Process for the fabrication of glass coatings for protection against heat

(54) Title: Process for the preparation of a semi-reflective tin oxide film (56) Published publications: SE 408 410 (C03C 17/22), DE 2 628 227 (C03C 17/22)

The numbers in brackets indicate the international identification code. INID code Letter mom clamp indicates international document code

7801761-3

Parties in the present invention relate to. coating of transparent refractory materials, such as sheets of glass or glass ceramic, with an adherent semi-reflective tin oxide film, which provides the transparent substrate with heat protection by reflection of infrared rays while maintaining acceptable transmission coefficient in the visible range of the solar spectrum.

It has previously been proposed to produce such transparent tin oxide films on glass sheets or other transparent substrates penetrated to the substrate, which is kept at high temperature, but below the softening point, an organic tin compound or mineral which, upon contact with the heated substrate, is decomposed by pyrolysis. and forms a transparent tin oxide film on the substrate.

So far, this technique has been applied by various methods, which essentially consist of spraying a solution of a tin compound in water or an organic solvent against the substrate.

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These processes have so far not been entirely satisfactory in that they all have some drawbacks, either because the quality of the thin tin oxide film obtained (adhesion, uniform thickness, transparency, optical properties or electrical conductivity) is insufficient or because they are difficult or complicated to implement: preparation of the surface to be coated, chemical auxiliary reagents, preparation of solutions to be atomized, removal of excess solution and solvent vapors or decomposition products.

The process according to the invention eliminates these drawbacks, and it consists in applying to the surface to be coated and maintained at a temperature of 400 to 650 ° C a solid organic tin compound which at this temperature can decompose into tin oxide in the form of powder having a maximum of 20 microns of grain size, suspended in an anhydrous carrier gas stream containing a certain amount of gaseous fluorine compound, preferably a fluoride such as boron trifluoride, bromine pentafluoride, chlorine trifluoride, silicon tetrafluoride, tungsten hexafluoride or molybdenum fluoride or especially anhydrous hydrogen fluoride.

The fluorine-containing gas according to the invention is preferably added at the same time as the application by application in the line through which the suspended particles of organic tin compound are conducted upstream of the spray nozzle.

When operating in accordance with the invention, tin organic dioxide can be used as an organic tin compound, which is a particularly economical compound introduced with a stream of dry air under pressure. · 3

Depending on the dimensions of the glass slab or glass strip to be treated, one or more fixed or movable spray nozzles can be used, in front of which one guides the substrate to be coated.

The process according to the invention differs from older methods in that it is simple and inexpensive. You do not need to prepare any syringe solution. No solvents are needed, and no chemical aids other than the gaseous fluorine compound, preferably fluorine hydrogen, which is economical and very easy to produce by evaporation of liquid anhydrous fluorine whose boiling point is below 20 ° C at atmospheric pressure are needed.

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Experience also shows that the tin oxide film obtained according to the invention has good adhesion and satisfactory corrosion resistance. It further has the desired optical properties in terms of transparency in the visible range of the spectrum and reflectivity in the infrared range, especially for wavelengths over 2 microns.

The resulting tin oxide film has good electrical conductivity, so that glass sheets with such coating can be used as heating windows.

Another advantage of the method according to the invention is that it can be carried out with the glass at a temperature of about 500 ° C, so that it can be applied to panes coming from a thermosetting station, or to panes which have undergone chemical curing.

An embodiment of the invention is described below.

Powdered tin dibutyl oxide is taken into a container on a porous bottom. Compressed air is used as carrier gas and is introduced below the porous bottom, and when the air is penetrated through it, it carries a certain amount of tin compound barley into a supply line for the spray nozzle (s). The feed air is used at ambient temperature, and it is under a pressure of 0.5 bar.

Upstream of each nozzle is an inlet for gaseous anhydrous fluorine hydrogen from liquid fluorinated hydrogen bottles maintained at a temperature of the order of 0 ° C. The spray nozzles are arranged at a distance of 25 cm from each other and: directed horizontally. In front of the nozzles are mounted vertically hanging floating glass sheets of the format 500 * 500 mm and 6 mm thickness, which have previously been heated by passing vertically hanging through an oven held at 550 ° C.

As the glass sheets pass in front of the nozzles, their temperature is about 610 to 620 ° C. Their velocity at passage is controlled after feeding, so that 50 g of tin dibutyl oxide is consumed per square meter of treated glass (only part of that amount is stuck to the glass in the form of tin oxide). 35 g of fluorine hydrogen is consumed per square meter of treated glass.

Specimens with tin oxide coatings so prepared are examined for reflectance and transmission coefficient as a function of wavelength. The results are shown as curves on the attached figures. Curve T represents the transmission of the test body in terms of percent light transmission for each wavelength. Curve R is the reflection curve of the sample.

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From this it can be seen that due to the high reflection, the transmission of the glass is very weak in the infrared range for wavelengths above about 1.5 µm.

The electrical resistance of the tin oxide film 5 was also measured at several points on the surface of the test body (points at 10 cm distance two perpendicular directions).

The table below shows the values ​​obtained in · ohm per square.

Electrical resistance in ohms, measured in the corners of 10 cm 10 squares

<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>

The values ​​correspond to an electrical conductivity, which makes the glass fully useful as heating glass panes.

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