Patent GB-622978-A (GB)
Title: Improvements in or relating to coating compositions
IPC: C09D101/18
Filed: 1947-02-28
Abstract: Hydrous iron oxide of an average particle diameter of less than 100 milimicrons and consisting of 0.2-5.0 per cent ferrous iron and 99.8-95.0 per cent ferric iron based on the total iron present is used as a pigment for transparent cellulose derivative coating compositions.  It may be obtained by precipitating a mixture of ferrous and ferric hydroxide and subsequently oxidizing the precipitate.  In an example, a solution made by mixing ferrous sulphate, sulphuric acid, sodium chlorate, and water, is heated to 180 DEG  F. and then run into caustic soda solution at 90 DEG  F. The mixture is heated to 130 DEG  F. and then an acid solution of sodium bichromate is added.  The mixture is heated to 180 DEG  F. and a further quantity of caustic soda is added.  The mixture is well stirred at 180 DEG  F. and then filtered.  The product is washed till free from sulphate.  Sodium chlorate may be used instead of bichromate.  The mixture containing precipitated iron hydroxides may be heated to boiling point during the treatment with oxidizing agent.ALSO:A stable coating composition comprises an organic film-forming vehicle containing a water-insoluble cellulose ester or ether and, as a pigment, hydrous iron oxide of an average particle diameter of less than 100 millimicrons and consisting of 0.2-5.0 per cent ferrous iron and 99.8-95.0 per cent ferric iron based on the total iron present.  The hydrous iron oxide pigment may amount to 2-10 per cent by weight of the total composition.  Black or gray coatings which are substantially transparent may be obtained. Metallic powders such as aluminium or nickel may be incorporated in the composition.  The pigment should preferably be transferred to the cellulose derivative vehicle direct from the wet pulp state, drying and sintering being avoided.  The pigment may be obtained by precipitating a mixture of ferrous and ferric iron and subsequently oxidizing the precipitate.  The precipitate, while still wet, is kneaded with the cellulose derivative and, if desired, with a blown non-drying vegetable oil and a solvent plasticizer.  Water which separates during the kneading is removed and then solvents, diluents and other desired ingredients are added.  In an example of the preparation of the pigment, a solution containing ferrous sulphate, sulphuric acid and sodium chlorate is heated to 180 DEG  F. and then run into warm caustic soda solution.  The mixture is heated to 130 DEG  F. and then a solution containing sodium bichromate and sulphuric acid is added.  The mixture is heated to 180 DEG  F. and more caustic soda solution is added.  The stirred mixture is filtered and the pigment is washed free from sulphate.  Sodium chlorate may be used instead of bichromate.  The mixture containing precipitated iron hydroxides may be heated to boiling point during the treatment with oxidizing agent.  In another example, water-wet cellulose nitrate is mixed with hydrous ferric-ferrous oxide pulp, blown castor oil and dibutyl phthalate, and after removal of the water, there is added ethyl alcohol, butyl acetate, butyl alcohol, and a solution in toluene of a glyceryl phthalate synthetic resin.  In another example, a paste of aluminium powder in mineral spirits is mixed with butyl acetate and then with cellulose nitrate, ethyl alcohol, methyl ethyl ketone, butyl alcohol, petroleum naphtha, blown castor oil, dibutyl phthalate, glyceryl phthalate synthetic resin, and malic acid.  A small proportion of this tinting solution is then added to a cellulose nitrate lacquer containing hydrous ferric-ferrous oxide. Specification 499,790 is referred to.