Patent GB-1375247-A (GB)
IPC: G21H5/00
Filed: 1972-03-13
Abstract: 1375247 Coated substrates DONALD MACPHERSON GROUP Ltd and S E YOUNG 5 March 1973 [13 March 1972] 11617/72 Heading B2E A process for coating a substrate surface comprises applying to the substrate a coating of a dispersion, emulsion or latex coating composition which comprises a mixture of at least one polymer or copolymer dispersion having a minimum film-forming temperature of at least 5‹C above ambient temperature and at least one polymer or copolymer dispersion having a minimum film-forming temperature at or below ambient temperature, the proportions thereof being such that the dispersion, emulsion or latex coating composition has a minimum film-forming temperature above ambient temperature, and drying the coating by heating with electromagnetic radiation having a wavelength longer than 780 nanometres. The invention also includes a process for coating a substrate comprising applying to the substrate surface a coating of an aqueous dispersion, emulsion or latex coating composition which comprises a mixture of at least one aqueous dispersion of a polymer or copolymer having a Tg above 40‹C and at least one aqueous dispersion of a polymer or copolymer having a Tg below 20‹C the proportions of dispersions being such as to provide a composition having an effective Tg in the range 20 to 40‹C and drying the said coating by heating with electromagnetic radiation of a wavelength longer than 780 nanometres. Generally the particles of the coating composition are of a particle size within the range 0.01 Ám to 6 Ám in diameter. The monomers used for production of the polymer or copolymer dispersion having the high film-forming temperature are styrene, methylmethacrylate, vinyl acetate. Monomers used for the production of the polymer or copolymer dispersions have a low minimum film-forming temperatures are the higher esters of acrylic and methacrylic acids, such as n-butyl-methacrylate, isobutylacrylate, &c., butadiene, ethylene, fumaric acid esters, maleic acid esters or vinyl esters. Reactive or polyfunctional monomers such as acrylamide, aminomethacrylate, hydroxy acrylates, hydroxy methacrylates, N-methanolacrylamides, acrylic and methacrylic acids may be used to produce polymers or copolymers capable of being linked internally or crosslinked with other polymers. The radiant energy used for drying the coating is preferably radiofrequency heating, although microwave heating and infra-red heating are also suitable. The drying may be by a two-stage process, the first being a preliminary drying step such as with warm air or by convection heating followed by the electromagnetic radiation heating. The use of additives such as pigments and dyestuffs, extenders, wetting agents, dispersing agents, may be added as well as colloids such as methyl cellulose and ether hydroxyether cellulose, and the viscosity, flow properties and application characteristics may be modified by addition of resin such as styrene-maleic acid copolymers, or solubilised alkyd resins. Fungicides, bactericides and anti-corrosion agents may also be present. In the Examples coatings are applied by spraying to veneered chipboard panels.