Process for optimising a gas barrier coating

Abstract

A process for enhancing the gas barrier properties of a composite laminate material whilst maintaining adequate bond strength, in which a gas barrier coating comprising a clay dispersion and a polymer solution or dispersion is positioned between two flexible plastics films using an adhesive, wherein a coating is applied to a first flexible polymer film at a coating weight (D), an adhesive is applied to either or both of the coated side of the first film or to a second polymer film and adhering the first and second films together to provide a material in which: (A/B). (C/D)>200, and in which: A/B>75; C>1.0; and D<1.5; wherein: A=Oxygen Transmission Rate for the laminate at 23 0C and 50% RH without the coating; B=Oxygen Transmission Rate for the laminate at 23 0C and 50% RH with the coating; C=Bond Strength in N/15 mm after the adhesive has fully cured; D=Coating Weight in g/m.sup.2 (dry).

Claims

1. A process of enhancing the gas barrier properties of a composite laminate material whilst providing an adequate bond strength between two flexible plastics films, in which a gas barrier coating comprising a clay and a polymer is positioned between the two flexible plastics films, wherein: a. a first flexible polymer film is coated with an aqueous dispersion of a clay, and a PVA and/or EVOH; b. an adhesive coating is applied to either or both of the coated side of the first film or to a second flexible polymer film; and c. the first and second films are adhered together, to provide a laminate material in which: (A/B).Math.(C/D)1500; and in which: A/B>75; C>1.0; and D<1.5, wherein: A is the Oxygen Transmission Rate for the laminate at 23 C. and 50% RH without the coating; B is Oxygen Transmission Rate for the laminate at 23 C. and 50% RH with the coating; C is the Bond Strength in N/15 mm between the first and second flexible plastics films after the adhesive has fully cured; and D is the Coating Weight in g/m2 (dry) of the gas barrier coating; wherein the PVA and/or EVOH is an aqueous solution or dispersion; and wherein the aqueous dispersion of the clay and the aqueous solution or dispersion of the PVA and/or EVOH are mixed prior to step a.

2. A process for preparing a gas barrier material of claim 1, in which C, the bond strength between the two films, is greater than 1.5N/15 mm after the adhesive has fully cured.

3. A process according to claim 1, in which some or all of the clay has been intercalated or exfoliated during dispersion.

4. A process according to claim 1, in which the clay has an aspect ratio from about 20 to about 10,000.

5. A process according to claim 1, in which the amount of polymer is from about 40 to about 95% of the total solids comprising polymer and clay.

6. A process according to claim 1, in which the amount of polymer is from about 50 to about 90% of the total solids comprising polymer and clay.

7. A process according to claim 1, in which the amount of polymer is from about 20 to about 45% of the total solids comprising polymer and clay.

8. A process according to claim 1, in which the thickness of the coating is from about 50 nm to about 3000 nm.

9. A process according to claim 6, in which the thickness of the coating is from about 200 to about 2000 nm.

10. The process for preparing a gas barrier material of claim 1, in which step a, is carried out within 24 hours of completing the mixing.

11. A process according to claim 10, in which steps a, b and c are carried out within 24 hours of completing the mixing.

12. A process according to claim 11, in which steps a, b and c are carried out within 6 hours of completing the mixing.

Description

EXAMPLES

(1) The oxygen transmission rates of the coated samples were determined on a Mocon Oxtran 2/21 gas permeability tester at 23 C. and 50% relative humidity. The coatings were applied with a No.2 K-bar (around 12 microns) and were dried in a warm flow of air (lab prints were dried with a hair dryer).

(2) The PET (polyethylene terephthalate) substrate film used in the examples was a freshly corona discharge treated 12 micron thick Melinex 800 film obtained from DuPont.

(3) The OPP (orientatied polypropylene) substrate film used was a 25 micron thick MB400 film obtained from Exxon Mobil Chemical.

(4) The PE film used in the examples to prepare the adhesively formed laminates was a lamination grade 30 m LDPE film obtained from BPI.

(5) The laminates were prepared by applying the coating to the treated side of the film; an adhesive was applied over the top of the dried coating and then laminated to the treated side of a 30 m gauge poly(ethene) film. The adhesive used was supplied by Henkel, UR3969/6055, was prepared according to the manufacturer's instructions and was applied so as to achieve a final dry film weight of 2.5 g/m.sup.2. The laminates were then stored for 10 days at 25 C. to ensure full cure of the isocyanate-based adhesive.

(6) The laminates were then tested for bond strength (N/15 mm) and oxygen barrier performance (cm.sup.3/m.sup.2/24 h at 23 C. and 50% RH). Where the film tears (FT) during the bond strength test, this shows that the adhesive bond is stronger than the plastics film and so the bond strength is necessarily greater than 1.5 N/15 mm, and probably in excess of 3.0 N/15 mm. The last measured bond strength (M) prior to film tear was recorded.

(7) Coating compositions 1 to 15 were prepared by blending a PVA/EVOH solution having 11% solids with a clay dispersion having a solids content of 4%. The polymer solution comprised 1.65% Mowiol 3-96, 9.35% of Exceval AQ-4104, and 15% n-propanol. The remainder of the solution was deionised water. The clay dispersion contained 4% (w/w) of Cloisite Na+ and 20% isopropanol; the remainder being deionised water. The clay was dispersed using a high shear blender (Dispermat CV).

(8) The coatings were adjusted to gravure application viscosity (19/20 seconds flow time from a Zahn-2 cup) by diluting with a 80/20 (w/w) blend of deionised water and isopropanol.

(9) The following Table 1 provides the detail of these coatings, along with their oxygen barrier performance, bond strength and calculated X values.

(10) TABLE-US-00001 TABLE 1 Performance in Barrier Laminates Solid Content Relative (% w/w)*/ content of Bond Strength; Bond Strength; Bond Strength; dry film Clay (% immediately after after 1 week of after 2 weeks of Coating weight (g/m.sup.2) w/w solids) Substrate OTR preparation; being blended being blended X none 0 0 PET 102 FT; M = 3.2 none 0 0 OPP 1350 FT; M = 4.2 none 0 0 PE 1600 FT; M = 3.8 1 9.0/1.08 0 PET 1.52 1.3 1.4 1.3 81 2 9.0/1.08 10 PET 0.63 1.4 1.2 1.2 210 3 8.7/1.04 15 PET 0.51 1.8 1.2 1.3 346 4 8.1/0.97 20 PET 0.26 1.6 1.2 1.1 647 5 7.4/0.89 25 PET 0.24 FT; M = 2.7 FT; M = 3.3 1.4 1289 5 7.0/0.84 30 PET 0.15 FT; M = 2.8 1.7 1.8 2267 7 6.6/0.79 35 PET 0.16 FT; M = 3.0 2.7 2.8 2421 8 5.5/0.66 40 PET 0.19 2.3 1.7 1.9 1870 9 5.2/0.62 45 PET 0.17 1.7 1.8 1.9 1645 10 4.9/0.59 50 PET 0.38 1.4 1.2 1.8 637 11 4.8/0.58 55 PET 0.50 0.7.sup. 0.5 0.6 246 12 4.5/0.54 60 PET 0.82 <0.1.sup. <0.1.sup. <0.1.sup. 13 5.5/0.66 40 OPP 1.44 0.4.sup. 568 14 5.5/0.66 40 PE 1.38 1.2 2108 15 Std. 2-pack/ 27.5 PET 0.36 FT; M = 2.8 FT; M = 3.0 1.1 1202 0.66 *Solid content varies owing to adjustments made to achieve application (gravure) viscosity. .sup.Figures noted fall outside the limits defined above.

(11) The Std 2-pack composition referred to in Table 1 is the 2-pack barrier coating supplied by Sun, under the trade name SunBar O.sub.2 Barrier Coating (ref.: 30504308 and 90108385)

(12) To better illustrate the influence of the clay concentration on the oxygen barrier performance, coating compositions 2 to 10 were coated onto a 25 micron thick OPP film (MB400) at 12 g/m.sup.2 (wet) and the oxygen transmission rates recorded. The results are shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Oxygen Transmission Rates on OPP Coating 2 3 4 5 6 7 8 9 10 OTR 1.29 1.25 0.63 0.58 1.04 1.06 1.44 2.31 3.22

(14) Considering the results contained within Tables 1 and 2 a preferred concentration of clay (on total solids) is preferably in the range of from 20 to 45%.

(15) To further understand the likely performance of these coatings, the oxygen transmission rates on coated PET were measured at 23 C. & 75% RH. The results are shown in Table 3.

(16) TABLE-US-00003 TABLE 3 Oxygen Transmission Rates on PET at 75% RH Coating 2 3 4 5 6 7 8 9 10 OTR 22.13 19.02 12.65 10.67 8.00 6.50 6.37 5.67 7.15

(17) These results indicate that at high RH, optimum performance is achieved with a concentration of clay of about 35-45%.

(18) Therefore, for both maximum barrier and laminate bond strength performance, with coatings prepared according to the procedure described here (with the components as specified), a relative concentration of clay in the range 25-45% (w/w) would appear optimum.