Electrodepositable coating compositions and related methods

In a method for preparing an electrodepositable coating composition comprising a resinous phase dispersed in an aqueous medium, said resinous phase comprising:

• (a) an active hydrogen-containing, cationic salt group-containing resin;
• (b) an at least partially blocked polyisocyanate curing agent;
• and
• (c) an organotin catalyst for effecting the cure of the resin (a) and the curing agent (b), said method comprising the steps of
• (1) preparing the resin (a) from a mixture of reactive components;
• (2) preparing the at least partially blocked polyisocyanate curing agent (b) separate from the resin (a) by reacting a polyisocyanate and a blocking agent;
• (3) admixing the resin (a) and the curing agent (b) to form a resinous admixture;
• (4) blending an organic and/or inorganic acid with the resinous admixture to form an acidified admixture;
• and
• (5) dispersing the acidified admixture of (4) in an aqueous medium,
• the improvement comprising incorporating the organotin catalyst (c) into the mixture of reactive components during the preparation of the resin (a) in step (1),
• wherein the catalyst (c) is or is derived from a dialkyltin compound having the following structure (I):
• [R1][R2]—Sn═O (I)
• where R1 and R2 are the same or different, and each independently represents a monovalent hydrocarbon group wherein the sum of the carbon atoms in R1 and R2 is greater than 8,
• said catalyst being present in the electrodepositable coating composition in an amount sufficient to effect cure of the electrodepositable composition at a temperature at or below 340° F. (171.1° C.).

In a method of electrocoating a conductive substrate serving as a cathode in an electrical circuit comprising said cathode and an anode, said cathode and anode being immersed in an aqueous electrocoating composition,

• said method comprising passing electric current between said cathode and anode to cause deposition of the electrocoating composition onto the substrate as a substantially continuous film, the aqueous electrocoating composition comprising a resinous phase dispersed in an aqueous medium, said resinous phase comprising:
• (a) an active hydrogen group-containing, cationic group-containing electrodepositable resin, and
• (b) at least partially blocked polyisocyanate curing agent,
• the improvement comprising the inclusion in the electrocoating composition of an organotin catalyst for effecting cure between the resin (a) and the curing agent (b), wherein said catalyst is or is derived from a dialkyltin compound having the following structure (I):
• [R1][R2]—Sn═O (I)
• where R1 and R2 are the same or different, and each independently represents a monovalent hydrocarbon group, wherein the sum of the carbon atoms of R1 and R2 is greater than 8,
• said catalyst being present in the electrocoating composition in an amount sufficient to effect cure of the electrocoating composition at a temperature at or below 340° F. (171.1° C.).