GB1339711A - Coating processes - Google Patents

Abstract

1339711 Coated products BOSTIK Ltd 21 Dec 1970 [22 Dec 1969] 60458/70 Heading B2E A method of producing a firmly adherent coating on a polymeric surface layer having a critical surface tension of not more than 35 dynes per centimeter as determined by contact angle measurements, in which method there is used a polymeric surface layer provided with a photo-sensitiser having a triplet state energy of at least 62K cal/mole, comprising the steps of irradiating the surface layer with ultraviolet light having a wavelength 2000-3500Š to an extent of not less than 980 watt-seconds per square foot of the surface layer and sufficient to promote generation of free radicals in molecules of said surface layer, and subsequently applying to the surface layer a coating composition in which the film forming component is essentially polymeric and which has chemical groups capable of combining with the molecules of said surface layer in which free radicals have been generated. Preferred photosensitisers are ketones, hydrocarbon multiple ring compounds, and halogenated hydrocarbons. The polymeric surface layer may be of polyethylene, polypropylene, a copolymer of ethylene and propylene, a copolymer of ethylene, propylene and a non- conjugated diene (EPDM), copolymers of ethylene or propylene with vinyl acetate or ethyl acrylate, polyvinyl fluoride or polyvinylidene fluoride. Other suitable materials are acetal resins, polyamides, polyurethanes, and metallic salts of an acrylic acid copolymer. The coating composition preferably comprises a polymer or copolymer of methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl acrylate. This type of coating composition may include 0.1% by weight polymerisable monomer having a vinyl or vinylidene radical. Polyurethane paints may also be used in which case a dosage of 5000 watt-secs./sq. ft. may be desirable. The ultraviolet radiation used is preferably at a wavelength of 2000-2800Š. Discussion of the bonding mechanism between the two polymeric materials is provided. The photosensitiser is generally applied to the polymeric surface layer in the form of a solution in a volatile solvent or as a pure liquid. The polymeric surface layer may be coated with a primer and then a top coat. Examples, some of which are comparative, refer to coating a) polyethylene with polymethyl methacrylate primer and top coats (1-13); b) ethylene butene-1 copolymer with polymethyl methacrylate primer (14-33); c) polyethylene with polymethyl methacrylate primer or top coat including metallic pigment, methane paint and acrylic primer (34-43); d) polyethylene or propylene optionally reinforced with glass fibres and polymethyl methacrylate primer and/or top coat, acrylic primer, and polyurethane paint (44-79); e) polyethylene with polymethyl methacrylate which optionally contains 0.1% acrylic acid (80-82); and f) acetal, polycaprolactam or polyamide with polymethyl methacrylate.