Patent GB-917030-A (GB)
Title: Improvements in or relating to pigments
IPC: C09C1/24
Filed: 1960-01-11
Abstract: A hydrophobic iron oxide pigment composition, suitable for use in coating compositions, comprises a dispersion in a water-immiscible organic liquid, of hydrous iron oxide particles having a molecularly thin surface coating of at least one aliphatic monocarboxylic acid having at least 6 carbon atoms per molecule which is soluble in said liquid, said particles having a surface area corresponding to 0,4 to 3,5% of extractable hydrophobic acid, and the content of extractable hydrophobic acid being 0,4 to 1,5% of the dry weight of pigment. Samples of pigment having surface areas corresponding to an extractable acid content greater than 3,5% may be mixed with samples having an extractable acid content less than 3,5% provided the upper limit of 3,5% for the mixture is not exceeded.  The term "per cent of extractable acid" is defined and the method of determining this factor described in detail.  The composition is preferably prepared by a method generally similar to that described in the parent Specification involving mixing the pigment with a solution of the acid in the organic liquid, heating and removing free water; a water-wet pigment of the above mentioned particle size is used with a total quantity of hydrophobic acid which may be determined by means of a graph (not shown).  If desired, the compositions of the invention may be spray dried to provide a mix-in pigment.  Suitable iron oxides, hydrophobic acids and organic liquids are some of those described in the parent Specification.  The particle sizes of iron oxide of the specified surface area range between about 1 and 300 millimicrons.  The compositions may be dispersed in liquid coating composition vehicles comprising a soluble organic film-forming polymer in a volatile organic solvent for the polymer consisting of, or including a major proportion of, a non-polar organic component such as toluol, xylol or petroleum naphtha.  In Example 1 a composition comprising hydrous ferric oxide pigment, coconut oil fatty acids and xylol is prepared which is employed in further examples to form coating compositions based on synthetic polymeric film-formers (see Group IV(a)).  Specifications 499,790, 622,978, 630,334, 676,696, and U.S.A. Specification 2,384,579, U.S.A. reissue Specification 23,757 also are referred to.ALSO:The coating compositions of the parent Specification comprising (a) a specified iron oxide composition (b) an organic film-forming vehicle and (c) a solvent for said vehicle are modified in that (a) comprises a dispersion in a water-dispersible organic liquid of hydrous iron oxide particles of specified surface area having a molecularly thin surface coating of at least one aliphatic monocarboxylic acid having at least 6 carbon atoms per molecule which is soluble in said liquid, and present in specified amount. The pigment compositions may be dispersed by simple mixing in the hydrophobic organic film-forming material together with a volatile organic liquid which is a diluent and/or solvent therefor. Suitable film-forming materials are: polymers and copolymers of C1-C4 alkyl acrylates and methacrylates and styrene, terpolymers of these monomers with methacrylic or acrylic acid, polymeric dimethacrylates of aliphatic diols, glycidyl methacrylate, copolymers of vinyl chloride and vinyl acetate, nondrying semi-drying and drying oil-modified alkyd resins and alkyd resins in combination with heat-reactive aldehyde condensation resins (urea- or melamine-formaldehyde), epoxyhydroxy polyether resins (epichlorhydrin and bis-phenol), and glyceride oil fatty acid esters of such polyether resins.  Various modifiers, solvents and other adjuvants may be employed, such as are specified in the parent Specification; the hydrophobic coating acids are also similar.  In Example 1 a composition comprising hydrous ferrous oxide pigment, coconut oil fatty acids and xylol is prepared which is employed in Example 2 to form a coating composition with a methyl methacrylate/methacrylic acid solution in toluol and acetone after thinning with xylol and toluol; in Example 3 the same composition is used to form a clear coating composition by thinning with xylol, mixing in a toluol/naphtha solution of a coconut oil-modified glycerylphthalate resin and mixing into the product a butyl alcohol solution of a melamine-formaldehyde resin; in Example 4 the same composition is used to form a clear coating composition by mixing with xylol and a calcium naphthenate solution in mineral spirits and mixing the product with a solution of soya oil-modified glycerylphthalate resin in naphtha and mineral spirits.  In Example 5, the coating composition of Example 2 is mixed with (a) a dispersion of phthalocyanine green pigment, amine-treated bentonite pigment, polymethyl methacrylate in toluol/acetone, and xylol, (b) a dispersion of aluminium flake pigment/mineral spirits and naphtha, polymethyl methacrylate/toluol and acetone, and xylol, (c) a further quantity of the copolymer solution of Example 2 and (d) benzyl butyl phthalate, and the resultant mixture is in turn mixed with a solution of cellulose nitrate in acetone/b -ethoxyethyl acetate. The products of Examples 1, 3 and 5 may be applied as top coat finishes over automobile sheet metal primer compositions.