GB672763A - Improvements in or relating to fluorescent materials - Google Patents

Abstract

A composition capable when applied as a coating of exhibiting daylight fluorescence, i.e. the projection in daylight of more light of a particular colour than is present in the incident light, is formed by dispersing in a transparent liquid vehicle a pigment insoluble therein, the pigment consisting of a finely-divided synthetic resin carrier in the individual particles of which is dispersed a dye capable of fluorescing in daylight when in dilute solution. The carrier can be a pulverized, unplasticized, polymerized resin of the class consisting of unmodified urea-formaldehyde and aliphatic alcohol - modified urea - formaldehyde. The difference in indices of refraction of the pigment and vehicle is less than substantially 15 per cent of either index. The maximum ratio of dye to carrier varies from substantially 0.025 grs. for dyes projecting yellow-green light to substantially 0.015 grs. for dyes projecting red light per c.cm. of carrier, and is preferably less than 0.01 grs. of dye per c.cm. of carrier. Articles having a daylight fluorescent surface are made by coating them with the composition so that the amount of dye present on the finished surface is not more than 0.0005 grs. per sq. cm., preferably more than 0.000015 grs. per sq. cm., and preferably 0.00003 to 0.00006 grs. per sq. cm. Examples of the dyes used are 4-amino-1,8-naphthal-p-xenylimide, ethyl ester of meta monoethyl amino - phenol - phthalein hydrochloride and meta diethylaminophenol - phthalein hydrochloride. Examples of the synthetic resin carriers are butyl alcohol modified urea-formaldehyde solution, aqueous dispersion of unmodified urea-formaldehyde, ethyl alcohol solution of butyl alcohol modified urea-formaldehyde, succinic anhydride, pentaerythritol, casein-modified urea-formaldehyde, melamine-formaldehyde, silicone resins (methylated from 1 to 1.9 methyls/silicon), methyl silicols copolymerized with butyl alcoholmodified urea-formaldehyde. The pigment is formed (a) by dissolving the dye in a solution of the completely or partly unpolymerized resinforming material and polymerizing the resin by heat alone or by heat in the presence of a catalytic agent, such as an acid, and grinding, or (b) by completely or partly polymerizing, and grinding the undyed resin and dispersing it in a dye bath. Polymerization may be completed by the heat employed in subsequent baking or moulding operations. Examples of coating composition vehicles are toluene solution of methyl methacrylate, solutions of butyl methacrylate, nitro-cellulose, nitro-cellulose modified by methacrylate resins or by drying or nondrying oil-modified alkyd resins, simple alkyd resins such as those derived from sebacic acid, or urea-formaldehyde modified for use in baking lacquers. An aqueous solution of ammonium caseinate is also referred to. The pigment may be dispersed in a vehicle which comprises two or more transparent mediums having sufficient difference in refractive indices to give diffuse reflection, e.g. dinaphthoxy ethane powder can be mixed with nitrocellulose dissolved in ethyl acetate and with a non-drying oil-modified alkyd resin in a toluene solution to provide when dry a self-diffusing vehicle for pigments having a butyl alcohol-modified urea-formaldehyde carrier. When the coating is preformed as a cast film, one surface may be etched or abraded to provide a diffusely-reflecting surface. The coating compositions may be applied to surfaces as inks, paints, lacquer-enamels, fabric coating and impregnating compounds applied by brushing, printing, screening, spraying, dipping, roll-coating, knife-coating, &c. The coating may cover the entire surface area or only portions thereof, as on white paper next to normally coloured portions to form a billboard poster.