Method of manufacture of transparent heat reflecting tin dioxide layers placed on glass

The invention relates to a process for the production of transparent thermally reflective layers of doped tin oxide on a glass, wherein a solution of a mixture of at least one thermally decomposable organic or inorganic tin compound and at least one thermally decomposable electrically active additive group is selected from fluorine and antimony.

Layers of semiconducting stannic oxide with considerably increased electron conductivity due to doping with suitable electrically active impurities are characterized by high reflectivity in the infrared part of the spectrum and at the same time relatively low absorption in the visible range.

For these properties, it is preferred; are used as so-called heat reflective layers. Applied in thicknesses of the order of hundreds of nanometers to the glass surface, they reflect up to 80% of incident heat radiation from sources with a temperature of about 20 to 1000 ° C.

Their use is multifaceted. On flat building glass to increase thermal insulating ability of windows and other glazing of buildings, for glass tubes to increase thermal efficiency of tubular solar collectors, for glass flasks to improve specific luminous intensity of sodium lamps, etc.

In MS. No. 220175 describes a method for producing transparent thermally reflective layers of tin oxide on glass. The glass is heated to a temperature above 570 ° C and its surface is contacted with a liquid or gaseous medium containing at least one degradable organic or inorganic tin compound and at least one doping degradable compound of an electrically active ingredient selected from the group consisting of fluorine and antimony by weight concentration of 0.5 to 5%.

This fluorine or antimony concentration range guarantees maximum thermal reflectance only at temperatures higher than 570 ° C, eg 640 to 650 ° C. However, for example, float glass which leaves the float bath and enters the cooling furnace may have a temperature of less than 570 ° C and at this temperature and a dopant concentration of 0.5 to 5% the coating has a lower reflectance in the range of 5 to 12 microns and is no more than 50%. ·

These disadvantages are eliminated or substantially reduced by the method according to the invention, which is characterized in that a solution containing 5 to 10% by weight of the electrically active ingredient is applied to the glass heated to 350 to 570 ° C.

In the method according to the invention, when applied to flat float glass, optimum reflectivity is obtained while utilizing the heat that the glass brings from the forming process. When applied to a tube or bulb, heating the glass to a lower temperature than previously is sufficient to save energy, while the material consumption is only slightly higher,

The method is described in more detail in the following examples:

He did

The borosilicate glass tube with a diameter of 50 mm is heated to a temperature of 570 ° C and sprayed on its inner surface with a special compressed air nozzle, a solution formed by mixing 100 g of stannous dimethyl dichloride / CH₃/₂SnCl₂100 ml of distilled water₂0 and 9.4 ml of HF.

A homogeneous layer of SnO is formed on the glass₂ with a 6% fluorine P content with a uniform light green color in reflection, with a visible transmittance in the range of 75 to 85% and a reflectance in the range of 5 to 12 in the range of 65 to 75%.

Example 2

A 5 mm thick strip of float glass is sprayed with an air spray gun in a gap between the float bath and the cooling furnace, where the glass has a temperature of about 560 ° C, by mixing 100 g of tin (II) -dimethyl dichloride / tin (III) monomethyltrichloride. CH 2 Cl 2, 100 ml of distilled H 2 O and 9.9 g of NH 4 F.

A homogeneous layer of tin (IV) SnOj containing 7% fluorine F is formed on the glass with a uniform light green color in reflection, with a visible transmittance in the range of 68 to 75% and a reflectance in the range of 5 to 12 µm in the range of 65 to 75%.

Example 3

A 4 mm 4 mm thick flat glass sheet is heated to 560 ° C and sprayed onto the surface with an air spray gun, a solution formed by mixing 80 ml of SnCl 2, 160 ml of ethyl alcohol. ^C2^H2 ° 5 '15 ml HCl hydrochloric acid and 9 g antimony trichloride SbClg.

A homogeneous layer of tin oxide SnOj containing 6% antimony Sb with a uniform light blue color in the view, with a visible transmission in the range of 63 to 70% and a reflectance in the range of 5 to 12yum in the range of 60 to 70% is formed on the glass.