FR2484991A1 - METHOD AND DEVICE FOR FORMING A UNIFORM COATING WITH MULTIPLE COMPONENTS - Google Patents

Abstract

In order to apply a uniform coating (5), containing at least two coating substances, onto a glass-like carrier (4), at least one coating-forming substance is sprayed separately from the or at least one other coating-forming substance, the separately sprayed coating-forming substances being sprayed onto essentially identical surfaces of the carrier (4), in order to form the uniform coating (5), at least one of these coating-forming substances being sprayed on in an aqueous solution. The apparatus for carrying out the process has conveyors (3) for the carrier (4) and at least one coating head (8) with at least two spray guns (10 and 11) fastened to the conveyor (7, 9). The spray guns (10, 11) are connected to at least two different coating-solution tanks (17, 19). The spray guns (10, 11) are inclined relative to the horizontal in such a way that the main horizontal component of the spray droplets points forwards or rearwards.

Description

 The present invention relates to a method for forming a uniform coating comprising at least two constituents, on a vitreous support, by spraying onto the hot support, substances generating the coating to form the coating by pyrolysis. The invention includes a device suitable for implementing such a method.

 Methods of the type indicated above ~ are used for example to form electrically conductive coatings which modify the effect of the support on the incident electromagnetic radiation of different wavelengths. Such coatings are used, among other things, to reduce the emissivity of the support vis-à-vis infrared radiation, especially radiation of wavelength greater than 5,000 nm. When used for such purposes, these coatings are typically doped with an additive which increases the conductivity of the coating so that it will have a marked influence on, for example, the reflection rate in the infra -red of the coated support. Methods of the type indicated above can also be used to form coatings which modify other properties of the support, for example its apparent color.

When using known methods, one encounters the fact that the speed at which a coating of given thickness can be constructed is inappropriately reduced. The coating speed can be increased within certain limits by increasing the concentration of the coating generating solution, but in many cases the coating solution becomes unstable at high.

concentrations and this has undesirable effects. In particular, certain solutions of coating-generating substances tend to form gels at high concentrations and can therefore practically no longer be sprayed. The coating speed can also be increased within certain limits by increasing the spray amount of a coating solution of given concentration. However, this involves the spraying of larger quantities of solvent which must evaporate when it reaches the hot vitreous support, thus stripping the support of amounts of heat which are therefore no longer available for the pyrolysis of the substances generating the coating. , above a certain spraying rate, it becomes impossible to form uniform coatings of good quality because the sprayed droplets are too large and / or because the droplets have too high an impact force on the support.

Attempts have been made to form good quality coatings at higher speeds by spraying quantities of coating solution simultaneously from two sprayers; but the results were not satisfactory given the large quantity of solvent sprayed and the large loss of heat from the support which ensued.

 One of the objects of the present invention is to provide a coating method which is applicable for forming multi-component coatings at higher speed than is possible by known methods, and / or for allowing greater latitude in the choice of coating generating substances.

 The present invention provides a method of forming a uniform coating comprising at least two constituents on a vitreous support by spraying onto the hot support, substances generating the coating to form the coating by pyrolysis, characterized in that at least one coating generating substance is sprayed separately from (at least one) other generating substance, in that these separately sprayed generating substances are sprayed simultaneously so as to substantially cover the same area of the support, to form a uniform coating, and in that at least one of them is sprayed in aqueous solution.

 For this reason, the present invention substantially avoids the risk of premature reaction between the coating generating substances sprayed separately, and this has the indirect effect that these substances can be sprayed at higher concentrations than has been possible. so far and therefore the coating can be formed at higher speed. The invention also allows a greater latitude in the choice of the generating substances of the coating. For example, using the present invention, it is possible to use generating substances which, if mixed in a common solution, would react together , with for example the formation of a precipitate, and even generating substances for which there is no single solvent in which they are sufficiently soluble for practical applications.

 In the preferred embodiments of the invention, the substances generating the coating are chosen so as to give rise to a coating, on a vitreous support, which reduces the emissivity of the coated surface with respect to infrared radiation. red.

This gives a product which is commercially highly desirable for its applications in glazing, buildings for example. Preferably, at least one substance generating the coating is chosen and sprayed so as to give rise to a minor constituent of the coating and this (these) substance (s) generating (s) is (are) sprayed (s) in aqueous solution. In fact, many of the minor constituents in question are soluble in water. Water is the cheapest and most universally available of all solvents.

In certain preferred embodiments of the invention, a substance generating the coating is chosen and sprayed so as to give rise to a main constituent of the coating and this generating substance is sprayed in a solution comprising water. It is however preferable not to use too large a quantity of water especially when the substance generating the main component is sprayed, having regard to its latent heat of vaporization and to the heat loss from the vitreous support which results therefrom, when the sprayed solvent is vaporized on contact with the support. For this reason, in the preferred embodiments of the invention, a coating generating substance is chosen and sprayed so as to give rise to a main constituent of the coating and this generating substance is sprayed in a solution comprising an organic solvent. The organic solvent can be used alone or in some cases, mixed with water. The organic solvent can be chosen for different properties outside of its capacity to dissolve the or a substance generating the main constituent of the coating. For example, the organic solvent can be chosen from those whose surface tension is lower than that of water. This facilitates the formation of smaller droplets in the spraying process which promotes a more uniform coating of the support. The organic solvent can be chosen from those which have a specific latent heat of vaporization lower than that of batten, in relation to their capacity to dissolve the main generating substance of the coating. In this way 11 evaporation of the solvent, when it reaches the support, will remove less thermal energy from the support. In fact, the organic solvent can be chosen from those which react exothermically at or below the temperature of the hot support, so that thermal energy is in fact released. Methanol satisfies these three conditions vis- vis-à-vis the coating generating substances particularly targeted and is a solvent especially preferred for its use in the present invention.
The present invention is of particularly suitable use in situations where one component of the coating is a metal oxide and another is a doping agent selected to increase the electrical conductivity of the metal oxide coating. For example, the present invention makes possible the formation of a coating of tin oxide (SnO2) doped with fluorine ions from tin dibutyldiacetate as generator of the main constituent of the coating and of ammonium bifluoride (NH4F. HF) as an additive generator. Tin dibutyldiacetate is substantially soluble in organic solvents only, while ammonium bifluoride is not substantially soluble in organic solvents.

While the year may use dibutyldiacetate, or in fact other organic metal salts as the metal oxide coating generating substance, for reasons of cost and availability it is preferred that the coating metal generating substance metal oxide is an inorganic metal salt, among which tin chloride and indium chloride are especially suitable for the formation of coatings of tin oxide and indium oxide respectively.

When operating according to the invention, any coating generating substance can be chosen solely as a function of the properties of the coating constituent to which it will give rise.

In embodiments of the invention in which the substance generating a constituent of a metal dioxide coating is tin chloride, it is advantageous to choose a substance generating doping agent from ammonium bifluoride and antimony chloride. In embodiments of the invention, where the generating substance of a constituent of a metal oxide coating is indium chloride, it is advantageous to use tin chloride as the generating substance. doping agent.

By way of example of the advantages which can be drawn from the present invention, mention may be made of the specific case of the formation of tin oxide coatings doped with fluorine from tin chloride and bifluoride. ammonium. According to a commonly used manufacturing process, an aqueous solution containing 375 gr / l of SnCl2. 2H2O and 55 gr / l NH4F. HF is sprayed at a rate of 20 liters per hour on a 3 m wide glass ribbon passing through a coating station at a rate of 1 m / minute, to give a coating of 750 nm thick. If it is desired to apply a coating similar to a glass ribbon produced on a larger scale moving faster, it would be necessary to increase the amount of solution applied to the glass, thereby subtracting heat from the glass, or to increase the concentration of the solution with as a consequence the risk of gel formation By spraying SnCl2 and
NH4F. HF separately according to the invention, it is possible to increase the concentration of the SnCl2 solution up to 1,800 gr / l in aqueous solution without giving rise to spraying difficulties.

NH4F. HF is very soluble in water and can be sprayed at any desired concentration. It will therefore be seen that without increasing the sprayed volume, it is possible to form a coating similar to that formed in the commonly used method cited above, without increasing the spraying rate and for a greater width and / or speed of ribbon of glass passing to the coating station
The invention is therefore particularly advantageous when the support is a glass ribbon which is subjected to spraying substantially over its entire width during its displacement. along a sound annealing gallery. The coating station can be located at a position in the gallery where the freshly formed glass ribbon is at a suitable temperature, so as to provide little or no additional heat, and for a given strip width and a forward speed, it is possible to form coatings of much greater thickness than has hitherto been possible.

 The invention extends to a glassy support carrying a uniform coating formed by the method and comprises a device for forming a uniform coating comprising at least two constituents on a hot glassy support by spraying, on the support, substances generating the coating to form the coating by pyrolysis, characterized in that the coating device comprises means for moving the support in a predetermined horizontal direction (hereinafter referred to as "forwards") and at least one coating head comprising at least two sprayers and means for moving the sprayers in tandem transversely to the path of the support, these sprayers being connected to at least two different coating solution tanks, which allows the sprayers of at least one coating head, to spray simultaneously on the support different solutions, which mix on or above the support, during each of their tra jour nsversaux, the sprayers being inclined horizontally so that the main horizontal component of the droplet streams is towards the front or towards the rear.

 This device is of simple construction and is well suited to carrying out the spray coating process of the invention.

When the sprayed droplets are ejected from the sprayers, they each form a cone and this cone meets the path of the support by forming spray ellipses. These ellipses can be separated or they can be tangent to each other or they can be partially or totally superimposed. The latter feature is preferred to provide a uniform, high quality coating and therefore it is preferred that the sprayers are arranged so that their axes converge in the spraying direction.

 Preferably, the spraying means are placed inside a sound annealing gallery to subject to spraying a glass ribbon moving in the gallery from a ribbon forming machine. It is relatively simple to place the spraying means in the gallery at a position where the temperature of the glass ribbon is at a suitable value to promote the desired pyrolysis and where little or no additional heating means should be used, in particular thereby saving energy.

 The present invention can be used to coat formed glass in any suitable manner, for example, using a ribbon forming machine in which the glass is drawn vertically from a bath of molten glass and then passed over a folding roller. horizontal to be conveyed along a horizontal annealing gallery, but it is preferred that the tape forming machine comprises a float tank.

 Preferably, the sprayers are arranged so that their discharge orifices are at a height of 15 to 40 cm above the path of the tape.

 Advantageously, the discharge orifices of at least one coating head are spaced at most 10 cm.

Preferably, the sprayers of at least one coating head are arranged so that the axes of their spray connes converge towards the path of the tape.

A preferred embodiment of a device according to the invention will now be described in more detail with reference to the accompanying schematic drawings in which
FIG. 1 is a schematic cross section of a device located at a coating station inside an annealing gallery, and
Figure 2 is a plan view of part of this device.

 In the drawings, an annealing gallery is provided with a roof 1 and a floor 2. At a certain distance above the floor 2 of the gallery, there is a roller conveyor 3 intended for transporting a ribbon of hot glass 4 through the gallery in the direction of the arrow. It is desired to provide the glass ribbon with a coating 5 with several constituents by pyrolysis in situ on the ribbon 4 while the ribbon passes below a coating station 6.

The coating station 6 comprises an endless track 7 along which the coating heads 8 are carried, carried by 'slides 9. Each coating head 8 comprises two sprayers 10, 11 which are oriented downwards in the direction of the path of the ribbon, so that the main horizontal component of the droplets sprayed by them from the coating head is parallel to the direction of progression of the glass ribbon. In addition, it will be noted in FIG. 2 that the axes 12, 13 respectively of the sprayers 10, 11 converge so that the contact ellipses of the spray cones 14, 15 emitted by these respective sprayers, with the moving glass ribbon 4 , substantially coincide at 16. In variants of the illustrated embodiment, the sprayers 10, 11 are directed in such a way that the contact ellipses of the jets sprayed with the ribbon simply overlap or are distinct.

 Each sprayer 10 is supplied by means of a first coating solution contained in a tank 17, by a conduit 18, and each sprayer 11 is supplied by means of a second coating solution from a second tank 19, by a conduit 20.

 The coating heads are arranged so as to circulate continuously along the endless track 7, and sealing means (not shown) can be incorporated in the device so that spraying occurs when the coating heads move the along a branch of the track only, when they cross the ribbon 4.

As an option, it is possible to have suction conduits such as 21 in front of the zone for meeting the spray cones 14, 15 for sucking excess spray droplets and decomposition products.

 Following are examples of methods according to the invention implemented by means of a device as described above.

Example 1
A coating device as described is used to deposit a coating on a glass ribbon 3 meters wide after its manufacture by a stretching process of the Libbey-Owens type while the still hot ribbon moves along a annealing gallery at the rate of approximately 4.5 meters / minute. The coating device is installed at a position in the annealing gallery, where the temperature of the glass at the point where it meets the cone of sprayed droplets is approximately 6000C.

The sprayers are conventional type guns and work at a pressure of around 6 bars. The coating heads are moved along the track at such a speed and relative spacing that there are 40 spray passes per minute.

The sprayers are placed so that their orifices are 35 cm above the glass ribbon when they pass through it and their spray axes are at 30C on the horizontal, that is to say on the plane of the ribbon of glass. The two spray holes at each coating head are spaced 8 cm apart and the two sprayers are directed so that their spray cones each meet substantially the same area of the tape.

 Suction forces in the discharge conduits 21 are adjusted to maintain a vacuum of about 981 Pa at their inlets which are placed at a distance of 1 to 20 cm above the tape.

 The first reservoir 17 is filled with an aqueous solution of tin chloride obtained by dissolving per liter of hot water 1,600 g of anhydrous tin chloride (SnCl2). The second tank 19 is filled with a solution containing 300 g of ammonium bifluoride (NH4F.HF) per liter of water.

The two coating solutions supply the respective sprayers of the coating heads on the spray branch of the track and are each discharged at the rate of 18 liters per hour in an amount of carrier gas of 15 Nm3 per hour. I1 forms on the glass ribbon a coating of tin oxide doped with fluorine ions, 750 nm thick.

 Examination of the coating shows - that it has a uniform thickness and optical properties and that it has a homogeneous structure. The coating has a neutral tint when viewed in reflected light. The coating has a high transmission vis-à-vis visible light and an appreciable reflectivity vis-à-vis infrared radiation in the wavelength range between 2.6 and 40vwm. The emissivity of the coating is 0.1.

 We get. similar results in a process in which the same coating process is applied to coat a ribbon of float glass.

xxxx
In a previously known process, a similar coating of similar thickness is formed by spraying a single coating solution containing 375 gr SnCl2.2H2O and 55 gr NH4F. HF per liter at a rate of 20 liters per hour and in 10 Nm3 / h of carrier gas, using a single sprayer making 18 spray passes per minute through a ribbon of the same width. In order to obtain a coating of the same thickness as that obtained by the process described in Example 1, it is necessary for the glass ribbon to move at a speed of approximately 1 meter / minute. The coating solution cannot be sprayed at a rate high enough to allow a similar coating to be applied to a tape moving at 4.5 meters per minute and the concentration of the single coating solution cannot be increased enough without an adverse reaction between tin chloride and ammonium bifluoride occurs.

Example 2
A strip of float glass about 2.5 meters wide is coated with a layer of tin oxide doped with fluorine having a thickness of 750 nm as it moves at a speed of about 4.5 m / minute, from the float tank, along a sound annealing gallery.

 The two sprayed coating solutions are respectively formed by adding tin dibutyldiacetate to an organic solvent, in this case methanol, at the rate of 1.180 grams per liter of solution and by adding ammonium bifluoride to l water at the rate of 300 grams per liter.

 The coating heads are arranged to make 40 spray passes per minute through the tape and are mounted so that the sprayer orifices are spaced 6 cm apart and located 35 cm above the tape. The axes of the sprayers of each head are parallel and inclined 30 over-horizontally.

The organic tin solution (the main coating solution) is sprayed at the rate of 37 liters per hour using 20 Nm3 / hour of carrier gas, and the NH F HF solution (the doping solution) is sprayed ~ at the rate of 15 liters per hour using 8 Nm3 / hour of carrier gas. Both solutions supply the sprayers, so that, for each coating head, the contact zone of the main coating solution with the glass ribbon is the same as that of the doping solution.

 It is not possible to form a coating using these two coating-generating substances in a single solution, because there is no solvent which dissolves them both in the required amounts.

 As a variant of this example, a main coating solution containing 1.180 grams of tin dibutyldiacetate per liter, dissolved in dimethylformamide, is sprayed at the rate of 37 liters per hour. The other conditions are the same and the resulting coating, of fluorine-doped tin oxide, has a thickness of 750 nm.

 The two coatings have a uniform thickness and uniform optical properties, have a homogeneous structure and a neutral shade in reflection. The emissivities of the two coatings are respectively 0.15 and 0.16 (approximately).

Example 3
Using a process similar to that of Example 1, a glass tape 3 meters wide, moving at a speed of 4.5 meters / minute, is subjected to spraying with a main coating solution containing 1. 600 grams of SnCl2 per liter of a solvent consisting of equal volumes of water and methanol, and with a coloring solution containing 90 grams FeCl3. 6H2O per liter of water as a solvent, to form a coating of tin oxide colored with iron oxide. The main coating solution is sprayed at the rate of 2 liters per hour and the coloring solution is sprayed at the rate of 1.5 liters per hour to give a colored coating 100 nm thick with uniform optical and physical properties. In fact, this coating is yellow-red in color.

The color of such a coating can be changed simply by changing the iron chloride solution and without changing the conditions under which the tin chloride is sprayed.

Example 4
A coating containing tin oxide and antimony oxide is formed on a 2.8 meter-wide glass ribbon moving at 4.5 meters / minute by a process similar to that given in the example 1.

A first coating solution containing 1,600 grams SnC12 per liter of water as the sole solvent is sprayed at the rate of 18 liters per hour. A second coating solution is sprayed simultaneously and contains 150 grams of SbC13 per liter of water. The second solution is sprayed at the rate of 18 liters per hour. The resulting coating is 750 nm thick and, when viewed in transmitted light, has a very intense blue tint.

 By modifying the amount of SbC sprayed on the glass, and this is much easier when it is in a separate solution with respect to SnC12, it is possible to modify the intensity of the color and the electrical resistance of the coating. . Such a modification can be obtained by spraying the antimony solution at a higher rate. high or lower or by increasing or reducing its concentration.

Claims (14)

1. Method for forming a uniform coating  comprising at least two constituents on a vitreous support by  spraying on the hot support, substances generating the coating to form the coating by pyrolysis, characterized in  that at least one coating generating substance is sprayed  laughed at separately from 1 '(at least one) other generating substance, in what these separately sprayed generators are  sprayed simultaneously so as to substantially cover the same area of the support (4), to form a uniform coating  (5), and in that at least one of them is sprayed in solution aqueous. 2. Method according to claim 1, characterized in  what the generating substances of the coating are chosen d-e so as to give rise to a coating, on the vitreous support,  which reduces the emissivity of the coated surface vis-à-vis the radiation infrared. 3. Method according to one of claims 1 or 2, ca  characterized in that at least one substance generating the coating  ment is chosen and sprayed so as to give rise to a  minor constituent of the coating and in that this (these) substance (s) generator (s) is (are) sprayed in aqueous solution.  4. Method according to claim 3, characterized in - that a substance generating the coating is chosen and sprayed laughed at in order to give birth to a main constituent of the  coating and in that this generating substance is sprayed  in a solution comprising an organic solvent.  5. Method according to one of claims 1 to 3, ca characterized in that a coating-generating substance is chosen and sprayed so as to give rise to a constituent  main coating and that this generating substance  is sprayed into a solvent which includes water.  6. Method according to one of claims 1 to 5, ca  characterized in that a component of the coating is a metal oxide  one and another is in doping agent chosen to increase the conduction  electrical susceptibility of the metal oxide coating. 7. Method according to claim 6, characterized er, that the substance generating the metal oxide coating is chosen from tin chloride and indium chloride.  8. Method according to one of claims 1 to 7, characterized in that the support is a glass ribbon (4) and in that the ribbon is subjected to spraying substantially over its entire width during its movement along an annealing gallery (1, 2). 9. Device for forming a uniform coating comprising at least two constituents on a hot vitreous support by spraying, onto the support, substances generating the coating to form the coating by pyrolysis, characterized in that the coating device comprises means (3) for moving the support (4) in a predetermined horizontal direction (hereinafter referred to as "forward") and at least one coating head (8) comprising at least two sprayers (10, 11) and means ( 7, 9) for moving the tandem sprayers transversely to the path of the support (4), these sprayers (10, 11) being connected to at least two different coating solution tanks (17, 19), which allows the sprayers (10 , 11) of at least one coating head (8), to spray simultaneously on the support (4) different solutions which mix on or above the support (4), during each of their transverse paths, the sprayers ( 10, 1 1) being inclined on the horizontal, so that the main horizontal component of the droplet streams is towards the front or towards the rear. 10. Device according to claim 9, characterized in that the sprayers (10, 11) are arranged so that their axes (12, 13) converge in the spraying direction. 11. Device according to one of claims 8 or 9, characterized in that the spraying means are placed inside an annealing gallery (1, 2) for subjecting to spraying a ribbon of glass moving in the gallery from a ribbon forming machine. '  12. Device according to one of claims 9 to 11, characterized in that the sprayers (10, 11) are arranged so that their discharge orifices are at a height of 15 to 40 cm above the path of the support ( 4). 13. Device according to one of claims 9 to 12, characterized in that the unloading orifices of at least one head, of coating are spaced at most 10 cm. 14. vitreous support which has been coated according to one of claims 1 to 8.