PACKAGING FOIL COMPRISING A LUMINESCENT COMPOUND

Abstract

The invention relates to a multi-layered packaging foil comprising a layer L-1 having an oxygen gas transmission rate OGTR-1; a luminescent compound having the property that its luminescence is capable of being quenched by oxygen; and a layer L-2 adhering to L-1 and to the luminescent compound. The layer L-2 has an oxygen gas transmission rate OGTR-2 that is at least 20 times higher than OGTR-1, and the luminescent compound is present between L-1 and L-2. The invention further relates to a packaging comprising a packaging foil of the invention and to a method for measuring the oxygen content in a packaging.

Claims

1. Multi-layered packaging foil comprising a layer L-1 having an oxygen gas transmission rate OGTR-1; a luminescent compound having the property that its luminescence is capable of being quenched by oxygen; a layer L-2 adhering to L-1 and to the luminescent compound, the layer L-2 having an oxygen gas transmission rate OGTR-2 that is at least 20 times higher than OGTR-1; wherein the luminescent compound is present between L-1 and L-2.

2. Multi-layered packaging foil according to claim 1, wherein a matrix material comprising the luminescent compound is present between L-1 and L-2.

3. Multi-layered packaging foil according to claim 2, wherein the matrix material comprises a material selected from the group of polystyrene, silicone gels, nitrocellulose and cellulose acetate butyrate.

4. Multi-layered packaging foil according to claim 1, wherein OGTR-1 is 50 cm.sup.3 m.sup.−2 day.sup.−or less at 25° C. and 0% RH at 1 atm oxygen partial pressure difference (ASTM D3985).

5. Multi-layered packaging foil according to claim 1, wherein OGTR-2 is at least 500 cm.sup.3 m.sup.−2 day.sup.−1 at 25° C. and 0% RH at 1 atm oxygen partial pressure difference (ASTM D3985), or at least 50,000 cm.sup.3 m.sup.−2 day.sup.−1 at 25° C. and 0% RH at 1 atm oxygen partial pressure difference (ASTM D3985).

6. Multi-layered packaging foil according to claim 1, wherein L-1 comprises a layer of a polymer selected from the group of low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, biaxially oriented polypropylene, poly(ethylene-vinyl acetate), poly(ethylene-vinyl alcohol), poly(ethyleneacrylic acid), polystyrene, poly(styrene-1,3-butadiene) oriented polystyrene, poly(vinyl alcohol), poly(vinyl chloride), poly(vinylidene chloride), poly(tetrafluoroethylene), poly(ethylene terephthalate), poly(ethylene naphthalate), polycarbonates, polyamides such as nylon-MXD6, polyacrylonitrile, regenerated cellulose and poly(lactic acid).

7. Multi-layered packaging foil according to claim 1, wherein L-2 comprises a layer of a polymer selected from the group of polyethylene, polypropylene, poly(ethylene-terephthalate) and oriented polyamide.

8. Multi-layered packaging foil according to claim 1, wherein OGTR-2 is at least 1,000 times or at least 10,000 times higher than OGTR-1

9. Multi-layered packaging foil according to claim 1, wherein the luminescent compound is selected from the group of ruthenium(II)-tris-4,7-diphenyl-1,10 phenantroline (Ru-DPP), platinum(II)-meso-tetra(pentafluorophenyl) porphine (Pt-TFPP), palladium coproporphyrin (PdCPP), platinum or palladium octaethylporphyrin (PtOEP,PdOEP), platinum or palladium tetraphenylporphyrin (PtTPP, PdTPP), iridium(III) acetylacetonato-bis(3-(benzothiazol-2-yl)-7-(diethylamino)-coumarin), camphorquinone and erythrosin B.

10. Multi-layered packaging foil according to claim 1, wherein the luminescent compound has a relative luminescence intensity I.sub.0/I or relative luminescence lifetime tau.sub.0/tau of 1.20 or higher, wherein I.sub.0 and tau.sub.0 represent the luminescence intensity and luminescence lifetime in the absence of oxygen, respectively, and wherein I and tau represent the luminescence intensity and luminescence lifetime in the presence of oxygen, respectively.

11. Method for preparing a multi-layered packaging foil according to claim 1, comprising providing a layer L-1 having an oxygen gas transmission rate OGTR-1; then applying on L-1 a luminescent compound having the property that oxygen quenches the luminescence; then laminating L-1 with a layer L-2 having an oxygen gas transmission rate OGTR-2 that is at least 20 times higher than OGTR-1, wherein L-2 completely covers the applied luminescent compound; or the method comprising providing a layer L-2 having an oxygen gas transmission rate OGTR-2; then applying on L-2 a luminescent compound having the property that oxygen quenches the luminescence; then laminating L-2 with a layer L-1 having an oxygen gas transmission rate OGTR-1 that is at least 20 times lower than OGTR-2, wherein L-1 completely covers the applied luminescent compound; or the method comprising providing a layer L-2 having an oxygen gas transmission rate OGTR-2; then applying on L-2 a luminescent compound having the property that oxygen quenches the luminescence; then laminating L-2 with a first layer of a material to produce an intermediate foil, wherein the first layer completely covers the applied luminescent compound; then applying a second layer on the first layer of the intermediate foil, wherein the second layer has an oxygen gas transmission rate OGTR-1 that is at least 20 times lower than OGTR-2, and wherein the second layer completely covers the first layer.

12. Method according to claim 11, wherein the luminescent compound is dissolved in a solvent and wherein the solvent is evaporated prior to the laminating.

13. Multi-layered packaging foil obtainable by the method of claim 11.

14. Packaging comprising a packaging foil according to claim 1.

15. Method for measuring the oxygen content in a packaging according to claim 14, comprising illuminating the luminescent compound present in the foil of the packaging with electromagnetic radiation of a wavelength at which luminescence occurs; then measuring the intensity or the lifetime of the luminescence of the luminescent compound present in the foil; then identifying which concentration of oxygen corresponds to the measured lifetime or intensity, by making use of the Stern-Volmer relationship of the particular foil that is used in the packaging.

Description

EXAMPLES

[0087] Preparation of the Foils

[0088] Two kilometers of foil having spots of luminescent compound were produced by making use of the technique of flexoprinting. The spots were printed as a circular shape with the dye dissolved in a UN1213 printing ink based on a technical printing varnish on a layer L-2 at a speed of 40 m/min. The ink was obtained from Sun Chemical, comprising (1) technical printing varnish of Sunprop Line 00LSF01, (2) Extender NC Flexo NC of 10LZD-05 and (3) adhesion promoter of 10-ZH-08. This layer L-2 comprised a polyethylene layer and a polypropylene layer, had a 37 μm thickness and an oxygen gas transmission rate (OGTR-2) of 3,000 cm.sup.3 m.sup.−2 day.sup.−1 at 25° C. and 0% RH at 1 atm oxygen partial pressure difference (ASTM D3985). The diameter of the spots is 1 cm. The concentration of the oxygen sensing dye (Pt(II)meso-tetra(pentafluorophenyl)porphine, Frontier Scientific) in the printing ink is 2 g/l. One spot required approximately 0.2 μl of ink. Subsequently (and after drying of the ink), a layer L-1 was laminated on the layer L-2 comprising the spot. The layer L-1 comprised a polyester layer with a silica coating, had a 12 μm thickness and an oxygen gas transmission rate (OGTR-1) of <1 cm.sup.3 m.sup.−2 day.sup.−1 at 25° C. and 0% RH at 1 atm oxygen partial pressure difference (ASTM D3985).

[0089] Characterization of the Foils

[0090] The obtained foil was transparent and had mechanical properties similar to known packaging foils. The spots enclosed in the foil retained their shape upon handling of the foil and could not be dislocated by passing an object over the surface of the foil (it could for example not be wiped away or deformed by brushing with a finger). FIG. 1 displays two photographs of the foil of the invention, each coming from the foil roll shown the background. The left photograph is taken under normal conditions (ambient light), demonstrating a spot that is darker than the foil (the spot is indicated with the vertical arrow). The right photograph is taken while the foil is illuminated by UV-light, while only the red channel is used for displaying the picture in black and white. This photograph displays a spot that is brighter than the foil (the spot is indicated with the vertical arrow).

[0091] The luminescence intensity of the sensor spot in the foil was measured under different oxygen atmospheres with a black and white 16 bit camera (Basler industrial vision) with a bandpass filter (665 nm±25 nm) mounted on the lens. The luminescence intensity was measured when the foil was exposed to a (gaseous) environment containing 0% of oxygen (I.sub.0), and when it was exposed to 20% of oxygen (I). FIG. 2 shows the luminescence at 0% of oxygen (left image) and at 20% of oxygen (right image). These images demonstrate that the luminescence intensity changed due to the variation of the oxygen concentration.

[0092] From both images it is possible to calculate the ratio I.sub.0/I. FIG. 3 displays this ratio over the entire spot (the diagram legend on the left displays the correlation of this ratio with the shades of grey in the spot). The average ratio of the spot appears to be 1.28.

[0093] For comparison, a couple of meters of the printed L-2 foil (i.e. L-2 foil provided with the luminescent compound) was not laminated with L-1. The non-laminated foil was put in a gas-tight container in which the gas (in particular oxygen) concentration could be changed. Accordingly, this foil had the luminescent compound in fluid communication with the atmosphere in the container. This provides a configuration wherein the lack of layer L-2 is mimicked, i.e. a packaging foil of the prior art. Luminescence measurements performed on this foil offer comparative data. This foil will be referred to by the term “non-coated”. A foil of the invention (which includes the layer L-2 as well as the layer L-1, with the luminescent compound therein between) will be referred to by the term “coated”.

[0094] Measuring the Oxygen Content in a MAP-Packaging

[0095] A MAP-packaging was prepared by sealing a container with a foil of the invention (“coated”). For comparison, a second MAP-packaging was prepared with a foil lacking the layer L-1 (“non-coated”). The containers had a gastight connection that allowed changing the gas concentration in the container. A series of nine oxygen concentrations was flushed continuously at 4 L h.sup.−1 through the containers fully replacing the headspace within 10 seconds. The gas mixtures were made by electronic mass flow controllers (Brooks Instruments) with a accuracy of 0.05% of the max flow rate of the mass flow controller. Measurement of the luminescence lifetime or intensity was determined after the spot reached steady state values.

[0096] With the obtained data, a Stern-Volmer plot could be made for the two foils used for the MAP-packagings. The plots are fit with the adapted Stern-Volmer equation (II), which plots are shown in FIG. 4. In Table 1, for each of the two foils the following quantities are given: (1) the non-quenchable fraction alpha with its standard error, (2) the Stern-Volmer quenching constant, (3) the fit quality of the plot, (4) the ratio tau.sub.0/tau and (5) the luminescence lifetimes under an anaerobic environment (100% N.sub.2) and under atmospheric environment (21% O.sub.2).

TABLE-US-00001 TABLE 1 Fit with adapted Stern-Volmer equation (II) Standard Standard Fit error of error of quality tau.sub.0/ lifetime (μs) α α K.sub.sv K.sub.sv (r.sup.2) tau 0% O.sub.2 21% O.sub.2 Coated 0.71608 0.0139 0.08731 0.00923 0.99497 1.20 66 55 Non-coated 0.30266 0.01253 0.15402 0.00784 0.99854 2.13 66 31

[0097] The data obtained with both foils show the effect of lamination (to thereby cover the luminescent compound) on the characteristics of the luminescent compound (as compared to known foils wherein the luminescent compound remains uncovered). When the luminescent compound is laminated (i.e. the luminescent compound is present between L-1 and L-2), then the result is in an increase of a, a decrease of K.sub.sv and a decrease of the ratio tau.sub.0/tau. The overall effect is that the sensor spot in a foil of the invention is somewhat less sensitive. However, the data also demonstrate that oxygen concentrations can still accurately and conveniently be determined with a foil of the invention. In addition, a foil of the invention has the advantages that result from the presence of layer L-2, such as the protection that this layer offers to the luminescent compound and the strongly reduced risk of contamination of the contents of the MAP-package.

[0098] Besides flexoprinting, foils were also prepared by making use of Continuous Ink Jet Printing (Linx printer). Two km of laminated foil was prepared using yellow printing ink (comprising 1 g of luminescent compound per liter ink) at a printing speed of 400 m/min. The ratio tau.sub.0/tau of the coated foil was 1.32 for the thus produced spots.