Process for the fabrication of glass coatings for protection against heat

(74) Agent:

D

Sale of booklets at IMPRIMERIE NATIONALE, 27, rue dé la Convention - 75732 PARIS CEDEX 15

The invention relates to the coating of refractory transparent materials such as glass sheets or glass-ceramic materials with an adherent semi-reflective film of tin oxide, conferring on the transparent support qualities of protection against heat by the reflection of infrared rays. while maintaining a satisfactory transmission coefficient in the visible range of the solar spectrum.

It has already been proposed to form such transparent tin oxide films on glass sheets or other transparent supports by projecting onto the sheet brought to a high temperature, but below the softening point, an organic tin compound. or mineral capable of decomposing by pyrolysis at the time of contact with the heated support to leave on this a transparent film of tin oxide.

Until now, th is technique has been carried out by various methods which generally involve spraying onto the support to be coated with a solution of a tin compound in an aqueous or organic solvent.

These processes have so far not given full satisfaction since they all have drawbacks, either as to the quality of the tin oxide film obtained (adhesion, uniformity of thickness, transparency, optical properties or electrical conduction ), either with regard to the difficulties or complications of implementation s preparation of the surface to be coated, auxiliary chemical reagents, preparation of the solutions to be sprayed, evacuation of excess solution as well as solvent vapors or decomposition products.

The process of the present invention, which makes it possible to avoid these drawbacks, consists in spraying onto the surface to be coated,

30 'maintained at a temperature of 400 to 650 · C, tin organic derivative of solid tin decomposable into tin oxide at this temperature, in the form of a powder whose particles do not exceed 20 microns, suspended in a stream of carrier gas in which an addition of fluorhydri35 acid than anhydrous is added at the time of spraying.

Adding gaseous hydrofluoric acid, characteristic of the invention, can be done by a tapping on the pipe transporting the particles of organo-stannic derivative in suspension, upstream of the spray nozzle.

In the implementation of the process, it is possible to use, advantageously, as organic derivative of tin, dibutyl tin oxide, a particularly economical compound which is entrained by a stream of dry air under pressure.

Depending on the dimensions of the sheet or glass ribbon 5 to be treated, one or more fixed or mobile projection nozzles can be used in front of which the support to be coated is passed.

The process according to the invention differs from the previous processes by its simplicity of implementation and its modesty: there is no need to prepare a spray solution; the use of solvent is avoided and no auxiliary chemical reagent is used, apart from gaseous hydrofluoric acid which is economical and very easy to produce by evaporation of anhydrous hydrofluoric acid in the liquid state, whose boiling point does not exceed

20 * c at atmospheric pressure.

Experience has also shown that the tin oxide film obtained according to the process of the invention has good adhesion and satisfactory resistance to corrosion. In addition, it has the desired optical qualities of transparency in the visible range of the spectrum and of reflection in the infrared, in particular for wavelengths greater than 2 microns.

Furthermore, the Applicant has found that the tin oxide films in question have good electrical conductivity, which allows the glazing thus coated to be used as heating glazing.

Yet another advantage of the process of the invention lies in the fact that this process can be carried out on glass, for example at one. temperature of the order of 500 ° C., which makes it possible to apply the process to glazing leaving a thermal quenching station or else to glazing having undergone a chemical reinforcement treatment.

An exemplary embodiment of the invention is given below.

The powdered dibutyl tin oxide is introduced into a tank on a porous bottom. Compressed air used as carrier gas is sent below the porous bottom and after passing through it, entrains a certain quantity of tin compound particles in a pipe supplying the spray nozzle (s). The drive air is used at room temperature and its pressure is 0.5 bar.

Upstream of each nozzle, the supply line includes an inlet of gaseous anhydrous hydrofluoric acid from bottles of liquid hydrofluoric acid maintained at a temperature of the order of 40^e C. The projection nozzles are spaced

25 cm · and directed horizontally. We pass in front of these projection nozzles sheets of float glass suspended vertically, 500 x 500 mm and 6 mm thick previously heated by passage in vertical suspension in an oven maintained at 650 · C.

The temperature of the glass sheets as they pass the projection nozzles is around 610 to 620 · C. The speed of movement of the glass is adjusted according to the supply so that 50 g of dibutyl tin oxide per m2 of treated glass (only part of this quantity is fixed on the glass in the state of tin oxide). The consumption of hydrofluoric acid is 35 g per m2 of treated glass.

The samples of glass coated with tin oxide thus obtained are examined from the point of view of the reflectivity and the transmission coefficient as a function of the wavelength.

The results are illustrated by the curves of the attached drawing.

In this drawing, the curve T is the transmission curve of the sample given as a percentage of light transmitted for each wavelength. Curve R is the reflection curve of the sample.

As can be seen, due to the high reflection, the transmission of the glass becomes very weak in the infrared for wavelengths greater than about 1.5 µtP-.

Furthermore, measurements were made of the electrical resistance of the tin oxide film at different points on the surface of the samples (points spaced 10 to 10 cm in both directions).

The values ​​obtained expressed in square Ohm are given in the table below t

Electrical resistance in Ohm / square every 10 cm

<td> 16</td><td> 12</td><td> 12</td><td> 13</td><td> 15</td>

<td> 13</td><td> 11</td><td> 11</td><td> 11</td><td> 14</td>

<td> 14</td><td> 11</td><td> 10</td><td> 12</td><td> 15</td>

<td> 12</td><td> 9</td><td> 9</td><td> 10</td><td> 13</td>

<td> 15</td><td> 11</td><td> 11</td><td> 11</td><td> 13</td>

It can be seen that these values ​​correspond to an entirely satisfactory electrical conductivity for the use of glazing as heating glazing.