Coating glass involving coating with an incompletely oxidized undercoat

(54) METHOD OF COATING GLASS (57) The invention relates to a method of forming a coating comprising a pyrolytically formed oxide layer on a moving hot glass substrate, wherein the substrate is contacted with coating precursor material in the presence of oxygen. To prevent interactions between the coating precursor material used to apply an upper stooping layer, and / or to facilitate the modification of the optical or other properties of the coating, For example, a first oxide layer as a sublayer is pyrolytically shaped in an incompletely oxidized state by contacting the substrate in a coating chamber with coating precursor materials in the presence of molecular oxygen in an amount insufficient for complete oxidation of the underlayer material on the substrate. Thereafter, the underlayer is coated with an upper CD coating layer while still in an incompletely oxidized state and while the substrate is still hot, thereby maintaining the underlayer in an incompletely oxidized state.

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AT 404 935 wtssrasiß

AT 404 935 Β

The invention relates to a method of forming a coating comprising a pyrolytically formed oxide layer on a slidable hot glass substrate by contacting the substrate with coating precursor material in the presence of oxygen.

It is known to coat glass for different purposes. Conductive coatings of various grades may be used to form part of an electrical circuit or to reduce the emissivity of the coated surface to infrared radiation. Reflective coatings, such as metal, such as absorbent coatings, may be used to shield solar radiation.

EP-A-174 727 describes the deposition of a layer containing silicon and oxygen by pyrolysis. For this purpose, electron donor gases are proposed, and particular reference is made to the use of unsaturated hydrocarbons. Due to this procedure, it can not be prevented that in the layer also carbon is present, whereby a different type of coating is formed at the same time insufficient control of the actual oxidation state.

GB-1 534 122 A shows and describes the production of glass with a coating of titanium dioxide of the rutile type. This is a high temperature separation of titanium by vacuum evaporation. In order to protect this titanium dioxide coating during subsequent high temperature treatment steps, an underlayer of silicon oxide is proposed which is also made by vacuum evaporation. In particular, in a high vacuum, the formation of SiO and at a relatively low vacuum (± 10^-4 mm Hg) the formation of Si₂O₃Coatings described.

More particularly, the invention relates to multilayer coatings in which a subbing layer of oxide is provided with one or more superimposed layers of an oxide or other material.

It is also known to prepare multilayer coatings having an oxide undercoat and one or more superposed coating layers. There are various reasons for using a multilayer pyrolytic coating, which is the principal object of modifying the manner in which the top layer or layers are deposited, or reducing interactions between the top coating material and the glass of the substrate and / or the substrate Modification of the properties of the entire coating, or to reduce interaction between an underlayer of the coating such as the oxide underlayer and the atmosphere to protect the underlayer from fouling or, indeed, abrasion, thus preserving the properties imparted to the underlayer of the wheel.

It may be useful to prevent interaction between the glass of the substrate and the material of an upper coating layer. For example, silicon oxide coatings may be used as undercoat layers to be coated with other coatings, which may be one or more different oxides or other materials such as metals. The presence of a silica underlayer on soda-lime glass has the particular advantage of inhibiting the migration of sodium ions from the glass, either by diffusion or otherwise into an upper coating layer, either during the formation of the upper layer or during a subsequent high temperature treatment. For example, it has been found that in the pyrolytic formation of a stannic oxide tin chloride coating on a soda-lime glass substrate, sodium chloride tends to become trapped in the coating as a result of the reaction, the glass with the coating precursor material or its reaction products, and this leads to clouding in the coating.

Alternatively, it is desirable to modify the optical properties of a coating when used for radiation shielding purposes. The radiation-repellent coatings, which are particularly in the field of vision, tend to be thin, and accordingly, their appearance -observed by transmitted or reflected light-is impaired by interfering effects, and small changes in coating thickness can have an important effect in modifying the visible color of the coating. In order to reduce the effect of thickness variations on the visible color of the coating, it has been proposed to provide an oxide underlayer and this can have a very beneficial effect of reducing unwanted interfering or have troublesome effects due to variations in the thickness of the entire coating, provided that the optical thickness of this underlayer itself is well selected.

Again, alternatively, it may be desirable to provide an oxide underlayer which gives the disc as a whole some special properties and the underlayer by an abrasion resistant

Coating protects, which also serves to protect the underlayer from chemical attack by the surrounding atmosphere.

AT 404 935 Β

It is therefore an essential object of the invention to provide a process for forming a pyrolytic multilayer coating on glass in which a sub-layer coating by itself has certain special properties, or which cooperates in conjunction with at least one other coating layer to give the coated glass certain special properties To give properties.

This object is achieved by the characterizing features of Anspuchs 1.

The subclaims further form the invention.

According to the invention there is provided a method of forming a coating comprising a pyrolytically shaped oxide layer on a slidable hot glass substrate by contacting the substrate with coating precursor material in the presence of oxygen, the method being characterized that a first oxide layer as underlayer is pyrolytically formed in an incompletely oxidized state by contacting the substrate in a coating chamber with coating precursor material in the presence of molecular oxygen in an amount insufficient for complete oxidation of the underlayer material on the substrate, and covering the underlayer with an upper coating layer; while still in an incompletely oxidized state, and while the substrate is still hot, thereby maintaining the underlayer in an incompletely oxidized state.

The invention therefore provides a method for forming an incompletely oxidized underlayer, followed by an upper cover layer which maintains the properties of the underlayer of incompletely oxidized material, thereby preserving the properties provided thereby. The term incompletely oxidized material is used herein to refer to a true suboxide containing an oxide of a lower valence state of a polyvalent element (eg VO₂ or TiO), and also to designate an oxide material containing oxygen vacancies in its structure: An example of the latter material is SiO 2_xwhere x is less than 2, which is the general structure of SiO₂ but has a fraction of gaps that can be filled with oxygen in the dioxide.

The precise nature of the particular properties that may be imparted by the undercoat of the incompletely oxidized material depends, at least in part, on the nature of that material.

For example, the underlayer may consist of a semiconductor layer. Semiconductor layers may be formed of zinc or cadmium oxides, titanium oxide or vanadium dioxide, and these layers may be rapidly formed to a given degree of oxidation by a method according to the invention, and then preserved in an incomplete oxidized state by the overcoat layer become. The overcoat layer or layers can be rapidly selected to protect the underlayer from further oxidation (due to atmospheric oxygen), from other chemical attack (due to the ambient atmosphere), and from abrasion.

At present, however, it is intended to apply the invention industrially to the formation of sub-layers of incompletely oxidized silica. It has been found that the presence of a silica coating on a soda-lime glass has a beneficial effect of reducing or eliminating sodium poisoning of a superposed coating layer. Furthermore, and this is also very important, the refractive index of silica varies according to its oxidation state and to the voids present in its structure. Therefore, the introduction of the invention provides an additional control parameter for the formation of the underlayer covering, eg of silicon oxide, which facilitates the control of the optical thickness of this underlayer. It is, of course, the optical thickness of the various coating layers that determines many of the optical and radiation-transmitting properties of the coating as a whole, and the optical thickness of a coating layer is the product of the actual thickness and refractive index of the material from which the coating layer is made. (In the case of interfering reflection, the important factor may be twice the product of actual thickness and refractive index.) Different oxides of different elements show different refractive indices, and therefore, the invention not only allows control of the actual thickness with which an underlayer is deposited is also a measure of independent control of its optical thickness by appropriate choice of the degree of oxidation, which has been allowed in the lower class.

It may be much easier to control the degree of oxidation of the material of a sub-layer than the precise thickness at which the sub-layer and the coating layer are deposited, particularly in the course of mass-production of coated glass on a large scale. The coating apparatus may be arranged to provide a uniform coating of approximately the required actual thickness, taking into account the nature of the coating material and adjusting to achieve the required optical thickness of that sublayer,

AT 404 935 Β simply by controlling the amount of oxygen allowed to enter the coating chamber.

If the undercoated glass substrate is exposed to an oxidizing atmosphere for a sufficiently long period of time, it must be expected that the underlayer will be completely oxidized to lose its desired properties. According to the invention, therefore, the underlayer is coated with an upper coating layer while it is in an incompletely oxidized state and while the substrate is still hot, whereby the underlayer is obtained in an incompletely oxidized state. The time while the freshly submerged or base coated glass substrate may be exposed to an oxidizing atmosphere such as air and before the overcoat is overcoated without destroying the underlayer properties will depend on the temperature of the glass during such exposure and on the nature of the underlayer. However, an exposure time of 15 seconds and possibly up to 1/2 minute is generally tolerated for silicas. Such periods of time may be insufficient to complete the oxidation of the underlayer, and the resulting increase in oxidation may be predictable and may therefore be accommodated by changing the degree of oxidation previously permitted in the underlayer step.

Advantageously, the process is carried out so that this coating chamber is surrounded by a reducing atmosphere. The introduction of this feature helps to allow ambient oxygen to enter the coating chamber, thus allowing better control of the oxidation conditions within that coating chamber.

The invention can therefore be used for the formation of a suboxide coating on pre-cut and reheated glass sheets, if necessary. However, when it is desired to produce pyrolytically coated flat glass, it is better to do so when the glass is freshly formed. This approach has economic advantages in that there is no need to re-heat the glass for the pyrolytic reactions that are to take place. This also has advantages for the quality of the coating, since it is ensured that the surface of the glass is in a virgin state. Preferably, therefore, this undercoat precursor material is brought into contact with an upper surface of a hot glass substrate of freshly formed flat glass.

For example, the coating chamber may be located in or adjacent the upstream end of a tunnel annealing furnace through which the strip is fed, and the glass ribbon may be formed in either a drawing machine or a float chamber.

However, the Applicant has found that certain problems arise in converting a furnace originally used to anneal uncoated glass to produce a furnace and two or more coating stations for the production of glass coated with multi-layer coatings. Such problems arise as a result of possibly different temperature conditions for forming the coating on the one hand and for proper annealing of the glass on the other hand, and as a result of efforts on the available spaces for placing the various coating stations. Furthermore, the coating reactions exert a cooling effect on the glass not only in that the glass is cooled everywhere, but also in that the coated surfaces tend to be cooled more than the uncoated surfaces: Therefore, more often a different temperature range has been set within a tunnel annealing furnace equipped with two or more coating stations when changing from the production of coated glass to uncoated glass and back again, and sometimes even when there is a substantial change in thickness the coating thickness used for the glass is made.

In order to alleviate these problems, the process of the present invention is carried out by contacting the coating precursor material with an upper surface of a float glass substrate in a coating chamber, which coating chamber is disposed in the float chamber in which the float glass is manufactured.

By operating in accordance with this preferred embodiment of the invention and forming the undercoat within the float chamber, there is no longer any need to locate a space for the undercoating station at or near the upstream end of the tunnel annealing furnace. Furthermore, the Applicant has found that it is possible to ensure that the temperature of the glass ribbon exiting the float chamber is substantially unaffected by whether or not the glass ribbon is undercoated, and accordingly there is no longer any need for the temperature range in a tunnel annealing furnace when the coating chamber is commissioned or shut down.

AT 404 935 B

It is a surprising proposal to form an oxide undercoating within a float chamber. Float chambers contain a bath of molten metal, wholly or substantially tin, which is fairly easily oxidized at the temperatures needed to expand the glass ribbon and which fused or is fire polished, and accordingly, it is a universal practice to maintain a reducing atmosphere within the float chamber, as any surface slag taken up by the glass ribbon from the surface of the metal bath is a source of defects in the glass produced. Typically, such an atmosphere contains about 92% to 95% nitrogen and about 8% to 5% hydrogen and is maintained at a slight overpressure to protect against oxygen entry into the float chamber from the surrounding atmosphere. There has been much research effort to remove Slag that almost always forms on the surface of the metal bath, despite all the precautions taken to prevent oxygen from entering the float chamber. It is therefore deliberate against the doctrine of making float glass to maintain oxidizing conditions in the float chamber. Applicant has found, however, that it is possible to produce oxidizing conditions within the float chamber without causing the expected problems. It is believed that this is due, at least in part, to the fact that this undercoating precursor material is brought into contact with this surface in a coating chamber. The use of a coating chamber facilitates the limitation of the oxidizing conditions of the undercoating precursor material and the undercoating reaction products so that their effect on the metal bath in the float chamber can be minimized or neglected.

Placing the coating chamber within a float chamber is also a very simple way of ensuring that the coating chamber is surrounded by a reducing atmosphere, and it does not require the provision of any additional arrangement to maintain that atmosphere.

The undercoating may be formed at any position along the float chamber downstream of the position where the glass ribbon has reached its final width, and the actual position selected will be from the desired temperature for initiation depend on the coating on the glass. The glass is removed from the float chamber to pass through the tunnel annealing furnace at a temperature usually in the range of 570 * C to 650'C. Glass ribbon temperatures above 570 ° C. are inherently suitable for the pyrolytic coating reactions that take place, so that the coating station may actually be located quite close to the exit of the float chamber. Preferably, however, the undercoat precursor material may contact the glass at a location along the float chamber at a temperature that is at least 50 ° C and preferably at least 100 ° C higher than the temperature at which the glass exits the float chamber, if not a coating is formed therein. The inclusion of this preferred feature of the invention provides the advantage that there is an extended period of time for the glass ribbon to regain the heat lost during the coating reactions so that as it exits the float chamber, its temperatures in the glass ribbon essentially unaffected by the underlayering process.

Even if the glass is not underlaid within a float chamber, it is preferred that the substrate reach the coating chamber at a temperature of at least 400 ° C. Such temperatures are very suitable for the rapid formation, for example, of a silicon oxide coating from a silane-containing or silane-containing coating precursor. It is also to be noted as a general rule that the higher the temperature of the glass during the coating formation, the faster the coating reaction is, so that the coating yield, that is the proportion of the coating precursor material that is converted into useful coating oxide, increases if desired, a thicker coating can be formed for a given rate of glass ribbon advance. For this reason, it is also preferred that the undercoating precursor material first contacts the glass 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 contacted by the underlayer precursor material.

The oxygen needed for the undercoating reactions may be supplied as pure oxygen, but this unnecessarily adds rusting, and it is accordingly preferred that air be supplied to the coating chamber to introduce oxygen.

Advantageously, this undercoat precursor material is selected from a silicon containing compound. There are thus formed silica coatings, which are used as undercoats for various

Purposes are useful. It is particularly advantageous if the underlayer precursor material is a silane.

AT 404 935 Β

The use of a silane, especially SiH₄ is well known per se 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 silicon oxide coating. For this reason, it is preferred that the silane react directly with oxygen. In order for this reaction to occur on the glass substrate rather than on some parts of the coating apparatus, all previously published proposals for using a silane containing coating precursor material in forming a silica coating insist that the coating precursor material should only be allowed to coexist To mix oxygen within a coating chamber, which is open to the substrate to be coated at a location where these materials are free to contact the substrate directly. Applicant has found, however, that this is not advantageous for the production of high quality silica coatings.

In the most preferred embodiments of the invention, the underlayer precursor material containing the silane is intimately mixed with molecular oxygen prior to contacting the glass. The Applicant has found that this early blending of the underlayer reagents provides great advantages in achieving a uniform sublayer across the width of the substrate. Surprisingly, this early blending does not result in such a premature reaction of the coating precursor material as is expected according to the teachings of the prior art, and indeed it is advantageous for the production of high quality silica coatings.

In preferred embodiments of the invention, silane coating precursor material is fed into the vapor deposition coating chamber in substantially an inert gas carrier stream and oxygen is introduced into the silane containing carrier gas stream prior to entering the coating chamber. While it is desirable that the oxygen and coating precursor silane be intimately mixed prior to entering the coating chamber, it is an advantage that it is possible to control the length of time that these reagents are mixed before being fed to the coating chamber become. Supplying the silane to the coating chamber in a substantially inert gas stream and then introducing oxygen to this carrier gas stream allows selection of the location where oxygen is introduced to achieve this control.

Advantageously, nitrogen is used as the essential inert carrier gas. Nitrogen is sufficiently inert for the purposes considered and it is not expensive compared to the noble gases.

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

In preferred embodiments, a swirling flow is introduced into the carrier gas stream to ensure intimate mixing of the carrier gas and the silane. A certain amount of swirling flow is introduced when using a Venturi tube, as stated above, but this can be enhanced, for example, by the use of a feed line which causes a constriction or Has cross-sectional constriction downstream of the coating precursor entry site. Such a constriction may be asymmetric. The intimate mixing of the precursor with the carrier gas is ensured by inducing vortex flow or turbulence.

For similar reasons, it is advantageous to induce a turbulent flow into the carrier gas stream after introduction of molecular oxygen therein to ensure intimate mixing of the silane-containing carrier gas and molecular oxygen.

The rate at which the coating reagents are supplied is dependent to a significant extent on the desired thickness of the subbing layer to be formed and on the rate at which the substrate passes through the coating chamber. Preferably, silane is introduced as undercoating precursor material into the coating chamber at a partial pressure of between 0.1% and 1.5%. A concentration within this range is suitable for forming underlays of from about 30 nm to about 240 nm on a substrate moving up to 20 m / min.

For the production of coated glass which moves at a rate of less than about 10 m / min, silane is advantageously introduced as undercoating precursor material into the coating chamber at a partial pressure of between 0.1% and 0.4%.

Preferably, steps are taken to limit heat energy transfer to the underlayer precursor material as it moves toward the glass. This maintains the temperature of the coating reagents at a lower level than would otherwise dictate environmental conditions, and this further aids in reducing any tendency for premature reaction.

Advantageously, the underlayer precursor material is supplied via at least one slot which extends across at least a portion of the width of the glass substrate. This facilitates

AT 404 935 Β the formation of a sub-layer having a uniform thickness across the width of the glass substrate.

With particular advantage, the inventive method is carried out so that the lower layer precursor material contacts the glass within this coating chamber, wherein the chamber is bounded by the substrate web and a downwardly inclined opening cap and wherein the coating chamber is sucked off over substantially its entire outer surface. This prevents leakage of unused undercoating precursor and coating reaction products from the undercoating chamber into the surrounding space.

With particular advantage, this aspiration induces an inward flow of ambient atmosphere surrounding substantially the entire outer surface of the coating chamber. This forms a pneumatic seal between the oxidizing conditions within the coating chamber and the surrounding atmosphere, which is particularly valuable in preventing the escape of oxidizing atmosphere from the undercoating chamber when this chamber is placed inside a float chamber.

The invention will now be further described by way of example with reference to the accompanying drawings.

Show it

FIG. 1 is a cross-sectional view taken along an undercoating device disposed in a float chamber.

FIG. 2 is a cross-sectional view taken along the underlayer apparatus of FIG. 1;

Figure 3 is a diagrammatic plan view of the underlayer device, and

Figure 4 shows the delivery of underlayer reagents to a feed line feeding the underlayer station.

In the drawings, a glass ribbon 1 is advanced along a path also shown at 1 as it is carried by a molten metal bath 2 contained within a float chamber 3. An underlay station is surrounded by a wall and a roof structure, shown generally at 4. The underlayer station or Site 4 includes a hood 5 which defines an undercoating chamber 6 with an opening downwardly onto the glass sheet 1, a feed line 7 for feeding undercoating reagents to the undercoating chamber 6, and a chimney 8 for peripheral suction around the undercoating chamber.

Feed line 7 is fed with a strong inert carrier gas, such as nitrogen, from a source, not shown, and the undercoating precursor material, such as silane, is introduced into the carrier gas stream at a first venturi 9. The feed line 7 shown is specifically designed for feeding silane to the undercoating chamber. The sub-layered precursor carrier gas stream flows along the feed line 7 to a first restriction 10 arranged to impart turbulence to the carrier gas stream to ensure intimate mixing of the carrier gas and the entrained underlayer precursor material. Further downstream, a second Venturi tube or a second Venturi nozzle 11 is provided for introducing oxygen, for example as part of air. Another turbulence inducing cross-sectional constriction 12 ensures intimate mixing of oxygen and the entrained underlayer precursor material in the carrier gas stream. The underlayer reagents are fed through a supply line 7 to a flow control block 13 having an exit slot 14 which extends across the major part of the width of the hood 5.

It is useful to supply undercoating precursor material and oxygen to the feed line 7 outside of the float chamber 3. At all parts within the float chamber 3, the supply line is surrounded by a cooling jacket 15, which is equipped with a cooling water inlet 16 and outlet 17, as shown in FIG. If desired, the cooling jacket may extend within the flow control block 13, as shown at 18 in FIGS. 2 and 4 in broken lines, so that the undercoating reagents may overheat until they exit the slot 13 for contact with the glass ribbon 1 in the undercoating chamber 6 come into contact, are protected.

As shown in FIG. 2, the hood 5 and the flow control block 13 are suitably held by means of struts 19 from the roof of the float chamber 3. It is desirable to use threaded struts 19 so that the height of the base of the hood 5 for a small recess, eg 2 cm or less, can be adjusted by the glass ribbon 1.

The hood 5, the undercoating chamber 6 and the flow control block 15 are surrounded by a peripheral passage 20 over which, if desired, undercoating reaction products and unused undercoating precursor material, together with inwardly drawn ambient atmosphere material, are aspirated upwardly through the chimney 8 from the float chamber can be. The hood 5 and the wall structure 4 of the underlayer station are if necessary, with peripheral

AT 404 935 Β extending edges 21 at the base of the peripheral passage 20 equipped. These edges are suitably made of flexible refractory curtains, which may be made, for example, from Refrasil (trademark).

After the glass ribbon has left the float chamber 3, it is directed to an overlay station (not shown) that sits close to the exit end of the float chamber. The superposing chamber itself may be made of a type known per se and located at or in front of the upstream end of a horizontal tunnel annealing furnace through which the glass ribbon is passed before it is cut into sheets. It is desirable that there be a closed passageway between the exit end of the float chamber and the entrance to the superposing chamber, especially if this passageway is more than a few meters long, and which also fills the passageway with a non-oxidizing or reducing atmosphere can be. This can be completed quickly by blowing in nitrogen along and in contact with the newly formed backsheet and can be supplemented by leaks in the float chamber atmosphere along that passageway.

EXAMPLE 1

In a specific practical embodiment for coating float glass, which is conveyed along a float chamber at a speed of 7 m / min, a coating station is located at a location along the float chamber where the glass is at a temperature of about 700 'C is located. The feed line is fed with nitrogen and silane is introduced there at a partial pressure of 0.2% and oxygen is introduced at a partial pressure of 0.36% (ratio 0.55). A coating of silicon oxide SiOx, wherein x is approximately equal to 1.8, is obtained with a refractive index of about 1.69. The coating that is formed has a thickness of 75 nm. The coating precursor material in its carrier gas is fed along the feed line 7 to exit from a slot approximately 4 mm wide at a rate at which the feed material flows along between the glass and the hood 5, which is 15 mm above the glass ribbon 1 at a speed of about 2 to 3 m / sec in both directions parallel to the direction of the glass ribbon advance. 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 produce an upward flow of gases into the peripheral passage 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 base of the passage 20 around the entire environment of the coating chamber 6, so that escape of the coating reagents or their reaction products in the float chamber is prevented. Of course, such aspiration also removes coating reaction products and unused coating reagents.

In a subsequent coating step carried out in a manner known per se in a coating station located close to the exit of the float chamber and upstream of the upstream end of a horizontal tunnel annealing furnace, an upper doped SnO coating layer is formed₂ to a thickness of 225 nm by pyrolysis of SnCl₂ formed in aqueous solution. A tolerance of ± 45 nm in the thickness of the SnO₂Coating and ± 4 nm in the lower layer can be accepted without giving rise to unwanted color changes due to interference effects.

In the absence of a subcoating, such a tin oxide layer in reflection exhibits a dominant greenish wavelength and may appear greenish yellow or greenish blue according to the precise thickness from location to location. A quantitative assessment of the light modifying power of the coating can be given in terms of the known Hunter coordinates. In the absence of the underlayer, a tin oxide coating has a Hunter a coordinate of between -6 and -7, and a Hunter b coordinate of between -7 and +5. In the case of the two-layer coating of this example, but with a silicon oxide underlayer of about 75 nm with a refractive index of 1.69 to 1.7, the Hunter a and b coordinates were between +2 and -2, thus giving a more uniform neutral product.

EXAMPLE 2

There is a need to produce a layer of doped tin oxide having a thickness of about 500 nm for shielding long-wave infrared radiation. Such a coating can be formed quickly by a technique known per se. Thickness variations can show deviations in hue across the coated slice from green (Hunter-a "coordinate -15) to reddish (Hunter-a-coordinate +7), which are believed to be commercially unacceptable. Therefore

AT 404 935 B, the glass is first provided with a sub-layer of incompletely oxidized silica having a thickness of 80 nm and a refractive index of 1.75 Â £ 0.01. This is quickly established by adjusting the flow rates of the silane and oxygen in the undercoating chamber in the process of Example 1. This sublayer has the effect of reducing color aberrations due to interfering effects such that for thickness variations in the upper layer of up to ± 30 nm, the Hunter a and b coordinates are both between +2 and -2 of a more uniform neutral product. This remains true for deviations of up to + 5 nm in the thickness of the underlayer.

EXAMPLE 3

A low emissivity coating of doped zinc oxide is formed from a thickness of 310 nm by pyrolysis of zinc acetate dissolved in aqueous isopropanol as a coating precursor material. Indium chloride is added to the coating precursor material to provide the required doping ions.

According to the invention, the glass is first provided with an underlayer, in this example incompletely oxidized silica having a thickness of 73 nm and a refractive index of 1.79, and the coating is used to preserve this incomplete oxidation state. This is accomplished quickly by adjusting the flow rates of the silane and oxygen into the undercoating chamber in the process of Example 1. This also has the effect of noticeably reducing color deviations due to variation in the thickness of the coating layer. The Hunter a and b coordinates were both between +2 and -2.

Deviations in the thickness of the coating of up to ± 10 nm, and variations in the thickness of the difference of up to 3nm can be tolerated without causing noticeable changes in the hue of the coated glass when viewed in reflection.

EXAMPLE 4

A low emissivity coating of doped zinc oxide is formed to a thickness of 505 nm, again by pyrolysis of zinc acetate dissolved in aqueous isopropanol as a coating precursor material. Indium chloride is added to the coating precursor material to provide the required doping ions.

According to the invention, the glass is first provided with an underlayer, in this example incompletely oxidized silica having a thickness of 78 nm and a refractive index of 1.8, and the coating layer is used to preserve this incomplete oxidation state. This is done quickly by adjusting the flow rates of the silane and oxygen into the undercoating chamber in the process of Example 1. This also has the effect of markedly reducing color deviations due to variations in the thickness of the coating layer. The Hunter a and b coordinates were both between +2 and -2.

Changes in the thickness of the coating of up to five angstroms and changes in the thickness of the undercoat of up to two angstroms can be tolierated without causing noticeable changes in the hue of the coated glass when viewed in reflection.

EXAMPLE 5

A low emissivity coating of indium tin oxide is formed to a thickness of 300 nm by pyrolysis of indium chloride and stannous chloride dissolved in dimethylformamide as a coating precursor material by a coating technique known per se.

In accordance with the invention, the glass is provided with an underlayer, in this example incompletely oxidized silicon oxide having a thickness of 74 nm and a refractive index of 1.77, and the overcoat layer is used to preserve this incomplete oxidation state. This is done quickly by adjusting the flow rates of the silane and oxygen into the undercoating chamber in the process of Example 1. This also has the effect of noticeably reducing color deviations due to variations in the thickness of the coating layer. The Hunter a '' and "b coordinates were both between +2 and -2.

Deviations in the thickness of the coating of up to 10nm and variations in the thickness of the underlayer of up to 2nm can be tolerated without appreciable variations in the hue of the coated glass when viewed in reflection.

AT 404 935 B

EXAMPLE 6

A low emissivity coating of indium tin oxide is formed to a thickness of 500 nm.

According to the invention, the glass is first provided with an underlayer, in this example incompletely oxidized silica having a thickness of 85 nm and a refractive index of 1.8, and the coating is used to preserve this incomplete state of oxidation. This is done quickly by adjusting the flow rates of the silane and oxygen into the undercoating chamber as described in Example 1. This also has the effect of markedly reducing color deviations due to variations in the thickness of the overcoat layer. The Hunter a and b coordinates were both between +2 and -2.

Deviations in the thickness of the coating of up to ± 5 nm, and variations in the thickness of the undercoat of up to ± 1 nm can be tolerated without visible changes in the hue of the coated glass when viewed in reflection.

EXAMPLE 7

A semiconducting sub-layer is formed of incompletely oxidized zinc by contacting a glass ribbon in an undercoating chamber within a float chamber with metallic zinc vapor in the presence of oxygen in an insufficient amount to fully oxidize the zinc coating thus formed on the glass.

The ZnOx semiconductive sublayer is then overcoated by a 500 nm thick conductive coating formed of doped tin oxide, which serves to preserve the ZnOx layer in an incompletely oxidized state to function as a semiconductor, and the like Time as an electrode in the finished product is used.

EXAMPLE 8

A glass ribbon within a float chamber is first equipped with an underlayer of silicon dioxide having a thickness of 90 nm. This can be done by modifying the method of Example 1 so that enough oxygen is used to completely oxidize the silicon. To accomplish this, silane is introduced into the undercoat coating station at a partial pressure of 0.25%, and oxygen at a partial pressure of 0.5% (ratio 0.5) is introduced.

This underlayer serves to prevent sodium poisoning of a sub-layer of a vanadium suboxide subsequently applied thereto. A vanadium dioxide underlayer is formed in an underlayer station also located in the float chamber, downstream of the underlayer coating station, by contacting the underlayer on the glass with vanadium trichloride in the vapor phase in the presence of insufficient oxygen to fully oxidize the vanadium in the suboxide underlayer. which has been formed on the lower layer shaped.

According to the invention, the vanadium dioxide is overcoated while still in a state of incomplete oxidation. A 500 nm thick coating of tin oxide is applied to the underlayer, outside the float chamber, prior to annealing the glass ribbon.