Process for the fabrication of glass coatings for protection against heat

© Start of patent period: 1984 10 15 Longest possible duration:

© Issued: 1985 05 28 © inventor:

© dependence:

AT 377 968 ​​© References contemplated by the prior art:

U.S. Patent 2,567,331

Nr.377968

The invention relates to the coating of heat-resistant transparent materials, such as the coating of glass or glass ceramic materials, with a semi-reflective adhesive film of tin oxide, which enables the transparent substrate to provide protection against heat rays by the Infrared beams reflected while still having a sufficiently large transmission coefficient in the visible range of the solar spectrum.

It has already been proposed to apply such transparent films of tin oxide to glass or other transparent substrates by first heating the disk to a high temperature but lower than the softening point, and then heating it to the temperature Disc sprays an organic or inorganic tin compound which decomposes by pyrolysis the moment it contacts the heated substrate, so that a transparent film of tin oxide remains on the substrate.

Heretofore, this production of tin oxide films has been carried out using various methods which typically involve spraying the tin compound onto the substrate to be coated using a solution consisting of an aqueous or organic solvent and the tin compound dissolved therein. Such a process is described, for example, in US Pat. No. 2,567,331, which relates to a process for producing an electrically conductive tin oxide film on the surface of a glass sheet. The glass sheet is heated to a temperature of the order of 1200 ° F (about 650 ° C) and a solution of an organic tin compound is atomized over the glass surface. At this time, the solvent evaporates and the tin compound is decomposed in contact with the hot glass surface to form an electroconductive tin oxide film. As the organic tin compound, dibutyltin diacetate is preferable, and as the solvent, isopropyl alcohol.

So far, however, these methods have not given entirely satisfactory results, since these methods have all the disadvantages, be it with regard to the quality of the resulting tin oxide film (adhesiveness, thickness uniformity, transparency, optical properties or electrical conductivity), with regard to the difficulty or the inconvenience of carrying out the procedure: Preparation of the surface to be coated, chemical auxiliary reagents, preparation of the solutions to be atomized, removal of the excess solution and the solvent vapors or the decomposition products.

The invention is intended to provide a method for producing a semi-reflective film of tin oxide on a transparent substrate, in which the above-described disadvantages are eliminated.

This object is achieved in a process for producing a semi-reflective film of tin oxide by pyrolysis on the surface of a substrate, such as a glass or glass ceramic disc, wherein the surface to be coated to a temperature of 400 to 650 ° C or is brought in the case of a thermally or chemically tempered glass to a working temperature of at most 520 ° C, after which is applied to the thus heated surface at this temperature to tin oxide decomposing organic tin compound, according to the invention achieved in that the organic tin compound in the form of a powder is used, whose particles have a size of not more than 20 gm, and that the powder in an anhydrous, gaseous carrier stream containing an admixture of a gaseous fluorinated inorganic compound.

In the mentioned U.S. Patent No. 2,567,331, there is nowhere mentioned or even hinted at any use of a fluorine compound; rather, it is said that the presence of hydrogen chloride vapors would cause a strong disturbance on the glass surface. Thus, the cited US patent does not impart the teaching of the invention to use an organic tin compound which is dry, solid and finely divided, nor to apply this solid compound as a suspension in an anhydrous carrier gas containing a gaseous fluorinated inorganic compound To use.

The admixing of a fluorinated gas, which constitutes a characteristic feature of the invention, preferably takes place at the moment of spraying, to which end a branch line leading into the transport line for the suspended particles of the organic tin compound upstream of the spray nozzle is used.

Nr.377968

In carrying out the process according to the invention is preferably as organic

Tin compound tin dibutyl oxide used. This tin compound is particularly interesting from the economic point of view. The Zinndibutyloxyd is carried by a stream of dry compressed air.

Depending on the dimensions of the glass sheet to be treated or the glass sheet to be treated, only a single spray nozzle or a plurality of spray nozzles is used, which can be fixed or can be arranged to be movable. Before these spray nozzles, the substrate to be coated is allowed to pass.

The method according to the invention differs from the known methods in its simple applicability and its low costs: it is not necessary to prepare a solution suitable for sputtering; the use of a solvent is dispensable and no auxiliary chemical reagents are needed except for the gaseous fluorinated compound, preferably hydrofluoric acid. The latter, however, is cheap and can be prepared very simply by evaporating anhydrous hydrofluoric acid in the liquid state.

Its boiling point is not above 20 ° C at atmospheric pressure.

Experience shows, on the other hand, that obtained by the process according to the invention

Tin oxide film adheres very well to the substrate and has a good corrosion resistance. The tin oxide film produced by the process according to the invention also has the desired optical properties, namely transmission in the visible region of the spectrum and good

Reflection in the infrared region of the spectrum, especially for beams with wavelengths greater than 2 pm.

It has also been found that the tin oxide films produced by the process of this invention have very good electrical conductivity. Thus, the coated by the novel process glass sheets can be used as heating disks.

A further advantage of the method according to the invention is that it can be carried out on glass which is at a temperature of the order of 500 ° C. This can be done on glass panes running out of a thermal tempering station; it can also be carried out on glass sheets which have undergone a chemical treatment to increase their mechanical strength.

The invention will be explained in more detail with reference to an embodiment.

Powdered tin dibutyloxide is added to a container placed over a porous bottom. Compressed air used as the carrier gas is put on the underside of the porous bottom, and after passing through the porous bottom, the compressed air entrains some of the particles of the tin compound in a conduit through which the

Spray nozzle or the spray nozzles are fed. The air used as carrier gas is at room temperature, its pressure is 0.5 bar.

Upstream of each of the spray nozzles, the feed line is provided with an inlet opening through which gaseous, anhydrous hydrofluoric acid is obtained, coming from bottles maintained at a temperature of the order of 40 ° C., in which liquid hydrofluoric acid is present. The spray nozzles are 25 cm apart and aligned horizontally. In front of these spray nozzles, slices of float glass are suspended, suspended in a vertical orientation, having a size of 500 χ 500 mm and a thickness of 6 mm, previously heated by passing them through a furnace suspended in a vertical orientation, whose temperature is maintained at 650 ° C.

As the glass panes pass the spray nozzles, their temperature is on the order of 610 to 620 ° C. The rate of conveyance of the glass sheets past the spray nozzles is adjusted depending on the flow rate through the spray nozzles such that 50 grams of tin dibutyl oxide are consumed per square meter of treated glass (only a portion of this amount remains adhered to the glass in the form of tin oxide). The consumption of hydrofluoric acid be50 carries 35 g / m² of the treated glass.

The thus-obtained tin oxide-coated glass samples are examined, reflecting the reflectivity and the transmission coefficient as a function of the wavelength.

Nr.377968

The results obtained are shown in the curves of the drawing.

In the drawing, the curve T represents the transmission coefficient as a function of the wavelength. The transmission coefficient is given in percent and indicates which

Part of the light at a given wavelength is passed through the sample. The⁵ Curve R represents the reflection coefficient of the sample as a function of the wavelength.

As can be seen from the drawing, in the infrared for wavelengths of more than about 1.5 pm, one has a high reflectivity and thus a very low transmission coefficient of the glass.

On the samples, the electrical resistance of the tin oxide film was further measured at various W points on the sample surface, with the measuring points being 10 cm apart in both directions.

The measurement results obtained, expressed in ohms / square, are given in the following table:

Electrical resistance in ohms / 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>

¹⁵ It can be seen that these values ​​for the electrical conductivity are quite sufficient in order to be able to use the glass panes as heating disks.