Properties / Applications: Desmodur BL 3175A blocked polyisocyanate is used with hydroxyl-functional coreactants in the formulation of light-stable one-component baking systems with relatively low curing temperatures. Coatings based on Desmodur BL 3175A blocked polyisocyanate are used for the industrial finishing of appliances, coil coating, and can coating, and in the automotive industry for chip-resistant primer-surfacers and topcoats. The properties of coatings based on Desmodur BL 3175A blocked polyisocyanate can be influenced, as with two-component polyurethane systems, by the degree of crosslinking and the choice of the polyol. The cure time and temperature required are also dependent upon the choice of coreactant. Combining Desmodur BL 3175A with hydroxyl-functional polyesters such as Desmophen 670BA gives coatings with high flexibility and hardness. The cure rate can be varied by catalysis without adverse effects on storage. Crosslinking with polyamines or amides may result in limited storage stability. In coil coating systems, adequate crosslinking may be achieved without catalysis at 465°F peak metal temperature (P.M.T.). With the addition of 1% dibutyl tin dilaurate (DBTDL) based on solid resin, a crosslinking temperature of 435°F P.M.T. is possible. Thermal yellowing may occur at temperatures above 320°F (160°C), depending on the baking time and the polyol used. Testing in Florida indicates that Desmodur BL 3175A polyisocyanate provides excellent weather stability comparable to Desmodur N 3390A BA/SN polyisocyanate. Desmodur BL 3175A may also be used as additive to upgrade the flexibility and adhesion of conventional baking systems. As with any product, use of Desmodur BL 3175A in a given application must be tested (including but not limited to field testing) in advance by the user to determine suitability.

Information provided by Covestro