Crosslinkable binders for solvent based intumescent coatings
Self-crosslinkable binder compositions which include a copolymer obtained by reacting a mixture of monomers in the presence of an organic solvent, wherein the monomer mixture includes a carboxylic acid monomer, a polymerizable ethylenically unsaturated monomer, and a crosslinkable acrylamide monomer. Intumescent coatings containing the self-crosslinkable binder, and substrates coated with the intumescent coatings are also disclosed.
1. An intumescent coating composition comprising:
(a) a self-crosslinkable binder composition comprising a copolymer obtained by reacting a monomer mixture in the presence of an organic solvent, the monomer mixture comprising:
(i) 0.5 to 10 percent by weight of a polymerizable ethylenically unsaturated carboxylic acid monomer;
(ii) 50 to 90 percent by weight of a polymerizable ethylenically unsaturated monomer different from (i); and
(iii) 7 to 50 percent by weight of a crosslinkable acrylamide monomer,
wherein the percent by weight is based on the total weight of the monomer mixture, and wherein the binder has an acid value of less than 100 mg KOH/g and the copolymer has a weight average molecular weight of greater than 20,000 as determined by gel permeation chromatography relative to polystyrene standards with the unit of g/mol;
(b) an acid source;
(c) a carbon source; and
(d) a gas source.
2. The intumescent coating composition of claim 1 , further comprising (e) a pigment, an inorganic filler, or an inorganic nucleating agent.
3. The intumescent coating composition of claim 1 , wherein the self-crosslinkable binder composition comprises at least 30% solids by weight of the copolymer, based on the total weight of the self-crosslinkable binder (a).
4. The intumescent coating composition of claim 1 , wherein the polymerizable ethylenically unsaturated carboxylic acid monomer (i) comprises (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, or combinations thereof.
5. The intumescent coating composition of claim 1 , wherein the polymerizable ethylenically unsaturated monomer (ii) comprises styrene, α-methyl styrene, t-butylstyrene, vinyl toluene, or a combination thereof.
6. The intumescent coating composition of claim 1 , wherein the crosslinkable acrylamide monomer (iii) comprises n-butoxymethyl acrylamide, which is present in an amount of 10 to 30 percent by weight based on the total weight of the monomer mixture.
7. The intumescent coating composition of claim 1 , wherein the coating composition, following application to a substrate, achieves a shore A hardness of greater than 90 as measured according to ASTM D2240 after 160 hours of drying time at ambient conditions (22.2° C.) or 25 hours of drying time at 40° C.
8. The intumescent coating composition of claim 1 , wherein the coating composition, following application to a substrate, has a time to 620° C. of greater than 50 minutes for a 1000 um coating on a W6×16 mild steel H-column tested according to EN13381-8.
9. A substrate coated at least in part with the intumescent coating composition of claim 1 .