Gas barrier coatings

Abstract

The use of a colloidal silica having a specific surface area greater than 300 m.sup.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.

Claims

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.sup.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.sup.2/g.

5. The composition according to claim 4, in which said silica has a specific surface area greater than 450 m.sup.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.

Description

EXAMPLES

(1) The raw materials used to prepare these examples were;

(2) 1. A 7.1% (w/w) aqueous solution of polyviol P-6060, ex. Wacker, a silylated polyvinyl alcohol;

(3) 2. A 8.0% (w/w) solution of Exceval AQ-4104 in a 90/10 blend of water/IPA, a water soluble ethylene/vinyl alcohol copolymer;

(4) 3. Bindzil 15/500, ex. EKA. This anionic colloidal silica has a solids content of 15%, a specific surface area of 500 m.sup.2/g, a claimed particle size range of 3-5 nm, and a measured mean particle size of about 10 nm;

(5) 4. Bindzil 30/360, ex. EKA. This anionic colloidal silica has a solids content of 30%, a specific surface area of 360 m.sup.2/g, a claimed particle size range of 8-20 nm, and a mean particle size of about 20 nm;

(6) 5. Bindzil 40/220, ex. EKA. This anionic colloidal silica has a solids content of 40%, a specific area of 220 m.sup.2/g, a claimed particle size range of 7-25 nm, and a mean particle size of about 25 nm;

(7) 6. An 8.0% (w/w) solution of Exceval AQ-4104: Mowiol 4-98 (70:30 w/w) in a 95/5 blend water IPA.

(8) 7. Crystal L40, a lithium silicate solution, ex. Ineos silicas, containing 25% solids in water.

(9) Various coating compositions were prepared by simple mixing of the ingredients. The formulations used are shown in Table 1

(10) TABLE-US-00001 TABLE 1 Coating Examples C1-C7 Deion- AQ- Exam- ised P-6060 4104 Bindzil Bindzil Bindzil ple Water IPA Solution Solution 15/500 30360 40/220 C1 29.1 4 5.6 1.35 C2 22.1 4 11.3 2.6 C3 15.1 4 16.9 4.0 C4 20.4 4 11.3 4.3 C5 23.3 4 10 2.6 C6 23.4 4 11.3 1.3 C7 23.7 4 11.3 1.0

(11) These coatings were applied at 4, 6 or 12 gsm wet applied film weight to the metallised surface of an Al-PET film comprising a coating of aluminium vacuum deposited (amount of Al deposited will vary from day to day on a 12 m thick film of polyethylene terephthalate (PET). The coated film was then dried under a flow of warm air. Morchem 614A/614C adhesive was then applied to the coated surface and a laminate was formed by applying a sealing PE film to the adhesive. The laminates were allowed to cure at 25 C. for 7 days before being tested. The laminates were assessed for oxygen barrier ability, and the bond strengths were measured as a function of the time they were immersed in room temperature water. Table 2 provides the results of these tests. Bond Strengths in Table 2b are given as the force (N/15 mm) required to peel apart the PE layer from the coated metallised surface of the Al-PET after being immersed in water for varying times.

(12) TABLE-US-00002 TABLE 2a Examples 1-10: Evaluation of 2-ply A/B/C/D 2-ply laminates - Oxygen Barrier (A = Al-PET, B = Coating, C = adhesive, D = PE) Wet Film Dry Film OTR (23 C./50% RH) Example Coating Weight Weight (cm.sup.3/m.sup.2/day) 1 none 5.38 2 C1 4 gsm 0.06 gsm 3 C1 6 gsm 0.09 gsm 0.34 4 C1 12 gsm 0.18 gsm 0.17 5 C2 12 gsm 0.36 gsm <0.10 6 C3 12 gsm 0.54 gsm 0.12 7 C4 12 gsm 0.65 gsm 8 C5 12 gsm 0.36 gsm 0.14 9 C6 12 gsm 0.36 gsm 0.16 10 C7 12 gsm 0.36 gsm

(13) TABLE-US-00003 TABLE 2b Examples 1-10: Evaluation of 2-ply laminates - Wet Bond Strengths v. Immersion time 0 30 60 120 180 240 420 Example mins mins mins mins mins mins mins 1 2.8 (FT) 1.5 (FT) 1.7 0.4 0.2 0.1 0.1 2 2.2 (FT) 0.2 0.2 0.1 0.1 0.1 0.1 3 2.1 (FT) 0.6 0.3 0.1 0.1 0.1 0.1 4 2.8 (FT) 2.2 (FT) 2.2 0.9 0.8 0.6 0.4 5 2.3 (FT) 2.4 (FT) 2.8 (FT) 1.4 0.8 0.8 0.9 6 2.0 (FT) 1.4 (FT) 1.3 (FT) 1.9 (FT) 1.7 1.5 1.2 7 4.0 (FT) 2.2 (FT) 2.3 (FT) 2.2 (FT) 1.9 (FT) 1.1 1.1 8 3.7 (FT) 1.9 (FT) 2.3 (FT) 1.8 (FT) 1.7 (FT) 1.3 1.1 9 <0.5 10 <0.5

(14) It is clear from Table 2a that only Bindzil 15/500 provided any degree of bond strength in the laminate, even prior to immersion in water. Table 2a also indicates that these coatings can actually enhance the laminates resistance to water immersion.

(15) TABLE-US-00004 TABLE 3 Coating Examples C11-C20; Used in the preparation of 3-ply laminates AQ4104- Deionised 4-98 Bindzil Lithium Coating water IPA solution 15/500 Silicate C11 8 4 20 8.77 C12 5 4 30 5.58 C13 10 4 25 5.85 C14 13 4 15 13.15 C15 9 30 5.85 2 C16 9 30 8.85 2 C17 9.35 30 5.85 1.65 C18 9.75 30 5.85 1.25 C19 10 30 5.85 1 C20 10.5 30 5.85 0.5

(16) These coatings were applied at 12 gsm wet applied film weight to the metallised surface of the Al-PET and dried under a flow of warm air. Coim 2525/2526 adhesive was then applied to both surfaces of the coated Al-PET film and layers of sealing PE were applied to both surfaces. The laminates were allowed to cure at 25 C. for 7 days before being tested. The laminates were assessed for oxygen barrier ability, and the bond strengths were measured as a function of the time they were immersed in room temperature water. Table 4 provides the results of these tests. Bond Strengths in Table 2b are given as the force (N/15 mm) required to peel apart the PE layer from the coated metallised surface of the Al-PET after being immersed in water for varying times.

(17) TABLE-US-00005 TABLE 4a Examples 11-20: Evaluation of 3-ply D/C/A/B/C/D laminates - Oxygen Barrier (A = Al-PET, B = Coating, C = adhesive, D = PE) Wet film OTR (23 C./50% RH) Example Coating weight (cm.sup.3/m.sup.2/day) 11 C11 12 gsm 0.3 12 C12 12 gsm 0.01 13 C13 12 gsm 0.2 14 C14 12 gsm 1.5 15 C15 12 gsm 0.01 16 C16 12 gsm 0.01 17 C17 12 gsm 0.2 18 C18 12 gsm 0.1 19 C19 12 gsm 0.01 20 C20 12 gsm 0.2

(18) TABLE-US-00006 TABLE 4b Examples 11-20: Evaluation of 3-ply laminates Wet Bond Strengths v. Immersion time Exam- ple 0 30 60 120 180 240 300 Control 2.8 (FT) 1.5 (FT) 1.7 0.4 0.2 0.1 0.1 11 3.2 (F.T) 3.0 3.0 1.2 0.8 0.9 0.5 12 3.5 (F.T) 3.0 (F.T) 2.0 1.5 1.0 1.0 1.0 13 3.4 (F.T) 2.9 3.1 3.0 1.2 0.9 0.8 14 3.5 (F.T) 3.5 (F.T) 2.8 2.5 1.8 1.9 1.8 15 .sup.4 (F.T) .sup.4 (F.T) 4 3 3 2.5 1.5 (F.T) 16 4.5 (F.T) 4.2 3.8 3.5 2.75 2.5 1.0 17 3.5 (F.T) 3.3 (F.T) 3.0 3.0 2.7 2.5 2.5 18 3.3 (F.T) 3.2 (F.T) 3.2 3.4 2.3 2.2 1.6 (F.T) (F.T) 19 3.0 3.1 3.1 3 2.5 1.8 1.4 20 2.8 3 2.8 3.0 2.0 1.9 1.0