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

(54) METHOD AND APPARATUS FOR PYROLYTICALLY FORMING OXID COATING ON A HOT GLASS SUBSTRATE (57) A method of pyrolytically forming a silicon dioxide layer on a hot glass substrate while passing through a coating chamber comprises contacting the substrate with a silane-containing coating precursor material in the presence of oxygen , The silane-containing coating precursor material is in the vapor phase and it and gaseous oxygen are intimately mixed prior to entering the coating chamber to contact the backing. Silane as a coating precursor material can be passed to the coating chamber in vapor phase in a substantially inert carrier gas stream, and oxygen is introduced into the silane-containing carrier gas stream before entering the coating chamber.

The coating process may take place within a coating chamber in a float chamber in which the glass is formed into a ribbon. The coating chamber may be bounded by the tape path and a downwardly opening hood, and it may be vacuumed to substantially its entire circumference.

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The invention relates to a method and apparatus for pyrolytically forming a silica coating on top of a hot glass substrate.

The invention is based on the study of various problems associated with the pyrolytic formation of silica coatings on glass. Silica coatings can be used either as a single coating on glass for various purposes or as a layer of a multilayer coating. For example, silica coatings can be used as sub-layers overcoated with other coatings consisting of one or more different oxides or other materials, such as metals, or as a coating layer deposited on top of one or more such sub-layers. The presence of a silica coating on soda-lime glass has the particularly beneficial effect of preventing the migration of sodium ions, whether by leaching in the case of a disc with no further coating, or by diffusion or otherwise, into an upper coating layer, either during the formation thereof upper layer or over the course of time inhibited. By way of example, it has been found that in the pyrolytic formation of a stannic chloride tin oxide coating on a soda lime glass substrate, sodium chloride tends to be incorporated into the coating as a result of reacting the glass with the precursor material of the coating or its reaction products a haze in the coating. The presence of the silica underlayer or overcoat may also have a very beneficial effect in reducing undesirable interference effects due to changes in the thickness of the overall coating.

The use of a silane, particularly SiFU, as a coating precursor material is well known in the art for the formation of pyrolytic coatings on glass. 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 silica coating. For this reason, it is preferred to react the silane directly with oxygen. In order for this reaction to proceed with deposition of silica on the glass substrate, rather than in any part of the coating apparatus, all known proposals for using a silane-containing coating precursor material in forming a silica coating require that the coating precursor material be mixed only with oxygen in a coating chamber suitable for the to be coated is open at one point, where these materials can contact the pad directly freely. However, it has been found that this is not favorable for the preparation of high and uniform grade silica coatings and that, in particular, there are problems in obtaining a coating of uniform thickness across the entire width of the substrate.

It is an object of the invention to solve these problems.

According to the invention, there is provided a process for pyrolytically forming a silica coating on a hot glass substrate as it passes through a coating chamber into which the substrate is contacted with silane-containing coating precursor material in the presence of oxygen, characterized in that the silane-containing coating precursor material is incorporated in the vapor phase and gaseous oxygen are intimately mixed, before entering the coating chamber for contact with the substrate.

A method according to the invention offers great advantages for achieving a uniform coating across the width of the substrate due to the early mixing of the coating reagents. Surprisingly, early mixing does not result in premature reaction of the coating precursor material, as one would expect from the prior art, but is indeed favorable for producing high quality silica coatings.

Preferably, the pad reaches the coating chamber at a temperature of at least 400 ° C. It is known that such temperatures are very suitable for the rapid formation of a silicon dioxide coating from a silane-containing coating precursor. It should also be noted that, as a general rule, the higher the temperature of the glass during the film formation, the faster the coating reaction takes place, so that the coating yield, that is the proportion of coating precursor material converted to a useful coating oxide, is increased, and for a given belt advance speed it is possible, if desired, to achieve a thicker coating. For this reason, it is also preferred that the coating precursor material contacts the glass for the first time when the glass has a temperature of at least 650 ° C. For many purposes, the glass may have a temperature of between 700 "C and 750 ° C when first contacting the coating precursor material.

The invention may serve to form a silicon dioxide coating on pre-cut and reheated glass sheets, if necessary. However, if one wishes to produce pyrolytically coated flat glass, it is best to do so on the freshly formed glass. Has to do this

AT 403 909 B, there is no need to reheat the glass for draining the pyrolytic reactions, and it is also beneficial to the quality of the coating, since it ensures that the surface of the glass is in a fresh state. Preferably, therefore, such a premix of the oxygen and coating precursor material is brought into contact with the upper side of a hot glass substrate consisting of a freshly formed flat glass.

For example, the coating chamber may be in or near the upstream end of a cooling path, eg, a channel cooling furnace, through which the belt passes, and the belt may be formed in either a drawing machine or a float chamber.

However, it has been found that certain problems arise when using a cooling line previously used to cool uncoated glass as the cooling line and coating station for the production of coated glass. Such problems arise as a result of the possible different temperature conditions to form a pyrolytic coating on the one hand and for proper cooling of the glass on the other hand, and as a result of limitations on the available space for the placement of a coating station. The problem is compounded when one wants to form a multilayer coating where two or more different coating stations are required. Moreover, the coating reactions have a cooling effect on the glass, not only cooling the glass as a whole, but the coated surface also tends to be cooled more than the uncoated surface. Thus, it is often necessary to set up a different temperature program in a cooling line equipped with one or more coating stations, switching from the production of coated glass to uncoated glass and back again, and sometimes even when there is a substantial change in thickness the glass applied coating is made.

To facilitate these problems, it is most preferred that such premix of the oxygen and coating precursor material be brought into contact with a top of a hot float glass base while the glass is in a float chamber in which it is made.

By operating according to this preferred embodiment of the invention and forming the coating within the float chamber, the need to find space for the coating station in or near the upstream end of a cooling path is avoided. From this it has been found that it is possible to ensure that the temperature of the glass ribbon leaving the float chamber is virtually unaffected, whether the strip is coated or not, and accordingly there is no need to change the temperature program in the cooling path, when putting the coating chamber into operation or out of service.

It is quite surprising to suggest forming an oxide coating within a float chamber. Float chambers contain a bath of molten metal which consists entirely or mainly of tin, which is quite easily oxidizable at the temperatures required for spreading the glass ribbon and for its fire polishing, and accordingly it is common practice to have a reducing in the float chamber Atmosphere, since any surface contaminants that are absorbed by the glass ribbon from the surface of the metal bath, a source of defects in the glass produced. Typically, such an atmosphere contains about 95% by volume of nitrogen and about 5% by volume of hydrogen and is maintained at a slight overpressure to prevent oxygen from entering the float chamber from ambient temperature. Much research has been done to To avoid impurities that almost always form on the surface of the metal bath, despite all the precautions that are taken to prevent the access of oxygen in the Fioatkammer. It is therefore contrary to all knowledge about the production of float glass, intentionally maintain oxidizing conditions in the float chamber. It has been found, however, that it is possible to produce oxidizing conditions within a float chamber without causing the expected problems. It is believed that this is at least partially due to the fact that this coating precursor material in a coating chamber is brought into contact with this side of glass. The use of a coating chamber facilitates confinement of the oxidizing conditions, the coating precursor material and the coating reaction products so that their effect on the metal bath in the float chamber can be made small or negligible.

The coating may be formed anywhere along the float chamber downstream of where the tape has reached its final width, and the actual location chosen will depend on the temperature one wants to initiate the coating of the glass. The glass is removed from the float chamber for onward flow to the cooling path at a temperature usually in the range of 570'C to 650'C. Strip temperatures above 570 ° C. are suitable from the outset for the passage of pyrolytic coating reactions, so that the coating station can actually be arranged quite close to the exit of the float chamber. Preferably, however, that contacts

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Coating precursor material deposits the glass at a location along the float chamber such that the glass has a temperature that is at least 50 ° C and preferably at least 100 ° C higher than the temperature at which the glass would exit the float chamber if no coating was formed thereon would. The choice of this preferred feature of the invention provides the advantage of leaving ample time for the strip to recover heat released during the coating reactions, so that as it exits the float chamber, its temperature is virtually unaffected by the coating operation.

Advantageously, the coating precursor material contacts the glass within such a coating chamber, the chamber being bounded by the path of the backing and a downwardly opening hood and the coating chamber being evacuated by substantially its entire circumference. This helps to prevent leakage of unused coating precursor and reaction products of the coating from the coating chamber into the surrounding space.

Preferably, such an exhaust induces an inwardly directed stream of ambient atmosphere which surrounds virtually the entire circumference of the coating chamber. This creates a pneumatic seal between the oxidizing conditions in the coating chamber and the ambient atmosphere.

In preferred embodiments of the invention, silane coating precursor material is fed to the coating chamber in vapor phase in a substantially inert carrier gas stream and oxygen is introduced into the silane-containing carrier gas stream prior to entering the coating chamber. While it is essential in operation according to the invention that oxygen and the coating precursor silane be intimately mixed prior to entering the coating chamber, it is also an advantage to be able to control the length of time for which these reagents are mixed before being fed to the coating chamber. The promotion of the silane to the coating chamber in a substantially inert carrier gas stream and then the introduction of oxygen into this carrier gas stream allows the choice of the location where the oxygen is to be introduced to achieve this control.

Advantageously, nitrogen is used as a substantially inert carrier gas. Nitrogen is sufficiently inert for the purposes here to be considered, and it is cheap to compare it to noble gases.

The required oxygen may be introduced as pure oxygen, but this unnecessarily increases the cost, and preferably, air is supplied to the carrier gas stream to introduce the oxygen.

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

In preferred embodiments, turbulence is induced in the carrier gas stream to ensure intimate mixing of the substantially inert carrier gas and silane. A certain amount of turbulence is generated when using a venturi as mentioned above, but it can be increased, for example, by using a feedline having a throat downstream of the coating precursor introduction site. Such a narrowing can also be asymmetric. The intimate mixing of the precursor into the carrier gas is ensured by the generation of turbulence.

For similar reasons, it is advantageous to cause turbulence in the carrier gas stream after introduction of oxygen therein to ensure intimate mixing of the silane-containing carrier gas and oxygen.

The rate at which the coating reagents are to be added depends to some extent on the desired thickness of the coating to be formed and on the rate at which the support passes through the coating chamber. Preferably, silane is introduced as a coating precursor into the coating chamber at a partial pressure of between 0.1% and 1.5%. A concentration in this range is suitable for forming coatings of from about 30 nm to about 240 nm on a pad running at up to 20 m / min.

Advantageously, for the production of coated glass running at a rate of less than 10 m / min, silane as a coating precursor material is introduced into the coating chamber at a partial pressure of between 0.1% and 0.4%.

Preferably, oxygen is introduced into the coating chamber at a partial pressure of between 0.6% and 20%. Concentration within this range is again useful for forming coatings of from about 30 nm to about 240 nm on a pad running at up to 20 m / min.

For the production of coated glass running at a rate of less than about 10 m / min, it is advantageous for oxygen to be 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 thermal energy to the coating precursor material as it is fed to the glass. This maintains the temperature of the

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Coating reagents at a lower level than the ambient conditions would otherwise dictate and further aids in reducing any tendency for premature reaction.

Advantageously, in a manner known per se, coating precursor material is fed so as to contact the glass via at least one slot which extends together over at least the major part of the width of the coating to be formed on the glass. This facilitates the formation of a uniform thickness coating across the width of the glass substrate.

The invention extends to an apparatus for pyrolytically forming an oxide coating on top of a hot glass substrate having support means for transporting the substrate along a path through a coating chamber bounded by the path of the substrate and a downwardly opening hood. A method for supplying coating precursor material in vapor phase to the coating chamber and means for the extraction of atmosphere, including coating reaction products and unconsumed precursor material from the coating chamber, characterized in that the apparatus comprises means for introducing the coating precursor material into a carrier gas stream and for the subsequent introduction of oxygen in the carrier gas stream containing the precursor material, before it enters the coating chamber has.

Such a device may be constructed very simply to effect the premixing of the gaseous oxygen and coating precursor material before they reach the coating chamber. In turn, it has been found that this early mixing of the vapor phase coating reagents brings about a very beneficial effect in achieving a uniform coating across the width of the substrate. Surprisingly, early mixing does not result in the premature reaction of the coating precursor material that would be expected and, in fact, is favorable for producing high quality coatings. Namely, in this way, the period of time for which these reagents are mixed can be controlled before being supplied to the coating chamber. The promotion 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 allow the choice of the location where the oxygen is introduced to achieve this control.

If desired, such a device may be used to coat individual reheated glass sheets. Alternatively, as is the case with some preferred embodiments of the invention, this coating station is located within or upstream of a horizontal cooling path which is supplied with glass from a glass ribbon forming machine. This has the advantage of avoiding the need for a reheating device.

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

Such a device has the advantage of simplifying the construction of a cooling track which is supplied with glass from the float chamber. This is because, during the time required for the glass ribbon to travel from the coating station farther along the float chamber and into the cooling path, the temperature profile of the coated ribbon may return to an equilibrium state that has been disturbed by the heat released during the time actual coating process was deducted. Accordingly, the device for adjusting the temperature in the cooling path does not have to compensate for differences that arise between the production of glass when the coating station is in operation or out of service, so that the temperature control in the cooling path can be greatly simplified. The advantage of the simplified construction of a cooling track which is supplied with the glass is even greater if one wants to produce glass which has a multilayer coating which, in the case of an existing glass-producing plant outside the float chamber, simply has no room for the required number of Coating stations can be without subjecting this system to a major conversion.

Advantageously, this coating chamber is delimited by the path of the backing and a downstream opening hood, and suction means are provided around virtually the entire circumference of the coating chamber. This helps to prevent the leakage of unused coating reagents and coating reaction products that could have a detrimental effect on the device near the coating station.

Preferably, these suction means are adjusted to cause an inward flow of ambient atmospheric material surrounding virtually the entire circumference of the coating chamber. This facilitates avoidance of material leakage from underneath the hood and creates a pneumatic seal around the coating chamber.

Preferably, at least one venturi is provided for introducing at least one of these materials, coating precursor material and gaseous oxygen into the carrier gas stream. This is a very simple way of introducing the respective material into a carrier gas stream in

AT 403 909 B such that the introduced material is mixed with this gas stream.

In preferred embodiments, means are provided for generating turbulence in the carrier gas stream to ensure intimate mixing of the carrier gas and the coating precursor material. For example, turbulence may be generated by use of a delivery conduit having a restriction downstream of the coating precursor introduction site. Such a narrowing can be asymmetric. The intimate mixing of the precursor into the carrier gas is ensured by the generation of turbulence.

For similar reasons, it is advantageous that means be provided for generating turbulence in the carrier gas stream after the introduction of oxygen to ensure intimate mixing of the carrier gas contained in the precursor and the oxygen.

Advantageously, for the introduction of the coating precursor material into the coating chamber, at least one slot is provided which extends or extends together over at least the greater part of the width of the coating chamber. This facilitates the formation of a coating of uniform thickness across the width of the pad. For example, a single slot in the center of the hood may be provided perpendicular to the path of the pad.

Preferably, means are provided to limit the transfer of thermal energy to the coating precursor material as it is fed to the coating chamber. This maintains the temperature of the coating reagents at a low level than otherwise dictated by environmental conditions and further aids in reducing any tendency for premature reaction.

A preferred embodiment of the invention will now be described in more detail by way of example with reference to the accompanying schematic drawing.

FIG. 1 is a cross-sectional view across the width of a coating apparatus according to the invention arranged in a float chamber;

FIG. 2 is a longitudinal section of the coating apparatus of FIG. 1;

Figure 3 is a schematic plan view of the coating apparatus, and

Figure 4 shows the supply of coating reagents to a supply line for the supply of the coating station.

In the drawing, a band 1 of glass is guided along a path which is also designated 1, while it is supported by a bath of molten metal 2 contained in a float chamber 3. A coating station is surrounded by a wall and roof structure, indicated generally at 4.

The coating station 4 comprises a hood 5 delimiting a coating chamber 6 which opens downwardly on the path of the belt 1, a supply conduit for the supply of coating reagents to the coating chamber 6 and a chimney 8 for the peripheral suction around the coating chamber.

The feed line 7 is supplied with a substantially inert carrier gas, such as nitrogen, from a source, not shown, and the coating precursor material, such as silane, is introduced into the carrier gas stream at a first venturi 9. The carrier gas stream with coating precursor dispersed therein flows along the supply line 7 to a first throat 10 which is installed to create turbulence in the carrier gas stream and to ensure intimate mixing of the carrier gas and the entrained coating precursor material. Further downstream, a second air funnel 11 is provided for the introduction of oxygen, for example as part of air. Another turbulence-generating restriction 12 ensures intimate mixing of the oxygen and the entrained coating precursor material in the carrier gas stream. The coating reagents are fed through the supply line 7 to a flow control block 13 having an exit slot 14 which extends over the major part of the width of the hood 5.

It is expedient to supply coating precursor material and oxygen to the supply line 7 outside the float chamber 3. At all parts within the float chamber 3, the supply line is surrounded by a cooling jacket 15 equipped with a cooling water inlet 16 and outlet 17 as shown in FIG. If desired, the cooling jacket may also extend into the flow control block 13, as indicated by 18 in FIG. 2 and 4, so that the coating reagents are protected against overheating until they exit the slot 14 for contact with the belt 1 in the coating chamber 6.

As shown in Fig. 2, hood 5 and flow control block 13 are suitably suspended on the roof of the float chamber 3 by struts 19. It is convenient to use threaded struts 19, so that the height of the bottom of the hood 5 can be adjusted to small distances, for example 2 cm or less, from the path of the belt 1.

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The hood 5, the coating chamber 6 and the flow control block 13 are of a

Circumferential passage 20 surrounded by which coating reaction products and unused coating precursor material together with optionally inwardly sucked material of the ambient atmosphere of the float chamber can be sucked up through the chimney 8. The hood 5 and the wall structure 4 of the coating station are shown as being provided with possibly existing, circumferentially extending skirts 21 at the bottom of the peripheral passage 20. These aprons are expediently made of flexible fireproof curtains, eg Refrasil (trademark).

EXAMPLE 1

In a specific practical embodiment for the coating of float glass, which with a

At a rate of 7 m / min through a float chamber, the coating station is located at a location along the float chamber where the glass is at a temperature of about 700 ° C. The feed line is fed with nitrogen and silane is introduced at a partial pressure of 0.25% and oxygen at a partial pressure of 0.5% (ratio 0.5). The coating precursor material and its carrier gas are passed through the supply conduit 7 and exit through a slot about 4 mm wide at such a rate that the material supplied is between the glass and the hood 5, which is about 15 mm above the path 1 of the glass , flows at a speed of about 2 to 3 m / sec in both directions parallel to the direction of tape advancement. The hood 5 has a length in this direction of about 40 cm. Atmospheric material is exhausted through the chimney 8 at such a rate as to generate an upward flow of gases in the peripheral passage 20 at a rate of about 7 to 8 m / sec, and this causes a continuous inward flow of gas from the float chamber into the bottom of the passage 20 around the entire circumference of the coating chamber 6, thus preventing the escape of coating reagents or their reaction products into the float chamber. Of course, such a suction also removes coating reaction products and unused coating reagents.

The formed coating consists of silicon dioxide of about 90 nm thickness. At a following

Coating step, which takes place in a conventional manner in a coating station, which is close to the upstream end of a horizontal cooling path, an upper coating layer of doped SnÜ2 is formed in a thickness of about 500 nm. The combined coating is virtually free of unwanted color changes due to interference effects.

In various embodiments according to the second aspect of this invention, the seated in the

Drawings shown coating station in a cooling line. In the description of the drawing, therefore, references to the float chamber may also be replaced by references to a cooling track, and references to the track of molten metal may be replaced by references to transport rollers.

EXAMPLE 2

In a specific practical embodiment for coating float glass after it has been withdrawn from the float chamber, the coating station is seated in a cooling path where the temperature of the glass is about 500 ° C., downstream of another coating station to form a doped SnO.sub.2 coating layer of about 350 nm thickness. The hood has a length of about 1 m. The coating precursor reagents are introduced in the same amounts as in Example 1 to form a silicon dioxide overcoat of about 100 nm thickness. Again, this combined coating is free from unwanted color changes due to interference effects.