Coating glass involving coating with an incompletely oxidized undercoat

Method of forming a coating on glass

The present invention relates to a coating forming method comprising an oxide layer deposited by pyrolytic route on a hot moving glass substrate, by contacting the substrate with coating forming material in the presence of oxygen.

It is well known to coat glass for various reasons. Different types of conductive coatings can be deposited in order to form part of the electrical circuit or to reduce the emissivity of the coated surface with respect to infrared radiation. Reflective coatings, made for example of metal, or absorbent coatings, can be deposited in order to protect from solar radiation.

The invention relates particularly to multilayer coatings, in which there is an oxide sublayer surmounted by a layer or several layers of oxide or of another material.

It is also well known to form multi-layer coatings comprising an oxide sublayer and one or more upper layers. There are various reasons for depositing a multi-layer pyrolytic coating, the main purpose of which is to modify the manner of deposit the upper layer (s), or reduce the interaction between the material of the upper layer and the glass of the substrate, and / or modify the properties of the coating, or reduce the interaction between an underlayment of the coating, such as an oxide underlayment, and the atmosphere to protect this underlayment from pollution or abrasion and thus retain the properties that this underlay gives the panel.

It may be useful to prevent the interaction between the glass of the substrate and the material of an upper layer of the coating. For example, a layer of silicon oxide can be used as a sublayer on which other layers are deposited which may be of different oxides or other materials, such as metals. The presence of a silicon oxide sublayer on soda-lime glass has the particular advantage of inhibiting the migration of sodium ions from the glass, whether by diffusion or by any other mechanism, to a layer upper coating, during the formation of this upper layer or during a subsequent treatment at high temperature.

For example, it has been found that during the pyrolytic formation of a coating of tin oxide from tin chloride on a soda-lime glass substrate, sodium chloride tends to be incorporated into the coating, as a product of the reaction of glass with the coating-forming material or with its reaction products, and this causes the appearance of haze in the coating.

Alternatively, one may wish to modify the optical properties of a coating which is deposited on glass for the purpose of protection against radiation. Radiation protective coatings are often thin, and therefore their appearance, whether seen in transmission or reflection, is influenced by interference effects, and minor variations in their thickness can have a significant effect. modification of the apparent color of the coating. In order to reduce the effects of variations in thickness on the apparent color of the coating, it has been proposed to deposit an oxide sublayer, and this can have a very advantageous effect in reducing the undesirable interference effects due to variations in the thickness of the total coating, provided that the optical thickness of the undercoat is itself well selected.

Alternatively, again, one may wish to deposit an oxide undercoat which gives certain special properties to a panel, and protect this undercoat with an abrasion resistant coating which also serves to protect the undercoat from chemical attack by the ambient atmosphere.

One of the main objects of the present invention is to provide a process for the pyrolytic formation of a multilayer coating on glass, in which an underlay has in itself certain special properties, or acts in combination with at minus another layer of the coating to impart certain special properties to the coated glass.

The present invention provides a process for forming a coating comprising an oxide layer deposited by pyrolytic route on a hot moving glass substrate, by bringing the substrate into contact with coating-forming material in the presence of oxygen, characterized in that an oxide layer in an incompletely oxidized state (the undercoat ”) is formed by pyrolytic means, by bringing the substrate into contact, in a treatment enclosure, with undercoat forming material in the presence of an insufficient quantity of oxygen to completely oxidize the material of the undercoat on the substrate, and in that it is deposited on the undercoat, when it is in an incompletely oxidized state and the substrate is still hot, an intended top coating layer which maintains said undercoat in an incompletely oxidized state.

The invention therefore provides a process for forming an incompletely oxidized sublayer, surmounted by an upper layer which will preserve the properties of this sublayer of incompletely oxidized material. The term incompletely oxidized material is used here to describe a true sub-oxide, i.e. an oxide of a multi-valent element which is in a lower valence state (for example VO₂ or TiO), and to describe an oxide which contains oxygen vacancies in its structure: a

JO example of such a material is SiO_x, where x is less than 2, which can have the general structure of SiO₂, but which has a certain proportion of gaps which would be filled by oxygen in the dioxide.

The precise nature of the special properties which can be imparted by the undercoat of incompletely oxidized material will depend at least in part on the nature of this material.

For example, the sublayer may consist of a semiconductor layer. Semiconductor layers can be formed from zinc or cadmium oxides, titanium oxide or vanadium dioxide, and such layers can be easily formed by a process according to the present invention at a given oxidation level , and they can be preserved in a state of incomplete oxidation by the upper layer. The upper layer (s) can be easily chosen to protect the undercoat against subsequent oxidation due to atmospheric oxygen, against any other chemical attack due to the ambient atmosphere, and against abrasion.

However, it is considered that an important use of the present invention is the formation of sublayers of incompletely oxidized silicon oxide. As mentioned, the presence of a layer of silicon oxide on soda-lime glass has the advantageous effect of reducing or eliminating the sodium poisoning of an upper coating layer. . In addition, and this is also very important, the refractive index of silicon oxide varies according to its oxidation state and in relation to the gaps present in its structure. Therefore, the adoption of the present invention offers an additional control parameter in the formation of a sublayer, for example of silicon oxide, which facilitates the control of the optical thickness of this sublayer. It is obviously the optical thicknesses of the different layers of the coating which determine a large part of the optical and radiation transmission properties of the coating as a whole, and the optical thickness of a coating layer is the product of the actual thickness and the refractive index of the material of which the layer is made. (In the case of interference reflection, the important factor may be twice the product of the actual thickness and the refractive index.) Different oxides of different elements have different refractive indices, and therefore the present invention not only allows control of the actual thickness of the undercoat being deposited, but also a control measure independent of its optical thickness by an appropriate selection of the degree of oxidation of the undercoat.

It can be a much simpler way to control the degree of oxidation of the material of an undercoat, than to control the precise thickness of undercoat and topcoat which are deposited, especially during manufacturing. glass coated in large series. The coating forming device can be adjusted to deposit a uniform layer approximately of the desired actual thickness, taking into account the nature of the coating material, and the adjustment to obtain the desired optical thickness of this underlay. can be done simply by controlling the amount of oxygen that is allowed to enter the processing enclosure.

If the glass substrate carrying the undercoat is exposed to an oxidizing atmosphere for a sufficiently long time, it can be expected that the undercoat will become completely oxidized, which would cause the desired properties to be lost. Consequently, according to the present invention, an upper coating layer which maintains said undercoat in an incompletely oxidized state is deposited on the sublayer, while it is in an incompletely oxidized state and the substrate is still hot. The time during which the glass substrate carrying the freshly deposited undercoat can be exposed to an oxidizing atmosphere such as air and before it is covered by an upper layer, without damaging the properties of the undercoat, depends on the temperature of the glass during such exposure and the nature of the undercoat. However, in general, for silicon oxides, an exposure time of 15 seconds, and sometimes up to half a minute, can be tolerated. Such periods may be insufficient to complete the oxidation of the sublayer and the increase resulting from the oxidation can be predicted, and therefore taken into account by modifying the degree of oxidation permitted in the deposition step of the underlay itself.

Advantageously, said treatment enclosure where the deposition of the sub-layer takes place is surrounded by a reducing atmosphere. The adoption of this characteristic contributes to preventing ambient oxygen from entering the treatment enclosure and therefore allows better control of the oxidation conditions in the treatment enclosure.

The present invention can be used to form a sub-oxide coating on pre-cut and reheated glass sheets, if desired. However, if it is desired to manufacture flat glass coated by pyrolysis, it is better to do so while the glass is freshly formed. To act in this way is economically advantageous since it is not necessary to reheat the glass for the pyrolytic reactions to occur, and is also advantageous with regard to the quality of the coating, since the surface of the glass is pristine. For this reason, preferably, said undercoat forming material is brought into contact with an upper face of a hot glass substrate consisting of freshly formed flat glass.

The processing enclosure can for example be located in or near the upstream end of an annealing gallery through which the ribbon advances, and the ribbon can be formed in a drawing machine or in a float tank. .

However, it has been found that certain problems arise when converting an annealing gallery previously used to anneal uncoated glass to form a gallery and one or more processing station (s) to produce glass having a multi-layer coating of such problems arise due to the temperature conditions which may be different for forming the coating on the one hand and for the annealing of the glass itself on the other hand, and due to constraints of space available to arrange the various treatment stations. In addition, the coating formation reactions have a cooling effect on the glass, not only that the glass is cooled everywhere, but also, the coated surface tends to be cooled more than the uncoated surface: therefore, a different temperature regime must often be established inside an annealing gallery provided with one or more treatment station (s) when the production changes from coated glass to uncoated glass, and vice versa, and sometimes even when there is a substantial change in the thickness of the coating that is applied to the glass.

In order to solve these problems, preferably, said underlaying forming material is brought into contact with an upper face of a hot float glass substrate in a treatment enclosure arranged inside a float tank in which float glass is formed.

By operating according to this preferred embodiment of the invention and by forming the sub-layer inside the float tank, any need to find a space for the treatment station in or near ό is avoided.

the upstream end of an annealing gallery. Furthermore, it has been found that it is possible to ensure that the temperature of the glass ribbon leaving the float tank is not substantially unchanged, whether or not the ribbon is coated, and therefore there is no need to modify the temperature regime in an annealing gallery when the treatment station is operated or when its operation is stopped.

It is quite surprising to propose forming an oxide sublayer inside a float tank. The float tanks contain a bath of molten metal, consisting entirely or mainly of tin, which is fairly easily oxidizable at the temperatures required for spreading and fire polishing the glass ribbon, and therefore it is practical universal to maintain a reducing atmosphere inside the float tank, because any surface impurity of the metal bath captured by the glass would be a source of defects in the glass produced. Typically, such an atmosphere contains approximately 92 to 95% nitrogen and 8 to 5% hydrogen, and is maintained at slight overpressure to prevent oxygen from the ambient atmosphere from entering the pressure vessel. floating. Much research has also been carried out for the removal of impurities which almost always form on the surface of the metal bath despite all the precautions taken to avoid the penetration of oxygen into the float tank. It therefore goes against the teaching relating to the production of float glass to deliberately maintain oxidizing conditions in the float tank. However, we have found that it is possible to create oxidizing conditions inside a float tank without causing the expected problems. We believe this is due at least in part to the fact that said undercoat forming material is brought into contact with said face in a treatment enclosure. The use of a treatment enclosure facilitates the confinement of the oxidizing conditions, of the undercoat forming material, and of the products of the undercoat deposition reaction, so that their effect on the metal bath in the float tank can be made weak or negligible.

Placing the treatment enclosure where the underlay is deposited inside a float tank is also a very simple way to ensure that this enclosure is surrounded by a reducing atmosphere , and not to require additional equipment to maintain this atmosphere.

The undercoat can be deposited anywhere in the float tank located downstream from where the tape has reached its final width, and the position actually chosen will depend on the temperature desired to initiate the coating on the glass. The glass is extracted from the float tank to pass into the annealing gallery at a temperature which is usually between 570 ° C and 650 ° C. Ribbon temperatures above 570 ° C are inherently suitable for the development of pyrolytic coating reactions, so that the treatment station can in fact be arranged very close to the outlet of the float tank. Preferably, however, the underlay forming material comes into contact with the glass at a location in the float tank such that the glass has a temperature of at least 50 ° C higher, and preferably at least 100 ° C, at the temperature at which the glass would leave the float tank if no coating was formed there. The adoption of this preferred feature of the invention has the advantage of a long delay for the ribbon to recover the heat lost during the coating formation reactions, so that when it leaves the float tank , its temperature is not substantially affected by the deposition of the undercoat.

Even if the glass does not undergo undercoating in the float tank, it is preferable for the substrate to reach the processing enclosure where the undercoating is carried out when its temperature is at least 400 ° C. Such temperatures are well suited for rapidly forming, for example, a silicon oxide coating from a coating forming material containing silane. Π It should also be noted that, as a general rule, the higher the temperature of the glass during the formation of the coating, the faster the coating reaction, so that the coating deposition yield, i.e. the proportion coating form material which is converted into a useful oxide coating, is increased, and for a given tape run speed, it is possible to form a thicker coating if desired. Also for this reason, it is preferred that the undercoat forming material comes into contact with the glass for the first time when the temperature of the latter is at least 650 ° C. For many uses, glass can have a temperature between 700 ° C and 750 ° C when it comes into contact with the coating forming material for the first time.

The oxygen necessary for underlayer formation reactions is preferably present in molecular form. It can be supplied in the form of pure oxygen, but this unnecessarily increases costs, and it is therefore preferable for air to be introduced into the treatment enclosure where the underlay deposition takes place, in order to bring oxygen there.

Advantageously, the under-layer forming material contains silicon to form on the glass an under-layer of silicon oxide. Silicon oxide coatings are useful as undercoats for various uses. Particulièrement is particularly suitable to use a coating forming material which contains a silane.

The use of a silane, in particular SiH₄, is well known per se for forming pyrolytic coatings on glass. The silane decomposes at temperatures above 400 ° C, and silicon coatings can be formed. It is difficult, however, to oxidize such a silicon coating in situ to form a silicon oxide coating. For this reason, it is preferred that the silane reacts 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 processing device, all previously published proposals for the use of a silane-containing coating forming material in the formation of a silicon oxide coating have insisted that the coating forming material be allowed to mix only with oxygen only inside a treatment enclosure which is open on the substrate to be coated, at a place where these materials can directly contact the substrate. However, we have found that this is not conducive to the production of high quality silicon oxide coatings.

In preferred embodiments of the invention, the silane-containing undercoat forming material is intimately mixed with oxygen before coming into contact with the glass. It has been found that this early mixing of the undercoating reagents offers many advantages for obtaining a uniform undercoat across the width of the tape. Surprisingly, early mixing does not cause the coating forming material to react prematurely as suggested by prior art teaching, and is in fact favorable to the production of high quality silicon oxide coatings.

In certain preferred embodiments of the invention, the silane used as an undercoat forming material is conveyed to the treatment enclosure where the undercoat is deposited, in the vapor phase in a gas stream carrier substantially inert and in that oxygen is introduced into the carrier gas stream containing the silane before it enters said enclosure. Although it is desirable that the oxygen and the coating forming silane are thoroughly mixed before entering the treatment enclosure, it is also advantageous to be able to control the time during which these reagents are mixed before entering the treatment enclosure. The routing of the silane to the treatment enclosure in a substantially inert carrier gas stream and the subsequent introduction of oxygen into this carrier gas stream makes it possible to choose the place where the oxygen must be introduced in order to obtain this control.

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

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

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

For similar reasons, advantageously, turbulence is induced in the stream of carrier gas after the introduction of oxygen to ensure the intimate mixing of the carrier gas containing the silane and oxygen.

The flow rate under which the reagents are supplied depends to some extent on the desired thickness of the undercoat to be formed and on the speed of movement of the substrate in the treatment enclosure. Preferably, silane used as an undercoat forming material is introduced into the treatment enclosure where the undercoat is deposited, under a partial pressure of between 0.1% and 1.5%. A concentration within these limits is suitable for forming sublayers of about 30 nm to about 240 nm on a substrate which moves at a speed up to 20 meters per minute.

Advantageously, to coat glass which moves at a speed of less than about 10 meters per minute, silane is introduced into said enclosure under a partial pressure of between 0.1% and 0.4%.

Preferably, measures are taken to limit the transfer of heat energy to the undercoat forming material as it moves towards the glass. This keeps the temperature of the reagents lower than that which ambient conditions would otherwise dictate, and further helps to reduce any tendency for the development of a premature reaction.

Advantageously, under-layer forming material comes into contact with the glass via at least one slot which extends, or the whole of which extends, through at least most of the width of the under-layer. -layer that must be formed on the glass. This facilitates the formation of an underlay having a uniform thickness across the width of the substrate.

Advantageously, the under-layer forming material comes into contact with the glass inside a treatment enclosure delimited by the path of the substrate and a hood open towards the bottom, and in that substantially the entire periphery of said enclosure is kept under suction. This helps to avoid the escape of unused underlay forming material and coating reaction products from the processing enclosure to the surrounding space.

Preferably, said suction induces a flow of the ambient atmosphere surrounding substantially the entire periphery of the enclosure, towards the interior thereof. This creates a pneumatic seal between the oxidizing conditions inside the treatment enclosure and the ambient atmosphere, which is particularly advantageous for avoiding the escape of oxidizing atmosphere from the treatment enclosure, when this enclosure is placed in a float tank.

The invention will now be described in more detail with reference to the accompanying drawings, and by way of example only.

FIG. 1 is a cross-sectional view of a treatment device where deposition of undercoat is carried out, placed in a float tank,

FIG. 2 is a view in longitudinal section of the processing device in FIG. 1,

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

FIG. 4 illustrates the supply of the treatment station with reagents for undercoating deposition by means of a supply line.

In the drawings, a ribbon 1 of glass moves along a path also indicated in 1, while it is supported by a bath of molten metal 2 contained in a float tank 3. A treatment station is surrounded by walls and a roof structure indicated as a whole in 4.

The treatment station 4 comprises a hood 5 which delimits a treatment enclosure 6 opening downwards on the path of the strip 1, a supply line 7 for conveying reagents for depositing undercoat in the enclosure treatment 6, and a chimney 8 for the peripheral aspiration of the treatment enclosure.

The supply line 7 is supplied with substantially inert carrier gas, such as nitrogen, from a source which is not shown, and the undercoat forming material, such as silane, is introduced into the stream. carrier gas to a first venturi 9. The supply line 7 illustrated is specially adapted for conveying silane into the treatment enclosure. The carrier gas stream and the formative material dispersed therein flow along the supply line 7 to a first constriction 10 which is arranged to induce turbulence in the carrier gas stream to ensure the intimate mixing of the carrier gas and entrained underlayer forming material. Further downstream, a second venturi 11 is intended for the introduction of oxygen, for example as a constituent of Fair. Another turbulence-inducing shrinkage 12 ensures the intimate mixing of the oxygen and the under-layer forming material entrained in the carrier gas stream. The undercoating deposition reagents are brought by the supply line to a flow control block provided with an outlet slot 14 which extends through most of the width of the hood 5.

D is necessary to bring the under-layer forming material and the oxygen into the supply line 7 outside the float tank 3. At all places inside the float tank 3, the line d The supply is surrounded by a cooling jacket 15 which is provided with a water inlet 16 and a cooling water outlet 17, as shown in FIG. 1. If desired, the cooling jacket can be extended to the interior of the flow control block 13, as shown in 18 in dashed lines in Figures 2 and 4, so that the reactants are protected against overheating until they exit through the slot 14 to come into contact with the ribbon 1 in the treatment enclosure 6.

As shown in Figure 2, the hood 5 and the flow control block 13 are suspended from the roof of the float tank 3 by means of rods 19. Π it is desirable to use threaded rods 19 so that adjust the height of the base of the hood 5 to obtain a small gap, for example 2 cm or less, up to the path of the tape 1.

The hood 5, the treatment enclosure 6, and the flow control block 13 are surrounded by a peripheral passage 20 through which the products of the underlayer formation reaction and the non-underlaying forming material used with, if desired, material from the ambient atmosphere sucked inside and coming from the float tank can be sucked up by the chimney 8. The hood 5 and the walls 6 of the treatment station are shown provided with optional peripheral skirts 21 at the base of the peripheral passage 20. These skirts are suitably made up of flexible refractory curtains produced for example in Refrasil (commercial brand).

After the glass ribbon has left the float tank 3, it passes through a processing station where the deposition of the upper layer (not shown) takes place near the outlet end of the float tank. The upper layer deposition enclosure itself may be of a type known per se and disposed at or before the upstream end of a horizontal annealing gallery through which the ribbon is conveyed before being cut in sheets. It is desirable that there is a closed passage between the outlet end of the float tank and the inlet of the treatment chamber where the top layer is deposited, especially if this passage is more than a few meters long, but also that this passage is filled with a non-oxidizing or reducing atmosphere. This can be easily achieved by blowing nitrogen on the freshly formed undercoat, and can be supplemented by an escape from the atmosphere of the float tank along this passage.

EXAMPLE 1

In a specific practical embodiment, to coat float glass moving at a speed of 7 meters per minute in a float tank, the treatment station where the deposition of the underlay is carried out is placed in a place the along the float tank where the glass is at a temperature of around 700 ° C. The supply line is supplied with nitrogen, and silane is introduced into it under a partial pressure of 0.2%, and oxygen is introduced under a partial pressure of 0.36% (ratio of 0.55). A coating of silicon oxide SiO is obtained_x where x is approximately equal to 1.8, which has a refractive index of approximately 1.69. The layer formed has a thickness of 75 nm. The coating-forming material in its carrier gas is conveyed along the supply line 7 to exit through a slot about 4 mm wide at a rate such that the material delivered flows between the glass and the hood 5 , which is located 15 mm above the path 1 of the glass, at a speed of approximately 2 to 3 meters per second, in the two directions parallel to the direction of movement of the ribbon. The hood 5 has a length in this direction of about 40 cm. Atmospheric material is sucked through the chimney 8 at a rate such that it generates an upward flow of gas in the peripheral passage 20, at a speed of approximately 7 to 8 meters per second, and this causes a continuous flow gas from the float tank in the base of the passage 20 over the entire periphery of the treatment enclosure 6, which prevents the escape of coating reagents or their reaction products to the float tank. Obviously, such aspiration also extracts unused coating reaction products and coating reagents.

In a subsequent coating step, implemented in a manner known per se in a coating station located near the outlet of the float tank, and before the upstream end of a horizontal annealing gallery, an upper coating layer made up of SnO₂ doped, 225 nm thick, is formed by pyrolysis of an aqueous solution of SnCl₂. A thickness tolerance of ± 45 nm for the upper layer of SnO₂ and ± 4 nm for the undercoat can be accepted without giving rise to unwanted color variations due to interference effects.

In the absence of an undercoat, such a tin oxide layer has a dominant greenish wavelength in reflection, and it may appear greenish yellow or greenish blue depending on the precise thickness of a place at the other. A quantitative estimate of the power of the light-modifying layer can be given in terms of the well-known Hunter coordinates. In the absence of an undercoat, such a tin oxide coating has a Hunter a coordinate between -6 and -7 and a Hunter b coordinate between -7 and +5. In the case of the two-layer coating of this example, however, with the silicon oxide sublayer of approximately 75 nm thick, and with a refractive index between 1.69 and 1.7, the coordinates a and b of Hunter are both between +2 and -2, which gives a much more uniformly neutral product,

EXAMPLE 2

It is desired to produce glass coated with a layer of doped tin oxide approximately 500 nm thick to protect from long wavelength infrared radiation. Such a coating can be easily formed by a technique known per se. Variations in thickness can cause variations in color across the coated panel from greenish (Hunter's coordinate of -15) to reddish (Hunter's coordinate of +7), which is believed to be commercially unacceptable . To do this, the glass is first provided with an under-layer of incompletely oxidized silicon oxide, having a thickness of 80 nm and a refractive index of 1.75 ± 0.01. This is easily obtained by adjusting the flow rates of silane and oxygen brought inside the treatment enclosure in the process described in Example 1. This sub-layer has the effect of reducing the color variations due to interference effects so that, for thickness variations up to ± 30 nm of the upper layer, the Hunter coordinates a and b are both included. between +2 and -2, which gives a much more uniformly neutral product. This remains true for variations up to ± 5 nm in the thickness of the undercoat.

EXAMPLE 3

We want to form a low emissivity coating with a thickness of 310 nm, consisting of doped zinc oxide, by pyrolysis of zinc acetate dissolved in a mixture of water and isopropanol as a formative material for the upper layer. coating. Indium chloride is added to the upper layer forming material to provide the required doping ions.

In accordance with the invention, the glass is first provided with an undercoat, constituted in this example of incompletely oxidized silicon oxide having a thickness of 73 nm and a refractive index of 1.79, and the upper layer is there applied to preserve this incomplete oxidation state. This is easily achieved by adjusting the flow rates of silane and oxygen supplied inside the treatment enclosure in the process described in Example 1. This also has the effect of significantly reducing the color variations due to variations in the thickness of the upper layer. Hunter's a and 'b coordinates are both between +2 and -2.

Variations in thickness up to ± 10 nm from the top layer, and variations in thickness up to ± 3 nm from the undercoat can be tolerated without causing discernible variations in the tint of the coated glass when is seen in reflection.

EXAMPLE 4

We want to form a low emissivity coating with a thickness of 505 nm, consisting of doped zinc oxide, by pyrolysis of zinc acetate dissolved in a mixture of water and isopropanol as a formative material for the upper layer. coating. Indium chloride is added to the upper layer forming material to provide the required doping ions.

In accordance with the invention, the glass is firstly provided with an undercoat, constituted in this example of incompletely oxidized silicon oxide having a thickness of 78 nm and a refractive index of 1.8. and the upper layer is applied to it to preserve this incomplete oxidation state. This is easily achieved by adjusting the flow rates of silane and oxygen supplied inside the treatment enclosure in the process described in Example 1. This also has the effect of significantly reducing the color variations due to variations in the thickness of the upper layer. Hunter's a and b coordinates are both between +2 and -2.

Variations in thickness up to ± 5 nm from the top layer, and variations in thickness up to ± 2 nm from the undercoat can be tolerated without causing discernible variations in the tint of the coated glass when is seen in reflection.

EXAMPLE 5

We want to form a low-emissivity coating with a thickness of 300 nm, consisting of indium tin oxide, by pyrolysis, according to a technique known per se, of indium chloride and dissolved tin chloride in dimethylformamide as a top coating layer forming material.

In accordance with the invention, the glass is firstly provided with an undercoat, constituted in this example of incompletely oxidized silicon oxide having a thickness of 74 nm and a refractive index of 1.77. and the upper layer is applied to it to preserve this incomplete oxidation state. This is easily achieved by adjusting the flow rates of silane and oxygen supplied inside the treatment enclosure in the process described in Example 1. This also has the effect of significantly reducing the color variations due to variations in the thickness of the upper layer. Hunter's a and b coordinates are both between +2 and -2.

Variations in thickness up to ± 10 nm from the top layer, and variations in thickness up to ± 2 nm from the undercoat can be tolerated without causing perceptible variations in the tint of the coated glass when is seen in reflection.

EXAMPLE 6

We want to form a low emissivity coating with a thickness of 500 nm, consisting of indium tin oxide.

In accordance with the invention, the glass is firstly provided with an undercoat, constituted in this example of incompletely oxidized silicon oxide having a thickness of 85 nm and a refractive index of 1.8. and the upper layer is applied to it to preserve this incomplete oxidation state. This is easily achieved by adjusting the flow rates of silane and oxygen supplied inside the treatment enclosure in the process described in Example 1. This also has the effect of significantly reducing the color variations due to variations in the thickness of the upper layer. Hunter's a and b coordinates are both between +2 and -2.

Variations in thickness up to ± 5 nm from the top layer, and variations in thickness up to ± 1 nm from the undercoat can be tolerated without causing perceptible variations in the tint of the coated glass when is seen in reflection.

EXAMPLE 7

A semiconductor undercoat of incompletely oxidized zinc oxide is formed by bringing a glass ribbon with metallic zinc vapor into contact in a treatment vessel located in a float vessel, in the presence of insufficient oxygen to cause complete oxidation of the zinc layer deposited on the glass.

The ZnO semiconductor underlay_x is then surmounted by a 500 nm thick conductive coating made of doped tin oxide which serves to protect the ZnO layer_x in an incompletely oxidized state, so that it can function as a semiconductor, and at the same time serves as an electrode in the finished product.

EXAMPLE 8

A glass ribbon in a float tank is first provided with a bottom layer of silicon dioxide 90 nm thick. This can be done by modifying the process described in Example 1, so that a sufficient amount of oxygen causes the complete oxidation of the silicon. To do this, silane is introduced into the treatment station where this lower layer is deposited under a partial pressure of 0.25%, and oxygen is introduced under a partial pressure of 0.5% (ratio of 0.5) .

This lower layer serves to avoid the poisoning by sodium of a sublayer of a vanadium sub-oxide deposited subsequently. A vanadium dioxide sublayer is formed, in a sublayer deposition station also placed in the float tank, downstream of the first station, by bringing the lower layer into contact with vanadium trichloride in vapor phase in presence of an insufficient quantity of oxygen to completely oxidize the vanadium in the sub-oxide sub-layer deposited on the lower layer.

In accordance with the invention, the vanadium dioxide is covered by an upper layer, while it is still in an incomplete oxidation state. An upper layer of tin oxide 500 nm thick is formed on the sub-layer, outside the float tank, before the annealing of the ribbon.