Dual cure thermoformable coating and coated articles
A coating has dual curing mechanisms wherein the first cure reaction and second cure reaction become active due to differing reaction mechanisms.
1 . A dual-curable, coating composition that is castable from an alcohol solvent, the coating composition comprising:
a blocked polyisocyanate having a blocking group selected from the group consisting of diethyl malonate, 3,5 dimethyl pyrazole, methyl ethyl ketoxime, and caprolactam,
a polyol with a hydroxy functionality greater than 2,
a monomeric or oligomeric reactant having both ethylenically unsaturated acrylate and/or methacrylate functionality and pendant and/or terminal isocyanate reactive groups, and
a photoinitiator;
wherein the composition undergoes an initial curing reaction via the photoinitiator and actinic radiation, causing the ethylenically unsaturated acrylate and/or methacrylate functionality of the monomeric or oligomeric reactant to undergo free-radical polymerization, resulting in is a tack-free, deformable coating; and
wherein the composition undergoes a secondary curing reaction by heating the tack-free deformable coating at an elevated temperature, causing the blocked polyisocyanate to unblock and initiate a urethane exothermic reaction with the polyol and the pendant and/or terminal isocyanate reactive groups of the polymerized monomeric or oligomeric reactant, resulting in a rigid coating having high hardness, good scratch resistance and good abrasion resistance with high optical transparency.
2 . The composition of claim 1 , wherein the tack-free, deformable coating has a glass transition temperature (Tg) of about 38° C. to about 115° C. and a tanδ of about 1.7 to about 3.30, and the rigid, coating has a Tg of about 80° C. to about 130° C. and a tanδ of about 0.50 to about 2.50.
3 . The composition of claim 1 , further comprising at least one of a polyurethane catalyst, an alcohol solvent, a UV light inhibitor, a hindered amine light stabilizer, a flow control agent, an amine synergist, or inorganic oxide particles.
4 . The composition of claim 1 , further comprising an alcohol solvent, wherein the alcohol solvent is not reactive with a substrate.
5 . The composition of claim 1 , wherein the monomeric or oligomeric reactant has a hydroxy functionality greater than 2.
6 . The composition of claim 1 , wherein the composition is applied to a thermoformable substrate, wherein the initial curing reaction occurs on the thermoformable substrate prior to thermoforming, and the secondary curing reaction occurs on the thermoformable substrate during thermoforming.
7 . The composition of claim 1 , wherein the blocked polyisocyanate comprises at least one of a blocked hexamethylene diisocyanate, blocked hexamethylene diisocyanate biuret, blocked hexamethylene diisocyanate trimer, blocked isophorone diisocyanate, or a blocked isocyanate functional urethane acrylate resin.
8 . The composition of claim 7 , wherein the blocked polyisocyanate is blocked with 3,5 dimethyl pyrazole.
9 . The composition of claim 1 , wherein the polyol has a hydroxyl equivalent weight of about 200 to about 6000 grams/mole.
10 . The composition of claim 9 , wherein the polyol is derived from at least one of pentaerythritol, glycerol, or caprolactone.
11 . The composition of claim 1 , wherein the pendant and/or terminal isocyanate reactive groups of the monomeric or oligomeric reactant comprise hydroxyl groups.
12 . The composition of claim 11 , wherein the monomeric or oligomeric reactant has a hydroxyl equivalent weight of about 200 to about 6000 grams/mole and an acrylate and/or methacrylate functionality of about 2 to about 8.
13 . The composition of claim 1 , wherein the rigid coating is substantially crack-free and has a total light transmittance of at least about 86% as measured at a wavelength of 400 to 700 nm in accordance with ASTM D1003, a delta haze in accordance with ASTM D1003 of about 8.0% or less, a yellow index in accordance with ASTM E313 of 3 or less, and an adhesion of 3B or greater in accordance with ASTMD3359.
14 . The composition of claim 1 , wherein the monomeric or oligomeric reactant is a urethane monomer or oligomer having both ethylenically unsaturated acrylate and/or methacrylate functionality and pendant and/or terminal isocyanate reactive groups.
15 . A coated substrate comprising a substrate coated with the dual-curable, coating composition of claim 1 .
16 . The coated substrate of claim 15 , wherein the tack-free, deformable coating has a glass transition temperature (Tg) of about 38° C. to about 115° C. and a tanδ of about 1.7 to about 3.30, and the rigid coating has a Tg of about 80° C. to about 130° C. and a tanδ of about 0.50 to about 2.50.
17 . The coated substrate of claim 15 , wherein the blocking group of the blocked polyisocyanate forms a UV stabilizer that is latent when the polyisocyanate is blocked, and is effective in absorbing damaging UV radiation when the polyisocyanate is unblocked, thereby protecting the substrate from UV radiation.
18 . The coated substrate of claim 15 , wherein the substrate is a thermoformable substrate, the initial curing reaction occurs on the thermoformable substrate prior to thermoforming, and the secondary curing reaction occurs on the thermoformable substate during thermoform; wherein the rigid coating is substantially crack-free and has a total light transmittance of at least about 86% as measured at a wavelength of 400 to 700 nm in accordance with ASTM D1003, a delta haze in accordance with ASTM D1003 of about 8.0% or less, a yellow index in accordance with ASTM E313 of 3 or less, and an adhesion of 3B or greater in accordance with ASTMD3359.
19 . The coated substrate of claim 15 , wherein the substrate is formed from an optically transparent polymer.
20 . The coated substrate of claim 19 , wherein the optically transparent polymer comprises at least one of polymethyl methacrylate, polycarbonate, or PET.
21 . The coated substrate of claim 15 , wherein the monomeric or oligomeric reactant is a urethane monomer or oligomer having both ethylenically unsaturated acrylate and/or methacrylate functionality and pendant and/or terminal isocyanate reactive groups.
22 . An article comprising the coated substrate of claim 15 , wherein the article is a protective visor, a windshield for a motor vehicle, a lens, a decorative automotive trim, window, roof, door system, or molding.