The present invention relates to a method for applying a UV activated oxidising agent indicator to a printing substrate and products derived therefrom. In particular, the present invention relates to a method for applying a UV activated oxygen sensitive ink to a blank for a package, or to a printing substrate for forming a blank for a package. The products derived therefrom include, for example: a printing substrate, a blank, and a package to which the ink has been applied.

Perishable goods, and in particular drinks and foodstuffs, are often provided in some form of air-tight packaging. This packing can be applied in a modified atmosphere (known as modified atmosphere packaging (MAP)), which limits the presence of oxygen. Alternatively, perishable goods may be packaged in normal atmospheric conditions.

Items that are packaged in air-tight packaging include: food, beverages, works of art, pharmaceuticals, medical diagnostic kits and sterilised packages. As mentioned, it is particularly desirable in the food industry to package goods such that their exposure to oxygen after packaging is minimised. This can be used to effectively extend the shelf life of many perishable items.

It is useful to be able to determine the length of time for which a package containing perishable goods has been opened. To this end, many different sensors for detecting oxidising agents, and in particular for detecting oxygen, have been produced. Several of these sensors have been adapted for attachment to packages containing perishable goods. For example, GB 2419868, FR 2836677, WO 2006/077413, GB2344101 and US 2006/0110835 disclose the use of oxygen sensitive dyes that are covered by a seal, the seal being broken by the opening of a package, and the dye changing colour over a set period of time to indicate the duration for which the package has been opened.

WO 03/021252 (incorporated herein by reference) discloses a sensor for oxidising agents which is activated using UV light. This patent application discusses the use of a particular chemical composition which can be in the form of an ink, and which may be printed onto a variety of supports. However, the indicator disclosed is necessarily sensitive to oxygen. It is not apparent from reading the application how such an indicator may be effectively integrated with, or printed onto, packaging in the reduced form. In addition, it is unclear as to how such an indicator may be applied in the reduced form in atmospheric, or in modified atmospheric, conditions.

Therefore, it is an object of the present invention to obviate or mitigate at least some of the disadvantages of the prior art.

A further object of the invention is to provide a method for applying an oxygen sensitive ink to a printing substrate.

According to first aspect of the present invention there is provided a method for applying a UV activatable oxidising agent indicator to a printing substrate, the method comprising the steps of: providing a printing substrate to a printing assembly; applying to the printing substrate a UV activatable oxidising agent indicator for detecting oxidising agents, the indicator comprising at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms; providing a coating configured to seal at least a portion of the printing substrate having the indicator applied thereto; and exposing the UV activatable oxidising agent indicator to light having a wavelength of about 200-400 nm thereby effecting reduction of the redox sensitive material therein.

The method may be carried out in the presence of oxygen, and in particular may be carried out in atmospheric conditions. This is in contrast to known methods of applying UV activatable indicators for detecting oxidising agents. Such known methods must generally be carried out in an atmosphere having a reduced oxygen content. This increases the cost and inconvenience of such known methods. Furthermore, if the amount of oxygen present in the atmosphere is not sufficiently low, the reliability of the indicator may be adversely affected. Therefore, the method disclosed herein is more cost effective than known methods. Also, the present method enables activation of the indicator at any time as chosen by the manufacturer. For example, the activation may take place some time after the printing process, and printed packages can be stored and transported in normal atmospheric conditions.

Preferably the coating provides a seal having a very low oxidising agent permeability thereby preventing oxidation of the indicator.

According to one embodiment, the coating provides a semi-permeable seal configured to allow controlled flow of oxidising agent to the indicator.

The seal may be selected from one or more of the group consisting of: PET, EVOH, PVDC or regenerated cellulose.

Preferably the seal is configured to be selectively removable. The oxidising agent may be oxygen. Preferably the indicator is in the form of an ink.

Optionally the ink is applied to the printing substrate in the form of a LOGO or text.

The indicator may further comprise an electron donor. The electron donor may be a mild reducing agent, such as an amine, a reducing saccharide, a readily oxidisable polymer, or other general anti-oxidants.

In particular, the electron donor may be selected from one or more of the group consisting of: NaEDTA, TEOA, glucose, fructose, polyvinyl alcohol, ascorbic acid or citric acid.

The indicator may further comprise at least one semiconductor material specifically sensitive to light having a wavelength of about 200-400nm, and wherein upon irradiation of said semiconductor material by light having a wavelength of about 200-400nm an electron is donated by the electron donor to the semiconductor material which in turn provides an electron to the redox sensitive material causing the redox sensitive material to become reduced.

The semiconductor material may be an oxide of: titanium, tin, tungsten, and zinc and mixtures thereof.

In particular the semiconductor material may be selected from one or more of the group consisting of: titanium (IV) oxide (TiOa), strontium titanate (SrTiO ₃ ), tin (IV) oxide (SnO ₂ ), tungsten (IV) oxide (WO ₃ ), and zinc (II) oxide (ZnO) and mixtures thereof. In one embodiment, a printing substrate is prepared wherein a portion of the seal covering the indicator is detachable from the printing substrate by a user. For example, when the printing substrate is configured as a fruit drink package, the portion of the seal is attached to the lid of the package, and is automatically removed from the package when the package is opened by a user. Therefore, the seal is configured to be selectively removable.

The method of the present invention enables application of an oxygen sensitive indicator in the oxidised form, and potentially in the presence of oxygen. Once applied to a printing substrate, the indicator is sealed using a material that inhibits oxygen, or oxidising agents, from reacting with the indicator. After sealing, the indicator is exposed to UV light which converts the indicator to the reduced form. The indicator remains sealed from the atmosphere until such time that the package is opened, at which point the seal is broken or removed thus exposing the indicator to the atmosphere. Once exposed to the atmosphere, the indicator will change colour at a particular rate dependent on the particular composition of the indicator, and optionally the temperature.

Alternatively, the seal may be semi-permeable, and may be configured to allow ingress of an oxidising agent at a predetermined rate, without the requirement of removing or breaking the seal.

The present invention enables the application of an oxygen sensitive ink to a printing substrate using commonplace printing techniques. There is no requirement for the atmosphere to be modified, as is the case with modified atmosphere packaging. However, it will be appreciated that the technique could also be used in a modified atmosphere packaging process. The method described herein is used in the manufacture of printing substrates (such as paper and card), blanks and packages. Optionally the printing substrate is configured to prepare a blank for use in the manufacture of a package.

According to a second aspect of the present invention there is provided a printing substrate obtainable according to the method as described herein.

According to a further aspect of the present invention there is provided a method for manufacturing a blank for a package comprising a UV activatable oxidising agent indicator, the method comprising the steps of: providing a printing substrate comprising a blank to a printing assembly; applying to the blank a UV activatable oxidising indicator for detecting oxidising agents, the indicator comprising at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms; providing a coating configured to seal at least a portion of the blank having the indicator applied thereto; and exposing the indicator to light having a wavelength of about 200-

400 nm thereby effecting reduction of the redox sensitive material therein.

According to a further aspect of the present invention there is provided a blank obtainable according to the method as described herein.

According to a still further aspect of the present invention there is provided a method for manufacturing a package comprising a UV activatable oxidising agent indicator, the method comprising the steps of: providing a printing substrate comprising a blank to a printing assembly; applying to the blank a UV activatable oxidising agent indicator for detecting oxidising agents, the indicator comprising at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms; providing a coating configured to seal at least a portion of the blank having the indicator applied thereto; exposing the indicator to light having a wavelength of about 200- 400 nm thereby effecting reduction of the redox sensitive material therein; and arranging the blank to form a package.

According to a further aspect of the present invention there is provided a package obtainable according to the method as described herein.

The method of the present invention, and the products derived thereform, will now be described by way of example only.

Example 1

The method of the present invention can be carried out using conventional printing apparatus, for example as used in Gravure printing.

The indicator is provided to a Gravure printer in the form of a printable ink. The Gravure printer is equipped with laminated paper and the printing process is commenced. The printable indicator is applied to the laminated paper in the form of a LOGO or text in the conventional manner using an etched printing cylinder and an impression cylinder as is common in the Gravure process. Once printed, the area of the laminated paper printed with the indicator is sealed by application of polyethylene terephthalate (PET). The section of the laminated paper which is printed with the indicator is then exposed to UV light having a wavelength of about 200- 400 nm thereby effecting reduction of a redox sensitive material in the indicator.

It will be appreciated that the method can be applied using different types of printing assembly and alternative printing regimes such as web offset printing. Whilst laminated paper is used in the example given, other suitable printing substrates known in the art can be used. Also, it will be understood that the printable indicator may be applied to the whole, or only a section of, the laminated paper, and that the seal may be applied to the whole, or only a section of, the laminated paper and/or section of the laminated paper to which the indicator is applied. In this embodiment, the printing substrate contains blanks which can be folded to manufacture packages.

In the example given, the indicator is sealed using PET. However, it will be appreciated that any suitable seal having a very low oxidising agent permeability (thereby preventing oxidation of the indicator) can be used. Alternatively, the seal may be chosen to provide a semi-permeable seal configured to allow controlled flow of oxidising agent to the indicator.

Examples of suitable materials for providing a seal are polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), and regenerated cellulose. In the embodiment described, the indictor is in the form of a printable ink and comprises a thiazine dyestuff, sodium ethylenediamine tetraacetic acid (NaEDTA), and titanium (IV) oxide (TiO ₂ ). The thiazine dyestuff acts as a redox sensitive material, having different visual properties in the oxidised and reduced forms. Other suitable redox sensitive materials include an oxazine dyestuff, an azine dyestuff, a triphenylmethane dyestuff, an indophenol dyestuff, and indigo dyestuff, viologen and/or mixtures thereof. The NaEDTA acts as an electron donor. Other suitable electron donors include mild reducing agents such as an amine, a reducing saccharide, a readily oxidisable polymer, or other general antioxidants.

The TiO ₂ acts as a semiconductor material specifically sensitive to light having a wavelength of about 200-400nm. Irradiation of the semiconductor material by light having a wavelength of about 200-400nm causes an electron to be donated by the electron donor to the semiconductor material which in turn provides an electron to the redox sensitive material causing the redox sensitive material to become reduced. Alternative semiconductor materials include oxides of: titanium, tin, tungsten, and zinc and mixtures thereof. In particular the semiconductor material may be selected from one or more the group consisting of: titanium (IV) oxide (TiO ₂ ), strontium titanate (SrTiO ₃ ), tin (IV) oxide (SnO ₂ ), tungsten (IV) oxide (WO ₃ ), zinc (II) oxide (ZnO) and mixtures thereof.

In one embodiment, the ink is printed directly onto a film layer which is the outer layer of a laminate used, for example, in modified atmosphere packaging. The outer layer acts as an oxygen barrier. An inner layer is then applied to the ink such that the ink is sandwiched between the outer layer and the inner layer. The inner layer has at least some degree of permeability to oxygen. Thus, in use, the inner layer will enable the ink to detect the oxygen content inside the packaged goods. This is particularly useful for detecting when, and for how long, modified atmosphere packaging has been breached. Modified atmosphere packaging for cooked meats has around 0.2% oxygen content after gas flushing. Therefore, the indicator will only start to change colour when the pack is opened. Thus, this embodiment is useful for "consume within" dates. This can also be applied to any foods packaged in a low oxygen content atmosphere such as bacon, salads, dried cereals, cured meats, and some uncooked white meats.

The embodiment described above can be manufactured using the method as described herein using one layer of the laminate as a printing substrate to which the ink is applied, one layer of the laminate as a coating, and activating the ink using UV light. As the ink is activated after it is sealed in the laminate, it does not need to be stored in oxygen free conditions.

The method described can be used to manufacture a blank for a package. In addition, the method described can be used to manufacture a package by folding or arranging a printing substrate or a blank produced using the method.

Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention which are obvious to those skilled in the art are intended to be covered by the present invention.