Fluoropolymer coatings comprising aziridine compounds and non-fluorinated polymer
A fluoropolymer coating composition is described comprising an aqueous liquid medium, fluoropolymer particles dispersed in the aqueous liquid medium, and at least one aziridine compound. The aziridine compound comprises at least two aziridine groups (i.e. polyaziridine) or at least one aziridine group and at least one alkoxy silane group. In another embodiment, an article is described comprising a substrate wherein a surface of the substrate comprises a coating comprising fluoropolymer particles; and a reaction product of at least one aziridine compound comprising at least two aziridine groups or at least one aziridine group and at least one alkoxy silane group. The coating can be utilized as a primer for bonding a non-fluorinated substrate to a fluoropolymer film and/or the coating can be used as an (e.g. outer exposed) surface layer. In some embodiments, the article may be the (e.g. backside) film of a photovoltaic module.
1. A fluoropolymer coating composition consisting of
a basic aqueous liquid medium;
at least 50 wt. % solids fluoropolymer particles comprising a fluorine content of at least 60 wt. % dispersed in the aqueous liquid medium,
5 to 50 wt. % solids non-fluorinated polymer particles dispersed in the aqueous liquid medium;
at least one aziridine compound comprising at least two aziridine groups or at least one aziridine group and at least one alkoxy silane group; and
optional additives selected from the group consisting of organic cosolvent, inorganic oxide nanoparticles, thickeners, surfactants, pigments, fillers, light stabilizers, thermal stabilizers, and barrier particles.
2. The fluoropolymer coating composition of claim 1 wherein the aqueous liquid medium is basic.
3. The fluoropolymer coating composition of claim 1 further comprising inorganic oxide nanoparticles.
4. The fluoropolymer coating composition of claim 3 wherein the inorganic oxide nanoparticles comprise silica, clay, or a mixture thereof.
5. The fluoropolymer coating composition of claim 3 wherein the inorganic oxide nanoparticles have an average particle size of less than 100 nm.
6. The fluoropolymer coating composition of claim 1 wherein the aziridine compound has the general structure:
wherein R is a core moiety having a valency of Y;
L is a bond, a divalent atom, or a divalent linking group;
R 1 , R 2 , R 3 , and R 4 are independently hydrogen or a C 1 -C 4 alkyl; and
Y ranges from 2 to 6.
7. The fluoropolymer coating composition of claim 6 wherein R-L is a residue of a multi(meth)acrylate compound.
8. The fluoropolymer coating composition of claim 6 wherein the aziridine compound is free of hydrolyzable groups including ester groups.
9. The fluoropolymer coating composition of claim 1 wherein the aziridine compound has the general structure:
wherein R″ is hydrogen or a C 1 -C 4 alkyl;
X is a bond, a divalent atom, or a divalent linking group;
n is 0, 1 or 2;
m is 1, 2, or 3;
and the sum of n+m is 3.
10. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises 15 to 35 mole-% of monomeric units derived from VF, VDF or a combination thereof; at least 45 mole-% of monomeric units derived from TFE; and monomeric units derived from HFP.
11. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises at least 50 mole-% of monomeric units derived from VF, VDF or a combination.
12. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises at least 50 mole-% of repeat units derived from TFE and monomeric units derived from alkyl vinyl ether.
13. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises at least 45 mole-% of repeat units derived from TFE and monomeric units derived from perfluoroalkyl vinyl ether.
14. The fluoropolymer coating composition of claim 1 wherein the non-fluorinated polymers comprise polyurethane polymer, acrylic polymer, or a mixture thereof.
15. A coated substrate comprising a substrate wherein a surface of the coated substrate comprises a dried coating composition according to claim 1 .
16. The coated substrate of claim 15 wherein the fluoropolymer is phase separated as an outer surface layer.
17. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises polar functional groups selected from hydroxyl and carboxylate groups.
18. The fluoropolymer coating composition of claim 1 wherein the fluoropolymer comprises reactive functionality derived from inclusion of a cure-site monomer; wherein the reactive functionality is selected from bromo-, iodo-, or nitrile.
19. The coated substrate of claim 15 wherein the dried coating can be heat laminated to a fluoropolymer film exhibiting an adhesion peel force of at least 2.4 lbf/inch.