Primer coating for metallized gas barrier films

Abstract

A primer coating is provided for use on polymeric substrates to enhance the adhesion of metallized coatings to the substrates. The primer coating also improves the gas barrier properties of the substrate when used in combination with a metallized coating. The primer coating includes an amorphous polyvinyl alcohol, polyethyleneimine, and optionally, an aqueous dispersion of polyurethane. The primer coating may be applied to a variety of polymeric substrates including polylactic acid, polyethylene terephthalate, biaxially oriented polyethylene terephthalate, oriented polypropylene, biaxially oriented polypropylene, and biaxially oriented polyamide. When used in combination with the subsequently applied metallized coating, an oxygen transmission rate of about 0.1 and 5.0 cc/m2/day at 0% relative humidity is achieved.

Claims

1. A primer coating comprising a blend of an amorphous polyvinyl alcohol and a polyethyleneimine.

2. The primer coating of claim 1, wherein the primer coating comprises from about 5% to about 15% by weight amorphous polyvinyl alcohol.

3. The primer coating of claim 1, wherein the primer coating comprises from about 0.1% by weight to about 0.15% by weight polyethyleneimine.

4. The primer coating of claim 1, further comprising a wetting agent, a defoaming agent, or a preservative.

5. A coated polymeric substrate having first and second major surfaces, with at least one of the first and second major surfaces having the primer coating of claim 1 coated thereon.

6. The coated polymeric substrate of claim 5, wherein the coated polymeric substrate exhibits an oxygen transmission rate of less than about 8 cc/m.sup.2/day.

7. A method of applying a primer coating to a polymeric substrate comprising: providing a polymeric substrate having first and second major surfaces; and applying a primer coating to at least one of the first and second major surfaces of said substrate, the primer coating comprising a blend of an amorphous polyvinyl alcohol and a polyethyleneimine.

8. The method of claim 7, further comprising: depositing a metallized coating on the at least one of the first and second major surfaces.

9. The method of claim 8, wherein the metallized coating is deposited over the primer coating.

10. The method of claim 8, wherein the metallized coating comprises aluminum.

11. The method of claim 8, wherein the primer coating and metallized coating, in combination, exhibit an oxygen transmission rate of about 0.1 and 5.0 cc/m.sup.2/day at 0% relative humidity.

12. The method of claim 7, further comprising: treating the at least one of the first and second major surfaces with a corona discharge treatment prior to applying the primer coating.

13. The method of claim 7, wherein the primer coating comprises from about 5% to about 15% by weight amorphous polyvinyl alcohol.

14. The method of claim 7, wherein the primer coating comprises from about 0.1% by weight to about 0.15% by weight polyethyleneimine.

15. A coated polymeric substrate comprising: a polymeric substrate having first and second major surfaces; and a primer coating disposed on at least one of the first and second major surfaces, the primer coating comprising an amorphous polyvinyl alcohol and a polyethyleneimine.

16. The coated polymeric substrate of claim 15, further comprising: a metallized coating.

17. The coated polymeric substrate of claim 16, wherein the metallized coating is disposed over the primer coating.

18. The coated polymeric substrate of claim 16, wherein the metallized coating comprises aluminum.

19. The coated polymeric substrate of claim 16, wherein the coated polymeric substrate exhibits an oxygen transmission rate of about 0.1 and 5.0 cc/m.sup.2/day at 0% relative humidity.

20. The coated polymeric substrate of claim 15, wherein the primer coating comprises from about 5% by weight to about 15% by weight amorphous polyvinyl alcohol and from about 0.1% by weight to about 0.15% by weight polyethyleneimine.

Description

DETAILED DESCRIPTION

(1) Embodiments of the primer coating described herein provide advantages over the use of metallized coatings alone on polymeric substrates in that they provide good adhesion of the metallized coating as well as enhancing the gas barrier properties of the polymeric substrate when used in combination with the subsequently applied metallized coating.

(2) Unless otherwise indicated, the disclosure of any ranges in the specification and claims are to be understood as including the range itself and also values subsumed therein, as well as endpoints.

(3) One primer coating comprises about 10.5% by weight of an amorphous polyvinyl alcohol, about 0.10% polyethyleneimine, and the balance deionized water. It should be appreciated that the primer coating may also include additives such as preservatives (about 0.02% to 0.20% by weight), defoaming agents (about 0.1% to 0.05% by weight), and wetting agents (about 0.20% to 1% by weight).

(4) Another primer coating comprises about 10.5% by weight of an amorphous polyvinyl alcohol, about 0.10% polyethyleneimine, about 0.1% to 5% of an aqueous dispersion of polyurethane having a solids content of about 33% by weight, and the balance water. Alternatively, the primer coating may comprise from about 0.03 to 2.5% by weight polyurethane, preferably in the form of an aqueous dispersion having a solids content of about 33 to about 50% by weight.

(5) A suitable amorphous polyvinyl alcohol for use in the primer coating is commercially available from Nippon Gohsei under the designation G-Polymer OKS-8049 or AZF-8035W. OKS-8049 has a melting point of 185 C. and a viscosity of 4.5 mPa.Math.s at 4% aqueous solution at 20 C., and AZF8035W has a melting point of 171 C. and a viscosity of 3.0 mPa.Math.s at 4% aqueous solution at 20 C.

(6) The polyethyleneimine acts as an adhesion promoter to achieve good adhesion of the coating to a polymeric substrate. A suitable polyethyleneimine is Lupasol P from BASF. Another suitable polyethyleneimine is Polymin P, available from BASF.

(7) Suitable polyurethane dispersions include NeoRez R-600 and NeoRez R-605, both available from DSM NeoResins.

(8) The primer coating is preferably prepared by adding the components to a mixing vessel and mixing at ambient temperatures until all of the components are adequately blended.

(9) The primer coating may be applied by gravure coating, rod coating, or flexographic printing at ambient temperature to polymeric substrates. Prior to applying the primer coating, it is preferable to use a corona discharge pre-treatment on the substrate to ensure that the coating will wet out the surface of the film and achieve adequate coverage. This treatment may be applied either in-line or off-line.

(10) Suitable polymeric substrates include polylactic acid (PLA), polyethylene terepthalate (PET), biaxially oriented polyethylene terepthalate (BOPET), oriented polypropylene (OPP), biaxially oriented polypropylene (BOPP), and biaxially oriented polyamide (BOPA). Typically, for food packaging applications, the polymer films will range in thickness from about 10 to about 100 m.

(11) The primer coating may be applied to one or both sides of the substrate as desired. After the primer coating has dried, the primer coated substrate is then preferably stretched (oriented) prior to deposition of the metallized coating to improve the gas barrier properties. The stretching is preferably accomplished by heating the film to a molten state followed by stretching in the machine direction, followed by stretching in the transverse direction (90 degrees from machine direction), followed by quenching.

(12) The primer coated polymeric substrates are then vacuum deposited with a metallized coating such as aluminum. The optical density of the vacuum-deposited aluminum is preferably about 2.0.

(13) In order that the invention may be more readily understood, reference is made to the following examples which are intended to illustrate the invention, but not limit the scope thereof.

Example 1

(14) Primer coatings were prepared in accordance with an embodiment of the invention using the following components: amorphous polyvinyl alcohol (G-Polymer) polyethyleneimine, and deionized water.

(15) See formulations 1 and 2 below.

(16) Formulation 1

(17) TABLE-US-00001 Component Wt. % of total composition deionized water 89.3 amorphous PVOH.sup.1 10.5 50% polyethyleneimine.sup.2 0.1 preservative.sup.3 0.1 .sup.1G-polymer AZF8035W from Soarus LLC (supplied as a solid powder) .sup.2Lupasol P from BASF (supplied as a 50% aqueous solution) .sup.3Proxel GXL from Arch Chemicals (supplied as an 18-20% active solution
Formulation 2

(18) TABLE-US-00002 Component Wt. % of total composition deionized water 89.3 amorphous PVOH.sup.1 10.5 50% polyethyleneimine.sup.2 0.1 preservative.sup.3 0.1 .sup.1G-polymer OKS-8049 from Soarus LLC .sup.2Lupasol P from BASF .sup.3Proxel GXL from Arch Chemicals
The following comparative formulations were also prepared:
Comparative Formulation 3

(19) TABLE-US-00003 Component Wt. % of total composition deionized water 89.5 50% polyethyleneimine.sup.1 8.9 Formaldehyde crosslinker 1.5 preservative.sup.2 0.1 .sup.1Lupasol P from BASF .sup.2Proxel GXL from Arch Chemicals
Comparative Formulation 4

(20) TABLE-US-00004 Component Wt. % of total composition deionized water 91.35 PVOH.sup.1 8.5 Preservative.sup.2 0.15 .sup.1Elvanol 90-50 from DuPont (semi-crystalline PVOH) .sup.2Proxel GXL from Arch Chemicals

(21) Additional primer coatings were prepared in accordance with another embodiment of the invention using the following components: amorphous polyvinyl alcohol (G-Polymer), polyethyleneimine, a polyurethane dispersion, and deionized water. See formulations 5-7 below.

(22) Formulation 5

(23) TABLE-US-00005 Component Wt. % of total composition deionized water 89.00 amorphous PVOH.sup.1 10.5 Polyurethane dispersion.sup.2 0.400 Polyethyleneimine.sup.3 0.100 .sup.1G-polymer OKS-8049 from Soarus LLC .sup.2NeoRez R-600 from DSM NeoResins (33% solids) .sup.3Polymin P from BASF (50% solids)
Formulation 6

(24) TABLE-US-00006 Component Wt. % of total composition deionized water 88.60 amorphous PVOH.sup.1 10.5 Polyurethane dispersion.sup.2 0.800 Polyethyleneimine.sup.3 0.100 .sup.1G-polymer OKS-8049 from Soarus LLC .sup.2NeoRez R-600 from DSM NeoResins .sup.3Polymin P from BASF
Formulation 7

(25) TABLE-US-00007 Component Wt. % of total composition deionized water 87.60 amorphous PVOH.sup.1 10.3 Polyurethane dispersion.sup.2 2.0 Polyethyleneimine.sup.3 0.100 .sup.1G-polymer OKS-8049 from Soarus LLC .sup.2NeoRez R-600 from DSM NeoResins .sup.3Polymin P from BASF
A comparative formulation was also prepared:
Comparative Formulation 8

(26) TABLE-US-00008 Component Wt. % of total composition deionized water 83.10 amorphous PVOH.sup.1 9.8 Polyurethane dispersion.sup.2 7.0 Polyethyleneimine.sup.3 0.100 .sup.1G-polymer OKS-8049 from Soarus LLC .sup.2NeoRez R-600 from DSM NeoResins .sup.3Polymin P from BASF

(27) All formulations were prepared by adding the components to a mixing vessel at ambient temperature until all components were blended. The liquid formulas were then applied at room temperature onto various polymeric substrate samples using a 2 BCM gravure cylinder. For samples 7-9, formulation 3 was coated on the film samples, dried at 190 F. in a hot air oven, rewound, and then coated with formulation 4.

(28) The polymeric substrates were corona discharge treated prior to primer coating. The primer coated samples were then tested for oxygen transmission. The results are shown in Table 1 below.

(29) TABLE-US-00009 TABLE 1 Coating Coat Sample Film Formulation weight (dry gsm) OTR (cc/m.sup.2/day) 1 BOPET 1 0.21 3.76 2 BOPP 1 0.21 6.56 3 PLA 1 0.27 7.97 4 BOPET 2 0.23 0.53 5 BOPP 2 0.23 7.07 6 PLA 2 0.31 5.65 7 BOPET 3 and 4 0.1 40.15 8 BOPP 3 and 4 0.1 61.76 9 PLA 3 and 4 0.1 22.43 10 BOPET 5 0.3 3.0 11 BOPET 6 0.3 2.7 12 BOPET 7 0.3 0.60 13 BOPET 8 0.3 35.70

(30) As can be seen, samples which were coated with formulations 1-2 and 5-7 exhibited lower oxygen transmission rates than comparative formulations 3-4, which did not include a combination of an amorphous polyvinyl alcohol and polyethyleneimine, and formulation 8, which included 7 wt % of the polyurethane dispersion.

Example 2

(31) Various polymeric substrates were coated with primer formulation 1 as described in Example 1 and with comparative primer formulations 9 and 10 below:

(32) Comparative Formulation 9

(33) TABLE-US-00010 Component Wt. % of total composition Polyurethane dispersion.sup.1 99.97 Defoamer 0.03 .sup.1NeoRez R-600 from DSM NeoResins
Comparative Formulation 10

(34) TABLE-US-00011 Component Wt. % of total composition Ethylene acrylic acid dispersion.sup.1 46.7 Polyurethane dispersion.sup.2 16.6 Ethylene acrylic acid dispersion.sup.3 36.7 .sup.1Michem Prime 4990R from Michelman .sup.2NeoRez R-600 from DSM NeoResins .sup.3Primacor 5990 from Dow (dispersed in sodium hydroxide) at 20% solids

(35) Selected primer coated samples were metallized by placing the samples on a web in an industrial vacuum chamber for deposition with aluminum. The oxygen transmission (OTR) measurements of primer coated films with and without metallized coatings is shown below in Table 2.

(36) TABLE-US-00012 TABLE 2 Coat OTR OTR Coating weight Metallized (cc/m.sup.2/24 hrs) (cc/m.sup.2/24 hrs) Sample Film Formulation (dry gsm) coating 1.sup.st measurement 2.sup.nd measurement No stretching 1 PET 1 0.5 No 1.516 1.03 2 PLA 1 0.5 No 0.258 0.167 3 OPP 1 0.5 No 0.36 0.4 4 PET 1 0.5 Yes 0.03 0.079 5 PLA 1 0.5 Yes 0.7 1.045 6 OPP 1 0.5 Yes 0.34 0.32 After stretching 7 PET No coating Yes 2.7 2.37 8 PET 1 0.04 Yes 0.36 0.22 9 PET 1 0.1 Yes 0.91 0.36 10 PET 6 0.1 Yes 9.73 9.01 11 PET 6 0.25 Yes 21.38 16.21 12 PET 9 0.1 Yes 8.5 7.56 13 PET 10 0.3 Yes 9.75 9.28

(37) As can be seen, the samples which included both a primer coating formulation of the present invention and a metallized coating had lower oxygen transmission rates than the samples which did not include the primer coating and/or the metallized coating. It can also be seen that samples which contained the comparative primer formulations had higher oxygen transmission rates in comparison with the primer formulations of the present invention.

(38) Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention.