One-component, dual-cure conformal coating compositions
Disclosed are one-component compositions that include: (1) an isocyanate-functional urethane acrylate and (2) a polyisocyanate containing allophanate and/or uretdione groups, wherein the one-component composition has a viscosity of less than or equal to about 800 mPa·s and an isocyanate content of greater than about 5% by weight, based on the weight of the one-component composition. Also disclosed are circuit boards and electronic components that are coated with such compositions.
1. A one-component composition comprising two components, wherein:
a first component is an isocyanate functional urethane (meth)acrylate, which is a reaction product of a composition comprising: (a) a polycaprolactone hydroxy ethyl (meth)acrylate; and (b) a di- or polyisocyanate, and
a second component is a polyisocyanate containing allophanate and/or uretdione groups,
which is different from the first component, and
wherein the one-component composition has:
(i) a viscosity of less than or equal to about 800 mPa·s according to ASTM Standard D 7395-07 using a Brookfield R/S Rheometer at 25° C., 100 s-1 shear rate for 2 minutes with a C-50-1 spindle, and
(ii) an isocyanate content of greater than about 5% by weight, based on the weight of the one-component composition.
2. The one-component composition of claim 1 , wherein a solids content of the composition is at least 90 percent by weight, based on the total weight of the one-component composition.
3. The one-component composition of claim 1 , wherein the polycaprolactone hydroxy ethyl (meth)acrylate is a poly(c-caprolactone) ester of 2-hydroxyethyl acrylate.
4. The one-component composition of claim 1 , wherein the first component is present in an amount of at least 40 percent by weight, based on the total weight of the composition.
5. The one-component composition of claim 1 , wherein the first component is present in an amount of no more than 60 percent by weight, based on the total weight of the composition.
6. The one-component composition of claim 1 , wherein the second component comprises a polyisocyanate containing uretdione groups.
7. The one-component composition of claim 1 , wherein the second component is present in an amount of at least 10 percent by weight and no more than 30 percent by weight, based on the total weight of the composition.
8. The one-component composition of claim 1 , further comprising a reactive diluent comprising a mono-functional (meth)acrylate monomer containing at least 6 carbon atoms in the alkyl moiety that is present in an amount of up to 50 percent by weight, based on the total weight of the composition.
9. The one-component composition of claim 1 , wherein the composition has an isocyanate content of greater than about 6% by weight and a solids content of at least 95 percent by weight, based on the total weight of the composition.
10. A method for conformal coating of a substrate, comprising depositing the composition of claim 1 over at least a portion of said substrate and exposing the coated substrate to actinic radiation.
11. The method of claim 10 , wherein the substrate comprises a circuit board or electronic component.
12. A substrate coated with a coating obtained from the composition according to claim 1 , wherein the microhardness of the coating is above 100 mN/mm2 measured using the method DIN 14577.