Device and method for forming a coating by pyrolysis

(54)

PATENT INVENTOR INVENTOR'S OFFICE NAME

Glaverbel, Brussels BE Robert Terneu, Thimeon BE, H Albihns Patent Office AB Device and methods for coating metal or (56) (57) glass substrates

CALLED PUBLICATIONS: - Secondo Franceschi, Gosselies BE through pyrolysis to form a metal compound on a surface of a

SUMMARY:

An apparatus is described for the formation by pyrolysis of a metal or metal compound coating on a surface of a hot glass substrate by contacting the surface with a gaseous reagent. The device comprises support means (20) for passing the substrate (16) through a coating chamber (14). At least one reagent gas input in the form of a gap (12) which opens directly into the coating chamber and extending across the path of the substrate is provided to supply and distribute reagent gas to the coating chamber. At least one exhaust outlet (18) is provided for discharging exhaust gas from the coating chamber. The invention is characterized by movable screen device (40) located in the coating chamber adjacent to its roof (38) to reduce the formation of deposits on the roof of the coating chamber.

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The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

504 491

The present invention relates to a device for forming, by pyrolysis, a coating of metal or metal compound on a surface of a hot glass substrate by contacting the surface with a gaseous reagent, comprising support means for transporting the substrate through a coating chamber, at least one reagent gas input for supplying and distributing reagent gas to the coating chamber and at least one suction outlet for discharging output gas from the coating chamber and also for a method of forming a metal or metal compound coating on a hot glass substrate by pyrolysis of a reagent in the gas phase.

The metal or metal compound coating formed on a hot glass substrate by pyrolysis is used to modify the visible color of the glass and / or to provide other properties required for incident radiation, such as the property of reflecting infrared. A simple coating on the glass substrate can be used for these purposes or a multilayer coating. Examples would be tin oxide SnO coatings₂, tin oxide SnO₂ doped with fluorine, titanium dioxide TiO₂, titanium nitride TiN, silicon nitride Si₃N₄, silica SiO₂ or SiÖ_x, alumina A1₂O₃, vanadium pentoxide V₂O₅ or tungsten oxide WO₃ or molybdenum oxide Mo0₃ and generally oxides, sulfides, nitrides or carbides and a layer of two or more of these coatings.

The coating can be formed on a sheet of glass moving in a tunnel oven or on a glass band during formation, while it is still warm. The coating can be formed inside the cooling duct that follows the glass band forming device or inside the float water on the upper surface of the glass band while the latter floats on a bath of molten tin.

504 491

To form the coating, the substrate is contacted in a gaseous medium coating chamber comprising one or more substances in the gas phase. The coating chamber is fed with a reagent gas through one or more slots, the length of which is at least equal to the width to be coated, fed through one or more outflow nozzles. Depending on the type of coating to be formed and the reactivity of the substances used, if several substances must be used, these are distributed either in the form of a mixture through a single effluent nozzle in the coating chamber via a slot or separately through several outflow nozzles via separate slots.

Methods and devices for forming such a coating are described, for example, in French Patent No. 2,348,166 (BFG Glassgroup) or in French Patent Application No. 2,648,453 A1 (Glaverbel). These methods and devices lead to the formation of particularly strong coatings with advantageous optical properties.

While such devices may be capable of forming coatings of acceptable quality, it is a disadvantage of such devices that certain coating materials are deposited falsely on other surfaces adjacent to the coating chamber, especially in its roof, and over time such deposits may build up and interfere with the flow of the reagent gas through the coating chamber and thereby result in uneven coating or may also fall onto the glass surface thereby causing even more serious defects.

It is an object of the present invention to provide a device and method whereby the aforementioned disadvantage is easier to avoid.

We have discovered that this object can be achieved by providing a moving screen in the coating chamber.

Thus, according to the invention, an apparatus for forming, by pyrolysis, a coating of metal or metal compound on a surface of a moving hot glass substrate by contacting the surface with a gaseous reagent, is intended.

504 491 comprising support means for transporting the substrate through a coating chamber, at least one reagent gas inlet in the form of a slot, which opens directly into the coating chamber and extending transversely of the substrate path to supply and distribute reagent gas to the coating chamber and at least one extraction output to exhaust exhaust from the coating chamber characterized by the presence of a movable screen device; located in the coating chamber near its roof to reduce the formation of deposits on the roof of the coating chamber.

The device according to the invention is a simple device which enables continuous deposition of a coating on a glass band with minimal contamination of the roof of the coating chamber, thereby providing an advantage expressed in settling time required for cleaning and consequently improving the device's productivity. Surprisingly, the introduction of a movable screen device into the coating chamber does not interfere with the coating process. This is especially true since the roof of the coating chamber is close to the glass substrate, as is generally the case with CVD methods (Chemical Vapor Deposition).

The device further comprises means for moving the screen device in and out of the coating chamber, thereby avoiding the need to move the screen device by hand.

In one embodiment of the invention, the screen device comprises a plurality of lines extending across the coating chamber across the direction of movement of the hot glass substrate. When a plurality of ropes are used as the shielding device, the diameter of the ropes and their relative spacing are an important factor for successfully shielding the coating chamber roof from the reagent gas. We prefer that the diameter of the lines should correspond to from 20% to 60% of the distance (Δ) between the coating surface and the roof of the coating chamber and is spaced apart at a distance equivalent to between 1 and 5 times Δ.

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In a modification of this embodiment, the screen assembly comprises smooth bars extending across the width of the coating chamber and movable into and out of the coating chamber for cleaning purposes. Although it may be easier to remove deposition material from smooth rods compared to ropes, rods are more difficult to keep straight under the high temperature conditions prevailing in the coating chamber.

In a further modification, the screen device comprises a band, for example made of steel cloth, extending across the coating chamber across the direction of movement of the hot glass substrate.

The device preferably includes a cleaning device located outside the coating chamber to remove deposits from the screen device. Thus, during operation, any litter deposited on the screen device can be removed therefrom by the cleaning device which allows the screen device to be returned in a clean state to the coating chamber.

Most preferably, the cleaning device comprises a cooling chamber and control means for causing the screen devices to pass therethrough. For example, the temperature of the coating chamber may be about 60 ° C. By rapidly cooling the screen device, the heat shock thus imparted thereto may be sufficient to cause any adhered coating material to be dissolved therefrom and thereby effectively clean the screen device. This is a particularly advantageous way to clean when the screen device is in the form of ropes. The cooling chamber may comprise a water jacket or may be in the form of a water container through which the screen device passes.

As an alternative or additional method of cleaning, the screen device is contacted with a cleaning device, such as a brush or scraper located outside the coating chamber to remove deposits from the screen device.

504 491

The use of ropes, a band or other flexible element as the shielding device enables the shielding devices to be tensioned to ensure that it lies in a straight, predetermined plane, which is preferably parallel to both the substrate surface and the coating chamber roof. Thus, in a preferred embodiment of the invention, the screen device comprises a flexible element and device for clamping the same in the coating chamber.

The flexible element may be in the form of a continuous loop which is constantly driven as the coating process continues.

The device may comprise means for moving the screen device in and out of the coating chamber and thereby in and out of the cleaning device located outside the coating chamber. In the case of ropes, a motor driven disc may be provided for this purpose. In the case of a belt, a motor driven roller can be used.

In an alternative embodiment, the screen assembly comprises a moving inert gas curtain adjacent to the roof of the coating chamber. In particular, the inert gas curtain flows in the same direction as the flow of the reagent gas into the coating chamber.

The inert gas curtain can generally suppress the formation of deposits. The use of an inert gas curtain is advantageous in that it does not require the presence of moving mechanical elements. It is really surprising that the supply of a gas stream into the coating chamber does not decrease the efficiency of the coating method.

By the term inert gas we mean a gas which does not significantly affect the reaction of the reagent gas at the substrate surface and will usually be selected from nitrogen, carbon dioxide, argon and mixtures thereof. The inert gas is preferably dry since any present vapor may react with the reagent gas depending on the nature of the latter.

504 491

The inert gas flow through the coating chamber should generally be parallel to the reagent gas flow and should be such that significant mixing with the reagent gas is avoided so that the inert gas effectively forms a curtain, shielding the reagent gas from the roof of the coating chamber. Nevertheless, some mixing between the inert gas and the reagent gas will inevitably occur at their mutual limit. We have found that a relatively cold gas curtain, for example with a temperature below about 400 ° C when entering the coating chamber, is effective with an inert gas flow rate of from 0.4 to 1.5 Nm.³/ cm.h such as about 0.7 m³/ cm width of substrate / h.

The inert gas can be injected into the coating chamber by a plurality of inlet openings in the roof of the coating chamber and extracted therefrom through the gas extraction outlet. This can be achieved according to an embodiment of the invention in that the device comprises an inert gas feeding chamber, the roof of the coating chamber being provided with a plurality of inert gas openings in communication with the inert gas supply chamber and opening in the coating chamber. A distance between the entrance openings of between 5 and 70 mm has been found to be suitable. It is preferred to make this distance as small as possible, such as from 5 mm to 20 mm.

Instead of openings mentioned above, the coating chamber may be provided with porous roof portions separating the coating chamber from the inert gas supply chamber, this construction providing a particularly simple way to achieve uniform injection of the inert gas.

The flow rate of the inert gas through the coating chamber is preferably controlled by using a variable speed pump and / or by arranging a variable gas limiting valve in the inert gas circuit.

We have found it particularly advantageous to combine the various embodiments of the screen devices, ie through

504 491 to use both movable ropes and an inert gas curtain fed through porous roof portions of the coating chamber.

The invention also relates to a method for forming, by pyrolysis, a metal or metal compound coating on a surface of a hot glass substrate by contacting the surface with a gaseous reagent, comprising:

transporting the substrate through a coating chamber;

supplying and distributing reagent gas to the coating chamber by at least one reagent gas input in the form of a gap which opens directly into the coating chamber and extends across the path of the substrate; and

- exhaust is emitted from the coating chamber, which is characterized by moving screen device in the coating chamber adjacent to its ceiling to reduce the formation of deposits on the coating chamber roof.

The reagent gas inlet or inputs preferably comprise an outflow nozzle having a gap which opens directly into the coating chamber, the gap extending across the path of the substrate, the length of the gap being at least substantially equal to the coating width of the substrate (i.e., the width of the portion). the substrate which one wishes to coat). In one embodiment of the invention, the gap is formed by a longitudinally extending distributor, whose longitudinal inner walls are substantially parallel to each other and, with the plane of movement of the substrate, form an angle between 20 'and 40'.

The axial plane of the nozzle may be inclined at an angle of between 20 'and 40' to the plane of movement of the substrate. Preferably the axial plane of the nozzle is substantially perpendicular to the plane of movement of the substrate to avoid congestion.

Two types of installations have been developed which allow for continuous coating formation in line by pyrolysis of a reagent or vapor phase (CVD) reagents on a hot glass band made by the float process. Two types of installations for depositing a coating can be described

504 491 as an asymmetrical installation and a symmetrical installation.

An asymmetric installation has already been described in patent specifications GB 1,524,326 and GB 2,033,374 (BFG Glassgroup), while a symmetrical installation has been described in patent specifications GB 2,234,264 and GB 2,247,691 (Glaverbel).

Both types of installation can be placed above the glass band after it exits from the float water or over the glass while it is still in the float water.

They enable essentially the entire width of the glass strip, eg about 3.2 m, to be coated.

These installations could be removable. They can therefore be positioned to produce coated glass and removed whenever necessary.

A system for depositing a layer in a float water can include apparatus for ensuring accurate geometry and functioning even at the high temperatures prevailing in a float water. The coating deposition device may be coupled to a bogie which carries a plurality of rollers adapted to engage in fixed guide beams. Preferably, the device further comprises means for adjusting the height of the coating chamber above the glass substrate. Thus, piston devices may be provided to allow adjustment of the distance between the glass and the CVD coating chamber (Chemical Vapor Deposition) to a distance generally less than 50 mm (preferably between 3 and 30 mm).

The float water may be sealed at the point where the device passes by a bellows system.

The invention will now be described with reference to the accompanying drawings in which:

504 491 Fig. 1 shows in vertical cross-section an asymmetric installation according to the invention;

Figure 1A is a schematic cross-section taken along line II of Figure 1; and Fig. 2A finally shows in vertical cross section part of an alternative asymmetric installation according to the invention.

Figures 1 and 1A show the whole of an asymmetric installation comprising three main parts:

(i) two steam or gaseous reagent effluent nozzles 10, each with a height of 85 cm and including a slot 12a, 12b, each slot having a gas flow path of 15 cm, an opening dimension of 8 mm and a distance between the walls of the gap of 4 mm;

(ii) a coating chamber 14, consisting of a flat arch which limits a channel open to the bottom above the glass 16; and (iii) a slot 18 for drawing out the used vapors.

The glass band 16 is supported by rollers 20 and driven in the direction indicated by arrow A.

The flow of vapors in the coating chamber 14 along the glass 16 is controlled mainly by suction.

Since hot reagents must be contacted with the glass 16 at a point located outside the float water, the entire installation is preferably insulated.

The number of consecutive reagent delivery slots 12a, b depends on the nature of the coating to be formed. These slots 12a, b are inclined to the coating chamber 14.

504 491

This device can be placed over the glass 16 so that the reagents flow in the direction of movement of the strip A or in the opposite direction.

The delivery device for the gaseous reactants consists of a supply line 22 connected to an adapter 26 which leads into the nozzle 10.

The vault or ceiling 38 of the coating chamber 14 is at a distance (Δ) of 20 mm from the glass 16. The width of each of the slots 12a and 12b is 4 mm. The length of the coating chamber 14 is chosen so that the reagent remains in contact with the glass 16 for 6 to 10 seconds. In practice, the length of the coating chamber 14 is chosen once for all according to the most common rate of movement of the glass 16 - ie about 14 m / minute for 4 mm glass - and the reagent concentration is adjusted whenever necessary according to the nature and thickness of the coating to be obtained.

The installation is sealed by carbon fiber joints (especially when the installation is located in a float water) or by Refrasil (trademark) or Cerafelt (trademark) skirts.

In order to prevent contamination of the coating chamber 14 by litter deposits which may fall on the glass 16 and create defects in the coating formed thereon, the installation includes systems for collecting litter deposits. A number of stainless steel metal ropes 40 are disposed below the vault 38 of the coating chamber 14. Preferably, these ropes collect the solid material formed above the glass 16 and divert the gas streams away from the vault which remains clean. The ropes move transversely as the glass 16 moves, thus making it possible to retract the contaminated portion progressively and replace it with a clean portion.

The installation is formed of annealed metal pieces attached to each other by bolts rather than welding to avoid heat warping.

504 491

Referring to Fig. 1A, it appears that each metal line 40 passes through a cooling chamber 42 located outside the coating chamber 14. The cooling chamber 42 comprises upper and lower cooling coils 44, 46 through which a coolant such as water of room temperature flows. Upon exiting from the cooling chamber 42, each line passes over a motor-driven switch plate 48. A clamping device, generally designated by the reference numeral 50, applies voltage to the line 40 to ensure that the latter has a straight path through the coating chamber 14 parallel to both the coating surface of the glass substrate 16 and the coating chamber roof 38.

The clamping device 50 may be in the form of counterweights on either side of the glass band.

Although not shown in Fig. 1A, similar cooling chambers and clamping devices may be located on the other side of the coating chamber 14, which allows the line to first move in one direction through the coating chamber and then in the opposite direction, the extent of movement in each direction being sufficient the entire line passing through the coating chamber is then passed through one or both of the cooling chambers. However, we prefer to use a closed loop of the rope, thereby enabling movement in only one direction, where there is a need for only one motor driven break disk and clamping device for each rope.

Instead of the cooling chamber 42, the lines 40 can pass through a water bath, where direct contact with the water therein produces the required heat shock to release the deposited material.

In the design alternatives shown in Figures 1 and 1A, the ropes 40 can be replaced by an endless steel cloth or steel strip or by smooth steel rods.

In the embodiment shown in Fig. 2, a glass band 216 is supported on rollers 220 and the device comprises screen device including a nitrogen curtain adjacent to the roof of the coating chamber. The roof 238 of the coating chamber 214 is formed with a plurality of nitrogen inlet openings 243 which conduct

504 491 from a nitrogen storage chamber 241. The openings 243 each have an opening dimension of 2 mm and are arranged at a distance of 2 cm from each other.

The openings are angled in the direction of the reagent gas flow through the coating chamber 214 from the reagent gas inlet nozzle 212. Thus, the nitrogen passing through the openings 243 is caused to flow through the coating chamber 214 in the same direction as the reagent gas. Nitrogen is supplied to the storage chamber 241 at room temperature at a flow rate of about 0.7 Nm³/ cm width of substrate / h. Since the device is at an elevated temperature, the temperature of the nitrogen rises up to about 300 ° C as it enters the coating chamber 214. Nevertheless, the nitrogen is at a temperature in the coating chamber 214 which is less than that of the reagent gas. The nitrogen forms a curtain 240 which separates the reagent gas from the roof 238. of the coating chamber 214. Both the reagent gas and the nitrogen exits the coating chamber through the gas outlet 218.

In an alternative embodiment, the openings 243 can be replaced by porous metal roof parts in the coating chamber.

We have found it particularly advantageous to combine the features of Figures 1 and 2, ie using both moving lines and a nitrogen curtain fed through porous roof sections in the coating chamber.

Example

The following example illustrates the use of an asymmetric installation as described in connection with Figures 1 and 1A. This installation enables, for example, deposits of tin oxide SnO to be deposited₂, tin oxide SnO₂ doped with fluorine, titanium dioxide TiO₂, titanium nitride TiN, silicon nitride Si₃N₄ and, in general terms, oxides, sulfides, nitrides or carbides.

To form tin oxide coatings SnO₂ or titanium dioxide TiO₂, two consecutive slots 12a, 12b were used. The reagents carrying the metal (Sn or Ti) (fed into it)

504 491 first slot 12a) is a tetrachloride, liquid at ambient temperature, evaporated in a stream of anhydrous nitrogen gas at a temperature of about 600 ° C. Evaporation is facilitated by atomizing these reagents in the carrier gas.

To produce the oxide, the tetrachloride molecules are introduced into the presence of water vapor led to the second gap 12b. The water vapor is superheated to about 600 ° C and is also injected into a carrier gas which is air heated to about 600 ° C. Twist₂ can be formed, for example, using the proportions of SnCl₄ and H₂O as disclosed in British Patent Specification GB 2,026,454 (Glaverbel).

When it comes to the formation of conductive tin oxide SnO₂, the dopant is fluorine: HF is added to the water vapor. HF's partial pressure is pHF = 0.2 pSnCl₄. Another dopant may also be introduced: liquid antimony chloride SbCl₅, which is directly mixed with the tin chloride SnCl₄, with which it is miscible in any proportion. The presence of the antimony chloride SbCl₅, makes it possible to dye tin oxide, SnO₂coating, which can then absorb (and reflect) a portion of the near infrared solar radiation.

The flow rate of gas (carrier gas + reagent) in each slot 12 is 1 m³/ cm per run / h at operating temperature.

To deposit tin oxide SnO₂- or titanium dioxide TiO₂coatings, the Inconel 600 or, optionally, an even more heat-resistant alloy (Hastelloy) is chosen for the device parts that are in contact with tin chloride SnCl₄ or titanium chloride TiCl₄and Monel 220 for the gap with water vapor and HF.

The ropes 40 have a diameter of 8 mm and are spaced at a mutual distance parallel to each other by 50 mm. They are located near the roof 38 of the coating chamber 14 and are subjected to a tension of two counterweights one on each side of 15 kg weight each to ensure their straight and parallel arrangement. It is recommended to take steps to avoid shocks to the ropes during their movements to avoid the release of material deposited on the surface of the ropes;

504 491 which would cause failure of the coating formed on the glass. The lines are driven through the coating chamber at a rate of 1 m / second, while the substrate is moving at a rate of 10 m / minute.

The contamination of the roof of the coating chamber during operation of the device is low, thereby reducing the need to stop the device for cleaning purposes.

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