Process or preparing organic solvent-based dispersions, coating compositions and coated metal substrate useful for packaging applications
The invention relates to a process for preparing an organic solvent-based dispersion comprising a melt-blended network of an epoxy-functional and/or amino-functional polymer having a polymer-O—Si—O-polymer linkage and a polyolefin (co)polymer having carboxylic acid and/or carboxylic acid anhydride groups, the process comprising the steps of a) forming the melt-blended network from a prepolymer, a silane-functional compound and the polyolefin (co)polymer in the absence of a solvent, b) mixing the melt-blended network with an organic solvent to make the organic solvent-based dispersion, and c) cooling the organic solvent-based dispersion. The invention further relates to a coating composition and to a coated metal substrate.
1. An organic solvent-based coating composition comprising
a) an organic solvent-based dispersion comprising a melt-blended network of particles of an epoxy-functional and/or amino-functional polymer having a polymer-O—Si—O-polymer linkage and a polyolefin (co)polymer having carboxylic acid and/or carboxylic acid anhydride groups obtained by,
i) forming the melt-blended network from a prepolymer, a silane-functional compound and the polyolefin (co)polymer in the absence of a solvent,
ii) mixing the melt-blended network with an organic solvent to make the organic solvent-based dispersion, and
iii) cooling the organic solvent-based dispersion,
b) a film-forming polymer,
c) a crosslinker, and
d) an acid catalyst;
wherein the film-forming polymer is a polyester.
2. A coating composition according to claim 1 , wherein the coating composition is substantially free of Bisphenol A, Bisphenol F, and aromatic glycidyl ethers.
3. The coating composition according to claim 1 , wherein the acid catalyst comprises phosphoric acid.
4. The coating composition according to claim 1 , wherein the mean particle size of the melt-blended network particles is from 4 to 6 μm.
5. The coating composition according to claim 1 , wherein the crosslinker is a phenolic resin.
6. A metal substrate coated with a coating composition according to claim 1 .
7. The metal substrate according to claim 6 , wherein the organic solvent-based coating composition is the only coating composition applied directly or indirectly to the metal substrate and is cured to produce the coated metal substrate.
8. The metal substrate according to claim 6 , wherein the metal substrate is an easy-open end for a food or beverage container.
9. The organic solvent-based coating according to claim 1 , wherein i) is performed by simultaneously melt blending the prepolymer, the polyolefin (co)polymer and the silane-functional compound to form the melt-blended network.
10. The organic solvent-based coating according to claim 1 , wherein the silane-functional compound comprises an epoxy-silane-functional compound.
11. The organic solvent-based coating according to claim 1 , wherein the epoxy-functional silane compound comprises a diethoxysilane compound.
12. The organic solvent-based coating according to claim 1 , wherein the silane-functional compound comprises an amino-silane-functional compound.
13. The organic solvent-based coating according to claim 1 , wherein the prepolymer is a polyester comprising a cyclic diol as building block.
14. The organic solvent-based coating according to claim 1 , wherein the melt blending is performed at a temperature in the range 100-250° C. in an extruder.