Phosphonate-containing two-component coating system and the production and use thereof

A two-component coating system comprising

• a component (a) comprising a polyisocyanate selected from the group consisting of alkylene diisocyanate, oligomerized alkylene diisocyanate, and combinations thereof;
• a component (b) comprising one or more oligomeric and/or polymeric compounds that are reactive with component (a), which component (b) has an acid number of up to 30 mg KOH/g, wherein component (b) comprises at least one member selected from the group consisting of a polyester having at least two hydroxyl groups or a poly(meth)acrylate having at least two hydroxyl groups;
• and
• a component (c) comprising one or more phosphonates selected from the group consisting of phosphonic diesters and diphosphonic diesters, where
• (i) component (b) contains all oligomeric and/or polymeric compounds that are present in the two-component coating system and are reactive with component (a) and
• (ii) component (b) contains not more than 15% by weight, based on the total weight of component (b), of oligomeric and/or polymeric compounds which carry isocyanate-reactive amino groups;
• wherein component (c) is capable of reacting with moisture to suppress secondary reactions of polyisocyanates with condensation that give rise to unwanted gelling.