ULTRA-HIGH BARRIER METALLIZED FILM

Abstract

A metallized multi-layer film having ultra-high oxygen and moisture barrier properties includes a core layer and a metal bonding layer preferably formed by coextruding. The metal bonding layer includes a preponderance, by weight, of a propylene/butene-1 copolymer free of particulates. A metal coating adhered to the metal bonding layer having a metal adhesion strength to the metal coating in excess of 90%, and the metallized film includes an oxygen barrier of less than 15.0 cc/m2/day and a water barrier of less than 0.1 gms/m2/day.

Claims

1. A metallized multi-layer film having ultra high oxygen and moisture barrier properties, said film comprising a core layer, a metal bonding layer including a preponderance, by weight, of a propylene/butene-1 copolymer and being free of particulates, and a metal coating, said metal bonding layer having one surface adhered to a first surface of said core layer and an opposed surface, said metal coating adhered to said opposed surface of said metal bonding layer, said metal bonding layer having an optical density in excess of 2.4, said film having an oxygen barrier of less than 15 cc/m2/day and a water barrier of less than 0.1 gms/m2/day.

2. The metallized multilayer film of claim 1, wherein the metal adhesion between the metal coating and the metal bonding layer is over 90% and said optical density is in excess of 2.6, said metal bonding layer having a thickness of less than 1 micron and the water barrier is in the range of 0.047-0.0775 gms/m2/day.

3. The metallized multilayer film of claim 1, wherein the metal adhesion between the metal coating and the metal bonding layer is over 90% and said optical density is in excess of 2.6, said metal bonding layer having a thickness of less than 1 micron and the oxygen barrier is in the range of 6.2-7.75 cc/m2/day.

4. The metallized multilayer film of claim 2, wherein said metal bonding layer includes at least 60% by weight of a propylene/butene-1 copolymer.

5. The metallized multilayer film of claim 2, wherein said metal bonding layer includes 100% by weight of a propylene/butene-1 copolymer

6. The metallized multilayer film of claim 2, further including an additional layer adhered to a second surface of the core layer opposite said first surface.

7. The metallized multilayer film of claim 2, further including an additional layer adhered to a second surface of the core layer opposite said first layer, said additional layer being a sealant layer.

8. The metallized multilayer film of claim 2, further including an additional layer adhered to a second surface of the core layer opposite said first layer, said additional layer being a sealant layer comprising an ethylene/propylene/butene-1 terpolymer, a non-migratory antiblock agent being included in the sealant layer in the range of 1,200-4,000 ppm of a non-spherical 4.5 micron synthetic silica, and a non-migratory slip agent in the range of 3,600-6,000ppm of a spherical 4 micron cross-linked polymethylmethacrylate.

9. The metallized multilayer film of claim 2, further including an additional layer adhered to a second surface of the core layer opposite said first layer, said additional layer being a sealant layer comprising an ethylene/propylene/butene-1 terpolymer, a non-migratory antiblock agent in about 15% by weight of the sealant layer, and a non-migratory slip agent in about 8% by weight of the sealant layer.

10. The metallized multilayer film of claim 2, wherein said core layer includes conventional polypropylene.

11. The metallized film of claim 2, wherein said core layer includes high crystalline polypropylene.

12. The metallized film of claim 2, wherein said core layer includes conventional polypropylene and up to 10% of a hard resin.

13. The metallized film of claim 2, wherein said core layer includes high crystalline polypropylene and up to 10% of a hard resin.

14. The metallized film of claim 2 having an optical density of at least 2.8.

15. A metallized multi-layer film having ultra high oxygen and moisture barrier properties, said film comprising a core layer, a sealant layer on one side of said core layer, a metal bonding layer on a side of the core layer opposed to said one side, said bonding layer including a preponderance, by weight, of a propylene/butene-1 copolymer and being free of particulates, and a metal coating, said metal bonding layer having one surface adhered to a first surface of said core layer and an opposed surface, said metal coating adhered to said opposed surface of said metal bonding layer, said metal bonding layer having an optical density in excess of 2.6, said sealant layer comprising an ethylene/propylene/butene-1 terpolymer, a non-migratory antiblock agent being included in the sealant layer in the range of 1200-4000 ppm, and a non-migratory slip agent in the range of 3600-6000 ppm, said film having an oxygen barrier of less than 15 cc/m2/day and a water barrier of less than 0.1 gms/m2/day.

16. The metallized multilayer film of claim 15, wherein said sealant layer comprises the non-migratory slip agent in about 4800 ppm and a non-migratory antiblock agent in about 3000 ppm.

17. The metallized film of claim 15, wherein said non-migratory antiblock agent is a non-spherical 4.5 micron synthetic silica, and the non-migratory slip agent is a spherical 4 micron cross-linked polymethylmethacrylate.

18. The metallized film of claim 16, wherein said non-migratory antiblock agent is a non-spherical 4.5 micron synthetic silica, and the non-migratory slip agent is a spherical 4 micron cross-linked polymethylmethacrylate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0020] Reference throughout this application to the multi-layer film or films being “heat set” identifies films which, in the plastic film art, are not considered to be heat shrinkable.

[0021] Reference throughout this application to the “metal coating” being part of the metallized films of this invention is limited (1) to a metal coating that is tenaciously adhered to film (i.e., it is not transferable from the film of this invention to another substrate), and (2) to a metal coating that is applied by a deposition process such as sputtering, vacuum, vapor deposition and electroplating, and not as a metal layer formed separately from the multi-layer films of this invention, either alone or laminated to another carrier layer or film.

[0022] Reference to “high crystallinity polypropylene” means a polypropylene having intermolecular stereoregularity greater than 93%. Reference to “conventional polypropylene” means polypropylene having an intermolecular stereoregularity no greater than 93%.

[0023] More preferably the multi-layer metallized film of this invention is formed by providing a metal coating on a coextruded film including at least two layers: a core layer and a metal bonding layer coextruded with the core layer.

[0024] Most preferably the multi-layer coextruded film is at least a three layer structure having a sealant layer on the side of the core layer opposite the metal bonding layer.

[0025] In the preferred embodiments of this invention the core layer preferably either is a conventional polypropylene or a high crystalline polypropylene either with or without commonly known hard resins. If desired a hard resin can be included in an amount of up to about 10% by weight of the polymer composition of the core. The inclusion of a hard resin in the core improves the mechanical properties of the film, when utilized in conjunction either with normal polypropylene or high crystalline polypropylene. When used with high crystalline polypropylene the hard resin also improves the drawability or stretch properties of the film.

[0026] In accordance with the broadest aspects of this invention the coextruded film can include more than three layers. However, an important feature of this invention is that the metal bonding layer is a thin skin layer having a thickness of less than one micron. Providing a thin copolymer layer gives a smooth surface for metal lay down; thereby enhancing the bond strength of the metal coating to the copolymer layer.

[0027] Another important feature of this invention is that the metal bonding layer includes a preponderance, by weight, of a propylene/butene-1 copolymer; more preferably at least 60%, by weight, and most preferably 100%, by weight. A representative propylene/butene-1 copolymer usable in this invention is ADSYL 3C30FHP, manufactured by Lyondellbasell, Italy, having its main office in Milan Italy.

[0028] It is highly desirable in this invention that the metal bonding layer is free of antiblock additives, which, if present, can adversely affect the smoothness of the metal bonding layer. This, in turn, can adversely affect the adhesion between the metal coating and the metal bonding layer. However, as noted earlier herein, the inclusion a minor amount and type of a particulate (e.g., reclaim material, antiblock additive, etc.) that does not affect the adhesion between the metal coating and the metal bonding layer is considered to be within the scope of the invention.

[0029] In accordance with this invention the core layer preferably is polypropylene having a thickness preferably in the range of 12-25 microns. The core layer can be formed through a single manifold die or multi-manifold die, depending upon the design of the extrusion equipment. A representative polypropylene is HP516J, a conventional polypropylene sold by Lyondellbasell, Geelong, Australia. However, it should be understood that high crystallinity polypropylenes also can be employed in this invention. Exemplary high crystalline polypropylenes are disclosed in Su et al. U.S. Pat. No. 6,844,078, which previously was incorporated by reference herein.

[0030] Most preferably the polypropylene that can be employed in the core is free of any reclaim material or other particulates. It is very desirable that the polypropylene polymers employed in the core be virtually free of particulates, since the particulates will enhance the roughness of the bonding layer; thereby impairing the barrier properties in the completed, metallized films of this invention. Most preferably the polypropylene in the core layer is completely free of particulates, such as reclaim material and antiblock agents.

[0031] As noted above, in the preferred embodiment of this invention the coextruded film includes a sealant layer opposed to the metal bonding layer, and this addition sealant layer preferably includes an ethylene/propylene/butene-1 terpolymer, preferably including an anti-block agent and a slip agent. A representative terpolymer useable in this invention is Ineos KS357, manufactured by Ineos Olefins and Polymers Europe, located in Brussels, Belgium.

[0032] A representative slip agent used in the additional sealant layer is Schulman ABVT 22SC, a masterbatch including 5% spherical 4 micron crosslinked polymethylmethacrylate in a C2C3 copolymer, manufactured by A Schulman, located in East Java, Indonesia.

[0033] A representative antiblock used in the additional sealant layer is Lehmann and Voss 33 Konz, a masterbatch including 2% non-spherical 4.5 micron synthetic silica in a C3C2C4 terpolymer, manufactured by Lehmann and Voss KG, located in Hamburg, Germany.

[0034] In the most preferred embodiment of this invention the sealant layer includes 6-10% (3,600-6,000 ppm), and more preferably about 8%, by weight, (about 4,800 ppm) of the above-identified polymethylmethacrylate master batch, and 6-20% (1,200-4,000 ppm), and more preferably aboutl5%, by weight, (about 3,000 ppm) of the above-identified synthetic silica masterbatch. The balance, by weight, of the sealant layer is the above-identified terpolymer. In the most preferred embodiment in which the polymethylmethacrylate master batch is 8% of the weight of the sealant layer and the synthetic silica masterbatch is 15% of the masterbatch the terpolymer is 77%, by weight of the sealant layer.

[0035] Applicants' have discovered that in order to obtain the ultra high barrier properties achieved in a three layer structure of this invention employing a sealant layer, a heavy loading of a slip agent and antiblock agent are required. To applicants' knowledge such a heavy loading of a slip and antiblock agent has not been recognized in the prior art as being necessary for achieving the ultra high barrier properties achieved in this invention. While the mechanism for achieving the ultra high barrier properties is not completely understood it is believed that without the high loading of the slip and antiblock additives the sealant layer will cause picking of the metal layer when the film is being unwound; thereby impairing the barrier properties of the film.

[0036] It is important in this invention that agents added to any of the layers, such as the antiblock and slip additives employed in the additional sealant layer opposed to the metal bonding layer, are not migratory agents that can migrate into other layers and adversely affect the properties of those other layers. The representative slip and antiblock additives for use in this invention, as identified early, are non-migratory additives, which, as noted earlier, is very important in this invention.

[0037] The coextruded multi-layer films of this invention preferably are biaxially oriented films formed in any desired or convention extrusion equipment, such as a tenter machine. As is well known in the art, the coextruded films formed in a tenter machine first are oriented in the machine direction and then in the transverse direction. After transverse-direction orientation the film is heat set to stabilize the structure against undesired shrinkage.

[0038] After the biaxially oriented film is formed (including corona treated as specified earlier) it generally is wound into a roll for subsequent off-line metallization to thereby form the metallized film of this invention.

[0039] In accordance with one embodiment of this invention the metal bonding layer is corona treated to provide a dyne level in the range of 42 dynes-50 dynes prior to applying the metal coating thereon.

[0040] In the preferred embodiment of this invention the oxygen barrier of the metallized film is less than 15 cc/m2/day and the water barrier is less than or equal to 0.1 gms/m2/day. More preferably the oxygen barrier is less than 9.3 cc/m2/day and even more preferably is in the range of 6.2 to 7.75 cc/m2/day. The water barrier more preferably is less than 0.0775 gms/m2/day and even more preferably in the range of 0.047 to 0.0775 gms/m2/day.

[0041] The ultra-high barrier properties are achieved in this invention in a film structure wherein the optical density of the metallized coating is greater than 2.4, more preferably greater than 2.6 and most preferably at least 2.8. The metal adhesion strength (i.e. the strength of the metal bond between the metal coating and the metal bond layer) is at least 90%. A high optical density of the above-stated values is important in achieving the high barrier properties of this invention. The most consistent ultra high barrier properties are achieved in this invention when the optical density is at least 2.8.

[0042] The oxygen barrier reported herein identifies oxygen permeability and was determined in accordance ASTM D3985 (23C-0%RH).

[0043] The moisture barrier reported herein identifies water vapor permeability (WVTR) and was determined by ASTM F1249 (38C-90%RH).

[0044] The optical density reported herein is determined as follows:

1. Obtain a transverse direction sample strip having a length equal to the full width of the metallised roll and a width of at least 300 mm wide.
2. Take three square shaped sub samples of minimum size 100 mm×100 mm, from the full width sample, Two, are taken from 200 mm from each edge, and one from the center.
3. Place these sub-samples on the testing table with the metallised side facing up.

[0045] They must be clean and free from finger marks, damage from sampling, and loose material in the test area.

4. Using a marker pen, two parallel lines are marked in the center of each sub-sample, in the MD direction, approximately 50 mm apart.
5. Zero the Densitometer (example: Tobias TBX Densitometer) by pressing the Sensing Arm down so that it comes in contact with the Light Table and depressing the button on the back of the Sensing Arm. 0.00 should be displayed.
6. Measure the optical density of the film at three positions in the area between the two marked lines for all three sub-samples. Record all results and note the lowest which must be above the specified minimum value for the film.
7. Grade the roll against Optical Density specification

[0046] The metal adhesion between the metal coating and the metal bonding layer reported herein was determined as follows:

1. Average the initial measurements of optical density for each sub-sample above to obtain a base level (A) for the metal adhesion test.
2. Apply Scotch Premium Grade 610 adhesive tape to the metallized film in the machine direction between the two lines marked as above, for approximately 30-40 cm in length, smoothing down using finger pressure. Ensure that the tape has a tail, or free end that is not adhered to the metallized test sub-sample, to permit easy removal of the tape from the test sub-sample.
3. Hold the film firmly with one hand and with the other hand peel the tape away from the film at an angle of about 45° in a sharp brisk manner ensuring that the film is not torn.
4. Measure the Optical Density every 5 cm along the area where the tape was removed and record and average the results to give the tested value (B).
5. The post tape removal measurements should be done within the marked lines, but directly adjacent to the positions initially measured. These initial positions will have had a degree of damage to the metal surface as a result of the measurement process.
6. The degree of metal adhesion is then calculated by the following formula:

% Metal Adhesion=(B/A)*100

The lowest result from the three sub-samples is recorded as the determined adhesion figure.

[0047] While the invention has been described with respect to various specific embodiments thereof, it will be understood that it is not intended that the invention be limited to such specific embodiments. The invention is limited only as required by the following claims.