Gas barrier coatings
The use of a colloidal silica having a specific surface area greater than 300 m 2 /g in a gas barrier coating additionally comprising polyvinyl alcohol and/or ethylene vinyl alcohol copolymer and/or a silylated derivative thereof improves wet bond strength.
1. A composition for preparing a gas barrier coating, said composition comprising an aqueous solution or dispersion of a polyvinyl alcohol and/or an ethylene-vinyl alcohol copolymer and/or a silylated derivative thereof, a colloidal silica, in which said silica has a specific surface area greater than 300 m 2 /g, and an alkali metal silicate;
wherein the ratio (w/w) of the polyvinyl alcohol and/or ethylene-vinyl alcohol copolymer and/or silylated derivative to silica is 1.5:1 to 3:1.
2. The composition according to claim 1 , in which the colloidal silica has a particle size less than 20 nm.
3. The composition according to claim 1 , in which the colloidal silica has a particle size less than 10 nm.
4. The composition according to claim 1 , in which said silica has a specific surface area greater than 400 m 2 /g.
5. The composition according to claim 4 , in which said silica has a specific surface area greater than 450 m 2 /g.
6. The composition according to claim 1 , in which said alkali metal silicate is lithium silicate.
7. A method of preparing a gas barrier material comprising applying to a substrate a coating composition according to claim 1 , and removing the water.
8. A gas barrier material prepared by a method according to claim 7 .
9. The material according to claim 8 , additionally comprising a flexible plastics material laminated to the coated side of the substrate.
10. The material according to claim 8 , in the form of a liquid container.
11. A bag-in-the-box container having a bag comprising a material according to claim 8 .