MASKING COMPOSITIONS FOR CHEMICAL MILLING AND METHOD FOR APPLYING THE SAME

摘要

MASKING COMPOSITIONS FOR CHEMICAL MILLING AND METHOD FOR APPLYING THE SAME A method of coating a metal part with a peelable mask which is resistant to attack by the strong acid and strong base etchants used in chemical milling is disclosed in which the metal part is surfaced with a layer of polyvalent metal salt, such as calcium nitrate, and then immersed in a high solids content anionic emulsion of coalescent rubbery particles heavily pigmented to contain at least about 45% total solids content and at least 20% pigment, the pigment to binder ratio being from 0.75:1 to 1:0.57. The salt-surfaced metal part is held in the anionic emulsion until the desired coating thickness has been anodically deposited thereon, and then the coated part is removed and baked to complete the formation of the mask. The rubbery particles are preferably constituted by an anionic polychloroprene homopolymer emulsion which is used in admixture with a curing Anita for the homopolymer, like zinc oxide, and a polyvinylidene chloride latex. Sodium bichromate is included with the polyvalent metal salt to enhance corrosion resistance, and a silicone release agent is included to control adhesion to the metal substrate.