Photodegradation-resistant electrodepositable coating compositions with improved throw power and processes related thereto

Abstract

The invention provides a photodegradation resistant curable electrodepositable coating composition which includes one or more ungelled, active hydrogen-containing cationic sulfonium salt group-containing resins which are electrodepositable on a cathode, and one or more curing agents having cationic groups or groups which are capable of forming cationic groups. The invention also provides processes for coating an electroconductive substrate with the coating composition, to form single layer or multi-layer composite coatings. Also provided is a multi-layer composite coating in which the electrodepositable coating composition is used to form the primer layer. The compositions have improved throw power versus typical sulfonium salt electrodepositable compositions.

Description

FIELD OF THE INVENTION [0001] The present invention is directed to an electrodepositable composition and a process for coating an electroconductive substrate using the composition. More particularly, the present invention is directed to single and multi-layer composite coatings comprising a photodegradation-resistant, high throw power electrodepositable composition with an optional top coat thereover, and to a process for forming such a coating on the substrate. BACKGROUND OF THE INVENTION [0002] Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection and low environmental contamination. [0003] Initially, electrodeposition was conducted ...

AI Technical Summary

Benefits of technology

The composition achieves high throw power and photodegradation resistance, preventing delamination even under concentrated solar spectral irradiance, equivalent to two years of outdoor weathering, with the top coat maintaining 80% light transmission at 400 nanometers.

Problems solved by technology

However, excessively high voltage will cause dielectric breakdown and film defects commonly known as film ruptures.

One disadvantage of sulfonium salt group-containing coating compositions, however, is their low throw power, due in large part to low bath conductivity.

If the top coat(s) do not provide sufficient protection, photodegradation of the electrodeposited primer coating can result in delamination of the subsequently applied top coats from the cured electrodeposited primer coatings producing catastrophic failure of the cured coating system.

However, if a thin top coat and / or a top coat which is not ultraviolet light absorbing is applied to the cured electrodeposited primer coating, ultraviolet light can pass through the top coat(s) resulting in photodegradation of the cured electrodeposited primer coating.

Such a problem is likely to occur when a top coat is lightly pigmented with metal flake pigments which tend to allow transmission of ultraviolet light to the previously applied and cured electrodeposited primer coating.

Although the aforementioned references disclose photodegradation resistant coating systems which can provide many advantages, each of the respective coating system disclosed therein can have one or more deficiencies, including low throw-power, excessive cost, toxicity issues, or marginal effectiveness.