Modified Crush Resistant Latex Topcoat Composition for Fiber Cement Substrates
A final topcoat coating composition and method employs a multistage latex polymer having acetoacetyl or ketone functionality and a hydrazide, hydrazine or polyamine crosslinking agent that provides a crush resistant final topcoat composition. The compositions may be used to coat a variety of substrates including wood, cement and fiber cement.
1 . A coated fiber cement article comprising an unattached fiber cement board substrate having a first major surface at least a portion of which is covered with a crush resistant topcoat composition comprising a multistage latex polymer having ketone functionality or acetoacetoxy functionality and a hydrazide, hydrazine or polyamine crosslinking agent.
2 . The article of claim 1 , wherein the multistage latex polymer comprises at least one soft stage having a Tg less than about 40° C. and at least one hard stage having a Tg greater than about 40° C.
3 . The article of claim 2 , wherein the soft stage is functionalized.
4 . The article of claim 2 , wherein the hard stage is functionalized.
5 . The article of claim 2 , wherein the hard and soft stages are functionalized.
6 . The article of claim 1 , wherein the ketone functionality is derived from diacetone acrylamide.
7 . The article of claim 1 , wherein the acetoacetoxy functionality is derived from acetoacetoxyethyl methacrylate.
8 . The article of claim 1 , wherein the multistage latex polymer comprises about 0.05 to about 1 wt. % reactive ketone or acetoacetyl functionality based on the total multistage latex polymer weight.
9 . The article of claim 1 , wherein the hydrazide is a dihydrazide.
10 . The article of claim 1 , wherein the dihydrazide is adipic acid dihydrazide.
11 . The article of claim 1 , wherein the polyamine is a diamine.
12 . The article of claim 1 , wherein the crosslinking agent comprises less than about 10 wt. % based on the weight of the latex polymer.
13 . The article of claim 1 , wherein the reactive equivalent ratio of crosslinking agents to crosslinkable groups of the reactive functionality is at least about 0.25:1.
14 . The article of claim 1 , wherein the topcoat when crosslinked, dried or otherwise hardened has a Crush Resistance value of at least 3 when two face-to-face coated embossed fiber cement board substrates are subjected to a pressure of about 8 kg/cm 2 .
15 . The article of claim 1 , wherein the composition is in the form of a layer atop a cementitious substrate.
16 . A method of making a crush resistant coated fiber cement article, which method comprises:
providing an unattached fiber cement board substrate having a first major surface;
providing a topcoat coating composition comprising a multistage latex polymer having ketone functionality or acetoacetoxy functionality and a hydrazide, hydrazine or polyamine crosslinking agent;
applying the topcoat coating composition to at least a portion of the first major surface;
crosslinking, drying or otherwise hardening the coating composition to form a crush resistant final topcoat; and
stacking two or more of the thus-coated boards on a pallet or other horizontal supporting surface.
17 . A method according to claim 16 further comprising placing a pair of the coated boards in face-to-face relationship with a protective liner between the coated surfaces.
18 . A method according to claim 17 comprising stacking a plurality of such pairs on a pallet.
19 . A method according to claim 18 comprising stacking a plurality of such pallets atop one another.
20 . A method according to claim 16 wherein the final topcoat has a Crush Resistance value of at least 3 when two face-to-face coated embossed fiber cement board substrates are subjected to a pressure of about 8 kg/cm2.