Patent GB-1406410-A (GB)
Title: Metal phosphate coating of glass articles
IPC: C03C17/22
Filed: 1971-07-20
Abstract: 1406410 Metal phosphates IMPERIAL CHEMICAL INDUSTRIES Ltd 11 Sept 1972 [20 July 1971 29 Oct 1971 4 Nov 1971 26 Nov 1971 (2) 20 Dec 1971 2 June 1972] 47607/74 47608/74 47609/74 47610/74 47611/74 47612/74 and 47613/74 Divided out of 1406233 Heading C1A [Also in Division B2] A method of applying a metal phosphate coating to the surface of a glass article comprising applying to the surface of the article a coating of a liquid composition comprising a solution of a metal compound, the metal being iron, titanium, a mixture of iron and titanium or a mixture of iron and chromium, an oxyacid phosphorus or a compound capable of forming such an oxyacid in solution, the oxyacid being an ortho- or meta-acid of the structure where X<SP>1</SP> and X<SP>2</SP> are the same or different and may be hydrogen, hydroxide, halide or have the structure to provide pyrophosphoric acid and (c) a solvent which comprises at least in part an organic compound and converting the coating to the metal phosphate. The composition may be obtained by dissolving the metal and the oxyacid or phosphorus, or a source thereof in a solvent for at least one of the components and for the reaction product and in the presence of an organic solvent. The metal compound may be a phosphate and so provide the oxyacid or phosphorus in which case additional acid may be required such as hydrochloric or nitric acid. The metal compounds may be inorganic salts such as oxides, hydroxides, halides, carbonate, nitrate, phosphate, perchlorate and cyanate. Salts of organic acids such as acetates, benzoates, oxylates, propionates or formates may also be used as well as alkoxides. Co-ordination complexes of a metal may also be used such as complexes having ligands derived from acetyl azidone, ethylene dithiol, ethanolamine, carbon monoxide or phosphines. The oxyacid or phosphorus is preferably of the phosphoric acid although metalphosphoric acid and para-phosphoric acids may be used. The organic solvent is preferably an alcohol, ester, ketone, aldehyde, nitro-compound or ether. Particularly preferred are monohydric alcohols ROH and esters of the structure R<SP>1</SP>COOR<SP>2</SP> where R, R<SP>1</SP> and R<SP>2</SP> are alkyl groups or substituted alkyl groups containing 1-10 carbon atoms, ethers of the structure R<SP>1</SP>OR<SP>2</SP> and ketones of the structure R<SP>1</SP>COR<SP>2</SP>, nitro-compounds of the structure R<SP>1</SP>NO 2  and cyclic ethers of the structure OR<SP>3</SP> where R<SP>3</SP> is a divalent alkyl group having 4-7 carbon atoms one of which may be replaced by an oxygen atom. Suitable specific compounds are specified. Up to 50% of aromatic or halogenated hydrocarbon diluents may also be present. In the composition the meta- and oxyacids are desirably present in atomic ratios of metal to phosphorus in the range 1 : 0À1 to 1 : 2À9 and the composition may be prepared over a wide range of temperatures, for example 50-150‹ C., preferably being mixed at below 60‹ C. The processes may be carried out at pressures above normal atmospheric pressure. Pigments, polymers, colorants, surfactants or sources of ions and other additives may be included. Suitable polymers are diene polymers, acetylene polymers, vinyl and vinylidene polymers, e.g. acrylic acid and methacrylic acid polymers, acrylate and methacrylate polymers, polyacrylonitrile, polyethers, polysulphones, formaldehyde resins, polyesters, polycarbonates, polyamides, polyureas and polyurethanes, natural polymers and modified natural polymers and polysiloxanes. The glass article may be in the form of a fibre, filament, sheet, granule, powder, tube, bulb or bottle. The composition may be applied by dip-coating, spraying, roller- or brush-coating. Heating to decompose the composition may be at up to 150‹ C., but even high temperatures up to 1000‹ C. may be used. The compositions may be applied to the hot surface. The coating may be prepared in relatively thick layers, for example up to 10 microns, of coatings of thickness 0À1 to 5 microns are preferred. A thicker coating may be obtained by repeated coatings with or without conversion to metal phosphate between each stage. The coating may be applied to the inside and/or the outside surface of glass or quartz bulbs or tubes for use in lighting equipment when they increase resistance to attack by alkali-metal vapours, mercury vapour and halogens.