Patent GB-858072-A (GB)
Title: Improvements in or relating to pigments
IPC: C09D7/62
Filed: 1958-04-02
Abstract: Coating compositions comprise (a) a hydrophobic iron oxide pigment composition which comprises a dispersion of iron oxide-containing particles which are not capable of scattering visible light (i.e. having a particle size less than about 30 millimicrons), in a water-immiscible volatile organic liquid, said particles having a molecularly thin surface coating of at least one aliphatic monocarboxylic acid which is soluble in the organic liquid and contains at least 6 carbon atoms (see Group III), (b) an organic film-forming vehicle and (c) a solvent for said vehicle.  The invention is described in relation to particles of ferric oxide, but is equally applicable to ferric oxide which has been prepared by coprecipitation with hydrous oxides of ferrous iron, chromium, aluminium, manganese and nickel.  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: cellulose nitrate, cellulose acetate, cellulose propionate, cellulose acetobutyrate, ethyl cellulose, polyester resins, oil-modified alkyd resins, urea/formaldehyde resins, melamine/formaldehyde resins, polyether resins such as those derived from bisphenol and epichlorohydrin, vinyl acetate homopolymer and copolymers, vinyl propionate homopolymer and copolymers, vinyl chloride homopolymers and copolymers, vinyl acetal polymers, methyl methacrylate polymers, butyl methacrylate polymers, ethyl acrylate polymers, acrylonitrile/acrylic ester copolymers, acrylonitrile/methacrylate ester copolymers, styrene/acrylic ester copolymers, 1, 3-butadiene homopolymer, 1, 3-butadiene/acrylonitrile copolymers, 1, 3-butadiene/styrene copolymers and polymeric dihydric alcohol diesters of methacrylic acid.  The proportion of pigment to total organic film-forming material is preferably between about 1 and 4 to 10.  The above-mentioned organic film-forming materials can be in admixture with compatible modifiers, such for example as plasticizers.  The composition can also include other adjuvants at the conventional concentration, such as metallic driers, silicone fluid, fungicides, thixotropy agents, and ultra-violet screening agents.  When the pigment composition contains an aromatic hydrocarbon, the volatile organic solvent or diluent for the film-forming material preferably contains initially a proponderance of volatile hydrocarbon.  After uniform mixing, esters, ketones, alcohols and petroleum naphthas may be added. Aluminium flake pigment or bronze flake pigment may be added to the iron oxide compositions to provide metallic finishes and thereby enhance the brilliance and increase the two-tone effect.  Specified monocarboxylic acids are: lauric acid, coconut oil fatty acids, capric, caprylic, caproic, myristic, palmitic, stearic, carnaubic, behenic, margaric, pentadecanoic, tridecanoic, undecanoic, pelargonic, nonadecanoic, arachidic, lignoceric, oleic, erucic, palmitoleic, linoleic, linolenic, dehydrated castor oil acids, and tall oil fatty acids. From 0,2 to 1,2 parts by weight of acid may be used per part of ferric oxide.  Toluene, xylene, high solvency petroleum naphtha and mineral spirits are preferably used to dissolve the carboxylic acid. The following formulations suitable for use as automobile finishes or tinting enamels are exemplified, the portions indicated by numerals being mixed successively: (a) (i) a mixture of high solvency petroleum naphthas, blown castor oil, cellulose nitrate in isopropyl alcohol, methyl isobutyl carbinol, (ii) pigment composition according to the invention in xylene (iii) butyl acetate, methyl amyl acetate, methyl isobutyl ketone and (iv) methyl isobutyl ketone, methyl ethyl ketone, dibutyl phthalate, coconut oil modified alkyd resin solution in toluene, silicone solution in toluene, isopropyl alcohol; (b) (i) ferric oxide composition according to the invention in xylene, calcium naphthenate in mineral spirits and xylene and (ii) soya oil modified alkyd resin in hydrocarbon solvent; (c) (i) ferric oxide composition according to the invention in xylene, toluene, a solution in acetone and toluene of a methyl methacrylate/methacrylic acid copolymer resin (ii) the same acrylic resin solution in acetone and toluene, benzyl butyl phthalate and a dispersion of montmorillonite clay in methyl methacrylate homopolymer dissolved in xylene, toluene and acetone, (d) (i) ferric oxide composition according to the invention in xylene, (ii) coconut oil modified alkyd resin in toluene and naphtha, (iii) melamine/formaldehyde resin in butyl alcohol and (iv) a second portion of melamine/formaldehyde resin in butyl alcohol.  It is stated that aluminium flake or paste pre-dispersed in a similar composition in the place of the ferric oxide may be mixed therewith for the preparation of metallic finishes. Specification 622,978 and 630,334 are referred to.ALSO:A hydrophobic iron oxide pigment composition, suitable for use in coating compositions, comprises a dispersion of particles comprising iron oxide which are not capable of scattering visible light (i.e. having a particle size less than about 30 millimicrons), in a waterimmiscible volatile organic liquid, said particles having a molecularly thin surface coating of at least one aliphatic monocarwhich is soluble in the organic liquid and contains at least 6 carbon atoms.  The composition is preferably prepared by treating a water-wet hydrous iron oxide pigment pulp having an average particle size less than 100 millimicrons with 0.2 to 1.2 parts by weight of said acid for each part by weight of iron oxide in solution in said organic liquid, removing water from the resulting composition and separating from the composition pigment particles whose size is such that they scatter visible light centrifugally by means of a centrifugal force of at least 6000 g.  The invention is described in relation to hydrous ferric oxide, but is equally applicable to ferric oxide co-precipitated with hydrous oxides of ferrous iron, chromium, aluminium, manganese and nickel.  A suitable pigment may be prepared by oxidising in solution a ferrous salt such as ferrous sulphate, precipitating ferric oxide with caustic soda and washing out water-soluble salts.  The methods of Specifications 622,978 and 630,334 may be employed.  Preferably the starting material has an average particle size between 10 and 30 millimicrons.  Suitable monocarboxylic acids are saturated or ethylenically unsaturated and have from 6 to 24 carbon atoms per molecule; lauric acid and coconut oil fatty acids are preferred and capric, caprylic, caproic, myristic, palmitic, stearic, carnaubic, behenic, margaric, pentadecanoic, tridecanoic, undecanoic, pelargonic, nonadecanoic, arachidic, lignoceric, oleic, erucic, palmitoleic, linoleic and linolenic acids, dehydrated castor oil and tall oil fatty acids are specified. 0.2 to 1.2 parts by weight of acid may be used per part of ferric oxide.  Toluene, xylene, high solvency petroleum naphthas and mineral spirits are preferably used to dissolve the carboxylic acid; 25 to 75% wt. of this solvent based on the total composition may be used.  The water-wet pigment is preferably treated with the fatty acid solution at 50 to 70 DEG C., the major proportion of free water removed by decantation and the temperature then raised to remove the remaining free water by azeotropic distillation; the resulting dispersion is then centrifuged after addition of a further quantity of the organic liquid if desired.  Centrifugal forces varying between 600 g. and 70,000 g. are referred to.  The above compositions may be dispersed by a simple mixing in liquid compositions comprising hydrophobic organic film-forming material and a volatile organic liquid which is a diluent and/or solvent therefor.  Suitable film-forming materials include cellulose nitrate, celulose acetate, cellulose propionate, cellulose acetobutyrate, ethyl cellulose, polyester resins, oil modified alkyd resins, urea/formaldehyde resins, melamine/formaldehyde resins, polyether resins such as those derived from bisphenol and epichlorohydrin, vinyl acetate homopolymer and copolymers, vinyl propionate homopolymer and copolymers, vinyl chloride homopolymers and copolymers, vinyl acetal polymers, methyl methacrylate polymers, butyl methacrylate polymers, ethyl acrylate polymers, acrylonitrile/acrylic ester copolymers, acrylonitrile/methacrylate ester copolymers, styrene/acrylic ester copolymers, 1,3-butadiene homopolymer, 1,3-butadiene/acrylonitrile copolymers, 1,3-butadiene/styrene copolymers, polymeric dihydric alcohol diesters of methacrylic acid, oleoresinous varnishes, and glyceride drying and semi-drying oils.  These organic film-forming materials can be in admixture with plasticizers.  The compositions can also include metallic driers, silicone fluid, fungicides, thixotropy agents, and ultra-violet screening agents.  It is preferred that the proportion of pigment to total organic film-forming material should be between about 1 and 4 to 10.  When the pigment composition contains an aromatic hydrocarbon the volatile organic solvent or diluent for the film-forming material preferably contains initially a preponderance of volatile hydrocarbon. After uniform mixing, esters, ketones, alcohols and petroleum naphthas may be added to obtain the desired solvent balance. Aluminium flake pigment or bronze flake pigment may be added to the iron oxide composition to provide metallic finishes and thereby enhance the brilliance and increase the two tone effect.  The following formulations suitable for use as automobile finishes or tinting enamels are exemplified (the portions indicated are mixed successively):-(a) (i) a mixture of high solvency petroleum naphthas, blown castor oil, cellulose nitrate in isopropyl alcohol, methyl isobutyl carbinol, (ii) pigment composition ac