Patent GB-1179636-A (GB)
Title: Process and Apparatus for Forming Metal Oxide Coatings
Inventor: PLUMAT EMILE
IPC: C04B41/87
Filed: 1967-04-10
Abstract: 1,179,636. Coating; coating apparatus. GLAVERBEL 10 April, 1967 [18 May, 1966], No. 16377/67. Heading B2K. Metal oxide surface coating on an object is formed by uniformly applying a solution of another compound or compounds of the metal to the surface in an inert atmosphere while this surface is already superficially wetted with a solvent for the dissolved metal compound, such solvent being the same as or compatable with the solvent used in such solution, and then converting the compound or compounds to the metal oxide or oxides. The object may be of glass, ceramic, polished metal, plastics. The surface may be superficially wetted by exposing it to the vapour of the selected solvent, or by dipping or rinsing with the solvent and then drying the surface to a point at which a uniform solvent film remains. The solvent may contain a wetting agent. The metal compound solution may be applied by spraying or pouring onto the surface maintained in the solvent vapour atmosphere by which the preparatory superficial wetting was brought about. Titanium oxide coatings may be formed by hydrolysis of a solution of titanium chloride in ethyl alcohol, followed by heating to 450‹C until all the solvent has evaporated. In Fig. 1 apparatus for coating a glass sheet with a metal oxide comprises three superimposed chambers 1, 2, 3. The bottom chamber 1 is equipped with pipes 9a, 9b, 9c, 9d and 10a, 10b, 10c, 10d for charging it with solvent vapour and at the upper portion with a spray pipe for discharging metal compound solution onto a glass sheet suspended, whilst held in a solvent vapour atmosphere, from bar 39 in the chamber. An evacuation conduit 13 extends through the base of the chamber 1. Between the chamber 1 and the chamber 2 there are four shutters 15 which can be retracted. The chamber 2 has lower and upper pipes corresponding to the pipes 9a-9d and 10a-10d of chamber 1. Between chamber 2 and the top chamber 3 there are four retractable shutters 23. Chamber 3 likewise has four lower and four upper pipes and at the top of the chamber there are four retractable shutters 31. The sheet of glass 41 suspended from the bar can be lowered into and raised through the chambers 1, 2 and 3. After the sheet has been lowered into chamber 1 the shutters 15 are closed to isolate the chamber from chamber 2. Solvent vapour is then admitted into chamber 1 through the pipes. Subsequently a solution of titanium chloride in alcohol is discharged in the form of sprays 49a over one face of the glass sheet. Chamber 1 is subsequently evacuated and charged with air having relative humidity of 30% to hydrolyse the coating solution. After evacuation of the alcohol vapours, shutters 15 are retracted and the coated glass sheet raised into chamber 2 and shutters 15 and 23 are then closed. The valves of the lower pipes of chamber 2 are opened and air heated to 70‹C is charged into the chamber to eliminate organic solvent still remaining in the coating. After the drying in chamber 2 the shutters 23 are retracted and the sheet of glass raised into chamber 3 for firing of the coating. This chamber is preheated to 70‹C with heated air admitted through pipes 27a, 27b. The heaters used for heating the air admitted to chamber 3 are then stepped up and the temperature in chamber 3 raised to 450‹C., the titanium hydroxide becoming converted to titanium oxide. In another embodiment of the apparatus (Fig. 3, not shown) the three chambers are mounted side by side. In a further embodiment (Figs. 4 and 5, not shown) the apparatus includes a conveyor for conveying sheets in a horizontal position through three chambers mounted side by side.