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 to 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 various purposes, or as one of the layers of a multi-layer coating. For example, silicon oxide coatings can be used as sub-layers which are to be surmounted by other layers which can be of one or more different oxide (s) or other materials. such as metals, or as top layers deposited on top of 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 sodium. other coating, or whether by diffusion or by some other mechanism, in a top coating layer, during the formation of this top layer or over time. For example, it has been found that in the pyrolytic formation of a tin oxide coating from stannic chloride on a soda lime glass substrate, sodium chloride tends to incorporate. in 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 an underlayer or top layer of silicon oxide can also have a very advantageous effect in reducing inoppor25 tuns interference effects due to variations in temperature. total coating thickness.

The use of a silane, in particular of SiH₄, as a coating forming material is well known per se for forming pyrolytic coatings on glass. Silane decomposes at temperatures above 400 ° C. and silicon coatings can be formed. However, it is difficult to oxidize in situ such a silicon coating 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 the coating equipment, all of the 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 within a 5 coating chamber which is open on the substrate to be coated, at a location where these materials can contact the substrate directly. We have, however, found that this is not favorable for producing high quality and uniform 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 of pyrolytically forming a coating of silicon oxide on a hot glass substrate as it passes through a coating chamber by contacting, in the presence of oxygen, the substrate. with a coating-forming material 75 containing silane, characterized in that the coating-forming material containing vapor phase silane and oxygen gas 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 in obtaining a uniform coating across the width of the substrate. Surprisingly, the early mixing does not lead to a premature reaction of the coating-forming material as suggested by the teaching of the prior art, and it is in fact favorable to the production of high silicon oxide coatings. quality.

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 silicon oxide coating from a coating-forming material containing silane. It will also be appreciated 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 of coating forming material which is converted to the useful coating oxide is increased, and for a given tape feed rate it is possible, if desired, to form a thicker coating. Also for this reason, preferably, the coating-forming material first comes into contact with the glass when the latter has a temperature of at least 650.^sC. For many

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Uses, glass may have a temperature between 700 ° C and 750 ° C when it first comes into contact with the coating-forming material.

The invention can be used to form a coating of silicon oxide on pre-cut and heated glass sheets, if desired. However, when it is desired to make pyrolytically coated flat glass, it is preferable to proceed when the glass is freshly formed. Acting in this way provides economic advantages because it is not necessary to heat the glass for the pyrolysis reactions to occur, as well as advantages with regard to the quality of the coating, since it is ensured that the surface of the blank glass. Preferably, therefore, the mixture of oxygen and coating forming material is contacted 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 tape advances, and the tape 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 to produce coated glass. Such problems arise due to the temperature conditions which may be different to form a pyrolytic coating on the one hand and to anneal glass proper on the other hand, and due to space constraints available to have a heating 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 required. 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 often has to be established within an annealing gallery equipped with one or more coating station (s) when switching from coated glass to glass production. uncoated 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 a top face of a hot float glass substrate while the glass is in a tank.

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float chamber in which it is formed.

By operating in accordance with this preferred embodiment of the invention and forming the liner within the float chamber, the need to find a space for the liner station in or near the upstream end of the float chamber is avoided. the annealing gallery. Further, we have found 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 speed. temperature in an annealing gallery when the coating chamber is operated or stopped.

It is quite surprising to propose to form 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 the spreading of the glass and for its fire polishing, and therefore it is of universal practice. to maintain a reducing atmosphere inside the float chamber, because any surface impurity from 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 to infiltrate the float chamber. Much research has also been done on the removal of impurities which almost always form on the surface of the metal bath despite all precautions taken to avoid the entry of oxygen into the float chamber. It is therefore against the teaching of float glass production to deliberately maintain oxidizing conditions in the float chamber. However, we have found 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 containment 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 actual position chosen will depend on the temperature desired to initiate the coating.

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on the glass. Glass is removed from the float chamber to pass through 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 may in fact be located 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 one. temperature at least 50 ° C, and preferably at least 100 ° C, higher than the temperature at which the glass would leave the float chamber if no coating was formed therein. Adopting this preferred feature of the invention offers the advantage that there is a significant amount of time for the ribbon to regain waste heat 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 at the bottom. and in that the coating chamber is maintained under suction substantially around its entire periphery. This helps to prevent the escape of formative material from 20. coating and coating reaction products from the coating chamber to the surrounding space.

Preferably, said suction induces an incoming flow of ambient atmosphere substantially surrounding 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 stream of substantially inert carrier gas and oxygen is introduced into the stream of carrier gas. 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. Conveying the silane to the coating chamber in a stream of substantially inert carrier gas and then introducing oxygen into this stream of carrier gas allows selection of the point where

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oxygen must be introduced in order to achieve this control.

Advantageously, nitrogen is used as a substantially inert carrier gas. Nitrogen is sufficiently inert for the intended purpose, 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.

Coating-forming material and / or oxygen may suitably be introduced into the carrier gas stream by means of a venturi.

In preferred embodiments of the invention, turbulence is induced in the stream of carrier gas to ensure 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 constriction downstream of the immoducnon point of the. coating forming material. Such shrinkage can be asymmetric. Intimate mixing of the coating forming material in the carrier gas is provided by inducing turbulence.

For similar reasons, advantageously, turbulence is induced in the carrier gas stream after oxygen is introduced to provide an intimate mixture of silane-containing carrier gas and oxygen.

The rate at which the coating reagents are to be supplied depends to some extent on the desired thickness of the coating to be formed and the rate at which the substrate ishes over the coating chamber. Preferably. the silane as 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 between about 30nm and 240nm on a substrate at a speed of 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, the 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 about 30nm to

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240nm on a substrate going at a speed of 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 at 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 maintains the temperature of the coating reagents below that which ambient conditions would otherwise dictate, and further helps to reduce any tendency for premature reaction.

Advantageously, the coating-forming material contacts the glass via at least one slit which extends, or which extends together, over at least the major part of the width of the coating which is to be formed over. the vene. This facilitates the formation of a coating having a uniform thickness across 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 at the bottom, means for supplying into the coating chamber vapor phase coating forming material which is premixed with oxygen and means for aspirating out of the coating chamber the atmosphere containing products of the coating reaction and unused coating-forming material.

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

Such a device can be used to coat individual heated glass sheets if desired. Alternatively, as well as in certain preferred embodiments of the invention, the coating chamber is disposed within, 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 warming device.

However, it is generally preferred that said supporting means is a bath of molten metal in a float chamber, and that the coating chamber is disposed within 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 taken by the ribbon to pass from the coating station, further into in the float chamber and in the annealing gallery, the temperature profile of the coated tape can return to a state of equilibrium 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 does not have to take into account the differences between the production of glass when this coating station is operating or not. so that the temperature control inside the gallery can be greatly simplified. The advantage of simplifying the construction of an annealing gallery which is supplied with glass is even greater when it is desired to produce glass having a multilayer coating. because in the case of a pre-existing glass production facility there may simply be no room outside the float chamber for the desired number of coating stations without major rebuilding of the facility.

Advantageously, said coating chamber is delimited by the path of the substrate and a box open at the bottom, and there are suction means substantially around the entire periphery of the coating chamber. This helps to prevent the escape of unused coating reagents and coating reaction products which could adversely affect the device in the vicinity of the coating station.

Preferably, said suction means are adapted to maintain an inward flow of ambient atmospheric material 30 surrounding substantially the entire periphery of the coating chamber. This aids in preventing the escape of material from below the casing, and creates an air seal around the coating chamber. .

Advantageously, there are means for introducing the coating forming material into a carrier gas stream and then introducing oxygen into the carrier gas stream containing the forming 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 where the reacuffs are mixed before being delivered to the coating chamber. Feeding the silane to the coating chamber in a stream of substantially inert carrier gas and then introducing oxygen into this stream of carrier gas allows selection of the point where oxygen should be introduced in order to achieve this control. . .

. Preferably, at least one venturi is provided for introducing said coating-forming material and / or oxygen gas into the carrier gas stream. This is a very simple way of introducing the respective material into the carrier gas stream so that the introduced material is mixed with that 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 forming material. Turbulence can be induced, for example, by using a supply line having a constriction downstream of the point of introduction of the coating-forming material. Such shrinkage can be asymmetric.

Intimate mixing of the coating forming material in the carrier gas is provided by inducing turbulence.

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

Advantageously, there is, in order to introduce the coating-forming material into the coating chamber, at least one slot which extends, or which extends together, above at least the major part of the width of the chamber. coating. This facilitates the formation of a coating having a uniform thickness across the width of the substrate. 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 to the coating chamber. This maintains the temperature of the coating reagents at a level lower than that ambient conditions would otherwise dictate, and further helps to reduce any tendency for 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 accompanying schematic drawings in which:

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

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

Figure 3 is a schematic plan view of the coating device, and Figure 4 illustrates the supply of coating reagents to the coating chamber through a supply line.

In the drawings, a ribbon 1 of glass advances along a path also indicated at 1 while it is supported by a bath of molten metal 2 contained within a float chamber 3. A coating chamber is surrounded by a wall and a roof structure indicated as a whole at 4..

The coating station comprises a casing 5 which delimits a coating chamber 6 open downward above the tape path, a supply line 7 for supplying coating reagents into the coating chamber 6 and a chimney 8. to aspirate peripherally around the coating chamber.

The feed line 7 is supplied with a 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 stream. carrier gas to a first venturi 9. The carrier gas stream and dispersed forming material flow along the supply line 7 to a first constriction 10 which is arranged to impart turbulence to the carrier gas stream to ensure an intimate mixture of carrier gas. and entrained coating forming material. Further downstream, a second venturi 11 30 is arranged to introduce oxygen, for example as a constituent of air. Another turbulence inducing constriction 12 provides for the intimate mixing of oxygen and entrained coating forming material in the carrier gas stream. The coating reagents are supplied through the feed line 7 to a flow control block 13 provided with a loudness slit 14 which extends through most of the width of the vessel 5.

The coating-forming material and oxygen should be fed into the feed line outside of 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 sleeve 15 which is provided with a cooling water inlet 16 and an outlet 17, as shown figure 1. If desired, the cooling sheath can be extended inside the flow control block 13, as shown in phantom 18 in Figures 2 and 4, so that the reagents of coating are protected from overheating until they exit through slot 14 to contact tape 1 in coating chamber 6.

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

The casing 5, the coating chamber 6, and the flow control block 13 are surrounded by a peripheral passage 20 through which the products of the coating reaction and unused coating-forming material with, if any. desire, atmospheric matter sucked in and coming from the float chamber can be sucked upwards 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 liners are suitably made of flexible refractory curtains made for example of Refrasil (trade mark).

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 disposed at a location along the float chamber where the The glass is at a temperature of about 700 ° C. The feed line is supplied with nitrogen, and silane is introduced therein at 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 to exit from a slit of approximately 4 mm wide at a rate such that the conveyed material flows between the glass and the casing 5. , which is located 15mm above the path of lens 1. at a speed of about 2 to 3 meters per second in the two directions parallel to the direction of advance of the tape. The box 5 has a length in this direction of about 40cm. Atmospheric matter is sucked through the chimney 8 at a rate such that it generates an upward gas flow into

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the peripheral passage 20 with a speed of about 7 to 8 meters per second, and this causes a continuous inward flow of gas from the float chamber into 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 suction also extracts coating reaction products and unused coating reagents.

The coating formed consists of silicon dioxide approximately 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, a top coating of doped SnC> 2 is formed in a thickness of approximately 500nm. . The combined coating is substantially free from undesirable color variations due to interference effects.

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

EXAMPLE 2

In a specific practical embodiment, to coat float glass after leaving the float chamber, the coating station is disposed 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 SnO-, doped with a thickness of about 350nm. The box is approximately 1 meter long. Coating-forming reagents are introduced in the same proportions as in Example 1 in order to form a top layer of silicon dioxide about 100 nm thick. Again the combined coating is substantially free from undesirable color variations due to interference effects.