stations without major reconstruction of the installation.

Advantageously, said coating chamber is delimited by the path of the substrate and a box open downwards, and there are suction means substantially around the entire periphery of the coating chamber. This helps to avoid the escape of unused coating reagents and coating reaction products which could have an adverse effect on the device in the vicinity of the coating station.

Preferably, said suction means are adapted to maintain an inward flow of ambient atmospheric material surrounding substantially the entire periphery of the coating chamber. This facilitates the prevention of material escaping from below the box, and creates a pneumatic seal around the coating chamber.

Advantageously, there are means for introducing the coating formative material into a stream of carrier gas and then introducing oxygen into the carrier gas stream containing formative material before entering the coating chamber. Although desirable when proceeding according to the first aspect of the present invention, and even

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essential when proceeding according to the second aspect of the invention, to provide means for mixing the oxygen and the coating forming silane before they enter the coating chamber, it is also advantageous to be able to control the period of time during which reagents are mixed before being delivered to the coating chamber. The routing of the silane to the coating chamber in a substantially inert carrier gas stream and the subsequent introduction of oxygen into this carrier gas stream allows the selection of the point where the oxygen must be introduced in order to obtain this control. .

Preferably, at least one venturi is provided to introduce said coating forming material and / or gaseous oxygen into the carrier gas stream. This is a very simple way to introduce the respective material into the carrier gas stream in such a way that the introduced material is mixed with this gas stream.

In preferred embodiments of the invention, there are means for inducing turbulence in the carrier gas stream to ensure intimate mixing of the carrier gas and the coating formative material. Turbulence can be induced for example by using a supply line having a narrowing downstream of the point of introduction of the coating formative material. Such a narrowing can be asymmetrical. An intimate mixture of coating formative material in the carrier gas is ensured by inducing turbulence.

For similar reasons, advantageously, there are means for inducing turbulence in the stream of carrier gas after oxygen has been introduced into it to ensure an intimate mixture of carrier gas containing the formant material and oxygen.

Advantageously, there is, for introducing the coating-forming material into the coating chamber, at least one slot which extends, or which extends together, above at least most of the width of the chamber. coating. This facilitates the formation of a coating having a uniform thickness over the width of the substrate. Π for example, there may be a single slot in the center of the box, perpendicular to the path of the substrate.

Preferably, there are means for limiting the transfer of heat energy to the coating forming material during its movement towards the coating chamber. This keeps the temperature of the coating reagents lower than that which ambient conditions would otherwise dictate, and further contributes to reducing any tendency for a premature reaction.

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A preferred embodiment of the invention will now be described in more detail, by way of example and with reference to the appended schematic drawings in which:

Figure 1 is a cross-sectional view of a coating device according to the invention, arranged in a float chamber.

FIG. 2 is a longitudinal section of the coating device of FIG. 1.

FIG. 3 is a schematic plan view of the coating device, and

FIG. 4 illustrates the supply of coating reagents to the coating chamber by means of a supply line.

In the drawings, a ribbon 1 of glass advances along a path also indicated in 1 while it is supported by a bath of molten metal 2 contained inside a float chamber 3. A coating chamber is surrounded by a wall and a roof structure indicated as a whole by

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The coating station comprises a box 5 which delimits a coating chamber 6 open downwards above the path of the tape, a supply line 7 for bringing coating reagents into the coating chamber 6 and a chimney 8 for vacuum peripherally around the coating chamber.

The supply line 7 is supplied with substantially inert carrier gas such as nitrogen from a source which is not shown, and the coating-forming material such as silane is introduced into the gas stream carrier to a first venturi 9. The carrier gas stream and the dispersed formatter flow along the supply line 7 to a first constriction 10 which is arranged to impart turbulence to the carrier gas stream to provide an intimate mixture of carrier gas and entrained coating formative material. Further downstream, a second venturi 11 is arranged to introduce oxygen, for example as a constituent of air. Another turbulence-inducing shrinkage 12 provides for the intimate mixing of the oxygen and the coating-forming material entrained in the carrier gas stream. The coating reagents are brought via the supply line 7 to a flow control block 13 provided with an outlet slot 14 which extends through most of the width of the box 5.

The coating formative material and oxygen should be brought into the supply line outside the float chamber 3. To all

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the places inside the float chamber 3, the supply line is surrounded by a cooling sheath 15 which is provided with a cooling water inlet 16 and an outlet 17, as shown Figure 1. If desired, the cooling jacket can be extended inside the flow control block 13, as shown at 18 in dashed lines in Figures 2 and 4, so that the coating reagents are protected against overheating until they come out through the slot 14 to come into contact with the tape 1 in the coating chamber 6.

As shown in Figure 2, the box 5 and the flow control block 13 should be suspended from the roof of the float chamber by means of rods 19. It is desirable to use threaded rods 19 so as to ability to adjust the height of the base of the box 5 to obtain a small gap, for example 2cm or less, from the path of the tape 1.

The housing 5, the coating chamber 6, and the flow control block 13 are surrounded by a peripheral passage 20 via which the products of the coating reaction and unused coating formative material with, if desired , atmospheric material sucked inside and coming from the float chamber, can be sucked up through the chimney 8. The box 5 and the walls of the coating chamber 4 are shown provided with peripheral skirts 21 at the base of the peripheral passage

20. These shirts are suitably made up of flexible refractory curtains made for example of Refrasil (commercial brand).

EXAMPLE 1

In a specific practical embodiment, for coating float glass advancing at a speed of 7 meters per minute along a float chamber, the coating station is arranged at a location along the float chamber where the glass is at a temperature of about 700 ° C. The supply line is supplied with nitrogen, and silane is introduced into it under a partial pressure of 0.25%, and oxygen is introduced under a partial pressure of 0.5% (ratio 0.5). The coating-forming material in its carrier gas is conveyed along the supply line 7 out of a slit about 4mm wide at a rate such that the conveyed material flows between the glass and the box 5 , which is located 15mm above the path of the glass 1, at a speed of approximately 2 to 3 meters per second in the two directions parallel to the direction of advancement of the ribbon. The box 5 has a length in this direction of about 40cm. Atmospheric material is sucked through the chimney 8 at a rate such that it generates an upward gas flow in

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the peripheral passage 20 with a speed of approximately 7 to 8 meters per second, and this causes a continuous inward flow of gas coming from the float chamber in the base of the passage 20 around the entire periphery of the coating chamber 6, which prevents the escape of coating reagents or their reaction products to the float chamber. Obviously, such aspiration also extracts unused coating reaction products and coating reagents.

The coating formed consists of silicon dioxide about 90nm thick. In a subsequent coating step, carried out in a manner known per se in a coating chamber arranged near the upstream end of a horizontal annealing gallery, an upper coating of doped SnC 4 is formed in a thickness of approximately 500 nm. The combined coating is substantially free of undesirable color variations due to interference effects.

In alternative embodiments of the second aspect only of the present invention, the coating station shown in the drawings is arranged in an annealing gallery. In the description of the drawings, for this reason, the references to the float chamber can be replaced by references to an annealing gallery, and the references to the molten metal bath can be replaced by references to conveyor rollers.

EXAMPLE 2

In a specific practical embodiment, for coating float glass after it leaves the float chamber, the coating station is arranged in an annealing gallery where the glass is at a temperature of about 500 ° C., downstream of 'another coating chamber to form a layer of doped SnC> 2 with a thickness of about 350nm. The box has a length of about 1 meter. Coating forming reagents are introduced in the same proportions as in Example 1 in order to form an upper layer of silicon dioxide about 100 nm thick. Again the combined coating is substantially free of unwanted color variations due to interference effects.