GB1019658A - Method for the electrical deposition of synthetic resin coatings - Google Patents

Abstract

Metallic or other conductive supports are coated with synthetic resins by anodic electro-deposition from aqueous solutions of synthetic resins having an acid number above 10 and neutralized or rendered slightly alkaline with ammonia or an amine or of a lacquer or varnish containing a synthetic resin which has been so treated. The resin may be a polyacrylate or polymethacrylate resin or an alkyd resin of acid number up to 70 formed from phthalic acid or its anhydride, isophthalic or terephthalic acids, maleic, adipic, succinic acids or their anhydrides, citric or aconitic acids and glycerol, pentaerythritol, or trimethylol propane modified by the incorporation of saturated or unsaturated fatty acids, such as linseed, castor, coconut, peanut, wood, oiticica, cottonseed or dehydrated castor oils, or colophony or copal resin acids, these resins being rendered soluble by neutralizing the acid groups. If necessary, the alkyd resins may be made water soluble by substituting polyethylene glycols for part of the polyalcohols used in preparing the resin. Neutralization may be effected with ammonia; primary, secondary, or tertiary mono- or poly-amines or mono-, di-, or trialkanolamines; or quaternary ammonium bases produced from these amines, while to improve the solubility of the neutralized resins the coating solutions may contain small quantities of an alcohol or a glycol or polyglycol or an ether formed from them. The coating solution may also include pigments, dyes, fillers, and metal powders and may also contain an aqueous solution of a water-miscible urea-, phenol-, or melamine-formaldehyde resin, e.g. a melamine-formaldehyde-methanol condensation resin. The solid content of the solution should be between 10% and 70% by weight, a preferred coating composition consisting of 2.2% pigment, 21.8% synthetic resin, 8.8% organic solvent and the remainder water. Iron, steel, copper, zinc and phosphated iron plates may be coated electrophoretically on both sides by anodic deposition employing a constant current density, say of 1.5 mA/cm.2 with increase of voltage as required up to 150 volts, and the resulting coatings, which are thickest at the edges, may be hardened by baking at 80-220 DEG C. Metal sheets, bands or wires may be coated by continuous passage as anode through the bath.ALSO:An aqueous solution or a water-thinnable lacquer or varnish suitable for coating an electrically conductive support by anodic electrodeposition includes an alkyd resin of acid number between 10 and 70 which has been made water-soluble by treatment with ammonia or an amine to neutralize the solution or make it slightly alkaline. The alkyd resin may be formed from phthalic acid or its anhydride, isophthalic or terephthalic acids, maleic, adipic, succinic acid or their anhydrides, citric or aconitic acids and glycerol, pentaerythritol or trimethylol propane, and may be modified by the incorporation of saturated or unsaturated fatty acids such as linseed, castor, coconut, peanut, wood, oiticica, cottonseed or dehydrated castor oils, or colophony or copal resin acids. Polyethylene glycols may be substituted for part of the polyalcohols used in making the resins to improve the water-solubility. Neutralization may be effected with ammonia; primary, secondary, or tertiary mono- or poly-amines or mono-, di- or tri-alkanolamines; or quaternary ammonium bases derived from these amines. To improve solubility, the coating solutions may contain small quantities of an alcohol or a glycol or polyglycol or an ether formed from them. The coating solution may also include pigments, dyes fillers, and metal powders, and may also contain an aqueous solution of a water-miscible or water-soluble urea-, phenol- or melamineformaldehyde resin, e.g. a resin formed by condensing melamine with formaldehyde and methanol. The solids content of the solution should be between 10 and 70% by weight, a preferred coating composition consisting of 2.2% pigment, 21.8% synthetic resin, 8.8% organic solvent and the remainder water. In specific examples there are employed for anodic deposition a water-thinned solution in hexyl and n-butyl monoethers of diethylene glycol of a dehydrated castor oil alkyd resin, neutralized with methyl isopropanolamine; a similar solution containing also a melamine-formaldehyde-methanol condensation resin; a solution of a similar alkyd resin neutralized with diethanolamine and mixed with a water-soluble phenol-formaldehyde resin or neutralized with methyl isopropanolamine and mixed with a melamine-formaldehyde-methanol resin together with a red iron oxide pigment; a solution of a linseed oil alkyd resin neutralized with dimethyl ethanolamine and mixed with an aqueous solution of a melamine resin; or a solution of a maleinized wood oil neutralized with ammonia.