INDICATOR FILM

Abstract

A self-supporting film (10) comprises a gas barrier layer (20); a semi-permeable layer (40); and an indicator material (30), preferably a colorimetric indicator material, is provided between the gas barrier layer (20) and the semi-permeable layer (40). The indicator material (30) is in direct contact with the gas barrier layer (20). The film (10) is particularly useful as an item of packaging, particularly in packaging for perishable materials.

Claims

1. A self-supporting film comprising: (i) a gas barrier layer; (ii) a semi-permeable layer, wherein the semi-permeable layer comprises a polymeric material; and (iii) an indicator material provided between the gas barrier layer and the semi-permeable layer; wherein the indicator material is in direct contact with the gas barrier layer.

2. The self-supporting film of claim 1, wherein the gas barrier layer and semi-permeable layer are of substantially equal surface area.

3. The self-supporting film of claim 1, wherein the self-supporting film does not comprise a release layer or an outer adhesive layer.

4. The self-supporting film of claim 1, wherein the indicator material is a colourimetric indicator material and/or wherein the indicator material is capable of changing colour when exposed to a first substance, wherein the gas barrier layer is less permeable to the first substance than the semi-permeable layer.

5. (canceled)

6. The self-supporting film of claim 4, wherein the first substance is carbon dioxide.

7. The self-supporting film of claim 1, wherein the gas barrier layer has an oxygen transmission rate from about 0.01 to about 40 cc/m.sup.2/day.

8. The self-supporting film of claim 1, wherein the semi-permeable layer has an oxygen transmission rate from about 30 to about 200 cc/m.sup.2/day.

9. The self-supporting film of claim 1, wherein the gas barrier layer has a carbon dioxide transmission rate from about 0.01 to about 20 cc/m.sup.2/day.

10. The self-supporting film of claim 1, wherein the semi-permeable layer has a carbon dioxide transmission rate from about 5 to about 200 cc/m.sup.2/day.

11. The self-supporting film of claim 1, wherein the self-supporting film further comprises at least one reference material.

12. The self-supporting film of claim 11, wherein the at least one reference material is positioned at the same depth as the indicator material, and adjacent to the indicator material.

13. The self-supporting film of claim 1, further comprising an adhesive layer.

14. The self-supporting film of claim 13, wherein the indicator material is positioned between the gas barrier layer and the adhesive layer.

15. The self-supporting film of claim 13, wherein the adhesive layer is not in contact with the indicator material.

16. The self-supporting film of claim 1, further comprising a contrast material adjacent to the indicator material, optionally on a side of the indicator material opposite the gas barrier layer.

17. The self-supporting film of claim 1, wherein the gas barrier layer comprises a coating that reduces the permeability of the gas barrier layer to a first substance and/or oxygen.

18. The self-supporting film of claim 1, wherein the gas barrier layer is transparent or semi-transparent.

19. The self-supporting film of claim 1, wherein the gas barrier layer is provided as, forms or comprises an upper or outermost layer of the self-supporting film.

20. The self-supporting film of claim 1, wherein the semi-permeable layer is provided as, forms or comprises a lower or innermost layer of the self-supporting film.

21. The self-supporting film according to claim 1, where the self-supporting film is a food packaging film.

22. An item of food packaging comprising the packaging film of claim 21.

23. (canceled)

24. A method of manufacturing a self-supporting film, the method comprising: (i) providing a gas barrier layer; (ii) providing a semi-permeable layer; (iii) applying an indicator material onto the gas barrier layer or the semi-permeable layer; and (iv) bonding and/or laminating the gas barrier layer and the semi-permeable layer; wherein the indicator material is positioned between the gas barrier layer and the semi-permeable layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0167] Embodiments of the invention will now be given by way of example only, and with reference to the accompanying drawings, in which:

[0168] FIG. 1 is a cross-section of a self-supporting film according to a first embodiment;

[0169] FIG. 2 is a cross-section of a self-supporting film according to a second embodiment, wherein the gas barrier layer comprises a coating;

[0170] FIG. 3 is a cross-section of a self-supporting film according to a third embodiment, including reference materials;

[0171] FIG. 4 is a cross-section of a self-supporting film according to a fourth embodiment, including an adhesive layer positioned between the indicator material and the semi-permeable layer;

[0172] FIG. 5 is a cross-section of a self-supporting film according to a fifth embodiment, including an adhesive layer positioned between the indicator material and the semi-permeable layer;

[0173] FIG. 6 is a cross-section of a self-supporting film according to a sixth embodiment, including a contrast material and an adhesive layer that are adjacent to one another;

[0174] FIG. 7 is a cross-section of a self-supporting film according to a seventh embodiment, including a sealing layer, which allows the self-supporting film to seal to a container;

[0175] FIG. 8 is a working example of a self-supporting film according to another embodiment;

[0176] FIG. 9 is a graph of the hue on the yellow/blue axis of the indicator material as a function of time (days) for a working example of a self-supporting film.

DETAILED DESCRIPTION

[0177] The following are examples of specific embodiments.

Drawings

[0178] FIG. 1 is a schematic cross-section of a self-supporting film 10 according to a first embodiment, comprising a gas barrier layer 20, a semi-permeable layer 40, and an indicator material 30 positioned between gas barrier layer 20 and semi-permeable layer 40. Gas barrier layer 20 and semi-permeable layer 40 are of substantially equal surface area and indicator material 30 is in direct contact with gas barrier layer 20.

[0179] Indicator material 30 is positioned in a discrete section of film 10, between gas barrier layer 20 and semi-permeable layer 40. It is to be understood that indicator material 30 of film 10 may span substantially the entire surface area of film 10, by which is meant that indicator material 30 may extend across at least 95% of the surface area of film 10. Typically, however, indicator material 30 spans a smaller surface area than gas barrier layer 20 and semi-permeable layer 40, and is positioned in discrete sections of film 10.

[0180] A first substance in an environment 90, positioned below semi-permeable layer 40 is able to flow to or from indicator material 30, but is blocked by gas barrier layer 20. If environment 90 changes, by increasing or decreasing the concentration of the first substance, then indicator material 30 may sense this change in a time-controlled manner, at a rate that is dependent on the flow of the first substance through semi-permeable layer 40.

[0181] FIG. 2 is a cross-section of a self-supporting film 110 according to a second embodiment. Film 110 is generally similar to film 10, like part denoted by like numerals, but incremented by ‘100’, and comprises a gas barrier layer 120, a semi-permeable layer 140, and an indicator material 130 positioned between gas barrier layer 120 and semi-permeable layer 140. Gas barrier layer 120 and semi-permeable layer 140 are of substantially equal surface area and indicator material 130 is in direct contact with gas barrier layer 120. However, in this embodiment, gas barrier layer 120 comprises a coating 121. Coating 121 preferably spans substantially the entire surface area of the self-supporting film. It is to be understood that coating 121 may be positioned on the outer surface of gas barrier layer 120, or on the inner surface of gas barrier layer 120. However, coating 121 is typically positioned on the inner surface of gas barrier layer 120, adjacent to indicator material 130, as shown in FIG. 2. Coating 121 may decrease the permeability of gas barrier layer 120 to a first substance in order to prevent gas flow through gas barrier layer 120.

[0182] FIG. 3 is a schematic cross-section of a self-supporting film 210 according to a third embodiment. Film 210 is similar to film 110, like part denoted by like numerals, but incremented by ‘100’, and comprises a gas barrier layer 220, a semi-permeable layer 240, an indicator material 230 positioned between gas barrier layer 220 and semi-permeable layer 240, and a coating 221. In this embodiment, the film 210 further comprises reference materials 250 positioned in discrete sections of film 210, in the same layer as indicator material 230, and adjacent to indicator material 230. Any number of reference materials 250 may be positioned adjacent to indicator material 230. Conveniently, reference materials 250 may assist the user in assessing the concentration of a first substance at indicator material 230. However, when not present, a user could instead refer to a separate reference scale, or simply estimate the concentration.

[0183] The change in signal from indicator material 230 is time-controlled. Reference materials 250 may be used to assess the concentration of the first substance at indicator material 230, which corresponds to the amount of time that has passed since the concentration of the first substance changed.

[0184] FIG. 4 and FIG. 5 each show a schematic cross-section of a self-supporting film 310 and 410, according to a fourth a fifth embodiment respectively. Films 310 and 410 are similar to film 210, like part denoted by like numerals, but incremented by ‘100’ ad ‘200’ respectively, and each comprise a gas barrier layer 320,420, a semi-permeable layer 340,440, an indicator material 330,430 positioned between gas barrier layer 320,420 and semi-permeable layer 340,440, a coating 321,421 and reference materials 350,450, positioned in discrete sections of each film 310,410 in the same layer as indicator material 330/430.

[0185] Films 310 and 410 further comprise an adhesive layer 360,460 positioned between indicator material 330,430 and respective semi-permeable layer 340,440. It is to be understood that adhesive layer 360,460 could alternatively be positioned between coating 321,421 and indicator material 330,430. In the embodiment of FIG. 4, the adhesive layer 360 is continuous, i.e. it spans substantially the entire surface area of film 310. In the embodiment of FIG. 5, the adhesive layer 460 is non-continuous/patterned. Some adhesives are known to release carbon dioxide on curing. A benefit to adhesive layer 460 over adhesive layer 360 is that it may be positioned within film 410 so that it is not in contact with indicator material 430. This avoids any interference to indicator material 430 that may result from carbon dioxide release when the adhesive layer cures. Owing to ease of manufacture, a continuous adhesive layer such as 360 is more convenient and/or less expensive.

[0186] FIG. 6 is a schematic cross-section of a self-supporting film 510 according to a sixth embodiment. Film 510 is similar to film 310, like part denoted by like numerals, but incremented by ‘200’ and comprises a gas barrier layer 520, a semi-permeable layer 540, an indicator material 530 positioned between gas barrier layer 520 and semi-permeable layer 540, a coating 521, reference materials 550, positioned in discrete sections of film 510 in the same layer as indicator material 530, and an adhesive layer 560.

[0187] In this embodiment, the film 510 further comprises a contrast material 570 positioned between indicator material 530 and adhesive layer 560. Adhesive layer 560 is positioned between contrast layer 570 and semi-permeable layer 540. It is to be understood that adhesive layer 560 could alternatively be positioned between coating 521 and indicator material 530. Contrast material 570 may enhance the visibility of indicator material 530 to the user. The user typically views film 510 from above the gas-barrier layer, with a user's view 595. To enhance the visibility of indicator 530 to the user, contrast material 570 is positioned at a greater depth than indicator material 530 (otherwise indicator material 530 may be blocked from user's view 595). Alternatively, contrast material 570 may be combined with indicator material 530. Contrast material 570 may also be combined with reference materials 550, although this may not be necessary if reference materials 550 are opaque.

[0188] FIG. 7 is a schematic cross-section of a self-supporting film 610 according to a seventh embodiment. Film 610 is similar to film 510, like part denoted by like numerals, but incremented by ‘100’, and comprises a gas barrier layer 620, a semi-permeable layer 640, an indicator material 630 positioned between gas barrier layer 620 and semi-permeable layer 640, a coating 621, reference materials 650, positioned in discrete sections of film 610 in the same layer as indicator material 630, an adhesive layer 660, and a contrast material 670. It is to be understood that adhesive layer 660 could alternatively be positioned between coating 621 and indicator material 630.

[0189] In this embodiment, the film 610 further comprises a sealing layer 680, which may allow film 610 to seal to a container, for example by applying heat.

[0190] FIG. 8 is an above-view of a working example of a self-supporting film 710 according to an eighth embodiment. The Film 710 is used to seal a container, thus providing a sealed container 800. In this embodiment, an indicator material 730, which comprises Cresol red, is positioned in a circular portion of the film (yellow circle) and three reference materials 750 are positioned in discrete sections of the film in the same layer as and around indicator material 730 (blue, yellow and green arrows). A contrast material 770 (white square) is positioned beneath indicator material 730 and reference materials 750. Film 710 is part of a MAP and the first substance (flushing gas) is carbon dioxide.

[0191] Film 710 encloses and seals a 30% carbon dioxide environment, such that the carbon dioxide environment is adjacent to the semi-permeable layer of film 710 and is within the sealed container 800. A standard atmospheric environment is adjacent to the gas barrier layer of film 710 and around sealed container 800. The carbon dioxide environment is able to permeate the semi-permeable layer, the adhesive and contrast material 770, and flows to and from Cresol red indicator material 730. When exposed to a carbon dioxide environment, Cresol red is yellow in colour, and when exposed to standard atmospheric conditions, it is blue in colour. In this embodiment, since Cresol red indicator material 730 is yellow, it may be inferred that the environment around cresol red indicator material 730 is high in carbon dioxide, and therefore that the integrity of the sealed container has not been compromised.

[0192] Reference materials 750 are either printed in such a way to expose contrast material 770 and form a label or text (blue and green arrows reading “past best” and “still fresh”, respectively), or are printed together with inert ink of a different colour to form a label or text (yellow arrow reading “fresh” in black ink).

[0193] FIG. 9 is a graph showing the hue on the yellow/blue axis (in an L*a*b colour scale) of indicator material 730 as a function of time (days) for the embodiment shown in FIG. 8. The time is measured from opening film 710, i.e. breaking the seal, thereby changing the environment within sealed container 800 from a carbon dioxide environment to a standard atmospheric environment. The environment within container 800 quickly changes—carbon dioxide may diffuse out of the break in the seal and other gases may diffuse into the break, forming a standard atmospheric environment. However, the concentration of carbon dioxide at indicator material 730 changes more slowly, owing to the controlled rate of carbon dioxide flow through the semi-permeable layer.

[0194] FIG. 9 shows that the b* value (the hue on the yellow/blue axis) decreases with time. In accordance with the conventional L*a*b colour scale, a more positive b* value corresponds to a more yellow colour, whereas a more negative b* value corresponds to a more blue colour. Thus, the decrease in the b* value corresponds to cresol red indicator material 730 becoming more blue in colour, as shown in the photographs of the insert. This is in agreement with a decreasing concentration of carbon dioxide at cresol red indicator material 730. In this example, the colour change of cresol red indicator material 730 takes approximately 3 days. Consequently, self-supporting film 710 may be useful as an indicator of the freshness of perishable material with a use by date of approximately 3 days from opening the packaging.

Indicator Material Formulations

[0195] Tables 1 and 2, below, exemplify suitable formulations of the indicator material for use in a self-supporting film. The formulation given in Table 1 is for a transparent composition, whilst that given in Table 2 is for an opaque composition in which the contrast material is combined with the indicator material.

TABLE-US-00001 TABLE 1 Example transparent composition of indicator material suitable for use in a self-supporting film, comprising Cresol Red Percentage in Component composition (%) Water 27.0 Tetrabutylammonium hydroxide (base) 18.5 (40% in water) Cresol Red 3.5 Joncryl ® FLX 5010 (self-crosslinking 40.0 acrylic emulsion) Syloid ® 244 (hydrophilic silica) 10.0 Aerosil ® R972 (hydrophobic silica) anti- 1.0 settlement agent

TABLE-US-00002 TABLE 2 Example opaque composition comprising the indicator material suitable for use in a self-supporting film, comprising Cresol Red Percentage in Component composition (%) Water 18.5 Tetrabutylammonium hydroxide (base) 18.5 (40% in water) Cresol Red 3.5 Joncryl ® FLX 5010 (self-crosslinking 35.0 acrylic emulsion) Syloid ® 244 (hydrophilic silica) 9.5 Titanium dioxide (whitener for opaque 15.0 indicator)

TABLE-US-00003 TABLE 3 Example transparent composition of the indicator material suitable for use in a self-supporting film, comprising m-Cresol Purple Percentage in Component composition (%) Water 27.0 Tetrabutylammonium hydroxide (base) 18.5 (40% in water) m-Cresol Purple 3.5 Joncryl ® FLX 5010 (self-crosslinking 40.0 acrylic emulsion) Syloid ® 244 (hydrophilic silica) 10.0 Aerosil ® R972 (hydrophobic silica) anti- 1.0 settlement agent

TABLE-US-00004 TABLE 4 Example transparent composition of the indicator material suitable for use in a self-supporting film, comprising Phenol Red Percentage in Component composition (%) Water 27.5 Tetrabutylammonium hydroxide (base) 18.5 (40% in water) Phenol Red 3.0 Joncryl ® FLX 5010 (self-crosslinking 40.0 acrylic emulsion) Syloid ® 244 (hydrophilic silica) 10.0 Aerosil ® R972 (hydrophobic silica) anti- 1.0 settlement agent