Device and method for forming a coating by pyrolysis

Device and method for forming a coating by pyrolysis

The present invention relates to a device for the formation, by pyrolysis, of a coating of metal or metal compound on a face of a hot glass substrate in motion by bringing the face into contact with a gaseous reagent, comprising support means for conveying the substrate through a coating chamber, at least one reagent gas inlet in the form of a slot opening directly into the coating chamber and extending transversely to the path of the substrate to supply and distribute gaseous reagent to the coating chamber and at least one outlet orifice gas to evacuate reaction gas from the coating chamber, as well as to a process of formation, by pyrolysis, of a coating of metal or metal compound on one face of a hot glass substrate in motion by bringing said face into contact with a reagent in the gas phase.

The coating of metal or metal compound formed on a hot glass substrate by pyrolysis is used to modify the apparent color of the glass and / or to exhibit other properties required with respect to the incident radiation, for example the property of reflect infrared. A single coating on the glass substrate, or a multi-layer coating, can be used for these purposes. Mention may be made, as examples, of tin oxide coatings SnO₂, tin oxide SnO₂ doped with fluorine, titanium dioxide

TiO₂, titanium nitride TiN, silicon nitride Si₃NOT₄, silica SiO₂ or SiO_x, alumina A1₂O₃, vanadium pentoxide V₂O₅ or tungsten oxide WO₃ or molybdenum oxide MoO₃, and oxides, sulfides, nitrides or carbides in general, and a stack of two or more of these coatings.

The coating can be formed on a sheet of glass which moves in a tunnel oven or on a glass ribbon during its formation, while it is still hot. The coating can be formed inside the gallery which follows the device for forming the glass ribbon, or inside the float tank on the upper face of the glass ribbon while it floats on a water bath. 'molten tin.

To form the coating, the substrate is brought into contact, in a coating chamber, with a gaseous medium comprising one or more substance (s) in the gas phase. The coating chamber is supplied by a gaseous reagent through one or more slit (s) whose length is at least equal to the width to be coated, it (s) itself supplied by one or more several ejection nozzles. Depending on the type of coating to be formed and the reactivity of the substances used, if several substances are to be used, these will be distributed either as a mixture by a single ejection nozzle into the coating chamber via a slot, or separately by several ejection nozzles via separate slots.

Processes and devices for forming such coatings 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 these devices lead to the formation of particularly resistant coatings which have advantageous optical properties.

Although such devices may be capable of forming coatings of acceptable quality, they have the disadvantage that coating material is wasted by deposition on other surfaces adjacent to the coating chamber, in particular on the roof of said chamber and that such deposits can over time accumulate and disturb the flow of reactive gas through the coating chamber causing a non-uniform coating and can even fall on the surface glass causing even greater defects.

One of the objects of the present invention is to provide a device and a method which facilitates the elimination of this disadvantage.

We have discovered that this objective could be achieved by using mobile means of protection in the bedroom.

Therefore, the present invention relates to a device for the formation, by pyrolysis, of a coating of metal or metal compound on one face of a hot moving glass substrate by bringing the face into contact with a reagent gaseous, comprising support means for conveying the substrate through a coating chamber, at least one reagent gas inlet in the form of a slot opening directly into the coating chamber and extending transversely to the path of the substrate to supply and distribute gaseous reagent to the coating chamber and at least one outlet orifice gas for discharging reaction gas from the coating chamber, characterized in that it is provided with mobile protection means arranged in the coating chamber adjacent to the 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 allows the continuous deposition of a coating on a glass ribbon with minimal soiling of the roof of the coating chamber, which gives an advantage from the point of view of wasting time. caused by cleaning and therefore improves the productivity of the device. It is surprising that the introduction of mobile protective means into the coating chamber does not disturb the coating process. This is particularly true when the roof of the coating chamber is close to the glass substrate, as is generally the case in CVD processes.

Preferably, the device further comprises means for moving the protective means in and out of the coating chamber, which avoids the need to move the protective means by hand.

In one embodiment of the invention, the protection means comprise a plurality of cables which extend through the coating chamber transversely to the direction of movement of the hot glass substrate. When a plurality of cables are used as protective means, the diameter of the cables and their relative spacing is an important factor in the effectiveness of the protection against the reactive gas of the roof of the coating chamber. The diameter of the cables will preferably correspond to 20% to 60% of the distance (Δ) between the surface of the coating and the roof of the coating chamber and they are spaced a distance equivalent to 1 to 5 times Δ.

In a variant of this embodiment, the protection means comprise smooth bars which extend across the width of the coating chamber and which are movable in and out of the coating chamber for cleaning. Although it is easier to remove material deposits from smooth bars rather than cables, bars are more difficult to keep straight under the high temperature conditions prevailing in the coating chamber.

In another variant, the protection means comprise a belt which extends through the coating chamber transversely to the direction of movement of the hot glass substrate.

Preferably, the device further comprises cleaning means arranged outside the coating chamber to remove deposits located on the protection means. Therefore, in use, any parasitic deposits formed on the protective means can be removed by the cleaning means, which allows the protective means to return, in a clean state, in the coating chamber.

Preferably, the cleaning means comprise a cooling chamber and guide means for causing the protection means to run there. The temperature in the coating chamber can be, for example, about 600 ° C. By rapid cooling of the protection means, the thermal shock thus imparted may be sufficient to release any coating material which adheres thereto, causing effective cleaning of the protection means. This is a particularly advantageous cleaning process when the protection means are in the form of cables. The cooling chamber may include a water jacket or be in the form of a water tank through which the protection means pass.

As a variant or in addition to the cleaning process, the protective means are brought into contact with a cleaning tool, such as a brush or a scraper, arranged outside the coating chamber to remove deposits from the cleaning means. protection.

The use of cables, a strap or other flexible element as protective means allows them to be tensioned, so as to ensure that they remain in a predetermined straight plane, which is preferably parallel to the surface of the substrate and to the roof of the coating chamber. Consequently, in a preferred embodiment of the invention, the protection means comprise a flexible element and means for tensioning it in the coating chamber.

The flexible element can be in the form of a continuous loop which is constantly animated during the coating process.

The device may include means for moving the protective means into and out of the coating chamber, and therefore into and out of the cleaning means disposed outside of the coating chamber. In the case of cables, a motorized pulley can be provided for this purpose. In the case of a belt, a motorized roller can be used.

In an alternative embodiment, the protection means consist of a movable curtain of inert gas adjacent to the roof of the coating chamber. In particular, the inert gas curtain flows in the same direction as the flow of reactive gas in 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 mobile mechanical elements. It is in fact surprising that the addition of a gas stream into the coating chamber does not reduce the efficiency of the coating process.

By the term inert gas is meant a gas which does not significantly affect the reaction of the gaseous reactant at the surface of the substrate. It will usually be selected from nitrogen, carbon dioxide, argon and their mixtures. The inert gas is preferably dry, since any water vapor present can react with the reactive gas, depending on the nature of the latter.

The flow of inert gas through the coating chamber will generally be parallel to the flow of the reactive gas and should be such that significant mixing with the reactive gas is avoided, so that the inert gas effectively forms a curtain , protecting the gaseous reagent from the roof of the coating chamber. However, some mixture of inert gas and reactive gas will inevitably occur at their mutual border. It has been found that a relatively cold gas curtain, for example having a temperature below 400 ° C when it enters the coating chamber, with an inert gas flow of between 0.4 and 1.5 Nm³/cm.h, for example 0.7 m³/ cm of substrate width, may be suitable.

The inert gas may be injected into the coating chamber by means of a plurality of inlets in the roof of the coating chamber and be evacuated therefrom by the gas exhaust duct. This can be obtained, according to an embodiment of the invention, in that the device comprises an inert gas supply chamber, the roof of the coating chamber being provided with a plurality of connected inert gas inlets to the inert gas supply chamber and opening into the coating chamber. It has been found that a spacing between the inlets of between 5 and 70 mm is appropriate. 11 it is preferable to make this spacing as small as possible, such as 5 to 20 mm.

Instead of the above-mentioned inlets, the coating chamber can be provided with porous roof pieces separating the coating chamber from the inert gas supply chamber, this construction providing a very simple way of obtaining an injection. inert gas uniform.

The flow of inert gas through the coating chamber is preferably controlled by the use of a variable speed pump and / or by a gas control valve located in the inert gas circuit.

It has been found that it is particularly advantageous to combine the various embodiments of the protection means, namely the simultaneous use of mobile cables and an inert gas curtain through porous roof parts in the coating chamber. .

The invention also relates to a process for the formation, by pyrolysis, of a coating of metal or of metallic compound on a face of a hot glass substrate in motion by bringing said face into contact with a gaseous reagent, comprising:

- the routing of the substrate through a coating chamber;

- the supply and distribution of gaseous reagent to the coating chamber using at least one reagent gas inlet in the form of a slot opening directly into the coating chamber and extending transversely to the path substrate; and

- the evacuation of reaction gas from the coating chamber, characterized in that protective means move in the coating chamber adjacent to its roof, to reduce the formation of deposits on the roof of the coating chamber .

The reagent gas inlet or inlets preferably comprise an ejection nozzle provided with a slit open directly in the coating chamber, the slit extending transversely to the path of the substrate, the length of said slit being at least substantially equal to the coating width of the substrate (ie the width of the part of the substrate that it is desired to coat). In one embodiment of the invention, the slot is formed by a longitudinal distributor, the internal longitudinal walls of which are substantially parallel to one another and form with the plane of movement of the substrate an angle between 20 ° and 40 °.

The axial plane of the nozzle can be inclined at an angle between 20 ° and 40 ° on 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 installation have been developed, which make it possible to form a coating by in-line pyrolysis of one or more vapor phase reagent (s) (CVD) on a strip of hot glass produced by the float process. The two types of installation for depositing a covering can be described as an asymmetrical installation and a symmetrical installation.

An asymmetrical installation has already been described in the British patents GB 1,524,326 and GB 2,033,374 (BFG Glassgroup), while a symmetrical installation is described in the patents GB 2,234,264 and GB 2,247,691 (Glaverbel).

Installations of both types can be placed above a glass ribbon after it leaves a float tank or above the glass while it is still in the float tank.

This makes it possible to cover substantially the entire width of the glass ribbon, for example around 3.2 m.

These installations can be removable. They can therefore be set up to produce coated glass, and removed whenever necessary.

A system for depositing a layer in a float tank may include means for ensuring precise geometry and operation even at the high temperatures prevailing in a float tank. Therefore, the coating deposition device can be coupled to a carriage carrying several rollers engaging on fixed guide beams. Preferably, the device further comprises means for adjusting the height of the coating chamber above the glass substrate. Therefore, pistons can be arranged to adjust the distance between the glass and the roof of the coating chamber to a value which is generally less than 50 mm (preferably between 3 and 30 mm).

The float tank can be closed, at the point of passage of the device, by a bellows system.

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

FIG. 1 represents a vertical section of an asymmetrical installation according to the invention;

Figure IA is a section along the line I -I of Figure 1; and

FIG. 2A represents a partial vertical section of an asymmetrical installation variant according to the invention.

Figures 1 and IA represent the whole of an asymmetrical installation which comprises three main parts:

(i) two ejection nozzles (10) of vaporized or gaseous reagent, each having a height of 85 cm and comprising a slot 12a, 12b, each slot having a path for the gas of 15 cm, an opening of 8 mm and a space between the slot walls of 4 mm;

(ii) a coating chamber 14, consisting of a flat arch delimiting a corridor open downwards, above the glass 16; and (iii) a slot 18 for extracting the used vapors.

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

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

When hot reagents are brought into contact with the glass at a point located outside the float tank, the entire installation is preferably isolated.

The number of successive reagent supply slots 12a, b depends on the nature of the coating to be formed. These slots 12a, b are inclined in the direction of the coating chamber 14.

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

The means for supplying gaseous reagents consist of a supply conduit 22 connected to a connector 26 leading to the nozzle 10.

The vault or the roof 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 and for all, according to the most common speed of movement of the glass, for example 14 m / min for glass of 4 mm - and the concentration of the reagent is adjusted if necessary. depending on the nature and thickness of the coating to be obtained.

The installation is sealed using carbon fiber seals when it is located in the float tank or by liners made of Refrasil (trademark) or Cerafelt (trademark).

To avoid soiling of the coating chamber 14 by parasitic deposits which can fall on the glass 16 and create defects in the coating which is formed therein, the installation includes a system for trapping parasitic deposits. Metallic cables 40, preferably made of stainless steel, are placed under the roof (38) of the coating chamber

14. These cables preferentially collect the solid matter which forms above the glass 16 and separate the gaseous current from the vault, which remains clean. The cables move transversely as the glass 16 advances, which makes it possible to gradually extract the soiled part and replace it with a clean part.

The installation is made up of annealed metal parts fixed to each other by means of bolts, rather than by welding, to avoid thermal distortions.

Referring to FIG. 1A, it can be seen that each metal cable 40 passes through a cooling chamber 42 disposed outside the coating chamber. The cooling chamber 42 comprises upper and lower cooling coils 44, 46 traversed by a cooling fluid, such as water at room temperature. At the exit of the cooling chamber 42, each cable passes through a motorized pulley

48. A tensioning device, indicated by the general reference 50, applies a tension to the cable 40, to ensure that it has a straight path through the coating chamber 14, parallel to the coating surface of the glass substrate 16 and to the roof of the coating chamber 38. The tensioning device 50 may be in the form of counterweights on either side of the glass ribbon.

Although not shown in Figure IA, similar cooling chambers and tensioning devices can be arranged on the other side of the coating chamber 14, allowing the cable to be moved first in one direction at the across the coating chamber, and then in the opposite direction, the length of the movement in each direction being sufficient to ensure that the entire cable which passes through the coating chamber then passes through one or the other of the cooling chambers. However, it is preferred to use a closed loop cable, which allows movement in one direction; all you need is a motorized pulley and a cable tensioning device.

Instead of the cooling chamber 42, the cables 40 can pass through a water bath, where direct contact with the water generates the thermal shock necessary for detachment of the deposited material.

In variants of the construction shown in FIGS. 1 and 1A, the cables 40 can be replaced by an endless belt made of steel lattice or of steel strip or by smooth steel bars.

In the embodiment shown in Figure 2, a glass ribbon 216 is supported by rollers 220 and the device comprises protective means consisting of a movable curtain of nitrogen adjacent to the roof of the coating chamber. The roof 238 of the coating chamber 214 is formed by a plurality of nitrogen inlets 243 opening out from a nitrogen supply chamber 241. The inlets 243 each have an opening of 2 mm and are spaced apart by one the other 2 cm.

The inlets are arranged angularly in the direction of flow of the reactive gas into the coating chamber 214 from the nozzle for injecting reactive gas 212. Nitrogen is then passed through the inlets 243 in the coating chamber 214 in the same direction as the gaseous reagent. Nitrogen is brought into the supply chamber 241 at ambient temperature at a flow rate of approximately 0.7 Nm³/ cm of substrate width / hour. Since the device is at high temperature, the temperature of nitrogen rises, up to about 300 ° C when it enters the coating chamber 214. However, the nitrogen is in the coating chamber at a temperature lower than that of the reactive gas. The nitrogen forms a curtain 240 which separates the gaseous reagent from the roof 238 of the coating chamber. The gaseous reagent and the nitrogen leave the coating chamber through the gas outlet 218.

In an alternative embodiment, the inlets 243 of the coating chamber may be replaced by roof pieces of porous metal.

It has been found that it is particularly advantageous to combine the characteristics of Figures 1 and 2, namely the simultaneous use of movable cables and a nitrogen curtain brought into the coating chamber by porous roof parts.

EXAMPLE

The following example illustrates the use of an asymmetrical installation as described with reference to Figures 1 and IA. Installation allows depositing, for example, tin oxide coatings SnO₂, tin oxide SnO₂ doped with fluorine, titanium dioxide TiO₂, titanium nitride TiN, silicon nitride Si₃NOT₄ and, in general terms, oxides, sulfides, nitrides or carbides.

To form SnO tin oxide coatings₂ or TiO titanium dioxide₂, two successive slots 12a, 12b are used. The reagent carrying the metal (Sn or Ti) (supplying the first slot 12a) is a tetrachloride, liquid at room temperature, vaporized in a current carrying anhydrous nitrogen gas at about 600 ° C. The vaporization is facilitated by the atomization of these reactants in the carrier gas.

To produce the oxide, the tetrachloride molecules are placed in the presence of water vapor supplied to the second slot 12b. The steam is superheated to about 600 ° C, and is also injected into a carrier gas, which is air heated to about 600 ° C. SnO₂ can be formed for example by means of SnCl proportions₄ and of H₂O given in the British patent

GB 2 026 454 (Glaverbel).

In the case of the formation of tin oxide SnO₂ conductive, the dopant is fluorine: HF is added to water vapor. The partial pressure of HF is pHF = 0.2 pSnCl₄. Another dopant can also be introduced: liquid antimony chloride SbCl₅ which is mixed directly with tin chloride SnCl₄, with which it is miscible in all proportions. The presence of antimony chloride SbCl₅ makes it possible to color tin oxide coating SnO₂, which can then absorb (and reflect) part of the near infrared of solar radiation.

The gas flow (carrier gas + reagent) in each slot 12 is 1 m³/ cm of slit / h, at working temperature.

To deposit SnO coatings₂ or TiO titanium dioxide₂, we choose Inconel 600, or even an even more refractory alloy (Hastalloy) for the parts of the device which are in contact with tin chloride SnCl₄ or titanium chloride TiCI₄ and Monel 220 for the slot distributing water vapor and HF.

The cables 40 have a diameter of 8 mm and are spaced 50 mm apart. They are arranged near the roof 38 of the coating chamber 14 and are stretched by two counterweights, one on each side, of 15 kg each, to ensure their straight and parallel arrangement. It is recommended to take precautions to avoid shocks to the cables during their movements, in order to prevent material which has been deposited on the surface of the cables from coming off, which would cause defects in the coating formed on glass. The cables are moved in the coating chamber at a speed of 1 m / sec, while the substrate moves at the rate of 10 m / min.

Soiling of the roof of the coating chamber during operation of the device is low, which reduces the need to stop the