Electrical insulation of metallic conductors

#The present invention relates to a process for coating wires with aqueous dispersions of coating materials.

#Metallic conductors are usually coated with synthetic resins which are applied in the form of solutions in organic solvents. On subsequent baking of the applied coating, the solvent evaporates and contributes to pollution of the environment.

#For this reason, attempts have been made to coat wires with aqueous dispersions. German Published Application No. 2,351,078 describes wire enamels based on aqueous polyester-imide dispersions wherein the preferred particle diameter is from 0.05 to 1.5.sub./ u. In the said Patent Application, the dispersion is prepared, and then applied to copper wires, in two separate steps. German Printed Application No. 1,285,081 describes wire enamels comprising aqueous polyester dispersions. Here again, the preparation of the dispersion and coating are carried out in two separate steps; to achieve a uniform coating, continuous filtration of the dispersion is recommended.

#The invention can best be understood by reference to the attached drawing in which:

#FIG. 1 is a schematic representation illustrating a preferred embodiment of a dispersing and coating system of the present invention;

#FIG. 2 is an enlarged sectional view of an embodiment of the dispersing zone B shown in FIG. 1;

#As is shown in FIG. 1, the starting dispersion is introduced via line 11 into the storage zone A from where it is withdrawn, advantageously by a pump 12, and fed to the dispersing zone B. The homogenized and comminuted dispersion is cooled in the cooling zone C and is then fed to the fractionating zone D, where it is separated into a coarse fraction and a fine fraction. The coarse fraction is recycled directly to the storage zone A via line 13; the fine fraction is also returned to the storage zone, via line 14, but through the coating zone E. Wires 15 are drawn through the coating zone E, and coated there.

#Resins which may be used for wire enameling according to the invention are any polymeric organic coating materials suitable for this purpose. The following are particularly suitable:

#Polyesters of aromatic dicarboxylic acids and polyhydric alcohols, which are preferably crosslinked by co-condensation of tris-hydroxyethyl-isocyanurate; polyamide-imides, manufactured by reacting trimellitic anhydride or its derivatives with aromatic diamines or diisocyanates, or by reacting diimide-dicarboxylic acids with diisocyanates, eg. in accordance with German Printed Application Nos. 1,256,418, 1,765,738 or 1,720,909; polyimides based on aromatic tetracarboxylic acid dianhydrides or their derivatives and aromatic diamines; polyurethanes of a mixture of a hydroxyl-containing polyester and a blocked polyisocyanate; polyamides of dicarboxylic acids and diamines; polyacrylates based on copolymers of esters of acrylic acid or methacrylic acid.