WO2007059902A2

WO2007059902A2 - Composite system provided with an oxygen scavenger/indicator function and the use thereof

Info

Publication number: WO2007059902A2
Application number: PCT/EP2006/011077
Authority: WO
Inventors: Horst-Christian Langowski; Thomas Wanner; Wolfgang Lohwasser
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2005-11-22
Filing date: 2006-11-17
Publication date: 2007-05-31
Also published as: DE102005055635A1; WO2007059902A3; DE102005055635B4

Abstract

The invention relates to a composite system provided with an oxygen scavenger/indicator function comprising at least one type of metal which is used in the form of an oxygen sorption agent and whose oxidation degree can be increased by oxygen. The inventive composite system also provided with an activator. The indicator function is carried out by modifying the physic al properties of oxygen sorption agent which is effected by metal oxidation.

Description

Composite system with oxygen scavenger / indicator function and its use

The invention relates to a composite system with the function as a scavenger / indicator for oxygen, which contains at least one metal as an oxygen sorbent, which is convertible by oxygen in a higher oxidation state. It also contains an activator. The indicator effect is caused by a change in the physical properties of the oxygen sorbent caused by the oxidation of the metal.

O ₂ scavengers are substances that can sorb oxygen. By sorption are meant all known sorption possibilities, eg adsorption, absorption, chemisorption and physisorption. The systems which are currently established according to the prior art can be classified here primarily according to the O ₂ scavenger substrate and according to their initialization mechanism. lifi grace. Here one differentiates the following groups:

• inorganic O ₂ scavengers, eg iron-based or sulfide-based systems

• low molecular weight organic O ₂ scavengers, eg ascorbotebased systems

• High molecular weight organic O ₂ scavengers, eg polyolefin-based or polyamide-based systems

O ₂ scavengers are initialized either by UV radiation or by moisture. This means that the O ₂ scavenging function is only available after exposure to UV radiation or water, ie air humidity.

Indicator systems can generally be classified into Time-Temperature-Indicator (TTI), Gas / Leakage-Indicator and Freshness-Indicator systems.

A TTI integrates the time-temperature history of a product and thus makes a direct statement about its storage conditions. The indicator effect is effected by a chemical reaction or by opposite diffusion of two dyes.

Gas leakage indicators detect the gas concentration of O ₂ , CO ₂ or H ₂ O in the packaging space. They thus make an indirect statement about the quality of the product. The indicator effect is caused by a chemical reaction with the reactants O ₂ , CO ₂ or H ₂ O.

Freshness indicators detect the metabolic products of microorganisms and thus make a direct statement about the quality of the product. The Indicator effect is caused by a chemical reaction of the metabolites.

All these indicator systems have in common that the indicator effect is reflected by a visible color change.

Thus, there are a variety of O ₂ scavenger systems in the prior art, but only a negligible number of gas leakage indicator systems.

Combined 0 ₂ scavenger / indicator systems are not currently known in the art. In these, the O ₂ scavenger works independently of the O ₂ indicator, ie the 0 ₂ indicator merely signals that a certain 0 ₂ concentration has been exceeded.

Based on this, it was an object of the present invention to provide a composite system which functions as an oxygen scavenger / indicator system, i. the residual capacity of an oxygen scavenger and the exceeding of a certain oxygen concentration span can signal visually or measurably.

This object is achieved by the composite system with the features of claim 1. Claims 37 and 38 indicate uses of such composite systems. The other dependent claims show advantageous developments.

According to the invention, there is provided a composite system comprising a substrate sheet and at least one scavenger / indicator layer deposited thereon as a thin film. The scavenger / indicator layer contains at least one metal as an oxygen sorbent, which is due to the sorption of Oxygen changes at least one physical property of the oxygen sorbent. Furthermore, the composite system contains at least one activator for the oxidation of the oxygen sorbent, which is in direct contact with the at least one scavenger layer.

According to the invention, a thin film is understood to mean all coating systems which can be produced by vacuum coating methods (CVD and PVD) as well as electrolytic deposition or coating in the nanoscale.

The disadvantages of the prior art that the oxygen scavengers or oxygen indicators described here have a very slow reaction kinetics can be eliminated according to the invention by applying the oxygen sorbent under reduced conditions by the vacuum-deposited scavenger / indicator layer becomes. This vacuum evaporation allows the metals acting as oxygen sorbents to be reduced and thus in elemental form, i. in the oxidation state 0. In the known from the prior art incorporation methods, such. extrusion or painting, however, metals are partially oxidized, i. Some of the incorporated metals have an oxidation state> 0 after the incorporation process.

The functioning of the composite system according to the invention is based on the fact that the oxygen sorbent in the presence of oxygen and moisture can bind the oxygen in the corresponding oxide compounds. In the case of iron, the following reaction represents a possible pathway for metal oxidation: 2 Fe + 3 H ₂ O + 1 MO ₂ - -> 2 Fe (OH) ₃

The oxygen sorbent can thus change one of its physical parameters under oxygen exposure. With regard to the physical properties concerned, there are no restrictions if they represent a visual or metrologically evaluable change.

As physical properties, here are e.g. magnetism, electrical conductivity and electromagnetic absorption are preferred.

In a first variant, the oxygen sorbent provides a magnetic or targeted magnetized material, such as e.g. elemental iron formed by contact with oxygen to a non-magnetic or less-magnetic compound, e.g. Iron oxide (s) is reacted. The resulting change in permeability or remanence can be reduced by e.g. a sensor can be detected. For the remanence, a magnetometer can be used here, while the change in permeability can be detected by an inductance measurement.

Another preferred variant provides that the oxygen sorbent is an electrically conductive material, such as elemental iron, and is converted by exposure to oxygen to a no or less electrically conductive compound, such as iron oxide (s). The change in the electrical conductivity can be detected for example by means of a sensor. The coupling of the current takes place on inductive or capacitive ways. The detection during the inductive coupling can preferably carried out via a Wirbelstrommesstechnik. In the case of capacitive coupling, detection can preferably take place according to the capacitor principle.

Another preferred variant provides that the electromagnetic absorption of the oxygen sorbent changes. Here, as the oxygen sorbent, e.g. elemental iron which, when exposed to oxygen, becomes an oxidic compound, e.g. Iron oxide (s) is reacted. This changes the electromagnetic absorption of the oxygen sorbent. This can e.g. be detected by a sensor. Preferably photometers or IR measuring devices are used as detectors for the UV / IR range. Detection is also possible in the VIS range (visual range) as well as in the microwave range. Particularly preferred is a visually perceptible color change of the oxygen sorbent.

The oxygen sorbents of the invention are based on materials which combine both the O ₂ scavenger and the O ₂ indicator functions. Thus, the O ₂ scavenger and indicator has the same reaction kinetics.

For the combined system according to the invention, this has the further advantage that the correlation of the absorbed amount of oxygen of the O ₂ scavenger with the color change of the O ₂ indicator is independent of the temperature.

A system with one material for the O ₂ scavenging function and another material for the

O ₂ indicator function, in contrast, has two Reaction kinetics and thus two different temperature dependencies. This means that the correlation of the residual capacity of the O ₂ scavenger with the color change of the 0 ₂ indicator is temperature-dependent.

Preferably, the oxygen sorbent is a metal selected from the group consisting of iron, zinc, aluminum, cobalt, copper, magnesium, chromium, nickel, titanium and tin.

Preferably, the activator contained in the composite system is an electrolyte, a water basic compound, and / or a more noble metal than the oxygen sorbent, i. a metal with a higher normal potential. These include e.g. Ag, Au and Cu.

As the electrolyte, all compounds are suitable which support the electron transfer of the redox reaction. Preference is given to using compounds from the group of alkali metal and alkaline earth metal halides. Likewise, it is also possible to use metallic and non-metallic sulfates and phosphates, but also non-metallic halides, such as ammonium chloride. These electrolytes can be in both liquid and solid form.

A further alternative according to the invention provides that the activator is a water-basic compound. The added base-reacting compound causes, upon contact with water, ie at a certain relative humidity of the air, a basic environment is created in which then the oxygen sorbent can sorb the oxygen. In the dry state, however, there is no oxygen sorption due to the lack of basic environment. The at least one water-basic compound is preferably selected from the group of hydroxides, carbonates, sulfides, thiosulfates, oxides, phosphates, polyphosphates of alkali or alkaline earth metals. Likewise, alkali or alkaline earth metal salts of organic acids are preferred. But it is also possible to use any other water-basic compounds. Most preferably, the oxygen scavenger / indicator contains magnesium hydroxide, sodium thiosulfate or calcium oxide as the basic reacting compound.

A further preferred variant provides that the oxygen scavenger / indicator contains a polymer electrolyte and / or a gel electrolyte. Polymers in combination with salts can be used in particular as polymer electrolytes, such as, for example, polyethyloxide (PEO) with LiPF ₆ , polypropylene oxide (PPO) with LiCF ₃ FO ₃ or polyethylene oxide with LiClO ₄ and optionally TiO ₂ . Systems of polyether, polycarbonate and LiBF ₄ , systems of polyacrylonitrile (PAN), polycarbonate (PC), electrochromic polymers and LiClO ₄ and systems of polyvinyl chloride (PVC), dioctyl adipate (DOA) and LiN (SO ₂ CF ₃ ) 2 used.

Likewise, it is also possible that an electrolyte and a water-basic compound are used together as an activator.

The deposited scavenger / indicator layers preferably have a layer thickness in the range of 10 to 1000 nm. The layer thickness used depends on the required scavenger capacity. A preferred variant provides that the scavenger / indicator layer is transparent in the visible region of the spectrum.

According to a further preferred variant, the composite system according to the invention may also have at least one further layer. This is preferably a lacquer layer, an adhesive layer, a further vapor-deposited layer or a polymer film. It is preferred that this further layer contains the above-described activator.

In the case that the further layer is a polymer film, this preferably consists of a polymer selected from the group of polyethylene terephthalate (PET), polyolefins, in particular polypropylene (PP) and polyethylene (PE), polyamides (PA), polystyrenes (PS ), Polycarbonates (PC) and their copolymers and polymer blends.

In a further variant, the polymer film used as a further layer is non-positively connected to the scavenger / indicator layer with a laminating adhesive. In this case it is then possible for the activator to be contained in the laminating adhesive.

In cases where the activator is embedded in a polymer layer, this layer can then be modified by foaming and / or stretching. In this way it is possible subsequently to influence the oxygen permeability of the composite system.

For metals as oxygen sorbent with poor adhesion to the substrate film it is preferred to use so-called mixed metal layers to ensure sufficient adhesion. Such mixed metal layers then consist of the oxygen sorbent and a spacer. The spacer can be another metal suitable as oxygen sorbent or also a metal without scavenger property. Preferred examples of spacers are Au, Ag, SiO _x where x = 1.0 to 2.0, AlO y where y = 1.3 to 1.6, B ₂ O ₃ , Cr-SiO ₂ , Cr ₂ Si ₂ , GeO ₂ , InO ₂ and TiO ₂ .

A further preferred variant provides that the substrate film itself is a composite film. In this case, it is then particularly preferred for the substrate film to have a barrier layer for oxygen. The barrier layer may contain SiO _x with x = 1.0 to 2.0, AlO _y with y = 1.3 to 1.6, ethylene vinyl alcohol copolymers (EVOH) and / or vinylidene chloride copolymers (PVDC). The barrier layers consisting of silicon oxides and aluminum oxides can be produced, for example, by a vacuum thin-layer method, the preferred layer thicknesses being in the range from 1 nm to 200 nm.

There are no restrictions whatsoever on the material of the substrate film, this preferably consisting of a polymer selected from the group of polyethylene terephthalates, polyolefins, in particular polypropylene and polyethylene, polyamides, polystyrenes, polycarbonates and / or their copolymers and polymer blends.

In a preferred embodiment, the at least one activator is integrated into the scavenger / indicator layer. In principle, the composite system according to the invention can be present in two variants, ie as a non-visible and visible variant. The visible variant enables a visual perception and evaluation, which is generally sufficient with regard to qualitative evaluations. The non-visible variant is in turn based on the change of other physical properties, which, as described above, can be evaluated with appropriate measuring instruments and thus can also provide additional quantitative results. Especially for the packer as well as the distributor of products, eg food, the information is often important, how the headspace atmosphere behaves in the packaging. Furthermore, with the establishment of active packaging with O ₂ scavengers, the knowledge of the residual consumption capacity of the scavengers in the packaging, eg at the time of packaging, is of highest interest. These requirements can be solved outstandingly well with the described composite systems.

The composite system according to the invention has the special feature that the weight ratio of oxygen sorbent to activator is adjustable so that the oxygen sorbent at a defined time, which represents the residual capacity of the oxygen sorbent, changes at least one of its physical properties. This particularly preferably includes a color change point.

A further variant according to the invention provides that the weight ratio of oxygen sorbent to activator is set so that the oxygen sorbent undergoes a change in its physical properties at a defined point in time, which exceeds a certain oxygen concentration. indicating onszeitspanne has. As a preferred physical property is also the electromagnetic absorption, ie the change in the color of the sorbent. By means of the color change point, a defined residual capacity of the oxygen sorbent is to be signaled visually or with the aid of a measurement.

A third variant according to the invention provides that the weight ratio of oxygen sorbent to activator is adjusted so that the oxygen sorbent changes at least one of its physical properties at a defined time, which indicates the exceeding of a certain oxygen concentration. The preferred physical property here too is the color transition point.

Of course, the three abovementioned variants according to the invention can also be combined with one another.

The composite systems described are very suitable as packaging films for any packaged goods, especially food. Likewise, the composite systems can be used to protect moisture sensitive components in electronic or electrical equipment.

The applications include the food industry, pharmaceutical products and devices, the electronics industry, the chemical industry as well as cultural and military sectors.

Reference to the following figures, the subject invention is to be explained in more detail, without wishing to limit this to the specific embodiment shown here. FIG. 1 shows the oxygen uptake over time, normalized to the O ₂ scavenger dimensions, of composite systems according to the invention. As oxygen sorbent here iron, aluminum and zinc were used. The substrate film in all three cases is a composite system of PET and SiO _x with x = 1.0 to 2.0. This substrate film thus has an oxygen barrier function.

FIG. 2 shows the oxygen uptake over time, normalized to the O ₂ scavenger dimensions, of a composite system according to the invention. This has as a substrate film a composite system of PET and SiO _x with x = 1.0 to 2.0, with oxygen barrier function. The scavenger / indicator layer vapor-deposited in vacuum is based on aluminum as the oxygen sorbent. In the present case, an activator is additionally integrated into the scavenger / indicator layer. As a sealing layer, the composite system according to the invention additionally comprises a film of polyethylene.

Claims

claims

Composite system comprising a substrate film, at least one vacuum deposited thereon scavenger Zlndikator layer as a thin layer containing at least one metal as oxygen sorbent, wherein the sorption of oxygen at least one physical property of the oxygen sorbent changes, and at least one in direct contact with the at least one scavenger layer standing activator for the oxidation of the oxygen sorbent.

2. Composite system according to claim 1, characterized in that the physical property is the magnetism, the electrical conductivity and / or the electromagnetic absorption of the oxygen sorbent.

3. Composite system according to one of the preceding claims, characterized in that the electromagnetic absorption of the microwave, the IR, the VIS or the UV range.

4. Composite system according to one of the preceding claims, characterized in that the change in physical properties is a color change of the oxygen sorbent.

Composite system according to one of the preceding claims, characterized in that the at least one metal is selected from the group consisting of aluminum, iron, zinc, cobalt, copper, magnesium, chromium, silicon, nickel, titanium and tin.

6. Composite system according to one of the preceding claims, characterized in that the at least one activator is selected from an electrolyte, a water-basic compound and / or a metal which has a higher normal potential compared to the oxygen sorbent.

7. Composite system according to one of the preceding claim, characterized in that the higher normal potential metal having gold, silver and / or copper.

8. Composite system according to the preceding claim, characterized in that the electrolyte is selected from the group of alkali and alkaline earth metal halides, the metallic and non-metallic sulfates and phosphates and the non-metallic halides.

9. Composite system according to claim 6, characterized in that the electrolyte is a polymer electrolyte.

10. Composite system according to claim 6, characterized in that the electrolyte is a gel electrolyte is,

11. A composite system according to any one of claims 6 to 10, characterized in that the water-basic compound is selected from the group of hydroxides, carbonates, sulfites, thiosulfates, oxides, phosphates, polyphosphates of alkali or alkaline earth metals and alkali or alkaline earth metal Salts of organic acids.

12. Composite system according to the preceding claim, characterized in that the water-basic compound is magnesium hydroxide, sodium thiosulfate and / or calcium oxide.

13. Composite system according to one of the preceding claims, characterized in that the scavenger / indicator layer has a thickness in the range of 10 to 1000 nm.

14. Composite system according to one of the preceding claims, characterized in that the scavenger / indicator layer is transparent in the visible region of the spectrum.

15. Composite system according to one of the preceding claims, characterized in that the composite system contains at least one further layer.

16. Composite system according to the preceding claim, characterized in that the further layer a lacquer layer, an adhesive layer, another vapor-deposited layer or a Polymerfo- lie is.

17. Composite system according to the preceding claim, characterized in that the further layer contains the activator.

18. A composite system according to any one of claims 16 or

17, characterized in that the polymer film consists of a polymer selected from the group of polyethylene terephthalates, polyolefins, polyamides, polystyrenes, polycarbonates and their copolymers and polymer blends.

19. Composite system according to one of claims 16 to

18, characterized in that the scavenger / indicator layer between the substrate film and the further layer is sandwiched at least partially frictionally enclosed.

20. Composite system according to one of claims 16 to

19, characterized in that the polymer film is non-positively connected to a Kaschierklebstoff with the scavenger / indicator layer.

21. Composite system according to the preceding claim, characterized in that the Kaschierklebstoff contains the at least one activator.

22. Composite system according to one of the preceding claims, characterized in that the activator is integrated in the scavenger / indicator layer.

23. Composite system according to one of the preceding claims, characterized in that the scavenger / indicator layer contains at least one spacer for improving the adhesion to the adjacent substrate film.

24. Composite system according to one of the preceding claims, characterized in that the at least one spacer is selected from the group consisting of Au, Ag, SiO _x with x = 1.0 to 2.0, AlO _y with y = 1.3 bis 1.6, B ₂ O ₃ , Cr-SiO ₂ , Cr ₂ Si ₂ , GeO ₂ , InO ₂ and TiO ₂ .

25. Composite system according to one of the preceding claims, characterized in that the substrate film is a composite film.

26. Composite system according to the preceding claim, characterized in that the substrate film has a barrier layer for oxygen.

27. Composite system according to the preceding claim, characterized in that the barrier layer contains SiO _x with x = 1.0 to 2.0, AlO _y with y = 1.3 to 1.6, ethylene vinyl alcohol copolymers and / or vinylidene chloride copolymers.

28. The composite system according to claim 1, characterized in that the substrate film consists of a polymer selected from the group of polyethylene terephthalates, polyolefins, polyamides, polystyrenes, polycarbonates and / or their copolymers and polymer blends.

29. Composite system according to one of the preceding claims, characterized in that the composite system in the visible region of the spectrum is transparent.

30. The composite system according to any one of the preceding claims, characterized in that the weight ratio of oxygen sorbent to the activator is set so that the oxygen sorbent is a change of at least one of its physical properties at a defined point, which represents the residual capacity of the oxygen sorbent , shows.

31. The composite system according to any one of the preceding claims, characterized in that the weight ratio of oxygen sorbent to the activator is set so that the oxygen sorbent has a color change point, which represents the residual capacity of the oxygen sorbent.

32. Composite system according to one of the preceding claims, characterized in that the weight ratio of oxygen sorbent to Akti vator is set so that the oxygen sorbent having a change in its physical properties at a defined point indicating the exceeding of a certain oxygen concentration period.

33. The composite system according to the preceding claim, characterized in that the weight ratio of oxygen sorbent to activator is set so that the oxygen sorbent has a color change point indicating the exceeding of a certain oxygen concentration period.

34. The composite system according to any one of the preceding claims, characterized in that the weight ratio of oxygen sorbent to the activator is set so that the oxygen sorbent a change of at least one of its physical properties at a defined point, the exceeding of a certain oxygen concentration shows, shows.

35. Composite system according to the preceding claim, characterized in that the weight ratio of oxygen sorbent to activator is adjusted so that the oxygen sorbent has a color change point indicating the exceeding of a certain oxygen concentration.

36. Composite system according to one of the preceding claims in the form of a film.

37. Use of the composite system according to one of the preceding claims as a packaging film or partially applied single film.

38. Use of the composite system according to one of claims 1 to 36 for the protection of oxygen-sensitive components in electronic or electrical devices.